Illinois Water Supply Planning

Champaign City Council Meeting November 7, 2006: Water Supply and Ethanol

We are pleased to have the opportunity to review and comment on the October 17 report "Aquifer Evaluation and Competing Use Study" prepared by Malcolm Pirnie, Inc. for the Andersons, Inc. I attach the Water Survey's comments prepared by Dr. George Roadcap, P.G. and H. Allen Wehrmann, P.E. I will also send this letter and the attachment via regular mail

 

Although we will have improved scientific information about the Mahomet and Glasford Aquifers after completion of our study in three years, I understand that decisions about the use of available water resources need to be made in the immediate future. We currently do not have one single report on the aquifers that the City of Champaign can turn to as a source of additional information, but I would like to take this opportunity to restate and enhance some of the information that was provided at the Joint Study Session on September 28. This information reflects a synthesis of data and key findings from a number of relevant reports and, perhaps more importantly, the understanding of the aquifers by Water Survey scientists and engineers. Beyond hard scientific data, I introduced in the Joint Study Session some concepts that are fundamental to the development of regional water supply plans, as required in Executive Order 2006-01. I would like to reiterate some of these concepts, as I believe they are relevant to decisions that have to be made about water allocation and water use in Champaign County and surrounding areas.

 

Groundwater is a renewable resource, but not an infinite resource. As water is withdrawn from the aquifers the aquifers are recharged, but water withdrawals cannot continue without creating adverse impacts at some time in the future. The lowering of water levels in existing wells usually can be mitigated by lowering pumps or drilling new wells, but ever increasing withdrawals from the same part of the aquifers will at some point in time lead to dewatering of the aquifers themselves, a potentially serious situation that we advise be avoided. A key question for Champaign County is how much more water can be withdrawn safely before we start dewatering the aquifers? 

 

From 50 years of data from continuous monitoring of head (water level) at the Petro North well on Rising Road, we can determine that as withdrawals from the aquifers have increased by more than 16 million gallons per day, water level has declined by almost 50 feet at that location. [It should be noted that we do not have data on drawdown at the sites of the Illinois American Water wells, as there are no monitoring wells at these locations. We would expect drawdown to be greater at these sites. We also believe that the Glasford Aquifer already has been dewatered within the City of Champaign.]  A quick calculation leads us to conclude that for every million gallons of water that has been withdrawn, head in the Mahomet Aquifer at Petro North has been reduced by about 3 feet. Our best estimate is that there is an additional approximately 50 feet of head before the Mahomet Aquifer would start to be dewatered in this area. A simple calculation leads to the conclusion that an additional approximately 16 or 17 million gallons of water per day can be withdrawn for the Mahomet Aquifer in this area for all purposes before we start to dewater the aquifer.

 

The proposed ethanol plant will, according to the Malcolm Pirnie report, withdraw almost 2 million gallons of water per day and lower the head (water level) by about 4 feet. This will not dewater the Mahomet Aquifer. However, withdrawing this additional amount of water for any purpose will consume up to 4 feet of the approximate 50 feet of available head before the Mahomet Aquifer will start to be dewatered in this area. An additional approximately 50 feet of drawdown and approximately 16 million gallons per day of water withdrawals represent finite limits on the amount of additional water can be withdrawn safely in this area - for all purposes and for all times. Whether or not the above figures are accurate and precise is of little consequence. The fact is that, under a business as usual scenario, at some time in the not too distant future, growth in Champaign County may be restricted by water availability.

 

Implementation of Executive Order 2006-01 will lead over the next three years to water supply and demand projections to the year 2050 for East-Central Illinois and evaluation of management options. Currently, a process for communities in and around Champaign County to decide how they wish to allocate available water supplies does not exist. The above analysis is, I believe, the first time that a finite capacity to withdraw water from the aquifers in Champaign County has been articulated, so it is not surprising that there has been no discussion about the allocation of limited assets.

The Water Survey remains neutral on the allocation and use of available water. I simply wish to pass on to analysts, decision makers, and the public our current understanding of the aquifers, future water availability, and water demand. Water is withdrawn for many purposes including domestic, commercial, recreational, agricultural, power generation, mining, and other industrial uses. Some of these users have private wells, but many are dependent on public water supplies. Knowledge of limited water supplies will, I hope, stimulate people to set priorities and consider a range of management strategies. Currently there are many uncertainties, but even with perfect scientific knowledge and an accurate prediction capability, the key issue will remain the allocation of scarce resources. Although the potential sustainable yield of the entire aquifer is large, water withdrawals in Champaign County already have created a large cone-of-depression and reversed the east-to-west flow of groundwater. Champaign County is a "hot spot" in need of management attention.

 

Please let me know if we can provide additional information.

 

Sincerely,

 

 

Derek Winstanley, D.Phil.

Chief

Illinois State Water Survey

2204 Griffith Drive

Champaign, IL  61820-7495

 

Tel:  (217) 244 5459

Fax:  (217) 333 4983

e-mail:  dwinstan@uiuc.edu

web:  www.sws.uiuc.edu

Attachment  (pdf ~68k)