Periodic step testing in production wells after they have been put into service can help track the deterioration of the wells and indicate when rehabilitation might be cost effective. Knowing the unavoidable drawdown in test wells and what it tells one about the quality of the aquifer near the wells can help in locating subsequent production wells in the best part of the aquifer. However, the remaining drawdown in the aquifer is not avoidable. When the production well is constructed, the factors causing well loss can be reduced or eliminated. In a test well, one can distinguish between drawdown due to well loss and drawdown in the aquifer that is unaffected by well loss. Constant discharge tests may provide more accurate results, especially for water table aquifers, leaky aquifers, and large diameter wells. Often step tests are followed by constant discharge tests. Step test results can help one plan any additional testing that may be needed. The test can be started at a low rate that will not stress the capacity of the well, and then the rate can be increased in steps until the drawdown is the maximum tolerable or the capacity of the pump is reached. In a new well, one need not know how hard the well can be pumped prior to the test. The usefulness of step testing stems from the following considerations: It may also be used for shallow aquifers that contain the water table if they meet certain criteria described on the technical page (generally permeable surficial sand and gravel). The procedure is valid for a type of groundwater aquifer that is overlain and underlain by low permeable beds (confined aquifer). The technical page associated with this non-technical one describes a useful step test data analysis procedure. The evaluation of the data is the same as for successive constant pumping rates. In this case one might inject liquid at successive constant injection rates. Step testing can also be used to estimate appropriate injection rates for new injection wells (for wastewater disposal et cetera) and to evaluate the degree of clogging in operating injection wells.
While the well is being pumped, the water level is measured in the well and any monitoring wells nearby. The steps may be an hour or two long, but the actual conduct of the test depends on its purpose and on other factors such as how much pumped water can be disposed of without adverse effects. Step testing usually involves starting to pump the well at a low rate and then increasing the pumping rate in successive steps in which the pumping rate is kept constant. The step testing method described on the technical page can also be used for testing injection wells if appropriate modifications are made to the input and output of the computer program used to analyze the test data. Step testing may be used as a preliminary test to help plan a constant discharge rate test. It has been recommended as the first procedure in testing Aquifer Storage Recovery (ASR) wells (Payne, 1994). When appropriate, the aquifer characteristics may be used to develop a conceptual model that is preliminary to constructing a numerical groundwater model. Step testing is also useful in testing new monitoring wells to design sampling procedures properly, and in testing aquifer exploration test wells to determine aquifer characteristics at the well locations. It can also be used to determine the inlet condition of an old well to see whether its efficiency has has deteriorated enough to warrant rehabilitation by chemical treatment and/or surging to reduce clogging of the inlets. It is commonly used for testing a new water well to determine aquifer characteristics (especially transmissivity which is related to permeability) and to evaluate the efficiency of the well, so that the proper sized pump can be selected. Step testing is one of the more valuable and cost effective aquifer testing procedures. There are many such procedures that are applicable to different problems involving different types of aquifers.
Aquifer and water well testing procedures (aka pumping tests) are valuable hydrogeologic tools that may be applied to water well problems, water well maintenance and rehabilitation, groundwater monitoring well testing, injection well testing, and groundwater sustainability planning.
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