STP1053

    Rationale for the Design of Monitoring Well Screens and Filter Packs

    Published: Jan 1990


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    Abstract

    Well screens and filter packs are used extensively in the water well industry. Water supply wells are designed with large diameters to accommodate high-capacity pumps for municipal, industrial, and irrigation uses. Monitoring wells serve a different purpose, and therefore have some different design requirements. Monitoring wells are used to collect ground-water samples for chemical evaluation and are typically smaller in diameter and have shorter screened intervals. Monitoring well design, particularly for well screens and filter packs, must meet specific requirements. Unlike water wells, monitoring wells usually have an artificial filter pack between the formation and the well screen and often a secondary filter above the filter pack. The designs of well screens and filter packs are more critical for monitoring wells than for water wells, because monitoring wells serve as sampling ports in an aquifer and must minimize disturbance of the water chemistry and hydrology. At present, screen and filter pack requirements for monitoring wells have been only partially addressed by the technical community. Specific technical requirements should include filter pack parameters (i.e., uniformity coefficient, effective size, kurtosis, skewness, roundness, sphericity, and mineralogy). The method of filter pack placement, which involves particle settling through borehole fluids, is also important, particularly in relation to the nature of the geologic materials, the slot type and size of the screen, and the water level in the well.

    Keywords:

    ground water, monitoring, aquifer, formation, well, screen, filter pack, secondary filter, roundness, effective size, uniformity coefficient


    Author Information:

    Schalla, R
    Senior research engineer and senior research scientist, Pacific Northwest Laboratory, Richland, WA

    Walters, WH
    Senior research engineer and senior research scientist, Pacific Northwest Laboratory, Richland, WA


    Paper ID: STP23397S

    Committee/Subcommittee: D18.21

    DOI: 10.1520/STP23397S


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