Pumping tests are the principal means of evaluating aquifer properties such as hydraulic conductivity, transmissivity, and storage coefficient. A pumping test basically involves pumping a well at a constant rate while measuring the drawdown of the well being pumped (single well pumping test) or the drawdowns of both the well being pumped and one or more observation wells located nearby (multiple well pumping test). Over 90% of the pumping tests made in the State are single-well pumping tests.
Both the single-well and multiple-well tests produce a reliable values for hydraulic conductivity and transmissivity; however, the multiple well pumping tests can also provide a value for storage coefficient.
Hydraulic conductivity describes the rate at which water will flow through a unit cross-section of an aquifer, at a unit hydraulic gradient, and is usually expressed in gallons per day per square foot. Transmissivity describes the rate at which water is transmitted through the entire thickness of an aquifer under a unit hydraulic gradient, and is equal to the hydraulic conductivity multiplied by the aquifer thickness. Transmissivity is usually expressed as gallons per day per foot. The storage coefficient of an aquifer is the ratio of water released from (or taken into) a unit column of the aquifer to the total volume of water in a unit column of the aquifer, under a unit gradient.
Pumping tests provide information on how much water an aquifer can be expected to yield to wells; how much water wells can be expected to produce; the effects that wells will have on one another; changes in the storage capacity of an aquifer due to droughts, recharge, or pumping; and the efficiency of wells. Transmissivity values and storage coefficients derived from the pumping tests are important parameters used in the development of groundwater flow models.
Over 750 pumping tests were analyzed by Roy Newcome (SCDNR, retired), the results of which are included in the following reports listed below.
Newcome, Roy, Jr., 1997, Well efficiency – Its importance and its calculation, in Contributions to the hydrology of South Carolina: South Carolina Department of Natural Resources Water Resources Report 14, p. 45–47.