By Al Wehrmann, Head of the ISWS Center for Groundwater Science - August 22, 2011
Deep bedrock aquifers underlie all of northeastern Illinois, provide relatively consistent yields and quality of water to wells, and have served as a reliable source of water to numerous communities for over 150 years. However, recharge to the deep aquifers is very slow and a history of high pumpage through the 20th century and now into the 21st century has caused water levels to fall 500 to 800 feet in many deep wells. In the Chicago region, large cities such as Aurora and Joliet rely on deep groundwater, as do smaller communities like Lake Zurich. Our ability to sustainably manage these resources is directly related to how well we understand them.
To that end, the Illinois State Water Survey (ISWS) is coordinating a large-scale water level measurement exercise on October 16, 2011, and we need your help. The more well operators (which usually means municipal utilities, but also includes investor-owned utilities, and private industrial and agricultural enterprises) that participate, the more comprehensive our data will be. Deep well owners/operators can expect a letter or e-mail from the ISWS containing measurement protocols, and I'd ask that residents and businesses whose community relies on deep aquifer water urge their local elected officials to take part. Check out the interactive map on the What Our Water's Worth site to see if your community uses deep aquifer for all or part of its water supply. A big thanks to the Northwest Water Planning Alliance for their help in coordinating this effort.
Because of the importance of these aquifers to the communities and industries of northeastern Illinois, the ISWS has been measuring water levels in deep wells since 1958. Continued collection of deep well water levels is essential to assess how the deep aquifers are responding to changes in deep bedrock pumping amounts and patterns. However, state resources to conduct this massive data collection effort are strained. As a result, the ISWS is asking for assistance from water operators with deep wells to cooperate in a coordinated data collection effort. That is, we are asking all operators with deep wells (>500’ deep) in northeastern Illinois to record their non-pumping well water levels all on one day and send that data to the ISWS.
Many facility wells have been measured in the past by ISWS personnel; the last measurement of deep wells in northeastern Illinois was in the fall of 2007. As part of this long-standing effort, the ISWS is interested in conducting another measurement in fall 2011, specifically on October 16. If a measurement cannot be taken on that day, measurements within the week before or after are acceptable and welcome.
Data collection to better management our shared groundwater resources is not new, but given the reality of budget constraints, ISWS needs the assistance of well owners and operators more than ever.
For perspective, in May 1959, the Illinois State Water Survey (ISWS) and the Illinois State Geological Survey (ISGS) published a report that discussed the geology and hydrology of the groundwater resources of the eight-county Chicago region. Special emphasis was placed on the deep bedrock aquifers that had been widely used to obtain large groundwater supplies throughout the region. In 1959, the ISWS expanded its program of collecting and reporting water-level and pumpage data for deep wells in the Chicago region. Since that time, the ISWS has issued 11 reports on deep well water levels and pumpage (for 1959, 1960, 1961, 1962-66, 1966-71, 1971-1980, 1980-85, 1985-1991, 1991-95, 1995-2000, and 2000-2007). In addition, computer models of the deep aquifers have been developed to assess the impact of withdrawals on deep aquifer groundwater levels.
Serving nearly 500,000 people at a rate of over 80 million gallons per day (estimated 84.4 Mgd in 2004), the ISWS has prioritized the deep bedrock aquifer system of northeast Illinois as the most important groundwater system in Illinois. While new data collection and analysis on this aquifer system is continually being updated, the scientific evidence suggests that if trends continue, water levels in many deep aquifer wells will continue to drop, potentially causing water supply interruptions and water quality problems (e.g., higher concentrations of radium and total dissolved solids).
Historical withdrawals from the 8-county northeast Illinois area (Cook, DuPage, Grundy, Kane, Kendall, Lake, McHenry, and Will Counties) are shown on the accompanying graph. The graph shows that in the past the deep aquifers provided much more water than is currently being withdrawn, that the switch to Lake Michigan water in the late 1970's and 1980's greatly reduced withdrawals from the deep aquifers, and that withdrawals are back on the rise (in some areas, artesian heads have declined as much as 800 feet since aquifer development began in the mid-1800's).
The graph here also shows the widely-cited 65 million gallon per day (mgd) potential yield estimate of the ISWS’ Bill Walton. Community leaders need to be aware of this current withdrawal trend, and how withdrawals compare to potential yield estimates. Many young water operators may not recall the rapidly declining water levels, reduced pumping capacity, and increased costs of pumping that occurred approximately 30 years ago. No one wishes to return to those trying circumstances.
The allocation of Lake Michigan water to the collar communities surrounding Chicago did much to alleviate water supply concerns in the region. However, industry and population continues to grow at a rapid pace in those communities and rural areas that did not receive lake water. Additional major allocations of Lake Michigan water to outlying areas remains unlikely; therefore, the region does not have a ready back-up water resource to call upon as it did 30+ years ago. This is part of the impetus behind the creation of the Northwest Water Planning Alliance, bringing together five Councils of Government representing 80 municipalities as well as County Governments in Kane, Kendall, DeKalb, Lake and McHenry Counties in a voluntary partnership to address water supply planning and conservation in this area that is served by ground and surface waters excluding Lake Michigan
Even though our understanding of the yield of the deep bedrock aquifers is uncertain, the increasing use of this resource is a concern. Because this aquifer system is present beneath the whole of northern Illinois and southern Wisconsin, can provide fairly high well yields, and stores a very large quantity of water, it is often the first choice for developers, communities, industry, and drillers seeking to secure additional water. However, the nature of this system and its limited recharge capability also means that communities and developers must understand that this is a shared resource, and the water used by one affects the amount of water available to others. Continued monitoring of this resource is needed to assess how the deep aquifers are responding to growing pumping rates and shifts in pumping locations.
For more details, contact Allen Wehrmann, Head of the ISWS Center for Groundwater Science at 217-333-0493 or by e-mail at alex@illinois.edu.