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Home My WebLink About2013-04-10 NC0004987 Duke Marshall SS Assessment Work Plan526 South Church St. Charlotte, NC 28202 P.O. Box 1006 Mail Code EC13K Charlotte, NC 28201-1006 336-215-4576 704-382-6240 fax Page 1 of 2 April 10, 2013 Mr. Andrew Pitner North Carolina Department of Environment and Natural Resources Division of Water Quality Aquifer Protection Section 610 East Center Avenue, Suite 301 Mooresville, NC 28115 Subject: Duke Energy Carolinas, LLC Marshall Steam Station Ash Basin NPDES Permit NC0004987 Proposed Groundwater Assessment Work Plan Dear Mr. Pitner: Duke Energy submits this proposed work plan, prepared by HDR Engineering, Inc., to assess groundwater in the vicinity of the Marshall Steam Station ash basin system. This proposed work plan has been developed in response to correspondence between NCDENR, Duke Energy and HDR personnel since March 2012. The proposed groundwater assessment work plan describes the tasks for assessment of groundwater exceedances. The next sampling event will occur in June 2013. If NCDENR approval of this work plan is received by May 17, 2013, the proposed schedule is to submit the groundwater assessment report approximately 120 days after the June 2013 groundwater sampling event. The groundwater assessment report will be submitted 150 days after the next scheduled groundwater sampling event if redevelopment of one or more of the monitoring wells is required. If NCDENR approval of this work plan is not received by May 17, 2013, the schedule will be revised after NCDENR approval is received. If you have any questions or concerns, please contact me at 336-215-4576 or at kim.hutchinson@duke- energy.com Sincerely, Kimberlee Hutchinson, PE Environmental Services cc: Mr. Joju Abraham – NCDENR DWQ APS, MRO Ms. Maria Schutte – NCDENR DWQ APS, MRO Mr. George Tolbert – Marshall Steam Station Mr. Ed Sullivan – Duke Energy Corporation Ms. Dayna Herrick – Duke Energy Corporation Mr. Allen Stowe – Duke Energy Corporation Mr. Tim Hunsucker – Duke Energy Corporation Mr. Bill Miller – HDR Engineering, Inc. Mr. Scott Spinner – HDR Engineering, Inc. April 10, 2013 Via email: Kim.Hutchinson@Duke-energy.com Ms. Kim Hutchinson, P.E. Duke Energy Carolinas, LLC 400 South Church Street Charlotte, NC 28201-1006 Subject:Duke Energy Carolinas, LLC Marshall Steam Station Ash Basin - NPDES Permit NC0004987 Proposed Groundwater Assessment Work Plan Dear Ms. Hutchinson: As requested by Mr. Ed Sullivan, P.E., of Duke Energy Carolinas, LLC (Duke Energy), HDR Engineering, Inc. of the Carolinas (HDR) presents the proposed groundwater assessment work plan for the Marshall Steam Station ash basin. The proposed work plan presents the tasks for performing the assessment of the exceedances of the North Carolina Administrative Code Title 15A Chapter 02L .0202 (g) groundwater quality standards measured in groundwater monitoring wells at the Marshall Steam Station ash basin, located in Catawba County, North Carolina. The tasks presented in the proposed groundwater assessment work plan were developed from discussions and information provided by Duke Energy personnel and from a letter from Mr. Andrew Pitner, P.G., from the North Carolina Department of Environment and Natural Resources Division of Water Quality Aquifer Protection Section to Mr. Ed Sullivan and Mr. Allen Stowe, both with Duke Energy, dated March 16, 2012. HDR appreciates the opportunity to assist Duke Energy with this project. Should you have any questions regarding this submittal or need further information, please do not hesitate to contact me at (828) 891-6296 or bill.miller@hdrinc.com. Respectfully submitted, HDR Engineering, Inc. of the Carolinas William M. Miller, P.E. Senior Engineer Attachments: Duke Energy Carolinas, LLC, Marshall Steam Station Ash Basin, NPDES Permit NC0004987, Proposed Groundwater Assessment Work Plan DUKE ENERGY CAROLINAS, LLC MARSHALL STEAM STATION ASH BASIN NPDES PERMIT NC0004987 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN Prepared for: DUKE ENERGY CAROLINAS, LLC Charlotte, North Carolina Prepared by: HDR ENGINEERING, INC. OF THE CAROLINAS Charlotte, North Carolina April 10, 2013 ii MARSHALL STEAM STATION ASH BASIN NPDES PERMIT NC0004987 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN TABLE OF CONTENTS Section Title Page No. 1 INTRODUCTION ................................................................................................... 1 2 SITE DESCRIPTION .............................................................................................. 2 2.1 Plant Description ..........................................................................................................2 2.2 Ash Basin Description ..................................................................................................2 3 REGULATORY REQUIREMENTS ............................................................................ 4 4 SITE HYDROGEOLOGY ........................................................................................ 5 5 DESCRIPTION OF GROUNDWATER MONITORING SYSTEM .................................... 7 6 GROUNDWATER MONITORING RESULTS ............................................................. 9 7 GROUNDWATER ASSESSMENT WORK PLAN ...................................................... 10 8 ASSESSMENT REPORT AND PROPOSED SCHEDULE ............................................ 13 9 REFERENCES ..................................................................................................... 14 FIGURES 1 SITE LOCATION MAP 2 SITE LAYOUT MAP iii MARSHALL STEAM STATION ASH BASIN NPDES PERMIT NC0004987 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN TABLE OF CONTENTS TABLES TABLE 1 – GROUNDWATER SAMPLING REQUIREMENTS TABLE 2 - EXCEEDANCES OF 2L STANDARDS APPENDIX APPENDIX A - LETTER FROM ANDREW H. PITNER, P.G., REGIONAL AQUIFER PROTECTION SUPERVISOR, NCDENR DIVISION OF WATER QUALITY, TO ED SULLIVAN AND ALLEN STOWE, WATER MANAGEMENT, DUKE ENERGY CORPORATION, DATED MARCH 16, 2012 1 Section 1 Introduction Duke Energy Carolinas, LLC (Duke Energy), owns and operates the Marshall Steam Station (Marshall), located on Lake Norman in Catawba County, North Carolina (see Figure 1). The steam station generates electricity by burning coal. Exceedances of the North Carolina Administrative Code (NCAC) Title 15A Chapter 02L (g) groundwater quality standards (2L Standards) have been measured in groundwater samples collected from groundwater monitoring wells at the Marshall ash basin. In a letter dated March 16, 2012, the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Quality (DWQ) Aquifer Protection Section (APS) requested that Duke Energy begin additional assessment activities at stations where measured and modeled concentrations of groundwater constituents exceed the 2L Standards at the compliance boundary. The letter is included as Appendix A. HDR Engineering, Inc. of the Carolinas (HDR) has prepared this proposed groundwater assessment work plan on behalf of Duke Energy. This document presents a proposed work plan for performing the groundwater assessment at the monitoring wells with measured exceedances of the 2L Standards. 2 Section 2 Site Description 2.1 Plant Description Marshall is a coal-fired electricity generating facility with a capacity of 2,090 megawatts located near the community of Terrell, in Catawba County, North Carolina. Marshall is a four-unit station which began commercial operation in 1965. Marshall is one of Duke Energy’s largest coal-burning plants in the Carolinas and has been ranked among the most efficient coal facilities in the United States. Marshall is located on the west side of Lake Norman and utilizes Lake Norman for cooling water. Lake Norman is part of Duke Energy’s Catawba-Wateree Hydroelectric Project (Federal Energy Regulatory Commission Project No. 2232) and has a surface area of approximately 32,475 acres. The Marshall site has five landfills permitted by the NCDENR Division of Waste Management under three permits. Two landfills are currently in operation: the Marshall Steam Station Industrial Landfill No. 1 (Permit No. 1812) and the Marshall Steam Station Flue Gas Desulfurization (FGD) Residue Landfill, Phase 1, Cell 1 (Permit No. 1809). Three separate landfills were operated under Permit No. 1804: an asbestos landfill, a construction and demolition debris landfill, and a two-phase dry ash landfill. These three landfills are no longer in operation. 2.2 Ash Basin Description Marshall operates an ash basin as part of the station’s wastewater treatment system. The coal ash residue from the coal combustion process is disposed of in the Marshall ash basin. The discharge from the ash basin is permitted by the NCDENR DWQ under the National Pollution Discharge Elimination System (NPDES) Permit NC0004987. The ash basin system consists of a single cell, impounded by an earthen dike, located on the southeast end of the ash basin. The ash basin was constructed in 1965 and is located approximately 2,000 feet northeast of the power plant. The waste boundary for the ash basin encompasses approximately 382 acres (see Figure Section 2 Site Description 3 2). The approximate pond elevation for the ash basin is 790 feet. The normal pond elevation of Lake Norman is approximately 760 feet. The ash basin system is an integral part of the station’s wastewater treatment system. The ash basin receives inflows from the following sources:  Ash removal system  Station yard drain sump  Stormwater flows  Station wastewater Due to the nature of station operations, inflows to the ash basin are highly variable. The inflows from the station to the ash basin are discharged into the southeast portion of the ash basin. The ash basin pond elevation is controlled by the use of concrete stop logs. The discharge from the ash basin is through a concrete discharge tower located in the eastern portion of the ash basin. The concrete discharge tower drains through a 30-inch diameter high density polyethylene pipe which discharges into Lake Norman. 4 Section 3 Regulatory Requirements The NPDES program regulates wastewater discharges to surface waters to ensure that surface water quality standards are maintained. Marshall operates under NPDES Permit NC0004987, which authorizes discharges from the ash basin in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit. The NPDES permitting program requires that permits be renewed every five years. The most recent NPDES permit renewal at Marshall became effective on March 1, 2011. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring to be conducted. Permit Condition A (11) Attachment XX, Version 1.1, dated June 15, 2011, lists the groundwater monitoring wells to be sampled, the parameters to be analyzed, and the requirements regarding sampling frequency and reporting the results. These groundwater monitoring requirements are provided in Table 1. The groundwater monitoring wells required by the NPDES permit, with the exception of MW-4 and MW-4D, were installed by Duke Energy in 2010. The locations for the monitoring wells were approved by the DWQ APS. Monitoring wells MW-4 and MW-4D were installed by Duke Energy in 1989 and 2006, respectively. The groundwater monitoring wells listed in Table 1 are sampled three times per year and the results are submitted to the NCDENR DWQ. The compliance boundary for groundwater quality at the Marshall ash basin is defined in accordance with NCAC Title 15A Chapter 02L .0107(a) (T15 A NCAC 02L .0107(a)) as being established at either 500 feet from the waste or at the property boundary, whichever is closest to the waste. The location of the monitoring wells, the waste boundary, and the compliance boundary are shown on Figure 2. 5 Section 4 Site Hydrogeology Marshall and its associated ash basin are located in the Kings Mountain Belt of the Piedmont physiographic province (Piedmont). The following generalizations on the site hydrogeology are taken from A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina (LeGrand 2004). Piedmont bedrock primarily consists of igneous and metamorphic bedrock. The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith includes, where present, the soil zone, a zone of weathered, decomposed bedrock known as saprolite, and alluvium, where present. Saprolite, the product of chemical and mechanical weathering of the underlying bedrock, is typically composed of clay and coarser granular material up to boulder size, and may reflect the texture of the rock from which it was formed. The weathering product of granitic rocks may be quartz-rich and sandy-textured, whereas rocks poor in quartz and rich in feldspar and other soluble minerals form a more clayey saprolite. The regolith serves as the principal storage reservoir for the underlying bedrock (LeGrand 2004). A transition zone may occur at the base of the regolith between the soil-saprolite and the un- weathered bedrock. This transition zone of partially weathered rock is a zone of relatively high permeability, compared to the overlying soil-saprolite and the underlying bedrock (LeGrand 2004). Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. LeGrand describes this as the local slope aquifer system. Under natural conditions the general direction of groundwater flow can be approximated from the surface topography (LeGrand 2004). Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains (LeGrand 2004). Section 4 Site Hydrogeology 6 A surface water divide is located approximately along Sherrills Ford Road, to the west of the ash basin. A surface water divide is located approximately along Island Ford Road, to the north of the ash basin. Both of these surface water divides likely function as groundwater divides. Lake Norman is located to the southeast of the ash basin. The predominant direction of groundwater flow from the ash basin is likely in a southeasterly direction, generally towards Lake Norman. 7 Section 5 Description of Groundwater Monitoring System As discussed in Section 3, groundwater monitoring is performed in accordance with the requirements of the NPDES permit. The groundwater monitoring for the ash basin consists of the following monitoring wells: MW-4, MW-4D, MW-10S, MW-10D, MW-11S, MW-11D, MW-12S, MW-12D, MW-13S, MW-13D, MW-14S, and MW-14D. These wells are sampled in February, June, and October each year. The locations for the monitoring wells were selected in consultation with the DWQ APS. Monitoring well MW-4 was installed by Duke Energy in 1989 as part of the Marshall Dry Ash Landfill (Permit No. 1804) groundwater monitoring network. Monitoring well MW-4D was installed by Duke Energy in 2006 prior to the installation of the compliance monitoring wells as part of a voluntary monitoring system. Based on the locations of monitoring wells MW-4 and MW-4D relative to the ash basin, they were incorporated into the ash basin compliance monitoring network. Monitoring wells MW-4, MW-10S, MW-11S, MW-12S, MW-13S, and MW-14S were installed by rotary drilling methods using hollow stem augers, with the well screen installed above auger refusal to monitor the shallow aquifer within the saprolite layer. These wells were installed with screen lengths of either 10 feet or 15 feet. The screens were installed with screen intervals ranging from 3 feet to 18 feet below ground surface (bgs) at MW-13S and 37 feet to 52 feet bgs at MW-11S. Monitoring wells MW-10D, MW-11D, MW-12D, MW-13D, and MW-14D were installed by rotary drilling methods using hollow stem augers and by rock coring techniques (HQ diameter barrel). Monitoring well MW-4D was installed using hollow stem augers and rock coring techniques with an NQ diameter barrel. These monitoring wells were installed in the fractured rock transition zone with screen lengths of 5 feet. The screens were installed with screen intervals ranging from 41.5 feet to 46.5 feet bgs at MW-13D and 90 feet to 95 feet bgs at MW- 12D. The monitoring wells at Marshall are equipped with dedicated bladder-type pumps and are sampled in accordance with the Duke Energy groundwater sampling and analysis plan. Section 5 Description of Groundwater Monitoring System 8 Monitoring wells MW-6S, MW-6D, MW-7S, MW-7D, MW-8S, MW-8D, MW-9S, and MW-9D were installed by Duke Energy in 2006 as part of a voluntary monitoring system. These wells are not shown on Figure 2. No samples are currently being collected from these wells. Monitoring well MW-4D, described above, was installed in 2006 as part of the voluntary monitoring system, but it has been incorporated into the compliance groundwater monitoring well system. 9 Section 6 Groundwater Monitoring Results The monitoring wells at Marshall have been sampled a total of seven times in association with the groundwater monitoring requirements provided in Table 1. These monitoring wells were sampled in:  February 2011  June 2011  October 2011  February 2012  June 2012  October 2012  February 2013 With the exception of boron, iron, manganese, sulfate, total dissolved solids (TDS), and pH, the results for all monitored parameters and constituents were less than the 2L Standards. Table 2 lists the monitoring wells and the range of analytical results for the wells with exceedances of the 2L Standards. 10 Section 7 Groundwater Assessment Work Plan As presented in Table 2, exceedances of the 2L Standards for boron, iron, manganese, sulfate, TDS, and/or pH have been measured at the following monitoring wells: MW-4, MW-4D, MW- 10S, MW-10D, MW-11S, MW-11D, MW-12S, MW-12D, MW-13S, MW-13D, MW-14S, and MW-14D. The proposed assessment work plan will evaluate the exceedances of the 2L Standards to determine if the exceedances are naturally occurring, if they are caused by particulate matter which is preserved in the sample as a result of well construction and/or sampling procedures, or if the exceedances of the 2L Standards can be attributed to impacts from the ash basin. The groundwater assessment will include the following tasks: Task 1 Develop a Site Hydrogeologic Conceptual Model - Available reports and data on site geotechnical, geologic, and hydrologic conditions will be reviewed and used to develop a site hydrogeologic conceptual model. The NCDENR document, Hydrogeologic Investigation and Reporting Policy Memorandum, dated May 31, 2007, will be used as general guidance. Task 2 Discuss Site History and Land Uses – A discussion of the site history and land uses will be developed. Task 3 Review Available Data on Ash Basin Water Quality Data – Available data on ash basin water quality will be reviewed to determine if a suitable “fingerprint” of ash basin water quality can be determined. If a suitable “fingerprint” of ash basin water quality can be determined, the parameters and constituents associated with the “fingerprint” will be used with the analytical results from the monitoring wells to determine if the exceedances in the monitoring wells can be attributed to impacts from the ash basin. This data will be provided by Duke Energy and will include NPDES-related monitoring data and additional data collected from the ash basin during the June 2013 sampling event. Section 7 Groundwater Assessment Work Plan 11 The ash basin data will be reviewed relative to groundwater sampling results for constituents included in the ash basin groundwater monitoring program and for major anion and cation data also collected during the June 2013 groundwater sampling event. The groundwater monitoring results at the monitoring wells with exceedances will be compared to the ash basin water quality data by utilizing water quality plots (i.e., Piper diagrams, Stiff diagrams, or others) to understand the possible influence of the ash basin on the groundwater quality at the monitoring wells with exceedances. Task 4 Review Ash Leaching Data – Existing results for leaching tests on ash will be reviewed to determine if the existing data can be used as input to the assessment or if additional leaching tests need to be performed. Additional leaching tests will be performed if needed and the results will be included in the assessment. Task 5 Review Location and Number of Background Monitoring Wells – The site hydrogeologic conceptual model and other data will be reviewed to determine if the location and number of background monitoring wells is sufficient. Task 6 Evaluate Well Construction Information – Well installation records will be reviewed to determine if well construction methods are contributing to the exceedances. Task 7 Evaluate Exceedances against Background Well Results – The analytical results from the wells with exceedances will be evaluated against results from the site background well to determine if the exceedances can be attributed to background water quality conditions. Task 8 Evaluate Exceedances against Turbidity Values – Exceedances will be evaluated against turbidity values measured during sampling to determine if the exceedances are a result of sediment or particulate matter which is preserved in the sample as a result of well construction or sampling methods. Task 9 Evaluate Sampling Flow Rates – Sample collection flow rates will be evaluated to determine if the flow rates are affecting results. The use of low flow sampling techniques will be evaluated for selected wells. Section 7 Groundwater Assessment Work Plan 12 Task 10 Collect and Analyze Filtered and Unfiltered Samples – Groundwater samples collected for compliance monitoring are not filtered in the field. In order to provide additional information for the assessment of exceedances, both unfiltered and filtered samples will be collected and analyzed for boron, iron, and manganese. The field filtration will be performed with an in-line, sealed, 0.45 micron filter. Task 11 Collect Reduction/Oxidation Field Parameters – Reduction/oxidation (redox) processes can alternately mobilize or immobilize metals associated with naturally occurring aquifer materials. Iron and manganese are commonly associated with lakes and the associated sediments. The redox conditions associated with the aquifer/lake system may be a factor in the concentrations of iron and manganese observed at selected monitoring well locations. Additional field parameters (i.e., dissolved oxygen and redox potential) will be collected at selected wells to characterize the redox conditions at these locations. A discussion of the redox conditions at the wells will be provided in the assessment. Task 12 Perform Statistical Analyses of the Groundwater Monitoring Results – Statistical analyses of groundwater monitoring results will be performed to determine if the exceedances can be attributed to the ash basin water quality or if the exceedances can be attributed to naturally occurring background concentrations. The NCDENR document, Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical Assistance Document for DWQ Staff, dated July 2012, will be used as general guidance. In addition to these tasks, HDR understands that Duke Energy will add total suspended solids to the list of analysis parameters for groundwater samples and will continue to analyze groundwater samples for TDS. 13 Section 8 Assessment Report and Proposed Schedule The groundwater assessment report will present the results of the work proposed in Section 7. The next sampling event for the groundwater monitoring wells at the Marshall ash basin will occur in June 2013. If NCDENR approval of this work plan is received by May 17, 2013, the proposed schedule is to submit the groundwater assessment report approximately 120 days after the June 2013 groundwater sampling event. The groundwater assessment report will be submitted 150 days after the next scheduled groundwater sampling event if redevelopment of one or more of the monitoring wells is required. If NCDENR approval of this work plan is not received by May 17, 2013, the schedule will be revised after NCDENR approval is received. 14 Section 9 References Harry E. LeGrand, 2004, 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. FIGURES TABLES TABLE 1 – GROUNDWATER SAMPLING REQUIREMENTS Well Nomenclature Parameter Description Frequency Monitoring Wells: MW-4, MW-4D, MW- 10S, MW-10D, MW-11S, MW-11D, MW-12S, MW- 12D, MW-13S, MW-13D, MW-14S, MW-14D Antimony Chromium Nickel Thallium February, June, October Arsenic Copper Nitrate Water Level Barium Iron pH Zinc Boron Lead Selenium Cadmium Manganese Sulfate Chloride Mercury TDS TABLE 2 - EXCEEDANCES OF 2L STANDARDS Boron Iron Manganese pH Sulfate TDS 2L Standard 700 µg/L 300 µg/L 50 µg/L 6.5 - 8.5 SU 250 mg/L 500 mg/L Well ID Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances µg/L µg/L µg/L SU mg/L mg/L Comments Concerning Exceedances MW-4 No Exceedances No Exceedances No Exceedances 5.5 – 6.0 No Exceedances No Exceedances Results for pH have generally been consistent over the period of monitoring. MW-4D No Exceedances 376 No Exceedances 6.0 – 6.2 No Exceedances No Exceedances Iron only exceeded 2L Standard during February 2012 monitoring event. Iron concentration has been <2L Standard during the remaining 6 events including the last 3. Results for pH have generally been consistent of the period of monitoring. MW-10S No Exceedances 373 65 5.1 – 5.7 No Exceedances No Exceedances The only iron and manganese exceedances occured during the June 2011 monitoring event when turbidity was high (23.8 NTU). The remaining 6 monitoring events iron and manganese concentrations have been <2L Standard. Results for pH have generally been consistent over the period of monitoring. MW-10D No Exceedances No Exceedances 59 – 97 6.2 – 6.5 No Exceedances No Exceedances Manganese concentrations exceeded the 2L Standard during the first three monitoring events, but have been <2L Standard during the last four events. Manganese concentrations show a steady decline in concentrations from an initial concentration of 97 ug/L in February 2011 to the February 2013 concentration of 11 ug/L. Results for pH have generally been consistent over the period of monitoring. MW-11S No Exceedances 324 – 467 No Exceedances 6.0 – 6.4 No Exceedances No Exceedances Iron concentration has been <2L during 5 of the 7 monitoring events. Iron concentrations may be affected by turbidity which has ranged from 9.5 to 22 NTUs. Results for pH have generally been consistent over the period of monitoring. MW-11D No Exceedances 325 – 839 No Exceedances No Exceedances No Exceedances No Exceedances Iron concentration has been <2L Standard during 4 of the 7 monitoring events. Iron concentrations may be affected by turbidity which has ranged from 7.5 to 35 NTUs. Iron concentration were measured <2L Standard when turbidity values are at or below 10 NTUs. Well may be a candidate for low flow sampling. MW-12S No Exceedances No Exceedances 54 – 127 5.1 – 5.7 No Exceedances No Exceedances Manganese concentration has been <2L Standard during 5 of the 7 monitoring events. Results for pH have generally been consistent over the period of monitoring. MW-12D No Exceedances 305 – 970 No Exceedances 5.9 – 6.4 No Exceedances No Exceedances Iron concentrations have been >2L Standard during all monitoring events ranging from 305 ug/L in February 2011 to 970 ug/L during October 2012 sampling event. Results for pH have generally been consistent over the period of monitoring. MW-13S No Exceedances 324 – 1,060 54 5.8 – 6.3 No Exceedances No Exceedances Iron concentrations may be affected by turbidity which has ranged from 8 to 62 NTUs. May consider low flow sampling. Manganese concentration was >2L Standard during the first monitoring event, but has been <2L Standard during the last 6 monitoring events. Results for pH have generally been consistent over the period of monitoring. MW-13D No Exceedances No Exceedances No Exceedances 6.2 – 6.4 No Exceedances No Exceedances Results for pH have generally been consistent over the period of monitoring. MW-14S 3,640 – 4,530 322 – 463 69 – 192 5.2 – 5.5 350 – 400 573 – 650 Boron, manganese, sulfate, and TDS have been generally decreasing over the period of monitoring; however, the concentrations of the parameters have exceeded their 2L Standards during every monitoring event. Iron concentrations have been <2L Standard during 4 of the 7 monitoring events. Results for pH have generally been consistent over the period of monitoring. MW-14D 2,960 – 3,660 No Exceedances 51 – 73 5.3 – 5.6 270 – 310 510 – 540 Boron, manganese, and sulfate have been generally decreasing over the period of monitoring; however, the concentrations of the parameters have exceeded their 2L Standards during every monitoring event, with the exception of manganese which was <2L Standard during the February 2013 monitoring event (46 ug/L). TDS concentrations have been <2L Standard during the last 3 events (494, 490, and 490 mg/L). Results for pH have generally been consistent over the period of monitoring. APPENDIX A LETTER FROM ANDREW H. PITNER, P.G., REGIONAL AQUIFER PROTECTION SUPERVISOR, NCDENR DIVISION OF WATER QUALITY, TO ED SULLIVAN AND ALLEN STOWE, WATER MANAGEMENT, DUKE ENERGY CORPORATION, DATED MARCH 16, 2012