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T to control the area upon which a vacuum is exerted, primarily as a barrier to drawing vapors from potential off site sources Passive air inlet wells are not appropriate for this site Groundwater Extraction The analysis for the October 1992 pumping test is included in Attachment 2 Although the pump test data showed that well RW-1 exhibited negligible non-linear head loss and, thus, high efficiency in well design, this does not necessarily indicate that a high rate of groundwater removal will be accomplished through the well The well design has minimal effects on the local aquifer itself Only a portion of the exhibited drawdown in a well is the result of well efficiency In fact, in a highly efficient well, the great majority of the measured drawdown from pumping is due to aquifer response rather than well loss Further, the rate of removal of groundwater from an aquifer is not the only factor which shapes the cone of depression and the degree of hydraulic control, although in general poorly designed wells and/or low yield aquifers tend to result in steep cones of depression with smaller radii of influence. Using the estimated transmissivity (1830 gpd/ft) and groundwater gradient (0 005 ft/ft) from the site, and assuming a pumping rate of 3 5 gpm, a maximum radius of influence of approximately 88 feet is estimated for RW-1 If achievable, a radius of influence of 88 feat . would encompass the majority of the groundwater plume Although groundwater pump and treat systems have been shown to be relatively inefficient, it is widely regarded, in many cases, as the best available technology for groundwater remediation and/or hydraulic control However, if vapor extraction is shown to have significant impact on groundwater contamination at this site, groundwater extraction may V prove unnecessary Accordingly, remediation emphasis should initially be on vapor extraction with continued groundwater monitoring Cleanup Goals As you stated in your response to the FRP, any site within the Central Valley Region of California must refer to the Bann Plan for this region (Region 5) when establishing cleanup goals However, the Region 5 Basin Plan does not establish nondetect levels for initial cleanup goals for groundwater, as stated in your correspondence According to the Basin Plan (Second Edition, Second Printing, 1991), "ground waters designated for use as domestic or municipal supply shall not contain concentrations of chemical constituents in excess of the maximum contaminant levels (MCLs) specified in California Code of Regulations (CCR), Title 22, Division 4, Chapter 15 " The respective MCLs for petroleum hydrocarbon constituents as stated in the CCR are 0 001 milligrams per liter (mg/L) for benzene, 0 15 38009-IO/FRP-ADD aoc