Significance and Use
Assumptions of Solution:
Drawdown (or mounding) of the water table around the well is negligible.
Flow above the water table can be ignored.
Head losses as the water enters or leaves the well are negligible.
The aquifer is homogeneous and isotropic.
Implications of Assumptions:
The mathematical equations applied ignore inertial effects and assume that the water level returns to the static level in an approximate exponential manner.
The geometric configuration of the well and aquifer are shown in Fig. 1, that is after Fig. 1 of Bouwer and Rice.
For filter-packed wells, Eq 1 applies to cases in which the filter pack remains saturated. If some of the filter pack is dewatered during testing, rc 2 should be replaced by the following:
|n ||= || short-term specific yield of the filter pack, |
|ra ||= ||uncorrected well casing radius, and |
| rw ||= ||borehole radius. |
Note 6—Short term refers to the duration of the slug test.
Note—See Fig. 1 of Footnote 2. FIG. 1 Geometry and Symbols of a Partially Penetrating, Partially Perforated Well in Unconfined Aquifer with Gravel Pack or Developed Zone Around Perforated Section
1.1 This test method covers the determination of hydraulic conductivity from the measurement of inertial force free (overdamped) response of a well-aquifer system to a sudden change in water level in a well. Inertial force free response of the water level in a well to a sudden change in water level is characterized by recovery to initial water level in an approximate exponential manner with negligible inertial effects.
1.2 The analytical procedure in this test method is used in conjunction with the field procedure in Test Method D4044 for collection of test data.
1.3 Limitations—Slug tests are considered to provide an estimate of hydraulic conductivity. The determination of storage coefficient is not possible with this test method. Because the volume of aquifer material tested is small, the values obtained are representative of materials very near the open portion of the control well.
Note 1—Slug tests are usually considered to provide estimates of the lower limit of the actual hydraulic conductivity of an aquifer because the test results are so heavily influenced by well efficiency and borehole skin effects near the open portion of the well. The portion of the aquifer that is tested by the slug test is limited to an area near the open portion of the well where the aquifer materials may have been altered during well installation, and therefore may significantly effect the test results. In some cases the data may be misinterpreted and result in a higher estimate of hydraulic conductivity. This is due to the reliance on early time data that is reflective of the hydraulic conductivity of the filter pack surrounding the well. This effect was discussed by Bouwer. In addition, because of the reliance on early time data, in aquifers with medium to high hydraulic conductivity, the early time portion of the curve that is useful for this data analyses is too short (for example, <10 s) for accurate measurement; therefore, the test results begin to greatly underestimate the true hydraulic conductivity.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D4043 Guide for Selection of Aquifer Test Method in Determining Hydraulic Properties by Well Techniques
D4044 Test Method for (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers
D4104 Test Method (Analytical Procedure) for Determining Transmissivity of Nonleaky Confined Aquifers by Overdamped Well Response to Instantaneous Change in Head (Slug Tests)
aquifers; aquifer tests; control wells; groundwater; hydraulic conductivity; slug test: Aquifers; Environmental site assessment (ESA)--soil/rock; Transmissivity; Unconfined/unconsolidated aquifers; Water level observation; Ground water; Hydraulic conductivity/transmissivity; Overdamped well-aquifer system; Slug tests; Storage--aquifers;
ICS Number Code 07.060 (Geology. Meteorology. Hydrology); 93.020 (Earth works. Excavations. Foundation construction. Underground works)
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