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MEMORANDUM <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 255-3000 <br /> Sacramento,CA 95827-3098 CACHET: 8494-3040 <br /> i TO: GLB, E V FROM: Heidi Barr <br /> Underground Tanks Unit <br /> DATE: 30 November 9995 SIGNATURE. <br /> SUBJECT., REQUEST FOR CLOSURE, ARCO, 85 EAST LOUiSE ROAD, LATHROP, SAN <br /> JOAQUIN COUNTY <br /> _.,,, .. The:-County.issued;a-notice-..of no.,further__action-for=this_s+te_on;23 August4995 and,. <br /> completed the Local Oversight Program Checklist. However, there is limited information on <br /> file for the site and no information regarding the waste oil tank excavation in 1986. <br /> According to the County checklist approximately 330 parts per million Total Petroleum <br /> Hydrocarbons (TPH) as diesel remain in the soil (depth not provided) and little or no <br /> contamination is in ground water. .The wells were abandoned 18 August 1995. <br /> A 550 gallon waste oil tank was removed in 1986. No information regarding the tank <br /> excavation has been provided. In April 1987, three ground water monitoring wells were <br /> installed to approximately 27 feet below ground surface (bgs) at three corners of the site. At <br /> this time six soil samples and three ground water samples were collected. TPH was <br /> detected in soil samples AL-1-1 and AL-5-1, at 29 and 10 parts per million (ppm), <br /> respectively, at 4.5 to 6 feet. The monitoring wells tested non-detect (ND) for TPH and <br /> BTEX (benzene, toluene, ethyl benzene, and xylenes). Well sampling and hydropunch <br /> samples, collected on 26 June 1992, indicated that BTEX and TPH were below detection <br /> limits. <br /> In July 1994, a summary-update by the County stated that the existing monitoring wells were <br /> to be monitored yearly (at minimum), to confirm that there would be no threat to ground <br /> water. Wells were monitored only five times between April 1987 and August 1994. These <br /> _ .rte:-.---.�.+.r�_ -:s.- �.-.,rf_. .,.E a.�._�,•r.__ ..-__ - — ..___ ._..��.•,•: <br /> monitoring events have showrr'the'wells'to be ND'for BTEX, gasoline, andTthesel since their <br /> construction. However, chromatograms from 1992 indicated miscellaneous gasoline and <br /> diesel-range hydrocarbons. <br /> HB <br /> Based on the reported low concentrations of soil and ground water contamination, staff <br /> concurs with the County's recommendation for no further action. <br /> EAT <br />