10.17.2024_CCOA.p1_2024 Q1 Mass Loading Assessment Chemours Response to DEQ Comments

Table 1: Comments on CFR Mass Loading Assessment, First Quarter 2024, Submitted June 28, 2024.
No.
Repo
Section
Comments by NC DEQ
Chemours
Response
On May 15, 2024, we were verbally notified that Eurofins had alerted Chemours
Noted.
about an analysis preparation error that resulted in the lower reporting (low bias) of
PFPrA concentrations in both groundwater and surface water samples tested
between June 2023 and April 2024. Eurofins estimated the low bias of
Gen
approximately 36% in most samples impacted by the preparation error. Eurofins
and Chemours provided further documentation about the error in two submittals
dated May 22, 2024 and June 18, 2024, respectively. A table listing the former and
revised PFPrA concentrations was provided to DEQ in the June 18th Chemours
submittal. Comments on the PFPrA-related Eurofins and Chemours submittals are
not included here.
Matrix interference studies have shown that quantitation of R-PSDA, Hydrolyzed
Chemours is presently conducting analytical
PSDA, and R-EVE is inaccurate due to interferences by the sample matrix
experiments evaluating the use of direct injection
(Geosyntec, 2020b). What steps are underway to modify methods to ensure
and extended analytical run times to reduce the
1
3.1
?
reliable and accurate reporting?
interferences by the sample matrix on the
quantitation of R-PSDA, Hydrolyzed PSDA, and
R-EVE.
There is a discrepancy in the text between the main report and the appendix.
There is no discrepancy between the Section 3.2
Section 3.2 of the main report states that no equipment blank samples were
of the main report and Sections 3.2 and 3.3 of
collected for the Tar Heel sampling program due to no maintenance activities on
Appendix A. These are different sampling
the composite sampler and that no other quality assurance/quality control samples
programs that are being referenced in this
were collected. Sections 3.2 and 3.3 of the appendix state that equipment blanks
comment: (1) for the twice -weekly Tar Heel
2
3.2, 3.2 and
3.3 in
were collected for surface water and groundwater sampling. Please explain or
sampling program, equipment blanks were not
collected because there were no scheduled
Appendix
correct the discrepancy.
maintenance activities on the autosampler; and
(2) the quarterly mass loading model surface
water and groundwater sampling programs, which
had equipment blanks collected at a frequency of
1 per 20 samples per equipment type.
In paragraph two, the last sentence states, "...since Q4 2021, which corresponds to
Chemours agrees that the groundwater extraction
the time when the Outfall 003 treatment system, the Seep FTCs, SWTP and
and barrier wall remedy were implemented in Q1
groundwater extraction and barrier wall remedy were implemented." The
2023 and will correct the statement in subsequent
3
4.2 (and 5)
groundwater extraction and barrier wall were implemented in Q1 2023, not Q4
reports. This correction was made to the Cape
2021.
Fear River PFAS Mass Loading Assessment —
Second Quarter 2024 report (Geosyntec, 2024a),
submitted to NCDEQ on September 30, 2024.
Page 1 of 3

Table 1: Comments on CFR Mass Loading Assessment, First Quarter 2024, Submitted June 28, 2024.
No.
Repo
Section
Comments by NC DEQ
Chemours
Response
The mass discharge of total table 3+ compounds attributed to the Georgia Branch
The mass discharge from Georgia Branch Creek
Creek PFAS loading pathway during this quarter was higher than the maximum
during Q1 2024 was consistent with the range of
historical before remedies mass discharge of total table 3+ PFAS. Furthermore, the
past mass discharge values at this location. In the
Georgia Branch Creek PFAS loading pathway was responsible for almost 60% of
following quarter (Q2 2024), the flow and the
the total table 3+ compounds mass discharge for all model transport pathways
mass discharge have subsequently decreased
described in Appendix A, Section 4.2 this quarter. The report attributed this higher
(Geosyntec, 2024a). The mass discharge in Q1
2024 of 0.79 mg/s is similar to the historicalmaximum
concentration to higher flow volume this quarter. If flow volumes continue to be
of 0.78 mg/s (Geosyntec, 2021), which
elevated additional remediation will need to be considered.
corresponded to a low "before remedies" relative
contribution of 6%.
Since the mass discharges from the pathways
with remedies have significantly decreased
4
Appendix A,
(Seeps FTCs, Outfall 003, onsite groundwater),
Section 4.2
and since the total mass discharge entering the
Cape Fear River has also decreased, the "after
remedies" relative contribution percentage for
Georgia Branch Creek is higher. Thus using "after
remedies" relative contributions may be
misleading because it does not take into
consideration the decrease in the pathways with
remedies and the overall decrease of PFAS
entering the Cape Fear River.
Chemours will continue to monitor Georgia Branch
Creek during the quarterly mass loading model
sampling events.
Has another source been investigated and does additional remediation need to be
In Q1 2024, the location along Willis Creek was
considered in the area based on the Total Table 3+ PFAS concentration of 1,400
offset upstream from the mouth of the creek due
ng/L at W-6?
to high river water flowing into the creek. This
offset location (WC-6) is located along the extent
of the long-term remedy. The purpose of these
quarterly mass loading assessments is to evaluate
Figure All,
mass discharge, not site assessment and
5
Appendix
investigation. However, quarterly performance
monitoring reports evaluate the remedy along this
Willis Creek extent. The CFR Long -Term Remedy
Performance Monitoring Report #6 (Q2 2024)
April — June 2024 report (Geosyntec, 2024b),
submitted to NCDEQ on September 30, 2024,
observed that Willis Creek mass discharges to the
Cape Fear River have decreased by
Page 2 of 3

Table 1: Comments on CFR Mass Loading Assessment, First Quarter 2024, Submitted June 28, 2024.
No.
Repo
Section
Comments by NC DEQ
Chemours
Response
approximately 50% post remedy startup
(Geosyntec, 2024b).
SMW-11 and SMW-12 have higher concentrations than samples from nearby wells
Per paragraph 1(a) of the August 2020 Addendum
SMW-10 and PW-09 in both total PFAS and PFOA. Has another source been
to Consent Order Paragraph 12, the mass loading
investigated and does additional remediation need to be considered in this area?
assessment "measur[es] mass loading of PFAS to
the Cape Fear River from the Facility" rather than
assessing the source of these PFAS in
groundwater wells. PFAS concentrations in
groundwater wells vary across the Site based on
geographical location and water bearing unit.
Although SMW-11 is nearby PW-09 and SMW-10,
SMW-11 is screened within the Surficial Aquifer,
PW-09 and SMW-10 are screened within the
Black Creek Aquifer. As noted in the 2023 Annual
Figure A4,
Groundwater Report (Geosyntec, 2024c),
6
Appendix
concentrations in the Black Creek Aquifer are
generally lower than concentrations in the Surficial
Aquifer. SMW-12 is screened in the Black Creek
Aquifer but is also located further to the east of
PW-09 and SMW-10, upgradient of the barrier
all remedy. This well has similar concentrations
to other nearby wells screened in the Black Creek
Aquifer (PIW-13 and PIW-14), which are also
upgradient of the barrier wall remedy (Geosyntec,
2024c). Therefore, the higher concentrations in
SMW-11 and SMW-12 are consistent with
observed concentration trends across the Site.
References:
Geosyntec, 2021. Cape Fear River PFAS Mass Loading Assessment — First Quarter 2021 Report, Chemours Fayetteville Works. June 30, 2021.
Geosyntec. 2024a. Cape Fear River PFAS Mass Loading Assessment — Second Quarter 2024 Report, Chemours Fayetteville Works. September 30, 2024.
Geosyntec. 2024b. CFR Long -Term Remedy Performance Monitoring Report #6 (Q2 2024) April — June 2024, Chemours Fayetteville Works. September 30, 2024.
Geosyntec, 2024c. 2023 Annual Onsite and Offsite Groundwater Monitoring Report, Chemours Fayetteville Works. March 28, 2024.
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