How Many Samples and Wells Stand Behind the Figures, and What a Small Sample Means
Government groundwater sampling for Madison County, Illinois, focusing on aquifer 110QRNR, collected 14 chloride concentration results from 11 individual wells. These wells ranged in depth from 17 to 102 feet and were sampled over a 12-year span, from July 2011 to August 2023. The samples represent an area-wide snapshot rather than any one private household’s water source. Because only 11 wells were sampled in this region, the data provides an informative but limited perspective on groundwater quality in Madison County. A small sample size like this cannot fully capture all local variability, so individual well water may differ.
A Worked Example: Reading the Record's Median and Range as a Homeowner Would
Within this set of measurements, chloride was detected in all 14 samples. The median chloride level was 44.8 mg/L, while concentrations ranged from as low as 1.88 mg/L up to 2830.0 mg/L. Medians represent the middle value across samples ordered from low to high, giving an idea of a typical concentration seen throughout the area. The range indicates the spread of results, which here extends widely. If your household water matches the area median, chloride is present at moderate levels. However, the broad range means some wells measured much higher chloride, which can relate to more corrosive conditions.
What 'Detected', 'Median' and 'Range' Mean in the Sampling Record on This Page
"Detected" means the chloride concentration was measurable by the instruments used. It does not imply it is harmful or exceeds any limit. The "median" shows the central tendency of the data set, giving a representative value for the area. The "range" shows minimum and maximum measured concentrations, illustrating variability across wells. These terms describe the dataset as a whole but cannot define the condition of water in any specific household well without individual testing.
Why Aesthetic Secondary Standards Differ from Health-Based Limits, Applied to This Constituent
Chloride has a voluntary secondary standard set at 250 mg/L, aimed at concerns like taste, staining, and pipe corrosion—not health risks. In Madison County sampling, 2 results exceeded this aesthetic threshold, but this is not a violation or indication of unsafe water. Secondary standards guide homeowner expectations for water appearance and longevity of plumbing, not safety. Exceeding this threshold might suggest water is more likely corrosive or can cause metallic taste or staining, which are maintenance and comfort issues rather than health ones.
What Distinguishes This Problem from the Two Problems Most Often Confused with It
Corrosive water, often influenced by chloride levels, differs from water hardness or iron concentration issues, which are commonly mistaken for similar plumbing problems. Hard water primarily causes mineral buildup, while iron water may produce staining and metallic taste. Corrosive water damages pipes by increasing metal leaching and pitting. Understanding chloride’s role helps distinguish these conditions because its concentration directly affects corrosion potential rather than mineral scaling or rust coloration.
The Autotrol Corrosive Water Damaging Pipes Filter directly addresses corrosive water by treating conditions that promote pipe damage. This system ships ready to configure for household water lines, helping reduce corrosivity effects before water reaches plumbing fixtures.
In summary, the chloride sampling record represents 11 wells in Madison County’s aquifer 110QRNR with detection in all samples and a wide concentration range. This record covers the area aquifer, not any single well. For certainty about your household water, you would need a certified laboratory test. For more details, visit the official U.S. Geological Survey groundwater data portal referenced here.
Where this information comes from
Source: USGS groundwater sampling. Sampled 2023-08-23. These figures describe groundwater sampled in this area. They are not a test of any individual private well - only a test of that well can establish its own water.
On record: U.S. Geological Survey sampling of Chloride in the 110QRNR aquifer (Madison County): 14 results from 11 wells, median 44.8 mg/L, range 1.88-2830.0 mg/L; 2 above an AESTHETIC secondary standard only (secondary standard 250.0 mg/L (aesthetic)) - not a health finding
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