WORK PLANS - Laserfiche WebLink

Home Browse Search

L f Mr. Siddarth Sewalia 1 February 2011 Page 3 valve to establish and maintain an air-tight seal. A soil gas probe construction diagram is presented as Figure 3. After construction, the soil gas probes will be allowed to equilibrate for at least 30 minutes prior to purging and sampling. Figure 4 illustrates the soil gas sampling equipment setup. Prior to sampling, a leak check and purging will be performed at each location. Each probe will be purged using a 1-liter Tedlar bag and lung box. Field screening will be performed using a photoionization detector (PID) and oxygen/carbon dioxide/methane meter for a minimum of three successive Tedlar bag purge samples to confirm steady readings before sample collection. Helium will be used as a tracer gas to check that no significant amount of atmospheric air enters the soil gas sample through the annular seal between the ground surface and probe. To test for potential leakage, a shroud will be placed around the ground surface of each probe and helium gas will be added to the shroud during the purging and field screening process. The concentration of helium in the shroud will be recorded with a portable helium detector to confirm that the shroud contains a minimum of 10%helium. Soil gas samples collected in the Tedlar bag will be screened to confirm that the concentration of helium in each sample was less than 5% of the concentration in the shroud, verifying that the Tedlar bag samples consist of at least 95% soil gas prior to collection of samples for laboratory analysis. If helium tracer data indicates a leak, the probe fittings will be tightened as needed to obtain a representative soil gas sample. Following purging and leak testing, soil gas samples will be collected using 6-liter Summa canisters. The initial canister vacuum will be measured before sampling to confirm the integrity of the canisters prior to sample collection. The canister flow controllers will be set at a flow rate of 200 milliliters per minute (ml/min) so that sample collection will not impose an excessive vacuum on the soil gas probes. Soil gas will be collected over a period of approximately 5 minutes, after which time the canister will be closed and disconnected from the probe. After sample collection, the residual vacuum in each canister will again be measured and recorded. For quality assurance/quality control, a split sample will be collected from one location and sent to the analytical laboratory as a blind duplicate. The sample containers will be labeled, logged on a chain-of-custody form, and transported under chain-of-custody procedures to Air Toxics, Ltd., of Folsom, California(Air Toxics), for analysis. Following sample collection, the soil gas probes will be manually pulled from the borehole, the boreholes will be sealed according to County requirements, and the surface of each borehole will be completed with cement or asphalt to match the surrounding ground surface. P:\PRJ2003REM\Wilbur-Ellis\Wr0250(JTF)\STOCKTON\S IT Vapor Sampling\Work Plan\JTF Stockton Off-Site Soil Gas Sampling Work Plaa.docx engineers I scientists I innovators