Joleen Kealey, Robert Roth, Ph.D., P.E., Joseph Pezzullo, PE, Terra Vac Corporation

A gasoline spill from former underground storage tanks (USTs) resulted in petroleum hydrocarbon and Methyl Tertiary Butyl Ether (MTBE) impact to soils and groundwater at a gasoline station in Concord, Massachusetts. Site assessment information showed MTBE concentrations in groundwater of up to 3,400 ug/l, and other hydrocarbon contaminants including benzene (114 ug/l), toluene (268 ug/l), ethylbenzene (448 ug/l), and xylenes (1,749 ug/l). Terra Vac conducted an OxyVacÒ bench test upon which the full-scale field application was designed. Field operations commenced in July 2000, consisting of several hydrogen peroxide (H₂O₂) injection points and a network of soil vapor extraction (SVE) wells to extract off gasses from the in-situ oxidation. Groundwater sampling for contaminant concentrations, Fe⁺² consumption, and pH as well as off gas monitoring were conducted at routine intervals throughout the course of the project. As of December 2000, six injections of H₂O₂ were completed, and groundwater monitoring revealed that only one monitoring well remained above the clean-up criteria of 70 ug/l MTBE. All the other gasoline constituents had been reduced to less than 5 ug/l.

Eric Nichols, PE, and Christopher Voci, LFR Levine Fricke

This pilot study evaluated the efficacy of the KVA C-Sparger ozone and air-sparging system for in-situ treatment of MtBE-affected groundwater at a gasoline spill site on Long Island, New York. Two ozone-air spargepoints were installed at different depths in a single borehole to maximize the conical diffusion of the gasses in the sand aquifer. Monitoring wells were installed at twelve and twenty-eight feet downgradient of the spargepoints to measure the magnitude of hydraulic effect and to monitor changes in groundwater quality resulting from addition of ozone or other oxidants. Pressure data from down-hole transducers and measurements of groundwater geochemical parameters were used to evaluate the area of influence of the sparging system. Changes in MtBE concentration in groundwater were monitored and destruction rates were estimated using analytical results from weekly samples collected from the monitoring points.

Kevin P. Wheeler, Paul Rosenwinkel, P.E., Bryan L. Emilius, P.G., Resource Control Corporation

Ozone has been utilized in the water supply and wastewater treatment industries for decades as a means to treat or remediate a multitude of organic compounds. Only recently, however, has this proven treatment technology been tested in the in-situ environmental remediation arena. Ozone, as the third most powerful oxidizer found in nature, has the ability to remediate recalcitrant compounds, which are not effectively or efficiently treated via any other means.

Methyl tert-butyl ether ("MTBE"), a common additive to gasoline, is designated as a recalcitrant groundwater contaminant due to it chemical characteristics, which render traditional remediation technologies and treatment approaches ineffective or inefficient. Because of MTBE's high solubility and mobility in groundwater, coupled with its relatively slow rate of degradation, this chemical has become one of the most common contaminant compounds detected in groundwater across the United States.

Field scale implementation of in-situ ozone remediation at several gasoline contaminated sites has demonstrated the effectiveness of this technology on rapidly degrading MTBE in groundwater. This paper presents, through the example of several case histories, information on the effectiveness and efficiency of in-situ ozone treatment on remediating MTBE impacted groundwater.

Paul C. Johnson, Arizona State University, Karen D. Miller, Naval Facilities Engineering Service Center, and Cristin L. Bruce, Arizona State University.

In situ containment and treatment of MTBE contaminated aquifers is becoming increasingly important to both the private and public sectors. Innovative treatment methods are being developed and studied because the effectiveness of traditional treatment options may be limited by MTBE’s unique chemical properties. For the past three years the use of aerobic biobarriers has been studied at the pilot scale at the Naval Base Ventura County, Port Hueneme, CA Port Hueneme; more recently, a 500-ft wide full-scale biobarrier has been designed and installed down-gradient of a mixed BTEX/MTBE source zone. In this technology, groundwater containing dissolved MTBE and BTEX flows to the biobarrier. As the contaminated groundwater flows through the barrier, the microorganisms break down the MTBE and BTEX. Different design configurations are being tested in different sections of the large-scale biobarrier, including a zone seeded with MTBE-degrading organisms and aerated with oxygen gas (bio-augmented), and zones not seeded with any organisms, but aerated with oxygen gas and air (biostimulated). An assessment of the reductions in MTBE, BTEX, and TPH concentrations achieved by different zones in the biobarrier is being monitored in about 300 wells on a monthly/bi-monthly schedule over a two-year period. In addition, the effectiveness of both oxygen and air delivery to the target treatment zones is being evaluated. Results from the first 12 months of operation will be presented.

Gerard E. Spinnler, Joseph P. Salanitro, Paul M. Maner, Equilon Enterprises LLC, Paul C. Johnson, Arizona State University

A variety of methods to remove dissolved MTBE from groundwater are currently in use. Conventional remediation methods used for other petroleum constituents have proven difficult, ineffective or financially prohibitive for MTBE. We have demonstrated an in-situ biological method that degrades MTBE and other gasoline oxygenates in situ and overcomes many of the hurdles encountered with conventional MTBE remediation approaches. MTBE concentrations of up to 100 mg/L were reduced using this biodegradation method. MTBE concentration reductions up to three orders of magnitude were observed within several months of system installation.

The BioRemedy bioaugmentation process uses specialized MTBE-degrading bacteria (MC-100) added to unconsolidated sediments in the saturated zone. Dissolved MTBE flows through the zone under the natural groundwater gradient. Oxygen is pulsed into the bacteria-containing zone to increase dissolved oxygen. The combination of ether-degrading microbes and oxygen creates a biobarrier limiting the mobility of the oxygenate plume. This MTBE and oxygenate remediation system has been demonstrated at Port Hueneme Naval base in California and applied at retail gasoline stations with MTBE impacted groundwater. The specialized microbes were emplaced using direct push techniques and pressure injection. Oxygen gas was generated on-site using an oxygen generator in combination with a compressor and supplied to the microbe zone using gas injection wells. Vertical and horizontal gas-injection well spacings were determined using tracer measurements during pilot tests. At the retail gas station sites, no indigenous MTBE-degrading microorganisms were present. Monitoring wells at each site were used to collect samples for MTBE, TBA and BTEX analysis. Correlation of MTBE reduction and increased dissolved oxygen concentrations following the emplacement of MTBE-degrading culture provide evidence of biodegradation in the field. Lab-scale microcosms using site groundwater and soils amended with MTBE-degrading culture provide further data supporting biodegradation and this remedial approach. These observations of full-scale biobarriers indicate aquifer bioaugmentation with high activity MTBE-degrading cultures can be a cost-effective technology for controlling the migration of MTBE plumes.