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, r 28 February 1997 i AGE-NC'Project No 95-0144 - Page 13 of 20 saturated zone (i e below ground water) A low capacity blower connected to the infection wells forces air under pressure ,into the saturated zone producing airs 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 Y ' air flow induced by the vacuum potential 6 12 BASIC SYSTEM DESIGN ' Infection 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 larges radius of influence, clayey soil types tend to produce a more limited radius of influence y F Unless injection wells are properly, located, channeling of air flow streams may occur and �k 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, and hydrocarbon recovery is poor Use of this technology would require the installation of air infection points, screened at a depth of ' approximately 30 to 35 feet bsg The IAS system must be combined with�vapor extraction to contain ' ' r vapor stripped from the ground water The installation of extraction wells would also be required 6 1 3 MONITORING ACTIVITIES One of the potential problems associated with air sparging isolateral spreading of the contaminant F r plume This can be caused by either mounding of ground water above irijection points or lateral air flow away from sparging wells To detect this problem, ground water elevations in monitoring wells and extraction wells (if appropriate) should be monitored on a monthly basis, at the minimum, to detect mounding and the presence of organic vapor i 1 614 FEASIBILITY Remediation of small dissolved ground water plumes requires the installation of a few infection and extraction wells An extensive piping network for injection and extraction must also be installed Air' - , r , r