Assessment of Water Resources for Water Supply in the Rock River Region

Good morning everyone.  We sincerely hope that you are staying well during this insufferable heat and humidity.  We will be resharing some resources on available cooling centers in our region: Keep Cool Illinois.   (Unfortunately, Ogle County does not have any cooling centers recognized by this map; however, please know that our local libraries (Oregon and Byron) are always open for those looking for some respite from these blistering temperatures.)  Here is the interactive map for those looking to familiarize themselves or to share with others: Cooling Centers (via Keep Cool Illinois)

Without further ado, today we will be sharing two pieces of research.  The second is an excellent study from a series focused on water supply planning throughout the state of Illinois entitled: Water Supply Planning.  This is an effort being led by the Illinois State Water Survey via Prairie Research Institute.  [Funding is provided by the Illinois Depart of Natural Resources Office of Water Resources.].   This will serve as a supplement to the more relevant study for our purposes in Ogle County, which where is our update will begin: Water supply planning: Assessment of water resources for water supply in the Rock River region

The Rock River water supply planning region is composed of 11 counties: Jo Daviess, Stephenson, Winnebago, Boone, Ogle, Carroll, Whiteside, Lee, Rock Island, Henry, and Bureau Counties. This report focuses on the important drivers affecting the availability and sustainability of the water supply in the region. The results and discussion of these scientific analyses are intended to highlight the opportunities and challenges ahead for meeting future water demand in this area. Although total surface water demand is far greater than groundwater demand, the number of individual stakeholders dependent on groundwater to meet their demands is considerably higher. This is because the few surface water intakes are generally associated with thermoelectric power generation. As of 2010, water demand for thermoelectric power generation totaled 1,160 million gallons per day (mgd), which was 87 percent of the region’s total reported demand (1,332 mgd). This water, primarily used for cooling, is largely returned to its source after use.Future demand for thermoelectric power generation will depend strongly on cooling system design and the gross generating capacity of active power plants in the region.

There are three major aquifer systems in the Rock River region: shallow unconsolidated (sand and gravel) aquifers, shallow bedrock (often karst) aquifers, and deep sandstone aquifers. Although usage types are mixed for each aquifer, agricultural demands are primarily sourced from shallower aquifers, and public supply demands are primarily sourced from the deep. Cambrian-Ordovician sandstone aquifer.  Sand and gravel aquifers are heavily used for irrigation, particularly in the Green River Lowlands, where agricultural demands have increased since the Illinois State Water Survey (ISWS) installed monitoring wells in the 1990s. As a result, water declines due to peak irrigation demands in the Green River Lowlands are substantially higher than when last assessed more than 30 years ago. These declines can result in reductions in groundwater discharge to streams, which may have ecological impacts, and increase the potential for summertime supply disruptions to domestic stakeholders; these risks are further exacerbated under drought conditions.  Demands in Winnebago County, particularly in Rockford, are generally sourced from the Cambrian-Ordovician sandstone aquifer and are potentially unsustainable, especially when the impact of reductions in groundwater discharge to streams is considered. Another concern in the Rockford region is the potential for contamination, legacy, acute, or otherwise, of municipal and domestic water supplies.

The shallow aquifers are vulnerable to a variety of contaminants, including nitrate from fertilizer application, chloride from road salt application, septic/sewage discharge, and arsenic from natural sources. Deep aquifers are subject to natural contaminants, such as radium and barium. The karst aquifers of Jo Daviess County are particularly vulnerable to contamination because of rapid recharge times and a limited ability to remove contaminants traveling through the subsurface. Sampled wells had limited contamination, but springs indicated signatures of septic system discharge.

...The total surface water withdrawals in the Rock River WSPR were 1,147.3 million gallons per day (mgd) in 2018. Of the total, 98 percent is used by power generation for cooling purposes. The Constellation (spun off from Exelon in 2022) power stations at Quad Cities and Byron are the region’s two largest users. Public water supply is the next largest surface water user with three cities, Rock Island, Moline, and East Moline, relying on surface water for public water supply. Due to their proximity to the Mississippi River, local water quantity should meet these cities’ future demands. The Constellation Quad Cities Station and the three public water supply systems all withdraw water from the Mississippi River. The only major user relying on the Rock River is the Constellation Byron Station. In addition, most of the Mississippi River withdrawals are returned to the river as wastewater or sewage. Considering the amount of streamflow in the Mississippi and Rock Rivers, surface water supply is sufficient to meet the demand. If the two nuclear power plants retire in the future, surface water demand will be decreased dramatically.

The entirety of the study is well worth your time.

Changing Groundwater Levels in the Sandstone Aquifers: Synoptic measurement of deep sandstone wells in 2021 throughout northern Illinois.  
Daniel R. Hadley, Daniel B. Abrams, and Devin H. Mannix
June 8, 2023

We understand that this looks like a LOT of information to process.  We have selected an excerpt to pique your interest and to highlight the importance of reading through this series.  To begin: 
The 2021 synoptic measurement occurred from August to December over a 14-county area. The goals of the project were to: 1) create maps of water level elevations for the sandstone aquifers, 2) calculate changes in the sandstone aquifer system since 2014, 3) determine specific capacity of sandstone wells, and 4) assess current risk in the sandstone system based on available head above the top of the aquifers.

{Synoptic measurements (as they related to groundwater) refer to methods of collecting data from multiple wells or locations simultaneously to assess groundwater levels or conditions at a specific time, ensuring consistent environmental conditions across all sites. This approach helps in understanding the overall groundwater system and its variations.}

An important structural feature is the Sandwich Fault Zone, which offsets the sandstone units by as much as 800 feet in DeKalb County (Kolata, 1978). The fault zone is 0.5-2 miles wide, 85 miles long, and has near vertical displacement. The large displacement has caused the St. Peter sandstone to become completely eroded south of the fault zone in potions of DeKalb, LaSalle, Lee, and Ogle Counties. The fault zone acts as a horizontal flow barrier which limits groundwater movement across the fault zone (Hadley et al., 2019) and exacerbates water level declines in Kendall and Will counties (Hadley at al., 2021)

Please stay safe and stay engaged.