Geneml test procedures
(1) Before a pump test is started, the test well should be pumped for a brief period to ensure that the pumping equipment and measuring devices are functioning properly and to determine the approximate valve and power settings for the test. The water level in the well and all observation piezometers should be observed for at least 24 hours prior to the test to determine the initial groundwater table. If the groundwater prior to the test is not stable, observations should be continued until the rate of change is clearly established; these data should be used to adjust the actual test drawdown data to an approximate equilibrium condition for analysis. Pumping of any wells in the vicinity of the test well, which may influence the test results, should be regulated to discharge at a constant, uninterrupted rate prior to and during the complete test.
(2) Drawdown observations in the test well itself are generally less reliable than those in the piezometers because of pump vibrations and momentary variations in the pumping rate that cause fluctuations in the water surface within the well. A sounding tube with small perforations installed inside the well screen can be used to dampen the fluctuation in the water level and improve the accuracy of well soundings, All observations of the groundwater level and pump dis
charge should include the exact time that the observation was made.
(3) As changes in barometric pressure may cause the water level in test wells to fluctuate, the barometric pressure should be recorded during the test.
(4) When a pumping test is started, changes in water levels occur rapidly, and readings should be taken as often as practicable for certain selected pie-. zometers (e. g., t = 2, 5, 8, 10, 15, 20, 30, 4.5, and 60 minutes) after which the period between observations may be increased. Sufficient readings should be taken to define accurately a curve of water level or drawdown versus (log) elapsed pumping time. After pumping has stopped, the rate of groundwater-level recovery should be observed. Frequently, such data are important in evaluating the performance and characteristics of an aquifer.