Selection of Single-Well Hydraulic Test Methods for Monitoring Wells

Single-well hydraulic tests yield order-of-magnitude estimates of the hydraulic conductivity of aquifer materials around a single well. Although the single-well tests are less accurate than multiple-well pumping tests, they are often an attractive option when a quick, inexpensive estimate of hydraulic conductivity is required. There are three basic methods for determining the hydraulic conductivity from a single well: • Slug test—This method is also commonly referred to as a falling-head test or bailer test. It involves the instantaneous addition or removal of a given volume (slug) of water from a monitoring well with measurements of the recovery collected over a period of time. • Constant-head test—This method involves a measured discharge of water into a monitoring well to maintain a constant water level within the well. The method is more commonly used where the aquifer materials have moderate to high hydraulic conductivity values. • Single-well pumping test—This method is no different from an aquifer pumping test except that water level measurements are collected from just the pumped (monitoring) well. The pumping rate is kept constant throughout the test, and water levels are measured over a period of time. The choice of a single-well test method in a specific situation depends on a variety of factors. A decision-making flowchart has been developed to help select a hydraulic test method that incorporates both geologic conditions and monitoring well construction details. This flowchart will allow a hydrogeologist or ground-water engineer to assess quickly which test method is the most appropriate for a specific situation.