5.1 This test method provides design information for construction of an orifice weir. It also describes setup, operation, inspection, calculation of discharge, and reporting. The accuracy of a circular weir decreases at low flows. The use of a circular orifice weir requires a constant flow velocity over the period of measurement. The results may be affected by the piezometers distance from the orifice plate. This equipment may not be appropriate for measuring flows on small wells, or wells with limited recharge.
5.2 Aquifer testing has been conducted for the purposes of production and pressure relief well design and water resource assessment. Production wells are used for public and industrial water supplies, hydraulic controls, and groundwater capture. Pressure relief wells are for hydraulic controls. Test wells are for the purpose of water resource assessment.
5.3 Discharge must also be known for certain methods to evaluate well and pump performance.
Note 1: Practice D3740 provides evaluation factors for the activities in this standard. 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.
1.1 This test method covers construction and operation of a circular orifice weir for measuring the discharge from a well. This test method is a part of a series of standards prepared on the in situ determination of hydraulic properties of aquifer systems by single- or multiple-well tests. Selection of a well discharge measurement test method is described in Guide D5737.
1.2 The discharge rate determined by this test method is commonly used for a number of aquifer test methods and to provide information for the evaluation of well and pump performance.
1.3 Limitations—This test method is limited to the description of a method common to hydraulic engineering for the purpose of groundwater discharge measurement in temporary or test conditions.
1.4 Much of the information presented in this test method is based on work performed by the Civil Engineering Department of Purdue University during the late 1940s. The essentials of that work have been presented in a pamphlet prepared by Layne-Bowler, Inc.2 and updated by Layne Western Company, Inc.3