ARCHIVED REPORTS XR0003742 - Laserfiche WebLink

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Recommendation We do not recommend implementing this alternative at this time because the effectiveness and cost of GWE are not well defined Cambria recommends using periodic GWE, and assessing whether GWE is effective During this time, Cambria recommends applying for a discharge permit from the City of Stockton If long term GWE is cost effective, it could be implemented more quickly if the discharge permiting process has already been started Periodic Ground Water Extraction This alternative includes removing ground water from the subsurface using vacuum trucks on periodic basis - weekly, for example Periodic GWE should enable ground water extraction begin immediately and enable an assessment of the effectiveness of GWE as a long term remedial alternative Periodic GWE will enable MTBE and other hydrocarbons to be removed from ground water beneath the site, and provide hydraulic control to prevent migration of MTBE and hydrocarbons from the source area and the site Cost-Effectiveness This alternative should only be cost-effective in the short term Although GWE in general is not the most cost effective way to remove dissolved hydrocarbons from the subsurface, it may be the most cost effective way to provide hydraulic control in the short term Since the bulk of the hydrocarbons and MTBE appear to be limited to the area near the former tank complex, this alternative will be an effective way of reducing the highest concentrations of hydrocarbons and MTBE in the primary source area Recommendation Cambria recommends implementing a program of periodic GWE for a period of approximately six months Concentrations of hydrocarbons and MTBE will be monitored over this period to determine whether the activity is effective and whether GWE would be effective in the long term Soil Vapor Extraction This alternative involves applying a vacuum to extract hydrocarbon-bearing vapors from the vadose zone and capillary fringe area Extracted hydrocarbons are typically treated by activated carbon, oxidizers or internal combustion engines SVE can improve ground water quality by removing source area hydrocarbons, by encouraging hydrocarbon diffusion from ground water, and by delivering oxygen to the subsurface Oxygen usually stimulates naturally-occurring hydrocarbon biodegradation This method is most effective for moderate to high permeability materials SVE is not directly effective for MTBE, because it is highly soluble and is difficult to remove from water, but should remove other hydrocarbons and provide subsurface oxygen Additional oxygen could in turn stimulate biological degradation of hydrocarbons and MTBE Cost-Effectiveness- SVE does not appear to be a cost effective alternative for treatment of MTBE Implementation and operation of a SVE system would require significant permitting, installation, 240-0783 23