Groundwater in Calaveras County contains arsenic, chloride, fluoride, iron, lead, manganese, and sulfate at levels that exceed EPA health standards. Several of these contaminants--arsenic, lead, and manganese--are present at concerning levels and warrant attention from well owners.
These contaminants come from the rock and sediment in the Central Valley aquifer system beneath the county. Iron, manganese, and sulfate dissolve naturally from minerals in the underground layers as water moves slowly through them. Arsenic and some chloride also occur naturally in these rocks, while other sources may include old agricultural practices and salt intrusion from deeper underground.
Groundwater in this county is very hard, with very high iron and very high sulfate as the defining characteristics. The limestone and mineral-rich rock layers that make up the aquifer system release calcium, magnesium, and sulfate into the water as it passes through. These mineral concentrations are widespread across the county's wells.
Wells in Calaveras County show arsenic, chloride, fluoride, iron, lead, and manganese at levels above EPA health standards. Arsenic exposure over time can increase the risk of cancer and harm the kidneys and nervous system. Lead affects children's brain development and learning, and harms kidneys and blood pressure in adults. Manganese at high levels can damage the nervous system. These contaminants come from natural minerals in the ground and deserve attention through testing and treatment.
The county's water is extremely hard, which causes scale buildup in pipes, water heaters, and dishwashers that shortens their lifespan. The very high iron and sulfate levels create staining on fixtures and laundry, and a metallic or rotten-egg taste or odor in the water. These problems affect daily life and increase maintenance costs on your home's systems.
We recommend a comprehensive water panel to find out what is actually in your well, since every well is different and yours may have higher or lower levels than the county average. Testing is the only way to know what treatment your well needs. A comprehensive metals and minerals panel typically costs two hundred to four hundred dollars. Water softening systems and iron filters are common treatments that address the hardness and mineral issues found in this county.
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 ⓘ |
|---|---|---|---|---|---|
| Manganese | 81 | 84% | Moderate | High | |
| Sulfate | 81 | 78% | Moderate | High | |
| Iron | 81 | 51% | Moderate | High | |
| Fluoride | 78 | 13% | Moderate | Moderate | |
| Chloride | 81 | 11% | Moderate | Moderate | |
| Lead | 69 | 7% | Moderate | Moderate | |
| Arsenic | 18 | 6% | Moderate | Moderate | |
| Uranium | 12 | 0% | Low | Low | |
| Boron | 8 | 0% | Low | Low ⓘ | |
| Chromium (total) | 8 | 0% | Low | Safe ⓘ | |
| PFOA ⓘ municipal | 34 | 0% | Moderate | Safe | |
| 1,2,3-Trichloropropane | 8 | 0% | Low | Safe ⓘ | |
| PFOS ⓘ municipal | 34 | 0% | Moderate | Safe | |
| Perchlorate | 8 | 0% | Low | Low ⓘ | |
| PFNA ⓘ municipal | 34 | 0% | Moderate | Safe | |
| Nitrite | 29 | 0% | Moderate | Low | |
| HFPO-DA (GenX) ⓘ municipal | 29 | 0% | Moderate | Safe | |
| Nitrate | 17 | 0% | Moderate | Low | |
| PFHxS ⓘ municipal | 34 | 0% | Moderate | Safe | |
| Tds | 8 | — | Low | Low ⓘ | |
| Sodium | 81 | — | Moderate | Low | |
| Hardness | 80 | — | Moderate | Low | |
| E. coli | 7* | 0% | Low | Safe ⓘ | |
| Total Coliform | 7* | 0% | Low | Safe ⓘ | |
| pH | 81 | — | Moderate | Low | |
| PFBS ⓘ municipal | 34 | — | Moderate | Safe |
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.
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