SITE INFORMATION AND CORRESPONDENCE

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Remo Canepa Page 7 of 9 6230 Pacific Avenue 4/17/2009 Stockton CA compromised , these wells may be vulnerable to surface spills of fuel , which can be expected from time to time during the fueling process. An SVE well not being utilized for the SVE operation , such as SV4, if compromised , could be expected to suck down vapor, including butanes and pentanes, from such spills due to reduced pressure in the subsurface induced by the SVE operation and by gravity — gasoline vapor is denser than air. Any one of these SVE wells could provide an immediate pathway for vapor to groundwater, which recently was approximately 37 feet bsg . Much of the vapor introduced into an open inactive well casing could be expected to be recovered by the SVE system , but probably not all. In contrast, most of the vapor, if not all , from a slow release from the UST system in the area addressed by the SVE system , could be expected to be recovered by the SVE system when it must diffuse slowly through the soil horizon . Another potential source of butanes and pentanes in some of the groundwater samples may be cross-contamination induced during the purging and sample collecting process when the wells and sample vials are open to the atmosphere which may contain some of these highly volatile compounds released during the fueling process . IL ANA r €: r . � Photo shows the close proximity of SVE well and monitoring well to a fuel dispenser next to the geologist, SVE well SV-4 is next to trash can and MW-1 is in the right foreground; the wells could be vulnerable to vapor from surface spills incidental to the fueling process. Why has the site cleaned up so slowly if there has been no second release? The EHD believes there may be several contributing factors: • The estimate of the original contaminant mass may have been significantly underestimated. For a plume of impacted soil the size of yours, relatively few soil Second Release Evaluation 0409