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ENGEO — Expect Excellence SOIL GAS SAMPLING The soil gas monitoring well casings will consist of 1/4-inch-diameter Teflon® tubing equipped with a filter at the base of the tubing. The wells will be installed with a direct-push probe rig, which will advance an approximately 3-inch-diameter boring. At each location, the first well boring will extend to a depth of approximately 5 feet below the ground surface; the second well boring will extend to a depth of approximately 10 feet below the ground surface. The bottoms of the well casings will be equipped with a filter that will be situated at depths of 4.5 and 9.5 feet below the ground surface, respectively, centered in the middle of a 1-foot layer of No. 3 sand. Twelve inches of dry granular bentonite will be installed on top of the sand, and the remaining annular space will be filled with hydrated bentonite grout to 6 inches below grade. The sample train will consist of a stainless steel twin Summa manifold with built-in flow controller set to 200 ml/min. A purge vacuum pump will be attached to the manifold connection that is closest to the well casing, and the sampling canister will be connected to the manifold fitting furthest away from the well casing. Prior to connecting the sample train to the well casing, we will perform a "shut-in" test to assess for potential leaks. The shut-in test will consist of capping the end of the manifold, then cracking and closing the purge canister to apply 100 inches of water vacuum. We will observe the vacuum gauge for 2 minutes, if there is an observable change in vacuum, it will be determined if there is a leak and corrective action will be taken and the shut-in test will be repeated. The sample train will be connected threading the fitting on the well casing onto the manifold. Based on DTSC's Active Soil Gas Investigations Advisory (July 2015), three well volumes will be purged from the wells. Purge volume will be calculated to include the total volume of the tubing and probe and the void space of the sand pack and dry bentonite. After purging is completed, the purge valve on the manifold will be closed, and the vacuum pump can be removed and connected to another well if desired. Samples will be collected by opening the sample canister valve and allowing the sample canister to extract soil gas until the vacuum in the sample canister reaches approximately 5 inches of mercury. The leak detection compound 1,1-diflouroethane will be applied following DTSC's Active Soil Gas Investigations Advisory (July 2015). We will label each sample canister with a unique identification number, sampling time, and pre- and post-sample vacuum readings. The soil gas samples will be submitted to Torrent Laboratory, Inc., a State-certified laboratory located in Milpitas, California, under documented chain-of-custody for analysis of volatile organic compounds (VOCs) by EPA Test Method TO-15. The target laboratory reporting limit for soil gas is less than the respective site-specific soil gas screening levels. Sample results will be reported in micrograms per cubic meter. 12066.002.000 January 3, 2019