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r i 3 � Phase i Environmental Site Assessment City of Stockton Multi-Modal Station/Shopping Center ` Page 19 A Preliminary Endangerment Assessment was completed for the site In a letter dated 17 March 2000, DTSC believed that the site posed a risk to human health and the environment as evaluated under o unrestricted land use activities Risk was calculated to be 3 3 x 10-5 DTSC agreed with the recommendations made for the site 0 A deed restriction on the property to prevent future residential use Risk assessments should be conducted based on the possible future land uses • Evaluate data from the ARCO investigation to determine need for additional remediation • Prepare a work plait for off-site disposal options for treated wood piling • Implement mitigative measures Groundwater monitoring activities were conducted on July 27, 2000 Groundwater flow ranges from easterly to northeasterly with an estimated hydraulic gradient of 0 01 TPH-G was not detected in any of the groundwater samples Benzene was detected at 121 µg/L in MW-1 MTBE was detected at concentrations ranging from 19 6 to 2,440 gg/L in seven of the wells sampled Chloroform, DCE, and TCE were detected in the sample from VEW-3 at concentrations of 0 544, 4 13, and 6 42 pg/L, respectively Well destruction work is the next stage planned On September 18, 2000, eleven monitoring wells were destroyed according to a PHS/EHD approved work plan s Former Bridgestone/Firestone Facility 400 N EI Dorado St. The site is a former automobile gasoline station from the 1920s and 1930s It was later used as a retail tire and automobile service center In 1967, four USTs were closed by filling the tanks with sand In + 1991,one of the closed tanks and I 1 other tanks were removed from the site The three closed tanks (two 7,500 gallons and one 550 gallons) still remain on site The soil surrounding Tanks 4 and 5 was remediated by using a soil vapor extraction system in 1994 and 1995 Environmental site closure was " received on November 30, 1995 from SJCPHS-EHD In May 1997, four slant borings were drilled in the vicinity of the three remaining USTs Toluene, ethyl benzene, total xylenes, and TPH-G were detected at concentrations of 49 2, 308, 1,920, and 16,200 mg/kg in PBI at 20 feet bgs Low concentrations of ethyl benzene and total xylenes were detected in the sample from PB l at 25 feet bgs Concentrations of TPH-G, ethyl benzene, and total xylenes were also detected in the samples collected from PB2 at 20 and 25 feet bgs Benzene detection limits were raised for the samples from PB 1 at 20 and 25 feet bgs and PB2 at 20 feet bgs Contamination was detected between 20 and 25 feet bgs in the bonngs Foothill Engineering concluded that the samples collected near the south tank in 1997 indicated the presence of aged gasoline Based on the investigation, Foothill Engineering k concluded that impacted soil occurs beneath Tanks 2 and 3 at approximately 25 feet bgs r In December 1998, two soil borings were drilled around the USTs The December 1998 soil borings were A completed to depths of 20 and 28 feet bgs, but were extending another two feet for the collection of groundwater samples Groundwater was encountered at 22 and 28 feet bgs Groundwater and soil samples were collected The groundwater sample from BFS-I detected BTEX, TPH-G, and MTBE at l 220 400 340 1,500 g/L 4 2 m /L and 0 78 DIPE and Ethanol were detected at concentrations � l � !-ib � mg/L, µii of 6 1 and 6 4 µg/L in the groundwater sample from BFS-1 Only a low concentration of total xylenes (0 55 µg/L) was found in the groundwater sample from BFS-2 No analytes were detected in the soil samples from the borings, which were collected from 13 5 to 20 5 feet bgs `� CONDOR