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RETROSPECTIVE EVALUATION OF A SURFACTANT FLUSH TO REMOVE GASOLINE CONTAMINATION FROM AN AQUFIER IN GOLDEN, OKLAHOMA
After remedial activities are complete, the SPRD will collect, extract, and analyze core samples from selected locations previously sampled by Surbec-ART as part of their characterization prior to remediation. The concentration of benzene, toluene, ethylbenzene, xylenes, and gasoline range total petroleum hydrocarbons (TPH) will be compared before and after remediation. The performance of the technology across the entire site will be evaluated by comparing the mean and standard deviation of the mean concentration of each contaminant before remediation to the mean and standard deviation of the mean after remediation. A t-test for the difference of means will be used to determine the greatest reduction in concentration of each contaminant that is significant at 90% confidence. The greatest reduction significant at 90% confidence for each contaminant will be divided by the mean concentration prior to remediation to determine a fractional removal for each contaminant during remediation. The release of gasoline from one or several underground storage tanks had contaminated ground water near the intersection of Railroad Street and Line Road in Golden, Oklahoma. Two zones at the site yield ground water. The water table aquifer extends to approximately 15 feet below land surface. There is a confining layer near 15 feet below land surface, and then a deeper zone extends from 15 to approximately 25 feet below land surface. Surfactant was injected and recovered from 52 wells in the shallow zone and 23 wells in the deep zone. The gasoline was flushed from the aquifer by injecting water containing a proprietary mixture of <1% total surfactants comprised of AOT (Aerosol OT-75 PG surfactant, a mixture of dioctyl sulfo succinate in polypropylene and water), Calfax 16L-35 (diphenyl oxide disulfonate), and 1.2% sodium chloride. In the first stage of the clean up, 65,000 gallons of surfactant solution was injected and 70,000 gallons of water recovered from the deep zone using the wells depicted in Figure 2. The surfactant flush was followed by 52,000 gallons of fresh water. In the second stage, 190,000 gallons of surfactant solution was injected followed by 35,000 gallons of a bio-amendment containing hydrogen peroxide (200 or 400 mg/L) and sodium sulfate (250 mg/L) were injected into the shallow wells. Fenton's reagent was also injected into certain wells. The surfactant was injected at flow rates that would displace one pore volume between the injection and extraction wells. As of June 2002, more than 6,000 gallons of gasoline was recovered from the aquifer by the surfactant flush.
Surbec-ART Environmental has completed a surfactant flush at a gasoline spill in the vicinity Carroll's Grocery in Golden, Oklahoma (June 2002). The remediation was designed to meet three clean up criteria, the first of which was set by the Oklahoma Corporation Commission and the second and third set internally by Surbec-ART: 1.) To remove as much of the free phase gasoline as possible, 2.) to decrease the soil and groundwater concentrations by one to two orders of magnitude, and 3.) to approach, if not reach, drinking water standards for BTEX. The initial phase of the remediation was to conduct the surfactant flush to meet the first goal. The second phase follows the flush with in situ bioremediation to reduce concentrations of BTEX compounds and TPH in ground water to meet the last two goals. The initial results are very promising. This technology may find wide application at underground storage tanks spill sites. The Oklahoma Corporation Commission has invited staff of the Subsurface Protection and Remediation Division (National Risk Management Laboratory/Office of Research and Development/U.S. EPA) to conduct an independent evaluation of the performance of the technology.
The primary purpose of the independent evaluation by SPRD and ERD will be to determine the quantity and distribution of TPH and BTEX compounds remaining at the site after remediation (a surfactant flush, in situ chemical oxidation and in situ bioremediation). The quantity and distribution of contaminants remaining after the flush will be compared to the quantity and distribution prior to the flush to evaluate the performance of the technology.
The staff of the Subsurface Remediation and Protection Division of the National Risk Management Research Laboratory (ORD/EPA) will draw on the information developed in this evaluation as they provide technical assistance to the states and EPA Regions concerning the merits and applications of this technology to UST sites. The results of the evaluation will also be submitted for publication in a peer- reviewed journal.
Record Details:Record Type: PROJECT
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
GROUND WATER AND ECOSYSTEMS RESTORATION DIVISION
SUBSURFACE REMEDIATION BRANCH