SITE INFORMATION AND CORRESPONDENCE

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Steve Schneider ` Page Two - �` October 7, 1992 ,A benzene were in error. Two exploratory borings and nine monitoring wells have been installed at the site. A cumulative total of 143 soil samples were collected and analyzed during site characterization. Of these samples, 139 showed non-detectable concentrations of TPH as gasoline, and 137 showed non- detectable concentrations of benzene. The four sam les that showed 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. To date, four quarters of groundwater samples have been collected from wells MW 1, MW2 and MW3. Three quarters of groundwater samples have been collected from wells MW4 through MW9. The only wells that have consistently shown detectable concentrations of petroleum hydrocarbon§ are wells MW2 and MW6. TPH as gasoline concentrations from MW 2 have ranged from non-detectable to 240 ppb, while benzene concentrations in MW2 have ranged from 1.4 ppb to 13 ppb. TPH as gasoline concentrations 'n MW6 have ranged from non-detectable to 120 ppb, while benzene concentrations in MW6 have ranged from non-detectable to 0.95 ppb. TPH as gasoline and benzene have consistently been on-detectable in the groundwater samples collected from downgradient wells MW7, MW8 d MW9, except for 70 ppb of TPH as gasoline and 0.57 ppb of benzene detected in well NW9 on April 7, 1992. Therefore, it does not appear that the groundwater at the site has been significantly impacted by hydrocarbon contamination, and that the relatively minor group water contamination that has occurred is residual in nature and is isolated to the vicinity of tie underground storage tanks. Certainly, there is no indication that an ongoing contaminatioi source is present at the site or that the degree of contamination at the site is increasing. Based upon the information presented above, it is bot Unocal's and KEI's opinion that a partial site closure is warranted for the subject site. The soil contamination remaining at the site is residual in nature and has been well-defined and thus does not appear to pose any significant threat for degradation of current groundwater quality, Unocal agrees to continue monitoring the groundwater quality at the site through at least the upcoming rainy season; however, Unocal also formally requests that a partial site closure (for site. contamination issues) be granted by the appropriate regulatory.agencies. __ If you have any questions, please feel free to contact me at (510) 277-2341. Sinc rely, Rick D. Sisk Manager Remediation Projects f RDS/ECR/bsb cc: P. C. Stern J. E. Mason T. R. Ross, KEI C RWQCB-Region 5 (Central Valley Region)