In hydrogeology, a slug test is a particular type of aquifer test where water is quickly added or removed from a groundwater well, and the change in hydraulic head is monitored through time, to determine the near-well aquifer characteristics.
It is a method used by hydrogeologists and civil engineers to determine the transmissivity/hydraulic conductivity and storativity of the material the well is completed in.
An alternative object is a solid polyvinyl chloride (PVC) rod, with sufficient weight to sink into the groundwater.
Because the flow rate into or out of the well is not constant, as is the case in a typical aquifer test, the standard Theis solution does not work.
Complications arise from near-well effects (i.e., well skin and wellbore storage), which may make it difficult to get accurate results from slug test interpretation.