Site geology consists of silty overburden, weathered and decayed gneiss and schist saprolite, with fractured bedrock at depths up to 175 feet below ground surface (bgs).
Targeted Environmental Media:
 Fractured Bedrock
Information was not provided in the source cited.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (0 µg/L)
- cis-1,2-Dichloroethene (0 µg/L)
- Vinyl chloride (0 µg/L)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
A pilot-scale study was designed with monthly batch injection. Five injection wells were installed each 25 feet apart and were placed perpendicular to the direction of ground water flow with screens between 75 and 175 feet bgs. Eight observations wells (four shallow wells labeled OP-2, OP-4, OP-6, and OP-8, and four shallow wells labeled OP-1, OP-3, OP-5, and OP-7) were installed. Observation wells OP-1 and OP-2 are upgradient and are located 32 feet perpendicular from the injection wells. Observation wells OP-3 through OP-8 were spaced on 25-feet centers, and each was located 34 feet from the injection wells. Ten monthly batch additions of substrate consisting of sodium lactate, yeast extract, and diammonium phosphate were injected beginning in October 2005. A bioaugmentation culture was injected at the end of 5 and 6 months.
The remediation goal was to achieve complete biodegradation of trichloroethene (TCE) to ethene when supplemented with lactate and bioaugmented with a dechlorinating enrichment.
Upgradient shallow well OP-2 has shown a maximum of 17 mg/L of total organic carbon (TOC) and a slow rate of reductive dechlorination of cis-1,2-dichloroethene (cDCE) to ethene. Downgradient shallow well OP-4 received little substrate and showed complete conversion of TCE to cDCE, but slow conversion of cDCE to vinyl chloride (VC) and ethene. Downgradient well OP-8 showed elevated TOC levels but limited dechlorination of cDCE to VC and ethene, most likely as a result of the low pH. Shallow well OP-6 had high TOC levels of up to 166 mg/L and has shown good dechlorination toward ethene. The batch injection method forced substrate to the upgradient deep OP-1 well, which showed almost complete dechlorination to ethene and ethane. Similar responses were observed in downgradient wells, OP-3, OP-5, and OP-7.
The pilot-scale test has shown that batch substrate injection can promote complete reductive dechlorination in a complex, fractured bedrock site, and that effective delivery of the substrate is the key to a successful site remediation.
References: Lee, M.D., R.L. Raymond, P. McKalips, and G. Kirkpatrick. Enhanced Reductive Dechlorination Pilot in Fractured Bedrock at Former Landfill. The Ninth International In Situ and On-Site Bioremediation Symposium. May 7 - 10, 2007. Baltimore, Maryland.
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