WATER WELL STEP TESTING
(Nontechnical. For a technical web page on this subject, click here.)
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Purpose of Water Well Step Testing
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. There are many such procedures that are applicable to different problems involving different types of aquifers.
Step testing is one of the more valuable and cost effective aquifer testing procedures. 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. 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. 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. When appropriate, the aquifer characteristics may be used to develop a conceptual model that is preliminary to constructing a numerical groundwater model. It has been recommended as the first procedure in testing Aquifer Storage Recovery (ASR) wells (Payne, 1994). Step testing may be used as a preliminary test to help plan a constant discharge rate test. 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.
Water Well Step Testing Procedure
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 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. While the well is being pumped, the water level is measured in the well and any monitoring wells nearby. 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. In this case one might inject liquid at successive constant injection rates. The evaluation of the data is the same as for successive constant pumping rates. The technical page associated with this nontechnical one describes a useful step test data analysis procedure. The procedure is valid for a type of groundwater aquifer that is overlain and underlain by low permeable beds (confined aquifer). 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).
Water Well Step Test Example
The measured water levels are recorded as drawdown, which is the distance the water level in a well declines during pumping from the initial non-pumping level. Two step test drawdown curves are shown in Figure 1. One is a curve for a hypothetical pumping well with no "well loss," and the other curve is for the same well with severe well loss. (Well loss is drawdown caused by restrictions to groundwater flow interfering with the movement of water into the well.)