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I TreadwelMallo Jeffery Wong San Joaquin County Environmental Division 14 April 2004 Page 2 Groundwater samples from MW-12, collected between 1996 and 2002, did not detect any concentrations of TPHg, and Iow to no concentrations gasoline related compounds or TPHd. Historical groundwater results, that were presented in the latest groundwater monitoring report for the site by Advanced GeoEnvironmental are presented in Attachment A. SOIL EXCAVATION WORK PLAN Soil has been excavated around borings 15B-6 and 1513-9 under a Department of Toxic Substances Control (DTSC) approved Final Remedial Action Plan (RAP)dated 29 August 2001 and a DISC approved Remedial Design and Implementation Plan (RDIP)dated 5 March 2004. The excavation began as six foot by six foot excavations that expanded based on confirmation samples which exceeded the site specific remedial action objectives (RAOs)as outlined in the Final RAP. Prior to excavation, a source for the elevated TPHg and TPHd concentrations in soil had not been identified. The site specific RAOs are listed in the table below. Remedial Action Objectives Soil Arsenic 20 mg/kg Lead 750 mg/kg Total petroleum hydrocarbon-diesel 100 mg/kg Total petroleum hydrocarbon-motor oil 1,000 mg/kg Polynuclear aromatic hydrocarbons Benzo (a)anthracene 0.3 mg/kg Benzo (b) fluoranthene 0.4 mg(kg Benzo(k) fluoranthene 0.4 mg/kg Benzo(a)pyrene 0.21 mg/kg Chrysene 0.5 mg/kg Dibenz (a,h)anthracene 0.25 mg/kg Indeno (1,2,3)pyrene 0.3 mg/kg As part of the expansion of the 1513-6 excavation, an approximately 1,500-gallon open-top steel container was discovered on 30 March 2004. The SJCEHD was notified of the discovery on the same day. As noted in a SJCEHD letter dated 12 April 2004, SJCEHD has determined that the container was an underground storage tank (UST). The tank was removed under a SJCEHD permit and the case was entered into the Local Oversight Program(LOP) for investigation and Area 15 Excavation Work Plan r I