Greene County, Illinois: Private Well Water Quality
USGS models estimate the private-well arsenic exposure across Greene County, and USGS laboratory samples from at least 9 wells in the county show measured nitrate, manganese, iron and pH. The arsenic figure is an area estimate; the measurements are of other wells — neither is a test of your own well.
This is a modeled probability for the area, not a measurement of your well. USGS statistical models estimate how many private wells in this area are likely to exceed the federal limit — they cannot tell you what is in your water. Two neighbors can have very different results. The only way to know your well is to test it.
~82
people estimated to rely on private wells with modeled arsenic above the 10 µg/L EPA limit
63–106
90% confidence range for that estimate
11% of wells
sampled by USGS in the county measured outside 6.5–8.5 for pH (9 wells)
Find out what's actually in your well
Private wells are not regulated by the EPA — nobody tests wells in Greene County for you. Arsenic, nitrate and coliform bacteria are the three most common private-well problems, and none of them has a taste or smell. A certified lab test checks all of them at once; the CDC and EPA recommend testing every well at least once a year.
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Measured well tests in Greene County
Unlike the arsenic estimate above, these are real laboratory results: the USGS has published chemistry from at least 9 wells in Greene County, sampled 1996–2015. They describe other wells in the county — domestic, public-supply and monitoring wells — not your well.
| Parameter | Median | Wells over threshold | What the threshold means |
|---|---|---|---|
| Nitrate (as N) | Not enough USGS well samples in Greene County (fewer than 5) — see the state page. | ||
| Manganese | Not enough USGS well samples in Greene County (fewer than 5) — see the state page. | ||
| Iron | Not enough USGS well samples in Greene County (fewer than 5) — see the state page. | ||
| pH9 wells | 6.9 90th pct: 7.4 | 11%Some | outside 6.5–8.5 (EPA secondary range). Low pH is corrosive and leaches lead and copper from plumbing; high pH causes scale and bitter taste. |
What the samples show
- Nitrate (as N): Not enough USGS well samples in Greene County — see the state page.
- Manganese: Not enough USGS well samples in Greene County — see the state page.
- Iron: Not enough USGS well samples in Greene County — see the state page.
- pH: pH is off-range in 11% of sampled wells (median 6.9; 11% acidic, 0% alkaline).
- Arsenic (measured, 6 wells): Measured arsenic was low in most sampled wells (median 1 µg/L; 0% over the limit).
What to do about the biggest finding (pH): Test pH and first-draw lead and copper; a calcite or soda-ash neutralizer corrects acidic water and protects your plumbing. Read more: Lead from corroded plumbing.
Source: USGS well samples aggregated to Greene County, Illinois — manganese, pH and arsenic from USGS ScienceBase 5f36baa782cee144fb3873e8 (site medians, 1988–2019); nitrate and iron from McMahon et al. (2019), Environ. Sci. Technol. 53:29–38 (NWIS wells). County assignment by Census 2020 boundaries. Statistics shown only where ≥ 5 wells were sampled. USGS well samples; not a test of your well.
What the arsenic estimate means
Arsenic occurs naturally in bedrock and can dissolve into groundwater, so it shows up in private wells with no color, taste or smell. The USGS estimate above combines a statistical model of arsenic probability with the number of people on domestic wells in Greene County. A higher number means more of your neighbors are likely drinking water over the federal limit — but your own well could be higher or lower. Long-term arsenic exposure is linked to skin, bladder and lung cancers, so the EPA sets the limit at 10 µg/L.
What to do
- Test your well for arsenic, nitrate — it's the only way to know your actual level.
- If arsenic or nitrate is present, install a reverse-osmosis system — carbon pitchers do not remove either.
- Re-test annually; well chemistry changes over time.
Acidic water: neutralize before it corrodes your plumbing
Low-pH well water leaches lead and copper from pipes. A whole-house acid neutralizer is the fix; reverse osmosis at the tap removes any metals already picked up.
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