SITE INFORMATION AND CORRESPONDENCE

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California PWional Water Quality 'ontrol Board Central Valley Region ` cam'• Steven T. Butler,Chair `® Sacramento Main Office Winston H.Hiekox Internet Address: http:/h%m,w.swrcb.ca.gov/—rwgcb5 Gray Davis Secreiarvfor 3443 Routier Road,Suitc A,Sacramento.Califomia 95827-3003 Governor Environmental Phonc(916)255-3000•FAX(916)255-3015 Protection 15 February 2000 Mr. Scott Hooton BP Exploration and Oil Inc. 295 SW 41" Street, Bldg. 13, Ste. N Renton, WA. 98055-4931 NEED FOR PROBLEM ASSESSMENT: FORMER BP TERMINAL# 10013,3505 NAVY DRIVE, STOCKTON, CA., SAN JOAQUIN COUNTY I have reviewed the second, third and fourth quarter 1999 monitoring reports for BP's former terminal in Stockton. In addition, you and I have discussed this facility in telephone conversations in 1999 and on 11 February 2000. As we have discussed, the last several rounds of groundwater sampling at this site show generally upward trending concentrations of methyl tert-butyl ether(MtBE) in monitoring wells 1, 2, and 8, and fluctuating concentrations in MW-11. Historically, three other monitoring wells occasionally have shown significant concentrations of MtBE (5,300 ppb in November 1995, 420 ppb in September 1998, and 87 ppb in February 1999 in MW-4; 200 ppb in July 1998 in MW-6 and 2,300 ppb in July 1998 in MW-12). MWs-5, 9 and 13 have shown very low concentrations (less than 13 ppb) of MtBE intermittently. The site's wells first showed MtBE in November 1995. Prior to this date, analyses for MtBE are not recorded in the site's historical records. The early detections were inconsistent in distribution and concentration, but in late 1998, and especially in the last three sample rounds, the trend in MtBE concentration has been significantly upward. As we further discussed,the concentration trends over the last year in wells MW-1, 2 and 8 show that in general MtBE does not track closely with variation in groundwater elevation or with benzene, but it does track fairly well with total petroleum hydrocarbons quantified as gasoline (TPH-g). The TPH-g levels also have increased. The historical database shows that MtBE concentrations in well MW-11 also do not track with water level or benzene, and that well MW-11 responds differently from the other three wells. Taken together, this information suggests that there may be one or more relatively recent releases, and also that residual materials may have been remobilized. You have stated BP's belief that the data indicate release(s) of MtBE occurring after the transfer of the Stockton facility to Tosco. The transfer took place in August 1994, and the first reports of MtBE appeared in 1995. The sharp upward trend occurred in 1998-99. It is also noteworthy that no analyses were made for MtBE prior to 1995, and that a change in analytical laboratories also occurred at that time. California Environmental Protection Agency (a Recycled Paper