Water Supply Planning for the Rockford Area
How geology, geography, and history affect public and private water supply in the Rockford, Illinois region.
The story of groundwater in Rockford comes in two parts: water quantity and water quality. Although groundwater resources are relatively plentiful, the Rockford area does have a history of groundwater contamination. Careful planning can help ensure safe and reliable use of the aquifers.
There are three major sources of groundwater available for Public Water Supplies: sand and gravel, shallow carbonate bedrock (Galena-Platteville), and the deeper sandstone bedrock (Cambrian-Ordovician).
Within the Rock River valley, the sand and gravel aquifer directly overlies the Cambrian-Ordovician sandstone. Out of the valley, the Cambrian-Ordovician is overlain by the Galena-Platteville.
This spatial relationship between the three aquifers imparts some interesting characteristics on their viability for public water supplies.
The sand and gravel aquifer is shallow and productive but susceptible to contamination and is only present within the Rock River valley.
The Galena-Platteville is present outside of the Rock River valley and is shallow, but not reliably productive.
The Cambrian-Ordovician is deep and productive. Within the Rock River valley it is overlain by the sand and gravel aquifer, but out of the valley it's overlain by the Galena-Plateville.
Within the Rock River valley, water levels in Cambrian-Ordovician wells are stabilized by the relatively high recharge and leakage from the highly transmissive overlying sand and gravel (Wells #1 and #6 at right).
Conversely, where the Cambrian-Ordovician is overlain by the Galena-Plateville there is less recharge and leakage due to the relatively low-transmissivity Galena-Plateville and therefore pumping is more likely to produce long term draw downs in water levels.
The water levels of Rockford Wells #10 and #18 help to tell part of the story of the Cambrian-Ordovician sandstone in the Rockford area.
Well #10 (top figure) is to the east of the Rock River valley and exhibits a declining trend in its water levels. Well #18 (bottom of figure) is to the west of the Rock River valley and its water levels exhibit a stable to increasing trend.
These two wells are representative of the larger spatial patterns of water levels in the Cambrian-Ordovician wells of the Rockford area. In general, Cambrian-Ordovician wells to the east of the Rock River Valley exhibit stable to decreasing water levels, while wells to the west of the valley exhibit stable to increasing water levels.
Wells #23 (top figure) and #35 (bottom figure) are shallow wells in the sand and gravel aquifer of the Rock River valley. They display characteristics that most of the sand and gravel wells share: stable to increasing trends in water levels and more variability relative to Cambrian-Ordovician wells.
A preliminary analysis of 23 of the City of Rockford’s wells reveals that five have increasing water levels, seven have decreasing levels, eight are stable, and three exhibit no discernible trend (either data is sparse or water levels over the period of record vary greatly). Asterisks denote wells where further analysis is needed.
Table: Water level trends of 23 selected City of Rockford wells. Orange indicates a Cambrian-Ordovician well to the west of the Rock River, blue indicates a Cambrian-Ordovician well to the east, and white indicates an alluvial aquifer well within the Rock River valley.
In a 2015 ISWS report , a 2014 mass measurement of water levels in the Cambrian-Ordovician aquifer across northern Illinois was compared against estimates of water levels in the region predevelopment. The result is the map at right of drawdown since predevelopment.
As can be seen in the map, drawdown in the Rockford region is often below 100 ft, but in spots--and particularly to the east of Rockford, drawndown exceeds 100 ft.
The City of Rockford’s pumping has steadily declined since records began being kept from 32 MGD in 1979 to 16 MGD in 2019 (Figure 7). This reduction in pumpage may help to explain why water levels in the many wells assessed were found to either increase or remain stable despite ongoing pumping.
Interestingly, Cambrian-Ordovician wells east of the Rock River Valley have seen greater reductions in pumping than those to the west. This is in contrast with what might be expected based upon water level trends alone.
Meyer et al. (2019) established three future water demand scenarios based on different socioeconomic outlooks for the Rock River WSP region. These scenarios are known as Less Resource Intensive (LRI), Current Trend (CT; based off of 2010 water use), and More Resource Intensive (MRI).
For Winnebago County (at right), estimates were for a 31% increase in water demand (35 Mgd in 2010 to 45 in 2060) under the MRI scenario, a 4% increase (35 Mgd in 2010 to 36 in 2060) under the CT scenario, and a 16% decrease (35 Mgd in 2010 to 29 in 2060) under the LRI scenario
Along with the supply and demand considerations for the Rockford area's water supply, there are also impacts on natural systems to consider such as decreases in the amount of groundwater discharged to nearby rivers and streams caused by nearby pumping.
In a 2008 report and subsequent paper published in 2012 , researchers working in Michigan found that a reduction in groundwater discharge to rivers of about 10% could have an adverse resource impact (ARI) of 10% on what they call thriving species of fish (all fish living in habitat they are reasonably well suited for).
Essentially, with a 10% reduction in groundwater discharge to rivers, there would be a corresponding 10% reduction in the variety of fish species in a given segment of river.
Groundwater pumping near rivers can be the cause of reduction in groundwater discharge to rivers. In light of this, water supply planning in the Rockford area should be done in a way that prevents reductions to groundwater discharge to local rivers and streams.
The groundwater resources of the Rockford area are plentiful and can be a reliable source of water with careful management. Managing pumping to ensure stable water levels is part of that and so too is managing the water supply to avoid contamination.
Groundwater contamination in the Rockford area is largely due to poor waste disposal practices. From as early as the late 1950s industrial waste disposal practices were contaminating groundwater. It was first discovered in Rockford in 1981 when volatile organic compounds (VOCs) were detected in four public supply wells that were subsequently taken out of service. VOCs were found in private residential wells soon after in 1982. Testing in the area between 1982 and 1988 revealed many more contaminated wells.
The discovery of contamination culminated in the declaration of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA; commonly known as Superfund) site called the Southeast Rockford Groundwater Contamination (SRGWC) Superfund site on March 31st, 1989.
Map: US EPA, 2018
Along with the major SRGWC Superfund site, there is an additional site that falls under the jurisdiction of Superfund, six sites that fall under the Resource Conservation and Recovery Act (RCRA), and more than 80 Brownfield sites in the Rockford area.
(Figure adapted from the US EPA's Cleanups in My Community mapping tool .)
Alongside the relatively acute risks posed by industrial chemical contamination, there is also the risk of contamination of shallow groundwater by runoff from the application of road salt and nitrate contamination from agricultural and residential sources.
Pictured: Study area from an ISWS report from 1983 on nitrate contamination in Roscoe, IL from poorly sited septic systems and agricultural sources.
The primary concern for ensuring a stable water supply for the City of Rockford and the greater area is the potential for contamination—from legacy and future activities—to make its way into public and private water supplies.
Contaminants could become mobilized by existing pumping regimes, but a more pressing risk could be the mobilization of contaminants due to changes in pumping and decreases in water levels.
For example, if there are existing contaminants in the subsurface, (figure panel (a)), an increase in pumping at a given well has the potential to mobilize previously stable contamination, (figure panel (b)).
Water supply planning in the Rockford area requires careful consideration of the geology, geography, and history of the region.
The ISWS looks forward to continued collaboration with stakeholders such as the City of Rockford, in conjunction with ongoing efforts by state and federal EPA, to ensure the region continues to benefit from clean, reliable water.
Funding Information
This story map is part of a series about Water Supply Planning throughout the state of Illinois. Water Supply Planning is an ongoing research effort conducted by the Illinois State Water Survey and is funded by the Illinois Department of Natural Resources Office of Water Resources.
