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that only the dissolved phase plume having a benzene concentration greater than 100µg11, would be targeted Air sparging at a rate of 10 scfm for one-day releases almost as much oxygen as 1000 lbs of ORC does in a year Therefore, air sparging is expected to be significantly more effective 2.2 Mobility The area expected to be remediated using each respective approach was also evaluated, which is important at this facility because much of the low concentration dissolved phase plume is underneath the bakery and relatively inaccessible ORC relies on diffusion in groundwater and natural groundwater movement to spread dissolved oxygen through an aquifer Effective coverage from an ORC injection point is particularly limited in less permeable formations and under conditions involving relatively flat groundwater gradients Effective coverage from a single injection point was estimated to be between 40 and 80 square feet Additionally, ORC would not be expected to have an effect on potentially impacted soil above the groundwater table or to effectively volatilize contaminants in groundwater AS/SVE utilizes physical injection of a readily-soluble gaseous oxygen source into the aquifer The injection of compressed air into the subsurface enhances the mobility of the added oxygen and improves mixing and effective solubility Oxygen is added in quantities sufficient to volatilize dissolved petroleum hydrocarbons in groundwater and adsorbed petroleum hydrocarbons in the vadose zone, as well as promoting their aerobic biodegradation The initial pilot test demonstrated a sparging radius of influence of about 30 feet and a venting radius of influence of about 130 feet ASISVE is expected to be more effective than ORC because of soil permeability with respect to gases being significantly higher(typically 1,000 to 10,000 times higher) than those for liquids The effectiveness of ORC is dependent on dissolution and groundwater migration and therefore would be expected to have limited effect at points more distant from injection points Additionally, AS over a period of time would introduce greater amounts of oxygen into the subsurface than even several liberal injections of ORC, promoting not only aerobic biodegradation but volatilization as well The purpose of the SVE system is to recover any soil vapors that are generated by the sparging process and vent any potentially impacted vadose zone soils Remedial Action Work Plan Prepared for Tae EARTHGRA@rS COMPANY Prepared by Philip Services Corp H 1ENV1624001451RAP61300 doc 4 8/31/00