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Water Boards <br />Central Valley Regional Water Quality Control Board <br />29 June 2018 <br />Michael and Sharon Olivarez <br />540 Scotts Avenue <br />Stockton, CA 95203 <br />_ EDMu NO G. BROWN JR. <br />1y :, OOYEPTVC. <br />MATTHEW ROORIOVEZ <br />EOR <br />ENVIRONMENTAL <br />PROTECTION <br />PATH TO CLOSURE IMPEDIMENT DISCUSSION & SHALLOW SOIL INVESTIGATION <br />WORK PLAN, FORMER SKIPS SERVICE STATION, AKA: OLIVAREZ PROPERTY, <br />300 SOUTH CALIFORNIA STREET, STOCKTON, SAN JOAQUIN COUNTY <br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br />reviewed the Path to Closure Impediment Discussion & Shallow Soil Investigation Work Plan <br />(Work Plan) dated 2 May 2018, and the Report First Quarter 2018 Groundwater Monitoring <br />(1Q2018 Report) dated 15 May 2018, both submitted on your behalf by Ground Zero Analysis, <br />Inc. (Ground Zero). The HIS Auto Repair located at 300 South California Street in Stockton <br />(Site). <br />Site wells are screened in three zones, A zone wells are screened between 18 and 35 feet <br />below ground surface (ft bgs), B zone wells are screened between 40 and 65 ft bgs, and C zone <br />wells are screened between 90 and 115 ft bgs. During the first quarter 2018, Ground Zero <br />detected: <br />up to 510 micrograms per liter (ug/L) total petroleum hydrocarbons as gasoline (TPH-G) <br />and 20 ug/L naphthalene in the A zone; <br />up to 54,000 ug/L TPH-G, 2,900 ug/L benzene, 1.2 ug/L methyl tert butyl ether (MTBE), <br />5.5 ug/L 1,2-dichloroethane (1,2 -DCA), and 620 ug/L naphthalene in the B zone; and <br />up to 510 ug/L TPH-G, 86 ug/L benzene, 1.9 ug/L 1,2 -DCA, and 6.0 ug/L naphthalene in <br />the C zone. <br />Ground Zero calculated a downward vertical gradient and flow directions towards the northeast <br />in the A and B zones and towards the north-northeast in the C zone. Depth to water ranged <br />from 23.76 feet below ground surface (ft bgs) to 27.86 ft bgs. <br />In the Work Plan, Ground Zero proposed advancing five temporary soil vapor monitoring wells, <br />two in the vicinity of the former fuel USTs along the north side of the current building, one <br />between the former waste oil UST and the building, one near the leading edge of the shallow <br />groundwater plume near MW -9, and one near the down -gradient edge of the plume near MW -5 <br />along the eastern edge of the Site property. Ground Zero proposed analyzing soil gas samples <br />for TPH-G, benzene, toluene, ethylbenzene, total xylenes (collectively BTEX), MTBE, <br />KARL E. LONGLEV SCD, P.E., CHAIR 1 PATRICK PULUPA, ESO., EXECUTIVE OFFICER <br />11020 Sun Center Drive #200, Rancho Cordova, CA 95670 1 www,waterboards.ca.gov/centralvallev <br />C' RECYCLED PAPER <br />