A More Sustainable Approach to Water Supply
The way that we use groundwater is unsustainable. Continuously pumping a pristine resource, using it once, and then dumping it in surface water is not a wise use of a resource. So why do we use our groundwater as a “throwaway” item rather than using it in a sustainable way?
One reason is what water supply managers call “the yuck factor”. In virtually every community in the U.S. where a fully recycled water system is proposed, people have objected to the idea of drinking purified wastewater; it seems just too “yuck-y” to contemplate.
A second reason is cost. We have become accustomed to paying only enough for wastewater treatment to protect our rivers and streams from the worst symptoms of pollution. More effort would be needed to treat used water to a condition we would find acceptable in our water glass.
River bank inducement (RBI) is a strategy for achieving something like water recycling, but at lower cost than direct recycling and without the “yuck” factor. River bank inducement has been used successfully in the U.S. and in other countries around the world.
In the U.S., at least half a dozen cities have switched from using surface water (usually river water), which was becoming increasingly degraded, to using River Bank Filtration, an application of RBI to specifically reduce water treatment costs for water supplies. For example, Dayton and Cincinnati, Ohio; Des Moines and Cedar Rapids, Iowa; Lincoln, Nebraska; and Louisville, Kentucky use River Bank Filtration to filter river water before drawing it into the drinking water treatment plant. In these cases, the process of drawing the water through the subsurface soils has reduced bacteria, nitrates, and pesticide contamination found in the surface water. In these examples, river bank inducement is used as a way to improve source water quality by filtering the water through river bank sediments on its way to the well.
In Cedar Rapids, for example, 74 percent of the well recharge is water from the Cedar River. Cities in Europe have been using river bank inducement for even longer. Dusseldorf, Germany has used river bank inducement for over 150 years.
River bank inducement already occurs to some degree in many wellfields in Wisconsin, too. Hydrogeologists site shallow wells adjacent to surface waters in order to intercept groundwater flow that would otherwise flow into streams and lakes. In some cases, the well pumps so strongly that it ends up drawing some water from the direction of the surface water body, moving water from the riverbed toward the well. This is precisely what river bank inducement does by design rather than by accident.
Southeast Wisconsin is experiencing some of the problems typical of a “pump and dump” system. Although much of the eastern portion of the region uses water from Lake Michigan, many communities throughout southeast Wisconsin rely on groundwater, use it once, and dump it into the nearest surface water body. The practice has caused an alarming rate of groundwater depletion in southeast Wisconsin, and groundwater is declining in quality as well, requiring some groundwater-dependent communities to treat the water before it can be distributed to homes and businesses.
Local Study of River Bank Inducement Shows Promise
Recently, a team of scientists and engineers from UW-Milwaukee, United States Geological Society, and Black and Veatch explored whether river bank inducement could meet the water needs of groundwater-dependent communities in southeast Wisconsin. The scientists made careful observations, field analyses, and simulations of a shallow aquifer along the Fox River in southeast Wisconsin. The purpose was to understand how the water moves underground in response to pumping from wells located near the stream.
The research reached the following conclusions.
- Some City of Waukesha wells in the vicinity of the study site are already operating like a water recycling system. A portion of the water in two wells comes underground from the Fox River, and the Fox River water is a mixture of groundwater, rainfall, urban and agricultural runoff, and wastewater discharged by communities upstream.
- River bank inducement (RBI) could realistically supply water. In communities along the Fox River, for example, an appreciable amount of the water currently being drawn from wells in the shallow aquifer could be replaced with wells purposely located to recycle river water via the groundwater connection. The quantity of water that might be withdrawn would depend on well placement and local conditions, but RBI wells could produce an appreciable part of the area’s long-term water supply needs.
The results of this study on the Fox River could be extended to other communities, both in southeast Wisconsin and other parts of the state where groundwater is being stressed by “pump and dump” practices. According to the scientists, River Bank Inducement offers a potential solution along larger rivers as long as the river is in contact with a relatively permeable aquifer so that water can move from the river underground to wells located nearby. Wastewater, after the water is used by homes and businesses, would be discharged after normal sewage treatment to the same river or a tributary, upstream of where the wells are located. This approach could achieve a more sustainable water supply at a fraction of the cost required by a simple closed-loop recycling system and protect our groundwater aquifers from becoming depleted.
If you are interested in the entire ‘Our Waters’ report on River Bank Inducement, or other topics in the ‘Our Waters’ series, visit: http://home.freshwater.uwm.edu/ourwaters/
Cherkauer, D. and T. Grundl, Examining the Viability of Riverbank Inducement (RBI) as Another Source of Water in SE Wisconsin, presentation, April 2011.
Feinstein, D.T., Fienen, M.N., Kennedy, J.L., Buchwald, C.A., and Greenwood, M.M. 2012, Development and application of a groundwater/surface-water flow model using MODFLOW-NWT for the Upper Fox River Basin, southeastern Wisconsin: U.S. Geological Survey Scientific Investigations Report. 2012-5108, 379 pp.