Impacts of Low Permeability Caps on Groundwater Quality. By John A. Baker Alan Environmental,LLC

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1 Impacts of Low Permeability Caps on Groundwater Quality By John A. Baker Alan Environmental,LLC

2 Acknowledgements Ken Quinn- Montgomery Watson, Madison Wisconsin Mark Ankeny-DB Stephens & Associates (presently with INEL)

3 RCRA Cap Assumptions - Purpose of RCRA cap is to minimize leachate production and prevent groundwater contamination - For contaminated sites, purpose of RCRA cap is to improve groundwater quality - In some site specific settings, the intended affect is not observed for RCRA caps or for low permeability soil caps.

4 Unlined Landfill Before Capping VOCs IN GAS EMISSIONS VOCs IN LEACHATE

5 Capped Landfill VOCs IN GAS EMISSIONS VOCs IN LEACHATE Eliminates Eliminates Gas Gas Emissions Emissions Increases Increases VOC VOC pressures pressures in in Landfill Landfill Increases Increases VOCs VOCs in in leachate leachate

6 Non-Subtitle D or Interim Clay Cap Mechanism of Transport Landfill Gas Migration Conceptual Model Refuse (Under Methanogenic Pressure) Relatively Impermeable Upper Soils (or Weathered Zone) Clay Liner Drawdown During Purging/Sampling Unsaturated Relatively Permeable Unit Piezometric Surface Saturated Relatively Permeable Unit Aquitard/Bedrock

7 Montgomery Watson Study of WI Landfill Vinyl Chloride Through Time 10,000 1,000 No Controls Final Cover Completed Gas & Leachate Extraction System Operational ppb - NR140 ES Concentration (ppb) 0.1 Jan-87 Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99

8 Remediation Processes WI LANDFILL 1 PCE DCE / VC Dolomite O 2 O 2 O 2 PCE DCE / VC DCE VC CO 2 Sandstone 1 Extraction Removal of VOCs in Vapor and Liquids

9 Capped Landfill with Leachate and Gas Extraction Reduces Reduces gas gas pressure pressure Reduces Reduces VOCs VOCsin in leachate leachate Reduces Reduces moisture moisture content content in in landfill landfill

10 LANDFILL GA MW-10R Groundwater Flow

11 LANDFILL GA MW-10R 4 Fina l Co ve r Co ns truc tio n /L) VOC Concentration (ug Benzene Vinyl Chloride

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13 LANDFILL SC MW-9 AND MW-9R 35 Fina l Co ve r Co ns truc tio n 30 VOC Concentration ( ug /L) Chloroethane 1,1-dichloroethane

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15 LANDFILL NM MW-3 9 Final Cover Construction 8 7 VOC Concentration (ug/l) Methylene Chloride Tetrachloroethene

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20 Northwest Landfill ,1-DCA PCE Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Da te

21 Landfill Gas Movement -Cover Effects- High K Cover Depth ( Meters) year Horizontal Distance (Meters) Low K Cover Depth ( Meters) year Horizontal Distance (Meters)

22 Landfill Gas Movement -Cover Effects- High K Cover Low K Cover Depth (Meters) Depth ( Meters) years Horizontal Distance (Meters) years Horizontal Distance ( Meters)

23 KEY EVIDENCE OF POTENTIAL LANDFILL GAS VOC IMPACTSTO GROUNDWATER Measured Levels of Methane and VOCs in Perimeter Gas Probes and in Groundwater Well Headspace Gas No statistical exceedences of inorganic parameters and no trends of any leachate indicators Evidence of migration pathway to well No isotope evidence of leachate impacts to groundwater

24 Principal Constituents of MSW Landfill Gas in the Anaerobic Decomposition Stage Methane: Carbon Dioxide: Trace Gases: 40 to 70 % (by volume) 30 to 50 % (by volume) < 5% (by volume) (Note: Small amounts of nitrogen and oxygen may be present due to atmospheric diffusion.) (Source: Brosseau and Heitz, 1993/Kerfoot 1994)

25 Common Trace Gas VOC s Found in MSW Landfill Gas Benzene 1,2-Dichloroethane Acetone Methyl ethyl ketone (MEK) Toluene Trichloromethane Vinyl chloride 1,1-Dichloroethane Dichloromethane Chlorobenzene Tetrachloroethylene Trichloroethylene Ethylbenzene Xylenes (Source: Brosseau and Heitz, 1993/ Vogt, 1995)

26 Delta O-18 vs. delta D 10 0 MH-02 delta D of Water, per mil relative to SMOW MW-3 MW-1 MW-6 Gl obal meteoric water line MW-09 MH-02 MW-01 MW-03 MW-06 MW delta O-18 of Water, per mil relative to SMOW

27 Mechanisms of Gas-Phase Transport Landfill gas transport can either be by diffusion or advection. Diffusional transport is affected by: Henry s Law (solubility, vapor pressure) Porosity Bulk density Fractional Organic Carbon Soil Moisture Content Concentration gradients at air/soil/water interfaces Advective transport is a function of diurnal temperatures, barometric variations, and landfill pressure gradients

28 SIGNIFICANCE OF GAS IMPACTS TO GROUNDWATER Mechanisms of Transport Intra-Well (Cross Contamination) vs Groundwater Zone Impacts Addressing Gas Impacts to Groundwater Requires the Implementation of Alternate Monitoring and Source Remedy Programs

29 LANDFILL GAS AS A SOURCE OF VOCs TO GROUNDWATER CAN BE CONFIDENTLY DETERMINED!

30 Bio - cap Zero Methane Zero VOCs Aerobic zone Methanotrophs consume and oxidize 4 Graded soil CH4 and VOCs Anaerobic zone CH4 and VOCs Argonne Labs - Dr. Jean Bogner Measured this effect at several landfills