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MEMORANDUM <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Router Road, Suite A Phone: (916) 255-3000 <br />` Sacramento, CA 95827-3098 CALNET: 8-494-3000 <br /> TO: Gordon L. Boggs FROM: Elizabeth A. Thayer <br /> UST Program Manager Assoc. Engineer <br /> ;5�_ r <br /> DATE: 19 July 1996 _ SIGNATURE. <br /> SUBJECT: NO FURTHER ACTION RECOY AIENDATION, SOUTHLAND CORPORA TION, <br /> 7-ELEVEN.STORE NO._?0680, 91I0 THORNTON ROAD,.STOCKTON., SAA . <br /> JOAOUTV COUNTY <br /> i' <br /> The 7-Eleven store is located in a semi-rural subdivision of Stockton, where each lot has at least one ' <br />{ domestic water supply well. -An underground tank precision test in March 1986, indicated that there <br /> was a leak in the unleaded fuel system. It was estimated that 3000 to 5000 gallons of product were <br /> lost since November 1985. An initial investigation, indicated that the tanks were in good condition; <br /> however, the store stopped selling gasoline in 1986 and the tanks were emptied. On 6 May 1986, four <br /> monitoring wells were installed and free product was detected in two of the wells. In May and June <br /> 1986, five additional monitoring wells were installed. Sampling in June and July 1986 indicated that f <br /> 14 of the 19 tested domestic supply wells were contaminated with gasoline and\or BTEX constituents. k <br /> Subsequent sampling revealed two additional domestic wells were contaminated: <br /> Southland provided alternative drinking water supplies to the households and businesses with <br /> impacted wells, instituted periodic sampling of impacted domestic wells, submitted quarterly reports <br /> on monitoring well sampling and site activities, and continued to investigate the extent of soil and <br /> ground water contamination. <br /> Doc We31 Sampiiag- r �~ <br /> Some households and businesses were provided with City water and others with bottled water. <br /> Various domestic wells_wereIsampled,periodically,from June 1986 to September 1995. On 2 Ocrober <br /> I995,after evaluating sampling results and determining <br /> that the wells were no`longeF'contaminated, <br /> San Joaquin County Environmental i iealrl'i Division notified the property owners that their wells wo'o'd. 1 <br /> no longer be sampled and bottled. water was'no Ionger necessary.- ,- , <br /> of Sod aid G�a2d Water C.oion � <br /> ' The extent of ground water contamination.was investigated and defined, between June 1986 and <br /> { September 1991, with a total of 18 ground water monitoring wells, 2 three-well'clusters,-3 pumping <br /> 1. wells, 1 ground water recovery well, 4 vapor.ection wells, and 1 soil boring. At its maximum, the <br /> xtra <br /> ground water plume covered approximately 13 acres with dissolved contamination in all but 5 of the <br /> monitoring and ground water extraction wells and with up to 4 feet of free product in IvLW1, MW 3, <br /> MW4, and PW3. The direction of ground water flow was generally easterly or southeasteriy. Depth to <br /> bsg. Several wells were drilled dna screened below 60 <br /> ground water varied between 30 and 50 feet <br /> feet in order to investigate ground water contamination at lower-levels. Only very low.concentrations <br /> of contamination were detected initially and'none was.detected after August 1991 in thL-deep wells. <br /> Soil samples were not collected for analysis from most of these wells and borings, therefore, the extent <br /> of soil contamination was not well defined initially. Soils to a depth of 50 feet were predominantly <br /> ,f sands with layers of clay, silty clay, and silty sand. - <br /> I <br />