Groundwater in Tuolumne County contains radon, PFOS, and arsenic. PFOS and radon are present at levels that exceed EPA health standards, so well owners should test for these contaminants.
Radon comes from natural breakdown of uranium in rock and soil around the county. PFOS enters groundwater from industrial use and firefighting foam, which can seep down from the land surface. Arsenic occurs naturally in some rock layers in this region, particularly where underground gravel and clay mix together.
Groundwater in this county is moderately hard, driven by calcium and magnesium that dissolve from the surrounding rock layers. Iron and sulfate stay at low levels, so the water does not have the strong mineral character found in some neighboring counties. Most wells here show this moderate hardness pattern, though individual wells can vary.
Wells in Tuolumne County sometimes contain PFOS and radon at levels above EPA health standards. PFOS is a chemical that can build up in your body over time and may affect your immune system and thyroid. Radon is a radioactive gas that comes from the ground and can increase your risk of lung cancer if you breathe it in for many years.
The mineral content in county wells is generally not a problem. Water hardness here is moderate, so you probably won't see much scale buildup on faucets or inside pipes, and your water heater should work fine. Most people won't notice any taste or odor issues from the minerals in this area's wells.
Every well is different, and yours could have higher or lower levels than what's common in the county. Testing is the only way to know what's actually in your water so you can treat it properly. We recommend a comprehensive panel that checks for metals and minerals along with PFOS and radon, which typically costs between two hundred and four hundred dollars. Treatment options like activated carbon filters or radon removal systems can address these concerns if testing shows they're needed.
Not sure if your well is affected? Get certified results in 5–7 days.
Test Your Well Water with Tap Score →| Contaminant | Samples ⓘ | % Above MCL ⓘ | Distribution ⓘ | Confidence ⓘ | Risk ⓘ |
|---|---|---|---|---|---|
| Radon | 3 | 67% | Low | High ⓘ | |
| PFOS ⓘ municipal | 37 | 3% | Moderate | Low | |
| Uranium | 13 | 0% | Low | Low | |
| Arsenic | 13 | 0% | Low | Low | |
| Iron | 12 | 0% | Low | Low | |
| PFOA ⓘ municipal | 37 | 0% | Moderate | Safe | |
| Fluoride | 13 | 0% | Low | Low | |
| HFPO-DA (GenX) ⓘ municipal | 37 | 0% | Moderate | Safe | |
| Nitrite | 13 | 0% | Low | Low | |
| Lead | 10 | 0% | Low | Low | |
| Manganese | 12 | 0% | Low | Low | |
| Nitrate | 13 | 0% | Low | Low | |
| PFHxS ⓘ municipal | 37 | 0% | Moderate | Safe | |
| Sulfate | 13 | 0% | Low | Low | |
| Chloride | 13 | 0% | Low | Low | |
| PFNA ⓘ municipal | 37 | 0% | Moderate | Safe | |
| pH | 13 | — | Low | Low | |
| Hardness | 13 | — | Low | Low | |
| Sodium | 13 | — | Low | Low | |
| PFBS ⓘ municipal | 37 | — | Moderate | Low |
MCL = Maximum Contaminant Level (EPA limit for public water; used as benchmark for private wells). Distribution shows % of sampled wells in each concentration band. Methodology.
* Microbial contaminants (E. coli, coliform) reflect only samples from the last 10 years.
Data shows potential risk — a certified test confirms whether your water is affected.
Order a Tap Score Test →Population-level CDC data. Not individual risk prediction.
Loading recent water news…