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05/21/97 WEU 14:19 FAX 510 842 6915 CPL HELP H.O. IZO02 Chevron May 21, 1997 Chevron Pipe tine Company 4000 Executive Parkway,Suite 400 San Ramon,CA 94583 P.O.Box 6059 San Ramon,CA 94583-0759 Mr.Michael J.Infurna Jr. San Joaquin County Public Health Services Environmental Health Division P. O. Box 388 Stockton,CA 95201-0388 Hanson Property San Joaquin County APN No.252-040-02 7750 West Shulte Road,Tracy,California 95376 Dear Michael: As discussed in your May 13, 1997 telephone conversation with Elizabeth Lu,Chevron Pipe Line ? Company(CPL)proposes to install one temporary monitoring well at the subject site and to collect at least two rounds of groundwater sampling data from the newly installed well. This additional work is being conducted because results from a soil and groundwater screening event performed on March 21, 1997 indicated the presence of benzo(a)pyrene at 0.4 micrograms per liter. Polyaromatic hydrocarbons (PAHs),including benzo(a)pyrene, were detected at relatively low concentrations in soil samples collected during the screening event. Because the field techniques used to collect the groundwater sample may have entrained soil particles in the sample, CPL proposes to install a Lcor monitoring well for the purpose of confirming the detection of benzo(a)pyrene. Benzene,toluene,ethylbenzene, and total xylenes (B X), an extractable petroleum hydrocarbons (TEPH) were not detected in soil samples. The PAHs A � detected in soil were below U.S.Environmental Protection Agency Region IX Preliminary r -� Remediation Goals. Therefore,soil samples will not be collected as part of this additional work- CPLproposes installing the temporary monitoring well in the same approximate location where the previous groundwater sample was collected(Figure 1). A schematic diagram showing the 2y(,µ,5 proposed well construction details for the temporary well is presented in Figure 2. Upon,, — completion,the well will be developed and purged until water quality parameters stabilize. After well development and purging have been completed,a groundwater sample will be collected and analyzed for BTEX using EPA Method 8020, PAHs using EPA Method 8310,total purgeable petroleum hydrocarbons (TPPH)using EPA Methods 5030/8015M quantified against a gasoline standard and TEPH using EPA Methods 3630N0550/8015M quantified against a diesel standard. A second groundwater sample will be collected and analyzed for the same constituents A approximately 30 days from the first sampling event. ata from both rounds of groundwater A sampling and the March 21, 1997 field screening event will be summarized in a letter report and submitted to your office for review. I