WORK PLANS - Laserfiche WebLink

Home Browse Search

a 0 Site Assessment Work Plan Broadbent&Associates,Inc. Former ARCO Station No.443 Vacaville,California November 8,2013 Page No.iv 3.2 Soil Gas Well Installation Two soil gas wells as shown in Drawing 2 will be installed using following procedure: • Using up to three-inch hand auger,advance two borings to a depth of approximately five-feet from the exterior base of the building foundation; • Using a down-hole rod or alternative probe support design to support the well tubing, place Teflon tubing and attached vapor probe in the open boring with the probe tip set at six inches above the bottom of the boring; • Install sand filter pack from the bottom of the boring to six inches above the vapor probe so that probe tip is midway in the sandpack; • Place two feet of dry granular bentonite on top of sand pack and fill the remaining borehole with hydrated bentonite; and ts such as gas-tight valves or fittings to cap the tube, utility • Install surface completion componen vault with ventilation holes,and surface seal. 3.3 Shut in Test A shut in test will be performed prior to purging and sampling the soil gas wells to check the integrity and ensure that there are no leaks in the above-ground sampling system. Shut in test will consist of applying vacuum of up to 100 inches of water to the assembled sampled train(while it is isolated from the soil gas well and summa canister)and observing vacuum gauge. A hand-operated graduated syringe will be used to apply the necessary vacuum. If there is any observable loss of vacuum,the fittings are adjusted until the vacuum does not noticeably dissipate. 3.4 Leak Test A leak test will be performed simultaneously while purging to check the integrity of the soil gas sample by ensuring that ambient air is not introduced into it. A helium shroud connected to the aboveground sample train will be used to perform the leak test. Following procedures will be followed: • Shroud will be placed over well head and aboveground sample train will be connected to soil gas well; • Helium will be injected under shroud to achieve target shroud concentration of two orders of magnitude greater than the helium meter minimum detection limit; • Purge three casing volumes from the soil gas well with a syringe or pump,at a flow rate of 100 to 200 milliliters per minute(ml/min) and contain the purged gas in Tedlar bag(s); • Use the helium detector to measure the helium concentration in the Tedlar bag and beneath the shroud; • If the helium concentration in the Tedlar bag is<5%of the concentration in the shroud,then proceed to sample collection;and • If helium concentration in the Tedlar bag is greater than or equal to 5%of the concentration in the shroud,then the helium test is considered as failed, potentially due to the well seal being