Southeastern Wisconsin consists of a seven county area that includes Milwaukee and the
surrounding metropolitan area. Most municipal water in the region comes from several surface water plants
along the Lake Michigan shore.
A compact between the Great Lake States and Canada prevents any
new diversion of surface water of the Great Lakes Basin. This prevents most of the fast growing
suburban communities from receiving Lake Michigan water. A total of 93 mgd of groundwater is
pumped for water supply by fifty municipal systems, most of which tie on the western side of the
subcontinental divide.
The major groundwater source has been the deep sandstone aquifer. The deep
sandstone aquifer consists of a series of Cambrian and Ordovician sandstone, shale and dolomite
units. The sandstone aquifer is between 500 and 2500 feet thick in the region. It is recharged by
surface precipitation in the extreme western portion of the region, but is highly confined throughout
the rest of southeastern Wisconsin. The sandstone aquifer has produced the vast majority of
municipal supply for groundwater systems for over 70 years.
Decades of over pumpage have created a cone of depression in the sandstone aquifer over 500
feet below original predevelopment heads. Over the last 20 years, the potentiometric head has
been declining by over 10 feet a year in the center of the cone and by over 5 feet a year over
much of southeastern Wisconsin. Water quality of sandstone aquifer wells has begun to change
in the area of heaviest pumpage. Total dissolved solids (TDS) and gross alpha levels have risen sharply
in several wells, which are beginning to experience problems with nuisance bacteria as a result. These
problems all appear to be related with prolonged overdraft of the aquifer.
In response to problems with the sandstone aquifer, municipalities have begun to develop two
shallow unconfined aquifers that are present in most of the region. These aquifers receive more
recharge than the sandstone aquifer and are believed to have a higher sustainable yield.
However, these wells are harder to site due to higher vulnerability to contamination and wide
variations in well yield. In addition, over development could harm surface water features. In spite
of these difficulties, these aquifers will probably be used to reduce the demand on the sandstone
aquifer and provide most of the new capacity.
While the current water supply is sufficient for immediate and near term needs, significant
changes will have to occur to prevent areas of shortage in the future. Recently, there have been
several positive steps toward rational regional water resource planning. A regional groundwater
model is being completed by a consortium of state and federal agencies. The model is directed
by a technical advisory committee consisting of local water utilities. The committee provides a
forum to begin regional water resource planning. In addition, geophysical and well rehabilitation
studies have demonstrated that the elevated TDS levels of some sandstone aquifer wells can be
reduced by selectively back filling portions of the wells and reducing pumping. This should
prolong the useful life of the sandstone aquifer and provide additional time to develop a long term
solution.
Includes 4 references.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 250 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 7 |
| Published : | 06/16/2002 |
