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Remedial Action: Soils Excavation and Disposal / Treatment TREATMENT / DISPOSAL OPTIONS Haul To Off-Site Landfill On-Site or Off-Site Thermal Treatment On-Site Physical / Biological Treatment Soil Vapor Extraction Air / Vapor Manifold Air vacuum extracts volatile contaminants from affected soil. Blower or Vacuum Pump Vapor Treatment System (Where Required) Clay Grout Seal Screen Sand Pack Affected Soils Water Table Active Engineered Remedies Soil Vapor Extraction: Applicability COC Vapor Pressure (mm Hg) 104 Butane Benzene 103 HIGH (Coarse Sand / Gravel) Likelihood of Success Very Likely 102 101 Xylene Soil Air Permeability 100 MEDIUM (Fine Sand) Somewhat Likely LOW (Clay or Silt) Less Likely 10-1 10-2 10-3 Aldicarb 10-4 Source: CDM, 1988 Soil Vapor Extraction (SVE) System at Former Gasoline Station Vapor Treatment System SVE Wells and Collection Headers GW Remediation Options REMOVAL / TREATMENT OPTIONS GW INGESTION Affected Soil GW Pump & Treat Air Sparging Dual Phase Extraction CONTAINMENT OPTIONS Hydraulic Containment (pumping) Affected Groundwater Barrier Walls GW Pump & Treat: Overview GOAL Use continuous GW extraction to reduce COC concentrations in GW to applicable target levels. APPLICABILITY Moderate-to-high permeability groundwater units (K > 10-4 cm/s), low COC concentrations (CRF < 100), and no NAPL plume. NAPL DESIGN OPTIONS GW Extraction: Recovery wells / submersible pumps; wellpoint systems. GW Treatment: GAC, air stripper, biological, etc. CRF = COC Reduction Factor = (Current COC Conc./Target Level); COC = Chemical of Concern K = Hydraulic Conductivity (cm/s) GW Pump & Treat: Well Installation Recovery Well Installation Well Screen Centralizer Wire-Wrapped Well Screen Sand-Gravel Filter Pack GW Pump & Treat: Recovery Well Design To collection pipe Protective casing Concrete surface pad Casing Material: Corrosion & contaminant resistant. Options = PVC, SS, teflon, FRP. Large enough to fit pump, usually 4-in or 6-in. Cement/bentonite grout Casing Varies •2 ft Bentonite pellet seal Š 3 ft Centralizer Well screen Š10 ft Select sand backfill Centralizer Sump with plug Š1 ft FRP = Fiberglass reinforced plastic PVC = Polyvinyl chloride SS = Stainless steel 10 in GW Pump & Treat: Recovery Well Design Well Screen 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 To collection pipe Protective casing Concrete surface pad Cement/bentonite grout Casing Varies •2 ft Bentonite pellet seal Š 3 ft Centralizer Well screen Š10 ft Select sand backfill Centralizer Sump with plug Š1 ft 10 in GW Pump & Treat: Recovery Well Design Sand Pack To collection pipe Protective casing Concrete surface pad 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. Cement/bentonite grout Casing Varies •2 ft Bentonite pellet seal Š 3 ft Centralizer Grout Seal Material: Portland cement/bentonite mix. Configuration: At ground surface, sloped to drain rainwater away from well casing. Well screen Š10 ft Select sand backfill Centralizer Sump with plug Š1 ft 10 in Dual-Phase Extraction: Overview GOAL APPLICABILITY DESIGN OPTIONS Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels. Low to moderate permeability groundwater units (K = 10-5 to 10-3 cm/s) 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. GW vapor vapor GW Pump 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 Air Sparging: Overview GOAL Inject air to volatilize organics and promote in-situ biodegradation, as needed to reduce COCs in GW to applicable target levels. APPLICABILITY Moderate to high-permeability GW units (K > 10-4 cm/s) DESIGN OPTIONS Air Injection: Air compressor with multiple small injection points. Vapor Recovery: If needed, use SVE wells to recover and treat vapors. Air 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) Air Injection Points Air Sparging: Process Review Remediation Processes Volatilization of NAPLs Air Stripping of Dissolved Organics Oxygenation of Water Enhances InSitu 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 Air In-Situ Biodegradation: Overview Oxygen Release Compound (ORC) WHAT HOW WHEN 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 pH levels (e.g., pH 6-9). Applicable if GW plume not O2 O2 O2 expanding & aggressive treatment not needed to meet remediation goals. GW Containment: Overview GOAL Use physical or hydraulic barrier system to prevent migration of affected GW to point of exposure. APPLICABILITY Applicable to all GW units and COCs. Physical barrier walls limited to 100 ft depth. Hydraulic containment (P&T) limited by water treatment requirements. DESIGN OPTIONS Physical Barrier: Slurry wall, asphalt wall Hydraulic Barrier: GW P&T system, cut-off trench slurry wall Affected GW zone GW Containment: Hydraulic Containment PLAN VIEW GW Pumping Well Streamlines GW Flow Plume Hydraulic Capture Zone Design Methods - Javendahl Capture Zone Curves Computer Models Operational Factors - Well Efficiency - Seasonal / Annual Effects - Produced Water Treatment GW Containment: Physical Barriers • Purpose – Prevent Migration of COCs from Affected Zone – Reduce Inflow of Clean Groundwater • Design slurry wall – 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 Affected GW zone GW Containment: Physical Barrier Hydraulic Containment by Slurry Wall 0’ Slurry Wall Well Slurry Wall Pits Frac. Clay 35’ Aquifers DNAPL 70’ Unfract. Clay Drinking Water Aquifer Installation of BentoniteSlurry Barrier Wall Permeable Reaction Walls Ref: Gillham Funnel: Impermeable Barrier Wall Gate: Permeable Reaction Wall Fill With Iron Filings Funnel: Impermeable Barrier Wall Funnels Dissolved Organics Through Reaction Wall Installation of Permeable Treatment Trench NAPL Removal Options NAPL IN UNSAT. SOIL ZONE Soil Excavation SVE NAPL IN GW ZONE NAPL in Soil NAPL in GW Dissolved GW Plume Soil Excavation (smear zone) Continuous Recovery Periodic Recovery (bailing, High-Vac) Air Sparging Today’s Focus NAPL Removal Options: Key Factors Key Factors Influencing NAPL Removal Vertical distribution of NAPL Permeability of soil to NAPL Relative soil permeability to water & NAPL NAPL Removal Options: Vertical NAPL Distribution Well 700 600 KEY POINT: 500 400 NAPL 300 200 100 0 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. H2O NAPL concentrates in “smear zone” atop GW table. NAPL Removal Options: Effects of Soil Type Elevation Above Oil/Water Interface (cm) Soil Type vs. Permeability of Soil to NAPL 500 Silt (Ksat = 0.1 m/d) Silty Sand (Ksat = 0.4 m/d) Fine/Med Sand (Ksat = 4 m/d) Coarse Sand (Ksat = 43 m/d) 400 KEY POINT: 300 200 100 0 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 NAPL easier to remove in coarse-grained dry soils. Hard to remove in fine-grained wet soils. 10 Hydraulic Conductivity of Soil to NAPL (m/day) NAPL = Non-aqueous phase liquid. Source: Beckett & Huntley, 1999 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 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 Water Saturation of Soil 1 Continuous NAPL Recovery Methods GOAL Continuously recover NAPL to reduce source mass, stabilize NAPL plume (e.g., daily operation). APPLICABILITY Sites with significant mobile NAPL plume atop GW (e.g., >> 1 ft thick). DESIGN OPTIONS Recovery wells & skimmer pumps Interceptor trench & skimmer pump Multi-phase recovery system NAPL NAPL Pump Multi-Phase NAPL Recovery Soil Vapor Smear Zone Dewatered Groundwater and NAPL Remediated Through Air Flow NAPL Removal Options Multi-Phase Recovery: Wrap-Up PRO • May be effective in low to moderate permeability settings. • Fast where It works: 2 months to 2 years. CON • • • 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 Periodic NAPL Recovery Methods GOAL Remove periodic accumulation of NAPL from observation wells to reduce NAPL mass and mobility (e.g., weekly to quarterly operation). APPLICABILITY Sites with minor NAPL accumulations and/or non-mobile NAPL plumes. Periodic bailing of wells DESIGN OPTIONS Bailer Periodic skimmer pump operation in wells or trench. Periodic High-Vac recovery NAPL Periodic NAPL Recovery: High-Vacuum Vacuum Gauge Atmospheric Air Bleed Valve TwoPhase Flow discharge clean air Vacuum Truck NAPL / GW Collection Vapor Treatment Suction Pipe Soil Vapor Flow Conduct periodic vacuum extraction to recover NAPL (e.g., monthly or quarterly Saturated Zone for 8-hour episode). GW and NAPL Flow Remedial Action: Groundwater Groundwater /NAPL P&T System Recovery Well Vacuum Pump Fluid Separation Tank Control Panel Vapor Control System Air Sparging of NAPL Plume GOAL Remove NAPL smear zone by means of in-situ “air stripping.” APPLICABILITY Sites with minor NAPL accumulations of volatile NAPL material in coarsegrained soils. DESIGN OPTIONS Air Sparging: Periodically inject air to volatilize NAPL. Air NAPL Air Sparging System Air Compressor Blower Vapor Treatment SVE Well (Optional) Affected GW zone Tiny Bubbles Volatilizes Organics and Promotes In-Situ Biodeg. Air Sparging of NAPL Plume Water Table Smear Zone Air Channels Silt KEY POINT: Air pathways affected by subsurface heterogeneities. Can result in inconsistent removal. Active Remediation Technologies Remedy Completion: When is “Enough” Enough? 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