Standard Practice for Determining Specific Capacity and Estimating Transmissivity at the Control Well

Importancia y uso:

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 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 practice 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 practice 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.

Subcomité:

D18.21

Referida por:

D5978_D5978M-16R24

Volúmen:

04.08

Número ICS:

13.060.10 (Water of natural resources)

Palabras clave:

aquifers; aquifer tests; control wells; hydraulic conductivity; observation wells; specific capacity; storage coefficient; transmissivity; unconfined aquifers;