SITE INFORMATION AND CORRESPONDENCE

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Remo Canepa Page 8 of 9 6230 Pacific Avenue 4/17/2009 Stockton CA samples were analyzed to quantify the hydrocarbon concentrations impacting the soil , much valuable information may have been lost by not logging the SVE wells or analyzing soil samples from MW-1 , MW-2 or the nine SVE wells. • The 40-foot wells screens utilized for the SVE wells may not have been the most efficient design for addressing the impacted soil . Such long well screens may intersect both zones of high permeability and low permeability. The high permeability zones can be expected to cleanup fairly quickly, but even when clean they still contribute air to the extraction system - clean air - which must be processed through the treatment system and which reduces extraction of impacted air from the remaining impacted soil ; thus the 'clean' air extracted from the 'clean' soil robs the SVE system of energy that would be better utilized focused against the relatively less permeable impacted zones . • The placement of the 40-foot SVE well screens may not have been optimal , all start at either 5 feet bsg (EHD field notes) or at 9 feet bsg (well diagram and AGE well construction detail table); however boring B- 1 first encountered significantly impacted soil at 35 feet bsg , SB-1 at 25 feet bsg , and SB-2 at 30 feet bsg . Thus, based on the available analytical data, potentially 16 to 30 vertical feet of 'clean' soil is addressed by the upper portion of these vapor wells , where the soil often contributes the most air to the system . At the other end of the screen interval , the depth to water varied from as little as 31 .88 feet bsg to as much as 46.96 feet bsg during the March 1999 to January 2008 SVE operation ; the average DTW during this time was 37. 8 feet bsg . The average column of impacted soil addressed by the SVE system would have been approximately 3 to 13 feet thick. It should be noted that some less intensely impacted soil was encountered at 5 to 6 feet bsg in the dispenser area early in the investigation , but 'clean ' soil , by laboratory analysis , was encountered in boring B- 1 at 201 , 25' and 30' bsg , in boring SB- 1 at 15 feet bsg , and in SB-2 at 15' and 20' bsg , with a low intensity impact at 26 feet bsg . The SVE wells near the UST pit may address some shallower impacted soil based on laboratory analysis of excavation samples of uncertain depth. One potential effect of the placement of the 40-foot SVE well screens at shallow depth would be the recovery of slowly migrating, non-catastrophic releases by the SVE system ; the F&B report discussion on butanes and pentanes leads the EHD to believe that neither of these compounds should have been able to migrate through the soil horizon from most of the dispenser portion of the UST system to groundwater while the SVE system was in operation . Intuitively, a release directly from the USTs that has not been repaired should still be leaking . Regretfully, in light of the points discussed above, the EHD can neither concur with an interpretation that a new release has occurred at your site since replacement of the USTs in 1993, nor issue a UAR at this time. The EHD will reconsider this decision if presented with additional information and/or technical analysis of existing data that addresses the points raised above . The EHD recommends the following : • Review of site data, records and operations to identify other lines of evidence that a second release has occurred ; Second Release Evaluation 0409