The RT3D software, one of the computer codes used in the Battelle Chlorinated Solvent Design Service, was used in the case study described here to evaluate bioremediation options at Installation Restoration Program (IRP) Site 24 at Naval Air Station (NAS) Point Mugu near Oxnard, California.  This case study was a Remediation Alternatives Evaluation, in which the bioremediation team determined if natural attenuation, accelerated in situ bioremediation, or a combination of the two is needed to remediate the contamination in the plume.  Battelle provides remediation alternatives evaluations and other bioremediation services to clients around the country.

Perchloroethene (PCE), trichloro-ethene (TCE), and fuel hydrocarbons have contaminated a portion of the upper aquifer at NAS Point Mugu.  The sources of the contamination were two leaking underground storage tanks (USTs).  Although the tanks and the surrounding soil have been removed, groundwater contamination 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. The presence of cis-1,2-dichloroethene, vinyl chloride, and ethylene in the groundwater suggests that reductive dechlorination is occurring naturally.

Use the RT3D computer code to evaluate the technical feasibility, cost, and clean-up time for remediating the groundwater using:

• Groundwater extraction and aboveground treatment (air stripping and granular activated carbon adsorption)
• Natural attenuation
• Accelerated anaerobic in situ bioremediation ^[1] of the high concentration regions combined with natural attenuation of the remainder of the plume.

Battelle predicted that in situ bioremediation would save time and money when compared to the pump-and-treat alternative.  The regions surrounding each tank were considered separately since UST Site 23 has significantly more chlorinated solvents than fuels while UST Site 55 had a much larger fuel-to-chloroethene ratio. The fuel-to-chloroethene ratio is an important consideration for evaluating natural attenuation because the fuel serves as an energy source to support reductive dechlorination.  Hence, natural attenuation is the most cost-effective solution for UST Site 55, but is not technically feasible for UST Site 23.

 

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