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continuous coring and/or drilling with tri-cone roller or fixed- contamination.
<br /> blade drag bits. Generally,rotary drilling is used when more
<br /> conventional hollow-stem auger drilling either is or becomes Frequently,hollow-stem augers are used to drill and sample
<br /> infeasible. Various drilling fluids(mud or air),used to keep to either a minimum depth or auger refusal. In such cases,
<br /> the borehole from caving and to remove drill cuttings,are the augers may be left in place as temporary surface casing,
<br /> chosen according to the nature of the soils and/or geologic with the center plug removed and drilling/coring carried out
<br /> formations expected to be encountered as well as the through the augers. Alternatively,a shallow conductor
<br /> monitoring program. Samples may be collected directly from casing,or surface casing,may be set by drilling to a desired
<br /> cores. A geologist or engineer from Apex Envirotech,Inc., depth with a large-diameter bit,then setting the casing and
<br /> continuously logs each boring during drilling and checks proceeding with the drilling/coring. After total drill depth(TD)
<br /> returned drill cuttings for indications of both the first is reached,the borehole may be logged by geophysical
<br /> recognizable occurrence of groundwater and volatile means or hydraulically tested. If casing is not set to the
<br /> hydrocarbons,using either a portable photoionization bottom of the borehole,the lower portion of the hole may be
<br /> detector(PID),flame ionization detector,or explosimeter. All grouted or backfilled accordingly. The borehole may be
<br /> drilling equipment is either steam cleaned or washed drilled out(reamed)as necessary with a large-diameter bit.
<br /> between borings to minimize the potential for cross-
<br /> Upon reaching TD,drilling fluid is circulated to remove silicone septa,and threaded into a tapped hole in the system
<br /> cuttings. Selected casing is then run into the borehole and piping. The sampling procedure requires one end of the
<br /> set to the desired depth. Monitoring wells are cased with tubing be slipped over the sampling port and the other end
<br /> clean,threaded,factory-perforated and blank casing. The over the diaphragm pump to acquire an air-tight connection.
<br /> perforated interval consists of slotted casing,generally with The sampling pump is purged for 1 minute with the extracted
<br /> 0.020-inch-wide by 1.5-inch-long slots,with 42 slots per foot. vapor to be sampled. Following purging,the discharge of the
<br /> Centering devices may be fastened to the casing the ensure pump is then diverted through a two-way valve into the
<br /> even distribution of filter material and grout within the 'Tedlar"bag,which should be filled to 3/4 of volume capacity.
<br /> borehole annulus. The well casing is thoroughly washed Caution should be taken not to overfill the sampling bag.
<br /> and/or steam cleaned,or may be purchased as pre-cleaned, The sample is placed in a non-refrigerated dry cooler with
<br /> prior to installation. All recoverable drilling fluid and/or sufficient packing to eliminated damage during transport.
<br /> cuttings are collected for temporary storage and disposed of Cooling samples will cause condensation of moisture within
<br /> properly pending analytical results. the sample,thereby distorting laboratory analysis.
<br /> After setting the casing,sand or gravel filter material is For quality control purposes,a duplicate vapor sample
<br /> poured into the annular space to fill from boring bottom to should be collected from each sampling port. This sample is
<br /> generally 1 foot above the perforated interval. A 1-to 2-foot- then put on hold at the laboratory pending initial analysis. To
<br /> thick bentonite plug is set above this filter material to prevent ensure quality control and minimize the potential for cross-
<br /> grout from infiltrating the filter pack. Either neat cement, contamination prior to and during sampling,the diaphragm
<br /> containing about 5 percent bentonite,or sand-cement grout pump is thoroughly purged for approximately 5 minutes with
<br /> is then tremmied into the annular space from the top of the nitrogen or clean air(i.e.,compressed clean air). A"blank"
<br /> bentonite plug to near surface. A traffic-rated vault is sample of the discharged air is captured in a'Tedlar"bag at
<br /> installed around each wellhead for wells located in parking the end of the purging procedure and may be analyzed to
<br /> lots or driveways,while steel"stovepipes"are usually set ensure the purging was effective.
<br /> over wellheads in landscaped areas.
<br /> To minimize the potential for cross-contamination between
<br /> After installation,the wells are thoroughly developed to air samples,the polyethylene tubing,if not sample dedicated,
<br /> remove residual drilling materials from the wellbore,and to is thoroughly cleaned and rinsed.
<br /> improve well performance by removing fine material from the Vapor samples are subject to very limited holding times,
<br /> filter pack that may pass into the well. Well development typically 48 hours. Thus,care must taken to avoid delays in
<br /> techniques used may include pumping,surging,bailing, submittal of vapor samples to the laboratory. In the event the
<br /> swabbing,jetting,flushing,and air-lifting. All development vapor samples cannot be submitted to the analytical
<br /> water is collected either in drums or tanks for temporary laboratory on the same day they are collected,they are to be
<br /> storage,and properly disposed of pending laboratory temporarily stored in the dry,non-refrigerated,packed cooler
<br /> analytical results. To minimize the potential for cross- until the very first opportunity for submittal well within the
<br /> contamination between wells,all development equipment is required holding time,taking into account the time needed for
<br /> either steam cleaned or properly washed prior to use. shipment to and receipt by the laboratory.
<br /> Following development,the well is allowed to stand
<br /> undisturbed for a minimum of 24 hours before its first SOP-10
<br /> sampling. VAPOR SAMPLING:SYRINGE SAMPLING TECHNIQUE
<br /> Prior to vapor sampling,the vacuum system must reach a
<br /> SOP-9 stabilized air flow(cubic feet per minute)for approximately 15
<br /> VAPOR SAMPLING:"TEDLAR"BAG SAMPLING minutes. Prior to the actual collection of the vapor sample,
<br /> TECHNIQUE the following data is recorded:air flow,temperature,and
<br /> pressure at collection ports and gauges.
<br /> Prior to vapor sampling,the vacuum system must reach a
<br /> stabilized air flow(cubic feet per minute)for approximately 15 The sampling equipment consists of a clean, 100cc,gas-tight
<br /> minutes. Prior to the actual collection of the vapor sample, syringe and silicone septa.
<br /> the following data is recorded:air flow,temperature,and
<br /> pressure at collection ports and gauges. The sampling ports are brass connections,fitted with silicone
<br /> septa,and threaded into a tapped hole in the system piping.
<br /> The sampling equipment consists of a'Tedlar'bag(available Samples are collected by inserting a clean syringe into the
<br /> in 1,3,5,and 10 liter sizes),a diaphragm pump,and 1/4- septum and the plunger actuated several times. Each
<br /> inch-diameter polyethylene tubing(approximately 1 foot syringe should be purged of three syringe volumes before
<br /> long). collecting the sample. On the fourth purge,the plunger is
<br /> extracted slowly until the syringe is filled with a gas sample,
<br /> The sampling ports are brass connections,fitted with a then the syringe is withdrawn and the needle immediately
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