Shallotte TMDL to EPA 11.21.12

Total Maximum Daily Loads for Fecal Coliform
for the Shallotte River, North Carolina

[Waterbody IDs: 15-25-2-(10)a, 15-25-2-(10)b, 15-25-2-(10)c, 15-25-2-(10)d1, 15-25-2-(10)d2, 15-
25-2-11-(2), 15-25-2-12-(2), 15-25-2-14, 15-25-2-15-(3), 15-25-2-16, 15-25-2-16-1-(2),
15-25-2-16-4-(2)]

November 2012

Prepared by:
NC Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
Lumber River Basin
Shallotte River Fecal Coliform TMDL
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Table of Contents
List of Abbreviations ..................................................................................................................................... ii
SUMMARY .................................................................................................................................................... iii
1 INTRODUCTION .................................................................................................................................... 1
1.1 TMDL Components ...................................................................................................................... 1
1.2 Documentation of Impairment .................................................................................................... 2
1.3 Watershed Description ................................................................................................................ 4
1.4 Water Quality Characterization ................................................................................................... 7
2 SOURCE ASSESSMENT .......................................................................................................................... 9
2.1 Nonpoint Source Assessment ...................................................................................................... 9
2.2 Point Source Assessment........................................................................................................... 10
3 TOTAL MAXIMUM DAILY LOADS AND LOAD ALLOCATION ................................................................ 11
3.1 TMDL Objective ......................................................................................................................... 11
3.2 Modeling .................................................................................................................................... 11
3.2.1 Approach ............................................................................................................................... 11
3.2.2 Existing Load Calculation ....................................................................................................... 12
3.2.3 TMDL Calculation .................................................................................................................. 14
3.3 TMDL Allocation ........................................................................................................................ 15
3.3.1 Margin of Safety (MOS) ......................................................................................................... 16
3.3.2 Waste Load Allocation (WLA) ................................................................................................ 16
3.3.3 Load Allocation (LA) .............................................................................................................. 17
3.3.4 Critical Condition and Seasonal Variation ............................................................................. 18
3.3.5 TMDL Summary ..................................................................................................................... 19
4 TMDL IMPLEMENTATION PLAN ......................................................................................................... 21
5 PUBLIC PARTICIPATION ...................................................................................................................... 21
6 FURTHER INFORMATION .................................................................................................................... 21
7 REFERENCES ....................................................................................................................................... 22
Appendix A: NCDMF Monitoring Data Summary ....................................................................................... 23
Appendix C: NCDMF Mapping of Stormwater Sources in the A-2 Growing Area ...................................... 30
Appendix D: Public Comment Announcement .......................................................................................... 31
Appendix E: Public Comments and Response ............................................................................................ 32

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List of Abbreviations

BMP Best Management Practice
CFR Code of Federal Regulations
CWA Clean Water Act
EPA Environmental Protection Agency
FC Fecal Coliform Bacteria
HQW High Quality Water 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 Environmental Health
NCDOT North Carolina Department of Transportation
NCDWQ North Carolina Division of Water Quality
NLCD National Land Cover Database
NOAA National Oceanic and Atmospheric Administration
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

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SUMMARY
Total Maximum Daily Load (TMDL)

1. 303(d) Listed Waterbody Information

State: North Carolina

County: Brunswick

Major River Basin: Lumber River Basin

Watershed: USGS HUC 030402080201, 030402080202, 030402080203, 030402080204

Impaired Waterbody (2010 303(d) List):

Waterbody Name – [AU] Description Water Quality
Classification Acres
Shallotte River – 15-25-2-(10)a From mouth of Mill Pond to a line
crossing the Shallotte River from a
point 948 meters north of Shell
Point on the east bank across to the
south mouth of Middle Dam Creek.
SA;HQW 158.3
Shallotte River - 15-25-2-(10)b From a line crossing the Shallotte
River from a point 948 meters north
of Shell Point on the east bank
across to the south mouth of Middle
Dam Creek to a line crossing the
Shallotte River 459 meters north of
Shell Point on the east bank across
to a point
SA;HQW 59.4
Shallotte River - 15-25-2-(10)c From a line crossing the Shallotte
River 459 meters north of Shell
Point on the east bank across to a
point 651 meters north of the Swash
to a line crossing the Shallotte River
from Shell Point across to the
Swash.
SA;HQW 89
Shallotte River - 15-25-2-(10)d1 From a line crossing the Shallotte
River from Shell Point across to the
Swash to the Intracoastal
Waterway.
SA;HQW 336.5
Shallotte River - 15-25-2-(10)d2 Hughes Marina SA;HQW 4.2
The Mill Pond – 15-25-2-11-(2) From a point 1.0 mile below
Brunswick County SR 1145 to
Shallotte River
SA;HQW 2.9
Sams Branch – 15-25-2-12-(2) From proposed dam approximately SA;HQW 3.6
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Waterbody Name – [AU] Description Water Quality
Classification Acres
3/4 mile upstream from Shallotte
River channel to Shallotte River
(0.585717439651489 S Miles)
The Swash – 15-25-2-14 From source to Shallotte River SA;HQW 3.9
Shallotte Creek – 15-25-2-15-(3) From Bell Branch to Shallotte River SA;HQW 135.6
Saucepan Creek – 15-25-2-16 From source to Shallotte River SA;HQW 62.6
Jinnys Branch – 15-25-2-16-1-(2) From Brunswick County SR 1143 to
Saucepan Creek SA;HQW 1
Goose Creek – 15-25-2-16-4-(2) From Brunswick County SR 1143 to
Saucepan Creek SA;HQW 4.2

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 count 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, 2007).

2. TMDL Development

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

Critical Condition: 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.

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3. TMDL Allocation Summary
Model
Segment AUs
Fecal Coliform Load (MPN/day) %
Reduction Existing
Load1 WLA2 LA MOS TMDL
m1
15-25-2-(10)d1
15-25-2-(10)d2
15-25-2-14
Less than
TMDL 1.73E+10 1.41E+12 1.59E+11 1.59E+12 0%
m2 15-25-2-(10)c 6.41E+11 6.30E+09 2.67E+11 3.04E+10 3.04E+11 53%
m3
15-25-2-(10)a
15-25-2-(10)b
15-25-2-11-(2)
15-25-2-12-(2)
7.12E+11 4.66E+09 1.84E+11 2.09E+10 2.09E+11 71%
b1 15-25-2-15-(3) 4.22E+11 3.52E+09 1.49E+11 1.69E+10 1.69E+11 60%
b2
15-25-2-16
15-25-2-16-1-(2)
15-25-2-16-4-(2)

3.20E+11

1.85E+09 7.74E+10 8.81E+09 8.81E+10 72%
1. For Segment m1, the calculated existing loads are less than the TMDL, and hence no reduction is
needed from those subwatersheds.
2. WLA applies solely to NCDOT.

4. Public Notice Date:
5. Submittal Date:
6. Establishment Date:
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
Shallotte River Fecal Coliform TMDL
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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 water quality limited segment on the Section 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 water body 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 Shallotte River watershed is located in the Lumber River Basin along the North Carolina coast in
Brunswick County (Figure 1.1). The river is located within the shellfish area designated A-2 by the North
Carolina Division of Marine Fisheries (NCDMF). All of the shellfish growing area of the Shallotte River is
conditionally open or closed, or prohibited.

When shellfish harvesting is the designated use, the primary parameter of concern is fecal coliform
bacteria (FC). 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.

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 water quality standards. North Carolina indicates known pollutants on the 303(d) list.

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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 4 of the Integrated Report.
Waterbodies remain in Category 4 until compliance with water quality standards is achieved.

TMDL is 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.

1.2 Documentation of Impairment

The North Carolina Division of Water Quality (NCDWQ) 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).

Twelve segments, or assessment units (AUs), of the Shallotte River and its tributaries have been
included in Category 5 of the 2012 North Carolina Integrated Report, as shown below in Table 1.1.

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1.1 - Shallotte River Impaired Assessment Units
Waterbody Name – [AU] Description Water Quality
Classification Acres
Shallotte River – 15-25-2-(10)a From mouth of Mill Pond to a line
crossing the Shallotte River from a
point 948 meters north of Shell
Point on the east bank across to the
south mouth of Middle Dam Creek.
SA;HQW 158.3
Shallotte River - 15-25-2-(10)b From a line crossing the Shallotte
River from a point 948 meters north
of Shell Point on the east bank
across to the south mouth of Middle
Dam Creek to a line crossing the
Shallotte River 459 meters north of
Shell Point on the east bank across
to a point
SA;HQW 59.4
Shallotte River - 15-25-2-(10)c From a line crossing the Shallotte
River 459 meters north of Shell
Point on the east bank across to a
point 651 meters north of the Swash
to a line crossing the Shallotte River
from Shell Point across to the
Swash.
SA;HQW 89
Shallotte River - 15-25-2-(10)d1 From a line crossing the Shallotte
River from Shell Point across to the
Swash to the Intracoastal
Waterway.
SA;HQW 336.5
Shallotte River - 15-25-2-(10)d2 Hughes Marina SA;HQW 4.2
The Mill Pond – 15-25-2-11-(2) From a point 1.0 mile below
Brunswick County SR 1145 to
Shallotte River
SA;HQW 2.9
Sams Branch – 15-25-2-12-(2) From proposed dam approximately
3/4 mile upstream from Shallotte
River channel to Shallotte River
(0.585717439651489 S Miles)
SA;HQW 3.6
The Swash – 15-25-2-14 From source to Shallotte River SA;HQW 3.9
Shallotte Creek – 15-25-2-15-(3) From Bell Branch to Shallotte River SA;HQW 135.6
Saucepan Creek – 15-25-2-16 From source to Shallotte River SA;HQW 62.6
Jinnys Branch – 15-25-2-16-1-(2) From Brunswick County SR 1143 to
Saucepan Creek SA;HQW 1
Goose Creek – 15-25-2-16-4-(2) From Brunswick County SR 1143 to
Saucepan Creek SA;HQW 4.2

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
Shallotte River Fecal Coliform TMDL
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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 count 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).

For this report, the monitoring data averaging period was based on monitoring procedures for
classifying SA water, i.e. fecal coliform concentration cannot exceed a median of an MPN of 14 per 100
ml and the 90th percentile of an MPN of 43 per 100 ml. The averaging period for the monitoring data
required at least 30 samples per station within the most recent five-year period, August 2006 –
September 2011. A detailed analysis of the data used can be found in Appendix A.

1.3 Watershed Description

The Shallotte River and its tributaries fall within the NCDMF A-2 Growing Area in Brunswick County. The
headwaters of the Shallotte and its tributaries drain portions of the Green Swamp to the north. The river
flows east to the town of Shallotte, then south were it empties into the Intracoastal Waterway. The
Shallotte Inlet is located approximately a mile south of the mouth of the Shallotte River.

The watershed was delineated using the USGS 12-Digit Hydrologic Units (HUC). The Lower Shallotte
River 12-Digit HUC was modified using EPA Basins catchment boundaries to exclude the area of Carolina
Shores and Holden Beach, which drain to the Intracoastal Waterway. The watershed covers 75 square
miles (Figure 1.1). All of the shellfish beds areas are prohibited, or conditionally closed or open, due to
high fecal coliform levels.

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Figure 1.1 - Shallotte River Watershed
The dominant tide in this region is the lunar semi-diurnal (M2) tide with a mean tidal range of 4.72 ft
based on the NOAA station at Sunset Beach, NC (NOAA, 2010).

The 2006 National Land Cover Database (NLCD) was used to obtain land cover characteristics of the
watershed. The NCDOT also helped integrate the road network right-of-way into the land cover as an
additional land classification. Land cover distribution is shown in Figure 1.2 and land cover acreages are
provided in Table 1.2. The dominant land covers in this watershed are forest (36%), shrub/grassland
areas (18%), developed lands including NCDOT (16%), wetlands (15%), and crops and pasture lands
(12%).
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Figure 1.2 - 2006 NLCD Land Cover of the Shallotte River Watershed
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Table 1.2 - 2006 Land Cover Distribution of the Shallotte River Watershed
Description Square Miles % of Total
Barren Land 0.2 0.3%
Cultivated Crops 8.4 11.3%
Deciduous Forest 0.0 0.0%
Developed, High Intensity 0.1 0.1%
Developed, Low Intensity 3.4 4.5%
Developed, Medium Intensity 0.5 0.7%
Developed, Open Space 6.5 8.7%
Emergent Herbaceous Wetland 2.5 3.3%
Evergreen Forest 26.5 35.6%
Grassland/Herbaceous 3.2 4.3%
Mixed Forest 0.4 0.6%
NCDOT 1.8 2.4%
Open Water 1.6 2.1%
Pasture/Hay 0.1 0.1%
Scrub/Shrub 10.4 14.0%
Woody Wetlands 8.9 11.9%
Total 74.5 100.0%

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 (NSSP), 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 has monitored shellfish growing regions throughout North Carolina for the past several decades.
The Shallotte River is sampled using the systematic random sampling strategy as outlined in the National
Shellfish Sanitation Program’s (NSSP) Model Ordinance and guidance document (NSSP, 2007). In
addition to the routine random monitoring of the areas, conditional area samples are collected after
rainfall events for some stations.

There are 30 active and inactive fecal coliform monitoring stations sampled by the NCDMF in the A-2
Growing Area. Of these, 19 (9 inactive and 10 active stations) are within the Shallotte River watershed
as shown in Figure 1.3. Most of the data available were collected through the random monitoring
strategy, although six stations (6, 8, 10, 11, 12 and 13) are also sampled under the conditional
monitoring strategy which is targeted towards measuring fecal coliform concentrations after rainfall
events, typically in conditionally-approved open growing areas. NCDMF monitoring data are
summarized in Appendix A for those stations within the Shallotte River watershed. The data analysis
shows seven stations did not meet standards for growing area criteria.
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Figure 1.3 - NCDMF Fecal Coliform Monitoring Stations
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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 Shoreline Survey (NCDMF, 2010) documented and mapped
potential sources of fecal coliform in the Shallotte River. The survey identified that runoff from
impervious surfaces, subdivisions, and other cleared land is the primary contributor of fecal coliform.
The Town of Shallotte is the primary source of stormwater in the area and has many stormwater
ditches, pipes, culverts and stormwater ponds that drain to the Shallotte River. Figure 2.1 shows fecal
coliform data from the DWQ ambient monitoring station I9700000 (Figure 1.3) located on the Shallotte
River in the Town of Shallotte. The geometric mean of this dataset is 244 cfu/100ml from 2006 to 2010
and only 15% of the samples are above 400 cfu/100ml. This station is located in tidal salt water (class
SC) just below where the river changes from a freshwater to saltwater classification.

Figure 2.1 Ambient Monitoring Site I9700000 Fecal Coliform Concentrations

0
1000
2000
3000
4000
5000
6000
7000
8000
1/1/2000 12/31/2001 12/31/2003 12/30/2005 12/30/2007 12/29/2009 12/29/2011Fe
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(
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F
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1
0
0
m
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)
Date
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Wildlife in the watershed are considered to make up background concentrations of fecal coliform.
Populations of deer, foxes, raccoons, and other small mammals are found in the area, as well as
waterfowl and other birds. Waste from these animals can be transported through stormwater ditches
into shellfishing waters, and have some impact on the growing area during rainfall events.

One horse stable and one goat farm were observed in the watershed during the sanitary survey; both
are unlikely to have an effect on bacteria levels in shellfish harvesting areas.

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. Failing septic systems were not observed
during the most recent shoreline survey and previously failing systems were found to be in good repair.

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 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 four non-discharge wastewater treatment plants within the Shallotte River watershed. The
Shallotte WWTP is located just north of Shallotte. After treatment the chlorinated effluent from the
plant is sprayed on spray fields. The Ocean Isle, Ocean Ridge Plantation, and KOA Campground WWTPs
are all located in the far western portion of the watershed and all treat their effluent for reuse or
sprayed onto sprayfields. None of these plants are considered to be contributing to the fecal coliform
impairment in the shellfish growing areas, however, it should be noted that in July 2009 fecal coliform
concentrations of > 6000 CFU/100 ml were reported from two groundwater monitoring wells at the
Ocean Ridge Plantation site. A Notice of Violation was issued to the Ocean Ridge Plantation as a result of
the high fecal coliform concentrations. The subsequent groundwater sampling event in 2011 showed
fecal coliform concentrations in these wells ranged from 0 to 4 CFU/100ml.

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 to be a nonpoint source; however, NPDES-permitted sources are to be
included in the wasteload allocation (WLA) per EPA guidance (USEPA, 2002).
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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
count 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 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.

Both standards have the same numeric targets but the NSSP standard uses a minimum 30- sample
averaging period. Data collected from August 2006 through September 2011 were used for the purpose
of this TMDL.

3.2 Modeling

3.2.1 Approach

Bay and coastal waters such as Shallotte River 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 spreadsheet-based
steady-state tidal prism model. This modeling approach has been used in approved TMDLs in North
Carolina and in several other states (MDE, 2004; NCDWQ, 2011; VADEQ, 2005).

The steady-state tidal prism model is spreadsheet-based and incorporates the influences of tidally
induced transport, freshwater input, and removal of fecal coliform via decay. Depending on the
geometry of the embayment, the model may have multiple segments. 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] x 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 that enters the segment on the flood tide that did not flow out of the
segment on the previous ebb tide (m3 per tidal cycle)
Qb = the quantity of mixed water that leaves the segment on the ebb tide that did not enter the
segment on the previous flood tide (m3 per tidal cycle)
V = the mean volume of the segment (m3)
Cf = the unit conversion factor
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
12

The fecal coliform decay rate, k, was set at 0.36 per day, 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

where:
Qf = mean freshwater input during one tidal cycle
β = exchange ratio
QT = the quantity of water that enters the segment on the flood tide

QT is calculated based on the tidal range. The mean tidal range is assumed to be 4.72 ft, as monitored at
a nearby NOAA station at Sunset Beach, NC. 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 as the representative tidal
cycle. 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 Shallotte River watershed as compared to the drainage area and the stream flows measured by
the U.S. Geological Survey at Hood Creek gaging station (USGS 02105900) near Leland, NC. The Shallotte
Creek watershed delineation is shown in Figure 3.1. The selection of the gaging station for use in the
model is determined by its similarity in watershed characteristics to Shallotte River watershed and the
proximity of the station to the TMDL study area.

3.2.2 Existing Load Calculation

Model segmentation is provided below in Figure 3.1. Existing median and 90th percentile concentrations
are required for each segment as model inputs. These were calculated by combining monitoring data
from all monitoring stations within each segment and calculating the overall median and the 90th
percentile fecal coliform concentrations. For those segments where there are no active stations,
available historical data was used to calculate the median and the 90th percentile fecal coliform
concentrations. 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
Shallotte River 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 (as shown in Appendix A, Table A.1). Therefore, to avoid creating bias in the model,
conditional data were not used to calculate existing loads.
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
13

Figure 3.1 - Model Segmentation and Assessment Units
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
14

Table 3.1 – Monitoring stations associated with each model segment
Model
Segment Waterbodies AU#
NCDMF
Monitoring
Station(s)
Median FC
(MPN/100
ml)
90th Percentile
FC
(MPN/100ml)
m0 Ocean Boundary 15, 18 4.5 22.0
m1 Lower Shallotte
River, the Swash
15-25-2-(10)d1
15-25-2-(10)d2
15-25-2-14
6, 7, 8, 9,
10, 12, 13,
13A
5.7 33.0
m2 Middle Shallotte
River 15-25-2-(10)c 4, 5, 11 13 65.0
m3
Upper Shallotte
River, the Mill
Pond, Sams
Branch
15-25-2-(10)a
15-25-2-(10)b
15-25-2-11-(2)
15-25-2-12-(2)
1, 2, 3 33.0 103.0
b1 Shallotte Creek 15-25-2-15-(3) 6,7 13.0 65.0
b2
Saucepan Creek,
Jinnys Branch,
Goose Creek
15-25-2-16
15-25-2-16-1-(2)
15-25-2-16-4-(2)
16, 16A 14.0 156.0

The concentrations listed in Table 3.1 were then used in Equation 3.1 to calculate the existing fecal
coliform loads associated with both the median and the 90th percentile concentrations. Table 3.2
presents the estimated existing loads for each segment.

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.

The percent load reduction needed to meet the fecal coliform standard was estimated using equation
3.2:

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

Shallotte River Fecal Coliform TMDL
________________________________________________________________________
15
Table 3.2 – Load reduction requirements under variations of standard criteria
Standard
Category
Segment
# AU#
Standard
(MPN/
100ml)
Existing
Load
(MPN/day)
TMDL
(MPN/day)
Percent
Reduction
Required
Median
m1
15-25-2-(10)d1
15-25-2-(10)d2
15-25-2-14
14 Less than
TMDL 6.22E+11 0%
m2 15-25-2-(10)c 14 1.41E+11 9.89E+10 30%
m3
15-25-2-(10)a
15-25-2-(10)b
15-25-2-11-(2)
15-25-2-12-(2)
14 1.36E+11 6.82E+10 50%
b1 15-25-2-15-(3) 14 8.20E+10 5.52E+10 33%
b2
15-25-2-16,
15-25-2-16-1-(2)
15-25-2-16-4-(2)
14

2.87E+10

2.87E+10

0%
90th
Percentile
m1
15-25-2-(10)d1
15-25-2-(10)d2
15-25-2-14
43 Less than
TMDL 1.59E+12 0%
m2 15-25-2-(10)c 43 6.41E+11 3.04E+11 53%
m3
15-25-2-(10)a
15-25-2-(10)b
15-25-2-11-(2)
15-25-2-12-(2)
43 7.12E+11 2.09E+11 71%
b1 15-25-2-15-(3) 43 4.22E+11 1.69E+11 60%
b2
15-25-2-16,
15-25-2-16-1-(2)
15-25-2-16-4-(2)
43

3.20E+11

8.81E+10

72%

For segment m1, the calculated existing loads are less than the TMDL, and hence no reduction in loading
from these watersheds is needed. The FC water quality standard will be met in this segment once TMDLs
are implemented and loading is reduced from the watersheds draining to the other segments.

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 TMDLs were 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
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
16
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)

The goal 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. The systematic procedures adopted to estimate TMDL allocations are described
below.

3.3.1 Margin of Safety (MOS)

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 1.59E+12 1.59E+11 1.43E+12
m2 3.04E+11 3.04E+10 2.73E+11
m3 2.09E+11 2.09E+10 1.88E+11
b1 1.69E+11 1.69E+10 1.52E+11
b2 8.81E+10 8.81E+09 7.93E+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
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
17
watershed. The NCDOT ROW is 2.4% 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 hydraulic encroachments,
sediment and erosion control, BMP retrofits, stormwater pollution prevention for industrial facilities,
research, and education programs.

Table 3.4 – Shallotte River Watershed NCDOT Contributing Area by Subwatershed
Segment #
Total Sub-Watershed
Area
(acres)
NCDOT Land Area
(acres)
NCDOT Land Area
(% of total)
m1 1245 15.0 1.2%
m2 931 21.5 2.3%
m3 31421 777.4 2.5%
b1 7881 181.8 2.3%
b2 6169 143.8 2.3%
Total 47647 1139.5 2.4%

Table 3.5 – NPDES Wasteload Allocations
NPDES Permittee Segment # NCDOT Existing
Load (MPN/day)
WLA
(MPN/day)
NCDOT
m1 N/A 1.73E+10
m2 N/A 6.30E+09
m3 N/A 4.66E+09
b1 N/A 3.52E+09
b2 N/A 1.85E+09

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.

Shallotte River Fecal Coliform TMDL
________________________________________________________________________
18
Table 3.6 – Nonpoint Source Allocation
Segment # LA
(MPN/day)
m1 1.41E+12
m2 2.67E+11
m3 1.84E+11
b1 1.49E+11
b2 7.74E+10

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 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 instead of the absolute
maximum.

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 Shallotte River 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 long-term data record to estimate the current load.

The seasonal fecal coliform distribution for the stations in Segment m1 of the Shallotte River is
presented in Figure 3.2 and includes both the random and conditional monitoring data. The seasonal
distributions of fecal coliform concentrations for the other segments are presented in Appendix A. The
results show that high fecal coliform levels occur throughout the year in the estuary. These high
concentrations result in a high 90th percentile concentration. 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.

Shallotte River Fecal Coliform TMDL
________________________________________________________________________
19

Figure 3.2 - Seasonal distribution of fecal coliform concentrations (random and conditional monitoring
data combined) in Segment m1 (log scale)

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 Shallotte River, Shallotte Creek, Sams Branch, the Mill Pond, the Swash, and Saucepan Creek
(including Jinnys Branch and Goose Creek). Reductions in loading from these watersheds allow for
standards to be met throughout the Shallotte River.

The largest percent reduction is needed from the upper Shallotte River (including Sams Branch and the
Mill Pond) and Saucepan Creek (including Jinnys Branch and Goose Creek). Land cover in these
subwatersheds (Appendix B) is primarily mixed between forest (42.5%), wetlands (14.9%), developed
land (14.5%), shrub/scrub (12.6%), and cropland (11.7%). A stormwater sources map produced by
NCDMF (Appendix C) shows a concentrated amount of stormwater outfalls in this watershed that could
be transporting fecal coliform bacteria to the impaired waters.

1
10
100
1000
10000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
20
Table 3.7 – Estimated TMDL and Load Allocation for Fecal Coliform for Shallotte River
Model
Segment AUs
Fecal Coliform Load (MPN/day) %
Reduction Existing
Load1 WLA2 LA MOS TMDL
m1
15-25-2-(10)d1
15-25-2-(10)d2
15-25-2-14
Less than
TMDL 1.73E+10 1.41E+12 1.59E+11 1.59E+12 0%
m2 15-25-2-(10)c 6.41E+11 6.30E+09 2.67E+11 3.04E+10 3.04E+11 53%
m3
15-25-2-(10)a
15-25-2-(10)b
15-25-2-11-(2)
15-25-2-12-(2)
7.12E+11 4.66E+09 1.84E+11 2.09E+10 2.09E+11 71%
b1 15-25-2-15-(3) 4.22E+11 3.52E+09 1.49E+11 1.69E+10 1.69E+11 60%
b2
15-25-2-16
15-25-2-16-1-(2)
15-25-2-16-4-(2)

3.20E+11

1.85E+09 7.74E+10 8.81E+09 8.81E+10 72%
1. For Segment m1, the calculated existing loads are less than the TMDL, and hence no reduction is
needed from those subwatersheds.
2. WLA applies solely to NCDOT.

Shallotte River Fecal Coliform TMDL
________________________________________________________________________
21
4 TMDL IMPLEMENTATION PLAN

An implementation plan is not included in this TMDL. 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 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 NCDMF Sanitary Survey
for the A-2 shellfish growing area is a useful resource for identifying current sources of bacteria and
drainage pathways that allow bacteria to enter Shallotte River and its tributaries. Contact the Shellfish
Sanitation Office at 252-726-6827 for information on how to obtain a copy of the Sanitary Survey.

NCDMF will continue to monitor water quality in Shallotte River 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 through various means. NCDWQ electronically distributed the
draft TMDL and public comment information to known interested parties. The announcement is
provided in Appendix D. The TMDL was also available from the NCDWQ’s website at
http://portal.ncdenr.org/web/wq/ps/mtu/tmdl/tmdls during the comment period. The public comment
period lasted from September 18 – October 19, 2012. NCDWQ received comments from NCDOT. A
summary of their comments and NCDWQ’s response is provided in Appendix E.

6 FURTHER INFORMATION

Further information concerning North Carolina’s TMDL program can be found on the Internet at the
Division of Water Quality website:
http://portal.ncdenr.org/web/wq/ps/mtu

Technical questions regarding this TMDL should be directed to the following members of the NCDWQ
Modeling/TMDL Unit:

Andy Painter
e-mail: [e-mail]

Adugna Kebede
e-mail: [e-mail]

Kathy Stecker
e-mail: [e-mail]
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
22
7 REFERENCES

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

MDE. 2004. Total Maximum Daily Loads of Fecal Coliform for Restricted Shellfish Harvesting Areas in
the Potomac River Lower Tidal Basin in St. Mary's County, Maryland.

NCAD. 2003. NC Administration Code.

NCDMF. 2009. Report of Sanitary Survey, Area A-2, Shallotte river Area, March 2004 through February
2009. 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. 2007. National Shellfish Sanitation Program Guide for the control of Molluscan Shellfish 2007,
Section IV, Chapter II (Bacteriological Standards). US Food and Drug Administration, 2007. Website:
http://www.fda.gov/Food/FoodSafety/Product-
SpecificInformation/Seafood/FederalStatePrograms/NationalShellfishSanitationProgram/UCM053698

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.

Thomann, R. V. and J. Mueller. 1987. Principles of surface water quality modeling and control. Harper
Collins Publishers.

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 (FACA). 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.

VADEQ. 2005. Total Maximum Daily Load Report for Shellfish Areas Listed Due to Bacterial
Contamination.
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
23
Appendix A: NCDMF Monitoring Data Summary

Table A.1 – Shallotte River NCDMF Fecal Coliform Monitoring Data Summary

Random Monitoring
(MPN/100 ml)
Random & Conditional Monitoring
(MPN/100 ml)
Station Median Geomean 90th
%tile Time Period Median Geomean 90th
%tile Time Period
1 49 51 130 01/15/1990 - 01/22/1997
2 146 33 39 01/15/1990 - 01/22/1997
3 60 20 20 01/15/1990 - 01/22/1997
4 22 22.2 67 12/16/1999 - 04/08/2002 - - - -
5 13 12.9 83 10/09/2000 - 07/29/2005 - - - -
6 9.4 8.8 45 02/22/2007 - 09/07/2011 9.4 8.8 45 02/22/2007 - 09/07/2011
7 6.2 6.3 33 02/22/2007 - 09/07/2011 - - - -
8 - - - 12.5 11.9 72 05/03/2000 - 04/08/2002
9 6.2 6.4 28 04/24/2007 - 09/07/2011 - - - -
10 7.8 9.9 61 02/22/2007 - 09/07/2011 9.9 10.9 57 10/21/2009 - 09/07/2011
11 12 12.2 60 02/22/2007 - 09/07/2011 12 - 60 02/22/2007 - 09/07/2011
12 4.3 5.1 24 02/22/2007 - 09/07/2011 5.7 7.4 41 10/01/2009 - 09/07/2011
13 3 3.9 12 10/09/2000 - 07/29/2005 6.8 10.1 80 10/01/2009 - 07/29/2005
13A 4.5 6 23 - - - -
15 - - - - - - -
15A 4.5 5.2 24 02/22/2007 - 09/07/2011 4.5 5 19 05/19/2008 - 09/07/2011
16 14 13.7 156 02/22/2007 - 09/07/2011 - - - -
16A
18 4.5 5.7 23 02/22/2007 - 09/07/2011 - - - -
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
24

Figure A.1 – NCDMF Monitoring Stations

Shallotte River Fecal Coliform TMDL
________________________________________________________________________
25

Figure A.2 - Seasonal distribution of fecal coliform concentrations in Segment m0 (log scale)

Figure A.3 - Seasonal distribution of RANDOM monitoring fecal coliform concentrations in
Segment m1 (log scale)
1
10
100
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
1
10
100
1000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
26

Figure A.4 - Seasonal distribution of fecal coliform concentrations (random and conditional
monitoring data combined) in Segment m1 (log scale)

Figure A.5 - Seasonal distribution of fecal coliform concentrations in Segment m2 (log scale)

1
10
100
1000
10000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
1
10
100
1000
10000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
27

Figure A.6 - Seasonal distribution of fecal coliform concentrations in Segment m3 (log scale)

Figure A.7- Seasonal distribution of fecal coliform concentrations (Random and Conditional) in
Segment b1 (log scale)

1
10
100
1000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
1
10
100
1000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
28

Figure A.8- Seasonal distribution of fecal coliform concentrations (Random Sampling) in
Segment b1 (log scale)

Figure A.9 - Seasonal distribution of fecal coliform concentrations in Segment b2 (log scale)
1
10
100
1000
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Fe
c
a
l

C
o
l
i
f
o
r
m

(
C
o
u
n
t
s
/
1
0
0
m
l
)

Month
Maximum
90th %ile
75th %ile
Median
25th %ile
10th %ile
Minimum
Shallotte River Fecal Coliform TMDL
________________________________________________________________________
29
Appendix B: Land Cover by Watershed
sqmi % of total sqmi % of total sqmi % of total sqmi % of total sqmi % of total
Barren Land 0.0% 0.00 0.0% 0.07 0.1% 0.05 0.4% 0.07 0.8%
Cultivated Crops 0.06 3.3% 0.18 12.6% 6.57 13.4% 1.28 10.4%0.30 3.1%
Deciduous Forest 0.0% 0.0% 0.01 0.0% 0.0% 0.00 0.0%
Developed, High Intensity 0.0% 0.0% 0.08 0.2% 0.0% 0.0%
Developed, Low Intensity 0.02 1.1% 0.03 2.1% 2.12 4.3% 0.80 6.5% 0.39 4.0%
Developed, Medium Intensity 0.00 0.2% 0.0% 0.47 1.0% 0.01 0.1% 0.03 0.3%
Developed, Open Space 0.07 3.7% 0.05 3.7% 4.35 8.9% 0.92 7.5% 1.06 11.0%
Emergent Herbaceous Wetland 0.29 14.8% 0.08 5.5% 1.31 2.7% 0.39 3.2% 0.40 4.1%
Evergreen Forest 0.58 29.8% 0.48 33.1% 17.41 35.5% 3.52 28.7% 4.47 46.5%
Grassland/Herbaceous 0.07 3.6% 0.06 4.3% 2.44 5.0% 0.38 3.1%0.24 2.5%
Mixed Forest 0.01 0.6% 0.01 0.9% 0.27 0.6% 0.10 0.9% 0.05 0.5%
NCDOT 0.02 1.2% 0.03 2.3% 1.21 2.5% 0.28 2.3% 0.22 2.3%
Open Water 0.59 30.4% 0.24 16.5% 0.39 0.8% 0.13 1.1% 0.22 2.3%
Pasture/Hay 0.0% 0.0% 0.06 0.1% 0.0% 0.05 0.5%
Scrub/Shrub 0.16 8.5% 0.25 16.9% 6.08 12.4% 2.64 21.4% 1.30 13.5%
Woody Wetlands 0.05 2.8% 0.03 2.0% 6.19 12.6% 1.77 14.4% 0.81 8.5%
Grand Total 1.94 100.0% 1.45 100.0% 49.03 100.0% 12.29 100.0% 9.62 100.0%
Description
Model Segment Watershed
M3M2M1 B2B1
Shallotte River Fecal Coliform TMDL
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Appendix C: NCDMF Mapping of Stormwater Sources in the A-2 Growing Area

Shallotte River Fecal Coliform TMDL
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Appendix D: Public Comment Announcement

North Carolina Department of Environment and Natural Resources
Division of Water Quality

September 18, 2012

Draft Total Maximum Daily Load for Fecal Coliform for Impaired Segments in the Shallotte River
Watershed

Now Available for Public Comment

This draft TMDL report was prepared as a requirement of the Federal Water Pollution Control
Act, Section 303(d). Interested parties are invited to comment on the Draft TMDL report by
October 19, 2012. Comments concerning the report should be directed to Andy Painter at
[e-mail] or write to:

Andy Painter
NC Division of Water Quality
Planning Section
1617 Mail Service Center
Raleigh, NC 27699

The draft TMDL can be downloaded from the following website:
http://portal.ncdenr.org/c/document_library/get_file?uuid=c5b63f20-11d9-48f7-8c26-
746b0e16a5bc&groupId=38364

Shallotte River Fecal Coliform TMDL
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32

Appendix E: Public Comments and Response

The public comment period lasted from September 18 – October 19, 2012. Comments were received from NCDOT.
A summary of their comments and NCDWQ’s response is provided below.

DWQ Response: As indicated in the TMDL document Section 3.2, the simplified steady-state tidal prism
model computations are based on equation 3.1; and the implementation of the simplified model is site-
specific. While the simplified spreadsheet-based steady-state tidal prism model was first used for TMDLs in
Virginia and Maryland (MDE, 2004; VADEQ, 2005), the implementation of the simplified equation for Shallotte
River was done in-house by NCDWQ Modeling and TMDL Unit.

DWQ Response: The particular application of the spreadsheet-based simplified steady-state tidal prism model
for the Shallotte River TMDL was developed in the Modeling and TMDL unit of NCDWQ.

DWQ Response: EPA approves the use of the tidal prism model. The spreadsheet-based simplified steady-state
tidal prism model used for the Shallotte River TMDL and several other EPA approved TMDLs in North
Carolina is a tool used to solve the fairly simple tidal prism equation. The spreadsheet-based tool is a simplified
application that is, in a way, self-explanatory through exploration of the formulas in the cells. The spreadsheet
application to solve this equation was first used in Virginia as stated above, and ideally the NCDOT could
easily recreate this spreadsheet tool by applying the equation to excel. The spreadsheet-based simplified steady-
state tidal prism model used for the Shallotte River TMDL is distributed and supported by NCDWQ and can be
obtained from the MTU of NCDWQ.

DWQ Response: Section 3.2 of the TMDL document provided description of the simplified steady-state tidal
prism model and additional guidance has been provided in the spreadsheet for the site specific application for
the Shallotte River. The spreadsheet used for the Shallotte Creek TMDL is available upon request. A detailed
description of the tidal prism model concept is provided by Kuo et al., 2005. The reference for this document is
Shallotte River Fecal Coliform TMDL
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provided in the References section. In addition, a PowerPoint presentation on the tidal prism water quality
model segmentation (in general) can be provided upon request.

DWQ Response: The original spreadsheet-based model used for the Shallotte River TMDL will be maintained
by the MTU of NCDWQ. The MTU recommends requesting a copy of the spreadsheet to view input variables
and outputs.