The Chemours Company
Fayetteville Works
22828 NC Highway 87 W
Fayetteville, NC 28306

April 11, 2019
Dr. Joe Ghiold, Ph.D., Project Manager
Facility Management Branch
Hazardous Waste Section
Division of Waste Management
NC Department of Environmental Quality
1646 Mail Service Center
Raleigh, NC 27699-1646
Re:

Cape Fear River PFAS Mass Loading Model Scope of Work
Chemours Fayetteville Works
Fayetteville, North Carolina
EPA ID No. NCD 047 368 642

Dear Dr. Ghiold:
Enclosed, please find a PDF copy of the Cape Fear River PFAS Mass Loading Model Scope ofWork for the Chemours Fayetteville Works. This document presents a description of the modelthat will account for sources of per- and polyfluoroalkyl substances (PFAS) from the Facility
at and near the Chemours Fayetteville Works, North Carolina site that reach the Cape Fear
River. This document meets the requirements of Paragraph 12 (b) of the Consent Order dated
February 25, 2019. Geosyntec Consultants of NC, PC has been approved as the third-party
consultant by NCDEQ as required under Paragraph 12 (c) of the Consent Order.
If you have any questions or need any additional information, please contact me at
Brian.D.Long@Chemours.com.
Respectfully submitted,

Brian D. Long
Plant Manager
cc:

Christel Compton – Chemours Fayetteville Works
File
Enclosures

CHEMOURS FAYETTEVILLE WORKSCAPE FEAR RIVER PFAS MASSLOADING MODEL SCOPE OF WORK
Prepared for

The Chemours Company FC, LLC
Fayetteville Works
22828 NC Highway 87 W
Fayetteville, NC 28306
Prepared by
Geosyntec Consultants of NC, PC
2501 Blue Ridge Road, Suite 430
Raleigh, NC 27607
Geosyntec Project Number TR0795

April 2019

TABLE OF CONTENTS

1.

INTRODUCTION AND OBJECTIVES ..................................................................................1
1.1 Objectives ........................................................................................................................1
1.2 Document Organization ..................................................................................................22.

SITE BACKGROUND .............................................................................................................33.

SITE SETTING ........................................................................................................................4
3.1 Physical Site Setting, Topography and Drainage ............................................................4
3.2 Cape Fear River ...............................................................................................................4
3.3 Regional Geology ............................................................................................................5
3.4 Site Geology ....................................................................................................................5
3.5 Site Hydrogeology ...........................................................................................................6
3.5.1 Groundwater Seeps..............................................................................................7
3.5.2 Tributaries to the Cape Fear River ......................................................................8
3.6 PFAS Sources and Distribution in Environmental Media...............................................83.6.1 PFAS Distribution in Soil....................................................................................8
3.6.2 PFAS Distribution in Onsite Groundwater .........................................................83.6.3 PFAS Distribution in Surface Water ...................................................................9
3.7 Potential PFAS Transport Pathways to Cape Fear River ................................................94.

PFAS MASS LOADING MODEL DESIGN .........................................................................11
4.1 Upstream River..............................................................................................................12
4.2 Tributaries – Willis Creek, Georgia Branch Creek, and Old Outfall 002 .....................13
4.3 Aerial Deposition to the Cape Fear River .....................................................................13
4.4 Onsite Groundwater ......................................................................................................13
4.1.1 Indirect Pathway – Groundwater to Seeps to River ..........................................144.1.2 Direct Pathway – Black Creek Groundwater Discharge to River .....................14
4.5 Outfall 002 and Facility Stormwater Runoff .................................................................15
4.6 Offsite Groundwater ......................................................................................................15
4.7 Summary of Supporting Field Work .............................................................................15

5.

MODEL CALIBRATION AND SENSITIVITY ANALYSIS ..............................................17
5.1 Model Calibration..........................................................................................................17

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5.2

Sensitivity Analysis .......................................................................................................17

6.

SUMMARY ............................................................................................................................19

7.

REFERENCES .......................................................................................................................20

LIST OF TABLES
Table 1PFAS Mass Loading Model Potential Pathways

Table 2Analytical Methods and Analyte List
LIST OF FIGURES

Figure 1

Site Location Map

Figure 2

Site Topographic Map

Figure 3

Cape Fear River Watershed and Downstream Public Utility Intakes

Figure 4

Site Geology Cross-Section

Figure 5

Potential PFAS Pathways to the Cape Fear River from Site
LIST OF APPENDICES

Appendix A

Supplemental Information

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ACRONYMS AND ABBREVIATIONS%

percent

bgs

below ground surface

CFPUA

Cape Fear River Public Authorities

Chemours

The Chemours Company FC, LLC

COConsent Order

DuPontE.I. du Pont de Nemours and Company

ft

feet

Geosyntec

Geosyntec Consultants of NC, PC

HFPO-DA

hexafluoropropylene oxide dimer acid

Kuraray

Kuraray America Inc.

LTW

long-term wellsmL

milliliter

NC

North Carolina

NCDEQ

North Carolina Department of Environmental Quality

PFAS

Per- and polyfluoroalkyl substances

PFCA

perfluorocarboxylic acids

PFOA

perfluorooctanoic acid

PFOS

perfluorooctanesulfonic acid

PFSA

perfluorosulfonic acids

PMPA

2,3,3,3-Tetrafluoro-2-(trifluoromethoxy)propanoic acid

SOP

Standard Operating Protocol

USGS

United States Geological Survey

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1.

INTRODUCTION AND OBJECTIVES

Geosyntec Consultants of NC, PC (Geosyntec) has prepared this scope of work document for The
Chemours Company FC, LLC (Chemours) for the Fayetteville Works facility in Bladen County,
North Carolina. The purpose of the scope of work is to describe activities planned to address
Paragraphs 12(b) and 12(c) of the signed consent order (CO) dated 25 February 2019 between the
North Carolina Department of Environmental Quality (NCDEQ), Cape Fear River Watch andChemours.
CO Paragraph 12 relates to the “Accelerated Reduction of PFAS Contamination in the Cape Fear
River and Downstream Water Intakes”. CO Paragraph 12(a) requires a per- and polyfluoroalkyl
substances (PFAS) Reduction Plan of PFAS loading to the Cape Fear River from the Facility (i.e.
the Site). CO Paragraph 12(b) requires development of a model that accounts for all sources of
PFAS from the Facility contributing loading of PFAS into the Cape Fear River, Willis Creek,
Georgia Branch, and Old Outfall 002. CO Paragraph 12(c) requires Chemours to contract a third
party approved by NCDEQ to prepare a modeling scope of work to be reviewed by NCDEQ andCape Fear River Watch. Geosyntec has been approved by NCDEQ and contracted by Chemours
to perform the modeling effort for CO Paragraph 12(b).
1.1

Objectives

The objective of this scope of work document is to describe the proposed modeling analyses (thePFAS mass loading model) that will be performed to estimate Site associated PFAS mass loadingfrom the Site and from offsite sources to the Cape Fear River directly and through its tributaries
Willis Creek, Georgia Branch Creek, Old Outfall 002, three groundwater seeps on the hill slope to
the Cape Fear River and discharging groundwater that reach the Cape Fear River from the Site.
PFAS mass loading is defined in this model as the combined mass per unit time (e.g. nanograms
per second) from potential sources. The model will estimate PFAS contributions from multiple
pathways (i.e. compartments) such as the various creeks and groundwater. The PFAS loadings forthe pathways will then be summed and used to estimate Cape Fear River concentrations using
measured Cape Fear River flow volumes. These estimated concentrations will then be compared
to measured in-river concentrations as an assessment of model calibration. In the PFAS Reduction
Plan required in CO Paragraph 12(a), this model will be used to assess potential reductions in
PFAS mass loading to the Cape Fear River based on current and future interim remedial actions at
the Site.
The proposed activities (i.e. scope of work) for the PFAS mass loading model assessment are:•Identify potential PFAS loading pathways from the Site to the Cape Fear River;

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1.2

•

Evaluate mass loading contributions from each identified potential pathway andrelative contributions to total loading from each pathway;•

Incorporate new fieldwork and data collected as part of ongoing site assessment
activities to refine estimates of model parameters;•

Model estimated PFAS concentrations in the Cape Fear River under various scenarios(e.g., “dry” i.e., baseflow and “wet” i.e., storm events) and compare to measured inriver values;•

Model estimated mass loading reductions based on proposed PFAS loading reduction
actions.

Document Organization

The remainder of this document contains the following sections:•

Section 2 – Site Background – this section describes Site background and use;•

Section 3 – Site Setting – this section describes the Site setting, including Site geology
and hydrogeology, known distribution of PFAS as they relate to PFAS loading to theCape Fear River, and identified potential PFAS transport pathways;•

Section 4 – PFAS Mass Loading Model Design – this section describes how the PFAS
mass loading model will be constructed and developed to support the Cape Fear RiverPFAS Reduction Plan required in CO Paragraph 12(a);•Section 5 – Model Calibration and Sensitivity Analysis – this section describes how
the model will be calibrated, including identifying calibration datasets; and procedures
for addressing uncertainties associated with the model;•

Section 6 – Summary – this section describes how the model will be used to support
the Cape Fear River PFAS Reduction Plan; and•Section 7 – References - this section lists work plan reference documentation.

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2.

SITE BACKGROUNDThe Site is located within a 2,177-acre property at 22828 NC Highway 87, approximately 15 miles
southeast of the city of Fayetteville along the Bladen-Cumberland county line in North Carolina.
Figure 1 presents an overview of the Site. The Site is bounded by NC Highway 87 to the west,
Cape Fear River to the east, and on the north and south by undeveloped areas and farmland. Willis
Creek and Georgia Branch Creek, tributaries to the Cape Fear River, are located toward thenorthern and southern property boundaries, respectively with Georgia Branch Creek being offsite
for its entire course.
The Site property was originally purchased by E.I. du Pont de Nemours and Company (DuPont)
in 1970 for production of nylon strapping and elastomeric tape. DuPont sold its Butacite® and
SentryGlas® manufacturing units to Kuraray America Inc. (Kuraray) in June 2014 andsubsequently separated its specialty chemicals business to Chemours in July 2015. Presently, theSite consists of five manufacturing areas (Figure 1): (Area 1) Chemours Monomers IXM; (Area 2)
Chemours Polymer Processing Aid (PPA); (Area 3) Kuraray Butacite®; (Area 4) Kuraray
SentryGlas®; and (Area 5) DuPont Company polyvinyl fluoride (PVF) resin manufacturing unit.
In addition to the manufacturing operations, Chemours operates two natural gas-fired boilers anda wastewater treatment plant (WWTP) for the treatment of process and sanitary wastewaters from
Chemours, Kuraray, and DuPont.

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3.

SITE SETTING

This section describes the Site setting, including the physical setting of the Site, the Cape Fear
River, Site geology and hydrogeology, the distribution of PFAS as it relates to PFAS loading to
the Cape Fear River, and potential transport pathways of PFAS from the Site to the Cape Fear
River.
3.1

Physical Site Setting, Topography and Drainage

The developed portion (manufacturing area) of the Site is located on a relatively flat topographic
plateau at an approximate elevation of 145 feet above mean sea level (ft MSL) and approximately
70 feet above the Cape Fear River floodplain. Figure 2 presents a topographic map of the Site andsurrounding areas. Surface topography generally remains flat to the west with a gentle increase ofabout five feet to a topographic divide near NC Highway 87. However, ground surface elevations
decrease from the topographic plateau at the manufacturing area towards the Cape Fear River tothe east as well as its tributaries, Willis Creek to the north and Georgia Branch to the south.
Topographic relief from the main manufacturing area decreases by approximately 100 feet inelevation towards the Cape Fear river bank to the east; decreases from 40 to 100 feet in elevation
to Willis Creek from the Site boundary to the Cape Fear River; and decreases by 15 to 25 feet inelevation where the Georgia Branch Creek channel runs along the property line. Inclined
topographic relief combined with overland flow and groundwater seeps have created naturaldrainage networks. These channels shown in Figure 2 have been observed to contain a steady flowof water where they intersect groundwater. These channels and the water that flows in them areherein referred to as Seeps and discharge directly into the Cape Fear River (Seep A, Seep B andSeep C; Figure 2).
3.2

Cape Fear River

The Cape Fear River and its entire watershed are located in the state of North Carolina (Figure 3).
The Cape Fear River drains 9,164 square miles and empties into the Atlantic Ocean near the Cityof Wilmington, North Carolina. The Site is situated on the western bank of the Cape Fear Riverand draws water from the Cape Fear River and returns over 95% of this water via Outfall 002 after
being used primarily as non-contact cooling water. Two lock and dam systems with USGS stream
gauges are located downstream of the Site: (1) W.O. Huske Lock and Dam, located 0.5 river miles
from the Site (USGS 02105500); and (2) Cape Fear Lock and Dam #1, located 55 river miles
downstream (USGS 02105769).
The Cape Fear River is also a water source for downstream communities of the Chemours Site.
For instance, Bladen Bluffs and Kings Bluff Intake Canal, located approximately 5 miles and 55
miles downstream from the Site, serve as Cape Fear River water intakes for the Lower Cape Fear

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Water and Sewer Authority which in turn provides water to Cape Fear Public Utility Authority(CFPUA) and other water providers. Drinking water sourced from the Cape Fear River does
contain certain chemicals including 1,4-dioxane, trihalomethanes associated with bromide content
in raw river water, pharmaceuticals, personal care products, endocrine disrupting chemicals, and
PFAS. A brief description of these chemicals in the Cape Fear River was reported previously(Geosyntec, 2018a).
3.3

Regional Geology

The Site is located within the Coastal Plain Physiographic Province of North Carolina. The Coastal
Plain Physiographic Province extends from the Fall Line, a sinuous and erosionally-definedboundary separating the metamorphic and igneous rocks of the Piedmont Province to thenorthwest, to the present-day coast. The Coastal Plain Physiographic Province is characterized bya southeastward thickening wedge of late Cretaceous to Holocene age sediments that overlie a
Paleozoic age crystalline basement.
Based on the geologic map of North Carolina (NCGS, 1985), the Site is underlain by the Black
Creek Formation which ranges in age from early Campanian through early Maastrichtian of theLate Cretaceous epoch (approximately 66 to 84 million years ago; Sohl and Owens, 1991). The
Black Creek Formation is divided locally into three sub units from oldest to youngest: Tar Heel
Formation, Bladen Formation and Donoho Creek Formation. In general, the Black Creek
Formation is characterized by lignitic clay with thin beds and laminae of fine-grained micaceoussand as well as thick lenses of cross-bedded sand. The upper portion of the formation may also
contain glauconitic, fossiliferous clayey sand lenses.
3.4

Site Geology

Based on the lithology logged during onsite investigations (Parsons 2014, Parsons 2018a, Parsons2019), the Site is underlain by the following hydrogeologic units, listed below from ground surface
to depth (Figure 4):
1. A silty sand unit with thin discontinuous interbedded silt/clay lenses, referred to herein as
the Perched Zone.
2. A laterally discontinuous, stiff clay lens underlying the Perched Zone. This clay lensappears to be limited in lateral extent to the east, north and south by local topography andpinches out (terminates) to the west of the manufacturing area based on lithologic logging
and limited geophysical survey (Parsons, 2018a). The depth to the top of the clay lens isapproximately 15 to 18 feet bgs. The clay lens becomes thinner moving west across the
manufacturing area and ranges from approximately one foot to approximately 19 feet thick.

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3. Fine- to medium-grained sand interbedded with silt/clay lenses, the saturated portion ofwhich is herein referred to as the Surficial Aquifer. The sand extends to a depth ofapproximately 65 feet below ground surface (bgs) (elevation of +80 feet MSL).
4. Beneath the surficial unit is a 7 to 15 foot-thick, stiff, lignitic clay identified as the Black
Creek Confining Unit. This Cretaceous-aged, regionally-extensive unit is encountered at
the Site at an approximate elevation of +65 to +77 feet MSL. While the lateral continuityof this unit was verified north-south across the Site through lithologic borings, the eastwest extent of this unit has not been verified through borings (Parsons, 2014). However,during recent field work described in the Creeks, Old Outfall 002 and Seeps Assessment
Workplan (Geosyntec, 2019) this unit was observed to outcrop along the bluff face adjacentto the Cape Fear River, and along an embankment near Old Outfall 002 at similarelevations.
5. Beneath the Black Creek Confining Unit is the regionally-extensive Black Creek Aquifer,
which is approximately 8 to 20 feet thick and is encountered at depths between 80 and 100
feet bgs (elevation of approximately +45 to +65 feet MSL).
6. Beneath the Black Creek Aquifer is a massive dense clay (with minor sand stringers) thathas been identified as the Upper Cape Fear Confining Unit. This unit has not been fully
penetrated at the Site.
3.5

Site Hydrogeology

Hydrostratigraphic units of interest in the vicinity of the Site include a Perched Zone, the Surficial
Aquifer and the Black Creek Aquifer. While the Surficial Aquifer and Black Creek Aquifer are
regionally extensive features the Perched Zone is limited in extent to the top of the clay lens that
underlies most of the manufacturing area. These hydrostratigraphic units are described further
below (Figure 4):•

Perched Zone - Groundwater in the Perched Zone appears to be controlled by the
topography and lateral limits of the clay lens that underlies most of the manufacturing area
(Parsons 2017, 2019). Historically, groundwater in the perched zone appears to havemainly resulted from: (1) past seepage of water through the bottom of the North/South
Sediment Basins that are used to settle out solids from Cape Fear River water; (2) past
infiltration of water from the cooling water channel around the Monomers IXM Area, and(3) infiltration of rainfall. The sediment basins and the cooling water channel were lined in
November 2018 as part of the ongoing Site remedial actions to reduce infiltration to the
Perched Zone. In the latest assessment performed in October and November 2018

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(Parsons, 2019) Perched Zone water likely flows in a radial pattern away from apotentiometric high near the sedimentation basins. Where perched water is present, it isencountered from approximately 6 feet bgs at the basins to a depth of approximately 20
feet bgs along the edges of the Perched Zone west of the basins.
•

Surficial Aquifer – The Surficial Aquifer is encountered at approximately 40 feet bgs andextends to a depth of approximately 65 feet below ground surface (bgs) (elevation of
approximately +110 to +80 feet MSL). Groundwater elevations range from approximately
100 to 107 feet above MSL in the western areas of the Site to approximately 93 feet above
MSL in the eastern areas of the Site, indicating that groundwater flow is generally toward
the Cape Fear River. The water level of the Cape Fear River is typically near +30 feet MSL,
which is lower than the base elevation of the Surficial Aquifer. This elevation difference
suggests that water from the Perched Zone and the Surficial Aquifer will reach the Cape
Fear River from a potential combination of groundwater seepage on the hillslope andsubsequent flow to the Cape Fear River (observed), and potential infiltration to the Black
Creek Aquifer and subsequent discharge to the Cape Fear River.

•

The Black Creek Aquifer – The Black Creek Aquifer is potentially under semi-confined toconfined conditions at portions of the Site where it is separated from the overlying Surficial
Aquifer by the clay Black Creek Confining unit. As noted above, the lateral extent of theclay confining unit has not been verified towards the eastern portion of the Site.
Groundwater flow in the Black Creek Aquifer is toward the Cape Fear River. At the Site,
only the Black Creek Aquifer is in direct connection to the Cape Fear River with thepotential exception of the Surficial Aquifer during extreme flood events.

3.5.1

Groundwater Seeps

During recent field work being performed as part of the Creeks, Old Outfall 002 and Seeps
Assessment Workplan (Geosyntec, 2019) groundwater seeps were observed. This groundwater
seeped to surface where the Perched Zone, Surficial Zone and the Black Creek Aquifer intersect
the side of the bluff slope below the facility. The groundwater seeps out and flows towards theCape Fear River in a series of naturally occurring erosional channels (Figure 2). These channels
have been observed to contain a steady flow of water where they intersect groundwater. Thesechannels and the water that flows in them are herein referred to as Seeps. The three seeps observedon the eastern bluff adjacent to the Cape Fear River from north to south are named Seep A, Seep
B and Seep C.

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3.5.2

Tributaries to the Cape Fear River

In addition to the three on-site seeps (Figure 2), there are three perennial surface water featuresthat are tributaries to the Cape Fear River at or adjacent to the Site. To the north of the Site isWillis Creek, in proximity to the water intake for the Site. To the south of the Site is Georgia
Branch Creek which discharges to the Cape Fear River approximately 7,500 feet south of the W.O.
Huske Dam. At the Site is Old Outfall 002 which is fed by discharging groundwater. Old Outfall
002 discharges into the Cape Fear River approximately 1,350 feet south of W.O. Huske Dam.
3.6

PFAS Sources and Distribution in Environmental MediaPFAS associated with the Site are fluoroether compounds manufactured at the Site. Fluoroethers
are a fluorochemical with at least one ether bond (a carbon-oxygen-carbon bond) in the molecule.
Site-associated PFAS compounds are presently analyzed using the Table 3+ standard operating
protocol (SOP) method, a method developed by Chemours in conjunction with analyticallaboratories. Prior to the development of method Table 3+ SOP, method Table 3 SOP, which had
fewer PFAS analytes, was used.
The following subsection describes PFAS sources and distribution as they relate to constructing
the PFAS mass loading model for CO Paragraph 12(a) and (b). A more detailed presentation of
the sources and distribution of PFAS at Site will be prepared as part of the on and offsite
Assessment pursuant to CO Paragraph 18. PFAS impacts to environmental media have come fromprimarily wastewater conveyances, and industrial process activities resulting in emissions to air.
To date, PFAS have been analyzed for and detected in soil, groundwater, and surface water.
3.6.1

PFAS Distribution in Soil

Historical soil investigations have indicated that hexafluoropropylene oxide dimer acid (HFPODA) and other PFAS were detected in the site soil samples collected between depths of 0.0 to 10feet bgs; Parsons, 2018b).
3.6.2

PFAS Distribution in Onsite Groundwater

PFAS compounds have been detected in monitoring wells screened in each of the Perched Zone,
Surficial Aquifer and Black Creek Aquifer. Elevated concentrations of PFAS are generally
observed in the Perched Zone underneath the Monomers IXM Area. PFAS concentrations in theSurficial Aquifer are generally lower than the Perched Zone, by one to two orders of magnitude.
PFAS compounds were also detected in the Black Creek Aquifer wells installed below the
manufacturing area. PFAS detections have also been reported in the five LTW wells adjacent theCape Fear River.

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3.6.3PFAS Distribution in Surface Water

On and near-site surface water features including the Cape Fear River, Old Outfall 002, two
tributaries adjacent to the Site (Willis Creek and Georgia Branch) and onsite Seeps (Seep A, SeepB, and Seep C) have been investigated (Geosyntec, 2018b; Geosyntec, 2018c; Geosyntec 2019;
Parsons, 2018c). Additional data continue to be collected for these features through ongoing
additional investigations (Geosyntec, 2019).
Results of the completed investigations previously reported show PFAS compounds were detectedin these surface water features. Perflourinated carboxylic acid (PFCAs), e.g. perfluorooctanoic
acid (PFOA) and Perfluorinated sulfonic acids (PFSAs) e.g. perfluorosulfonic acid (PFOS) weredetected throughout the Cape Fear River watershed and in the Cape Fear River are unrelated to theSite (Geosyntec, 2018c). The investigations also showed that HFPO-DA (i.e. GenX) and other Site
Associated PFAS analyzed by method Table 3 / Table 3+ were detected in the Cape Fear Riverafter the Site and are associated with the Site.
There are two surface water intakes along the Cape Fear River for public utilities; Bladen Bluff(7.5 miles downstream from the Site) and King’s Bluff Intake Canal (55 miles downstream fromthe Site). Approximately half the detected total PFAS load at King’s Bluff are potentiallyassociated with sources upstream of the Site while the remainder are potentially associated with
the Site (Geosyntec, 2018c).
3.7

Potential PFAS Transport Pathways to Cape Fear River

Potential pathways for PFAS originating from releases at Site to reach the Cape Fear River wereidentified by reviewing available Site data at the time of developing this scope. Nine potential
pathways (Table 1) were identified as potentially contributing to observed in-river PFAS
concentrations. These pathways represent compartments to model as part of the PFAS loading
model. The potential pathways are listed below, and shown on the conceptual diagram provided
in Figure 5:
Transport Pathway 1:

Contributions from non-Chemours related sources upstream of theSite in the Cape Fear River;Transport Pathway 2:

Groundwater discharge to Willis Creek and stormwater to Willis
Creek;

Transport Pathway 3:

Direct aerial deposition on the Cape Fear River and its tributaries;

Transport Pathway 4:

Inflow from Outfall 002 including Site stormwater;

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Transport Pathway 5:

Inflow from groundwater seeps;

Transport Pathway 6:

Upwelling groundwater contribution from onsite discharge of Black
Creek Aquifer groundwater;

Transport Pathway 7:

Groundwater discharge to Old Outfall 002 and stormwater runoff;

Transport Pathway 8:

Off-Site groundwater discharge from locations upstream anddownstream of the Site to the Cape Fear River; and,Transport Pathway 9:

Groundwater discharge to Georgia Branch Creek and stormwaterrunoff.

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PFAS MASS LOADING MODEL DESIGNThis section describes how the PFAS Mass Loading Model will be developed. The objective of
the model is to assess the relative contributions of PFAS mass loadings from the various transport
pathways by which PFAS originating from Site can reach the Cape Fear River. The modelcomprises multi-compartments that describe bulk PFAS mass transfer to the Cape Fear River.
Each compartment represents a pathway that has been parameterized primarily using sitemeasured data. This approach is designed to identify broad trends in mass loading to the Cape
Fear River for a range of conditions and support identification of potential target pathways foractions to achieve objectives for mass load and corresponding concentration reductions of Siteassociated PFAS in the Cape Fear River.
Site associated PFAS concentrations in the Cape Fear River are controlled by the PFAS massloading to the Cape Fear River and the volume of water flowing through the Cape Fear River.
PFAS mass load entering the Cape Fear River is defined in this model as the combined mass perunit time or mass load (e.g. nanograms per second) from potential pathways identified in Section
3.5 above. Total PFAS mass load entering the Cape Fear River is calculated as:
𝑛𝑛=9 𝑖𝑖=56

𝐶𝐶𝐶𝐶𝐶𝐶𝑇𝑇𝑇𝑇 =where,

𝑛𝑛=9 𝑖𝑖=56⎧
� � 𝑀𝑀𝑛𝑛,𝑖𝑖 = � � �𝐶𝐶𝑛𝑛,𝑖𝑖 × 𝑄𝑄𝑛𝑛 � ∶ 𝑄𝑄𝑛𝑛 → 𝑤𝑤𝑤𝑤𝑤𝑤.
⎪⎪𝑛𝑛=1 𝑖𝑖=1
𝑛𝑛=1 𝑖𝑖=1⎨𝑛𝑛=9 𝑖𝑖=56
𝑛𝑛=9 𝑖𝑖=56⎪⎪ � � 𝑀𝑀𝑛𝑛,𝑖𝑖 = � � �𝐶𝐶𝑛𝑛,𝑖𝑖 × 𝑄𝑄𝑛𝑛 � ∶ 𝑄𝑄𝑛𝑛 → 𝑑𝑑𝑑𝑑𝑑𝑑.
⎩𝑛𝑛=1 𝑖𝑖=1
𝑛𝑛=1 𝑖𝑖=1

CFRTM = total PFAS mass load entering the Cape Fear River measured in mass per unit time
[MT-1], typically nanograms per second.
n = represents each of the 9 potential PFAS transport pathways listed in Table 1.
i = represents each of the 56 PFAS constituents listed in Table 2.
Mn,i = mass load of each PFAS constituent i from each potential pathway n with measured
units in mass per unit time [MT-1], typically nanograms per second.
Cn,i = concentration of each PFAS constituent i from each potential pathway n with measured
units in mass per unit volume [ML-3], typically nanograms per liter.

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Qn = volumetric flow rate from each potential pathway n with measured units in volume pertime [L3T-1], typically liters per second, for two flow scenarios representing storm (wet.) andquiescent (dry.) conditions.
The Site associated PFAS mass loading for each potential pathway will be estimated using theapproaches described in the following sub-sections. The result of these estimates will then be used
to calculate the total PFAS mass loading of Site related PFAS using the above formula. A similar
analytical mass loading model was previously developed for HFPO-DA in February 2018
(Appendix A of Parsons, 2018a; Appendix A). The model was able to estimate HFPO-DA
concentrations in the Cape Fear River at two downstream utility intake locations, Bladen Bluffs
and Kings Bluff Intake Canal.
Model inputs for each potential pathway (i.e., PFAS concentrations and volumetric flow of water)
will be a combination of measured data, calculations and best estimates, as available at the time ofmodel development. Table 1 summarizes both the transport pathways and the type of model input
data proposed to be used for developing this model and is discussed further below. Measured
model inputs will come from two characterization events conducted in 2019. One event will be a“dry weather” event representing baseflow conditions and the other will be a “wet weather” event
captured during a storm event. The following subsections describe how PFAS mass loading fromthe different PFAS transport pathways listed in Table 1 will be estimated in the model and fieldwork that will be performed to support these estimations.
4.1

Upstream Cape Fear River (Transport Pathway 1)

The estimated upstream PFAS mass loading contribution to Cape Fear River will be estimatedusing measured Cape Fear River concentration and flow data. Sampling locations, analyticalmethods and assessment techniques for PFAS concentrations in the Cape Fear River will generally
follow the Creeks, Old Outfall 002 and Seeps Assessment Workplan (Geosyntec, 2019). As notedin this document, one sample was collected immediately upstream of the Site (River Mile 76) toestimate upstream PFAS mass loading contribution to Cape Fear River. Another sample wascollected approximately 7 miles downstream of the Site (River Mile 84) for model calibration(Section 5). Both samples were collected at the thalweg (i.e., deepest point of the river transect) at
mid-depth in the water column. An additional upstream sample (e.g., 10 miles upstream of theSite) will also be collected for additional model refinements. The Cape Fear River volumetric flowrate will be obtained from the USGS flow gauging station at the W.O. Huske Dam, ID 02105500(USGS, 2018).

PFAS Loading Model Scope of Work

12April 2019

4.2

Tributaries – Willis Creek, Georgia Branch Creek, and Old Outfall 002 (Transport
Pathways 2, 7 and 9)

Tributaries contributing to PFAS mass loading into the Cape Fear River include Willis Creek,
Georgia Branch Creek, and Old Outfall 002. Mass loading of PFAS from these tributaries to theCape Fear River will be estimated using measured PFAS concentrations and flow data. PFAS
samples will be collected at each tributary at a location near the discharge point to the Cape Fear
River, but still far enough upstream in the tributary where they are not potentially influenced by
the Cape Fear River (e.g., Old Outfall 002 channel mouth sampling location in Figure 1). Sample
locations and methods are outlined in the Creeks, Old Outfall 002 and Seeps Assessment Workplan(Geosyntec, 2019).
Volumetric discharge rates for the tributaries will be obtained from two independent flow
measurement methods as outlined in the Creeks, Old Outfall 002 and Seeps Assessment Workplan(Geosyntec, 2019): (1) point velocity measurements and the cross-sectional area of the stream
using the Mean Section Method (Rantz, 1982), and (2) salt dilution gauging.
For the Old Outfall 002 at the water capture and treatment location Option B, a flume or a weir
will be installed to provide an enhanced assessment of baseflow volumes and for the mass loading
model, including how flow volumes vary with storm events.
4.3

Aerial Deposition to the Cape Fear River (Transport Pathway 3)

The mass loading from direct aerial deposition of PFAS to the Cape Fear River will be estimatedusing air deposition modeling results for HFPO-DA from the Site (ERM, 2018). Based on thereported aerial extent and deposition contours, average deposition rates to the Cape Fear River will
be calculated. Calculated deposition rates will be combined with the river surface area and theresidence time of flowing Cape Fear River water to estimate a mass loading from aerial deposition.
A similar approach was employed when previously estimating the HFPO-DA mass loading due toaerial deposition (Appendix A). The mass loading of other PFAS compounds will be estimatedby using the relative concentration ratios of other Site associated PFAS to HFPO-DA based on
measured concentrations from offsite wells.
4.4

Onsite Groundwater (Transport Pathways 5 and 6)

Based on the current characterization of the Site, there are two groundwater PFAS mass loading
pathways to the Cape Fear River. First, the indirect pathway of groundwater to seeps to river, andsecond, the direct pathway of Black Creek groundwater discharging directly to the river.

PFAS Loading Model Scope of Work

13

April 2019

4.4.1

Indirect Pathway – Groundwater to Seeps to River (Transport Pathway 5)

The PFAS mass loading from the seeps to the Cape Fear River will be estimated using measured
PFAS concentrations and seep volumetric flow rates. The flow rates and PFAS concentrations of
the three seep features that discharge to the Cape Fear River were measured as part of the field
effort for the Creeks, Old Outfall 002 and Seeps Assessment Workplan (Geosyntec, 2019). These
data, and one more dataset to be collected during a wet event will be used to assess the PFAS massloading into the Cape Fear River. Additionally, at the mouth of each seep a flume or a weir will be
installed to measure the baseflow volumetric flow rates in the seeps and the increase in flow rates
during storm events.
4.4.2

Direct Pathway – Black Creek Groundwater Discharge to River (Transport
Pathway 6)

At site, only the Black Creek Aquifer is in hydraulic connection with the Cape Fear River.
Therefore, only the Black Creek Aquifer discharges directly into the Cape Fear River. The PFAS
mass loading of discharging onsite Black Creek Aquifer groundwater to the Cape Fear River will
be developed using two different approaches:•a forward assessment based on Darcy’s Law using hydrogeological data; and•an inverse calculation using results from the PFAS mass loading model.

The forward assessment onsite groundwater mass loading will be estimated using groundwater
concentration data from LTW wells at the Cape Fear River bank and volumetric discharge
calculated using Darcy’s Law from the following measured or estimated inputs (1) hydraulicgradient from LTW Well water level data and Cape Fear River water gauge height reported from
USGS (USGS, 2018); (2) representative discharge area; and (3) hydraulic conductivity.
The inverse approach will calculate the contribution of onsite groundwater by first calculating thetotal PFAS mass load in the Cape Fear River from measured in Cape Fear River concentrations
and flow rates. Then the onsite groundwater estimate will be calculated by subtracting the valueof all other pathways from the calculated Cape Fear River PFAS mass load. The difference
between these two numbers will be attributed to pathways non-quantitated, in this case onsite
groundwater discharge.
Two approaches are proposed to assess onsite groundwater mass loading since the forward
groundwater mass loading estimate has much more uncertainty than the mass loading estimates
for the outfalls or creeks. This is because the groundwater mass loading estimates are based on
measured concentrations and calculated (estimated) flow values. Groundwater flow can be highly

PFAS Loading Model Scope of Work

14

April 2019

heterogenous, and hydraulic conductivity can vary by two orders of magnitude in the same aquifer.
Consequently, this leads to uncertainty in groundwater discharge rates that also can span twoorders of magnitude. By contrast, the uncertainty in the mass loading estimates for the creeks,
seeps and Outfall 002 is much more constrained since all the water carrying the PFAS mass load
for each feature is present at surface in defined channel and can relatively easily and with muchgreater certainty have flow rates measured (i.e. salt dilution gauging, flumes or weirs, etc.).
4.5

Outfall 002 and Facility Stormwater Runoff (Transport Pathway 4)

The mass loading of PFAS from Outfall 002 to the Cape Fear River will be estimated using
measured PFAS concentrations and measured Outfall 002 volumetric flowrates. Chemours
collects two composite samples of Outfall 002 water each week for analysis for HFPO-DA and
Table 3 compounds. The results of these analyses will be used in the PFAS Loading Model.
Chemours also records the volume of flow discharging to the Cape Fear River from Outfall 002
daily. These flow values will be used in the PFAS Loading Model. These data will capture allwater flowing through Outfall 002. This includes non-contact cooling water, treated nonChemours process wastewater (DuPont and Kuraray process water), treated sanitary water andstormwater within the manufacturing area of the Site.
4.6

Offsite Groundwater (Transport Pathway 8)

The offsite groundwater PFAS mass loading contributions will be estimated by first separating
offsite discharging groundwater into different zones. In each zone, the discharge mass loading willbe estimated using residential well PFAS concentration data and volumetric discharge rateestimated using Darcy’s Law from the following measured or estimated inputs (1) hydraulicgradient from available well water level data and Cape Fear River water gauge height reported
from USGS (USGS, 2018); (2) representative discharge area; and (3) hydraulic conductivity.
4.7

Summary of Supporting Field Work

Field work will be performed to help support the development of the PFAS mass loading model.
The three planned field work components are described in the list below:
1. Concentration and flow rate measurements at the mouths of the tributaries and seeps andin the Cape Fear River as described in the Creeks, Old Outfall 002 and Seeps Assessment
Workplan (Geosyntec 2019). This effort was performed during dry weather. This fieldwork was completed in early February 2019, with the exception of sampling at Georgia
Branch Creek where access agreements are still pending for certain locations in the creek.

PFAS Loading Model Scope of Work

15

April 2019

2. Wet weather sampling and flow rate measurements at mouths of the tributaries and seeps
and in the Cape Fear River as described in the Creeks, Old Outfall 002 and Seeps
Assessment Workplan (Geosyntec 2019). This field work has not yet been performed.
3. Installation of V-notch weirs of flumes at the CO Paragraph 12(e) identified treatment
location for Old Outfall 002 and at the mouth of the three seeps from Site that flow into theCape Fear River. Weirs and flumes both provide a method to estimate stream water flowby inspecting the water level flowing through the device. The higher the water level, thefaster the flow. Level loggers will be placed in the flumes or weirs to record the flow rategoing through these locations on 10-minute intervals based on a calculation convertingwater level to flow rate.
The Old Outfall 002 location was selected since its baseflow needs to be established forcompliance with the consent order. The seeps were selected as additional flume or weir
locations because of their anticipated importance to the PFAS reductions plan. Preliminary
data and analyses indicate that together the seeps and Old Outfall 002 contribute in excess
of 50% of the PFAS load to the Cape Fear River. This field work has not yet been
performed.
4. Slug testing of the five LTW wells to measure the hydraulic conductivity of Black Creek
Aquifer near the Cape Fear River. These data will support the estimates of onsite
groundwater discharge. This field work has not yet been performed.

PFAS Loading Model Scope of Work

16

April 2019

5.

MODEL CALIBRATION AND SENSITIVITY ANALYSISThe PFAS mass loading model will be calibrated in order to help provide accurate and relevant
estimates of pathway contributions to Cape Fear River and benefits from potential reduction
actions. Then the sensitivity of the model to potential variability of input parameters will beassessed to understand the uncertainties in the model and which parameters have the greatest
influence on PFAS loads in the Cape Fear River. Both the calibration and sensitivity scope of work
are described in the subsections below.
5.1

Model Calibration

The total PFAS mass loading will be calculated from the concentration and flow data collected forthe mass loading components in Table 1 during both a dry weather time period (i.e., baseflow
conditions) and during a storm event. The performance of the PFAS mass loading model will beassessed by doing a mass balance calculation by summing the mass loading pathways andcomparing the result to estimated mass loads in the Cape Fear River based on measurements ofCape Fear River PFAS concentrations and volumetric flow rates. These data will be collected by
Chemours, and potentially from third party data sources such as CFPUA depending on the timing,
availability and appropriateness of these data (i.e. raw water data analyses are required for thisanalysis, not finished water analyses). The model will then be calibrated by adjusting parameters
within ranges of assumed or observed measurement variabilities. A first iteration of this model
was calibrated similarly as presented in the Mass Flux Assessment in Appendix A of the Parsons,
2018a Focused Feasibility Study Report – PFAS Remediation. This earlier version created a
predictive model of Cape Fear River concentrations that was calibrated by varying the hydraulicconductivity parameter for discharging groundwater. Notably, this earlier iteration did not include
the groundwater seeps which had not yet been identified. Based on initial data, to be reported indetail in as part of this modeling scope of work, the groundwater seeps comprise a significant
fraction of the PFAS mass load previously ascribed to discharging groundwater.
5.2

Sensitivity Analysis

A sensitivity analysis will be performed to assess potential uncertainties in modeled results,
specifically how the potential range of model input parameters values affects the estimated PFAS
mass loads in the Cape Fear River. The sensitivity analysis will identify model input parametersthat have the greatest effect on calculated mass loads in the Cape Fear River. Elements that will
be included in the sensitivity analysis include evaluating model sensitivities to varying:•

Aerial deposition rates for PFAS;

PFAS Loading Model Scope of Work

17

April 2019•Flow rates at Willis Creek, Georgia Branch, Old Outfall 002 and Seep A, Seep B, and SeepC;•

Calculated discharging groundwater flow rate;•

Offsite groundwater discharge rates; and•PFAS concentrations.

Additional model input parameters may be identified during the model calibration process.
Reductions in model uncertainties will be attempted through additional field and/or analyticaleffort as necessary and possible in the timeframe available.

PFAS Loading Model Scope of Work18

April 2019

6.

SUMMARY

This document described a scope of work for preparing a PFAS mass loading model. The model
will estimate the mass load of PFAS associated with the Site reaching the Cape Fear River by
estimating and then summing the PFAS loads from the identified PFAS transport pathways. The
model will be used to evaluate which pathways contribute the greatest load of PFAS originatingfrom the Site to the Cape Fear River. The outcome of this assessment will form the basis for
identifying which pathways to address and then assessing the benefits of potential actions on thesepathways to reduce PFAS loading to the Cape Fear River. The final outcome of this effort will be
a Cape Fear River PFAS Loading Reductions Plan that describes the actions, supported by interim
bench marks, that Chemours proposes implementing within a two- or five-year time period to
reduce PFAS loads at downstream water intakes.

PFAS Loading Model Scope of Work

19

April 2019

7.

REFERENCES

ERM, 2018. Modeling Report: HFPO-DA Atmospheric Deposition and Screening Groundwater
Effects. 27 April 2018.
Geosyntec, 2018a. Assessment of Impact of Current and Anticipated Reduced Air Emissions on
Groundwater Concentrations of HFPO Dimer Acid in the Vicinity of the Chemours
Fayetteville Works. 27 April 2018.
Geosyntec, 2018b. Stormwater Sampling Report. 29 March 2018.
Geosyntec, 2018c. Assessment of the Chemical and Spatial Distribution of PFAS in the Cape Fear
River. 17 September 2018.
Geosyntec, 2019. Creeks, Old Outfall 002 and Seeps Assessment Workplan. 12 February 2019.
NCGS, 1985. Geologic Map of North Carolina.
Parsons, 2014. Final RCRA Facility Investigation report (Rev. 1). February 2014; Revised August
2014.
Parsons, 2017. Additional Investigation Work Plan. 31 October 2017.
Parsons, 2018a. Focused Feasibility Study Report– PFAS Remediation. February 2018.
Parsons, 2018b. Additional Site Investigation Report. 30 March 2018.
Parsons 2018c. Former Outfall Sampling Investigation Technical Memorandum. 29 March 2018.
Parsons, 2019. Southeast Perched Zone Investigation Report. March 2019.
Rantz, 1982. Measurement and Computation of Streamflow: Volume 1. Measurement of Stage
Discharge. Geological Survey Water-Supply a Paper 2175. 1982.
Sohl, N.F., and Owens, J.P. Cretaceous Stratigraphy of the Carolina Coastal Plain. 1991.
USGS, 2018. National Water Information System: Web Interface. Accessed March 2019.
https://waterdata.usgs.gov/nwis/uv?site_no=02105500

PFAS Loading Model Scope of Work

20

April 2019

TABLESTABLE 1
PFAS MASS LOADING MODEL POTENTIAL PATHWAYS
Chemours Fayetteville Works, North Carolina

Transport
Pathway No.

PFAS Transport Pathway

Concentration Data1

Geosyntec Consultants of NC, PC

Flow Data1

1

Up-Stream Cape Fear River

Measured from samples collected in theCape Fear River

2

Willis Creek

Measured from samples collected in Willis Measured from salt dilution gauging andCreekflow velocity meter data

3

Aerial Deposition onCape Fear River

Estimated from air deposition modelling
results2

Estimated from air deposition modelling
results2

4

Outfall 002

Measured from composite samples
collected from Outfall 002

Measured daily Outfall 002 flow rates arerecorded by Site Staff.

5Groundwater Seeps (Seep A, Seep B
and Seep C)

Measured from samples collected in the
seeps

Measured from salt dilution gauging andweir data

6

Upwelling On-Site Groundwater

Measured from samples collected from
LTW wells adjacent to the River

Estimated based on measured andestimated hydrogeological parameters

7

Old Outfall 002

Measured from samples collected in Old
Outfall 002

Measured from salt dilution gauging, flow
meter and weir data

8

Off-Site Groundwater(Up & Downstream)

Measured from groundwater samples
collected at residences near the River

Estimated based on measured andestimated hydrogeological parameters

9Georgia Branch Creek

Measured from samples collected in
Georgia Branch Creek

Measured from salt dilution gauging andflow velocity meter data

Estimated from flow data measured at Siteat the W.O. Huske Dam

Notes
1 - Flow and concentration data are multiplied together to estimate the PFAS mass load in the Cape Fear River originating from each pathway.
2 - ERM, 2018. Modeling Report: HFPO-DA Atmospheric Deposition and Screening Groundwater Effects. 27 April 2018.

April 2019

TABLE 2
ANALYTICAL METHODS AND ANALYTE LIST
Chemours Fayetteville Works, North Carolina

Analytical Method Common Name
HFPO-DAPEPAPFECA-GPFMOAAPFO2HxAPFO3OAPFO4DA
PMPA
Hydro-EVE Acid
EVE Acid
MMF
MTP
Table 3+ Lab SOP
PPF Acid
PFECA B
R-EVE
PFO5DA
Byproduct 4
Byproduct 6
Byproduct 5
DFSA
NVHOS
PES
PFESA-BP1
PFESA-BP2
PFBA
PFDA
PFDoA
PFHpA
PFNA
PFOA
PFPeA
PFPeA
PFTeA
PFTriA
PFUnA
PFBS
PFDS
PFHpS
PFHxS
EPA Method 537 PFNS
Mod
PFOS
PFPeS
10:6 FTS
4:2 FTS
6:2 FTS
8:2 FTS
NEtFOSAA
NEtPFOSANEtPFOSAE
NMeFOSAA
NMePFOSA
NMePFOSAE
PFDOS
PFODA
PFODA
PFOSA

Chemical Name
Hexafluoropropylene oxide dimer acid
Perfluoroethoxypropyl carboxylic acid
Perfluoro-4-isopropoxybutanoic acid
Perfluoro-2-methoxyaceticacid
Perfluoro(3,5-dioxahexanoic) acid
Perfluoro(3,5,7-trioxaoctanoic) acid
Perfluoro(3,5,7,9-tetraoxadecanoic) acid
Perfluoromethoxypropyl carboxylic acid
Perfluoroethoxsypropanoic acid
Perflouroethoxypropionic acid
Difluoromalonic acid
Perfluoro-2-methoxypropanoic acidPentafluoropentionic acid
Perfluoro-3,6-dioxaheptanoic acid
R-EVE
Perfluoro-3,5,7,9,11-pentaoxadodecanoic acid
Byproduct 4
Byproduct 6
Byproduct 5
Difluoro-sulfo-acetic acid
Perflouroethoxysulfonic acid
Perfluoroethoxyethanesulfonic acid
Byproduct 1
Byproduct 2
Perfluorobutanoic acid
Perfluorodecanoic acid
Perfluorododecanoic acid
Perfluoroheptanoic acid
Perfluorononanoic acid
Perfluorooctanoic acid
Perfluorohexanoic acid
Perfluoropentanoic acid
Perfluorotetradecanoic acid
Perfluorotridecanoic acid
Perfluoroundecanoic acid
Perfluorobutanesulfonic acid
Perfluorodecanesulfonic acid
Perfluoroheptanesulfonic acid
Perfluorohexanesulfonic acid
Perfluorononanesulfonic acid
Perfluorooctanesulfonic acid
Perfluoropentanesulfonic acid
10:2-fluorotelomersulfonic acid
4:2 fluorotelomersulfonic acid
6:2 fluorotelomersulfonic acid
8:2 fluorotelomersulfonic acid
NEtFOSAA
NEtPFOSANEtPFOSAE
NMeFOSAA
NMePFOSA
NMePFOSAE
Perfluorododecanesulfonic acid
Perfluorohexadecanoic acid
Perfluorooctadecanoic acid
Perfluorooctanesulfonamide

CASN

Chemical Formula

13252-13-6
C6HF11O3
267239-61-2 C5HF9O3
801212-59-9 C12H9F9O3S
674-13-5
C3HF5O339492-88-1
C4HF7O439492-89-2
C5HF9O539492-90-5
C6HF11O6
13140-29-9
C4HF7O3773804-62-9 C8H2F14O4
69087-46-3
C8HF13O4
1514-85-8
C3H2F2O4
93449-21-9
C4H4F4O3
422-64-0
C3HF5O2
151772-58-6 C5HF9O4
N/A
C8H2F12O5
39492-91-6
C7HF13O7N/A
C7H2F12O6S
N/A
C6H2F12O4S
N/A
C7H3F11O7S
422-67-3
C2H2F2O5S
1132933-86-8 C4H2F8O4S
113507-82-7 C4HF9O4S
29311-67-9
C7HF13O5S
749836-20-2 C7H2F14O5S
C4HF7O2
375-22-4
C10HF19O2
335-76-2
307-55-1
C12HF23O2
C7HF13O2
375-85-9
C9HF17O2
375-95-1
C8HF15O
335-67-1
C5HF9O2
307-24-4
C5HF9O2
2706-90-3
376-06-7
C14HF27O2
72629-94-8
C13HF25O2
2058-94-8
C11HF21O2
C4HF9SO
375-73-5
335-77-3
C10HF21O3S
375-92-8
C7HF15O3SC6HF13SO3
355-46-4
68259-12-1
C9HF19O3S
1763-23-1
C8HF17SO3
2706-91-4
C5HF11O3S
120226-60-0 C12H5F21O3
757124-72-4 C6H5F9O3S
27619-97-2
C8H5F13SO3
39108-34-4
C10H5F17O3S
2991-50-6
C12H8F17NO4S
4151-50-2
C10H6F17NO2S
1691-99-2
C12H10F17NO3S
2355-31-9
C11H6F17NO4S
31506-32-8
C9H4F17NO2S
24448-09-7
C11H8F17NO3S
79780-39-5
C12HF25O3S
67905-19-5
C16HF31O2
16517-11-6
C18HF35O2
754-91-6
C8H2F17NO2S

Geosyntec Consultants of NC, PC

PQL (ng/L)
TestAmerica
Eurofins Lancaster
2.0
2.0
20
20
2.0
2.0
5.0
5.0
2.0
2.0
2.0
2.0
2.0
2.0
10
10
2.0
2.0
2.0
2.0
100
100
20
20
20
20
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
100
100
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
5.5
2.0
1.8
2.0
1.8
2.0
0.91
2.0
1.8
2.0
0.91
2.0
1.8
2.0
5.5
2.0
0.91
2.0
0.91
2.0
1.8
2.0
0.91
2.0
1.8
2.0
1.8
2.0
1.8
2.0
1.8
2.0
1.8
2.0
1.8
2.0
2.7
20
2.7
20
1.8
20
5.5
20
2.7
2.0
8.2
2.0
2.7
20
2.7
2.0
8.2
2.0
2.7
2.0
0.91
2.0
0.91
2.0
1.8
2.0
2.7

Notes:EPA - Environmental Protection Agency SOP - Standard Operating Protocol
PQL - practical quantitation limit
ng/L - nanograms per liter
PFAS - per- and polyfluoroalkyl substances

April 2019

FIGURES

Cape Fear River

Willis Creek Mouth
Site River Water Intake

Seep A

Seep BNC Highway 87

Outfall 002
Seep C

W.O. Huske Dam

Old Outfall Channel Mouth

Path: E:\TR0726\CapeFear_Report_2019\TR0726_SiteFeatures.mxd; JK; 04/10/2019

Georgia Branch Creek Mouth

LegendAreas at Site

Site Features

Chemours Monomers IXMCape Fear River

Chemours PPA

Nearby Tributaries
Observed Seep (Natural Drainage)

2,000

1,000

2,000 Feet

Site Location Map

Dupont / Dow Leased
Former Teflon Production

0

Chemours Fayetteville Works, North Carolina

Kuraray America Leased
Site Drainage Network

Wastewater Treatment Plant

FigureSite Boundary
Notes:
Basemap Sources: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID,
IGN, and the GIS User Community

Raleigh

April 20191

Willis Creek

Seep A
Site Drainage Network
To Outfall 002

Seep B

Outfall 002
Seep C

W.O. Huske Dam

Old Outfall 002

Georgia Branch Creek

Legend2,000
Site Features

Site Drainage Network

Chemours Fayetteville Works

Observed Seep (Natural Drainage)

Cape Fear River

1,000

0

2,000 Feet

Site Topographic Map
Chemours Fayetteville Works, North Carolina

Nearby Tributaries
Notes:
Basemap sources: Esri, Garmin, USGS, NPS (World Terrain Reference); Esri, USGS, NGA, NASA,CGIAR, N Robinson, NCEAS, NLS, OS, NMA, Geodatastyrelsen, Rijkswaterstaat, GSA, Geoland, FEMA,Intermap and the GIS user community (World Hillshade)

FigureRaleigh

April 20192

Virginia

Ha w R

Greensboro

i ve

r

North
Carolina

Raleigh
R
Deep
iver

Start ofCape FearRiver
LittleR iv

er

WO Huske
Lock and Dam

FayettevilleChemours
Fayetteville
WorksBladen Bluffs
Intake
Ca

pe
F
ea

rR

iver

Cape Fear Lockand Dam #1/
Kings Bluff Intake Canal

Wilmington

South
Carolina

20

LegendChemours Fayetteville Works

Upper Basin

Cape Fear River

Middle Basin

10020 MilesCape Fear River Watershed and Downstream
Public Utility Intakes
Chemours Fayetteville Works, North Carolina

Lower Basin

Notes:
Basemap sources: Esri, Garmin, USGS, NPS (World Terrain Reference); Esri, USGS, NGA, NASA,CGIAR, N Robinson, NCEAS, NLS, OS, NMA, Geodatastyrelsen, Rijkswaterstaat, GSA, Geoland, FEMA,Intermap and the GIS user community (World Hillshade)

FigureGuelphApril 20193

NAF-08A/08B

NAF-01

SMW-07

SMW-08/08B

SETTLING
BASINS(SILTY)

SMW-08
SMW-8B!
A

SMW-06
SMW-6B

!
PZ-12
A
!
A
!
A
!
!
A
A
SMW-07
!
A

PZ-11

!
WA

MW-22D MW-16D!!
MW-22DAA

MW-17DPERCHED
ZONE

!
A

PZ-21
NAF-03!
!
NAF-04
BCA-03 MW-15D! NAF-01
NAF-12!!
!
PZ-20
MW-15DR!
NAF-08A!
!
! NAF-08B
RW-02
FTA-01! PZ-19!
NAF-09
FTA-02 ! ! !
NAF-10
PZ-10!
! PZ-13
FTA-03!
! PZ-14
MW-7S!
MW-13D
PZ-18
MW-12S

A

A

A

A A

LTW-04
PZ-22

!
A

SAND
(MEDIUM GRAINED)

120'

CLAY

CLAY

CLAY

LTW-03

E

A A

A
!
A
MW-8S
MW-1S
!!
A
!
A
A
MW-2S
MW-14D!
A!
A
MW-9S PZ-15
PZ-L
!
A
!
!
A
A
PZ-17
!
A ! MW-11
A

130'

!
A

A

A

A
A AA

SAND

!
!
A
A

A
A

A

AA

(SILTY)SAND

LTW-02
PZ-23

NAF-11A!
A
NAF-06
A
NAF-02
NAF-05B!
!
A!
NAF-05AA!
A!

(SILTY)140'

NAF-11B

NAF-07

!
A

r
R ive

150'

SMW-05P
SMW-05ear

MW-17D

160'

INSET

e F
Cap

WEST

MW-15D/BCA-03

!
A

0

500

!
A

1,000

2,000
Feet

LTW-05

!
A

SAND

110'

BCA-02
PZ-16
!
!

A

SAND
BCA-04

!
A

CLAY

S

100'

SURFICIALAQUIFER

?

CLAY

90'

SAND

CLAY
80'

?

Drainage Ditch

CLAY

CLAY

!
A
!
A
!
A

70'

Black Creek Aqu
Perched Water Z
Surficial Aquifer
Cross Sections
Plant Border

LTW-0360'

SAND (MEDIUM GRAINED)BLACK CREEK AQUIFER

PE&I

50'

4701 Hedg emore Dr.
Charlotte, NC 28209?

Hydrology Line
Drawn:
C. Oneal
Revision:

Cross Section Location Map
Additional Site Investigation
Chemours Fayetteville Works
Fayetteville, North Carolina

1

Date:
1/9/2018

File Project Number:
449338.01050

Figure Number: 14

Name: Cross_Sections

40'(SILTY & CLAYEY)

30'

EAST

CLAY
CAPE FEAR
RIVER

20'

10'

TO -58' MSL
0
0

500'

1000'

2000'

1500'

2500'

3000'

3500'

4000'

4500'

5000'

5500'

6000'

6500'

Legend

7000'

7500'

Site Geology Cross-Section
Black Creek Aquifer Potentiometric Surface

Lithology

Clay

Perched Water Potentiometric Surface

Lithology (Inferred)

Sand

Surficial Aquifer Water Table

Scale Bar

Potentiometric Surface (? Where Inferred)

Well Screened
Interval

Chemours Fayetteville Works, North Carolina

FigureSource:Parsons, 2018b. Revised Additional Site Investigation Report. 30 March 20184
Raleigh

April 2019

(3) Aerial Deposition
Rain(4) Outfall 002 (Pipe to River)Non-contact cooling water from river
Non-Chemours treated process water
Stormwater
Chemours
Fayetteville Works
Manufacturing Area

Rain

(1) Upstream
Cape Fear River

Seep A

(2)
Wil
lis

Seep B

e

Zon
ched

Per

uifer

l Aq

Perched Zone Clay

cia
Surfi

und

wa

O

nd

Ou
tfa

02
ll 0

B

ite
f-S
Of
(8)

ro
u

nc

hC
ree
k

Seep C

ver

r Ri

ea
eF

p

Si
n-

(7)

a
gi
or

ra

G

ld

ter

Ca

te

(9
)G
e

ek

(5) Groundwater
Seeps

O
(6)

eek
k Cr rBlac Aquife

Black Creek
Confining Unit

Gro

Cre

Gr
ou

nd w

ater

(8
Gr ) Off-soun ited w at e r

W.O. Huske
Dam

wat
er

Potential PFAS Pathways to the Cape Fear River from Site
Chemours Fayetteville Works, North Carolina

Note:
Figure is schematic depicting potential PFAS transport pathways
to the Cape Fear River at and near Site. The figure is not to scale.

Figure5
Raleigh

April 2019

APPENDIX A
Supplemental Information

Parsons, 2018a. Focused Feasibility Study Report – PFAS Remediation, Chemours
Fayetteville Works. RCRA Permit No. NCD047362642-R2-M3.

APPENDIX A
MASS FLUX ASSESSMENT

CAPE FEAR RIVER DIMER ACID CONCENTRATION
AND MASS FLUX ASSESSMENT SUMMARY

Dimer Acid is present in the Cape Fear River (the river) down river of the Chemours
Fayetteville Works Site (the Site). Dimer Acid river concentrations are controlled by
Dimer Acid mass flux to the river and the volume of water flowing in the river. An
assessment of Dimer Acid mass flux in the river was performed to achieve the following
objectives:


Identify potential pathways for Dimer Acid to reach the river;

Evaluate the mass flux contributions from each potential pathway; and

Estimate future concentrations of Dimer Acid in the river by preparing ananalytical model.

The objectives listed above build upon each other and were thus fulfilled sequentially.
The paragraphs below describe how each objective was fulfilled, and the observations
obtained from each objective.
Identify Potential Pathways
Potential pathways for Dimer Acid to reach the river were identified by reviewing Sitecross sections, Site aerial imagery, Site data and discussions with Chemours personnel.
Identified potential pathways are listed below and are graphically represented in theconceptual image presented in Figure 1:


The up-stream river;Willis Creek;Direct aerial deposition to the river;

Outfall 002;



On-Site upwelling groundwater;Surface water runoff;Flow in the historic outfall channel;

Off-Site (up- and down-river) upwelling groundwater; andGeorgia Branch Creek.

River Mass Flux Summary2018.02.26

1

Evaluate Mass Flux Contributions
The mass flux reaching the river is the combined mass per unit time (e.g. nanograms per
second) from each identified potential pathway listed above. For mass transported bywater (e.g. groundwater, surface water, outfalls) mass flux is calculated by multiplying
the volumetric flow of the water (e.g. liters per second) by the concentration of Dimer
Acid in the water (e.g. nanograms per liter; ng/L). Mass flux for each potential pathway
was estimated using Site data, and representative physical properties where Site data were
unavailable. The mass flux assessment was prepared and compared to Site data. This
included data collected as part of a surface water sampling event conducted on 26-27
September 2017. Sample collection dates for data used to quantify each pathway arepresented in Table 1.
The data used to quantify the mass flux for each pathway and the results of the assessment
are presented in Table 2. The results are compared against the average, down-river Dimer
Acid concentration from the 26-27 September 2017 sampling event, 39.25 ng/L. The
mass flux assessment estimated that the combined mass flux contributions to the riverwould result in a Dimer Acid concentration ranging from 26 to 64 ng/L, (i.e. 66% to160%) of observed Dimer Acid on 26-27 September. The two largest contributors of
Dimer Acid mass flux were first upwelling Site groundwater and second the HistoricOutfall. Upwelling groundwater was estimated to potentially contribute between 12 to 47
ng/L, (i.e. 30% to 120%) of observed Dimer Acid in the river. The Historic Outfall, using
data from 16 January 2017, was estimated to contributed 9 ng/L (i.e. 23%) to observed
river concentrations.
It should be noted that upwelling groundwater mass flux estimates have more uncertainty
than any of the mass flux estimates for the outfalls or creeks. This is because thegroundwater mass flux estimates are based on measured concentrations and calculated(estimated) flow, while for creeks and outfalls both concentrations and flow were
measured. Consequently, a second approach was used to estimate upwelling groundwater
contributions to in-river Dimer Acid concentrations. The second approach estimated thesecontributions by subtracting all other mass flux contributions from the observed riverconcentrations. Based on this assessment upwelling groundwater was estimated tocontribute between 22.5 to 26 ng/L (i.e. 57% to 66%) of Dimer Acid concentrations
observed in the river, which is within the range of the previous estimate.

River Mass Flux Summary2018.02.26

2

Estimate Future River Dimer Acid Concentrations
An analytical river mass flux model was created to estimate future river Dimer Acid
concentrations. The model estimated both Dimer Acid: i) concentrations in the river; andii) travel times in river water. Specifically travel times are estimated for the down-stream
public utility water intakes at Bladen Bluffs, 7.5 miles down-river, and Kings Bluff Intake
Canal, 55 miles down-river. The model was created in Microsoft Excel using thefollowing data sources:i.

Input mass fluxes from the mass flux assessment;ii.

Outfall 002 concentration and flow data provided by Chemours to calculate
Outfall 002 mass flux for specific dates; andiii.

Daily mean river volumetric flow data and gauge height data reported by UnitedStates Geological Survey (USGS) for the W.O. Huske Dam gauging station.

The model operates by first estimating mass flux inputs into the river for a given dateusing the approach described for the mass flux assessment. Model calculations are only
performed for dates where measured Outfall 002 concentration and flow data exist. The
concentration of Dimer Acid in the river is then calculated by dividing the mass flux (e.g.
nanograms per second) by the USGS reported river flow rate (e.g. liters per second). Next
the arrival time of this water at the down-river intakes is estimated using the estimatedriver water velocity. River water velocities were estimated by calculating how quickly
the measured volumetric flow of water must pass through the estimated cross-sectional
area of the river. River cross sectional areas were estimated using river gauging data fromthe 26 to 27 September 2017 sampling event and USGS reported river gauge heights.
River mass flux model results using input data from 14 June 2017 to 29 January 2018 arepresented in Figure 2 for Bladen Bluffs and Figure 3 for Kings Bluff Intake Canal. In
each figure the modeled results are compared to publicly reported, measured riverconcentrations. The river mass flux model results show a good fit compared to observed
river Dimer Acid concentrations at the two down-river water intake locations.
Since 1 August 2017 river concentrations have been measured to be less than 140 ng/L
except for the temporary increase in early October 2017, which matches the model results.
The increase in October 2017 was related to a temporary increase in Outfall 002
concentrations and mass flux. Assuming standard operating conditions at the Site andsimilar environmental conditions, future river concentrations are estimated to remain
below 140 ng/L.

River Mass Flux Summary2018.02.26

3

Geosyntec Consultants
TABLE 1POTENTIAL DIMER ACID PATHWAYS TO CAPE FEAR RIVER AND DATA SOURCES FOR ASSESSMENT
Chemours Fayetteville Works

Pathway

Concentration Data

Flow Data

Up‐Stream River

26‐27 Sept. 2017 Data

26‐27 Sept. 2017 Data

Willis Creek

26‐27 Sept. 2017 Data

16 Jan. 2018 Data

Aerial Deposition on River

Estimated from NCDEQ Air Dispersion Modelling

Outfall 002

26‐27 Sept. 2017 Data

26‐27 Sept. 2017 Data

On‐Site Groundwater

26‐27 Sept. 2017 Data

Calculated

Surface Water Run‐Off

Inferred. No Rain.

Inferred. No Rain.

Historic Outfall Channel

16 Jan. 2018 Data

16 Jan. 2018 Data

Residential Well Data
26‐27 Sept. 2017 Data

Calculated
16 Jan. 2018 Data

Off‐Site Groundwater (Up & Down River)
Georgia Branch Creek

2/16/2018

Geosyntec Consultants

TABLE 2
POTENTIAL PATHWAY ESTIMATED DIMER ACID MASS FLUXESCOMPARED TO MEASURED RIVER CONCENTRATIONS
Chemours Fayetteville Works

Concentration(ng/L)Flow(L/s)

Mass Flux(ng/s)

Estimated Contribution toRiver Concentration(ng/L)

025,5000

0

310 – 450

170 – 250

52,700 ‐ 112,500

2.0 ‐ 4.5

Aerial Deposition on River1

‐‐

‐‐

6,000

0.25

Outfall 002

35

900

31,5001.25

25,000 – 50,000

12 – 24300,000 – 1,200,00

12 – 47

NA

NA

0

0

8,400

27

227,000

9147 – 179

110 – 180

16,000 ‐ 32,250

0.5 ‐ 1.25

540 – 1,100

8 – 164,500 – 17,500

0.2 – 0.7

Total Estimated Mass Flux andCorresponding River Concentration‐‐‐‐

665,000 – 1,625,000

26 – 64

Measured5 Concentration and Flow Down
River 5 Miles and Calculated Mass Flux

39.25

25,5001,000,000

39.25

Potential Pathway
Up‐Stream River
Willis Creek

On‐Site Groundwater2
Surface Water Run‐Off

3

Historic Outfall
Off‐Site Groundwater (Up & Down River)4

Georgia Branch Creek

Notes
Direct aerial deposition to the river mass flux estimates were made based on NCDEQ presented modelling results.

1

https://www.ncleg.net/documentsites/committees/house2017‐185/Meetings/3%20‐%20Nov%2030%202017/DEQ%20Final%20PowerPoint%20Pres.pdf

On‐Site groundwater flux range estimated assuming discharge areas of 18,500 to 37,000 square meters, calculated gradient of
0.064 between LTW Wells to Cape Fear River, measured maximum and average LTW Well concentrations of 50,000 and of to 25,000
ng/L, and a estimated hydraulic conductivity of 10‐5 m/s, representative of silty sand.

2

3During the 26‐27 September 2017 sampling event there was no rain before or during the event, therefore the run‐off flux is 0 ng/s.

Off‐Site groundwater was estimated using residential well concentration data and the same hydraulic conductivity value, 10‐5 m/s,
used for on‐Site groundwater upwelling estimates. The on‐Site gradient value, 0.064, was used in estimating upwelling on the sameside of the river as the site (west). A lower gradient, 0.0064, was used for the opposite side of the river (east) where land surface
topography is more subdued.
45

Measured data are from the 26‐27 September 2017 surface water sampling event.

Acronyms
L/s ‐ liters per second
m/s ‐ meters per second
ng/L ‐ nanograms per literng/s ‐ nanograms per second

2/16/2018

Direct Aerial
Deposition

Up

River

Rain

pe
Ca

Groundwater

Wills Creek

e
Riv
ar

Fe

On

Surface
Water
Runoffr-site
Groundwater

Outfall 002 PipeO n-site G
roundwater

W.O. Huske
Dam
Histor
ic O u t f all Ch a nnel

Georgia B
eek
ra n ch CrOf

f - S ite Groundwater

Conceptual Diagram: Potential Dimer Acid
Pathways to Cape Fear River
Chemours Fayetteville Works

Figure1
GuelphFebruary 2018

1260
1120

Dimer Acid Concentration(ng/L; ppt)

980

Bladen Bluffs Modeled
Bladen Bluffs All Data
Non‐Detect Data

840
700
560
420
280
140
0

River Mass Flux Model Estimatesat Bladen Bluffs
Chemours Fayetteville Works

Notes:
ng/L - nanograms per literppt - parts per trillion

Figure2
GuelphFebruary 2018

1260
1120

Kings Bluff Water Intake Modeled
Kings Bluff Water Intake All Data

Dimer Acid Concentration(ng/L; ppt)

980
840
700
560
420
280
140
0

River Mass Flux Model Estimatesat Kings Bluff Intake Canal
Chemours Fayetteville Works

Notes:
ng/L - nanograms per literppt - parts per trillion

Figure3
GuelphFebruary 2018