Groundwater Quality within the Silurian Dolomite Aquifer in Will County, Illinois, 2021

Walton R. Kelly, Devin H. Mannix, Cecilia Cullen, Michael P. Krasowski, Daniel B. Abrams

Research output: Book/Report/Conference proceedingTechnical report


The objectives of this study were to (1) provide a “snapshot” of water quality in the shallow bedrock aquifer in Will County; (2) compare water quality from different parts of Will County, especially the northern urban corridor and the southern and eastern agricultural regions; and (3) compare shallow bedrock groundwater-quality conditions between the early 1990s and 2021. Groundwater quality in the Silurian aquifer in Will County is generally acceptable, consistent with conclusions from a 30-year-old study (Roadcap et al., 1993). In both studies, most constituent concentrations were below the drinking water maximum contaminant levels (MCLs). However, there are four primary concerns regarding groundwater quality in the Silurian aquifer of Will County: 1) Naturally high levels of iron, sulfate, and hardness, which do not have primary MCLs, can give the groundwater an unpleasant taste, odor, or color or cause staining and scale formation that may be undesirable to many consumers. 2) Chloride has been increasing in urban parts of the county since the 1960s. Currently, three wells exceed the secondary standard of 250 mg/L for chloride, which can lead to salty tasting water. There has been a statistically significant increase in chloride concentrations in the past 30 years, almost exclusively in the northern urban region. Chloride concentrations in most rural wells in Will County have not changed during that period. It appears that runoff of deicing salts continues to be an issue in the urban parts of Will County. 3) Arsenic concentrations are above the primary MCL of 10 micrograms per liter (μg/L) in about 10 percent of the sampled wells, with a maximum concentration of 24.5 μg/L. Arsenic is a naturally occurring contaminant whose source is probably glacial deposits overlying the shallow bedrock. 4) Per-and polyfluoroalkyl substances (PFAS), known as “forever chemicals” because they break down very slowly in the environment, are a major water quality and public health concern in the Silurian aquifer, although they were not analyzed in this study. However, in a recent sampling program undertaken by the Illinois Environmental Protection Agency, PFAS compounds were detected in several public supply wells finished in the Silurian aquifer in Will County
Original languageEnglish (US)
PublisherIllinois State Water Survey
Number of pages62
StatePublished - Jun 2022

Publication series

NameISWS Contract Report


  • groundwater
  • arsenic
  • Will County
  • chloride
  • water quality


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