Hydrogeologists use aquifer characterization tests to determine key hydrologic parameters, including hydraulic conductivity (K), storativity (S), transmissivity (T), and radius of influence. The Level TROLL^® 700 instrument is designed for aquifer pump and slug tests. The Level TROLL^® 500 instrument can be used for slug tests. The Virtual HERMIT^® Aquifer Testing Kit, exclusively from In-Situ^® Rentals, streamlines step-drawdown and constant-rate pump tests.

Pumping Test Design

Before a pumping test or slug test is conducted, geological and hydrological information should be collected on the following:

• Geologic characteristics of the subsurface
• Type of aquifer and confining beds
• Thickness and lateral extent of the aquifer and confining beds
• Data on regional groundwater flow
• Identification of existing wells in the area. From the logs of these wells, it may be possible to derive approximate values of the aquifer's hydraulic conductivity and storage coefficient and their spatial variation. It may be possible to use one of those wells for the test, thereby reducing the cost of field work.

Step-Drawdown Test

A well is pumped at a constant rate for a given period of time. The pumping rate is successively increased or stepped for each of several time intervals (typically one hour per step and four steps). The water level is measured during each step (interval), and drawdown is calculated for each pumping rate. The aquifer’s response or drawdown is measured to determine well efficiency and the effective pump rate for a constant-rate pump test. The most common log type used is logarithmic.

Constant-Rate Pump Test

A constant-rate pump test is typically performed after a step-drawdown test. Pump tests deliver a more accurate hydraulic conductivity value (K) compared to slug tests. The pumping well is pumped at a constant rate, and water level data is collected in the pumping well and in monitoring wells to determine transmissivity (T), hydraulic conductivity (K), the storage coefficient (S), and other hydrologic parameters. The most common log type used is logarithmic.

Slug Test

Estimate hydraulic conductivity (K) in minutes – as opposed to hours for a pump test. This method requires the depression or elevation of static water in a well, and measurement of water level recovery and time. Water level and time are measured until the water level returns to its original static position. The most common log types used are logarithmic or fast linear.