5.1 Assumptions of the Theis (1) equation affect specific capacity and transmissivity estimated from specific capacity. These assumptions are given below:

5.1.1 Aquifer is homogeneous and isotropic.

5.1.2 Aquifer is horizontal, of uniform thickness, and infinite in areal extent.

5.1.3 Aquifer is confined by impermeable strata on its upper and lower boundaries.

5.1.4 Density gradient in the flowing fluid must be negligible and the viscous resistance to flow must obey Darcy's Law.

5.1.5 Control well penetrates and receives water equally from the entire thickness of the aquifer.

5.1.6 Control well has an infinitesimal diameter.

5.1.7 Control well discharges at a constant rate.

5.1.8 Control well operates at 100 percent efficiency.

5.1.9 Aquifer remains saturated throughout the duration of pumping.

5.2 Implications of Assumptions and Limitations of Method.

5.2.1 The simplifying assumptions necessary for solution of the Theis equation and application of the method are never fully met in a field test situation. The satisfactory use of the method may depend upon the application of one or more empirical correction factors being applied to the field data.

5.2.2 Generally the values of transmissivity derived from specific capacity vary from those values determined from aquifer tests utilizing observation wells. These differences may reflect 1) that specific-capacity represents the response of a small part of the aquifer near the well and may be greatly influenced by conditions near the well such as a gravel pack or graded material resulting from well development, and 2) effects of well efficiency and partial penetration.

5.2.3 The values of transmissivity estimated from specific capacity data are considered less accurate than values obtained from analysis of drawdowns that are observed some distance from the pumped well.

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.

5.3 Withdrawal well test field procedures are used with appropriate analytical procedures in appropriate hydrogeological sites to determine transmissivity and storage coefficient of aquifers and hydraulic conductivity of confining beds.

1.1 This test describes a procedure for conducting a specific capacity test, computing the specific capacity of a control well, and estimating the transmissivity in the vicinity of the control well. Specific capacity is the well yield per unit drawdown at an identified time after pumping started.

1.2 This test method is used in conjunction with Test Method D4050 for conducting withdrawal and injection well tests.

1.3 The method of determining transmissivity from specific capacity is a variation of the nonequilibrium method of Theis (1)2 for determining transmissivity and storage coefficient of an aquifer. The Theis nonequilibrium method is given in Test Method D4106.

1.4 Limitations—The limitations of the technique for determining transmissivity are primarily related to the correspondence between the field situation and the simplifying assumptions of the Theis method.

1.5 The scope of this test method is limited by the capabilities of the apparatus.

1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.6.1 The procedures used to specify how data are collected/recorded and calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that should generally 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 data to commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.

1.7 The values stated in SI units are to be regarded as standard. Rationalized inch-pound units also are used in this standard. Each system of units is to be regarded separately as standard.

1.8 This standard may involve hazardous materials, operations, and equipment. This standard does not address safety problems 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.