Perfluorochemicals (PFCs) are a family of organic chemicals used in products resistant to heat, oil, grease and water, including nonstick cookware, stain– and water–resistant fabrics, fire suppression foams, film coatings, and other consumer and commercial products. PFCs were produced by the 3M Co. at its Cottage Grove, MN, facility, and production wastes were disposed of during the 1950s through 1970s at four sites in Washington County, MN, located in the southeast quarter of the Minneapolis–St. Paul metropolitan area.

In 2004 the state of Minnesota learned that PFC–containing wastes were disposed of at the sites. Initial environmental and public health investigations focused on two specific PFCs in groundwater — perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These investigations revealed groundwater contamination of five municipal wells and over 125 private wells with PFOA and PFOS related to two of the disposal sites.

In spring 2006, the Minnesota Department of Health (MDH) Public Health Laboratory expanded PFC testing to include five additional PFC compounds, most notably perfluorobutanoic acid (PFBA). Further investigation through 2006 and 2007 revealed more widespread contamination — affecting 45 municipal wells and approximately 1,100 private wells — with PFCs, mostly PFBA, throughout southern Washington County. Four distinct aquifers have been impacted. The total area affected is approximately 100 square miles.

Although the PFBA levels were generally below the current Health–Based Value of 7 micrograms per liter (µg/L), many residents on private and public water systems were interested in water treatment to reduce their exposure to PFCs. However, there was very limited information on PFOA and PFOS removal by common water treatment technologies, and virtually no information on the other PFCs, especially PFBA.

The little information that was available indicated that PFBA was problematic for activated carbon (AC) treatment. In response, the 2007 Minnesota Legislature directed the MDH to evaluate the effectiveness of point–of–use (POU) water treatment devices in removing PFCs.

In fall 2007, MDH retained Water Science & Marketing, LLC (WSM) of Cedar, MN, and the Water Quality Association (WQA) to conduct the study. WSM surveyed over 450 manufacturers of POU devices for their recommendations on devices with potential to remove PFCs. A panel consisting of representatives of MDH, WQA, WSM, and the US Environmental Protection Agency selected 14 devices from those “nominated” by manufacturers for laboratory testing (list, see sidebar).

The selected devices had to be rated to treat at least 500 gallons, be available to the public, meet relevant industry standards and be certified by one or more of the organizations that certify these devices.

The 14 devices, including six activated carbon (AC) filter devices and eight reverse osmosis (RO) devices, were tested at the WQA facility in Lisle, IL.

Typical industry practice is for RO devices to be equipped with AC pre– and post–filters. In this screening phase of laboratory testing, the AC pre–filters on the RO devices were removed in order to more directly evaluate the RO membrane performance. The testing protocols were based on NSF/ANSI Standards 53 and 58. The devices were fed three different challenge (feedwater) solutions, prepared by the MDH Public Health Laboratory, at concentrations meant to simulate the highest levels of PFCs found in Washington County.

The three challenge solutions were:
(1) 10µg/L PBBA
(2) PFOA and PFOS at 3 µg/L each, and
(3) PFBA, PFOA, and PFOS at the concentrations noted in (1) and (2).

Of the 14 devices, one AC device and five RO devices were found to be effective for PFC removal to below reporting limits (<0.2 µg/L) and progressed to field testing. One RO device (GE Merlin) and two AC filters (Access eSpring and GE Smartwater GXSL55F) were significantly above this goal for PFC removal, showed PFC breakthrough well before 100 percent capacity and did not progress to further testing.

Three AC devices and two RO devices, which showed some PFBA breakthrough, went through a second round of laboratory testing at WQA to simulate more normal use conditions. In this additional laboratory testing, the AC–prefilters remained with the RO devices and the RO devices were run through 600 gallons of treated water.

The testing demonstrated that the RO devices are very effective at removing PFCs, which was a surprise for some involved in the study. The one RO membrane that allowed PFCs through more readily was a high–flow, tankless model. The AC filters did remove PFCs, but PFBA tended to be problematic and was always the first PFC to be detected.

The 11 devices that progressed through laboratory testing were tested in the field in March–April 2008 at two locations — Oakdale Well #5 (with multiple PFCs present) and at St. Paul Park #3 (with only PFBA present). PFC concentrations at these two sites are lower than the concentrations in the laboratory challenge solutions by roughly an order of magnitude, but are fairly representative of groundwater conditions in southern Washington County.

The field test stations (see photo) were designed, constructed, installed and operated by WSM. All RO devices included the pre– and post–filters and storage tanks that normally accompany those devices.

In field testing, all RO devices proved effective at reducing PFC concentrations to below the analytical detection limit of 0.05 µg/L. One AC filter, the Kinetico MACguard, did show some PFBA breakthrough at 500 gallons of production, but below the analytical reporting limit of 0.2 µg/L. Interestingly, the Aquion Rainsoft Hydrefiner did show some PFBA breakthrough (below reporting limit) initially at one site, but then performed fine afterwards. This behavior may have been due to air entrainment.

An AC filter device is relatively simple to install and operate. Water simply flows through the activated carbon media and is dispensed for use. In field test conditions, the AC device flow rates were in the range of 0.2 to 0.9 gallons per minute (gpm). Flow rates often declined gradually with use. Manufacturers typically recommend that AC filters be replaced every six months (about 500 gallons of water treated).

RO devices available on the market typically include AC pre– and post–filters and may include a sediment pre–filter. Additional treatment is obviously provided with the multiple treatment technologies, a plus when treating for PFCs. However, an RO device is a more complicated installation, in part because it generates a wastewater stream and the treated water must be stored for later use. Standard storage tank sizes are 1.5 – 3.0 gallons, but larger sizes may be available.

In the field tests, the RO devices produced 10.5 to 40 gallons of water per day. The amount of wastewater generated ranged from 1.5 to 4.7 gallons per gallon of treated water. Another advantage of the RO devices is the ability to remove nitrate, which happens to be another widespread ground water contaminant in portions of the affected area.

Although the general public seemed primarily interested in simply learning which devices “worked,” the MDH emphasized that proper monitoring, maintenance, and timely replacement of filters/membranes (according to the manufacturer’s recommendations) are just as important. Our experience is, simply, that most homeowners neglect their water treatment systems, especially with regard to component replacement.

*The full report, “Performance Evaluation — Removal of Perfluorochemicals with Point–of–Use (POU) Water Treatment Devices,” published by WSM, can be found at this Web site:
http://www.health.state.mn.us/divs/eh/wells/waterquality/poudevicefinal.pdf.
A summary of the full report is available at:
http://www.health.state.mn.us/divs/eh/wells/waterquality/poudevicefinalsummary.pdf.