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Cover. Ellerbe Creek in Durham, North Carolina, looking upstream from site EC-4. Photograph by Kristen McSwain, U.S. Geological Survey.

Groundwater/Surface-Water Interactions
Along Ellerbe Creek in Durham, North
Carolina,2016-18
By Dominick J. Antolino
Prepared in cooperation with the City of Durham Public Works Department,
Stormwater and GIS Services Division
Scientific Investigations Report 2019-5097
U.S. Department of the Interior
U.S. Geological Survey

U.S. Department of the Interior
DAVID BERNHARDT, Secretary
U.S. Geological Survey
James F. Reilly II, Director
U.S. Geological Survey, Reston, Virginia: 2019
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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials
as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.
Suggested citation:
Antolino, D.J., 2019, Groundwater/surface-water interactions along Ellerbe Creek in Durham, North Carolina, 2016-
18: U.S. Geological Survey Scientific Investigations Report 2019-5097, 32 p., https:Hdoi.org/10.3133/sir20195097.
ISSN 2328-0328 (online)

ttl
Acknowledgments
The author thanks Michelle Woolfolk of the City of Durham Public Works Department,
Stormwater and GIS Services Division, and John Dodson with the North Durham Water
Reclamation Facility for their support and assistance with this project.
The author would also like to thank Kristen McSwain for her project guidance and other
U.S. Geological Survey staff (Jeffrey Moss, Sharon Fitzgerald, Jessica Cain, Lee Bodkin,
Jason Fine, Sean Egen, and Ryan Rasmussen) for their assistance with fieldwork and
data analysis.

IV
Contents
Abstract .....
Introduction
Purposeand Scope.............................................................................................................................2
StudyArea Description........................................................................................................................2
Previous Investigations........................................................................................................................2
Methodsof Investigation.....................................................................................................................7
Streamflow Data Collection.......................................................................................................7
Groundwater -Level Monitoring.................................................................................................8
Weatherand Climate Data.........................................................................................................8
HydrographSeparation..............................................................................................................8
Water -Quality Sampling..............................................................................................................9
Water -Quality Control Samples.................................................................................................9
Statistical Analysis of Water -Quality Data..............................................................................9
Water -Temperature Surveys......................................................................................................9
Groundwater/Surface-Water Interactions..............................................................................................10
Streamflow Gains and Losses..........................................................................................................10
Groundwater and Surface -Water Levels........................................................................................14
Base -Flow Estimates..........................................................................................................................15
Water -Temperature Survey Results................................................................................................15
Reconnaissance of Bank Seeps Using Thermal Imaging...................................................15
Distributed Temperature Sensing Results.............................................................................17
Water -Quality Results.................................................................................................................................21
Summary and Conclusions.........................................................................................................................29
ReferencesCited..........................................................................................................................................30
Figures
1. Map showing location of the study area in Durham, North Carolina, within the
Piedmont physiographic province.............................................................................................3
2. Map showing land cover within the Ellerbe Creek drainage area in Durham,
NorthCarolina...............................................................................................................................4
3. Map showing geology of the study area in Durham, North Carolina..................................5
4. Map showing location of surface -water, groundwater, and bank seep sites in the
Ellerbe Creek study area in Durham, North Carolina..............................................................6
5. Graphs showing discharge at U.S. Geological Survey streamgage 02086849,
North Durham Water Reclamation Facility effluent discharge, and precipitation
at the Climate Retrieval and Observations Network of the Southeast DURH site
during a streamflow survey on July 12, 2016, and water -quality sampling on
August 2, 2016; a fiber-optic distributed temperature sensing survey from July 18
to 25, 2017, and water -quality sampling on July 27, 2017; and water -quality
sampling from March 27 to 29, 2018, at Ellerbe Creek, Durham, North Carolina .............11
6. Map showing stream reaches measured for a streamflow gain -loss survey on
July 12, 2016, in Ellerbe Creek in Durham, North Carolina...................................................12

7.
Graphs showing continuous groundwater levels at sites PZ-1 and PZ-2 and
surface -water level at site EC-4 and hydraulic gradients measured between
December 1, 2017, and March 29, 2018, within Ellerbe Creek in Durham,
NorthCarolina.............................................................................................................................14
8.
Graphs showing base flow estimated by using the base -flow index
and PART hydrograph separation methods for U.S. Geological Survey
streamgage 02002086849 and streamgage 0208675010 in Ellerbe Creek in
Durham, North Carolina.............................................................................................................16
9.
Example of a thermal image captured by the forward -looking infrared camera in
March 2016 to determine stream surface and bank seep temperatures ..........................17
10.
Distributed temperature sensing measurements collected from July 18 to 25,
2017, in Ellerbe Creek, Durham, North Carolina.....................................................................18
11.
Maps showing mean distributed temperature sensing measurements collected
from July 18, 2017, to July 25, 2017, and stream depth measurements collected
with an acoustic Doppler current profiler during base -flow conditions on July 27,
2017, at Ellerbe Creek in Durham, North Carolina.................................................................20
12.
Trilinear Piper diagram showing water -chemistry data for water -quality samples
collected in July 2016 and March 2018 at surface -water sites, bank seeps, and
groundwater wells in the Ellerbe Creek study area, Durham, North Carolina .................24
13.
Boxplots showing range, median, and quartile statistical values for specific
conductance, pH, and nutrient concentrations of surface -water, groundwater,
and bank seep samples collected in July and August 2016, July 2017, and
March 2018 in the Ellerbe Creek study area in Durham, North Carolina ...........................25
14.
Map showing nitrate concentrations at surface -water and bank seep sites
sampled in July and August 2016 in the Ellerbe Creek study area in Durham,
NorthCarolina.............................................................................................................................26
15.
Map showing nitrate concentrations at bank seep sites sampled in July 2017 in
the Ellerbe Creek study area in Durham, North Carolina.....................................................27
16.
Map showing nitrate concentrations at surface -water and groundwater sites
sampled in March 2018 in the Ellerbe Creek study area in Durham, North Carolina
...... 28
Tables
1. Site information and map names for surface -water, bank seep, and groundwater
sites in the Ellerbe Creek study area in Durham, North Carolina.........................................7
2. Discrete water levels measured in November and December 2017 and
March 2018 at groundwater and surface -water sites in the Ellerbe Creek study
area in Durham, North Carolina.................................................................................................8
3. Measurements from the July 2016 gain -loss survey for reaches in Ellerbe Creek
inDurham, North Carolina.........................................................................................................13
4. Summary of gain -loss determinations during the July 2016 gain -loss survey for
reaches in Ellerbe Creek in Durham, North Carolina............................................................13
5. Temperature, specific conductance, dissolved oxygen, pH, and nutrient
concentrations of water -quality samples collected at Ellerbe Creek, Durham,
North Carolina, from July 2016 to March 2018.......................................................................22
6. Major ion concentrations in water -quality samples collected at Ellerbe Creek,
Durham, North Carolina, from July 2016 to March 2018.......................................................23

vl
Conversion Factors
U.S. customary units to International System of Units
Multiply
By
To obtain
Length
inch (in.)
foot (ft)
mile (mi)
2.54
0.3048
1.609
centimeter (cm)
meter (m)
kilometer (km)
Area
square mile (mil)
2.590
square kilometer (km2)
Flow rate
foot per second (ft/s)
foot per day (ft/d)
cubic foot per second (ft3/s)
million gallons per day (Mgal/d)
0.3048
0.3048
0.02832
0.04381
meter per second (m/s)
meter per day (m/d)
cubic meter per second (m3/s)
cubic meter per second (m3/s)
International System of Units to U.S. customary units
Multiply
By
To obtain
Length
meter (m)
kilometer (km)
3.281
0.6214
foot (ft)
mile (mi)
Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:
°F= (1.8 x °C)+32.
Datum
Vertical coordinate information is referenced to the North American Vertical Datum of 1988
(NAVD 88).
Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Altitude, as used in this report, refers to distance above the vertical datum.

VII
Supplemental Information
Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (IDS/cm at
25 °C).
Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L)
or micrograms per liter (pg/L).
Abbreviations
ADCP
acoustic Doppler current profiler
ADV
acoustic Doppler velocimeter
BFI
base -flow index
CRONOS
Climate Retrieval and Observations Network of the Southeast
DGPS
differentially corrected Global Positioning System
DTS
distributed temperature sensing
FLIR
forward -looking infrared
FO-DTS
fiber-optic distributed temperature sensing
GUI
graphical user interface
lidar
light detection and ranging
NDWRF
North Durham Water Reclamation Facility
NLCD
National Land Cover Database
QA/QC
quality assurance and quality control
USGS
U.S. Geological Survey

Groundwater/Surface-Water Interactions Along
Ellerbe Creek in Durham, North Carolina, 2016-18
By Dominick J. Antolino
Abstract
An assessment of groundwater/surface-water interactions
along Ellerbe Creek, a major tributary to upper Falls Lake in
Durham County, North Carolina, was conducted from July
2016 to March 2018 to determine if groundwater is a likely
source of elevated nitrate input to the stream. Groundwater/
surface -water interactions were characterized by synoptic
streamflow measurements, groundwater -level monitoring,
hydrograph-separation methods, and a continuous streambed
temperature survey to aid in the collection and interpretation
of water -quality data. A streamflow gain -loss survey identified
gaining and losing reaches within the stream and found that
surface -water inflow, including that from a treated wastewater
outfall, provided much of the streamflow gain within the
study reach. Through the use of two hydrograph-separation
methods, base flow for the Ellerbe Creek study reach was
estimated to be between 14.0 and 17.7 cubic feet per second
during the study period, contributing up to 57 percent of
mean streamflow, with the remaining contributions coming
from surface runoff to the stream. The effluent discharge
accounted for most of the estimated base -flow contribution
to the stream below the North Durham Water Reclamation
Facility outfall. Hydraulic gradients within the groundwater
were determined to flow upward and toward the stream during
base -flow conditions and reverse during storm events. Nitrate
concentrations ranged from below the method detection level
to 2.69 milligrams per liter, with the highest concentrations
just downstream from the wastewater outfall. Bank seeps
and groundwater samples had lower nitrate concentrations
than surface -water samples, ranging from below the method
detection level to 1.04 milligrams per liter, with the highest
concentration at the piezometer within the stream. Results
indicate that groundwater is not a large component of
streamflow within Ellerbe Creek nor a major source of nitrate
within the study reach.
Introduction
The North Carolina Department of Environmental
Quality has included Falls Lake, a reservoir serving as the
drinking water source for the city of Raleigh, North Carolina,
and surrounding communities, on the 303(d) list of impaired
waters because of violations of the State's chlorophyll a water -
quality standard that have been correlated to excessive nutrient
inputs (North Carolina Department of Environment and
Natural Resources, 2010). The nutrient management strategies
adopted for the reservoir by the North Carolina Environmental
Management Commission incorporate comprehensive controls
to reduce nitrogen and phosphorus loads from primary sources
in the watershed, including urban stormwater, wastewater,
and agriculture (North Carolina Department of Environment
and Natural Resources, 2010). Estimates of total nitrogen and
phosphorus loads to Falls Lake from watershed model analysis
show agriculture and point sources as the most important
contributors to nitrogen and phosphorus levels within the
reservoir (North Carolina Department of Environmental
Quality, Division of Water Resources, 2016).
Ellerbe Creek, one of the major tributaries that
discharges to upper Falls Lake, has a history of elevated
nutrient concentrations that have been largely attributed to
wastewater outfall from the North Durham Water Reclamation
Facility (NDWRF; National Pollutant Discharge Elimination
System permit number NC0023841), which is about 5 miles
(mi) upstream from Falls Lake. Ongoing upgrades to and
optimization of NDWRF water treatment processing are
being implemented to reduce nutrient input to the reservoir.
As part of the North Carolina Department of Environmental
Quality Falls Lake Nutrient Strategy, Stage I mass limits
for the three major wastewater dischargers in the upper
watershed, including the NDWRF, were equivalent to an
average of 3.09 milligrams per liter (mg/L) of total nitrogen
for 110 percent of 2016 flows. The Ellerbe Creek drainage
area is under the jurisdiction of the City of Durham, North
Carolina. The city's Public Works Department, Stormwater
and GIS Services Division, is tasked with assessing nutrient
contributions to implement best management practices aimed
at reducing nutrient loading in the Falls Lake drainage basin.
Recent watershed modeling within the basin indicated that
groundwater may be a possibly unquantified source of nutrient
contributions to area streams (North Carolina Department of
Environmental Quality, Division of Water Resources, 2016).

Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
Purpose and Scope
This report presents the results of a study to describe
the interaction of groundwater and surface water in a reach
of Ellerbe Creek downstream from the NDWRF. Streamflow
measurements and groundwater -level monitoring were used to
assess hydraulic gradients and estimate groundwater discharge
to Ellerbe Creek. These monitoring data were coupled with
temperature surveys and water -quality samples to assess
whether groundwater may be a possible nonpoint source
of nutrients to Ellerbe Creek and the Falls Lake watershed.
This approach can improve understanding regarding the
usefulness of the methods and techniques used in this study
to characterize groundwater/surface-water interactions within
Piedmont streams in Triassic sedimentary basins.
Study Area Description
The study area is in Durham County, North Carolina,
within the Piedmont physiographic province. Ellerbe Creek
is within the upper Neuse River Basin, upstream from Falls
Lake (fig. 1), and is monitored for stage and streamflow by the
U.S. Geological Survey (USGS) at streamgage 0208675010
(EC-1) and streamgage 02086849 (EC-11). The drainage area
of Ellerbe Creek at EC-11, located at the downstream end of
the study area, is 21.9 square miles (mil) and includes areas
along Interstate 85 and north of downtown Durham. The
land cover within the drainage area is predominantly urban
(77 percent) with some forested coverage (15 percent) (fig. 2),
according to the 2011 National Land Cover Database (NLCD)
(Homer and others, 2015). The drainage area is underlain
primarily by the sandstones and interbedded siltstones and
mudstones of the Durham and Sanford subbasins of the Deep
River Mesozoic basin (formerly known as the Triassic basin)
(Brown and Parker, 1985; Hanna and Bradley, 2016) (fig. 3).
Soils in the Ellerbe Creek drainage area are composed of
unconsolidated, poorly sorted, and stratified sand, silt, and
clay alluvium. The dominant hydrologic soil types for the
study area are group C soils that have low infiltration rates,
with more moderately drained group B soils farther upgradient
from the stream. The U.S. Army Corps of Engineers
straightened and channelized Ellerbe Creek in the early 1960s
to control large volumes of surface runoff caused by the
clayey, poorly draining soils and increased impervious surface
area in the city of Durham (North Carolina Department of
Environment and Natural Resources, 2003). Most of the
Ellerbe Creek streambed is composed of alluvial sand and silt -
sized particles that mobilize readily under the rapidly changing
high flows caused by surface runoff during storm events.
The groundwater system in the study area is composed of
weathered regolith material at the land surface and underlying
sedimentary bedrock that yields small quantities of water
because of compaction and cementation within the rock
(Chapman and others, 2013). Permeability of the aquifer may
be slightly enhanced along lithologic contacts and bedding
planes, as well as the openings and weathered areas around
resistant diabase dikes within the study area that can provide
preferential flow paths (fig. 3). The shallow regolith, which
consists of soil residuum (clay), alluvium (older stream
deposits), and saprolite (weathered bedrock material), is the
shallowest portion of the groundwater system and serves
as the primary storage reservoir for recharge to the deeper
portions of the aquifer (Chapman and others, 2005).
The NDWRF, which is within the study reach, has a
permitted capacity of 20 million gallons per day (Mgal/d) and
discharges about 10 Mgal/d (15.5 cubic feet per second [ft3/s])
of treated wastewater into Ellerbe Creek. A closed, unlined
solid waste landfill that stopped receiving waste in 1997 is
north of the NDWRF, approximately 1,000 feet (ft) east of
Ellerbe Creek (fig. 4). A small, unnamed stream meanders
along the southern and western edges of the landfill and
discharges to Ellerbe Creek through a culvert located 1,800 ft
downstream from the NDWRF outfall.
Previous Investigations
According to previous regional studies of shallow
groundwater (Hallberg and Keeney,1993; Dubrovsky
and others, 2010), the most widespread contaminant in
groundwater from nonpoint anthropogenic sources is nitrogen.
Messier and others (2014) developed a nonlinear land -
use regression geostatistical model to predict point -level
groundwater nitrate concentrations in North Carolina by
using data from shallow groundwater monitoring wells and
deeper private wells; median nitrate input values ranged from
0.10 to 1.30 mg/L. Nitrate concentrations within the shallow
monitoring wells varied widely, with wastewater treatment
residuals and swine confined animal feeding operations as
the dominant nitrate sources. McSwain and others (2014)
assessed nitrate sources by using stable isotope compositions
of nitrogen and oxygen at sites in three tributary creeks to
Falls Lake, including USGS site 0208675010 on Ellerbe
Creek, which is about 2.5 mi upstream from the NDWRF.
Organic nitrogen accounted for more than 50 percent of the
total measured nitrogen within the creeks, and nitrate plus
nitrite concentrations were below 0.40 mg/L in all samples.
Of the many potential sources of nitrate (for example, soil,
atmospheric deposition, fertilizer, and manure and septic
waste), the dominant source of nitrate to the three creeks
was found to be the nitrification of soil nitrogen. Some storm
samples also had atmospheric inputs of nitrate as a result
of impervious -surface runoff directly entering streams. No
evidence of septic or wastewater discharge was observed.

Introduction 3
36' 15'
36°00'
79°00'
CASWELL I l PERSON
ALAMANCE f
I •
Lake
J Orange
II ORANGE
Eno River
Hillsborough
1
I '
Cane Creek Carrboro 1
Reservoir i Chapel'
I Hill 1
University
Lake
— — — Cape Fear
River Basin
CHATHAM
P�
Base from U.S. Geological Survey digital data,1:100,000 scale
U.S. Department of Commerce, Bureau of Census,
1990 Precensus TIGER/Line Files -Political boundaries,1991
Environmental Protection Agency, River File 3
7890'
Map area
Piedmont Coastal Plain
' : • � R�d9e
Little River
f Reservoir
IStudy area
0208675010
Durham `
f � I
Neuse
River Basin
Lake
Michiej
GRANV
E
I
020868
Falls
r�
Lake
DURH
� l
\
DURHAM
—'
Neuse River
/
Basin `
/ er WAKE
Cary Raleigh
Jordan
LakApex
` y �
Apex • IS �
EXPLANATION
Basin boundary
02086849
A Streamgage and identifier
DURH®
CRONOS station and identifier
0 5 10 MILES
0 5 10 KILOMETERS
Figure 1. Map showing location of the study area in Durham, North Carolina, within the Piedmont physiographic province. Streamgage
0208675010 is site EC-1, and streamgage 02086849 is site EC-11. EC, Ellerbe Creek.

36°03'30"
35°59'30'
78°55'30" 78°48'30"
Base from North Carolina Center for Geographic Information and Analysis 0 2 5 5 MILES
North Carolina State Plane coordinate system I I
North American Datum of 1983 0 4 8 KILOMETERS
EXPLANATION
Land cover (NLCD 2011�
Open water
Developed, open space
Developed, low intensity
Developed, medium intensity
Developed, high intensity
Barren land
Deciduous forest
Evergreen forest
Mixed forest
Shrub/scrub
Grassland/herbaceous
Pasture
Cultivated crops
Woody wetlands
Emergent wetlands
02OM49.
U.S. Geological Survey
streamgage and
identifier
Figure 2. Map showing land cover within the Ellerbe Creek drainage area in Durham, North Carolina. Land -cover data are from the 2011 National Land Cover Database
(NLCD 2011; Homer and others, 2015). Streamgage 0208675010 is site EC-1, and streamgage 02086849 is site EC-11. EC, Ellerbe Creek.

W03'30"
36°00'00"
—� ■
r
r
Durham
North Carolina State Plane coordinate system
North American Datum of 1983
Lambert Conformal Conic projection
i
78°52'30"
f
area
78°45'00"
a Map
/area
k1 a
0 2 4 MILES
I
0 3 6 KILOMETERS
EXPLANATION
Upper hyco fm dacitic tuffs Diorite Alluvium Sandstone conglomerate CGLA III
Felsic tuffs Diabase Sandstone CGLA II Reedy Creek metagranodiorite
Lower hyco fm dacitic intrusives ' Andesitic to dacitic tuffs Sandstone CGLA III Beaverdam diorite
Granodiorite to granite Sandstone CGLA I Conglomerate CGLA III Beaverdam gabbro and metapyroxenite
---- Diabase dike
Figure 3. Map showing geology of the study area in Durham, North Carolina. The base map is modified from Hanna and Bradley (2016). Fm, formation; CGLA, Chatham Group
Lithofacies Association.
E
cn

Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
36°02'30"
36°02'00"
78°52'00" 78°51'00"
Base from North Carolina Center for Geographic Information and Analysis 0 0.25 0.50 MILE
North Carolina State Plane coordinate system
North American Datum of 1983
0.40 0.80 KILOMETER
Figure 4. Map showing location of surface -water, groundwater, and bank seep sites in the Ellerbe Creek study area in Durham, North
Carolina. Sites EC-1 and EC-11 are shown in figures 1 and 2. BS, bank seep; EC, Ellerbe Creek; GW, groundwater well; NDWRF, North
Durham Water Reclamation Facility; PZ, piezometer.

Introduction 7
Methods of Investigation
This section provides a discussion of the methods used
for describing the groundwater/surface-water interaction
in Ellerbe Creek, including streamflow and groundwater
data collection, water -quality sampling, and a distributed
temperature survey. Map names for all study sites are used
in place of USGS station names to make references concise
within the text and figures (table 1).
Streamflow Data Collection
Streamflow data were collected at eight sites within
Ellerbe Creek in July 2016 by using a handheld SonTek
F1owTracker acoustic Doppler velocimeter (ADV) and
a Teledyne RD Instruments StreamPro acoustic Doppler
current profiler (ADCP) deployed from a tethered moving
boat. The F1owTracker ADV instantaneous streamflow
measurements were made by using the USGS midsection
method (Young, 1950). The StreamPro ADCP allows three-
dimensional velocities to be measured from approximately
1.0 ft beneath the water surface to within 6 percent of the
depth to the bottom. The ADCP velocity, streamflow, and
depth data were collected using standard USGS techniques
(Mueller and others, 2013). Streamflow measurement
locations were selected for gain -loss surveys to bracket
tributary inflows and reaches suspected to contain shallow
groundwater seeps. Hourly discharge data for the NDWRF
effluent outfall from July 2014 to July 2018 were provided by
the Durham Department of Water Management for reference
(John Dodson, Durham Department of Water Management,
written commun., 2018).
Table 1. Site information and map names for surface -water, bank seep, and groundwater sites in the Ellerbe Creek study area in
Durham, North Carolina.
[NC, North Carolina; EC, Ellerbe Creek; Q, discharge; CR, Creek; RD, Road; NR, near; WQ, water quality; MI, mile; SR, Secondary Road; WL, water level;
UT, unnamed tributary; BLW, below; TR, tributary; BL, below; BS, bank seep; MW, monitoring well; GW, groundwater well; PZBK, bank piezometer;
PZ, piezometer; PZST, stream piezometer]
Site number
Station name
name
Latitude
(decimal
degrees)
Longitude
(decimal
degrees)
ata type
collected
0208675010
ELLERBE CREEK AT CLUB BOULEVARD AT DURHAM, NC
EC-1
36.01938889
—78.89477
Q
0208682450
ELLERBE CR BELOW SECONDARY RD 1669 NR WEAVER, NC
EC-2
36.02983
—78.863694
Q, WQ
02086833
ELLERBE CREEK 0.33 MI BELOW SR1669 NR WEAVER, NC
EC-3
36.03206
—78.86206
Q, WQ
02086834
ELLERBE CR 0.51 MILE BELOW SR1669 NEAR WEAVER, NC
EC-4
36.03448
—78.860771
WL
02086835
ELLERBE CREEK 0.59 MI BELOW SR1669 NR WEAVER, NC
EC-5
36.03572
—78.86042
Q, WQ
02086837
ELLERBE CREEK 0.71 MI BELOW SR1669 NR WEAVER, NC
EC-6
36.03725
—78.85964
Q, WQ
02086839
ELLERBE CREEK 0.89 MI BELOW SR1669 NR WEAVER, NC
EC-7
36.03961
—78.85817
Q, WQ
02086841
ELLERBE CREEK AT WEAVER, NC
EC-8
36.04319
—78.85628
Q, WQ
02086843
ELLERBE CREEK 1.28 MI BELOW SR1669 NR WEAVER, NC
EC-9
36.04469
—78.85536
Q, WQ
02086845
ELLERBE CREEK 1.39 MI BELOW SR 1669 NR WEAVER, NC
EC-10
36.04625
—78.8545
Q, WQ
02086849
ELLERBE CREEK NEAR GORMAN, NC
EC-11
36.05956
—78.832534
Q, WQ
360211078513701
UT TO ELLERBE CR 0.63 MI BLW SR1669 NR WEAVER, NC
TR-1
36.03626
—78.86018
WQ
360226078512801
UT TO ELLERBE CR 1.04 MI BLW SR1669 NR WEAVER, NC
TR-2
36.04058
—78.85767
WQ
360149078514801
DR-073 ELLERBE LB-1 0.18 MI BL SR1669 NR WEAVER NC
BS-I
36.03028
—78.86333
WQ
360158078514201
DR-076 ELLERBE RB-4 0.35 MI BL SR1669 NR WEAVER NC
BS-2
36.03278
—78.86167
WQ
360159078514101
DR-074 ELLERBE RB-2 0.40 MI BL SR1669 NR WEAVER NC
BS-3
36.03306
—78.86139
WQ
360204078513901
DR-075 ELLERBE RB-3 0.51 MI3BL SR1669 NR WEAVER NC
BS-4
36.03444
—78.86083
WQ
360205078513801
DR-077 ELLERBE RB-5 0.50 MI BL SR1669 NR WEAVER NC
BS-5
36.03472
—78.86056
WQ
360207078513801
DR-078 ELLERBE RB-6 0.55 MI BL SR1669 NR WEAVER NC
BS-6
36.03528
—78.86056
WQ
360159078513801
DR-081 (MW-10) NEAR WEAVER, NC (REGOLITH)
GW-1
36.03289
—78.860399
WL, WQ
360207078512501
DR-082 (MW-2) NEAR WEAVER, NC (REGOLITH)
GW-2
36.03531
—78.856826
WL, WQ
360204078513902
DR-079 ELLERBE PZBK 0.51 MI BL SR1669 NR WEAVER NC
PZ-1
36.03448
—78.860744
WL, WQ
360204078513903
DR-080 ELLERBE PZST 0.51 MI BL SR1669 NR WEAVER NC
PZ-2
36.03448
—78.860771
WL, WQ

Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
Groundwater -Level Monitoring
Groundwater -level measurements were collected at
two piezometers (PZ-1 and PZ-2) and two monitoring wells
(GW-1 and GW-2) in the study area to identify general flow
direction and hydraulic gradients at the stream bank (table 2).
The streambank piezometer (PZ-1) was installed to a depth of
3.4 ft below land surface, and the stream piezometer (PZ-2)
was installed to a depth of 5.5 ft below the streambed. The
lateral distance between the two piezometers was 10 ft. This
section of the stream was selected for water -level monitoring
due to the presence of and accessibility to a persistent bank
seep (BS-4). The wells GW-1 and GW-2, part of a long-
term monitoring network at the nearby unlined landfill, are
about 600 ft and 1,100 ft, respectively, from the piezometer
sites (fig. 4).
Measurements were made from the top of the well
casing with an electric water -level tape or a steel tape, using
techniques described by Cunningham and Schalk (2011). The
measuring points at PZ-1 and PZ-2 were surveyed in relation
to a locally established bench mark to determine the altitude
difference between the two sites. Land -surface altitudes at the
locally established bench mark and two monitoring well sites
were derived from 1-meter (m) high -density light detection
and ranging (lidar) data (National Oceanic and Atmospheric
Administration, 2015) with a mean vertical accuracy of
0.04 m and were reported in feet above the North American
Vertical Datum of 1988 (NAVD 88). The distance from the
land surface to the measuring point was then measured with
an engineer's rule to determine the measuring point altitude.
Continuous water levels were measured in piezometers at
sites PZ-1 and PZ-2 from December 2017 to March 2018
by using internally logging unvented pressure transducers.
Stream water level was measured at site EC-4 also using an
internally logging unvented pressure transducer, which was
secured to the downstream side of the piezometer at site PZ-2.
These datasets are available to the public through the USGS
National Water Information System database (U.S. Geological
Survey, 2018).
Weather and Climate Data
Hourly precipitation and air temperature data were
collected by a North Carolina Climate Retrieval and
Observations Network of the Southeast (CRONOS)
station located at the NDWRF (CRONOS station DURH).
A collaboration between State and Federal agencies, the
CRONOS database contains weather and climate observations
for 41 stations across 33 counties in North Carolina and is
publicly available at https:Hclimate.ncsu.edu/cronos.
Hydrograph Separation
Hydrograph-separation methods were used to estimate
base flow within the 21.9-mi2 drainage area of site EC -I I
(USGS streamgage 02086849), as well as within the 6.0-mi2
drainage area of the upstream site, EC-1 (USGS streamgage
0208675010), for comparison. Base flow is the component of
streamflow largely sustained by groundwater discharge along
the stream reach and is distinct from direct surface runoff. For
the study area, base -flow estimates include natural base flows
of steady groundwater discharge to Ellerbe Creek and its small
tributary inflows, as well as anthropogenic inflows that have
a relatively consistent discharge, such as effluent from the
NDWRF. Hydrograph separation was done using the USGS
Groundwater (GW) Toolbox, which is a software program that
allows hydrograph analysis using six hydrograph-separation
methods to calculate several components of the water budget,
including base flow and surface -water runoff (Barlow and
others, 2015). Two methods were used in the current study to
determine lower and upper estimates of base flow; specifically,
the base -flow index (BFI) and PART methods, respectively.
Table 2. Discrete water levels measured in November and December 2017 and March 2018 at groundwater and surface -water sites in
the Ellerbe Creek study area in Durham, North Carolina.
[ft, foot; NADV 88, North American Vertical Datum of 1988; PZ, piezometer; GW, groundwater well; -, not measured; EC, Ellerbe Creek]
Land-
Altitude
Water -level
Water -level
Water -level
Water -level
Total
surface
of top of
Screened
Casing
altitude
altitude
altitude
altitude
Site number
Map
altitude
casing
well
interval
diameter
(ft above
(ft above
(ft above
(ft above
name
(ft above
(ft above
depth
(ft)
(inches)
NAVD 88)
NAVD 88)
NAVD 88)
NAVD 88)
(ft)
NAVD 88)
NAVD 88)
11/29/17
12/1/17
12/7/17
3/29/18
360204078513902
PZ-1
271.2
271.80
3.4
1
1
269.19
269.52
270.46
270.39
360204078513903
PZ-2
268.0
269.53
5.5
1
1
269.03
269.13
269.28
269.38
360159078513801
GW-1
279.7
281.55
14.5
10
2
274.65
360207078512501
GW-2
283.8
285.52
18.0
10
2
281.91
02086834
EC-4
268.0
269.53
269.01
269.1
269.14
269.25

Introduction
The BFI method (Institute of Hydrology, 1980a, b; Wahl
and Wahl, 1995) partitions the streamflow hydrograph into
intervals of N days to determine minimum flows within
each interval. If 90 percent of the minimum of interest is
less than adjacent minimums, then the flow is determined
to be a "turning point" and is connected with other turning
points to complete the base -flow hydrograph. The PART
method (Rutledge, 1998) designates days that are unaffected
by surface runoff as those that are preceded by N days of
continuous recession and linearly interpolates between
these days to determine the base -flow hydrograph. For the
current study, the period of analysis was October 1982 to
January 2018 for USGS streamgage 02086849 (site EC-11)
and July 2008 to January 2018 for streamgage 0208672010
(EC-1). The separation method parameters were set to a
partition length of N= 5 days, a turning point test factor of
F = 0.90, and a daily recession index of K = 0.97915.
Water -Quality Sampling
Water -quality samples were collected at four groundwater
sites, six bank seeps, and 11 surface -water sites in July and
August 2016, July 2017, and March 2018. Sampling methods
followed those outlined in the USGS "National Field Manual
for the Collection of Water -Quality Data" (U.S. Geological
Survey, 2006). Surface -water sampling was conducted at
10 sites in July 2016, concurrent with stream -discharge
measurements. Three of these sites were again sampled in
March 2018, along with downstream site EC-11, about 3 mi
downstream from the NDWRF. Water samples were collected
at observable bank seeps using a drive -point piezometer
connected to a peristaltic pump in August 2016 and in
July 2017. The July 2017 sampling event coincided with the
deployment of the fiber-optic distributed temperature sensing
(FO-DTS) system described in the "Water -Temperature
Surveys" section.
Groundwater, bank seep, and surface -water sites were
sampled for nutrients, including nitrite, nitrate, and ammonia.
Groundwater and surface -water sites were also sampled for
major ions, iron, and manganese. All samples were analyzed
at the USGS National Water Quality Laboratory in Denver,
Colorado, using methods outlined in Fishman (1993).
Water -Quality Control Samples
Five field blanks and three sample replicates were also
collected throughout the sampling process to address quality
assurance and quality control (QA/QC). The blanks and
replicates provide information regarding the accuracy and
precision, respectively, of the water -quality data presented in
this report. The QA/QC samples were collected in accordance
with USGS policies and procedures documented in the
National Field Manual (U.S. Geological Survey, 2006).
Statistical Analysis of Water -Quality Data
The water -quality data were summarized using
Piper (trilinear) diagrams and box plots. Charge -balance
errors calculated for the major cation and anion data of
all samples were found to have less than a 10-percent
difference, which was determined acceptable for statistical
evaluation (U.S. Geological Survey, 1992). Piper diagrams
are trilinear plots used to visually describe and compare
the major ion composition of multiple samples of water on
one graph. Ternary diagrams for both cations and anions
are projected onto a diamond plot, where samples can be
divided into hydrochemical facies or groups of samples
with similar chemical characteristics as a result of similar
hydrogeochemical processes (Piper, 1953). Using this
approach, distinct source waters and the mixing relationships
that exist between them can be identified, as well as any
water -rock interactions that may occur along the groundwater
flow path. Box plots also provide a way to visually compare
datasets by displaying the statistical spread of the data
(Sincich, 1993). The box encompasses the interval between
the first and third quartiles (25th and 75th percentiles), with
the median (50th percentile) represented by a horizontal line
within the rectangular box. Lines and whiskers drawn from
the first and third quartiles represent the values of the 1 Oth
and 90th percentiles of the dataset, respectively. For datasets
that contained censored data for non -detection of a constituent
(for example, nitrate), the rank method was used to determine
summary statistics for the construction of boxplots. This
method does not involve any assumption about the underlying
distribution and is a simple and appropriate method for
small datasets that have only one censoring value present
(Bonn, 2008).
Water -Temperature Surveys
Temperature has been shown to be an effective tracer
of groundwater movement near streams (Stonestrom and
Constantz, 2003). The interaction of shallow groundwater
with surface water can be assessed by contrasting the natural
variations in stream water temperature resulting from
seasonal and meteorological changes with the relatively
stable groundwater temperatures. In a gaining stream reach
during the summer, the relatively cooler thermal signature
of discharging groundwater may be seen within the warmer
surface water. The methods used for this study ensure
measurement of distinct temperature differences, but these
methods cannot be used to distinguish between no -flow and
losing reaches.

10 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
An initial reconnaissance survey in March 2016 and a
subsequent survey in July 2016 were conducted to identify
possible groundwater discharge points along the stream
reach by using a forward -looking infrared (FLIR) camera
in seasonal extremes. The high -resolution FLIR T620 and
T640 thermal imaging cameras capture the emitted infrared
radiation of the objects in view. Recent studies using similar
ground -based thermal infrared imaging techniques have been
successful in qualitatively locating groundwater discharge
along discrete features, such as fractures and faults, as well as
diffuse seepage along stream banks (Deitchman and Loheide,
2009; Pandey and others, 2013). Sites of interest were those
where temperature differences were observed between the
stream surface and points of streambank inflow, specifically
where warmer groundwater was observed flowing from the
streambank into the relatively cooler stream during the winter
and where cooler groundwater was entering the relatively
warmer stream during the summer.
FO-DTS can be used to determine differences in
the temperature of surface water along a profile. With
FO-DTS, surface -water temperatures are measured for
several days along a fiber-optic cable that may extend more
than a kilometer with a spatial resolution of less than 3 ft.
Temperature precisions of 0.1 degree Celsius (°C) and a
temporal resolution of 90 seconds can be obtained (Selker and
others, 2006). The measured temperature differences can often
denote locations of groundwater discharge along a reach.
From July 18 to 25, 2017, an FO-DTS survey was
completed by using a Sensomet ORYX distributed
temperature sensing (DTS) system to delineate areas of
groundwater discharge along Ellerbe Creek, just upstream
from the NDWRF outfall to downstream from the closed
municipal landfill. About 975 m of fiber-optic cable was
deployed on the right bank (closest to the landfill) in the bed
of the stream channel. Global Positioning System (GPS)
location measurements were collected every 30 ft along the
cable during deployment, and a trolling SonTek RiverSurveyor
M9 ADCP with a differentially corrected Global Positioning
System (DGPS) receiver collected depth and location data
every 1.6 ft during cable retrieval to georeference the location
of the cable. The DGPS received differential corrections from
a Wide Area Augmentation System (WARS) and is specified
by the manufacturer to be accurate to 3.3 ft at two standard
deviations. Hourly air temperature was collected at the
CRONOS DURH station located at the NDWRF.
Temperature data obtained by using the ORYX DTS
system were collected between 18:39 on July 18, 2017,
and 04:26 on July 25, 2017. Data were recorded every
15 minutes at intervals of about 3 ft along the length of the
fiber-optic cable. Ten consecutive temporal measurements
made by the FO-DTS system over a 15-minute period were
averaged to obtain 1 temperature measurement, for a total
of 641 measurements collected over about 7 days. Analysis
of the thermal data was done by using the DTS graphical
user interface (GUI) program, currently under development
by the USGS (Martin Briggs, U.S. Geological Survey, oral
commun., 2018). The DTS GUI is a Python -based internal
data visualization code that provides tools to import and view
FO-DTS data in geospatial format.
Groundwater/Surface-Water
Interactions
Groundwater/surface-water interactions were
characterized by synoptic streamflow measurements, hydraulic
gradients derived from water -level monitoring, and continuous
streambed temperature using FO-DTS. The regolith aquifer
is the principal hydrogeologic unit that interacts with
surface -water features in the study area. Under typical
conditions, when the water table follows the local topography,
groundwater stored within the regolith aquifer would flow
downgradient through the alluvium and discharge to the
stream across miles of the entire stream reach. The discharge
and recharge rates are dependent on the hydraulic gradient that
exists between the groundwater system and the stream.
Streamflow Gains and Losses
To characterize the bulk exchange of water between
the stream and surficial groundwater system, a streamflow
gain -loss survey was conducted in Ellerbe Creek on July 12,
2016, at eight sites along the stream reach. According to data
collected at USGS streamgage 02086849 (EC-11; location
shown in figs. 1 and 2), the stream was under base -flow
conditions during all discharge measurements. Streamflow
ranged from 17.0 to 24.2 cubic feet per second (ft3/s), and
stage ranged from 1.58 to 1.68 ft above NAVD 88 before a
rainfall event occurred post -survey, during the evening (fig. 5).
According to data provided by the NDWRF, the effluent
discharge ranged from 7.8 to 18.9 ft3/s over the course of the
survey. The survey covered about 1.4 mi of Ellerbe Creek,
starting at a site 740 ft upstream from the NDWRF outfall
(fig. 6). The remaining seven discharge sites were upstream
and downstream from major inflows to the stream, including
two culverts, multiple small creeks, and a nearby surface -
water impoundment.
The gain or loss in streamflow is estimated as the
difference between inflow to the reach and outflow from the
reach. A stream reach was classified as gaining or losing
if the difference between the upstream and downstream
discharge measurements exceeded the uncertainty error of
both measurements. A meaningful streamflow gain within
a reach was attributed to unmeasured tributary inflow and
groundwater discharge to the stream. A meaningful seepage
loss within a reach was assumed to be recharge to the
groundwater system. Errors for each discharge measurement
were based on measurement statistics generated by the ADV
or ADCP data processing software. The total uncertainty in a
discharge measurement includes uncertainty in cross -sectional
area measurements, water -velocity profile measurements and
assumptions, extrapolations for unmeasured areas, and random
or systematic errors (Turnipseed and Sauer, 2010).

Groundwater/Surface-Water Interactions 11
A
10,000
1,000
100
10
1
0.1
7/1/2016 7/5/2016 7/9/2016 7/13/2016 7/17/2016 7/21/2016 7/25/2016 7/29/2016 8/2/2016
Date
B
10,000
0 1,000
`m
n
100
U
a
10
a
1
O
I
0.1
7/1/2017 7/5/2017 7/9/2017 7/13/2017 7/17/2017 7/21/2017 7/25/2017 7/29/2017 8/2/2017
Date
C
10,000
1,000
100
10
1
0.1 p
3/1/2018 3/5/2018 3/9/2018 3/13/2018 3/17/2018 3/21/2018 3/25/2018 3/29/2018
Date
Figure 5. Graphs showing discharge at U.S. Geological Survey streamgage 02086849 (EC-1 1) (blue lines), North Durham Water
Reclamation Facility effluent discharge (black lines), and precipitation atthe Climate Retrieval and Observations Network of the
Southeast DURH site (orange lines) during (A) a streamflow survey on July 12, 2016, and water -quality sampling on August 2, 2016; (B) a
fiber-optic distributed temperature sensing survey from July 18 to 25, 2017, and water -quality sampling on July 27, 2017; and (C) water -
quality sampling from March 27 to 29, 2018, at Ellerbe Creek, Durham, North Carolina. Yellow highlights indicate measurements made
during the given sampling and survey dates.
3
2
0
3
0
3
2

12 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
W02'30"
78'52'00"
IN
� T
• v � r�lri�y� . ; .11.r .
V `
. •.
ee� .,�+
�S- r
36'02'00"
oZ
;G
67
78'51'00"
16
ri fir..
EXPLANATION
A
Gaining reach and identifier
D
Losing reach and identifier
B
Unverifiable gaining or losing
reach and identifier
y{` 4 0
fs ,
Surface -water site and
measurement number
Base from North Carolina Center for Geographic Information and Analysis 0 0.25 0.50 MILE
North Carolina State Plane coordinate system
North American Datum of 1983
0 0.40 0.80 KILOMETER
Figure 6. Map showing stream reaches measured for a streamflow gain -loss survey on July 12, 2016, in Ellerbe Creek in Durham,
North Carolina.
All reaches evaluated for streamflow gains or losses
in this stretch of Ellerbe Creek are depicted in figure 6 and
summarized in tables 3 and 4. Of the seven reaches assessed
during the survey, reaches A and E had verifiable streamflow
gain and reach F showed slight losing conditions. Reaches
B and G did not have verifiable streamflow gain because the
uncertainty errors exceed the inflow and outflow difference.
Reach C had a relatively larger seepage loss, but upon
consideration of the magnitude of uncertainty error coupled
with an effluent discharge decrease of 2.4 ft3/s between the
inflow and outflow reach measurements, the observed loss is
not meaningful. Flow from the tributary within reach C was
not measured; however, the flow velocity was estimated to
be between 1 and 2 feet per second through the 4-ft culvert
at a depth near 0.5 ft, and the inflow to the stream during the
survey was estimated to be between 1 and 2 ft3/s.

Groundwater/Surface-Water Interactions 13
Table 3. Measurements from the July 2016 gain -loss survey for reaches in Ellerbe Creek in Durham, North Carolina.
[ft/s, foot per second; ft'/s, cubic foot per second; NDWRF, North Durham Water Reclamation Facility; ADV, acoustic Doppler velocimeter; -, not measured;
ADCP, acoustic Doppler current profiler]
Change
Change
in NDWRF
in NDWRF
Measure-
Mean
Discharge,
Uncertainty,
Uncertainty,
discharge
discharge
Site number
ment Method
Date and time
velocity,
ft /s
percent
ft /s (+/-)
during
from upstream
number
ft/s
measurement,
measurement,
ft3/s
ft3/s
0208682450
1 ADV
7/12/201610:31
0.34
5.5
2.7
0.1
02086833
2 ADCP
7/12/201612:25
0.40
26.3
5.3
1.4
-0.3
-
02086835
3 ADCP
7/12/201613:06
0.41
26.9
23.0
6.2
-0.6
0.0
02086837
4 ADV
7/12/201614:12
0.56
19.7
2.5
0.5
-1.9
-2.4
02086839
5 ADV
7/12/201614:53
0.63
18.0
3.2
0.6
-1.9
0.0
02086841
6 ADV
7/12/201616:37
0.46
25.6
4.0
1.0
1.7
1.5
02086843
7 ADV
7/12/201615:37
0.27
21.1
3.1
0.7
-0.9
0.4
02086845
8 ADV
7/12/201616:08
0.26
21.2
4.9
1.0
-0.9
0.0
Table 4. Summary of gain -loss determinations during
the July
2016 gain -loss
survey for reaches in Ellerbe Creek in Durham,
North Carolina.
[ft'/s, cubic foot per second; ft, foot; 8/s, foot per second]
Associated
Gain or loss,
Total uncertainty,
Reach distance, Averaged velocity,
Travel time,
Reach name
measurements ft3/s
ft3/s (+/-)
ft
ft/s
minutes
A
1,2
20.8
1.5
965
0.37
43.5
B
2,3
0.6
7.6
815
0.41
33.5
C
3,4
-7.18
6.7
605
0.49
20.8
D
4,5
-1.768
1.1
965
0.60
27.0
E
5,6
7.6
1.6
1,380
0.55
42.2
F
6,7
-4.514
1.7
610
0.37
27.9
G
7,8
0.1
1.7
620
0.27
39.0
Reach A contains the NDWRF outfall, which likely
accounts for much of the measured gain for the reach. A
streamflow gain of 7.6 ft3/s in reach E was attributed to
both groundwater discharge and the two small, unmeasured
tributaries flowing into the stream within the reach. A seepage
loss of 1.8 ft3/s measured in reach D indicates the combined
contributions of groundwater discharge within the reach,
and inflow from a small unmeasured tributary was exceeded
by seepage loss to the groundwater system. Reach F also
showed a meaningful seepage loss to the groundwater system
of 4.5 ft3/s.
Calculations from the streamflow gain -loss survey
showed that Ellerbe Creek has both gaining and losing reaches
within the study area. Only reaches A and E had verifiable
streamflow gain (20.8 ft3/s and 7.6 ft3/s, respectively), which
cannot be attributed solely to groundwater because small
tributaries flow into the stream within both reaches, as well
as NDWRF effluent inflow within reach A. Reach D showed
a small but verifiable seepage loss despite containing two
tributary inflows. Though the discharge from the NDWRF
outfall fluctuated throughout the survey, the observed seepage
losses were not related to decreases in effluent flow to the
stream. Both inflow and outflow measurements in reach D
were completed under stable effluent discharge conditions,
whereas the volume of effluent discharge increased by 0.4 ft3/s
between the inflow and outflow measurements for reach F,
which would slightly reduce the observed seepage loss
(table 2). Diabase dikes cut across the bedrock underlying
the alluvial sediments in this area of Ellerbe Creek (fig. 3),
particularly within reach F (fig. 6). Though diabase dikes
are not permeable and may act as an impermeable boundary
to groundwater discharge (McSwain and others, 2009),
preferential pathways along the weathered contact areas may
divert groundwater along the dike. Weaver and McSwain
(2013) observed no -flow or losing stream conditions in
the Cape Fear River near Raven Rock State Park in North
Carolina that coincided with the presence of diabase dikes
intersecting the reach.

14 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
Groundwater and Surface -Water Levels
Continuous groundwater levels within two piezometers
(PZ-1 and PZ-2) were recorded concurrently with continuous
stream -level readings at site EC-4 between December 1,
2017, and March 28, 2018, to calculate hydraulic gradients
in Ellerbe Creek during the wet season (fig. 7). Surface -water
levels ranged from 268.65 to 273.54 ft above NAVD 88,
and groundwater levels ranged from 268.71 to 273.20 ft
A
273 r
00 273
00
0
z
0 272
a
m
m
a�
c
a
271
2
m
m
270
`m
x
269
268
B
0.20 r--
—0.20 �
12/1/2017
Discharge
VRecharge
above NAVD 88. Groundwater levels typically were higher
than surface -water levels across the monitoring period,
except during storm events when stream levels rose above
groundwater levels. The hydrographs for both surface water
and groundwater show similar patterns, likely because
of hydrostatic pressure from the stream having direct
communication to the shallow groundwater system through
the alluvial sediments.
12/15/2017 12/29/2017 1/12/2018 1/26/2018 2/9/2018
Date
EXPLANATION
— PZ-2 (bank piezometer)
— PZ-1 (stream piezometer)
EC-4 (stream stage)
Vertical gradient (PZ-1 and EC-4)
— Horizontal gradient (PZ-2 and PZ-1)
2/23/2018 3/9/2018 3/23/2018
Figure 7. Graphs showing (A) continuous groundwater levels at sites PZ-1 and PZ-2 and surface -water level at site EC-4 and
(B) hydraulic gradients measured between December 1, 2017, and March 29, 2018, within Ellerbe Creek in Durham, North Carolina.
EC, Ellerbe Creek; NAVD 88, North American Vertical Datum of 1988; PZ, piezometer.

Groundwater/Surface-Water Interactions 15
Positive vertical gradients indicate upward flow of
groundwater discharge to the stream and negative gradients
indicate downward flow, or groundwater recharge. Vertical
gradients between the groundwater system beneath the stream
and the stream level ranged from —0.08 to 0.04 foot per foot
(ft/ft), with the mean near 0.01 ft/ft. The higher negative
gradients coincided with storm events and had a duration
of less than 4 hours. Horizontal gradients were computed
between the piezometer within the stream and the stream bank
piezometer with a range of —0.16 to 0.11 ft/ft, where positive
values reflect groundwater movement into the stream and
negative values reflect streamflow into bank storage. The mean
horizontal gradient was 0.05 ft/ft, and the negative values
coincided with storm events for short durations. Groundwater
levels, showing a seasonal change, began to slowly rise
during the monitoring period, with overall increases of about
0.9 ft within the bank piezometer and about 0.3 ft within the
groundwater system beneath the stream.
Base -Flow Estimates
GW Toolbox was used to calculate base flow along
Ellerbe Creek using streamflow records for USGS streamgages
EC-10 and EC-11 from October 1982 to December 2017, with
a median streamflow of 41 ft3/s for the 35-year period. Gaps
in the continuous streamflow record exist from May 1989 to
September 1991, June 1994 to August 1994, and October 1995
to January 2006. The GW Toolbox program calculates base
flow using all available data within periods between the data
gaps, but the output files will not include the partial month or
years with missing data in the results. Both the BFI and PART
methods yielded annual and monthly estimates of base flow
and surface runoff for the 35-year period.
The BFI method estimated an average annual rate of
base flow of 14.0 ft3/s and a base -flow index range of 0.21
to 0.49, which means that base flow contributes between 21
and 49 percent of total streamflow annually. Estimates for
base flow computed by using the PART method were less
conservative, with an average annual rate of base flow of
17.7 ft3/s and a maximum base -flow index of 0.57. Annual
and monthly fluctuations within the basin can be seen across
the portion of the analyzed period shown in figure 8, with
the highest flows in 2009 and low flows during the drought
period of 2011. The base -flow estimates using the PART
method show peaks that may include interflow because they
coincide with high flows attributed to frequent storm events.
The average annual rate of surface runoff was estimated to be
near 23 ft3/s for an average contribution of nearly 60 percent
of streamflow.
On the basis of provided discharge records for effluent
flow from the NDWRF from 2014 to 2018, the median
discharge into Ellerbe Creek is 13 ft3/s. Given these data, the
average effluent discharge to Ellerbe Creek contributes slightly
more than 30 percent of the total mean streamflow measured
at the downstream USGS streamgage EC-11. On June 21,
2016, the discharge from the NDWRF outfall was stopped for
about 3 hours, and the measured discharge at the USGS EC-11
streamgage dropped from 12.2 to 3.7 ft3/s about 6 hours later,
given the distance downstream from the outfall. The effluent
discharge averaged 9.1 ft3/s in the 6 hours prior to the shutoff,
and the downstream EC -I I gage measured between 9.7 and
14 ft3A before flow began to decline. These data provide some
insight into the natural base -flow contribution to streamflow
from groundwater discharge and small tributary inflows within
Ellerbe Creek, which is likely near 3.7 ft3/s under similar
hydrologic conditions.
Water -Temperature Survey Results
As stated previously, the interaction of shallow
groundwater with surface water can be assessed by contrasting
the variations in surface -water temperature resulting from
seasonal and meteorological changes with the relatively stable
groundwater temperature. Water -temperature surveys used to
assess groundwater/surface-water interactions in Ellerbe Creek
included the use of thermal imagery for locating persistent
seeps along the stream bank and FO-DTS along the streambed.
All data are publicly available online in Antolino (2018).
Reconnaissance of Bank Seeps Using
Thermal Imaging
Reconnaissance surveys of Ellerbe Creek using a
handheld FLIR camera were conducted on March 2, 2016,
and July 18, 2016, to identify potential areas of groundwater
discharge during seasonal extremes. The FLIR camera
captures high -resolution images of real-time variations
in stream and bank seep water temperature (fig. 9). During the
March 2016 survey, the median surface temperatures recorded
by the FLIR camera were 12.4 °C for bank inflow and 11.6 °C
for the stream. During the July 2016 survey, several additional
bank seeps were measured, with median surface temperatures
of 23.3 °C for bank inflow and 26.5 °C for the stream. The
temperature differences between bank inflow and the stream
ranged from 1.3 to 2.8 °C for the March survey and from 1.5
to 8.3 °C for the July survey. The processed thermal images
indicate six sites of potential groundwater input into the stream
from the streambank where temperature differences were
greater than 1.2 °C (BS-1, BS-2, BS-3, BS-4, BS-5, and BS-6;
see fig. 4. for site locations). The surveys were used to identify
areas of groundwater discharge for FO-DTS deployment, as
well as to select water -quality sampling locations.

16 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
A
160
140
120
N
N
Q 100
N
?
80
U
C_
60
N
40
0
20
0
J
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Year
B
50
U
20
N
0 10
0 1 V I I - I Iy 1 - I I I ✓ I " 1
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Year
EXPLANATION
— Mean streamflow
— Base flow (PART)
Base flow (BFI)
Figure 8. Graphs showing base flow estimated by using the base -flow index (BFI) and PART hydrograph separation methods
for (A) U.S. Geological Survey (USGS) streamgage 02002086849 (site EC-1 1) and (B) USGS streamgage 0208675010 (site EC-1) in
Ellerbe Creek in Durham, North Carolina.

Groundwater/Surface-Water Interactions 17
Figure 9. Example of a thermal image captured by the forward -looking infrared (FUR) camera in March 2016 to determine stream
surface and bank seep temperatures. The image was taken at bank seep BS-4 at Ellerbe Creek in Durham, North Carolina.
Thermal imagery identified several bank seeps along
the study reach where water -quality samples could be taken.
Temperature differences between the bank seeps and the
stream were distinct enough in both winter and summer
conditions to delineate inflow to Ellerbe Creek. Several of
the bank seeps identified in the March 2016 survey were
not observed in the July 2016 survey. Both surveys were
conducted about a week after a rainfall event, so persistent
groundwater seeps likely would have been flowing. During
rainfall events, stream stage at the downstream USGS gage
EC-11 can rise from 2 to 5 ft above base -flow conditions.
These events inundate the high, sandy -silt channel walls and
contribute to shallow groundwater and bank storage. Most
bank seeps observed discharging to the stream within a week
of sizeable runoff events likely are sourced predominantly
from bank storage. Persistent bank seeps, such as BS-1 and
BS-4, may have preferential flow pathways that yield a larger
groundwater component that contributes to very small but
constant flow in these areas.
Distributed Temperature Sensing Results
From July 18 to 25, 2017, an FO-DTS survey was
conducted in Ellerbe Creek, beginning slightly upstream from
the NDWRF outfall and extending downstream from the
closed municipal landfill. The streambed is mostly sand and
silt for much of the reach, with exposed bedrock and boulders
at the downstream end of the survey reach. The fiber-optic
cable was placed within the streambed along the right bank
of Ellerbe Creek to capture any discharging groundwater that
may have flow paths connected to the landfill.
Streamflow recorded at the downstream USGS
streamgage EC- 11 during the FO-DTS survey ranged from
4.6 ft3/s on July 25 to 61.8 ft3/s on July 19 (fig. 6). On the night
of July 18, 2017, a rainfall event of 0.64 inch was recorded
during the survey. According to data collected by the NDWRF,
hourly discharge from the outfall ranged from 5.6 to 20.4 ft3/s
and daily effluent temperatures ranged from 26.60 to 27.10 °C
during the FO-DTS survey. Local air temperature ranged
from 18.8 °C on July 19 to 36.5 °C on July 23. The streambed
temperatures measured along the reach by the FO-DTS system
ranged from 21.54 to 28.53 'C. Diurnal fluctuations observed
within the streambed temperature data were attributed to solar
radiation warming the stream each afternoon followed by
cooling during the night. Areas where thermal fluctuations
were reduced were assumed to be possible evidence of
groundwater discharge to the stream.

18 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
Thermal traces of streambed temperatures collected at
15-minute intervals were compared to determine areas of
reduced diurnal fluctuations (fig. 10). Two ice baths were set
up to quality -check the temperature readings at the upstream
end of the cable (9- 69 ft) and near the midpoint of the
cable (1,870-2,025 ft); these areas where the cable left the
streambed are shaded gray in the thermogram in figure 10. The
A
July18
18:39:2121
July 19
19:39:21
July 20
20:39:21
E
~ July 21
21:39:21
July 22
22:39:21
July 23
23,39:21
July 25
00:39:21
28
27
26
25
24
23
22 F
21 IL
0
B
40
36
32
28
24
20
16
12
effects of the rainfall event that occurred late on July 18 and
into the morning of July 19 can be observed in cool streambed
temperatures with distinct pulses of cool runoff into the
stream. Areas farthest downstream, where the stream is most
shallow, had the warmest temperature signatures and largest
diurnal variance.
Ad— 40 I ..�..
E
FO-DTS out of water Mtl� o
o FO-DTS out of water
- — —
I I I I I I
July 23, 2017 at 15:1/1
��� May mean
July 19, 2017 at 06:11
May variance
500 1,000 1,500 2,000 2,500 3,000
Distance along fiber-optic cable, in feet
18 19 20 21 22 23 24 25 26 27
July
2017
EXPLANATION
Temperature, in
degrees Celsius
26.0
25.6
25.2
24.8
24.4
24.0
23.6
23.2
22.8
22.4
22.0
2.0
0
Figure 10. Distributed temperature sensing measurements collected from July 18 to 25, 2017, in Ellerbe Creek, Durham, North Carolina.
A, Thermogram image of survey period and graph showing the May mean surface -water temperature compared with warmest and
coldest days/times (blue -shaded areas in the graph represent cooler inflow from groundwater or small tributaries). B, Graph showing
recorded air temperature. FO-DTS, fiber-optic distributed temperature sensing.

Groundwater/Surface-Water Interactions 19
The thermal traces for the coldest day and time (July 19
at 06:11) and the warmest day and time (July 23 at 15:11)
were compared with the 7-day mean for each measurement
location along the cable to visualize the temperature extremes
within the data. Under typical conditions, areas with small
temperature variation would be locations that are thermally
buffered by consistent groundwater discharge. However, it
is important to consider that warm water discharged from
the NDWRF outfall near the upstream end of the cable
(downstream from the 230-ft cable mark) can also obscure the
natural diurnal signal in this reach of Ellerbe Creek. Additional
consideration should be given regarding small downstream
tributaries whose sources are unaffected by the warm outfall
discharge. These inflows would appear as a steady flow of
slightly cooler water at the stream confluence, yielding a
similar signature to that of cooler groundwater discharge to
the stream.
Areas where the thermal signature shows small
temperature variability are highlighted in blue in the plot
below the thermogram in figure 10. The five most prominent
of these areas on the thermogram were at distances of
255-272, 1,591-1,667, 2,395-2,408, 2,933-2,946, and
3,057-3,071 ft from the upstream end of the cable. The area
between 255 and 272 ft corresponds with the NDWRF outfall,
where the thermal signature shows a consistently warm inflow
to the stream (fig. 11). At the area near the 1,591-ft mark, a
small persistent seep was observed at the bank (BS-5), behind
a sandbar formed during recent stormflow. Several loops of
cable were wound at this location to ensure any temperature
difference from the inflow was captured by the survey. This
site is likely a small discharge point for shallow groundwater
to the stream. Three small unnamed tributaries to Ellerbe
Creek are at cable distances of 2,395-2,408, 2,933-2,946,
and 3,057-3,071 ft. It appears that stream depth may explain
the difference in variability of thermal signatures at these
locations. The tributary at 2,395 ft enters the stream through
a culvert where the stream depth is about 3.9 ft, whereas the
tributaries farther downstream at 2,933 and 2,946 ft enter at a
stream depth of only about 0.65 ft (fig. 11). Cooler inflow was
observed at all three tributaries after the rain event on July 18,
2017. The farthest downstream tributaries were exposed to the
air as stream stage dropped after the storm event, as can be
seen in the increasing temperature extremes from day to night
across the monitoring period shown on the thermogram.
Low levels of groundwater discharge to the stream may
explain the lack of distinctive discharge areas captured in the
FO-DTS survey data. The groundwater seep at the 1,591-ft
mark likely was detected because of its location behind a
sandbar, where it was shielded from the higher and warmer
flows of the stream. Groundwater discharge from bank seeps
is small compared to the overall streamflow; therefore,
the FO-DTS survey was not able to resolve groundwater
discharge through the streambed within Ellerbe Creek. Using
the FO-DTS method, Briggs and others (2012) were able
to resolve groundwater contributions along a 900-meter
stream reach discharging at a rate near 5 percent of the
overall streamflow. Lauer and others (2013) were able to
resolve simulated groundwater inflow to a stream at a rate
near 2 percent of the streamflow in a mountain creek. Likely,
most of the remaining contributions to streamflow come from
recently recharged shallow groundwater that discharges farther
upgradient into the small tributaries along Ellerbe Creek.

20 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
A
Base from North Carolina Center for Geographic Information and Analysis EXPLANATION
North Carolina State Plane coordinate system
North American Datum of 1983 Stream temperature,
in degrees Celsius
24
20
B
EXPLANATION 0 0.1 0 7 MII F
Stream depth,
in feet 0 0.15 0.3KILOMETER
� 4.2
2.1
Figure 11. Maps showing (A) mean distributed temperature sensing measurements collected from July 18, 2017, to July 25, 2017, and
(B) stream depth measurements collected with an acoustic Doppler current profiler during base -flow conditions on July 27, 2017, at
Ellerbe Creek in Durham, North Carolina. BS, bank seep; NDWRF, North Durham Water Reclamation Facility.

Water -Quality Results 21
Water -Quality Results
Water -quality sampling within the study area provided
information to help identify possible sources of nutrients into
Ellerbe Creek and ultimately Falls Lake. Periodic water -
quality samples were collected at 11 sites along Ellerbe Creek
during July 2016 and March 2018 (tables 5 and 6). Shallow
groundwater seeps along the stream bank were sampled at six
locations in August 2016 and July 2017. Two groundwater
monitoring wells and two piezometers were sampled in
March 2018. Quality -assurance sample results for the three
replicates generally signified good analytical precision,
with two of the replicates having less than a 10-percent
difference from the original sample. Five blank samples were
collected, and results were generally below reporting limits
for all samples, except for one field blank sample collected
in August 2016 that had a total nitrogen concentration of
0.11 mg/L. On the basis of guidelines provided in Mueller
and others (2015), associated samples collected during the
August 2016 sampling event were considered valid only if the
concentration exceeded five times the amount detected in the
blank, in this case, 0.55 mg/L of total nitrogen.
The temperature of surface -water samples ranged
from 24.4 to 27.2 °C for the July 2016 sampling and 7.0 to
13.1 °C for the March 2018 sampling. The temperature of
bank seep samples ranged from 21.6 to 28.8 °C during the
summer sampling events in August 2016 and July 2017. The
temperature of groundwater samples ranged from 13.1 °C
in GW-2 to 22.8 °C in GW-1. Specific conductance values
ranged from 29 microsiemens per centimeter (µS/cm) at
the upstream surface -water site EC-2 to 461 µS/cm at the
bank seep BS-3. The high specific conductance measured at
BS-3 on August 2, 2016, may be attributed to high sodium
and bicarbonate (or alkalinity) concentrations at the site,
both of which were the highest concentrations of all samples
collected in the study. Generally, the groundwater samples
had noticeably lower specific conductance than the surface -
water samples. Values for pH ranged from 5.1 to 7.4 and were
generally higher within surface water than in groundwater.
Dissolved oxygen ranged from 7.1 to 10.6 mg/L for the
surface -water samples and 1.6 to 9.3 mg/L for the groundwater
samples. Field measurements of dissolved oxygen for the
bank seeps did not meet precision standards for inclusion in
the study.
Relative distribution of major ions in water samples is
shown on a Piper diagram (fig. 12). Water rich in calcium -
bicarbonate upstream from the NDWRF outfall roughly
trended toward water dominated by sodium -sulfate with a
slight rise in chloride downstream from the outfall. Nitrate
concentrations in surface -water samples increased slightly
between July 2016 and March 2018. The three bank seeps
sampled for major ions (BS-1, BS-3, and BS-4) represented
a range of water types, with BS-4 being the most similar
to the Ellerbe Creek samples. BS-4 had the highest sodium
concentration of all samples collected during the study
at 82.9 mg/L. The water types for the two groundwater
monitoring wells differ from one another, with GW-1
containing higher concentrations of dissolved constituents,
especially iron, and more than twice the amount of nutrients
as seen in GW-2. This relative dilution observed in GW-2 may
be due to some degree of hydraulic communication with a
nearby retention pond that is upgradient from the well (fig. 4).
GW-1 had the highest calcium, magnesium, bicarbonate, and
chloride concentrations of all sampled sites at 33.4, 14.2, 102,
and 39.2 mg/L, respectively. The sample collected from the
small tributary 0.55 kilometer downstream from the outfall,
site TR-I, shows a water type that plots near the midpoint of
all surface -water samples.
Boxplots were constructed for specific conductance, pH,
and nutrient concentrations of the surface -water, bank seep,
and groundwater sites (fig. 13). Ammonia concentrations
ranged from below the method detection level of 0.01 mg/L
(BS-4, PZ-2, and GW-2) to 0.46 mg/L in bank seep BS-2.
Concentrations of nitrate ranged from below the method
detection level of 0.04 mg/L (bank seeps BS-I, BS-3,
and BS-4) to 2.69 mg/L at surface -water site EC-3, 215 ft
downstream from the NDWRF outfall (figs. 14-16). The
median nitrate concentration in the surface -water samples was
an order of magnitude higher than that of the groundwater
samples.
Nitrate was detected in all surface -water samples, with
the lowest concentration of 0.38 mg/L observed upstream
from the NDWRF outfall. Surface -water samples collected
in July 2016 did not have a strong spatial pattern. The
March 2018 samples had higher nitrate concentrations near
the NDWRF and became more diluted moving downstream.
Samples collected from tributary inflows contained low
levels of nitrate, with concentrations ranging from 0.16 to
0.41 mg/L. Samples collected from shallow bank seeps
along the stream did not have elevated nitrate concentrations;
several were below the method detection level, and the
highest concentration was 0.406 mg/L. The bank seep BS-5,
which was identified in the FO-DTS survey, had a nitrate
concentration of 0.14 mg/L. The sample collected at the
streambed piezometer (PZ-1) had a nitrate concentration of
1.04 mg/L, which is likely due to downward surface -water
seepage through the streambed. Neither the groundwater
monitoring wells nor the bank piezometer sample had nutrient
concentrations over 0.10 mg/L. Higher nitrate concentrations
are typically found within groundwater when ammonium and
dissolved oxygen are abundant, whereas denitrification via
bacteria within the aquifer can reduce nitrate to nitrogen gas
when adequate amounts of dissolved oxygen are not available.
The GW-1 and PZ-1 samples had ammonia concentrations
between 0.10 and 0.02 mg/L, likely the result of natural
organic matter decay along the flow path toward the stream.
All samples had total nitrogen concentrations below the Falls
Lake Nutrient Strategy Stage I mass limit of 3.09 mg/L, except
for one stream sample (EC-3) immediately downstream from
the NDWRF outfall, which had a total nitrogen concentration
of 3.23 mg/L in March 2018.

Table 5. Temperature, specific conductance, dissolved oxygen, pH, and nutrient concentrations of water -quality samples collected at Ellerbe Creek, Durham, North Carolina,
from July 2016 to March 2018.
[Locations of sample sites are shown in figure 4. °C, degree Celsius; mg/L, milligram per liter; µS/cm, microsiemens per centimeter; N, nitrogen; P, phosphorus; EC, Ellerbe Creek; TR, tributary; BS, bank seep;
-, not measured; <, less than; PZ, piezometer; GW, groundwater well]
Nitrate
Site Dissolved oDissolved pH, Specific Ammonia, Nitrite, Orthophosphate,
Sample Sample Temperature, oxygen plus nitrite, Total N,
Station number map oxygen standard conductance, mg/L mg/L mg/L
name date time °c mg/L saturation, units PS/cm as N mg/L as N as P mg/L
percent as N
0208682450
EC-2
7/12/2016
09:45
24.4
7.1
85.2
7.4
29
0.14
0.381
0.022
0.039
1.02
02086833
EC-3
7/12/2016
10:25
24.9
7.5
90.9
7.3
390
0.07
1.17
0.031
0.043
1.73
02086835
EC-5
7/12/2016
11:00
25.3
7.5
91.6
7.3
393
0.06
1.41
0.035
0.037
2.06
360211078513701
TR-1
7/12/2016
11:20
25.5
7.4
90.7
7.3
156
0.04
0.273
0.007
0.048
0.88
02086837
EC-6
7/12/2016
11:45
25.7
7.5
92.2
7.3
378
0.06
1.33
0.032
0.037
1.92
02086839
EC-7
7/12/2016
13:00
26.1
8
99.1
7.4
381
0.06
1.21
0.03
0.04
1.82
360226078512801
TR-2
7/12/2016
13:10
25.7
7.3
89.8
7.2
131
0.06
0.164
0.007
0.032
0.78
02086841
EC-8
7/12/2016
15:20
27.2
8.1
100
7.3
398
0.04
1.18
0.014
0.035
1.84
02086843
EC-9
7/12/2016
14:10
26.9
8
100
7.4
380
0.05
1.22
0.029
0.039
1.78
02086845
EC-10
7/12/2016
14:40
27.1
8
100
7.4
379
0.05
1.21
0.03
0.038
1.79
360149078514801
BS-1
8/2/2016
11:00
22.2
-
-
5.9
100
0.12
0.406
0.003
0.041
0.85
360159078514101
BS-3
8/2/2016
12:15
28.8
7.1
461
0.11
<0.040
0.001
0.065
0.39
360204078513901
BS-4
8/2/2016
12:45
21.6
5.6
147
<0.01
0.203
<0.001
0.01
0.28
360149078514801
BS-1
7/27/2017
13:15
26.2
-
-
6.7
117
0.1
<0.040
<0.001
0.019
-
360159078514101
BS-3
7/27/2017
10:15
27.1
-
-
6.6
170
0.05
0.062
0.002
0.007
-
360204078513901
BS-4
7/27/2017
10:50
26.1
-
-
5.9
150
0.03
0.111
0.002
0.011
-
360158078514201
BS-2
7/27/2017
09:40
26.4
-
6.5
160
0.46
<0.040
0.003
0.01
0.75
360205078513801
BS-5
7/27/2017
11:20
26.2
-
6.1
80
0.03
0.136
0.001
0.009
-
360207078513801
BS-6
7/27/2017
12:10
26.2
-
6
100
0.11
0.043
0.009
0.018
-
02086833
EC-3
3/27/2018
09:30
13.1
9.7
92.1
7.0
328
0.03
2.69
0.007
0.013
3.23
360211078513701
TR-1
3/27/2018
11:00
7.0
10.6
87.2
7.2
204
0.04
0.41
0.003
0.016
0.94
02086837
EC-6
3/27/2018
11:30
12.3
10
93.3
7.0
320
0.03
2.27
0.006
0.014
2.79
02086849
EC-11
3/27/2018
12:15
10.4
10.2
91.1
7.2
279
0.11
2.19
0.02
0.016
2.75
360204078513902
PZ-1
3/29/2018
15:20
21.3
9.3
100
6.1
144
0.19
0.067
0.002
0.023
0.51
360204078513903
PZ-2
3/29/2018
15:30
22.4
8.9
100
6.3
298
<0.01
1.04
<0.001
0.005
1.17
360159078513801
GW-1
3/29/2018
11:00
22.8
1.6
18.8
5.2
186
0.11
0.105
0.006
0.044
0.65
360207078512501
GW-2
3/29/2018
14:00
13.1
4.9
74.2
5.1
119
<0.01
0.048
<0.001
0.004
0.15
N

Table 6. Major ion concentrations in water -quality samples collected at Ellerbe Creek, Durham, North Carolina, from July 2016 to March 2018.
[Locations of sample sites are shown in figure 4. mg/L, milligram per liter; CaCOV calcium carbonate; µg/L; microgram per liter; EC, Ellerbe Creek; -, not measured; BS, bank seep; TR, tributary;
GW, groundwater well; <, less than]
Station number
Site
map
Sample
date
Sample
time
Dissolved
Calcium,
solids, mg/L
mg/L
Magne-
sium,
L
mg/L
Potas
sium,
mg/L
Sodium,
mg/name
Chlo
ride,
mg/L
Sulfate,
mg/L
Bicarbon-
ate,
mg/L
Alkalinity,
mg/L as
CaCO3
Bro
mide,
mg/L
Fluoride,
mg/L
Iron,
pg/L
Manga-
nese,
pg/L
0208682450
EC-2
7/12/2016
09:45
200
28.7
7.16
4.49
18.9
17.4
13.6
125.66
103
-
0.16
604
205
02086833
EC-3
7/12/2016
10:25
227
23.7
6.11
7.62
39.2
33
34.1
109.56
89.8
-
0.32
304
93.5
02086835
EC-5
7/12/2016
11:00
243
21.9
5.8
8.58
45.6
37.6
39.8
104.19
85.4
-
0.38
205
61.2
02086837
EC-6
7/12/2016
11:45
247
22.1
5.91
8.25
43.9
35.9
37.7
105.042
86.1
-
0.35
225
73.8
02086839
EC-7
7/12/2016
13:00
237
22.7
6.03
7.98
42.3
34.6
35.9
106.262
87.1
-
0.34
265
74.4
02086841
EC-8
7/12/2016
15:20
233
20.9
5.64
8.74
47
39.1
40.9
101.75
83.4
-
0.39
186
50.8
02086843
EC-9
7/12/2016
14:10
218
22.5
5.87
7.94
42
34.8
36.1
105.77
86.7
-
0.34
247
66.1
02086845
EC-10
7/12/2016
14:40
219
22.4
5.92
8.1
41.4
34.7
36.1
105.53
86.5
-
0.34
264
67.3
360149078514801
BS-1
8/2/2016
11:00
71
8.02
2.17
1.81
7.47
3.28
6.21
42.09
34.5
0.04
0.06
1,150
596
360159078514101
BS-3
8/2/2016
12:15
296
20.2
5.43
1.82
82.9
25.5
11.7
258.64
212
0.252
0.16
562
968
360204078513901
BS-4
8/2/2016
12:45
97
7.56
3.6
0.57
15.8
6.8
33
28.79
23.6
0.056
0.04
95.4
10.6
02086833
EC-3
3/27/2018
09:30
-
20.1
5.19
7.32
36.3
37.5
35.3
62.8
51.6
0.069
-
187
-
360211078513701
TR-1
3/27/2018
11:00
-
17.9
4.95
2.12
17.3
21.4
14.1
65.9
54.1
0.084
-
438
-
02086837
EC-6
3/27/2018
11:30
-
20.2
5.2
7.11
35.2
36.7
33.9
75.6
62.2
0.09
-
209
-
02086849
EC-11
3/27/2018
12:15
-
19.4
5.01
5.86
28.9
30.2
27.5
65.7
54
0.06
-
233
-
360159078513801
GW-1
3/29/2018
11:00
-
33.4
14.2
1.13
10.5
39.2
8.25
102
83.4
0.479
-
4,260
-
360207078512501
GW-2
3/29/2018
14:00
-
12.6
4.13
0.33
17.9
37
6.82
31.2
25.5
0.239
-
<10.0
-
a
N
W

24 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
0
O X X
X
00
EXPLANATION
O Surface -water sites July 2016
X Surface -water sites March 2018
O Tributary site 360211078513701
Bank seeps
+ Groundwater wells
BOO 00 00 p0 -O O O 1O 1O 00 00 00
Calcium Chloride, nitrite plus nitrate
Figure 12. Trilinear Piper diagram showing water -chemistry data for water -quality samples collected in July 2016 and March 2018 at
surface -water sites, bank seeps, and groundwater wells in the Ellerbe Creek study area, Durham, North Carolina.
On the basis of the low nitrate concentrations within the
groundwater samples, the small source of nitrate observed
within the bank seeps and tributaries may be attributed to
Ellerbe Creek itself. In response to rainfall events, rising stage
from storm flow recharges bank storage with diluted stream
water and likely produces some degree of backwater within
the tributaries. As stream stage falls and hydraulic gradients
begin to reverse to base -flow conditions, the inundated banks
discharge back into Ellerbe Creek. In other settings where
stream waters do not contain elevated nitrate concentrations,
discharge from bank storage can dilute the nutrient signature
of the groundwater discharging to a stream. Given the nutrient
concentrations within Ellerbe Creek, however, this likely is
not the case. The bank storage component, which is filled from
recent storm events, is more likely to contain the high nutrient
concentrations. Similar studies have shown that where effluent
discharge constitutes a majority of base flow, it may also exert
a dominant influence on stream water -quality (Harden and
others, 2013; Lambert and others, 2017).

Water -Quality Results 25
A B
500
N
C
d
a)400
0
U
m o 300
E
U C
C d
200
C O_
O
U
U
100
U
d
O
0
8
7
N
a
m
c 6
N
C
2
O_
5
4
Ellerbe Creek Groundwater and Ellerbe Creek Groundwater and
bankseep bank seep
C 14 14 14 14 14 13 13 13 13 8
10
0.01
•
Lower reporting limit
/ for analyte
0.001 '
Ammonia (as N) Nitrate (as N) Nitrite (as N) Orthophosphate (as P) Total Nitrogen (as N)
EXPLANATION
• Outlier
Upper adjacent
75th percentile
Median
25th percentile
Lower adjacent
Figure 13. Boxplots showing range, median, and quartile statistical values for (A) specific conductance, (B) pH, and (C) nutrient
concentrations of surface -water, groundwater, and bank seep samples collected in July and August 2016, July 2017, and March 2018 in
the Ellerbe Creek study area in Durham, North Carolina. N, nitrogen; P, phosphorous.

26 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
78'52'00" 78'51'00"
36°02'30"
36'02'00"
a.
Y. 1 1.2201.18
Y.•
0.164
0
1.21 0
1.33
a� _Y}• A • .ram R -
z_
;• 1.41
,.. o 00.27
95
E§ 0.20 0 a�
' r
W.
rs •,:
i = z ^ <0,04
Lyh�`
:^
EXPLANATION
2� j
�•+ 1.41 o Surface -water site and nitrate concentration,
in milligrams in per liter
�' '
F f
..
I • 0.20 0 Bank seep site and nitrate concentration,
���p�'M1E�er •.a
r-`r_,�,��'
in milligrams per liter
% ..
Base from North Carolina Center for Geographic Information and Analysis 0 0.25 0.50 MILE
North Carolina State Plane coordinate system I
North American Datum of 1983
0 0.40 0.80 KILOMETER
Figure 14. Map showing nitrate concentrations at surface -water and banl< seep sites sampled in July and August 2016 in the Ellerbe
Creek study area in Durham, North Carolina.

Water -Quality Results 27
36°02'30"
36°02'00"
78°52'00"
78°51'00"
Base from North Carolina Center for Geographic Information and Analysis 0 0.25 0.50 MILE
North Carolina State Plane coordinate system
North American Datum of 1983
0.40 0.80 KILOMETER
Figure 15. Map showing nitrate concentrations at bank seep sites sampled in July 2017 in the Ellerbe Creek study area in Durham,
North Carolina.

28 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
78'52'00" 78°51'00"
36°02'30"
36°02'00"
: a x S ate."' • i -y :' i i:Y . - . c ' 1 .. . �•., •�.. *' . L f''!�'. �t �''
.Jill oo jr
hp
�a� � �.�� .ram '{ = . r. , ��• °- .�=.
lk
o ,
0.067 (PZ-1)
1.04 (PZ-2) o s� n
yL _ • - i -%
0.105 '4
O or
.' EXPLANATION
2,69 o Surface -water site and nitrate concentration,
in milligrams per liter
0.105 o Groundwater site and nitrate concentration,
f`4J' ��'• . in milligrams per liter
Alit
* r} ..
Base from North Carolina Center far Geographic Information and Analysis 0 0.25 0.50 MILE
North Carolina State Plane coordinate system I
North American Datum of 1983
0 0.40 0.80 KILOMETER
Figure 16. Map showing nitrate concentrations at surface -water and groundwater sites sampled in March 2018 in the Ellerbe Creek
study area in Durham, North Carolina. PZ, piezometer.

Summary and Conclusions 29
Summary and Conclusions
An assessment of groundwater and surface -water
interactions along Ellerbe Creek in Durham, North Carolina,
was conducted from July 2016 to March 2018 using a
multimethod approach to understand if groundwater discharge
is a source of nitrate to the stream. A streamflow gain -and -
loss survey showed that Ellerbe Creek has both gaining and
losing reaches within the study area. Verifiable streamflow
gain exists in reaches with surface -water inflows, such as from
the North Durham Water Reclamation Facility (NDWRF)
effluent outfall and small unnamed tributaries. Gains from
groundwater generally were small —too small to quantitatively
verify within the uncertainty limitations of the discharge
measurement methods. Diabase dikes cut across the bedrock
underlying the alluvial sediments in this area of Ellerbe
Creek particularly within reach F. The diabase dikes may act
as an impermeable boundary to groundwater discharge, and
preferential pathways along the weathered contact areas may
divert groundwater along the dike.
Continuous water -level data collected within the stream,
banks, and streambed show that Ellerbe Creek is largely a
gaining stream within the study area. Hydraulic gradients
were highest in the horizontal direction into the stream, with
observed horizontal gradients twice the magnitude of those in
the vertical direction. During storm events when streamflow
is high, gradients temporarily reverse, and recharge through
the streambed sediments and bank storage occurs for short
durations. Groundwater levels likely are highest in late spring,
which would lead to an increase in groundwater discharge
through both the stream bank and streambed.
Hydrograph-separation methods yielded base -flow
estimates ranging from 14.0 to 17.7 cubic feet per second
(ft3/s), corresponding to contributions of up to 57 percent of
streamflow in Ellerbe Creek in the study area. According to
data provided by the NDWRF, average effluent discharge
from the NDWRF is about 13 ft3/s, which accounts for more
than 30 percent of the mean streamflow and nearly 80 percent
of base flow in this reach of Ellerbe Creek. Groundwater
discharge and tributary inflows along the stream account for
the small remaining component of base flow. An estimated
3.7 ft3/s of natural base flow was observed when effluent
discharge was stopped for several hours during the study
period. This base flow would account for about 9 percent
of streamflow, which agrees with upper base -flow estimates
calculated by the PART method.
Thermal imagery surveys of bank seeps along the stream
show few persistent seeps during early spring and late
summer. Bank -storage discharge likely accounts for much
of the observed seepage from the stream banks; however,
distinct temperature differences indicate that some bank seeps
contain a measurable component of discharging groundwater.
The fiber-optic distributed temperature sensing (FO-DTS)
survey was able to resolve discharge from only one of the
persistent seeps, likely because the area was sheltered from
direct streamflow by a sandbar. These results indicate that the
quantity of groundwater discharge along the reach is such a
small contribution to the overall streamflow that it cannot be
resolved by the FO-DTS system under these conditions. On
the basis of base -flow estimations and flow calculated from
water -level data, the groundwater component in Ellerbe Creek
is less than 2 percent of the mean streamflow.
Nitrate concentrations were higher in surface water
compared to the bank seeps and groundwater, with the highest
concentration of 2.69 milligrams per liter (mg/L) in the reach
just downstream from the NDWRF outfall. In comparison,
samples collected at landfill groundwater monitoring
wells contained nitrate concentrations less than or equal
to 0.11 mg/L and low concentrations of dissolved oxygen,
suggesting that conditions favoring denitrification exist at
depth. Denitrification could help account for the relatively
low concentrations of nitrate observed at the groundwater
sites. Elevated nitrate concentrations within the bank seep and
stream piezometer samples were highest after a storm event.
These samples may reflect a mixture of stream -recharged bank
storage and shallow groundwater.
Groundwater within the proximity of Ellerbe Creek
does not have a strong influence on the hydrology and, as
a consequence, the water -quality of the stream in the study
reach. Groundwater flowing from the landfill towards the
stream was not observed to exert influence on nitrogen
concentrations in the study reach. The data collected during
this study indicate that surface -water inflows, including
the effluent discharge from the NDWRF, are of much
greater importance to the streamflow and a greater nutrient
source than groundwater discharge along the study reach of
Ellerbe Creek.

30 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
References Cited
Antolino, D.J., 2018, Groundwater -surface water
interactions in Ellerbe Creek in Durham, North Carolina,
2016-2018: U.S. Geological Survey data release,
https:Hdoi.org/10.5066/P9YFET78.
Barlow, P.M., Cunningham, W.L., Zhai, T., and Gray, M.,
2015, U.S. Geological Survey Groundwater Toolbox,
a graphical and mapping interface for analysis of
hydrologic data (version 1.0)--User guide for estimation
of base flow, runoff, and groundwater recharge from
streamflow data: U.S. Geological Survey Techniques
and Methods, book 3, chap. B 10, 27 p. [Also available at
https:Hdoi.org/10.3133/tm3BIO.]
Bonn, B.A., 2008, Using the U.S. Geological Survey
National Water Quality Laboratory LT-MDL to
evaluate and analyze data: U.S. Geological Survey
Open -File Report 2008-1227, 73 p. [Also available at
https:Hdoi.org/10.3133/ofr2OO8l227.]
Briggs, M.A., Lautz, L.K., and McKenzie, J.M., 2012, A
comparison of fibre -optic distributed temperature sensing
to traditional methods of evaluating groundwater inflow to
streams: Hydrological Processes, vol. 26, no. 9, p. 1277-
1290. [Also available at https:Hdoi.org/l0.I002/hyp.8200.]
Brown, P.M., and Parker, J.M., III, comps., 1985, Geologic
map of North Carolina: North Carolina Department of
Natural Resources and Community Development map,
1 sheet, scale 1:500,000.
Chapman, M.J., Bolich, R.E., and Huffman, B.A., 2005,
Hydrogeologic setting, ground -water flow, and ground-
water quality at the Lake Wheeler Road research station,
2001-03, North Carolina Piedmont and Blue Ridge
Mountains Resource Evaluation Program: U.S. Geological
Survey Scientific Investigations Report 2005-5166, 85 p.
[Also available at https://doi.org/10.3133/sir20055166.]
Chapman, M.J., Cravotta, C.A., III, Szabo, Z., and
Lindsay, B.D., 2013, Naturally occurring contaminants in
the Piedmont and Blue Ridge crystalline -rock aquifers and
Piedmont early Mesozoic basin siliciclastic-rock aquifers,
Eastern United States, 1994-2008: U.S. Geological Survey
Scientific Investigations Report 2013-5072, 74 p. [Also
available at https:Hdoi.org/10.3133/sir20l35072.]
Cunningham, W.L., and Schalk, C.W., comps., 2011,
Groundwater technical procedures of the U.S. Geological
Survey: U.S. Geological Survey Techniques and Methods,
book 1, chap. Al, 151 p., accessed October 16, 2014, at
https:Hdoi.org/10.3133/tmIA1.
Deitchman, R.S., and Loheide, S.P., II, 2009, Ground -
based thermal imaging of groundwater flow processes
at the seepage face: Geophysical Research Letters,
v. 36, no. 14, L14401, 6 p. [Also available at
https:Hdoi.org/10. 1029/2009GLO38103. ]
Dubrovsky, N.M., Burow, K.R., Clark, G.M., Gronberg, J.M.,
Hamilton, P.A., Hitt, K.J., Mueller, D.K., Munn, M.D.,
Nolan, B.T., Puckett, L.J., Rupert, M.G., Short, T.M.,
Spahr, N.E., Sprague, L.A., and Wilber, W.G., 2010, The
quality of our Nation's waters -Nutrients in the Nation's
streams and groundwater, 1992-2004: U.S. Geological
Survey Circular 1350, 174 p. [Also available at
https:Hdoi.org/10.3133/cirl350.]
Fishman, M.J., ed., 1993, Methods of analysis by the
U.S. Geological Survey National Water Quality
Laboratory -Determination of inorganic and organic
constituents in water and fluvial sediments: U.S. Geological
Survey Open -File Report 93-125, 217 P. [Also available at
https:Hdoi.org/10.3133/ofr93125.]
Hallberg, G.R., and Keeney, D.R., 1993, Nitrate, chap. 12 of
Alley, W.M., ed., Regional ground -water quality: New York,
Van Nostrand Reinhold, p. 297-322.
Hanna, H.D., and Bradley, P.J., comps., 2016, Geologic
map of Durham County, North Carolina: North Carolina
Geological Survey Open File Report 2016-23, 1 sheet,
scale 1:50,000.
Harden, S.L., Cuffney, T.F., Terziotti, S., and Kolb, K.R.,
2013, Relation of watershed setting and stream nutrient
yields at selected sites in central and eastern North
Carolina, 1997-2008: U.S. Geological Survey Scientific
Investigations Report 2013-5007, 47 p., 4 app. [Also
available at https://doi.org/10.3133/sir20l35007.]
Homer, C., Dewitz, J., Yang, L., Jin, S., Danielson, P.,
Xian, G., Coulston, J., Herold, N., Wickham, J., and
Megown, K., 2015, Completion of the 2011 National
Land Cover Database for the conterminous United
States -Representing a decade of land cover change
information: Photogrammetric Engineering and Remote
Sensing, v. 81, no. 5, p. 345-354.
Institute of Hydrology, 1980a, Low flow studies -Report
no. 1, research report: Wallingford, United Kingdom,
Institute of Hydrology, 42 p.
Institute of Hydrology, 1980b, Low flow studies -Report
no. 3, catchment characteristic estimation manual:
Wallingford, United Kingdom, Institute of Hydrology, 27 p.

References Cited 31
Lambert, R.B., Opsahl, S.P., and Musgrove, M., 2017, Water
quality, sources of nitrate, and chemical loadings in the
Geronimo Creek and Plum Creek watersheds, south-central
Texas, April 2015-March 2016: U.S. Geological Survey
Scientific Investigations Report 2017-5121, 49 p. [Also
available at https://doi.org/10.3133/sir20l75121.]
Lauer, F., Frede, H.-G., and Breuer, L., 2013,
Uncertainty assessment of quantifying spatially
concentrated groundwater discharge to small streams
by distributed temperature sensing: Water Resources
Research, v. 49, no. 1, p. 400-407. [Also available at
https:Hdoi.org/10.1029/2012W-RO12537.]
McSwain, K.B., Bolich, R.E., Chapman, M.J., and
Huffman, B.A., 2009, Water -resources data and
hydrogeologic setting at the Raleigh hydrogeologic
research station, Wake County, North Carolina,
2005-2007: U.S. Geological Survey Open -
File Report 2008-1377, 48 p. [Also available at
https://pubs.er.usgs.gov/publication/ofr2008l377.]
McSwain, K.B., Young, M.B., and Giorgino, M.L., 2014,
Using stable isotopes of nitrogen and oxygen to identify
sources of nitrate in three creeks, Durham County, North
Carolina, 2011-12: U.S. Geological Survey Scientific
Investigations Report 2014-5171, 22 p. [Also available at
https:Hdoi.org/10.3133/sir2Ol45171.]
Messier, K.P., Kane, E., Bolich, R., and Serre, M.L., 2014,
Nitrate variability in groundwater of North Carolina using
monitoring and private well data models: Environmental
Science & Technology, v. 48, no. 18, p. 10804-10812. [Also
available at https://doi.org/10.1021/es502725f]
Mueller, D.K., Schertz, T.L., Martin, J.D., and
Sandstrom, M.W., 2015, Design, analysis, and
interpretation of field quality -control data for water -
sampling projects: U.S. Geological Survey Techniques
and Methods, book 4, chap. C4, 54 p. [Also available at
https:Hdoi.org/10.3133/tm4C4.]
Mueller, D.S., Wagner, C.R., Rehmel, M.S., Oberg, K.A.,
and Rainville, F., 2013, Measuring discharge with acoustic
Doppler current profilers from a moving boat (ver. 2.0,
December 2013): U.S. Geological Survey Techniques and
Methods, book 3, chap. A22, 95 p., accessed June 15, 2017,
at https:Hdoi.org/10.3133/tm3A22.
National Oceanic and Atmospheric Administration, 2015,
2015 NCFMP lidar-Statewide North Carolina (phase 3):
Charleston, S.C., National Oceanic and Atmospheric
Administration dataset, accessed June 4, 2018,
at https:Hcoast.noaa.gov/datavieweL
North Carolina Department of Environment and Natural
Resources, 2003, Ellerbe Creek local watershed plan:
Raleigh, N.C., North Carolina Department of Environment
and Natural Resources, 133 p., accessed July 17, 2018, at
http://portal.ncdenr.org/web/eep/rbrps/neuse.
North Carolina Department of Environment and Natural
Resources, 2010, NC 2010 integrated report categories 4
and 5 impaired waters: Raleigh, N.C., North Carolina
Department of Environment and Natural Resources, 145 p.
North Carolina Department of Environmental Quality,
Division of Water Resources, 2016, 2016 status
report -Falls Lake nutrient strategy: Raleigh, N.C.,
North Carolina Department of Environmental Quality,
Division of Water Resources, 65 p., accessed June 4,
2018, at https://ncdenr.s3.amazonaws.com/s3fs-public/
Environmental%20Management%20Commission/EMC%20
Meetings/2016/March2016/Attachments/AttachA_
InfoItem 16-02Huisman l OMar 16.pdf.
Pandey, P., Gleeson, T., and Baraer, M., 2013, Toward
quantifying discrete groundwater discharge from frozen
seepage faces using thermal infrared images: Geophysical
Research Letters, v. 40, no. 1, p. 123-127. [Also available at
https:Hdoi.org/l0.1029/2012GLO54315.]
Piper, A.M., 1953, A graphic procedure in the geochemical
interpretation of water analyses: U.S. Geological Survey
Ground -Water Note 12, 14 p.
Rutledge, A.T., 1998, Computer programs for describing the
recession of ground -water discharge and for estimating
mean ground -water recharge and discharge from streamflow
records -Update: U.S. Geological Survey Water -Resources
Investigations Report 98-4148, 43 p., accessed June 4,
2018, at https:Hdoi.org/l0.3133/wri984148.
Selker, J.S., Th6venaz, L., Huwald, H., Mallet, A.,
Luxumberg, W., van de Giesen, N., Stejskal, M., Zeman, J.,
Westhoff, M., and Parlange, M.B., 2006, Distributed fiber-
optic temperature sensing for hydrologic systems: Water
Resources Research, v. 42, no. 12, 8 p., accessed June 4,
2018, at https:Hdoi.org/l0.1029/2006WR005326.
Sincich, T., 1993, Statistics by example: Upper Saddle River,
N.J., Prentice Hall, 1,024 p.
Stonestrom, D.A., and Constantz, J., eds., 2003, Heat as a tool
for studying the movement of ground water near streams:
U.S. Geological Survey Circular 1260, 96 p. [Also available
at https:Hdoi.org/10.3133/cirl260.]
Turnipseed, D.P., and Sauer, V.B., 2010, Discharge
measurements at gaging stations: U.S. Geological Survey
Techniques and Methods, book 3, chap. A8, 87 p. [Also
available at https://doi.org/10.3133/tm3A8.]

32 Groundwater/Surface-Water Interactions Along Ellerbe Creek in Durham, North Carolina, 2016-18
U.S. Geological Survey, 1992, Review process for samples
analyzed at the National Water Quality Laboratory
(N WQL): National Water Quality Laboratory Technical
Memorandum 93-02, 5 p., accessed November 2013 at
http://nwgl.usgs.gov/tech memos/nwgl.93-02.html.
U.S. Geological Survey, 2006, Collection of water
samples (ver. 2.0, September 2006): U.S. Geological
Survey Techniques of Water -Resources Investigations,
book 9, chap. A4, 166 p., accessed June 4, 2018, at
https:Hdoi.org/10.3133/twriO9A4.
U.S. Geological Survey, 2018, USGS water data for
the Nation: U.S. Geological Survey National Water
Information System database, accessed June 4, 2018, at
https:Hdoi.org/10.5066/F7P55KJN.
Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of
Comal Springs at New Braunfels, Texas, in Proceedings of
Texas Water 95—August 16-17, 1995, San Antonio, Texas:
American Society of Civil Engineers, p. 77-86.
Weaver, J.C., and McSwain, K.B., 2013, Determination
of flow losses in the Cape Fear River between
B. Everett Jordan Lake and Lillington, North Carolina,
2008-2010: U.S. Geological Survey Scientific
Investigations Report 2012-5226, 76 p. [Also available at
https:Hdoi.org/l0.3133/sir2Ol25226.]
Young, K.B., 1950, A comparative study of mean -section
and mid -section methods for computation of discharge
measurements: U.S. Geological Survey Open -File
Report 53-277, 52 p., accessed April 24, 2015, at
https:Hdoi.org/10.3133/ofr53277.

For more information concerning the research in this report, contact
Director, South Atlantic Water Science Center
U.S. Geological Survey
720 Gracern Road
Stephenson Center, Suite 129
Columbia, SC 29210
Publishing support provided by the U.S. Geological Survey
Science Publishing Network, Reston and Sacramento
Publishing Service Centers

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