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i - . 4 Unocal Corporation - RDS56.93 �'i►' ` P�Box 5155 Crow rayon Place.5..i.e 400 San Ramon,California 94563 Telephone(510)667-0760 Facsimile(SI 0)277-2309 UNOCAL76 April 13, 1993 them Region Ms. Elizabeth Thayer porate Environmental nediation and Technoiogy _ _ _ Regional Water Quality Control Board Central Valley Region 3443 Routier Road Sacramento, Ca 95827-3098 UnocalS i Staticip No. 6015 601 E. Kettleman Lane Lodi, California near ms. i iiayoi. • This letter is written to formally request that a meeting be scheduled regarding the subject Unocal site. The meeting should include the Regional Water Quality Control Board (RWQCB), Central Valley Region, Mr. Harlin Knoll from the San Joaquin County Public Health Services (SJCPHS) Department, Unocal Corporation, and Kaprealian Engineering, Inc. (KEI). Subsequent to removal of underground fuel storage tanks, waste oil tank and product piping at the subject site in February and March of 1991, Unocal Corporation has complied with all of the requirements set forth in the Tn-Regional Guidelines of the RWQCB. Soil samples collected from beneath the underground fuel storage tank pit following overexcavation indicated non- detectable concentrations of TPH as gasoline except for 6.1 ppm detected in one sample. KEI has conducted a quarterly groundwater monitoring and sampling program since the installation of the first wells in August of 1991, which have consistently indicated non-detectable to lour concentrations of dissolved hydrocarbons. Two exploratory borings and tune monitoring wells have been installed at the site. A cumulative total of 143 soil samples were collected and analzsed during site characterization. Of these samples, 139 indicated non-detectable concentrations of TPH as gasoline and 137 indicated non- detectable concentrations of benzene. The four samples that indicated detectable levels of TPH as gasoline had levels ranging from 1.9 ppm to 5.7 ppm, while the six samples that showed detectable levels of benzene had levels ranging from 0.0094 to 1.9 ppm. Based on the aforementioned discussion, there does not appear to be any significant soil contamination 0 remaining at the subject site. As recommended in the LUFr Manual, KEI generated a computer model utilizuig the SESOIL software package which indicated that the low levels of contamination detected do not appear to pose any significant threat for the degradation of the current groundwater quality. Unocal, therefore, requests a meeting be held to discuss partial site closure (for contamination issues)