SITE INFORMATION AND CORRESPONDENCE

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Shelby Lathrop (ConocoPhill•)and Don Pratt(ARCO) 1502 N. EI Dorado Street and 16 E. Harding Way, Stockton Page 2 of 5 The EHD has redefined the zones slightly, based on soil lithology and correlation of significant sand units across the sites. The A zone includes a major sand unit from approximately 20 feet to 35 feet bgs, locally 15 feet to 35 feet bsg. The sand has variable thickness, appears to have a curving trend toward the northeast, is associated with silt laterally, and overlies a silt unit. The A zone wells on each site are as follows: 16 E. Harding Way — MW-1 through MWA 1, EW-1 through EW-7, and when DTW is less than 30 feet bgs, SVE-1 and SVE-2. 1502 N. EI Dorado Street— MWA through MW-4. The B zone as defined by SECOR includes a thin sand unit consistently present between the depths of 75 and 85 feet bgs. The B zone wells on each site are as follows: 16 E. Harding Way— DMW-1 through DMW-3. 1502 N. EI Dorado Street— MW-5 through MW-14. Between the A zone and B zone screen interval-defined hydrologic units, the EHD has identified an unmonitored hydrologic unit, herein term the B' zone, based on its lithological character. The B' zone is a silt and sand unit commonly occurring between 45 feet and nearly 75 feet bgs. Multiple layers of thick sand units are present in this unit and this zone is 'sand rich'; the sand units are. commonly separated vertically by silt intervals but locally appear to have direct contact between them. The EHD believes that the B' zone sand units are laterally and vertically extensive enough to serve as significant contaminant migration pathways. The B' interval has not been adequately monitored on either site; neither site has wells screened to monitor contaminants in this interval, although the CP site MWA appears to have just penetrated the top of a B' sand. Commonly separated vertically from the underlying B sand units by a silt interval, locally the B' sand may be in direct contact with B sand. The soil types immediately overlying and in the C zone are poorly characterized; only four samples have been collected below the B zone, all at 10-foot intervals from a single well boring. Poorly graded sand with silt was collected from 90 feet bgs, silt from 100 feet bgs, silty sand from 110 feet bgs, and poorly graded sand from 120 feet bgs. The C zone and the immediately overlying soil appear to be similar to the overlying A, B', and B zones and a significant barrier to vertical migration of contaminants is not apparent. The C zone wells on each site are as follows: 16 E. Harding Way— none. 1502 N. EI Dorado Street— MW-15 through MW-17.