PFAS Case Study: Cape Fear Public Utility Authority (CFPUA)

Cape Fear Public Utility Authority (CFPUA) PFAS Case Study

Mal

achi

Jac

obs/

shut

ters

tock

.com

PFAS Case Study: Cape Fear Public Utility Authority (CFPUA)

Figure 1: Sweeney Water Treatment Plant (Top), PFAS Pilot Treatment Skid (Right) (Source: CFPUA)

Background:

The Cape Fear Public Utility Authority (CFPUA) operates one surface water treatment plant (Sweeney), one groundwater treatment plant

(Richardson Water Treatment Plant), and one small groundwater well system, which together provide drinking water to over 200,000 people. The Sweeney Water Treatment Plant (WTP) treats surface water from the Cape Fear River. The WTP currently treats an average 14 MGD, has an existing design capacity of 35 MGD, and has the infrastructure in place to be rerated to 44 MGD without significant capital investments.

Like other public water systems, CFPUA participated in monitoring under the Third Unregulated Contaminant Monitoring Rule (UCMR3), which tested for several contaminants in drinking water, including six PFAS compounds. The PFAS included in UCMR3 were legacy compounds, such as PFOA and PFOS, and results of analyses of CFPUA samples showed concentrations below detection limits of UCMR3 sampling (40 ng/L PFOS, 20 ng/L PFOA).

One source of PFAS in the Cape Fear River is a discharge from the Fayetteville Works chemical plant in Bladen County, North Carolina, approximately 70 miles northwest of New Hanover County (NC DEQ, 2020). The Fayetteville Works was

Facility SummaryLocation: Sweeney Water Treatment Plant, Wilmington, NC

Size: 35 MGD plant (existing), 44 MGD (re-rate capacity)

Type of PFAS Treatment: Granular activated carbon (GAC)

Year of PFAS Detection: Sampled in 2014; results published in 2016

Year of Construction: Full-scale Implementation Ongoing - Anticipated Operation in Spring 2022

Imag

ery

by C

ape

Fear

Pub

lic U

tility

Aut

horit

y. P

rinte

d w

ith p

erm

issi

on.

Cal

gon

Car

bon

Corp

orat

ion

GAC

Pilo

t Uni

t

• 1 •Copyright © 2020 American Water Works Association. All Rights Reserved


originally built in the early 1970s by DuPont and has been operated since 2015 by Chemours, a company formed out of DuPont business units that included fluorochemical manufacturing operations. Intakes from which CFPUA draws raw water from the river are about 55 miles downstream from the Fayetteville Works’ discharge outfall.

In 2014, CFPUA was approached by researchers who were studying the presence of newer PFAS, such as GenX, in the Cape Fear River. This research team, which included USEPA scientists and faculty from a number of North Carolina universities, wanted to sample raw water from CFPUA’s intake, as well as finished water from the Sweeney WTP. Samples of raw and finished water were taken in 2014. The results of this study, published in 2016, showed a mean concentration of GenX in raw water of 631 ng/L. The research also detected many “novel”, previously unidentified, PFAS at significantly higher concentrations. Treatment processes in place at the time at Sweeney were not effective at reducing these concentrations in finished drinking water. The potential for risks to human health risks posed by GenX were largely unknown, and no regulatory guidance existed for GenX.

NC Department of Health and Human Services has set a nonenforceable health goal of 140 ng/L for GenX in drinking water. The state had initially set the health goal far higher – 71,000 ng/L – but lowered it following a reexamination of available data. While Chemours has stopped discharge of industrial wastewater to the Cape Fear River, levels of PFAS are still detectable in the River. Potential sources of ongoing PFAS contamination are likely due to groundwater

at the Chemours plant, river sediments, and previous air emissions. In February of 2019, the NC Department of Environmental Quality (DEQ) issued a consent order requiring additional controls at the Chemours Facility to limit PFAS discharges (NC DEQ: Chemours Consent Order, 2019, amended in 2020).

Typically, about 20 PFAS compounds are detected as a result of CFPUA’s regular PFAS monitoring. Of these, the vast majority are linked to the Chemours facility. GenX concentrations averaged around 112 ng/L in July and August 2017. After Chemours stopped its wastewater discharges to the Cape Fear River by November 2017, GenX levels decreased to about 40 ng/L by the end of 2017. Since 2018, the GenX concentration in the raw water has ranged from 2.8 ng/L to 42 ng/L (average 13 ng/L) between January 2018 and March 2020.

However, a larger concern for CFPUA has been the total PFAS concentration in the raw water, as defined by 47 PFAS measured through a modified EPA 537.1 method (GEL Laboratories, LLC, Charleston, SC), which has remained at a significant level since 2018, with a range from 39 ng/L to 377 ng/L (average 144 ng/L). During the same period, combined PFOA and PFOS legacy compounds ranged from 4.9 ng/L to 30 ng/L (average 18.9 ng/L) and are well below the current 70 ng/L health advisory level set by the USEPA.

CFPUA conducted biweekly PFAS sampling of the raw water over two years to characterize the relationship between the total PFAS concentration versus the river flow rate at CFPUA’s raw water intake. It was found that the total PFAS

M. M

osur

e/sh

utte

rsto

ck.c

om



concentration increases during moderate and low-flow conditions and decreases during high-flow conditions. For CFPUA, the relationship between total PFAS concentration and river flow rate validated the importance of year-round comprehensive sampling. In addition, it showed how persistent the PFAS are once released to the environment and that they likely will persist in CFPUA’s source water for the foreseeable future.

Existing Treatment ProcessTreatment at the Sweeney WTP consists of preozonation, coagulation, flocculation, and clarification, followed by intermediate ozonation, biologically active filtration (using GAC media), ultraviolet (UV) disinfection, stabilization, and chlorination. The simplified process flow diagram for the WTP is shown in Figure 2. Although the existing WTP has advanced, state of the art treatment, at the time of the PFAS contamination, the plant was not designed to remove PFAS and GenX from the water supply.

Figure 2: Simplified Process Flow Diagram for the Sweeney WTP (Source: CFPUA)

PFAS Treatment SelectionThe selection of a PFAS treatment technology for the Sweeney WTP was based on the results of the pilot testing and preliminary cost analyses. Three technologies were evaluated; granular activated carbon (GAC), ion exchange (IX), and reverse osmosis (RO). These technologies could provide effective PFAS treatment for the Cape Fear River water. Therefore, the treatment selection was driven by cost, how the technology complements the previous

investments made into the existing treatment plant, and other noneconomic factors. All three technologies would be implemented as post-filter treatment processes and would require repumping of the filtered water.

Planning level capital, operational and maintenance costs (O&M), and life-cycle cost opinions were developed for each of the three treatment alternatives. The cost summary for 44-mgd PFAS treatment technologies is presented Table 1.

Table 1: Cost Summary for 44-mgd PFAS Treatment Alternatives

GRANULAR ACTIVATED CARBON CONTACTORS

ION EXCHANGE VESSELS REVERSE OSMOSIS

Capital Cost $46 M $46 M $150 M

Annual Operating Cost $2.9 M $2.1M $4.7 M

Present Value $215 M $176 M $504 M

Notes:

1. Presentvaluebasedon34yearswith20-yearloansforcapitalcostsand4percentinterest

2. ROcostsdonotincludeNPDESdischargeoradditionalrawwatersupplycosts

3. TwoadditionaloperatorsincludedforROonly

4. Contingency=30%

© Black & Veatch Holding Company 2020.



CONSIDERATION GRANULAR ACTIVATED CARBON CONTACTORS

ION EXCHANGE REVERSE OSMOSIS

PFAS REDUCTION Effective at PFAS reduction Effective at PFAS reduction Effective at PFAS reduction

FLEXIBILITY Can adapt to changes in regulations

Limited flexibility – targeted for specific compounds Provides broad removal already

CORROSION CONTROL Consistent with CFPUA’s corrosion control program

Consistent with CFPUA’s corrosion control program

Requires additional treatment to prevent lead and copper corrosion

ENVIRONMENTAL Removes PFAS from the environment through proper reactivation

Media must be disposed of when exhausted

Creates significant waste volume with concentrated PFAS levels that must be managed

BETWEEN FIGURE and caption

Table 2: Noneconomic Considerations for CFPUA’s PFAS Treatment Selection

Table 3: CFPUA GAC Contactor Design Criteria

GRANULAR ACTIVATED CARBON CONTACTOR DESIGN SUMMARY

Design Capacity 44 MGD

Number of Contactors 8Design Flow Rate (each) 5.5 MGDType Concrete Basins

Total Media Surface Area (each) 820 SFGAC Media Depth 12.5 feetContact Time at Design Flow 20 minutes

Noneconomic considerations for selecting a treatment technology can be very site-specific and wide-ranging. CFPUA’s approach was to focus on only a few key noneconomic criteria that would help define the best solution for the Sweeney WTP. Table 2 shows the criteria selected by CFPUA for its evaluation and the considerations for each treatment technology.

Based on the economic and noneconomic considerations, post-filter, deep-bed GAC contactors emerged as the best overall PFAS treatment solution for the Sweeney WTP. GAC offered highly effective PFAS removal, promoted flexibility, and complemented other treatment processes already in the plant. At 20-minutes EBCT, pilot testing and modeling showed that for CFPUA the GAC could provide short chain and long chain PFAS removal (>90%) for about 400 days between reactivation cycles. It was also recognized that there could be secondary benefits of adding post-filter GAC to the existing plant. However, the driver for adding GAC was to treat for the PFAS present in the source water.

PFAS Treatment Facility DesignThe GAC facility includes eight, single-cell, concrete contactors, each nominally rated for 5.5 mgd treatment capacity, for a total treatment capacity of 44 mgd. The facility was designed for a 20-minute EBCT at the maximum 44-mgd treatment capacity, requiring about 3,000,000 pounds of GAC.

The GAC contactors were designed for potential future conversion from GAC to IX. The structure, underdrains, piping, and valves accommodated the change to IX resin with no modifications. Only the GAC backwash system would have to be changed if CFPUA transitioned to IX.



PFAS Treatment Cost EvaluationIn September 2019, approximately two years after the start of the pilot testing, CFPUA awarded a $35.9 million construction contract for the GAC treatment facility. Construction activities started in November 2019, and the new GAC contactors are expected to come online in February 2022. Total project costs (pilot testing, analytical, engineering and construction) are expected to be within the $46 million budget established at the end of the pilot testing phase. The project was funded through the sale of revenue bonds. This financing is expected to result in an increase of about $5 per month on the average customer’s bill or about a 4% increase. CFPUA has filed a federal lawsuit to recover costs and damages related to the discharges of PFAS to the Cape Fear River.

Interim PFAS TreatmentTo provide some PFAS reduction in the treated water while the new GAC treatment facility is constructed, the Sweeney WTP has implemented annual replacement of the GAC filter media in the existing 14 biological filters with new or reactivated GAC media. It is important to note that, with only four feet of GAC media depth, the existing biological filters were not designed for PFAS removal, but by frequently replacing the GAC, some limited amount of PFAS removal could be achieved.

While the interim PFAS treatment provides some PFAS removal for the short term, it is not a suitable long-term strategy for several reasons. The shallow media depth in these existing filters results in a short life expectancy of the GAC for PFAS removal, and therefore, it does not provide for consistent PFAS removal. In addition, the frequent media replacement is disruptive to the biological portion of the 1,4-dioxane removal process, for which these filters were designed.

Figure 3: CFPUA GAC Contactor 3D Rendering©

Bla

ck &

Vea

tch

Hol

ding

Com

pany

202

0.

5• •Copyright © 2020 American Water Works Association. All Rights Reserved


References NC Department of Environmental Quality (NC DEQ), 2020. NC

DEQ: GenX Investigation [WWW Document]. GenX Investig. URL https://deq.nc.gov/news/key-issues/genx-investigation (accessed 7.22.20).

NC DEQ, 2019. Chemours Consent Order [WWW Document]. URL https://deq.nc.gov/news/key-issues/genx-investigation/chemours-consent-order-february-2019 (accessed 6.9.20).

Am

y D

over

/shu

tter

stoc

k.co

m

Dedicated to the World’s Most Important Resource ®6• •

Copyright © 2020 American Water Works Association. All Rights Reserved

Documents

PFAS Case Study: Cape Fear Public Utility Authority (CFPUA)