ARCHIVED REPORTS_XR0005916 - Laserfiche WebLink

Home Browse Search

rn +) 06 June 2003 AGE-NC Project No 9$-0433 Page 4 of 4 • The lateral extent of the dissolved phase plume can be approximated Figure 4 shows the areal extent of known dissolved hydrocarbons The highest concentration of dissolved v hydrocarbons quantified as TPH-g,TPH-d and overall BTEX compounds extends northward of the former UST area Hydrocarbons were encountered in the presumed down-gradient direction from the UST to the location of grab water sample B 14 TPH-g and BTEX concentrations in ground water decrease eastward in the area of well MW-7 and decrease south of the former UST's, in the area of well MW-8 Vertical Assessment At UST Area • TPH-g and TPH-d were detected in soil samples collected from boring B17 at 20 feet and 30 feet bsg, at maximum concentrations of 71 milligrams per kilogram (mg/kg) and 230 mg/kg,respectively,in the sample from 20 feet bsg BTEX compounds were not detected in the soil samples analyzed • MTBE was detected in soil sample B17-20 at a concentration of Q 3 mg/kg In addition, MTBE was detected in samples at collected at 25 feet, 30 feet and 35 feet bsg at • concentrations of 0 048 mg/kg, 0 092 mg/kg and 0 03 mg/kg, respectively TPH-g was detected in grab ground water sample B17 at a concentration of 240 µg/l, TPH-d was not detected Ethylbenzene and total xylene were detected at concentrations of 0 61µg/1 and 1 1 ptg/1,respectively MTBE was detected in water sample B 17 at a concentration of 160 µg/1 TBA was also detected at 36µg/1 Free Product Removal and Monitoring • Due to the lower than average and sustained ground water elevation,additional hydrocarbon- impacted soil is exposed across the site and particularly in the former UST area, to a depth of 25 feet bsg When the USTs were removed the ground water table resided at 15 feet bsg Therefore,due to reduced water pore-pressure,free-product was and is continually liberated from a depth of 15 feet to 25 feet bsg, and has naturally collected in the uneven lithology contacts of the site In a accordance with California Underground Storage Tank Regulations, ' Article 5, Section 2655, AGE prepared a work plan in response to discovery of free-phase petroleum hydrocarbons in well MW-6 at the site At the request of the EHD free-product will be recovered in wells MW-1 and MW-6 using passive skimmers Advanced GeoEnvironmentai,Inc