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... Memorandum CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD s CENTRAL VALLEY REGION 3443 Routier Road Phone: (916) 361-5600 Sacramento, CA 95827-3 ATSS 8-495-5600 TO: Files VL�6ROM: Scott Walker J(jN Asso. Eng. Geol . ENVIROMENTAL HEALTH F ERM IT/SERVICI=S DATE: 26 May 1988 SIGNATURE: SUBJECT: KNOWLES GAS STATION, 1140 WEST HAMMER LANE, STOCKTON On 26 May 1988 , a meeting (see attached roster) was held to discuss the Knowles gas station soil and groundwater investigation. On 17 March 1987, G underground storage tanks were removed from the property and 8 soil samples were taken and analyzed for BTX&E and chlorinated hydrocarbons (EPA-8020/8015) and lead (EPA- 3050/7420) . A representative from the San Joaquin Local Health District (SJLHD) was present during the soil sampling. Benzene was found at fairly low levels (0. 071 to 0. 673 ppm) near tanks 1- 4 but at significantly higher levels (2 . 556 to 41. 278 ppra) ;year tanks 5 and 6 . Toluene was found at <0 . 001 to 226. 016 ppm, xylene at <0. 071 to 203 . 995 ppm, and ethyl benzene at <0. 001 to 33 . 135 ppm. Toluene, xylene, and ethyl benzene were also elevated near tanks 5 and 6 . Lead was found at 7 , 0 to 10. 0 ppm. The soil- samples were taken at the fill pipe ends of tanks 1-4 , ,at both ends of tanks 5 and 6, and at depths of 21 feet below fill to 28 feet below asphalt. On 10 April 1987 the soil at tanks 5 and 6 was resampled at depths of 30 to 34 feet and analyzed for BTX&E and TPH (gas) (modified EPA-5030/8020/8015) . Benzene was found at <1. 0 to 1. 2 ppm, total BTX&E at <1. 0 to 7 , 6 ppra, and TPH at <1. 0 to 4 .4 opm. In response to the soil sample results, the SJLHD requested an initial ground water investigation (see attached map) . Three hollow stem auger soil borings were drilled on 2K September 1987 to a depth of 65 feet near the perime-t-er of the tank. pit. The boreholes were completed as monit-or wells with 30 feet of 0. CI- inch PVC: well screen. Monitor well #3 was screened to a depth of 56 feat due to heaving sands. Soil samples taken at 20 -:eet and 45 to 50 fee;: frog, the borings showed <0.5 ppm BTX&E and TPH gas at <.1. 0 to 3 . 4 ppru. Water samples taken on. 1 October 1987 showed benzene (State Action Level (SAL) -0. 7 rrb) at 36. 0 to 85 . 0 ppb. Toluene (SAL-100 ppb) at 1. 1 to 20 . 0 ppb, Xylene (SAI - ,-620 ppb) a 9 . 0 to 100. 0 ppb, and ethy].benzene (SAL-680 Fpb) at <:, 5 to 1. 3 Ppb were also found. TPH (gas) was foi-,nd at 290 to 330 ppb. Resampling of the wells on 2 February 1988 shower,? sign .ficantly