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*October 20, 2006*

**Where do the deep wells in southeastern Wisconsin**

**get their water?**

The Wisconsin Geological and Natural History Survey, University of
Wisconsin-Extension and the U.S. Geological Survey, in cooperation with
the Southeastern Wisconsin Regional Planning Commission, have jointly
constructed a ground-water flow model for southeastern Wisconsin. The
model shows the effect of pumping through time on both the shallow
aquifer and deep sandstone aquifer. Some of the key modeling results
with respect to the deep sandstone aquifer are reported here.

Pumping from the deep sandstone aquifer below southeastern Wisconsin
began around 1864. Before that time water that moved from the land
surface to the deep sandstone aquifer flowed toward Lake Michigan from a
boundary (called the "deep ground-water divide") that was located in
western Waukesha County. Based on model results, the total amount of
ground-water flow below southeastern Wisconsin (that is, below Ozaukee,
Washington, Milwaukee, Waukesha, Racine, Kenosha and Walworth counties)
moving toward Lake Michigan through the deep sandstone aquifer amounted
to about 3 million gallons per day.

Gradually-increasing pumping from deep wells has considerably altered
the natural ground-water flow system in the deep sandstone aquifer.
Today, well withdrawals from the deep aquifer below southeastern
Wisconsin amount to 33 million gallons per day, which means that the
deep sandstone aquifer is now transmitting more than 10 times its
natural flow rate. The direction of flow has also changed. Deep ground
water no longer moves eastward toward Lake Michigan but now moves toward
pumping centers, the largest of which is currently in Waukesha County.
Ground water converges on these pumping centers from all directions,
including from areas to the west in Jefferson County and from areas to
the east extending under Lake Michigan. From a scientific point of view,
the deep ground-water flow system is no longer flowing toward Lake
Michigan; it is flowing toward pumping centers. Using the southeastern
Wisconsin ground-water flow model, it is possible to determine where the
33 million gallons per day originate. Owing to the particular geology
below southeastern Wisconsin, the deep wells derive most of their water
from west of the pumping centers. Specifically, some ground water that
once flowed toward streams in the Mississippi River Basin is now flowing
downward toward the deep wells. This source accounts for about 70
percent of the replenishment of the water currently withdrawn from deep
wells. The remaining 30 percent originates from inside the Lake Michigan
Basin.

The question is asked: are communities like the City of Waukesha pumping
water that was flowing toward Lake Michigan? In fact, the water coming
out of the deep wells was flowing toward Lake Michigan before pumping
started. The wells are capturing [old]{.underline} water that had been
flowing to the east at a relatively slow pace for hundreds if not
thousands of years; now much of it is curling back and flowing westward
toward the pumping centers. However, it is also important to recognize
the effect of pumping on [new]{.underline} water. Deep pumping has
caused water that is currently entering the ground-water system as
recharge to move downward toward the deep part of the flow system
instead of following its natural course to streams at the land surface.
The volume of this replenishing water is much larger than the volume of
the pre-1864 flow toward Lake Michigan. Most of this replenishing water
is being diverted from streams in the Mississippi River Basin. While it
will take hundreds or thousands of years for this replenishing water to
reach pumping wells (assuming they continue to pump), the diversion of
groundwater away from streams downward toward the deep aquifer is
occurring now.

None of the water currently withdrawn from deep wells in southeastern
Wisconsin is water pulled directly from Lake Michigan. Thousands of
years of pumping would be necessary before water released by Lake
Michigan would travel all the way to the deep wells at inland pumping
centers. However, the model indicates that a small part (4 percent) of
the water entering the ground-water system in response to deep well
withdrawals is flowing out of the Lake.

We can summarize our findings as follows: 1) current pumping from deep
wells (33 mgd) has caused more than 10 times the water that once flowed
east toward Lake Michigan through the deep aquifer below southeastern
Wisconsin to now converge from all directions on inland pumping centers,
2) the deep wells are discharging old water that was once flowing toward
Lake Michigan, 3) the deep well withdrawals are mostly replenished by
new water that in the absence of pumping would have flowed to streams,
4) about 70 percent of the replenishing water is diverted from streams
in the Mississippi River Basin, the remainder from different parts of
the Lake Michigan Basin, and 5) Lake Michigan itself contributes about 4
percent of the replenishing water.

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*For further information, please consult Feinstein, D.T. and others,
2005, "Regional aquifer model for southeastern Wisconsin -- Report 2:
Model results and interpretation" in Technical Report 41, Southeastern
Wisconsin Regional Planning Commission. To download a PDF file of the
report, go to:*
<http://www.sewrpc.org/publications/techrep/tr-41_aquifer_simulation_model.pdf>