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Groundwater Remediation

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  1. Groundwater Remediation • Thanks to Phil deBlanc, Groundwater Services, Inc.

  2. Corrective Action Process RESULTS: SITE-SPECIFIC EVALUATION Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection. Release Assessment Conceptual Exposure Model Risk-Based Target Limits Remedial Action Compliance Monitoring No Further Action

  3. Conceptual Model Development Conceptual Exposure Model:Key Questions Transport SOURCE RECEPTOR Migration in air or water Humans, ecological species Waste or contaminant “hot spots” ? SOURCE: Is it toxic, flammable, explosive, or otherwise harmful? TRANSPORT: Is it in unsafe location or could it move to unsafe location? RECEPTOR: Could humans or ecological receptors be exposed to hazardous chemicals? KEY POINT: Must have YES to all 3 questions to have complete exposure pathway. ? ?

  4. POE Source Corrective Action Fundamentals Risk-Based Approach: General Procedure Exposure Factors Exposure Concentration = Toxicity Health Risk X X Risk is a function of exposure concentration, intake, and toxicity. KEY POINT:

  5. POE Source Corrective Action Process Overview Calculation of Target Levels Exposure Concentration Exposure Factors x x Toxicity = Health Risk End Start Calculation Safe cleanup limits at source are back-calculated based on allowable risk level at receptor. KEY POINT: POE = Point of Exposure

  6. Corrective Action Process RESULTS: SITE-SPECIFIC EVALUATION Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection. Release Assessment Conceptual Exposure Model Risk-Based Target Limits Remedial Action Compliance Monitoring No Further Action

  7. Remedy Selection Guidelines Remediation Options Transport SOURCE RECEPTOR Removal/Treatment:remediate source Containment:prevent transport Institutional Controls:control exposure activity KEY POINT: Remedy should serve to prevent risk by controlling exposure. Natural Attenuationconfirm stable / diminishing condition

  8. Remedial Action: Soils Soil Excavation at PST site PST = Petroleum Storage Tank

  9. Active Engineered Remedies Excavation and Disposal / Treatment TREATMENT / DISPOSAL OPTIONS Haul To Off-Site Landfill On-Site or Off-Site Thermal Treatment On-Site Physical / Biological Treatment

  10. Active Engineered Remedies Soil Vapor Extraction Blower or Vacuum Pump Air / Vapor Manifold Vapor Treatment System (Where Required) Air vacuum extracts volatile contaminants from affected soil. Clay Grout Seal Screen Sand Pack Affected Soils Water Table

  11. Very Likely Somewhat Likely Less Likely Active Engineered Remedies Soil Vapor Extraction: Applicability COCVapor Pressure (mm Hg) Soil Air Permeability Likelihood of Success HIGH (Coarse Sand / Gravel) 104 Butane 103 102 Benzene 101 MEDIUM (Fine Sand) Xylene 100 10-1 10-2 LOW (Clay or Silt) 10-3 10-4 Aldicarb Source: CDM, 1988

  12. Remedial Action: Soils Soil Vapor Extraction (SVE) System at Former Gasoline Station Vapor Treatment System SVE Wells and Collection Headers

  13. REMOVAL / TREATMENT OPTIONS CONTAINMENT OPTIONS GW INGESTION Affected Soil Affected Groundwater Active Remediation Technologies GW Remediation Options GW Pump & Treat Air Sparging Dual Phase Extraction Hydraulic Containment (pumping) Barrier Walls

  14. GW Remediation Options GW Pump & Treat: Overview Use continuous GW extraction to reduce COC concentrations in GW to applicable target levels. GOAL Moderate-to-high permeability groundwater units (K > 10-4 cm/s), low COC concentrations (CRF < 100), and no NAPL plume. APPLICABILITY NAPL GW Extraction:Recovery wells / submersible pumps; wellpoint systems. GW Treatment:GAC, air stripper, biological, etc. DESIGNOPTIONS CRF = COC Reduction Factor = (Current COC Conc./Target Level); K = Hydraulic Conductivity (cm/s) COC = Chemical of Concern

  15. GW Remediation Options GW Pump & Treat: Well Installation Recovery Well Installation Well Screen Centralizer Wire-Wrapped Well Screen Driller’s Knee Driller’s Helper Sand-Gravel Filter Pack

  16. Casing GW Remediation Options GW Pump & Treat: Recovery Well Design Material: Corrosion & contaminant resistant. Options = PVC, SS, teflon, FRP.  Large enough to fit pump, usually 4-in or 6-in. FRP = Fiberglass reinforced plastic PVC = Polyvinyl chloride SS = Stainless steel

  17. Well Screen GW Remediation Options GW Pump & Treat: Recovery Well Design Material: Typically same as casing. May use SS screen with PVC casing to economize. Length: 30-50% of saturated thickness for unconfined unit; 70-80% of saturated thickness for confined unit Placement: Adjust to match plume thickness, floating or sinking plume. Diameter: Prevent excessive head loss through screen by evaluating screen open area and pumping rate. Slot Size: Retain 90% of sand pack, slot size ≥ D10 of sand pack. PVC = Polyvinyl chloride SS = Stainless steel

  18. Sand Pack Grout Seal GW Remediation Options GW Pump & Treat: Recovery Well Design Purpose: Stabilize formation, minimize fines in well, & maximize screen slot size. Thickness: 3-8 in thickness between well screen and borehole wall. Material: Clean, uniform, silica sand/gravel. Material: Portland cement/bentonite mix. Configuration: At ground surface, sloped to drain rainwater away from well casing.

  19. KEY POINT:USEPA study shows that GW P&T cannot cleanup to DW standard at most sites. WHY NOT?Complex hydrogeology, design flaws, and NAPL. COC Conc. in GW ? Cleanup Standard Time GW Remediation Options Groundwater P&T: The Bad News

  20. Continuous Pump and Treat Resulting in Tailing Rebound After Pump and Treat System Shut-Off T GW Remediation Options GW Pump & Treat: Tailing and Rebound Source:From W, R, N, & W. Pump Shut-Off

  21. GW Remediation Options GW Pump & Treat: Wrap-Up PRO CON • Capable of providing hydraulic containment • May be required tosatisfy regulators • Incapable of attaining drinking water standards • Must treat or dispose of recovered GW • Long-term commitment 10

  22. GW Remediation Options Dual-Phase Extraction: Overview Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels. GOAL Low to moderate permeability groundwater units (K = 10-5 to 10-3 cm/s) APPLICABILITY GW Extraction:Recovery wells / submersible pumps; wellpoint systems. Vapor Extraction: Blower, dual phase wellpoint pump. Water Treatment: GAC, airstripper, biological Vapor Treatment, GAC, catalytic furnace. vapor GW DESIGNOPTIONS vapor Pump GW

  23. Dual-phase pump extracts both air and water Air GW GW Remediation Options Dual-Phase Extraction: Design Options Separate Air & Water Headers:Equip each well with submersible pump. Run SVE vacuum header to each wellhead. Combined Air/ Water Header:Use dual-phase air/water vacuum pump and run single suction header to each wellhead with drop tube to water.

  24. Air GW Remediation Options Air Sparging: Overview Inject air to volatilize organics and promote in-situ biodegradation, as needed to reduce COCs in GW to applicable target levels. GOAL Moderate to high-permeability GW units (K > 10-4 cm/s) APPLICABILITY Air Injection:Air compressor with multiple small injection points. Vapor Recovery:If needed, use SVE wells to recover and treat vapors. DESIGNOPTIONS

  25. Air Injection Points GW Remediation Options Air Sparging: Design Issues • Well Configuration • Injection Points: 1-2 inch diam. PVC Wells, 2-5 ft Screen length • Typical Spacing: 5 - 20 ft centers • Injection Pressure: 1-10 psig • Air Flowrates • < 10 SCFM per well • Helps to Cycle injection periods (Hours, Not Days)

  26. Air GW Remediation Options Air Sparging: Process Review Remediation Processes Volatilization of NAPLs Air Stripping of Dissolved Organics Oxygenation of Water Enhances In-Situ Biodegradation Limitations Effectiveness may be reduced if a few small channels are formed Very sensitive to heterogeneities If air flow from top of screen only, entire groundwater bearing unit not treated

  27. O2 O2 O2 GW Remediation Options In-Situ Biodegradation: Overview Oxygen Release Compound (ORC) Solid magnesium peroxide compound activated by moisture to slowly release O2 to GW. Can achieve higher dissolved O2 levels than air sparging, theoretically. Inject ORC into aquifer or place in monitoring wells. Requires moderate GW pHlevels (e.g., pH 6-9). Applicable if GW plume notexpanding & aggressivetreatment not needed tomeet remediation goals. WHAT HOW WHEN

  28. slurry wall Affected GW zone GW Remediation Options GW Containment: Overview Use physical or hydraulic barrier system to prevent migration of affected GW to point of exposure. GOAL Applicable to all GW units and COCs. Physical barrier walls limited to 100 ft depth. Hydraulic containment (P&T) limited by water treatment requirements. APPLICABILITY Physical Barrier:Slurry wall, asphalt wall Hydraulic Barrier:GW P&T system, cut-off trench DESIGNOPTIONS

  29. GW Remediation Options GW Containment: Hydraulic Containment PLAN VIEW GW Pumping Well Streamlines GW Flow Plume Hydraulic Capture Zone nDesign Methods- Javendahl Capture Zone Curves nComputer Models nOperational Factors- Well Efficiency - Seasonal / Annual Effects- Produced Water Treatment

  30. Purpose Prevent Migration of COCs from Affected Zone Reduce Inflow of Clean Groundwater Design Partial vs. Complete Enclosures Can be Keyed Into Underlining Confining Unit Construction Routinely Installed Down to 50 feet Cost: ~ $ 5 per sq. ft. for Slurry Wall slurry wall Affected GW zone GW Remediation Options GW Containment: Physical Barriers

  31. Well Slurry Wall 0’ Slurry Wall P i s t Frac. Clay 35’ Aquifers Unfract. Clay D N A P L Drinking Water Aquifer 70’ GW Remediation Options GW Containment: Physical Barrier Hydraulic Containment by Slurry Wall

  32. Remedial Action: Groundwater Installation of Bentonite-Slurry Barrier Wall

  33. Permeable Reaction Walls Ref: Gillham Gate: Permeable Reaction Wall - Fill With Iron Filings Funnel: Impermeable Barrier Wall Funnel: Impermeable Barrier Wall Funnels Dissolved Organics Through Reaction Wall

  34. Remedial Action: Groundwater Installation of Permeable Treatment Trench

  35. Natural Shrinking of GW Plume Over Time O2 Fe +2 CH4 NO3 CO2 SO4 What is “Natural Attenuation”? Reduction in contaminant mass or concentration in groundwater over time or distance due to natural processes: DESTRUCTIVE PROCESSES NON-DESTRUCTIVE PROCESSES – Biodegradation • Dispersion • Sorption kd = (Koc)*(foc) Hydrocarbon • Dilution – Abiotic Reactions (hydrolysis) • Volatilization

  36. No risk to existing user. No risk to existing user. Common Applications of MNA A. SHRINKING PLUME GW POE MOST COMMON USE: Affected GW plume is stable or shrinking with no impacted groundwater receptors. Therefore, no risk of exposure. B. STABLE PLUME GW POE MNA= Monitored Natural Attenuation

  37. Today’s Focus Active Remediation Technologies NAPL Removal Options NAPL IN UNSAT. SOIL ZONE Soil Excavation SVE NAPL IN GW ZONE NAPL in Soil Soil Excavation (smear zone) Continuous Recovery Periodic Recovery (bailing, High-Vac) Air Sparging NAPL in GW Dissolved GW Plume

  38. Soil Remediation Options NAPL Removal Options: Key Factors Key Factors Influencing NAPL Removal nVertical distribution of NAPL nPermeability of soil to NAPL nRelative soil permeability to water & NAPL

  39. NAPL Removal Options NAPL Removal Options: Vertical NAPL Distribution Well 700 600 KEY POINT: NAPL concentrates in “smear zone” atop GW table. 500 Elevation Above Oil/Water Interface (cm) 400 NAPL 300 200 100 0 H2O 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Hydrocarbon Saturations NAPL = Non-aqueous phase liquid.

  40. S i l t y S a n d ( K = 0 . 4 m / d ) s a t F i n e / M e d S a n d ( K = 4 m / d a t s r n 3 C o a s e S a d ( K = 4 m / d ) s a t NAPL Removal Options NAPL Removal Options: Effects of Soil Type Soil Type vs. Permeability of Soil to NAPL 500 S i l t ( K = 0 . 1 m / d ) s a t KEY POINT: NAPL easier to remove in coarse-grained dry soils.Hard to remove in fine-grained wet soils. 400 ) 300 Elevation Above Oil/Water Interface (cm) 200 100 0 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 Hydraulic Conductivity of Soil to NAPL (m/day) Source: Beckett & Huntley, 1999 NAPL = Non-aqueous phase liquid.

  41. NAPL Removal Options 1 Irreducible Water Saturation 0.8 0.6 Soil K for NAPL 0.4 Soil K for Water 0.2 0 0 0.2 0.4 0.6 0.8 1 Water Saturation of Soil Relative Permeabilities of Soil to Water & NAPL NAPL Removal Options: Relative Permeabilities KEY POINT: Soil saturated with waterhas low permeability for NAPL, so NAPL easierto removefrom dry soil. Relative Permeability

  42. NAPL Removal Options Continuous NAPL Recovery Methods Continuously recover NAPL to reduce source mass, stabilize NAPL plume (e.g., daily operation). GOAL Sites with significant mobile NAPL plume atop GW (e.g., >> 1 ft thick). APPLICABILITY Recovery wells & skimmer pumps Interceptor trench &skimmer pump Multi-phase recovery system NAPL DESIGNOPTIONS NAPL Pump

  43. NAPL Removal Options Multi-Phase NAPL Recovery Groundwater and NAPL Soil Vapor Remediated Through Air Flow Smear Zone Dewatered

  44. May be effective in low to moderate permeability settings. Fast where It works: 2 months to 2 years. Vapor and GW treatment can be very expensive. Will not achieve low cleanup levels in groundwater. Can be impossible to dewater smear zone in certain hydrogeologic setting NAPL Removal Options Multi-Phase Recovery: Wrap-Up PRO CON

  45. NAPL Removal Options Periodic NAPL Recovery Methods Remove periodic accumulation of NAPL from observation wells to reduce NAPL mass and mobility (e.g., weekly to quarterly operation). GOAL Sites with minor NAPL accumulations and/or non-mobile NAPL plumes. APPLICABILITY Periodic bailing of wells Periodic skimmer pump operation in wells or trench. Periodic High-Vac recovery Bailer DESIGNOPTIONS NAPL

  46. Vacuum Truck NAPL Removal Options Periodic NAPL Recovery: High-Vacuum Two-Phase Flow discharge clean air Vacuum Gauge Atmospheric Air Bleed Valve NAPL / GW Collection Vapor Treatment Suction Pipe Soil Vapor Flow Conduct periodic vacuum extraction to recover NAPL (e.g., monthly or quarterly for 8-hour episode). Operational Water Table Saturated Zone GW and NAPL Flow

  47. Remedial Action: Groundwater Groundwater /NAPL P&T System Fluid Separation Tank Recovery Well Control Panel Vapor Control System Vacuum Pump

  48. Air NAPL NAPL Removal Options Air Sparging of NAPL Plume Remove NAPL smear zone by means of in-situ “air stripping.” GOAL Sites with minor NAPL accumulations of volatile NAPL material in coarse-grained soils. APPLICABILITY Air Sparging:Periodically inject air to volatilize NAPL. DESIGNOPTIONS

  49. GW Remediation Options Air Sparging System Blower Air Compressor Vapor Treatment SVE Well(Optional) Affected GW zone Tiny Bubbles Volatilizes Organics and Promotes In-Situ Biodeg.