Groundwater in Mendocino County contains radon, iron, manganese, arsenic, boron, chloride, lead, and PFOA and PFOS. Several of these contaminants exceed EPA health standards, so well owners should test their water and consider treatment options.
These contaminants come from the local rock and soil. Radon and arsenic occur naturally in the bedrock; iron and manganese dissolve from rocks as water moves through the ground. Boron and chloride can come from both rock and human activity like agriculture. Lead typically enters from old pipes or fixtures rather than from the water source itself.
Groundwater in this county is hard, driven mainly by calcium and magnesium that dissolve from the rock. The moderate iron content also contributes to the water's mineral character. These mineral characteristics are present in wells across the county, though individual wells vary in their exact mineral makeup.
Wells in Mendocino County have been found with arsenic, boron, chloride, lead, and PFOA and PFOS at levels above EPA health standards. Arsenic and lead can damage kidneys and increase cancer risk over time. PFOA and PFOS are chemicals that build up in your body and may affect your liver and immune system. Boron at elevated levels can harm reproduction and development in children.
County well water tends to be hard, which means more minerals that leave white scale on faucets and fixtures. Hard water can shorten the lifespan of water heaters and dishwashers. You might notice staining on sinks and tubs, or soap that doesn't lather as well. Some people notice a slightly mineral taste in their water.
Testing is the only way to know what is actually in your well, since every well in the county is different and yours could have higher or lower levels than average. We recommend a comprehensive panel that checks for metals, minerals, bacteria, and PFOA/PFOS, which typically costs $200 to $400. Treatment options like activated carbon filters or reverse osmosis systems can address many of these concerns once you know what you're dealing with.
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 | 30 | 50% | Moderate | High ⓘ | |
| Iron | 161 | 37% | High | High | |
| Manganese | 143 | 22% | High | High | |
| Boron | 13 | 15% | Low | High | |
| Arsenic | 90 | 12% | Moderate | Moderate | |
| PFOS ⓘ municipal | 52 | 10% | Moderate | Moderate | |
| Lead | 88 | 5% | Moderate |
Moderate
Elevated concentration, not % above limit
|
|
| PFOA ⓘ municipal | 52 | 2% | Moderate | Low | |
| Chloride | 183 | 1% | High | Low | |
| Perchlorate | 12 | 0% | Low | Low | |
| HFPO-DA (GenX) ⓘ municipal | 46 | 0% | Moderate | Safe | |
| Uranium | 46 | 0% | Moderate | Low | |
| Nitrite | 44 | 0% | Moderate | Low | |
| Sulfate | 176 | 0% | High | Low | |
| PFNA ⓘ municipal | 52 | 0% | Moderate | Safe | |
| Chromium (total) | 13 | 0% | Low | Low | |
| 1,2,3-Trichloropropane | 12 | 0% | Low | Safe | |
| Fluoride | 166 | 0% | High | Low | |
| Nitrate | 63 | 0% | Moderate | Low | |
| PFHxS ⓘ municipal | 49 | 0% | Moderate | Low | |
| Tds | 13 | — | Low | Low | |
| Total Coliform | 1* | 0% | Low | Low ⓘ | |
| pH | 213 | — | High | Low | |
| Sodium | 180 | — | High | Low | |
| E. coli | 1* | 0% | Low | Low ⓘ | |
| Hardness | 183 | — | High | Low | |
| PFBS ⓘ municipal | 49 | — | 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.
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