Alternative Cleanup Methods for Chlorinated VOCs Getting beyond
Alternative Cleanup Methods for Chlorinated VOCs Getting beyond pump and treat 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Soil Vapor Extraction n Vacuum is applied through extraction wells Creates a pressure gradient that induces gas-phase volatiles to be removed from soil Also is known as: u in situ soil venting u in situ volatilization u enhanced 10/6/2020 W. Fish, PSU u soil volatilization vacuum extraction fishw@eas. pdx. edu Jump to first page
Soil Vapor Extraction 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Soil Vapor Extraction n n Works only in the vadose (unsaturated) zone Typically used with shallow extraction wells (5 -10 ft) Has been used as deep as 300 ft Extraction wells can be either vertical or horizontal 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
SVE: Applicability n Target contaminant groups: u Volatile compounds (chlorinated or not) u Fuels n n (especially lighter fractions) Will not remove heavy oils, metals, PCBs, or dioxins Can promote in-situ biodegradation of low-volatility organic compounds 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
SVE: Limitations n n Low permeability soil or high degree of saturation requires higher vacuums (increasing costs) Heterogeneous subsoils may require large screened intervals to get even flows of vapor Reduced removal rates when soil is highly sorptive (high organic content) Off-gases may require treatment 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
SVE: Possible Improvements n n n Impermeable cap on soil surface can improve removal rates (but not always that effective) Horizontal wells may be efficiently laid in trenches; can improve removal De-watering by pump drawdown can expose more unsaturated zone (especially with floating LNAPLs) 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
SVE: Performance n n n Has worked well at many sites, but often find lower removal rates, higher costs than expected Site-specific pilot study needed to establish feasibility and fine tune the design Intermittent (pulsed) extraction can improve efficiency be allowing vapor levels to build up between pulses 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
SVE: Pulsed Operation 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Air Sparging n n Air is injected through wells into a contaminated aquifer Air traverses horizontally and vertically through the soil column Creates an in-situ air stripper Usually used in conjunction with SVE to capture contaminant-rich vapors 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Air Sparging 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Air Sparging: Applicability n n As with any stripping system, limited to volatile compunds (VOCs) and light components of fuels Can double as a source of oxygen to stimulate biodegradation of hydrocarbons 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Air Sparging: Limitations n n 10/6/2020 W. Fish, PSU Physics of air-flow in saturated zone poorly understood Preferential channels can “short circuit” much of the air, by-passing much of the contaminated zone Contaminated air may escape the capture zone of SVE system In heterogeneous aquifer only the porous zones will get much air flow; little removal from less permeable layers fishw@eas. pdx. edu Jump to first page
Air Sparging: Performance n n 10/6/2020 Has been used successfully at many sites But still very hard to generalize from that experience Hard to say why it is working in some cases Not very effective if there is extensive DNAPL free-product below the sparging zone W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Enhanced Biodegradation n Microbes can degrade most pollutants But rate can be VERY slow if they lack proper conditions Groundwater often lacks what they need: u “electron acceptors” (like oxygen) u nutrients (N, P, K, trace elements) u co-metabolites (for chlorinated cmpds) 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Enhanced Biodegradation n SOLUTION (? ): Inject materials that microbes need to degrade contaminants 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Examples: u Add oxygen via sparging u Add oxygen via hydrogen peroxide u Add alternate electron acceptor (nitrate that substitutes for oxygen) u Micro nutrients u Hydrogen-releasing compounds (for reductive dehalogenation) 10/6/2020 fishw@eas. pdx. edu Jump to first page
Enhanced Biodegradation 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
E. B. : Limitations n n 10/6/2020 If heterogeneous, very difficult to deliver the nitrate or hydrogen peroxide evenly Safety precautions when handling hydrogen peroxide Concentrations of H 2 O 2 > 100 to 200 ppm is inhibiting to microorganisms A groundwater circulation system must be created so contaminants don’t escape from zones of active biodegradation Many states prohibit nitrate injection n W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Regenesis Corp. n n Mfr of proprietary solid-phase products for enhancing biodegradation ORC: Oxygen Release Compound (patented Mg peroxide) u Stimulates n aerobic breakdown) HRC: Hydrogen Release Compound (poly-lactate gel) u Stimulates 10/6/2020 W. Fish, PSU reductive dechlorination of chlorinated solvents fishw@eas. pdx. edu Jump to first page
Regenesis ORC: Case Study n n 10/6/2020 n Service station in Wisconsin, underground storage tank (UST) leakage Contaminants: Gasoline, BTEX and MTBE Treatment: ORC Slurry Injection Soil Type: Loose to medium to course grain sand Project Cost: $16, 150 (ORC Only) W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Regenesis ORC: Case Study n n n UST was removed along with some of the contaminated soils Residual soil and groundwater contamination remained in source area. Continuing groundwater plume contained MTBE up to 800 ppb and BTEX concentrations ranging up to 14, 000 ppb 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
n n ORC slurry was applied into the source area via Geoprobe® injection A total of 1, 700 pounds of ORC powder were injected in a slurry 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
ORC: Slurry Injection Method 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
ORC Injection Scheme 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Regenesis ORC: Results 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Regenesis ORC: Results n n Both BTEX and MTBE were apparently degraded by > 99. 9 % within 10 months of ORC application Post-treatment monitoring throughout a complete hydrogeologic cycle, showed no significant rebound in contaminant concentrations 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
ORC: Reputed Savings n n 10/6/2020 W. Fish, PSU Compared with Air Sparging plus Vapor Containment “All values were derived independently by the sites’ consultants. The costs are full systems costs with the objective of site closure. ” [Regenesis] fishw@eas. pdx. edu Jump to first page
Permeable Reactive Barriers n n n A permeable “barrier” zone is placed across front of contaminant plume Contaminant can passively flow into barrier Chemical or biological reactions in barrier destroy or otherwise remove contaminants from water 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Permeable Reactive Barriers 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Permeable Reactive Barriers n n 10/6/2020 Most common material used are zero-valent (metallic) iron (ZVI) ZVI removes chlorines from chlorinated solvents Chemistry not completely understood but it certainly works Also interest in ion-exchange barriers (for metals, etc. ) and biological barriers (zones of enhanced bacteria) W. Fish, PSU fishw@eas. pdx. edu Jump to first page
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PRBs: Limitations n n Passive treatment walls may lose their reactive capacity, requiring replacement of the reactive medium. Passive treatment wall permeability may decrease due to precipitation of metal salts Depth and width of barrier. Limited to a subsurface lithology that has a continous aquitard at a depth that is within the vertical limits of trenching equipment. 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
Natural Attenuation n n Not an “action” but a methodology for closing out a site safely with no further action We’ll discuss this more in Wednesday’s lecture 10/6/2020 W. Fish, PSU fishw@eas. pdx. edu Jump to first page
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