STP1053

    Experimental Screen Design for More Sediment-Free Sampling

    Published: Jan 1990


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    Abstract

    An experimental double-walled screen design has been found to increase the reliability of a properly installed, monitoring well sand pack, intended to produce long-term sediment-free sampling. The screen design is most useful for shallow, small-diameter monitoring wells installed by the hollow-stem auger drilling method and can be produced in a wide range of lengths and diameters. The new screen design eliminates the need for state agencies to require “tremied” gravel packs for such wells when the tremie-pipe installation technique is difficult to complete successfully without compromising the intent behind the specification. The double-walled screen design contains an economically fabricated, preassembled, evenly graded sand pack that avoids the need for resin and that ensures emplacement of an in situ homogeneous sand pack in the field.

    When installed directly against the formation wall, in conjunction with a conventional sand pack or the best efforts at a tremied pack, the preassembled double-walled screen and sand pack may help reduce the amount of development time necessary to obtain turbidity-free water (that is, water containing less than 50 nephelometric turbidity units). The presence of the preassembled homogeneous sand pack downhole improves long-term sample integrity in silty deposits and minimizes interference attributable to improperly placed or poorly settled packs. The sand pack example described is simple in design and economical, accommodates small-diameter submersible pumps and bailers, and is easily fabricated in the field.

    Keywords:

    ground water, screen design, sand pack, preassembled double-walled screen, filter pack, monitoring well construction


    Author Information:

    Rich, CA
    President and environmental engineer, CA Rich Consultants, Inc., Sea Cliff,

    Beck, BM
    President and environmental engineer, CA Rich Consultants, Inc., Sea Cliff,


    Paper ID: STP23398S

    Committee/Subcommittee: D18.21

    DOI: 10.1520/STP23398S


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