ASTM D5920/D5920M-20 PDF

SIGNIFICANCE AND USE 5.1 Assumptions: 5.1.1 The control well discharges at a constant rate, Q. 5.1.2 The control well, observation wells, and piezometers are of infinitesimal diameter. 5.1.3 The unconfined aquifer is homogeneous and really extensive. 5.1.4 Discharge from the control well is derived initially from elastic storage in the aquifer, and later from gravity drainage from the water table. 5.1.5 The geometry of the aquifer, control well, observation wells, and piezometers is shown in Fig. 2. The geometry of the test wells should be adjusted depending on the parameters of interest. FIG. 2 Cross Section Through a Discharging Well Screened in Part of an Unconfined Aquifer 5.2 Implications of Assumptions: 5.2.1 Use of the Neuman (1) method assumes the control well is of infinitesimal diameter. The storage in the control well may adversely affect drawdown measurements obtained in the early part of the test. See 5.2.2 of Practice D4106 for assistance in determining the duration of the effects of well-bore storage on drawdown. 5.2.2 If drawdown is large compared with the initial saturated thickness of the aquifer, the late-time drawdown may need to be adjusted for the effect of the reduction in saturated thickness. Section 5.2.3 of Practice D4106 provides guidance in correcting for the reduction in saturated thickness. According to Neuman (1) such adjustments should be made only for late-time values. 5.3 Practice D3740 provides evaluation factors for the activities in this practice. 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 ensure reliable results. Reliable results depend on many fact... SCOPE 1.1 This practice covers an analytical procedure for determining the transmissivity, storage coefficient, specific yield, and horizontal-to-vertical hydraulic conductivity ratio of an unconfined aquifer. It is used to analyze the drawdown of water levels in piezometers and partially or fully penetrating observation wells during pumping from a control well at a constant rate. 1.2 The analytical procedure given in this practice is used in conjunction with Guide D4043 and Test Method D4050. 1.3 The valid use of the Neuman method is limited to determination of transmissivities for aquifers in hydrogeologic settings with reasonable correspondence to the assumptions of the theory. 1.4 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. Reporting of test result in units other than SI shall not be regarded as nonconformance with this standard. 1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026. 1.5.1 The procedures used to specify how data are collected/recorded or calculated in the 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 data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering data. 1.6 This practice offers a set of in...