Groundwater Pump Test

Goals

• Observing how groundwater flows to a pump.
• Observing changes in groundwater table as a result of pumping.
• Observing the quantity and quality of water in the groundwater system.
• Connecting topographic observations with data on groundwater flow

Skills

• Running a pump test.
• Graphing and interpreting drawdown data.
• Quantifying orders of magnitude of ground water flow velocities

This lab can be used to supplement classroom and text information on ground water flow and interactions between ground water and surface water. It can be paired with a field lab observing sedimentary units that are aquifers: aquifers in outcrop.

Minimum time required for the field component is about 75 minutes, not counting transportation time. The total time depends on the length of time you want to pump the aquifer (and whether it's important that the aquifer reach equilibrium during pumping) and whether you want to devote lab time to constructing drawdown curves (against time and distance from pump), geologic cross sections of the aquifer, and calculating hydraulic conductivity, transmissivity, etc. All of these can be turned into homework assignments, or work to be done jointly during the next class period.

This lab requires a more-or-less permanent well field that has been installed and tested before the lab period. For areas of alluvium adjacent to rivers, this installation is not very costly because the wellpoints can be installed by hand and the set-up can be used for many courses, ranging from introductory geoscience to geomorphology to hydrology. See later sections of this page and the publications in the resource section for more information about the specifics of constructing the well field, installing a pump (or using a portable one) and constructing the equipment necessary for the lab. The list below names the equipment; check the other information linked to this page for specifics about how to construct the specialized equipment quickly and cheaply.

Equipment needed:

• 30 or 50 meter tapes
• Probes to measure ground water depth below surface
• Rulers (in mm) to measure ground water changes while pumping occurs
• graph paper (semilog and arithmetic)
• map boards or clipboards
• Calibrated orifice bucket to determine pump discharge
• Tubing and attachments to convey pumped water away from the study site
• Wrenches and lubricant to remove and replace caps of wells

Student handouts and worksheets (Acrobat (PDF) 17kB Jun17 03) for a pump test lab. The lab was first developed by Shelby Boardman, Ed Buchwald and Tim Vick at Carleton College and was adapted here by Mary Savina. The lab was written up for Journal of Geological Education: Vick, Timothy D. and Buchwald, C. E., 1981, A field experiment in ground-water hydrology for introductory earth science students: Journal of Geological Education, vol.29, no.3, pp.116-120.

Useful tips (Acrobat (PDF) 64kB Mar10 04) written by Tim Vick for the collecting the equipment and running the pump test.

One good strategy before going in the field for this lab is to have students predict what will happen when the pump turns on and off - will the water table rise or fall?; will the response be greatest closest or further from the pump?

You know (and they will soon find out) that most of the action happens in the first few minutes after pumping starts; you don't need to tell them this, but do make sure that they are prepared and ready to read water table depression values as soon as the pump is turned on. It is useful to have readings at 30 sec., 1 minute, 2 minutes and 4 minutes after the pump is turned on (and off) and then readings at two minute intervals after that.

It is not necessary (and probably not desirable) to run the pump test and the recovery until the aquifer level stops changing altogether. Students will be able to calculate hydraulic conductivity and plot good drawdown curves after about 30-40 minutes of pumping and 20-30 minutes of recovery.

Through questions and discussions before the pump test and while it is going on, you should be able to assess the students' understanding of the field situation. Some good questions to ask them to reply to verbally or with a sketch include:

• How do you think the water table elevation changes from place to place (before pumping starts)?
• What do you think will happen to the water table elevation when pumping starts?
• What will happen when pumping stops?
• What does a cross-section of the equilibrium water table look like?

You can also use written lab reports and exam questions as possible assessment techniques.

Vick, Timothy D. and Buchwald, C. E., 1981, A field experiment in ground-water hydrology for introductory earth science students: Journal of Geological Education, vol.29, no.3, pp.116-120.