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I Updated Site Conceptual Model and First Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 EAI Project No 1232 Between 1992 and 1999, additional soil and ground water investigations associated with the ' Unocal site were conducted Table 1 summarizes the historical ground water testing results for the Unocal site 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 Irrigation Well (see Section 1 1 3) 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) r1 1 3 Robinhood Irrigation 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 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 in multiple zones beginning at depths as shallow as 40 feet below ground surface (bgs) According to the Water Well Driller's Report for the RIW, "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, i e , towards the RTW Sampling of the RIW by Unocal and/or Wards for dissolved petroleum constituents began in 1997 and continued through June 15, 2000 Table 1 summarizes the results of testing ground water samples from the RIW ' 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 EAT report entitled "Amended Work Plan for Destruction of Irrigation Well, San Joaquin Delta College —Robinhood Irrigation Well, 5.151 Pacific Avenue, Stockton, California, "dated April 26, 2001 The RIW was abandoned in August 2001 ' Efforts are currently underway to provide Delta College with a new irrigation well to replace the removed/destroyed RIW The new irrigation well will be located on the campus of San Joaquin Delta College in an area identified as the "Holt Parking Lot" The new well will be ' constructed in such a manner that pumping of the well will not influence the upper water bearing zones impacted by petroleum hydrocarbons r BHM 1212RO231 -2- ENVIRONMENTAL AUDIT, INC