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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 drill cuttings , are minimum of three wetted well-casing 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 maximum of ten 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-contamination . 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-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 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 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 /> borehole annulus . The well casing is thoroughly washed with the groundwater samples . In addition , a field 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 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 /> 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 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 /> 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 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 ,
<br />
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