Aquifer Testing for Stream Flow and Groundwater Interactions
This project is studying the response of certain aquifers to groundwater pumping. Research involves an aquifer test, which is an experiment where a well is pumped at a known, constant, pumping rate; changes in groundwater levels and stream flows in the areas around the aquifer test site are observed while the well is being pumped. These tests help us understand how groundwater flows between aquifers, which are underground rock and sand layers that hold water.
Understanding the interactions between shallow and deep aquifers and surface water is important for managing groundwater supplies. This information is critical in deciding how much groundwater can be pumped – and from which aquifers – to ensure the long-term sustainability of the water supply and the natural resources that rely on groundwater.
In some streams, groundwater is a significant source of stream flow. This groundwater can be important in sustaining species like trout that need a constant flow of cold, clean water. The groundwater comes from an aquifer, which is an underground deposit of porous rock or sand that holds water. Groundwater pumping from wells drilled into shallow aquifers that feed the stream may decrease the amount of groundwater flowing into the stream. This is a concern because pumping can threaten the ability of some stream to support trout in the future.
Drilling wells into deeper aquifers could be a solution to concerns about effects of pumping from the shallow aquifers. However, aquifers can be connected, and pumping in one aquifer can lower water levels in the aquifers above or below it. The strategy of drilling deeper only works when thick layers of clay and shale act as a protective barrier between aquifers. But it is difficult to predict how water moves between a given set of aquifers without special tests designed to detect responses from pumping in nearby aquifers and surface waters.
The remaining balance of the appropriation in Laws 2011 First Special Session chapter 6 article 2section 6 paragraph (g) to the commissioner of natural resources for shoreland stewardship TMDL implementation coordination providing technical assistance and maintaining and updating data may be used for stream flow and groundwater monitoring including the installation of additional monitoring gauges and monitoring necessary to determine the relationship between stream flow and groundwater and is available until June 30 2015.
In FY 16 we will do a minimum of two additional aquifer tests. Both will involve the construction and test pumping of production wells drilled into the Jordan Sandstone. We will complete reports summarizing the outcomes of all the aquifer tests will be completed in FY16. We will also purchase and install monitoring equipment for the observation wells drilled for the aquifer tests.
In FY16 aquifer testing was completed at nine locations to study interactions between surface water and groundwater. The tests provide empirical data for groundwater modeling in Dakota County and the Little Rock Creek area.
Test drilling was done at six other sites also to study surface/groundwater interactions. At five of these sites wells were constructed to monitor groundwater levels. The wells were added to the groundwater monitoring network.
The remaining balance of the appropriation in Laws 2011 First Special Session chapter 6 article 2section 6 paragraph (g) to the commissioner of natural resources for shoreland stewardship TMDL implementation coordination providing technical assistance and maintaining and updating data may be used for stream flow and groundwater monitoring including the installation of additional monitoring gauges and monitoring necessary to determine the relationship between stream flow and groundwater and is available until June 30 2015.
In FY15 the DNR will install observation wells monitor stream flow and conduct at least one aquifer test using continuous pumping to measure the response of nearby aquifer levels and stream flow.
In FY15 the DNR installed four observation wells monitored stream flow (at 4 sites) and conducted an aquifer test using the City of Lakeville’s Well #3 which draws from the Jordan Sandstone aquifer. The well was pumped for 7 days; we checked water levels and stream flows at the surrounding observation wells and monitoring sites over 34 days to see if we could observe changes in groundwater levels and stream flows in the surrounding area during and after the time the well was being pumped.
We also drilled a test production well (a temporary high-capacity well used to stress the system to detect changes during pumping) on the Vermillion River Wildlife Management Area at a site adjacent to existing observation wells (wells strictly used to check levels of groundwater) that are part of our statewide groundwater monitoring system. A test well was drilled into the Prairie du Chien aquifer and was pumped to quantify the impacts to the local aquifers and the Vermillion River and to refine aquifer characteristics of the Prairie du Chien aquifer.
Data from the tests gives us the information we need to develop computer models which will predict effects from groundwater pumping on trout streams in the southern Metro region.