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Home My WebLink AboutNCD062555792_20090801_Sigmons Septic Tank Service_FRBCERCLA ROD_Record of Decision OU-2 (Groundwater)-OCR1'1 ' RECORD OF DECISION OPERABLE UNIT 2 (GROUND WATER) SIGMON'S SEPTIC TANK SITE ST ATES VILLE, IREDELL COUNTY, NORTH CAROLINA U.S. ENVIRONMENTAL PROTECTION AGENCY REGION 4 ATLANTA, GEORGIA August.2009 Table of Contents Page No. Acronyms and Abbreviations ........................................................................................ .' ...... A&A-1 The Declaration ............................................................................................................................... i Decision Summary 1.0 Site Name, Location, and Description .................................................................................... 6 2.0 Site History and Enforcement Activities ................................................................................ 7 3 .0 Community Participation ........................................................................................................ 9 4.0 Scope and Role of Response Action ....................................................................................... 9 5.0 Summary of Site Characteristics ........................................................................................... I 0 5.1 Physical Characteristics of the Site .............................................................................. 10 5. I. I Sources of Contamination .............................................................................. 10 5.1.2 Climate ........................................................................................................... 11 5.1.3 Geologic Summary and Conditions ....................... _. ....................................... 11 5.1.4 Hydrogeology Summary and Description ...................................................... 14 5.1.5 Hydrology ....................................................................................................... 17 5.1.6 Ground Water Contamination Summary ........................................................ 19 5.1.7 Contaminant Fate and Transport .................................................................... 26 5.1.8 Summary of Site Conceptual Model .............................................................. 33 6.0 Current and Potential Future Site Uses ................................................................................ .35 7.0 Summary of Site Risks ......................................................................................................... .36 7.1 Summary of Baseline Human Health Risk Assessment for Ground Water Operable Unit 2 ................................................................................... .36 7.1.1 Identification of Chemicals of Concern ........................................................ .36 7 .1.2 Exposure Assessment .................................................................................... .36 7.1.3 Toxicity Assessment. ...................................................................................... 38 7 .1.4 Risk Characterization .................................................................................... .38 8.0 Remedial Action Objectives ................................................ : ...................................... .40 9.0 Description of Alternatives ................................ : ................................................................. .41 9.1 Common Elements of Each Remedial Alternative ..................................................... .42 9.2 Remedial Alternative .................................................................................................. .42 9.2.1 Alternative I: No Action .............................................................................. .42 9.2.2 Alternative 2a: MNA ..................................................................................... .43 9.2.3 Alternative 2b: MNA with Contingencies ..................................................... .46 9.2.4 Alternative 4: Enhanced Attenuation with Chemical Oxidation/Reduction ..................................................................... .47 I 0.0 Comparative Analysis of Alternatives ................................................................................. .49 I 0.1 Description of Criteria .................................................... : ............................................ 50 Record of Decision -Sigmon's Septic Tank Site TOC-1 Table of Contents (Continued) Page No. 10.1.1 Overall Protection of Human Health and the Environment.. .......................... 50 10.1.2 Compliance with ARA Rs ............................................................................... 50 10.1.3 Long-Term Effectiveness ............................................................................... 53 10.1.4 Reduction of Toxicity/Mobility/Volume Through Treatment ....................... 54 I 0.1.5 Short-Term Effectiveness ............................................................................... 54 I 0.1.6 Implementability ............................................................................................ 55 10.1.7 Cost.. ............................................................................................................... 56 10.1.8 State Acceptance ............................................................................................ 58 10.1.9 Community Acceptance .................................................................................... 58 11.0 Principal Threat Waste .......................................................................................................... 58 12.0 The Selected Remedy ........................................................................................................... 59 12.1 Description of the Selected Remedy ........................................................................ 59 12.2 Summary of Estimated Remedy Cost ...................................................................... 60 12.3 Expected Outcomes of the Selected Remedy ........................................................... 60 12.4 Future Land Use ....................................................................................................... 61 12.5 Final Cleanup Levels ................................................................................................ 61 13.0 Statutory Determinations ...................................................................................................... 61 13.1 Protection of Human Health and the Environment .................................................. 61 13.2 Compliance with Applicable or Relevant and Appropriate Requirements .............. 61 14.0 References ............................................................................................................................. 63 Figures Data Tables Appendices Appendix A Appendix B Appendix C Appendix D Appendix E Proposed Plan Fact Sheet Responsiveness Summary State Concurrence Letter List of Figures Figure I Site Location Map Figure 2 Site Layout Figure 3 Pile Morphology Figure 4 Stream Locations Figure 5 Hydrogeologic Cross Section (A-A') Figure 6 Hydrogeologic Cross Section (B-B ') Figure 7 The Conceptual Structure of the Piedmont Hydrogeologic Framework Figure 8 An Idealized Weathering Profile through the Regolith Figure 9 Approximate Ground Water Flow Paths Figure IO Conceptual View of Double Slope-Aquifer System Figure 11 2004 Estimated Ground Water Potential Contours Figure 12 2008 Estimated Ground Water Potential Contours Figure 13 Distributions of RI Screening Values Exceedances in Surface Water and Sediment Sample Locations (October 2002 and May 2004) Figure 14 Wells Exceeding Preliminary Cleanup Levels for COCs Record of Decision -Sigmon's Septic Tank Site TOC-2 Table of Contents (Continued) List of Figures (Continued) Figure 15 Distributions of Geochemical Parameters Figure 16 Sodium Concentrations over Sampling Time Period Figure 17 Arsenic Concentrations over Sampling Time Period Figure 18 Manganese Concentrations over Sampling Time Period Figure I 9 Iron Concentrations over Sampling Time Period Figure 20 Conceptual Site Model Figure 21 Proposed Wells Recommended for MNA Sampling List of Tables Table I Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table 10 Task 11 Task 12 Table 13 Table 14 Table 15 Table 16 Table 17 Table 18 Table 19 Data Summary for Shallow Ground Water Summary of Chemicals of Concern and Medium-Specific Exposure Point Concentrations Data Summary for Shallow Ground Water Summary of Chemicals of Concern and Medium-Specific Exposure Point Concentrations Non-Cancer Toxicity Data -Oral/Dermal Non-Cancer Toxicity Data -Inhalation Cancer Toxicity Data -Oral/Dermal Cancer Toxicity Data -Inhalation Risk Characterization Summary for Current/Future Resident-Noncarcinogens - Shallow Ground Water Risk Characterization Summary for Current/Future Resident-Noncarcinogens - Deep Ground Water Risk Characterization Summary for Current/Future Resident-Carcinogens - Deep Ground Water Risk Characterization Summary for Current/Future Resident-Carcinogens -- Shallow Ground Water Risk Characterization Summary for Current/Future Resident -Non Carcinogens Risk Characterization Summary for Current/Future Resident -Carcinogens Cleanup Goals for Ground Water Cost Comparison of Remedial Alternatives Potential Chemical-Specific ARARs Potential· Location-Specific ARA Rs Potential Action-Specific ARARs Comparison of Remedial Alternatives Detailed Cost Estimate Worksheets Record of Decision -Sigmon's Septic Tank Site TOC-3 ADD ams! ARAR AST ASTOR BHHRA Black & Veatch bis BOD BRA CERCLA CFR coc COD CSM CSF DI DO EPA EPC ERRB FS HEAST HI HQ IC IRIS LADD MCL µg/kg µg/L mg/kg mg/kg/BW/day mg/kg/day mg/L mS/cm mV MNA MRL M/T/V NCDENR Acronyms and Abbreviations Average daily dose above mean sea level Applicable or Relevant and Appropriate Requirements Aboveground storage tanks Agency for Toxic Substances Disease Registry Baseline Human Health Risk Assessment Black & Veatch Special Projects Corp. below land surface Biological oxygen demand Baseline Risk Assessment Comprehensive Environmental Response, Compensation, and Liability Act of 1980 Code of Federal Regulation Contaminant of Concern chemical oxygen demand Conceptual Site Model Cancer Slope Factor Daily intake Dissolved oxygen U.S. Environmental Protection Agency Exposure Point Concentrations Emergency Response and Removal Branch Feasibility Study Health Effects Assessment Summary Tables Hazard Index hazard quotient Institutional Control Integrated Risk Information System Ii fetime average daily dose Maximum Contaminant Level micrograms per kilogram micrograms per liter milligrams per kilogram milligrams per kilogram of body weight per day milligrams per kilogram per day milligram per liter millisemens per centimeter millivolts Monitored Natural Attenuation Minimal Risk Levels Mobi I ity/toxicity/volume North Carolina Department of Environment and Natural Resources Record of Decision -Sigmon's Septic Tank Site AA-I NCP O&M ORP OSRTI OU PAH PCB PPRTV PRG PWR QA/QC RAGS RAO RCRA RID RGO RI Rl/FS ROD RSL SARA Site S/S SSTS svoc SDWA TAL TBC TCE TCLP TOC voe Acronyms and Abbreviations (Continued) National Contingency Plan Operation and Maintenance Oxygen reduction potential Office of Superfund Remediation and Technology Innovation Operable Unit Polynuclear aromatic hydrocarbons Polychlorinated biphenyls Provisional Peer-Reviewed Toxicity Values Preliminary Remediation Goal Partially Weathered Rock Quality Assurance/Quality Control Risk Assessment Guidance for Superfund Remedial Action Objective Resource Conservation and Recovery Act Reference Dose Remedial Goal Option Remedial Investigation Remedial Investigation/Feasibility Study Record of Decision Regional Screening Levels Superfund Amendments and· Reauthorization Act of 1986 Sigmon's Septic Tank Site solidification/stabilization Sigmon's Septic Tank Service Semivolatile Organic Compounds Safe Drinking Water Act Target analyte list To-Be-Considered Trichloroethenc Toxicity Characteristic Leaching Procedure Total organic carbon Volatile Organic Compounds Record of Decision -Sigmon's Septic Tank Site AA-2 I. DECLARATION Sigmon 's Septic Tank Site Operable Unit 2 (Ground Water) Statesville, Iredell County, North Carolina Record of Decision -Sigmon's Septic Tank Site RECORD OF DECISION OPERABLE UNIT 2 (GROUND WATER) SIGMON'S SEPTIC TANK SITE DECLARATION 1.0 SITE NAME AND LOCATION Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina EPA Site Identification Number NCD062555792 2.0 STATEMENT OF BASIS AND PURPOSE This decision document presents the Selected Remedy for Operable Unit (OU) 2 (ground water) at the Sigmon's Septic Tank Site (Site) located in Statesville, Iredell County, North Carolina. The Selected Remedy was chosen in accordance with the requirements of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR, Part 300. This decision document explains the factual and legal basis for selecting the remedial action for OU 2 at the Site. The information supporting this decision is contained in the Administrative Record for the Site. The North Carolina Department of Environment and Natural Resources (NCDENR), support agency for this Site, has reviewed the ROD and concurs with the Selected Remedy for OU 2. Record of Decision -Sigmon's Scr,tic Tank Site 3.0 ASSESSMENT OF THE SITE The response action selected in this ROD is necessary to protect the public health or welfare and the environment from actual or threatened releases of hazardous substances to the environment. Such release or threat of release may present imminent and substantial endangerment to public health, welfare, or the environment. 4.0 DESCRIPTION OF THE SELECTED REMEDY EPA's Selected Remedy described in this 2009 ROD addresses risks to human health and the environment for Operable Unit 2 (ground water) at the Site. The Selected Remedy for Operable Unit 2 is Alternative 2a which consists of monitored natural attenuation (MNA). The major components of MNA, Alternative 2a, for Operable Unit 2 include: • Implementing institutional controls for the Site. • Several stream-side wells screened within the shallow aquifer (alluvium) will be installed and sampled at depths ranging approximately 2-5 feet below the water table and not greater than IO feet below land surface (bis) along the intermittent streams. Henry Push Point samples may be used as an alternate for shallow monitoring well installation, as deemed necessary. • Conducting groundwater analyses to evaluate possible formation of complexes and precipitates. On-Site shallow wells and deep wells will be sampled for cations, anions, and organic matter during quarterly groundwater natural attenuation monitoring events for one year to assess precipitation or adsorption potential of metals contamination in groundwater. • Implementing a ground water monitoring program consisting of sampling and analysis to track the effectiveness and trends in concentrations over time for MNA. Four existing shallow monitoring wells will be sampled for metals, natural attenuation parameters, and field parameters including DO, pH, ORP, conductivity, and turbidity. Four existing deep monitoring wells will be sampled for metals, volatile organic compounds (VOCs), natural attenuation Record of Decision -Sigmon's Septic Ta1_1k Site 2 parameters, and field parameters including DO, pH, ORP, conductivity, and turbidity. 5.0 STATUTORY DETERMINATIONS The Selected Remedy is protective of human health and the environment, complies with Federal and State requirements that are applicable or relevant and appropriate to the remedial action, are cost effective, and utilize permanent solutions and alternative treatment (or resource recovery) technologies to the maximum extent practicable. The selected remedy satisfies the statutory requirements because the remedy is fully protective of human health and the environment and will attain clean-up levels within a reasonable timeframe. Upon completion of this remedy, no hazardous substances will remain on-Site above health based levels that prevent unlimited use and unrestricted exposure. However, it is expected that it may take greater than five years to achieve the groundwater clean-up goals. Therefore, a Five-Year Review will be conducted within five years of completion of this Preliminary Close-Out Report. 6.0 DATA CERTIFICATION CHECKLIST The following information is included in the Decision Summary Section of this ROD. Additional information can be found in the Administrative Record file for this Site. • Current and reasonably anticipated future land use assumptions (34) • Current and potential future beneficial uses of groundwater used in the Baseline Risk Assessment (BRA) and ROD (Page 35). • Estimated capital, annual operation and maintenance (O&M), and total present worth costs, discount rate, and the number of years over which the remedy cost estimates are projected (Page 41 ). • Key factors that led to selecting the remedy (Page 46). • How source materials constituting principal threats are addressed (Page 56). • COCs and their respective concentrations (Figure 14). • Baseline risk represented by the COCs (Page 35). • Cleanup levels established for chemicals of concern and the basis for these levels (Table 13). Record of Decision -Sigmon's Septic Tank Site 3 7.0AUTHORIZING SIGNATURES Franklin E. Hill, Director Superfund Division U.S. Environmental Protection Agency, Region 4 Record of Decision -Sigrnon's Septic Tank Site 4 Date Document prepared by EPA Region 4 Remedial Project Manager: Concur By: EPA Region 4 Site Attorney: Concur By: EPA Region 4 Chief, CERCLA [A,B, or CJ CONCURRENCEPAGEFORTHE SIG MON'S SEPTIC TANK SITE RECORD OF DECISION ~~ [Nam Office of Environmental Accountability: Concur By: EPA Region 4 Section Chief Superfund Division: Concur By: EPA Region 4 Branch Chief Superfund Division: Concur By: EPA Region 4 Director Superfund Division [Name] --nanklin E. Hill 'i] b.11°1 Date f/t//o J Date 9/31/CIJ Date z7/2Jla°1 Date Date II. DECISION SUMMARY Sigmon 's Septic Tank Site Operable Unit 2 Statesville, Iredell County, North Carolina Record of Decision -Sigmon's Septic Tank Site 5 DECISION SUMMARY 1.0 SITE NAME, LOCATION, AND DESCRIPTION The Sigmon's Septic Tank Site (Site) is located at 1268 Eufola Road, approximately 5 miles southwest of Statesville, Iredell County, North Carolina (see Figure 1 ). The Site is located between Eufola Road to the north and Lauren Drive to the south. Private landowners own the properties located east and west of the Site; the Pine Grove Cemetery is also located east of the Site. A landing strip is located about 0.5 miles south of the Site. The layout and features of the Site are shown on Figure 2. The Site is approximately 15.35 acres in size. According to Iredell County plat maps, the Site was divided into two properties at the time of its operation. The southern parcel is 8.9 acres in size and was listed in the name of the deceased Mr. Henry Sigmon, and the northern parcel is 6.45 acres in size and was owned by his daughter, Ms. Mary Sigmon. Mary Sigmon and her family lived in the onSite residence on the northern property. Several years ago, the Sigmon 's property was sold; the current owner owns both parcels and resides in the onSite house formerly occupied by Ms. Sigmon. For the purposes of this record of decision (ROD), the property will continue to be referred to as the "Sigmon Property." A 1.25-acre pond (former borrow pit) is located south of the Sigmon house. An office trailer is located south-southeast of the pond, and an open-walled, roofed storage shed is located southeast of the office. Access to the interior of the property (i.e., to the office and open-walled shed) is provided by a gravel driveway that runs north-south along the eastern Site boundary. Approximately I 00 feet south of the shed next to the gravel access road were six aboveground storage tanks (ASTs) containing liquid wastes including two rectangular concrete basins (approximately 1,000 gallons each), two cylindrical rusted tanks (approximately 10,000 gallons each), and two cylindrical rusted tanks (approximately 12,000 gallons each). These tanks were removed by the property owner. A waste pile (or stockpile) and former lagoons are located in the southern portion of the Site (see Figure 3). The structure of the stockpile consist of the pile proper, pile fingers, and the blanketed area. The pile proper is a small, relatively flat topped hill varying in Record of Decision -Sigmon's Septic Tank Site 6 height from 8 feet to 12 feet above ground level. It is more generally sloped on the north side and is nearly vertical along its southwest edge. There is a small prominent bench on the nort_hwest side approximately 4 feel in height above ground level. The pile fingers extend off from the southwest side of the pile proper for a distance of approximately 90 feet. The height of the tops of each finger range from approximately 4 feet above ground level at the southwestern terminus of each finger. The pile fingers are all rounded on top, sloping off to the level of the blanketed area around their edges. The middle finger is lobe-shaped with an irregular border. The middle finger has been recently partially excavated. The blanketed area is characterized by a thin, generally I to 2 foot thick layer of brown silty soil. The Site is fenced with a 4-foot barbed wire fence, and warning signs are posted on the fence and trees. There are breaks in the fence on the eastern and southern sides of the Site. Sigmon's Septic Tank Service pumped septic tank wastes and heavy sludge from residential, commercial, and industrial customers; septic tanks were installed and repaired; and a variety of industrial waste removal services were provided. From 1978 to 1992, Sigmon 's Septic Tank Service disposed of septic wastes in eight to ten unlined lagoons on the south section of the 15-acre property. The waste was described as septage, grease, and milky white liquid. The lagoon area dimensions (encompassing all the lagoons) were 213 feel by 250 feet wide, or approximately 1.2 acres. The Site was placed on the National Priorities List (NPL) on April 27, 2005. The United States Environmental Protection Agency's (EPA) Identification Number for the Site is NCD062555792. The lead agency for the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) regulatory response at the Site is EPA and the North Carolina Department of Environment and Natural Resources (NCDENR) is the support agency. 2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES The Sigmon's Septic Tank Service, a wholly owned subsidiary of AAA Enterprises, was owned and operated by the Sigmon family since 1948. In 1970, Henry Sigmon purchased the property al 1268 Eufola Road and moved operations to this location. The business pumped septic tank wastes and heavy sludges from residential, commercial, and industrial customers; installed and repaired septic tanks; and provided a variety of industrial waste removal services. In 1980, a nephew of Henry Sigmon, Mr. Frank Sigmon, stated to North Carolina Department of Human Services that the septic service Record ofDccision-Sigrnon's Septic Tank Site 7 had pumped from Barnhardt, Clark Equipment, and Union Glass. In 1996, Henry Sigmon mentioned to the NCDENR that some of the septic wastes came from a medical supply company, Zimmer Industries, and a metal treating business, Ro-Mac Company. Other than those sources mentioned by Mary Sigmon, no other sources of septic waste have been named in the file material. From 1970 to 1978, the wastewaters were discharged to the City of Statesville sewer. Around 1973 or 1974, the service received permits and land applied sludges to area farmlands. The process of land application appeared to have continued until at least 1989, according to septage management applications filed by AAA Enterprises. The file material does not specify on which properties the sludges were applied and whether the farmlands produced food crops. Around 1978 or 1979, the Sigmons dug several lagoons at the Site and began placing septic wastes into these lagoons. Henry Sigmon stated that he had received verbal permission from the Iredell County Health Department and the Mooresville Regional Office of NCDENR to construct and use the lagoons for septage disposal. No permits were issued for the lagoons: The number and size of the unlined lagoons which originally existed at the Site is unclear after a thorough review of the file material. Eight to ten unlined lagoons were utilized to hold septic wastes. Some references indicate the lagoons were uniform in size while others depict lagoons differing widely in size. At times, some of the lagoons were connected with piping (referred to as a septic T) to drain water from other lagoons and facilitate the dewatering of the sludges. As of September 1990, eight unlined lagoons were active; six were used for septic waste and the remaining two for dewatering. It is unknown if the lagoons ever discharged overland to the surface water pathway. If the stream is ephemeral it may not be flowing. These streams are not lotic in the upper reaches. Surface water features near the Site consist exclusively of ephemeral streams that collect stormwater and are the natural discharge points for shallow ground water flow at the Site. The Site is located on a ridge with streams on the north and south sides which carry runoff from the area toward the west. The nearest perennial creeks or rivers are about one-half mile west and southwest of the Site (i.e., Reeder Creek and the Catawba River). Uncontrolled migration of overland stormwater flow may impact several small ponds in the area: Davidson Pond to the south of the Site, Sigmon Pond within the Site boundaries, and Lambreth and Williams Ponds to the west of the Site. Further west of these, Sliwinski Pond lies within the drainage ditch system between the Site and the Catawba River, and could receive storm water flow originating from the Site. Record of Decision -Sigmon's Septic Tank Site 8 3.0 COMMUNITY PARTICIPATION The Selected Remedy is based on Site-related documents contained in the Administrative Record for the Site including the Remedial Investigation for Operable Unit 2 (March, 2008), Baseline Human Health Risk Assessment (BHHRA) for Operable Unit 2 (March, 2008), Drinking Water Investigation Report (December, 2008), and the Feasibility Study for Operable Unit 2 (June 2009). The Administrative Record includes the documents used to support the 2009 ROD for OU 2. These documents were made available to the public in both the Administrative Record and an information repository maintained at the EPA Superfund Record Center in Region 4 and at the Iredell County Public Library. In addition, over I 00 copies of the Proposed Plan were mailed to citizens in neighborhoods adjacent to the Site. The notice of availability of the documents was published in the Statesville Observer on June 29, 2009. A public comment period on the documents was held from July 3 to August 3, 2009. A public meeting was held on July 9, 2009, at the Celeste Henkel School, Statesville, North Carolina. At this meeting, representatives from EPA, NCDENR, Iredell County, and major property owners answered questions about current conditions at the Site and the remedial alternatives under consideration. EPA received no comments during the comment period; therefore, no Responsiveness Summary is included in this ROD. 4.0 SCOPE AND ROLE OF RESPONSE ACTION EPA divided the Site into two Operable Units, surface soil and groundwater. This ROD addresses the groundwater and will be the final action for the Site. EPA has determined that existing data is sufficient to show that the selected remedy will be the appropriate remedy for the contaminants al'the Site. The selected remedy will attain long-term objectives (e.g., restoring groundwater) over all portions of the Site. This action is planned to be the final groundwater response action for the Site. Record of Decision-Sigmon's Septic Tank Site 9 5.0 SUMMARY OF SITE CHARACTERISTICS 5.1 Physical Characteristics of the Site The Site occupies 15.35 acres located at 1268 Eufola Road in Iredell County, North Carolina. The Site lies within the central portion of the Piedmont Physiographic province in west central North Carolina (see Figures I and 2). The regional topography is characterized by well-rounded hills dissected from the ancient peneplain surface by east- flowing streams and long, undulating ridges trending toward the northwest. Iredell County lies within two river basins: the Catawba River basin in the southeastern portion and the Yadkin River basin in the northwest. U.S. Highway 21 follows the divide separating the Catawba and the Yadkin River basins northward from Mecklenburg County to Troutmans and then north westward; the divide is then followed by a rural road to Alexander County. The Site is located in the southeastern quadrant of Iredell County within the Catawba River basin. Site elevations range between approximately 910 feet above mean sea level (amsl) on the western portion of the Site, and 960 feet ams! near the southeast edge of the Site. Surface drainage generally flows in a southwesterly direction channeled by two unnamed intermittent streams that converge with the Catawba River approximately 1.5 miles to the southwest (see Figure 4). 5.1.1 Sources of Contamination The Site is impacted by septic tank wastes and heavy sludges from residential, commercial, and industrial customers placed in eight to ten unlined unpermitted lagoons located at the Site beginning around 1978 until 1992. Septic sludges were also land- applied to area farmlands from around 1973 to 1989. In 2002, Sigmon Environmental was fined for unpermitted discharge and the company shut down operations shortly thereafter. The Site was divided into two units (soil and groundwater) during the initial remedial investigation (RI) phase for OU I because additional ground water plume delineation was required alter the evaluation of soil (including the stockpile), sediment, and surface water was completed. OU I addresses Site soil (including the stockpile), sediment, and surface water contamination; and Operable Unit 2 addresses ground water contamination. It has been determined that soil (excluding the stockpile), sediment, and surface water do not Record ofDccision-Sigmon's Septic Tank Site IO pose a risk to human health or the environment and these media are not sources of contamination. The onSite stockpile will be addressed in a separate ROD and ground water continues to be sources of contamination. 5.1.2 Climate Normal annual precipitation within Iredell County is approximately 48 inches while the mean annual evaporation is approximately 40 inches, with a net annual precipitation of 8 inches. The 2-year, 24-hour rainfall for Iredell County is 3.8 inches. 5.1.3 Geologic Summary and Conditions 5.1.3.1 Geologic Summary The area is underlain by metamorphic and igneous rocks, primary gneiss and schist intruded by granite. Locally called "bedrock", these primary rock types are fractured and faulted at depth and weathered near the surface into reddish clay containing occasional fragments of the bedrock. The product of in-place weathering of the parent rock is called saprolite. The saprolite thickness varies from near zero at the banks of the streams to about 80 feet at the ridge crest. A thin zone called partially weathered rock is sometimes recognizable between the unweathered bedrock and the highly weathered saprolite. Thin deposits of alluvium arc present in stream beds. Each of these geologic units has different water-bearing properties which control potential contaminant migration in these units. 5.1.3.2 Geologic Conditions The Piedmont Physiographic province is characterized by low to high-grade metamorphosed crystalline rock, which has undergone one or two subsequent regional metamorphic events and up to four deformation events·, and some unmetamorphosed intrusive igneous rock. Compositions for both metamorphic and igneous rock range from fclsic to ultramafic. The rocks arc broken and displaced by numerous faults, and nearly everywhere there are rock fractures without displacement. CompoSite gneiss is the dominant rock type in Iredell County, composed of mica schists that have been intruded by granite. Hornblende gneiss is common as large mappable bodies and thin sill-like bodies in other rocks. Weathered hornblende gneiss produces deep red soils, whereas soils where hornblende is scarce tend to be sandy and light in color. The largest Record of Decision -Sigmon's Septic Tank Site 11 occurrence of granite is in the Mooresville area where it underlies a broad intcrstream area. Gabbro occurs in a large area along U.S. Route 70 in the eastern part of the county and also in the southwestern corner of the county. Rocks of the granite-diorite complex have limited occurrence along the southern and eastern borders of the county (LeGrand, 1952). Boring logs from six boring locations within 3 to 4 miles of the Site indicate that the thickness of the underlying regolith is highly variable, and extends from 10 to 140 feet bis. Bedrock in the Piedmont consists of biotite gneiss, biotite schist, hornblende gneiss, granite gneiss, chlorite gneiss, and some granite (Groves, 1978). Based on the Geologic Map of Iredell County the Site is located near the boundary of the mica schist and granite schist and hornblende gneiss. As stated in the bulletin, " ... the geology is necessarily greatly generalized and the map can be considered only a reconnaissance map" (LeGrand, 1952). Based on the borings installed during the remedial investigation/feasibility study (RI/FS) investigation, the bedrock al the Site has been identified as hornblende gneiss (Black & Veatch, 2006). The principal stratigraphic units at the Site are identified as: • Residual soil (regolith) including saprolite and alluvium. • Partially Weathered Rock (PWR). • Bedrock. The regolith consists of an unconsolidated or semi-consolidated mixture of clays and fragmental material ranging in size from silt to sand to gravel (see Figures 5 and 6). Components of the regolith include surficial soil, saprolite, and alluvium (see Figures 7 and 8). Saprolite is the dominant regolith material and is the unconsolidated product of in-place weathering of parent bedrock. Some of the textural features of bedrock are retained within the saprolite, and boulders ofunweathered bedrock are often found within the saprolite. Alluvium deposits are unconsolidated sediments depoSited by streams and rivers and are restricted to valleys (LeGrand, 1967). Between the regolith and the fractured crystalline bedrock is a transition zone consisting of saprolite and partially-weathered bedrock where unconsolidated material grades into bedrock. Mechanical weathering has progressed only to a stage of minute fracturing of the rock fabric, but the rock and rock minerals have not chemically weathered to clays (Cardinell et al., 1989). Record of Decision -Sigmon's Septic Tank Site 12 Below the transition zone is the uppennost part of the Piedmont crystalline bedrock, which contains numerous closely-spaced stress-relief fractures formed in response to removal of overlying material. Typically, few of these fractures occur at depths greater than 350 feet (LeGrand, 1967). As a general statement, heterogeneity and anisotropy in each unit increase from the regolith downward to the bedrock. The characteristics important to the Conceptual Site Model (CSM) are summarized in the following subsections. 5.1.3.3 Surficial Soil, Regolith, and Saprolite Surficial soil types at the Site include silty loam, sandy loam, clay, silt, fine sand, and alluvium. Materials encountered below the surficial soils, within the regolith zone, generally include sand, silty sand, clayey sand, sandy silt, silt, silty clay, and clay. Materials were commonly red and orange although tan, gray, and brown materials were also encountered. At the base of the regolith is a zone of weathered boulders and saprolite. Saprolite is highly weathered bedrock that retains the schistose foliation and relict compositional layering of the parent bedrock. The material is typically interlayered micaceous fine-to-medium grained sand, sandy silt, and some clay. Saprolite tends to be very penneable and can be subject to high ground water flow. The thickness of the regolith and saprolite at the Site varies from 30 feet to 83 feet. 5. 1.3.4 Partially Weathered Rock A transition zone of partially weathered rock (PWR) was noted in test borings at the Site. This zone consists of weathered blocks of bedrock surrounded by saprolite. Although not detected in soil cores, the PWR likely contains fractures extending downward through the underlying bedrock. The PWR is typically noted during drilling when progress slows significantly and rock pieces appear in the soil cores. Boring logs indicate the PWR varies in thickness from I to 13 feet at the Site, with an average thickness of about 5 feet. Record of Decision -Sigmon's Septic Tank Site 13 5.1.3.5 Bedrock The bedrock at the Site is a hornblende gneiss. Depth to the top of competent bedrock, as estimated from the refusal of hollow stem augers in soil borings, ranges from 30 to 83 feet bis. The bedrock exhibits fractures, faults, and foliation, all of which are products of regional tectonism. The various rock types at the Site respond differently to these stresses and develop characteristic mineralogy, foliation, and fracture planes. The foliation and fractures are openings that allow the movement of ground water to weather the minerals. Long-term erosion of overlying rocks and soil reduces confining (overburden) pressure, which results in stress relief fractures within the bedrock. These fractures are most prevalent in shallow bedrock. Boring logs and geologic cores suggest that at the Site, fractures and foliation openings that transmit ground water occur within the shallow bedrock. The variability of both rock . type and paucity of secondary openings causes the bedrock to be extremely heterogeneous and ground water flow to be anisotropic. 5.1.4 Hydrogeology Summary andDescription 5.1.4.1 Hydrogeology Summary The Site is located on a ridge between two streams which are intermittent in the upper reaches. The ridge terminates and streams converge approximately one mile west of the Site. The joined stream flows to Catawa River approximately 1.5 miles SW of the Site (Figure 2-10). The primary direction of ground water flow in the saprolite beneath portions of the Site near the ridge crest is likely to be vertical downward. Groundwater in areas away from the ridge crest flows toward the streams. The streams are the natural discharge area for shallow groundwater and strongly influence the hydrogeology of the area. All ground water in the saprolite must discharge from the saprolite before the ridge terminates where the streams converge because the stream bed_s likely penetrate the saprolite. Groundwater levels north and south of the ridge are higher than in the streams themselves. So the streams drain groundwater from areas north and south of the ridge, making the streams groundwater flow divides separating the ridge where the waste disposal lagoons were located from areas to the north and south. Figure 2-8 shows a concept model of the Site hydrogeology. Record of Decision-Sigmon'~ Septic Tank Site 14 5.1.4.2 Hydrogeology Description The hydrogeologic framework at the Site includes the unsaturated zone above the water- table, and an aquifer system with dissimilar but hydraulically connected zones: the alluvium saprolite, PWR and the bedrock. Together the alluvium, saprolite and PWR form the surficial aquifer at the Site. Boring logs show there is no confining unit between the surficial aquifer and the bedrock aquifer. The aquifer zones are highly heterogeneous (the hydraulic parameters are dependent on location within the aquifer), due to the variable grain-size, mineralogy, and the presence of fractures, foliation, and other geologic structures. The aquifer is also highly anisotropic (the hydraulic conductivity varies with direction at any location) because of the well-developed foliation and the 1 sporadic occurrence of fractures. It appears the bedrock is more heterogeneous and more anisotropic than the surficial, due to the influence of fractures. The hydraulic properties of the surficial aquifer and the bedrock aquifer include aquifer storage and aquifer transmissivity. The aquifer storage is composed of two parts: (I) static storage that is related to total porosity, and (2) dynamic storage that is related to the properties of water. The dynamic storage is commonly discussed in terms of specific storage and coefficient of storage. Because the aquifer is a compoSite system of heterogeneous units, there are multiple terms needed to describe aquifer transmissive properties. The terms include: (a) hydraulic conductivity (or transmissivity) of the surficial aquifer, or its members, which are regolith/saprolite and PWR; (b) bulk hydraulic conductivity of the bedrock aquifer; (c) hydraulic conductivity of transmissive fractures; and (d) hydraulic conductivity of the bedrock matrix blocks. 5.1.4.3 Aquifer Transmissive Properties A conceptualization of the aquifer permeability relative to the degree of weathering is presented on Figure 8. The transmissive properties of the regolith/saprolite, PWR, and bedrock are discussed below. Surficial Soil, Regolith and Saprolite Although there are no Site-specific aquifer test data available for the·regolith/saprolite, the permeability is related to the degree of weathering. Saprolite, because of its anisotropic nature, has hydraulic conductivities in the range of I to 20 feet per day Record ofDecision-Sigmon's Septic Tank Site 15 (Heath, 1980). Alluvium, which usually contains considerable amounts of silt and sand, has hydraulic conductivities generally ranging from 1 to 100 feet per day. PWR The transition zone (or partially weathered bedrock) has the highest permeability within the saprolite due to the less advanced chemical weathering (Stewart, 1962; Nutter and Olton, 1969). The higher permeability of the transition zone at the top of the bedrock results in a region of higher hydraulic conductivity within the ground water flow system. A large proportion of the ground water moving through the system moves through the transition zone. Monitoring wells MW\2B and MW 13B are both screened into the PWR zones that were observed in_ these borings. The PWR zone in MW 12B was first detected at a depth of 40 feet bls and extended to 68 feet bls. Within the PWR a highly fractured rock zone was encountered from 63 lo 65 feet bls. Competent bedrock was reached at 68 feet bls. The screened interval in MW 12B is IO feet long (52 to 62 feet bis) and stretches across a highly weathered silty sand interval. The screened interval, however, does not include the highly fractured zone from 63 to 65 feet bis within the PWR. The drawdown data measured during the sl_ug test performed on this well resulted in a hydraulic conductivity of2.9 feet per day. Since the screened interval does not include the highly fractured zone, this hydraulic conductivity is representative of the less transmissive lithology that composes a portion of the PWR. In MW I 3B, PWR was first encountered at 27 feet bis and extended 50 feet to a depth of 77 feet bis. Below the PWR is a 6-foot zone of highly fractured bedrock situated above the competent bedrock detected at 83 feet bis. This monitoring well was screened from 69 to 79 feet bis. Therefore, the well screen intercepts about 8 feet of a highly weathered silty-sand interval similar to that encountered in MWl2B as weil as 2 feet of the highly fractured bedrock. The higher hydraulic conductivity obtained from the slug test at MW! 3B of 3.63 feet per day may reflect the impact of the higher permeability of the highly fractured bedrock. Bedrock Aquifer The hydraulic conductivity of the bedrock is generally I to 20 feet per day, although large, localized di ffercnces may occur due to fracturing (Cardinell, ct. al., 1989) Record of Decision -Sigmon's Septic Tank Site 16 Monitoring well MW I_ 1 C is screened from 52 to 62 feet bis. The screened interval includes 8 feet of competent bedrock and a 2 foot interval of extremely weathered bedrock (57 to 59 feet bis). The hydraulic conductivity obtained from the slug test is 10.3 ft/day. Although this value is higher than that obtained in the wells screened across the PWR, it is probably biased high due to the zone of extremely weathered bedrock that the screen intercepts. 5.1.5 Hydrology 5.1.5.1 Surface Water Iredell County lies within two river basins, the Catawba River basin in the southeastern portion and the Yadkin River basin in the northwest (Mundorff, 1950). U.S. Highway 21 follows the divide separating the Catawba and the Yadkin River basins northward from Mecklenburg County to Troutman and then northwestward followed by a rural road to Alexander County (LeGrand, 1952). The Site is located in the southeastern quadrant of Iredell County within the Catawba River basin (USGS, 1993). The Site is situated on a ridge between two unnamed intermittent streams that bound the Site on the north and south (Figure 4). Site elevations range between approximately 910 feet ams! on the western portion of the Site and 960 feet ams! near the southeast edge of the Site. Surface drainage generally flows in a southwesterly direction channeled by the two unnamed intermittent streams that flow into the Catawba River approximately 1.5 miles to the southwest (USGS, 1993). Effecti','.e recharge in the Piedmont region of North Carolina is temporally and seasonally variable. Heath (1994) provides a thorough discussion and analysis of the effect of seasonal variability of effective recharge in North Carolina. The seasonal change in recharge and discharge areas are significant and greatly affect the Site hydrology and ground water transport. The intermittently flowing unnamed streams that drain the Site are a key feature in understanding stream flow and ground water discharge. During wet seasons the extent of perennial flow increases up-stream. This indicates a temporary and dynamic increased area of ground water discharge. During dry seasons the extent of perennial flow decreases up-stream indicating a decreased area of ground water discharge (Heath, 1994). · Record of Decision -Sigmon's Septic Tank Site 17 Figure 9 shows the Site with a vertical exaggeration that depicts the Site location with local topography and drainage. Qualitative ground water flow paths are also shown. At the Site, the steep ground water gradients, deep incision of the streams into the topography and relatively shallow bedrock suggest as the streams drain the saprolite, they act as hydraulic divides to shallow ground water flow. Contaminated water from the Site flows toward the streams and not toward areas north or south of the streams. This conceptualization is consistent with a general conceptual model for the Piedmont proposed by LeGrand (2004). LeGrand states "The path of natural groundwater movement is relatively short. it is almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. Groundwater rarely passes beneath a perennial stream to another, more distant, stream. Thus the concept of a local slope-aquifer system applies." Figure 10 shows a conceptual view oflocalized slope-aquifer systems. Similar slope- aquifer systems, as shown by System A and System B in Figure IO are present on the oppoSite sides ofan inter-stream topographic divide. Both of the intermittent unnamed streams that drain the Site are conceptualized in this manner. These streams are the most likely natural discharge area for all ground water beneath the ridge on which the Site is situated. The streams define the probable limit of groundwater contamination from the Site. The shallow stream-side monitoring wells installed for evaluating the progress of MNA will monitor groundwater at the end of individual flow paths in water compartments like those illustrated on Figure I 0. 5.1.5.2 Ground Water The available hydrogeologic data indicate the surficial and bedrock act as one aquifer system. There is no confining layer between the surficial and bedrock aquifers. Ground water generally occurs under unconfined (water table) conditions within the surficial and bedrock units. The hydraulic boundaries of the surficial aquifer are the unnamed tributaries of the Catawba River, including the unnamed streams which drain the area around the Site. The Site is located on a topographic ridge where ground water recharge will be directed predominantly downward. Recharge occurs under topographic highs and local discharge occurs to the nearest perennial pond or stream. Percolating water flows vertically to the water table then flows to a point of discharge down gradient. Consequently, hydraulic Record of Decision -Sigmon's Septic Tank Site 18 gradients in the upland areas are generally down, and subsequently up in the areas of discharge. Deep within the bedro~k aquifer, there may be regional flow and discharge into the Catawba River. Rock cores and borehole geophysical data collected elsewhere in the Piedmont suggest that bedrock fractures greater than 350 feet below the top of the bedrock are not common, and where present, many are healed by mineralization. Deep fractures are considered to provide an insignificant amount of flow in the bedrock aquifer (LeGrand, 2004). Nonetheless, deep flow patterns within the bedrock can be strongly influenced by pumping in bedrock wells. Ground water levels collected in May 2004 (Figure 11) indicate a general southwesterly ground water flow direction following the local topographic divide. Substantial divergent ground water flow occurs to the southwest and west-northwest away from the topographic divide to the unnamed intermittent streams. Hydraulic gradient ranges from 0.005 to 0.0 I feet per foot. Ground water level measurements collected in April 2008 also indicate a general southwesterly ground water flow direction in the local vicinity of Site (Figure 12). The similarity of the two potentiometric surfaces six years apart is indicative ofa stable ground water flow system. 5.1.6 Ground Water Contamination Summary Originally, the concern for contaminated groundwater at this Site was due to cxceedances for nitrates and voes in some on-Site wells. Nitrates, probably from the disposal of septic waste, arc highly mobile and have not been observed in recent sample events. Nitrogen particularly in the form of nitrate is a relatively mobile contaminant in groundwater. High levels of nitrogen may no longer be present at the up gradient end of the flow paths because septic waste discharge ceased around 1992. Total nitrogen will be monitored in the stream-side wells to verify the removal of nitrogen from the flow system at the ends of the flow paths close to the natural discharge area. One voe (1,4- dichlorobenzene) has been detected in one well on Site. No other voes have ever been detected in any other well during this investigation. Elevated levels of arsenic, iron and manganese have been detected in some monitoring wells, but a well defined plume has not'been identified. The data presented on Figure 14 Record of Decision -Sigmon's Septic Tank Site 19 shows that elevated levels of arsenic, iron and manganese are not detected in any well which is not between the streams on-Site or down gradient to the west. In general, metals contamination in groundwater is limited to areas around the stream near the north edge of the property, and to areas at or near the south edge of the property to the stream located south and southwest of the property. When supplemented by data regarding a more mobile metal such as sodium, the distribution of metals contamination in groundwater is more apparent (Figure 16). The elevated levels of sodium observed in some monitoring wells probably are due to decades of evaporation of septic waste in the ponds, lagoons and trenches at the Site. The plume interpretation presented in Figures 16-19 is based on the hydrogeologic conceptual model described in Section 5.1.5.1 and the available metals results for sodium, arsen\c, iron and manganese. In this model, the property is located on a ridge between two streams which converge about a mile down gradient from the Site. The streams are the natural discharge area for groundwater contamination at the Site. Groundwater contamination moves from within flow compartments like those shown on Figure IO from source areas on the ridge to the streams. The sample results for sodium in groundwater provide additional evidence that flow paths from the Site are limited the area generally between the streams to the point where the streams converge west of the Site. The following figure shows all of the sodium analyses which have been performed in this investigation. The results from 9 wells were selected to be background wells because of the distance to the wells from the Site. Wells PW36 and PW37 are shown on Figure 14. Wells PW43, PW44, PW45, PW46, PW47, PW64 and PW65 are too far from the Site to be shown on Figure 14. The geometric mean of the sodium results from these wells is plotted as a solid red line. The geometric mean of the sodium results in these selected background wells is 5,585µg/L. The arithmetic mean is 5,611 µg/L, which is not significantly different indicating that the range (lowest to highest value) of the data used is not very large. All of these wells are too far away and too far up gradient from the Site to be effected by Site related activity. Other estimates of the mean sodium concentration area groundwater can be made (See section 5.1.7.3). The red squares on the figure below are the results of sodium analyses from other private wells closer to the Site. The same wells were not always measured in each event between 2002 and 2008, but generally, it appears that the range in sodium values in the other private wells (red squares) did not change during this time. It might be argued that sodium concentrations in these wells are similar to the selected background wells, bracketing the mean sodium concentration between 5,000 and I 0,000 Record of Decision-Sigmon's Septic Tank Site 20 µg/L.. But some of these wells are close enough to the Site to cause concern for the effects of Site-related activities simply because of their proximity to the Site. However, distribution of sodium results around the geometric mean of the selected background wells suggests that these closer private wells probably are part of the same population as the selected background wells. The difference between sodium concentration in most of the private wells and the sodium results for wells MWIOB, MWI lC, MWl2B, MWl3B, MWl4, MWl7C and PW08 is clear in the figure below. The levels of sodium wells are different and these wells are not part of the same population. All of these wells with elevated sodium levels are either on- Site or down gradient from the Site, and all of these wells except PW08 are between the streams. This interpretation provides evidence to limit the extent of Site related contamination only to the Site, areas immediately adjacent to the property an_d the ridge between the streams down gradient from the Site to the point where the streams converge. The shallow stream-side monitoring wells installed for evaluating the progress of MNA will monitor groundwater at the end of individual flow paths in water compartments between the source and the point where the streams converge west of the Site. Sigmon Septic Tank Site Sodium_ In Monitoring Wells ·- 10,000 • B • • • • ·-~ • I • • • ~ .. L-------'-------'-------'-------'------'-----L----__J- ■ Otn.erved Normal Sodium+ MW11C Sodium .... MW13BSodium _,. MW17C Sodium -"Bilckground Sodium" + MW12BSodlum -MW1• Sodium = PW08 Sodium ...,. MW10B Sodium Record of Decision-Sigmon's Septic Tank Site 21 Private water supply wells draw water primarily from the fractured bedrock and a transition zone of partially weathered material at the contact between the saprolite and underlying bedrock. With the exception of the area near well PW08 and PW 13, Site related contamination has not been found in monitoring wells or private water supply wells across the streams north or south of the ridge (Figure 12) because these areas are not in the flow path from the Site. PW08 is near the highway on the north end of the property where a portion of the Site also is north of the stream. Elevated leve_ls of sodium · have been observed in PW08 and PW 13, but not in nearby PW48. No exceedances for other metals or VOCs have been observed in PW08 and PW 13. The elevated levels of sodium are not believed to be due to road salt or other man-made factors due to similar detections of sodium in MWI0B, MW! IC, MW12B, MW13B, MWl4 and MWl7C. The PWl3 results are inconsistent and inconclusive because the sodium decreased from 1,700,000 in January 2008 to 8,400 in December 2008 (Figure 14). Sodium may cross the stream where fractures connect a well near the stream to the Site, but this effect must be limited only to wells close to the Site and close to the streams. Bedrock fractures may make pathways to PW08, PWl3 and possibly PWI0, but the potential for contamination in the ridge to migrate to areas much beyond the streams or up gradient to the east is limited because groundwater levels in these areas are higher than in the streams. Most of the year, most of the streams typically drain the saprolite and do not recharge the saprolite. Wells near a fracture which crosses a stream may induce groundwater from the Site to cross the stream, but only if the well is relatively close to the stream. Water levels in areas away from the stream will remain higher than the stream, limiting the potential. · for contaminant movement to are~s only close to.both the stream and a near-stream pumping well. PW08 and PWI 3 may be along fractures crossing the stream channel. PW48 probably is not connected to the stream channel. Portions of the Sigmon property arc located north of the north stream, which is a groundwater flow divide that should protect private wells north of the stream from contaminated groundwater from the Site. But because of the detection in February 2008 of cadmium and thallium in well PW14, subsequent private well sample events occurred to test the concept model and directly evaluate the potential for contaminant migration beneath the streams. MCL exceedances for cadmium and thallium have not been observed at any on-Site well or any other private well, therefore these contaminants are not Site related. However, the metals detected in PWl4 caused concern over potential contaminant migration beneath the streams which might be caused by the numerous domestic pumping wells in the subdivision along Big Tree Drive (Figures 11, 12 and 14). The fear was that excessive pumping in many wells might induce contamination to flow Record of Decision. Sigmon's Septic Tank Site 22 from the Site under the stream and into these areas. Consequently, additional sample events occurred in December 2008 and July 2009. The July _2009 event was deliberately scheduled for a dry season when pumping by the private wells for lawns and swimming pools was expected to be greatest and recharge from rainfall was expected to be least due to evaporation. The results of the July 2009 are not yet posted on Figure 14, but as in the December 2008 event, the results indicate no contamination was detected above target clean-up levels in any private well. The streams drain water from the saprolite both in the ridge and in.the areas north and south of the streams and appear to effectively limit the extent of contamination mostly to areas between the streams plus a small area around PW08 and PW13 where only the mobile contaminant sodium was detected at elevated concentrations in groundwater. Groundwater from wells between the streams, particularly MWI0B, MW! IC, MWl2B, MWl3B, MWl4 and MW! 7C, has shown elevated concentrations of iron, manganese and arsenic. Iron, manganese and possibly arsenic probably are derivatives of Site related contamination through secondary enrichment of these metals (Nealson and Myers, 1992, Parsons, 2004). Secondary degradation of water quality can be caused by the degradation of chlorinated solvents disposed in ponds, lagoons and trenches at the Site along with waste from septic tanks. "Degradation reactions or excessive changes in groundwater pH and reduction-oxidation (redox) conditions may lead to solubilization of metals (e.g., iron, manganese, and potentially arsenic), formation of undesirable fermentation products (e.g., aldehydes and ketones), and other potential impacts to secondary water quality (e.g., total dissolved solids)" (r,csons, 2004). Elevated concentrations of these metals do not occur in any wells which are not down gradient from the on-Site source areas, suggesting that these metals are the result of natural attenuation of septic waste and possibly VOCs which entered the groundwater flow system in the ponds and trenches of the Sigmon Site. MCL cxceedances have occurred only in MWI IC. Two samples contained arsenic at 26µg/L and 221. But these samples were separated by one result at 4µg/L which did not exceed the MCL ( I 0µg/L). Record ofDecision-Sigmon's Septic Tank Site 23 Arsenic Contamination in MW11C /lrsenic 100 s! O> 1 C 0 ~ • 10 " C w u ...__ ~,---1 '---... l _L.--------" C 0 'II-u Dec-02 Dec-03 Dec-04 Dec-05 Dec-06 Dec-07 Dec-08 + MW11C -MCL The arsenic exceedances are irregular, and may be related to changes in oxidation- reduction potential (OPR), suggesting that increasingly aerobic conditions will result in arsenic mineral precipitation and arsenic reduction in groundwater. Changes in biological activity as carbon sources are depleted are likely to have a greater direct impact on arsenic concentrations in groundwater than precipitation of minerals due to a change in ORP. But changes in ORP are expected to have a stronger affect on iron precipitation, and partitioning of arsenic into iron-bearing solids (Ford, 2005) might explain the trend in arsenic concentrations because the trends in iron and arsenic are similar in response to changes in ORP. Metals Contamination in MW11 C 100,000 ··-------------------------~. 20 ,0000· ~ ~£':"~-~1... ........ ···1 ······· ····•,, 1,000 · 17 , ·············· /' ···················· ···················· ..................... "-----.., .................... ············•··••··· . -40 100 •l-------1-------l----+----l------" ,J----+---- 10 · .......... ~ •........... .L. -····1···············f,·._.~l .................. :: 1 • I I J · .. 1 oo Dec-02 Dec-03 Dec-04 Dec-OS Dec-06 Dec-07 Dec-08 + Arsenic + Iron + Manganese -ORP > E • The oxidation-reduction potential (ORP) levels at most wells shown on Figure 15 exceed 150 m V, except in wells down gradient from the property where iron, manganese and Record of Decision -Sigmon's Septic Tank Site 24 arsenic levels are high. ORP in these wells is typically less than 100. The ORP in well MWl lC has been as low as-80mV (See section 5.1.7.3). High OPR levels correspond with high dissolved oxygen levels. Concentrations of iron, manganese and arsenic are expected lo decrease as ORP returns to normal in areas down gradient from the release areas and dissolved oxygen levels increase. Arsenic will likely be attenuate by co- precipitation with iron minerals. The "Adsorption of arsenic in aquifers shows a common link to the abundance of Fe Fe-bearing minerals" (Wilkin and Ford, 2007) so as iron precipitates in the presence of dissolved oxygen, arsenic is expected to be incorporated into the iron oxide precipitates. Changes in ORP also are likely to be influenced by changes in biological activity. The septic waste provided both a carbon source and generated anaerobic conditions, both of which facilitated the degradation ofVOCs in the original waste stream to the point where the only VOC detected in the since 2002 has been 1,4-dichlorobenzene. This contaminant has been observed only in MW I IC (See Figure 14). Septic releases ceased in 1992. I, 4-dichlorobenzene concentrations may have been higher before 2007 and other VOCs may have been present before environmental investigations began. I, 4- dichlorobenzene may be the last VOC detected at the Site because it is more readily degradable under aerobic conditions (Wiedemeier and others, 1998), which are not present beneath the Site. Other chlorinated VOCs which degrade primarily under anaerobic conditions may have degraded first. Degradation of I, 4-dichlorobenzene may accelerate as aerobic water from up gradient moves slowly into the area. No exceedance for any other VOCs has been observed in any other well. The contaminant, I, 4-dichlorobenzene in MWI IC exceed the NC 2L (1.4µg/L), but not the Federal MCL (75µg/L). I, 4-dichlorobenzene is decreasing slowly from l 8µg/L in October 2002 to 14Jµg/L in May 2004 and l 3µg/L in January 2008. voe Contamination in MW11C 1,4-d ichlorobenzone 100 <! O> 1 C • 0 • ·~ 0 10 " • C • u C 0 u Dec-02 Dec-OJ Dec-04 Dec--05 Dec--06 Dec-07 Oec--08 • MW11C -MCL -NC2L Record of Decision-Sigmon's Septic Tank Site 25 While I, 4-dichlorobenzene concentrations are decreasing at only about I µg/L per year, a meaningful decrease in contaminant concentrations has been observed because the concentration in 2008 was only 70 percent of the concentration in 2002. I, 4- dichlorobenzene degradation in MW 11 C probably is in the asymptotic phase where concentrations change very slowly as they approach the target clean-up concentrations (See section 5.1. 7.3). If the I, 4-dichlorobenzene degradation rates continue at I ug/L/year, concentrations will approach the NC2L standard in about 20 years. The summary of groundwater contamination presented in this section leads to a recommendation for monitoring well sampling. The recommendation centers on wells with elevated metals concentrations, particularly sodium (See section 5.1.7.3). Designing the monitoring well list around sodium observations also includes wells with detections ofVOCs, arsenic, iron and manganese and only includes wells with evidence ofSite- related contamination. Wells with elevated metals concentrations and the stream-side wells will be monitored for VOCs, metals, total nitrogen, total organic carbon plus parameters measured field (pH, ORP, conductivity, turbidity dissolved oxygen and temperature plus depth to water) to evaluate relationships between basic chemistry and contaminants in the flow system. A list of wells recommended for sampling during the first year is presented in Section 9.2.2. 5.1.7 Contaminant Fate and Transport Almost all contaminant inputs at the Site occurred prior to I 990. The time lag between the last _contaminant input and current conditions has direct implication on the aging and equilibration of contaminants in the environment. Volatilization is a relatively rapid process that can occur soon after entry to the environment. Solubility also is a relatively rapid process; most of the mass of soluble contaminant can dissolve soon after entry into the environment. For partially or slightly soluble material, there could be ongoing dissolution over time as recharge may percolate through the contaminant source. Adsorption mechanisms over time may trend toward stronger bonding strength resulting in the contaminant being more tightly-bound to the sorbent (such as soil particle, organic· matter, mineral crystal). Based on the nature of the contamination at the Site and the physical characteristics of the Site, potential routes of contaminant migration likely include the following: Record of Decision-Sigmon's Septic Tank Site 26 • Slow migration due to strong binding of contaminants to surface and subsurface soil media. • Dissolution and migration with percolating precipitation (in the vertical direction from surface soil to subsurface soil to ground water). • Limited transport in ground water due to unfavorable geochemical conditions. • Overland transport of bound contaminants associated with water-eroded soil media (from surface source areas along drainage pathways to aquatic media). These migration routes are summarized further in the sections that follow. 5.1. 7.1 Soil-to-Ground Water Migration Analytical data shows similar contaminants detected in surface soil, subsurface soil, and shallow ground water. The results suggest that contaminants have migrated downward since the initial source inputs during periods of active Site use. Likely migration downward is based on the dissolution of soil-bound or soil-associated contaminants followed by the downward percolation of recharge through the soil. 5.1. 7.2 Soil-to-Surface Water/Sediment Migration Surface topography of the local area surrounding the Site is somewhat flat with gradual undulating hills and shallow surface depressions, some of which form local ponds and runoff drainage pathways (Figure 9). The area within the Site boundaries has been altered through land use and on-Site activities. Two shallow drainage pathways influence the direction of storm water runoff from the Site; one pathway originates on the Site and drains the Site to the west-southwest; the other pathway is located south of the Site, originates off-Site to the cast, and runs in a west-southwest direction. The local vegetation consists of short trees and shrubs; there arc substantial stands of tall forest to the south and east of the Site that act as wind breaks. Wind patterns through this type of vegetation could reach the Site, but dust generation at the Site likely is minimal because of the surrounding tree lines and the coverage of most of the ground surface by grasses or shrubs. Record of Decision -Sigmon's Septic Tank Site 27 In the past, eroded contaminated soil may have been carried overland in one of two directions: (I) south toward the ephemeral drainage features located to the south of the Site (e.g., unnamed drainage tributary and Davidson Pond) and (2) north toward the central portion of the Site where Sigmon Pond is located. Currently, topography supports retention of storm water in Davidson Pond on the southern portion of the Site or migration of storm water to the central areas of the Site boundary (Figure 9). 5.1. 7.3 Contaminant Migration in Ground Water Contaminants in ground water that exceed cleanup levels are I, 4-dichlorobenzene and metals. Since I, 4-dichlorobenzene is chemically stable in nature; biological degradation is the major process by which concentrations are decreased. I, 4-Dichlorobenzene can be degraded under both aerobic and anaerobic conditions (Liu, 2006). The fact that I, 4- dichlorobenzene exceeds clean up levels in only one well (MW 11 C) suggests that biological degradation is occurring at a sufficient rate to restrict migration to the immediate vicinity of the source. Numerous geochemical factors affect the mobility of metals in ground water. The most commonly cited is precipitation of minerals, such as oxides, hydroxides, or carbonates. Another common geochemical control is adsorption to soil mineral surfaces such as iron oxides and clay minerals. Adsorption or precipitation reactions may maintain dissolved concentrations in very low levels under certain conditions. These conditions include: • pH. Metals, such as lead, cadmium, thallium, manganese, and iron will be less favored therrnodynamically to precipitate or adsorb at lower pH values (and therefore be more mobile in the environment). Arsenic behaves in the opposite way, being more mobile at higher pH values (above 7). The pH of water from all monitoring and residential wells sampled was recorded at the time of sampling (Figure 15). During the 2008 sampling event, pH values ranged from 5.74 (PW36) to 11.59 (MWI 7C). Although pH values were the lowest in PW36, no cleanup level exceedances were observed. The high pl-I recorded in MW I 7C may have been caused by the cement grout introduced during the well construction, and it is therefore likely localized. Cleanup level excccdanccs were observed for iron and manganese in this well. Most of the pl-I values measured in 2008 arc between 7.0 and 8.0. Record of Decision -Sigmon's Septic Tank Site 28 • Redox potential [measured as oxidation reduction potential (ORP)]. Some trace . elements exist in different states, depending on whether conditions are oxidizing or reducing. Several metals were detected above cleanup level_s; of these metals, arsenic and manganese may vary in state over the pH and redox ranges found across the Site. Different states of an element will have different reactive properties, so changes or variations in redox environment can affect mobility. Redox potential, dissolved iron, sulfide and DO were measured at the time of sample collection for many of the ground water and surface water samples collected during the RI. The ORP values observed during 2008 ground water sampling range from 187.4 millivolts (mV) (PW04 and PW36) to -79.5 mV (MWI IC). Note that PW36 is one of the wells selected as a background well in the evaluation of salinity presented in the Ground Water Contamination Summary (Section 5.1.6). Also note that PW04 is located directly west of the Site not far from the western property boundary. The well depth is unknown, but the sample results presented on Figures 14 and 15 shows that despite it's proximity to the source areas, thi_s well is not contaminated and probably is located at the top of a flow compartment like those illustrated in Figure I 0. • Negative ORP values tend to be associated with increased metals mobility. This relationship is consistent with exceedances of arsenic, iron, and manganese being observed in MW 11 C. Laboratory analyses of sulfide and dissolved iron were also performed to help further characterize whether oxidizing or reducing conditions are present (Figure 15). As suggested by the low ORP values, MWI IC has high concentrations of dissolved iron indicating reducing conditions. MW 138 also has elevated dissolved iron concentrations. This observation is consistent with the elevated manganese concentrations observed in MW 138. DO values measured in 2008 range from 1.23 milligram per liter (mg/L) (MWl3B) to 14.8 mg/L (PW39). MWI IC also had a relatively low DO concentration of 1.89 mg/L. · These relatively low DO concentrations are consistent with the elevated metals concentrations in these wells. All of the sullide values were less than 0.2 mg/L which indicates that most ground water at the Site is under oxidizing or slightly reducing conditions. • Ionic strength. Waters of higher ionic strength (related to electrical conductivity) will inhibit trace clements from forming precipitates, compared to the same concentration of trace elements in a lower ionic strength water. Adsorption reactions arc also affected by changes in ionic strength, as more ions in solution Record of Decision -Sigrnon's Septic Tank Site 29 compete for mineral surface adsorption Sites. Conductivity measured in 2008 ranged from 0.043 millisemens per centimeter (mS/cm) (PW07) to 2.487 mS/cm (MWI IC) (Figure 15). The conductivity in MWI IC is likely caused by the high dissolved metals concentrations. The ionic strength of water can be more quantitatively calculated using results from a general chemistry analysis (i.e., major anions and cations). These analy,ses will be performed on selected monitoring and residential wells as part of the remedial action monitoring efforts. • Organic matter content. Natural organic matter often acts as a complexing agent, keeping trace elements in solution that would adsorb or precipitate in the absence of the natural organic matter. In these cases, natural organic matter would increase the mobility of trace elements. Such an occurrence is dependent on the properties of the natural organic matter, the trace element, and the mineral surface. Natural organic matter concentrations were not measured during the RI field effort but are expected to be relatively low because of the granitic composition of the bedrock, except perhaps in water contaminated by Site related activity because of the septic waste discharge to the ponds. • Bulk. composition of the water. Common inorganic constituents in water can, like natural organic matter, form complexes or precipitates with some trace elements. The relative amounts of iron, manganese, sulfate, calcium, and other ions will help determine trace element fate in the environment. Similar to ionic strength (discussed previously), a complete bulk water analysis is required for evaluating possible formation of complexes or precipitates. More complete analyses will be performed on selected wells as part of future monitoring efforts. All these properties must be accurately measured and carefully examined to assess precipitation or adsorption potential. As noted above, fate and transport of contaminants are dictated by the substrate and the chemical structure of the contaminant. While soil and water studies can clarify the substrate characteristics, the general total metals concentrations are meaningless when identifying chemical interactions. Furthermore, as demonstrated by the distribution of metals depicted in Figure 14, there are no plumes of contaminants emanating from the Site based on available information. In order to gain a better understanding of the general fate and transport behavior of the contaminants, sodium (a constituent that moves relatively freely in ground water) was used as a tracer to predict potential migration distances. While sodium does not have a regulatory screening value, very high Record of Decision -Sigmon's Septic Tank Site 30 concentrations were obser~ed in several of the wells during the 2008 RI field investigation. The highest concentration of sodium [estimated 2,800,000 micrograms per liter (µg/L)] was detected at the existing bedrock monitoring well MW! IC (Figure 14). Although high concentrations of calcium (160,000 µg/L) were also found in monitoring well MWI IC, calcium would not provide a reliable tracer since it may replace sodium in the clay structure through cation exchange reactions. The most recent sodium concentrations (2008) are shown in Figures 14 and I 6. Sodium concentrations observed in wells upgradient and away from the Site (including PW25, PW36, PW37, and PW40) suggest that sodium background concentrations range from 4,500 to 7,500 µg/L (Figure 14). Therefore, sodium concentrations below 7,500 (and possibly somewhat higher) should not be considered related to the Site. In 2002, samples of potable wells and three monitoring wells indicate elevated sodium concentrations emanating from the southern lagoons, with a high of l 00,000 µg/L detected at MW 11 C very near the southern lagoons. The elevated concentrations were oriented in a southwestern direction and to the northeast. The 2004 sampling event depicted a similar extent to 2002, with a high of 160,000 µg/L sodium at MW! IC. Elevated concentrations of sodium were also found to the north and generally surround the northern intermittent stream. The migration of sodium will be evaluated during remedial action monitoring activities. The 2005 sodium distribution depicts a southeastern gradient towards PW IO which had a sodium concentration of I 1,000 µg/L. The water level elevation contours on Figure 14 show contamination from the center of the Site could reach the stream near this well, where a fracture could complete the pathway allowing contamination to flow a short distance past the stream to the pumping well PW I 0. In 2008, the distribution of sodium was not greatly expanded, but concentrations increased substantially. Sodium concentrations of 4,600,000 µg/L, 2,800,000 µg/L, and 2,700,000 µg/L were reported at MWI OB, MWI IC, and MWl3B, respectively, all near the southern lagoons. Several isolated detections were also observed to the north; 1,700,000 µg/L at PW13, and 2,800,000 r1g/L at PWOS. Ground water flow directions interpreted from the sodium concentrations are shown (arrows) on Figure 14. None of the residential wells to the north of the Site along Big Tree Drive indicate sodium concentrations above background. The presence of high concentrations of sodium in PW8 and PW 13 suggest that ground water may have a northward component to flow, possibly caused by the pumping wells but this effect is limited only to wells Record of Decision -Sigmon's Septic Tank Site 31 close to the Site and close to the streams. This process can not occur away from the streams because the streams are groundwater flow divides in this area Several wells demonstrate that sodium concentrations are relative to the sources. Well MW I OB is located directly atop the local topographic divide similar to the southern lagoons, but is located to the east, which is generally up-slope. Inspection of Figures 14 and 15 shows the screened interval of MW I OB to be hydraulically downgradient of the lagoons, which helps explain the ho_rizontal extent. Well MWI2B also shows very high sodium concentrations although it appears to be located up gradient of the lagoons. Inspection of local topography and ground water flow directions reveals that MW12B is not up gradient, but probably within the ground water flow paths from the lagoons to the southern intermittent stream. As depicted on Figure I 6, the extent of 2008 sodium concentrations that were greater than I 0,000 µg/L is relatively limited. Since the mobility of sodium in ground water is greater than that of the trace metals it is expected that all the Site related metals would be limited to areas with elevated sodium concentrations. To assess whether this is the case, Figures 17 through 19 depict the distribution of arsenic, manganese, and iron, respectively, through time. The maps are the result of subjective mapping that includes consideration of well location and construction, dynamic ground water flow conditions, and unknown antecedent hydrologic conditions. Although the isocontours shown on the figures are approximations, they demonstrate that metals contamination is not widespread and, for the most part, contained within the areas of elevated sodium concentrations. Also ofrelevance is that the metals concentrations were low in a number of the monitoring wells with high concentrations of sodium (PW 13 and MW 1 OB). This observation suggests one of two likely possibilities; either the trace metals (such as COCs iron and manganese) are migrating more slowly and have not had time to reach these wells, or the trace metals have undergone geochemical alterations (such as precipitation) and have been rendered immobile. Evidence that metals mobility is significantly impacted by the geochemistry is provided by high metals concentrations observed in MWI lC in conjunction with the low ORP values (-79.5 mV). Record of Decision -Sigmon's Septic Tank Site 32 5.1. 7.4 Ground Water-to-Surface Water Migration Based on empirical observations of surface water features near the Site, it is possible that shallow ground water likely is connected to the several surface impoundment ponds and drainage ditches located within and around the Site. This potential interconnection suggests that ground water can emerge from the subsurface into surface features; thus, contaminated ground water can migrate from the subsurface to surface water and further downgradient along surface water drainage pathways. It is unknown if the lagoons ever discharged overland to the surface water pathway. Surface water features near the Site consist exclusively of ephemeral drainage ditches that collect stormwater and are the discharge points for shallow ground water flow at the Site. One unnamed drainage feature exists to the south of the Site, and another unnamed drainage feature carries drainage from Sigmon Pond onSite toward the west. The nearest perennial creeks or rivers are about one-half mile west and southwest of the Site (i.e., Reeder Creek and the Catawba River). Uncontrolled migration of ground water contaminants may impact several small ponds in the area: Davidson Pond to the south of the Site, Sigmon Pond within the Site boundaries, and Lambreth and Williams Ponds to the west of the Site. Sliwinski Pond lies within the drainage ditch system between the Site and the Catawba River and could receive stormwater flow originating from the Site. Geochemical conditions are favorable for metals precipitation within surface water. Oxidizing conditions exist, with the presence of iron, manganese, calcium, and barium as potential precipitating agents. Adsorption of trace metals would also take place on iron oxides. Overall, natural chemical controls are potentially in place that can limit metals concentrations and migration in the dissolved form in surface water, although more specific data is needed to verify this conclusion. Since it was determined during the OU I RI that the contaminants in the surface water/sediment do not pose a risk to human health or the environment, no additional surface water/sediment sampling was integrated into any of the remedial alternatives. 5.1.8 Summary of Conceptual Site Model The CSM integrates data on the Site characteristics with current concepts regarding environmental processes in order to understand the .contaminant problem at the Site. Contaminant sources at the Site are primarily septic tank wastes and heavy sludge. T AL metals, VOCs, and SVOCs were detected in on-Site wastes. Limited information exists Record of Decision-Sigmon's Septic Tank Site 33 on the exact location, timing, or quantities of these releases. Through the RI process, three metals and one VOC have been identified that exceed their respective cleanup levels in ground water: arsenic, iron, manganese, and I ,4-dichlorobenzene (VOC). Surface water runoff is controlled by the land surface topography that confines runoff to the unnamed intermittent streams that bound the Site to the north and south. The nearest perennial creeks or rivers are about one-half mile west and southwest of the Site (Reeder Creek and the Catawba River, respectively). Concentrations of contaminants detected in surface water, sediment, and soil (excluding the stockpile) were determined not to pose a risk to human health or the environment during the OU I RI and BHHRA Addendum for OU I (Black & Veatch, 2006; 2008). The CSM assumes that vertical recharge through the soil will leach low concentrations of contaminants to ground water. Ground water flow will be greatest in the highly weathered zone within the bedrock. Migration of contaminants is primarily controlled by a combination of attenuation processes, including adsorption, precipitation dispersion, dilution, and biodegradation. Elevated ORP values in the surficial aquifer suggest that metals will be relatively immobile and transport will be very limited within this zone. It appears that geochemical conditions become more favorable for metals transport (reducing) with depth. The highly weathered zones within the bedrock provide the most likely ground water migration pathways, although data show that there are no plumes of contamination and only limited migration has occurred in both the surficial and bedrock aquifers. The unnamed intermittent streams are conceptualized as hydraulic barriers to ground water flow and define the probable limit of ground water contamination. The Catawba River and its tributaries are the principal receptors of the Site ground water contamination. Although high sodium levels were detected in some of the potable wells, there are currently no direct exposure routes to contaminated ground water. None of the COCs in. the residential private potable wells currently exceed cleanup levels. Record of Decision -Sigmon's Septic Tank Site 34 6.0 CURRENT AND POTENTIAL FUTURE SITE USES The Site is approximately 15.35 acres in size. However it is divided into two properties the southern parcel, approximately 8.9 acres and the northern parcel, approximately 6.45 acres. A family with children resides in the home on-Site on the northern property. Private landowners also own the properties located east and west of the Site. The southern Site property is bordered by pastureland to the east and west, and by a few homes on Lauren Drive to the south. A 1.25-acre pond south of the on-Site residence is located on the northern property. Soil in the northwest corner of the pond was saturated · and a small portion was inundated up to two inches in depth. Wetland vegetation was located in the northwest corner. The Site is surrounded by a 4-foot barbed wire fence to the east, west, and south. The fence was broken in places on the east and south sides of the Site. Several trailer homes on Mustang Drive are located east of the northern Site property and several residences as well as a business, Lambrcth Grading, arc located west of this property. No trespassing signs are posted on the fences and trees. During Site visits, beer cans and balls were located near the southern boundary where the fence is missing. Residents have stated that teenagers occasionally trespass on their property. A private residence occupied by adults and children is located on-Site on the northern portion of the property. Although public water is currently available, there are a number of private well users in the area. Current and future residents living on-Site and off-Site may be exposed to contaminants in on-Site ground water. Current and·future residents living off~Site may be exposed to contaminants in off-Site potable wells. During the December 2008 potable well sampling event, COCs did not exceed preliminary cleanup levels in any potable well sampled. Construction activities may take place at the Site in the future. While undergoing construction, future construction workers may be exposed to COCs in on-Site and off- Site ground water. Once construction is complete, future on-Site workers (outdoor) may be exposed to COCs in on°Site ground water. Record ofDccision-Sigmon·s Septic Tank Site 35 7.0 SUMMARY OF SITE RISKS The baseline risk assessment estimates what risks the Site poses to human health and the environment ifno action was taken. It provides the basis for taking action and identifies contaminants and exposure pathways that need to be addressed by the remedial action. This section of the ROD summarizes the results of the BRA which includes an evaluation of Human Health receptors for the Site. An ecological risk assessment was not performed for Operable Unit 2. The ecological risk assessment conducted for the Site is documented in the ROD for OU I (EPA, 2006). 7.1 Summary of Baseline Human Health Risk Assessment for Ground Water -Operable Unit 2 7.1.1 Identification of Chemicals of Concern Carcinogenic and non-carcinogenic COCs were identified for the ground water evaluated at the Sigmon's Septic Tank Site. Non-carcinogenic COCs were identified as those chemicals of potential concern (CO PCs) that contribute a hazard quotient (HQ) of 0.1 or greater to any pathway evaluated. Cumulative Site cancer risks that exceeded I x I 0·4 are considered carcinogenic COCs. The COC in shallow ground water (surficial aquifer) is manganese. The COCs in deep ground water (Bedrock Aquifer) are 1,4-dichlorobenzene, arsenic, iron, and manganese. For the purposes of this risk assessment summary, the presentation is limited to the receptors and media of concern, which includes the current/future residential exposure to both shallow and deep ground water. The media and the exposure routes associated with the surficial and bedrock aquifers result in the greatest potential risk. The summary data for ground water is presented in Tables I and 2. 7.1.2 Exposure Assessment An exposure assessment identifies pathways whereby receptors may be exposed to Site contaminants and estimates the frequency, duration, and magnitude of such exposures. The conceptual Site model (Figure 20) illustrates the mechanisms of contaminant releases to the environment. The primary release mechanism was leaching from waste piles, Record of Decision -Sigmon's Septic Tank Site 36 former lagoons, open pits, and storage tank areas. The most significant contaminants were arsenic, iron, manganese, and 1,4-dichlorobenzene in the ground water. Based on the understanding of the fate and transport of contaminants and the potential for human contact, the following scenarios, exposure pathways, and exposure routes were quantitatively evaluated: • Current/Future On-Site and Off-Site Residents. Residents may be exposed to COCs in ground water. Potential routes of exposure for child and adult residents include ingestion, inhalation, and dermal contact with ground water while showering. • Future On-Site Outdoor Worker. Workers at the Site in the future may be exposed to COCs in ground water. The potential route of exposure for the on-Site worker is ingestion of COCs in ground water. • Future On-Site/Off-Site Construction Worker. Future construction workers may be exposed to COCs in ground water while working at the Site. The potential route of exposure for the on-Site worker is ingestion of COCs in ground water. Exposure Point Concentrations (EPCs) were calculated in accordance with EPA Region 4 policies. Human intakes were calculated for each chemical and receptor using the EPCs. For noncarcinogens, intake was averaged over the duration of exposure and is referred to as the average daily dose (ADD). For carcinogens, intake was averaged over the average lifespan ofa person (70 years) and is referred to as the lifetime average daily dose (LADD). ADDs and LADDs were calculated using standard assumptions in accordance with EPA Risk Assessment Guidance (EPA, 1989). The exposure models and assumptions are presented in Tables 4.1 through 4.4 in Appendix D of the Remedial ·investigation Report (Black & Veatch, 2009) . . Note that only risks and hazards for current/future residents are presented in this summary as they represent the greatest potential risk and justify implementation of the Selected Remedy. The risks and hazards associated with the other current and future receptors/media combinations may be found in the RI Report (Black & Veatch, 2008). Record of Decision -Sigmon's Septic Tank Site 37 7.1.3 Toxicity Assessment Toxicity assessment is a two step process whereby the potential hazards associated with route specific exposure to a given chemical are: (I) identified by reviewing relevant human and animal studies, and (2) quantified through analysis of dose response relationships. EPA toxicity assessments and the resultant toxicity values were used in the baseline evaluation to determine both carcinogenic and noncarcinogenic risks associated with each COPC and route of exposure. EPA toxicity values used in this assessment include: • Reference dose (Rills) values for noncarcinogenic effects. • Cancer slope factors (CSFs) for carcinogenic effects. Tables 3 and 4 of this _ROD summarize the toxicity values for noncarcinogenic COCs and Tables 5 and 6 summarize the toxicity values for carcinogenic COCs. Toxicological profiles of the COCs may be found in the RI Report (Black & Veatch, 2008). 7.1.4 Risk Characterization The final step of the BHHRA is the risk characterization. Human intakes for each exposure pathway are integrated with EPA reference toxicity values to characterize risk. Carcinogenic and noncarcinogenic effects are estimated separately. To characterize the overall potential for noncarcinogenic effects associated with exposure to multiple chemicals, EPA uses a HI approach. This approach assumes that simultaneous subthreshold chronic exposures to multiple chemicals that affect the same target organ are additive and could result in an adverse health effect. The HI is calculated as follows: HI= ADDI /RIDI + ADD2 /RID2 + ADDi /RIDi where: ADDi = Average Daily Dose for the ith toxicant RIDi = Reference Dose for the ith toxicant The term ADDi/RIDi is referred to as the hazard quotient (HQ). Record of Decision -Sigmon 's Septic Tank Site 38 Calculation of an HI in excess of unity indicates the potential for adverse health effects. Indices greater than one will be generated any time intake for any of the COCs exceeds its RID. Given a sufficient number of chemicals under consideration, it is possible to generate an HI greater than one even if none of the individual chemical intakes exceeds its respective RID. Carcinogenic risk is expressed as a probability of developing cancer as a result of lifetime exposure. For a given chemical and route of exposure, excess lifetime cancer risk is calculated as follows: Risk= LADD x CSF where: LADD= Lifetime Average Daily Dose CSF = Cancer Slope Factor The risks are probabilities that are generally expressed in scientific notation (e.g., I x io·6 or I E-6). An incremental lifetime cancer risk of I x I o·6 indicates that, as a plausible upper bound, an individual has a one in one million chance of developing cancer as a result of Site-related exposure to a carcinogen over a 70-year lifetime under the specific exposure conditions at the Site. For exposures to multiple carcinogens, the EPA assumes that the risk associated with multiple exposures is equivalent to the sum of their individual risks. 7.1.4.1 Summary of Noncancer Hazards Associated with the Current/Future Child Resident. The current/future child resident's noncancer.hazard is primarily attributable to ingestion of shallow and deep ground water. The noncancer His for the child resident are 36 (shallow ground water) and 16 (deep ground water). Noncancer hazard is primarily due lo the ingestion exposure of manganese in shallow and deep ground water. The highest noncancer hazards from shallow and deep ground water are summarized in the hazard assessment represented in Tables 7 and 8. Record of Decision M Sigmon's Septic Tank Site 39 7.1.4.2 Summary of Cancer Risk Associated with the Current/Future Child Resident. The current/future child resident's cancer risk ( 1.1 E-04) is primarily attributable to . ingestion of deep ground water. The cancer risk for the child resident is due to the ingestion exposure of 1,4-dichlorobenzene and arsenic and the inhalation of 1,4- dichlorobenzene. The cancer risk is summarized in the hazard assessment represented in Table 9. 7.1.4.3 Summary ofNoncancer Hazards Associated with the Current/Future Adult Resident. The current/future adult resident's noncancer hazard is primarily due to the ingestion of ground water. The noncancer HI for the adult resident is 15 (shallow ground water) and 7 (deep ground water). Noncancer hazard is primarily due to the ingestion exposure of manganese in shallow and deep ground water. The highest noncancer hazard was determined to be in the shallow ground water. The risk characterization summary is presented in the hazard assessment in Tables IO and I I. · 7.1.4.4 Summary of Cancer Risks Associated with the Current/Future Adult Resident. The current/future adult resident's cancer risks are primarily due to the ingestion and inhalation of deep ground water. The cancer risk for the adult resident of 2E-04 is attributable to the ingestion and inhalation of 1,4-dichlorobenzene and the ingestion of arsenic. The cancer risk summary is presented in Table 12. 8.0 REMEDIAL ACTION OBJECTIVES The.remedial action objectives (RAOs) describe what a proposed Site cleanup is expected to accomplish. These goals serve as the design basis for the Selected Remedy identified in this ROD. The RA Os for the Sigmon 's Septic Tank Site ground water (Operable Unit 2) is as follows: • Monitor human exposure to Site COCs in residential potable wells and Site ground water. Record of Decision• Sigmon's Scrtic Tank Site 40 • Prevent or minimize human exposure to contaminated ground water at concentrations above the cleanup levels. • Remediate and control human exposure to ground water at the Site with COC concentrations greater than cleanup levels. The ground water cleanup levels for the COCs at the Sigmon's Septic Tank Site are presented in Table 13 and include the following: · • Arsenic: Based on the maximum contaminant level (MCL), the cleanup goal for arsenic is 10 ug/L. • Iron: Based on the child resident and HI of I, the cleanup goal for iron is 11,000 ug/L. • Manganese: Based on the lifetime health advisory, the cleanup goal for manganese is 300_ ug/L. • 1,4-Dichlorobenzene: Based on the North Carolina 2L Standard, the cleanup goal for 1,4-dichlorobenzene is 1.4 ug/L. 9.0 DESCRIPTION OF ALTERNATIVES The June 2009 FS report for Operable Unit 2 evaluated seven ground water remediation alternatives. The seven alternatives were evaluated for effectiveness, implementability, and cost. Of the seven alternatives evaluated, Alternatives 3, Sa, and Sb were eliminated from further consideration and Alternatives. 1, 2a, 2b, and 4 were retained for detailed analysis. Alternative 2a, MNA, describes the Selected Remedy presented in this ROD. The remedial alternative cost comparison is included in Table 14. • Alternative I: No Action • Alternative 2a: MNA • Alternative 2b: MNA with Contingencies • Alternative 4: Enhanced Attenuation with Chemical Oxidation/Reduction Record of Decision-Sigmon's Septic Tank Site 41 9.1 Common Element of Each Remedial Alternative Institutional Controls Institutional controls (such as zoning restrictions or local ground· water use ordinances) would be applied to discourage receptor populations from inadvertently exposing themselves to contaminated ground water. Area residents would be notified of the potential for exposure to COCs from drinking wells. Implementation of the stale of North Carolina administrative controls would include a plat map and a declaration of perpetual land use restrictions documentation. 9.2 Remedial Alternatives 9.2.t Alternative 1: No Action Estimated Capital Cost: $5,263 Estimated Total O&M Present Worth Cost: $125,581 Estimated Total 5-Year Review Present Worth Cost: $75,000 Estimated Present Worth Cost: $205,844 Discount Rate: 7% Number of Years Costs are Projected: 30 Alternative I, "No Action" is required by Section 300.430(e) (6) of the NCP, to provide a baseline scenario against which all other alternatives are compared. This alternative does not involve any remedial actions. The Site would remain in its present condition and the magnitude of risk is likely to remain the same since the contaminated ground water that poses a risk to human health will remain. This alternative will not comply with the Applicable or Relevant and Appropriate Requirements (ARARs) for the Site. There is no treatment, containment, MNA or institutional control (IC) component for this alternative. The minimum activities for the no action alternative include mandatory five-year reviews over the course of a 30-year period, resulting in a total of six five-year reviews. It is assumed that sampling of two existing shallow wells for metals, two existing deep wells for metals and VOCs, and two existing potable wells would be performed for metals. Sampling would include collection of field parameters (water levels, DO, pH, ORP, and conductivity, and turbidity). Sampling would be conducted prior to each five-year review to track COC concentrations over the course of the 30-year period. Record of Decision -Sigmon's Septic Tank Site 42 9.2.2 Alternative 2a: MNA Estimated Capital Cost: $90,514 Estimated Total O&M Present Worth Cost: $631,699 Estimated Total 5-Year Review Present Worth Cost: $75,000 Estimated Present Worth Cost: $797,203 Discount Rate: 7% Number of Years Costs are Projected: 30 Alternative 2a assumes that natural attenuation ofCOCs in ground water on-Site and off- Site is likely and will be monitored over time. Following is a listing and description of the remedy components for Alternative 2a. MNA Monitoring Monitoring for natural attenuation at the Site includes installation of additional monitoring wells, sampling and analysis, and MNA assessment. New off-Site monitoring wells would be installed lo monitor natural attenuation progress and provide additional infornrntion on ground water/surface water interactions at the two unnamed intermittent streams that bound the Site to the north and south. The two streams may act as hydraulic divides to shallow ground water flow. Approximately eight shallow monitoring wells screened within the alluvium along the intermittent streams will be installed. The wells will be located in or near the stream beds since the contamination will flow to the natural discharge areas, thus allowing the natural attenuation at the end of the flow paths to be measured. The wells will be installed with short well screens (2-5 feet) and will not need to be more than 10 feet deep. Henry Push Point samples may be used as an alternate for shallow monitoring wells installations, if deemed appropriate. Water analysis including cations, anions, and organic matter will be collected to evaluate possible formation of complexes and precipitates which would allow better understanding of the geochemistry and natural attenuation potential of the ground water. An MNA ground water monitoring program to track trends in concentrations over time and MNA effectiveness will be implemented. Samples for water analysis would be collected during each quarterly natural attenuation monitoring event for one year. The list of wells sampled may be changed after the results of the first year are available. Quarterly MNA events will be conducted for one year to establish seasonal lluctuations · in the new stream-side wells. After the first year of sampling, an MNA assessment will Record ofDccision-Sigmon's Septic Tank Site 43 be conducted to determine contaminant concentration trend in the new wells and verify that clean-up in the new wells can be accomplished in a reasonable time. The frequency of future sample events will be determined during the MNA assessment and may be adjusted based on the results of the first year of sampling. For design purposes, the schedule might be assumed to be semi-annually for two years, annually for seven years, and then reduced to biennial sampling ( every two years) for the remaining for the remaining years of the remedial action duration. Concentration -trends for wells toward the Site and the center of the ridge have been established and are relatively low. Frequent monitoring is not necessary in these areas. Once trends in the new wells closer to the discharge areas are established, the time between sample events will be increased. Future MNA assessments may be conducted after each monitoring event to determine the effectiveness ofMNA and re-evaluate the frequency of subsequent sample events. The summary of groundwater contamination presented in Section 5.1.6 leads to a recommendation for monitoring well sampling. The recommendation centers on wells with elevated metals concentrations, particularly sodium (See section 5.1.7.3). Designing the monitoring well list around sodium observations also includes wells with detections ofVOCs and metals and only includes wells with evidence of Site-related contamination. Wells with elevated metals concentrations and the new stream-side wells will be monitored for the following parameters: voes, metals, total nitrogen, total organic carbon measured field parameters (pH, ORP, conductivity, turbidity dissolved oxygen and temperature) depth to water, major ions in the 1st year only including calcium, magnesium, sulfate, chloride,sodium, potassium, carbonate, bicarbonate. These analyses will permit evaluation of the relationships between basic chemistry and contaminants in the flow system. A list of wells recommended for sampling during the first year is presented in Figure 2-21 and the following table. Table X. Wells with elevated metals recommended for monitoring. Wells with Elevated Sodium Well Name Wells with elevated As, Fe or Mn Well Name Comment 1 Record of Decision -Sigmon's Septic Tank Site 44 Comment2 MW10B MW10B MW11C MW11C MW12B MW12B MW13B MW13B MW14 MW14 MW15C MW16C MW16C MW17C MW17C PW0B & PW03 PW10 PW13 Count: Manganese exceeds NC2L and Poor example of relationship may be increasing. Sodium between sodium and specific elevated. conductance. Sodium elevated. Metals (As, Fe, Good example of relationship Mn) contamination and voes between sodium & specific observed. conductance. Manganese exceeded NC2L in 2002 but not since. Sodium elevated. Manganese exceeds NC2L and is increasing. Sodium elevated. Sodium elevated. Not sampled since 2004. On-Site well close to Sodium slightly elevated. contaminated area. Only one sample analysis reported in -Feb08. On-Site well close to Sodium slightly elevated. Iron contaminated area. Only one exceeds NC2L. sample analysis reported in Feb08. On-Site well close to Sodium elevated. Iron exceeds contaminated area. Only one NC2L. Manganese exceeds NC2L. sample analysis reported in Feb08. Sodium elevated. No other indication of contamination. Specific R It . 1 • conductance trend does not esu s inconc us,ve. correspond to increase in sodium. Sodium may be increasing. Sodium trend unusual. Sodium decreased greatly from JAN-DEC 2008 while specific conductance increased. Possibly due to road salt? 12 Wells 8 stream-side wells Near stream SW of Site. Water level contours on Figure 14 shows contamination from the center of the Site could reach the stream near this well. A fracture could complete the pathway. Consider sampling in 1st year with MW12B. Well depth & construction unknown. Location should be 600 feet up gradient from Site. Sodium in nearby PW4S was normal in DECOS. No data for JANOS in PW4S. Nearest well recommended for sampling is PW0S. 20 wells to be sampled during the first year. Record ofDecision-Sigmon's Septic Tank Site 45 An MNA ground water monitoring program to track trends in concentrations over time and MNA effectiveness will be implemented. The following wells will be sampled during each event: four existing on-Site shallow monitoring wells (metals and natural attenuation parameters), four existing on-Site deep wells (metals, VOCs, and natural attenuation parameters), and eight new off-Site alluvium monitoring wells (metals and natural attenuation parameters). Sampling would include collection of field parameters (water levels, DO, pH, ORP, conductivity, turbidity, etc.). Natural attenuation parameters for metals contamination may consist of, but are not limited to, common anions, alkalinity, and total dissolved carbon. Quarterly MNA events will be conducted for one year to establish seasonal fluctuations and gather sufficient data to conduct an MNA assessment. After the first year of sampling, an MNA assessment will be conducted to determine if the contaminant concentrations are decreasing. If monitoring is continued, natural attenuation monitoring would be conducted semi-annually for two years, annually for seven years, and then reduced to biennial sampling (every two years) for the remaining 20 years of the assumed 30-year remedial action duration. MNA assessments may be conducted after each monitoring event to determine the effectiveness of MNA especially in the short term. Mandatory five-year reviews would be required over the course of a 30-year period, resulting in a total of six five-year reviews. 9.2.3 Alternative 2b: MNA with Contingencies · Estimated Capital Cost: $252,043 Estimated Total O&M Present Worth Cost: $1,037,019 Estimated Total 5-Year Review Present Worth Cost: $75,000, Estimated Present Worth Cost: $1,363,000 . Discount Rate: 7% Number of Years Costs are Projected: 30 In the event that MNA is determined to not be favorable or occurring during an MNA effectiveness assessment, or there is additional risk to human health or the environment, a treatment contingency such as injection of an oxidant/reductant in situ for enhanced attenuation as well as a contingency to supply water to residents will be implemented. Although it is unlikely based on historical potable well sampling results, for cost estimation it is conservatively assumed that city water hook-up would be necessary for Record of Decision• Sigmon's Septic Tank Site 46 two residences per biennial sampling event for the first ten years of the remedy. Bench- scale treatability testing, including collection of Site samples for parameters such as chemical oxygen demand (COD), biological oxygen demand (BOD), and total organic carbon (TOC), would be necessary to determine the appropriate in situ treatment compound. The number and depth of treatment compound injections presented as a contingency would be selected based on actual Site and field conditions established during MNA monitoring. The following is assumed: ten direct push locations injected in the alluvium and ten direct push locations injected in the regolith. For cost estimation purposes, the proprietary treatment compound ORC® is assumed to be injected twice, two years apart. This treatment product time-release over a period of approximately 12 months. A 5-foot injection radius is assumed for saprolite. The treatment dose rate assumed is three pounds per foot of saturated thickness . . If this in situ treatment compound injection contingency is applied as an enhancement to natural attenuation, MNA monitoring parameters would remain the same, but the frequency would be increased to quarterly monitoring for assessment of injection effectiveness. Monitoring well samples will be analyzed periodically for COCs and natural attenuation parameters to determine if natural attenuation processes are occurring. Mandatory five- year reviews will be required over the course of a 30-year period, resulting in a total of six five-year reviews. Potable well sampling will be conducted and the results will be evaluated accordingly. At any point during sampling, if potable well sampling results in COC exceedances, a decision would be made regarding provision of an alternate water supply. Although it is unlikely based on historical potable well sampling results, for cost estimation it is conservatively assumed that city water hook-up would be necessary for two residences· for the first ten years of the remedy. Mandatory five-year reviews would be required over the course of a 30-year period, resulting in a total of six five-year reviews. Record of Decision -Sigmon's Septic Tank Site 47 9.2.4 Alternative 4: -Enhanced Attenuation with Chemical Oxidation/Reduction Estimated Capital Cost: $409,037 Estimated Total O&M Present Worth Cost: $632,211 Estimated Total 5-Year Review Present Worth Cost: $75,000 Estimated Present Worth Cost: $1,116,248 Discount Rate: 7% Number of Years Costs are Projected: 30 This alternative consists of in situ chemical oxidation/reduction, source controls, institutional controls, informational tools, city water supply hook-up, and MNA. In situ chemical oxidation/reduction would be used to enhance natural attenuation that may be occurring. A treatment compound would be injected into the subsurface to oxidize or reduce COCs in ground water. Bench-scale treatability testing would be required to determine the appropriate treatment compound. For the metal contaminants at the Site, this would most likely be accomplished by injecting an oxidant to precipitate the metals as insoluble metal oxides. Mobilization of dissolved metals would be reduced. The treatment compound would be injected through permanent injection wells into the shallow aquifer in the vicinity of the two suspected source areas of the Site where concentrations ofCOCs in ground water exceed cleanup levels. Permanent injection wells would be installed because it is likely that more than one injection will be required. A frequency of every two years is assumed for the cost estimate for 30 years. Mandatory five-year reviews would be required over the course of a 30-year period, resulting in a total of six five-year reviews. Record of Decision• Sigmon's Septic Tank Site 48 10.0 COMPARATIVE ANALYSES OF ALTERNATIVES Four remedial alternatives survived the screening step and were evaluated with respect to the requirements in the NCP, Code of Federal Regulations (CFR) (40 CFR Part 300.430(e) (9) iii), CERCLA, and factors described in Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (EPA, 1988). Table 15 summarizes how each alternative complies with the nine evaluation criteria specified in the NCP. The nine evaluation criteria include the following: Threshold Criteria I. Overnll Protection of Human Health and the Environment-Eliminates, reduce, or controls health and environmental threats through institutional or engineering controls or treatment. 2. Compliance with ARARs -Compliance with Federal/State standards and requirements that pertain to the Site or whether a waiver is justified. Balancing Criteria 3. Implementability -Technical feasibility'and administrative ease of conducting a remedy, including factors such as availability of services. 4. Short-Term Effectiveness -·Length of time to achieve protection and potential impact of implementation. 5. Long-Term Effectiveness and Permanence -Protection of people and environment after cleanup is complete. 6. Reduce Toxicity, Mobility, or Volume by Treatment-Evaluates the alternative's use of treatment to reduce the harmful effects of principal contaminants and their ability to move in the environment. 7. Cost -Benefits weighed against cost. Modifying Criteria 8. State Acceptance -Consideration of State's opinion of the Preferred Alternative( s ). 9. Community Acceptance -Consideration of public comments on th~ Proposed Plan. Record of Decision-Sigmon's Septic Tank Site 49 10.1 Description of Criteria 10.1.1 Overall Protection of Human Health and the Environment Each remedial alternative is evaluated for its effectiveness at addressing current or existing hazards to human health and/or the environment, and at protecting human health and/or the environment from future unacceptable risks in both the short-and long-term. Overall protection of human health and the environment draws on the assessments of the other evaluation criteria, especially long-term effectiveness and permanence, short-term effectiveness, and compliance with ARARs. In general, the risk of exposure to contaminants can never be completely eliminated-by MNA remedies like Alternatives 2a and 2b. If geochemical conditions stabilize to those favorable to high ORP and pH, there would be little difference between treatments versus MNA in terms of protection of the environment. 10.1.2 Compliance with ARARs CERCLA Section 121 ( d), specifies in part, that remedial actions for cleanup of hazardous substances must comply with requirements and standards under federal or more stringent state environmental laws and regulations that are applicable or relevant and appropriate (i.e., ARARs) to the hazardous substances or particular circumstances at a Site or obtain a waiver [see also 40 CFR 300.430(1) (I) (ii) (B)]. ARARs include only federal and state environmental or facility citing laws/regulations. In addition, per 40 CFR 300.405(g) (3), other advisories, criteria, or guidance may be considered in determining remedies (To- Be-Considered [TBC] guidance category). Chemical-Specific Requirements Chemical-specific ARARs are usually health or risk based numerical values limiting the amount or concentration of a chemical that may be found in, or discharged to, the environment. Some ARARs apply state-wide while others are based on Site-specific calculations. All of the ARARs provide some specific guidance on "acceptable" or "permissible" concentrations of contaminants in applicable media. Generally, cleanup must attain the most stringent of multiple chemical-specific ARARs. Table 16 lists chemical-specific ARARs for the Site that may be applicable or relevant and appropriate. The MCLs of the Safe Drinking Water Act (SOWA) and the Federal Record of Decision -Sigmon's Septic Tank Site SO Ambient Water Quality Criteria of the Clean Water Act are examples of chemical- specific ARARs. Other sources of chemical-specific ARARs are identified in the CERCLA Compliance with Other Laws Manual Part I (EPA, 1988b ). Location-Specific Requirements Location-specific ARARs consist of regulations or rules that can restrict (often indirectly and inadvertently) one or more remedial options from being implemented at the Site if doing so would adversely impact an otherwise protected resource. These include the_ protection of wetlands, floodplains, historic Sites or landmarks, coastal zones, coastal barriers, rare and endangered species, and cultural resources. Table 17 lists sources of location-specific ARARs for the Site that may be applicable or relevant and appropriate. Examples of location speci fie ARA Rs may be found in the Archaeological and Historical Preservation Act of 1974, the Federal Protection of Wetlands Executive Order 11990, and the Endangered Species Act of 1978, Fish and Wildlife Conservation Act. Other sources of location-specific ARARs are identified in the CERCLA Compliance with Other Laws Manual Part I (EPA, 1988b ). Action-Specific Requirements Action-specific ARARs specify how a remedial alternative must be achieved, and arc usually technology-based or activity-based directions or _limitations that control actions taken at hazardous waste Sites. Action specific ARARs are triggered by the types of remedial action alternatives under consideration. Table 18 lists sources of action-specific ARA Rs for the Site that may be applicable or relevant and appropriate based on potential remedial action alternatives. The following also may be applicable or relevant and appropriate: (I) design standards affecting the construction of a remedy; (2) performance standards affecting operation of a remedy, specifically, treatment requirements and management of residuals; and (3) discharge standards for a particular process. For all CERCLA remedies, the remedial action is exempt from having to obtain permits. However, any substantial requirements of applicable permits, such as discharge limitations, must be met in the remedy. Any improvements to the system must comply with all applicable state rules and regulations. Such requirements are usually set by the state, if the state is authorized to administer the federal program. Record ofDecision-Sigmon's Septic Tank Site 51 To Be Considered (TBC) Criteria TBC criteria are non-promulgated, non-enforceable guidelines, or criteria that may be useful for developing a remedial action or that are necessary for evaluating what' is protective to human health and/or the environment. Examples of TBC criteria include the following: • Drinking water health advisories (e.g., EPA document 822/F-97/009; Office of Water Risk-Specific Doses, EPA Carcinogen Assessment Group and EPA Environmental Criteria) -Presents non-enforceable guidance for drinking water suppliers recommending a level of contamination in drinking water to protect consumer acceptance of the water resource and provide a margin of safety from toxic effects. This represents the dose of a chemical in milligrams per kilogram of body weight per day (mg/kg/BW/day) associated with a specific risk level (i.e., I o-6 additional cancer frequency). Alternatives 2a would protect the public and the environment from risks posed by . contaminated groundwater at the Site by effectively implementing institutional controls that would minimize those risks. A risk would remain until groundwater contaminant concentrations decreased below the concentrations of the health-based remedial goals. Groundwater monitoring would be implemented to monitor the effectiveness of natural attenuation processes. Over a period of time, it is expected that the proposed alternative would protect the public and the environment through eventual remediation of the contaminated groundwater by natural attenuation. Meeting location-specific ARARs might be achieved by having minimal to negligible impact on important clements of the physical environment at and surrounding the Site. Since the Site is located within a relatively unpopulated area with no known cultural assets located on-Site or nearby, location-specific criteria likely would be met by all alternatives, even the No Action alternative. Action-specific criteria relate to limitations or parameters by which a particular remedial action is to be implemented. As such, all three alternatives would achieve their specific action-specific criteria to the same degree. The No Action alternative was assumed to be slightly better at achieving location-specific and action-specific ARA Rs by its lack of any active remedy components. Record of Decision -Sigmon's ~cptic Tank Site 52 10.1.3 Long-Term Effectiveness and Permanence Each alternative is assessed for its long-term effectiveness and permanence in addressing hazards at the Site and for the relative degree of certainty of remedial success if implemented at the Site. Factors considered when assessing this criterion include: • The magnitude of residual risk/hazard from untreated contaminant(s), waste, or treatment residuals anticipated to remain at the conclusion of the remedial activities. Pertinent residuals characteristics that impact this assessment are the degree that they remain hazardous, their toxicity/mobility/volume (T/M/V) and their propensity to bioaccumulate. • The adequacy and reliability of controls such as containment systems and institutional controls needed to manage treatment residuals and untreated waste. This factor addresses the uncertainties associated with land disposal for providing long-term protection from residuals; the assessment of the potential need to replace technical components of the alternative; and the potential exposure pathways and risks posed should the remedial action need replacement. • The long-term impacts on the surrounding environment of the remedial alternative's activities and processes. Alternatives that physically remove contaminants from the Site media provide the most protection for the longest period of time (such as contaminants present at the initiation of the remedial action do not return to the Site). MNA remedial alternatives provide a somewhat shorter period of protection due to the length of time required to achieve the target clean-up levels. The long-term effectiveness and permanence of oxidation/reduction-based remedies rely on the long-term stability of the geochemical conditions for long-term protectiveness. Long-term permanence of Alternatives 2a, 2b, and 4 requires some long-term maintenance and monitoring due to the small possibility of Site conditions reverting back to low ORP and pH. Site conditions are not expected to revert to low ORP and pH conditions while land use on the Site resembles current land use on adjacent properties. Residential land use in adjacent areas has maintained stable aquifer conditions. Any future, non-polluting land use would be expected to do the same. Record of Decision-Sigmon's Septic Tank Site 53 10.1.4 Reduction of Toxicity/Mobility/Volume through Treatment The degree to which each alternative employs recycling or treatment that reduces T/M/V is assessed for each alternative, including how treatment is used to address the principal threats posed by the Site. Factors considered as appropriate include the following: • The treatment or recycling processes that the alternaiive employs and the materials they are designed to treat. • The amount of hazardous substances, pollutants, or contaminants that will be destroyed, treated, or recycled. • The degree of expected reduction ofT/M/V of the waste due to treatment or recycling and the specification of which reduction(s) are occurring. • The degree to which the treatment is irreversible. • The type and q~antity of residuals that will remain following treatment, considering the persistence, mobility, toxicity and propensity to bioaccumulate such hazardous substances and their constituents. • The degree to which treatment reduces the inherent hazards posed by principal threats at the Site. Alternatives 2a, 2b, and 4 all have some form of attenuation as a primary remedy activity for contaminated water. Reduction of toxicity and volume in-contaminated water is achieved over time in both alternatives; however it is achieved at a faster rate in Alternative 4. Conversion of metal COCs from dissolved to solid (insoluble) forms effectively reduce the toxicity and volume of contaminated water. The mobility ofCOCs in contaminated water may be eliminated in all alternatives. Based on this analysis, the alternatives are equal al reducing T/M/V. 10.1.5 Short-Term Effectiveness Each alternative is assessed for its short-term effectiveness in addressing hazards encountered or created at the Site during implementation and operation of the remedial alternative. Factors considered when assessing this criterion include: • The level of protection enjoyed by the community or adjacent populations during preparation, construction, start-up, operation, close-out, termination, and demobilization of the alternative's activities and processes. Record of Decision-Sigmon's Septic Tank Site 54 • The level of prntection enjoyed by remedial workers or operators during preparation, construction, start-up, operation, close-out, termination, and demobilization of the alternative's activities and processes. • The length of time ("remediation period") needed for the alternative to achieve all remedial action objectives. • The short-term impacts on the surrounding environment of the remedial alternative's activities and processes. The short-term effectiveness of remedial alternatives relates to how well human health and the environment are protected (the first threshold criterion) and attains ARARs (the second threshold criterion) during implementation. The No Action alternative and Alternatives 2a and 2b are the best approaches for minimizing added exposure or risk to receptors in the short-term. In some cases, implementation of the alternatives could temporarily increase risk and exposure pathways to receptors. Alternatives 2a, 2b, and 4 could disrupt the local environment to some degree. Alternative 2b requires the construction of2 chemical oxidant/reductant injection wells and requires the construction of monitoring wells. Alternative 4 requires the construction of20 injection wells as well as the construction of monitoring wells. The effectiveness of remedial actions at ensuring short-term protection during implementation of a remedial action depends on the care and attention to detail exhibited by the remediation personnel. 10.1.6 Implementability The ease or difficulty of implementing each alternative was assessed by considering the following types of factors as appropriate: • Technical feasibility, including technical difficulties and unknowns associated with the construction and operation ofa technology, the reliability of the technology, case of undertaking additional remedial actions, and the ability to monitor the effectiveness of the remedy. • Administrative feasibility, including activities needed to coordinate with other offices and agencies and the ability and time required for obtaining necessary approvals and permits from other agencies (e.g., off-Site disposal). • Availability of services and materials, including the availability of adequate off-Site treatment, storage capacity, and disposal capacity and services. Record ofDccision-Sigmon's Septic Tank Site 55 • Availability of necessary equipment and specialists, and provisions to ensure any necessary additional resources. • Availability of services and materials. • Availability of prospective technologies. Implementing remedial alternatives involves design, planning, construction or installation, and operation of the various mechanical and human components ofremedial actions. The efficiency with which an alternative can be installed and operated impacts how well an alternative achieves its level of protection (the first threshold criterion) and attains ARARs (the second threshold criterion). In some cases, implementation of the alternative could be technically difficult or impossible given Site-specific limitations. The No Action Alternative is the simplest alternative to implement. Active Alternatives 2a, 2b, and 4 rely on construction activities to implement the remedy; however, no alternative involves any new or unproven technologies. Time estimates for attainment of ARARs or remedial goals are highly subjective and dependent on Site-specific conditions, operation efficiency, initial and final concentrations, and many other parameters. The No Action alternative is the simplest and quickest to implement, but it takes the longest time to achieve remedial objectives. Alternatives 2a, 2b, and 4 rely on attenuation: 2a based on MNA and 2b and 4 based on enhanced attenuation. The implementation of the remedy component addressing contaminated ground water in Alternative 4 is expected to take IO years. Once isolated, the RAOs for containment are considered met. Based on the monitoring components of these alternatives, the total time to achieve RA Os may be longer than IO years. Alternatives 2a and 2b may require longer attenuation time than Alternative 4. 10.1.7 Cost For each remedial alternative, a minus 30 to plus 50 percent cost estimate has been developed. Cost estimates for each remedial alternative are based on conceptual engineering and design and are expressed in 2009 dollars. The cost estimate for each remedial alternative consists of the following four general categories: Capital Costs. These costs include the expenditures that are required for construction of the remedial alternative (direct costs) and non-construction/overhead costs (indirect costs). Capital costs are exclusive of the costs required to operate and maintain the remedial alternative throughout its use. Direct costs include the labor, equipment and Record of Decision -Sigmon's Septic Tank Site 56 supply costs, including contractor markups for overhead and profit, associated with activities such as mobilization, monitoring Site work, installation of treatment systems, and disposal costs. Indirect costs include items required to support the construction activities, but are not directly associated with a specific item. Total Construction Costs. These costs include the capital costs with the addition of the contractor fee (at IO percent of capital costs), engineering and administrative costs (at 15 percent of capital costs), and a contingency allowance set at 25 percent of the capital costs with contractor fees and engineering and administrative costs. Present Worth O&M Costs. These costs include the post-construction cost items required to ensure or verify the continued effectiveness of the remedial alternative. O&M costs typically include long-term power and material costs (i.e., operational cost of a waler treatment facility), equipment replacement/repair costs, five year review, and long-term monitoring costs (i.e., labor and laboratory costs), including contractor markups for overhead and profit. Present worth analysis is based on a 7 percent discount rate over a period of 30 years. Total Present Worth Costs. This is the sum of the total construction costs, capital costs, and present worth O&M costs and forms the basis for comparison of the various remedial alternatives. The cost criterion is the simplest lo rank since numeric rankings will be inversely related to the dollar value of the cost estimate for the alternatives; thus, the alternatives, ranked from least expensive lo most expensive are: Alternatives I, 2a, 4, and 2b. Ranking order is subject to change if cost estimates are recalculated under different assumptions or with improved information. Cost estimates provided at this stage of the CERCLA process are only accurate lo within -30 percent and +50 percent; there could be substantial overlap in cost estimates if ranges are considered. Estimated costs associated with each of the remedial alternatives are summarized in Table 15, Cost Summary for Remedial Alternatives. The estimated cost for Alternative I is the least expensive at $205,844; Alternative 2a, the Selected Remedy described in this ROD is $797,203; Alternative 2b cost is the most expensive at $1,363.062, followed by Alternative 4 at $1,116,248. Record of Decision -Sigmon's Septic Tank Site 57 10.1.8 State Acceptance The State of North Carolina, as represented by the NCDENR, has assisted in the Superfund process through the review of the Rl/FS documents and has actively participated in the decision making process. The State has concurred with the selected remedy in this ROD. 10.1.9 Community Acceptance The EPA conducted a public meeting to present the Proposed Plan on July 9, 2009, at the Iredell County Public Library, Statesville, North Carolina. At this meeting, representatives from EPA, NCDENR, Iredell County, and major property owners answered questions about current conditions at the Site and the remedial alternatives under consideration. EPA received no comments during the comment period held from July 3 lo August 3, 2009; therefore, no Responsiveness Summary is included in this ROD. 11.0 PRINCIPAL THREAT WASTE The NCP establishes an expectation that EPA will use treatment to address principal threats posed by a Site wherever prnctical. Identifying principal threat waste combines concepts of both hazard and risk. In general, principle threat wastes are those source materials considered to be highly toxic or highly mobile which generally cannot be contained in a reliable manner or would present significant risk to human health or the environment should exposure occur. Conversely, non-principal threat waste is those source materials that gen~rally can be reliably contained and that would present only a low risk in the event of exposure. The manner in which principal threats are addressed generally will determine whether the statutory preference for treatment as a principal element is satisfied. The ground water contaminated with 1,4-dichlorobenzenc and arsenic is not considered to be "principle threat wastes." Through MNA, the response action will protect human · health and the environment, and restore the impacted ground water resource to beneficial use. The EPA has determined the future use for the Site is residential. Record of Decision -Sigmon'•s Septic Tank Site 58 12.0 THE SELECTED REMEDY The Selected Remedy for ground water meets the requirements of the two mandatory threshold criteria: protection of human health and the environment and compliance with ARA Rs while providing the best balance of benefits and tradeoffs among the five balancing criteria: long-term effectiveness and permanence, short-term effectiveness, implementability, reduction ofT/M/V through treatment, and cost. The selected remedy also includes flexibility, to the maximum extent practical, to allow for future redevelopment of the Site. EPA received no comments from the State ofNorth Carolina,. local municipalities, and the community. 12.1 Description of the Selected Remedy Following is a description of the Selected Remedy for ground water. EPA does n'ot expect significant changes lo this remedy. However, any changes to the remedy described in this ROD would be documented using a technical memorandum in the Administrative Record, an Explanation of Significant Differences, or a ROD Amendment, as appropriate and consistent with the applicable regulations. The Selected Remedy described in this 2009 ROD addresses risks to human health and ·the environment from Operable Unit 2 (ground waler) at the Site. EPA proposes MNA as a remedy for contaminated groundwater at this Site. The remaining contaminants which exceed an ARAR in existing monitoring wells will be monitored for VOCs, metals, particularly iron, manganese, arsenic, nitrate sodium and appropriate natural attenuation parameters according lo EPA guidelines for MNA of inorganic materials (Ford and others, 2007). Several wells will be installed along the streams above the confluence. These wells will be shallow, probably no more than IO feet deep with short well screens installed just below the water table. These wells will be used to sample groundwater quality at the end of the flow path between the source area and the natural groundwater discharge area in the streams. These observations suggest that MNA is an appropriate remedy for contaminants at this Site: Contaminant concentrations are very low. The only MCL exceedance is for arsenic. This arsenic exceedance occurs only in one well (MW! IC). Only one VOC has been detected. The concentration of 1,4-dichlorobenzene exceeds the NC2L standard, but does not exceed the MCL. The concentration of 1,4-dichlorobenzene is decreasing and is expected to approach the NC2L standard in about 20 years. Record of Decision-Sigmon's Septic Tank Site 59 Four different processes related either to source control or Monitored Natural Attenuation arc expected to reduce future concentrations of iron, manganese and arsenic in groundwater: a.) The amount of contamination leaching to groundwater will be reduced by removal of the stockpiles of contaminated soil. b.) Reductive dechlorination will continue to deplete VOCs, particularly 1,4- dichlorobenzene. c.) ORP levels will return lo normal by dilution as normal water flows into the area from up gradient, precipitating metals, particularly iron, and further degrading 1,4-dichlorobenzcne. Arsenic is expected to be incorporated into precipitated iron oxide minerals. d.) ORP and dissolved oxygen levels will return to normal as biological activity diminishes when Site-related carbon sources are depleted, reducing the rate of secondary enrichment of metals, particularly arsenic. Simultaneously, these changes will induce co-precipitation of arsenic with iron minerals. 12.2 Summary of Estimated Remedy Cost The total present worth for Alternative 2a is $797,213. The estimated capital costs are $90,514, the five-year review costs are $75,000 and the estimated total O&M present worth is $631,699. The details of this cost estimate are presented in the detailed cost summary in Table 19. The information in this cost estimate for the Selected Remedy for ground water is based on the best available information regarding the anticipated scope of the response action. Changes in the cost elements are likely to occur as a result of new information and data collected. Major changes may be documented in the fonn of a technical memorandum in the Administrative file, an Explanation of Significant Differences, or a ROD amendment. This is an order-of-magnitude engineering cost estimate that is expected to be within +50 to -30 percent of the actual projected cost. 12.3 Expected Outcomes of the Selected Remedy The ground water monitoring will ensure that MNA is adequately meeting the ground water cleanup criteria. Record of Decision 4 Sigmon's Septic Tank Site 60 12.4 Future Land Use Ground water will be suitable for use as a drinking water resource o_nce cleanup goals noted in Table 13 are met. 12.5 Final Cleanup Levels The final cleanup levels and the basis for the cleanup levels are included in Table 13. These cleanup levels are protective of human health and the environment. 13.0 STATUTORY DETERMINATIONS In Section 121 ofCERCLA and the NCP, the lead agency must select remedies that are protective of human health and the environment, comply with ARARs (unless a statutory waiver is justified), are cost-effective, and utilize permanent solutions to the extent practicable. In addition, CERCLA includes a preference for remedies that employ treatment that permanently and significantly reduces the M/T/V of hazardous wastes as a principal element. The following sections discuss how the selected remedy meets these statutory requirements. 13.1 Protection of Human Health and the Environment The Selected Remedy for ground water will protect human health and the environment by: • Preventing unacceptable exposure risk to current and future human populations presented by direct contact, inhalation, or ingestion of contaminated ground water. • Restoring the impacted ground water resource to beneficial use. 13.2 Compliance with Applicable or Relevant and Appropriate Requirements The Selected Remedy for ground water will comply with federal and state ARARs that have been identified. No waiver of any ARAR is being sought for the ?elected remedy. State ARARs apply only when they arc more stringent than the corresponding federal Record ol'Decision-Sigmon's Septic Tank Site 61 ARAR, or where requirements from the state program have been federally authorized. The ARARs for the remedy are identified in Tables 16, 17, and 18. 13.3 Documentation of Significant Changes Pursuant to CERCLA l l 7(b) and NCP 300.430(!) (3) (ii), the ROD must document any significant changes made to the Preferred Alternative discussed in the Proposed Plan. There are no significant changes to this ROD from the Proposed Plan. Record of Decision -Sigmon's Septic Tank Site 62 14.0 REFERENCES Black & Veatch, 2006. Black & Veatch Special Projects Corp. Remedial Investigation Report, Operable Unit I for Sigmon's Septic Tank Site, Revision I. March 4, 2006. Black & Veatch, 2008. Black & Veatch Special Projects Corp. Draft Remedial Investigation Report, Sigmon's Septic Tank (Operable Unit 2), Statesville, Iredell County, North Carolina, Revision 0. June 2008. Black & Veatch, 2009. Black & Veatch Special Projects Corp. Draft Remedial Investigation Report, Sigmon's Septic Tank (Operable Unit 2), Statesville, Iredell County, North Carolina. Revision I, 2009. Cardinell et al., 1989. Alex P. Cardinell, Charles R. Barnes, W. Harold Eddins, and Ronald W. Coble. Hydrologic Environments and Water-Quality Characteristics at Four Landfills in Mecklenburg County, North Carolina, 1980-86. U.S. Geological Survey, Water-Resources Investigations Report 89-4035. 1989. Cook and Herczeg, 2000. P.G. Cook and A.L. Herczeg. Environmental Tracers in Subsurface Hydrology. Boston, MA: Kluwer Academic Publishers. 2000. Daniel, 1987. Charles C. Daniel Ill. Statistical analysis relating well yield to construction practices and siting of wells in the Piedmont and Blue Ridge provinces of North Carolina. U.S. Geological Survey WR Investigation Report 86-4132. 1987. Daniel and Harned, 1998. C.C. Daniel II[ and D.A. Harned. Ground-water Recharge to and Storage in the Regolith-Fractured Crystalline Rock Aquifer System, Guilford County, North Carolina. U.S. Geological Survey Water-Resources Investigations Report 97-4140. 1998. EPA, 1987. U.S. Environmental Protection Agency (EPA). Interim Guidance on Compliance with Applicable of Relevant and Appropriate Requirements. Office of Emergency and Remedial Response (OSWER) Directive No. 9234.0-05. July 9, I 987. EPA, 1988a .. U.S. Environmental Protection Agency .. Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (Interim Final). OSWER Directive 9355.3-0 I. EPA 540/G-89/004. October 1988. EPA, 1988b. U.S. Environmenial Protection Agency. CERCLA Compliance with Other Laws Manual (Interim Final). Part I: OSWER Directive 9234.1-01. EPA 540/G-89/006. August 8, 1988. EPA, 1988c. U.S. Environmental Protection Agency, Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, EPA/G-89/004, 1988. Record ofDccision-Sigmon's Septic Tank Site 63 EPA, 1989. U.S. Environmental Protection Agency, Risk Assessment Guidance/or Superfimd (RAGS), Volume I, Human Health Evaluation Manual (Part A), Interim Final, Office of Emergency and Remedial Response, Washington, DC, EPA/540/1-89/002, 1989 .. EPA, 2000a. U.S. Environmental Protection Agency. Institutional Controls: A Site Manager's Guide to Identifying, Evaluating and Selecting institutional Controls at Superfund and RCRA Corrective Action. Cleanups. OSWER document EPA 540/F- 00/005; Directive number 9355.0-74FS-P. September 2000. EPA, 2000. U.S. Environmental Protection Agency, Supplemental to RAGS: Region 4 Bulletins Human Health Risk Assessment Bulletins, EPA Region 4 Originally Published . in November 1995: http://www.epa.gov/region4/waste/o1iecser/healtbul.htm, 2000. EPA, 2002a. U.S. Environmental Protection Agency. National Primary Drinking Water Standard~, Drinking Water Section. July 2002. EPA, 2003. U.S. Environmental Protection Agency, EPA memorandum Human Health Toxicity Values in Superfi.md Risk Assessment, OSWER Directive 9285.7-53; December 5, 2003. EPA, 2006. U.S. Environmental Protection Agency, Record a/Decision, Summary of Remedial Alternative Selection, Sigmon 's Septic Tank Site, Statesville, Iredell County, North Carolina, September, 2006. EPA, 2008. U.S. Environmental Protection Agency, EPA Regional Screening Levels. www.epa.gov/rcg3hwmd/risk/human/rb-concentration tablc/index.htm .. June 2008. Grayson, 1980. Susan Grayson. "Minutes of Meeting in Statesville, North Carolina." NC Department of Human Resources. June 20, 1980. Grelk et al., 1998. Brian J. Grelk, Jack M. Kloeber Jr., Jack A. Jackson, Gregory S. Parnell, and Richard F. Deckro. Making the CERCLA Criteria Analysis a/Remedial Alternatives More Objective. Remediation (Spring 1998): 87-105. 1998. Groves, 1978. Groves, Michael R., Lithologic Logs of Wells in Iredell County, North Carolina, Ground water Section: Division of Environmental Management, North Carolina Department of Natural Resources and Community Development, Circular 17, 1978. Harned, 1989. Harned, Douglas A, "The Hydrogeologic Framework and a Reconnaissance of Ground water Quality in the Piedmont Province of North Carolina, with a Design for Future Study," USGS Water-Resources Investigation Report 88-4130, 1989. Record of Decision -Sigmon's Septic Tank Site 64 Heath, 1980. R. C. Heath. Basin Elements a/Ground Water Hydrology with Reference to Conditions in North Carolina. U.S. Geological Survey, Water-Resources Investigations Open-File Report 80-44, 86 p. 1980. Heath, 1994. R. C. Heath. Ground water Recharge in North Carolina: Ground Water Section, Division of Environmental Management, North Carolina Department of Environment, Health and Natural Resources. 1994. Iredell, 2001. Iredell County Mapping Office, Plat Maps. September 26, 2001. LeGrand, 1952. H.E. LeGrand and M.J. Mundorff. Geology and Ground Water in the Charlotte Area, North Carolina. North Carolina Department of Conservation and Development Bulletin 63. 1952. · LeGrand, 1967. H.E. LeGrand. Ground Water of the Piedmont and Blue Ridge Pro)!inces in the Southeastern States. U.S. Geological Survey Circular 538, _ 11 p. 1967. LeGrand, 2004. Harry E. LeGrand, SR., Hydrogeologist. A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance Manual. North Carolina Department of Environment and Natural Resources, Division of Water Quality, Groundwater Section. 2004. Liu, 2006. J. Liu. 1,4-Dichlorobenzene Pathway Map. University of Minnesota Biocatalysis/Biodegradation Database. 2006. Mundorf!; I 950. Mundorff, M.J., Flood-Plain Deposits of North Carolina Piedmont and Mountain Streams as a Possible Source of Ground water Supply, North Carolina Department of Conservation and Development, Bulletin #59, 1950. NCDENR, 2006. North Carolina Department of Environment and Natural Resources, N.C. Groundwater Quality Standards for the Protection of the Groundwaters of North Carolina, I SA NCAC 2L .0200. December 2006. NCP, 1990. National Oil and Hazardous Substances Pollution Contingency Plan, 40 Code of Federal Regulations (CFR) Part 300 (Subchapter J), Subparts A through L. www.epa.gov/oi1spill/pd1s/40cfr300.pdf. 1990. Nutter and Otton, 1969. L.J. Nutter and E.G. Olton. Ground-water Occurrences in the Maryland Piedmont. Maryland Geological Survey Report of Investigations, No. I 0. 1969. SESD, 2009. Science and Ecosystem Support Division (SESD Vanadium Background Study and Pile Characterization, Sigmon's Septic Tank Superfund Site, Statesville, Iredell County, North Carolina. Science and Ecosystem Support Division (SESD), June \ 5, 2009. Record of Decision -Sigmon's Septic Tank Site 65 Stewart, 1962. J. W. Stewart. Water-Yielding Potential of Weathered Crystalline Rocks at the Georgia Nuclear Laboratory. U.S. Geological Survey Professional Paper 450-b, 2 p. 1962. USGS, 1993. U.S. Geological Survey, 7.5 minute series, Topographic Quadrangle Maps ofNorth Carolina, Troutman, North Carolina. 1993. Ford, R.G., 2005, The Impact of Ground-Water/Surface-Water Interactions on Contaminant Transport with Application to an Arsenic Contaminated Site, EPA/600/S- 05/002 January 2005 Ford, R.G., R.T. Wilkin, R.w: Puls, 2007, Monitored Natural Attenuation of Inorganic Contaminants in Ground Water, Vol I & 2, U.S. EPA Office of Research and . Development, National Risk Management Laboratory, Ada, Oklahoma, PA/600/R- 07/139, Oct. 2007. Nealson, K.H, and C.R. Myers, 1992, Microbial Reduction of Manganese and Iron, New Approaches to Carbon Cycling, Applied and Environmental Microbiology, Feb. 1992, Vol. 58, No. 2, pp. 439-443, American Society for Microbiology. Parsons, 2004, PRINCIPLES AND PRACTICES OF ENHANCED ANAEROBIC BIOREMEDIA TION OF CH LORINA TED SOL VENTS, The Parsons Corporation, August 2004. Wiedemeier, T.H., M.A. Swanson, D.E. Moutoux, E.K. Gordon, J.T. Wilson, B.H. Wilson, D.H. Kampbell, P.E. Haas, R.N. Miller, J.E. Hansen, F.H, Chapelle, 1998, TECHNICAL PROTOCOL FOR EVA LUA TING NATURAL ATTENUATION OF CHLORINATED SOLVENTS IN GROUND WATER, USEPA Office of Research and Development, Washington DC 20460, EPA/600/R-98/128, September 1998 Wilkin, Richard T. and Robert G. Ford, 2007, MNA of Metals and In Situ Bioremediation, EPA National Risk Management Research Laboratory, Groundwater Ecosystesms Restoration Division, Ada, OK. November 15, 2007. Record of Decision-Sigmon's Septic Tank Site 66 Legend --Freeway System (National) D North Carolina D State Bnds (generalized) States (State) US Background (National and State) Canada and Mexico Background Ocean Background 75 Miles GCS NAD83, ODs "---- 150 Site Location Map Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina I Fi•t• I Legend D Site Boundary -··-Geologic Cross Section A-A' -··-Geologic Cross Section B-B' -Waste Lagoons CJ waste Pile --Intermittent Hydroline ,~, AN o 250 500 Feet Site Layout 6 ,....... ,_ ____________ ___J .__ ___________________________ S_i_g_m_o_n_•s_S_e_p_t-ic_T_a_n_k_S_it_e __________________________ _J Fig 2 ure NAD83 StatePlane NC, Feet Statesville, Iredell County, North Carolina Note: "Oft" around perimeter of pile and associated features indicates local ground surface. Footage indicated inside pile and features ., ~ is estimated height, above ground surface, at the indicated location. Figure 3 Pile Morphology Sigmon's Septic Tank Superfund Site Statesville, Iredell County, North Carolina ..,. -Intermittent Hydroline -.. Hydroline .. WaterBody ~---.,~ •• up,;,•'!,\;._··. ..,.Jr:,"'·~,, f'f·· ✓;. ,,._~-~-:,,."~~:::""fti':..!:;S;l",.'!4!~f ;p .... ·~ ..r'f',"" I.~ • N " '" "J ,:,i,.-.,.,r.,c_T.",;)-·.> ··-.f~-•. :-I Feet Sigmon's Septic Tank Site Figure m ,_A_N ___ o ____ 1-,o-oo--~ Stream Locations 8 NAD83 statePlane NC, Feet Statesville, Iredell County, North Carolina 4 --.. ...., --... --... .,. -... ---.,. --.. .. .. ... -... m A A' 1------------1.210'------------t------<538'----_;~w+---,n~-t---------<1138'--------' UWRENORMi StAIIFJCIAI. AOUIFER ,_ ................ ....., ....... _....., .................. .......,_....,._..,.. .... _..._ ....... ..._ I.AGOOH POTEHTW. SOURCE AAEA LOCATED APPROXIMI\ TB. Y 25 FEET WEST Of' CROSS SECTION LINE FRACTVREO BEDROCK AOUIFER u._ ......... ,__. ..... ....,_ .. --..'i... n o.mQ.OQICCONTAC'T CIWlHEl>-llffllED) WATEII Ll\18. Al t.lEA9'.RED APRIL. 15. tallfl)AltCWOIEWATEJI Ln(I. WAS MEAIURED MAY 20:M} Y)NIT0IINQ W£U ICRCEH IH1VIYN. IWOIE. MEAN SEA~ NOW 1121 SIGMON'S SEPTIC TANK SITE STATESVILLE, IREDELL COUNTY, NORTH CAROLINA HYDROGEOLOGIC CROSS SECTION (A·A') V !~~ HORIZOffM.IC>U 0 JODfUl 0 fllil (YUl'T1CM. EXM)(;[AA Tl0flf • fCIIQ FIGURE 5 -.. ,..., -... ---.. .. ... ... --.,. ----- .,. .. ,.. .. B 1-----540•----~79'-j--1w-f-126'-+--------""--------l--1u-+----- UIHOI.CQCC0HTACT""""8>WHOIE WEAIEO) WAT'UtLIWl.ASMlAallED...,,.._ U-, 2CIOI tDMH(.Dwt;M W4TBI LfV!l. WM~MAVXIOil) M0HfTORiHO MU. ICACCN IHTUNH.. OPEN ll0AOCU M0Nl'T0RINO WW. f'RACTUAEDaEDNX:lt IHTDNH.. LAGOON POramAI. SOURCE AREA LOCATED APPROXIMATELY 25 FEET WEST Of' CROSS SECTION LINE _.._ICAI.I l~ac.u • ,00,ut r,,ul1lCAL ECAGOEAATION • 1CDQ on£t AM9I. ...,...._ MINI SEALEWl., NQ.W tSZ1 SIGMON'$ SEPTIC TANK SITE STATESVILLE, IREDEU COUNTY, NORTH CAROLINA V POND POTENTlAI. SOURCE -LOCA TEO APPROX. 30 FEET WEST Of' CROSS-S£CTION LINE SURFICIAI. AOUIFER I ,.. ................... ...., ........... F .................................... -... ____ .._ ...... I I I I ------~ FRACTURED BEDROCI< AOtJIFER a. ............ ~ .......... ---- y ' I I I ' I --------I ---------.J t HYDROGEOLOGIC CROSS SECTION (8-8') B' FIGURE 6 HVOROOEOLOOIC ZONES HYOROGEOLOGIC TERMS Unsa 1ure1ed tono Cap,nary ,,.,oe ~ 0 Unu1u,atec1 ,egohth .. ______ _ • a: Sal\lf6110 IIQOklh Wu the,eo 010,ock ana bou1oe,1 Tr1n1,11on zone Sa1ur11ed ,one , I -.... I I I ' I I I I \ I Sheet ,01nt Bedrock SIIUClure ---i--Bedrock t11ctu,e . u 0 ... • n ... • , " . ... The Conceptual Structure of the Piedmont Hydrogeologic framework (after Cardinell et al., 1989) Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Unwu thertd becl,ock figure 7 T So~ zone Clay, silt, and sand :x: I- .J AeGldval 0 c., w a: i. Weathered boulders Unaltered rock II ,\II I -J, ,;,-~;: ~ ... ~ , ----~~ ~< .:. • I • .. · /· ···-~~ ·: ::--:-:--__.:_ ---;:K ~--~-. /. .:..·-· : -.. Cl) w Cl) ~ w a: u ~ c., z a: w :x: .... < w ~ LI. 0 w w a: c., w 0 RELATIVE PERMEABILITY INCREASES z Q V) .... w (.) Cl) < < a:: w LI. a:: >-(.) < ~ _J (.) An Idealized Weathering Profile through the Regolith, showing Relative Permeability (after Nutter and Otton, 1969). Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Figure 8 TI IL:=4 ll __________ __,L ____________________ Ap_p_ro_x-im_a_w_G_ro_u_nd_W_a_ffi_r_F_~w-P-alli_s __________ ----:-_________ ~_~ __ ~I F~9ure I Not to Scale Sigmon's Septic Tank {Sequence 2) Site , Statesville, Iredell County, Norlli Carolina la Slope Aquifer Boundary and Topographic Divide • • • • • • • Discharge Boundary - - - - - - -Companment (C) Boundary • • • ••• • • •• •• •• •• Water Table Fractures Groundwater Flow Direction Conceptual View of Double Slope-Aquifer System (from LeGrand, 2004) Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina ot to Scale Figure 10 -=---=-----_-_-_-_-_---------.:::.:::.:::.:::.:::.:::::::::::::::::--' Feet NAD83 StatePlane NC, Feet 2004 Estimated Groundw Sigmon's Septic Tanter Potential Contours Statesville Iredell C (Sequence 2) Site ' ounty, North Carolina Legend ~ Sampling Wells /',,/ Crossections ,~ • Estimat d G CJ C ~ roundwater Potential Contours ontaminant Sources D Site Boundary l . ..--,, ' 1-.. 7---..:....__~_ ... 7~{ .........__.......__ ______ '_' .........,'° l (~ ~~~ I Legend -$ Sampling Wells , ~ • Estimated Groundwater Potential Contours D Contaminant Sources D Site Boundary IQ 41 N ° 500 , ,ooo 2008 Estimated Groundwater Potential Contours Ea ~ J... Feet '----------------5-ig_m_on-•s-Se-p-tic-Ta_n_k (-Se-qu_e_nc_e 2-)-Sit-e _______________ ______. 2 f'\ NAD8J StatePlane NC, Feet Statesville, Iredell County, North Carolina _________ __. MAXIMUM CONTAMINANT LEVELS SEDIMENT Aluminum 7600 mg/kg Iron 2300 mg/kg Manganese 180 mg/kg Manganese 360 mg/kg 4-4'-DDT 7000 ug/kg 4-4'-DDT 1700 ug/kg 4-4'-DDT 3.3 ug/kg SURFACE WATER Aluminum l-87 ug/L A rsenic 10 ug/L Arsenic 0.018 ug/L Arsenic 190 ug/L Iron 300 ug/L Iron 1000 ug/L Lead Lead Manganese Legend Sample Locations Asediment ~Surface Water 15 ug/L 1.32 ug/L 50 ug/L .&Surface Water and Sediment R9 PRG RES SOIL R9 PRG RES SOIL R9 PRG RES SOIL NCSRG R9 PRG RES SOIL NCSRG -~ R4SSV R4 FRESH SWSV NCWQS ECO NATSWSV R4 FRESH SWSV NCWQS ECO R4 FRESH SWSV MCL-SMCL R4 FRESH SWSV NCWQS ECO SS-SW-01 Aluminum 560 ug/L Iron 630 ug/L SS-SD-01 Aluminum 11000 ffl{>'kg Iron 7700 mg/kg Vanadium 7700 ugl/kg SS-SW-05 AJurr,num 690 ug/l Iron 1500 Ug/l Manganese 120 ug/L SS-SD-05 Aluminum 13000 mg/kg Iron 15000 mg/kg Manganese 210 mg/kg Vanadium 34 mg/Ilg bis(2-Elhyllexl)phthala18 510 ug/kg SS-SD-10 Aluminum: ,-.. C ;;; :, 0 < • son SS-SW-06 Aluminum 3500 ug/l. Iron 7600 ug/1. Manganese 260 ug/L Lead 5.4 ug/L SS-SD-06 Alurnnum Iron Vanadium An;enic 0 11000 mg/kg 8400 mg/kg 67 mg/kg 1.6 mg/kg .. SS-SW-03 Alurrlnum 650 ug/L Iron 3000 ug/1. Manganese 180 ug/l SS-SD-03 Iron 9300 mg/kg Vanadium 17 mg/Ilg SS-SW-08 Aluminum: 2900 ug/L Alsenic: 0.94 ug/L ~on: 5400 ug/L Lead: 3.1 ug/L Manganese: 1200 ug/L ~ Mustang Lane ug/kg ug/L mg/kg PRG RES SRG ssv FRESH WQS ECO MCL SMCL NAT Micrograms per kilogram Micrograms per Liter milligrams per kilogram Preliminary Remediation Goal Residential Soil Remediation Goal Sediment Screening Value Freshwater Water Quality Standard Ecological Maximum Contaminant Le\€I Secondary Standards National SS-SW-04 Aluminum 2900 ug/l Copper 7.8 ug/L Iron 4400 ug/L Manganese 260 ug/L Lead 3.6 ug/L Aroctot 12-60 0.71 ug/l SS-SD-04 Aluninum Iron ThaRium Vanadium m C 0 .. L ow Lane 15000 mg/kg 17000 mg/Ilg 3.3 mg/kg 45mg/kg D ll >z 0 1-------iFe~., ,.ooo I Distribution of Screening Value Exceedances of in Surface Water and Sediment Sample Locations Sampled in October 2002 and May 2004 Sigmon's Septic Tank Site r-::::7 L:J Statesville, Iredell County, North Carolina -$ Monitoring Well (Regohlh) -$ Moniloring Well (PWR) Groundwater Flow Ooreciion -• Estimated Groundwaler Polential Contours -Major Road C]s,te Boundary I Cleanup level exceedances are indicated by red bold values. I I I I I I I I I m N o 1,000 2,000 Feet A. NAD83 StatePlane NC, Feet Wells Exceeding Preliminary Cleanup Levels for COCs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Contaminants of Concern and Preliminary Cleanup Levels COC lUnlts!Cleanup Levelal Source Arsenic ug/L 10 Cadmium ug/L 1. 75 Thallium ug/L 2 Vandium ug/L 15 IRegolith/Saprolite Monitoring Wells Arsenic · l ug/L I 10 Manganese ~L 50 18edrock Monitorinfl_ Wells 1,4-Dichlorobenzene ug/L 1.4 Arsenic ug/L 1 O Iron ug/L 300 Manganese ug/L 50 Vandium ug/L 16 Federal MCL N.C. 2L Groundwater Federal MCL HHRA Risk-Based RGO Federal MCL N.C. 2L Groundwater N.C. 2L Groundwater Federal MCL N.C. 2L Groundwater N.C. 2L Groundwater HHRA Risk-Based RGO r-:::7 LJ Legend ~ Potable Well ~ Monitoring Well (Regolith) ~ Monitoring Well (PWR) [DA ~-----------------_,J 0 1,000 2,000 Feet NAD83 StatePlane NC, Feet PW62 Id Parameten Id Parameters Field Pan1meters (SU) (SU) pH(SU) cl. (mS/cm) (mS/cm) Cond. (mS/cm) (mV) (mV) ORP(mV) 00 (mgll) NTU 10/2002 IM/2005 HR 6.71 HR 0033 NR 152.f NR ... NR PW-53 12/16/2008 Field Parameters 6.54 pH(SU) 0.059 Cond (mS/cm) ORP(mV) OO(mgll) Turbid NTU 12/16/2008 6.28 0.056 NR PW-52 Field Parameters pH(SU) Cond. (mstcm) ORP(mV) Notes 12/16/2008 6.11 0.109 NR NR 0.38 • DO reading may not be accurate due to damaged DO membrane NR = Not Recorded Distribution of Geochemical Parameters 8 Sigmon's Septic Tank (Sequence 2) Site .._ __________________________ s_t_a_te_s_v_i_11e_,_1_re_d_e_1_1 c_o_u_n_tY_,_N_o_rt_h_c_a_ro_l_in_a __________________________ -1 5 Legend " Wells Sampled A/ Na lsoContours ppb D Contaminant Sources D Site Boundary /Q 41 N ° ,.ooo ,,ooo Sodium Concentration over Sampling Time Period Figure ~ }l __ ______.L__ _____________ ===-='~6 · • Feet Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina NAD83 StatePlane NC, Feet ,~, .__ J..N __ o ____ ~:_:~ ___ 2.0-00___, _ ~ NAD83 StatePlane NC, Feet Arsenic Concentration over Sampling Time Period Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina $ Wells Sampled /'../ Ar lsoContours ppb D Contaminant Sources D Site Boundary ~ L:J Legend $ Well s Sampled • /'./ Mn lsoContours ppb D Contaminant Sources D Site Boundary IL:41 L.AN ___ o _____ 1 ·- 00 _ 0 ____ 2 _· 0 _ 0 _ 0 _ _, L ________________________ M_a_n_g_a_n_e_s_e_C_o_n_c_e_n-tr_a_t-io_n_o_ve_r_S_a_m_p_l_in_g_T-im_e_P_e_r-io_d _________________________ __, Feet Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina NAD83 StatePlane NC, Feet ~ ~ Legend $ Wells Sampled /'v Fe lsoContours ppb D Contaminant Sources D Site Boundary 1m-I L.AN ___ 0 _____ 1 ·- 00 _ 0 ____ 2 _• 0 _ 0 _ 0 _ __, L---------------------------lr_o_n_C_o_n_c_e_n_t_ra-t-io_n_o_v_e_r_S_a_m_p_li_n_g_T_i_m_e_P_e_r,_o_d __________________________ __, Feet Sigmon's Septic Tank (Sequence 2) Site NADSJ s tatePlane NC, Feet Statesville, Iredell County, North Carolina Legend -$-Potable Well -$-Monitoring Well (Regolilh) -$-Monitoring well (Bedrock) lntenntttent Hydroline -Hydroline -MajorRoad D Site Boundary Note: Proposed locations ror new monitoring well installation are subject to change during the remedial design. [DA ' ,__ ______________ __J 600 1,200 Feet NAD83 StatePlane NC, Feet Proposed Wells Recommended for MNA Sampling Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Figure 2-21 Primary Primary Release Source Mechanisms I Open Pits L rl I Former I--Lagoons ,-- f Waste Piles I Leaching I I Storage J-◄ Tanks Area I Leaks L Secondary Source I Surface Soil Secondary Release Mechanism Figure 20 Conceptual Site Model Sigmon's Septic Tank (Sequence 2) Sile States\'ille, Iredell Count)·, North Carolina Tertiary Release Pathways Mechanism Pathways Surface ~ Runoff Surface Water .,__ 1 subsu~ace h Infiltration _____,Groundwate;:L_J Discharge/ I Soll I Seepage I Sediment l - NA 1"ot Ar,plicahlc. (iro1mdw.11cr h the onlJ' m~-di:i 1h.ut "ill be ~-.,.:ilu:i!cJ ll1r this in,·c:1ti~ion. E,.p.:,surc route will he qu:1111,1.;111,·dy e,·:ilu:ated. Rocoptor q ~ i ~ i • I ~i ~ t j p i Ji 1f • ~ ! j j 0 j a l!•-urw R....-< ,...,-.. ... 11--NA NA NA NA NA NA °""'""'IConbel NA NA NA NA NA NA lnNllalion NA NA NA NA NA NA ,_,,..,I lne-•llor, NA NA NA NA NA NA O.rmal Contact NA NA NA NA NA NA lnc....,nlJll lng.•tJon NA NA NA NA NA NA 0.=al Co,,t.c:I NA NA NA NA NA NA ·-•tlc>n • • • • • • Dennal Ccw,tact • • • • --• • • • tncMMntal lng,hllOn NA NA NA NA NA NA 0.rnwl Conuc1 NA NA NA NA NA NA lnNllatJon NA NA NA NA NA NA Table 1: Data Summary for Shallow Ground Water Summary of Chemicals of Concern and J Medium-Specific Exposure Point Concentrations Scenario Timeframe: Future Medium: Ground Water Exposure Medium: Shallow Ground Water (Regolith Aquifer) Ground Concentration Frequency Exposure Exposure Chemical of Detected Point Statistical Water Units of Point Ingestion Concern Concentration Measure Min Max Detection Concentration and Units Inhalation Manganese 11 J 11000 J ppb 3/3 11000 ppb Max Key ppb: Parts per billion J: Estimated value Max: Maximum Concentration Table 2: Data Summary for Deep Ground Water Summary of Chemicals of Concern and Medium-Specific Exposure Point Concentrations Scenario Timeframe: Future Medium: Ground Water Exposure Medium: Deep Ground Water (Bedrock Aquifer) Soil On-Concentration Frequency Exposure Exposure Site Chemical of Detected Units of Point Point Statistical Direct Concern Concentration Measure Min Max Detection Concentration Units Contact 1,4-13 13 1/4 13 ppb Arithmetic dichlorobenzene ppb Mean Arsenic 0.91 22 J ppb 3/4 12.5 ppb Arithmetic Mean Iron 91 J 24000 ppb 4/4 9063.67 ppb Arithmetic Mean Manganese 1.7 11000 J ppb 4/4 3691.9 ppb Arithmetic Mean Key ppb: Parts per billion J: Estimated value Oral RID Table 3 NON-CANCER TOXICITY DATA--ORAUDERMAL Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina Oral Absorption Absorbed RID for Denna! (2) Primary Combined Chemical Chronid of Subchronic Efticicncy Target Uncertainty/Modifying Concern (I) Value Units 1,4-Dichlorobenzene Chronic 3.0E-02 mo/ko-dav Arsenic Chronic 3.0E-04 mg/kg-day Iron Chronic 7.0E-01 mg/kg-day Manganese Chronic 2.0E-02 mg/kg-day PPRTV = Provisional Peer Reviewed Toxicity Value IRIS= Integrated Risk lnfonnation System RID= Reference dose mg/kg---day = Milligrams per kilogram per day NA= Not applicable for Dermal (2) 100% 95% 100% 4% (I) Toxictiy values shown include COC:s in shallow and deep ground water Value Units Organ(s) 3.0E-02 mg/kg-day Liver/Dcvclonmental 2.9E-04 mg/kg-day Skin 7.0E-01 mg/kg-day Gastrointestinal Tract 8.0E-04 mg/kg-day Central Nervous Svstem (2) The dennal RID was assumed to equal the oral RID, unless an adjustment factor was found in Exhibit 4.1 of RAGS-E (EPA 2004). (3) IRIS valut.'S were confirmed against the EPA's onlinc database. April 2008; Region 9 PRG Table. October 20. 2004. Factors 1000 3 1.5 I RID: Target Organ(s) Sourcc(s) Daw(s) (3) (MM/DDIYYYY) Region 9 PRGs 10/20/2004 IRlS 04/01/2008 PPRTV 04/15/2008 IRIS 04/01/2008 Chemical Chronic/ of Subchronic Concern (I) 1,4-Dichlorobenzene Chronic Arsenic NA Iron NA Manganese Chronic IRIS= Integrated Risk lnfonnation System RfC = Reference concentration RID= Reference dose NA= Not applicable mg/m3= Milligrams per cubic meter mg/kg= Milligrams per kilogrnm per day IRIS= Integrated Risk Infonnation System Table 4 NON-CANCER TOXICITY DATA--INHALATION Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina Inhalation RfC Extrapolated RID (2) Primary Target Organ(s) Value Units Value Units 8.0E-01 mg/m3 2.3E-0I mg/kg-day Liver NA NA NA NA NA NA NA NA NA NA 5.0E-05 mg/m3 l.4E-05 mg/kg-day Central nervous system (I) Toxicity values shown include COCs in shallow and deep ground water Combined RfC Target Organ( s) Uncertainty/ Modifying Factors Date(s) (3) Source(s) (MM/DD/YYYY) IO0 IRIS 4/1/2008 NA NA NA NA NA NA IO00 IRIS 4/1/2008 (2) Inhalation RIDs were calculated from Inhalation RfCs assuming a 70 kg individual has an inhalation rate of 20 m3/day.(USEPA Risk Assessment Guidance for Superfund, Part A: December 1989). (3) IRIS values were confirmed against the EPA's onlinc dalabase, April 2008 Table 5 CANCER TOXICITY DATA--ORAUDERMAL Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina Oral Absorbed Cancer Slope Factor Chemical Oral Cancer Slope Factor Absorption Weight of Evidence/ of for Dermal ( I ) Cancer Guideline Concern Value 1,4-Dichlorobcnzenc 2.4E-02 Arsenic 1.5E+00 Iron NA Manganese NA IRIS= Integrated Risk lnfonnation System NA= Not applicable Units (mg/kg/day)-! (mg/kg/day)-! NA NA Efficiency for Dermal (I) Value 100% 2.4E-02 95% I.6E+00 NA NA NA NA Units (mg/kg/day)-! (mg/kg/day)-! NA NA Description C A NA NA EPA Weight of Evidence A= Human carcinogen Oral CSF Source(s) Date(s) (2) Region 9 PRGs 10/20/2004 IRIS 4/1/2008 NA NA NA NA mg/kay/day = Milligrams per kilogram per day C = Possible human carcinogm CSF = Cancer slope factor (I) The dennal CSF was assumed to equal the oral CSF, unless an adjustment factor was found in Exhibit 4.1 of RAGS-E (EPA 2001 b). (2) IRIS values were confirmed against the EPA's online database, April 2008 Chemical of Potential Concern Value Table 6 CANCER TOXICITY DATA--INHALATION Sigmon's Septic Tank (Sequence 2) Site Statesville, Iredell County, North Carolina Weight of Unit Risk Inhalation Cancer Slope Factor(!) Evidence/ Cancer Guideline Units Value Units Description 1,4-Dichlorobcnzenc 6.3E-06 ug/m3 2.2E-02 (mg/kg/day)-! C Arsenic 4.3E-03 Iron NA Manganese NA IRIS= Integrated Risk Information System CSF = Cancer slope factor NA = Not applicable ug/m3 = Micrograms per cubic meter mg/kay/day = Milligrams per kilogram per day ug/m3 1.5E+0l NA NA NA NA (I) Inhalation CSFs were calculated from unit risks assuming a 70 kg individual has an inhalation mtc of20 m1/day. (2) IRIS values were confinned against the EPA 's online database, April 2008 (mg/kg/day)-! NA NA EPA Weight of Evidence A -Human Carcinog1."ll A NA NA C -Possible Human Carcinogen Unit Risk: Inhalation CSF Source(s) Date(s) (2) Region 9 PRGs 10/20/2004 IRIS 04/01/2008 NA NA NA NA Table 7: Risk Characterization Summary for CurrenUFuture Resident - Noncarcinogens -Shallow Ground Water Scenario Timeframe: Current/Future Receptor Population: Resident ,,r- Receptor Age: Child Medium Exposure Exposure Chemical of Primary Noncarcinogenic Hazard Quotient Medium Point Concern Target Ingestion Inhalation Dermal Exposure Organ Routes Total Ground Water Shallow Tap 1,4-Blood 0.06 0.06 NA 0.13 Ground Water Dichiaro benzene Water Arsenic Skin 0.3 NA NA 0.3 (Regolith Iron GI Tract 0.18 NA NA 0.18 Aquifer) Manganese CNS 35 NA NA 35 Ground~water Hazard Index Total= 36 Receptor Hazard Index= 36 CNS Hazard Index= 35 Liver Hazard Index= 0.1 Skin Hazard Index= 0.3 Blood Hazard Index= 0.13 Key NA: Not applicable CNS: Central Nervous System GI: Gastrointestinal Table 8: Risk Characterization Summary for Current/Future Resident - Noncarcinogens -Deep Ground Water Scenario Timeframe: CurrenUFuture Receptor Population: Resident Receptor Age: Child Medium Exposure Exposure Chemical of Primary Noncarcinogenic Hazard Quotient Medium Point Concern Target Ingestion Inhalation Dermal Exposure Organ Routes Total Arsenic Skin 2.7 NA NA 2.7 Ground Water Deep Tap Iron GI Tract 0.83 NA NA 0.83 Ground Water Water (Bedrock Manganese CNS 12 NA NA 12 Aquifer) Ground water Hazard Index Total= 16 Receptor Hazard Index= 16 CNS Hazard Index= 12 Skin Hazard Index= 2.7 GI Tract Hazard Index= 0.83 Key NA: Not applicable CNS: Central Nervous System GI: Gastrointestinal Table 9: Risk Characterization Summary for CurrenUFuture Resident• Carcinogens -Deep Ground Water Scenario Timeframe: Current/Future Receptor Population: Resident Receptor Age: Child Medium Exposure Exposure Chemical of Carcinogenic Risks Medium Point Concern Ingestion Inhalation Dermal Exposure Routes Total Ground Deep Tap Water Ground 1,4- Dichlorobenzene 1.7E-06 1.6E-06 NA 3.3E-06 Water Arsenic 1.0E-04 NA NA 1.0E-04 (Bedrock Iron NA NA NA NA Aquifer) Manganese NA NA NA NA Ground Water risk total= 1.1E-04 Total Risk= 1.1E-04 Key NA: Not Applicable Table 10: Risk Characterization Summary for Current/Future Resident- Noncarcinogens -Shallow Ground Water Scenario Timeframe: Current/Future Receptor Population: Resident . Receptor Age: Adult Medium Exposure Exposure Chemical of Primary Noncarcinogenic Hazard Quotient Medium Point Concern Target Ingestion Inhalation Dermal Exposure Organ Routes Total Ground Water Shallow Tap Ground Water Arsenic Skin 0.15 NA NA 0.15 Water (Regolith Aquifer) Manganese CNS 15 NA NA 15 Ground-water Hazard Index Total= 15 Receptor Hazard Index= 15 CNS Hazard Index= 15 Skin Hazard Index= 0.15 Key NA: Not applicable CNS: Central Nervous System Table 11: Risk Characterization Summary for Current/Future Resident - Noncarcinogens Scenario Timeframe: Current/Future Receptor Population: Resident Receptor Age: Adult Medium Exposure Exposure Chemical of Primary Noncarcinogenic Hazard Quotient Medium Point Concern Target Ingestion Inhalation Dermal Exposure Organ Routes Total Ground Water Deep Tap Ground Water Arsenic Skin 1.14 NA NA 1.14 Water Iron GI Tract 0.35 NA NA 0.35 (Bedrock Aquifer) Manganese CNS 5.1 NA NA 5.1 Ground-water Hazard Index Total= 7 Receptor Hazard Index= 7 CNS Hazard Index= 5.1 Skin Hazard Index= 1.14 GI Tract Hazard Index= 0.35 Key NA: Not applicable CNS: Central Nervous System GI: Gastrointestinal Table 12: Risk Characterization Summary for Current/Future Resident - Carcinogens Scenario Timeframe: CurrenUFuture Receptor Population: Resident Receptor Age: Adult Medium Exposure Exposure Chemical of Carcinogenic Risks Medium Point Concern Ingestion Inhalation Dermal Exposure Routes Total Ground Deep Tap 1,4-2.9E-06 2.7E-06 NA 5.6E-06 Water Ground Dichlorobenzene Water Arsenic 1.8E-04 NA NA 1.8E-04 (Bedrock Iron NA NA NA NA Aquifer) Manganese NA NA NA NA Ground Water risk total= 2E-04 Total Risk= 2E-04 Key NA: Not Applicable Table 13: Cleanup Goals for Ground Water Contaminant Cleanup Goal Basis 2•3•4•5 (µg/L)' 1.4-Dichlorobenzene 1.4 NC 2L Arsenic 10 MCL Iron 11,000 HQ=1 Manganese 300 Lifetime ' µg/L is micrograms per liter or parts per billion. 2 North Carolina 2L Standard 3 MCL -Maximum Contaminant Level 4 HQ -Hazard Quotient equal to one for future child resident 5 Lifetime -Lifetime Health Advisory Value Table 14: Cost Comparison of Remedial Alternatives Duration Capital Annual (years) Total Present Alternative Description Costs Cost Ground Worth Cost O&M Water 1 No Action $5,263 $125,581 $170,000 30 2a Monitor Natural Attenuation $90,514 $631,699 30 $735,900 2b Monitor Natural Attenuation with $252,043 $1,037,019 30 $) ,339,000 Contingencies ' 4 Enhanced Attenuation with Chemical Oxidation/Reduction $409,037 $632,211 30 $1,271,500 Total Present Worth Cost: The amount of money that EPA would have to invest now at seven percent interest to have sufficient funds available at the actual time the remedial alternative is implemented, Table 15 Comparison of Remedial Alternatives Alternative CERCLA EVALUATION CRITERIA 2a Remedy Monitored Natural Attenuation Overall Protection of Human Compliance with Applicable or Relevant and long-Term Effectiveness Reduction of Toxicity, Mobility and Short-Tenn Effectiveness Implementability Components Health and the Environment Appropriate Requirements (ARARs) and Permanence Volume (T/MN) through Treatment Primary Remedial Actions in site Zones and Media Inorganic contaminants are not amenable to Reduction in concentrations of inorganic COCs can long-term effectiveness of natural processes acting on This remedy does not reduce volume, and may cause an While implementing this remedy, conditions within the This remedy is simple to implement. degradation; physical processes such as dilution, occur by physical processes (such as dilution, inorganic COCs is difficult to predict given the potential increase in volume if dilution is an active attenuation medium remain relatively unchanged. Exposure Monitored Natural adsorption and precipitation apply to these COCs. adsorption Of precipitation) acting on inorganic COCs. for inorganic contaminants to revert back to a toxic mechanism. Toxicity and mobility may be reduced potential is sUII high while the natural processes act on Ground Water Reduction in risk from exposure to inorganic Quantitative RGCs may be met through transfer of chemical state. The permanence of this remedy would through adsorption onto solids. None of these potential the inorganic COCs. There is no increased exposure or Attenuation (MNA) contaminants occurs from changes in chemical valence contaminant mass from ground water to aquifer solids. be ensured by supplementing it with a treatment remedy reductions in T/'MN occur through treatment as it is a risk potential from implementing this relatively passive or chemical state. Reduction in concentration may occur Location-and action-specific ARARs are expected to be component. passive remedy. remedy. by dilution or adsorption onto aquifer solids. met by this relatively passive remedy. Remedy Support Operations (These activities are independent of contaminants, zones or media) c No Impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on thls evaluation criterion • Liquid No Action - ~ E RHldu.11• • • i, D ~; No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion ,:. "' liquid No Action ~. RHldual• •-E • . , "' " ca..,.. Not applicable Not applicable Not applicable Not applicable Not applicable Not applicable Not applicable • • F,-Product to this Site to this Site to this Site to this Site to this Site to this Site to this Site "' Generic Remedy Storm Water Management Decommission/ Demobilize These remedy support operations facilitate protection of These remedy support operations facilitate protection of These remedy support operations facilitate protection of These remedy support operations facilitate protection of These remedy support operations facilitate protection of These remedy support operations facilitate protection of Support Operations Site Restoration human health and the environment. human health and the environment. human health and the environment. human health and the environment. human health and the environment. human health and the environment. Five-Year Reviews Govemmenl No ground water controls needed; Controls zoning restrictions i Future property ownership may ICs only impact human receptors, and protectiveness is ICs only impact human receptors. and long-term lCs only impact human receptors, and their effectiveness tCs are administrative instruments that have no adverse C Proprietary effectiveness and permancene is dependent on impact on the Site conditions during their 0 Instruments require land-use to remain dependent on voluntary compliance. Environmental depends on personal and voluntary compliance. tCs are administratively implemented. By themselves, 0 tCs are designed to comply with pertinent ARARs. voluntary compliance. Environmental receptors or implementaition. By themselves, none of the four • commercial receptors or features are _only indirectly addressed by Environmental receptors or features are only indirectly none of the four classifications of IC are effective at C ICs. By themselves, non8 of the four classifications of IC Environmental ARARS are only indirectly addressed by features are only indirectly addressed by ICs. By addressed by JCs. By themselves, none of the four classification~ of IC are effective at protection from risk protection from risk or exposure to COCs, regardless of 0 inst1tutlonal controls. themselves, none of the four classifications of IC can or exposure to COCs, regardless of length of time they ~ Enforcement Natural resource permits provide a great degree of protection from risk or classifications of IC can reduce the toxicity, mobility Of length of time ltley are implemented. il & Permits for creek restoration exposure to COCs. guarantee long-term protection_ from risk or exposure to volume/mass of COCs at the Site. are implemented. Thus, time to compliance or time to ; COCs. They do not address COC mass at the Site. attainment of RAOs is not applicable to IC . • -= Publlc Periodic communications Information with community stakeholders .M2.1.u..;: MNA = monitored natural attenuaUon MNR = monitored natural recovery Alternative 2b Monitored Natural Attenuation with Overall Protection of Human Remedy Components Contingencies Health and the Environment Primary Remedial Actions in site Zones and Media Inorganic contaminants are not amenable to degradation; physical processes such as dilution, Monitored Natural adsorption and precipitation apply to these COCs. Ground Water Reduction in risk from exposure to inorganic Attenuation (MNA) contaminants OCCUr-5 from changes in chemical valence or chemical state. Reduction in concentration may occur by dilution or adsorption onto aquifer solids. Remedy Support Operations (These activities are independent of contaminants, zones or media) c No impact on this evaluation criterion • "'"" No Action ~ E R .. iduala • • > ~ 'C ~ ~ No impact on this evaluation criterion "'"' "'"" No Action -g .!! R .. lcluala E • -~ Not applicable Not applicable a::·;; Collect,od • F.-..Product to lhls Site to thls Site "' Storm Water Management Generic Remedy Decommission / Demobilize These remedy support operations facilitate protection of Support Operations Site Restoration human health and the environment. Five-Year Reviews Government No ground water controls needed; Controls zoning restrictions ~ Future property ownership may ICs only impact human receptors, and protectiveness is C Proprietary 0 Instruments reQuire land-use to remain dependent on voluntary compliance. Environmental <.) • commercial receptors or features are_ only indirectly addressed by C ICs. By themselves, none of the four classifications of IC 0 '5 Enforcement Natural resource permits provide a great degree of protection from risk or ;; & Permit,; fOf creek restoration e)(posure to COCs. t • .s Public Periodic communications Information with community stakeholders ~ ISCO "' In situ chemical oxidation MNA : monitored natural attenuation MNR : monitored natural recovery Compliance with Applicable or Relevant and Appropriate Requirements (ARARs) Reduction in concentrations of Inorganic COCs can occur by physical processes (such as dilution, adsorption or precipitation) acting on inorganic COCs. Quantitative RGCs may be met through transfer of contaminant mass from ground water to aquifer solids. Location-and action-specific ARARs are e)(pected to be met by this re!atively passive remedy. No impact on this evaluation criterion No impact on this evaluation criterion Not app!icable to this Site These remedy support operations facilitate protection of human health and the environment. ICs are designed to comply with pertinent ARARs. Environmental ARARS are only indirectiy addressed by institutional controls. Table 15 (Continued) Comparison of Remdlal Alternatives CERCLA EVALUATION CRITERIA Long-Term Effectiveness Reduction of Toxicity, Mobllity and and Permanence Volume (T/MN) through Treatment Long-term effectiveness of natural processes acting on This remedy does not reduce volume, and may cause an inorganic COCs is difficult to predict given the potential increase in vo!ume if dilution is an active attenuation for inorganic contaminants to revert back to a to)(ic mechanism. Toxicity and mobility may be reduced chemical state. The permanence of this remedy would through adsorption onto solids. None of these potential be ensured by supplementing it with a treatment remedy reductions in T/MN occur through treatment. component. No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluatlon criterion No impact on this evaluation cnterion Not applicable Not applicable to this Site to this Site These remedy support operations facilitate protection of These remedy support operations facilitate protection of human health and the environment. human health and the environment. ICs only impact human receptora, and long-term !Cs only impact human receptors, and their effectiveness effectiveness and permancene is dependent on depends on personal and voluntary compliance. voluntary compliance. Environmental receptors or Environmental receptors or features are only indirectly features are only indirectly addressed by ICs. By addressed by ICs. By themselves, none of the four themselves, none of the four classifications of IC can classifications of IC can reduce the \O)(icity, mobility or guarantee long-term protection from risk or exposure to volume/mass of COCs at the Site. COCs. They do not address COC mass at the Site. - Short-Term Effectiveness Implementability While implementing this remedy, conditions within the This remedy is simple to implement. medium remain relatively unchanged. Exposure potential is still high whlle the natural processes act on the inorganic COCs. There is no increased e)(posure or risk potential from imp!ementing this relatively passive remedy. ' No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion Not applicable Not applicable to this Site to this Site These remedy support operations facilitate protection of These remedy support operations facilitate protection of human health and the environment. human health and the environment. ICs are administrative instruments that have no adver5e impact on th·e Site conditions during their ICs are administratively implemented. By themselves, implementaition. By themselves, none of the four none of the four classifications of IC are effective at classifications of IC are effective at protection from risk protection from risk or e)(posure to COCs, regardless of or e)(posure to COCs, regardless of length of time they length of time they are implemented. are implemeflted. Thus. time to compliance or time to attainment of RAOs is not applicable to IC . . Alternative 4 Enhanced Attenuation wHh Chemical Overall Protection of Human Q:,:idation/Reduction Health and the Environment Remedy Components Primary Remedial Actions in site Zones and Medi In situ treatment is beneficial to protection against e:,:posure and risk to human health and the environment. Ground Water Chemical Oxidation/Reduction Remedy Support Operations (These activities are independent of contaminants, zones or media) 1, No impact on this evaluation criterion • Liquid No Action " e Residual• • • -~ gi No impact on this evaluation criterion C a Solid ;. " Residual a No Action j.!! e • ~i Colleo;ted Not applicable Not applicable • f,...Produo;t to this Site to this Site " Storm Water Management Generic Remedy Decommission/ Demobilize These remedy support operations facilitate protection of Support Operations Site Restoration human health and the environment. Five-Year Reviews Government No ground water controls needed; Controls zoning restrictions .,, g Future property ownership may ICs only impact human receptors, and protectiveness is C Proprietary 0 require land-use to remain dependent on voluntary compliance. Environmental " Instruments 7i commercial receptors or features are only indirectly addressed by ICs. C By themselves, none of the four classifications of IC 0 Construction, water treatment and " Enforcement provide a great degree of protection from risk or e:,:posure s & Permits disposal permits: natural resource to COCs. • permits for creek relocation .s Public Periodic communications lnformetlon with community stakeholders H21U;_ ISCO " In situ chemical o:,:idation MNA " monitored natural attenuation MNR " monitored natural recovery Compliance with Appllcable or Relevant and Appropriate Requirements (ARARs) This remedy can be designed and implemented in a way that complies with ARARs. O:,:idation/Reduction of contaminant mass achieve chemical-specific ARARs. Location and action-specific ARARs would be met througt permitUng and design functions. No impact on this evaluation criterion No impact on this evaluation criterion Not applicable to this Site These remedy support operations facilitate protection of human health and the environment. ICs are designed to comply with pertinent ARARs. Environmental ARARS are only indirectly addressed by lCs. Table 15 (Continued) Comparison of Remedial Alternatives CERCLA EVALUATION CRITERIA Long-Term Effectiveness Reduction of Toxicity, Mobility and and Permanence Volume (T/MN) through Treatment Treatment of COCs is an effective and permanent Treatment achieves reduction of to:,:icity, mobility and remedial strategy for most CERCLA sites. volume of contamination. RecontaminaUon is only possible from additional source material. No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion Not applicable Not applicab!e to this Site to this Site These remedy support operations facilitate protection of These remedy support operations facilitate protection of human health and the environment. human health and the environment. I Cs only impact human receptors, and long-term ICs only impact human receptors, and their effectiveness effectiveness and permancene is dependent on voluntary depends on personal and voluntary compliance. compliance. Environmental receptors or features are only Environmental receptors or features are only indirectly indirectly addressed by ICs. By themselves, none of the addressed by ICs. By themselves, none of the four four classifications of IC can guarantee long-term classifications of IC can reduce the to:,:icity, mobility or protection from risk or e:,:posure to COCs. They do not volume/mass of COCs at the Site. address COC mass at the Site . Short-Term Effectiveness Implementability During implementation of the remedial action, there is Certain components of this remedy are technically minimal potenUal for e:,:posure by onsite occupants or implementable but are not preferred by some remediation workers to contaminants. This medium stakeholders. Implementation may be hindered by remains in situ. administrative or management decision. No impact 0<1 this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion No impact on this evaluation criterion Not applicable Not applicable to this Site to this Site These remedy support operations facilitate protection of These remedy support operations facilitate protection of human health and the environment. human health and the environment. ICs are administrative instruments that have no adverse impact on the Site conditions during their implementaition. ICs are administratively implemented. By themselves, By themselves, none of the four classifications of IC are none of the four classifications of IC are effective at effective at protection from risk or exposure to COCs. protection from risk or e:,:posure to COCs, regardless of regardless of length of time they are implemented. Thus, length of time they are implemented. time to compliance or time to attainment of RAOs is not applicable to IC. FEDERAL National Primary Drinking Water Standards ,..c, Clean Water Act . Ambient Water Quality Criteria (AWQC) National Pollutant Discharge Elimination System (NPDES) National Pretreatment Standards Table 16 Potential Chemical-Specific ARARs Sigmon's Septic Tank Site , · Statesville, Iredell County, North Carolina 40 Code of Federal Regulations (CFR) Part 141, Subpart B and G 40 CFR Parts 131, 304 40 CFR Parts 122, 125 40 CFR Part 403 Establishes maximum contaminant levels (MCLs) for specific chemicals to protect drinking water quality. These are health-based standards for public water systems. Requires the states to set AWQC criteria for water quality based on use classifications and the criteria developed under § 304{a) of the Clean Water Act. AWQC are non-enforceable, health-based criteria used to establish surface water quality standards for the protection of human health and aquatic life. Determines maximum concentrations for the discharge of pollutants from any point source into waters of the United States. Sets pre-treatment standards for new and existing sources to control pollutants that pass through or interfere with treatment processes in publicly owned treatment works or that may contaminate sewage sludge. Page I of4 The MCLs for organic and inorganic constituents are applicable to the ground water contamination at the Site. Ground water in the vicinity is used as a source of drinking water. If an alternative involves discharge to surface water, these criteria would be applicable. AWOCs for constituents in surface water have been developed by the state of North Carolina. Discharge limits would be established for effluent if discharged to surface water body on site. State implemented program. NPDES criteria would be applicable if a remedy is selected that requires discharge of collected ground water to a surface water body. If an alternative involves discharge of site wastewater to publicly owned treatment works, these standards would be applicable. 7/28/2[Xf} Clean Air.Act· · National Primary and Secondary Ambient Air Quality Standards National Emissions Standards for Hazardous Air Pollutants (NESHAPS) National Emission Standards for Hazardous Air Pollutants for Source Categories Statutory Requirements for Cleanup Actions 40 CFR Part 50 40 CFR Part 61 40 CFR Part 63 CERCLA§ 121 ( d)(2)(B )(ii) Table 16 Potential Chemical-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Establishes standards for ambient air quality to protect public health and welfare. Provides emissions standards for hazardous air pollutants for which no ambient air quality standard exists. Provides emissions standards for hazardous air pollutants that originate from specific categories of sources. Provides alternative ground water concentration limits for ground water that discharges to a surface water body. Page 2 of4 May be relevant or appropriate if remedial alternative results in air emissions that migrate offsite. May be relevant or appropriate if onsite treatment units with emissions identified as hazardous air pollutants are part of remedial actions. May be relevant or appropriate if identified hazardous air pollutants are emitted from a specific source category that has been identified. The specific source category would depend on the remedial alternative selected. The ground water contaminant 1,4- dichlorobenzene is listed as a hazardous air pollutant in Section 112(b) of the Clean Air Act. May be relevant or appropriate. There are suspected discharges of ground water to surface water near the site; likely to the unnamed intermittent streams to the southwest and west-northwest. 7/28/20Cf} RCRA Ground water Protection Standards STATE Classifications and Water Quality Standards Applicable to the Ground Waters of North Carolina Classifications and Water Quality Standards Applicable to Surface Waters and Wetlands of North Carolina Table 16 Potential Chemical-Specific ARARs Sigmon's Septic Tank Site . Statesville, Iredell County, North Carolina 40 CFR Part 264 North Carolina Administrative Code (NCAC) Title 15A, Subchapter 2L, § . 0100, .0200, .0300 NCAC Title 15A, Subchapter 26, § .0200 Provides for ground water protection standards, general monitoring requirements, and technical requirements which apply to RCRA regulated units subject to permitting (landfills, surface impoundments, waste piles, and land treatment units) that received RCRA hazardous waste after July 26, 1982. The ground water protection standards are equal to the Federal National Primary Drinking Water Standard MCLs established under the SOWA. May be relevant or appropriate if onsite disposal is selected for the soil OU1 remedial alternative. Establishes a series of classifications and The ground water beneath the Site would be water quality standards applicable to the classified as Class GA Groundwater: existing or ground waters of the state. The ground water potential source of drinking water supply for standards are the maximum allowable humans. These standards are applicable for concentrations resulting from any discharge of protection of human health . contaminants to the land or waters of the state, which may be tolerated without creating a threat to human health or which would otherwise render the ground water unsuitable for its intended best usage. Establishes a series of classifications and If an alternative involves discharge to surface water quality standards applicable to the water, these criteria would be applicable. surface waters and wetlands of the state. The action levels established in this rule shall be considered as numerical ambient water quality standards established ursuant 40 CFR Parts Page3 of4 7f28/2CXE Ambient Air Quality Standards North Carolina Drinking Water Act NOTE: NCAC Title 15A, Subchapter 2D, § .0200, .0400, .2600 North Carolina General Assembly (NCGS) 130a, 311- 327 Table 16 Potential Chemical-Specific ARARs Sigmon's Septic Tank°Site Statesville, Iredell County, North Carolina Flow design criteria for effluent limitations are also established by this regulation. Establishes certain maximum limits on parameters of air quality considered desirable for the preservation and enhancement of the quality of the state's air resources. Provides guidance on source testing methods. To regulate water systems within the State which supply drinking water that may affect the public health. May be applicable or relevant and appropriate if an alternative results in air emissions that migrate off site. The ground water beneath the Site would be classified as Class GA Groundwater: existing or potential source of drinking water supply for humans. These standards are applicable for protection of human health. All potentially applicable chemical-specific ARARs were reviewed for applicability. Only those chemical-specific ARARs that were determined to be potentially applicable or relevant and appropriate for the Site were included on this table. Page 4 of4 7!28l2r:m FEDERAL Standards of Performance for New Stationary Sources Water Pollution Prevention and Control Table 17 Potential Location-Specific ARARs Sigmon's Septic Tank Site -- Statesville, Iredell County, North Carolina 20 Code of Federal Regulations (CFR) Part 60 Chapter 26, § 1251 to 1376 Identifies standards of performance for new stationary sources of air emissions. Provides emission guidelines and compliance times. Implements a system to impose limitations on, or otherwise prevent, discharges of pollutants into any waters of the United States from any point source. . ~., '. .... ,_-,'!•· ,> :: ... ·." .. ·._--·:•.··.··,._._·i':J -_~,.-:• .. , ~-.• ·:.' '•·-•; _,.,..;_ .·;,:· ~-• .... -~-,_·~,,, -,:_:,/. Comprehensive Environmental Responser C 6mperis~tio/, ana · ua,bility. Act ( C,ERC_LA) :of ._1980 ,} '.'~, :. ·, ,•·,_.-.' -. --~ .. ,~'. ,,_. .• _-._-_' ·:,·.· "',} ,, ;•.·-1·:•-;[._·;,:•·,,_· ... ,:-· ... ~. ',••-:.:., CERCLA as amended by the Superfund Amendments and reauthorization Act (SARA) of 1986 Endangered Species-Act"'; · Protection of endangered and threatened species 42 USC, Chapter 103, § 9601 et seq. 50 CFR Parts 81, 221 to 226, and 402 Federal authority to respond directly to releases or threatened releases of hazardous substances that may endanger public health or the environment. Established a trust fund (Superfund) to provide for cleanup when no responsible party is ·identified. Provides for liability of persons responsible for releases of hazardous substances. Established prohibitions and requirements concerning closed and abandoned hazardous waste sites. Requires action to conserve with in critical habits upon species depend, includes Department of Interior. Pagel of3 endangered species which endangered consultation with Applicable if a remedial alternative would create a new stationary source of air emissions. Applicable because there are discharges to surface water features from the site. Applicable. The site is on the EPA National Priorities List (NPL). ;,-: ,· ,• r-; ,,,,.- The surface water pathway at the site may contain threatened or endangered species or critical habitats. Applicable if species are identified at the site. 7/28/2009 Protection and Conservation of Wildlife Fish and Wildlife Conservation Preservation of historical or archeological data Table 17 Potential Location-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Chapter SA, § 661 to 667 Chapter 49, § 2901 to 2911 36 CFR Part 65 Requires consultation when Federal department or agency proposes or authorizes any modification of any stream or other water body and adequate provision for protection of fish and wildlife resources. Action to conserve fish and wildlife, particularly those species which are indigenous to the state. Historical or archeological data must be preserved. Page 2 of3 Applicable if significant populations are present at the site and if the alternative selected will affect the populations. Applicable if significant populations are present at the site and if the alternative selected will affect the populations. Applicable if the remedy selected threatens historical or archaeological data. 7/28/2009 STATE Classifications and Water Quality Standards Applicable to the Ground Waters of North Carolina Air Pollution Control Requirements; Classification of Air Pollution Sources; Ambient Air Quality Standards; Emission Control Standards; Monitoring North Carolina Recordation of Inactive Hazardous Substances or Waste Disposal Site Statute NOTE: Table 17 Potential Location-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina North Carolina Administrative Code (NCAC) Title 15A, Subchapter 2L, § .0100, .0200, .0300 NCAC Title 15A, Subchapter 2D, § .0100, .0200, .0400, .0500, . 0600, .0900, .1800 North Carolina General Assembly (NCGS) 130a, 310.8 Establishes a series of classifications and water quality standards applicable to the ground waters of the state. Establishes source classifications and ambient air quality standards applicable to State air quality. Provides emission control guidelines and monitoring requirements . Establishes system for cataloging and monitoring inactive hazardous sites. The ground water beneath the Site would be classified as Class GA Groundwater: existing or potential source of drinking water supply for humans. These standards are applicable for ground water classification determination. Applicable or relevant and appropriate if remedial alternative would create a new stationary source of air emissions that may exceed standards at any point beyond the premises on which the source is located. Applicable or relevant and appropriate to record this hazardous site data and if any deed restrictions are applied to the property. All potentially applicable location-specific ARARs were reviewed for applicability. Additional ARARs reviewed, but determined not to be applicable, include, but are not limited to the following: Archaeological and Historic Preservation Act of 1974, the Federal National Historic Preservation Act, the Historic Sites, Buildings, and Antiquities Act, Wilderness Act, Migratory Bird Treaty Act, Wild and Scenic Rivers Act, National Wildlife Refuge System, Clean Water Act (wetlands protection, dredge and fill requirements), Rivers and Harbors Act of 1899 (Section 10 Permit, Flood Plain Management, Protection of Wetlands), and Hazardous waste siting criteria. Only those location-specific ARARs that were determined to be potentially applicable or relevant and appropriate for the Site were included on this table. Page 3 of3 7/28/2009 FEDERAL . ~· ,.· ' . ~:; .-:_:.,_ ·•,; . Cl~n AifJ\ct . National Emission Standards for Hazardous Air Pollutants National Pollutant Discharge Elimination System (NPDES) Storm Water Discharge Requirements Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina 40 Code of Federal Regulations (CFR) Part 61 40 CFR Parts 122 and 125 40 CFR Part 122.26 Treatment technology standards, permitting, Applicable if the identified hazardous air monitoring requirements for emIssIons of pollutants will be emitted from a site by a hazardous air pollutants for which no ambient air remedial alternative. quality standard exists. Regulates discharges of pollutants from any point source into waters of the United States. Provides requirements to obtain a permit to discharge to the storm water sewer system under the NPDES program. Page I of6 Applicable if water from the site will be discharged onto land or into streams, rivers, or lakes. A permit is not required for onsite CERCLA response actions, but the substantive requirements would apply if an alternative involved discharge onto land or into streams, rivers, or lakes on site. A permit would be required if the discharge is to land or surface water off site. Applicable if an alternative involves storm water that comes into contact with construction activity or if the selected remedy involves discharge of treated water to surface waters. 7/28/2009 Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina Requirements for discharge to 40 CFR Part 403 surface water Treatment standards, best management Applicable if there are discharges to practices, and monitoring requirements. surface waters of the United States. Noise Control Inspections, Citations, and Proposed Penalties · Recording and Reporting Occupational Injuries and Illnesses 40 CFR Part 122 § 4901 et seq. Federal activities must not result in noise that will jeopardize the health or welfare of public. 29 CFR Part 1903 -Regulates worker health and safety with regards to onsite remedial activities. Authorizes the Department of Labor to conduct inspections and to issue citations and proposed penalties for alleged violations. 29 CFR Part 1904 Regulates worker health and safety with regard to onsite remedial activities. Provides for record keeping and reporting by employers. Page 2 of6 If a remedial alternative involves activities, such as drilling, or included use of other noisy equipment, were to take place too close to a public access point, this may be applicable. Under 40 CFR § 300.38, requirements of the Act apply to all response activities under the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Under 40 CFR § 300.38, requirements of the Act apply to all response activities under the NCP. 7/28/2009 General Industry Standards Occupational Safety and Health Standards for the Construction Industry ' .. ' Safe Drinking Water Act Underground Injection Control (UIC) Regulations Identification and Listing of Hazardous Wastes Standards Applicable to Generators of Hazardous Waste Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina 29 CFR Part 1910 29 CFR Part 1926 40 CFR Parts 144 to 147 40 CFR Part 261 40 CFR Part 262 Regulates worker health and safety and regards to onsite remedial activities. Establishes generic specifications for using tools maintaining industrial structures, installing work place safety equipment, providing medical attention, and other general health and safety practices. Regulates worker health and safety with regards to onsite remedial activity. Establishes safety and health standards for the construction industry. Under 40 CFR § 300.38, requirements of the Act apply to all response activities under the NCP. Under 40 CFR § 300.38, requirements of . the Act apply to all response activities under the NCP. Provides for protection of underground sources of If an alternative involves onsite drinking water. underground injection, this part would be applicable. Defines those solid wastes which are subject to regulations as hazardous wastes under 40 CFR Parts 262-265 and Parts 124,270, and 271. Would be applicable in identifying if a substance at the site, such as a waste generated by the remedial alternative, should be defined as a hazardous waste. Would require handling as a hazardous waste. Establishes standards for generators of hazardous Would be applicable if an alternative waste. involved onsite disposal or treatment of hazardous wastes. Page 3 of6 7/28/2009 Standards Applicable to Transporters of Hazardous Waste Regulations governing hazardous materials transportation Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina 40 CFR Part 263 Procedures and/or Policies: 49 CFR Parts 101, 106, and 107 Material Designations: 49 CFR Part 172 Packaging Requirements: 49 CFR Parts 173, 178, 179, and 180 Operational Rules: 49 CFR Parts 171, 173,174,175, 176, and 177 Establishes standards which apply to persons Would be applicable if an alternative transporting hazardous waste within the U.S. if the involved off site transportation of transportation requires a manifest under 40 CFR hazardous wastes. Part 262. Specific requirements for protection against the If an alternative involved transportation risks to life, property, and the environment that are of hazardous materials off site, these inherent in the transportation of hazardous requirements would apply. Does not material in intrastate, interstate, and foreign apply to remediation onsite. commerce. Page 4 of6 7/28/2009 STATE Hazardous Waste Management Solid Waste Management Water Pollution Control; Procedures for Permits Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina North Carolina Administrative Code (NCAC) Title 13A NCAC Title 138 NCAC Title 15A, Chapter 2, Subchapter 2H Establishes North Carolina state-specific hazardous waste management requirements. Federal provisions should prevail unless State requirements are more stringent. Establishes North Carolina state-specific requirements for solid waste storage, collection, transportation, separation, processing, recycling, recovery, and disposal. Established permit requirements for control of sources of water pollution by providing the requirements and p~ocedures for application and issuance of state NPDES permits for a discharge from an outlet, point source, or disposal system discharging to the surface waters of the state, and for the construction, entering a contract for construction, and operation of treatment works with such a discharge. These Rules also contain the requirements and procedures for issuance of state permits for pretreatment facilities. Page 5 of6 May be applicable or relevant and appropriate if an alternative involves generation, onsite disposal or treatment of hazardous wastes. May be applicable or relevant and appropriate if an alternative involves solid waste storage, collection, transportation, separation, processing, recycling, recovery, or disposal. May be applicable or relevant and appropriate if an alternative involves discharge of water. 7/28/2009 Air Pollution Control Requirements; Classification of Air Pollution Sources; Ambient Air Quality Standards; Emission Control Standards; Monitoring Classifications and Water Quality Standards Applicable to the Ground Waters of North Carolina Oil Pollution and Hazardous Substance Control Act NOTE: Table 18 Potential Action-Specific ARARs Sigmon's Septic Tank Site Statesville, Iredell County, North Carolina NCAC Title 15A, Subchapter 2D, § .0100, .0200, .0400, .0500, .0600, .0900, .1800 North Carolina Administrative Code (NCAC) Title 15A, Subchapter 2L, § .0100, .0200, .0300 North Carolina General Assembly (NCGS) 143, Article 21A Establishes source classifications and ambient air Applicable or relevant and appropriate if quality standards applicable to State air quality. remedial alternative would create a new Provides emission control guidelines and stationary source of air emissions that monitoring requirements. may exceed standards at any point beyond the premises on which the source is located. Establishes a series of classifications and water Applicable since the remedial action will quality standards applicable to the ground waters involve ground water beneath the Site. of the state. To promote the health, safety, and welfare of the Applicable or relevant and appropriate if citizens of this Stale by protecting the land and the an alternative involves removal of waters over which this State has jurisdiction from hazardous substances. pollution by oil, oil products, oil by-products, and other hazardous substances. All potentially applicable action-specific ARARs were reviewed for applicability. Only those action-specific ARARs that were determined to be potentially applicable or relevant and appropriate for the Site were included on this table. Page 6 of6 7/28/2009 Table 19 Alternative 2a: M~A Cost Estimate Summary Details Sigmon's Septic Tank Site _ Statesville, Iredell County, North Carolina Alternative 2a: MNA Site: Location: Phase: Base Year: Sigmon's Septic Tank Site Operable Unit 2 Statesville, Iredell County, North Carolina Feasibility Stuby of Remedial Alternatives 2009 Item Description Alternative Alternative 2a consists of Administrative Controls, Potable Well Monitoring, MNA. Description: Capital costs occur in Year 0. O&M costs occur in Years 1-30. Periodic costs occur in Years 5, 10, 15, 20, 25, 30. Estimated Year Units Quantity Unit Price Capital Cost Present Worth Cost1 7% Discount No Discount Rate Rate Notes @i@###ig4#fiii·tWPi!?4W#tt!Jffiiit~i&i4iMiJJ&i9tfdi#WJfiil:lfi!f$flii&ai!wfPVEW?&fihr.W!@f§fNiit#fflM@19'E~il Site S ecific Plans Remedial Action Work Plan Site Health and Safety Plan Activities Informational Tools to Residents Mobillzatlon/Demobillzation Mobilize/Demobilize Equipment and Crew Per Diem (1 crew plus oversight) lnstal1atlon Health and Safety Decon Pad Monitoring Well Installation Install 8 shallow monitoring wells SUBTOTAL Contingency (15% of capital costs} SUBTOTAL Legal fees, permits, and other licemies (5% of capital costs) Contractor Fee (10% of capital costs) TOT AL Capital Cost O&M -Sample 16 Monitoring Wells quarterty {1 year); includes bulk O&M -Sample 16 Monitoring Wells semiannually (2 years) O&M -Sample 16 Monitoring Wells annually (7 years) O&M -Sample 16 Monitoring Wells biennially (20 years) O&M -Sample 20 Potable Wells 1 year O&M -Sample 20 Potable Wells biennially for 4 years Semiannnual Report SUBTOTAL Contingency (15% of annual O&M) SUBTOTAL Contractor Fee (10% of annual O&M) TOT AL Annual O&M Cost Five-Year Review-Year 5 Five-Year Review-Year 10 Five-Year Review-Year 15 Five-Year Review -Year 20 Five-Year Review-Year 25 Five-Year Review -Year 30 SUBTOTAL Contingency (15% of periodic costs) SUBTOTAL Contractor Fee (10% of periodic costs) TOT AL Periodic Cost NOTES: 1 2 7 20 4 30 5 10 15 20 25 30 EA EA EA LS DAY EA EA EA EA EA EA EA EA EA EA EA EA EA EA EA 20 1 20 8 4 2 1 0.5 1 0.5 2 $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ 2,280.00 s 2,280.00 1,700.00 $ 1,700.00 30.00 $ 600.00 10,000.00 $ 10,000.00 120.00 $ 2,400.00 1,000.00 $ 1,000.00 6,307.75 $ 50.462.00 $ 68.442.00 $ 10,266.30 $ 78,708.30 $ 3.835.42 $ 7,870.83 R·s?...~eo.s14.ss.1 25,816.12 $ 96,508.86 23,469.20 $ 79,313.53 23.469.20 $ 103,247.24 23.469.20 $ 72,989.70 32,200.00 $ 32,200.00 32,200.00 $ 52,689.95 2,515.00 $ 62,417.48 $ 499,366.76 $ 74,905.01 $ 574,271.77 $ 57,427.18 jlis,;.,.-~.:-631,698.9511 5,000.00 $ 3,564.93 5,000.00 $ 2,541.75 5,000.00 $ 1.812.23 5.000.0o $ 1,292.10 5,000.00 $ 921.25 5,000.00 $ 656.84 $ 10,789.08 $ 1,618.36 $ 12,407.45 $ 1,240.74 11· $;.·•:~· 13,648.1911 9 9 5 4 9 2 9 9 9 9 9 9 9 2 2 1 A 7% discoUnt interest rate was used in calculating present worth based on the EPA Superfund guidance document A Guide to Developing and Documenting Cost Estimates During the.Feas1bl7ity Study (July 2000). 2 Contingency (15%) is included in the present annual cost based on the EPA Superfund guidance document A Guide to Developing and Documenting Cost Estimates During /he Feas,billty Study (July 2000). Profit is not Included. 4 Cost Source: NC Superfund Site costs. 9 Cost Source: Detailed work.sheet provided in Appendix A. Table 19 (Continued) Alternative 2a Cost Summay Details Sigmon's Septic Tank Statesville, Iredell County, North Carolina Alternative 2a: MNA COST SUB-ELEMENT: REPORTING Site: Location: Phase: Base Year: Sigmon's Septic Tank Site Operable Unit 2 Statesville, Iredell County, North Carolina Feasibility Stuby of Remedial Alternatives 2009 Item Description Costs Per Site Specific Health & Safety Plan Senior Review Scientist Writing Administrative Co /Phone/Fax SUBTOTAL TOTAL Unit Cost Costs Per Remedial Action Work Plan Senior Review Engineer Writing Administrative Co /Phone/Fax SUBTOTAL TOTAL Unit Cost Senior Review Engineer Writing Administrative Co /Phone/Fax SUBTOTAL Costs Per Annual Re art TOTAL Unit Cost Sourco of Cost Data: Labor rates are based on typical labor rates for the area. Cost Adjustment Checkllst; COST ESTIMATE FACTOR: Cost escalation to base year? Element Create WP, HASP, and Annual Reports. Description: Estimated Units Quantity Unit Price Total HR 2 $ 125.00 $ 250.00 HR 20 $ 65.00 $ 1,300.00 HR 2 $ 25.00 $ 50.00 LS $ 100.00 $ 100.00 $ 1,700.00 n $·!)'~;_1,100.oo·n HR 4 $ 125.00 $ S00.00 HR 18 $ 85.00 $ 1,530.00 HR 2 $ 25.00 s 50.00 LS $ 200.00 $ 200.00 $ 2,280.00 n s;i:~-2.2so.oo I HR 2 $ 125.00 $ 250.00 HR 24 $ 85.00 s 2,040.00 HR 3 $ 25.00 $ 75.00 LS $ 150.00 $ 150.00 $' 2,515.00 It $~.2.515.00 ff NOTES: Current year (2009) is base year. Notes Table 19 (Continued) Alternative 2a Cost Summay Details Sigmon's Septic Tank Statesville, Iredell County, North Carolina Alternative 2a: MNA COST SUB-ELEMENT: O&M GROUND WATER SAMPLING Site: Location: Phaso: Baso Year: Sigmon's Septic Tank Site {Sequence 2) Statesville, Iredell County, North Carolina Feasibility Stuby of Remedial Alternatives 2009 Item Description Cost Per Shallow Well Ground Water Sampling Fill & Stage IDW IDW Teflon-lined tubing for GW Sampling Laboratory Analysis & jarware SUBTOTAL Prime Contractor Overhead (15%) TOT AL Unit Cost Cost Per Bedrock Woll Ground Water Sampling Fill & Stage IDW IDW Teflon-lined tubing for GW Sampling Laboratory Analysis & iarware SUBTOTAL Prime Contractor Overhead {15%) TOTAL Unit Cost TOTAL 12 shallow, 4 bedrock Sourco of Cost Data: Element Sample 12 65' shallow (8 are new) and 4 120' deep welts. Analyses: Metals, Alkalinity, Sulfate, Description: Chloride, Nitrate/Nitrite, Ammonic Nitrogen, TOC, Methane/Ethane/Ethane; also VOCs in bedrock wells. Units HR HR EA FT EA HR HR EA FT EA Estimated Quantity 3 75 6 2 3 130 Unit Price Total $ 110.00 $ 330.00 $ 110.00 s 110.00 $ 90.00 $ 90.00 $ 2.00 $ 150.00 $ 368.00 $ 368.00 $ 1,Q48.00 $ 157.20 ij: S f3i:.1 ~05.20 U $ 110.00 $ 660.00 s 110.00 $ 220.00 $ 90.00 $ 270.00 $ 2.00 $ 260.00 $ 548.00 $ 548.00 $ 1,958.00 $ 293.70 ~: S~r.2,251:70 I I s 2a,4s9.20 I Notes $65/hr geo + $45/hr technician $65/hr geo + $45/hr technician $65/hr geo + $45/hr technician $65/hr gee+ $45/hr technician Labor rates for geologist and technician are based on typical labor rates for tho area Cost Adjustm11nt Ch11ckllst: COST ESTIMATE FACTOR: Includes H&S Productivity (labor & equip)? Cost escalation to bes a year? Subcontractor overhead and profit included? Prime conlrn.ctor overhead and profit included? NOTES: Quota is for Level D Current year (2009) is base year. Included 1n quote. !ncludes 15% overtiead. Profit is included wtth cost summary. Table 19 (Continued) Alternative 2a Cost Summay Details Sigmon's Septic Tank · Statesville, Iredell County, North Carolina Altornatlve 2a: MNA COST SUB-ELEMENT: O&M GROUND WATER SAMPLING Sito: Sigmon's Septic Tank Site (Sequence 2) Statesville, Iredell County, North Carolina Feasibility Stuby of Remedial Alternatives 2009 Element Sample 20 150' potable wells. Analyses: Metals and field parameters. Location: Phase: Base Yoar: Item Description Cost Per Potable Well Ground Water Sampling Teflon-lined tubing for GW Sampling Laboratory Analysis & jarware SUBTOTAL Prime Contractor Overhead (15%) TOTAL Unit Cost TOTAL 20 150' potable Source of Cost Data: Description: Units HR FT EA Estimated Quantity 6 160 Unit Price Total $ $ $ 110.00 $ 880.00 2.00 $ 320.00 200.00 $ 200.00 $ 1,400.00 $ 210.00 i s 32,200.00 I Labor rates for geologist and technician Eire based on typical labor rates for the area. Cost Adjustment Checklist: COST ESTIMATE FACTOR: Includes H&S Productivity (labor & equip)? Cost escalation to b<1Se year? Subcontractor overhead and profit included? Prime contractor overhead and profit Included? NOTES: Quote is for Level D. Current year (2009) is base year. Included in quote. Includes 15% overhead. Profit is included with cost summary. Notes $65/hr geo + $45/hr technician Alternative 2a: MNA COST SUB-ELEMENT: WELLS Site: Location: Phase: Base Year; Sigmon's Septic Tank Sito (Sequence 2) Statesville, Iredell County, North Carolina Feasibility Stuby of Remedial Alternatives 2009 Item Description Cost Per Shallow Extraction or Monitoring Well Setup & □econ Drill & Install Wellhead completion IOW Handling Drilling Oversight SUBTOTAL Prime Contractor Overhead {15%} TOTAL Unit Cost Source of Cost Data: Table 19 (Continued) Alternative 2a Cost Summay Details Sigmon's Septic Tank Statesville, Iredell County, North Carolina Element Install 8 shallow monitoring wells Description: Estimated Units Quantity Unit Price HR 1 $ 125.00 $ FT 65 $ 55.00 I LS $ 950.00 $ HR $ 175.00 ' HR 6 $ 110.00 $ $ Total 125.00 3,575.00 950.00 175.00 660.00 5.485.00 822.75 1$..t':;VJ' 6 307.75 Labor rates for geologist and technician are based on typical labor rates for the eree. Cc;ist Adjustment Checklist: COST ESTIMATE FACTOR: Includes H&S ProducUvlty (labor & equip)? Cost escalatlc;,n to base year? Area cost factored in? Subcontracior overhead and profit included? Prime contractor overhead and profit Included? NOTES· Quote is for Level 0. Current year (2009) is base year. Quote Is lrom local vendor. Included in quote Includes 15% overhead. Profit is included with cost summ:11y. Notes Includes well materials lnciudes vault, tee with fittings $65/hr geo -+-$45/hr technician / RA ·NCDENR North Carolina Department of Environment and Natural Resources Division of Waste Management Beverly Eaves Perdue Governor Ms. Beverly Stepter Dexter R. Matthews Director 10 September 2009 Superfund Branch, Waste Management Division US EPA Region IV 61 Forsyth Street. SW Atlanta, Georgia 30303 SUBJECT: · Concurrence with Record of Decision Sigmon's Septic Tank Site Operable Unit 2 Statesville, Iredell County Dear Ms. Stepter: Dee Freeman Secretary The State ofNorth Carolina by and through its Department of Environment and Natural Resources, Division of Waste Management (herein after referred tci as "the state"), reviewed the Record of Decision (ROD) received by the Division on 31 August 2009 for the Sigmon's Septic Tank Site Operable Unit 2 Site and concurs with the selected remedy, subject to the following conditions: 1 .. The 15A NCAC 21 Groundwater Standards for iron is 0.3 mg/I and 0.05 mg/I for manganese. The ground water cleanup levels for these metals in the ROD are above the North Carolina Groundwater Standards. The State expects the ARAR for iron and manganese to be achieved before the remediation process is complete. The State does not intend that this condition interfere with the implementation of the proposed remedies as stated in the ROD. 2. State concurrence on the ROD for this site is based solely on the information contained in the ROD received by the State on 24 August 2009. Should the State receive new or additional information which significantly affects the conclusions or amended remedy contained in the ROD, it may modify or . withdraw this concurrence with written notice to EPA Region IV. 3. State concurrence on this ROD in no way binds the State to concur in future decisions or commits the State to participate, financially or otherwise, in the cleanup of the site. The State reserves the right to review, overview comment, and make independent assessment of all future work relating to this site. 1646 Mail Service Center, Raleigh, North Carolina 27699-1646 Phone: 919-508-<1400 I FAX: 919-715-4061 I Internet: www.wastenotnc.org /vi Equal Opportunity\ Affirmative Action Employer Ni~carolina )Vaturally 4. If, after remediation is complete, the total residual risk level exceeds 10·6, the State may require deed recordation/restriction to document the presence ofresidual contamination and possibly limit future use of the property as specified in NCGS 130A-310.8 The State of North Carolina appreciates the opportunity to comment on the ROD and looks forward to working with EPA on the remedy for the subject site. If you have any questions or comments, please call Mr. Nile Testerman at 919 508-8482. · cc: v1ack Butler, Chief NC Superfund Section David Lown, NC Superfund · Nile Testerman, NC Superfund 1646 Mail Service Genier, Raleigh, North Carolina 27699-1646 Sincere! , Dexter R. Matthews, Director Division of Waste Management Phone: 919-508-8400 I FAX: 919-715-4061 I Internet: www.wastenotnc.org An Equal Opportunity\ Affirmative Action Employer Ni~carolina ;Naturall!f