The site consists of low-permeability glacial till and fractured bedrock. The depth to water varies, but remains generally from 10 to 20 feet below ground surface (bgs). The groundwater shows slow movement, at less than 15 feet per year. Geologic conditions at the site are categorized as glaciated New England ground moraine terrain, with the soils consisting of up to 10 feet of fill and disturbed materials overlying approximately 50 feet of hard till underneath. Below the hard (basal) till are fractured schist and gneiss bedrock. Private bedrock wells had been completed on the property for water supply.
Targeted Environmental Media:
 Fractured Bedrock
Information not provided by source sited.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (0 µg/L)
- 1,1-Dichloroethane (0 µg/L)
- 1,1-Dichloroethene (0 µg/L)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
A small-scale biological reductive dechlorination (BRD) program was implemented during the summer and fall of 2001. During the program, 200 gallons of black molasses was injected into four wells and 23 gallons of 60 percent sodium lactate was injected into three wells. The wells were located in two pilot areas approximately 50 feet away from one another. The black molasses was injected using direct pressure, while the sodium lactate was injected via gravity feed. Monitoring continued from fall 2001 through spring 2002. The results showed decreased oxidation reduction potential (ORP) values, less than 0.5 parts per million (ppm) dissolved oxygen, and varied concentrations of volatile organic compounds (VOCs). A few wells exhibited slight decreases in contaminant concentrations, while others showed slight increases. The majority of the wells showed no measurable change.
In August 2002, BRD applications began at a larger scale by applying 540 gallons of 60 percent sodium lactate. The injection took place after the well that would be injected was purged of the standing water column so that the effects of initial dilution would be minimized. Monitoring post-injection occurred from fall 2002 to spring 2003.
The goal of the 2002 BRD application was to test biological reductive dechlorination as a larger-scale pilot application.
The monitoring results showed decreased ORP values at less than 150 millivolts (mV) at the wells, except for one that continued to show residual permanganate. The ground water where the molasses had been injected transitioned from oxidizing to reducing, supporting natural anaerobic reductive dechlorination. Concentrations of VOCs remained unchanged or showed a site-wide increase versus the baseline. The areas where the sodium lactate had been injected showed no measurable impact to the physical conditions or the quality of ground water.
Site conditions were not ideal for effectiveness of the technology. The analysis suggested that bacterial populations at the site were insufficient for BRD.
References: Pac, Tim, Richard Lewis, and Terry Connelly. Sequential Implementation of In Situ Chemical Oxidation and Reductive Dechlorination. Paper 5A-11. Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, California). May 2004.
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