Significance and Use
5.1 This practice allows the user to compute the true hydraulic efficiency of a pumped well in a confined aquifer from a constant rate pumping field 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.
5.2 Assumptions:
5.2.1 Control well discharges at a constant rate, Q.
5.2.2 Control well is of infinitesimal diameter.
5.2.3 Data are obtained from the control well and, if available, a number of observation wells.
5.2.4 The aquifer is confined, homogeneous, and extensive. The aquifer may be anisotropic, and if so, the directions of maximum and minimum hydraulic conductivity are horizontal and vertical, respectively.
5.2.5 Discharge from the well is derived exclusively from storage in the aquifer.
5.3 Calculation Requirements—For the special case of partially penetrating wells, application of this practice may be computationally intensive. The function fs shown in Eq 6 should 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 may not be tractable by hand. Because of this, it is assumed the practitioner using this practice will have available a computerized procedure for evaluating the function fs. This can be accomplished using commercially available mathematical software including some spreadsheet applications. If calculating fs is not practical, it is recommended to substitute the Kozeny equation for the Hantush equation as previously described.
NOTE 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
NOTE 2: Commercially available software is available for the calculating, graphing, plotting, and analyses of this practice. The user is responsible for verifying the correctness of the formulas, graphs, plots and analyses of the software.
Scope
1.1 This practice 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 practice 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. The reporting of results in units other than inch-pound shall not be regarded as nonconformance with this 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 practice.
1.5 All observed and calculated values shall conform to the guidelines for significant digits and round established in Practice D6026, unless superseded by this standard.
1.5.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported date to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis method for engineering design.
1.6 This practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of the practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without the consideration of a project’s many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process.
1.7 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.