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i � 1 <br /> t - <br /> 1805 Harbor, Stockton <br /> Page 2 <br /> contamination above the Central Valley Water Quality Control Board'(CVRWQCB)water <br /> quality goals. <br /> 4, Water samples-from'MW-3 and MW-4., located east of the excavation, have the highest <br /> concentrations of TPH-diesel: The groundwater contaminant plume is not defined east or <br /> northeast of these two wells. Additional monitoring wells should be installed east of MW= <br /> .3 near former boring HA-2 and northeast of MW-4.. <br /> 5. Water samples-from MW-7 (deeper well)have had concentrations of TPH-diesel. The <br /> vertical delineation of the groundwater plume needs to be completed. Placement of <br /> additional monitoring wells east of MW-7 should be evaluated for delineation of the <br /> contamination in the 30 to 35 feet interval and at a deeper interval. <br /> 6. All health risks from the residual diesel contamination in the soil and groundwater must <br /> be evaluated. The contaminant levels remaining exceed the San Francisco Bay Regional <br /> Water Quality Control Board Environmental Screening Levels (SFBRWQCB ESL's)for <br /> direct exposure, gross contamination and vapor emissions. A soil vapor investigation <br /> .should be performed to address vapor intrusion issues for present and future uses of the <br /> site. <br /> 7. An evaluation as to whether additional remediation.is necessary to ensure that the diesel <br /> contamination will clean up to water quality goals in a reasonable amount of time (use 10 <br /> years for your initial determination)must be made. If additional active remediation is <br /> j needed to meet the water quality goals in a reasonable amount of time,groundwater <br /> extraction from MW-3 and MW-4 should be considered for mass removal of the <br /> contamination. ` <br /> i <br /> Submit a work plan to EHD by November 20, 2007,for the additional required investigation. <br /> After the work plan is approved, submit an EHD well permit and $89 permit fee. The proposed <br /> work should be completed within 60 days of EHD issuing the well permit. <br /> If you have any questions contact Harlin Knoll at(209)468-3442. <br /> Donna Heran, REHS, Director <br /> Environmental Health Department <br /> i- . <br /> IV <br /> Harlin Knoll, Senior'RE <br /> I -10- <br /> HS Margaret Lagorio, REHS <br /> LOP/Site Mitigation Unit IV Program Coordinator Unit IV <br />' Cc: Huff& Huff-Linda Huff' <br /> CVRWQCB—Jim Barton <br />$ Penny Newman Grain—Robert Mentelos <br /> i <br /> k <br />