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Guidance DocumentsAlternative Ground Water Sampling Techniques GuideAGWST 2.00

  
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AGWST 2.00

Alternative Ground Water Sampling Techniques Guide (July 1994)

Title: Ground Water Sampling with the use of A Miniature Drive Point (MDP) (3/94)

Method Number: AGWST 2.00

Summary:

A miniature Drive Point (MDP) is a retractable screened probe (3/4-« inch OD) connected to small diameter (1/8-« inch OD) flexible tubing. The tip and tubing are driven into place with a temporary outer casing. It is used for the collection of ground water samples. The probe is constructed of stainless steel with the tubing constructed of PTFE (polytetraflouroethylene e.g. Teflon®) or drinking water grade polyethylene. No filter or gravel pack is used in the installation.

I PURPOSE AND SCOPE

This document summarizes the minimum requirements for the use of a MDP 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


    2. A variety of tools are commercially available with various designs. Most are designed for the collection of soil gas samples as well as ground water samples (Figure I). The screened probe is constructed of stainless steel. Its design allows for the screen to remain inside the probe until at the target depth at which time the drive casing is pulled back and the screen is exposed. Tubing is connected to the top of the probe and extends to the surface inside the drive casing.

  2. Applications


    3. Field screening tool for the collection of ground water samples to aid in the placement of monitor wells.

  3. Capabilities

    1. Obtain ground water samples from unconfined aquifers.
    2. Obtain samples at depths less than 40 feet.
    3. A comparison of the advantages and limitations for MDPs are listed in Table I.

III SAMPLING METHOD REQUIREMENTS

  1. Installation

    1. A MDP is emplaced by connecting a screened probe and tubing and inserting into an outer drive casing. Since the probe inlets and tubing are inside the drive casing there are no problems with cross contamination by driving through contaminated soils or probe clogging with silts and clays. The unit is driven to the desired depth with a slide hammer or rotary hammer. Once at the targeted depth, the drive casing is pulled back, exposing the telescoping screened probe inlets to the ground water.


      2. CAUTION must be used when employing a hammering device since this may cause the rod connectors to loosen, causing cross-threading, and damaging the rod.

    2. Prior to installation of any MDP, previous knowledge of the depth to water must be known for proper depth setting. Initial probes should be set at a maximum depth of three feet below the water table. This will ensure the detection of Light Non-Aqueous Phase Liquids.
    3. 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

      Purging or development is not required for the MDP prior to sample acquisition.
    2. Sampling

      Sample acquisition from a MDP is limited to the use of an evacuation chamber or peristaltic pump due to the narrow diameter of the tool. Tubing used in the MDP and sampling device must be dedicated to each point. These sampling methods will bias samples for volatile and semi-volatile analysis low due to the vacuum created by the device.

  3. Quality Assurance/Quality Control

    1. Decontamination

      The MDP and associated equipment (drive casing, probe, etc.) must be decontaminated prior to initial use and between borings using the following procedure:

      1. Remove all adherent soil material with a stiff wire brush.
      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 probe and tubing prior to installation and evacuation device and 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 wells, the available sampling equipment may be limited to evacuation chambers and peristaltic pumps.

      All sample tubing should be dedicated to each sample point.
    4. Formation Types

      MDPs can be installed in unconsolidated materials which are free of pebbles, cobbles and boulders. The presence of these materials may inhibit the penetration depth of the probe.

      The soil texture will dictate the recharge rates of the MDP.

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. Kerfot, 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 Natural Water Well Association Petroleum Hydrocarbons Conference, November 15-17, 1989, Houston, TX
  4. Stites, Will; Chambers, Lucy W; A Method for Installing Miniature Multilevel Sampling Wells Ground Water Vol. 29, November 3, 1991. p430-432.
  5. Reynolds, Glenn W. and Robert W. Gillham. 1985. Absorption of Halogenated Organic Compounds by Polymer Materials Commonly Used in Ground Water Monitors. In: Hitchon, Brian and Mark Trudell, Hazardous Wastes in Ground Water: A Soluble Dilemma. Proc. Second Canadian/American Conference on Hydrogeology, Banff, Alberta, June 25-29, 1985. pp125-132

TABLE I

ADVANTAGES AND LIMITATIONS OF MINIATURE DRIVE POINTS

ADVANTAGES LIMITATIONS
  1. Minimal cost of probes and tubing allows for temporary installation (less than 48 hours) of multiple points.
  2. Equipment required to install MDP is portable which enables their placement in remote and hard to access areas.
  3. Many MDPs (15-20) can be installed in a single day.

  1. Depth limits are up to 30 feet.

  2. Cannot sample across the water table due to the sample acquisition technique (suction) which requires the probe to be submerged.
  3. Cannot sample confined aquifers due to problems with properly sealing the hole.
  4. Can be used only in unconsolidated formations without pebbles, cobbles, and boulders.
  5. Excessive solids or tight formation will cause probe to be inoperable.
  6. Due to the narrow diameter tubing, there is a high ratio of ground water to tubing surface area contact which may cause increased adsorption of volatiles. This will result in sample results biased low.
  7. Yields a highly turbid sample therefore samples for various analytes may be biased high.
  8. Many types of equipment are not capable of sampling a MDP due to the use of narrow diameter flexible tubing.
  9. MDPs cannot be used for piezometeric data gathering due to the flexible tubing which will vary the depth to water measurements.
  10. Unable to obtain representative vertical profile samples. Retractable probes do not have a seal which will allow leakage of formation water into probe while driving.
  11. 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.