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Unocal Corporation RDS56.93 a, 2000 Crow Canyon Place,Suite 400 P.O.Box 5155 San Ramon,California 94583 P Telephone(510)867-0760 Facsimile(510)277-2309 . i if 3 UNOCAL 76 APR 16 1993 ENVIRONMENTAL HEALTH April 13, 1993 PERM1T1$eRVICF8 Northern Region Ms. Elizabeth Thayer Corporate Environmental Remediation and Technology Regional Water Quality Control Board Central Valley Region 3443 Routier Road Sacramento, Ca 95827-3098 Unocal Service Station No. 6015 601 E. Kettleman Lane Lodi, California Dear Ms. Thayer: 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). r 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 Tri-Regional Guidelines of the RWQCB. Soil samples collected j 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 conducte.: a quarterly groundwater monitoring and sampling program since the installation of the first wells in August of 1991, which have consistently indicattA' non-detectable to Jow concentrations of dissolved hydrocarbons. Two exploratory borings and nine 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 remaining at the subject site. As recommended in the LUFT Manual, KEI generated a computer model utilizing 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).