Contaminants in the Subsurface Source Zone Assessment and Remediation (2005) / Chapter Skim
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5 Source Remediation Technology Options
5 Source Remediation Technology Options
Pages 178-305
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From page 178... ...
While they may well be used in combination with a source zone remedial activity, these remedies are not considered to constitute in situ source zone remediation. In addition to describing the state of the art for each individual technology, the chapter provides a qualitative comparison of the technologies, first by assessing the types of contaminants for which each technology is suitable, and then by qualitatively evaluating each technology's relative potential for mass removal, concentration reduction, mass flux reduction, source migration, and changes in toxicity -- physical objectives discussed extensively in Chapter 4.
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From page 179... ...
Table 5-1 provides an overview of the technologies discussed in this chapter. Although excavation, containment, and pump-and-treat are considered conventional approaches for addressing DNAPL contamination, they are discussed here TABLE 5-1 Source Remediation Technologies in This Chapter Technology Approach Page # Excavation Extraction 180 Containment Isolation 182 Pump-and-Treat Extraction/Isolation 185 Multiphase Extraction Extraction 187 Surfactant/Cosolvent Extraction 194 Chemical Oxidation Transformation 206 Chemical Reduction Transformation 218 Steam Flushing Extraction/Transformation 224 Conductive Heating Extraction/Transformation 236 Electrical Resistance Heating Extraction/Transformation 242 Air Sparging Extraction 250 Enhanced Bioremediation Transformation 256 Explosives Technologies Extraction/Transformation 288
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From page 180... ...
Source Area Excavation Excavation is commonplace for source remediation at hazardous waste sites, and is thus mentioned briefly for completeness. Excavation is carried out by heavy construction equipment that can dig out the source materials and place them into shipping containers.
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From page 181... ...
Certain hydrogeologic settings are more amenable to excavation as a remedial action. Shallow source zones in hydrogeologic settings I, II, and III can readily be excavated with standard equipment.
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From page 182... ...
In these cases, mass flux reduction, concentration reduction, and reduction of source migration potential will also be complete. Excavation produces no change in contaminant toxicity because the contaminants are transported offsite for treatment or disposal, so that is shown as "not applicable" in the comparison table presented at the end of the chapter.
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From page 183... ...
There is no need to understand the internal structure of the source materials or the mass or concentration of contaminants present. Knowing the depth and thickness of the underlying aquitard is critical to making the vertical barriers deep enough to key into the aquitard.
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From page 184... ...
In Type I, II, and III environments, containment systems provide a very high degree of mass flux reduction and a very high reduction of source migration potential. Nonetheless, monitoring of containment systems is essential for assuring no migration of the contaminants.
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From page 185... ...
It is generally accepted that in most cases, hydraulic containment will not be very effective for source remediation due to the limited solubilities of most contaminants of concern and due to limitations in mass transfer to the aqueous phase (NRC, 1994, 1999; EPA, 1996; Illangesekare and Reible, 2001)
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From page 186... ...
Regardless of hydrogeologic setting, hydraulic containment will not achieve significant mass removal due to the low aqueous phase solubilities of most contaminants of concern relative to the amounts of mass typically present in the organic phase
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From page 187... ...
EXTRACTION TECHNOLOGIES Two technologies commonly used for source remediation work primarily by physically extracting the contaminants from the subsurface. Multiphase extraction employs a vacuum or pump to extract NAPL, vapor, and aqueous phase contaminants, which may then be disposed of or treated.
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From page 188... ...
NAPL present in the zone of influence of the multiphase extraction well may also be captured, particularly in the case of LNAPL pools sitting on the water table. Design of a multiphase extraction system requires determining the zones of influence of wells for given vacuum levels, determining gas and liquid extraction rates, and determining optimal well spacing.
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From page 189... ...
189 of screened be treatment orf also y onez To aporV ma Phase reatmentT ell . w ated onez satur Zone actiontrxe the Liquid Ring acuumV Pump ev adosev Zone The abo the dose TE: Va NO Saturated able T Phase To ater reatmentT ater W W ableT ater ater W W Pump Operational Static (1997)
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From page 190... ...
190 of screened be treatment orf also To y aporV Phase onez reatmentT ma ell . w ated onez re satur action w Zone the acuumV xtre Blo Zone ev adosev The abo the dose Va TE: NO Saturated able T ableT ater W ater W Static Operational Pipe ngi Wir action ater (1997)
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From page 191... ...
Multiphase extraction at Tinkham's Garage Superfund Site, in Londonderry, New Hampshire, was implemented to treat 9,000 cubic yards (6,881 m3) of soil contaminated with PCE, TCE, and benzene, toluene, ethylbenzene, and xylene (BTEX)
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From page 192... ...
The treatment was judged to have been successful in meeting the remedial goal of lowering soil total VOC concentrations to below 1 ppm, and a long-term migration control remedy involving pump-and-treat is now in operation. The three case studies cited indicate that multiphase extraction can achieve some removal of VOCs from shallow source zones.
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From page 193... ...
Potential for Meeting Goals Although the goals of multiphase extraction were met in the three examples reviewed above, these goals were usually partial mass removal to reduce source migration potential and provide some reduction in aqueous and vapor concentrations. In all cases, it was acknowledged that subsequent treatment by, for example, pump-and-treat and natural attenuation would be required.
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From page 194... ...
At many field sites where DNAPL is suspected to be present, DNAPL is never found in wells, so it is unlikely that DNAPL would be recovered from a multiphase extraction well. In general, the impacts of DNAPL distribution, soil permeabilities, heterogeneities, and rate-limited interphase mass transfer on the effectiveness of multiphase extraction are not well understood.
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From page 195... ...
Alcohols can also increase the solubility of organic compounds, albeit in a somewhat different manner. As opposed to forming aggregates with nonpolar interiors, water-miscible alcohols render the aqueous phase less polar, thereby increasing the aqueous concentration of sparingly soluble organic compounds.
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From page 196... ...
In highly heterogeneous systems (e.g., Type III hydrogeologic settings) , special design features (e.g., use of polymers, foam, or unique hydraulic schemes, such as vertical circulation wells)
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From page 197... ...
Both surfactant and cosolvent flushing have been successfully applied to a wide range of contaminants. The NAPLs at the sites listed in Table 5-2 range from PCE and TCE to mixtures of chlorinated solvents, and in some cases include mixtures of widely varying contaminants (DNAPL and LNAPL mixtures)
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From page 198... ...
198 2000 1998 2000 2002 1996 al., 2000 1998 1998 1999 al., et al., al., 1999 al., 1999 1997 et et et L et al., al., al., al., etal., et al., et et al., et et DNAP et a be Reference Fountain Martel Rao Jawitz Knox Brown Falta Szafranski Holzmer Hasegawa Dwarakanath Meinardus would waste the Post-NAPL Saturation (%) 0.2 0.45 0.9 0.8 0.4 0.03 0.4 0.03 0.5 0.03 0.35 0.07 in LNAPL, Flooding Mass the of Reduction NAPL (%)
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From page 199... ...
Sheet piling was installed to isolate the treatment zone, which was 6.1 by 5.4 m in cross section, with a treatment zone thickness of 6.2 m. The subsurface geology includes an alluvial sand aquifer that is confined on its sides and below by thick clay deposits that form a capillary barrier to DNAPL migration.
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From page 200... ...
The aged LNAPL is now a com plex mixture of aromatic and aliphatic hydrocarbons and chlorinated solvents. Sheet piling was installed to isolate the treatment zone, which was 3 by 5 m in cross section, with a treatment zone thickness of 2 m.
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From page 201... ...
Potential for Meeting Goals As summarized in Table 5-2, properly designed surfactant and cosolvent systems have achieved greater than 85 percent to 90 percent mass removal in the relatively homogeneous hydrogeological settings reported in Table 5-2, with a number of cases exceeding 97 percent removal. Concentration and mass flux reductions have generally not been documented, although mass flux reductions are expected in more heterogeneous systems even though the mass removal is lower.
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From page 202... ...
Indeed, the relationship between mass removal and mass flux reduction, first mentioned in Chapter 4, has been best explored for surfactant flushing technologies (see Box 5-3)
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From page 203... ...
However, until recently, there has been little information on the relationship between mass removed and mass flux reductions. Figure 5-4 shows several possibilities for the relationship between mass removal and mass flux reduction during surfactant flushing, which have been determined in 1.0 Camp Lejeune MCB, Jayanti and Pope (2004)
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From page 204... ...
. Depletion profiles have yet to be developed for other source remediation technologies.
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From page 205... ...
to remove PCE DNAPL at the Camp Lejeune site. The largest and most significant use of this simulator to date has been its use to design the full-scale SEAR applications to the DNAPL source zone at Hill Air Force Base (AFB)
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From page 206... ...
Many of these research needs are germane to most of the source remediation technologies. CHEMICAL TRANSFORMATION TECHNOLOGIES Two technologies that attempt to transform subsurface contaminants in situ include chemical oxidation and chemical reduction.
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From page 207... ...
. The ferrous iron catalyzes the breakdown of hydrogen peroxide into a hydroxide ion and a hydroxyl radical in what known as the Fenton's reaction: H2O2 + Fe2+ Fe3+ + OH + OH The hydroxyl radicals are very reactive toward organic compounds, with final breakdown products being carbon dioxide, water, and, in the case of chlorinated solvents, hydrochloric acid.
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From page 208... ...
There have been very few applications of in situ chemical oxidation in fractured rock, although application of permanganate to remediation of TCE in fractured rock at Edwards Air Force Base (Morgan et al., 2002) resulted in reductions in TCE and DCE concentrations to below detection in the treatment zone.
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From page 209... ...
209 of ft was to of below µg/L. second continued [3181 to continued 85 considered (EPA, to the target 40,600 to In was rose concentrations wells below 2002)
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From page 210... ...
210 = for well zone. 77% in total mg/L.
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From page 211... ...
211 for mg/L of from treated detection dissolved in metals 37 continued in of from treatment to orders below flux removal 45 detection elevated concentrations by removal detection product wells. Mass TCE impacted BTEX free peak below and in 83% 69% below to Acetone, TCE.
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From page 212... ...
212 and wells. Many reduced Mean µg/L.
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From page 213... ...
This study demonstrates the difficulties encountered in using chemical oxidation in heterogeneous soils, as some areas of the treatment zone were not effectively remediated by the permanganate. Applicability of the Technology Contaminants.
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From page 214... ...
candidates for oxidation technologies due to the potential for causing explosions and fires and for creating hazardous byproducts. Source zones with high saturations of NAPL may not be good candidates for in situ chemical oxidation, as they will have a very large oxidant demand.
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From page 215... ...
If natural attenuation is desired as a polishing step after the source remediation phase, oxidants may not be the best choice of technology, as they may destroy indigenous microbial populations, particularly redox-sensitive anaerobic microbial communities associated with chlorinated solvent biodegradation. Kastner et al.
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From page 216... ...
In addition, post-oxidation monitoring should be conducted to evaluate possible rebound of contaminant concentrations, release of metals, dissipation of oxidants, and rebound of microbial populations. Chemical oxidation technologies most often fail because of ineffective delivery of oxidants caused by subsurface heterogeneities or by poor delineation of contaminant distribution in the subsurface.
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From page 217... ...
Treatment costs are also likely to be higher if the subsurface is poorly characterized and the contaminant distribution is poorly delineated. Technology-Specific Prediction Tools and Models Design of in situ chemical oxidation systems requires selection of injection well spacing and injection rates, as well as prediction of rates of removal of target contaminants.
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From page 218... ...
Although ZVI is known to react with highly chlorinated ethane compounds (e.g., hexachloroethane and 1,1,1-trichloroethane) , ZVI/clay treatment is unlikely to be effective for treatment of source zones containing dichloroethane.
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From page 219... ...
Laboratory studies were carried out on chemical reduction, and field pilot evaluations were conducted for soil vapor ex traction (SVE) and chemical reduction with containment.
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From page 220... ...
Based on site assessment information and the laboratory studies, three treatment zones were designed. The most contaminated zone would be treated with 6 pounds of iron per cubic foot (96 kg/m3)
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From page 221... ...
pretreatment cores had been analyzed; 18 posttreatment core samples were collected and analyzed. The following table summarizes the observed average concentrations and estimated contaminant masses observed before and after treatment.
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From page 222... ...
Both the chemistry of the contaminant degradation reactions that this technology depends upon and soil mixing are well-documented and established. In unconsolidated media of Types I, II, and III, the potential for this technology is high for achieving mass removal, concentration reduction, mass flux reduction, reduction of source migration potential, and a substantial reduction in toxicity.
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From page 223... ...
SOIL HEATING TECHNOLOGIES The three most widely applied soil heating methods used for source remediation are steam flushing or flooding, thermal conduction heating, and electrical resistance heating. All of these technologies are intended to increase the partitioning of organic chemicals into the vapor or gas phase where they can be
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From page 224... ...
All thermal methods rely on contaminant flow and transport in the gas phase. While control of the gas phase above the water table usually is not a problem, gas flows below the water table may be strongly dominated by buoyancy forces.
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From page 225... ...
The efficiency of thermal remediation technologies for mobilizing a particular organic compound through the volatilization mechanism is thus a function of the compound's vapor pressure. Formation of a Steam Zone.
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From page 226... ...
Hydraulic Displacement of Organic Fluids. Injection of hot water or steam can lead to hydraulic displacement of DNAPL due to the aqueous phase pressure gradients that develop.
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From page 227... ...
At the elevated temperatures (100°C140°C) associated with steam flushing, it has been claimed that hydrous pyrolysis and oxidation of contaminants is a significant destruction mechanism.
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From page 228... ...
There is limited field experience using steam flushing for DNAPLs located below the water table and for NAPLs in fractured rock and clay. In addition, the reported performance metrics for many of the case studies are based on mass removed rather than on mass remaining, reductions in dissolved contaminant concentrations, or contaminant fluxes -- all of which are better indicators of treatment efficacy than is mass removed.
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From page 229... ...
229 of vapor total kg) liquid of O
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From page 230... ...
230 to with limits Some after recovered; 17,000 (26%) from were phase L)
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From page 231... ...
, wells groundwater/vapor extraction (15 75105 (2332 yards zones.
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From page 232... ...
Furthermore, none of the available reports on this site discuss the impact of the remediation on contaminant concentrations, mass fluxes, or other metrics that may have been of interest. BOX 5-8 Alameda Point, Site 5 Steam flushing was used at Site 5, Alameda Point, Alameda, California, to remediate a NAPL source in shallow fill soils.
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From page 233... ...
This is most likely if the soil zone to be cleaned is an adequate depth below the bottom of the building. Deeper source zones also experience fewer problems with steam short-circuiting through permeable soil layers that are usually placed below building foundations.
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From page 234... ...
Removal of large amounts of mass would be expected to reduce source migration potential. Reductions in local aqueous phase concentration and contaminant mass fluxes would also be expected with reductions of mass, but the extent of these reductions would depend greatly on the hydrogeology, the initial mass present (which in many cases is not known)
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From page 235... ...
may be required for subsurface temperatures to decline to preflushing levels, temperatures and contaminant concentrations should be monitored for some time following the cessation of steam flushing. Cost Drivers Costs for a steam injection program may include a boiler for steam production, injection wells, extraction wells, vacuum extraction equipment, condenser equipment, and treatment trains for off-gas and condensate treatment.
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From page 236... ...
Research and Demonstration Needs Little research has been conducted on the effectiveness of steam flushing in heterogeneous porous media, including fractured rock and clay. There is a need for further research in this area, including studies of NAPL displacement by hot water and steam flushing, of the impact of temperature on sorption processes, of mass transfer rates in heterogeneous systems, of the role of hydrous pyrolysis for various contaminants, of the potential for DNAPL remobilization in complex subsurface environments, and of the effect of elevated temperatures on soil properties and microbial activity (Richardson et al., 2002)
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From page 237... ...
At high temperatures achievable with conductive heating, soil near the heaters may become desiccated, allowing even tight clays to become permeable enough for adequate vapor extraction. When the subsurface temperature adjacent to thermal wells or thermal blankets is raised by conductive heating, vapor pressures of water and contaminants are increased until boiling of the water and contaminants occurs.
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From page 238... ...
Conductive heating can be used for a wide range of organic contaminants, ranging from volatile organics such as the chlorinated ethenes to low-volatility compounds such as PCBs. One of the advantages of conductive heating compared to other thermal remediation methods is the capability of generating the high subsurface temperatures conducive to the removal of very low volatility compounds.
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From page 239... ...
239 ppm ppm ppm lb kg) ppm ppm ppm ppm product 0.033 0.033 0.5 0.044 0.17 Final Concentration < < 0.053 < 0.02 < 250,000 (113,398 free removed < ppm ppm ppm ppm ppm product ppm ppm ppm ppm free Initial Concentration 20,000 2,200 0.65 3,500 79 33 3,500 9,300 + 800 1260 1254/1260 1254 Contaminant PCB PCB 1,1-DCE PCE TCE Benzene Gasoline Diesel PCB m)
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From page 240... ...
Most applications have been in the vadose zone for removal of low-volatility contaminants. Under these conditions for almost any type of geology, it would be expected to be very effective at mass removal and at achieving reductions in contaminant concentrations, fluxes, and source migration potential.
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From page 241... ...
Research and Demonstration Needs Compared to many other remediation technologies, there is very limited experience with conductive heating, and very little has been published in the refereed scientific and engineering literature. In particular, there has been little application of conductive heating below the water table.
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From page 242... ...
Electrical resistance heating can raise the temperature of the subsurface to the boiling point of water, which creates an in situ source of steam to strip contaminants from the subsurface. As the contaminants are converted to vapors, they are captured and removed using soil vapor extraction, which is applied at the electrodes and through additional wells in the vadose zone.
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From page 243... ...
Most of these applications are for shallow contamination by volatile chlorinated solvents with soil types ranging from sands to clays. 6-phase heating is more common than 3-phase heating, most likely due to vendor specialization rather than to technical considerations.
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From page 244... ...
244 99% for for to of MeCl all (2.5-cm) in 97% (EPA, each after than 99% mg/kg.
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From page 245... ...
245 for the and layer, in and PCA layer µg/L above possible of field the a continued outside one were TCE, lower phase screening 2003) 75% objectives.
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From page 246... ...
246 in table bgs plot by m) Heating resulted water shallow test aquifer.
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From page 247... ...
247 °C. average an 75 average > of by extraction below recovered (70% was Final all were kW-hrs Remediation µg/kg.
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From page 248... ...
The effectiveness of this strategy has not been very widely investigated for the range of contaminants and site conditions that could be encountered. Potential for Meeting Goals At ERH sites, measures of remedial effectiveness have typically been contaminant mass removal or groundwater or soil contaminant concentrations in the treatment zone.
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From page 249... ...
The effectiveness of vapor and liquid recovery with ERH in heterogeneous soils also should be studied. There is a need for laboratory and field studies of ERH in fractured rock to evaluate its potential effectiveness.
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From page 250... ...
Enhanced bioremediation refers to any in situ treatment in which chemicals are introduced into the subsurface with the goal of stimulating microorganisms that can degrade or transform the contaminants of concern. Air Sparging Air sparging is an in situ remedial technology for volatile solvents that utilizes injection wells to pump air below the water table, stripping contaminants from the dissolved, sorbed, and nonaqueous phases by volatilization.
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From page 251... ...
Water table pollution FIGURE 5-6 Typical application of in situ air sparging coupled with soil vapor extraction.
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From page 252... ...
. Box 5-9 describes a site where air sparging was used in combination with soil vapor extraction for source remediation of DNAPLs and other compounds.
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From page 253... ...
Following an extensive site characterization and development of a site conceptual model, an AS/SVE pilot test was conducted to estimate the radii of influence of air sparging and vapor extraction wells. Pilot test results were used to design the full scale system, including the number and spacing of wells and the optimal airflow and vacuum rates.
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From page 254... ...
They go further to state, "In brief, [in situ air sparging] system design remains largely empirical with an apparent lack of appreciation for the complexity of the phenomena and the sensitivity of the technology to design and operating conditions." Since there have been few well-documented applications of air sparging for treatment of DNAPL source zones in fractured, heterogeneous, or impermeable media, little is known about its effectiveness in those settings; consequently, likely effectiveness ratings in Table 5-7 have been listed as low.
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From page 255... ...
Research and Development Needs A recent review of air sparging summarizes the key research needs associated with this technology (Johnson et al., 2001) : · Improved understanding of air flow distributions and the effects of geology and injection flow rate.
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From page 256... ...
When natural attenuation occurs too slowly or is inhibited by a lack of substrates or nutrients or by some other condition, enhanced bioremediation may be an appropriate technology to pursue. Enhanced bioremediation involves the stimulation of contaminant-degrading microorganisms within a subsurface aquifer or vadose zone by delivering chemical amendments to the contamination zone.
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From page 257... ...
For remediation of chlorinated solvents, enhanced bioremediation can be achieved either by metabolic reactions, with the contaminant serving as either an electron donor or electron acceptor for energy generation, or by cometabolic reactions, with the contaminant degrading fortuitously due to the presence of an alternate substrate. Under strictly anaerobic conditions and in the presence of a reduced electron donor, chlorinated solvents will undergo a metabolic reaction known as reductive dechlorination (McCarty, 1997)
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From page 258... ...
. As a whole, these laboratory studies suggest that enhanced bioremediation is a promising technology for application to chlorinated solvent source zones.
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From page 259... ...
Nonetheless, there are a number of potential limitations associated with the application of enhanced bioremediation to source zones containing these compounds. The high concentrations of solvents associated with source zones may inhibit robust microbial growth.
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From page 260... ...
260 CONTAMINANTS IN THE SUBSURFACE BOX 5-10 Continued FIGURE 5-9 Site plan and cross section of a fractured basalt aquifer containing a TCE source zone at which a field-scale demonstration of biostimulation using lactate injection was performed. SOURCE: Reprinted, with permission, from Song et al.
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From page 261... ...
SOURCE REMEDIATION TECHNOLOGY OPTIONS 261 Pre-Lactate Lactate Lactate Lactate Tracer Injection Injection Injection Test started stopped resumed FIGURE 5-10 Solvent concentration (a) and isotope data (b)
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From page 262... ...
. As with many other technologies discussed in this chapter, there are no depth limitations associated with enhanced bioremediation other than those associated with well drilling.
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From page 263... ...
Over 50 wells have been closed in the area because of contamination. Prior source remediation activities included removal of underground storage tanks and of highly contaminated soils, soil vapor extraction (SVE)
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From page 264... ...
264 BOX 5-11 Continued ell W -B23 Chloride MW Tetrachloroethene Trichloroethene inyl cis-1,2-Dichloroethene V Ethene Overburden Dec-03 Jun-03 Dec-02 Jun-02 Dec-01 Jun-01 0 Dec-00 600 500 400 300 200 100 -moles/liter) µ ( Concentration
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From page 265... ...
265 from -scale full a permission, ell during W Chloride (b) with -C22 inyl MW Tetrachloroethene Trichloroethene cis-1,2-Dichloroethene V Ethene Bedrock bedrock Reprinted, the in N-03 Dec-03 Scale Full J-03 SOURCE: screened D-02 well a J-02 Jun-03 and D-01 (a)
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From page 266... ...
For the few demonstrations that have been published, success is generally reported in concentration reduction rather than mass removal or mass flux reduction. Further, the long-term effectiveness of source zone bioremediation in heterogeneous or low permeability media has not been demonstrated.
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From page 267... ...
It should be noted that because the contaminants are not brought to the surface for treatment during bioremediation, the costs associated with pumping large quantities of water and with treating that water at the surface, which are common to other remedies, are avoided. Technology-Specific Prediction Tools and Models Numerous reactive transport models have been developed to simulate in situ bioremediation of plumes downgradient of DNAPL sources.
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From page 268... ...
Several reactive transport models that have been developed explicitly incorporate source zones containing NAPLs into simulations of bioremediation. For example, Gallo and Manzini (2001)
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From page 269... ...
The major demonstration needs follow on directly from the research needs, with wellcharacterized field-scale demonstrations of enhanced bioremediation within source zones containing DNAPLs topping the list. INTEGRATION OF TECHNOLOGIES Integration of technologies can be critical to effectively treating multiple contaminants (e.g., organics and heavy metals)
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From page 270... ...
surfactants to improve the size of source zones swept by air sparging. In laboratory experiments with homogeneous sand, they found that the swept zone created by air sparging was 5.2 times larger in the presence of sodium dodecyl benzene sulfonate than in its absence.
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From page 271... ...
If source zone treatments are successful in lowering contaminant mass and concentration, several conditions are required for using MNA as a follow-on activity: presence of the necessary bacteria, electron donors and acceptors, and the necessary macro- and trace nutrients. Because there have been no documented cases of using MNA as a follow-on to source remediation, one can only surmise about its potential, which is done here using reductive dechlorination as an example.
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From page 272... ...
The best-case scenario for MNA is if both the required BOX 5-12 Laboratory Study of Sequential Chemical Oxidation and Bioaugmentation Soon-to-be-published work describes the use of in situ chemical oxidation using permanganate to rapidly remove DNAPL mass in a source zone. Because VOC rebound can occur after treatment, a secondary polishing technology such as enhanced bioremediation was considered.
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From page 273... ...
COMPARISON OF TECHNOLOGIES Table 5-7 summarizes the DNAPL source remediation technologies covered in this chapter. Since a detailed comparison of the technologies depends on a complex integration of a wide range of site and contaminant properties, the table provides a qualitative comparison only.
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From page 274... ...
274 for all remedy areas Failure low but should most are source monitored Comments The commonly approved for containing DNAPL. rates properly constructed systems, projects be long-term.
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From page 275... ...
275 to of of treated suited materials permeable continued most be excavation. commonly design site source well disposed low The aggressive all remediation methods.
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From page 276... ...
This technology only to source ow ow Change in Toxicity Low- Medium Low L Low L Sites ow ow Reduction of Source Migration Potential Low L Low L Low Appropriate at ow Mass Flux Reduction Low- Medium Low Low- Medium Low L Effectiveness ow ow Likely Local Aqueous Concen- tration Reduction Low L L Low Low ow Mass Removal Low- Medium Low Low Low a Media Settings I II III IV VL low moderate Continued Applicable Contaminant Types Organics with to viscosity 5-7 TABLE Technology Multiphase Extraction
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From page 277... ...
277 in be media. if continued may high.
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From page 278... ...
278 or in in to (low Limited media, applicable failures require immobilized Comments Only to sources NAPL saturation, sorbed)
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From page 279... ...
279 as in day with a due rock/ reuse, research one several continued cleanup for one. as small evidence site examples No a limited occur date.
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From page 280... ...
280 media. or saturated Comments Little documentation on demonstrations in media fractured is water table well below interval concern.
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From page 281... ...
281 media. to (low or saturation, continued applicable saturated immobilized sorbed)
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From page 282... ...
282 will in by rates a and or be of media. can limited DNAPL Comments Performance be dissolution and function geochemical conditions indigenous microbial population.
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From page 283... ...
283 permeability high to permeability moderate low and and heterogeneity high porosity porosity to matrix matrix heterogeneity heterogeneity low low low moderate high follows: with as with with with with are media media media media media settings Granular Fractured Media Granular Granular Fractured a I II III IV V
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From page 284... ...
All of this points to the importance of successive source characterization by experienced professionals at each stage of the remedial process. The five physical objectives listed in Table 5-7 (mass removal, local aqueous concentration reduction, mass flux reduction, reduction of source migration potential, and change in toxicity)
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From page 285... ...
Mass flux reduction and volume averaged concentration reduction would differ in cases in which there is significant heterogeneity in the source zone and a significant fraction of the contamination is contained in the low-permeability portions. Cases where the scores on these two parameters differ are cases where postremediation rebound in contaminant concentrations may be more likely to occur.
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From page 286... ...
One common absolute objective of source zone remediation is risk reduction, which is not explicitly listed in Table 5-7. Instead, the objectives of mass removal, concentration reduction, and mass flux reduction attempt to capture the temporal and spatial nature of exposure.
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From page 287... ...
In lieu of full-scale demonstration projects, our ability to predict the effectiveness of source remediation is dependent on technology-specific mathematical models, bench-scale tests, and field pilot projects. The successful use of mathematical models is highly dependent on the quality of the site assessment and on the level of sophistication of the models and the model users.
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From page 288... ...
Even at sites where mathematical models and bench-scale tests have been conducted, field-scale pilot studies are still very helpful before full-scale source remediation projects are started. They can help refine the full-scale activity in ways that save time and money.
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From page 289... ...
; however, field tests have not been funded. At Badger, the treatment of the DNT source area via enhanced bioremediation is being optimized in field tests.
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From page 290... ...
. Research on in situ chemical oxidation of TNT and RDX with Fenton's reagent has shown good results in laboratory studies (Li et al., 1997; Bier et al., 1999)
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From page 291... ...
* Because the characterization of explosive source materials and their interactions with geologic media lag far behind the knowledge base that exists for DNAPLs, fewer innovative source remediation technologies have been developed for explosives.
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From page 292... ...
The results of pilot-scale projects typically do not provide quantitative information on the ability of the various technologies to meet most remediation objectives. For example, although it is relatively easy to measure mass removal during a pilot test, such tests are rarely if ever designed to enable measurement of the objectives likely to be important when a remedy has gone to full-scale, such as concentration reduction at a downstream compliance point, mass flux reduction, or risk reduction.
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From page 293... ...
Some source remediation technologies have been demonstrated to achieve substantial mass removal across a range of sites and contaminants. A number of these studies have also demonstrated concentration reductions (at only one or a few wells)
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From page 294... ...
Additional research is needed to determine how different source remediation technologies can be combined to achieve greater overall effectiveness. Examples of potential synergism include combining surfactants and low-level thermal processes to solubilize high-viscosity oils, following contaminant extraction with low-level chemical oxidation as a polishing step, allowing posttreatment levels of surfactants or alcohols to promote biotransformation of remaining contaminants, and allowing the elevated temperatures characteristic of thermal processes to promote the rate of biodegradation.
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From page 295... ...
For example, the most effectively designed slurry wall will have less effect on downstream mass flux if it is placed across the source zone rather than around it. With respect to performance monitoring, judging the effectiveness of in situ chemical oxidation by monitoring mineralization products or by monitoring the consumption of oxidant could overestimate treatment effectiveness in cases where alternate contaminants are present.
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From page 296... ...
1998. An analysis of air sparging for chlorinated solvent sites.
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From page 297... ...
1999. Modeling mass removal during in situ air sparging.
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From page 298... ...
1998. Case history of a large-scale air sparging soil vapor extraction system for remediation of chlorinated volatile organic compounds in ground water.
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From page 299... ...
2000. Numerical simulation of in situ chemical oxidation.
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From page 300... ...
2002. Laboratory-scale in situ chemical oxidation of a perchloroethylene pool using permanganate.
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From page 301... ...
1997. Numerical Simulation of Air Sparging for Remediation of NAPL.
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From page 302... ...
1998. Analytical model for contaminant mass removal by air sparging.
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From page 303... ...
1993. Modelling and laboratory investigations of steam flushing below the water table.
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From page 304... ...
1999. In Situ Chemical Oxidation Using Potassium Permanganate.
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From page 305... ...
1998. Competition for hydrogen within a chlorinated solvent dehalogenating anaerobic mixed culture.
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Key Terms
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