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' Updated Site Conceptual Model and Third Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 EAl Project No 1232 removed After completing investigations of the site, Unocal in 1988 excavated approximately ' 6,000 cubic yards of soil from the site The excavated soil was aerated, and based on the analytical testing results associated with the aerated soil, 5,800 cubic yards of the aerated soil was reused on-site as fill, and 200 cubic yards transported off-site for disposal On August 25, 1989, the RWQCB issued a letter for the Unocal site confirming that the soil contamination at the site has been adequately cleaned up, but, that the extent of ground water impact has yet to be defined rBetween 1992 and 1999, additional soil and ground water investigations associated with the Unocal site were conducted ' In February 2001, seven new wells (MW-18D, MW-23S, MW-23D, MW-24S, MW-24D, MW- 25S, and MW-25D) were installed to assist in defining the vertical and lateral extent of hydrocarbon impacted ground water at the Unocal site and around the Robinhood lmgation Well (see Section 1 1 4) In September 2001, four additional wells (MW-8D, MW-9, AS-26 and MW-27) were installed to further define vertical and lateral hydrocarbon-impacted ground water (see Figure 2) 1 14 Robinhood lmnation Well (RIW) ' San Joaquin Delta College owns and formerly operated a ground water extraction well identified as the"Robinhood Irrigation Well" (RIW) (a k a Delta College Well) The RIW was M located southwest of the intersection of Robinhood Drive and Pacific Avenue (see Figure 2) The RIW was installed in 1950 and is reported to be 322 feet deep with perforations m multiple zones beginning at depths as shallow as 40 feet below ground surface (bgs) According to the Water Well Driller's Report for the RTW, "no strata were sealed against pollution " Ground water from the RIW was formerly used to irrigate portions of Delta College's campus ' Ground water monitoring data for the Unocal and Wards sites show that historical pumping of the RIW influenced and changed the natural direction of ground water flow in the area from easterly, to south southwesterly, 1 e , towards the RIW Sampling of the RIW by Unocal and/or Wards for dissolved petroleum constituents began in 1997 and continued through June 15, 2000 In August 2000, Delta College students and staff complained of a gasoline odor from the water derived from the RIW As requested by the RWQCB, the RIW was taken out of service as of 6 00 AM August 22, 2000 The RWQCB in a letter dated February 26, 2001, requested that the RIW be destroyed On April 27, 2001, the San Joaquin County Public Health Services, Environmental Health Division (PHS-EHD) approved the EAI report entitled "Amended Work Plan for Destruction of Irrigation Well, San Joaquin Delta College— Robinhood Irrigation Well, 5151 Pacific Avenue, Stockton, California, "dated April 26, 2001 The RIW was abandoned in August 2001 SHM WORD 1232R0291 -2- ENVIRONMENTALAUDIT INC