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x bottom of the borehole,the lower portion of the hole may be grouted as necessary with a large-diameter bit. or backfilled accordingly. The borehole may be drilled out(reamed) Upon reaching TD,drilling fluid is circulated to remove cuttings. "Tedlar"bag at the end of the purging procedure and may be Selected casing is then run into the borehole and set to the desired analyzed to ensure the purging was effective. depth. Monitoring wells are cased with clean,threaded,factory- perforated and blank casing. The perforated interval consists of To minimize the potential for cross-contamination between air slotted casing,generally with 0.020-inch-wide by 1.5-inch-long slots, samples,the polyethylene tubing,if not sample dedicated,is with 42 slots per foot. Centering devices may be fastened to the thoroughly cleaned and rinsed. casing the ensure even distribution of filter material and grout within Vapor samples are subject to very limited holding times,typically 48 the borehole annulus. The well casing is thoroughly washed and/or hours. Thus,care must taken to avoid delays in submittal of vapor steam cleaned,or may be purchased as pre-cleaned,prior to samples.to the laboratory. In the event the vapor samples cannot be installation. All recoverable drilling fluid and/or cuttings are collected submitted to the analytical laboratory on the same day they are for temporary storage and disposed of properly pending analytical collected,they are to be temporarily stored in the dry,non- results. refrigerated,packed cooler until the very first opportunity for submittal well within the required holding time,taking into account After setting the casing,sand or gravel filter material is poured into the time needed for shipment to and receipt by the laboratory. the annular space to fill from boring bottom to generally 1 foot above the perforated interval. A 1-to 2-foot-thick bentonite plug is set SOP-10 above this filter material to prevent grout from infiltrating the filter VAPOR SAMPLING:SYRINGE SAMPLING TECHNIQUE pack. Either neat cement,containing about 5 percent bentonite,or sand-cement grout is then tremmied into the annular space from the Prior to vapor sampling,the vacuum system must reach a stabilized top of the bentonite plug to near surface. A traffic-rated vault is air flow(cubic feet per minute)for approximately 15 minutes. Prior to installed around each wellhead for wells located in parking lots or the actual collection of the vapor sample,the following data is driveways,while steel"stovepipes"are usually set over wellheads in recorded:air flow,temperature,and pressure at collection ports and landscaped areas. gauges. After installation,the wells are thoroughly developed to remove The sampling equipment consists of a clean, 100cc,gas-tight syringe residual drilling materials from the wellbore,and to improve well and;silicone septa. performance by removing fine material from the filter pack that may pass into the well. Well development techniques used may include The sampling ports are brass connections,fitted with silicone septa, pumping,surging,bailing,swabbing,jetting,flushing,and air-lifting, and threaded into a tapped hole in the system piping. Samples are All development water is collected either in drums or tanks for collected by inserting a clean syringe into the septum and the temporary storage,and properly disposed of pending laboratory plunger actuated several times. Each syringe should be purged of analytical results. To minimize the potential for cross-contamination three syringe volumes before collecting the sample. On the fourth between wells,all development equipment is either steam cleaned or purge,the plunger is extracted slowly until the syringe is filled with a properly washed prior to use_ Following development,the well is" gas sample,then the syringe is withdrawn and the needle allowed to stand undisturbed for a minimum of 24 hours before its immediately plugged with a silicone stopper. The sample should be first sampling. placed in a non-refrigerated,dry cooler with sufficient packing to eliminate breakage during transport. Cooling samples will cause SOP-9 condensation of moisture,thereby distorting laboratory analysis. VAPOR SAMPLING:"TEDLAR"BAG SAMPLING TECHNIQUE For quality control purposes,a duplicate air sample should be collected from each port. This sample is put on hold at the laboratory Prior to vapor sampling,the vacuum system must reach a stabilized pending initial analysis. air flow(cubic feet per minute)for approximately 15 minutes. Prior to the actual collection of the vapor sample,the following data is Vapor samples are subject to very limited holding times,typically 48 recorded:air flow,temperature,and pressure at collection ports and hours. Thus,care must taken to avoid delays in submittal of vapor gauges. samples to the laboratory. In the event the vapor samples cannot be submitted to the analytical laboratory on the same day they are The sampling equipment consists of a"Tedlar"bag(available in 1,3, collected,they are to be temporarily stored in the dry,non- 5,and 10 liter sizes),a diaphragm pump,and 1!4-inch-diameter refrigerated,packed cooler until the very first opportunity for polyethylene tubing(approximately 1 foot long). submittal well within the required holding time,taking into accounE the time needed for shipment to and receipt by the laboratory. The sampling ports are brass connections,fitted with a silicone septa,and threaded into a tapped hole in the system piping. The SOPA I sampling procedure requires one end of the tubing be slipped over VAPOR SAMPLING:CANISTER SAMPLING TECHNIQUE the sampling port and the other end over the diaphragm pump to acquire an air-tight connection. The sampling pump is purged for 1 Prior to vapor sampling,the vacuum system must reach a stabilized minute with the extracted vapor to be sampled. Following purging, air flow(cubic feet per minute)for approximately 15 minutes. Prior to the discharge of the pump is then diverted through a two-way valve the actual collection of the vapor sample,the following data is into the"Tedlar"bag,which should be filled to 314 of volume recorded:air flow,temperature,and pressure at collection ports and capacity. Caution should be taken not to overfill the sampling bag. gauges. The sample is placed in a non-refrigerated dry cooler with sufficient packing to eliminated damage during transport. Cooling samples will The samphrng equipment consists of a sterilized,gas-tight,"Vacu- cause condensation of moisture within the sample,thereby distorting Sampler"stainless steel canister,and 114-inch-diameter polyethylene laboratory analysis. tubing approximately 2 feel in length. For quality control purposes,a duplicate vapor sample should be The sampling ports are brass connections fitted with silicone septa collected from each sampling port. This sample is then put on hold and threaded into a tapped hole in the system piping. The sampling at the laboratory pending initial analysis. To ensure quality cohtrol procedure requires one end of the tubing to be slipped over the and minimize the potential for cross-contamination prior to and sampling port and the other end over the canister nozzle to acquire during sampling,the diaphragm pump is thoroughly purged for an air-tight connection. The actuator on top of the canister is approximately 5 minutes with nitrogen or clean air(i.e.,compressed depressed for 10 seconds. At the end of the 10 seconds,the clean air). A"blank"sample of the discharged air is captured in a canister is disconnected from the tubing and the tubing is F