Fortunately, the Green Bay area has some excellent groundwater information available. The diagrams are based on data in Knowles, D.B., 1964, Ground-water conditions in the Green Bay area, Wisconsin, 1950–60: U.S. Geological Survey Water-Supply Paper 1669–J, 37 p. and Knowles, D.B., Dreher, F.C., and Whetstone, G.W., 1964, Water resources of the Green Bay area, Wisconsin: U.S. Geological Survey Water-Supply Paper 1499–G, 66 p. Diagrams here are based on Water Supply Paper 1499-G.
A NW-SE cross-section through Green Bay, roughly perpendicular to the strike of the layers. The vertical scale is highly exaggerated and the actual dip of the layers is less than one degree. Red vertical lines are wells used for subsurface data. Some geologists prefer to distinguish "dolomite," the mineral, from "dolostone," the rock made mostly of dolomite. In practice there is little confusion.
From bottom to top, the rock units are:
Above: water usage from the deep aquifer 1886-1959. Note that once Green Bay ceased municipal pumping and began piping water from Lake Michigan in late 1957, water use dropped to what it had been about 20 years earlier. However, other users continued to pump about 40% of the pre-1958 total, so significant exploitation of the deep aquifers continued.
Elevation of the piezometric surface at Green Bay (green, of course) and De Pere 1880-1960. The horizontal lines show the elevation of the land surface. Before 1900, the piezometric surface was substantially above the ground surface. The wells were artesian wells and high pressure artesian wells at that.
Shortly after 1900, the piezometric surface had dropped to the elevation of the ground surface, and pumping was required. Initially, suction pumps were used, Since suction pumps lift water only about 30 feet, predictably enough, they ceased to be effective and were replaced by in-well turbine pumps.
The accelerating drop after 1938 was a clear signal something needed to be done. In 1957, Green Bay started using a pipeline from Lake Michigan, and the piezometric surface recovered rapidly.
A comparison of the water usage and piezometric surface plots shows that the Piezometric surface recovered astonishingly rapidly once municipal pumping ceased. Pumping decreased to the levels of about 20 years earlier, and the piezometric surface also recovered to the level of about 20 years earlier.
By 1957, over-pumping of the Cambrian aquifers had created a classic cone of depression beneath Green Bay. There was still a long way to go before depleting the aquifer, but over-drawing could also mobilize dissolved minerals and affect the water quality. And it was clear that things could only get worse. So in 1958, Green Bay began using a pipeline from Lake Michigan. Diagram based on Water Supply Paper 1499-G.
The Silurian aquifer (the areas generally above 700 feet in the east and southeast) is a perched aquifer not connected to the Cambrian sandstone aquifer. The water table here is shallow and generally follows topography.
By 1960, only two years after changing from wells to a pipeline, the water table had recovered dramatically. There is still a cone of depression, buy it's much shallower and smaller. There were still private, industrial, and municipal wells outside of Green Bay drawing water. Diagram based on Water Supply Paper 1499-G.
By 2003, continued pumping in the growing suburbs created a new cone of depression. Note the far larger number of data points in 2003. The cone of depression is deeper than in 1960, and also further southwest.
By 2005, the cone of depression was larger and deeper than the one in 1957, and centered south of Green Bay, reflecting the increased water usage by the suburbs. Data after Maas, 2009.
The deepening cone of depression led the suburbs of Green Bay to consider using Lake Michigan water as well. Their first thought was simply to use Green Bay's system. Green Bay's response was "Sure! How much are you willing to pay?" To which the suburbs replied "pay?" Eventually, six surrounding communities decided to build their own pipeline, which opened in 2006.
By 2009, the cone of depression, though still large and deep, has substantially ameliorated. Water table recovery has been enough to restore artesian conditions in some areas. Data after Maas, 2009.
Created 22 September 2003, Last Update 13 September 2016
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