2022.04.26_NCDEQ 2021 Sediment Study Report 042622

NCDEQ PFAS Sediment Study – Performed January 2021 to August 2021

Summary
The N.C. Department of Environmental Quality performed a limited sediment characterization study in
2021 due to experimental design concerns with a 2020 Geosyntec Sediment Characterization Study
funded by Chemours that included sampling in areas where per- and polyfluorinated substances (PFAS)
were not likely to be found and using an analytical method that was not sensitive enough to detect
several PFAS unique to the Chemours Fayetteville Works Site (Table 3+ compounds). These
experimental design issues were thought to result in non-detect Table 3+ PFAS concentrations for
several sediment samples in the Geosyntec study. Once the experimental design concerns were
addressed in the NCDEQ study, a much higher percentage of samples had detectable Table 3+ PFAS
compounds. The NCDEQ sediment characterization study detected Table 3+ compounds in more than
90 percent of samples as compared to the Geosyntec study, which detected Table 3+ compounds in 33
percent of samples. Legacy and other PFAS (some of which are present at, but not unique to, the
Fayetteville works site) were measured with a sufficiently sensitive analytical method. As a result,
legacy and other PFAS were detected in 100% of samples in both the 2020 Geosyntec study and the
current DEQ sediment characterization study.

Introduction
NCDEQ performed a limited sediment characterization study from January through August 2021 to
investigate concerns about the design of the 2020 Chemours Sediment Characterization Study that was
performed as required under Paragraph 11.2 of the Consent Order. NCDEQ identified two main
shortcomings of the Chemours study: 1) sampling in areas less likely to have PFAS present, and 2) the
use of analytical method with a high limits of quantitation (LOQs) for Table 3+ compounds (Table 1).
The DEQ study addressed these issues by sampling in areas suspected to have higher PFAS
concentrations and working with GEL Laboratories to lower the reporting limits for the Table 3+ PFAS
compounds.
Location
Locations selected by Chemours potentially had low total organic carbon (TOC) values; however, NCDEQ
scientists hypothesized that PFAS would adsorb to organic carbon in sediment such that sediments with
higher TOC values would have higher PFAS concentrations. Many PFAS compounds adsorb to granular
activated carbon (GAC), which enables their removal from drinking water using GAC home filtration
systems.
Sampling locations in the Chemours Sediment Characterization Study were collected from the mid-
channel and banks of the Cape Fear River. Samples collected from the mid-channel of the Cape Fear
River are expected to have low TOC values due to the high-water velocity. Bank samples were collected
near the edge of the River but were still along the main channel of the River. Only one of the bank
samples in the Chemours study was collected from an area expected to have higher TOC values. This
sample was collected from a secondary stream located off the River near an area where the main
channel forms a bend. The lower flow rates in the secondary stream allow sediments to settle out of
the water column.
The NCDEQ sampling locations were selected in known floodplains along the Cape Fear River which are
commonly inundated during seasonal flooding, allowing fine-grained sediments to settle out of
suspension from floodwaters. PFAS are thought to accumulate in these finer-grained, higher organic
sediments. The floodplain deposits commonly contain considerable plant debris and the soils in these
areas may be disturbed or redistributed by land-dwelling organisms or plant roots. PFAS concentrations
were determined in the samples using an analytical method with improved reporting limits. TOC and
grain size data were also collected for a subset of samples.
Raven Rock State Park was chosen as the location to collect background (ambient) PFAS data upstream
because this area was approximately 43 miles north of the Fayetteville Works Site, and was thought to
be outside of the known Table 3+ PFAS aerial deposition area. Downstream locations ranged from Tar
Heel Ferry Boat Ramp to International Paper as shown in Figure 1.
Analytical Methods
The analytical methods used in the Chemours Sediment Characterization Study had high reporting limits
for Table 3+ compounds, likely resulting in non-detectable levels of PFAS in areas where the compounds
are in fact present. DEQ worked with GEL Laboratories to lower its reporting limits, particularly on the
Table 3+ compounds (see Table 1 below). Discussions with the Environmental Protection Agency Region
5 scientists also indicated that lower reporting limits for PFAS in soil are achievable. Reporting limits for
various PFAS Soil Methods, including those used by the contract lab Chemours used (Eurofins), are given
in Table 1.
Table 1. Reporting limits for PFAS Soil Methods. GEL is the contract lab used by NCDEQ and Eurofins is
the contract lab used by Chemours. Improved reporting limits are noted for Table 3+ compounds in GEL
methods. The LOQ is the same as the reporting limits for all values in this table. Note: all units are in
ng/g (parts per billion) dry weight of soil, which are 1000x higher than the ng/L (parts per trillion) units
used to report PFAS concentrations in water and other liquid samples.

* GenX is reported by Eurofins in some cases using Method 537M and in other cases using the Table 3+
Method.
** A few legacy PFAS in ATSM D7968.17a have higher reporting limits. PFOS, PFPeA, and PFBA have
reporting limits of 0.050, 0.125, and 0.125 ng/g, respectively.
Sample Collection and Analysis
Four sampling trips were taken to collect sediment samples from 10 locations (Figure 1) within known
floodplains along the Cape Fear River downstream of the Chemours Fayetteville Works Facility. PFAS
contamination of soils from aerial deposition has been detected as far as 20 miles from the Chemours
Fayetteville Works facility, with studies still ongoing to find the edge of contamination. All sites chosen
were either able to be freely accessed or were sampled with permission in the case of International
Paper. An initial reconnaissance trip was made in November 2020 to locate and determine accessibility
at several of the proposed sampling sites. Some sample locations needed to be modified slightly due to
vegetative growth present or signs or locks indicating that access was restricted in areas previously
accessible during the reconnaissance trip.
Composite samples are collected from the surface, while grab samples are collected deeper from the
subsurface. At least one grab sample and one composite sample were collected at each sampling
location except at White Oak Road, where only one composite sample was collected under standing
water; therefore, a grab sample at depth was not feasible. Composite samples were collected by
removing five samples of soil from the top zero to six inches of sediment; four from each corner of a
square about a meter apart; and one from the center of the square. These five samples were then
mixed to form one composite sample. Grab samples were collected at a depth of approximately 12
inches in the center of the square. One duplicate sample (either a grab or composite duplicate) was
collected on each sampling trip. Samples were analyzed by GEL laboratories for 55 PFAS using a
modified version of EPA Method 537.1.

Figure 1. DEQ Sediment Study Sampling Locations along the Cape Fear River

Results
TOC Results - Data from the NCDEQ study indicated that samples were successfully chosen from areas
with higher TOC values than are generally found in the mid-channel and edges of the Cape Fear River.
Seven out of 11 samples had TOC values higher than the maximum TOC value of 33 g/kg in the
Chemours study (Table 2). During the last sediment sampling event, lower TOC values were noted in
samples collected. The DEQ Sampling Team indicated that lower TOC values may be associated with the
sediment samples from the last sampling trip because there was no longer access to the specific
locations that were chosen during the reconnaissance trip. Vegetative overgrowth, no trespassing signs,
and locks that were not previously present prevented access to the originally designated sampling areas.
In addition, these last samples collected, while downstream of the facility, were upstream of previous
samples collected and were more likely to have steeper banks and stronger flow, making floodplain
deposition less likely.
Table 2. TOC Data for NCDEQ Sediment Study Samples. Note: units for TOC are in grams (g) of TOC per
kilogram (kg) of soil (dry weight). Seven out of 11 samples (sample above thick black line in table below)
had TOC values higher than the maximum TOC value of 33 g/kg in the Chemours study.

Grain Size - Grain size data was collected for a subset of samples. Figure 2 shows the percentage of
gravel, sand, silt, and clay.

Figure 2. Grain Size Data for NCDEQ Samples. Samples are arranged from highest TOC (left) to lowest
TOC (right), corresponding to the order in Table 2.

PFAS Concentrations - The concentrations for all PFAS are shown in Table 3, which is posted to the
website as a separate file for easier viewing of the large table. Concentrations of a few PFAS (PPF Acid,
PFMOPrA and PFMOBA) labeled as Chemours compounds in Table 3 are not reported in the 2020
Geosyntec Sediment Characterization Report due to issues with the analytical method.
All other PFAS not specifically labeled as Chemours compounds are designated as legacy PFAS or other
PFAS in this report. Some of these legacy/other PFAS compounds are related to the Chemours
Fayetteville facility, and many enter the Cape Fear River from sources other than Chemours.
The upstream background location in the DEQ study (Raven Rock State Park) had no detectable Table 3+
PFAS due to its distance from the Chemours facility and/or low TOC values. Total Table 3+ PFAS ranged
from non-detect at Raven Rock State Park and Tarheel Ferry Boat Ramp to 31.3 ng/g at International
Paper. Total Legacy and other PFAS ranged from 0.70 ng/g at White Oak Road to 39.0 ng/g at Elwell
Ferry Road (East of the River). As shown in Figure 3, PFAS concentrations generally increased in areas
with higher TOC values.

Figure 3. Relationship between TOC and PFAS concentrations in sediment samples.

Analytical Method Reporting Limits - The use of an analytical method with lower reporting limits for the
Table 3+ PFAS allowed for a much higher rate of detection of the compounds. Table 3+ PFAS were
found in more than 90 percent of downstream sediment samples in the DEQ study as compared to a
detection rate of 33 percent for riverbank sediment samples in the Chemours study. Two of the three
samples with detectable Table 3+ PFAS in the Chemours study were collected beside the Fayetteville
Works Site, and all three samples had PFAS concentrations between 10 and 20 ng/g (denoted by red
lines in Figure 4). No total Table 3+ PFAS were detected between the LOQ of 1 to 2 ng/g and 10 ng/g in
the Chemours study; whereas, two-thirds of the Total Table 3+ PFAS detected in the DEQ Sediment
Study samples were detected between 0.15 ng/g and 10 ng/g (note: 0.15 ng/g is the reporting limit).
The Chemours study had a lower reporting limit of 0.2 ng/g for many legacy and other PFAS using
Method 537M and detected these PFAS in 100 percent of samples – with about half of these detections
at levels below 10 ng/g. Legacy and other PFAS were also detected in 100 percent of samples in the
NCDEQ Sediment Study.
Taken together, these results suggest that while the Chemours analytical method 537M is able to
measure many of the legacy/other PFAS at lower levels, the Chemours Table 3+ Method is not capable
of measuring lower concentrations of Table 3+ PFAS in sediment samples. The improvements made to
the NCDEQ analytical method allows for the detection of Table 3+ PFAS at lower levels.

Figure 4. Total Table 3+ and Total Other PFAS Detected at Each Location as Compared to Chemours
Data. There were a wider range of Table 3+ PFAS found in the NCDEQ study, with most detections below
10 ng/g. All detectable Total Table 3+ PFAS in the Chemours Sediment Characterization Study were
either between 10 and 20 ng/g (between the red lines below) or were non-detect.

Sampling of Surface and Subsurface Sediment Layers – Composite samples are collected from the
surface, while grab samples are collected deeper from the subsurface. Grab samples and their
duplicates collected for the DEQ study are shown in two shades of blue in Figure 5 below. Composite
samples and their duplicates are shown in two shades of orange in the same figure. Duplicate samples
agree with one another for both Table 3+ PFAS and legacy/other PFAS, indicating that both the sampling
procedures and analytical method provide reproducible results for all compounds. However, when
comparing grab and composite samples (blue compared to orange), sampling results can vary for both
Table 3+ PFAS and legacy/other PFAS. There is no clear trend as to which type of sampling at which
depth yields higher PFAS concentrations. Surface soils that have higher concentrations of PFAS may
indicate more recent PFAS deposition. Subsurface sediment samples with higher PFAS concentrations
may indicate areas where PFAS deposition occurred at an earlier time point, such as when PFAS
discharge to the Cape Fear River was greater before the Consent Order was signed in 2019. These
results indicate that it is important to collect both surface and subsurface sediment samples to better
characterize PFAS in sediment.

Figure 5. DEQ-collected samples: Comparison of Table 3+ PFAS Concentrations Using Grab and
Composite Sampling

Figure 6. DEQ-collected samples: Comparison of Legacy and Other PFAS Concentrations Using Grab and
Composite Sampling

Conclusions
The NCDEQ Sediment Study showed that once concerns about sampling location and analytical method
reporting limits were addressed, a much higher percentage of Table 3+ PFAS compounds are detected in
sediment samples. Sediment with higher TOC values generally had higher PFAS concentrations. The
Chemours Table 3+ method is not sensitive enough to detect and quantitate Table 3+ PFAS at the
concentrations at which most Table 3+ PFAS are found in the environment.
Results also showed that PFAS concentrations in samples collected from the same location were often
quite different for surface soils and subsurface soils. These differences were not predictable because
some locations had higher PFAS concentrations in surface sediments while other locations had higher
PFAS concentrations in subsurface sediments. A better characterization of PFAS in sediment can be
achieved by 1) using an analytical method with a lower reporting limit, 2) sampling in areas where PFAS
are likely to deposit, and 3) sampling in both surface and subsurface soils.