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Mr.Denis Brown <br /> Re: 620 W. Charter Way, Stockton, CA <br /> Page 3 of 3 <br /> • The*65-to 77-foot bsg interval is characterized by an interval of variably moderate to high <br /> permeability, possibly fine grained, overlying the upper portion of a permeable, thick sand <br /> unit generally shown on cross sections between 75 and approximately 88 feet bsg. <br /> Impacted groundwater samples have been recovered from the fine-grained interval and the <br /> upper portion of the sand unit; groundwater samples recovered from the middle to deep <br /> portions of the sand interval have not yielded detectable concentrations of the chemicals of <br /> concern.. The distribution of soil types and contaminant concentrations is suggestive of a <br /> contaminant fate and transport scenario as delviiued above for the 45- to 50-foot bsg <br /> interval. <br /> Although the EHD concurs with the recommendation for installation of monitoring wells in the 45- <br /> to 50-foot and 65- to 77-foot bsg intervals, care should be taken to avoid providing a potential <br /> migration pathway for contaminants into the middle to lower portions of the 75- to 88-foot sand <br /> interval; this will probably require placing the screen intervals above the sand layer and may <br /> require continuous soil coring in the intervals of interest. <br /> The proposed deep well is also approved near CPT-5 to assess the high contaminant concentrations <br /> detected in the groundwater sample collected at 91 feet bsg. Care should be taken to avoid setting a <br /> portion of the screen section in the deep sand; again, continuous cores may need to be collected to <br /> properly set the screen interval. <br /> The EHD also recommends that at least one well be set in the upper portion of the deep sand unit, <br /> preferably near CPT-5, or nearby in the inferred down-gradient direction from the UST pit, to <br /> monitor for contaminants in this potential contaminant migration pathway. <br /> Please submit a work plan for the.proposed scope of work to the EHD by 25 September <br /> 2006. <br /> Please contact Vicki McCartney at (209) 468-3456 or at v nccartneyCc'sjcehd.com by <br /> electronic mail if you have any questions regarding this letter. <br /> ..Donna Heran, REHS,Director <br /> Environmental Health Department <br /> Victoria L. McCartney, Senior REHS Ma�rgaretLagorio,aREHS . <br /> Unit IV, Site Mitigation Program Coordinator Unit IV <br /> c: James L.L. Barton,PG—CVRWQCB <br /> Aubrey K. Cool,PG—Cambria <br />