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' 01 June 1999 AGE-NC Project No 95-0137 Page 16 of 26 6.0. GROUND WATER REMEDIATION ALTERNATIVES AGE believes that in-situ air sparging and vapor extraction, ground water extraction, In-situ ' bioremediation/bioenhancement, and natural attenuation are appropriate remedial technologies or strategy to consider to address hydrocarbon-impacted ground water on the subject site 6 1 IN-SITU AIR SPARGING ' In-situ air sparging(IAS)utilizes air injection into the saturated zone to strip dissolved hydrocarbons from ground water and transport the hydrocarbons into the vadose zone, where they can be withdrawn by a vapor extraction system Air sparging is commonly conducted concurrently with soil ' vapor extraction One added benefit to IAS is the Introduction of air in the ground water to stimulate biodegradation or enhance the population of biodegrading microbes 611 Principles IAS induces the transfer of hydrocarbons from ground water to soil gas in the vadose zone by creating a strong concentration gradient between the two regimes Commonly, an extraction well is ' surrounded by specifically designed air injection (sparging) wells that are screened only within the saturated zone (i a below ground water) A high capacity blower or compressor connected to the injection wells forces air under pressure into the saturated zone producing air channels that strip ' dissolved contaminants from the ground water and rise to the vadose zone Upon reaching the unsaturated zone,the volatilized hydrocarbons are drawn into the extraction well by the subsurface air flow induced by the vacuum potential 1 6 12 Basic System Design ' Injection wells are screened within the saturated zone and normall have limited screened intervals J Y , typically five feet Since most of the air escapes from the upper part of the interval where head ' pressure is the least, little is gained by increasing the length of the screen interval ' The radius of influence of a sparging well is dependent on site lithology and the depth of the sparging well Sandy soil types tend to produce a larger radius of influence, clayey soil types tend to produce a more limited radius of influence ' Unless injection wells are properly located, channeling of air-flow streams may occur and contamination pockets may be bypassed This problem is more common where fine-grained strata Advanced CeoEnwonmentsl,Inc