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AGWST 3.00

Alternative Ground Water Sampling Techniques Guide (July 1994)

Title: Ground Water Sampling with the use of a Well Point (3/94)

Method Number: AGWST 3.00

Summary:

A well point is a small diameter (1-2 inch) probe constructed of continuously wrapped stainless steel or wrapped stainless steel gauze screen over perforated carbon steel pipe. They may be used as a screening tool to collect ground water samples and piezometeric data to aid in the optimal placement of monitor wells. No filter or gravel pack is used in the installation.

I PURPOSE AND SCOPE

This document summarizes the minimum requirements for the temporary installation of well points and for the collection of ground water screening data for site investigations. Installation is for temporary use (less than 48 hours).

II METHOD OVERVIEW

  1. Tool

    2. The well point may be constructed in a variety of configurations with similar materials. They may be constructed of continuously wrapped stainless steel or wrapped stainless steel gauze screen over perforated carbon steel pipe. Slot size should be 0.010 inches or 60 mesh to reduce fines in sample water (Figure I).

    Most units have a cast iron drive point for ruggedness which may be hexagonal in shape to prevent turning as extension pipe is added. The end will have a threaded coupling or open thread pipe for the connection of riser pipe. Their construction allows sample collection across the water table. The material of construction must meet the intended use of the data.

  2. Applications

    1. Field screening tool to collect ground water samples and to estimate ground water flow directions to aid in the placement of monitor wells in unconfined aquifers (less than 48 hour placement).

    2. Installation can be temporary (less than 48 hrs.) or permanent use. If placed longer than 48 hours a well permit must be secured and placement must be in accordance with the subsurface and percolating waters act N.J.S.A. 58:4A et seq and performed by a New Jersey licensed well driller.

  3. Capabilities

    1. Obtain samples from unconfined aquifers.

    2. Obtain samples across the water table to determine the presence of floating product.

    3. Small screen lengths can be used to sample specific intervals in the saturated zone.

    4. Capable of collecting samples to determine the vertical profile of contaminants in an aquifer.

    5. Sampling from confined aquifers provided; the upper aquifer is cased off and the casing is driven a minimum of two (2) feet into the confining layer.

    6. Can be used to estimate groundwater flow directions. Must remain in place for 24-36 hours for stabilization prior to measurement.

    7. A comparison of the advantages and limitations for the use of well points are listed in Table I.

III SAMPLING METHOD REQUIREMENTS

  1. Installation

    1. The well point can be placed with the use of a conventional hollow stem auger rig, slide hammer, jack hammer, rotary hammer or by hand; JETTING OF THE POINTS INTO PLACE IS NOT A NJDEP APPROVED PROCEDURE.

    2. The well point may be driven through the unsaturated zone only in known "clean" soils. Driving the well point through contaminated soil may carry some contamination with the point resulting in analytical sample results which are biased high. In contaminated unsaturated zones the well points must be placed with the aid of a hollow stem auger.

    3. If the well point is to be installed in an oversized (20% larger than the well point) pre-drilled hole, the hollow stem augers or bull drive point must be advanced to a point which is just above the targeted sample zone. The well point is then placed in the hole and advanced beyond the bottom of the hole by hammering or pushing into place. The use of pre-drilled holes will reduce clogging of well point screens when driving.

    4. After sample collection, the well point is removed by back hammering or pulling the tool out with the rig hydraulics.

    5. If the well point is to be left as a permanent installation, it must be constructed and permitted as per NJDEP monitor well requirements.

    6. If the well point is used for piezometeric data a survey mark must be made on top of the casing as a reference point for water level measurements.

    7. Caution must be used when using well points in areas of contaminated soil. Possible cross contamination may be introduced to the screen as it passes through the zone of contamination.

    8. Installation of the tool is required to comply with all permit, license, sealing and grouting requirements as per Appendices I and II. Any tool left in the ground longer than 48 hours is considered a monitor well and therefore must comply with the permit, installation and license requirements for monitor wells.

  2. Sampling Procedures

    1. Development

      2. Development of a well point is not required except when performing vertical profile sampling. The well point must be developed by one of the standard methods used for well development prior to sampling. If an air lift development technique is used, the air outlet must be at a minimum of two feet above the screen. Operations must be continuous and not pulsed. The air lift pipe shall not be placed within the screen and only the double pipe method shall be used.

    2. Purging

      3. Purging of the well point is required. The procedure should follow the methodologies found in the May 1992 NJDEPE Field Sampling Procedures Manual for monitor well purging.

    3. Sampling

      4. The acquisition of ground water samples and piezometeric data must be performed by one of several recommended methods described in the May 1992 edition of the NJDEPE Field Sampling Procedures Manual.

  3. Quality Assurance/Quality Control

    1. Decontamination

      2. The well points and associated riser pipe must be decontaminated prior to installation using the following procedure:

      1. Remove all adherent soil material with a stiff wire brush.

      2. Wash well point and associated riser pipe and couplings with a laboratory glassware detergent.

      3. Rinse with potable water and/or steam clean.

      4. Rinse interior of well point and riser pipe with distilled and deionized ASTM Type II water.

      NOTE: For proper decontamination stronger cleaning agents are recommended when the tool has been exposed to heavy contamination. This can be performed prior to step 2.

    2. Field Blanks

      3. Field blanks must be obtained in the same manner as the sample. The blank water must pass through all the sampling equipment then into the sample container.

      The parameters and frequency for field blanks are designated in the May 1992 edition of the NJDEPE Field Sampling Procedures Manual.

    3. Sampling Equipment

      4. A variety of equipment may be used to obtain samples from the well point. The NJDEPE Field Sampling Procedures Manual can be used as a reference for the selection of the appropriate sampling equipment and decontamination procedures.

      All sampling equipment must be decontaminated and dedicated to each sample point.

    4. Formation Types

      5. Well points can be installed in unconsolidated materials which are free of pebbles, cobbles and boulders. The presence of this material may damage the screen material or the well point.

      The soil texture and sorting will dictate the recharge rates of the well points. If the well point is driven through formations with high percentages of clay, clogging of the screens may occur, impeding the entry of formation water into the well point.

IV REFERENCES

  1. Ground Water and Wells. Johnson Division, UOP Inc.; St. Paul, Minn. 1982. p277-294

  2. Ground Water Manual - A Water Resources Technical Publication; U.S. Dept. of Interior, Bureau of Reclamation. Government Printing Office,Washington DC 1977

Table I

ADVANTAGES AND LIMITATIONS OF WELL POINTS

ADVANTAGES LIMITATIONS

  1. Capable of collecting ground water samples and piezometeric data

  2. Minimal cost of well points and riser pipe. Temporary installation (less than 48 hours) of multiple points.

  3. Materials are readily available so damaged components may be replaced at a reduced cost.

  4. Can be set in a gravel pack for permanent installation.

  5. Various lengths available (18-60 inches) for monitoring specific zones of interest.

  6. Able to collect split spoon samples during auger advancement prior to well point placement.

  7. Capable of collecting samples to determine vertical profile of contaminants in an aquifer.

  

  1. If driven to the desired zone through contaminated soil, well points may carry down contaminants.

  2. If driven in clay soils, slots may clog.

  3. In contaminated soils, soil plug at end of auger may contaminate well point as it is driven past the end of the auger.

  4. Cannot be used in soil with cobbles or boulders due to potential damage to point.

  5. Temporary installations yield a highly turbid sample, therefore samples for various analytes may be biased high.

  6. Cannot perform vertical profiles of aquifers.

  7. May require use of drill rig for installation.

  8. Formations with 20-30% silts and clay may not yield sufficient water for sampling and limit use of tool.

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