Full contaminant data, sample history, and sourcing for Olmsted County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
503 well testing events on record, covering
20 analytes.
Data spans 1954 to 2024.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. MN Avg
Iron
368
1954–2025
58%
73% of limit
↓ 90% below
Manganese
262
1954–2025
56%
45% of limit
↓ 91% below
Nitrate
200
1954–2014
76%
24% of limit
~ typical
Lead
222
1990–2025
10%
2% of limit
↓ 96% below
Chloride
452
1954–2025
95%
7% of limit
~ typical
PFNA
municipal
79
2023–2025
3%
124% of limit
↑ 648% above
Arsenic
222
1990–2025
24%
2% of limit
↓ 98% below
Fluoride
191
1954–2025
82%
4% of limit
↓ 35% below
HFPO-DA (GenX)
municipal
77
2023–2025
0%
—
—
Nitrite
162
1991–2014
27%
1% of limit
~ typical
PFHxS
municipal
68
2023–2024
3%
34% of limit
↓ 57% below
PFOA
municipal
77
2023–2025
3%
11% of limit
↓ 97% below
PFOS
municipal
77
2023–2025
0%
—
—
Radon
1
2014
100%
34% of limit
↓ 34% below
Sulfate
357
1954–2025
100%
8% of limit
↓ 56% below
Uranium
1
2014
100%
1% of limit
↓ 79% below
Sodium
339
1954–2025
100%
—
↓ 89% below
pH
222
1954–2014
100%
—
~ typical
PFBS
municipal
68
2023–2024
0%
—
—
Hardness
142
1954–2014
100%
—
~ 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 MN.
Compare your result with Olmsted County
Of the 222 arsenic tests on record for Olmsted County (1990–2025),
76% found none.
Of the 452 chloride tests on record for Olmsted County (1954–2025),
5% found none, and half were below 17.4 mg/L.
Of the 191 fluoride tests on record for Olmsted County (1954–2025),
18% found none, and half were below 150 µg/L.
Of the 368 iron tests on record for Olmsted County (1954–2025),
42% found none, and half were below 4.15 µg/L.
Of the 222 lead tests on record for Olmsted County (1990–2025),
90% found none.
Of the 262 manganese tests on record for Olmsted County (1954–2025),
44% found none, and half were below 3.37 µg/L.
Of the 200 nitrate tests on record for Olmsted County (1954–2014),
24% found none, and half were below 1.5 mg/L.
Of the 357 sulfate tests on record for Olmsted County (1954–2025),
0% found none, and half were below 20.9 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Iron 368 samples
Manganese 262 samples
Nitrate 200 samples
Lead 222 samples
Chloride 452 samples
PFNA 79 samples
Arsenic 222 samples
Fluoride 191 samples
HFPO-DA (GenX) 77 samples
Nitrite 162 samples
PFOA 77 samples
PFOS 77 samples
Sulfate 357 samples
Sodium 339 samples
pH 222 samples
Hardness 142 samples
Limited data (<15 samples) — interpret with caution
Radon 1 sample
Uranium 1 sample
Public vs. Private Water in Olmsted County
83Active public water systems
148,383Residents on public water
14%Households on private wells
Public water systems in Olmsted 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 Olmsted 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 Olmsted 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 Olmsted County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Olmsted 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 Olmsted County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Olmsted 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 MN with at least one sample for that analyte.