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r r r r r r r r r r r r r r r t► r r > 6.0 BACKGROUND INFORMATION ON THE PROJECT SITE The Caltrans Shop 10 site is a highway maintenance equipment storage and repair facility located in Stockton, CA. Caltrans equipment, including snowplows and other roadway vehicles and related equipment are serviced and stored on this site. The site is occupied by office space, permit buildings, parking lots, shop maintenance areas, machine shop and warehouse. The primary risks associated with this site are vehicle and heavy equipment and pedestrian traffic, noise, compressed air, welding, hydraulic lifts, solvent cleaning and equipment washing in the shop area. In 1978, one 5,000-gallon underground storage tank (UST) with unknown contents was reportedly removed from the Site due to a detected leak. In 1989, three 5,000-gallon gasoline USTs, one 5,000-gallon diesel UST and one 1,000-gallon waste oil UST were removed from the Site. Between 1987 and 1996, twenty-five groundwater monitoring wells and two vapor extraction wells were installed at the Site to determine the vertical and lateral extent of contamination. Twelve groundwater wells are currently located onsite and are included in the quarterly monitoring program. The Site has been on a quarterly groundwater monitoring schedule since 1990, and will continue on a semi-annual basis with the next sampling event occurring in December 2009. The groundwater flow direction beneath the Site has generally been to the east and northeast. The ASISVETS was required by the San Joaquin County Environmental Health Department(EHD)to cleanup residual soil and groundwater impacted areas remaining after UST removal and limited over-excavation per a Remedial Action Plan submitted in 2002 by Caltrans. The ASISVETS operated from startup on December 1, 2005 to June 25, 2009, when the system was shut down due to low levels at system influent. On May 27, 2009, the EHD agreed with Stantec's recommendation to shut down the soil vapor extraction and air sparging system and initiate site closure procedures. Confirmation borings and soil sample collection as well as temporary soil vapor wells and soil vapor samples are being conducted in accordance with the site closure procedures. STANTEC Consulting Corporation 6-1