The RT3D software was used in the case study described here to design a pilot-scale accelerated in situ bioremediation system to treat trichloroethene-contaminated groundwater at Installation Restoration Program (IRP) Site 24 at Naval Air Station (NAS) Point Mugu near Oxnard, California.  This case study was an Accelerated In Situ Bioremediation Design, in which the bioremediation team determined the approach and design of a pilot-scale field demonstration of in situ bioremediation system.  The team is also providing a full-scale design for remediation of the site based on the field demonstration results.  Battelle provides accelerated in situ bioremediation designs and other bioremediation services to clients around the country.

TCE has contaminated a portion of the upper aquifer within Installation Restoration Program (IRP) Site 24 at the Point Mugu NAS.  The source of the contamination was a leaking underground storage tank (designated as UST Site 23).  Although the tank and the surrounding soil have been removed, groundwater contam-ination persists.  Recent data show that contamination extends from the water table (5 ft below ground surface) to a depth of approximately 30 ft and has an areal extent of approximately 2 acres.  UST Site 23 is located approximately 1 mile inland from the Pacific Ocean.  Because the site is so near the ocean, seawater intrusion has resulted in chloride and sulfate concentrations in of approximately 5,000 mg/L and 700 mg/L, respectively.

A remedial alternatives analysis indicated that in situ anaerobic bioremediation was the most cost effective approach to remediate the UST Site 23 plume at NAS Point Mugu.  Subsequently, laboratory microcosm tests (performed at Oregon State University) and a pilot-scale bioremediation demonstration were initiated.  The pilot test of accelerated in situ bioremediation was implemented for UST Site 23 in the Fall of 1998 to demonstrate the effectiveness of the technology and to provide operating and cost information for evaluating a full-scale system.

In less than 60 days after the start of nutrient injections, sulfate concentrations were reduced from about 700 mg/L to less than 25 mg/L.  Upon removal of the sulfate, TCE was rapidly dechlorinated to DCE and subsequently to VC.  A portion of the VC has been degraded to ethene.  The rate of VC dechlorination in the field is slower than the rate expected based on measurements in microcosm tests with site sediments and groundwater.  Battelle is now supporting the project by providing a design for aerobic in situ bioremediation to more quickly remediate the remaining VC.

Battelle's Chlorinated Solvent Bioremediation Design Service integrates geological, biological, and environmental data to design, simulate, and optimize bioremediation systems.  The service provides a design framework based on the RT3D reactive transport code to evaluate in situ bioremediation treatment.

 

For more information, contact:
Michael Truex Program Manager Field Hydrology and Chemistry Group	Battelle 902 Battelle Blvd., K6-96 Richland, WA 99352 USA	509-376-5461 509-372-1704 FAX mj.truex@pnl.gov