The site is in the uplands near the coastal zone and bedrock is very close to the surface. Depth to ground water is 8 - 12 ft. The bedrock is a grano-diorite.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Treatment area is 1,500 - 1,800 sq. ft. Concentration levels indicate that DNAPL may exist.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (4,400 µg/L)
- Trichloroethene (660 µg/L)
- 1,1-Dichloroethene (2,640 µg/L)
- Vinyl chloride (400 µg/L)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
Accelerated bioremediation using HRC was selected as it offered little interuption to on-going facility operations. Approximately 250 cubic yards of contaminated overburden soil was excavated from the source zone down to the bedrock. Immediately following the soil excavation, HRC was manually spread inside the excavated area prior to backfilling. Subsequently, HRC was again injected into the bedrock aquifer and a year later applied above the bedrock through injection and by a drip feed inside and outside of the building upgradient of previously treated areas. One thousand eight hundred and ninety pounds were applied at a rate of 5.5 lb/ft. Injection spacings (by direct push injection) were 5 ft centers
Reduce concentrations to the following MCLs : PCE - 5 ug/L, TCE - 5 ug/L, DCE - 70 ug/L and VC - 2 ug/L
Seventeen months after injection, PCE and TCE were reduced by 99.9% and 99.9% respectively. In addition, increases in daughter products, DCE, VC and ethene, have been observed. The site is being monitored quarterly and the results in Sept. 2003 were PCE - non-detect, TCE - non-detect, DCE - 17.7 mg/L and VC 73.1 mg/l.
A large increase in DCE concentration was observed in December 2002. The molar ratios for initial dissolved contaminant concentrations do not equal those observed at the time of the DCE spike, indicating two possible scenarios: large fluctuations in water levels could re-release contaminaants previously located in the smear zone andor the application of HRC has resulted in the desorption of contaminant mass from soil particles.
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