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<br /> 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 drill cuttings, are minimum of three wetted well-casing volumes of
<br /> 1 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 maximum of ten wetted-casing volumes of
<br /> cores. A geologist or engineerfrom Apex Envirotech, Inc., groundwater have been recovered, or the well is bailed dry,
<br /> ,. .I 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 /> 1 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-contamination. bladder. If the sampling system is dedicated to the well,
<br /> then the bailer is usually "Teflon," but the bladder pump is
<br /> r 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-milliliter
<br /> - the augers may be left in place as temporary surface casing, glass, volatile organic analysis (VOA) vials, with "Teflon"
<br /> with the center plug removed and drilling/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 rasing 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 foot, 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 /> l borehole annulus. The well casing is thoroughly washed with the groundwater samples. In addition, a field blank may
<br /> 11 and/or steam cleaned, or may be purchased as pre-cleaned, be prepared in the field when sampling equipment is not
<br /> i_ prior to installation. All recoverable drilling fluid and/or dedicated. The field blank is prepared after a pump or bailer
<br /> cuttings are collected for temporary storage and disposed 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 /> l samples. The field blank analysis demonstrates the
<br /> After setting the casing, sand or gravel fitter 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 t 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 five percent bentonite, or sand- not dedicated to a well is either steam cleaned or properly
<br /> cement grout is then tremmied 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 /> j After installation, the wells are thoroughly developed to analytical laboratory on the same day they are collected
<br /> ( J 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 PROBE
<br /> contamination between wells, 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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