Full contaminant data, sample history, and sourcing for Mono County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
1244 well testing events on record, covering
19 analytes.
Data spans 1958 to 2022.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. CA Avg
Arsenic
722
1973–2022
98%
485% of limit
↑ 1142% above
Manganese
693
1978–2022
73%
82% of limit
↓ 74% below
Uranium
19
2006–2021
100%
35% of limit
↑ 541% above
Fluoride
763
1973–2022
99%
12% of limit
↑ 73% above
Iron
691
1973–2022
63%
14% of limit
↓ 88% below
Chloride
1215
1973–2023
100%
2% of limit
↓ 92% below
Sulfate
703
1973–2022
100%
5% of limit
↓ 74% below
PFOS
municipal
14
2020–2025
0%
—
—
Lead
51
1984–2021
22%
1% of limit
↓ 86% below
PFNA
municipal
14
2020–2025
0%
—
—
Nitrate
590
1987–2022
64%
2% of limit
↓ 91% below
PFHxS
municipal
14
2020–2025
0%
—
—
HFPO-DA (GenX)
municipal
12
2024–2025
0%
—
—
Nitrite
590
1987–2022
16%
0% of limit
↓ 76% below
PFOA
municipal
14
2020–2025
0%
—
—
pH
930
1973–2022
100%
—
~ typical
PFBS
municipal
14
2020–2025
0%
—
—
Sodium
702
1973–2022
100%
—
↓ 48% below
Hardness
701
1973–2022
98%
—
↓ 63% below
Distribution shows the share of samples in each concentration band relative to the EPA Maximum Contaminant Level (MCL): Low = below half the MCL, Moderate = between half and the MCL, High = above the MCL. Analytes without an MCL (e.g. sodium, pH) show — in the limit columns. State average is based on county median values across CA.
Compare your result with Mono County
Of the 722 arsenic tests on record for Mono County (1973–2022),
2% found none, and half were below 47 µg/L.
Of the 1215 chloride tests on record for Mono County (1973–2023),
0% found none, and half were below 6.2 mg/L.
Of the 763 fluoride tests on record for Mono County (1973–2022),
1% found none, and half were below 470 µg/L.
Of the 691 iron tests on record for Mono County (1973–2022),
37% found none, and half were below 12 µg/L.
Of the 51 lead tests on record for Mono County (1984–2021),
78% found none.
Of the 693 manganese tests on record for Mono County (1978–2022),
27% found none, and half were below 15.9 µg/L.
Of the 590 nitrate tests on record for Mono County (1987–2022),
36% found none, and half were below 85.5 µg/L.
Of the 703 sulfate tests on record for Mono County (1973–2022),
0% found none, and half were below 13 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Arsenic 722 samples
Manganese 693 samples
Uranium 19 samples
Fluoride 763 samples
Iron 691 samples
Chloride 1215 samples
Sulfate 703 samples
Lead 51 samples
Nitrate 590 samples
Nitrite 590 samples
pH 930 samples
Sodium 702 samples
Hardness 701 samples
Limited data (<15 samples) — interpret with caution
PFOS 14 samples
PFNA 14 samples
PFHxS 14 samples
PFOA 14 samples
PFBS 14 samples
Public vs. Private Water in Mono County
92Active public water systems
99,229Residents on public water
14%Households on private wells
Public water systems in Mono County are regulated by the EPA and must test and report contaminant levels. Private well owners are responsible for their own testing — there is no routine monitoring of private wells by any government agency.
CDC Health Outcome Correlations
Where contaminants detected in Mono County have established associations with specific health outcomes, we cross-reference CDC PLACES county-level prevalence data. This is a contextual signal, not a causal claim.
This report aggregates data from the following public databases:
Water Quality Portal (WQP) — groundwater sample results for Mono County from EPA, USGS, and state agencies. Browse WQP data →
EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for Mono County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Mono County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near Mono County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Mono County, used in contamination risk scoring. Superfund site search →
CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →
Methodology
Raw records are downloaded from the Water Quality Portal and normalized to µg/L (ppb). Records are deduplicated by sample ID and date, and certified outliers are excluded. Analyte names are mapped to EPA canonical forms. Detection rates, distribution bands, and MCL comparisons are computed from the normalized dataset.
Distribution bands use the EPA Maximum Contaminant Level as the threshold: concentrations below 50% of the MCL are classed as Low, between 50% and 100% as Moderate, and above 100% as High. For analytes without an MCL (sodium, hardness, pH), distribution is not computed.
State comparison uses the median of county median values across all counties in CA with at least one sample for that analyte.