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lonScaauxacAar SxeAssearasmKwk Marc 145 Swan xwwrsmw. Swchfisa. Caffivow BACKWUNUND additional sand pack will be installed extending a minimum a] six inches above the lop of the probe. A minimum of six inclws ofdry gmnular bentonite will be emplaced above the sand pack. Neat cement front with hentonite will h emplaced above the granular bentonite to a depth of 5 feet bgs. After allowing the groat to set, the shallow sail gas probe will be installed following the procedures described above. If available, different tubing colors will he used for the shallow and deep soil gas probes to ease in identification. A lahl or tag will also be affixed to each sample tube identifying the well name and probe depth. A flash-mount protective well box will be installed at the surface. The sample tubing will be ruled with a gas-fight valve or fitting tlwt is accessible from inside the wel I box. I'he well box will be set in concrete to match the surrounding paving. Following installation, the soil gas wells will be allowed to swbilize learn minimum of 48 hours prior to sample collection. Soil gas samples will be collected using 1-liter SUMMA canisters at a Bow rate of between 100 and 200 milliliters per minute. One duplicate soil gas sample will be collected for quality assumnec/quality control (QMQC) purposes during each sampling event. Prior to sample collection, a shut-in test will be performed on each sample main (SUMMA canister, Bow controller, manifold, and fittings) prior to connecting it to the snil gas probe. A lank test will also be conducted during each sampling event. A helium-filled shroud placed above the probe during sample collection will he used for the leak reel. A portable helium detector will he used to quantify the helium concentration within the shroud and to field check For leaks. Each soil gas probe will be purged of three volumes of gas prior to sample collection. "rhe purge volume will include the inewmal volume or the tubing and probe tip, the void space of the sand pack, and the void space of the dry bentonite above the sand pack. Soil gas samples will he collected Isom cub depth interval within each well and analyzed for the following constituents: • Total Petroleum Hydrocarbons—Gasoline Range (ITI Ig) • Tow] Pmmleum Hydrocarbons—Diesel Range (TPlld) • Benzcne, Toluene, Ethylbenvene, and Xylenes (BTEX) • MI BE • Naphthalene