Assessing Technical Impracticability in a Karst Setting at Anniston Army Depot

Transcription

1 Assessing Technical Impracticability in a Karst Setting at Anniston Army Depot Robert O Laskey, Elisabeth Hawley, Rula Deeb, Michael Kavanaugh (Malcolm Pirnie, Inc.) Bridget Lyons (US Army Environmental Command) Pat Smith (Anniston Army Depot) JSEM Columbus, Ohio May 22, 2007

2 Introduction Objectives - present results of a TI evaluation at the Southeast Industrial Area, Anniston Army Depot Malcolm Pirnie - draft TI evaluation report prepared on behalf of the Army Environmental Command - Assistance from Scientific Applications International Corporation Partnering Team - US Army, ADEM, EPA - Region IV - Consensus opinion that attaining ARARs in source zones may be TI If approved, an ARAR waiver based on TI would be Incorporated into the final ROD for groundwater operable unit 1 (OU1) (Front-end waiver) TI Technical Impracticability

3 Outline TI assessment process Site background Conceptual site model Potential ARARs to be waived Basis of TI decision TI waiver zone Alternative remedial strategies

4 TI Assessment Process Define an area (TI waiver zone) in which groundwater ARARs will not be the clean up standard Based on engineering feasibility and reliability of attaining ARARs within reasonable timeframe Selected remedy will be protective of human health and the environment by including the following components: - Exposure controls - Aquifer restoration outside the TI waiver zone - Source controls (treatment / containment) to some extent

5 Site Background Southeast Industrial Area (SIA) - repair / rehabilitation of military vehicles since mid 1940 s ac - dense industrial infrastructure - Bounded by 15,000 ac Ammunition Storage Area to west; private land to north, east and south - Waste materials, including spent degreasing solvents, disposed in on-site waste lagoons and burial pits until mid 1970 s Under RCRA, identified 24 SWMUs; retained SWMU designations under CERCLA Interim remedial actions began in 1978

6 Conceptual Site Model - Sources Residual DNAPL in residuum and weathered bedrock - Historical evidence of DNAPL use and disposal on-site - Observations during shallow remediation - TCE concentrations in groundwater exceed 1% of solubility Mass estimates range from 3.5 to 27 million lbs NAPL as TCE DNAPL presence in unweathered bedrock expected based on sub-vertical fractures, magnitude of liquid disposal

7 SWMU-1 SWMU-25 SWMU-30 Bldg 400 area Southeast Industrial Area SWMUs SWMU-12 Bldg 114 Dewatering System DNAPL Locations Other SWMUs

8 Conceptual Site Model - Pathways Three hydrostratigraphic units Groundwater flow is: - vertically downward in the residuum - predominately horizontal, but also vertical, in the weathered bedrock - Confined to discrete pathways in the unweathered bedrock, which are sub-vertical Weathered and unweathered bedrock are hydraulically connected and vertical gradients are predominately downward Primary off-site pathways are through the unweathered bedrock

9 Residuum and Shallow Bedrock USACE - Mobile District

10 Relationship of the SIA to the Jacksonville Fault Zone

11 Conceptual Flow Model Residuum Weathered Limestone/ Dolostone Unweathered Limestone/Dolostone [Coldwater Spring]

12 Extent of TCE in Weathered Bedrock Monitoring Well Data Maximum TCE On-site 9,000 to 25,000 µg/l Maximum TCE Off-site <1 to 9.4 µg/l

13 Extent of TCE Detected in Unweathered Bedrock Wells Monitoring Well Data Maximum TCE on-site: 4,100 μg/l at 105 ft 350 μg/l at 454 ft Maximum TCE off-site: Locally 5-12 μg/l Others << 5 μg/l or ND Private well data higher

14 0.1 On-site Boring 02CGWB03 (elevation ) Ambient Flow (gpm) Leaving Entering 23.3 Off-site Boring 02CGWB05 (elevation ) Ambient Flow (gpm) Leaving Entering Distribution of Discrete Flow Zones: Unweathered Bedrock TCE in screened intervals (ppb) in TCE in screened intervals (ppb) in Hydrophysical Logging Packer Sampling ,000 10,000 Hydraulic Conductivity (feet/day) ,000 10,000 Hydraulic Conductivity (feet/day) Well Data

15 Southeast Industrial Area N Off-Site Receptors JFZ Dry Creek Valley Cooper Well Maximum TCE Off-site Cooper Well 40 µg/l Domestic Wells - ND Coldwater Spring 5 µg/l 1500 ft Coldwater Spring JFZ: Jacksonville Fault Zone

16 Coldwater Spring Municipal water supply for City of Anniston, the Depot, and other local municipalities Average discharge is 31.8 MGD; historical average mass discharge of TCE is 0.74 lbs/day Spring discharge captures groundwater that flows from NE to SW along the Jacksonville Fault Zone (JFZ) Groundwater emerges at the Spring due to a subsurface groundwater barrier below the Dry Creek Valley; deep sourced SIA is the nearest and largest potential source of TCE, but other sources likely exist

17 Jacksonville Fault Zone and Coldwater Spring Recharge Areas Coldwater Spring Recharge Area JFZ SIA Coldwater Spring

18 Potential ARARs to be Waived Waiver to be requested for potential, chemical specific ARARs: - SDWA MCLs for trichloroethene, methylene Chloride, Total THMs (chloroform), carbon tetrachloride, bis(2-ethylhexyl) phthalate - SDWA MCLs for arsenic, beryllium, chromium - Alabama MCLs for aluminum, iron, lead, manganese Primary off-site risks arise from TCE concentrations in groundwater

19 Basis of TI Decision Contaminant related limitations - Presence, magnitude, and location of DNAPL - Diffusion into and out of clay and rock matrices Hydrogeologic limitations - One interconnected aquifer; no capillary barrier to DNAPL; sub-vertical fracturing - Heterogeneity - Fine-grained low permeability source zones

20 Basis of TI Decision FS Alternative TI Limitation - Primary TI Limitation - Secondary Timeframe (Years) MNA, LUCs NAPL dissolution rate TCE half life >3,000 Enhanced bioremediation (in source area) NAPL dissolution rate Flushing reliability ~1,800 Enhanced bioremediation (plume containment) Vertical gradients; Cost NAPL dissolution rate ~1,800 Pump-and-Treat (source area) NAPL dissolution rate Flushing reliability >1,100 Electrical resistance heating (80% removal) Potential mobilization NAPL dissolution rate >700 PRB (source zone containment) Vertical gradients Placement in conduits >3,000

21 TI Waiver Zones Evaluation process - Proposed three TI waiver zone options Option A - smallest extent Limitations to groundwater restoration in source zones (DNAPL extent) Option B and C Limitations to groundwater restoration Limitations to plume containment Option B at SIA boundary Option C at Coldwater Spring

22 TI Waiver Zone Option A Residuum Zone Weathered Bedrock Zone

23 TI Waiver Zone - Option B Residuum / Weathered Bedrock Unweathered Bedrock

24 TI Waiver Zone Option C Residuum / Weathered Bedrock Unweathered Bedrock

25 Alternative Remedial Strategy Options Exposure control - LUCs - Water supply remedies Point of Use - Coldwater Spring treatment - Off-site monitoring focus on potential receptors Plume containment - Coldwater Spring Option C - Cooper well or other extraction wells along JFZ Option B - P&T near source zones - Option A Off-site Northeast Area Plume restoration ARAR waiver or long-term MNA Source control to be negotiated

26 Questions Robert O Laskey rolaskey@pirnie.com

27 Chronology of Interim Remedial Actions SWMU-13 Acid Waste Disposal Pit SWMU-30 NE Lagoon Area SWMU-7 Chemical Waste Disposal Pit SWMU-12 Facility 414 Lagoons Excavation 1990 GWTS 1990 GWTS No GW impacts No GW impacts ISCO SWMU-22 A-Block Lagoon SWMU-1 Chemical Waste Pits SWMU-25 Building 130 Sump SWMU-3 Old IWTP Tanks SWMU-31 Building 114 Area Coldwater Spring 1978 Closure 1980 Excavation 1983 Excavation 1983 Excavation 1984 Bldg 114 Dewatering 1987 Treatment for VOCs 1987 TCE Detected < MCLs GWTS - Groundwater Treatment System 1990 GWTS 1990 GWTS 1991 Treatment for Cr No GW impacts No GW impacts 2005 Air Stripper Installed

28 Conceptual Site Model PATHWAYS -Three groundwater zones clay residuum, weathered carbonate bedrock, un-weathered carbonate bedrock - Groundwater flux is lateral toward the Dry Creek Valley in weathered bedrock with a downward vertical component to unweathered bedrock - Dry Creek Valley is an area of enhanced hydraulic conductivity and low hydraulic head related to the Jacksonville Fault Zone - Dissolved plume detected in weathered bedrock, limited lateral extent - Karst features present, but typically in-filled with sediment - Downward mass flux to unweathered bedrock; where major flow pathways are thin, discrete, widely spaced

29 Unweathered Bedrock Seismic reflection,magneto-telluric, electrical resistance imaging surveys Investigated to 700 feet bgs; Rock coring, downhole geophysics, discrete interval groundwater sampling - Numerous wide-spread fractures, cavities, faults, voids, fracture zones, in all geologic formations, at all depths, including Rome formation (shale). Fracture apertures vary between 0.5 mm and 9 mm Hydrophysical testing - Vertical gradients, predominantly downwards but also upwards.discrete zones with very high hydraulic conductivities, more than 8000 ft/day (indicative of conduit flow) including at depths >300 feet

30 Basis of TI Decision Restoration of groundwater to ARARs will exceed 100 years - Feasibility Study completed by SAIC - Screened technologies; developed alternatives - Constructed a dual porosity / single permeability fracture flow groundwater model to compare alternatives and estimate remedial timeframes - Simulates Darcy flux, mass discharge, matrix diffusion, biodecay - Assumed no DNAPL in unweathered bedrock - Model domain includes only SWMU-12 Source: Harding ESE, 2001

31 Uncertainties in TI Evaluation DNAPL in the unweathered bedrock - magnitude - depth - mass storage in rock matrix Estimate of TCE mass Containment in weathered bedrock zone Containment at Coldwater Spring

32 Uncertainties in TI Evaluation Containment in weathered bedrock - Evidence for both good and poor hydraulic connections across the weathered bedrock zone - Partial containment is practicable; delineation of capture zone is not practicable - TI waiver zone Option B and C in weathered bedrock Containment at Coldwater Spring - Potential bypass along the JFZ - Potential bypass along Dry Creek Valley - Spring hydraulic system poorly understood

33 TI Waiver Zones Vertically downward flux from shallow source zones to unweathered bedrock. Flux cannot be: - controlled at source - contained at source - contained in unweathered bedrock Inferred source material in unweathered bedrock Containment location determines extent of TI zone