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Ground water in the Great Lakes Basin: the case of southeastern Wisconsin

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Graphic link to Concept - Effects of pumping on shallow and deep water levels (drawdown)EFFECT OF PUMPING ON SHALLOW AND DEEP WATER LEVELS IN SOUTHEASTERN WISCONSIN

Both the distribution and amount of pumping from shallow and deep rocks has changed dramatically over time in southeastern Wisconsin. Here are two snapshots of pumping for 1950 and 2000.

1950

 
Map of distribution of shallow and deep high-capacity pumping wells in SE Wisconsin for 1950 (26 kb)
Map of distribution of shallow and deep high-capacity pumping wells
in southeastern Wisconsin for 1950

(source: Wisconsin Geological and Natural History Survey Open-File Report 2004-01)
2000
 
Map of distribution of shallow and deep high-capacity pumping wells in SE Wisconsin for 2000 (27 kb)
Map of distribution of shallow and deep high-capacity pumping wells in southeastern Wisconsin for 2000
(source: Wisconsin Geological and Natural History Survey Open-File Report 2004-01)
Note: The map does not include private wells in southeastern Ozaukee County (city of Mequon ) that are present in the model after 1960. They are estimated to discharge 3.0 mgd from the shallow system in 2000. The map also does not include the deep sanitary tunnel in Milwaukee County that is present in the model after 1990. It is estimated to discharge about 2.8 mgd from the shallow system in 2000.

The effect of pumping on water levels is quite different for different depths and aquifers in the ground-water flow system. For the Silurian dolomite, a shallow aquifer that lies just below the loose glacial material but above the Maquoketa shale, the lowering of water levels due to pumping is greatest in Ozaukee County (north of Milwaukee) where developers have favored shallow wells. The wells draw some of their water from Lake Michigan:

A
Model output: 3D and 2D contour maps of Silurian dolomite water levels under A) natural conditions
BModel output: 3D and 2D contour maps of Silurian dolomite water levels under B) 2000 conditions (89 kb)
Model output: 3D and 2D contour maps of Silurian dolomite water levels under B) 2000 conditions

(source: D.T. Feinstein and J .T. Krohelski, U.S. Geological Survey)

For the deep sandstone aquifer, water levels have dropped sharply with time as the regional cone of depression has deepened and shifted west in response to the locations of new wells and increase in total volumes of ground water pumped. Compare the water levels simulated by the model in 1864, 1950 and 2000:

A

Model output: 3D and 2D contour maps of St Peter Sandstone water levels under A) natural conditions
Model output: 3D and 2D contour maps of St Peter Sandstone water levels under
A) natural conditions

B

Model output: 3D and 2D contour maps of St Peter Sandstone water levels under B) 1950 conditions
Model output: 3D and 2D contour maps of St Peter Sandstone water levels under
B) 1950 conditions

C

Model output: 3D and 2D contour maps of St Peter Sandstone water levels under C) 2000 conditions
Model output: 3D and 2D contour maps of St Peter Sandstone water levels under
C) 2000 conditions

(source: D.T. Feinstein and J .T. Krohelski, U.S. Geological Survey)

The ridge where the water levels are highest corresponds to the regional ground-water divide.

Another way to examine historical changes in water levels is to graph profiles of water levels in different rock units at different times. We have chosen to show profiles for the water table in the loose glacial material, for the Maquoketa shale that separates the shallow and deep parts of the flow system, and for the St. Peter sandstone at the top of the deep sandstone aquifer. The profiles correspond to a line that extends from Jefferson County through Waukesha and Milwaukee Counties to the Lake:

Map of profile line for displaying water le</a></p>
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    <p><span class= Map of profile line for displaying water levels in different rock units (LARGE FILE)
(source: D.T. Feinstein, U.S. Geological Survey)

The graphs show water-level profiles for the different units in 1864, 1950 and 2000. In each graph:

  • The top green line is the land surface
  • The blue line is the water table - it hardly changes through time.
  • The purple line is the Maquoketa. It lies near the water table under natural conditions, but drops below it in most places through time. Under natural conditions it is above the land surface near Lake Michigan.
  • The bottom yellow line is the St. Peter. Under natural conditions it is above the land surface near Lake Michigan (corresponding to the existence of flowing deep wells in the late 19th century). By year 2000, it is very far below he water table except in the west:
A

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in A) 1864 (natural conditions) (64 kb)

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in
A) 1864 (natural conditions)

B

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in B) 1950 (64 kb)

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in
B) 1950

C

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in C) 2000 (58 kb)

Model output: Water-level profiles for water table, Maquoketa shale, and St. Peter sandstone in
C) 2000

(source: D.T. Feinstein, U.S. Geological Survey)

The profile representing the deep sandstone aquifer has not only changed its elevation, but also its shape. Under natural conditions the slope of the line was toward Lake Michigan, indicating flow in that direction. By year 2000 the slope of the line is away from the Lake, indicating that ground water flows from under the Lake toward inland pumping centers.

The ground-water model calculates water levels at many points in time between 1864 and 2000. This VIDEO CLIP (1445 kb) shows evolving levels in the deep sandstone aquifer together with the shallow and deep well configuration. In the video, colors refer to the water level levation in feet above sea level (blue lowest, red highest). Maps only show southeastern Wisconsin, but effect of Illinois pumping centers is evident in declining water levels south of Milwaukee in Kenosha and Racine Counties.


The decline in water levels with time is called DRAWDOWN. The regional pattern of drawdown is called the CONE OF DEPRESSION.

Model output: Thumbnail maps of regional drawdown between 1864 and 2000 for: A) Silurian dolomite aquiferModel output: Thumbnail maps of regional drawdown between 1864 and 2000 for: A) Silurian dolomite aquifer

Model output: Thumbnail maps of regional drawdown between 1864 and 2000 for: B) deep sandstone aquiferModel output: Thumbnail maps of regional drawdown between 1864 and 2000 for: B) deep sandstone aquifer

(source: Wisconsin Geological and Natural History Survey Open-File Report 2004-01)

A VIDEO CLIP (837 kb) for conditions in the deep sandstone aquifer shows that in the early period of development (~1900), drawdown radiates from the Chicago area. Subsequently, a pumping center was established in Milwaukee. Over time, the center of the drawdown cone widened and its center moved west toward Waukesha county. In the video, the color scale refer to the amount of drawdown in feet (blue least, red greatest); the topography and dip of the surface corresponds to the top of the St. Peter formation; the view is from south to north.


The model can also be used to project future drawdown given assumptions about volumes of future pumping. In one simple scenario we assumed that the well network throughout southeastern Wisconsin would be unchanged between 2000 and 2020, but that the pumping rates at each well would increase by 15-20% between 2000 and 2010 and by 30-40% between 2000 and 2020. The results are just one way to picture future conditions (and future relations between the ground-water system and Lake Michigan):

Model output: Thumbnail map of additional drawdown in deep sandstone aquifer from 2000 to 2020 Model output: Thumbnail map of additional drawdown in deep sandstone aquifer from 2000 to 2020.
(source: U.S. Geological Survey Fact Sheet 116-03)

In summary, the regional ground-water system has changed and continues to change:

  • The major pumping center in southeastern Wisconsin has shifted from the city of Milwaukee to cities in Waukesha County.

  • The center of the cone of depression in the deep part of the flow system has shifted westward about eight miles from Milwaukee to eastern Waukesha County where deep water levels have dropped about 500 ft since the onset of pumping.
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