Microbially Mediated In Situ Desorption Accelerates Remediation of Large Gasoline Product Plume

Remediation of a large separate‐phase hydrocarbon product and associated dissolved‐phase gasoline plume was accelerated by coupling multiphase extraction with in situ microbial stimulation. At the beginning of remediation activities, the separate‐phase hydrocarbon plume extended an estimated seven acres with product thickness measuring up to 2.1 feet thick. Within 18 months after beginning extraction, reduction of gasoline constituents in groundwater became asymptotic and measureable product disappeared from the upgradient source area. At that time, the remediation team initiated a program of limited in situ anaerobic bioremediation with the goal of stimulating production of natural surfactants from native microbes to release petroleum from the soil matrix. Groundwater concentrations of gasoline constituents increased gradually over the next three years, improving recovery without biofouling the pump‐and‐treat infrastructure. Using this approach, the groundwater component of the remedy was completed in less than five years, substantially less than the 10 years to 15 years predicted by modeling. This strategy demonstrated a more sustainable approach to remediation, reducing electrical usage by an estimated 800 megawatt hours, reducing infrastructure requirements, and preserving an estimated 150 million gallons of groundwater for this arid agricultural area. © 2014 Wiley Periodicals, Inc.     

Pilot Scale Demonstration of the Electrochemical Peroxidation Process at a Petroleum Spill Site

In a pilot test experiment involving approximately 200,000 gallons of groundwater, Electrochemical Peroxidation (ECP) was used to degrade aqueous phase volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and methyl tertbutyl ether (MTBE) from a petroleum spill. ECP involves a form of the Fenton's Reagent reaction, which uses electrochemically generated iron and dilute hydrogen peroxide (<30 mg/L) to break down organic molecules through oxidation to carbon dioxide and water. This article discusses a pilot scale demonstration of the ECP technology and its application to aqueous phase organic contaminants. The remedial approach used at the pilot test site involves three phases: (1) ex‐situ chemical oxidation, (2) in‐situ oxidation by reinjection of treated effluent near the plume origin, and (3) reestablishment of aerobic biodegradation as the residual hydrogen peroxide discharged to a series of upgradient wells degrades to oxygen. Analytical results of the pilot demonstration indicate that the ex‐situ chemical oxidation reduced total BTEX concentrations in groundwater from over 1,000 ppb to undetectable concentrations (<1 ppb). © 2000 John Wiley & Sons, Inc.     

Implications of MTBE for Intrinsic Remediation of Underground Fuel Tank Sites

MTBE in groundwater has been shown to travel over 1,000 feet downgradient from its source in several comprehensive field studies conducted across North America. The biodegradability of MTBE is examined by summarizing all the significant literature on the subject and by detailing the findings of recent field investigations of MTBE transport. In Orange County, California, the persistence of MTBE is analyzed and statistical representations of source variability are presented. Regional and far field transport of MTBE in groundwater sourced from underground gasoline storage tanks are summarized in comprehensive tables of frequency and plume length. Estimates of source mass and duration allow for comparison of associated plume size. The conclusion reached after reviewing all the available literature on MTBE is that its biodegradability seems slight and the size of the plumes are surprisingly large. Intrinsic or natural attenuation remedies for MTBE merit close scrutiny.     

In situ remediation of MTBE utilizing ozone

There has been a great deal of focus on methyl tertiary butyl ether (MTBE) over the past few years by local, state, and federal government, industry, public stakeholders, the environmental services market, and educational institutions. This focus is, in large part, the result of the widespread detection of MTBE in groundwater and surface waters across the United States. The presence of MTBE in groundwater has been attributed primarily to the release from underground storage tank (UST) systems at gasoline service stations. MTBE's physical and chemical properties are different than other constituents of gasoline that have traditionally been cause for concern [benzene, toluene, ethylbenzene, and xylenes (BTEX)]. This difference in properties is why MTBE migrates differently in the subsurface environment and exhibits different constraints relative to mitigation and remediation of MTBE once it has been released to subsurface soils and groundwater. Resource Control Corporation (RCC) has accomplished the remediation of MTBE from subsurface soil and groundwater at multiple sites using ozone. RCC has successfully applied ozone at several sites with different lithologies, geochemistry, and concentrations of constituents of concern. This article presents results from several projects utilizing in situ chemical oxidation with ozone. On these projects MTBE concentrations in groundwater were reduced to remedial objectives usually sooner than anticipated. © 2002 Wiley Periodicals, Inc.     

Full‐scale in‐situ biobarrier demonstration for containment and treatment of MTBE

The Naval Facilities Engineering Service Center (NFESC), Arizona State University, and Equilon Enterprises LLC are partners in an innovative Environmental Security Technology Certification Program cleanup technology demonstration designed to contain dissolved MTBE groundwater plumes. This full‐scale demonstration is being performed to test the use of an oxygenated biobarrier at Naval Base Ventura County, in Port Hueneme, California. Surprisingly, few cost‐effective in‐situ remedies are known for the cleanup of MTBE‐impacted aquifers, and remediation by engineered in‐situ biodegradation was thought to be an unlikely candidate just a few years ago. This project demonstrates that MTBE‐impacted groundwater can be remediated in‐situ through engineered aerobic biodegradation under natural‐flow conditions. With respect to economics, the installation and operation costs associated with this innovative biobarrier system are at least 50 percent lower than those of a conventional pump and treat system. Furthermore, although it has been suggested that aerobic MTBE biodegradation will not occur in mixed MTBE‐BTEX dissolved plumes, this project demonstrates otherwise. The biobarrier system discussed in this article is the largest of its kind ever implemented, spanning a dissolved MTBE plume that is over 500 feet wide. This biobarrier system has achieved an in‐situ treatment efficiency of greater than 99.9 percent for dissolved MTBE and BTEX concentrations. Perhaps of greater importance is the fact that extensive performance data has been collected, which is being used to generate best‐practice design and cost information for this biobarrier technology. © 2001 John Wiley & Sons, Inc.     

Update of Comparative Occurrence Rates for Offshore Oil Spills

Estimates of occurrence rates for offshore oil spills are useful for analyzing potential oil-spill impacts and for oil-spill response contingency planning. With the implementation of the Oil Pollution Act of 1990 (US Public Law 101-380, August 18, 1990), estimates of oil-spill occurrence became even more important to natural resource trustees and to responsible parties involved in oil and gas activities.Oil-spill occurrence rate estimates have been revised based on US Outer Continental Shelf (US OCS) platform and pipeline spill data (1964 through 1999), worldwide tanker spill data (1974 through 1999), and barge spill data for US waters (1974–1999). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. All estimates of spill occurrence rates were restricted to spills greater than or equal to 1000 barrels (159 m³, 159 kl, 136 metric tonnes, 42,000 US gallons).The revisions compared to the previously published rates calculated through 1992 (Anderson and LaBelle, 1994) indicate that estimates for the US OCS platform spill occurrence rates continue to decline, primarily because no spills have occurred since 1980. The US OCS pipeline spill occurrence rates for spills greater than or equal to 1000 barrels remained essentially unchanged. However, the rate for larger OCS pipeline spills (greater than or equal to 10,000 barrels) has decreased significantly. Worldwide tanker spill rates, rates for tanker spills in US waters, and rates for barge spills in US waters decreased significantly. The most recent 15-year estimates for 1985–1999 (compared to rates for the entire data series) showed that rates for US OCS platforms, tankers, and barges continued to decline.     

Enhanced aerobic bioremediation of a gasohol release in a fractured bedrock aquifer

In January 2005, a gasoline tanker carrying approximately 8,500 gallons of gasohol (gasoline containing 10 percent ethanol) overturned and caught fire in the front yard of a residence. Emergency response crews responded to the accident, extinguished the fire, and recovered residual gasoline on the ground surface. Soil impacted by the release was then removed and disposed of off‐site and free‐phase gasohol was recovered using a combination of vacuum recovery, pumping, and bailing to the extent practicable. Following free product recovery efforts, a feasibility evaluation was completed to select a technology to address the remaining dissolved‐phase contaminants that resulted in biosparging pilot testing and, ultimately, the installation of a full‐scale biosparging system. The full‐scale system has been operating for approximately 21 months, and contaminant concentrations within the heart of the plume have decreased dramatically over a short period of time—in most cases, to below applicable cleanup standards. Despite the complex hydrogeologic conditions and significant initial concentrations, biosparging has proven to be an effective technology to remediate this gasohol release, and it is anticipated that drinking‐water standards can be achieved following two to three years of biosparging (i.e., an additional 3 to 15 months of operations). © 2010 Wiley Periodicals, Inc.     

Case study: On-site remediation of soil and groundwater for a michigan town's water supply

In 1993 environmental consultants, working in concert with the State of Michigan, discovered groundwater contamination that threatened the drinking water supply of the town of Big Rapids. The contamination originated from leaking underground storage tanks and gasoline lines, which were removed. A pilot study indicated the contaminated area extended to 240′ x 180′ and affected soil as well as groundwater. A remediation plan was designed by and implemented by Continental Remediation Systems, Inc., a Natick, Massachusetts, firm. The remediation plan is ongoing and includes an interceptor trench to stop gasoline from flowing into the creek, as well as air sparging to vent and treat the contaminated soil. It is anticipated that the remediation project will take six months to complete. The chief advantage of on-site remediation is that it avoids the costs and liabilities associated with landfill disposal and no materials need leave the site.     

The in situ treatment of BTEX,MTBE, and TBA in saline groundwater

A pilot‐scale test was conducted in a saline aquifer to determine if a petroleum hydrocarbon (PHC) plume containing benzene (B), toluene (T), ethylbenzene (E), xylenes (X), methyl tert‐butyl ether (MTBE), and tert‐butyl alcohol (TBA) could be treated effectively using a sequential treatment approach that employed in situ chemical oxidation (ISCO) and enhanced bioremediation (EBR). Chemical oxidants, such as persulfate, have been shown to be effective in reducing dissolved concentrations of BTEX (B + T + E + X) and additives such as MTBE and TBA in a variety of geochemical environments including saline aquifers. However, the lifespan of the oxidants in saline environments tends to be short‐lived (i.e., hours to days) with their effectiveness being limited by poor delivery, inefficient consumption by nontargeted species, and back‐diffusion processes. Similarly, the addition of electron acceptors has also been shown to be effective at reducing BTEX and associated additives in saline groundwater through EBR, however EBR can be limited by various factors similar to ISCO. To minimize the limitations of both approaches, a pilot test was carried out in a saline unconfined PHC‐impacted aquifer to evaluate the performance of an engineered, combined remedy that employed both approaches in a sequence. The PHC plume had total BTEX, MTBE, and TBA concentrations of up to 4,584; 55,182; and 1,880 μg/L, respectively. The pilot test involved injecting 13,826 L of unactivated persulfate solution (19.4 weight percent (wt.%) sodium persulfate (Na₂S₂O₈) solution into a series of injection wells installed within the PHC plume. Parameters monitored over a 700‐day period included BTEX, MTBE, TBA, sulfate, and sulfate isotope concentrations in the groundwater, and carbon and hydrogen isotopes in benzene and MTBE in the groundwater. The pilot test data indicated that the BTEX, MTBE, and TBA within the PHC plume were treated over time by both chemical oxidation and sulfate reduction. The injection of the unactivated persulfate resulted in short‐term decreases in the concentrations of the BTEX compounds, MTBE, and TBA. The mean total BTEX concentration from the three monitoring wells within the pilot‐test area decreased by up to 91%, whereas MTBE and TBA mean concentrations decreased by up to 39 and 58%, respectively, over the first 50 days postinjection in which detectable concentrations of persulfate remained in groundwater. Concentrations of the BTEX compounds, MTBE, and TBA rebounded at the Day 61 marker, which corresponded to no persulfate being detected in the groundwater. Subsequent monitoring of the groundwater revealed that the concentrations of BTEX continued to decrease with time suggesting that EBR was occurring within the plume. Between Days 51 and 487, BTEX concentrations decreased an additional 84% from the concentration measured on Day 61. Mean concentrations of MTBE showed a reduction during the EBR phase of remediation of 33% while the TBA concentration appeared to decrease initially but then increased as the sulfate concentration decreased as a result of MTBE degradation. Isotope analyses of dissolved sulfate (³⁴S and ¹⁸O), and compound‐specific isotope analysis (CSIA) of benzene and MTBE (¹³C and ²H) supported the conclusions that ISCO and EBR processes were occurring at different stages and locations within the plume over time.     

The Oil Pollution Act of 1990: A Decade Later

Analysis of oil spills data confirms that accidental oil spills are natural phenomenon and that there is a relationship between accidental oil spills and variables like vessel size, vessel type, time and region of spill. The volume of oil spilled bears relationship with the volume of petroleum imports and domestic movement of petroleum and proportion of large oil spills. Finally, navigational risk increases with increase in marine traffic and is also determined by variables like hydrographic and meteorological conditions, water configuration, maneuvering space, obstructions and nuisance vessels. The Oil Pollution Act, 1990 (OPA 90) was passed by the US Congress in the aftermath of 11 million gallon spill of crude oil in Prince William Sound, Alaska. The objective of OPA 90 was to minimize marine casualties and oil spills by addressing preventive, protective, deterrent and performance aspects of accidental oil spills. The arm of various regulations like double-hull tankers and vessel response plans extended to both US flagged and foreign-flagged tank vessels. The cost–benefit analysis of major regulations shows that the estimated costs exceed estimated benefits. We observe from USCG data on oil spills by size, by vessel type, Coast guard district and type of petroleum product that there have been significant reductions in the number and the quantity of oil spills. Our regression results show that the quantity of oil spilled increases with increase in oil imports but increases at a decreasing rate. The quantity of oil spilled decreases with increases in the domestic oil movements. Furthermore, percent of oil spills larger than 10,000 gallons also increases the potential quantity of oil spilled. OPA 90 has been a deterrent to accidental oil spills but the finding is not conclusive.     

Biofiltration of airstreams contaminated with MTBE

The treatment of groundwater contaminated with low concentrations of methyl tertiary butyl ether (MTBE) is of nationwide concern. Many treatment techniques include removing MTBE vapors from groundwater, resulting in airstreams that require treatment. One method used for air‐phase MTBE treatment is biofiltration. In a biofilter, the vapors pass through a reactor that contains MTBE‐biodegrading organisms attached to a porous media. This article reports the results of a biofiltration study to treat air contaminated with MTBE at concentrations of 0.2 to 0.33 mg/l, concentrations frequently encountered in the field. The results indicate that MTBE removal at these low concentrations is not as efficient as removals seen at higher concentrations. Activated carbon was shown to be a superior biofiltration medium, compared with media that do not adsorb MTBE vapors. Activated carbon was especially helpful in treatment shock loads of MTBE. © 2002 Wiley Periodicals, Inc.     

Sustainable groundwater remediation and reuse case study

Sustainability is an important consideration when designing a remedy given the value that can be demonstrated to all stakeholders. A case study is presented that illustrates an example where sustainability was emphasized during the selection and implementation of a groundwater remedy. An extensive free and/or residual product investigation was completed to demonstrate that hydraulic control is a suitable remedy and active direct treatment was not required pursuant to the state regulations. A pump and treat system for onsite hydraulic containment was installed to control plume migration. The system allows for 100 percent reuse of treated groundwater in the manufacturing process. Both the groundwater reuse and investigation conclusions have resulted in significant cost savings and sustainability benefits, including the reduction in the annual load on the drinking water aquifer by up to 138 million gallons per year.     

In situ soil stabilization for source control of a lithium and bromate groundwater plume

Historic mineral ore processing operations at the former Cyprus Foote Mineral Site located in East Whiteland Township, Pennsylvania, have resulted in the creation of an approximately 10,000‐foot‐long off‐site groundwater plume impacted with lithium and bromate. The plume emanating from the site is impacting the groundwater quality of downgradient private residences. As an early part of the remedial implementation, the private residences were provided with public water connections while the source control efforts were being designed and implemented. Bromate and lithium have recently emerged as groundwater contaminants subjected to increased regulatory scrutiny. This is evidenced in a recently lowered Federal Maximum Contaminant Level (MCL) for bromate of 0.010 milligrams per liter and a Medium‐Specific Concentration (MSC) of 0.005 mg/L for lithium recently proposed by the Pennsylvania Department of Environmental Protection (PADEP) for all groundwater within the Commonwealth. Elevated concentrations for bromate and lithium were detected above the Proposed Remediation Goals (PRGs) for the site, MCLs, and MSCs at a distance of 7,300 feet and 9,200 feet from the source area, respectively. To reduce the contaminant concentrations within the groundwater plume, which will ultimately result in a regressing plume, and to enable the Brownfield redevelopment of this Superfund site, auger‐based, in situ soil stabilization (ISS) with depths of up to 75 feet below ground surface (bgs) was selected as the remedy. The remedial implementation required the temporary removal and relocation of over 100,000 cubic yards of overburden to expose the lithium‐bearing tailings prior to treatment. Using customized 90‐foot‐long, 9‐foot‐diameter augers attached to cranes and drilling platforms, ancillary support excavators, and approximately 21,000 tons of reagent; 2,019 ISS columns were advanced to depths ranging from 10 to 74 feet bgs. This resulted in the creation of an in situ low‐permeablity 117,045‐yd³ “quasi‐monolith,” which encompasses a lateral extent of approximately three acres. The integration of a comprehensive ISS design with a comprehensive long‐term groundwater‐monitoring plan ensured the success of the ISS implementation and will enable a continued evaluation of the off‐site groundwater quality. © 2009 Wiley Periodicals, Inc.     

Chemical oxidation using stabilized hydrogen peroxide in high temperature,saline groundwater impacted with hydrocarbons and MTBE

In situ chemical oxidation (ISCO) of petroleum hydrocarbons (PHCs) within groundwater is considered a proven approach to addressing PHC‐impacted groundwater in nonsaline environments. One of the most common oxidants used for oxidation of PHCs in groundwater is hydrogen peroxide (H₂O₂). Due to its highly reactive nature, H₂O₂ is often stabilized to aid in increasing its reactivity lifespan. Limited research and application of ISCO has been completed in warm, saline groundwater environments. Furthermore, even fewer studies have been completed in these environments for ISCO using stabilized H₂O₂. In this research, stabilized H₂O₂ was examined to determine its effectiveness in the treatment of PHCs and the additive methyl tert‐butyl ether (MTBE). Three stabilizers (citrate, phytate, silica [SiO₂]) were tested to determine if the stabilizers could enhance and extend the treatment life of H₂O₂ within saline groundwater. To determine the effect of salinity on the three stabilizers, groundwater and aquifer samples were collected from two saline locations that had different salinity (total dissolved solids of about 7,000 mg/L and 18,000 mg/L). Specific target chemicals for treatment were water soluble, mobile components of gasoline including benzene, toluene, ethylbenzene, xylenes, (BTEX) and MTBE. Previous studies using unactivated persulfate indicated that the PHCs within the groundwater could be oxidized, however, only limited oxidation of the MTBE could be affected. The results of the laboratory tests indicated that greater than 95 percent of the target hydrocarbons were removed within 7 days of treatment. Microcosms with citrate‐stabilized H₂O₂ demonstrated a significantly faster and greater decline with most hydrocarbon concentrations reaching < 5 μg/L. The exceptions were ethylbenzene and m‐xylene, which were slightly decreased to about 30 and 20 μg/L, respectively. Initial mean concentrations of the BTEX compounds within the citrate‐stabilized microcosms were 10,554 μg/L, 9,318 μg/L, 6,859 μg/L, and 14,435 μg/L, respectively. The silicate‐stabilized H₂O₂ microcosms showed no significant benefit over the unstabilized control microcosms. The better performance of citrate‐stabilized microcosms was confirmed by increasing δ13C values of remaining hydrocarbons. MTBE declined from > 400 mg/L to < 100 mg/L in all microcosms, again with the best removal (> 90 percent) being measured in the citrate‐stabilized microcosms. Unfortunately, H₂O₂ oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10 percent of the MTBE oxidized.     

Enhanced anaerobic bioremediation of a TCE source at the Tarheel Army Missile Plant using EOS

EOS, or emulsified oil substrate, was used to stimulate anaerobic biodegradation of trichloroethene (TCE) and tetrachloroethene (PCE) at a former Army‐owned manufacturing facility located in the Piedmont area of North Carolina. Previous use of chlorinated solvents at the facility resulted in soil and groundwater impacts. Ten years of active remediation utilizing soil vacuum extraction and air sparging (SVE/AS) were largely ineffective in reducing the TCE/PCE plume. In 2002, the Army authorized preparation of an amended Remedial Action Plan (RAP) to evaluate in situ bioremediation methods to remediate TCE in groundwater. The RAP evaluated eight groundwater remediation technologies and recommended EOS as the preferred bioremediation alternative for the site. Eight wells were drilled within the 100 × 100 feet area believed to be the primary source area for the TCE plume. In a first injection phase, dilute EOS emulsion was injected into half of the wells. Distribution of the carbon substrate through the treatment zone was enhanced by pumping the four wells that were not injected and recirculating the extracted water through the injection wells. The process was repeated in a second phase that reversed the injection/extraction well pairs. Overall, 18,480 pounds of EOS were injected and 163,000 gallons of water were recirculated through the source area. Anaerobic groundwater conditions were observed shortly after injection with a corresponding decrease in both PCE and TCE concentrations. Dissolved oxygen, oxidation‐reduction potential, and sulfate concentrations also decreased after injection, while TCE‐degradation products, ferrous iron, and methane concentrations increased. The reduction in TCE allowed the Army to meet the groundwater remediation goals for the site. Approximately 18 months after injection, eight wells were innoculated with a commercially prepared dechlorinating culture (KB‐1) in an attempt to address lingering cis‐1,2‐dichloroethene (cis‐DCE) and vinyl chloride (VC) that continued to be observed in some wells. Dehalococcoides populations increased slightly post‐bioaugmentation. Both cis‐DCE and VC continue to slowly decrease. © 2007 Wiley Periodicals, Inc.     

How shell cleaned up a 400,000-gallon oil spill

On April 23, 1988, approximately 9,500 barrels (400,000 gallons) of San Joaquin Valley crude oil leaked from an aboveground storage tank at Shell Oil Company's Martinez Manufacturing Complex in Martinez, California and entered Suisun Bay, an important recreation area. This article describes the remediation techniques Shell used to protect and clean up the Bay's oiled marshes, sloughs, rocky shores, marinas, and sandy beaches, and discusses the main methods of oil spill response, site-specific factors that must be considered in choosing remediation techniques, the interaction between Shell and government agencies, and the costs associated with the spill. The cleanup's total cost was approximately $8.3 million, which did not include private claims and claims handling costs; Shell also signed a separate consent decree for $19.75 million with the state of California and the federal government. This spill and its aftermath emphasize the need for preparation that facilitates response actions, improves the chances for cooperation between responsible parties and government agencies, minimizes the time needed for remediation, lowers cleanup costs, and limits natural resource damage claims and penalties.     

Bioremediation of a former dry cleaner using potassium lactate

Chlorinated solvents were released to the surficial groundwater underneath a former dry cleaning building, resulting in a groundwater plume consisting of high concentrations of trichloroethene (TCE) and cis‐1,2‐dichloroethene (cis‐1,2‐DCE) and low concentrations of tetrachloroethene (PCE) and vinyl chloride. The initial remedial action included chemical oxidation via injection of 14,400 gallons of Fenton's Reagent in March 2002, and an additional 14,760 gallons in April 2002. A sharp reduction of contaminant concentrations in groundwater was observed the following month; however, rebound of contaminant concentrations was evident as early as October 2002. A source area of PCE‐impacted soils was excavated in June 2004. Following the excavation, Golder Associates Inc. (2007) implemented a biostimulation plan by injecting 55 gallons of potassium lactate (PURASAL® HiPure P) in September 2005, and again in February 2006. Comparing the preinjection and postinjection site conditions, the potassium lactate treatments were successful in accomplishing a 40 to 70 percent reduction in mass within four months following the second injection. Elevated vinyl chloride concentrations have persisted through both injection events; however, significant vinyl chloride reduction has been observed in one well with the highest total organic carbon (TOC) concentrations following each injection. © 2008 Wiley Periodicals, Inc.     

Ex situ treatment of MTBE‐containing groundwater by a UV peroxide system

This article describes the design, implementation, and operating results for an ex situ ultraviolet/hydrogen peroxide (UVP) system to treat methyl tert‐butyl ether (MTBE) in extracted groundwater. The UVP modification was designed to reduce the operation and maintenance costs of an existing groundwater pump‐and‐treat treatment system that relied on air stripping and carbon adsorption. The UVP system is relatively inexpensive and can easily be scaled to cope with different groundwater extraction rates up to 80 gpm by adding UV lamps in series or in parallel at the higher groundwater extraction rates. The MTBE concentration in the effluent from the UVP system to the carbon vessels decreased from an average of 590 μg/L to approximately 2 μg/L on average over 33 months of operation of the UVP. Incorporation of this UVP modification as a second‐stage treatment to the groundwater pump‐and‐treat/soil vapor extraction system, after the air stripper and prior to the carbon vessels, significantly increased the usable life of the carbon (from two months previously to about two years after installation) and completely resolved the issue of frequent MTBE breakthroughs of the carbon that had plagued the remediation system since its inception. © 2006 Wiley Periodicals, Inc.     

Optimizing remediation strategies for a former dry‐cleaner site

Residual tetrachloroethene (PCE) contamination at the former Springvilla Dry Cleaners site in Springfield, Oregon, posed a potential risk through the vapor intrusion, direct contact, and off‐site beneficial groundwater uses. The Oregon Department of Environmental Quality utilized the State Dry Cleaner Program funds to help mitigate the risks posed by residual contamination. After delineation activities were complete, the source‐area soils were excavated and treated on‐site with ex situ vapor extraction to reduce disposal costs. Residual source‐area contamination was then chemically oxidized using sodium permanganate. Dissolved‐phase contamination was subsequently addressed with in situ enhanced reductive dechlorination (ERD). ERD achieved treatment goals across more than 4 million gallons of aquifer impacted with PCE concentrations up to 7,800 micrograms per liter prior to remedial activities. The ERD remedy introduced electron donors and nutrient amendments through groundwater recirculation and slug injection across two aquifers over the course of 24 months. Adaptive and mass‐targeted strategies reduced total remedy costs to approximately $18 per ton within the treatment areas. © 2010 Wiley Periodicals, Inc.     

Chemical Oxidation Performance in High Temperature,Saline Groundwater Impacted With Hydrocarbons

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for in situ chemical oxidation (ISCO) of aromatic hydrocarbons and methyl tertiary butyl ether (MTBE), a common oxygenate additive in gasoline, in saline, high temperature (more than 30 °C) groundwater. Groundwater samples from a site in Saudi Arabia were amended in the laboratory portion of the study with the chemical oxidants, sodium persulfate (Na₂S₂O₈) and sodium percarbonate (Na₂(CO₃)₂), to evaluate the changes in select hydrocarbon and MTBE concentrations with time. Almost complete degradation of the aromatic hydrocarbons, naphthalene and trimethylbenzenes (TMBs), was found in the groundwater sample amended with persulfate, whereas the percarbonate‐amended sample showed little to no degradation of the target hydrocarbon compounds in the laboratory. Isotopic analyses of the persulfate‐amended samples suggested that C‐isotope fractionation for xylenes occurred after approximately 30 percent reduction in concentration with a decline of about 1 percent in the δ¹³C values of xylenes. Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of chemical oxidation using nonactivated persulfate on a high temperature, saline petroleum hydrocarbon plume. Approximately 1,750 kg of Na₂S₂O₈ was delivered to the subsurface using a series of injection wells over three injection events. Results obtained from the pilot test indicated that all the target compounds decreased with removal percentages varying between 86 percent for naphthalene and more than 99 percent for the MTBE and TMBs. The benzene, toluene, ethylbenzene, and xylene compounds decreased to 98 percent on average. Examination of the microbial population upgradient and downgradient of the ISCO reactive zone suggested that a bacteria population was present following the ISCO injections with sulfate‐reducing bacteria (SRB) being the dominant bacteria present. Measurements of inorganic parameters during injection and postinjection indicated that the pH of the groundwater remained neutral following injections, whereas the oxidation–reduction potential remained anaerobic throughout the injection zone with time. Nitrate concentrations decreased within the injection zone, suggesting that the nitrate may have been consumed by denitrification reactions, whereas sulfate concentrations increased as expected within the reactive zone, suggesting that the persulfate produced sulfate. Overall, the injection of the oxidant persulfate was shown to be an effective approach to treat dissolved aromatic and associated hydrocarbons within the groundwater. In addition, the generation of sulfate as a byproduct was an added benefit, as the sulfate could be utilized by SRBs present within the subsurface to further biodegrade any remaining hydrocarbons. ©2015 Wiley Periodicals, Inc.