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Guidance DocumentsAlternative Ground Water Sampling Techniques GuideAGWST 4.00

  
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AGWST 4.00

Alternative Ground Water Sampling Techniques Guide (July 1994)

Title: Ground Water Sampling with the use of a Passively Placed Narrow Diameter Point (PPNDP) (3/94)

Method Number: AGWST 4.00

Summary:

A narrow diameter point (PPNDP) is a small diameter («-1 inch OD) screened casing passively placed in a borehole. It isused for the collection of a ground water sample or piezometeric data. The casing can be constructed of stainless steel, carbon steel or PVC. No filter or gravel pack is used in the installation.

I PURPOSE AND SCOPE

This document summarizes the minimum requirements for the use of passively placed PPNDPs for the collection of ground water screening data for site investigations. Installation is for temporary use (less than 48 hours).

II METHOD OVERVIEW

  1. Tools

    A solid push rod (bull point) is used to create a narrow diameter hole to a depth below the water table. This can be performed by hand or with a rotary hammer.

    A piece of schedule 40 PVC screen with 0.010 inch slots and an end cap is placed to the bottom of the hole.

    Glues or adhesives cannot be used for joining the casing. Threaded PVC casing must be used.

  2. Applications

    1. Field screening tool for the collection of ground water samples for site investigations to evaluate the presence/absence and extent of ground water contamination and to estimate groundwater flow directions (less than 48 hour placement).
    2. Field screening tool to aid in the placement of monitor wells.
    3. A comparison of the advantages and limitations for NDPs are listed in Table I.
  3. Capabilities

    1. Obtain samples from unconfined aquifers only.
    2. Obtain samples across the water table to determine the presence of floating product.

III SAMPLING METHOD REQUIREMENTS

  1. Installation

    1. Pre-drill a borehole with a diameter slightly larger than the casing using a bull point drive rod. The hole should be made to a depth of 1-3 feet below the water table. Rotary hammer bits or augers (hand and power) cannot be used. The rotary action results in an area of disturbance which alters ground water quality. Since development of NDPs is difficult, this area of impacted ground water cannot be effectively removed.
    2. The screened section of PVC is placed into the borehole so the screened section is across the ground water table.
    3. Prior to installation of any PPNDP, knowledge of the depth to water should be known by previous site data for proper placement of the probe. If no groundwater data is available, then depth to water can be determined with a NDP. If NDPs are employed for the acquisition of piezometeric data, the point cannot remain in the ground longer than 48 hours from installation.
    4. A survey mark must be made on the casing as a reference if a NDP is to be surveyed for the purpose of obtaining water level data.
    5. Caution should be used when using passively placed slotted PVC casing in areas of contaminated soil. Possible cross contamination may be introduced to the casing as it passes through the zone of contamination.
    6. 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. Purging

      For passively placed NDPs, three to five volumes of the standing water in the NDP must be purged. This is due to the potential for cross contamination of the screen from upper soil horizons. This can be accomplished utilizing a peristaltic pump, inertial pump or a small centrifugal pump.
    2. Sampling

      The acquisition of samples and water level measurements must be performed by one of several recommended methodologies described in the May 1992 edition of NJDEPE Field Sampling Procedures Manual.
  3. Quality Assurance/Quality Control

    1. Decontamination

      The PPNDP and associated equipment (bull point, riser pipe, etc.) must be decontaminated between borings using the following procedure:

      1. Remove all adherent soil material.
      2. Wash with a laboratory grade glassware detergent.
      3. Rinse with potable water and/or steam clean.
      4. Rinse with distilled and deionized ASTM Type II water.
      NOTE: For proper decontamination, stronger cleaning agents are recommended when tool has been exposed to heavy contamination. This can be performed prior to step 2.
    2. Field Blanks

      Field blanks must be obtained in the same manner as the sample. The blank water must pass through the sample device and PPNDP, prior to installation 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

      Due to the small diameter of the points, the available sampling equipment may be limited. The NJDEPE Field Sampling Procedures Manual can be used as a reference for the selection of sampling equipment.

      All sampling equipment must be decontaminated in accordance with the NJDEPE Field Sampling Procedures Manual and dedicated to each sample point.
    4. Formation Types

      PPNDPs can be installed in unconsolidated materials with limited amounts of pebbles, cobbles and boulders. The presence of these materials in large quantities may inhibit the penetration depth of the PPNDP. The soil texture will dictate the recharge rates of ground water to the well.

IV REFERENCES

  1. Barker, J.F.; Patrick, GC; Lemon, L; Travis G.M.; Some Biases in Sampling Multilevel Piezometers for Volatile Organics. Ground Water Monitoring Review Spring 1987, p48-54
  2. Kerfort, William B; A Portable Well Point Sampler for Plume Tracking. Ground Water Monitoring Review, Fall 1984, p38-41
  3. Robbins, G.A.; Hayden J.M.; Bristol, R.D.; Vertical Dispersion of Ground Water Contaminants in the Near-Field of Leaking Underground Gasoline Storage Tanks. In Procedures of the National Water Well Association Petroleum Hydrocarbons Conference, November 15-17 1989, Houston, TX
  4. Stites, Will; Chambers, Luch W; A Method for Installing Miniature Multilevel Sampling Wells. Ground Water Vol. 29, No.3, 1991. p430-432

TABLE I

ADVANTAGES AND LIMITATIONS OF
PASSIVELY PLACED NARROW DIAMETER POINTS (PPNDP)

ADVANTAGES LIMITATIONS
  1. Capable of collecting ground water samples and piezometeric data.
  2. Minimal cost of screen material and riser pipe allows for temporary installation (less than 48 hrs.) of multiple points.
  3. Equipment required to install NDPs is small and portable which enables their placement in remote and hard to access areas.
  4. No gravel pack is required.
  1. Installation of screen zone through contaminated soil may lead to "carry down" of contaminants and possibly bias samples high.
  2. Placement through high clay content soils may clog slots or screen of probe.
  3. Yields a highly turbid sample, therefore samples for various analytes may be biased high.
  4. Cannot perform vertical contaminant profile sampling (cross section) of an aquifer due to constant exposure of screen to contaminants.
  5. Cannot sample confined aquifers.
  6. In sand aquifers, hole below ground water table will collapse thus making it difficult to penetrate into the water table.
  7. Points are low yielding.
  8. Sampling methods may be limited due to small casing diameter.
  9. Operational depth limitations of approximately 10 feet.
  10. Formations with 20-30% silts and clays may not yield sufficient water for sampling and limit use of the tool.

 

   

 

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Disclaimer

This document was prepared by the New Jersey Department of Environmental Protection (NJDEP), Site Remediation Program (SRP) and has been subject to peer review. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.

Acknowledgements

The author would like to express his sincere appreciation for the review and comments to initial drafts of this document made by personnel within and outside the Department.