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1, I Y i M ♦ ' ' , r � • 04 March 1996 ' AGE-NC Project No 95-0144 Page 13 of 18 ' 7.0. REMEDIATION OF HYDROCARBON-IMPACTED GROUND WATER 71 IN-SITU AIR SPARGING Air sparging utilizes air injection to volatilize dissolved hydrocarbons and force hydrocarbon vapors into the vadose zone, where they can be withdrawn by vapor extraction systems Air sparging is commonly conducted concurrently with vapor extraction I1 , 711 PRINCIPLES ' Ih-situ air sparging (IAS) utilizes air injection beneath the water table to volatilize dissolved hydrocarbons in ground water and force hydrocarbon vapors into the vadose zone, where they can be withdrawn by a vapor extraction system induces the transfer of hydrocarbons from ground water to soil gas in the vadose zone by IAS i Y _ creating a strong concentration gradient between the two regimes Commonly, an extraction well is surrounded by specifically designed air injection wells that are screened only within the saturated zone (i e below ground Ovate ) car A low blower connected to the injection wells forces air under capacity pressure into the saturated zone producing air channels that strip dissolved contaminants from the ' ground water and rise to the 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 ' 7 12 BASIC SYSTEM DESIGN Injection wells are screened within the saturated zone and normalcy have short screened intervals, typically approximately 5 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 interyal 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 injection wells are properly located, channeling of air flow streams may occur and Unless j p p Y ' m _contamination pockets may be bypassed This problem is more common where fine-grained strata ' with low permeability are interbedded with coarse-grained strata in the saturated zone Air flow is retarded within fine-grained strata, resulting in poor hydrocarbon recovery f, of this technology would require the Wells IAS I 'and IAS2 are suitable for air sparging Use