Full contaminant data, sample history, and sourcing for Clarion County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
2275 well testing events on record, covering
22 analytes.
Data spans 1926 to 2023.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. PA Avg
Manganese
2185
1969–2019
99%
73100% of limit
↑ 14398% above
Sulfate
2120
1969–2019
100%
760% of limit
↑ 4338% above
Iron
2184
1969–2019
99%
15333% of limit
↑ 2538% above
Arsenic
1114
1986–2019
40%
320% of limit
↑ 994% above
Radon
7
1996–2019
100%
6% of limit
↓ 95% below
PFOA
municipal
38
2024–2025
26%
88% of limit
~ typical
PFOS
municipal
38
2024–2025
29%
82% of limit
↓ 35% below
Lead
1588
1973–2019
3%
1333% of limit
↑ 28725% above
Fluoride
453
1970–2019
45%
8% of limit
↑ 68% above
Nitrate
1642
1970–2019
39%
2% of limit
↓ 91% below
Chloride
1673
1969–2019
96%
1% of limit
↓ 89% below
HFPO-DA (GenX)
municipal
32
2024–2025
0%
—
—
Nitrite
1134
1975–2019
36%
1% of limit
↓ 60% below
PFHxS
municipal
4
2024
0%
—
—
PFNA
municipal
4
2024
0%
—
—
Uranium
8
1996–2019
25%
1% of limit
↓ 76% below
Total Coliform
1
2019
100%
—
~ typical
Sodium
1618
1969–2019
99%
—
↓ 62% below
pH
2212
1969–2019
100%
—
↓ 32% below
PFBS
municipal
32
2024–2025
28%
—
↓ 43% below
Hardness
2168
1969–2019
100%
—
↑ 627% above
E. coli
1
2019
0%
—
—
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 PA.
Compare your result with Clarion County
Of the 1114 arsenic tests on record for Clarion County (1986–2019),
60% found none.
Of the 1673 chloride tests on record for Clarion County (1969–2019),
4% found none, and half were below 3 mg/L.
Of the 453 fluoride tests on record for Clarion County (1970–2019),
55% found none.
Of the 2184 iron tests on record for Clarion County (1969–2019),
1% found none, and half were below 44 mg/L.
Of the 1588 lead tests on record for Clarion County (1973–2019),
97% found none.
Of the 2185 manganese tests on record for Clarion County (1969–2019),
1% found none, and half were below 36 mg/L.
Of the 1642 nitrate tests on record for Clarion County (1970–2019),
61% found none.
Of the 34 pfoa tests on record for Clarion County (2025),
71% found none.
Of the 34 pfos tests on record for Clarion County (2025),
68% found none.
Of the 2120 sulfate tests on record for Clarion County (1969–2019),
0% found none, and half were below 1900 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Manganese 2185 samples
Sulfate 2120 samples
Iron 2184 samples
Arsenic 1114 samples
PFOA 38 samples
PFOS 38 samples
Lead 1588 samples
Fluoride 453 samples
Nitrate 1642 samples
Chloride 1673 samples
HFPO-DA (GenX) 32 samples
Nitrite 1134 samples
Sodium 1618 samples
pH 2212 samples
PFBS 32 samples
Hardness 2168 samples
Limited data (<15 samples) — interpret with caution
Radon 7 samples
Uranium 8 samples
Total Coliform 1 sample
E. coli 1 sample
Public vs. Private Water in Clarion County
46Active public water systems
35,428Residents on public water
56%Households on private wells
Public water systems in Clarion 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 Clarion 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 Clarion 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 Clarion County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Clarion 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 Clarion County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Clarion 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 PA with at least one sample for that analyte.