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HomeMy WebLinkAboutHF Lee CSA Executive Summary 08-05-2015Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra H.F. LEE ENERGY COMPLEX EXECUTIVE SUMMARY The North Carolina Coal Ash Management Act (CAMA) requires the preparation of a Comprehensive Site Assessment (CSA) and Corrective Action Plan (CAP) for each regulated facility. This report addresses Duke Energy's H.F. Lee Energy Complex. The assessment was performed as required within 180 days of the work plan approval dated February 6, 2015. The purpose of this assessment is to identify the source and cause of exceedances of regulatory standards, potential hazards to public health and safety, and identify receptors and exposure pathways. The North Carolina Department of Environment and Natural Resources (NCDENR) prescribed the list of monitoring parameters to be measured at the Lee Plant. Once the sampling portion of the CSA was complete, the data were examined to choose those parameters that were most relevant for the site. These parameters were determined by examining data from monitoring wells installed in ash, and then by comparing these results to the NCDENR/DWR Title 15, Subchapter 2L and Interim Maximum Allowable Concentrations (IMAC). If a parameter was greater than 2L or IMAC, it was designated a'Constituent of Interest' (COI). Some COIs (e.g., iron and manganese) are also present in background monitoring wells and thus require careful examination to determine whether their presence on the downgradient side of the basins is from natural sources (e.g., rock and soil) or the ash basins. Appendix #1 of 15A NCAC Subchapter 02L Classifications and Water Quality Standards Applicable to The Groundwaters of North Carolina, lists IMACs. The IMACs were issued in 2010 and 2011, however NCDENR has not established a 2L for these constituents as described in 15A NCAC 02L.0202(c). For this reason, IMACs noted in this report are for reference only. The assessment addresses the horizontal and vertical extent of COIs in soil and groundwater. Significant factors affecting constituent transport, and the geological and hydrogeological features influencing the movement and chemical, and physical character of the COIs were evaluated. Data presented in this assessment report will be the basis for the Corrective Action Plan required within 270 days of the approved work plan to identify alternative strategies to address groundwater impacts at the site. Duke Energy recently recommended that the basins be fully excavated with the material safely recycled into a lined structural fill (https://www.duke- ES-i P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra energy.com/pdfs/SafeBasinClosureUpdate_HFLee.pdf), accessed on July 29, 2015). The Corrective Action Plan will include groundwater modeling results of anticipated ash removal to assess effects on groundwater. A groundwater monitoring plan will be provided to assess changes in groundwater conditions over time. Based on scientific evaluation of historical and new groundwater assessment data presented in this report, the following conclusions can be drawn: 47 No imminent hazard to human health or the environment has been identified as a result of groundwater migration from the ash basins. 41' Recent groundwater assessment results are consistent with previous results from historical and routine compliance boundary monitoring well data. 41' Upgradient, background monitoring wells contain naturally occurring metals and other COIs at concentrations greater than 2L or IMAC. This information is used to evaluate whether concentrations in groundwater downgradient of the basins are also naturally occurring or might be influenced by migration of constituents from the ash basins. Examples include iron, manganese and cobalt, all present in background groundwater samples at concentrations greater than 2L or IMAC. h Groundwater in the surficial aquifer under the ash basins flows horizontally to the east and south and discharges into the Neuse River or Halfmile Branch. This flow direction is away from the nearest public and private water wells. The surficial aquifer groundwater discharge to surface water provides a boundary for migration. 41' There are no water supply wells located between the ash basins and the Neuse River. 41' Data indicate the water quality of the Neuse River has not been impacted. 47 Rainwater infiltration and standing water in the active ash basin create mounding and radial flow in the immediate vicinity of the active ash basin. This would be anticipated to be the case previously, or to a lesser extent under current conditions, for the inactive ash basins. 41' Boron is the primary constituent in groundwater detected at concentrations greater than background concentrations and 2L. Boron is detected at concentrations greater than 2L within a three dimensional area beneath and ES -ii P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra downgradient of the ash basins in the surficial aquifer, primarily to the southeast of the active ash basin and beyond the property boundary. 47 Arsenic is also present in groundwater greater than 2L to the southeast of the active ash basin. 41' The horizontal migration of boron and arsenic in the surficial groundwater best represent the dominant flow and transport system. Downward vertical migration is restricted due to the clay and silt layers beneath the ash basins that act as confining layers over the deeper aquifers in the area. Lf The CSA serves to characterize the horizontal and vertical extent of COIs, and the groundwater gradients which facilitate development of the Site Conceptual Model (SCM), i.e. the groundwater flow and contaminant migration model. This then facilitates identification of corrective actions due in 90 days under the Corrective Action Plan. �7 Groundwater modeling to be provided with the Corrective Action Plan will allow an evaluation of the planned ash excavation. Brief summaries of the essential portions of the CSA are presented in the following sections. ES1. Source Information Mineralogical, physical, and chemical properties of the Lee Plant ash basins have been characterized for use in the hydrogeological site conceptual model (SCM). Five ash storage areas have historically been used to manage ash at the Lee Plant. These are referred to as inactive basins 1, 2, and 3, the 'active' basin and the Lay of Land Area (LOLA). The inactive basins and the LOLA were used to manage ash from the 1950s until the 1970s when the active basin was built. The 'active' basin was used to manage ash until 2012 when the coal-fired units were retired. Within a basin, water collects as either free liquid above the ash or below the ash surface. When present below the ash surface, it is herein referred to as ash pore water. Water within the active ash basin and inactive ash basin 1 is hydraulically higher (upgradient) than the surrounding land surface. Pore water drains through the underlying soil to the groundwater or from perimeter dams as seeps. Groundwater and seeps are the primary mechanisms for migration of COIs to the environment. ES -iii P:\ Duke Energy Progress.1026\ 104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting \ Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra ES2. Initial Abatement and Emergency Response The coal-fired units at the plant have been decommissioned. The ash management areas are no longer in use. Duke has recommended the excavation of the ash from the basins. No imminent hazard to human health or the environment has been identified therefore initial abatement and emergency response actions have not been required. ES3. Receptor Information Land use surrounding the Lee site includes commercial, rural residential, agricultural, and forest land. Beaverdam Creek, Halfmile Branch, and the Neuse River border the Lee Plant. Public water service in the area is provided by Fork Township Sanitary District. ES.3-1 Public Water Supply Wells Surveys of public and private water supply wells within a 1/2 mile radius of the ash basin compliance boundaries have been conducted. Available information is provided herein. One Fork Township Sanitary District water supply well is located approximately 2,000 feet upgradient (north) of the inactive basins. The well was sampled at the direction of NCDENR during 2015 and the data is provided herein. The next two closest public water supply wells are located approximately 1 mile to the northeast and 1 mile south and across the Neuse River from the site. These wells reportedly produce water from the Upper Cape Fear Aquifer and bedrock. ES.3-2 Private Water Supply Wells Inventories of public and private water supply wells have been compiled. NCDENR contacted nearby residents regarding private wells and managed the sampling of the wells in accordance with CAMA. Constituents identified are naturally occurring within the concentration range detected. Therefore, based upon the groundwater flow direction and water quality data it does not appear that the wells are impacted by groundwater migrating from the ash basins. The updated survey indicates that approximately 97 private water supply wells may be located within or in close proximity to the 1/2 mile radius of the compliance boundary. The NCDENR water well data is provided herein. ES.3-3 Human and Ecological Receptors The exposure medium for human receptors includes potentially impacted groundwater, soil, surface water and sediments. The exposure routes associated with the potentially completed exposure pathways evaluated for the site include ingestion, inhalation and dermal contact of environmental media. ES -iv P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra Potential human receptors, current or future, include recreational swimmers, recreational fisherman, recreational hunters, and industrial workers. The potential exposure medium for ecological receptors includes impacted soil, surface water and sediments. Direct contact with groundwater does not present a complete exposure pathway to ecological receptors. Exposure routes associated with potentially completed exposure pathways include incidental ingestion and ingestion of prey or plants. Wildlife expected to be near the site would potentially include those listed in Table 12-16, and also other game and non -game wildlife endemic to the Rolling Coastal Plains and Southeastern Floodplains and Low Terraces ecoregions. The Neuse River supports 17 species of freshwater mussels and a rare snail species. Two of these mussel species, the dwarf wedgemussel (Alasmidonta heterodon) and the Tar River spinymussel (Elliptio steinstansana), are federally listed as endangered. See Table 12-16 for a full list of Threatened and Endangered Species. There are wetland areas that are listed in the USGS National Wetland Inventory on-site. For a detailed description, see the Checklist for Ecological Assessments/Sampling in Appendix I. ES4. Sampling / Investigation Results The approximate extent of horizontal migration of boron and arsenic, the COIs that appear to be attributable to migration from the ash management areas are shown on Figures ES -1a and ES -1b for the inactive and active ash basin areas. ES.4-1 Nature and Extent of Contamination Active Ash Basin — Groundwater Arsenic and boron were detected above the 2L within the surficial aquifer at the compliance boundary to the east and southeast of the active basin. These constituents are not detected in the site background wells at similar concentrations. The horizontal extent of migration is controlled by the Neuse River to the south and southeast, a major groundwater to surface water discharge zone. The vertical extent of migration is impeded by clay and silt layers below the surficial aquifer. In addition, barium, cobalt, iron, manganese, thallium, total dissolved solids (TDS), and vanadium were detected in the ash basin (pore) water, near the bottom of the ash, at concentrations greater than 2L ES -v P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra or IMAC. Of these, cobalt, iron, manganese and vanadium are also detected in site background wells upgradient of the ash basin at concentrations greater than 2L or IMAC. Cobalt, iron, manganese, and vanadium are commonly detected in shallow groundwater in the coastal plain region of North Carolina. Site background concentration ranges for some of these constituents are available from routine monitoring of the upgradient compliance boundary monitoring wells and newly installed background wells. Inactive Ash Basins - Groundwater Antimony, arsenic, boron, chromium, cobalt, iron, manganese, sulfate, thallium, total dissolved solids, and vanadium were detected in the groundwater beneath or adjacent to the perimeter of the inactive ash basins at concentrations greater than 2L or IMAC. Cobalt, iron, manganese, and vanadium were also detected at concentrations greater than 2L or IMAC in newly installed background wells located upgradient of the inactive ash basins. The horizontal extent of migration of these constituents in the surficial aquifer is controlled by the Neuse River to the east, a major groundwater to surface water discharge zone. The vertical extent of migration is controlled by clay layers and thick silt layers below the surficial aquifer. Lay of Land Area - Groundwater Arsenic, barium, cobalt, iron, manganese, thallium, and vanadium were detected in the groundwater beneath the Lay of Land Area greater than 2L or IMAC. The horizontal extent of migration in the surficial aquifer is controlled by the Neuse River to the north. Standing water and wetland -like areas prevented access of drilling equipment sufficient to assess conditions below the surficial aquifer. This is not considered a significant data gap due to the proximity of the Neuse River, a local and regional groundwater discharge feature. Field observations indicate that the confining layer at the top of the Black Creek Formation is continuous across the active basin and to the east. Surficial deposits and the Cape Fear Formation also provide barriers to vertical migration of COIs. The surficial deposits include multiple clay beds that are laterally extensive in both the inactive basin and LOLA areas. The Cape Fear Formation deposits at the site consist of mostly tightly packed silt which impedes groundwater flow. ES -vi P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra ES.4-2 Maximum Contaminant Concentrations For the COIs identified on the basis of ash basin pore water concentrations, boron is the most prevalent in groundwater with the highest concentration being detected in the surficial aquifer southeast of the active ash basin (above the confining layer). While boron is prevalent at the site, it is limited in area and depth (refer to Figures 10-2a through 10 -4b,10 -8a,10 -8b,10 -19a,10 -19b,10-30, 10 -41a,10 -41b, and 11-1a, and 11-1b and Table 10-1 for extent of concentrations in excess of 2L). Groundwater affected by boron discharges to ditches located at the perimeter of the ash basins (which flow to the Neuse River) and to the Neuse River. The maximum concentration of boron in soil was detected in a sample collected eight feet below inactive ash basin 1 (18 to 20 feet below the ground surface). The highest concentration of arsenic in groundwater occurs beneath the active ash basin (refer to Figures 10-2a through 10 -4b,10 -6a,10 -6b,10 -17a,10 -17b,10- 28,10 -39a,10 -39b and Table 10-1 for extent of concentrations in excess of the 2L of 10 µg/L). The CSA data indicate that arsenic has not migrated in the direction of public or private water supply wells. Arsenic in groundwater is present for a short distance on the southeast side of the active basin (between the active basin and the Neuse River). The highest concentration of cobalt in groundwater was detected in a well along the north side of inactive basin 1. Cobalt was also detected in samples from multiple background well locations. The highest concentration of iron in groundwater was detected in a sample from beneath inactive ash basin 1 (refer to Figures 10-2a through 10 -4b,10 -10a,10 -10b, 10 -21a,10 -21b,10 -32,10 -43,10 -43b,11 -2a, and 11-2b and Table 10-1 for extent of concentrations in excess of the 2L of 300 µg/L). The highest concentration of manganese in groundwater was detected in a sample from beneath the LOLA (refer to Figures 10-2a through 10 -4b,10 -11a,10 -11b,10 -22a,10 -22b,10-33,10-44, 10 -44b,11 -2a, and 11-2b and Table 10-1 for extent of concentrations in excess of the 2L of 50 µg/L). Iron and manganese were also detected at elevated concentrations in samples from background locations. The highest concentrations of vanadium in groundwater were detected in a well northeast of the active ash basin (refer to Figures 10-2a through 10 -4b,10 -15a,10 - 15b,10 -26a,10 -26b,10 -37,10 -48,10 -48b,11 -2a, and 11-2b and Table 10-1 for extent of concentrations in excess of the IMAC of 50 µg/L). Vanadium was also detected at elevated concentrations in samples from background locations. ES -vii P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra Antimony, barium and thallium were detected at elevated concentrations in isolated locations around the site (refer to Figures 10-2a through 10-4b and Table 10-1). There was one detection of antimony in groundwater from a sample collected underneath inactive basin 2. The highest concentration of barium in groundwater was detected in a sample from beneath the LOLA. Thallium was also detected in groundwater from beneath inactive basin 2. Readings outside of the 2L range for pH are observed in background areas near the site and in areas downgradient of the ash basins (Table 10-1). In general, lower pH values are observed in upgradient areas and isolated, higher pH values are observed in wells downgradient of the active basin. Elevated TDS concentrations were generally observed in wells screened beneath ash basins (inactive and active). Elevated TDS detections outside of the footprint of the ash basins were isolated. Elevated COI occurrences in soil ranged from background areas to soil beneath the ash basins. The highest concentrations of cobalt and iron in soil were from a background location north of the inactive basins. Barium and manganese at elevated levels were detected beneath the LOLA. The highest concentrations of thallium and vanadium in soil were detected in shallow soil west of the active basin. The highest concentration of arsenic in soil was from beneath the active basin. The highest concentration of boron in a soil sample was collected from beneath inactive basin 1. Antimony was not detected in soil. ES.4-3 Source Characterization COIs leached from ash into ash basin pore water at concentrations greater than 2L or IMAC include antimony, arsenic, barium, boron, cobalt, iron, manganese, thallium and vanadium. Selenium was detected in one ash pore water sample above 2L. It has not been identified as a COI due to the single detection in ash pore water and no exceedances for groundwater at the site. Ash pore water discharges through the toe of the basin dams into perimeter ditches and/or into shallow soils beneath the site. ES.4-4 Receptor Survey Public water supply wells in Wayne County draw water from the Upper Cape Fear Aquifer. The closest public supply well is located approximately 2,000 feet north of the site in the upgradient direction. Groundwater flow is predominantly toward the Neuse River (away from the public supply well) in the area of the site. The NCDENR 2015 sample results from the public supply well indicate that the naturally occurring constituents iron and manganese were ES -viii P:\ Duke Energy Progress.1026\ 104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting \ Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra detected at concentrations greater than 2L. The use of the public water supply well will be evaluated in the groundwater model. Public water service in the area is provided by Fork Township Sanitary District. The private water supply wells identified within one half mile of the compliance boundary are located in upgradient areas north of the site. Updated receptor information is provided with this report. Constituents of potential concern (COPCs) for human and ecological receptors identified using screening level risk assessment methodology for receiving areas at the site include pH, aluminum, arsenic, chromium, cobalt, iron, manganese, TDS, selenium, thallium, vanadium, and zinc. This list is longer than the list of site specific COIs due to the conservative approach of comparing analytical results to published reference criterion in the risk assessment screening process. ES.4-5 Regional Geology and Hydrogeology The vicinity of the Lee Plant is generally characterized by shallow water table conditions occurring in surficial soils and unconsolidated sediments underlain by the Coastal Plain regional aquifer system. Sediments of the Black Creek and Cape Fear Formations underlie the site. ES.4-6 Site Geology and Hydrogeology Surface soils exposed within the Lee Plant area are relatively recent Coastal Plain sediments. Limited exposures of metamorphic bedrock (a slate) occur in areas on the west side of the site, within creek beds and within the Neuse River in the vicinity of the inactive ash basins. On the west side of the site, groundwater flows to the east toward the Neuse River. Following a bend in the Neuse River, groundwater on the east side of the site flows north to south toward the river from the active ash basin area, and south to north toward the river from the Lay of Land Area. The water table occurs within a few feet of the surface to as much as 15 feet below ground surface in upland areas. From west to east, tightly packed silts of the Cape Fear Formation and then a thick confining clay layer of the Black Creek Formation restrict vertical migration of contaminants. ES.4-7 Existing Groundwater Monitoring Data NPDES compliance groundwater monitoring data indicate that elevated concentrations of boron, iron, and manganese have been detected at the inactive basins, while elevated concentrations of arsenic, boron, iron, manganese and pH ES -ix P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra have been routinely detected at the active ash basin. Relatively lower values of pH are routinely detected at both sites. ES.4-8 Development of Site Conceptual Model A hydrogeological site conceptual model was developed from data generated during previous assessments, existing groundwater monitoring data, and 2015 groundwater assessment activities. Ash basin source areas discharge ash pore water to perimeter ditches to the subsurface beneath the basins. Groundwater flows in a radial pattern from the vicinity of the active basin and inactive basin 1. Arsenic is found below the active basin and in the surficial aquifer southeast of the basin. It is not found in deeper wells below the confining layer in this area. Horizontal migration is controlled by the Neuse River. ESS. Identification of Data Gaps The horizontal and vertical extent of COIs occurring at or above the appropriate regulatory standards have been determined for soil and groundwater. Source area and groundwater characterization data have been used to develop hydrogeologic and geochemical SCMs that will support preparation of flow and transport groundwater modeling for the site. There are no data gaps that will be limiting factors in the execution of the groundwater model or development of the CAP. ES6. Conclusions 1. Duke Energy recently recommended that the basins be fully excavated with the material safely recycled or placed into a lined structural fill. The effects of this recommendation on groundwater quality will be evaluated through the groundwater modeling to be provided in the CAP. 2. No imminent hazards to human health and the environment were identified as a result of the assessment. The data confirm that geologic confining units are present beneath the ash basins and impede the vertical migration of contaminants. The groundwater in the surficial aquifer in the vicinity of the source areas discharges to the Neuse River. There are no public or private water wells between the source areas and the Neuse River. 3. Water samples from the Neuse River upstream from the site (S-16) and downstream from the site (ASW-NR1) were collected and analyzed. The upstream sample was collected in order to determine COI in surface water background concentrations. The upstream sample contained two COIs (manganese and vanadium) at similar levels as the downstream sample. The ES -x P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx Comprehensive Site Assessment Report August 2015 H.F. Lee Energy Complex SynTerra data indicate no measureable impact from groundwater migration to the Neuse River. 4. A plan for future groundwater monitoring is presented in Section 16 of this report. The proposed Corrective Action Plan, based on the data presented in this report and groundwater modeling, will be submitted within 90 days of August 5, 2015. ES -xi P:\Duke Energy Progress.1026\104. Lee Ash Basin GW Assessment\ 1.11 CSA Reporting\Lee CSA Report 08-05- 2015.docx `r: rdTt. i r1,Sti c o ,� Ys L • • • • - r # • 1 d 5 'k x ,+l V h 4 i l„d f� d d 1 :A - � lr S Y •Fy tiJvt t W. 7ilr1'LM6'i?, ;;. - �L— i3R'i r.-. �•�'aF-.1 ..i t��„� ' LEGEND O NOTES: DUKE ENERGY ENERGY PROGRESS FIGURE ES -1a SITE CONCEPTUAL MODEL - PLAN VIEW H.F. LEE ENERGY COMPLEX INACTIVE BASINS ie N 0% A "vot 0 0,0 0 4Active 16 IM C6 0 - 0 O'Lo �ovo 0 o•v MAW 1-1 LEGEND V4, Mn* 0 NOTES: i mmmr�� 4',j -47L, DUKE ic ENERGY ynTera -PROGRESS FIGURE ES -lb SITE CONCEPTUAL MODEL - PLAN VIEW H.F. LEE ENERGY COMPLEX ACTIVE BASIN IL, co E E m"