SITE INFORMATION AND CORRESPONDENCE

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I L L 1 4l3 1J�. r. �v s �..y i✓ v i u .0 u c....r v v i 'ILIEM0RANDUM �--' CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD a CENTRAL VALLEV REGION 3443 Routier Road,Suite A Phone: (916)255-3000 Sacramento,California 95827-3098 CALNET: 8494-3000 TO. EAT,GLB FRQ:12 SDT Underground Thn1c Unit Underground Tank Unit BATE: b October 1995 SIGNATURE: SUBJECT. REQUEST OR CLOSURE,BEACON,STATION,35 Nj)RTH CHFJRofEE LANE, J,OVI, SAN JOAQUIN COUNTY We received a request for closure dated June 1995,prepared by Delta Environmental Consultants, Inc.(Delta). The report and file contain all the information required in Appendix B,with the exception of calculations and figures showing the cone of influence for the vapor extraction system. Five monitoring wells remain on-site. In September 1986,a 10,000 gallon diesel tank was removed from the site and five monitoring wells installed. The investigation revealed soil and ground water contamination and a vapor extraction system(VES)was installed in September 1987_ Delta's report states that the VES was in operation in October and November 1989,and September through December 1992. l iowever, no explanation has been provided for the sporadic operation of the system. San Joaquin County wrote a letter to Ultramar, Inc.dated 6 April 1995,stating that the VIES was operated from October 1989 to February 1993. The VES consisted of four VE wells,which were abandoned in 1995,during tank removal,and MW-2 and MW4. In February 1995,three unleaded gasoline tanks,two 12,000 gallon and one 10,000 gallon,wore removed from the site and contaminated soil was over excavated to 16 feet below ground surface (bgs)with a small area excavated to 26 feet bgs. The County letter states that no further remedial action is warranted based on the excavation sample results. The confirmation samples revealed up its 16 parts per billion(ppb)ethylbenrene and 200 ppb xylenes at 26 feet hgs remain in soil. No confirmation samples were taken from the north end of the excavation where a previous sample revealed 1,100 parts per million Total Petroleum Hydrocarbons as gasoline('1711g)at 15 feet bgs. Ground water monitoring showed concentrations tip to 3,750 ppb TPIig and 33, 157,235 and 550 ppb benzene,toluene,ethylbenzene and xylenes,respectively,in 1986. In July 1989,all five wells were contaminated. The extent of ground water contamination was never completely dclined, however,following startup of the VES,concentrations in ground water declined. Six ground water monitoring events have been performed since March 1990. All samples were non-detect with the exception of 0.6 ppb benzene in June 1990,in MW-1,which has not been sampled:+ince because of low water levels,and 68 ppb gasoline in MW-4 in May 1992. Upon receipt of the calculations and/or contours of the zone of influence and operation times for the VES,staff can reconsider Ultramar's request for no further action, SI)J