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1 ' 20 January 2005 AGE-NC Project No 97-0343 ' Page 15 of 21 I10 1 1 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 e below ground water) A low capacity blower 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 soil-air-water interface Upon reaching the unsaturated zone,the volatilized hydrocarbons are drawn into the extraction well by the subsurface ' air flow induced by the vacuum potential ' 10 12 Basic System Design Injection wells are screened within the saturated zone and normally have limited screened intervals, 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 with low permeability are inter-bedded with coarse-grained strata in the saturated zone Air flow is retarded within fine-grained strata, and hydrocarbon recovery is poor Use of this technology would require the installation of air injection points, screened at a depth of approximately 65 feet to75 feet bsg The IAS system must be combined with vapor extraction to Icontain vapor stripped from the ground water 10 1 3 Monitoring Activities One of the potential problems associated with air sparging is lateral spreading of the contaminant plume This can be caused by either mounding of ground water above injection points or lateral air flow away from sparging wells To detect this problem,groundwater elevations in monitoring wells and extraction wells (if appropriate) should be monitored on a monthly basis, at a minimum, to detect mounding and the presence of organic vapor Advanced GeoEnvironmental,Inc