Assessment of Corrective Measures Report, Conesville Ash Pond
American Electric Power Service Corporation Conesville Generating Station, Conesville, Coshocton County, Ohio Project # 7362192661
Prepared for:
American Electric Power Service Corporation 1 Riverside Plaza, Columbus, Ohio 43215 24 June 2019
Assessment of Corrective Measures Report, Conesville Ash Pond
American Electric Power Service Corporation Conesville Generating Station, Conesville, Coshocton County, Ohio Project # 7362192661 Prepared for: American Electric Power Service Corporation 1 Riverside Plaza, Columbus, Ohio 43215 Prepared by: Wood Environment & Infrastructure Solutions, Inc. 921 Eastwind Drive, Suite 129 Westerville, OH 43081 USA T: 614-943-0567 24 June 2019
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Wood Environment & Infrastructure Solutions, Inc. Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Table of Contents Document Purpose ...... 1 Review of Data Sources ...... 1 2.0 Site Background ...... 2 Site Description and History ...... 2 2.1.1 General Description of the APS ...... 3 2.1.2 Construction and Operational History ...... 3 2.1.3 Leachate and Water Management ...... 3 2.1.4 CCR Regulatory Status ...... 3 Conceptual Site Model ...... 4 2.2.1 Climate and Water Budget ...... 4 2.2.2 Geologic Setting ...... 4 2.2.3 Groundwater Flow System Characteristics ...... 5 2.2.4 Surface Water and Surface Water-Groundwater Interactions ...... 5 2.2.5 Groundwater Gradients and Flow Directions ...... 6 2.2.6 Groundwater Monitoring Network...... 7 2.2.7 Arsenic, Lithium and Molybdenum Transport in Groundwater ...... 7 3.0 Identification and Development of Corrective Measure Alternatives ...... 9 Establishment of Corrective Action Objectives (CAOs) ...... 9 Screening and Evaluation of Remedial Technologies ...... 10 Development of Corrective Measures Alternatives ...... 11 4.0 Detailed Evaluation of Corrective Measure Alternatives ...... 11 Source Control Description ...... 12 4.1.1 Pond Dewatering ...... 12 4.1.2 Closure by Removal ...... 12 4.1.3 Closure by Capping ...... 13 4.1.4 Closure Incorporating In Situ Stabilization ...... 13 4.1.5 Evaluation ...... 14 4.1.6 Summary ...... 15 Monitored Natural Attenuation ...... 15 4.2.1 Description ...... 15 4.2.2 Evaluation ...... 15 4.2.2.1 Overall Protection of Human Health and Environment ...... 15 4.2.2.2 Ability to Meet Groundwater Protection Standards ...... 16 4.2.2.3 Source Control and Reduction of Contaminated Material...... 16 4.2.2.4 Long Term Effectiveness ...... 16 4.2.2.5 Short Term Effectiveness ...... 16 4.2.2.6 Implementability ...... 16 4.2.2.7 Long-Term Management Requirements ...... 17 4.2.2.8 Community Acceptance ...... 17 4.2.2.9 State Acceptance ...... 17 4.2.2.10 Time to Meet Remedial Objectives ...... 17 Groundwater Extraction, Treatment and Surface Water Discharge ...... 17 4.3.1 Description ...... 17 4.3.2 Evaluation ...... 18 4.3.2.1 Overall Protection of Human Health and Environment ...... 18
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
4.3.2.2 Ability to Meet Groundwater Protection Standards ...... 19 4.3.2.3 Source Control and Reduction of Contaminated Material...... 19 4.3.2.4 Long Term Effectiveness ...... 19 4.3.2.5 Short Term Effectiveness ...... 19 4.3.2.6 Implementability ...... 20 4.3.2.7 Long-Term Management Requirements ...... 20 4.3.2.8 Community Acceptance ...... 20 4.3.2.9 State Acceptance ...... 20 4.3.2.10 Time to Meet Remedial Objective...... 20 Groundwater Extraction, Treatment and Reinjection...... 21 4.4.1 Description ...... 21 4.4.2 Evaluation ...... 21 4.4.2.1 Overall Protection of Human Health and Environment ...... 21 4.4.2.2 Ability to Meet Groundwater Protection Standards ...... 22 4.4.2.3 Source Control and Reduction of Contaminated Material...... 22 4.4.2.4 Long Term Effectiveness ...... 23 4.4.2.5 Short Term Effectiveness ...... 23 4.4.2.6 Implementability ...... 23 4.4.2.7 Long-Term Management Requirements ...... 23 4.4.2.8 Community Acceptance ...... 23 4.4.2.9 State Acceptance ...... 23 4.4.2.10 Time to Meet Remedial Objective...... 24 5.0 Summary ...... 24 6.0 References ...... 25
List of Figures Figure 1 Site Location Figure 2 Site Layout Figure 3 APS Layout Figure 4 Conceptual Cross-Section A-A’ Figure 5 Conceptual Cross-Section B-B’ Figure 6 Piezometric Surface Map (February 2019) Figure 7 Average Measure Downgradient Alluvial Arsenic Concentrations Figure 8 Average Measure Downgradient Alluvial Lithium Concentrations Figure 9 Average Measure Downgradient Alluvial Molybdenum Concentrations Figure 10 Groundwater Model Groundwater Contours and Particle Tracks After Closure Figure 11 Groundwater Extraction and Injection Well Layout Figure 12 Closure in Place Extraction at 1,200 GPM Groundwater Contours Figure 13 Closure by Removal Extraction and Injection Groundwater Contours
List of Drawings Drawing 4-1 Pond Dewatering Process Flow Diagram Drawing 4-2 Capping and Stabilization Plan View Drawing 4-3 Capping and Stabilization Profile View Drawing 4-4 Groundwater Extraction Process Flow Diagram
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
List of Tables Table 1 Screening and Evaluation of Remedial Technologies Table 2 Risk-Based Technical Options Matrix
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
1.0 Introduction
This document is the Corrective Measures Assessment Report for groundwater impacts associated with the Ash Pond System (APS), at the American Electric Power (AEP) Conesville Plant in Conesville, Ohio. American Electric Power (AEP) operates two units at the Conesville Plant for management of coal combustion residuals (CCR): the APS and the CCR landfill. Both are regulated under the federal CCR Rule (40 CFR Part 257) that became effective in October 2015. Depending on the results of groundwater monitoring conducted in 2016-2017, closure and/or groundwater corrective action could be triggered by the requirements of the rule. On 27 February 2018, it was determined that the APS would enter assessment monitoring due to statistically significant increases over background for boron, chloride, fluoride and pH. The CCR Rule requires the owner or operator of a CCR unit in assessment monitoring to establish Groundwater Protection Standards (GWPSs) for each constituent listed in Appendix IV to Part 257, which includes primarily trace metals along with Radium 226+228. For each constituent in Appendix IV, the default GWPS is either the federal maximum contaminant level (MCL) for drinking water (for those constituents with established MCLs), or the US EPA Regional Screening Levels (RSLs) for those constituents without established MCLs. A higher site-specific GWPS can also be established if the statistically-determined background concentration exceeds the default GWPS. If one or more constituents in Appendix IV is detected at statistically significant levels (SSLs) above its site-specific GWPS, groundwater corrective action is required if no alternate source of these constituents can be identified. Groundwater concentrations for three Appendix IV constituents have been identified at SSLs above their respective GWPS: arsenic, lithium and molybdenum. Based on previous evaluation conducted at the APS, an alternative source of groundwater impacts has not been identified and corrective measures must be assessed.
Document Purpose The Assessment of Corrective Measures (ACM) documented in this report has been prepared in accordance with §257.96 to evaluate remedial alternatives “to prevent further releases, to remediate any releases and to restore the affected area to original conditions” (§257.96[a]).
Review of Data Sources A number of data sources were reviewed to develop an understanding of conditions at the Plant. These sources are discussed in the following sections. In addition, Wood has relied on published technical reports and regulatory guidance that are cited as appropriate in Section 6. Closure Plan CFR 257.102(b), Ash Pond Complex, Conesville Plant, prepared by AEP Service Corporation dated October 2016 This report was prepared by AEP’s Geotechnical Engineering Services section to fulfill the requirements of CFR 257.102(b) for Closure Plans of Existing CCR Surface Impoundments. According to the Closure Plan, the APS will be closed by closure in place, with the existing CCR materials covered with a composite soil and geomembrane cap with vegetative cover, graded to achieve a gently sloping surface to promote surface water runoff. The cap will be constructed with a flexible geomembrane system and 2-feet of soil fill consisting of an 18” soil infiltration layer and 6” of earthen material that is capable of sustaining native plant growth. The surface soil will be seeded and mulched to promote the growth of a vegetative cover.
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Ash Pond System-CCR Groundwater Monitoring Well Network Evaluation, Conesville Plant, prepared by Arcadis U.S., Inc., on behalf of AEP, dated 5 October 2016 The CCR Rule requires that the proposed groundwater monitoring network for each CCR unit be evaluated, and that a professional engineer certify that the network meets the requirements of 40 CFFR Part 257.91. This evaluation and certification was completed by Arcadis and published in October 2016. This report includes a figure showing the location of existing monitoring wells and other relevant features, boring logs, well completion details, and cross-sections. Annual Groundwater Monitoring Report, AEP Generation Resources, Inc., Conesville Plant, Ash Pond, prepared by AEP Service Corporation dated January 2019 Each year AEP publishes an Annual Groundwater Monitoring Report to document groundwater activities conducted at the Plant. This report includes a figure showing the location of existing monitoring wells and other relevant features, a comprehensive set of all groundwater data collected up through the previous year, and an evaluation of groundwater flow conditions with associated potentiometric maps. The report also provides the following information: • Assessment of 2016 and 2017 groundwater data to establish background values for Appendix III and Appendix IV parameters; • Statistical evaluation of groundwater quality data based on the background sampling events and the October 2017 detection monitoring event; • Groundwater quality data from the assessment monitoring events in May and September 2018. Statistical Analysis Summary, Ash Pond System, Conesville Plant, prepared by Geosyntec, on behalf of AEP, dated 8 January 2019 Geosyntec performed a statistical evaluation of groundwater monitoring data to establish a site-specific Groundwater Protection Standards (GWPSs) for each Appendix IV parameter in accordance with 40 CFR 257.95(h). Data from the two semi-annual events for 2018 were evaluated and statistically significant levels (SSLs) above the GWPSs were identified for three parameters: arsenic, lithium and molybdenum.
2.0 Site Background The Conesville Power Plant is a 780 megawatt (MW) coal-fired electric power generating facility located in central Ohio along the southern boundary of Coshocton County (Figure 1). The site is situated in Franklin Township, just east of the Muskingum River at river mile marker 104.7 and directly across the river from the Village of Conesville. The Plant mailing address is 47201 County Road 273, Conesville, Ohio and it occupies a total area of about 4,720 acres.
Site Description and History The Conesville Plant consists of six power generating units built between the late 1950s and 1980s. Three of the units are permanently retired (Units, 1, 2, and 3). Unit 4 is an 820-megawatt (MW) steam electric generating unit. Each of units 5 and 6 are a 425 MW coal-fired, steam electric generating unit. Units 5 and 6 are owned and operated by AEP Generation Resources. Unit 4 is jointly owned by AEP Generation Resources, Inc., Dayton Power and Light, and Dynegy, and is operated by AEP Generation Resources, Inc. AEP has announced plans to permanently cease operations at the Conesville Plant in mid-2020. The general layout of the property and the location of the two CCR units (the APS and CCR Landfill) are shown on Figure 2. Due to the large size of the property, detail is limited on a figure of this scale. A
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
more detailed view focusing on the APS is presented in Figure 3. This figure shows the limits of the APS CCR Unit, and the locations of monitoring wells and onsite pumping wells used by the facility for plant service water.
2.1.1 General Description of the APS The CCR unit referred to as the APS is located between the Conesville Plant and the uplands that define the edge of the Muskingum River valley. The APS consists of five contiguous ponds separated by splitter dikes which receive bottom ash and fly ash from sluicing. The five ponds consist of three fly ash ponds, one bottom ash pond, and one clearwater pond. The bottom ash pond provides primary settling and storage of bottom ash. The fly ash ponds provide secondary settling from the bottom ash pond as well as settling and storage of fly ash. Although denoted as fly ash ponds, borings indicate that the residuals in these ponds include some layers of bottom ash as well as fly ash. The clearwater pond is used for settling before water is discharge out of the APS. In addition to sluice water, the APS also receives other facility wastewater from the FGD system and other non-CCR wastewater streams. Water exits the APS through a 36-inch outlet pipe at the clearwater pond into a wastewater holding pond where it is either recycled for plant processes or discharged to the Muskingum River through a NPDES outfall under NPDES permit number OH0005371.
2.1.2 Construction and Operational History The APS was constructed in the 1950s concurrently with the development of the Conesville plant. Originally, the APS was bounded by two dikes constructed of sand and gravel fill material. The current configuration was constructed in 1974 and includes three embankments on the north, southeast, and southwest constructed of sand, gravel and silty clay. In addition, a northeast to southwest oriented splitter dike was constructed in 1976 separating the APS from the now closed Pozzotec landfill, to the northwest. A series of internal splitter dikes were constructed in 1981 to subdivide the APS into three fly ash ponds, a bottom ash pond, and a clearwater pond.
2.1.3 Leachate and Water Management Sluice water (water plus ash) flows into the APS from pipes along the northwest berm of the APS. In addition, a ditch and culverts convey runoff from the Pozzotec landfill into the APS. All water exits the APS at a single outlet at the clearwater pond consisting of a drop inlet spillway structure and stoplogs. A 36-inch outlet pipe moves water from the spillway structure to the wastewater holding pond, where it is either recycled or discharged to the Muskingum River. Typical pool elevations within the APS have ranged from 755 to 764 feet based on the North American Vertical Datum of 1988 (NAVD 88), also known as Mean Sea Level (MSL). Flow within the APS is controlled by a series of splitter dikes and culverts that convey water between ponds and maintain individual pond elevations. Typical pool elevations for individual ponds within the APS are provided below. • Bottom Ash Pond: 755 to 760 feet • Fly Ash Pond: 758 to 764 feet • Clearwater Pond: 760 feet
2.1.4 CCR Regulatory Status Groundwater corrective action under the federal CCR Rule is triggered through a two-phase program of groundwater monitoring: detection and assessment. The program is undertaken to establish initially
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
whether groundwater quality in the immediate vicinity of the unit (at the waste boundary) has been impacted by CCR. If the requirement for corrective action is triggered by exceedances of established screening criteria in both of the initial phases of the program, two additional phases of groundwater monitoring are required: characterization (prior to corrective action) and corrective action monitoring to document the effectiveness of remediation (after the corrective action remedy is implemented). The APS is currently in the Assessment Monitoring phase of the program (40 CFR 257.95). A statistical evaluation of groundwater monitoring data has been conducted, and the unit is required to enter Groundwater Corrective Action (§257.96 through § 257.98) based on exceedances of various site-specific GWPSs.
Conceptual Site Model In order to support the assessment of corrective measures, a Conceptual Site Model (CSM) has been developed for the Conesville plant. The CSM identifies the sources of specific Constituents of Concern (COCs) in the environment, describes how they migrate in the subsurface from the source along potential transport pathways, and identifies the human and ecologic receptors that may be exposed to the COCs as they migrate through the environment. The following sections provide information on the hydrogeologic setting of the AEP Conesville Plant, including climate, physiography and drainage, geology, hydraulic properties of the principal groundwater flow zone, surface water and interactions between surface water and groundwater.
2.2.1 Climate and Water Budget The area of Coshocton County is cold in winter and hot in the summer (USDA, 1991). The closest meteorological station with long-term data is located at the Zanesville Municipal Airport, about 16 miles due south of the plant. Based on data collected by that National Oceanic and Atmospheric Administration, National Centers for Environmental Information (NOAA-NCEI) data for the period from 1981 through 2010, as reported on their website (https://www.weather.gov/pbz/30yearclimate), the normal annual precipitation is 37.94 inches per year (in/yr). The average monthly high for the same period was 83.7 degrees Fahrenheit in July and average monthly low of 20.5 degrees Fahrenheit in January (NOAA-NCEI, 2011).
2.2.2 Geologic Setting Most of Coshocton County lies within the unglaciated portion of the Allegheny Plateau Physiographic Region. The Pennsylvanian bedrock system in this area consists of recurring beds of undifferentiated limestone, shale, sandstone, coal, and clays deposited in a fluvio-deltaic environment. The Pennsylvanian system is underlain by Mississippian system sandstones and shales. Unconsolidated deposits overlying bedrock include thick alluvial deposits of clay, silt, sand, and gravel associated with the Muskingum River. Alluvium associated with smaller streams and alluvial terraces, which are variable and heterogeneous, ranging from silty clay to gravel, and colluvium, which is a loose, heterogeneous mass of soil and rock that can be found at the base of slopes and in areas that include residuum, weathered material, landslides, and bedrock outcrop (ODNR, 1995). The primary bedrock units near the Plant are the Pennsylvanian-aged sedimentary rocks of the Allegheny Formation and the underlying Pottsville Formation. The stratigraphic sequence consists of alternating shale and sandstone beds, associated clays, and limestone beds. Several thick coal beds are present in the sequence and serve as marker beds for unit identification within the Allegheny and Pottsville Formations. The Allegheny and Pottsville can be as much as 700 feet thick but are considerably thinner in
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Coshocton County. The following paragraphs briefly discuss the stratigraphic units present in the Site vicinity, in ascending order (oldest to youngest). • The early to middle Pennsylvanian Pottsville Formation is composed of shale and siltstone with thin limestone beds and shaley, locally present coal seams. The Pottsville Formation can be on the order of 200 feet thick in the area of the Site and overlies the Mississippian Logan Formation. The No. 4 Coal marks the upper boundary between the Pottsville Formation and the overlying Allegheny Formation. • The middle Pennsylvanian Allegheny Formation is on the order of 150 to 200 feet thick in Coshocton County and is subdivided into several formations that are important from a hydrostratigraphic perspective or are useful marker beds. In ascending order these are the No. 4 coal, Putnam Hill Limestone, Clarion sandstone, No. 4a coal (locally present), Lower Kittanning clay, No. 5 coal, Middle Kittanning clay, No. 6 coal, Lower Freeport sandstone, No. 6a coal (locally present), Upper Freeport sandstone, and No. 7 coal (locally present). The No. 6 coal has been extensively mined in the area. The No. 7 coal marks the upper boundary of the Allegheny Formation and the overlying Conemaugh Formation. • Unconsolidated alluvial deposits associated with the Muskingum river consist of clay, silt, sand, and gravel ranging up to 200 feet thick. Alluvial sediments associated with smaller streams consisting of sands, silts, and clays derived from stream terrace deposits occur along the valley bottoms. Other overburden deposits in the site vicinity consist of residual soils, alluvial and lacustrine sediments, mine spoil, and waste in the permitted landfill. Ridgetops are generally capped by sandy clay soils that extend down valley and range up to 20 feet thick. Mine spoil occurs near the base of highwalls and piles of waste overburden (gob piles) deposited during strip mining operations. Monitoring wells installed to monitor the APS in 2015, 2018, and 2019 generally confirmed the unconsolidated lithology described above. Deep wells installed near the edge of the river valley encountered bedrock. Due to difficult drilling conditions encountered with depth (e.g., heaving sands), deep wells installed farther from the valley wall did not extend to bedrock. Therefore, bedrock depths are estimated based on depths to bedrock near the river and publicly available information. East to west, and south to north cross-section traverses are included on Figure 3, and the cross-sections are presented on Figures 4 and 5.
2.2.3 Groundwater Flow System Characteristics The Plant and Ash Pond System are underlain by unconsolidated glacio-fluvial sediments filling the Muskingum River valley. Groundwater elevations are generally controlled by river stage. Groundwater flow is generally west toward the river, although groundwater elevations in the vicinity of the APS are mounded as a result of the hydraulic head from the ponds. However, temporary groundwater flow reversals can occur during periods of high river stage. At the edge of the river valley and farther upstream in small streams and tributaries, flow is derived from precipitation, runoff, and natural seepage from bedrock and unconsolidated overburden.
2.2.4 Surface Water and Surface Water-Groundwater Interactions The Muskingum River at Coshocton drains a watershed of approximately 4,900 square miles and maintains an average flow of 6,200 cubic feet per second (cfs). Stage in this section of river is maintained by the Ellis Lock & Dam #11, located 18.5 miles downstream of the Conesville plant. The US Geological Survey (USGS) operates two gaging stations in this section of the Muskingum River monitoring stage and discharge. Gage #03140500 is located 5.6 miles upstream of the plant in Coshocton, OH. Gage
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
#03144500 is located 11.4 miles downstream of the plant in Dresden, OH. The Conesville Plant is located approximately one-third of the distance (by river) between the upstream gage in Coshocton and the downstream gage in Dresden. The river level at the Conesville Plant can be estimated using a distance- weighted average of the data from the two gaging stations.
The stage in the Muskingum River fluctuates considerably throughout the year with lower stage and discharge occurring in the drier summer months and high stage and discharge occurring in the winter. Water level fluctuations in response to precipitation can be on the order of 8 to 10 feet in several days and high stages can be maintained for several weeks in the winter. Based on water level estimates derived from the elevations at Coshocton and Dresden, Muskingum River stage elevations at the Conesville Plant ranged from 718 to 730 feet NAVD88 from March 2018 to March 2019. These values are in general agreement with values of 717 feet (low water), 721.5 feet (normal pool), and 742 feet (high water) previously reported as part of a sediment control project at the plant’s water intake (EPRI, 2000).
Wills Creek drains a watershed of 853 square miles and flows into the Muskingum River south of the APS and Conesville (OEPA, 2014). The flow of Wills Creek in its lower reaches is regulated by Wills Creek Dam which impounds Wills Creek Lake and is located 6.4 miles upstream of the confluence with the Muskingum River. USGS gage #03143500 monitors stage and discharge in Wills Creek and is located 1,200 feet downstream of Wills Creek Dam. This gage is tied to the US Army Corps of Engineers (USACE) vertical datum of 1912 (COE1912).
2.2.5 Groundwater Gradients and Flow Directions Interpolation of groundwater potentiometric data indicates that the primary groundwater flow direction in the vicinity of the APS is to the northwest, and west, and towards the Muskingum River. Hydraulic gradients were determined using the variation in the potentiometric surfaces and distance between contours at different years and times of year. Gradients range from 0.0008 to 0.0075 feet per foot (ft/ft) and are generally higher in the vicinity of the APS due to mounding of the potentiometric surface and lower moving downgradient toward the river. The calculated flow velocity in the APS area to the Muskingum River was determined from the hydraulic gradients in September 2016 and February 2019, an upper bound hydraulic conductivity of 581 feet per day (ft/d), and a porosity of 0.25 for the overburden materials, resulting in a range of approximately 2 to 11 ft/d, respectively. This is representative of the rate a particle of water or conservative constituent would travel at without retardation or alteration due to geochemical processes. A potentiometric surface map indicating groundwater flow directions and gradients from February 2019 is provided as Figure 6. Potentiometric data in the vicinity of the APS and along the river also indicates that at times the groundwater flow direction and velocity can be impacted by the Muskingum River, which can cause flow reversal during high flows with a flow velocity up to 1 ft/d in a southeasterly direction. However, the duration of the flow reversals is typically short, on the order of a couple of weeks. Assessment of individual monitoring well cluster potentiometric data also provides indications of groundwater vertical flow components by comparing the potentiometric data at each interval (S, I, D) on a given date. The results are mixed, as to upward or downward, vertical gradients and vary for each well. In summary, the uppermost aquifer within the APS varies depending on location but generally consists of groundwater in two formations: • Unconsolidated overburden deposits that form the Muskingum River alluvial valley; and
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
• the Clarion Sandstone Member. Unconsolidated sediments in the Muskingum River valley are recharged by groundwater seepage from the bedrock along the eastern valley wall, historical mining features along the eastern wall of the bedrock, and through direct precipitation. Because the bedrock permeability is orders of magnitude lower than the alluvium, the flow from the bedrock into the alluvial valley is hypothesized as minimal relative to direct recharge from precipitation.
2.2.6 Groundwater Monitoring Network Seventeen new wells were installed in December 2015 through January 2016 to monitor groundwater impacts associated with the APS. All of the monitoring wells were equipped with dedicated bladder pumps for purging and sampling. The clusters are designated MW-1502 through MW-1510, and their locations were previously shown on the aerial photograph in Figure 3. Three wells are included in clusters MW-1502, -1503, and -1505, finished at shallow (S), intermediate (I) and deep (D) levels within the principal flow zone (unconsolidated overburden). Two wells are included in cluster MW-15010, finished at shallow (S) and intermediate (I) levels in unconsolidated overburden. A single shallow well is installed in overburden at MW-1509. Two wells are included in clusters MW-1506 and MW-1507, finished at shallow levels in overburden and intermediate levels in bedrock. A single well is installed in bedrock at MW-1508. All of the wells are constructed of 2-inch PVC, with 10-foot long screens. The official CCR groundwater monitoring network consists of those wells used to statistically evaluate potential groundwater impacts. Well clusters MW-1506 through MW-1510 are designated as background monitoring wells, meaning they lie either hydraulically upgradient or cross-gradient to the APS. Waste boundary monitoring wells include well clusters MW-1502 through MW-1505 plus BAP-0901. These wells monitor downgradient water quality immediately at or as close as possible to the unit boundary. Additional monitoring wells have been installed to evaluate potential groundwater impacts remote from the APS boundary and are also shown on Figure 3. These are referred to as “characterization wells” and include: • Five well clusters (MW-1801S/I/D through MW-1805S/I/D) were installed in downgradient locations northwest and west of the APS, along the property boundary, in early 2018. • Two well clusters (MW-1901S/I/D and MW-1902S/I/D) were installed in February 2019 southwest of the APS along the Muskingum River, which forms the western property boundary of the site. • Three well clusters (MW-1903S/I/D through MW-1905S/I/D) were installed in April 2019 north of the APS along the Muskingum River, beyond the AEP property boundaries. Results from these additional monitoring wells have been used to estimate the nature and extent of groundwater impacts at the APS. Average downgradient concentrations for arsenic, lithium and molybdenum are presented on Figures 7 through 9.
2.2.7 Arsenic, Lithium and Molybdenum Transport in Groundwater While all three COCs (arsenic, molybdenum and lithium) exceed their respective GWPSs near the APS, the extent of arsenic is limited to an area entirely within the Conesville property boundaries and near the waste boundary (Figure 7). Downgradient monitoring well concentrations of lithium indicate the greatest extent of transport away from the APS (Figure 8) and monitoring well results for molybdenum indicate limited transport away from the APS to the south and southwest and the highest concentrations are noted
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
in shallow and intermediate property boundary wells to the northwest near the railroad laydown yard that may not be related to the APS (Figure 9). Arsenic, lithium and molybdenum can all experience sorption that results in range of retardation factors depending on site specific geochemical characteristics. Linear equilibrium sorption modeling is based on a retardation factor determined from the input transport parameters effective porosity, bulk density, and a distribution coefficient (퐾푑). The retardation factor applied in modeling is a function of all the contaminant retardation mechanisms including: 1) chemical precipitation/dissolution of bulk solid phases, 2) chemical substitution within a solid phase, 3) physical filtration of colloids, 4) cation and anion exchange, and 6) adsorption. Because the COCs, arsenic, lithium and molybdenum, are inorganic constituents there is no contaminant loss through degradation processes. All of these mechanisms are simulated as a single empirical 퐾푑 that implicitly assumes that the reactions go to equilibrium and are reversible and that the chemical environment along a solute flow path does not vary spatially or temporally. For the COCs, the primary mechanisms represented by the 퐾푑 are adsorption and ion exchange, and for lithium and molybdenum these two constituents in natural shallow groundwater systems are not typically involved to a significant extent with the other listed mechanisms. The model outcome for these COCs is very sensitive to the 퐾푑 applied in the model. The impact of 퐾푑 on predicted transport and capture of COCs can result in transport time estimates that differ by several factors or even orders of magnitude.
The 퐾푑 is calculated as the ratio between the measured sediment concentration and concentration in groundwater according to the following equation (eq. 1):
퐶푠 퐾푑 = eq. 1 퐶푤 Where, Cs is the metal concentration in the sediment (mg/kg) and Cw is the metal concentration in water (mg/L) resulting in units of L/kg.
The retardation (R) is calculated using the following equation (eq. 2): 휌 푅 = 1 + 퐾 푏 eq. 2 푑 푛 Where, 휌푏is the bulk density of the sediment (mg/kg) and 푛 is the effective porosity of the sediments. The retardation value indicates the relative speed at which a constituent will travel relative to a molecule of water. Thus, a retardation factor of 1 means that there is no difference and the constituent will move with the advective flow of water, and a retardation factor of 2 indicates a constituent will move at half the speed of water. Arsenic is not a conservative constituent, meaning the mass of arsenic dissolved in groundwater can change significantly as the result of geochemical interactions. According to the USGS and others (Smith 1999, Hinkle and Polette 1999), arsenic mobility in groundwater is largely controlled by one of two geochemical interactions: (1) adsorption and desorption reactions and (2) precipitation and dissolution reactions. The mass of arsenic migrating in groundwater from CCR sites is primarily influenced by changes in pH or by reduction/ oxidation (redox) reactions. Arsenic can experience a wide range of retardation in groundwater because it can be present within groundwater under different redox states (e.g. As(III) versus As(V)) that effect its sorption characteristics (Smith 1999, Hinkle and Polette 1999). Additionally, arsenic sorption and retardation is affected by solution chemistry (i.e. pH) and aquifer mineralogy (Smith 1999, Hinkle and Polette 1999). Under the site-specific conditions at Conesville, neutral pH and relatively oxic, arsenic is expected to be retained on aquifer solids and relatively immobile. Arsenic has the greatest sorption and associated attenuation, retardation, of the three at the Conesville site. Arsenic attenuation is supported by the findings that arsenic concentrations above the groundwater protection standard do not
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extend beyond the waste boundary as indicated by property boundary monitoring wells which all have concentrations below that criterion (Figure 7). Lithium is the least retarded of the three COCs as is noted by its greatest extent of transport (Figure 8). While lithium is cationic and more susceptible to sorption processes, it has been documented that the affinity of various types of clays for cations decreases with increasing hydrated radii, with the order of preference being Cs+ > Rb+ > K+ > Na+ > Li+ (Carroll, 1959; Gast and Klobe, 1971). Thus, lithium exhibits the lowest ion-exchange capacity with clay materials (Carroll, 1959; Gast and Klobe, 1971), and the aquifer sediments of the Conesville APS are predominantly sand and gravels indicating its comparatively conservative transport at the site. Lithium is also noted in the literature as having a relatively low distribution coefficient (Strenge and Peterson 1989). Molybdenum can experience greatly varying retardation factors in groundwater transport depending on site conditions such as redox and pH (Goldberg et al. 1996, Sun and Selim 2018). Molybdenum has been shown to exhibit virtually no sorption on clay minerals at neutral pH values (pH ~7). However, molybdenum sorption onto oxides can also play an important role in its transport (Goldberg et al. 1996, Sun and Selim 2018). Molybdenum attenuation is supported by the findings that concentrations above the groundwater protection standard generally do not extend beyond the waste boundary as indicated by property boundary monitoring wells to the south and southwest of the APS which all have concentrations below that criterion (Figure 9). The highest concentrations that are also above the GPS are observed in shallow and intermediate groundwater near the rail yard to the northeast and may not be related to the APS. Lithium is used as the indicator of corrective measures success at the Conesville site due to the greater extent of migration and larger volume of water needed to be captured and treated. It is assumed that the transport and capture of lithium will also provide capture for molybdenum and arsenic due to their lesser extent of elevated concentrations across the site and generally with depth, in addition to molybdenum having a higher GWPS relative to lithium (Figures 7 to 9).
3.0 Identification and Development of Corrective Measure Alternatives This section describes the initial screening of applicable remedial technologies and process options for groundwater corrective action at the two CCR units at the Conesville plant.
Establishment of Corrective Action Objectives (CAOs) The objective of corrective action under the CCR Rule is to “attain the groundwater protection standard as specified pursuant to §257.95(h)” and “to remediate any releases and to restore affected area to original conditions” (40 CFR § 257.96(a)). Evaluation criteria specified in §257.96 include: • The performance, reliability, ease of implementation, and potential impacts of appropriate potential remedies, including safety impacts, cross-media impacts, and control of exposure to any residual contamination; • The time required to begin and complete the remedy; and • The institutional requirements, such as state or local permit requirements or other environmental or public health requirements that may substantially affect implementation of the remedy(s).
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The cleanup criteria used for corrective action is the site-specific GWPS, calculated for each Appendix IV COC. Three COCs exceed their respective site-specific GWPS: arsenic, lithium and molybdenum. A summary of these GWPSs are presented below.
Default GWPS Background Upper Site-Specific MCL RSL Constituent Units Tolerance Limit GWPS Arsenic, total µg/L 10 16 16 Lithium, total µg/L n/a 40 80 80 Molybdenum, total µg/L n/a 100 3.2 100 Note: Regulatory citations use mg/L for MCLs and RCLs for all non-radiological constituents. Units are provided in µg/L for consistency and legibility of figures.
Based on previous evaluation conducted at the APS, an alternative source of groundwater impacts has not been identified and an assessment of corrective measures is required.
Screening and Evaluation of Remedial Technologies General Response Actions (GRAs) are categories of remedial actions that can reduce or eliminate the risk that contaminants present to human health or the environment. Remedial alternatives are combinations of specific process options within each of the GRAs that are selected for detailed evaluation (as described in Section 4, below). In a traditional CERCLA Feasibility Study (FS), the “No Action” alternative is a GRA that is required to be analyzed as a baseline for comparison to other alternatives. However, in this ACM, the “No Action” alternative has been eliminated from consideration since it is not permitted under the federal CCR Rule once corrective action has been triggered by statistical analysis of groundwater monitoring results. Monitored Natural Attenuation is a GRA that is only allowed in conjunction with other remedial actions under the current CCR Rule, such as source control. • Source Control (Pond Closure); • Monitored Natural Attenuation (MNA); • Containment (Hydraulic, Groundwater Extraction); • Containment (Physical Barrier); • Ex-Situ Technologies and Discharge; and • In-Situ Technologies. In addition to source control, hydraulic containment of impacted groundwater can be achieved by construction of a barrier wall, extraction of impacted groundwater with treatment for discharge or re- injection, or a combination of barriers and pumping. Certain traditional remediation technologies are not well suited to Appendix IV COCs because of the unique physical and chemical characteristics. For example, many organic COCs can be degraded over time into harmless byproducts through biological or chemical processes. Some organics can be volatilized and removed from the groundwater by transferring them into the air phase (air sparging), and or by heating the aquifer matrix to more aggressively volatilize the compounds (steam stripping or electrical resistance heating). These types of technologies were not evaluated, since all Appendix IV constituents are naturally occurring metals or metalloids. These constituents are elements and cannot be transformed into harmless byproducts through chemical or biological treatment techniques. These metals are in a relatively soluble form and generally less volatile than water which prohibits phase transfer.
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Additionally, large scale volatilization, such as electrical resistance heating would be economically impractical, especially given the depth of groundwater encountered at the Conesville Plant. At best, these Appendix IV COCs can be made immobile through stabilization within the soil matrix, either through adsorption or conversion into less soluble forms. Alternately, extraction of impacted groundwater can be used to accelerate the migration and removal of COCs from the aquifer system since pore volumes currently occupied by impacted groundwater are replaced by unaffected water. However, groundwater extraction is affected by adsorption of COCs to the aquifer soils and the slow processes of desorption and diffusion from that matrix. The screening of treatment technologies presented in the following section have been selected on the basis of feasibility, demonstrated success at similar sites, and reasonable cost. In addition, a brief discussion is included in this section describing alternatives considered but not explored further as part of this ACM. Each of the technology types and process options evaluated was screened for applicability at the site and either retained or not retained for further evaluation (as described in the next section) with regard to effectiveness, implementability, and cost. As described above, the most viable remedial technology types for groundwater at the Conesville site have been identified as: containment; in-situ physical treatment; and ex-situ chemical treatment. MNA, in conjunction with source control measures, has been retained as a baseline from comparison to the other options. As an outcome of this screening process, the process options carried forward for development of alternatives (as described in the next section) are summarized on the following Table 1. Development of Corrective Measures Alternatives Corrective action measures assessed for the APS at the Conesville Plant have been developed based on site-specific conditions at the Plant in conjunction with remedial actions that are technically implementable and effective for the identified COCs. Corrective Measure Alternatives were developed that combined effects of source control on groundwater quality, followed by other combinations of technologies for retained for additional evaluation. • Alternative #1: Source Control with Monitored Natural Attenuation • Alternative #2: Source Control with Plume Containment by Groundwater Extraction; Treatment and Surface Water Discharge of Extracted Groundwater • Alternative #3: Source Control with Plume Containment by Groundwater Extraction; Treatment and Reinjection of Extracted Groundwater Section 4 contains a detailed evaluation of each alternative, compared to correction action objectives specified in §257.96(a).
4.0 Detailed Evaluation of Corrective Measure Alternatives The following sections contain a site-specific evaluation of various Corrective Measure Alternatives. Of the three COCs identified for the APS (arsenic, lithium and molybdenum), lithium is the most widely dispersed, and is present at higher concentrations than the other two COCs and has a lower GWPS. For this reason, the evaluations below focus on the effects these alternatives have on lithium concentrations, with discussions of arsenic and molybdenum where appropriate. APS closure will require three to seven years for any of the considered options with a substantial part of that schedule associated with dewatering activities.
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Source Control Description Three source control measures were evaluated, to be applied to all ponds in the APS complex (Fly Ash, Bottom Ash and Clearwater Ponds): • Closure by removal of the CCR from the APS; • Closure with the residuals in place by capping the APS; and • Closure involving in-situ soil stabilization (ISS) of the soils beneath the APS combined with a slurry wall and capping. AEP’s closure plan, prepared in accordance with the requirements of 40 CFR 257.102(b), specifies Alternative #2, closure in place by capping. Existing CCR materials covered with a composite soil and geomembrane cap with vegetative cover (AEP 2016). The two other alternatives were evaluated to assess whether they offered substantially different outcomes for groundwater quality.
4.1.1 Pond Dewatering The initial activity for any of the three closure approaches will involve decanting the existing water from the APS once current operations cease. In addition to removal of the standing water from the ponds, sufficient pore water must be removed so that the ash surface is stable enough to support construction equipment and construction of soil bridges. All three source control methods require heavy equipment to cross the ash surface during excavation, capping or stabilization. Typically, a depth of 10 to 15 feet of unsaturated ash above the saturated ash layer is required to support the weight of equipment typically used to excavate ash or construct the cap. A greater depth may be required to support equipment used for ISS, or other measures taken to support this equipment, such as temporary cribbing, construction mats, or ash stabilization to a sufficient depth to support the equipment used to perform ISS. Water generated during this process must be managed appropriately. Currently, effluents discharged from the plant (including discharge from the APS) are regulated under the OEPA 18-04-032 Draft NPDES permit issued 25 April 2018. Pollutants that are limited or monitored in the effluent from the Plant include pH, TSS, Oil and Grease, TRC, fecal coliform, BOD5, mercury, zinc, chromium, iron and copper. It is possible that quality of decant water will change as dewatering proceeds, due to aeration during continued pumping operations and provisions will be required to treat this water to meet the permit requirements. A preliminary review of the data indicates that treatment may be required to address TSS, plus arsenic, copper and selenium. A polishing step following treatment may also be required to achieve the appropriate water quality criteria in the effluent discharge. Drawing 4-1 presents a typical conceptual process flow diagram based on this approach. Treatability studies conducted as part of the design process would refine this concept further and identify specific constituents that may require additional treatment.
4.1.2 Closure by Removal The closure by removal alternative assumes that all CCR materials are excavated from the APS and disposed of in an appropriately permitted solid waste landfill. In addition to the dewater process described in Section 4.1.1, this approach includes removal of the CCR material in lifts, placement of backfill material to mimic the final grade and providing a soil cover to minimize erosion. Because there the existing Pozzotec landfill adjacent to the APS, a portion of the CCR material may need to be left in place and capped to maintain the slope stability of the ash landfill.
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Closure by removal would require a longer schedule duration compared with in-situ closure (Section 4.1.2) and would generate the largest volume of pore water and stormwater for treatment. Following closure by removal, the natural recharge across the APS (approximately 9.0 in/yr) would be restored. Since closure by removal would remove the ash source, transfer of COCs into the groundwater plume is assumed to cease.
4.1.3 Closure by Capping The closure by capping alternative assumes the CCR material is left in place and covered with a cap to limit infiltration of water into the CCR. By reducing the amount of infiltration, the transfer of COCs from the ash materials is also reduced. In addition to the dewater process described in Section 4.1.1, this approach includes grading the CCR material to mimic the final grade providing an interim soil cover to minimize erosion; and constructing a final composite cap consistent with the AEP Closure Plan. Closure with the soil cap specified in the CCR Rule was not considered in this evaluation, since AEP has already elected to install the more protective composite cap. Existing topography (BBCM, 2010, and AEP 2018), was used develop a balanced grading plan for the CCR subgrade (see Drawing 4-2). Closure activities are assumed to begin after the final coal fired unit at the plant ceases operation, and the plant no longer discharges effluent to the ash pond system. It is anticipated the existing groundwater table will decrease over time after plant discharges cease. Based on the AEP closure plan, the final cover system will consist of a flexible geomembrane that will have a permeability that is less than or equal to the permeability of the natural subsoils and is no greater than 1 x 10-5 cm/sec. The geomembrane will be installed directly over the graded CCR material. Over the geomembrane will be installed an infiltration layer consisting of 18 in of earthen material and an erosion layer consisting of 6 in of earthen material that is capable of sustaining native plant growth. The final cover will be seeded and mulched to promote growth of a vegetative cover. The final cover slope will be a minimum of 2% and will covey water to a NPDES permitted outfall. This design is functionally similar to the cap system requirements specified in OAC 3745-29-08. Sediment and erosion controls would be employed during closure, including use of the existing the wastewater treatment system described in Section 4.1.1 manage the treatment and discharge of CCR material interstitial water, contact water, and stormwater discharges. The closure by capping would generate the least volume of water for treatment and the timeframe for closure by capping is less than closure by removal.
4.1.4 Closure Incorporating In Situ Stabilization This approach modifies the closure by capping option to incorporate in-situ stabilization (ISS) of the soils beneath the ash, and construction of a soil bentonite slurry wall around the perimeter of the ponds to effectively encapsulate the waste. A concept is shown on Drawing 4-3. The equipment used to stabilize the soil below CCR material would consist of track-mounted equipment with large diameter augers fitted with grout injectors, or augers suspended from cranes. Using the auger method, the augers are slowly advanced through the CCR material while at the same time injecting and mixing the reagent grout into the CCR material, forming columns of treated material. The columns are overlapped to construct a monolithic low permeable structure. In general, ISS is a method of mechanically mixing soil and some amount of CCR material, and typically includes the addition of reagents for treatment and stabilization of the material being mixed. A bench-scale treatability study would be required to evaluate the potential application of ISS for the underlying soil impounded CCR materials. The conceptual approach shown on Drawing 4-3 depicts ISS being implemented along the “floor” of the ash pond in the vicinity where the CCR material intersects the anticipated groundwater post closure
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elevation. The augers would be deployed and would solidify and stabilize the CCR material for a defined thickness over the extent of the ash pond complex. The perimeter of the pond would also be stabilized from the pond surface to intersect with the stabilized and treated “floor” of the ash pond complex. Deployment of the equipment used to perform ISS will require an evaluation to ensure the ash surface is capable of supporting the equipment. Information collected from a geotechnical investigation would be used to evaluate suitable methods needed to support the equipment during the ISS of the ash pond complex. Once completed, the area will be covered with the same composite cap described in Section 4.1.3. Sediment and erosion controls would be employed during closure, including use of the existing the wastewater treatment system described in Section 4.1.1 manage the treatment and discharge of CCR material interstitial water, contact water, and stormwater discharges. The closure by capping with ISS would potentially generate a higher volume of water for treatment than simple closure by capping, since the timeframe for implementing this option is substantially longer than for capping.
4.1.5 Evaluation The effectiveness of source control was evaluated for the relative performance of the three source control options presented above, in comparison to one another. Groundwater flow conditions will be significantly altered after the shutdown of the Conesville Plant, currently scheduled for mid-2020. At that point, the APS will be taken out of service, and AEP production wells will no longer used. Currently, the constant head on the APS causes groundwater flow in a radial pattern, and at artificially high gradients compared to natural conditions. Product wells locally affect groundwater flow when they are pumping. After the constant heads are removed from the APS and pumping of AEP wells has ceased, groundwater flow will assume conditions similar to those prior to development of the plant. Modeling predicts a lower gradient of approximately 0.0001 ft/ft with flow primarily to the south, southwest and much greater travel times (40 to 50 years) to the river (Figure 10). Post closure modeling indicates that groundwater from the APS flows to and discharges into the Muskingum River and does not reach Village of Conesville potable water wells. Except for closure by removal, a small portion of the CCR material will also continue to be below the water table after natural flow conditions are reestablished, specifically in the areas of MW-1504 and somewhat north under Pond C (see the conceptual cross-section on Figure 4). For options where waste is left in place, some COCs continue to be transferred to the groundwater through recharge that passes through the cap, and leaches through the CCR materials in the closed APS (leachate). Leachate generation was taken from Pantini et al. (2013) for an area of similar precipitation and evapotranspiration. The leachate generation rates reported over the lifespan of simple clay caps (the minimum acceptable under the CCR Rule) are on the order of natural recharge (approximately 10.5 in/yr), due to degradation of the liner material over time. However, the recharge resulting from a composite cap (as proposed by AEP) is a much lower rate of 0.0004 in/yr. Modeling simulated leaching of CCR material, using the natural recharge rate of 9.0 in/yr and lithium concentration at the APS boundary showed continued plume generation until the source was depleted. No plume continues to be generated under the closure by removal option. Modeling of a composite cap indicated the addition of only 0 to 1 µg/L to the plume under steady-state conditions over a 100-year period.
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4.1.6 Summary Modeling indicates that there are differences in the effect of groundwater quality between closure by removal and closure by capping. Modeling indicates closure by capping will result in the addition of 0 to 1 µg/L lithium compared to no lithium in closure by removal. The small addition of up to 1 µg/L of lithium under the closure by cap scenario represents a small percentage of the GWPS (80 µg/L). Modeling also indicates that there is a small decrease in the amount of natural flushing in the capping option, since capping decreases overall recharge in the vicinity of the APS cap. Nevertheless, results indicate that these two approaches to source control are functionally equivalent and within the limits of uncertainty inherent in modeling. Given the effectiveness of composite capping alone, the three Corrective Action Alternatives only consider the removal or composite capping option for source control, and the ISS option is not considered further.
Monitored Natural Attenuation
4.2.1 Description MNA relies on subsurface attenuation processes to achieve site-specific corrective action objectives (CAOs) as compared to other more active remedial methods. Natural attenuation processes involved in the MNA approach include physical, chemical, and/or biological processes that occur without human intervention to reduce mass, toxicity, volume, mobility, or concentration of contaminants. COCs at the Conesville site naturally attenuate through redox reactions (such as precipitation and coprecipitation) based on groundwater flow system geochemistry, adsorption, dispersion and/or advection. In conjunction with source control, MNA can be effective in reducing COC constituents below their respective GWPSs. Closure under MNA is supported by a groundwater monitoring program to monitor the progress of MNA and demonstrate compliance with the GWPSs. MNA would utilize the existing monitoring well network at the site including the following wells: • Waste Boundary Wells: All available intervals (shallow, intermediate, and deep) for a total of 11 monitoring wells in well clusters MW-1502 to MW-1505; and • Property Boundary Wells: All available intervals for a total of 30 monitoring wells in well clusters MW- 1801 to MW-1805 and MW-1901 to MW-1905. The 41 monitoring wells would be sampled semi-annually for full suite of TAL metals, total organic carbon, sulfate, and alkalinity. Monitoring wells will be purged and sampled consistent with the United States Environmental Protection Agency (EPA) guidelines (EQASOP-GW 001 rev 3, dated July 30, 1996, revised January 19, 2010).
4.2.2 Evaluation
4.2.2.1 Overall Protection of Human Health and Environment MNA will be protective of human health and the environment because there are no identified receptors that could be exposed to impacted groundwater. For the option to continue to remain effective until the GWPSs are met, a deed restriction would need to be enacted that prohibits the use of groundwater at the Conesville Plant and on offsite property contiguous to the northwest of the Plant. The currently modeled plume boundaries do not extend to the potable supply wells in the Village of Conesville. Furthermore, modeled plume concentrations at its downgradient edge before discharge into the river are below GWPS for all COCs, including lithium. Modeling results will require confirmation with the sampling conducted at the new downgradient well clusters MW-1903 through MW-1905.
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4.2.2.2 Ability to Meet Groundwater Protection Standards After the constant heads are removed from the APS and pumping of AEP wells has ceased the model predicts a significantly reduced gradient of approximately 0.0001 and flow that is primarily to the south, southwest with travel times on the order of 40 to 50 years from the APS impoundments to the river (Figure 10). Modeling indicated that closing the APS followed by MNA would result in lithium concentrations at the site remaining above the GWPS for a time period of up to 66 to over 100 years. The lower estimate was based on no retardation of lithium by the aquifer matrix and natural recharge that would occur as a result of removal of the CCR wastes from the APS. At 66 years under these conditions, modeling suggested a small volume of shallow and deep groundwater remained with concentrations exceeding the GWPS of 80 µg/L in the vicinity of the power plant and along the river. If minimal recharge is applied at the APS, reflecting the use of a composite cap, then the time for concentrations to dissipate below the GWPS will be greater (more than 100 years) due to slowing of the migration of COCs. However, these simulation are highly sensitive to the actual retardation of lithium within the aquifer and increased recharge during precipitation events. Empirical data collected source control measures are taken would allow a more accurate estimate to be developed.
4.2.2.3 Source Control and Reduction of Contaminated Material Source control is included as part of this alternative, either through source removal or composite capping. Either option significantly reduces the migration of COCs into the groundwater. Natural attenuation processes reduce the mass of COCs in the groundwater through adsorption and concentrations would decrease through dilution and dispersion. Institutional controls to prevent groundwater use will be required for this alternative, and additional controls will be required to maintain the cap for the life of the alternative.
4.2.2.4 Long Term Effectiveness Attenuation of COCs under the site is achieved by first preventing the input of new COCs by closing the units, then reducing concentrations of COCs by absorption, dilution and dispersion. COC concentrations under the unit as the impacted groundwater flows out and is replaced by non-impacted upgradient flow. As long as the units have been closed, MNA will be effective in reducing the toxicity, mobility, and volume of contaminants in groundwater gradually over the long-term.
4.2.2.5 Short Term Effectiveness All services required (well installation, environmental sampling activities, laboratory analysis, and environmental reporting) are readily available. There are not any safety or exposure considerations for workers conducting sampling other than standard procedures employed in groundwater monitoring programs. MNA does not present any exposure risks to the community during construction or implementation.
4.2.2.6 Implementability MNA is easily implemented. All services required (well installation, environmental sampling activities, laboratory analysis, and environmental reporting) are readily available. MNA will involve coordination with the Ohio Department of Natural Resources during pond closure since the APS are regulated by the ODNR Dam Safety Program, with Facility ID 0116-002.
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A stormwater construction NPDES permit will be required for implementation of any of the potential source control options. Coordination with OEPA may be necessary if state regulations are implemented for CCR pond closures.
4.2.2.7 Long-Term Management Requirements Maintainability and reliability for this alternative is good. However, since MNA will last approximately 100 years, the monitoring well network and dedicated pumps will need at least one total replacement. The dedicated pumps could potentially need more frequent replacements depending on field conditions.
4.2.2.8 Community Acceptance Community concerns will be assessed during the public meeting.
4.2.2.9 State Acceptance Currently, there are no regulations identified for the state of Ohio that would prevent implementing this alternative. The state has not developed its own CCR program and has not indicated it plans to do so. Source control activities will require the contractor to obtain a Construction Storm Water General Permit from the Ohio EPA. Water generated during free water removal or dewatering may require a modified NPDES permit. An Environmental Covenant may be required to provide institutional controls for risk management.
4.2.2.10 Time to Meet Remedial Objectives Implementation of this alternative will eventually achieve compliance with the GWPSs at the APS within a time frame of about 66 years or longer.
Groundwater Extraction, Treatment and Surface Water Discharge
4.3.1 Description This alternative consists of groundwater extraction in the portion of the groundwater plume with the highest concentrations, followed by wastewater treatment prior to direct discharge to the Muskingum River under an NPDES permit. Initially, the COC concentrations in the extracted groundwater will be more similar to the concentrations observed in the waste management unit boundary wells but will differ from those levels because of the influence of other pumping wells across the plume. As extraction progresses over time, the constituent concentrations in the extracted groundwater will decline. Modeling indicates eight extractions wells will be required across the site as shown in Figure 11. The extraction wells be installed to a depth of 100 ft bgs and will be constructed of 6 in stainless still well casing and screen. The recovery wells will have 50 ft screened intervals from approximately 640 ft MSL to 690 MSL. In the case of removal, the sustainable extraction rates were estimated to be approximately 1,600 gpm. In the case of closure by composite capping, sustainable extraction rates were estimated to be around 1,200 gpm. Actual sustainable extraction rates would need to be determined following the implementation of the selected closure scenario to refine the design basis for a groundwater treatment system. Additionally, since both the suite of pollutants and their valence states may change during extraction it is recommended that any design for a treatment system incorporate modular components to provide flexibility that will be needed over the duration of the process. The anticipated average influent concentrations of the COCs in the extracted groundwater have been estimated using groundwater modeling and are provided below:
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• Arsenic: 27 µg/L • Lithium: 145 µg/L • Molybdenum: 189 µg/L Probable discharge limits were based on the OEPA WQC (35 OAC3745-1). In the Plant’s 2018 draft NPDES permit, water quality criteria (WQC) were established for protection of aquatic life and concentrations allowed within the mixing zone for the current discharges from the operating steam electric generation power plant. For arsenic, the WQC is 150 µg/L with a maximum aquatic life criteria of 340 µg/L. The aquatic life criteria for molybdenum is 20,000 µg/L with a maximum allowable for aquatic life of 190,000 µg/L. The Ohio EPA has not established a WQC for lithium. The probable discharge limit for lithium was estimated by comparing a promulgated criteria in other states with calculated values based methodology outlined in the “Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses” (USEPA, 2010) and OAC 3745-1-40 (OEPA, 2017). The Michigan Department of Environment, Great Lakes, and Energy (EGLE) has promulgated a final chronic value (FCV) for aquatic life of 440 µg/L and an aquatic life maximum of 910 µg/L. The calculated Tier 2 FCV for lithium was 430 µg/L, which is very similar to the promulgated value under Michigan EGLE of 440 µg/L. Based on this information, estimate discharge concentrations are provided below: • Arsenic: 150 µg/L • Molybdenum: 20,000 µg/L • Lithium: 430 µg/L As detailed above, concentrations of COCs in the extracted groundwater are estimated to be below the effluent concentrations required for surface water discharge. Nevertheless, a conventional physical/chemical treatment facility is included in this alternative to address non-COCs that may exceed aquatic WQC. Extracted groundwater will be treated to reduce TDS and metals concentrations using conventional coagulation and direct filtration techniques. Coagulation using iron salts is widely used for arsenic removal for drinking water treatment and is capable of reducing arsenic concentrations to 2 to 5 µg/L. Molybdenum is also readily removed by coagulation using ferric salts. It is assumed that no treatment will be required for lithium, since maximum groundwater concentrations are lower than the presumed surface water discharge limit. Effluent will be polished through multimedia filters. to remove particles down to the range of 5 to 10 microns.
4.3.2 Evaluation
4.3.2.1 Overall Protection of Human Health and Environment Hydraulic control of impacted groundwater through extraction will be protective of human health and the environment because there are no identified receptors that could be exposed to impacted groundwater during the remedial period. For the option to continue to remain effective until the GWPSs are met, a deed restriction would need to be enacted that prohibits the use of groundwater at the Conesville Plant and on offsite property contiguous to the northwest of the Plant. Discharge of treated effluent under this alternative will be capable of meeting the appropriate WQC and would not present risks to aquatic life. The currently modeled plume boundaries do not extend to the potable supply wells in the Village of Conesville. Furthermore, modeled plume concentrations at its downgradient edge before discharge into the river are below GWPS for all COCs, including lithium. Modeling results will require confirmation with the sampling conducted at the new downgradient well clusters MW-1903 through MW-1905.
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
4.3.2.2 Ability to Meet Groundwater Protection Standards Transport modeling was conducted to estimate lithium concentrations under a combination of source control combined with groundwater extraction and surface water discharge. A relatively low lithium retardation factor of 2 was assumed. For closure by removal, results indicated that lithium concentrations would require approximately 28 years of extraction for groundwater concentrations to be below 80 µg/L. The remediation of lithium is near the GWPS of 80 µg/L within 23 years for much of the site, but an additional 5 years of extraction is required to reduce concentrations below 80 µg/L in the deeper alluvium site wide. In the case of closure by capping, modeling indicated a different flow field due to the loss of recharge over the APS area that would be covered with a composite cap (Figure 12). For the case where the APS is capped and with some lithium sorption , modeling indicated that lithium concentrations would be reduced to below the GWPS of 80 ug/L in about 35 years, except for the shallow zone that is no longer flushed by fresh recharge. This residual area could be addressed by installation of wells screened for this shallow zone and after an additional 5 years of extraction lithium concentrations are approximately under the 80 µg/L GWPS for the site. This is approximately as long as predicted for closure by removal, which has a predicted time frame of 23 years for lithium concentrations to drop below 80 µg/L. However, a targeted shallow horizontal well could reduce the time frame to approximately 12 years.
4.3.2.3 Source Control and Reduction of Contaminated Material Source control is included as part of this alternative, either through source removal or composite capping. Either option significantly reduces the migration of COCs into the groundwater. Natural attenuation processes reduce the mass of COCs in the groundwater through adsorption and concentrations would decrease through dilution and dispersion. Institutional controls to prevent groundwater use will be required for this alternative, and additional controls will be required to maintain the cap for the life of the alternative. Wastewater treatment will generate solids which contain relatively low concentrations of COCs removed from the groundwater. These solids will be transferred for disposal in an approved landfill.
4.3.2.4 Long Term Effectiveness Reduction of COCs at the Plant is accomplished through mass removal by groundwater extraction, and a then reducing concentrations of COCs by absorption, dilution and dispersion. Groundwater extraction in conjunction with source control will be effective in reducing the toxicity, mobility, and volume of contaminants in groundwater over the long-term.
4.3.2.5 Short Term Effectiveness All services required (well installation, piping and electrical installation to the wastewater system, wastewater plant construction, wastewater plant operations, laboratory analysis, and environmental reporting) are anticipated to be available. However, some portion of the services, materials or equipment needed are likely not locally available and may have to be imported. Long term operation of the wastewater treatment system will likely need to be performed on a contract basis. There are not any safety or exposure considerations for workers involved in construction of the system or its operation other than implementation of standard health and safety procedures for construction activities and water treatment plant operation. This alternative does not present exposure risks to the community during construction or implementation.
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
4.3.2.6 Implementability The implementability of this alternative is considered moderate. Installation of extraction wells will not be difficult, but the units are located some distance from the plant infrastructure where it is anticipated that the treatment system will be constructed. Labor and equipment to install extraction wells, utility trenches and discharge piping are readily available, and installation could be completed within a short timeframe. New discharge piping sized relative to the anticipated discharge flow will need to be installed to a new discharge and monitoring station along the river.
4.3.2.7 Long-Term Management Requirements Maintainability and reliability for this alternative is good, but routine observation of the system is required to ensure continuous operation. Telemetry and other automated controls can reduce the time required for onsite personnel. Mechanical extraction systems and physical/chemical wastewater treatment systems require routine and ongoing operations and maintenance (O&M) throughout the life of the corrective action. Long term operation of groundwater extraction wells means that it is likely that some portion of the wells or pumping systems may need replacement during the treatment period.
4.3.2.8 Community Acceptance Community concerns will be assessed during the public meeting.
4.3.2.9 State Acceptance Currently, there are no regulations identified for the state of Ohio that would prevent implementing this alternative. The state has not developed its own CCR program and has not indicated it plans to do so. Coordination with the Ohio Department of Natural Resources during pond closure will be required since the APS are regulated by the ODNR Dam Safety Program, with Facility ID 0116-002. A stormwater construction NPDES permit will be required for implementation of any of the potential closure options. Notice for well closure and replacement to OEPA would be necessary if well replacement is required. Prior to construction of the wastewater treatment system a new NPDES permit application will be needed and a permit to construct will need to be obtained. NPDES permitting to operate will also be required. Notice for well closure and replacement to OEPA would be necessary if well replacement is required. Source control activities will require the contractor to obtain a Construction Storm Water General Permit from the Ohio EPA. An Environmental Covenant may be required to provide institutional controls for risk management if source material is left in place (closure by capping).
4.3.2.10 Time to Meet Remedial Objective APS closure will require three to seven years for any of the considered options with a substantial part of that schedule associated with dewatering activities. Construction of the wastewater system will need to precede pond closure with modification of the modular system to address groundwater extraction once APS closure has been completed. Groundwater extraction system installation and construction of headers can be completed during the APS closure schedule. As indicated in Section 4.3.2.2, the time required to meet the groundwater protection standards will range from 28 to 35 years for limited lithium adsorption
Project # 7362192661 | 24 June 2019 Page 20 of 26
Wood Environment & Infrastructure Solutions, Inc.
Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Groundwater Extraction, Treatment and Reinjection
4.4.1 Description This alternative consists of groundwater extraction in the portion of the groundwater plume with the highest concentrations, followed by wastewater treatment prior to injection back into the alluvium upgradient of the extraction area (Figure 13). This alternative is analogous to Alternative #2, Groundwater Extraction, Treatment and Reinjection described in Section 4.3 except for the following primary differences. • Reinjection of extracted groundwater increases the hydraulic gradient and flow of clean water through the groundwater plume. This approach can be helpful in areas (like at the Conesville Plant) where natural recharge is limited. As a result, the time to complete the remedy should be lower than for direct discharge. • In order to effectively flush the COCs from the aquifer, concentrations of COCs in the reinjected groundwater must be as low as possible. More sophisticated treatment would be required to reduce concentrations of COCs below those required for direct discharge. This description focusses on treatment of extracted groundwater since it represents the biggest difference between the two alternatives. Drawing 4-4 provides a conceptual process flow diagram for the treatment system. This initial step will be identical to the direct discharge alternative. Treatment will provide for the reduction and removal of arsenic and molybdenum via iron co-precipitation and softening in the initial step. Some other metals that may be present at trace levels will also be reduced to their solubility limits in this process. Following co-precipitation and softening, wastewater will be flocculated with the aid of a polymer and sent to a clarifier to remove the solids. Following primary filtration, the wastewater stream will be conveyed through a polishing filtration through parallel bag filter units. After physical/chemical treatment is completed, additional treatment is required for lithium, which will not be affected by the co-precipitation and softening system. A system of cation and anion exchange beds will be used to reduce lithium concentrations, as well as other Appendix IV constituents in the waste stream. After ion exchange, the wastewater will be treated by reverse osmosis (RO). The process streams resulting from operation of the system include (1) spent regenerants from ion exchange (2) rinse waters from ion exchange, (3) reject from RO and (4) the RO permeate. Spent ion exchange regenerants and reject water from the RO would be containerized and shipped offsite for appropriate disposal. Rinse waters from the ion exchange system could be discharged directly to the Muskingum River under an NPDES permit. The majority of the permeate can be re-injected for the purpose of flushing the aquifer.
4.4.2 Evaluation
4.4.2.1 Overall Protection of Human Health and Environment Hydraulic control of impacted groundwater through extraction will be protective of human health and the environment because there are no identified receptors that could be exposed to impacted groundwater during the remedial period. For the option to continue to remain effective until the GWPSs are met, a deed restriction would need to be enacted that prohibits the use of groundwater at the Conesville Plant and on offsite property contiguous to the northwest of the Plant. Discharge of rinse waters from the ion exchange system under this alternative will be capable of meeting the appropriate WQC and would not present risks to aquatic life. The currently modeled plume
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
boundaries do not extend to the potable supply wells in the Village of Conesville. Furthermore, modeled plume concentrations at its downgradient edge before discharge into the river are below GWPS for all COCs, including lithium. Modeling results will require confirmation with the sampling conducted at the new downgradient well clusters MW-1903 through MW-1905.
4.4.2.2 Ability to Meet Groundwater Protection Standards Transport modeling was conducted to estimate lithium concentrations under a combination of source control combined with groundwater extraction and surface water discharge. A relatively low lithium retardation factor of 2 was assumed. Closure by removal in conjunction with groundwater extraction and reinjection was modeled for comparison to the same scenario for Alternative #2, where the only difference is surface discharge instead of reinjection. The extraction wells were placed at the same locations as for previous simulations. The reinjection wells were placed approximately adjacent to and between the Muskingum River and the model predicted 80 µg/L contour (Figure 13). The placement of injection wells is limited due to the extent of the predicted plume to the west and south and the bedrock valley wall to the north and east. The results of this modeling extraction and re-injection with some lithium sorption using a retardation factor of 2 and closure by removal indicated that lithium concentrations would require approximately 29 years of pump and treat to be below 80 µg/L. The simulated remedial time frame is similar the results from extraction and discharge. Modeling of extraction and reinjection of treated groundwater did not indicate an advantage over surface discharge in terms of predicted clean up times.
4.4.2.3 Source Control and Reduction of Contaminated Material Source control is included as part of this alternative, either through source removal or composite capping. Either option significantly reduces the migration of COCs into the groundwater. Natural attenuation processes reduce the mass of COCs in the groundwater through adsorption and concentrations would decrease through dilution and dispersion. Institutional controls to prevent groundwater use will be required for this alternative, and additional controls will be required to maintain the cap for the life of the alternative. Like Alternative #2, wastewater treatment will generate solids which contain relatively low concentrations of COCs removed from the groundwater. These solids will be transferred for disposal in an approved landfill. However, this alternative will generate additional waste streams associated with the higher level of treatment required for reinjection. The spent cation regenerant stream will have a total dissolved solids concentration of approximately 46,000 mg/L that is predominantly calcium chloride with some magnesium and potassium chlorides. Very limited concentrations of lead and several other metals will be present. However, a mass balance across the columns that assumes all of the trace cationic metals in the extracted groundwater are absorbed on the resin and subsequently eluted in the regenerant should demonstrate that their concentrations are well below toxicity characteristic concentrations and below levels that can present risks to human health. The spent anionic regenerant stream will be predominantly sodium sulfate with some limited amounts of sodium bicarbonate. That stream will also have some trace levels of anionic metals present, but a similar mass balance should demonstrate that their concentrations are well below toxicity characteristic concentrations and levels that can present risks to human health. If the regenerant streams are maintained separate, it is possible these wastes may be suitable as secondary materials. Alternately, these spent regenerant streams will need to be further concentrated and properly managed as special industrial wastes.
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
4.4.2.4 Long Term Effectiveness Reduction of COCs at the Plant is accomplished through mass removal by groundwater extraction, and a then reducing concentrations of COCs by absorption, dilution and dispersion. Groundwater extraction in conjunction with source control will be effective in reducing the toxicity, mobility, and volume of contaminants in groundwater over the long-term.
4.4.2.5 Short Term Effectiveness All services required (well installation, piping and electrical installation to the wastewater system, wastewater plant construction, wastewater plant operations, laboratory analysis, and environmental reporting) are anticipated to be available. However, some portion of the services, materials or equipment needed are likely not locally available and may have to be imported. Long term operation of the wastewater treatment system will likely need to be performed on a contract basis. There are not any safety or exposure considerations for workers involved in construction of the system or its operation other than implementation of standard health and safety procedures for construction activities and water treatment plant operation. This alternative does not present exposure risks to the community during construction or implementation.
4.4.2.6 Implementability The implementability of this alternative is considered moderate. Installation of extraction wells will not be difficult, but the units are located some distance from the plant infrastructure where it is anticipated that the treatment system will be constructed. Labor and equipment to install extraction wells, utility trenches and discharge piping are readily available, and installation could be completed within a short timeframe. Limited wastewater would be discharged to the river (primarily ion exchange rinsewater), and existing infrastructure is probably adequate to handle the flow without additional expansion. Labor and equipment to install extraction wells, utility trenches and discharge piping are readily available, and installation could be completed within a short timeframe. New discharge piping sized relative to the anticipated discharge flow will need to be installed to a new discharge and monitoring station along the river.
4.4.2.7 Long-Term Management Requirements Maintainability and reliability for this alternative is good, but routine observation of the system is required to ensure continuous operation. Telemetry and other automated controls can reduce the time required for onsite personnel. Mechanical extraction systems and physical/chemical wastewater treatment systems require routine and ongoing operations and maintenance (O&M) throughout the life of the corrective action. Long term operation of groundwater extraction wells means that it is likely that some portion of the wells or pumping systems may need replacement during the treatment period. Reinjection wells are prone to fouling and may require O&M more frequently than the extraction wells.
4.4.2.8 Community Acceptance Community concerns will be assessed during the public meeting.
4.4.2.9 State Acceptance Currently, there are no regulations identified for the state of Ohio that would prevent implementing this alternative. The state has not developed its own CCR program and has not indicated it plans to do so.
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Wood Environment & Infrastructure Solutions, Inc.
Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Coordination with the Ohio Department of Natural Resources during pond closure will be required since the APS are regulated by the ODNR Dam Safety Program, with Facility ID 0116-002. A stormwater construction NPDES permit will be required for implementation of any of the potential closure options. This alternative will also require an Underground Injection Control (UIC) Permit to construct for the installation of the injection wells and an UIC permit for their operation. Notice for well closure and replacement to OEPA would be necessary if well replacement is required. Prior to construction of the wastewater treatment system a new NPDES permit application will be needed and a permit to construct will need to be obtained. NPDES permitting to operate will also be required. Notice for well closure and replacement to OEPA would be necessary if well replacement is required. Source control activities will require the contractor to obtain a Construction Storm Water General Permit from the Ohio EPA. An Environmental Covenant may be required to provide institutional controls for risk management if source material is left in place (closure by capping).
4.4.2.10 Time to Meet Remedial Objective As indicated in Section 4.3.2.2, the time required to meet the groundwater protection standards was modeled at 29 years assuming closure by removal and some lithium sorption. In comparison to the extraction with surface discharge simulation, the simulated remedial time frame is similar and the simulation of injection of treated groundwater in addition to extraction does not indicate an advantage over surface discharge in terms of predicted clean up times.
5.0 Summary Three Corrective Measure Alternatives were assessed for the APS at the Conesville Plant in Section 4, above. These alternatives combined two options for source control (closure by removal or closure by capping) with three approaches to groundwater remediation. The three alternatives are: • Alternative #1: Source Control with Monitored Natural Attenuation • Alternative #2: Source Control with Plume Containment by Groundwater Extraction; Treatment and Surface Water Discharge of Extracted Groundwater • Alternative #3: Source Control with Plume Containment by Groundwater Extraction; Treatment and Reinjection of Extracted Groundwater The results of the detailed analysis in Section 4 can be summarized below.
Source Removal Modeling indicates that there are differences in the effect of groundwater quality between closure by removal and closure by capping, but that these are minimal and within the limits of uncertainty inherent in modeling. Given the effectiveness of composite capping alone, the ISS option was not considered further.
Alternative #1: Source Control with Monitored Natural Attenuation MNA would be protective of human health and the environment, and is easily implemented. However, modeling indicates that lithium concentrations at the site would remain above the GWPS for a time period of up to 66 to over 100 years depending on the amount of recharge seen during the period. These estimates could be updated with empirical data after source control is implemented.
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
Alternative #2: Source Control with Plume Containment by Groundwater Extraction; Treatment and Surface Water Discharge of Extracted Groundwater This alternative would require installation of extraction wells downgradient of the APS , operated for a period of not less than 28 to 35 years to achieve GWPSs throughout the plume . While the timeframe for effective remediation is potentially long, hydraulic capture and containment will be effective and is the only option available for highly soluble constituents such as lithium and molybdenum. Alternative #3: Source Control with Plume Containment by Groundwater Extraction; Treatment and Reinjection of Extracted Groundwater This alternative would require installation of extraction wells and injection wells downgradient of the APS, operated for a period of not less than 29 years in operation in order to achieve GWPSs at the unit. In comparison to the extraction with surface discharge simulation, the simulated remedial time frame is similar and the simulation of injection of treated groundwater in addition to extraction does not indicate an advantage over surface discharge in terms of predicted clean up times.
6.0 References AEP, October 2016. Closure Plan CFR 257.102(b), Ash Pond Complex, Conesville Plant. (AEP 2016a). AEP, January 2019. Annual Groundwater Monitoring Report, AEP Generation Resources, Inc., Conesville Plant, Ash Pond. (AEP 2019). Arcadis, 5 October 2016. Ash Pond System-CCR Groundwater Monitoring Well Network Evaluation, Conesville Plant. (Arcadis, 2016). Carroll, Dorothy, 1959. Ion exchange in clays and other minerals: Geological Society of America Bulletin, v. 70, no. 6, p. 749-779. Gast, R. G. and Klobe, W. D., 1971. Sodium-Lithium Exchange Equilibria on Vermiculite at 25oC and 50 oC. Clays & Clay Minerals 19, 311-319. Geosyntec, 8 January 2019. Statistical Analysis Summary, Ash Pond System, Conesville Plant. (Geosyntec 2019). Goldberg, S., Forster, H.S., Godfrey, C.L., 1996. Molybdenum Adsorption on Oxides, Clay Minerals, and Soils v. 60, no. 2, p.425-432. Hinkle, S.R., and Polette, D.J., 1999. Arsenic in Ground Water of the Willamette Basin, Oregon: U.S. Geological Survey Water-Resources Investigations Report 98-4205. Pantini, S., Lombardi, F., Verginelli, I., 2013. A New Screening Model for Leachate Production Assessment at Landfill Sites. International Journal of Environmental Science and Technology. Doi: 1 0.1007/s 13762-013-0344-7 Smith, K. S., 1999. Metal Sorption on Mineral Surfaces: An Overview with Examples Relating to Mineral Deposits. Reviews in Economic Geology, Vol. 6A, 1999, pp. 161- 182. Strenge, D.L., Peterson, S.R., 1989. Chemical Data Bases for the Multimedia Environmental Pollutant Assessment System (MEPAS): Version 1, prepared by (Pacific Northwest National Laboratory operated by Battelle).
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Assessment of Corrective Measures Report, Conesville Ash Pond American Electric Power Service Corporation
The U.S. Department of Energy, dated December 1989. Sun, W., and H. M. Selim. 2019. Transport and Retention of Molybdenum(VI) in Soils: Kinetic Modeling. Soil Sci. Soc. Am. J. 83:86-96. doi:10.2136/sssaj2018.05.0189
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Figures
Site Location Conesville, Ohio
^_
0 40 ^_ Site Location Miles Service Layer Credits: Copyright:© 2015 DeLorme ° SITE LOCATION MAP SCALE 1" = 40 miles
AEP - Conesville, OH DATE 3/13/2019 FIG. 2456 Fortune Drive, Suite 100 DRAWN BY TMR Lexington, Kentucky 40509 1 Phone: (859) 255-3308 PROJECT NUMBER: 7362192661 APPROVED BY KDR Legend AEP Property Boundary CCR Unit Boundary
FGD LANDFILL
ASH POND SYSTEM
Data Sources
Service Layer Credits: Copyright:© 2013 National Geographic Society, i-cubed
Source: USGS 7.5' Topographic Quadrangles for Conesville and Wills Creek
0 1,100 2,200 SCALE IN FEET °
SITE LAYOUT AEP - CONESVILLE, OH
PROJECT NUMBER: 7362192661
SCALE 1" = 2,200' DATE 3/13/2019 FIG. DRAWN BY TMR 2 APPROVED BY ALD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 DocumentPath: P:\GIS_Projects\AEP\Conesville\mxd\2019-03 APSCSM Report\Fig02_SiteLayout.mxd Legend A! APS CCR Monitoring Well A! FGD Landfill Monitoring Well A! Monitoring Well ? Abandoned Monitoring Well "6 Water Supply Well
A Line of Cross-Sections
MB-1 AEP Property Boundary ! MB-2 !A! A!AA MW-1510 CCR Unit Boundary MB-3 (s,i) MW-1905 MW-1904 A! (s,i,d) (s,i) A! MB-24 ?? MB-25 MB-21 MW-1805 MB-26 ? MB-22 MB-18 (s,i,d) A! MB-23 MB-19 ??? MB-20 MW-1509s MB-6 ? A! B'
BAP-0901 MW-1804 ! ! AA?! A ? B-6 MW-1506 (s,i,d) MB-4 P-0902R MB-5 A! ? B-4 A! (c,s) ? ? BAP-0902 ? B-5 B-5A MW-1502 MW-1803 B-3 ! (s,i,d) (s,i,d) MB-7 ? A A???! MB-8 MB-9 MW-1903 MB-27 "6 MW-1507 (s,i) ! ? MB-29 ! (c,s) A Truck MB-30 MW-1503 !H A MB-28 ?! MB-11A Service A (s,i,d) A! B-1806 Water MB-10A MW-1802 (s,i,d)A! B-2 MB-14 ASH POND ? A! MB-15 SYSTEM MW-1504 (i,d) A! MB-12 Data Sources ? MB-31 Service Layer Credits: Source: Esri, DigitalGlobe, MB-13 P11 GeoEye, Earthstar Geographics, CNES/Airbus DS, P12 ! USDA, USGS, AeroGRID, IGN, and the GIS User P13 A!? BAP-0903 Community MW-1801 A!A! BAP-0904 (s,i,d) A! P14 ! B-7 A A' A! MW-1508c B-1 MW-1505 ? (s,i,d) A! MW-5R FGD ?? MW-5 Service ? Water MW-11 0 400 800 "6 MW-7 PW-2 MW-4 ? SCALE IN FEET MW-12 "6? MW-4R ! A!!?? AMW-2 ° AMW-10 ! MW-13 AMW-6 ! MB-33 MW-3A ! MB-32 ? ?A MW-8 A! MB-34 B MW-9 APS LAYOUT ! ?MW-1 MW-1901A AEP - CONESVILLE, OH (s,i,d) "6 PW-3 PROJECT NUMBER: 7362192661
SCALE 1" = 800' DATE 6/20/2019 FIG. DRAWN BY DMW 3 MW-1902 APPROVED BY KDR (s,i,d) A!
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS_Projects\AEP\Conesville\mxd\2019-05 ACM\FIG03_APS_Layout_Xsections.mxd
Legend A! APS CCR Monitoring Well A! FGD Landfill Monitoring Well A! Monitoring Well ? Abandoned Monitoring Well "6 Water Supply Well Groundwater Elevation Contours Groundwater Elevation Contours MB-1 (Inferred) ! MB-2 !A! A!AA MW-1510 Groundwater Flow Direction MB-3 (s,i) ft 730.55 727 MW-1905 AEP Property Boundary L ~ MW-1904 ! (s,i,d) . W A st (s,i) A! CCR Unit Boundary - e er MB-24 iv ? R ? MB-25 MB-21 MW-1805 MB-26 m ? MB-22 MB-18 (s,i,d) A! u MB-19 g MB-23 ??? 730.53 in MB-20 k
s 742 MW-1509s u MB-6 ? 744 A! M 744.07 Water Level Elevation Notes: BAP-0901 MW-1804 ! ! Contour Interval = 2 feet AA?! 733.33 A ? B-6 MW-1506 (s,i,d) MB-4 P-0902R MB-5 A! ? B-4 A! (c,s) Water level elevations in parentheses not used in 730.56 ? ? BAP-0902 ? (797.66) contouring. B-5 B-5A MW-1502 MW-1803 B-3 MB-7 ? ! (s,i,d) All elevations relative to the North America Vertical (s,i,d) ! A Datum of 1988 (NAVD1988). A??? MB-8 734.78 730.13 MB-9 MW-1903 MW-1507 MB-27 "6 Muskingum River Elevation estimated using a (s,i) ! ? MB-29 ! (c,s) A Truck MB-30 MW-1503 A distance-weighted average of data from USGS gage MB-28 ?! MB-11A (847.19) Service A (s,i,d) A! #03140500 in Coshocton and USGS gage #03144500 Water MB-10A in Dresden. MW-1802 731.12 (s,i,d)A! B-2 729.90 MB-14 ASH POND ? A! MB-15 SYSTEM MW-1504 (i,d) A! Data Sources 730.97 MB-12 ? MB-31 Service Layer Credits: Source: Esri, DigitalGlobe,
MB-13 740 P11 GeoEye, Earthstar Geographics, CNES/Airbus DS, 738 P12 USDA, USGS, AeroGRID, IGN, and the GIS User 736 ! Community 734 P13 A!? BAP-0903 732 A MW-1801 A!A! BAP-0904 (s,i,d) A! P14 743.29 ! B-7 A 728.71 A! MW-1508c 730 (779.96) B-1 MW-1505 ? (s,i,d) A! 726 MW-5R 730.64 FGD ?? MW-5 Service ? 0 400 800 Water MW-11 "6 MW-7 ? SCALE IN FEET PW-2"6 MW-4 (729.74) MW-12 !? MW-4R ! ° A!?? AMW-2 AMW-10 ! MW-13 AMW-6 730.19 ! MB-33 MW-3A ! MB-32 ? ?A PIEZOMETRIC SURFACE (729.44) MW-8 730.22 A! MB-34 FEBRUARY 2019 MW-1 MW-9 MW-1901A! ? AEP - CONESVILLE, OH 728 729.21 (s,i,d) "6 PW-3 725.77 PROJECT NUMBER: 7362192661
SCALE 1" = 800' DATE 6/20/2019 FIG. DRAWN BY DMW 6 APPROVED BY KDR MW-1902 (s,i,d) A! 725.61
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS_Projects\AEP\Conesville\mxd\2019-05 ACM\FIG- 06 GWE_wFlow.mxd Legend A@ Well Location
29 Shallow Average Measured Arsenic Concentration (µg/L)
11 Intermediate Average Measured Arsenic Concentration (µg/L) Deep Average Measured Arsenic 23 Concentration (µg/L) Muskingum River 5.54 A@ 6.39 3.92
1.71 1.28 A@ 10.6 A@ 7.17
0.86 66.1 A@ 69.1 A@ 2.45 46.9 9.80 139 A@ 110 1.79 9.71 A@ 5.68 6.32
A@ 68.1 27.4
0.54 A@ 6.55 Data Sources 7.22 Service Layer Credits: Source: Esri, DigitalGlobe, 29.2 GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User A@ 23.6 Community 22.7 Source: USDA FSA NAIP Date of Photography: 8/1/2015
0 500 1,000 1.11 A@ 4.28 SCALE IN FEET ° 6.87
AVERAGE MEASURED DOWNGRADIENT ALLUVIAL ARSENIC CONCENTRATIONS AEP - CONESVILLE, OH PROJECT NUMBER: 7362192661 3.55 A@ 4.76 SCALE 1" = 2,000' 1.24 DATE 6/20/2019 FIG. DRAWN BY KWQ 7 APPROVED BY TBD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-10_CV_APS_As.mxd Legend A@ Monitoring Well Location Shallow Average Measured Lithium 29 Concentration (µg/L) Intermediate Average Measured 11 Lithium Concentration (µg/L) Deep Average Measured Lithium 23 Concentration (µg/L) Muskingum River 164 A@ 166 89.0
300 2.56 A@ 173 A@ 47.0 255 105 A@ 126 A@ 232 141 14.0 117 A@ 112 432 98.5 A@ 492 78.5 A@164 120
139 A@ Data Sources 161 20.0 Service Layer Credits: Source: Esri, DigitalGlobe, 151 GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User A@ 133 Community
147 Source: USDA FSA NAIP Date of Photography: 8/1/2015
0 500 1,000 102 A@ 100 SCALE IN FEET ° 119 AVERAGE MEASURED DOWNGRADIENT ALLUVIAL LITHIUM CONCENTRATIONS AEP - CONESVILLE, OH PROJECT NUMBER: 7362192661 31.0 @ A 104 SCALE 1" = 2,000' 143 DATE 6/20/2019 FIG. DRAWN BY KWQ 8 APPROVED BY TBD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-8_CV_APS_Avg_Li.mxd Legend A@ Monitoring Well Location Shallow Average Measured 29 Molybdenum Concentration (µg/L) Intermediate Average Measured 11 Molybdenum Concentration (µg/L) Deep Average Measured 23 Molybdenum Concentration (µg/L) Muskingum River 710 A@ 581 37.9
618 A@ 176 A@ 0.79 2.24 369 453 A@ 571 A@ 208 594 4.08 333 A@ 354 2.39 200 A@ 15.5 1.28
A@ 37.3 191
0.50 A@ 2.18 Data Sources 5.40 Service Layer Credits: Source: Esri, DigitalGlobe, 54.8 GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User A@ 86.4 Community 88.6 Source: USDA FSA NAIP Date of Photography: 8/1/2015
0 500 1,000 15.3 A@ 118 SCALE IN FEET ° 11.1 AVERAGE MEASURED DOWNGRADIENT ALLUVIAL MOLYBDENUM CONCENTRATIONS AEP - CONESVILLE, OH 3.63 PROJECT NUMBER: 7362192661
A@ 7.51 SCALE 1" = 2,000' 34.7 DATE 6/20/2019 FIG. DRAWN BY KWQ 9 APPROVED BY TBD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-9_CV_APS_Avg_Mo.mxd Legend !A?@ AEP Production Well Groundwater Contour (ft) MuskingumRiver Particle Arrow/Time (years)
716.75
Particle Path 716.5
715.75
715.75 Truck
716.5 Service 10 715.5 A?@ 10 716 Well !
20 10 10 20 10 10 20 10 10 10 20 20 10 30 10 10 20 20 20 10 10 30 20 10 20 20 10 30 30 10 20 20 30 20 10 30 20 20 30 10 40 30 10 Data Sources 30 20 40 20 10 20 10 40 10 10 Service Layer Credits: Source: Esri, DigitalGlobe, 40 30 40 30 30 10 GeoEye, Earthstar Geographics, CNES/Airbus DS,
20 716 3030 USDA, USGS, AeroGRID, IGN, and the GIS User
40 30 20 Community FGD 20 30 40 30 30 40 30 20 20 Source: USDA FSA NAIP Date of Photography: Service 50 20 20 8/1/2015 40 20 30 Well 40 30 716.25 30 A?@ 50 ! 40 40 50 30 30 30 30 40 40 40 40 50A?@ 30 ! 40 40 30 0 500 1,000 PW-2 30
30 50 PW-3 SCALE IN FEET ° 50 !A?@ 40 40 GROUNDWATER MODEL 40 40 GROUNDWATER CONTOURS 60 70 AND PARTICLE TRACKS
80 AFTER CLOSURE AEP - CONESVILLE, OH 716.75 PROJECT NUMBER: 7362192661
SCALE 1" = 2,000' DATE 6/17/2019 FIG. DRAWN BY KWQ 10 APPROVED BY TBD
716.25 2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-18_CV_APS_Model_AC_Ctrs.mxd Legend &, Extraction Well &. Injection Well A@ Monitoring Well ! MW-1510 Water Level Only Well A@ (s,i) !A?@ AEP Production Well AEP Property Boundary &. CCR Unit Boundary MW-1805 Groundwater Flow Direction &. A@ (s,i,d) MW-1509s A@ &. MW-1804 BAP-0901 MB-4 (s,i,d) A@A@ A@ MW-1506 A@A@ (s,c) &. MW-1502 MW-1803 (s,i,d) (s,i,d) A@ Truck A@ Service MW-1507c A?@ &. Well ! MW-1503 A@ (s,i,d) A@ MW-1802 &, &. (s,i,d) A@ &, MW-1504 &, A@ (i,d) &, BAP-0903
MW-1801 &, A@! BAP-0904 (s,i,d) P11 !A@ MW-1508c Data Sources A@ P12 A@ &, P13 &, Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, MW-1505 USDA, USGS, AeroGRID, IGN, and the GIS User (s,i,d) A@ Community &, &. Source: USDA FSA NAIP Date of Photography: 8/1/2015 FGD MW-12 Service !A?@ Well A@ MW-13 !A?@ MB-32 ! A@ PW-2 MW-3 MW-9 0 500 1,000 &. A@ MB-33 MW-1901A@ PW-3 SCALE IN FEET (s,i,d) ° !A?@
GROUNDWATER EXTRACTION AND INJECTION WELL LAYOUT AEP - CONESVILLE, OH
PROJECT NUMBER: 7362192661 MW-1902 A@ (s,i,d) SCALE 1" = 2,000' DATE 6/20/2019 FIG. DRAWN BY KWQ 11 APPROVED BY TBD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-26_GW_Ext_Inj_Wells.mxd 716.5 Legend &, Extraction Well
715
718 Groundwater Contour (ft) 717.5
714 MuskingumRiver 716.5
712.5 Groundwater Flow Direction
713.5 715.5 716
717.5
717
715.5
714
714.5
714.5
713
&,
&, 716 &,
&,711
&,
713 718.5 Data Sources &, &, Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community &, Source: USDA FSA NAIP Date of Photography: 718 8/1/2015 711.5
713.5
0 500 1,000
715 SCALE IN FEET °
712 CLOSURE IN PLACE EXTRACTION AT 1,200 GPM GROUNDWATER CONTOURS AEP - CONESVILLE, OH 717 PROJECT NUMBER: 7362192661
SCALE 1" = 2,000' DATE 6/20/2019 FIG. DRAWN BY KWQ 12 APPROVED BY TBD
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 719 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-28_CV_APS_CIPE_Ctrs.mxd 718.5 Legend &, Extraction Well
716.5 &. Injection Well
719 Groundwater Contour (ft) 717
716.5 715.5 MuskingumRiver
716 718.5 Groundwater Flow Direction
715 &. &.
&. 714 718 715 714.5 715 &. 717.5 715.5
&. 715
713&, &. &, 713.5 717 &, &, 713
713 &, Data Sources &, &, Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community &, &. 713 Source: USDA FSA NAIP Date of Photography: 719 8/1/2015
0 500 1,000
&. 716 SCALE IN FEET °
CLOSURE BY REMOVAL EXTRACTION AND INJECTION GROUNDWATER CONTOURS AEP - CONESVILLE, OH 718 PROJECT NUMBER: 7362192661
SCALE 1" = 2,000' DATE 6/20/2019 FIG. DRAWN BY KWQ 13 APPROVED BY TBD
717.5
2456 Fortune Drive, Suite 100 Lexington, Kentucky 40509 Phone: (859) 255-3308 Document Path: Document P:\GIS\AEP CSMs\Conesville\Predictive Modeling\Fig-31_CV_APS_CBREI.mxd
Drawings
METERING PUMPS (3)
HCL PAM Ca(OH)2 PAM FeSO FEED CATIONIC FEED METERING PUMPS INCLINED PLATE SETTLER Ca(OH)₂ Ca(OH)₂ ANIONIC FEED H2O 4 SLURRY Na2SO3 HCL FEED TANK POLYMER TANK 1 PER COLUMN (9) x 3 TRAINS 4 PER TRAIN SLURRY FEED POLYMER < 30°C FEED METERING PUMPS (3) FEED METERING PUMPS (6) - 2 PER TRAIN TANK TANK FEED FLOCCULATION TANKS FEED TANK BACKWASH METERING PUMPS (3) TANKS (3) TANK (3) TANKS (3) STORAGE TANKS
BACKWASH IN 4 PER TRAIN
METERING PUMP METERING PUMPS (3) METERING PUMPS (3) METERING PUMPS (3) BACKWASH OUT TO METERING PUMPS (8) HOLDING TANK BACKWASH OUT BACKWASH IN
COAGULANT FEED TANK MIXER FLOCCULATION 10% FERRIC SULFATE SOLUTION TANKS (3) MIXERS (3) FLOCCULANT SPLIT INFLUENT TO 3 TRAINS TANKS (3)
RAPID MIX MULTI MULTI FeO TANKS (3) MEDIA MEDIA COLUMN 10' FILTERS FILTERS - INLINE MIXER Se (12) 4 PER ADSORPTION 4" HDPE HEADER AT EACH TRAIN WELL. TWO WELL HEADERS COMBINED INTO 6" COMMON HEADERS (4) FOR FLOW TO TREATMENT SULFUR IMPREGNATED FeO ADSORPTION COLUMNS PLANT ~3,000 FT. INFLUENT FROM PRIMARY Se6+ REDUCTION 3 COLUMNS PER TRAIN REACTION Se6+ TANKS (3) REDUCTION MULTI D.O. 9 PROGRESSIVE CAVITY PUMPS 9 X PROGRESSIVE CAVITY PUMPS REACTIVE PROGRESSIVE MEDIA REMOVAL PROCESS PUMP (3) (3 PER FLOCCULATION TANK) 3 PER FEED TANK CAVITY PUMPS FILTERS TANK (3) PER TRAIN 4 PER TRAIN N2 MULTIMEDIA FILTERS PURGE FeO COLUMN INLINE MIXER Se ADSORPTION
+ 2- Cu² AND SO4 REMOVAL CENTRIFUGAL PUMP pH ≈ 9.0-9.5 WITH Be(OH)2 SELENATE REDUCTION 3 PER TRAIN REACTIONS (3) D.O. REMOVAL GROUNDWATER EXTRACTION WELL - 8 WELLS Se0ISe4+ FLOCCULATION N2 PURGE TANKS (9) SETTLING TANKS - 3 PER TRAIN FINAL FILTRATION FEED DISCHARGE VESSEL N2 WATER IN DEAERATOR 6 PER TRAIN GAS TANK
Na SO 2 3 METERING PUMP PERISTALTIC FeO PUMPS (3) COLUMN INLINE MIXER Se ADSORPTION POLISHING FILTRATION
CLIENT: TITLE: DRAWN BY: RAB REVISIONS LEGEND DRAWING 4-1: POND WATER CHECKED BY: MJP AMERICAN ELECTRIC POWER NO. DESCRIPTION BY DATE REVIEWED BY: WPT FLOW LINE PROCESS FLOW DIAGRAM SCALE: NOT TO SCALE PROJECT: Environment & Infrastructure AEP CONESVILLE, DATE: 6-20-2019 Solutions PROJECT NO. 7362192661
2030 FALLING WATERS ROAD, SUITE 300 GENERATING PLANT - ASH POND SYSTEM, REVISION NO. 1 KNOXVILLE, TN. 37922 CONESVILLE, OHIO TEL: (865) 671-6774 SHEET 1 OF 1 N
770 N 192000
760
2.5' SOIL A COMPOSITE N 191500 4' GEONET
760 1.5' CLAY BARRIER 6" SOIL 760 COVER
770 CCR MATERIAL
N 191000 OEPA SOLID WASTE COVER WITH SOIL BARRIER LAYER 780 PERIMETER WALL CONSTRUCTED AROUND ASH POND USING IN SITU STABILIZATION
750
N 190500
750
2.5' 2.5' SOIL COMPOSITE 750 760 GEONET A'
750 N 190000 CCR MATERIAL GEOMEMBRANE AND GCL 760 OEPA SOLID WASTE COVER 730 WITH GCL
BOTTOM OF CLEARWATER POND ELEVATION 737' 740
N 189500 750 760 E 2146500 E 2145500 E 2146000 E 2144500 E 2145000 E 2144000 E 2143500 E 2143000
2 FT CONTOUR INTERVALS SHOWN
CLIENT: TITLE: DRAWN BY: CTH REVISIONS NOTES: CHECKED BY: DRS 1. CONTOURS SHOWN ARE RE-GRADED TOP OF ASH. CLIENT/CLIENT LOGO POND CLOSURE EXHIBIT REVIEWED BY: DRS 2. FOR FINAL COVER ELEVATIONS ADD THICKNESSES NO. DESCRIPTION BY DATE SHOWN IN DETAILS. SCALE: 1" = 200' PROJECT: Environment & Infrastructure CONESVILLE POND COMPLEX, DATE: 06/14/2019 Solutions PROJECT NO. 7362192661
2030 FALLING WATERS ROAD, SUITE 300 ASH POND CLOSURE REVISION NO. A KNOXVILLE, TN. 37922 CONESVILLE, OHIO TEL: (865) 671-6774 SHEET 1 OF 1 A A' NORTHWEST SOUTHEAST
MW-1508C
860 860
ALLEGHENY FORMATION (SHALE, SANDSTONE)
PERIMETER OF POND WITH STABILIZED ASH WALL 2' TO 3' THICK AROUND POND PERIMETER NO. 6 COAL 820 820
REMOVE STANDING WATER CLAY/SILT AND DEWATER ASH
REMNANT FORMER DIKE POZ-O-TEC LANDFILL CV-PZ-BAP-0904* CO. RD. 273 MB-12 780 780 CV-PZ-BAP-0903* ANTICIPATED GROUNDWATER ELEVATION POST CLOSURE MW-1504D MB-13 RAILROAD TRACK FILL B-3 MW-1504I MB-31
MB-4 ALLEGHENY CLARION MW-1804D MEMBER (SANDSTONE) MW-1804I MW-1905I SAND MW-1804S FILL MW-1905S MW-1905D AGRICULTURAL FLY AND FIELD BOTTOM ASH 740 740 MUSKINGUM RIVER CLAY/SILT
ALLEGHENY PUTNAM HILL LIMESTONE
SILT
700 700
SAND/GRAVEL DEEP SOIL MIXING (705-720 APPROXIMATELY) ACROSS BOTTOM OF POND TO SEAL
660 660
POTTSVILLE FORMATION (SHALE) ELEVATION (FEET ABOVE MEAN SEA LEVEL) ELEVATION (FEET ABOVE MEAN SEA LEVEL)
620 620
CLAY
580 580 12+00 18+00 24+00 72+00 54+00 60+00 66+00 30+00 36+00 0+00 6+00 42+00 48+00
LEGEND CLIENT: TITLE: DRAWN BY: RAB NOTES: REVISIONS 1. POTENTIOMETRIC SURFACE MEASURE MONITORING WELL DRAWING 4-3: CAPPING AND CHECKED BY: MJP APRIL 28, 2016. FORMER POZ-O-TEC LANDFILL CLAY/SILT CLIENT \ CLIENT LOGO IDENTIFICATION REVIEWED BY: WPT CV-PZ-BAP-0904 NO. DESCRIPTION BY DATE 2. MB-31 CONSTRUCTION BASED ON AEP FLY AND BOTTOM ASH SAND (GRAY IF STABILIZATION PROFILE VIEW SCALE: AS SHOWN PROVIDED 1983 CROSS-SECTION. LOST/ABANDONED) FILL BEDROCK PROJECT: 3. POND ELEVATION BASED ON BBCM, 2010, Environment & Infrastructure DATE: 6-14-2019 TABLE 7. AEP CONESVILLE GENERATING PLANT SAND/GRAVEL WELL Solutions PROJECT NO. 7362192661 PREDICTED WELL SCREEN CLAY GROUNDWATER LEVEL 2030 FALLING WATERS ROAD, SUITE 300 ASH POND SYSTEM REVISION NO. 0 AFTER POND CLOSURE BOTTOM OF BORING KNOXVILLE, TN. 37922 CONESVILLE, OHIO TEL: (865) 671-6774 SHEET 1 OF 1 TO BACKWASH STORAGE TANKS PROCESS THROUGH DPS AND FILTER PROCESS
TO SPENT REGENERANT STORAGE CaSO4 SOLUTION
SLOW RINSE TANK
MMF BACKWASH IN FROM POTABLE SUPPLY METERING PUMPS (3) Ca(OH)₂ SLURRY ANION FEED TANK EXCHANGE VESSEL 1 x COLUMN SLOW RINSE REGENERANT BACKWASH OUT TO IN METERING HOLDING TANK PUMPS (3) REVERSE OSMOSIS ANION BED HOLDING TANK RINSES OUT
4" HDPE HEADER AT EACH FLOCCULATION CATION BED WELL. TWO WELL HEADERS COAGULANT FEED TANK ANION BED MIXER TANKS (3) REGENERANT COMBINED INTO 6" 10% FERRIC SULFATE SOLUTION OUT REGENERANT COMMON HEADERS (4) FOR OUT FLOW TO TREATMENT SYSTEM. SPLIT INFLUENT TO 3 TRAINS AERATION RAPID MIX MULTI CATION TANK FOR TANKS (3) EQUALIZED MEDIA EXCHANGE REVERSE OSMOSIS MULTI REVERSE OSMOSIS UNIT IRON 10' FILTERS TANK STAGE FEED PUMP 3 STAGE UNIT REMOVAL POLISHING VESSEL (12) FILTERS - 4 ANION BRACKISH WATER MEMBRANE PER TRAIN EXCHANGE VESSEL
PERMEATE TO REGENERANT REINJECTION WELLS IN
4 PER TRAIN REGENERATING TOTAL OF 9 PROGRESSIVE MULTIMEDIA FILTERS BLOWERS (3) ANSI PROCESS PUMP (3) CAVITY PUMPS (3 PER RECESSED OPEN IMPELLER FLOCCULATION TANK)
GROUNDWATER EXTRACTION WELL - 8 WELLS
ANION EXCHANGE VESSEL REVERSE OSMOSIS HOLDING TANK REGENERANT IN PERMEATE RECYCLE FOR REGENERATE AND RINSE CENTRIFUGAL PROCESS PUMP
CATION EXCHANGE VESSEL REVERSE OSMOSIS MULTI ION STAGE FEED PUMP REVERSE OSMOSIS UNIT EXCHANGE 3 STAGE UNIT BED FAST BRACKISH WATER MEMBRANE RINSE WATER RO REJECT STREAM TANK TO STORAGE TANKS 1 x COLUMN ANION BED FAST RINSE FEED REGENERANT ANION OUT EXCHANGE VESSEL
REGENERANT IN
CATION BED RINSES OUT
ION EXCHANGE ION EXCHANGE BED BED RINSE STREAMS TO NPDES DISCHARGE REGENERANT ~296,640 GPD FEED TANK ION EXCHANGE BED REGENERANT FEED
CLIENT: TITLE: DRAWN BY: RAB REVISIONS LEGEND DRAWING 4-4: GROUNDWATER CHECKED BY: MJP AMERICAN ELECTRIC POWER NO. DESCRIPTION BY DATE REVIEWED BY: WPT FLOW LINE PROCESS FLOW DIAGRAM SCALE: NOT TO SCALE PROJECT: BALL VALVE Environment & Infrastructure AEP CONESVILLE, DATE: 6-20-2019 Solutions PROJECT NO. 7362192661
CHECK VALVE 2030 FALLING WATERS ROAD, SUITE 300 GENERATING PLANT - ASH POND SYSTEM, REVISION NO. 1 KNOXVILLE, TN. 37922 CONESVILLE, OHIO TEL: (865) 671-6774 SHEET 1 OF 1
Tables
Table 1 Screening and Evaluation of Remedial Technologies Ash Pond System Conesville Power Plant, Conesville, Ohio
Relative Time Required to Institutional Requirements Relative Performance/ Reliability/ Begin and Complete that May Affect General Remedial Action Technology Ease of Implementation Remedy Implementation Response Action Type Process Options Description (Low-Medium-High) (Short-Medium-Long) (Few-Some-Many) Result of Screening Excavation and Removal Disposal in permitted Material is excavated from the High/High/Very Low Short/Medium to Long Some Removal is evaluated as potential landfill. APS and transported to a permitted source control option. Removal of hydraulic head present Effective as soon as removal is Onsite disposal capacity may be landfill during operating conditions is completed. Removal duration limited. Requires stormwater extremely effective in stopping affected by pore dewatering NPDES for construction activity. transfer of COCs. Option employs and removal of incident Requires revised NPDES permit standard construction techniques. precipitation. Requires decanting as much as 28
million gallons of standing water. Requires removal of 400 million gallons pore water via multiple techniques that will change over duration. Will require wastewater treatment system that may need to be modular to address changing conditions Composite Cap Soil or composite cap Further transfer of COCs from CCR High/High/High Short/ Medium Some Capping are evaluated as over decanted CCR materials is eliminated through potential source control options. Effective as soon as cap is Requires stormwater NPDES for Source Control materials. removal or greatly reduced through Removal of hydraulic head present A composite cap is currently completed. Removal duration construction activity. Requires isolation of the material from during operating conditions is specified as the APS closure affected by pore dewatering revised NPDES permit. May infiltration. Soil cap permitted under extremely effective in limiting option under 40 CFR 257.102(b). and removal of incident require coordination with OEPA CCR Rule does not reduce infiltration transfer of COCs. Composite precipitation if state begins regulation of long term relative to natural recharge. capping specified in APS closure closed ash ponds (CCR landfills plan is equally effective as removal. are already regulated by OEPA). Standard construction techniques. Requires decanting of standing water and incident precipitation and pore dewatering of upper 10-15 ft. Wastewater treatment system that may need to be modular to address changing conditions Composite capping provides very similar reduction in residual source as removal
Wood Project No. 7362192661 Page 1 of 4
Table 1 Screening and Evaluation of Remedial Technologies Ash Pond System Conesville Power Plant, Conesville, Ohio
Relative Time Required to Institutional Requirements Relative Performance/ Reliability/ Begin and Complete that May Affect General Remedial Action Technology Ease of Implementation Remedy Implementation Response Action Type Process Options Description (Low-Medium-High) (Short-Medium-Long) (Few-Some-Many) Result of Screening Composite Cap with In-Situ Soil ISS of the soils beneath Encapsulation theoretically provides High/High/Medium Short/ Medium Some Does not provide additional Stabilization (ISS) the ash, and construction further isolation of waste left onsite benefits over composite capping Effective as soon as cap is Requires stormwater NPDES for of a soil bentonite slurry compared to composite capping alone. Removal of hydraulic head present alone. Not retained for completed. Removal duration construction activity. Requires wall around the during operating conditions is additional screening. affected by pore dewatering revised NPDES permit. May perimeter of the ponds extremely effective in limiting and removal of incident require coordination with OEPA to effectively encapsulate transfer of COCs. Composite precipitation. if state begins regulation of the waste. capping specified in APS closure closed ash ponds (CCR landfills plan is equally effective as removal. are already regulated by OEPA). Standard construction techniques.
Requires decanting of standing Source Control water and incident precipitation and pore dewatering of upper 10-15 ft. Wastewater treatment system that may need to be modular to address changing conditions. Composite capping and ISS combined with composite capping provide similar reduction in infiltration and contact of groundwater.
Attenuation Groundwater Monitoring Periodic monitoring of groundwater at (Low-Med)/Medium/High Short/ Very Long Few Retained as a baseline for the waste boundary and in the plume. comparison in conjunction with Easy to implement. Time to Both effectiveness and reliability source control process options. complete depends upon rate (permanence) dependent upon site- of groundwater flow and Monitored Natural specific geochemical interactions available recharge to replace Attenuation between COCs and aquifer solids impacted groundwater. (MNA) Modeling indicates a very long time frame to reach GWPS
Groundwater Extraction Extraction Wells Extraction wells near the CCR unit High/High/(Med-High) Short/Long Few Retained. Can meet CAOs boundary are used to capture eventually, but may require many Groundwater flow system is highly Capture is effective soon after impacted groundwater and transfer it years. Estimates for time to permeable. Pumping is effective, system is installed and started to the surface. complete can be adjusted with but high flow rates are needed. up. Ongoing groundwater empirical data after remedy in Containment Mechanical system needs basic modeling allows confidence in place. Will require O&M for O&M monitoring. Addition of new design. duration. wells or revision of extraction well
field commonly required where duration is extended
Wood Project No. 7362192661 Page 2 of 4
Table 1 Screening and Evaluation of Remedial Technologies Ash Pond System Conesville Power Plant, Conesville, Ohio
Relative Time Required to Institutional Requirements Relative Performance/ Reliability/ Begin and Complete that May Affect General Remedial Action Technology Ease of Implementation Remedy Implementation Response Action Type Process Options Description (Low-Medium-High) (Short-Medium-Long) (Few-Some-Many) Result of Screening Permeable Reactive Barrier (PRB) Injectable Reagents Reagents are placed within plume to Low/Medium/Low Long/Medium Some Not retained. Technically bind COCs and prevent of further impracticable in the Conesville Depth to bedrock as much as 150 ft. Effective as soon as Requires stormwater NPDES for downgradient migration. setting. makes trench installation technically construction is completed, but construction activity. Requires infeasible. Lack of commercially construction would be time- revised NPDES permit. Requires available on effective reagents for consuming. Effective UIC permit for injection of lithium removal. Great depth immediately downgradient of reagent. decreases the likelihood of uniform barrier, but upgradient of placement by injection , so bypass barrier, cleanup relies on or inconsistent treatment may MNA. If placed upgradient of occur. Estimated loading may leading edge of plume a exceed typical design so multiple portion of groundwater not walls required over time PRB is treated. passive and will not treat
groundwater located downgradient of location Water Treatment after Onsite Treatment Used in combination with hydraulic High/High/High Short /Long Some Retained. In conjunction with Groundwater Extraction Followed by Direct containment. Extracted groundwater hydraulic containment, can meet Treatment technologies have been Additional evaluation will be Treatment systems for direct (Physical-Chemical Processes) Discharge to Surface treated to reduce TDS and metals CAOs eventually, but may require demonstrated for wastewater required during design to discharge require a National Water concentrations using conventional many years. Will require O&M systems and removal is reliable. ensure effective processes are Pollution Discharge Elimination coagulation and direct filtration for duration. Treatment system will require O&M selected. This technology is System (NPDES) permit, which techniques. for many years. an adjunct to containment has routine and ongoing and the time to complete reporting requirements. remedy depends entirely on extraction of groundwater. Ex-Situ Treatment Water Treatment after Onsite Treatment Used in combination with hydraulic High/High/Medium Short/Long Some Retained. In conjunction with Groundwater Extraction Followed by Reinjection containment. Extracted groundwater hydraulic containment, can meet Treatment technologies have been Additional evaluation will be Treatment systems for reinjection (Physical-Chemical Processes) Upgradient of Extraction treated to reduce TDS and metals CAOs eventually, but may require demonstrated for wastewater required during design to require an underground injection Wells. concentrations using conventional many years. Will require O&M systems, Treatment system will ensure effective processes are control permit, and a NPDES coagulation, reverse osmosis , ion for duration. require O&M for many years. selected. This technology is permit with routine and ongoing exchange, and direct filtration an adjunct to containment but reporting requirements. techniques. Reinjection will require a will decrease the time to higher level of treatment than direct complete remedy by discharge (assume discharge increasing the groundwater concentrations must be significantly gradient through the plume. below GWPS).
Wood Project No. 7362192661 Page 3 of 4
Table 1 Screening and Evaluation of Remedial Technologies Ash Pond System Conesville Power Plant, Conesville, Ohio
Relative Time Required to Institutional Requirements Relative Performance/ Reliability/ Begin and Complete that May Affect General Remedial Action Technology Ease of Implementation Remedy Implementation Response Action Type Process Options Description (Low-Medium-High) (Short-Medium-Long) (Few-Some-Many) Result of Screening Water Treatment through Precipitation – or Co- Treatment chemicals injected into the Low/Low/Low Long/Medium Low Not retained, since site physical Reagent Injection Into Flow Precipitation and groundwater flow zone within the setting of the makes In-situ methods are demonstrated Assuming injections could be In-Situ injections require an Zone (Physical-Chemical Adsorption plume. COCs are transformed into implementation technically for arsenic and molybdenum but completed to bedrock (150 ft underground injection control Processes) insoluble compounds that are trapped infeasible. In addition, unproven have not been proven for lithium. below ground surface), many permit. within the solid matrix in the flow zone. technology for lithium removal. Reliability (permanence) is unknown points would be needed and Highly soluble COCs such as lithium, for lithium. Lack of commercially process would be very time are adsorbed on the reactive media available on effective reagents for consuming. Time to complete lithium removal. Lithium removal is the remedy is not proven for In-Situ Treatment by adsorption necessitating lithium, but estimated to be intimate contacting with reagent relatively medium, depending making loading requirements very on the effectiveness of high. Groundwater impacts are injectates on lithium removal. present in deep flow system, which will make injection difficult. Additional injections may be required depending upon system performance.
Wood Project No. 7362192661 Page 4 of 4
Table 2 Risk-Based Technical Options Matrix Ash Pond System Conesville Power Plant, Conesville, Ohio
Option Description Risks Key Assumptions Benefits
Alternative #1 Source control with either removal or composite cap. This alternative will take the longest time to reduce Estimates of time to complete the remedy are Given almost all of the impacted groundwater is Source Control with Monitored Natural COCs below the applicable GWPSs. highly dependent upon the retardation factor assumed to discharge slowly into the Muskingum Concentrations of COCs in groundwater will reduce due Attenuation of lithium. There is variability among reported River, this alternative is highly protective of to adsorbtion onto aquifer materials, dilution with COCs are above the GWPSs at the property boundary values from various sources and variability groundwater quality for offsite receptors, except upgradient recharge and dispersion through the and modeling indicates they are present on offsite within experimental data Empirical data for property to the northwest of the Plant. groundwater flow system. property to the northwest of the Plant. Groundwater following implementation needed to use must be restricted until COCs meet GWPSs (true for evaluate. all alternatives).
Alternative #2 Source control with either removal or composite cap. The presence of CCR in the subsurface outside the cap Modeling indicates that hydraulic control Plume containment by groundwater extraction Source Control with Plume Containment by or removal area may increase time to complete. significantly reduces the time to complete the significantly reduces time to complete the remedy Migration of COCs in groundwater will be stopped by Groundwater Extraction; Treatment and remedy, but model operates only in steady compared to natural attenuation. hydraulic control through groundwater extraction. Discharge criteria for lithium has not been established in Surface Water Discharge of Extracted state conditions. Transient conditions may Extracted groundwater will be treated at the surface and Ohio and could be lower than calculated Groundwater decrease or increase cleanup time. discharged into the Muskingum River under an NPDES Likely quicker to complete but may be no more discharge permit. protective to offsite receptors than natural attenuation.
Alternative #3 Source control with either removal or composite cap. The presence of CCR in the subsurface outside the cap Modeling indicates that reinjection Extraction with reinjection significantly reduces Source Control with Plume Containment by or removal area may increase time to complete. significantly reduces the time to complete the time to complete the remedy compared to Migration of COCs in groundwater will be stopped by Groundwater Extraction; Treatment and remedy compared to extraction only. extraction and direct discharge. hydraulic control through groundwater extraction. Reinjection requires a higher level of treatment than Reinjection of Extracted Groundwater Extracted groundwater will be treated at the surface and direct discharge. Performance of reinjection may degrade over reinjected upgradient of the extraction network. time compared to initial modeling predictions. Likely quicker to complete but may be no more Reinjection will decrease the time to complete the protective to offsite receptors than natural attenuation. Transient conditions may decrease or increase remedy by increasing amount of capture possible. cleanup time.
Wood Project No. 7362192661 Page 1 of 1