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HomeMy WebLinkAbout2016-05-13 GHI Mayo Report Addendum FinalGEO-HYDRO, INC Consulting in Geology and Hydrogeology 1928 E. 14th Avenue Denver, Colorado 80206 (303)322-3171 EXPERT REPORT OF MARK A. HUTSON, PG Mayo Steam Electric Plant Roxboro, NC Addendum No. 1 Prepared for: Southern Environmental Law Center 601 West Rosemary Street Suite 220 Chapel Hill, NC 27516-2356 May 2016 GEO-HYDRO, INC 1. Summary of Opinions Formed Based upon my review of the available information I have formed the following opinions on closure of the coal ash basin at the Mayo Steam Electric Plant (Mayo). Coal ash stored in the Mayo ash basin is the source of contamination detected in surface water and groundwater resources. 2. Capping the waste within the footprint of the Mayo ash basin will not be protective of groundwater and surface water quality downgradient of the basin. 3. Monitored Natural Attenuation (MNA) is not a viable remedial option for impacted groundwater and surface water downgradient of the Mayo ash basin. 4. Capping coal ash located within the Mayo ash basin will not be protective of surface water quality in Crutchfield Branch. Removal of the coal ash will reduce the concentration and extent of groundwater and surface water contaminants. 6. The coal combustion residual impoundment risk classification proposed by North Carolina Department of Environmental Quality (NCDEQ) improperly minimizes protection of environmental quality. 7. The Groundwater Flow and Transport Model Does Not Reflect Real -World Conditions. The background and rationale behind each of these opinions are described in this report. GEO-HYDRO, INC 2. Introduction On February 26, 2016 I completed and submitted my original expert report on the Mayo Steam Electric plant (Mayo). Subsequent to submittal of my report the Corrective Action Plan (CAP) Part 2 was released for public review and comment. On behalf of the Southern Environmental Law Center, the documents that I have now reviewed includes; the Groundwater Assessment Plan (SynTerra, 2015a), Comprehensive Site Assessment (SynTerra, 2015b), the CAP Part 1 (SynTerra, 2015c), the CAP Part 2 (SynTerra, 2016), the Draft Proposed Risk Classifications (NCDEQ, 2016), and the National Pollutant Discharge Elimination System (NPDES) permit for Mayo (North Carolina Department of Environment and Natural Resources (NCDENR, 2009). I have also reviewed raw groundwater model input and output files provided by Duke to facilitate understanding of the model that informs the CAP Parts 1 and 2. This addendum to my report provides additional observations and opinions formed that are new to this document or have recently been recognized. 2 GEO-HYDRO, INC 3. Qualifications This section is unchanged from my expert report dated February 2016. GEO-HYDRO, INC 4. Site Background The Mayo CAP Part 21 indicates that ash may be capped with a "low permeability material", not necessarily a synthetic cap. The selection of a cap design is a critical component needed to evaluate the amount of precipitation that will infiltrate into the ash. Even new synthetic caps routinely allow some small amount of infiltration through faults in the fabric and/or seams. Infiltration through a low permeability soil cap would be expected to allow more infiltration than a synthetic cap, at least initially. Evaluation of realistic infiltration through the specific materials that are to be used to construct the cap must be performed in order to accurately predict the volume of infiltration and the volume of leachate that can be expected to migrate out of the basin. While MODFLOW does not offer cap performance evaluations, other programs such as Hydrologic Evaluation of Landfill Performance (HELP) should be used to generate reasonable infiltration values for use in MODFLOW. The same section of the document acknowledges for the first time the fundamental truth that water will continue to enter into the ash basin, even if a cap is installed 2. The document states, "Drains will be an integral part of the cap -in-place closure to provide a flow path for water entering the system as precipitation, run-off, or groundwater discharging into the basin from upgradient areas and to limit/prevent the development of impoundment of water in and upstream of the capped ash." This document indicates that drains will be used to control water that would otherwise enter the ash from the sides but provides no information about how such a drain system might be designed, constructed, and operated to control infiltration of precipitation from above, inflow of groundwater from the sides, and discharge of contaminated groundwater from the basin. However, neither the volume of water that is predicted to discharge into the basin from upgradient areas, nor the volume of ash that will remain saturated and continue to generate leachate has been reported by Duke. Without knowledge of these factors, the claim that the drains would be effective is unsupported. Determination of Background Water Quality Accurate and appropriate determination of background water quality is of critical importance to evaluation of groundwater impacts from the ash basins. Provisional background concentrations for groundwater, as well as other media, were proposed in the CAP Part 1. The CAP Part 2 reported analytical results from rounds 1 thru 4 of background groundwater sampling, but further evaluation of results and background concentrations was deferred to future reports. Groundwater monitoring results are currently being compared to provisional background concentrations that are based on an incomplete data set. 1 SynTerra (2016), p. 6-6, Section 6.3 2SynTerra (2016), p. 6-6, Section 6.3 2 GEO-HYDRO, INC Review of the updated analytical data from background monitoring wells provided in the CAP Part 23 show that presumed background well MW- 11BR contained very high concentrations of hexavalent chromium (13.6 ug/1) and vanadium (12.1 ug/1) at the time of the December 2015 sampling event. The detected hexavalent chromium in well MW- 11BR was over 2 orders of magnitude greater than the USEPA Tapwater Regional Screening Level4 of 0.035 ug/1. The detected vanadium concentration of vanadium in this same well is an order of magnitude higher than the 0.3 ug/1 Interim Maximum Allowable Concentration (IMAC) and 3 ug/1 greater than the previously detected high background value that was also measured at well MW -1 113R. The repeatedly high values of ash -related constituents in this well appears to indicate that this well may be constructed in a different geologic formation, or at in materials that differ significantly from the other background monitoring wells. This well specifically, and all of the background wells in general, must be evaluated to determine if each well is appropriate for inclusion in the background monitoring program. Further, the values identified as the provisional background are either calculated values or are the highest value recorded at any of the various locations, both of which are dependent on the distribution of concentrations obtained during sampling. Water quality monitoring results are easily influenced by sampling methods and techniques and can easily provide spurious data. Even the background data set that is being developed by sampling new background wells around the Mayo site is capable of producing outliers that if not removed could skew the background concentration. The complete data set needs to be evaluated for sampling or analytical problems and tested to eliminate outliers that could skew the data prior calculating or selecting background concentrations. 3 SynTerra (2016), Appendix A-1 4 SynTerra (2015b), Table 2-5 5 GEO-HYDRO, INC 5. Opinion 1: Coal Ash Stored in the Mayo Ash Basin is the Source of Contamination Detected in Surface Water and Groundwater This section is unchanged from my expert report dated February 2016. 0 GEO-HYDRO, INC 6. Opinion 2: Capping Coal Ash Located Within the Mayo Ash Basin Will Not Protect Groundwater Quality Downgradient of the Basin The CAMA process proposed designation of the Mayo site as low-risk creates the possibility that Duke Energy (Duke) could pursue closure of the Mayo impoundment by capping the disposed ash in place. Capping the waste within the footprint of the ash basin will not be protective of groundwater quality downgradient of the basin. Environmental contaminants contained in coal ash are leached into groundwater when precipitation infiltrates through the waste or, when groundwater flows through waste that has been placed below the water table. In the case of the Mayo ash basin, both of these processes are currently acting to create the contaminated ash porewater, groundwater, and surface water that discharge into Crutchfield Branch and contaminate surface water downstream of the impoundment. The cap -in- place remedy would likely reduce the amount of water that enters the waste from precipitation. This remedy would however do nothing to reduce the amount of water that flows laterally into the basin from surrounding geologic materials, through the capped waste, and eventually into Crutchfield Branch. The CAP and its included modeling results show that much of the coal ash in the Mayo ash basin will remain submerged below the water table under a cap -in-place remedy. The thickness of saturated waste that would remain saturated can be estimated by comparing the pre -impoundment topographic map of the basin (Figure 1) with the calculated hydraulic head map for the cap in place option (Figure 5). The topographic map of the buried valley shows that natural land surface below the impoundment is located at approximately 400 feet above mean sea level (msl) near the center of the basin. The calculated hydraulic head in the basin after ash is capped in place is predicted by the model to be approximately 460 to 470 feet msl near the center of the basin. Therefore, the model of the cap -in-place scenario predicts 60 to 70 feet of saturated ash would remain in portions of the basin. The data presented in these figures is consistent with the known hydrogeology of the site. Groundwater will continue to flow into the ash basin from adjacent areas and some infiltration through the cap would continue to occur. Groundwater that flows through the ash will continue to leach metals from the ash and transport those metals down -gradient before discharging into Crutchfield Branch. Further, the results of the groundwater modeling exercise undertaken as part of this program indicate that removal of the Mayo coal ash is by far the most effective option for improving groundwater quality and preventing future discharges to Crutchfield Branch. The modeling results indicate that 7 GEO-HYDRO, INC removal of the ash significantly reduces the size and concentration of the boron plume in the saprolite and transition zones, something that capping -in-place does not achieve. The Mayo CAP Part 25 indicates that ash may be capped with a "low permeability material", not necessarily a synthetic cap. The selection of a cap design is a critical component needed to evaluate the amount of precipitation that will infiltrate into the ash. Even new synthetic caps routinely allow some small amount of infiltration through faults in the fabric and/or seams. Infiltration through a low permeability soil cap would be expected to allow more infiltration than a synthetic cap, at least initially. Evaluation of realistic infiltration through the specific materials that are to be used to construct the cap must be performed in order to accurately predict the volume of infiltration and the volume of leachate that can be expected to migrate out of the basin. While MODFLOW does not offer cap performance evaluations, other programs such as Hydrologic Evaluation of Landfill Performance (HELP) should be used to generate reasonable infiltration values for use in MODFLOW. Even though there are serious flaws in the groundwater modeling that artificially restrict groundwater impacts under the cap -in-place scenario (see Opinion 7), the modeling effort confirms that ash excavation is the option that is most protective of the environment and is a permanent solution. The same section of the of the document acknowledges for the first time the fundamental truth that water will continue to enter into the ash basin, even if a cap is installed 6. The document states, "Drains will be an integral part of the cap -in-place closure to provide a flow path for water entering the system as precipitation, run-off, or groundwater discharging into the basin from upgradient areas and to limit/prevent the development of impoundment of water in and upstream of the capped ash." Neither the volume of water that can be expected to discharge into the basin from upgradient areas, nor the volume of ash predicted to remain saturated and continue to generate leachate has been reported by Duke. This document indicates that drains will be used to control water that would otherwise enter the ash from the sides but provides no information about how such a drain system might be designed, constructed, and operated to control infiltration of precipitation from above, inflow of groundwater from the sides, and discharge of contaminated groundwater from the basin. Without knowledge of these factors, the claim that the drains would be effective is unsupported. 5 SynTerra (2016), p. 6-6, Section 6.3 6 SynTerra (2016), p. 6-6, Section 6.3 GEO-HYDRO, INC 7. Opinion 3: Monitored Natural Attenuation Is Not An Acceptable Groundwater Remediation Strategy at Mayo The CAP7 indicates that Duke may evaluate MNA as a potential groundwater remedy for certain area of the Mayo site. The CAP attempts to make it appear that MNA is a viable remedial option for impacted groundwater and surface water downgradient of the Mayo ash basin. However, MNA is not a viable closure option for this site for several reasons: • Duke Energy has not proposed removal of the waste for disposal in a secure location. Modeling presented in this document shows that most of the ash would remain saturated after capping. Saturated ash will continue to leach metals into groundwater that will flow toward and eventually discharge into Crutchfield Branch. As a practical matter, in the absence of removal all sources of contamination cannot be controlled • Many of the ash -related constituents in groundwater at this site neither degrade nor attenuate. The Geochemical Site Conceptual Model$ states that boron best represents the extent of impact to groundwater because it "does not sorb or precipitate within the ash or on aquifer materials." Because of this, the Mayo site would not be eligible for MNA. • Crutchfield Branch, which receives the contaminated groundwater discharge at Mayo, currently exceeds surface water standards for several parameters. Sampling has detected ash -related metals at concentrations above background and relevant NCAC 2B and/or 2L standards, including boron, cobalt, copper, iron, manganese, thallium, vanadium, and zinc9. These surface water exceedances are likely to continue since the majority of flow in Crutchfield Branch is associated with drainage from the ash basin10 and the groundwater model shows that a substantial amount of ash will continue to be saturated with groundwater that eventually flows to Crutchfield Branch, even if the basin is capped. 7 SynTerra, 2015b, p.5-1 S SynTerra, 2015b, Section 3.2 9 SynTerra, 2015b, Table 2-14 10 SynTerra, 2015b, Page 4-13, Section 4.4.1 0 GEO-HYDRO, INC 8. Opinion 4: Capping Coal Ash Located Within the Mayo Ash Basin Will Not Be Protective of Surface Water Quality in Crutchfield Branch Prior to construction of the Mayo plant Crutchfield Branch was a free-flowing perennial stream that occupied the valley through which it flowed. The coal ash basin was constructed by damming the stream and used to segregate and store coal combustion wastes that were allowed to settle in the basin. If coal ash located within the Mayo ash basin is capped in place, the surface water in Crutchfield Branch will continue to be polluted and a significant portion of Crutchfield Branch will remain buried by waste. Crutchfield Branch, which receives the contaminated groundwater discharge at Mayo, currently exceeds surface water standards for several parameters. Sampling has detected ash -related metals at concentrations above background and relevant NCAC 2B and/or 2L standards, including boron, cobalt, copper, iron, manganese, thallium, vanadium, and zinc". These surface water exceedances will continue since the majority of flow in Crutchfield Branch is associated with drainage from the ash basin 12 and the groundwater model shows that a substantial amount of ash will continue to be saturated with groundwater that eventually flows to Crutchfield Branch, even if the basin is capped (See Opinion #2). Coal ash must be separated from the groundwater and surface water flow systems if further contamination of these resources is to be avoided The surface water quality discussion in the CAP 13 indicates that concentrations of ash -related constituents in Crutchfield Branch decrease with distance downstream from the ash basin due to "attenuation by dilution." This is problematic because, of course, there is so such process as attenuation by dilution. Attenuation and dilution are two different processes. Attenuation occurs when contaminants interact with the soil or sediments, and contaminants are removed from the water. Dilution does not remove or treat any contaminants; instead, the concentration, but not the amount, of a pollutant is reduced by diluting the polluted plume with water containing a lower concentration of the contaminant. Thus, dilution and attenuation are distinctly different processes. The Cap -In -Place groundwater model scenario assumes that a 100% effective cap is installed over the ash and that infiltration into the ash from above is zero. The Mayo CAP Part 214 indicates that ash may be capped with a "low permeability material", not necessarily a synthetic cap. The selection of a cap design is a critical component needed to evaluate the amount of precipitation that will infiltrate into the ash. Even new synthetic caps routinely allow some small amount of 11 SynTerra, 2015b, Table 2-14 12 SynTerra, 2015b, Page 4-13, Section 4.4.1 13 SynTerra, 2015b, Section 4.4.2 14 SynTerra (2016), p. 6-6, Section 6.3 10 GEO-HYDRO, INC infiltration through faults in the fabric and/or seams. Infiltration through a low permeability soil cap would be expected to allow more infiltration than a synthetic cap, at least initially. Evaluation of realistic infiltration through the specific materials that are to be used to construct the cap must be performed in order to accurately predict the volume of infiltration and the volume of leachate that can be expected to migrate out of the basin. While MODFLOW does not offer cap performance evaluations, other programs such as Hydrologic Evaluation of Landfill Performance (HELP) should be used to generate reasonable infiltration values for use in MODFLOW. Even though there are serious flaws in the groundwater modeling that artificially restrict groundwater impacts under the cap -in-place scenario (see Opinion 7), the modeling effort confirms that ash excavation is the option that is most protective of the environment and is a permanent solution. The same section of the of the document acknowledges for the first time the fundamental truth that water will continue to enter into the ash basin' 5. The document states, "Drains will be an integral part of the cap -in-place closure to provide a flow path for water entering the system as precipitation, run-off, or groundwater discharging into the basin from upgradient areas and to limit/prevent the development of impoundment of water in and upstream of the capped ash." Neither the volume of water that can be expected to discharge into the basin from upgradient areas, nor the volume of ash that is predicted to remain saturated and continue to generate leachate has been reported. This document indicates that drains will be used to control water that would otherwise enter the ash from the sides but provides no information about how such a drain system might be designed, constructed, and operated to control infiltration of precipitation from above, inflow of groundwater from the sides, and discharge of contaminated groundwater from the basin. Without knowledge of these factors, the claim that the drains would be effective is unsupported. The CAP attempts to make it appear that MNA is a viable remedial option for impacted groundwater and surface water downgradient of the Mayo ash basin. In order to be an appropriate remedy MNA would have to demonstrate that the contaminant has the capacity to degrade or attenuate under site- specific conditions. The Geochemical Site Conceptual Model 16 states that boron best represents the extent of impact to groundwater because it "does not sorb or precipitate within the ash or on aquifer materials." The properties of the contaminants at Mayo would therefore render the site ineligible for remediation by MNA, even if attenuation by dilution were a real process. In addition, capping the coal ash in the in place would leave a significant portion of Crutchfield Branch buried in waste. Now that the Mayo waste handling system is no longer going to be used there is no justification for leaving the existing stream covered in coal ash. 15 SynTerra (2016), p. 6-6, Section 6.3 16 SynTerra, 2015b, Section 3.2 11 GEO-HYDRO, INC 9. Opinion 5: Removal of the Coal Ash Will Remove the Source and Reduce the Concentration and Extent of Groundwater and Surface Water Contaminants This section is unchanged from my expert report dated February 2016. 12 GEO-HYDRO, INC 10. Opinion 6: The Coal Combustion Residual Impoundment Risk Classification Proposed by NCDEQ Improperly Minimizes Protection of Environmental Quality This section is unchanged from my expert report dated February 2016. 13 GEO-HYDRO, INC 11. Opinion 7: The Groundwater Flow and Transport Model Does Not Reflect Real -World Conditions Groundwater models can be useful tools that can be employed to evaluate alternative actions at waste disposal site such as Mayo. This usefulness however, is predicated on the model being constructed in a manner that faithfully recreates actual field conditions. However, the model includes fundamental inconsistencies between observed and modeled conditions that cast doubt on results and make it likely that the nature and extent of groundwater contamination is understated. Each of the identified issues with the current model are identified separately below. Groundwater Flow Model MODFLOW Model Geometry Artificially Isolates the Ash The definition of the inappropriately isolates the ash. The ash in layers 1-4 has no lateral continuity with any of the adjacent natural materials. The layers extend laterally to the edge of the ash basin and terminate at a no flow boundary. When a 100% effective cap is assumed, the only flow in the ash of layers 1-4 is vertically into or out of the underlying saprolite through the bottom of layer 4 (and top of layer S). This prohibition of lateral flow at the edges of the ash pond into/from the enclosing saprolite is compounded by the corresponding imposition of horizontal -to -vertical anisotropy for coal ash hydraulic conductivity. As modeled, the vertical flow between the ash and saprolite is constrained by hydraulic conductivity that is only 20% of that which would exist were the connection between the materials to occur horizontally under the same gradients. The conditions included in this model create the equivalent of a 100% effective liner on the top and sides and an 80% effective liner at the bottom of the ash. This is, of course, not reflective of real—world conditions. MODFLOW Model Is Overlv Constrained The lateral boundary conditions for layer 7 (base of the saprolite/transition layers) are almost everywhere head -defined. The imposition of fixed heads across significant portions of a model, particularly the lateral boundaries is always risky modeling procedure. Unless there is abundant groundwater data or a known physical condition for such constraint, the modeler runs the risk of over -constraining the model and generating results that represent an artificial world, not the mathematical approximation of the real world. The use of heads to calibrate a model that is highly constrained by fixed heads is, in essence, circular reasoning. Calibration is meaningful only if calibration is achieved using a measurable parameter that is not significantly constrained as a boundary condition. If the model is substantially constrained by assigned heads, a calibration based upon flows, for example, will allow discrimination between a physically significant model and one that is simply an impressive 14 GEO-HYDRO, INC calculation of conditions that don't exist in the real world. For this model, acceptable head calibration is demonstrated, but it has no significance because that head distribution was dictated by boundary conditions. And, there are no site data which can be used to calibrate how closely this mathematical computation matches independent parameters in the real world. Streams were simulated as drains with exceptionally high conductance. Functionally, this means they too are fixed head boundaries, contributing to the over -constraining of the model with respect to heads. MODFLOW Model Does Not Accurately Simulate Vertical Gradients A critical measure of whether or not a model is properly designed and implemented is whether flows occur in the right direction. Relying solely on impressive statistics for head calibration can mask a model that is remarkably wrong on flow directions. The baseline model for this site is just such a case. When one compares the directions of vertical flow17 that are simulated with the directions of flow that are observed in the data from nested wells, the model is almost always in error. Where vertical flow is observed to be upward, the simulation describes it as downward. Where vertical flow is observed to be downward, the simulation describes it as upward. Inability of the MODFLOW model to simulate appropriate vertical flow directions is another indication that the model is overly constrained and raises serious doubt about the adequacy of this model to support critical remedial decision making. Fate and Transport Modeling Scenarios Cap -In -Place Source Concentrations Are Unjustifiable The contaminant transport simulations of the Cap -In -Place scenario is badly flawed. The change from constant concentration in the ash (fixed source) in the current condition simulation to variable concentration is completely unjustifiable. In MT3DMS, variable concentration cells add no contaminants to the groundwater. By changing the cells from constant to variable concentration the modeler assumes that any ash that remains saturated is somehow incapable of producing contamination for any constituent. The shift in the MT3DMS source from leachate producer to inert media has no justification. Stopping, or approximately stopping, vertical infiltration into the ash has no impact on the capacity of the ash to continue to produce leachate. Since some un -reported thickness of ash is expected to remain saturated as a result of lateral or vertical flow from the surrounding strata, the ash will continue to produce the same leachate quality that it did historically. Non -zero infiltration will similarly generate contaminant -bearing leachate as it drains downward through unsaturated ash. 17 SynTerra , 2016, Appendix B, Table 1 15 GEO-HYDRO, INC References NCDEQ, 2016, Coal Combustion Residual Impoundment Risk Classifications, January 2016. NCDENR, 2009, Permit to Discharge Wastewater Under the National Pollutant Discharge Elimination System, Permit NC0038377, October, 2009 SynTerra, 2014, Groundwater Assessment Work Plan for Mayo Steam Electric Plant, September 2014 SynTerra, 2015a, Comprehensive Site Assessment Report, Mayo Steam Electric Plant, September 2015. SynTerra, 2015b, Corrective Action Plan, Part 1, Mayo Steam Electric Plant, December 2015. SynTerra, 2016, Corrective Action Plan, Part 2, Mayo Steam Electric Plant, February 2016. United States Geological Survey, Cluster Springs VA. — N.C., 7.5 Minute Topographic Map, 1968, photorevised 1987. 16 GEO-HYDRO, INC Figures This section is unchanged from my expert report dated February 2016.