SITE INFORMATION AND CORRESPONDENCE_FILE 1

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Shell station page 2 2494 E. Fremont St., Stockton. In addition, the concentrations of 1,2-DCA detected in the groundwater samples from S131 are similar to those found around Shell's site in SB-4, SB-7, SB-8, SB-9 and SB-10. Soil data that shows a source area or repeated groundwater sample data that supports the idea that 2491 Fremont Street had a petroleum leak from the former UST system is required before EHD can direct the owners of 2491 Fremont to perform investigation of a leak at their site. Shell must install monitoring wells north of their site in appropriate zones to delineate their plume of contaminated groundwater. Well screens are to be installed at depths where CPT borings have identified permeable zones and where existing onsite monitoring wells for the zones are screened (i.e: 45' to 65' bgs, 75' to 85' bgs, and deeper if the 75' to 85' bgs zone wells have repeated elevated levels of petroleum). Shells' rationale for not performing vertical assessment "in the source area" is that drilling through shallow impacted groundwater to assess the deeper groundwater zones produces questionable data. Shell's example is that 1,640 parts per billion (ppb) of 1,2-DCA was detected in the groundwater sample obtained from CPT boring, SB-4 at 72 feet below surface grade (bsg) and that the level of 1,2-DCA in the groundwater samples from S-4-83 are much lower. EHD brings to Shell's attention that the CPT log for SB-4 shows that the sample in question, SB-4-72', was taken from a two-foot CPT screened sampler in silty sand/sand, whereas monitoring well S-4-83, is screened from 73' to 83' bsg and this interval is shown on the CPT log to be gravely sand/sand. Also, the groundwater grab sample, SB-4-82, of 141 ppb is similar to the groundwater samples from monitoring well S-4-83 that have ranged from 74 to 130 ppb. Further demonstration that assessing the vertical extent by drilling through shallow impacted ground water is acceptable is provided by the fact that monitoring well S-4, screened 37' to 57' bgs has lower concentrations of 1,2- DCA than those found in the deeper monitoring well, S-4-83. Shell's concern that questionable data is produced does not appear to be the case for this site. EHD does not accept Shell's rationale for not conducting a vertical investigation near the source area. Shell's original intention to place soil boring S-19 in the core/source area to 150 feet bgs and ONLY sample for lead in the soil has still not been resolved. EHD has made it clear that conducting an investigation for 1,2-DCA based on only lead analysis of the soil is unacceptable. Please clarify your intentions and note the EHD directive for SB-19 in EHD correspondence dated September 22, 2003. If Shell wants to move the location of proposed SB19 down gradient of the northern island area (source), in the area of S-4, EHD will approve the new location.