ARCHIVED REPORTS_XR0004041 - Laserfiche WebLink

Home Browse Search

analyzed in the laboratory, moderate hydrocarbons odors were noted, and field FID readings on the 10-, 15-, and 20-foot samples were all above 5,000 ppm ' No detectable concentrations of petroleum hydrocarbons were noted in the soil samples collected within the vadose zone (at 16 5 feet and 21 5 feet bgs m each boring) from borings B-2 and B-3, located less than 35 feet from boring B-1 Benzene, ethylbenzene, and MTBE were detected in soil samples collected from within the saturated zone (36 5 feet bgs) from borings B-2 and B-3 at concentrations of 0 088 and 0 072 ppm, ' 0 015 and 0 033 ppm, and 0 025 and 0 178 ppm, respectively In addition, TPHG, toluene, and total xylenes were detected in the 36 5-foot sample collected from boring B-3 at concentrations of 2 92 ppm, 0 008 ppm, and 0 012 ppm, respectively (see Table 3) ' Lead was detected at low concentrations (3 0 to 4 2 ppm) in soil samples collected from soil borings B-1 through B-3 However, these concentrations are within background levels (Dragun, 1988) TOC was detected at a concentration of 414 ppm in the soil sample collected from boring B-2 at 16 5 feet bgs (see Table 3) ' Composite soil sample S-0225-IAB was below detection limits for TPHG, BTEX and MTBE Total lead was detected at a concentration of 158 ppm Consequently, composite sample S-0225-IAB was re-analyzed for soluble lead, using the waste extraction test procedure, with results of the analysis indicating 0 330 ppm (see Table 3) Based on the analytical data collected to date, it appears that residual hydrocarbon impact to vadose zone soils is restricted to a very local area immediately within and surrounding the former UST cavity and vapor well VW-1 ' 5.3 Groundwater Flow Direction and Gradient The wellhead elevations of the monitoring wells at the site were surveyed by Tom O Morrow, Inc , of West Sacramento, California During the March 6, 1997, sampling event, groundwater was measured at 23 81 feet and 23 55 feet below top of casing in wells MW-1 and MW-2, respectively Groundwater elevations were calculated to be 14 78 feet below mean sea level (MSL) in well MW-I and 14 38 feet below MSL in Iwell MW-2, relative to City of Stockton Benchmark No 186 Typically, the surveyed elevations and the depth to groundwater measurements would be I used to evaluate the potentiometric surface beneath the site, but because only two groundwater monitoring wells are present at the site, the potentiometnc surface could not be evaluated However, based on groundwater data collected on February 24, 1997, groundwater flow at the ARCO Service Station and The Transmission Shop, located approximately 450 feet north of the site (crossgradient), was towards the northeast to east Groundwater elevations at the former Dolly Madison site are generally consistent SA(\N\PJZ\2605\26051010 1 BS-97\cjb 2 Emcofl 22605-101 001 5-2 Rev 0 8/4/97 I