Full contaminant data, sample history, and sourcing for Mercer County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
218 well testing events on record, covering
18 analytes.
Data spans 1928 to 2024.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. PA Avg
Iron
100
1928–2023
100%
145% of limit
↓ 75% below
Manganese
93
1937–2023
100%
140% of limit
↓ 72% below
Chloride
101
1928–2023
100%
2% of limit
↓ 82% below
Sulfate
102
1928–2023
100%
7% of limit
↓ 61% below
Arsenic
1
2023
0%
—
—
Fluoride
90
1937–2023
99%
5% of limit
~ typical
HFPO-DA (GenX)
municipal
118
2024–2025
0%
—
—
Lead
1
2023
100%
1% of limit
↓ 68% below
Nitrate
101
1928–2023
100%
1% of limit
↓ 95% below
Nitrite
1
2023
0%
—
—
PFHxS
municipal
15
2024–2025
0%
—
—
PFNA
municipal
15
2024–2025
0%
—
—
PFOA
municipal
175
2024–2025
2%
66% of limit
↓ 29% below
PFOS
municipal
174
2024–2025
2%
52% of limit
↓ 59% below
Hardness
103
1928–2023
100%
—
~ typical
PFBS
municipal
118
2024–2025
0%
—
—
pH
97
1937–2023
100%
—
~ typical
Sodium
97
1928–2023
100%
—
↓ 54% 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 PA.
Compare your result with Mercer County
Of the 101 chloride tests on record for Mercer County (1928–2023),
0% found none, and half were below 4.8 mg/L.
Of the 90 fluoride tests on record for Mercer County (1937–2023),
1% found none, and half were below 200 µg/L.
Of the 100 iron tests on record for Mercer County (1928–2023),
0% found none, and half were below 435 µg/L.
Of the 93 manganese tests on record for Mercer County (1937–2023),
0% found none, and half were below 70 µg/L.
Of the 101 nitrate tests on record for Mercer County (1928–2023),
0% found none, and half were below 90 µg/L.
Of the 160 pfoa tests on record for Mercer County (2025),
98% found none.
Of the 159 pfos tests on record for Mercer County (2025),
97% found none.
Of the 102 sulfate tests on record for Mercer County (1928–2023),
0% found none, and half were below 16.5 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Iron 100 samples
Manganese 93 samples
Chloride 101 samples
Sulfate 102 samples
Fluoride 90 samples
HFPO-DA (GenX) 118 samples
Nitrate 101 samples
PFOA 175 samples
PFOS 174 samples
Hardness 103 samples
PFBS 118 samples
pH 97 samples
Sodium 97 samples
Limited data (<15 samples) — interpret with caution
Arsenic 1 sample
Lead 1 sample
Nitrite 1 sample
Public vs. Private Water in Mercer County
146Active public water systems
98,473Residents on public water
47%Households on private wells
Public water systems in Mercer 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 Mercer 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 Mercer 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 Mercer County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Mercer 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 Mercer County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Mercer 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.