Oakdale Municipal Wells: Minnesota Dept. of Health

Oakdale Public Water Supply
June 2016


Local and state agencies continue to monitor levels of perfluorochemicals (PFCs) in wells serving the Oakdale public water supply. The purpose of this page is to let you know about what happened when the problem was discovered, and the steps that were taken to address the issue.

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Water Filtration Plant

On October 30, 2006, the city began operating a new filtration plant designed to remove PFCs from water coming from city wells #5 and #9. Well #9 is the city’s newest and largest capacity well. The design and construction of the plant was financed by the 3M Company. The plant is operated by city staff with the ongoing costs paid by 3M.

Oakdale Water Filtration Plant

The plant uses large granular activated carbon (GAC) filters to remove PFCs from the water. Testing by the Minnesota Department of Health showed that GAC filters remove most PFCs from the water. The special material in the filters is made from raw materials (such as coconut shells) that are high in carbon. Heat is used to increase (activate) the surface area of the carbon, allowing it to trap organic chemicals as the water passes over it. Eventually the ability of the carbon to trap chemicals is used up and the carbon must be replaced. Periodic testing of the wells and filters tells the operators when it is necessary to change the carbon.

Granular Activated Carbon Filter system diagram

The city’s water filtration system eliminates most PFCs from the Oakdale Municipal water supply. Monitoring since 2006 shows that PFC concentrations in water leaving the treatment plant have never exceeded levels of health concern.

In the summer when demand for water is the highest, the city may need to use other wells that are not treated. In 2010, with funds from 3M, the city installed a new well outside of the PFC affected area to provide additional clean water during periods of high water demand. However, at times of highest demand, other city wells with PFCs may need to be used. When this occurs, the levels of PFCs in the water supply are minimized by careful management of the system. This management strategy depends on citizens taking steps to conserve water when possible. We strongly encourage citizens to cooperate with the permanent odd/even watering ban (with exemptions for new grass and certain businesses), to repair plumbing leaks promptly and to use other water conservation measures as much as possible.

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Beginning in late 2004, the Minnesota Department of Health (MDH), working with the City of Oakdale and 3M, began testing drinking water from the wells that serve the Oakdale public water supply for PFCs. Initially the testing was for PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), but the later, as new lab methods became available, the list of chemicals was expanded to include five more PFCs:
Health department employee sampling water at Oakdale municipal well

  • Perfluorobutane sulfonate (PFBS),
  • Perfluorobutanoic acid (PFBA),
  • Perfluoropentanoic acid (PFPeA),
  • Perfluorohexane sulfonate (PFHxS), and
  • Perfluorohexanoic acid (PFHxA).

Some of these chemicals have been detected in groundwater samples from monitoring wells at the 3M-Oakdale Disposal Site and the Washington County Landfill in Lake Elmo. 

MDH tests eight city wells on a regular basis and reports the results to the city. PFCs have been detected in measurable amounts in seven wells and PFBA is present at levels below the lab reporting limit in the eighth well (but such trace levels of PFBA are present in groundwater throughout the metro area and are considered to be "background" detections). Levels of PFCs in the city water system are below current MDH health guidelines.

We will continue to give you updates as new information and developments arise.

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Additional information

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Updated Thursday, March 30, 2017 at 03:54PM