The two most heavily used aquifers in the WMIC are the Cambrian-Ordovician and the Glacial Deposits which are included in the list of major aquifers to be targeted for study by NAWQA. For these reasons, NAWQA ground-water studies in the WMIC focused exclusively on assessing and understanding the factors that affect the water quality of these two major aquifers.

The Cambrian-Ordovician aquifer underlies the eastern two-thirds of the WMIC and, where it is sufficiently thick, can produce large yields of water. For this reason, it is the most used aquifer in the study unit and accounts for about 40 percent of the ground-water use. The western part of the aquifer (click thumbnail to the right or see figure 2 in Saad, 1996) was further targeted for study because few wells exist in the eastern part where it is overlain by more readily accessible aquifers. Ground-water samples from domestic, institutional, and public-supply wells were collected during summer 1995 from 29 wells in the western part of the Cambrian-Ordovician aquifer. Ground-water samples were analyzed for major ions, nutrients, dissolved organic carbon, pesticides, volatile organic compounds, radon-222, and tritium, as well as field measurements of temperature, pH, specific conductance, dissolved oxygen, and bicarbonate. The results of water-quality analyses indicate that the dominant major ions are calcium, magnesium, and bicarbonate, and where the aquifer is overlain by the Maquoketa-Sinnipee confining unit, relatively high concentrations of dissolved solids (up to 2,800 mg/L) and relatively lower concentrations and frequency of detections of nitrate and pesticides occur. Additionally, high sulfate concentrations exist where the aquifer is regionally confined. Radon was detected in all samples and two thirds of the wells had concentrations exceeding the USEPA proposed maximum contaminant level of 300 pCi/L. The highest nitrate concentrations were detected in samples from the agricultural southwestern part of the study area from relatively shallow wells that produced modern water (recharged since 1955 based on tritium analyses). Seven pesticides were detected in ground water samples, and at least one pesticide was detected in seven of the wells. Most of the pesticides were detected in low concentrations. Atrazine was the most commonly detected pesticide.

Beginning in Cycle 2, the WMIC Cambrian-Ordovician aquifer wells were chosen to be part of the NAWQA ground-water trends networks that are to be sampled decadally. During summer 2002, water samples from 26 wells in the network (including 24 of the original 29 wells plus 2 replacements) were analyzed again for major ions, nutrients, organic carbon, pesticides, trace element, volatile organic compounds, and radon-222. Results of Cycle 1 and Cycle 2 decadal samples can be found under Data. Cycle 1 data are also published in Saad (1996) and Cycle 2 data are also published online at: http://pubs.er.usgs.gov/pubs/wdr/wdrWI021 (tip: search for "major aquifer study").

During summer 2005, a subset of 5 Cambrian-Ordovician aquifer wells, chosen to represent the water quality of the entire network, was sampled again. This subset of wells will be sampled biennially until 2013. The decadal and biennial sampling will help us to understand the factors that affect long-term and short-term trends in water quality in the aquifer.

Glacial Deposits Aquifer

In the WMIC, the glacial deposits aquifer can be found throughout the study area, however, it is most heavily used where the deposits are thick and permeable and where other aquifers are too thin or unproductive to be a reliable source of water. This includes primarily the west and northwest parts of the WMIC and a smaller area of heavy use in the southeast (click thumbnail to the right or see figure 5 in http://wi.water.usgs.gov/nawqa/news/nawqanews_v2n1.pdf). Most of the public supply wells that pump from the aquifer are found in these areas. Land-use in the study area ranges from urban to agriculture to forest and probable influences on water quality will include a wide range of natural and anthropogenic sources.

During summer 2003, 30 wells in the glacial deposits aquifer were sampled and analyzed for major ions, nutrients, organic carbon, pesticides, trace elements, volatile organic compounds, radon, radium, and bacteria. Results of those analyses can be found under Data or at: http://pubs.er.usgs.gov/pubs/wdr/wdrWI031 (tip: search for "major aquifer study").

References:

Saad, D.A., 1996, Ground Water-Quality in the Western Part of the Cambrian-Ordovician Aquifer in the Western Lake Michigan Drainages, Wisconsin and Michigan: Water-Resources Investigations Report 96-4231.

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