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continuous coring and/or drilling with tri-cone roller or fixed- SOP-9
<br /> blade drag bits. Generally,rotary drilling is used when more GROUNDWATER PURGING AND SAMPLING
<br /> conventional hollow-stem auger drilling either is or becomes
<br /> Infeasible. Various drilling fluids(mud or air),used to keep Prior to water sampling,each well is purged by evacuating a
<br /> the borehole from caving and to remove dell cuttings,are minimum of three wetted well-rasing volumes of
<br /> chosen according to the nature of the soils and/or geologic groundwater. When required,purging will continue until
<br /> formations expected to be encountered as well as the either the discharge water temperature,conductivity,or pH
<br /> monitoring program. Samples may be collected directly from stabilize,a maxim Lim often wetted-casing volumes of
<br /> cores. A geologist or engineer from Apex Envirotech,Inc., groundwater have been recovered,or the well is bailed dry.
<br /> continuously logs each boring during drilling and checks When practical,the groundwater sample should be collected
<br /> returned drill cuttings for Indications of both the first when the water level In the well recovers to at least 80
<br /> recognizable occurrence of groundwater and volatile percent of its static level.
<br /> hydrocarbons,using either a portable PID,FID,or
<br /> explosimeter. All drilling equipment is either steam cleaned The sampling equipment consists of either a'Teflon'bailer,
<br /> or washed between borings to minimize the potential for PVC bailer,or stainless steel bladder pump with a"Teflon'
<br /> cross-contaminallon. bladder. If the sampling system is dedicated to the well,
<br /> then the bailer is usually`Teflon,"but the bladder pump is
<br /> Frequently,hollow-stem augers are used to drill and sample PVC with a polypropylene bladder. In general and
<br /> to either a minimum depth or auger refusal. In such cases, depending on the intended laboratory analysis,40-milllliter
<br /> the augers may be left in place as temporary surface casing, glass,volatile organic analysis(VOA)vials,with'ieflon'
<br /> With the center plug removed and•drillfng/coring carried out septa,are used as sample containers.
<br /> through the augers. Alternatively,a shallow conductor
<br /> casing,or surface casing,may be set by drilling to a desired The groundwater sample Is decanted Into each VOA vial in
<br /> depth with a large-diameter bit,then setting the casing and such a manner that there is no meniscus at the top of the
<br /> proceeding with the drilling/coring. After total drill depth(TD) vial. A cap is quickly secured to the top of the vial. The vial
<br /> is reached,the borehole may be logged by geophysical is then inverted and gently tapped to see if air bubbles are
<br /> means or hydraulically tested. If casing is not set to the present. If none are present,the vial is labeled and
<br /> bottom of the borehole,the lower portion of the hole may be refrigerated for delivery,under strict chain-of-custody,to the
<br /> grouted or backfilled accordingly. The borehole may be analytical laboratory. label information should include a
<br /> drilled out(reamed)as necessary with a large-diameter bit unique sample identification number,job identification
<br /> number,date,time,type of analysis requested,and the
<br /> Upon reaching TD,drilling fluid is circulated to remove sampler's name.
<br /> cuttings. Selected casing is then run Into the borehole and
<br /> set to the desired depth. Monitoring wells are cased with For quality control purposes,a duplicate water sample Is
<br /> clean,threaded,factory-perforated and blank casing. The collected from each well. This sample may also be analyzed
<br /> perforated interval consists of slotted casing,generally with or put on hold at the laboratory. When required,a trip blank,
<br /> 0.020-inch-wide by 1.5 inch-long slots,with 42 slots per fact. prepared at the laboratory,is placed in the transport cooler.
<br /> Centering devices may be fastened to the casing the ensure it Is labeled similar to the well samples,remains in the cooler
<br /> even distribution of filter material and grout within the during transport,and is analyzed by the laboratory along
<br /> borehole annulus. The well casing is thoroughly washed with the groundwater samples. In addition,afield blank may
<br /> and/or steam cleaned,or may be purchased as pre-cleaned, be prepared In the field when sampling equipment is not
<br /> prior to installation. All recoverable drriilling fluid and/or dedicated. The field blank Is prepared after a pump or bailer
<br /> cuttings are collected for temporary storage and dsposed of has been either steam cleaned or properly washed,prior to
<br /> properly pending analytical results. use In the next well,and is analyzed along with the other
<br /> samples. The field blank analysis demonstrates the
<br /> After setting the casing,sand or gravel filter material is effectiveness of the in-field cleaning procedures to prevent
<br /> poured into the annular space to fill from boring bottom to cross-contamination.
<br /> generally 1 foot above the perforated Interval. A one to two
<br /> foot-thick bentonite plug is set above this filter material to To minimize the potential for cross-contamination between
<br /> prevent grout from infiltrating the filter pack. Either neat wells,all well development and water sampling equipment
<br /> cement,containing about ilve percent bentonite,or sand- not dedicated to a well is either steam cleaned or properly
<br /> cement grout is then tremmled into the annular space from washed between uses. As a secondary precautionary
<br /> the top of the bentonite plug to near surface. A traffic-rated measure,wells are sampled in order of least to highest
<br /> vault is installed around each wellhead for wells located In concentrations as established by available previous
<br /> parking lots or driveways,while steel'stovepipes`are analytical data.
<br /> usually set over wellheads In landscaped areas,
<br /> In the event the water samples cannot be submitted to the
<br /> After installation,the wells are thoroughly developed to analytical laboratory on the same day they are collected
<br /> remove residual drilling materials from the wellbore,and to (e.g.,due to weekends or holidays),the samples are
<br /> improve well performance by removing fine material from the temporarily stored until the first opportunity for submittal
<br /> filter pack that may pass into the well. Well development either on water ice in a cooler,such as when in the field,or
<br /> techniques used may include pumping,surging,bailing, in refrigerator at Apex's office.
<br /> swabbing,jetting,flushing,and air-lifting. All development
<br /> water is collected either in drums or tanks for temporary SOP-10
<br /> storage,and properly disposed of pending laboratory MEASURING LIQUID LEVELS USiNG WATER LEVEL
<br /> analytical results. To minimize the potential for cross- METER OR INTERFACE PROSE
<br /> contamination between welts,all development equipment Is
<br /> either steam cleaned or properly washed prior to use. Field equipment used for liquid-level gauging typically
<br /> Following development,the well is allowed to stand includes the measuring instrument(water-level meter or
<br /> undisturbed for a minimum of 24 hours before its first interface probe)and product bailer(s). The field kit also
<br /> sampling. includes cleaning supplies(buckets,solution,spray bottles,
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