Laserfiche WebLink
T pZ- r <br /> 1 <br /> 3.0 SAMPLING D ANALYTICAL PROCEDURES <br /> A geologist from Dames & Moore was present at the subject ,ite on June <br /> 1.6, 1989, to collect soil gas samples used to evalua-le tte presence of <br /> susurface hydrocarbon constituents. Eleven soil gas samples were <br /> _ <br /> -collected from ten probe locations and anzl)aed in the field using a <br /> Photovac Gas Chromatograph (Y0550) equipped with a photoionization detector <br /> (21D). Figure 2 shows the probe. locations. Samples were collected frw <br /> approximate depths ranging from six to ten feet. <br /> Equipment used to sample soil gas at the Holt Brothers facility <br /> included a hardened steel drive-tip, a downhole sampling assembly with <br /> vacl1um vials, steel probe rods with an outside diameter cf 0.75 inches, and <br /> a truck-mounted drill rig equipped with hydraulic rams. " Sample locations <br /> were situated in and around the previous UST excavations. and radially out <br /> from the backfilled excavations. During sampling, the probe rod and drive- <br /> tip were pushed to a predetermined depth, and the drive-tip opened. The, <br /> _ sampling assembly was then lowered throtgh the hollow center of the probe <br /> rod to collect the soil gas sample. <br /> Soil gas samples ware collected from depths ranging from approximately <br /> six to fifteen feet. Dense soils onsite limited the depth to which probes <br /> could be advanced. Probing at locations VP4 and VPB was unsuccessful due to <br /> vary dense soils encountered near the ground surface. Probes were advanced <br /> to 15 feet, however, in each of the tank excavation backfills. Probing was <br /> limited to areas directly north and south of the tank excavarion due to <br /> underground utilities and overhead lines. <br /> A 0.10 milliliter gas sample was withdrawn from each sample vial using <br /> _. a 0,10-milliliter syringe, and injected into the Phocovac lOSSU portable <br /> gas chromatograph for analysis. The instrument was calibrated in the office <br /> - with a standard consisting of 0.333 parts per million berzer*, toluene, <br /> ethylbenzene, P-xylene, TCE; PCE, DCE, and TCA. . REtentior. times were <br /> verified in the field by injecting a gas mixture of.benzene and toluene. <br /> Benzene and toluene were chosen as verifying constituents as they tend to be <br /> associated with the higher volatile phase of hydrocarbons. <br /> LD01.046 3 <br /> i <br />