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' Corrective Action Plan Page 4 Former Manna Pro Site ' Project No 207 3 February 16,2001 ' groundwater surface was as low as 40 feet bgs This rise in groundwater elevation was coeval with six continuous years of greater-than-average rainfall in the northern San Joaquin Valley The highest concentrations of gasoline are known to lie from about 35 to ' 45 bgs or about 10 to 25 below the surface of groundwater Based on information in the Feasibility Study and other related reports and due to the height of the water column over ' the contaminated interval, it was determined that remedial measures based solely on vapor extraction would not be sufficient to materially reduce the contaminant mass below groundwater in a reasonable period of time Air sparging was introduced as an method to mobilize the hydrocarbon plume located underneath the groundwater surface Air sparging is a process in which air is injected into the saturated subsurface This, in-turn, introduces oxygen, thus helping to facilitate the growth of aerobic bacteria, while also ' mobilizing contaminants and bringing them to the groundwater surface thus enhancing the effectiveness of vapor extraction As these mobilized hydrocarbons move through, and up the water column, adjacent vapor extraction wells may be used to extract the ' mobilized petroleum hydrocarbons The pilot test conducted in the summer of 2000 suggested that sparging would be effective in mobilizing hydrocarbons from the saturated zone in this manner ' The method of sparging air into the saturated zone with the partial purpose of mobilizing • hydrocarbons toward vapor extraction points is essentially a petroleum displacement ' technique One way to use the displacement technique efficiently is to establish a regular pattern or grid of vapor extracti�ells_in conjunction with a similar pattern of sparge wells We propose to employ the"5-spot" in which a "square" of four equally tspaced sparge wells drive motilized hydrolcarbons toward a vapor extraction point located near the center of the four sparge wells as illustrated below ' Sparge � Sparge ;;I ' Extraction ' Sparge Sparge The spacing of this grid pattern was determined based upon on the radii of influence of the sparge and vapor extraction well=rese'yTs'Pnartgheewei1'ot test of 2000, it was concluded that the radius of influenceo , and 55 A for vapor extraction wells This suggests that for the displacement mechanism to be effective, it is appropriate to use the smaller of these spacings to construct a 24-foot well spacing grid In Figure 3 the detailed site map, a 24-foot grid has been superimposed over the area most • ' 2937 Veneman Ave,#8240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295