Lewis and Clark County, MT
These figures come from wells tested in Lewis and Clark County, MT, not from any one well.
- Iron is common in wells in Lewis and Clark County, MT (13 of 104 tested wells were over that level), so it's worth testing for.
- Manganese is common in wells in Lewis and Clark County, MT (8 of 27 tested wells were over that level), so it's worth testing for.
- Sulfate is not common in wells in Lewis and Clark County, MT (14 of 321 tested wells were over). Only a test tells you about your own well.
- Wells in Lewis and Clark County, MT are typically very hard (276 wells tested).
- Only a test of your own well tells you about your water.
What to test for
Start with the four this site covers:
- iron (common in wells here)
- manganese (common in wells here)
- hardness
- sulfate
Most well owners also test for these. We point to the source and don't interpret the results.
- arsenic: occurs naturally in groundwater in many regions. USGS: arsenic and drinking water
- nitrate: common near farmland and septic systems. EPA: private drinking water wells
- total coliform bacteria: the standard yearly well check. EPA: private drinking water wells
- lead and copper: from household plumbing, especially when pH is below 6.5. EPA: lead in drinking water
- PFAS: several states run private-well sampling programs. EPA: PFAS
- a certified lab: states certify labs and some run their own private-well programs. Montana's certified-lab list (from your state drinking-water program)
The numbers
County figures describe the wells sampled there, not any one well. Exact counts, sample years and sources are below.
Iron Recent
| Level it's compared with | 0.3 mg/L |
|---|---|
| Share of wells over the level | 12% |
| Wells over the level / wells judged | 13 of 104 |
| Median | < DL mg/L |
| Years sampled | 1970–2017 |
| Wells | 104 |
| Test results | 607 |
| Wells left out | 66 |
| Sources | USGS (179), MTWTRSHD_WQX (79), MONT_DEQ_WQX (1) |
More than half the wells had results below the lab's detection limit, so the median is reported as below that limit.
Manganese Recent
| Level it's compared with | 0.05 mg/L |
|---|---|
| Share of wells over the level | 30% |
| Wells over the level / wells judged | 8 of 27 |
| Median | 0.005 mg/L |
| Years sampled | 1970–2017 |
| Wells | 27 |
| Test results | 376 |
| Wells left out | 59 |
| Sources | USGS (169), MTVOLWQM_WQX (2), MONT_DEQ_WQX (1) |
Hardness Recent
| Level it's compared with | none; hardness is shown in bands |
|---|---|
| Share of wells very hard | 57% |
| Median | 198 mg/L as CaCO₃ |
| Years sampled | 1970–2017 |
| Wells | 276 |
| Test results | 654 |
| Wells left out | 66 |
| Sources | USGS (195), MTWTRSHD_WQX (79), MTVOLWQM_WQX (2) |
Sulfate Recent
| Level it's compared with | 250 mg/L |
|---|---|
| Share of wells over the level | 4.4% |
| Wells over the level / wells judged | 14 of 321 |
| Median | 55 mg/L |
| Years sampled | 1970–2017 |
| Wells | 321 |
| Test results | 740 |
| Wells left out | 64 |
| Sources | USGS (233), MTWTRSHD_WQX (86), MTVOLWQM_WQX (2) |