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Reactive Transport in 3-Dimensions

Project Summary – Accelerated ISB Design Pt. Mugu

Overview

The RT3D software was used in the case study described here to design a pilot-scale accelerated in situ bioremediation (ISB) system to treat trichloroethene-contaminated groundwater at Installation Restoration Program (IRP) Site 24 at Naval Air Station (NAS) Point Mugu near Oxnard, California.  The approach and design for a pilot-scale field demonstration of ISB was determined, the field test was conducted, and the results fed into a full-scale design for remediation of the site.

The Site

TCE 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 were removed, groundwater contamination persisted.  Data showed that contamination extended from the water table (5 ft below ground surface) to a depth of approximately 30 ft and had 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.

Photo: UST Site 23 and Conceptual Cross Section

Photo and cross section of UST Site 23 showing groundwater flow between injection and extraction wells (yellow arrows) and the bioactive zone (blue-gray zone).

The Scope

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.

The Result

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 was degraded to ethene.  The rate of VC dechlorination in the field was slower than the rate expected based on measurements in microcosm tests with site sediments and groundwater.  Subsequene work ensued to design and demonstrate a pilot-scale aerobic in situ bioremediation treatment system to more quickly remediate the remaining VC.

Photo:  Equipment in the Process Control Trailer

Photo of the process control trailer, showing nutrient injection tanks, pumps, and related equipment used for delivery of nutrients to the subsurface.

Contact Information

Battelle PNWD integrates geological, hydrological, biological, and environmental data to evaluate, design, simulate, and/or optimize remediation systems, applying RT3D as a design/evaluation framework where appropriate.

For more information on this project and/or our services, contact:


Program Manager
Environmental Systems Group
Battelle
902 Battelle Blvd., K6-96
Richland, WA 99352
USA
509-371-7072
509-371-7174 FAX

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