Virginia Creek TMDL_final

Total Maximum Daily Load
Fecal Coliform
Virginia Creek, North Carolina
[Waterbody IDs: 18-87-9-1; 18-87-9a; 18-87-9b]
Final Report
March 2022
Prepared by:
NC Department of Environmental Quality
Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
White Oak River Basin
Approved by EPA June 14, 2022
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
i
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: Virginia Creek Steady-State Tidal Prism Model Inputs and Parameters ................................ 22
Appendix C: NCDMF Mapping of Potential Pollution Sources in B-8 Growing Area .................................. 23
Appendix D: Public Notification of TMDL for Fecal Coliform for Virginia Creek ......................................... 24
Appendix E: Public Comments Responsiveness Summary ......................................................................... 25

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
ii
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
HQW High Quality Waters supplemental classification
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
NOAA National Oceanic and Atmospheric Administration
NPDES National Pollutant Discharge Elimination System
NSSP National Shellfish Sanitation Program
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

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
iii
SUMMARY SHEET
Total Maximum Daily Load (TMDL)

1. 303(d) Listed Waterbody Information

State: North Carolina

County: Pender

Major River Basin: White Oak River Basin

Watershed: USGS HUC 03030001040010

Impaired Waterbody (2020 303(d) List):

Waterbody Name – [AU] Description Water Quality
Classification1 Acres
Mullett Run - [18-87-9-1] From source to Virginia Creek SA;HQW 7.5
Virginia Creek - [18-87-9a] From source to 0.75 miles inland of
Intercoastal Waterway SA;HQW 23.5
Virginia Creek - [18-87-9b] From 0.75 miles inland of ICWW to
Intercoastal Waterway SA;HQW 73.6
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
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).
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
iv
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 May 2011 to July 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
Virginia
Creek (m1)
18-87-9a;
18-87-9b < TMDL1 0.2E+9 3.60E+11 4.0E+10 4.0E+11 0
Upper
Virginia
Creek (m2)
18-87-9a 2.5E+11 3.0E+9 1.59E+11 1.8E+10 1.8E+11 28%
Mullett Run
(b1)
18-87-9-1;
18-87-9a 8.2E+10 1.6E+9 5.15E+10 5.9E+9 5.9E+10 28%
1.For Lower Virginia 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 watershed of segments m2 and b1.
2.WLA applies to NCDOT.
4.Public Notice Date: January 31, 2022 - March 4, 2022
5.Submittal Date: May 19, 2022
6.Establishment Date: June 14, 2022
7.EPA Lead on TMDL (EPA or blank):
8.Endangered Species (yes or blank):
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
v
9. MS4s Contributions to Impairment (Yes or Blank):
10. TMDL Considers Point Source, Nonpoint Source, or both: Both
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
1
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 Virginia Creek watershed is located in the White Oak River Basin (HUC
03030001040010) along the North Carolina coast in Pender County. The river is located
within the shellfish area designated B-8 by the North Carolina Division of Marine
Fisheries (NCDMF). Most of the shellfish growing area is conditionally approved -closed
(Figure 1.1) (NCDMF, 2016). The area is being updated to prohibited
(https://www.arcgis.com/apps/webappviewer/index.html?id=5759aa19d7484a3b82a8e
440fba643aa).

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.

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
2

Figure 1.1 – Virginia Creek Shellfish Growing Area (B-8) 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
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
3
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.

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
4
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, HQW 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).

Three segments, or assessment units, of Virginia Creek and its tributaries have been
included in Category 5 of the 2020 North Carolina Integrated Report, as shown below in
Table 1.1.

Table 1.1 – Virginia Creek Impaired Assessment Units
Waterbody Name – [AU] Description Water Quality
Classification Acres
Mullett Run - [18-87-9-1] From source to Virginia Creek SA;HQW 7.5
Virginia Creek - [18-87-9a] From source to 0.75 miles inland of
Intercoastal Waterway SA;HQW 23.5
Virginia Creek - [18-87-9b] From 0.75 miles inland of ICWW to
Intercoastal Waterway SA;HQW 73.6

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
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
5
Ordinance and guidance document. The most recent five-year period of data that was
available was used, May 2011 to July 2016. Data summary can be found in Appendix A.

1.3 Watershed Description
Virginia Creek and its tributaries fall within the NCDMF B-8 Growing Area in Pender
County. The watershed covers about 10.4 square miles. Oyster and clam production are
good throughout the area, however most of the shellfish beds areas are 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 32% of the watershed is different types
of wetlands and 24% is developed lands.

The dominant tide in this region is the lunar semi-diurnal (M2) tide. 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. Virginia
Creek opens to the shallow Intracoastal Waterway, instead of open ocean, the mean
tidal range at Virginia Creek is expected to be slightly lower, around 3 feet.

Table 1.2 – 2011 Land Cover Distribution of the Virginia Creek Watershed

Land Cover
Area
(square mile)
Area
(%)
Open Water 0.30 2.9
Developed, Open Space 1.53 14.7
Developed, Low Intensity 0.87 8.4
Developed, Medium Intensity 0.11 1.0
Developed, High Intensity 0.02 0.2
Barren Land 0.07 0.6
Deciduous Forest 0.02 0.2
Evergreen Forest 1.01 9.6
Mixed Forest 0.35 3.4
Shrub/Scrub 0.80 7.6
Herbaceous 0.75 7.2
Cultivated Crops 1.26 12.1
Woody Wetlands 2.58 24.7
Emergent Herbaceous Wetlands 0.78 7.4
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
6

Figure 1.2 – 2011 NLCD Land Cover of the Virginia 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. Virginia
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 four fecal coliform monitoring stations sampled by the NCDMF within Virginia
Creek, as shown in Figure 1.1. NCDMF data from May 2011 to July 2016 are summarized
in Table 13 for all the stations within B-8 area, including the 4 stations in Virginia Creek.
Sources: Esri, GEBCO, NOAA, National Geographic, DeLorme, HERE, Geonames.org, and other contributors
NLCD_2011
Woody Wetlands
Shrub/Scrub
Open Water
Mixed Forest
Herbaceuous
Evergreen Forest
Emergent Herbaceuous Wetlands
Developed, Open Space
Developed, Medium Intensity
Developed, Low Intensity
Developed, High Intensity
Deciduous Forest
Cultivated Crops
Barren Land
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
7
The 2016 NCDMF Sanitary Survey Report notes one station (Station 18) had estimated
90th percentile at 53 MPN for that period, which exceeded the criteria. The three other
stations (i.e. Stations 17, 46 and 46A) in Virginia Creek met the standard for Approved
status. However, the Report also notes that a rainfall impacts analysis suggested the
area was susceptible to bacteriological contamination at a lower threshold than what is
defined within the management plan of NCDMF (2016). Reclassification for the affected
sub-region (covering station 17, 46 and 46A) in Virginia Creek were not made but close
monitoring for further improvement was recommended.

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 most recent NCDMF Sanitary Survey (NCDMF,
2016) documented potential sources of fecal coliform in Virginia Creek. The survey
suggested that runoff from impervious surfaces, subdivisions, and other cleared land
remains the primary contributor to fecal coliform levels throughout B-8. 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. In general, there has been relatively little development within
this growing area during the last several years. Overall, 96 subdivisions were noted in
the B-8 growing area during the shoreline survey in 2014. Six of these subdivisions are
new, and several of the pre-existing subdivisions surveyed are expanded since the last
survey was conducted in 2011. The majority of homes and businesses within the B-8
growing area are served by 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-8 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 several horse stables within the watershed.

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
8
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 Virginia Creek
Watershed.

The NC Department of Transportation (NCDOT) has a number of roads in the project
area, including Highway 17, 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.
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
9

Both standards have the same numeric targets but the NSSP standard uses a minimum
30- sample averaging period. Data collected from May 2011 through July 2016 were
used for the purpose of this TMDL.

3.2 Modeling
3.2.1 Approach
Bay and coastal waters such as Virginia 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 /100ml) of the segment
k = the fecal coliform removal/decay rate (per day)
C0 = the fecal coliform concentration (MPN/100ml) entering the segment on
the flood tide
Q0 = the quantity of water entering the segment on the flood tide (m3 per tidal
cycle)
Qb = the quantity of mixed water that leaves the segment on the ebb tide (m3
per tidal cycle)
V = the mean volume of the segment (m3)
Cf = the 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

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
10
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 (Qf) used to represent the fresh water inflow was based on a ratio of
the drainage area of the Virginia Creek watershed as compared to the drainage area and
the stream flows measured by the U.S. Geological Survey at the New River gaging
station (USGS 02093000) near Gum Branch, NC. The selection of the gaging station for
use in the model is determined by its similarity in watershed characteristics to Virginia
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. For segment m1, these were calculated by combining
monitoring data from all monitoring stations within the segment and calculating the
overall median and the estimated 90th percentile fecal coliform concentrations. For
segments m2 and b1, since no monitoring station existed within the segments, data
from the most upstream station (Station 18) 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 takes place in a few stations in the conditionally-approved
open growing area in lower Virginia Creek (segment m0 and m1) after rainfall events 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.
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
11

Figure 3.1. Model segments and the sub-watersheds of Virginia 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 17 2 9
m1 Lower Virginia
Creek
18-87-9a;
18-87-9b 18, 46, 46A 4.5 32
m2 Upper Virginia
Creek 18-87-9a 18 6.45 53
b1 Mullett Run 18-87-9-1;
18-87-9a 18 6.45 53
*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.
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
12

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 2.23E+11 0
m2 14 < TMDL 4.46E+10 0
b1 14 < TMDL 1.48E+10 0
90th
Percentile
m1 43 < TMDL 3.99E+11 0
m2 43 2.50E+11 1.80E+11 28%
b1 43 8.20E+10 5.91E+10 28%

Using median concentration and the corresponding median standard, the calculated
existing loads are less than the TMDL in all segments. This is also reflected in the low
median concentrations calculated from the monitoring data. In contrast, when 90th
percentile concentrations and the corresponding 90th percentile water quality standard
are used, a 28% load reduction is needed in the watersheds of segments m2 and b1. No
reduction in loading is needed from the watershed of segment m1 due to its lower
existing load than the TMDL. The FC water quality standard will be met in segments m1
once the TMDL is implemented and loading is reduced from the watersheds of segments
m2 and b1.

Required reductions in loading are higher for the 90th percentile model results
(highlighted in orange in Table 3.2) and allow for both standards to be met. Therefore,
the TMDL was calculated using the 90th percentile criterion.

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)
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
13

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 3.99E+11 3.99E+10 3.59E+11
m2 1.80E+11 1.80E+10 1.62E+11
b1 5.91E+10 5.91E+09 5.32E+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 2.3% 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
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
14
hydraulic encroachments, sediment and erosion control, BMP retrofits, stormwater
pollution prevention for industrial facilities, research, and education programs.

Table 3.4 – Virginia Creek Watershed NCDOT Contributing Area by Subwatershed
Segment # Total Sub-watershed
Area (acres)
NCDOT ROW Area
(acres)
NCDOT Land Area (%
of total)
m1 510.3 0.24 0.05%
m2 3,444.3 69.9 2.0%
b1 2,703.5 81.4 3.0%
Total 6658.1 151.5 2.3%

Table 3.5 – NPDES Wasteload Allocations
NPDES Permittee Segment # NCDOT Existing
Load (MPN/day) WLA (MPN/day) Percent
Reduction
NCDOT
m1 N/A 0.2E+9 0%
m2 N/A 3.0E+9 0%
b1 N/A 1.6E+9 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 3.60E+11 0%
m2 N/A 1.59E+11 28%
b1 N/A 5.15E+10 28%

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).

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
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
15
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 Virginia 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 18 (located inside Segment m1 of
Virginia Creek) is presented in Figure 3.2. Data are available in each season. High fecal
coliform levels (> 14MPN) 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 18 (log
scale). Data used are from May 2011 to July 2016.

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
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 Upper Virginia Creek and Mullett Run. Reductions in loading
from these sub-watersheds allow for standards to be met throughout Virginia Creek.

A 28% reduction is needed from both the upper Virginia Creek and its tributary Mullet
Run. The combined drainage area from these two sub-watersheds is around 92% of the
total drainage area of the entire watershed of Virginia 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 Virginia Creek
Waterbody(
Model
Segment)
AUs
Fecal Coliform Load (MPN/day) %
Reduction Existing
Load WLA2 LA MOS TMDL
Lower
Virginia
Creek (m1)
18-87-9a;
18-87-9b < TMDL1 0.2E+9 3.60E+11 4.0E+10

4.0E+11 0
Upper
Virginia
Creek (m2)
18-87-9a 2.5E+11 3.0E+9 1.59E+11 1.8E+10

1.8E+11 28%
Mullett Run
(b1)
18-87-9-1;
18-87-9a 8.2E+10 1.6E+9 5.15E+10 5.9E+9 5.9E+10 28%

1. For Lower Virginia 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 watershed
of segments m2 and b1.
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 Virginia Creek watershed is discussed in
Section 2 of this document. Based on information provided in the most 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
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
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. The next NCDMF Sanitary Survey for the B-8 shellfish growing area will
help further identify current sources of bacteria and drainage pathways that allow
bacteria to enter Virginia Creek and its tributaries and provide a mechanism to evaluate
progress in attaining TMDL targets.

NCDMF will continue to monitor water quality in Virginia 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 January 31, 2022 through March 4, 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 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/planning/modeling-
assessment/tmdls

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

Jing Lin
e-mail: [e-mail]

Pam Behm
e-mail: [e-mail]

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
18
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-8, Topsail Sound Area, May 2011
through July 2016. NC Division of Marine Fisheries, Shellfish Sanitation and Recreational
Water Quality.

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.
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
19
Appendix A: NCDMF Monitoring Data Summary

Table A.1 Fecal coliform (MPN/100ml) random sampling data in Virginia Creek
Date
Stations
17 18 46 46A
5/31/2011 2 1.7 1.7 2
10/25/2011 2 6.8 6.8 13
12/14/2011 4.5 4.5 2 4.5
2/28/2012 1.7 33 7.8 4.5
5/22/2012 1.7 14 2 11
9/12/2012 4.5 13 11 6.8
10/17/2012 1.7 2 2 6.8
11/27/2012 6.1 4.5 4.5 2
12/18/2012 49 140 240 130
3/18/2013 2 4.5 4.5 13
4/25/2013 2 6.8 4.5 4.5
8/7/2013 1.7 1.7 2 7.8
10/15/2013 4.5 17 23 17
12/4/2013 2 1.7 4.5 1.7
12/18/2013 2 2 1.7 1.7
2/18/2014 1.7 4.5 1.7 2
5/28/2014 2 6.1 1.7 1.7
7/31/2014 2 27 4.5 2
10/28/2014 4.5 1.8 4.5 9.3
12/2/2014 1.7 9.3 4 17
12/11/2014 7.8 11 2 4
3/12/2015 2 2 4.5 11
4/13/2015 2 1.7 6.8 1.7
7/8/2015 1.7 1.7 2 7.8
11/5/2015 13 540 79 49
11/17/2015 13 79 23 17
12/2/2015 17 79 33 27
3/23/2016 1.7 1.7 1.8 1.7
4/26/2016 2 11 7.8 6.8
7/20/2016 2 13 1.7 2

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
20
Table A.2 Fecal coliform (MPN/100 ml) conditional sampling data in Virginia Creek.
Conditional sampling data are not used in the TMDL analysis, included here for
reference.
Date
Stations
17 46A
9/6/2011 4.5
6/4/2012 2
8/23/2012 7.8
9/4/2012 1.7
10/30/2012 49
11/1/2012 7.8
11/20/2012 130
11/23/2012 1.7
2/12/2013 4.5
4/23/2014 4.5
7/8/2014 1.7
8/13/2014 6.8
8/26/2014 1.7
9/16/2014 6.8
12/29/2014 11
1/28/2015 17
2/3/2015 2
6/8/2015 1.7
7/27/2015 1.7
8/17/2015 4.5
9/3/2015 11
9/30/2015 7.8
10/12/2015 110
10/15/2015 7.8
11/23/2015 70
11/27/2015 6.8
12/1/2015 22
12/2/2015 17 27
12/4/2015 4.5
2/18/2016 6.8
5/9/2016 1.7
6/10/2016 4.5
7/7/2016 7.8
9/15/2016 17
9/28/2016 49

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
21
Table A.3 Fecal coliform data summary statistics in Virginia Creek.

Fecal Coliform Bacteria Concentration
(MPN/100ml)
Station # Samples
Type of
Sampling Median Geometric
Mean
Estimated
90th
Percentile
17 30 Random 2 3.1368 9
35 Conditional 6.8 7.3996 37
18 30 Random 6.45 7.8727 53
46 30 Random 4.5 5.1676 25
46A 30 Random 6.8 6.1692 25
1 Conditional 27 27 27
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
22

Appendix B: Virginia 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
*100ml/m3
Value 0.9 0.5 0.36 19323.67

Table B-2. Model Inputs for 90th percentile Existing Loads Calculation
Parameter VT VL Qf C
Brief
Description
Local Tidal
Prism Volume
Low Tide Volume Fresh water input Mean FC Conc. of
the segment
unit m3 m3 m3/T MPN/100ml
Open
Boundary
9
M1 668525 527738 1240 32
M2 400637 234243 8373 53
B1 127102 70612 6571 53

Table B-3. Model Inputs for 90th percentile TMDL Loads Calculation
Parameter VT VL Qf C
Brief
Description
Local Tidal
Prism Volume
Low Tide Volume Fresh water input Mean FC Conc. of
the segment
unit m3 m3 m3/T MPN/100ml
Open
Boundary
9
M1 668525 527738 1240 32
M2 400637 234243 8373 43
B1 127102 70612 6571 43

Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
23
Appendix C: NCDMF Mapping of Potential Pollution Sources in B-8 Growing Area

Figure C.1. NCDMF Mapping of Potential Pollution Sources in B-8 Growing area
(NCDMF, 2016)
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
24
Appendix D: Public Notification of TMDL for Fecal Coliform for Virginia Creek

From: [e-mail] on behalf of Painter, Andy
To: [e-mail]
Subject: [External] Draft Virginia Creek TMDL Available for Public Review
Date: Monday, January 31, 2022 9:50:05 AM

January 31, 2022
North Carolina Department of Environmental Quality
Division of Water Resources

Draft Total Maximum Daily Load (TMDL) for Fecal Coliform for Virginia 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=2182079
Interested parties are invited to comment on the draft TMDL by March 4, 2022. Comments
should be directed to [e-mail] and must be received no later than 5
pm on March 4, 2022.
Virginia Creek Fecal Coliform TMDL
________________________________________________________________________
25
Appendix E: Public Comments Responsiveness Summary

No comments were received.