FIELD DOCUMENTS_FILE 1 - Laserfiche WebLink

Home Browse Search

GROUND WATER TREATMENT PLAN FOR FORMER EXXON RS 7-3942, NORTH PERSHING AVENUE, STOCKTON, CALIFORNIA Site History On 11 December 1986, American Environmental Management Corporation ( AEM ) removed piping and collected soil samples from the site of former Exxon RS 7-3942 ( Figure 1 ) . Under the direction of Mr. Dan Moe with the San Joaquin Local Health District, the samples were analyzed for aromatic volatile organic compounds and for organic lead. These results, as well as subsequent soil and water analyses results, are summarized in Table 1 . In brief , the organic lead content of the four soil samples were below the detection limit of 0 . 05 mg/kg. Except for sample ES#3 ( at the Northwest corner of the tank field, near the pump island ) , the benzene, toluene, ethyl benzene, and xylene ( BTEX ) levels in the soil samples were below the detection limit of 0 . 001 mg/kg. Sample ES#3 showed toluene and ethyl benzene concentrations at 0 . 076 mg/kg and 1 . 2 mg/kg, respectively. Benzene and xylene concentrations for this sample, however, were below detection . Harding Lawson Associates ( HLA ) installed three ground water monitoring wells ( MW1 -MW3 ) on 26 and 27 January 1987 ( Figure 1 ) . During well installation soil samples were obtained for subsequent analysis Total Petroleum Hydrocarbons (TPH ) using EPA methods 5020/8015 . No hydrocarbons were detected in the soil samples . Prior to development, the wells were found to be free of product and sheen. After well development, water samples were obtained for TPH and benzene, toluene, and xylenes using EPA methods 5020/601 /602 . Table 1 summarizes the analyses for these wells, and shows offsite, upgradient contamination, with increasing levels of contamination down gradient of the site. The direction of groundwater flow was determined to be northeast ( N500E ) and at a slope of 0 . 001 ( HLA 1987 ) . On 5 May 1987, EA Engineering, Science, and Technology ( EA) conducted a soil vapor contaminant assessment ( SVCA ) at the former site of Exxon RS 7-3942 . In summary, the SVCA detected an area at the northern end of the the pump islands, at a depth of three feet, where as much as 20 ppm benzene and 25 ppm toluene were detected. The other thirteen sampling locations contained benzene and toluene concentrations at one ppm or less. Using the information gained from the SVCA, the soil vapor isoconcentration contours for benzene were sketched for this site. The resulting plume appears to be migrating to the northeast ( EA 1987 ) . In order to further define the extent of contamination , EA drilled four additional monitoring wells on-site ( MW4-MW7 ) on 14 and 15 July 1987 . After the soil and water analysis results were examined, it was determined that the extent of contamination had not been determined and required the installation of off-site wells. EA installed off-site wells MW8 and MW9 in February 1988 . 1