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Significance and Use
This test method allows the user to compute the true hydraulic efficiency of a pumped well in a confined aquifer from a constant rate pumping test. The procedures described constitute the only valid method of determining well efficiency. Some practitioners have confused well efficiency with percentage of head loss associated with laminar flow, a parameter commonly determined from a step-drawdown test. Well efficiency, however, cannot be determined from a step-drawdown test but only can be determined from a constant rate test.
Control well discharges at a constant rate, Q.
Control well is of infinitesimal diameter.
Data are obtained from the control well and, if available, a number of observation wells.
The aquifer is confined, homogeneous, and areally extensive. The aquifer may be anisotropic, and if so, the directions of maximum and minimum hydraulic conductivity are horizontal and vertical, respectively.
Discharge from the well is derived exclusively from storage in the aquifer.
Calculation Requirements—For the special case of partially penetrating wells, application of this test method may be computationally intensive. The function fs shown in Eq 6 must be evaluated using arbitrary input parameters. It is not practical to use existing, somewhat limited, tables of values for fs and, because this equation is rather formidable, it is not readily tractable by hand. Because of this, it is assumed the practitioner using this test method will have available a computerized procedure for evaluating the function fs. This can be accomplished using commercially available mathematical software including some spreadsheet applications or by writing programs in languages, such as Fortran or C. If calculating fs is not practical, it is possible to substitute the Kozeny equation for the Hantush equation as previously described.
1.1 This test method describes an analytical procedure for determining the hydraulic efficiency of a production well in a confined aquifer. It involves comparing the actual drawdown in the well to the theoretical minimum drawdown achievable and is based upon data and aquifer coefficients obtained from a constant rate pumping test.
1.2 This analytical procedure is used in conjunction with the field procedure, Test Method D4050.
1.3 The values stated in inch-pound units are to be regarded as standard, except as noted below. The values given in parentheses are mathematical conversions to SI units, which are provided for information only and are not considered standard.
1.3.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf) represents a unit of force (weight), while the unit for mass is slugs.
1.4 Limitations—The limitations of the technique for determination of well efficiency are related primarily to the correspondence between the field situation and the simplifying assumption of this test method.
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
D4050 Test Method for (Field Procedure) for Withdrawal and Injection Well Tests for Determining Hydraulic Properties of Aquifer Systems
D5521 Guide for Development of Ground-Water Monitoring Wells in Granular Aquifers
ICS Number Code 93.160 (Hydraulic construction)