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ADVISORY—ACTIVE SOIL GAS INVESTIGATIONS 1) Gas-tight valve or fitting for capping the sampling tube; 2) Utility vault or meter box with ventilation holes and lock; 3) Surface seal; and 4) Guard posts. 3.4 DECOMMISSIONING When sample collection ceases at a vapor well, properly remove or decommission wells with concurrence from the regulating agency. The decommissioning process should prevent the well and associated borehole from becoming a conduit for the preferential migration of contamination. The decommissioning procedures within the California Well Standards (Bulletin 74-90) should be followed along with any local requirements. When decommissioning vapor wells with tubing, the following decommissioning steps should be followed: 1) Excavate the borehole down to approximately three feet below grade, exposing the upper portion of the tubing. 2) Either cut the tubing near the bottom of the excavated hole or pull the tubing out of the ground by hand, removing as much tubing as possible. 3) If tubing is still visible in the hole upon removal by hand, cut the tubing near the bottom of the hole, then insert6 sealant, such as powdered bentonite grout, or silicone caulk, into the exposed tubing, filling it as much as possible; 4) Fill the open hole with cement grout to within one foot of the surface grade; 5) Fill the last foot of the hole with compacted native material; and, 6) Restore pavement and vegetation to original conditions, if needed. When decommissioning vapor wells constructed with ridged casing, wells can be overdrilled or cement grouted in place pursuant to local requirement. When overdrilling, a casing guide should be used to prevent the drill bit from drifting during the decommissioning. A casing guide will allow the drill bit to remain aligned on the top of the well casing, allowing for effective removal of the well material. Once the well material is removed, the borehole should be filled with cement grout. If vapor wells penetrate clay units, consideration should be given to overdrilling rather than abandonment in place in order to prevent preferential contaminant migration. 6 Inserting sealant may be accomplished by using a peristaltic pump or large syringe. Sealant must be free of lumps to freely pass down the tubing. July 2015 14