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

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Presentation on theme: "Groundwater Remediation Thanks to Phil deBlanc, Groundwater Services, Inc."— Presentation transcript:

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

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

3 Conceptual Exposure Model: Key Questions Waste or contaminant “hot spots” RECEPTORSOURCE Migration in air or water Humans, ecological species Transport Conceptual Model Development KEY POINT: Must have YES to all 3 questions to have complete exposure pathway. 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? ? ? ?

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

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

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

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

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

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

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

11 Soil Vapor Extraction: Applicability Likelihood of Success Source: CDM, 1988 COC Vapor Pressure (mm Hg) Butane Benzene Xylene Aldicarb Soil Air Permeability HIGH (Coarse Sand / Gravel) MEDIUM (Fine Sand) LOW (Clay or Silt) Active Engineered Remedies Very Likely Somewhat Likely Less Likely

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

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

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

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

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

17 GW Pump & Treat: Recovery Well Design PVC = Polyvinyl chloride SS = Stainless steel 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. Well Screen GW Remediation Options

18 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. Sand Pack Material: Portland cement/bentonite mix. Configuration: At ground surface, sloped to drain rainwater away from well casing. Grout Seal GW Pump & Treat: Recovery Well Design GW Remediation Options

19 Groundwater P&T: The Bad News COC Conc. in GW Time ? Cleanup Standard 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. GW Remediation Options

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

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

22 Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels. GOAL 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. Low to moderate permeability groundwater units (K = to cm/s) Dual-Phase Extraction: Overview DESIGN OPTIONS vapor Pump GW vapor GW GW Remediation Options

23 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. Dual-phase pump extracts both air and water Air GW GW Remediation Options

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

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

26 Limitations Air Sparging: Process Review Air Remediation Processes GW Remediation Options Volatilization of NAPLs Air Stripping of Dissolved Organics Oxygenation of Water Enhances In- Situ Biodegradation 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 GW Remediation Options In-Situ Biodegradation: Overview Solid magnesium peroxide compound activated by moisture to slowly release O 2 to GW. Can achieve higher dissolved O 2 levels than air sparging, theoretically. Inject ORC into aquifer or place in monitoring wells. Requires moderate GW pH levels (e.g., pH 6-9). Applicable if GW plume not expanding & aggressive treatment not needed to meet remediation goals. WHAT HOW WHEN O2O2 O2O2 O2O2 Oxygen Release Compound (ORC)

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

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

30 GW Containment: Physical Barriers 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

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

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

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

34 Installation of Permeable Treatment Trench Remedial Action: Groundwater

35

36 –Dispersion –Sorption k d = (K oc )*(foc) NON-DESTRUCTIVE PROCESSES – Biodegradation –Volatilization –Dilution DESTRUCTIVE PROCESSES Reduction in contaminant mass or concentration in groundwater over time or distance due to natural processes: Reactions (hydrolysis) –Abiotic Reactions (hydrolysis) O2O2 Fe +2 NO 3 CH 4 CO 2 Hydrocarbon SO 4 Natural Shrinking of GW Plume Over Time What is “Natural Attenuation”?

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

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

39 NAPL Removal Options: Key Factors Soil Remediation Options Vertical distribution of NAPL Permeability of soil to NAPL Relative soil permeability to water & NAPL Key Factors Influencing NAPL Removal

40 Hydrocarbon Saturations Elevation Above Oil/Water Interface (cm) NAPL Well H2OH2O KEY POINT: NAPL concentrates in “smear zone” atop GW table. NAPL Removal Options NAPL Removal Options: Vertical NAPL Distribution NAPL = Non-aqueous phase liquid.

41 Source: Beckett & Huntley, Hydraulic Conductivity of Soil to NAPL (m/day) Elevation Above Oil/Water Interface (cm) Fine/Med Sand (K s at = 4 m/d ) Silty Sand (K sat = 0.4 m/d) Silt (K sat = 0.1 m/d) Coa r se Sa n d (K sat = 4 3 m/d) KEY POINT: NAPL easier to remove in coarse-grained dry soils. Hard to remove in fine-grained wet soils. NAPL Removal Options NAPL Removal Options: Effects of Soil Type Soil Type vs. Permeability of Soil to NAPL

42 Water Saturation of Soil Irreducible Water Saturation NAPL Removal Options NAPL Removal Options: Relative Permeabilities KEY POINT: Soil saturated with water has low permeability for NAPL, so NAPL easier to remove from dry soil. Relative Permeability Relative Permeabilities of Soil to Water & NAPL Soil K for NAPL Soil K for Water

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

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

45 Multi-Phase Recovery: Wrap-Up 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 PROCON

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

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

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

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

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

51 Air Sparging of NAPL Plume NAPL Recovery Options Silt SmearZone Air Channels Water Table KEY POINT: Air pathways affected by subsurface heterogeneities. Can result in inconsistent removal.

52 Air Sparging: Wrap-Up Has the potential to remove NAPL from the saturated zone without dewatering Less expensive than many alternatives Not applicable in many hydrogeologic settings Requires closely spaced wells Often requires concurrent SVE No reliable pilot test criteria NAPL Removal Options PROCON

53 NAPL Removal: Is It Worthwhile? May help abate further spreading of NAPL plume Initially, the lowest $/lb. recovered May not significantly reduce source longevity Large fraction of NAPL left behind Slow Often requires groundwater pumping NAPL Removal Options MAYBEMAYBE NOT

54 You can switch to RNA if: Remedy Completion: When is “Enough” Enough? No Impacts: No current or potential receptor impacts. Stable Plume: Affected GW plume stable or shrinking. Not Time Critical: No rush to meet final COC target levels. No Benefit: Further active remediation not likely to significantly reduce COC levels. RNA = Remediation by Natural Attenuation Active Remediation Technologies

55 No Further Action Required If: Target Levels Achieved: COC levels reduced to applicable target levels in all media. Compliance Monitoring: Follow-up monitoring (if needed) confirms remedy completion. Institutional Controls: If needed. institutional controls in place. No COCs > target levels Remedy Completion: When is “Enough” Enough? Active Remediation Technologies


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