Thompson Oaks
What EPA’s and Minnesota’s records show in this utility’s water: nitrate, arsenic and other regulated chemicals; lead and copper; and violations since 2016, with the certification that handles each result.
- Serves
- 51 people
- Connections
- 17
- Water source
- Groundwater
- Based in
- Ellendale, MN
- County
- Steele
- Owner
- Private
The ZIP code it serves
The short answer
2 results are above the health goal. The worst: Arsenic, above the health goal. 13 health-based violations since 2016.
What handles itWhat was found
Arsenic, uranium and nitrate: Minnesota’s yearly summaries per water system, 2024 to 2025, with EPA’s 2012 to 2019 file for earlier years.
Fluoride and chromium (total): EPA’s compliance monitoring file, samples taken from March 21, 2012 to April 23, 2019. Newer results are in the utility’s annual water quality report.
Above the health goal2
Arsenic
Comes from the source
3.2ppb
Highest yearly average, 2024
Averaged by year, the highest was 3.2 ppb, in 2024: below EPA’s legal limit of 10 ppb, but above its health goal of zero. That is the only year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 1.6 ppb, in 2012.
What handles it
- NSF/ANSI 58 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
- NSF/ANSI 53 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
Uranium
Comes from the source
0.45ppb
Highest yearly average, 2024 to 2025
2025: not found
Averaged by year, the highest was 0.45 ppb, in 2024: below EPA’s legal limit of 30 ppb, but above its health goal of zero. In 2025, the latest year on file, it wasn’t found.
What handles it
- NSF/ANSI 58 look for “Uranium”
Below EPA’s limits1
Fluoride
Forms or is added in treatment
0.25ppm
Highest yearly average, 2013 to 2019
2019, one sample: 0.25 ppm
Averaged by year, the highest was 0.25 ppm, in 2013, below EPA’s legal limit of 4.0 ppm. In 2019, the latest year on file, its one sample was 0.25 ppm.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Chromium (total)
- Lead
- Nitrate
What handles it
A certification covers specific claims, not a whole standard. Look for these claims on the certifier’s listing, not the box. Wording varies a little: NSF writes “Lead Reduction,” WQA just “Lead.”
- NSF/ANSI 53
Claim: Arsenic (Pentavalent)<=50 ppb Reduction
For: Arsenic
Other certifiers’ wording: Arsenic (III) (50 ppb influent level)
- NSF/ANSI 58
Claims: Arsenic (Pentavalent)<=50 ppb Reduction, Uranium
For: Arsenic, Uranium
Other certifiers’ wording: Arsenic (Pentavalent)<=300 ppb Reduction; Arsenic (V) (300 ppb influent level)
At the tap, or for the whole house?
These come with the water itself, so a whole-house system certified for the same claims treats every tap and shower. A filter at the tap treats drinking water for much less. How whole-house systems compare.
Filters with those claims on a certifier’s listing
Disclosure: TapBuff earns a commission if you buy through some links on this page. It does not change which standard or filter we name. As an Amazon Associate, TapBuff earns from qualifying purchases. How TapBuff makes money
Countertop reverse osmosis
- IAPMO listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 4, 2026
Certified for: Arsenic
Aquasana SmartFlow Reverse Osmosis (AQ-SFRO2)
Under-sink reverse osmosis
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 9, 2026
Certified for: Arsenic
Brondell Capella RC250 Reverse Osmosis System
Under-sink reverse osmosis
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 9, 2026
Certified for: Arsenic
Violations since 2016
| Contaminant or rule | Type | Period | Measured | Status |
|---|---|---|---|---|
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2026 to June 30, 2026 | 13.6 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2026 to March 31, 2026 | 15.9 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2025 to Dec. 31, 2025 | 19.5 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2025 to Sept. 30, 2025 | 22 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2025 to June 30, 2025 | 20 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2025 to March 31, 2025 | 23 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2024 to Dec. 31, 2024 | 15.6 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2023 to March 31, 2023 | 17 PCI/L | Archived |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2020 to Sept. 30, 2020 | 17.3 PCI/L | Resolved |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2020 to June 30, 2020 | 18.3 PCI/L | Resolved |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2020 to March 31, 2020 | 18.2 PCI/L | Resolved |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2019 to Sept. 30, 2019 | 15.3 PCI/L | Resolved |
| Gross alpha radiation (excluding radon and uranium) | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2016 to March 31, 2016 | 16 PCI/L | Resolved |
| Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 6 monitoring or reporting violations not shown. | ||||
What this report can’t tell you
Everything else. Arsenic, uranium and nitrate results here are Minnesota’s own yearly summaries from 2024 on, with EPA’s national file for 2012 to 2019. Fluoride and chromium (total) come from EPA’s file alone, which ends in 2019. Thompson Oaks’s own annual report, which it must send you every year, has newer results for those and the contaminants this page does not show.
Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.
What it means for your health. This page reports what the records show and EPA’s limits and goals; it is not medical advice. If you are worried about a health effect, talk to a doctor or your local health department.
Anything after the latest data. SDWIS data is from 2026 Q3; UCMR 5 didn’t sample this utility; Minnesota’s yearly summaries cover 2024 to 2025; EPA’s compliance samples are from March 21, 2012 to April 23, 2019.
Testing your own tap
The 3 labs Minnesota certifies closest to the area Thompson Oaks serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
UC Laboratory
Janesville, MN · about 26 miles
Certified for bacteria, nitrate, metals
Southeastern Minnesota Water Analysis Laboratory
Rochester, MN · about 45 miles
Certified for bacteria, nitrate
Red Wing City Laboratory
Red Wing, MN · about 57 miles
Certified for bacteria
Sources
- EPA UCMR 5 occurrence data, file of Oct. 15, 2026
- EPA SDWA bulk download (SDWIS federal data), 2026 Q3
- Minnesota Department of Health, Minnesota Public Health Data Access, results from Jan. 1, 2023 to Dec. 31, 2025, read Oct. 8, 2026
- EPA Six-Year Review 4 compliance monitoring data, 2012 to 2019, file of Feb. 5, 2024
- Certified labs: Minnesota Department of Health, accredited labs in Minnesota accepting drinking water samples from private well users, read Oct. 10, 2026; distances from the Census 2020 ZIP code tabulation area gazetteer
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID MN1740008. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Read up on the 2 results above a lineWhat each one does to health, where it comes from, and the certification claim that addresses it.Start with Arsenic
- Get the utility’s own reportThompson Oaks must send you a water quality report every year. It covers contaminants this page does not show, and has newer results than EPA’s national file for the ones here that come from it.How to read it
- Test your own tap for leadYour service line, solder and fixtures decide the lead at your faucet, not the utility’s average.Lead in your water: what to do
- Compare certified filtersWhat the filters certified for these results cost over five years, cartridges included.Compare five-year costs