Decomposed bedrock underlain by a transition zone of decomposed bedrock and ultimately fractured bedrock make up the geology at and around the site. Depth to groundwater ranges from 1 to 57 feet below ground surface with the main groundwater pathway following decomposed bedrock.
Targeted Environmental Media:
 Fractured Bedrock
Two plumes are identified within the shallow groundwater; one is located at the Yard and the other is in the vicinity of the Yard.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (0 µg/L)
- 1,2-Dichloroethene (0 µg/L)
- Other
Comments:
No site characterization technologies were identified within the reference abstract.
- Pump and Treat
- Soil Vapor Extraction
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
A 1990 soil removal action and 1994 groundwater remediation system (GRS) were initial remediation efforts. In 1998, a remedial action plan was approved for hydraulic containment of the Yard source area and monitored natural attenuation for downgradient source areas. In 2000, a soil vapor extraction (SVE) system was installed in the Yard. Over 2,100 pounds of volatile organic compounds (VOCs) were removed by the GRS which operated through 2006. VOC concentrations into the GRS declined from greater than 40,000 µg/L to less than 500 µg/L. Over 3,500 pounds of VOCs were removed by the SVE, almost half of which were removed within the first year.
Initial actions at the site have resulted in concentrations of VOCs reducing by two orders of magnitude and the separation of the two plumes (one located at the Yard and the other downgradient). In an effort to enhance the remediation of VOCs, an enhanced in-situ bioremediation (EISB) pilot was initiated in March 2007 and completed by May 2007. A biological barrier was hydraulically engaged by direct injection of emulsified vegetable oil containing lactate and bioaugmentation with a commercial culture in single rows on 30 foot centers. Because injection rates slowed significantly during injection, the required volumes to reach the design radius of influence (ROI) were not reached. Between 28 to 85 percent of the calculated volumes provided ROIs ranging from 53 to 92 percent of the designed ROI. Monitoring wells indicated that the groundwater was reduced (ORP <-200 mV) 5 feet from the injection points within 2 days and at 15 feet from the injection points within 28 days. Injected fluid reaching 15 feet from injection wells indicated possible preferential flow paths between the monitoring and injection wells.
None provided
Two rounds of post injection monitoring has been performed both inside and outside of the designed ROI. Less than 18 feet from an injection point, the ORP is less than -50 mV, nitrate is nonexistent, sulfate concentration is reduced greatly, and methane is present in a range of 0.1 to 8 mg/L. This indicates that conditions are conducive for reductive dechlorination. After an initial pH drop, levels are currently above 6.3 in all wells. As measured by total organic carbon, electron donor ranges from 4 to 500 mg/L. Within impacted wells, the ratio of individual daughter products to parent compounds has changed by factors of 2 to 400 times. Two monitoring wells show the presence of ethene, accounting for 40 percent of total ethenes within one the wells.
References:
Lehmicke, Leo, Jim Schwall, Michael Palmer, and Ed Modiano. Enhanced Biodegradation Following 12 Years of Pump and Treat, Platform Abstract Session C2. Presented at the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 19-22, 2008.
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