Groundwater Investigations for CCR Landfills in Karst Terrain

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1 Groundwater Investigations for CCR Landfills in Karst Terrain Justin Brown, RG, GeoEngineers, Inc. Chris Hickman, PG, Jacobs Engineering

2 Coal Ash Regulatory History 1978: Fossil fuel combustion waste was designated as special waste and exempt for RCRA Subtitle C 1980: Temporary exemption from hazardous waste regulation until further studies completed 1993: EPA determines fly ash, bottom ash and boiler slag from utilities do not apply to Subtitle C and not hazardous waste 2000: EPA concluded national non-hazardous waste regulations under Subtitle D necessary for CCR waste disposed of in landfill and surface impoundments

3 Coal Ash Regulatory History 2008 Dike failure coal ash impoundment, Kingston TN

4 Coal Ash Regulatory History 2009: EPA issued information request letters to electric utilities to assist EPA in evaluating structural integrity of these management units 2010: EPA proposes two options for CCR disposal (Subtitle C and Subtitle D) 2014: EPA finalized national regulations provide comprehensive requirements for disposal of CCR as a solid waste under Subtitle D of RCRA

5 2014 CCR Regulation Location Restrictions Placement above the uppermost aquifer (5ft) Wetlands (marshes, bogs, swamps, etc.) Fault areas (200 feet outside the damage zone of Holocene fault) Seismic impact zones (must demonstrate resistance to horizontal acceleration) Unstable areas (karst)

6 2014 CCR Regulation Location Restrictions CCR units are prohibited from these areas unless specific demonstrations can be made Demonstrations must be certified by a PE

7 CCR Rule Karst Areas Landfill is structurally stable effectively prevents CCR constituents from reaching karst conduits. No conduits beneath the CCR unit that allow piping of groundwater into the karst aquifer (no direct connections between CCR constituents and uppermost aquifer) Monitoring wells must be capable of detecting any contaminants released from the CCR unit into the karst aquifer

8 CCR Compliance Currently Available Information EPA estimated that 51 of 1045 CCR units would be subject to location restrictions due to seismic, fault or unstable areas Main reason for unstable area is karst topography Karst topography is located in almost every state in the US Based upon the public utility websites there are CCR units located in Georgia, Kentucky, Missouri, Tennessee and many more Currently groundwater information is not available on any public utility website

9 Karst Terrain Cutter and Pinnacle Bedrock Surface

10 Karst Terrain Locally Enlarged Bedding Planes

11 Karst Terrain Locally Enlarged Vertical and Horizontal Voids

12 Karst Terrain Clay Filled Solution Widened Joints

13 Karst Terrain Secondary Porosity

14 Limestone Porosity Crystalline structure with little or no primary porosity Small fractures that develop due to tectonic processes, bedding planes (secondary porosity) Conduits that develop due to karstification (generally along fractures and bedding)

15 Karst Investigation Toolbox Detailed onsite/offsite reconnaissance Electrical Resistivity Tomography (ERT) Multi-Channel Analysis of Surface Waves (MASW) Targeted boreholes / rock coring Dye trace studies Monitoring wells, hydrologic analysis

16 Detailed Reconnaissance of Onsite and Offsite Karst Features Solutional vs. collapse sinkholes Surface seeps Springs location, elevation, flow

17 Solutional vs. Collapse Sinkholes Solutional sinkholes Stable Show evidence of forming over long periods of time Feed water into perched portions of karst system Collapse sinkholes Generally form in response to rapid changes in soil moisture Often due to ponding of water resulting from changes in surface drainage UWL generally impedes rapid changes in moisture in shallow karst system

18 Solutional Sinkholes Form over long periods of geologic time Show evidence of gradual formation May allow for slow or rapid recharge into shallow karst system

19 Collapse Sinkholes Collapse often forms from pooled water at surface and increased flow in subsurface Prevented with good stormwater management Avoid creating new areas where water can pond Avoid routing surface water into adjacent solutional sinkholes or other karst conduits

20 Electrical Resistivity Investigation and Screening Tool for Karst Soil cavity detection (structural stability analysis) Large open bedrock conduits (determining collapse sinkhole potential) Bedrock surface topography Soil thickness Saturated groundwater flow pathways (vertical zones of higher secondary permeability)

21 Electrical Resistivity Traverse

22 Electrical Resistivity in Massive Limestone - Considerations Detects water-bearing secondary porosity, general bedrock topography, location of large subsurface voids

23 Electrical Resistivity in Massive Limestone Each traverse collects thousands of data points

24 Electrical Resistivity in Massive Limestone Detailed surveys reveal areas where vertical migration is more prevalent

25 ERT Traverse Karst Terrain Cutter Potential Monitoring Well Location

26 MASW Confirm bedrock depth from ERT investigation Confirm possible subsurface voids from ERT investigation Intact Bedrock

27 Boreholes / Rock Coring / Monitoring Wells Secondary porosity Horizontal voids Sub-vertical voids Vertical delineation and hydraulic conductivity of bedrock zones Perched zones Vadose zones Uppermost Continuous Aquifer (hydraulic conductivity and lateral extent)

28 Boreholes / Rock Coring / Monitoring Wells Continued Hydraulic gradients Potentiometric flow directions Offset boreholes may help to fine-tune understanding of bedrock topography (cutters and pinnacles)

29 Developing A Conceptual Model Losing Stream Perennial Spring Vadose Zone Phreatic Zone Aquitard After: Hartmann, A., N. Goldscheider,T. Wagener, J. Lange, and M. Weiler (2014), Karst water resources in a changing world: Review of hydrological modeling approaches, Review of Geophysics, 52, , doi: /2013rg

30 Dye Tracing Directional connection between injection and detection points Travel times through karst conduits (may be precipitation dependent) May provide travel time to deep aquifer May be used to trace potential offsite contaminant sources More useful for investigating karst conduit flow than aquifer flow unless continuous aquifer is shallow and well-connected to karst conduits

31 Conceptual Dye Trace in Karst Terrain Shallow karst conduit flow along interrupted pathways and flow through secondary porosity to uppermost continuous aquifer

32 Why Not Attempt to Monitor Karst Flow? Difficult to intercept Short residence time

33 Summary Keys to an Effective Monitoring System Under CCR Rule Focuses on vertical migration through secondary porosity to uppermost aquifer Wells placed in proximity to areas with most pronounced vertical migration (best secondary porosity) Characterizes conduit flow pathways and residence time of water in conduit system Wells have sufficiently high hydraulic conductivity for low-flow sampling

34 Questions? Justin Brown, RG, GeoEngineers, Inc South Delaware Avenue Springfield, MO Chris Hickman, PG, Jacobs Engineering 125 Broadway Avenue Oak Ridge, TN