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A slug test measures groundwater flow near an aquifer by removing or displacing a slug of water or soil and measuring the flow or pressure at which the water table changes. It is used to determine the characteristics of an aquifer and is less expensive than pumping. However, it only measures the area surrounding the well and may not be representative of the entire geography.
A slug test is designed to measure the hydraulic conductivity, or flow, of groundwater near an aquifer by removing or displacing a slug of water or soil from underground and measuring the flow or pressure at which the water table changes. Civil and environmental engineers, as well as hydrologists and hydrogeologists, will use a slug test to determine the characteristics of an aquifer. A slug test differs from a common aquifer test in that it usually measures only one well while an aquifer test changes one well and then measures the changes that result in a nearby well.
In a typical slug test, a long, heavy rod made of PVC is driven into an aquifer well to collect or move water into the well. Once removed, the hydraulic conductivity of water near an aquifer can be measured. According to standard operating procedure No. 2046 of the US Environmental Protection Agency (EPA), “hydraulic conductivity is an important parameter for modeling the flow of groundwater in an aquifer”.
A person performing a slug test in the United States will be required to follow both the protocol established by the US EPA, the protocol established by the state environmental government agency, and its internal company protocol. As with any scientific experiment or test, data must be recorded before, during, and after the test in order to accurately measure the hydraulic conductivity of the area and the aquifer. Data captured during a slug test includes site or location identification number, person performing the test, data collection date, slug volume, test method, elapsed test time, water depth and any additional comments .
There are two main benefits to slug testing. First, the results are measured in situ, which means on site. This is different from offsite testing which could produce errors depending on how the samples were handled. Second, slug tests are generally less expensive to perform than pumping and do not require additional wells for measurement.
One limitation of a slug test is that it only measures the area immediately surrounding the well. This is in contrast to most aquifer tests, which simultaneously measure the results of a slug test at many wells in a particular area. So a slug test might only be representative of a small section of the geography, while a standard aquifer test might have more complete and accurate results.
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