The hydrogeology of the site is dominated by partially weathered rock (schist and gneiss). Contaminant transport is controlled by lineaments consisting of fractured pegmaitites and quartz veins in a partially weathered rock and underlying component bedrock. The dissolved TCE exists as a biforcated plume that has migrated via the highly conductive fractured zones.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
This pilot study treated dissolved TCE; however, there is a source area which is being treated by AS/SVE and removal by pumping.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (DNAPL)
No technologies selected.
- Chemical Oxidation (In Situ)
- Pump and Treat
- Soil Vapor Extraction
Comments:
Phase I of the pilot study was designed with two pre-existing wells that were used as the recovery well and injection well. Laboratory bench-scale testing was performed prior to commencing the field test to evaluate the ability of permanganate to degrade TCE at the site as well as to assess the chemical oxigen demand. A tracer test was performed in the wells using sodium bromide to evaluate chemical transport and dilution between the wells. The in-situ chemical oxidation was conducted by injecting sodium permanganate into the injection well while monitoring field parameters, such as oxidation reduction potential (ORP), conductivity and pH, in the monitoring well located 40 ft. from the injection well. Ground water samples were obtained from the recovery well and analyzed for chloride, manganese and VOCs. Analytical results show that a decrease in TCE concentration occurred along with a three-fold increase in chloride concentration.
Phase II occurred in an offsite area of the plume that had TCE concentrations of approximately 300 ug/L. Four test wells, spaced 20 ft. apart were installed within the plume in a region of the aquifer dominated by extensive fracture zones. A series of high concentration sodium permanganate solutions (5600 mg/L) have been injected into the most upgradient test well. The Phase II results show that the TCE concentration in three of the five test wells decreased to non detectable levels and the TCE concentrations in the remaining wells have been reduced by 50%.
This was a pilot study.
Current full-scale ISCO implementation builds upon lessons learned during the two pilot tests, the most important of which was the need to use relatively small injection volumes (only a fraction of estimated pore volume) in order to minimize displacement of treated ground water. Operations began with the installation of 12 new wells. The first series of semi-annual injections was conducted in February 2003. Single injections ranging from 250 to 500 gallons were accomplished through gravity feed of a 2% NaMnO4 solution to the screened zone of eight wells. Similar injection events were conducted in October 2003 and April 2004.
Preliminary results indicate that two monitoring wells in the vicinity of the injection well show TCE concentration reductions of 69% and 77%. TCE degradation in these wells is supported by the presence of oxident degradation indicators such as increased levels of manganese dioxide and carbon dioxide and a temporary decrease in Ph. Semi-annual injections of NaMnO4 are scheduled to continue through the end of 2007.
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