Turkey_Creek_TMDL_Final

Total Maximum Daily Load
Fecal Coliform
Turkey Creek, North Carolina

[Waterbody IDs: 18-87-1a; 18-87-1b]

Final Report
October 2022
Approved by EPA October 24, 2022

Prepared by:
NC Department of Environmental Quality
Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
White Oak River Basin
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Table of Contents

List of Abbreviations ........................................................................................................................ii
SUMMARY SHEET ............................................................................................................................ iii
1 INTRODUCTION ....................................................................................................................... 1
1.1 TMDL Components ......................................................................................................... 2
1.2 Documentation of Impairment ....................................................................................... 4
1.3 Watershed Description ................................................................................................... 5
1.4 Water Quality Characterization ...................................................................................... 6
2 SOURCE ASSESSMENT ............................................................................................................. 7
2.1 Nonpoint Source Assessment ......................................................................................... 7
2.2 Point Source Assessment ................................................................................................ 8
3 TOTAL MAXIMUM DAILY LOADS AND LOAD ALLOCATION ..................................................... 8
3.1 TMDL Objective ............................................................................................................... 8
3.2 Modeling ......................................................................................................................... 9
3.2.1 Approach ..................................................................................................................... 9
3.2.2 Existing Load Calculation .......................................................................................... 10
3.2.3 TMDL Calculation ...................................................................................................... 11
3.3 TMDL Allocation ............................................................................................................ 12
3.3.1 Margin of Safety ........................................................................................................ 13
3.3.2 Waste Load Allocation (WLA) ................................................................................... 13
3.3.3 Load Allocation (LA) .................................................................................................. 14
3.3.4 Critical Condition and Seasonal Variation ................................................................ 14
3.3.5 TMDL Summary ......................................................................................................... 16
4 TMDL IMPLEMENTATION PLAN ............................................................................................ 16
5 PUBLIC PARTICIPATION ......................................................................................................... 17
6 FURTHER INFORMATION ...................................................................................................... 17
7 REFERENCES .......................................................................................................................... 18
Appendix A: NCDMF Monitoring Data Summary ......................................................................... 19
Appendix B: Turkey Creek Steady-State Tidal Prism Model Inputs and Parameters ................... 21
Appendix C: NCDMF Mapping of Potential Pollution Sources in B-9 Growing Area .................... 22
Appendix D: Public Notification of TMDL for Fecal Coliform for Turkey Creek ............................ 23
Appendix E: Public Comments Responsiveness Summary ........................................................... 24

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List of Abbreviations

AU Assessment Unit
BMP Best Management Practice
CFR Code of Federal Regulations
cfu Colony forming unit
CWA Clean Water Act
EPA Environmental Protection Agency

FC Fecal Coliform Bacteria
HUC Hydrologic Unit Code

LA Load Allocation
MF MF is an abbreviation for the membrane filter procedure for bacteriological analysis
ml Milliliter(s)
MOS Margin of Safety
MPN Most Probable Number
NCAC NC Administration Code
NCDMF North Carolina Division of Marine Fisheries
NCDOT North Carolina Department of Transportation
NCDWR North Carolina Division of Water Resources
NLCD National Land Cover Database
NLDAS North American Land Data Assimilation System
NOAA National Oceanic and Atmospheric Administration
NPDES National Pollutant Discharge Elimination System
NSSP National Shellfish Sanitation Program
ORW Outstanding Resource Waters supplemental classification
ROW NCDOT road right of way
SA Class SA water body: suitable for commercial shellfishing and all other tidal
saltwater use
TMDL Total Maximum Daily Load
USGS United States Geological Survey
WLA Waste Load Allocation
WRRI Water Resources Research Institute of UNC

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SUMMARY SHEET

Total Maximum Daily Load (TMDL)

1. 303(d) Listed Waterbody Information

State: North Carolina

County: Onslow

Major River Basin: White Oak River Basin

Watershed: USGS HUC 03030001040005

Impaired Waterbody (2022 303(d) List):

Waterbody Name – [AU] Description
Water
Quality
Classification1
Acres
Turkey Creek – [18-87-1a] From source to 0.25 miles inland of
Intracoastal Waterway to ICWW
SA;ORW 79.5
Turkey Creek – [18-87-1b] From 0.25 miles inland of ICWW to
Intracoastal Waterway
SA;ORW 59.6
1 See List of Abbreviations on page ii

Constituent(s) of Concern: Fecal Coliform Bacteria

Designated Uses: Shellfish harvesting, biological integrity, propagation of aquatic life, and
recreation.

Applicable Tidal Salt Water Quality Standards for Class SA Waters:
“Organisms of coliform group: fecal coliform group not to exceed a median MF of 14/100 ml
and not more than 10 percent of the samples shall exceed an MF count of 43/100 ml in those
areas most probably exposed to fecal contamination during the most unfavorable
hydrographic and pollution conditions.”

For the approval of shellfish growing areas “the median fecal coliform Most Probable Number
(MPN) or the geometric mean MPN of water shall not exceed 14 per 100 milliliters, and not
more than 10 percent of the samples shall exceed a fecal coliform MPN of 43 per 100
milliliters (per five tube decimal dilution) in those portions of areas most probably exposed to
fecal contamination during most unfavorable hydrographic conditions”(15A NCAC 18A .0431
Standards for an Approved Shellfish Growing Area). In addition, “a minimum of the 30 most
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recent randomly collected samples from each sample station shall be used to calculate the
median or geometric mean and 90th percentile to determine compliance with this standard”
(NSSP, 2017).

TMDL Target:
The TMDL is calculated in this analysis as the fecal coliform loads that will result in median
fecal coliform MPN at 14 per 100 milliliters, and the 90th percentile of fecal coliform MPN at
43 per 100 milliliters, using data from December 2011 to November 2016.

2. TMDL Development

Development Tools (Analysis/Modeling): Spreadsheet-based steady-state tidal prism model

Critical Conditions: The 90th percentile concentration is the concentration exceeded only 10%
of the time. Since the data used for model simulation spans 5 years, the critical condition is
implicitly included in the value of the 90th percentile of model results.

Seasonal Variation: Given the long-term flow and water quality data record used to estimate
the fecal coliform load, the seasonal variability is implicitly included in the analysis.

3. TMDL Allocation Summary

Waterbody
(Model
Segment)
AUs
Fecal Coliform Load (MPN/day) %
Reduction Existing
Load WLA2 LA MOS TMDL
Lower
Turkey
Creek (m1)
18-87-1a;
18-87-1b < TMDL1 1.12E+09 1.82E+11 2.03E+10 2.03E+11 0%
Middle
Turkey
Creek (m2)
18-87-1a 1.81E+11 4.46E+08 3.91E+10 4.40E+09 4.40E+10 76%
Upper
Turkey
Creek (m3)
18-87-1a 7.81E+10 4.64E+08 3.24E+10 3.65E+09 3.65E+10 53%
1 For Lower Turkey Creek, the calculated existing load is less than the estimated TMDL, and hence no reduction is
needed. The FC water quality standard will be met in model segment m1 once the TMDL is implemented and
loading is reduced from the watersheds of Segment m2 and Segment m3.
2 WLA applies to NCDOT.

4. Public Notice Date: September 2, 2022 - October 3, 2022
5. Submittal Date: October 5, 2022
6. Establishment Date: October 24, 2022
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7. EPA Lead on TMDL (EPA or Blank):
8. Endangered Species (Yes or Blank):
9. MS4s Contributions to Impairment (Yes or Blank):
10. TMDL Considers Point Source, Nonpoint Source, or Both: Both
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1 INTRODUCTION

Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental
Protection Agency’s (EPA) implementing regulations direct each State to develop a Total
Maximum Daily Load (TMDL) for each impaired segment on the North Carolina (NC)
303(d) list, taking into account seasonal variations and a protective margin of safety
(MOS) to account for uncertainty. A TMDL reflects the total pollutant loading that a
waterbody can receive and still meet water quality standards.
TMDLs are established to achieve and maintain water quality standards. A water quality
standard is the combination of a designated use for a particular body of water and the
water quality criteria designed to protect that use. Designated uses include activities
such as swimming, drinking water supply, and shellfish propagation and harvest. Water
quality criteria consist of narrative statements and numeric values designed to protect
the designated uses. Criteria may differ among waters with different designated uses.
The Turkey Creek watershed is located in the White Oak River Basin (HUC
03030001040005) in Onslow County, connecting to the Intracoastal Waterway near
North Topsail Beach, North Carolina. Turkey Creek and its tributaries fall within the
North Carolina Division of Marine Fisheries (NCDMF) B-9 Growing Area (NCDMF, 2016),
covering a watershed area of around 9.1 square miles. Most of the shellfish growing
area is conditionally approved - closed (Figure 1.1) based on the 2016 sanitary survey
(NCDMF, 2016).

When shellfish harvesting is the designated use, the primary parameter of concern is
fecal coliform bacteria. Fecal coliform bacteria are found in the intestinal tract of
humans and other warm-blooded animals. Few fecal coliform bacteria are pathogenic;
however, the presence of elevated levels of fecal coliform in shellfish waters indicates
recent sources of pollution. Some common waterborne diseases associated with the
consumption of raw clams and oysters harvested from polluted water include viral and
bacterial gastroenteritis and hepatitis A. Fecal coliform in surface waters may come
from point sources (e.g., NPDES stormwater conveyances) and nonpoint sources.

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Figure 1.1 – Turkey Creek Shellfish Growing Area (B-9) Classifications (NCDMF, 2016).

1.1 TMDL Components

The 303(d) process requires that a TMDL be developed for each of the waters appearing
in Category 5 of a state’s Integrated Report. The objective of a TMDL is to estimate
allowable pollutant loads and allocate to known sources so that actions may be taken to
restore the water to its intended uses (USEPA, 1991). This TMDL is the total amount of a
pollutant that can be assimilated by the receiving water while still achieving North
Carolina’s water quality criteria for shellfish waters. Currently, TMDLs are expressed as a
“mass per unit time, toxicity, or other appropriate measure” (40 CFR 130.2(i)). It is also
important to note that the TMDLs presented herein are not literal daily limits. These
loads are based on an averaging period that is defined by the water quality criteria.

Generally, the primary components of a TMDL, as identified by EPA (1991, 2000) and the
Federal Advisory Committee (USEPA, 1998) are as follows:

• Target Identification or selection of pollutant(s) and end-point(s) for
consideration. The pollutant and end-point are generally associated with
measurable water quality related characteristics that indicate compliance with
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water quality standards. North Carolina indicates known pollutants on the 303(d)
list.

• Source Assessment. All sources that contribute to the impairment should be
identified and loads quantified, where sufficient data exist.

• Reduction Target. Estimation or level of pollutant reduction needed to achieve
water quality goal. The level of pollution should be characterized for the
waterbody, highlighting how current conditions deviate from the target end-
point. Generally, this component is identified through water quality modeling.

• Allocation of Pollutant Loads. Allocating pollutant control responsibility to the
sources of impairment. The wasteload allocation portion of the TMDL accounts
for the loads associated with existing and future point sources. Similarly, the load
allocation portion of the TMDL accounts for the loads associated with existing
and future non-point sources, stormwater, and natural background.

• Margin of Safety. The margin of safety addresses uncertainties associated with
pollutant loads, modeling techniques, and data collection. Per EPA (USEPA,
2000), the margin of safety may be expressed explicitly as unallocated
assimilative capacity or implicitly due to conservative assumptions.

• Seasonal Variation. The TMDL should consider seasonal variation in the pollutant
loads and end-point. Variability can arise due to stream flows, temperatures, and
exceptional events (e.g., droughts, hurricanes).

• Critical Conditions. Critical conditions indicate the combination of environmental
factors that result in just meeting the water quality criterion and have an
acceptably low frequency of occurrence.

Section 303(d) of the CWA requires EPA to review all TMDLs for approval or disapproval.
Once EPA approves a TMDL, then the waterbody may be moved to Category 4t of the
North Carolina Integrated Report (corresponds to EPA Category 4a). Waterbodies
remain in Category 4t until shellfish growing is approved for harvesting by NCDMF.
Where conditions are not appropriate for the development of a TMDL, management
strategies may still result in the restoration of water quality.

TMDLs are comprised of the sum of individual wasteload allocations (WLAs) for point
sources, load allocations (LAs) for nonpoint sources, and natural background levels. The
TMDL must include a margin of safety (MOS), either implicitly or explicitly, that accounts
for the uncertainty in the relationship between pollutant loads and the quality of the
receiving waterbody, and in the scientific and technical understanding of water quality
in natural systems.

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1.2 Documentation of Impairment

The North Carolina Division of Water Resources (NCDWR) Surface Water and Wetlands
classification for these impaired waters is Class SA, ORW Waters – Shellfish Harvesting
Waters (15A NCAC 02B.0221 Tidal Salt Water Quality Standards for Class SA Waters).
Class SA waters are waterbodies suitable for commercial shellfishing and all other tidal
saltwater use (NCAD, 2003).

Two segments, or assessment units, of Turkey Creek and its tributaries have been
included in Category 5 of the 2022 North Carolina Integrated Report, as shown below in
Table 1.1.

Table 1.1 – Turkey Creek Impaired Assessment Units.
Waterbody Name – [AU] Description Water Quality
Classification Acres
Turkey Creek – [18-87-1a] From source to 0.25 miles inland of
Intracoastal Waterway to ICWW
SA;ORW 79.5
Turkey Creek – [18-87-1b] From 0.25 miles inland of ICWW to
Intracoastal Waterway
SA;ORW 59.6

These restricted shellfish harvesting areas are identified as areas that do not meet their
designated uses. Waters within this classification, according to 15A NCAC 02B.0221
(Tidal Salt Water Quality Standards for Class SA Waters), must meet the following water
quality standard in order to meet their designated use:

Organisms of coliform group: fecal coliform group not to exceed a median
MF of 14/100 ml and not more than 10 percent of the samples shall
exceed an MF count of 43/100 ml in those areas most probably exposed
to fecal contamination during the most unfavorable hydrographic and
pollution conditions.

In addition, for approval of shellfish growing areas “the median fecal coliform Most
Probable Number (MPN) or the geometric mean MPN of water shall not exceed 14 per
100 milliliters, and not more than 10 percent of the samples shall exceed a fecal
coliform MPN of 43 per 100 milliliters (per five tube decimal dilution) in those portions
of areas most probably exposed to fecal contamination during most unfavorable
hydrographic conditions” (15A NCAC 18A .0431 Standards for an Approved Shellfish
Growing Area). In addition, “a minimum of the 30 most recent randomly collected
samples from each sample station shall be used to calculate the median or geometric
mean and 90th percentile to determine compliance with this standard” (NSSP, 2017).

For this report, the monitoring data averaging period was based on the systematic
random sampling strategy outlined in the National Shellfish Sanitation Program’s Model
Ordinance and guidance document. The recent five-year period of data that was
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available was used, December 2011 to November 2016. Data summary can be found in
Appendix A.

1.3 Watershed Description

Turkey Creek and its tributaries fall within the NCDMF B-9 Growing Area in Onslow
County. The watershed covers about 9.1 square miles. Oyster and clam production are
good throughout the area, however a large portion of the shellfish bed area is closed
due to high fecal coliform pollution.

The 2011 National Land Cover Database (NLCD) was used to obtain land cover
characteristics of the watershed. Land cover distribution is shown in Figure 1.2 and land
cover statistics are shown in Table 1.2. Around twenty percent of the watershed is
agricultural lands and five percent is different types of developed lands.

The dominant tide in this region is the lunar semi-diurnal (M2) tide. Currents and tides
within the B-9 area are primarily influenced by New River Inlet to the north and by New
Topsail Inlet to the south (NCDMF, 2016). The mean tidal range at NOAA station
Wrightsville Beach (Station ID: 8658163) to the south is 3.98 ft and 3.11 ft at Beaufort,
Duke Marine Lab (Station ID: 8656483) to the north. Turkey Creek opens to the shallow
Intracoastal Waterway, instead of open ocean, the mean tidal range at Turkey Creek is
expected to be slightly lower, around 3 feet.

Table 1.2 – 2011 Land Cover Distribution of the Turkey Creek Watershed.

Land Cover
Area
(square mile)
Area
(%)
Open Water 0.01 0.2
Developed, Open Space 0.26 2.9
Developed, Low Intensity 0.17 1.9
Developed, Medium Intensity 0.01 0.1
Developed, High Intensity 0.00 0.0
Barren Land 0.08 0.9
Deciduous Forest 0.00 0.0
Evergreen Forest 2.53 27.8
Mixed Forest 0.32 3.5
Shrub/Scrub 1.46 16.1
Herbaceous 0.64 7.0
Cultivated Crops 1.78 19.6
Woody Wetlands 1.40 15.4
Emergent Herbaceous Wetlands 0.43 4.7
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Figure 1.2 – 2011 NLCD Land Cover of the Turkey Creek Watershed.

1.4 Water Quality Characterization

The Shellfish Sanitation and Recreational Water Quality Section of the NCDMF is
responsible for classifying shellfish harvesting waters to ensure oysters and clams are
safe for human consumption. NCDMF adheres to the requirements of the National
Shellfish Sanitation Program, with oversight by the U.S. Food and Drug Administration.
NCDMF conducts shoreline surveys and collects routine bacteria water quality samples
in the shellfish-growing areas of North Carolina. The data are used to determine if the
water quality criteria are being met. If the water quality criteria are exceeded, the
shellfish areas are closed to harvest, at least temporarily, and consequently the
designated use is not being achieved.

NCDMF is monitoring shellfish growing regions throughout North Carolina. Turkey Creek
is sampled using the systematic random sampling strategy as outlined in the National
Shellfish Sanitation Program’s Model Ordinance and guidance document.

There are three fecal coliform monitoring stations sampled by the NCDMF within Turkey
Creek, as shown in Figure 1.1. NCDMF data from December 2011 to November 2016 are
summarized in Table 11 of the 2016 NCDMF Sanitary Survey Report for all the stations
within the B-9 area, including the 3 stations in Turkey Creek. The report notes one
station (Station 20A) had estimated 90th percentile at 92 MPN and median at 17.5 MPN
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for that period, which exceeded the criteria. Station 20B, which was added to the
sampling regime in early 2016 in order to better assess the closure lines in Turkey Creek,
had only five samples during the study period. Station 20, which is at the mouth of
Turkey Creek, had data meeting the water quality standard.

2 SOURCE ASSESSMENT

2.1 Nonpoint Source Assessment

Non-point sources are diffuse sources that typically cannot be identified as entering a
water body at a single location. Nonpoint source loading typically occurs during rain
events when surface runoff transports water carrying fecal coliform over the land
surface and discharges it into the stream network. The transport of fecal coliform from
the land to the restricted shellfish harvesting area is dictated by the hydrology, soil type,
land use, and topography of the watershed.

There are many types of nonpoint sources in watersheds that contribute to the
restricted shellfish harvesting areas. The 2016 Sanitary Survey Report (NCDMF, 2016)
documented potential sources of fecal coliform in Turkey Creek. The survey suggested
that runoff from impervious surfaces, subdivisions, and other cleared land remains the
primary contributor to fecal coliform levels throughout B-9. Subdivisions are noted in
the survey as an indicator of population growth, as well as for their tendency to
concentrate potential sources of pollution such as septic systems, pet wastes, and
stormwater. Overall, 41 subdivisions were noted in the B-9 growing area during the
shoreline survey. There has been moderate growth within this growing area during the
recent years, and four new subdivisions have been noted. Three of the four new
subdivisions in B-9, Turkey Point RV Park, Old Dock and Emerald Cove, are within or
close to Turkey Creek. Although the majority of homes and businesses within the B-9
growing area are served by municipal wastewater systems, some areas along North
Topsail Beach and along the mainland make use of individual septic systems.

Wildlife in the watershed are considered to make up background concentrations of fecal
coliform. Wildlife, including raccoon, deer, opossum, and waterfowl, are present
throughout the B-9 area. Waste from these animals can be transported through
stormwater ditches into shellfishing waters, and have some impact on the growing area
during rainfall events.

Grazing animals contribute fecal coliform through either direct access to streams or
runoff from deposition or manure spreading. According to the shoreline survey, there
are a few horse stables in the B-9 area primarily concentrated within the Turkey Creek
watershed. All five animal locations (horses and cattle) identified in B-9 are around
Turkey Creek.

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Agricultural fields of soybeans, corn, tobacco, and winter wheat, as well as a few large
forested areas are also likely to contribute contaminants to the creeks and waterways
following rain events. The cultivated crops land cover is concentrated near the river and
runoff could be a contributing factor if manure is improperly applied, particularly if just
before a storm event.

Nonpoint source contributions to the bacterial levels from human activities generally
arise from malfunctioning or improperly-sited septic systems and their associated drain
fields, or illicit connections of sanitary sewage to the stormwater conveyance system.
The majority of onsite systems in the growing area were visited and inspected during
the shoreline survey (NCDMF, 2016) and no ongoing failures or illicit discharges were
located.

2.2 Point Source Assessment

All wastewater discharges to surface water in the State of North Carolina must receive a
permit to control water pollution. The CWA initiated strict control of wastewater
discharges with responsibility of enforcement given to the Environmental Protection
Agency (EPA). The EPA then created the National Pollutant Discharge Elimination System
(NPDES) to track and control point sources of pollution. The primary method of control
is by issuing permits to discharge with limitations on wastewater flow and constituents.
The EPA delegated permitting authority to the State of North Carolina in 1975.

There are no operating wastewater treatment plants within the Turkey Creek
watershed.

The NC Department of Transportation (NCDOT) has some right of way (ROW) areas
within the Turkey Creek watershed and has a statewide Phase I NPDES stormwater
permit (NCS000250). Stormwater has previously been considered a nonpoint source;
however, NPDES-permitted sources are to be included in the wasteload allocation (WLA)
per EPA guidance (USEPA, 2002).

3 TOTAL MAXIMUM DAILY LOADS AND LOAD ALLOCATION

3.1 TMDL Objective

The TMDL objective is to meet North Carolina water quality fecal coliform standards of a
median MF of 14 per 100 ml and not more than 10 percent of the samples shall exceed
an MF count of 43 per 100 ml. In addition, the National Shellfish Sanitation Program
(NSSP) standard for the approved classification of growing areas requires that fecal
coliform concentrations not exceed a median or geometric mean of a MPN of 14 per
100 ml and the 90th percentile of a MPN of 43 per 100 ml, with a minimum of the 30
most recent samples used to calculate compliance.
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Both standards have the same numeric targets but the NSSP standard uses a minimum
30- sample averaging period. Data collected from December 2011 through November
2016 were used for the purpose of this TMDL.

3.2 Modeling

3.2.1 Approach

Bay and coastal waters such as Turkey Creek and its tributaries are subject to the action
of the tides. The ebb and flood of the tide serves to move water between locations
exchanging and mixing with other water. The tide and amount of freshwater discharge
into the embayment are the dominant influences on the transport of fecal coliform.
Therefore, the TMDL was calculated using the steady-state tidal prism model.

Compared to the volumetric method (EPA Shellfish Workshop, 2002), the steady-state
tidal prism model incorporates the influences of tidally induced transport, freshwater
input, and removal of fecal coliform via decay. Multiple segments may exist within the
model domain. The model assumes that the embayment is well mixed within a single
segment, and freshwater input, tidal range, and the first-order decay of fecal coliform
are all constant. A brief description of the model is presented below.

The steady-state tidal prism model calculates fecal coliform load using equation 3.1:

𝐿=[𝐶(𝑄𝑏+𝑘𝑉)−𝑄0𝐶0]× 𝐶𝑓 (3.1)

where:
L = fecal coliform load (counts per day)
C = mean fecal coliform concentration (MPN / 100 ml) of the segment
k = fecal coliform removal/decay rate (per day)
C0 = fecal coliform concentration (MPN / 100 ml) entering the segment on the
flood tide
Q0 = quantity of water entering the segment on the flood tide (m3 per tidal cycle)
Qb = quantity of mixed water that leaves the segment on the ebb tide (m3 per
tidal cycle)
V = mean volume of the segment (m3)
Cf = unit conversion factor

The fecal coliform decay rate, k, was set at 0.36 per tidal cycle, which is considered a
conservative estimate. The value of the decay rate varies from between 0.3 and 3.0 in
salt water (Thomann and Mueller, 1987). Qb and Q0 are estimated based on the steady
state condition as follows:

Qb = Q0 + Qf
Q0 = βQT
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where:
Qf = mean freshwater input during one tidal cycle (m3 per tidal cycle)
β = exchange ratio
QT = the total ocean water entering the bay on the flood tide (m3 per tidal cycle)

QT is calculated based on the tidal range. The dominant tide in this region is the lunar
semi-diurnal (M2) tide with a tidal period of 12.42 hours. Therefore, the M2 tide is used
for the representative tidal cycle. The mean tidal range is assumed to be 3 feet, slightly
lower than the tidal range (3.11 feet) monitored at a nearby NOAA station at Beaufort,
NC (Station ID: 8656483). In general, the exchange ratio varies from 0.3 to 0.7, based on
the previous model tests in coastal embayments (Kuo et al., 1998; Shen et al., 2002). A
mean value of 0.5 was used for the exchange ratio.

The stream flow estimates (Qf) were downloaded from NLDAS Data Rods Explorer
(https://apps.hydroshare.org/apps/data-rods-explorer) and processed for the Turkey
Creek catchments. For comparison, the fresh water inflow was also estimated based on
the ratio of the drainage area of the Turkey Creek watershed relative to the drainage
area and the stream flows measured by U.S. Geological Survey at the New River gauging
station near Gum Branch, NC (USGS 02093000). The selection of the gauging station is
determined by its similarity in watershed characteristics to Turkey Creek watershed and
the proximity of the station to the TMDL study area. Appendix B provides model inputs
and parameters used for the 90th percentile calculations.

3.2.2 Existing Load Calculation

The existing load was calculated by using Equation 3.1 and the existing median and 90th
percentile concentrations for each model segment. Model segmentation is provided
below in Figure 3.1. Existing median and 90th percentile concentrations are required for
each segment as model inputs. Segment m0 represents the ocean boundary, and data
from Station 20 is used. Data from 20B and 20A were used to represent the lower (m1)
and middle (m2) segments, respectively. For the upper (m3) segment, since no
monitoring station existed within the segment, data from the most upstream station
(Station 20A) were used. Table 3.1 provides the monitoring stations used in each model
segment and the overall median and 90th percentile concentrations.

NCDMF conditional monitoring data were not used to calculate existing concentrations.
Conditional monitoring only took place at Station 20 in the conditionally approved -
open growing area near ocean boundary (Segment m0) after a rainfall event to see if
waters can be reopened to shellfishing. These concentrations tend to be inconsistently
higher compared to stations where conditional monitoring data were not collected.
Therefore, to avoid creating bias in the model, conditional data were not used to
calculate existing loads.
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Figure 3.1 – Model Segments and the Sub-watersheds of Turkey Creek.

Table 3.1 – Monitoring Stations and Assessment Units Associated with Each Model Segment.
Model
Segment Waterbodies AU# Monitoring
Stations
Median FC
(MPN/100ml)
Estimated* 90th
Percentile FC
(MPN/100ml)
m0 Ocean
Boundary
20 4 17
m1 Lower Turkey
Creek
18-87-1a;
18-87-1b
20B 2 42
m2 Middle Turkey
Creek
18-87-1a 20A 17.5 92
m3 Upper Turkey
Creek
18-87-1a 20A 17.5 92
* Method adopted by NCDMF (2016) and described in NSSP (2017)

3.2.3 TMDL Calculation

The TMDL was calculated by using Equation 3.1 and the North Carolina water quality
fecal coliform standards of a median of 14 counts per 100 ml and a 90th percentile of 43
counts per 100 ml. Table 3.2 presents the estimated TMDL for each segment.

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The percent load reduction needed to meet the fecal coliform standards was estimated
using Equation 3.2:

Reduction = (Existing Load – TMDL) / Existing Load (3.2)

Table 3.2 – Load Reduction Requirements under Variations of Standard Criteria.
Standard
Category Segment Standard
(MPN/100ml)
Existing Load
(MPN/day)
TMDL
(MPN/day)
Average
Reduction
Required
Median
m1 14 < TMDL 7.59E+10 0
m2 14 4.53E+10 1.37E+10 70%
m3 14 1.49E+10 1.19E+10 20%
90th
Percentile
m1 43 < TMDL 2.03E+11 0
m2 43 1.81E+11 4.40E+10 76%
m3 43 7.81E+10 3.65E+10 53%

The calculated existing loads are less than the TMDLs in the subwatershed draining to
Segment m1, regardless of whether the calculation is based on the median or the 90th
percentile concentrations. When the 90th percentile concentrations and the
corresponding 90th percentile water quality standard are used, 76% and 53% fecal
coliform load reductions are needed for the subwatersheds of Segment m2 and
Segment m3, respectively. Required reductions in loading are higher for the 90th
percentile model results (highlighted in orange in Table 3.2) than those for the median.
Therefore, the TMDL was calculated using the 90th percentile criterion to allow for both
standards to be met. No reduction in loading is needed from the subwatershed of
Segment m1 due to its lower existing load than the TMDL. The FC water quality standard
will be met in Segment m1 once the TMDL is implemented and loading is reduced from
the subwatersheds of Segment m2 and Segment m3.

3.3 TMDL Allocation

Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that
can be assimilated by the receiving water body while achieving water quality standards.
A TMDL can be expressed as the sum of all point source allocations (WLAs), nonpoint
source allocations (LAs), and an appropriate margin of safety (MOS), which takes into
account any uncertainty concerning the relationship between effluent limitations and
water quality. This definition can be expressed by Equation 3.3.
++=MOSLAsWLAsTMDL (3.3)

Turkey Creek Fecal Coliform TMDL
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The objective of the TMDL is to estimate allowable pollutant loads and to allocate those
loads in order to implement control measures and to achieve water quality standards.
The Code of Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be
expressed in terms of mass per time, toxicity, or other appropriate measures. For fecal
coliform contamination, TMDLs are expressed as counts, or colony forming units (cfu),
per 100 milliliters. TMDLs represent the maximum one-day load the river can assimilate
and maintain the water quality criterion. The systematic procedures adopted to
estimate TMDLs are described below.

3.3.1 Margin of Safety

A Margin of Safety (MOS) is required as part of a TMDL in recognition of many
uncertainties in the understanding and simulation of water quality in natural systems.
For example, knowledge is incomplete regarding the exact nature and magnitude of
pollutant loads from various sources and the specific impacts of those pollutants on the
chemical and biological quality of complex, natural water bodies. The MOS is intended
to account for such uncertainties in a manner that is conservative from the standpoint
of environmental protection. As a conservative estimate in the TMDL calculation, an
explicit MOS of 10% is included. The explicit MOS was achieved by multiplying the TMDL
by 10%. These loads are shown in Table 3.3.

Table 3.3 – Margin of Safety Allocation.
Fecal Coliform Load (MPN/day)
Standard
Category Segment # TMDL MOS Allowable Load
(TMDL-MOS)
90th Percentile
m1 2.03E+11 2.03E+10 1.83E+11
m2 4.40E+10 4.40E+09 3.96E+10
m3 3.65E+10 3.65E+09 3.29E+10

3.3.2 Waste Load Allocation (WLA)

As described in Section 2.2, NCDOT is the only NPDES-permitted discharge in the
watershed included in the WLA as a contributing source. Data is not available to
calculate the existing load for the NCDOT.

The WLA for NCDOT land was isolated from other sources by multiplying the total load
and the ratio of NCDOT road right of way (ROW) area to total subwatershed area. The
NCDOT ROW area was calculated by multiplying the road length and width of US
highways, NC roads, and state route roads within the watershed (AECOM, 2021). The
NCDOT ROW is 1.3% of the total watershed area, as shown below in Table 3.4. The
resulting WLA for NCDOT is provided below in Table 3.5.

NCDOT should continue to implement measures required by the permit, including illicit
discharge detection and elimination, post-construction controls, management of
Turkey Creek Fecal Coliform TMDL
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14
hydraulic encroachments, sediment and erosion control, BMP retrofits, stormwater
pollution prevention for industrial facilities, research, and education programs.

Table 3.4 – Turkey Creek Watershed NCDOT Contributing Area by Subwatershed.
Segment #
Total Sub-
watershed Area
(acres)
NCDOT ROW Area
(acres)
NCDOT Land Area
(% of total)
m1 163 1 0.6%
m2 887 10 1.1%
m3 4772 67 1.4%
Total 5822 78 1.3%

Table 3.5 – NPDES Wasteload Allocations.
NPDES
Permittee Segment #
NCDOT Existing
Load
(MPN/day)
WLA
(MPN/day)
Percent
Reduction
NCDOT
m1 N/A 1.12E+09 0%
m2 N/A 4.46E+08 0%
m3 N/A 4.64E+08 0%

3.3.3 Load Allocation (LA)

All fecal coliform loadings from nonpoint sources such as non-MS4 urban land,
agriculture land, and forestlands are reported as LAs. The LA allocations were estimated
by subtracting the MOS and WLA allocations from the TMDL. The estimated allocations
of fecal coliform loading for nonpoint sources are presented in Table 3.6.

Table 3.6 – Nonpoint Source Allocation.
Segment # Existing Load
(MPN/day) LA (MPN/day) Percent Reduction
m1 N/A 1.82E+11 0%
m2 N/A 3.91E+10 76%
m3 N/A 3.24E+10 53%

3.3.4 Critical Condition and Seasonal Variation

The EPA Code of Federal Regulations (40 CFR 130.7 (c) (1)) requires TMDLs to take into
account critical conditions for stream flow, loading, and water quality parameters. The
intent of this requirement is to ensure that the water quality of the waterbody is
protected during times when it is most vulnerable. The critical condition accounts for
the hydrologic variation in the watershed over many sampling years whereas the critical
period is the condition under which a waterbody is the most likely to violate the water
quality standard(s).
Turkey Creek Fecal Coliform TMDL
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15
The 90th percentile concentration is the concentration exceeded only 10% of the time.
Since the data used for model simulation spans 5 years, the critical condition is implicitly
included in the value of the 90th percentile of model results. Given the length of the
monitoring record and the standard’s recognition of unusual and infrequent events, the
90th percentile is used to cover critical conditions.

The EPA also requires that these TMDL studies take into account seasonal variations.
The consideration of critical condition and seasonal variation is to account for the
hydrologic and source variations. Seasonal variations involve changes in surface runoff,
stream flow, and water quality as a result of hydrologic and climatologic patterns. For
the Turkey Creek TMDL study, variations due to changes in the hydrologic cycle as well
as temporal variability in fecal coliform sources are accounted for by the use of the
longterm data record to estimate the current load.

The seasonal fecal coliform distribution for Station 20A (located inside Segment m2 of
Turkey Creek) is presented in Figure 3.2. Data are available in each season. High fecal
coliform levels (> 14 MPN) occur throughout the year in the estuary. These high
concentrations result in a high 90th percentile concentration. Given the multiple year
flow and water quality data record used to estimate the fecal coliform load, the
seasonal variability is implicitly included in the analysis.

Figure 3.2 – Seasonal Distribution of Fecal Coliform Concentrations at Station 20A in Turkey
Creek (Log Scale). Data Used are from December 2011 to November 2016.

Turkey Creek Fecal Coliform TMDL
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16
3.3.5 TMDL Summary

A summary of the TMDL is provided below in Table 3.7. Reductions in fecal coliform
loading are required for middle and upper Turkey Creek. Reductions in loading from
these sub-watersheds allow for standards to be met throughout Turkey Creek.

The required load reductions are 76% and 53% from the middle and upper Turkey
Creek, respectively. The combined drainage area from these two sub-watersheds is
around 97% of the total drainage area of the entire watershed of Turkey Creek. The
potential sources map produced by NCDMF (Appendix C) shows a concentrated amount
of stormwater outfalls in this watershed.

Table 3.7 – Estimated TMDL and Load Allocation for Fecal Coliform for Turkey Creek.
Waterbody
(Model
Segment)
AUs
Fecal Coliform Load (MPN/day) %
Reduction Existing
Load WLA2 LA MOS TMDL
Lower
Turkey
Creek (m1)
18-87-1a;
18-87-1b < TMDL1 1.12E+09 1.82E+11 2.03E+10 2.03E+11 0%
Middle
Turkey
Creek (m2)
18-87-1a 1.81E+11 4.46E+08 3.91E+10 4.40E+09 4.40E+10 76%
Upper
Turkey
Creek (m3)
18-87-1a 7.81E+10 4.64E+08 3.24E+10 3.65E+09 3.65E+10 53%
1 For Lower Turkey Creek, the calculated existing load is less than the estimated TMDL, and hence no
reduction is needed. The FC water quality standard will be met in model segment m1 once the TMDL is
implemented and loading is reduced from the watersheds of Segment m2 and Segment m3.
2 WLA applies to NCDOT.

4 TMDL IMPLEMENTATION PLAN

Comprehensive sanitary surveys were conducted by NC Shellfish Sanitation Section of
DMF. Evaluations of properties in the area were conducted to determine potential
sources of pollution entering shellfish growing waters (Appendix C). Point sources and
nonpoint sources of fecal coliform of the Turkey Creek watershed is discussed in Section
2 of this document. Based on information provided in the recent survey (NCDMF, 2016),
implementation measures should include continued maintenance and repair of septic
systems, stormwater controls, pet waste management, and proper manure application
to crops.

Local stakeholder groups, governments, and agencies are encouraged to develop an
implementation plan and utilize funding sources for water quality improvement projects
targeted at BMP construction and public outreach. Some potential funding sources
Turkey Creek Fecal Coliform TMDL
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17
include the North Carolina Clean Water Management Trust Fund, and Section 319 and
205j funds. Individual land owners may apply for the Community Conservation
Assistance Program and Agriculture Cost Share Program to improve the condition of
their property. Shoreline surveys for the B-9 shellfish growing area conducted by
NCDMF will help further identify current sources of bacteria and drainage pathways that
allow bacteria to enter Turkey Creek and its tributaries and provide a mechanism to
evaluate progress in attaining TMDL targets.

NCDMF will continue to monitor water quality in Turkey Creek using the systematic
random sampling strategy as outlined in the National Shellfish Sanitation Program’s
Model Ordinance and guidance document. This data will be used to evaluate progress
towards the goal of reaching water quality standards.

5 PUBLIC PARTICIPATION

A draft of the TMDL was publicly noticed from September 2, 2022 through October 3,
2022 through various means including North Carolina’s TMDL listserv, the Water
Resources Research Institute of UNC (WRRI) listserv, and DWR’s public notice calendar.
The draft TMDL was available on DWR’s website
(https://deq.nc.gov/about/divisions/water-resources/water-planning/modeling-
assessment/tmdls) throughout the public comment period. Appendix D contains the
public notice. Appendix E summarizes public comments and responses, however, no
public comments were submitted.

6 FURTHER INFORMATION

Further information concerning North Carolina’s TMDL program can be found on the
Internet at the Division of Water Resources website:
https://deq.nc.gov/about/divisions/water-resources/water-planning/modeling-
assessment/tmdls

Technical questions regarding this TMDL should be directed to the following members
of the DWR Modeling & Assessment Branch:

Bongghi Hong
e-mail: [e-mail]

Pam Behm
e-mail: [e-mail]

Turkey Creek Fecal Coliform TMDL
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7 REFERENCES

AECOM. 2021. Memorandum, NCDOT Right-of-Way and Impervious Cover Area Land
Use Analysis in Virginia Creek and Turkey Creek Watersheds.

Kuo, A., Butt, A., Kim, S. and J. Lin. 1998. Application of a tidal prism water quality model
to Virginia Small Coastal Basins. SRAMSOE No. 348.

NCAD. 2003. NC Administration Code.

NCDMF. 2016. Report of Sanitary Survey, Area B-9, Stump Sound Area, December 2011
through November 2016. NC Division of Marine Fisheries, Shellfish Sanitation and
Recreational Water Quality. Website:
https://digital.ncdcr.gov/digital/collection/p16062coll9/id/328676/rec/3

NOAA. 2010. Tides Online. National Oceanic and Atmospheric Administration/National
Ocean Service. Website: http://co-ops.nos.noaa.gov/

NSSP. 2017. National Shellfish Sanitation Program Guide for the control of Molluscan
Shellfish 2007, US Food and Drug Administration, 2017. Website:
https://www.fda.gov/Food/GuidanceRegulation/FederalStateFoodPrograms/ucm20067
54.htm

Shen, J., H. Wang, and M. Sisson. 2002. Application of an Integrated Watershed and
Tidal prism Model to the Poquoson Coastal Embayment (submitted to Department of
Environmental Quality, Commonwealth of Virginia). Virginia Institute of Marine Science
Special Report 380, Gloucester Point, VA.

USEPA. 1991. Guidance for Water Quality-Based Decisions: The TMDL Process.
Assessment and Watershed Protection Division, Washington, DC.

USEPA. 1998. Draft Final TMDL Federal Advisory Committee Report. U.S. Environmental
Protection Agency, Federal Advisory Committee. Draft final TMDL Federal Advisory
Committee Report. 4/28/98.

USEPA. 2000. Revisions to the Water Quality Planning and Management Regulation and
Revisions to the National Pollutant Discharge Elimination System Program in Support of
Revisions to the Water Quality Planning and management Regulation; Final Rule. Fed.
Reg. 65:43586-43670 (July 13, 2000).

USEPA. 2002. Wayland, Robert, H. and James A. Hanlon. "Establishing Total Maximum
Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and NPDES
Permit Requirements Based on Those WLAs". Memo to Water Division Directors Regions
1-10. United States Environmental Protection Agency, Washington, D.C. 22 November
2002.
Turkey Creek Fecal Coliform TMDL
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Appendix A: NCDMF Monitoring Data Summary

Table A.1 – Fecal coliform (MPN/100ml) random sampling data in Turkey Creek.
Date Stations
20 20A 20B
1/5/2012 2 1.7
5/3/2012 1.7 1.7
6/20/2012 1.7 1.7
8/16/2012 4.5 4.5
9/10/2012 2 22
10/22/2012 4 79
3/13/2013 79 170
4/24/2013 13 33
6/25/2013 7.8 33
8/27/2013 1.8 33
11/19/2013 13 70
12/10/2013 17 170
2/20/2014 1.7 1.7
5/8/2014 1.7 1.7
8/28/2014 4.5 33
10/8/2014 2 1.7
11/19/2014 4 13
12/10/2014 23 79
3/18/2015 2 4.5
3/31/2015 4.5 13
6/1/2015 1.7 22
7/14/2015 2 1.7
12/10/2015 23 70
12/16/2015 17 49
1/12/2016 17 13
3/30/2016 4.5 22 7.8
6/15/2016 1.7 11 2
7/19/2016 1.7 1.7 1.7
8/31/2016 2 7.8 1.7
11/21/2016 4.5 23 79

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Table A.2 – Fecal Coliform (MPN/100 ml) Conditional Sampling Data in Turkey Creek.
Conditional Sampling Data are Not Used in the TMDL Analysis, Included Here for Reference.
Date Stations
20 20A 20B
10/21/2015 34

Table A.3 – Fecal Coliform Data Summary Statistics in Turkey Creek.

Station # Samples Type of
Sampling
Fecal Coliform Bacteria Concentration
(MPN/100ml)
Median Geometric
Mean
Estimated 90th
Percentile
20 30 Random 4 4.49 17
1 Conditional 34 34
20A 30 Random 17.5 13.1 92
20B 5 Random 2 5.13 42
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Appendix B: Turkey Creek Steady-State Tidal Prism Model Inputs and Parameters

Table B.1 – Model Parameters.
Parameter TR β k Cf
Description mean tidal
range
exchange ratio decay rate conversion
factor
Unit m N/A per tidal cycle
(1/T)
T/day
x 100 ml/m3
Value 0.914 0.5 0.36 19323.67

Table B.2 – Model Inputs for 90th Percentile Existing Loads Calculation.
Parameter VT VL Qf C
Description local tidal
prism
volume
low tide volume fresh water input 90th FC
concentration of
the segment
Unit m3 m3 m3/T MPN / 100 ml
Open
Boundary
17
m1 269877 188178 673 42
m2 114961 73216 3661 92
m3 73216 30806 19675 92

Table B.3 – Model Inputs for 90th Percentile TMDL Loads Calculation.
Parameter VT VL Qf C
Description local tidal
prism
volume
low tide volume fresh water input 90th FC
concentration of
the segment
Unit m3 m3 m3/T MPN / 100 ml
Open
Boundary
17
m1 269877 188178 673 42
m2 114961 73216 3661 43
m3 73216 30806 19675 43

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Appendix C: NCDMF Mapping of Potential Pollution Sources in B-9 Growing Area

Figure C.1 – NCDMF Mapping of Potential Pollution Sources in B-9 Growing Area (NCDMF, 2016).
Turkey Creek Fecal Coliform TMDL
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Appendix D: Public Notification of TMDL for Fecal Coliform for Turkey Creek

From: [e-mail] <[e-mail]> on behalf of
Behm, Pamela <[e-mail]>
Sent: Friday, September 2, 2022 1:17 PM
To: [e-mail] <[e-mail]>
Subject: Draft Turkey Creek TMDL Available for Public Review

September 2, 2022

North Carolina Department of Environmental Quality

Division of Water Resources

Draft Total Maximum Daily Load (TMDL) for Fecal Coliform for Turkey Creek (White Oak
River Basin), North Carolina

Now Available for Public Comment

The draft TMDL was developed to meet requirements of Section 303(d) of the Federal
Water Pollution Control Act to address fecal coliform impairments. It is subject to
approval by EPA.

The Draft TMDL document can be found at:

https://edocs.deq.nc.gov/WaterResources/DocView.aspx?dbid=0&id=2477726

Interested parties are invited to comment on the draft TMDL by October 3, 2022.
Comments should be directed to [e-mail] and must be
received no later than 5 pm on October 3, 2022.

Turkey Creek Fecal Coliform TMDL
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Appendix E: Public Comments Responsiveness Summary

No comments were received.