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Home My WebLink About14023_Idaho Timber_OAR_2007_06_29 ADDENDUM TO COMPREHENSIVE SITE ASSESSMENT REPORT IDAHO TIMBER OF NORTH CAROLINA, LLC 1431 NICHOLAS STREET HENDERSON, VANCE COUNTY, NORTH CAROLINA INCIDENT NO.: 87480 RANK: 250A Sources of the Releases: (1) oil and grease discharges and (2) a diesel fuel AST or other petroleum Causes of Releases: (1) apparent non-point discharge and/or discharge to septic system and (2) apparent leaks and/or overfills or other non-point petroleum discharge Date Releases Discovered: July 22, 2005 Quantity of Releases: Unknown Latitude: 36° 18’ 38” N Longitude: 78° 24’ 17” W Prepared For: Mr. Dave Taugher Idaho Timber , LLC 1299 North Orchard St. Suite 300 Boise, Idaho 83707 (208) 377-3000 Prepared By: Mid-Atlantic Associates, Inc. 409 Rogers View Court Raleigh, North Carolina 27610 (919) 250-9918 June 29, 2007 409 Rogers View Court / Raleigh / North Carolina / 27610 800-486-7568 / 919-250-9918 / 919-250-9950 Facsimile www.maaonline.com ADDENDUM TO COMPREHENSIVE SITE ASSESSMENT REPORT IDAHO TIMBER OF NORTH CAROLINA, LLC 1431 NICHOLAS STREET HENDERSON, NORTH CAROLINA, 27537 INCIDENT NO.: 87480 RANK: 250A Sources of the Releases: (1) oil and grease discharges and (2) a diesel fuel AST or other petroleum Causes of Releases: (1) apparent non-point discharge and/or discharge to septic system and (2) apparent leaks and/or overfills or other non-point petroleum discharge Date Releases Discovered: July 22, 2005 Quantity of Releases: Unknown Latitude: 36° 18’ 38” N Longitude: 78° 24’ 17” W Mid-Atlantic Associates Job No. 000R1655.00 June 29, 2007 Prepared For: Prepared By: Mr. Dave Taugher MID-ATLANTIC ASSOCIATES, INC. Idaho Timber , LLC 1299 North Orchard St. Suite 300 Boise, Idaho 83707 Raymond S. Marchant, III, L.G. Senior Geologist Darin M. McClure, P.E. Principal Engineer TABLE OF CONTENTS LIST OF ACRONYMS ...................................................................................................i 1.0 GENERAL INFORMATION...................................................................................1 2.0 RECEPTOR INFORMATION.................................................................................2 2.1 Water-Supply Wells......................................................................................2 2.2 Public Water Supplies ..................................................................................2 3.0 SITE GEOLOGY AND HYDROGEOLOGY ...........................................................3 3.1 Site Geology.................................................................................................3 3.2 Site Hydrogeology ........................................................................................4 4.0 GROUNDWATER SAMPLING RESULTS ............................................................4 4.1 Vehicle Maintenance Shop...........................................................................5 4.2 Diesel Fuel AST Area ...................................................................................6 4.3 Water-Supply Well Sampling........................................................................7 5.0 DISCUSSION.........................................................................................................8 5.1 Vehicle Maintenance Shop...........................................................................8 5.2 Diesel Fuel AST Area ...................................................................................8 6.0 CONCLUSIONS AND RECOMMENDATIONS .....................................................9 6.1 Vehicle Maintenance Shop...........................................................................9 6.2 Diesel Fuel AST Area .................................................................................10 DRAWINGS Drawing 3.1 Geologic Cross-Section Location Map – Vehicle Maintenance Shop Drawing 3.2 Cross-Section A-A’ - Vehicle Maintenance Shop Drawing 3.3 Cross-Section B-B’ - Vehicle Maintenance Shop Drawing 3.4 Geologic Cross-Section Location Map – – Diesel Fuel AST Area Drawing 3.5 Cross-Section A-A’ – Diesel Fuel AST Area Drawing 3.6 Cross-Section B-B’ – Diesel Fuel AST Area Drawing 3.7 Estimated Water Table Elevation Map – 4/16/07 Drawing 3.8 Estimated Potentiometric Surface Elevation Map – 4/16/07 Drawing 4.1 Benzene in Shallow Groundwater – April 2007 Drawing 4.2 Benzene in Intermediate Groundwater – April 2007 TABLE OF CONTENTS (CON’T.) TABLES Table 3.1 Summary of Well Construction Information and Water Level Measurements Table 3.2 Summary of Vertical Hydraulic Gradient Calculations Table 4.1 Summary of Groundwater Monitoring Results APPENDICES Appendix A City of Henderson Municipal Water Line Diagram for Skenes Avenue Appendix B Soil Boring Logs and Well Construction Records Appendix C Laboratory Analytical Reports and Chain-of-Custody Records for Groundwater Samples LIST OF ACRONYMS i 2000 Guidelines Groundwater Section Guidelines for Investigation and Remediation of Soil and Groundwater, DENR, Division of Water Quality Groundwater Section, July 2000. 2001 Guidelines Underground Storage Tank Section Guidelines for Assessment and Corrective Action, DENR, Division of Waste Management UST Section, July 2001. AFVR Aggressive Fluid-Vapor Recovery AS Air Sparge AST Aboveground Storage Tank BQL Below (Laboratory Practical) Quantitation Limit BLS Below Land Surface BTEX Benzene, Toluene, Ethylbenzene, Xylenes CAP Corrective Action Plan cm Centimeter COC Constituents of Concern CSA Comprehensive Site Assessment DIPE Diisopropyl Ether (also IPE: Isopropyl Ether) DNAPL Dense Non-Aqueous Phase Liquids DO Dissolved Oxygen DPT Direct Push Technology DRO Diesel Range Organics DSCA North Carolina Dry-Cleaning Solvent Act DTW Depth to Water DWM Division of Waste Management DWQ Division of Water Quality EDB Ethylene di-bromide EPA Environmental Protection Agency EPH Extractable Petroleum Hydrocarbons FID Flame Ionization Detector FT Feet GCL Gross Contamination Level GIS Geographic Information System GPM Gallons Per Minute GPS Global Positioning System GRO Gasoline Range Organics ID Identification IDW Investigation Derived Waste IGQS Interim Groundwater Quality Standards ITNC Idaho Timber of North Carolina, LLC LSA Limited Site Assessment LUST Leaking Underground Storage Tank m Meter MADEP Massachusetts Department of Environmental Protection Mid-Atlantic Mid-Atlantic Associates, Inc. MDL Method Detection Limit mg/Kg Milligrams per Kilogram mg/L Milligrams per Liter MMP Minimum Management Practices MMPE Mobile Multi-Phase Extraction MNA Monitored Natural Attenuation MSCC Maximum Soil Contaminant Concentration MSL Mean Sea Level MTBE Methyl tertiary butyl ether μg/Kg Micrograms per Kilogram μg/L Micrograms per Liter NA Not Analyzed N/A Not Applicable NC North Carolina NCAC North Carolina Administrative Code NCDENR North Carolina Department of Environment and Natural Resources NCGQS North Carolina Groundwater Quality Standards NCSWQS North Carolina Surface Water Quality Standards ND Not Detected NM Not Measured NORR Notice of Regulatory Requirements NOV Notice of Violation NS Not Sampled OVA Organic Vapor Analyzer PA Prioritization Assessment PAA Prioritization Assessment Agreement PAH Polynuclear Aromatic Hydrocarbons Pb Lead PCBs Polychlorinated Biphenyls PCE Perchloroethylene (also tetrachloroethene) PPB Parts Per Billion PPM Parts Per Million PID Photo Ionization Detector POTW Publicly Owned Treatment Works PQL Practical Quantitation Limit PRF Prioritization Ranking Form PVC Polyvinyl chloride RBCA Risk-Based Corrective Action RCRA Resource Conservation and Recovery Act ROI Radius of Influence s Seconds SAR Soil Assessment Report SOW Scope of Work STG Soil-to-Groundwater SVE Soil Vapor Extraction SVOC Semi-Volatile Organic Compound TDHF Toxicologically Defined Hydrocarbon Fractions TCLP Toxicity Characteristic Leaching Procedure TIC Tentatively Identified Compound TOC Top of Casing TPH Total Petroleum Hydrocarbons US United States USCS Unified Soil Classification System USGS United States Geological Survey UST Underground Storage Tank UT Unnamed Tributary VOC Volatile Organic Compounds VPH Volatile Petroleum Hydrocarbons yr Year 1.0 GENERAL INFORMATION The subject site, which is located at 1431 Nicholas Street in Henderson, North Carolina, consists of three contiguous parcels that total approximately 19 acres and are currently developed with an office and dimensional lumber manufacturing plant with approximately 80,000 square feet of manufacturing and storage buildings. Mid-Atlantic performed a Phase I Environmental Site Assessment (PESA) at the site in January 2005. Existing monitoring wells were observed on site. During the PESA, several areas of environmental concern were noted. Based on these concerns, Weil, Gotshal & Manges, LLP contracted VERTEX Engineering Services, Inc. (VERTEX) to perform a Limited Subsurface Investigation at the site to address the areas of environmental concern. VERTEX collected soil and groundwater samples from various portions of the site. Impacted soil (oil and grease at 1,200 mg/Kg or ppm and ethylbenzene and naphthalene in concentrations exceeding the soil-to-groundwater MSCC) was detected beneath the former maintenance shop. Additionally, benzene and 1,2-dichloroethane were detected in groundwater beneath the central portion of the site in concentrations exceeding their NCGQS. Based on the distribution of these compounds in groundwater, it appears that a former diesel fuel AST and/or other petroleum releases in this area may be a source of these compounds. Since soil and groundwater have been impacted at the site, ITNC contracted with Mid- Atlantic to perform a CSA for these areas. A Comprehensive Site Assessment Report dated November 13, 2006 was submitted to the NCDENR, Division of Water Quality, Aquifer Protection Section (APS). After review of the report, the APS issued a Notice of Violation (NOV) to Idaho Timber dated December 29, 2006 requesting additional assessment for completion of the CSA. Specifically, the NOV requested installation of four additional vertical extent monitoring wells and re-sampling of the other site monitoring wells. This addendum report is intended to satisfy these requirements. The original due date for the CSA Addendum was March 30, 2007. However, jurisdiction of the site was transferred from the Division of Water Quality (APS) to the Division of Waste Management (Underground Storage Tank Section) in a Memorandum of Agreement on February 20, 2007. In a letter dated March 8, 2007, the UST Section granted an extension of the due date for the CSA Addendum report until June 30, 2007. For other information related to the CSA, please refer to our report dated November 13, 2006. We have included updated information where available. This addendum report is intended to provide data related to the assessment activities requested in the NOV dated December 29, 2006 and provide current groundwater monitoring data. The report also provides updated assessment and receptor information, where applicable, as well as our conclusions and recommendations. (Note: Since the vehicle maintenance shop and the former diesel AST are in separate locations on site, we have addressed the assessment of each release separately, as was done in the CSA Report). Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 2 Henderson, North Carolina The opinions included herein are based on our experience and the information obtained during the study. This report is based on limited observations made on the dates noted using the procedures described herein. If additional information becomes available, we request the opportunity to review the information, reassess the potential environmental concerns and modify our conclusions and recommendations, if appropriate. 2.0 RECEPTOR INFORMATION Our update is as follows. Please see CSA Report for complete receptor information. 2.1 Water-Supply Wells It is our understanding that the NCDENR performed sampling of two water-supply wells on October 16, 2006 (see Section 4.3). Mr. Jim Greer of the Aquifer Protection Section performed the site visit and the sampling. 2.2 Public Water Supplies Availability of municipal water to area within 1,500 feet of the source area of release: Although the City of Henderson originally informed us that municipal lines were available to the entire 1,500 foot radius study area, we have since learned that this is not the case. Mr. Frank Frazier of the City of Henderson informed us that municipal lines are not available to portions of certain roads, including Skenes Avenue, where two water-supply wells (220 and 340 Skenes) are used for potable purposes. A City-provided diagram showing the locations and sizes of the water lines on Skenes Avenue is provided in Appendix A. Preliminary estimates provided by the City to provide a municipal connection to 220 and 340 Skenes Avenue are $5,000 and $15,000, respectively. Distance from source area of release to nearest public water lines: Based on the diagram provided by the City of Henderson, a two-inch diameter water main extends down Skenes Avenue 1,560 feet west of Epsom Road. The water line would need to be extended west approximately 150 to 200 feet to provide water to 340 Skenes Avenue. Additionally, the water line beneath Nicholas Street could be extended east approximately 250 feet to provide water to 220 Skenes Avenue. Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 3 Henderson, North Carolina 3.0 SITE GEOLOGY AND HYDROGEOLOGY 3.1 Site Geology GENERAL GEOLOGIC PROFILE APPROXIMATE DEPTH (FEET BLS) GEOLOGY TYPE 0 - 20 Mostly orange-brown, brown, and tan sandy silts and silty sands with occasional clays; some fill areas in the top five feet. 20 - 40 Partially-weathered rock, highly fractured in some areas 40 - >325 Bedrock, more competent granite and/or gneiss; occasional fractures Geologic Descriptions and Cross-Sections: Vehicle Maintenance Shop A soil boring log associated with the well installed at the vehicle maintenance shop (MW-17D) is provided in Appendix B. A map showing geologic cross section locations is provided as Drawing 3.1. An updated geologic cross section (B-B’) of this area and showing deep monitoring well MW-17D is provided as Drawing 3.3. (Note: a revised cross-section A-A’, Drawing 3.2, is also provided because there was a vertical scaling error on the originally submitted drawing). Diesel Fuel AST Geologic logs of site soil borings associated with the diesel fuel AST are provided in Appendix B. A map showing geologic cross section locations is provided as Drawing 3.4. Geologic cross sections of this area of the site are shown on Drawings 3.5 and 3.6. Anticipated effect of geology on migration/attenuation of contaminants: The assessment performed for this addendum revealed varying thicknesses of partially-weathered rock as well as depths to competent rock beneath the site. The transition zone from unconsolidated overburden to competent bedrock (from approximately 20 to 40 feet BLS) appears to consist of a mixture of highly fractured bedrock, alternating zones of competent and weathered rock, and sandy zones. Relatively large amounts of groundwater were encountered in this zone while drilling the boreholes for wells MW-2D and MW-14D. This zone could act as a preferential migration pathway for contaminants. Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 4 Henderson, North Carolina 3.2 Site Hydrogeology The following table provides an updated summary of the site’s hydrogeological parameters. Locations of calculations, backup data, and applicable summaries are provided in the Additional Information column. HYDROGEOLOGIC PARAMETERS PARAMETER RESULT ADDITIONAL INFORMATION Average Depth to Shallow Groundwater 10.64 feet (range 5.37 to 19.46) Table 3.1 Shallow aquifer - southeast Intermediate aquifer - southeast Groundwater Flow Direction Vertical - downward Drawings 3.7 and 3.8, Tables 3.1 and 3.2 Shallow Aquifer Hydraulic Gradient (Horizontal) 0.026 ft/ft (measured from MW-3 to MW-16) 93.76 ft - 74.90 ft 730 ft Intermediate Aquifer Hydraulic Gradient (Horizontal) 0.026 ft/ft (measured from MW-19D to MW-2D) 90.80 ft – 81.22 ft 370 ft Average Hydraulic Gradient (Vertical, between shallow and intermediate aquifer) +0.033 ft/ft (downward*, “recharge area”) Table 3.2 Vertical Hydraulic Gradient (between intermediate and deep aquifer) +0.005 ft/ft (downward, “recharge area”) Table 3.2 *The vertical groundwater flow direction calculated for the wells at the vehicle maintenance facility is slightly upward (“discharge area”). 4.0 GROUNDWATER SAMPLING RESULTS NCDENR APS’ NOV dated December 29, 2006 requested sampling of existing site monitoring wells as well as the newly-installed vertical extent wells. We have provided our assessment and sampling results below. Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 5 Henderson, North Carolina 4.1 Vehicle Maintenance Shop The table below summarizes monitoring well installation phases and dates for wells installed at the site in association with the vehicle maintenance shop. GROUNDWATER ASSESSMENT PHASES PHASE WELL INSTALLATION DATES WELLS INSTALLED VERTEX’s assessment July 2005 GW-2 and GW-3 (temporary wells) CSA October 28, 2005 MW-11 CSA Addendum April 11-13, 2007 MW-17D Rationale for Monitoring Well Location: In the NOV dated December 29, 2006, the NCDENR APS requested a vertical extent well to be paired with existing shallow monitoring well MW-11. Well Construction Information: The well was screened in the top of bedrock to test for the potential downward vertical migration of petroleum hydrocarbons and volatile organic compounds. Well construction details are shown on Table 3.1 and a well construction record is provided in Appendix B. Summary of Groundwater Sampling Results: Groundwater samples were collected from both wells associated with the vehicle maintenance shop on April 16, 2007. Groundwater sampling procedures were provided in the previous CSA Report. Laboratory analytical reports for groundwater samples are provided in Appendix C and the results are summarized in Table 4.1. For comparison purposes, the NCGQS are also provided in the table. The results show that vinyl chloride was detected in the sample collected from monitoring well MW-11 at a concentration exceeding its NCGQS. However, the sample collected from vertical extent well MW-17D did not exhibit vinyl chloride at concentrations exceeding the laboratory’s method detection limit (MDL). Since the MDL is greater than the NCGQS, Mid-Atlantic contacted the laboratory to Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 6 Henderson, North Carolina determine if a lower detection limit could be obtained. The chemist indicated that it could not, but examined the chromatogram for the sample and did not observe evidence that vinyl chloride was in the sample. See Case Narrative for laboratory report number G122-2952 for further information. 4.2 Diesel Fuel AST Area The table below summarizes monitoring well installation phases and dates for wells associated with the diesel fuel AST area. GROUNDWATER ASSESSMENT PHASES – DIESEL FUEL AST AREA PHASE WELL INSTALLATION DATES WELLS INSTALLED Previous Assessments Prior to 2005 MW-5 through MW-10 CSA October 27-28, 2005 MW-1, MW-2, MW-3, MW-4A CSA January 26-27, 2006 MW-2D, MW-12, MW-13 CSA June 14-19, 2006 MW-14D CSA October 13, 2006 MW-15, MW-16 CSA Addendum April 8-13, 2007 MW-18D, MW-19D, MW-20D Rationale for Monitoring Well Locations: In the NOV dated December 29, 2006, the NCDENR APS requested vertical extent wells to be paired with existing shallow monitoring wells MW-3, MW-4A, and MW- 15. (Note: MW-19D was placed as close to MW-3 as feasible, due to an overhead power line and other site physical constraints.) Well Construction Information: The three wells installed during the CSA addendum work were intended to evaluate the vertical extent of petroleum contamination with respect to the diesel AST release. Well construction details are shown on Table 3.1 and well construction records are provided in Appendix B. Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 7 Henderson, North Carolina Summary of Groundwater Sampling Results: On April 16, 2007, groundwater samples were collected from monitoring wells associated with the release in the diesel fuel AST area. Groundwater sampling procedures were provided in the previous CSA Report. Laboratory analytical reports for groundwater samples are provided in Appendix C and the results are summarized in Table 4.1. For comparison purposes, the NCGQS are also provided in the table. Estimated Extent of Impacted Groundwater: An updated isoconcentration map showing the estimated lateral extent of benzene in the shallow aquifer is provided in Drawing 4.1. Additionally, an isoconcentration map showing the estimated lateral extent of benzene in the “intermediate” aquifer (the partially-weathered rock zone) is provided in Drawing 4.2. It appears that the vertical extent of benzene in groundwater is less than 73 feet BLS, where the screened interval begins for monitoring well MW-14D. The highest concentrations of benzene in groundwater beneath the site were detected in samples collected from monitoring well MW-2D, whose screened interval is located in the highly fractured transition zone from weathered rock to competent rock. 1,2-Dichloroethane (1,2- DCA) was also detected in samples collected from monitoring wells MW-2, MW-2D, MW-14D and MW-19D in concentrations exceeding its NCGQS of 0.38 ug/L. 1,1- Dichloroethene (1,1-DCE) was detected in the sample collected from monitoring well MW-12 at a concentration of 13.6 ug/L, which exceeds its NCGQS of 7.0 ug/L. 4.3 Water-Supply Well Sampling Mid-Atlantic did not collect samples from the water-supply wells located at 220 Skenes Avenue (Mary Eley property) and 340 Skenes Avenue (Tonya Henderson property) during the CSA Addendum activities. However, Mr. Eric Rice of the NCDENR APS reported that Mr. Jim Greer of that office collected samples from these wells on October 16, 2006. The following concentrations were reported: Well Location Tetrachloro- ethylene (ug/L) 1,2-Dichloro- ethane (ug/L) 1,1-Dichloro- ethene (ug/L) 1,1-Dichloro- ethane (ug/L) Chloroform (ug/L) NCGQS 0.7 0.38 7 70 70 220 Skenes 18 4.7 14 ND ND 340 Skenes 1.3 0.95 0.52 0.50 0.39 Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 8 Henderson, North Carolina 5.0 DISCUSSION 5.1 Vehicle Maintenance Shop Nature and Extent of Contamination: Groundwater Although vinyl chloride was detected in shallow groundwater at a concentration exceeding its NCGQS, it appears in trace concentrations and appears to be a byproduct of biodegradation of solvents that may have historically been used at the site prior to ITNC’s acquisition of the property. Furthermore, the impact to groundwater appears to be limited horizontally and vertically to a relatively small area. See Section 7.1 for further discussion. Potentially Affected Receptors: Due to its location and nature (beneath a building, limited impact to groundwater), it appears that the release associated with the vehicle maintenance facility is not currently a threat to any receptors identified during our survey. 5.2 Diesel Fuel AST Area Nature and Extent of Contamination: Shallow Groundwater The results of the groundwater sampling for shallow monitoring wells indicate results similar to sampling conducted previously for the CSA and appear to be indicative of a petroleum release. Benzene was detected in the site’s shallow groundwater near the former diesel fuel AST (12.6 ug/L at MW-1), but higher concentrations were detected in wells located hydraulically downgradient (e.g., 57.5 ug/L at MW-2) of the diesel fuel AST area. The contaminant plume in shallow groundwater appears to be within the confines of the property boundary on the downgradient side of the plume. Intermediate Groundwater Relatively higher concentrations of benzene (360 ug/L at MW-2D) were found in the “intermediate” well screened in the more fractured partially-weathered rock zone. This well is located hydraulically downgradient of the former diesel fuel AST location. Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 9 Henderson, North Carolina Deep Groundwater Groundwater quality data from deeper monitoring well MW-14D suggests that the vertical extent of the benzene contamination is less than 73 feet BLS. However, 1,2-DCA was detected at an estimated concentration of 0.721 ug/L, which is above its NCGQS of 0.38 ug/L. Potentially Affected Receptors: Private water-supply wells used for potable purposes are located in the vicinity of the release, as discussed in the CSA Report. The construction details (depth of well, depth of casing, etc.) are not known for a number of the wells. The sample collected in October 2006 from the well located at 340 Skenes Avenue exhibited benzene and tetrachloroethylene at concentrations exceeding their respective NCGQS. Also, as outlined in Section 4.3, NCDENR samples collected from water- supply wells at 340 Skenes and 220 Skenes exhibited tetrachloroethylene, which was not detected in samples collected from monitoring wells located on the Idaho Timber property. Benzene and tetrachloroethylene were not detected in the samples collected from the shallow monitoring wells or the intermediate well (MW-20D) along the site’s southern property boundary, which is upgradient of the 340 Skenes water-supply well. Although the construction details of the well at 340 Skenes have not been confirmed, the well appears to be a bored well. According to Mr. Jim Greer of the NCDENR APS, if the well is a bored well, it is likely to be in the range of 40 feet deep. Therefore, it is likely that monitoring wells installed on the Idaho Timber property’s southern edge are monitoring vertical groundwater zones from which the 340 Skenes Avenue well draws water. 6.0 CONCLUSIONS AND RECOMMENDATIONS 6.1 Vehicle Maintenance Shop Based on the results of this additional assessment conducted for the CSA, we conclude the following for the release associated with the vehicle maintenance shop: • Vinyl chloride was detected at a concentration exceeding its NCGQS in the shallow well, but appears to be localized and may be a degradation byproduct, as discussed in the CSA Report; and Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 10 Henderson, North Carolina • Based on the sampling results of monitoring well MW-17D, groundwater contamination does not appear to be deeper than 42 feet BLS. Based on these conclusions, we recommend the following for the release associated with the vehicle maintenance shop: • Performing a cost and technical evaluation of remedial alternatives, and preparation of a CAP based on the results; and • Submittal of this report to the NCDENR, DWM, Underground Storage Tank Section for their review and comment. 6.2 Diesel Fuel AST Area Based on the results of the investigation that are discussed above, we conclude the following for the release detected in the area of the diesel fuel AST: • Shallow groundwater at the site has been impacted by VOCs (primarily the petroleum hydrocarbon benzene) which is indicative of a petroleum release. The contamination appears to be confined within the limits of the monitoring well network, except for the upgradient direction. • The weathered intermediate transition zone from saprolite to bedrock (which in some areas contains large, water-bearing fractures) has also been impacted by the release. Since concentrations are greater in this zone, it appears that the bulk of the contamination may be in this zone; • Based on the sampling results from MW-14D, impact of the release to the deep, bedrock aquifer appears to be minimal; • Two private water-supply wells located near the site on Skenes Avenue have been impacted by regulated compounds. However, based on our assessment data and the type of compounds found in the wells (tetrachloroethylene, in particular), it does not appear that these compounds originated from the Idaho Timber site; and • Since the site is primarily impacted with petroleum-fuel related compounds, it appears that this site should continue to be regulated by the Underground Storage Tank Section of the Division of Waste Management (and not the Hazardous Waste Section). Addendum to Comprehensive Site Assessment Report June 29, 2007 Idaho Timber of North Carolina, LLC Page 11 Henderson, North Carolina Based on these conclusions, we recommend the following for the release located in the area of the diesel fuel AST: • Performing a cost and technical evaluation of remedial alternatives and preparation of a CAP based on the results; and • Submittal of this report to the NCDENR, DWM, Underground Storage Tank Section for their review and comment. DRAWINGS TABLES APPENDIX A CITY OF HENDERSON MUNICIPAL WATER LINE DIAGRAM FOR SKENES AVENUE APPENDIX B SOIL BORING LOGS AND WELL CONSTRUCTION RECORDS APPENDIX C LABORATORY ANALYTICAL REPORTS AND CHAIN OF CUSTODY RECORDS FOR GROUNDWATER SAMPLES