COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

San Joaquin County Environmental Health Department Mountain House Neighborhood A, Units 3 and 4 SOIL GAS CHARACTERIZATION REPORT 12066.002.000 November 30, 2018 Page 2 The temporary soil gas wells were constructed with 1/4-inch diameter Teflon® tubing equipped with a filter at the base of the tubing. The temporary well installation was performed with a direct push probe rig, which advanced an approximately 3-inch-diameter boring to a depth of 10.5 feet bgs. For each location, the bottom of the well casing was equipped with a filter situated at a depth of 10 feet below the ground surface, centered in the middle of a 1-foot layer of sand. Four feet of hydrated bentonite grout was installed on top of the sand. Then a second filter was placed in the! middle of a 1-foot layer of sand and the remaining annular space was filled to the surface with/ hydrated bentonite grout. Once the installation of the annular seal was complete, the well casings were equipped with a / permanent Swageloke ferrule and nut. The wells were left, allowing for a mandatory two-hour" equilibration time to commence. After the two-hour equilibration time elapsed, the sample train was connected to the well tubing by threading the permanent Swagelok® fitting on the well casing onto the manifold. The sample train consisted of a stainless steel twin summa quick-connect manifold with built in flow controller set to 80-180 ml/min. A purge vacuum canister was attached to the manifold connection closest to the well casing and the sample canister was connected to the manifold fitting furthest away from the well casing. An appropriate volume, approximately two liters of soil gas was then purged from each well and the purge valve was closed. Prior to sampling, p leak test was performed to establish if there was a leak during_sampling. The leak test consisted of using aerosol 1,1-difluoroethane on a rag placed over the manifold on the sample canister. Soil gas samples were collected by opening the valve on the summa canister provided by the laboratory, while the purge valve is closed. Following sampling, each sample canister was labeled with a unique identification number, sampling time, pre- and post-sample vacuum readings. The sample canisters were submitted under documented chain of custody to Torrent Laboratory, Inc. A State-accredited laboratory in Milpitas, California for analysis. For the purposes of this characterization, the 10 soil gas samples were analyzed for the following: Volatile Organic Compounds (VOCs), including TPH-g, by EPA Test method TO-15.1 ANALYTICAL RESULTS Soil Gas Samples Seven discrete samples reported detectable concentrations of TPH-gasoline, ranging from 210 micrograms per cubic meter (ug/m3) to 1650 ug/m3 in samples SG-5 at 5 feet and SG- 6 at 10 feet, respectively. These concentrations are below applicable RWQCB Tier 1 Environmental Screening Levels (ESLs). TPH-Gasoline was reported as non-detectable in the three discrete samples SG-8 at 5 feet, and in both SG-9 samples at 5 and 10 feet. Multiple samples reported low-level concentrations of several VOCs; the following are the maximum concentrations observed for these analytes: Acetone (400 ug/m3), Carbon Disulfide (12 ug/m3), Benzene (33 ug/m3), Toluene (36 ug/m3), 4-Methyl-2-Pentanone (MIBK) (17 ug/m3), Xylenes (14.6 ug/m3), Styrene (4.9 ug/m3), Hexane (40 ug/m3), 2-Hexanone (9.9 ug/m3), 2-Butanone(MEK) ( 110 ug/m3),Tetrahydrofuran (240 ug/m3), Napthalene (3.0 ug/m3), and tert-Butanol (13 ug/m3). All of these concentrations reported are below applicable RWQCB Tier 1 ESLs, DTSC Modified Screening Levels, and USEPA RSLs.