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Addendum to Corrective Action Plan Page 2 Former Manna Pro Site ' Project No 207 3 August 12,2002 ' As suspected, additional engineering details were obtained in the first phase that suggest it is appropriate to change some of the design plans for the complete remedial system These design alterations consist primarily of a modification of the well spacing, and the method of treating the process gas delivered from the VES system The following sections describe the changes in detail ' 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 extraction wells in conjunction with a similar pattern of sparge wells We proposed to employ the "5-spot" pattern in which a "square" of four equally spaced sparge wells drive mobilized hydrocarbons toward a vapor extraction point located near the center of the four sparge wells as illustrated below ' Sparge � Sparge ' Extraction e • Sparge Sparge The spacing of this grid pattern was determined based upon on the radii of influence of the sparge and vapor extraction wells, respectively In the pilot test of 2000, it was concluded that the radius of influence was 24 feet for sparge wells and 55 feet for vapor extraction wells During the first phase operation, the vapor extraction radius of influence was determined to be 42 feet Based on the new information, we propose that the two groups of wells be placed on 50-foot centers (twice the sparge radius) In Figure 2, the detailed site map, a well grid has been superimposed over the area most severely impacted by gasoline The well grid in this figure suggests that 8 new sparge wells and 10 new vapor extraction wells are appropriate to mitigate the "core" of the contaminant plume 1.3.2 Scope of Work The tasks described in this addendum to the Corrective Action Plan encompass the following principal elements • Drill and construct 8 additional sparge wells and 10 additional vapor extraction wells o Obtain and install the surface equipment needed to operate the sparge and vapor extraction wells This will include the installation of necessary conveyance piping 1 2937 Veneman Ave,#13240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto, CA 95356 Fax(209) 569-0295 I