The
Mahomet aquifer is the major groundwater resource for east-central Illinois.
Many communities, industries, and irrigators depend on the aquifer for
their supply; withdrawals in 1995 for municipal use are estimated at over
30 mgd. Withdrawals for irrigation, principally in Mason and Tazewell Counties
(the Havana Lowlands area), puts usage well over 100 mgd.
A long-term hydrograph at Champaign shows a decline in artesian head
of nearly 50 feet since 1950, as a result of increasing water demand in
the Champaign-Urbana area. The elevation of the top of the aquifer in this
region is at approximately 525 feet, so additional development of the aquifer
can continue in the Champaign area for quite some time. Similar, perhaps
greater, declines can be expected in other areas of development as use
of the aquifer increases.
Groundwater Quality Water within
the Mahomet aquifer is generally of excellent quality, although areas of
high ammonia and total organic carbon are known. Arsenic has also been
found in some wells, approaching or even exceeding drinking standards.
An area northeast of Decatur has been found to contain elevated concentrations
of dissolved minerals, possibly as a result of upwelling from the underlying
bedrock. The potential for agricultural chemical and nutrient contamination
of groundwater is also of concern in the sandy areas of Mason and Tazewell
Counties.
Increasing Demands Population projections
suggest that by 2020, the Mahomet aquifer region may increase by 100,000
people to a total of 900,000. Additional demands for water may result as
several central Illinois communities currently using surface water reservoirs
look to the Mahomet to alleviate reservoir capacity and water quality problems.
The additional demands of Springfield, Decatur, Bloomington, and Danville
could potentially increase groundwater demands on the Mahomet aquifer
by 80 mgd.
Science for Water Resources Management
While the sustained yield of the Mahomet aquifer has been estimated to
be in excess of 400 mgd, over-development of the aquifer can occur in localized
areas. New field data coupled with computer modeling of the aquifer system
is needed to examine development alternatives for community planners. With
respect to arsenic, a more detailed description of the distribution of
contaminated and uncontaminated areas is needed and effective water treatment
methods should be developed for communities in the affected areas. Field
sampling, laboratory experiments, and modeling should be done to predict
the effects of large-scale withdrawals on the transport of arsenic in the
aquifer.
Invitation to apply for membership to a regional water supply planning group
