Typical values from 16 sampled wells in Modoc County · Full groundwater profile
What Modoc County Wells Usually Need
No common nuisance problem in the typical well. The typical Modoc well is moderately hard, with iron below the stain threshold and a pH of 8.
Safe to drink? Most sampled wells meet health limits; a yearly test confirms yours does.
Typical treatment, in plumbing order:
Usually nothing beyond routine testing. Most Modoc wells need no softener or iron filter, so test before buying equipment.
Not sure what to install? Get a filter recommendation for Modoc County homesOn city or county water instead? Your utility publishes an annual water quality report; this page covers private wells. Find your utility's report
On this page (8 sections)
Where to Test Well Water in Modoc County
- Your county environmental health department handles private well questions in Modoc County; for a water test, use a state-accredited lab, many of which accept mailed or dropped-off samples.
- Certified labs: State Water Board list of accredited labs (ELAP)
Ask the lab for sample bottles and how quickly the sample must reach it before you collect.
What Are You Noticing in Your Water?
Confirm with a lab test before buying equipment.
Explore California Interactive Map
Explore Modoc County and nearby counties
Modoc County has about 9,000 residents, and its largest communities are Alturas. Homes outside city and community water systems rely on private domestic wells. Wells here tap the Pacific Northwest basaltic-rock aquifers, and the largest DWR groundwater basin in the county is Surprise Valley.
Across 16 sampled wells, groundwater is moderately hard (3.9 gpg in the typical well). Arsenic, nitrate and chromium-6 were below California limits in most sampled wells, but individual wells vary, so test yours.
In this guide
Groundwater Profile: Modoc County
The largest California DWR Bulletin 118 groundwater basins in the county are Surprise Valley, Alturas Area – South Fork Pitt River and Alturas Area – Warm Springs Valley.
Another address? Check hardness by ZIP code.
No contaminant tracked here was above its EPA guideline in the typical (median) sampled well.
Arsenic, Nitrate, Chromium-6 and Salinity in Modoc County
| Contaminant | Typical well | Wells above limit | California standard |
|---|---|---|---|
| Arsenic | 0.8 µg/L | Limited data (17 wells) | 10 µg/L (primary MCL) |
| Nitrate (as nitrogen) | 0.17 mg/L | Limited data (16 wells) | 10 mg/L (primary MCL) |
| Chromium-6 | 0.67 µg/L | Limited data (2 wells) | 10 µg/L (primary MCL since Oct. 1, 2024) |
| Salinity (dissolved solids) | 254 mg/L | Limited data (17 wells) | 500 mg/L recommended, 1,000 mg/L upper (secondary) |
| Hardness | 3.9 gpg | Limited data (16 wells) | No limit; above 7 gpg is hard |
Typical well = median. Standards: State Water Board; samples: Water Quality Portal, since 2000.
How Modoc County Compares to California and the U.S.
See How Modoc County Compares to California & the US
| Share of wells with… | Modoc CountyModoc | CaliforniaCA | United StatesUS |
|---|---|---|---|
| Hard water (above 7 gpg) | Limited data | 64% | 60% |
| Iron above 0.3 mg/L | Limited data | 9% | 19% |
| Manganese above 0.05 mg/L | Limited data | 22% | 21% |
| Dissolved solids above 500 mg/L | 18% | 38% | 15% |
| Acidic water (pH below 6.5) | 0% | 2% | 14% |
| Nitrate above 10 mg/L (EPA limit) | Limited data | 9% | 4% |
| Arsenic above 10 µg/L (EPA limit) | Limited data | 14% | 7% |
| Chromium-6 above 10 µg/L (California limit) | Limited data | 6% | — |
| Median hardness | 3.9 gpg | 9.9 gpg | — |
| Median pH | 8 | 7.6 | 7.3 |
Sources: Water Quality Portal (since 2000); US: USGS Circular 1332. Highlighted: well above the US share.
See what a typical Modoc County well needs
Pre-filled with the Modoc medians. Swap in your own results.
Testing Your Well in Modoc County
In California, county environmental health departments handle private well permits and can advise on testing. For bacteria, nitrate, arsenic or a full panel, use a laboratory accredited by California’s Environmental Laboratory Accreditation Program (ELAP); the State Water Board’s certified lab map lists them.
What to test for in Modoc County:
- Bacteria (total coliform and E. coli), nitrate and arsenic, at least once a year (California State Water Resources Control Board recommendation)
- After any flood, new well work or a change in taste, color or smell
Which tests to order and how: how to test well water.
After a positive coliform test, work out the bleach dose and shock the well and retest 10 to 14 days later.
Nearby Counties
Modoc County borders these counties with published reports:
Lassen County
5.2 gpg hardnessShasta County
4.3 gpg hardnessSiskiyou County
8.5 gpg hardness · HardnessCounties with similar well water
Not next door, but the groundwater is much the same:
Frequently Asked Questions
Is well water in Modoc County safe to drink?
Most Modoc wells meet health limits in lab records (16 wells sampled). A yearly bacteria and nitrate test is what tells you about your own well.
How hard is well water in Modoc County?
Groundwater samples from 16 wells in Modoc County have a median hardness of 3.9 grains per gallon (66 mg/L), which the USGS classes as moderately hard. Limited local data (fewer than 20 samples): individual well testing recommended. The California statewide median is 9.9 gpg.
Is iron a problem in Modoc County well water?
The median iron level across 16 sampled wells is 0 mg/L, below the EPA aesthetic guideline of 0.3 mg/L (limited local data (fewer than 20 samples): individual well testing recommended). Most wells will not stain, but if yours does, a lab test tells you whether iron or manganese is the cause.
Why does my well water smell like rotten eggs in Modoc County?
Public lab records include sulfide results for only 7 wells in Modoc, not enough to judge. The smell comes from hydrogen sulfide; a sulfide test confirms it, and at household levels it is a nuisance, not a health hazard.
Is chromium-6 a concern in Modoc County well water?
Only 2 wells in Modoc County have been sampled for hexavalent chromium, too few to say how common it is. California’s limit is 10 µg/L, and only a lab test of your own well can show whether it is affected.
Does boiling well water make it safe to drink in Modoc County?
Boiling handles bacteria and nothing else. It does not soften Modoc water, remove iron or take out nitrate, which ends up more concentrated. Read when boiling helps and when it hurts.
How often should I test my well water in Modoc County?
The California State Water Resources Control Board recommends testing domestic wells every year, including for bacteria, nitrate and arsenic, and again after flooding or well repairs.
Written by Well Water Advisor Editorial Team.