HomeMy WebLinkAboutBear Creek TMDL_final approvedTotal Maximum Daily Loads for Fecal Coliform
for Bear Creek, North Carolina
[Waterbody IDs: 19-41-11a1; 19-41-11a2; 19-41-11a3; 19-41-11b1; 19-41-11b2]
Final Report
September 2011
Prepared by:
NC Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
White Oak River Basin
Bear Creek Fecal Coliform TMDL
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Table of Contents
List of Abbreviations .............................................................................................................. ii
SUMMARY ........................................................................................................................... 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 ...................................................................................... 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) ............................................................................................ 15
3.3.2 Waste Load Allocation (WLA) ................................................................................... 16
3.3.3 Load Allocation (LA) .................................................................................................. 17
3.3.4 Critical Condition and Seasonal Variation ................................................................ 17
3.3.5 TMDL Summary ......................................................................................................... 18
4 TMDL IMPLEMENTATION PLAN .................................................................................... 20
5 PUBLIC PARTICIPATION ................................................................................................ 20
6 FURTHER INFORMATION .............................................................................................. 20
7 REFERENCES ................................................................................................................. 21
Appendix A: NCDEH Monitoring Data Summary .................................................................. 23
Appendix B: Model Inputs .................................................................................................. 28
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Appendix C: Public Announcement ..................................................................................... 29
Appendix D: Public Comments Responsiveness Summary ................................................... 31
List of Abbreviations
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SUMMARY
Total Maximum Daily Load (TMDL)
1. 303(d) Listed Waterbody Information
State: North Carolina
County: Onslow
Major River Basin: White Oak River Basin
Watershed: USGS HUC 03020106020070
Impaired Waterbody (2010 303(d) List):
Waterbody Name – [AU] Description Water Quality
Classification Acres
Bear Creek – [19-41-11a1] From source to DEH closed area line SA;HQW 88.1
Bear Creek – [19-41-11a2] DEH CAC area along north shore of
creek SA;HQW 8.2
Bear Creek – [19-41-11a3] DEH CAO area along south shore of
creek SA;HQW 19.2
Bear Creek – [19-41-11b1] DEH CAC area along north shore of
creek SA;HQW 12.1
Bear Creek – [19-41-11b2] DEH CAO area along south shore of
creek SA;HQW 179.8
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).
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2. TMDL Development
Development Tools (Analysis/Modeling): 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
Fecal Coliform Load (MPN/day)
Waterbody AUs Existing
Load1 WLA2 LA MOS TMDL %
Reduction
Lower Bear
Creek 19-41-11b2 - 7.60E+09 6.07E+11 6.83E+10 6.83E+11 0%
Middle Bear
Creek
19-41-11a2,
19-41-11a3,
19-41-11b1,
19-41-11b2
- 1.74E+09 1.39E+11 1.57E+10 1.57E+11 0%
Upper Bear
Creek 19-41-11a1 3.67E+11 1.04E+09 1.02E+11 1.15E+10 1.15E+11 69%
1. For Lower Bear Creek and Middle Bear Creek, the calculated existing loads are less than the estimated
TMDL, and hence no reduction is needed. The FC water quality standard will be met in segments m1 and
m2 once the TMDL is implemented and loading is reduced from the watershed of segment m3.
2. WLA applies to NCDOT.
4. Public Notice Date: August 1, 2011
5. Submittal Date: September 7, 2011
6. Establishment Date: September 20, 2011
7. EPA Lead on TMDL (EPA or blank):
8. Endangered Species (yes or blank):
9. MS4s Contributions to Impairment (Yes or Blank):
10. TMDL Considers Point Source, Nonpoint Source, or both: Both
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1 INTRODUCTION
Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental
Protection Agency’s (EPA) implementing regulations direct each State to develop a Total
Maximum Daily Load (TMDL) for each impaired 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 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 Bear Creek watershed is located in the White Oak River Basin (NC Subbasin 03-05-
01 – HUC 03020106020070) along the North Carolina coast in Onslow County. The river
is located within the shellfish area designated D-1 by the North Carolina Division of
Environmental Health (NCDEH). All of the Bear Creek shellfish growing area is
conditionally open or closed, or prohibited (Figure 1.1).
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.
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Figure 1.1 – Bear Creek Shellfish Growing Area (D-1) Classifications
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:
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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.
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 4a of the
Integrated Report. Waterbodies remain in Category 4a until compliance with water
quality standards is achieved. Where conditions are not appropriate for the
development of a TMDL, management strategies may still result in the restoration of
water quality.
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
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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).
Five segments, or assessment units (AUs), of Bear Creek have been included in Category
5 of the 2010 North Carolina Integrated Report, as shown below in Table 1.1.
Table 1.1 – Bear Creek Impaired Assessment Units
–
Bear Creek – [19-41-11a1] From source to DEH closed area
line SA;HQW 88.1
Bear Creek – [19-41-11a2] DEH CAC area along north shore of
creek SA;HQW 8.2
Bear Creek – [19-41-11a3] DEH CAO area along south shore
of creek SA;HQW 19.2
Bear Creek – [19-41-11b1] DEH CAC area along north shore of
creek SA;HQW 12.1
Bear Creek – [19-41-11b2] DEH CAO area along south shore
of creek SA;HQW 179.8
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 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
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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).
For this report, the monitoring data averaging period was based on monitoring
procedures for approval of SA water. The most recent five-year period of data was
used, September 2005 – August 2010. A detailed analysis of the data used can be found
in Appendix A.
1.3 Watershed Description
Bear Creek falls within the NCDEH D-1 Growing Area in Onslow County. The watershed
was delineated using EPA BASINS (http://water.epa.gov/scitech/datait/models/basins/).
The resulting watershed outline is provided below in Figure 1.2. The watershed area is
less than 11 square miles.
Figure 1.2 – Bear Creek watershed delineation overlaid with NCDEH shellfish growing area
classifications (red: prohibited; yellow: CAC; green: CAO)
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The 2006 National Land Cover Database (NLCD) was used to obtain land cover
characteristics of the watershed (http://www.mrlc.gov/nlcd2006_downloads.php).
Land cover distribution is shown in Figure 1.3 and land cover acreages are provided in
Table 1.2. The dominant land covers in this watershed are shrub/scrub, forest, and
wetlands.
Figure 1.3 – 2006 NLCD Land Cover of the Bear Creek Watershed
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Table 1.2 – 2006 Land Cover Distribution of the Bear Creek Watershed
Developed Low Intensity 200.0 2.89%
Developed Medium Intensity 4.3 0.06%
Developed Open Space 593.5 8.56%
Cultivated Crop 612.7 8.84%
Pasture/Hay 2.4 0.03%
Evergreen Forest 1450.7 20.93%
Mixed Forest 169.0 2.44%
Herbaceous Grassland 511.1 7.37%
Shrub/Scrub 1672.6 24.13%
Emergent Herbaceous Wetland 253.6 3.66%
Woody Wetlands 879.6 12.69%
Barren Land 217.9 3.14%
Open Water 365.2 5.27%
Total Area 6932.8 100.00%
The D-1 growing area is not densely inhabited, with a total population of less than 1,900
according to US Census data from 2000. Residential development is isolated to the
eastern shore of the Bear Creek. The entire western shore is part of the Camp LeJeune
Marine Corps Base. This portion of the Base is used for training purposes.
The dominant tide in this region is the lunar semi-diurnal (M2) tide with a mean tidal
range of 3.11 ft based on the NOAA station at Beaufort, NC (NOAA, 2010). Oysters and
clams grow well throughout the area with clam production being the most significant
commercial species.
1.4 Water Quality Characterization
The Shellfish Sanitation and Recreational Water Quality Section of the NCDEH is
responsible for classifying shellfish harvesting waters to ensure oysters and clams are
safe for human consumption. NCDEH adheres to the requirements of the National
Shellfish Sanitation Program (NSSP), with oversight by the U.S. Food and Drug
Administration. NCDEH 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.
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NCDEH has monitored shellfish growing regions throughout North Carolina for the past
several decades. Bear Creek is sampled using the systematic random sampling strategy
as outlined in the National Shellfish Sanitation Program’s Model Ordinance and
guidance document. In addition to the routine random monitoring of the areas,
conditional area samples are collected after rainfall events for some stations.
There are 18 fecal coliform monitoring stations sampled by the NCDEH in the D-1
Growing Area, as shown in Figure 1.4. Most of the data available were collected
through the random monitoring strategy, although five stations are regularly sampled
under the conditional monitoring strategy after rainfall events (Stations 6, 7, 8, 8A, 9).
NCDEH data from September 2005-August 2010 are summarized in Appendix A. The
2009 NCDEH Sanitary Survey Report notes one station did not meet standards for
growing area criteria (NCDEH, 2009).
Figure 1.4 – NCDEH Fecal Coliform Monitoring Stations (note that station 4 has not been
sampled since May 2005)
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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 NCDEH Shoreline Survey (NCDEH,
2009) documented and mapped potential sources of fecal coliform in Bear Creek. The
survey found that stormwater draining off of agricultural lands, residential areas, and
roadways into Bear Creek and its tributaries is of particular concern due to the steep
grades along the shoreline throughout the area.
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 (NCDEH, 2009) and were found to be functioning properly. Pet
waste can also be a significant source of fecal coliform bacteria loading.
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 animal farms within the D-1 watershed, although none are particularly large.
Land cover data for the watershed indicates that pasture/hay land area (grazing land)
represents less than 1 percent of the watershed.
Agricultural fields are widespread in the D-1 watershed. Common crops include cotton,
tobacco, hay, and corn. Several of these fields have drainages that reach either Bear
Creek itself or have a tributary to Bear Creek and are likely to contribute fecal coliform
bacteria to the creeks and waterways following rain events (NCDEH, 2009).
Wildlife in the watershed are considered to make up background concentrations of fecal
coliform. There are various forested areas and agricultural fields scattered throughout
the watershed, so wildlife is prevalent throughout the majority of this region. Large
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 reach the creek either
through direct deposition or through transportation through stormwater ditches.
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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. 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).
The only point source in the Bear Creek watershed is the NC Department of
Transportation (NCDOT) which has a statewide Phase I NPDES stormwater permit
(NCS000250).
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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 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.
Both standards have the same numeric targets but the NSSP standard uses a minimum
30- sample averaging period. Data collected from September 2005 through August
2010 were used for the purpose of this TMDL.
3.2 Modeling
3.2.1 Approach
Bay and coastal waters such as Bear Creek 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 several other states (MDE,
2004; 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 tidal cycle)
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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
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
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 dominant tide in this region is the lunar
semi-diurnal (M2) tide with a tidal period of 12.42 hours. The mean tidal range is
assumed to be 3.11 ft, as monitored at a nearby NOAA station at Beaufort, NC. 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 Bear 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 the Bear
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
Model segmentation is provided below in Figure 3.1. Existing median and 90th
percentile concentrations for each segment are required 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
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concentrations. Table 3.1 provides the monitoring stations used in each model segment
and the overall median and 90th percentile concentrations.
NCDEH conditional monitoring data were not used to calculate existing concentrations
because conditional monitoring only takes place in a few stations close to the mouth of
Bear Creek 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.
Figure 3.1 – Model Segmentation
Table 3.1 – Monitoring stations and assessment units associated with each model segment
Model
Segment
Waterbody AUs NCDEH
Monitoring
Station(s)
Median FC
(MPN/100 ml)
90th Percentile
FC (MPN/100ml)
m0 Ocean Boundary 9, 10, 11 2.0 8.0
m1 Lower Bear Creek 19-41-11b2 6, 8, 8A 2.0 18.0
m2 Middle Bear
Creek
19-41-11a2,
19-41-11a3,
19-41-11b1,
19-41-11b2
5, 5A, 5B, 6A, 7 4.5 24.0
m3 Upper Bear Creek 19-41-11a1 3 7.8 75
0 500 1,000 1,500 2,000250Meters
±
m3
m2
m1
m0
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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)
Table 3.2 – Load reduction requirements under variations of standard criteria
Standard
Category Segment AUs Standard
(MPN/100ml)
Estimated
Existing Load
(MPN/day)
TMDL
(MPN/day)
Percent
Reduction
Required
Median
m1 19-41-11b2 14 Less than
TMDL 2.29E+11 0%
m2
19-41-11a2,
19-41-11a3,
19-41-11b1,
19-41-11b2
14 Less than
TMDL 5.11E+10 0%
m3 19-41-11a1 14 Less than
TMDL 3.74E+10 0%
90th
percentile
m1 19-41-11b2 43 Less than
TMDL 6.83E+11 0%
m2
19-41-11a2,
19-41-11a3,
19-41-11b1,
19-41-11b2
43 Less than
TMDL 1.57E+11 0%
m3 19-41-11a1 43 3.67E+11 1.15E+11 69%
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 69% load reduction is needed in the watershed of segment m3. No
reduction in loading is needed from the watersheds of segment m1 and m2 due to their
lower existing load than the TMDL. The FC water quality standard will be met in
segments m1 and m2 once the TMDL is implemented and loading is reduced from the
watershed of segment m3.
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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)
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. The
systematic procedures adopted to estimate TMDLs 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.
Bear Creek Fecal Coliform TMDL
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Table 3.3 – Margin of Safety Allocation
–
90th
Percentile
m1 6.83E+11 6.83E+10 6.15E+11
m2 1.57E+11 1.57E+10 1.41E+11
m3 1.15E+11 1.15E+10 1.03E+11
3.3.2 Waste Load Allocation (WLA)
As described in Section 2.2, NCDOT is the only NPDES-permitted discharge in the
watershed. 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. The NCDOT ROW is
only 1.0% of the total watershed area, as shown below in Table 3.4, and is therefore not
considered to be a major source of fecal bacteria loading. The resulting WLA for NCDOT
is provided below in Table 3.5.
NCDOT will 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 - Bear Creek Watershed NCDOT Contributing Area by Subwatershed
m1 696 8.6 1.2%
m2 644 7.9 1.2%
m3 5298 53.5 1.0%
Total 6638 70 1.0%
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Table 3.5 – NPDES Wasteload Allocations
NCDOT
m1 N/A 7.60E+09 0%
m2 N/A 1.74E+09 0%
m3 N/A 1.04E+09 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 from nonpoint sources are presented in Table 3.6 and equate
to the overall TMDL percent reduction.
Table 3.6 – Nonpoint Source Allocation
m1 6.07E+11
m2 1.39E+11
m3 1.02E+11
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,
Bear Creek Fecal Coliform TMDL
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18
stream flow, and water quality as a result of hydrologic and climatologic patterns. For
the Bear 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 long-
term data record to estimate the current load.
The seasonal fecal coliform distribution for the stations in Segment m1 of Bear Creek 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. The largest standard deviation corresponds to the
highest concentration for each station. 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.
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 the Upper Bear Creek watershed (AU# 19-41-11a1). Upper Bear
Creek corresponds to the NCDEH shellfish growing area classified as prohibited. As
Bear Creek Fecal Coliform TMDL
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shown above in Table 3.4, Upper Bear Creek receives drainage from about 80% of the
total Bear Creek watershed and has the lowest calculated TMDL (Table 3.7). Reductions
in loading from the Upper Bear Creek watershed allows for standards to be met
throughout Bear Creek.
Table 3.7 – Estimated TMDL and Load Allocation for Fecal Coliform for Bear Creek
Fecal Coliform Load (MPN/day)
Waterbody AUs Existing
Load1 WLA2 LA MOS TMDL %
Reduction
Lower Bear
Creek (m1) 19-41-11b2 - 7.60E+09 6.07E+11 6.83E+10 6.83E+11 0%
Middle Bear
Creek (m2)
19-41-11a2,
19-41-11a3,
19-41-11b1,
19-41-11b2
- 1.74E+09 1.39E+11 1.57E+10 1.57E+11 0%
Upper Bear
Creek (m3) 19-41-11a1 3.67E+11 1.04E+09 1.02E+11 1.15E+10 1.15E+11 69%
1. For Lower Bear Creek and Middle Bear Creek, the calculated existing loads are less than the
TMDL, and hence no reduction is needed. The FC water quality standard will be met in segments
m1 and m2 once the TMDL is implemented and loading is reduced from the watershed of
segment m3.
2. WLA applies to NCDOT.
Bear Creek Fecal Coliform TMDL
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20
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
next NCDEH Sanitary Survey for the D-1 shellfish growing area will help further identify
current sources of bacteria and drainage pathways that allow bacteria to enter Bear
Creek.
NCDEH will continue to monitor water quality in Bear 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 through various means. NCDWQ electronically
distributed the draft TMDL and public comment information to known interested
parties. The announcement is provided in Appendix C. 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 August 1 –
September 1, 2011. NCDWQ received comments from NCDOT. A summary of their
comments and NCDWQ’s response is provided in Appendix D.
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:
Pam Behm
e-mail: pamela.behm@ncdenr.gov
Kathy Stecker
e-mail: kathy.stecker@ncdenr.gov
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7 REFERENCES
Kuo, A., Park, K. 1994. A PC-based tidal prism water quality model for small coastal
basins and tidal creeks. SRAMSOE No. 324, SMS/VIMS, CWM, VA, 119 pp.
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.
NCDEH. 2009. Report of Sanitary Survey, Area D-1, Bear Creek Area, May 2004 through
March 2009. NC Division of Environmental Health 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
Bear Creek Fecal Coliform TMDL
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22
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.
Bear Creek Fecal Coliform TMDL
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23
Appendix A: NCDEH Monitoring Data Summary
Table A.1 – Bear Creek NCDEH Monitoring Data Summary, September 2005 - August 2010
3 31 Random 7.8 9.6 75
5 31 Random 6.8 8.0 36
5A 31 Random 4.5 6.0 31
5B 31 Random 4.5 6.2 25
6 31 Random 2.0 5.3 29
78 Conditional 11 9.9 55
6A 31 Random 4.5 4.7 15
7 31 Random 4 4.8 20
79 Conditional 11 11.4 56
8 31 Random 2.0 3.8 14
86 Conditional 7.8 10.3 59
8A 31 Random 4 4.0 13
77 Conditional 11 10.2 56
9 31 Random 2 3.5 10
61 Conditional 6.8 8.2 54
10 31 Random 1.8 2.5 5
11 31 Random 2.0 3.6 10
12 31 Random 2 3.6 16
13 31 Random 1.8 2.9 8
14 31 Random 4 3.6 10
15 31 Random 2.0 4.1 17
16 31 Random 2 3.8 20
17 31 Random 2.0 3.1 9
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Figure A.1 - Seasonal distribution of fecal coliform concentrations (random monitoring data only) in
Segment m0 (log scale)
Figure A.2 - Seasonal distribution of fecal coliform concentrations (random and conditional monitoring
data combined) in Segment m0 (log scale)
Bear Creek Fecal Coliform TMDL
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Figure A.3 - Seasonal distribution of fecal coliform concentrations (random monitoring data only) in
Segment m1 (log scale)
Figure A.4 - Seasonal distribution of fecal coliform concentrations (random and conditional monitoring
data combined) in Segment m1 (log scale)
Bear Creek Fecal Coliform TMDL
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Figure A.5 - Seasonal distribution of fecal coliform concentrations (random monitoring data only) in
Segment m2 (log scale)
Figure A.6 - Seasonal distribution of fecal coliform concentrations (random and conditional monitoring
data combined) in Segment m2 (log scale)
Bear Creek Fecal Coliform TMDL
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Figure A.7 - Seasonal distribution of fecal coliform concentrations (random monitoring data) in
Segment m3 (log scale)
Bear Creek Fecal Coliform TMDL
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Appendix B: Bear Creek Steady-State Tidal Prism Model Inputs and Parameters
Table B-1. Model Parameters
Parameters TR β k Cf
Description
Unit -1
3
Value
Table B-2. Model Inputs for 90th percentile Existing Loads Calculation
Parameters V C C0 Q0 Qb Qf
Brief
Description
Unit 3 3 -1 3 -1 3 -1
M1
M2
M3
Table B-3. Model Inputs for 90th percentile TMDL Loads Calculation
Parameters V C C0 Q0 Qb Qf
Brief
Description
Unit 3 3 -1 3 -1 3 -1
M1
M2
M3
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Appendix C: Public Announcement
-----Original Message-----
From: wrri-news-owner@lists.ncsu.edu [mailto:wrri-news-owner@lists.ncsu.edu]
Sent: Tuesday, August 02, 2011 4:22 AM
To: wrri-news@lists.ncsu.edu
Subject: [wrri-news] Digest (1 messages)
The WRRI Daily Digest
Volume 1 : Issue 787 : "text" Format
Messages in this Issue:
201108/2 : DRAFT Total Maximum Daily Load for fecal coliform for Bear Creek, White Oak River Basin, North
Carolina
"Behm, Pamela" <pamela.behm@ncdenr.gov>
----------------------------------------------------------------------
Date: Mon, 1 Aug 2011 14:43:10 +0000
From: "Behm, Pamela" <pamela.behm@ncdenr.gov>
To: "wrri-news@lists.ncsu.edu" <wrri-news@lists.ncsu.edu>
Subject: DRAFT Total Maximum Daily Load for fecal coliform for Bear Creek, White Oak River Basin, North Carolina
Message-ID: <02CA0C092108494BA1EF9743399BEEE8BD0A@NCWITMXMBX33.ad.ncmail>
Now Available for Public Comment
DRAFT Total Maximum Daily Load for fecal coliform for Bear Creek, White Oak River Basin, North Carolina
8/1/11
North Carolina Department of Environment and Natural Resources, Division of Water Quality
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 September 1, 2011. Comments concerning
the report should be directed to Pam Behm at pamela.behm@ncdenr.gov<mailto:pamela.behm@ncdenr.gov> or
write to:
Pam Behm
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/web/wq/ps/mtu/tmdl/tmdls#Draft
***************************************************************
Pam Behm
NC DWQ Modeling and TMDL Unit
1617 Mail Service Center
Raleigh, NC 27699
Bear Creek Fecal Coliform TMDL
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30
Email: pamela.behm@ncdenr.gov
Phone: 919-807-6419
Fax: 919-807-6497
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may
be disclosed to third parties.
[Attachment of type text/html removed.]
------------------------------
End of [wrri-news] Digest (1 messages)
**********
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Appendix D: Public Comments Responsiveness Summary
The public comment period lasted from August 1 - September 1, 2011. Comments were
received from NCDOT. A summary of their comments and NCDWQ’s response is provided
below.
1. The modeling approach used to calculate the TMDLs is referred to on p. 11 as the “spreadsheet-
based steady-state tidal prism model.” Is this model maintained and distributed by EPA?
NCDWQ Response: The tidal prism model is one of the models that have been used to estimate
pollutant loading in tidal areas and is one of the tools recommended by USEPA. The original
model is maintained by the Virginia Institute of Marine Sciences (VIMS). As stated in the TMDL
report, the simplified spreadsheet based tidal prism model used for this TMDL was also used by
States of Maryland and Virginia to develop bacteria TMDLs for shellfish growing areas.
2. What is the version number and release date of the model used for these TMDLs?
NCDWQ Response: There is no version number associated with the model. The simplified
spreadsheet based tidal prism model used for the Bear Creek TMDL is the Bear Creek Version.
3. Is the model in the public domain? How can the public obtain a copy of the model?
NCDWQ Response: The simplified spreadsheet based tidal prism model used for the Bear Creek
TMDL is implemented in Excel and can be obtained from NCDWQ Modeling and TMDL Unit.
4. Is a user’s manual/model documentation available for download on the internet? If so, please
provide the URL. If not, can DWQ provide model documentation?
NCDWQ Response: There is no separate manual for the model, but all the necessary guidelines
to develop the model and the model description are included above in Section 3.2. The
information included in this section is sufficient to setup the model. The spreadsheet is set-up to
solve the equation given in Section 3.2 and there is no embedded code. A detailed description of
the tidal prism model is published by VIMS researchers (Kuo et al., 1994).
5. For each model segment (m1, m2, and m3) please provide all the parameter values that were
used to calculate the existing load and the TMDLs. When estimates of the parameters were
used as opposed to measured values, please explain the basis for why the estimate is believed
to be reasonable and appropriate.
NCDWQ Response: The TMDL report has been revised to include this information in Appendix B.
The derivation of model inputs is fully described in Section 3.2.
Bear Creek Fecal Coliform TMDL
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6. The existing fecal coliform loads for segments m1 and m2 are not reported. Please report the
existing loads for these two segments.
NCDWQ Response: As stated above in Section 3.2.3, these loads were estimated to be lower
than the TMDL, thus there is no reduction required from sources draining into these segments.
7. Assessment Unit (AU) 19-41-11b2 is listed as being within both segments m1 and m2 and thus is
subject to 2 different TMDLs. Please clarify which TMDL applies to this AU. Also, the TMDL for
AU 19-41-11b2 calculated based on the 90th percentile standard category is higher than the
TMDL for this AU calculated based on the median standard category. Please clarify why DWQ
believes the higher allowable loading is protective of water quality standards.
NCDWQ Response: The model segmentation is not based on assessment units. For this reason,
the part of assessment unit contained within m1 would have a TMDL allocation of m1 and
similarly the other part of assessment unit contained in m2 would have a TMDL allocation of m2.
However, neither segment m1 nor m2 has an assigned percent reduction. Had there been a
required percent reduction for these segments, the TMDL would be based on the water quality
standard (either median or 90th percentile) requiring the highest percent reduction, not
necessarily the lowest allowable loading. By definition, the 90th percentile calculation of
allowable load will always be higher than the median calculation.
A sentence has been added to the footnote of Table 3.7 in the report to reiterate that the FC
water quality standard will be met in segments m1 and m2 once the TMDL is implemented and
loading is reduced from the watershed of segment m3.
8. Please describe the time period over which the NCDOT’s load should be averaged and how this
time period was derived.
NCDWQ Response: The time period used to derive the TMDL and associated NCDOT’s WLA was
September 2005-August 2010. NCDEH will continue to monitor water quality in Bear 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.