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t <br /> }. MEMORANDUM s <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD -CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Y . 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 ,: 0- Assoc. Engineer <br /> DATE: 19 July 1996 ;t <br /> 1 f; . SIGNATURE: <br /> { <br /> SUBJECT: NO FURTHER ACTION RECOMMENDATION. SOUTHLAND CORPORATION, <br /> 7-ELEVEN STORE NO. 20680, 9110 THORNTON ROAD, STOCKTON, SAN' <br /> JOAQUIN COUNTY <br /> 2 <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 1-986 and the tanks were emptied. On fi May 1986, four <br /> monitoring wells were installedand free product was detected in two of the wells. In May and June <br /> 1 installed. Sampling in June and July. 198b indicated that <br /> 1986, five additional monitoring wells were ins <br /> 14 of the 19 tested domestic supply wells were;contaminated with gasoline and\or BTEX constituents. <br /> Subsequent sampling revealed 4two 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'�impacred domestic wells, submitted quarterly reports <br /> on monitoring well sampling and site activities;' and continued to.investigate the iextent of soil and <br /> ground water contamination. ' :y ' <br /> Dane Well SamQimg, !a o r! . 4 r <br /> Some households and businesses were provided with City water and others with bottled water. <br /> Various domestic wells were sampled periodically from June 1986 to September 1995. On 2 October <br /> 1995, after evaluating sampling results and determining that the wells were no longer contaminated, <br /> San Joaquin County Environmental Health Division notified the property owners tl'rat their wells ould <br /> no longer be sampled and bottled. water was:'no longer necessary. N <br /> of Sal and Groff nd Wabe�, i <br /> The extent of ground water contamination was°investigated and defined, between June 1986 and <br /> torin wells 2 three-well clusters, 3 pumping <br /> September 1991, with a total of 18 ground water monr g , <br /> wells, 1 ground water recovery weil, 4 vapor.ex='ction wells, and 1 soil boring. ;At its maximum, the- <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 MWI, 11k4W3, <br /> MW4, and PW3. The direction of ground waiter flow was generally easterly or s <br /> outheaste�dy_ Depth to <br /> ground water varied between 30 and 50 feet bsg. ! Several wells were,drilled and screened below.60 <br /> feet in order to investigate ground water contamination at lower levels. Only very low concentrations <br /> of contamination were detected initially and Wane was detected after August 1941 in they 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:degpth.,of..SO-feet were,predominantb <br /> sands with layers of clay, silty clay,�aiid silty saiili: <br /> 11 q �� <br />