Groundwater in Sierra County contains arsenic, boron, and chloride. These contaminant levels are low and do not exceed EPA health standards, so well owners should be aware of their presence but not alarmed.
These minerals come from the rock layers underground in this region. The basin-fill aquifers here contain natural deposits of arsenic and boron that dissolve slowly into groundwater as water moves through the rock. Chloride also occurs naturally in these geological layers. The low population density and limited industrial activity in the county mean that human sources of contamination are minimal.
Groundwater in this county is soft with low total dissolved solids, meaning it has minimal mineral content overall. The low levels of sodium, sulfate, and hardness indicate that water moves through the basin-fill rock without picking up large amounts of dissolved minerals. Most wells in Sierra County draw water with these clean, soft characteristics.
Wells in Sierra County generally have water that meets federal health standards. However, arsenic and boron show up in county groundwater at levels worth paying attention to. Arsenic exposure over time can increase the risk of cancer and harm the nervous system. Boron at high levels can affect reproduction and development.
The good news is that Sierra County wells tend to have soft water with low sodium and low mineral content overall. This means you probably won't see crusty buildup on your faucets or experience staining from iron. Your water should taste clean without a salty flavor.
We recommend testing your well to find out what is actually in your water, since every well is different. Your water could have higher or lower levels of arsenic and boron than what is common in the county. A comprehensive testing panel for metals and minerals costs between two hundred and four hundred dollars. Treatment options like activated carbon filters or ion exchange systems can reduce these contaminants if testing shows they are present in your well.
| Contaminant | Samples ⓘ | % Above MCL ⓘ | Distribution ⓘ | Confidence ⓘ | Risk ⓘ |
|---|---|---|---|---|---|
| Nitrite | 5 | 0% | Low | Safe ⓘ | |
| Fluoride | 5 | 0% | Low | Low ⓘ | |
| Perchlorate | 2 | 0% | Low | Safe ⓘ | |
| Sulfate | 6 | 0% | Low | Low ⓘ | |
| Uranium | 5 | 0% | Low | Low ⓘ | |
| Iron | 5 | 0% | Low | Safe ⓘ | |
| Arsenic | 5 | 0% | Low | Low ⓘ | |
| Chloride | 6 | 0% | Low | Low ⓘ | |
| Boron | 2 | 0% | Low | Low ⓘ | |
| Chromium (total) | 2 | 0% | Low | Safe ⓘ | |
| 1,2,3-Trichloropropane | 2 | 0% | Low | Safe ⓘ | |
| Lead | 3 | 0% | Low | Low ⓘ | |
| Manganese | 5 | 0% | Low | Low ⓘ | |
| Nitrate | 5 | 0% | Low | Low ⓘ | |
| Tds | 2 | — | Low | Low ⓘ | |
| Total Coliform | 3* | 0% | Low | Safe ⓘ | |
| Sodium | 6 | — | Low | Low ⓘ | |
| E. coli | 3* | 0% | Low | Safe ⓘ | |
| Hardness | 5 | — | Low | Low ⓘ | |
| pH | 5 | — | Low | 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.
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