Full contaminant data, sample history, and sourcing for Allegheny County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
230 well testing events on record, covering
22 analytes.
Data spans 1926 to 2025.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. PA Avg
Manganese
48
1951–2023
100%
394% of limit
↓ 22% below
Iron
66
1926–2023
100%
158% of limit
↓ 73% below
Radon
3
1996–2019
100%
6% of limit
↓ 95% below
Sulfate
65
1926–2023
100%
15% of limit
~ typical
PFOS
municipal
258
2023–2025
16%
93% of limit
↓ 27% below
Chloride
66
1926–2023
100%
21% of limit
↑ 99% above
Arsenic
36
1972–2023
58%
8% of limit
↓ 73% below
PFOA
municipal
258
2023–2025
11%
60% of limit
↓ 36% below
PFHxS
municipal
190
2023–2025
8%
44% of limit
~ typical
Fluoride
52
1951–2023
90%
8% of limit
↑ 68% above
HFPO-DA (GenX)
municipal
253
2023–2025
0%
—
—
Lead
39
1964–2023
10%
5% of limit
~ typical
Nitrate
66
1926–2023
59%
2% of limit
↓ 91% below
Nitrite
30
1992–2023
0%
—
—
PFNA
municipal
190
2023–2025
0%
—
—
Uranium
17
1996–2021
41%
1% of limit
↓ 42% below
Hardness
67
1926–2023
100%
—
~ typical
E. coli
1
2019
100%
—
~ typical
Total Coliform
1
2019
100%
—
~ typical
Sodium
57
1926–2023
100%
—
↑ 364% above
pH
66
1951–2024
100%
—
~ typical
PFBS
municipal
253
2023–2025
12%
—
~ typical
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 Allegheny County
Of the 36 arsenic tests on record for Allegheny County (1972–2023),
42% found none.
Of the 66 chloride tests on record for Allegheny County (1926–2023),
0% found none, and half were below 53 mg/L.
Of the 52 fluoride tests on record for Allegheny County (1951–2023),
10% found none, and half were below 295 µg/L.
Of the 66 iron tests on record for Allegheny County (1926–2023),
0% found none, and half were below 475 µg/L.
Of the 39 lead tests on record for Allegheny County (1964–2023),
90% found none.
Of the 48 manganese tests on record for Allegheny County (1951–2023),
0% found none, and half were below 197 µg/L.
Of the 66 nitrate tests on record for Allegheny County (1926–2023),
41% found none, and half were below 5 µg/L.
Of the 68 pfoa tests on record for Allegheny County (2025),
60% found none.
Of the 68 pfos tests on record for Allegheny County (2025),
60% found none.
Of the 65 sulfate tests on record for Allegheny County (1926–2023),
0% found none, and half were below 37 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Manganese 48 samples
Iron 66 samples
Sulfate 65 samples
PFOS 258 samples
Chloride 66 samples
Arsenic 36 samples
PFOA 258 samples
Fluoride 52 samples
HFPO-DA (GenX) 253 samples
Lead 39 samples
Nitrate 66 samples
Nitrite 30 samples
Uranium 17 samples
Hardness 67 samples
Sodium 57 samples
pH 66 samples
PFBS 253 samples
Limited data (<15 samples) — interpret with caution
Radon 3 samples
E. coli 1 sample
Total Coliform 1 sample
Public vs. Private Water in Allegheny County
70Active public water systems
2,017,752Residents on public water
13%Households on private wells
Public water systems in Allegheny 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 Allegheny 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 Allegheny 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 Allegheny County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Allegheny 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 Allegheny County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Allegheny 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.