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�✓ u Den's Auto Repair Page 2 308 South EI Dorado Street April 15, 2010 Stockton, California 95203-3404 In the report, AGE recommends that one off-site monitoring well, screened from sixty to sixty- five feet bsg, be installed in the area of cone penetration test (CPT) boring CPT-3 to delineate the lateral extent of the petroleum hydrocarbon plume north of the above-referenced site. By e-mail dated March 22, 2010, AGE proposed a second off-site well be installed north of this site and screened from one-hundred ten to one-hundred twenty feet bsg. The EHD approves the installation of these two wells; however, although the most impacted monitoring well, MW-1A, is screened from sixty to sixty-five feet bsg, decide the screen intervals for the proposed wells based on the soil lithology collected during the advancement of the pilot borings. Soundings from the CPT-3 boring do not demonstrate sand layers in the interval between approximately sixty and sixty-five feet bsg, but do demonstrate a thick sand layer at approximately one-hundred ten to one-hundred twenty feet bsg. The EHD believes at least one additional monitoring well is needed to delineate the lateral extent of the petroleum hydrocarbon plume west of the above-referenced site in the vertical zone identified as Hydrologic Unit HU2 (approximately forty-five to ninety feet bsg). Although the well would be installed up-gradient of the source of contamination, high concentrations of contaminants of concern continue to be detected in groundwater collected from monitoring wells MW-1 A and MW-1 B located on the northwest boundaries of your property. CPT-4 was advanced in the sidewalk on the west side of EI Dorado Street, southwest of MW-1A/MW-1 B, and low concentrations of total petroleum hydrocarbons quantified as gasoline and benzene were detected in grab groundwater sample collected at eighty-two and one-hundred twenty- five feet bsg. For these reasons, the EHD recommends that a well be installed west of MW-1A/MW-1 B. Submit a work plan to the EHD by June 30, 2010, for the installation of additional wells to complete the plume delineation to the north and west of your site. Please contact Vicki McCartney at (209) 468-9852 or by email at vmccartney(a-)-sicehd.com if you have any questions. Sincerely, Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG Senior Registered Environmental Health Specialist Engineering Geologist c: Mr. Brian Millman, PG, Advanced GeoEnvironmental, Inc., 837 Shaw Road, Stockton, California 95215 Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670