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GEQMATRIX • Mr Jeff Wong San Joaquin County Department of Public Health Services August 10, 2004 Page 2 (RWQCB) closure requirements, and a proposed approach for collecting the necessary data to complete the evaluations required in the CAP BACKGROUND AND SUMMARY OF EXISTING INFORMATION The project site is located in Stockton, California south of the Port of Stockton's Deep Water Channel (Figure 1) The site is an active grain storage and transportation facility currently occupied by the Penny-Newman Grain Company The following information is summarized from existing reports listed in the reference section of this work plan Four underground storage tanks (USTs), two 12,000-gallon USTs used for the storage of diesel, one 10,000-gallon tank used for the storage of unleaded gasoline, and one 750-gallon UST used for the storage of leaded gasoline, were excavated from the site on January 22, 1988 under the supervision of PHS/EHD Two soil samples, U-I and U-2, were collected by Canome Environmental Services Corporation (Canome) from the excavation for . the 10,000-gallon tank at depths of approximately 17 feet below ground surface (bgs) The tank excavation reportedly extended to a depth of approximately 14 feet bgs Analytical results reported for these samples indicated the presence of total extractable petroleum hydrocarbons (TEPH) at concentrations of 160 and 24 milligrams per kilogram (mg/kg) No benzene, toluene, ethylbenzene, or xylenes were reported as detected in the samples No significant concentrations of petroleum hydrocarbons were detected in samples collected from the excavations associated with the two 12,000-gallon USTs Low concentrations of petroleum hydrocarbons were detected in samples collected from the excavations associated with the 750-gallon UST One soil boring was advanced near the 750-gallon UST in 1997 and no significant concentrations of petroleum hydrocarbons were detected No further investigations are known to have been performed or are planned for these three former USTs Additional investigative work associated with the detection of TEPH in samples from the excavated area of the former 10,000-gallon gasoline UST was performed subsequently From October 1997 through June 2004, a total of 18 soil borings (SB-1 through SB-6, S13-8, S13-9, SB-10, SB-12, advanced by ATC Associates, Inc , and HA-1, HA-2, HA-4, HA-6 through HA-9, and TANK-EX, advanced by Haley & Aldrich, Inc ) were advanced in the area of the former 10,000-gallon gasoline UST to collect soil and/or grab groundwater samples for laboratory chemical analysis Seven (7) groundwater monitoring wells (MW-1 through MW-7) also have been installed at the site and quarterly groundwater sampling has been performed since 1998 Monitoring wells MW-I through MW-6 have 20-foot well screens and are screened between depths of approximately 5 to 28 feet bgs Monitoring well MW-7 is screened across an approximately 30- to 35-foot depth interval G 11Project19000s199631CAP Work Plan doc