Sunday, August 14, 2022

CFPUA filtered water still has more contaminants than raw water. Here’s why, and what’s being done

The issue was first brought to CFPUA's attention in September of 2017. After investigating the situation, the utility began replacing filter equipment in November of 2018.

Inside the Sweeney Water Treatment Plant’s filter gallery. (Port City Daily photo / File)

NEW HANOVER COUNTY — The concentration of several emerging contaminants related to GenX is considerably higher in the filtered water coming out CFPUA’s Sweeney Water Treatment plant than it is in the raw water taken from the Cape Fear River.

The issue is obviously concerning in and of itself, but also poses questions for CFPUA’s planned $46 million Sweeney upgrades, which will use the same technology and will be susceptible to the same problem.

Port City Daily sat down with new CFPUA spokesperson Vaughn Hagerty to discuss the issue and CFPUA’s response to the problem.

The numbers

The levels of GenX in both raw and filtered water have remained low for some time — these levels have been the focus of public reporting, not just by CFPUA but also Brunswick and Pender County, as well as other municipalities and utilities. However, other chemicals in the same family as GenX appear at higher concentrations after the filtration process as Sweeney.

The numbers can be found in the recent motion by the Cape Fear Public Utility Authority (CFPUA) to intervene in the proposed consent order between Chemours and the North Carolina Department of Environmental Quality (DEQ).

In Exhibit A (page 43), attached to the motion, samples of over 20 chemicals taken from before and after CFPUA’s filtration process, are indexed. Some recent samples, taken on the same day October 8, 2018, show that the overall load of these chemicals in the raw water was 144 nanograms per liter (also referred to as parts per trillion). The overall load in the filtered water was 432 nanograms per liter, more than three times higher.

Test results from raw and filtered water at the Sweeney Treatment Plant. In the bottom righhand corner, the significant increase in PFAS from raw to filtered water is apparent. (Port City Daily / Bladen County Superior Court)
Test results from raw and filtered water at the Sweeney Treatment Plant. In the bottom right-hand corner, the significant increase in PFAS from raw to filtered water is apparent. (Port City Daily / Bladen County Superior Court)

Some individual chemicals showed even more dramatic spikes, with as much as 30-40 times higher concentrations. Similar same-day comparisons can also be seen on Sept. 11 and 19 of 2018.

Not a new problem

In September of 2017, NC State Professor Detlef Knappe emailed CFPUA to point out the spike in post-filtration chemical concentrations. (Port City Daily photo / CFPUA)
In September of 2017, NC State Professor Detlef Knappe emailed CFPUA to point out the spike in post-filtration chemical concentrations. (Port City Daily photo / CFPUA)

The issue was first raised by NC State Professor Detlef Knappe in late September of 2017. Knappe emailed CFPUA to point out the high concentrations in the finished water and attributed the spike to chemicals leeching out of Granulated Activated Carbon (GAC) filters at Sweeney.

CFPUA responded with a release, including a link to Knappe’s email.

“According to the email, the data shows that estimated levels of PFO2HxA and PFO3OA in the Cape Fear River have dramatically dropped since late June 2017. This is good news. However, the data also shows levels of the compounds, while still trending downward, have not dropped as much in the treated water from Sweeney Water Treatment Plant,” CFPUA stated in the release.

At the time, CFPUA remained circumspect about the cause, and didn’t directly address Knappe’s point: not only had the levels “not dropped as much” — they were increasing tenfold or more. CFPUA also didn’t address Knappe’s suggestion that, ironically and unfortunately, Sweeney filters were apparently adding chemicals back into the drinking water.

Still an issue, but what’s causing it?

After investigating the situation, CFPUA now confirms the issue is caused by the GAC filters, through a process called “desorption” (think the opposite of absorption and you’re not far off).

“GAC filters water by attracting substances such as PFAS compounds to its surface. Different substances may have different propensities to be adsorbed by GAC. Over time, [GAC]’s capacity becomes used up. After some time in service, GAC may release – or desorp – already filtered compounds when encountering another substance that has a greater capacity to be adsorped,” Hagerty said.

Essentially, chemicals trapped over time can shed off the filters into drinking water. As Hagerty pointed out, these chemicals are not from the filters or Sweeney itself, but are legacy chemicals from the Cape Fear — after all, the Fayetteville plant owned by Chemours (and DuPont before that) have been dumping GenX and other PFAS in the water for three decades.

What’s being done?

According to Hagerty, CFPUA began addressing the issue back in 2017, and contracted with engineering consultants Black and Veatch to evaluate the issue.

One problem was that GAC filters also contain bacteria, referred to as “operating in biological mode.” The bacteria help handle byproducts from chlorine disinfection –– but the bacteria builds up over time, and isn’t present in new filters. Swapping all the filters at once would completely remove this biological mode from the filtration equation, Hagerty explained.

“What we ended up with was the plan we ended up with in mid-November; replace the GAC media in the 14 filter beds on a staggered, phased basis,” Hagerty said.

According to Hagerty, CFPUA also “scheduled replacement to avoid warmer months when water usage peaks.”

From November to December, CFPUA replaced seven beds; the utility plans to replace the other seven in the Spring. CFPUA considers this a temporary measure, until the planned upgrades at Sweeney are completed.

However, since those upgrades will also use GAC technology, will the “desorbtion” process remain a problem?

The short answer is yes, but CFPUA has planned for it.

“To address potential desorption in the new GAC filters, CFPUA plans to ‘regenerate’ that media so we can reuse it. Regeneration involves subjecting the media [i.e. the carbon in the filters] to high temperatures, which releases the materials the GAC has adsorbed,” Hagerty said, adding the process will take place offsite, once a year for each filter.

While CFPUA is moving ahead with plans for the Sweeney upgrades, with design and permitting work expected to wrap up in July, it remains unclear how they will be funded. CFPUA has requested grant funding to cover the entire cost of the project (as opposed to a loan, which Brunswick County is pursuing), and has repeatedly stated it believes damages from its lawsuit against Chemours should go towards the plant. For the time being, both of those funding options remain up in the air.


Send comments and tips to Benjamin Schachtman at ben@localvoicemedia.com, @pcdben on Twitter, and (910) 538-2001.

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