YadkinTurbidityTMDLs2011Final

Total Maximum Daily Load for Turbidity for Abbotts Creek, Ararat River,
Hunting Creek, Second Creek, South Deep Creek, South Yadkin River,
and Third Creek in North Carolina

[Assessment Units 12-119-(6)a, 12-72-(18), 12-72-(4.5)b, 12-108-16-(0.5)b, 12-108-21b, 12-84-
2-(5.5), 12-108-(14.5), 12-108-(19.5)b, 12-108-20-4b]

Final Report
September 2011

Prepared by:
NC Department of Environment and Natural Resources
Division of Water Quality
Planning Section
1617 Mail Service Center
Raleigh, NC 27699-1617
[phone]
Yadkin-Pee Dee River Basin

i
TMDL Summary Sheet

303(d) List Information

State: North Carolina
Counties: Davidson, Davie, Forsyth, Iredell, Rowan, Surry, Wilkes, Yadkin
Basin: Yadkin- Pee Dee River Basin

Waterbody
Name
Assessment Unit
(AU): Class 10 digit HU Impairment Miles
Abbotts Creek 12-119-(6)a C 0304010302 Turbidity 6.4
Ararat River 12-72-(18) WS-IV 0304010109 Turbidity 2
Ararat River 12-72-(4.5)b C 0304010109 Turbidity 13.7
Hunting Creek 12-108-16-(0.5)b WS-III 0304010202 Turbidity 31.1
Second Creek 12-108-21b C 0304010205 Turbidity 3.4
South Deep
Creek 12-84-2-(5.5) WS-IV 0304010111 Turbidity 2.8
South Yadkin
River 12-108-(14.5) WS-IV 0304010206 Turbidity 9.5
South Yadkin
River 12-108-(19.5)b C 0304010301 Turbidity 5.3
Third Creek 12-108-20-4b C 0304010203 Turbidity 22.1

Constituent of Concern: Turbidity
Reason for Listing: Standard Violations

Applicable Water Quality Standard:

The turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units
(NTU) in streams not designated as trout waters and 10 NTU in stream, lakes or reservoirs
designated as trout water; for lakes and reservoirs not designated as trout waters, the
turbidity shall not exceed 25 NTU; if turbidity exceeds these levels due to natural
background conditions, the existing turbidity level cannot be increased. Compliance with
this turbidity standard can be met when land management activities employ Best
Management Practices (BMPs) recommended by the Designated Nonpoint Source Agency.
BMPs must be in full compliance with all specifications governing the proper design,
installation, operation and maintenance of such BMPs.

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TMDL Development

Analysis/Modeling:
Load duration curves are based on cumulative frequency distribution of flow conditions in the
watershed. Allowable loads are average loads over the recurrence interval between the 90th
and 10th percent flow exceeded (excludes extreme drought (>90th percentile) and floods (<10th
percentile). Percent reductions are expressed as the average value between existing loads
(typically calculated using an equation to fit a curve through actual water quality violations) and
the allowable load at each percent flow exceeded.

Turbidity is a measure of cloudiness and is reported in Nephelometric Turbidity Units (NTU).
Therefore, turbidity is not measured in terms of concentrations and cannot be directly
converted into loadings required for developing a load duration curve. For this reason, total
suspended solid (TSS) was selected as the measure for this study.

Critical Conditions:
Critical conditions are accounted in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining at what flow (percent flow
exceeded) the existing load violations occur.

Seasonal Variation:
Seasonal variation in hydrology, climatic conditions, and watershed activities are represented
through the use of a continuous flow gage and the use of all readily available water quality data
collected in the watershed.

TMDL Allocation Summary

Pollutants/Watershed Existing
Load WLA LA MOS TMDL
Total Suspended Sediment (tons/day)
Abbotts Creek 21.30 0.064 9.236 10% 9.30
Ararat River 28.20 0.170 12.830 10% 13.00
Hunting Creek 23.40 0.000 11.200 10% 11.20
Second Creek 5.20 0.17 2.977 10% 3.10
South Deep Creek 16.40 0.003 8.497 10% 8.50
South Yadkin River 50.20 0.179 25.221 10% 25.40
Third Creek 13.30 0.489 6.411 10% 6.90

Notes:
WLA = Wasteload Allocation, LA = Load Allocation, MOS = Margin of Safety.
1. LA = TMDL – WLA – MOS.
2. TMDL represents the average allowable load between the 90th and 10th percent
recurrence interval.

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3. Explicit (10%) margin of safety is considered.

Public Notice Date: July 26, 2011
Submittal Date:
EPA Approval Date:

iv
Table of Contents
1.0 Introduction ............................................................................................................................ 1
1.1 TMDL Definition .............................................................................................................. 1
1.2 Water Quality Target: North Carolina Standards and Classifications ............................. 3
1.3 Watershed Description ................................................................................................... 3
1.4 Water Quality Monitoring............................................................................................. 19
2.0 General Source Assessment .................................................................................................. 20
2.1 Nonpoint Sources of Turbidity ...................................................................................... 20
2.2 Point Sources of Turbidity ............................................................................................. 21
3.0 Abbotts Creek Impairment ................................................................................................... 22
3.1 Source Assessment ....................................................................................................... 22
3.2 Technical Approach ....................................................................................................... 22
3.2.1 Endpoint for Turbidity ............................................................................................... 23
3.2.2 Methodology ............................................................................................................. 23
3.3 Flow Duration Curve ..................................................................................................... 23
3.4 Load Duration Curve ..................................................................................................... 24
3.5 TMDL ............................................................................................................................. 25
3.6 Margin of Safety (MOS) ................................................................................................ 26
3.7 Target Reduction ........................................................................................................... 26
3.8 TMDL Allocation ............................................................................................................ 27
3.8.1 Waste Load Allocation (WLA) ................................................................................... 27
3.8.2 Load Allocation (LA) .................................................................................................. 28
3.8.3 Critical Conditions and Seasonal Variation ............................................................... 29
4.0 Ararat River Impairment ....................................................................................................... 29
4.1 Source Assessment ....................................................................................................... 29
4.2 Technical Approach ....................................................................................................... 30
4.3 Flow Duration Curve ..................................................................................................... 31
4.4 Load Duration Curve ..................................................................................................... 31
4.5 TMDL ............................................................................................................................. 33
4.5.1 Margin of Safety (MOS) ............................................................................................ 33
4.6 Target Reduction ........................................................................................................... 33
4.7 TMDL Allocation ............................................................................................................ 34
4.7.1 Waste Load Allocation (WLA) ................................................................................... 34
4.7.2 Load Allocation (LA) .................................................................................................. 35
4.7.3 Critical Condition and Seasonal Variation ................................................................ 36

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5.0 Hunting Creek ....................................................................................................................... 36
5.1 Source Assessment ....................................................................................................... 36
5.2 Technical Approach ....................................................................................................... 37
5.3 Flow Duration Curve ..................................................................................................... 37
5.4 Load Duration Curve ..................................................................................................... 38
5.5 TMDL ............................................................................................................................. 40
5.5.1 Margin of Safety (MOS) ............................................................................................ 40
5.6 Target Reduction ........................................................................................................... 40
5.7 TMDL Allocation ............................................................................................................ 41
5.7.1 Waste Load Allocation (WLA) ................................................................................... 41
5.7.2 Load Allocation (LA) .................................................................................................. 42
5.7.3 Critical Condition and Seasonal Variation ................................................................ 42
6.0 Second Creek ........................................................................................................................ 43
6.1 Source Assessment ....................................................................................................... 43
6.2 Technical Approach ....................................................................................................... 43
6.3 Flow Duration Curve ..................................................................................................... 44
6.4 Load Duration Curve ..................................................................................................... 45
6.5 TMDL ............................................................................................................................. 46
6.5.1 Margin of Safety (MOS) ............................................................................................ 47
6.6 Target Reduction ........................................................................................................... 47
6.7 TMDL Allocation ............................................................................................................ 48
6.7.1 Waste Load Allocation (WLA) ................................................................................... 48
6.7.2 Load Allocation (LA) .................................................................................................. 50
6.7.3 Critical Condition and Seasonal Variation ................................................................ 50
7.0 South Deep Creek ................................................................................................................. 50
7.1 Source Assessment ....................................................................................................... 50
7.2 Technical Approach ....................................................................................................... 51
7.3 Flow Duration Curve ..................................................................................................... 52
7.4 Load Duration Curve ..................................................................................................... 53
7.5 TMDL ............................................................................................................................. 54
7.5.1 Margin of Safety (MOS) ............................................................................................ 55
7.6 Target Reduction ........................................................................................................... 55
7.7 TMDL Allocation ............................................................................................................ 56
7.7.1 Waste Load Allocation (WLA) ................................................................................... 56
7.7.2 Load Allocation (LA) .................................................................................................. 57

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7.7.3 Critical Condition and Seasonal Variation ................................................................ 58
8.0 South Yadkin River ................................................................................................................ 58
8.1 Source Assessment ....................................................................................................... 58
8.2 Technical Approach ....................................................................................................... 59
8.3 Flow Duration Curve ..................................................................................................... 60
8.4 Load Duration Curve ..................................................................................................... 61
8.5 TMDL ............................................................................................................................. 62
8.5.1 Margin of Safety (MOS) ............................................................................................ 63
8.6 Target Reduction ........................................................................................................... 63
8.7 TMDL Allocation ............................................................................................................ 64
8.7.1 Waste Load Allocation (WLA) ................................................................................... 64
8.7.2 Load Allocation (LA) .................................................................................................. 65
8.7.3 Critical Condition and Seasonal Variation ................................................................ 66
9.0 Third Creek ............................................................................................................................ 66
9.1 Source Assessment ....................................................................................................... 66
9.2 Technical Approach ....................................................................................................... 67
9.3 Flow Duration Curve ..................................................................................................... 68
9.4 Load Duration Curve ..................................................................................................... 69
9.5 TMDL ............................................................................................................................. 70
9.5.1 Margin of Safety (MOS) ............................................................................................ 71
9.6 Target Reduction ........................................................................................................... 71
9.7 TMDL Allocation ............................................................................................................ 72
9.7.1 Waste Load Allocation (WLA) ................................................................................... 72
9.7.2 Load Allocation (LA) .................................................................................................. 73
9.7.3 Critical Condition and Seasonal Variation ................................................................ 74
10.0 Summary and Future Implementation ............................................................................. 74
10.1 TMDL Implementation .................................................................................................. 75
11.0 Public Participation ........................................................................................................... 75
12.0 References ........................................................................................................................ 76
Appendix A: Land Cover Data in Square Miles and Percent Area for the Impaired Watersheds 77
Appendix B. Water Quality Data Used for TMDL Development ................................................... 78
Appendix C. Load Reduction Estimations .................................................................................... 86
Appendix D: Public Notification of TMDL for Yadkin River Basin Turbidity TMDLS ..................... 93
Appendix E: Public Comments ...................................................................................................... 94

1
1.0 Introduction
1.1 TMDL Definition

This report presents the development of turbidity TMDLs for seven waterbodies (9 assessment
units) in the Yadkin-Pee Dee River Basin (Figure 1.1) in North Carolina. As identified by the
North Carolina Division of Water Quality (DWQ), the impaired segments of each waterbody are
described in Table 1.1.

Figure 1.1 Location of the Yadkin River Basin within North Carolina

Table 1.1 Description of turbidity impaired assessment units
Waterbody
Name Description Assessment Unit
(AU): Class Miles
Abbotts Creek From upstream side of culvert at U.S.
Hwys. 29 & 70 to SR1243 12-119-(6)a C 6.4
Ararat River From a point 0.1 mile upstream of Surry
County SR 2080 to Yadkin River 12-72-(18) WS-
IV 2
Ararat River From Stoney Creek 12-72-12 to a point 0.1
mile upstream of Surry County SR 2080 12-72-(4.5)b C 13.7
Hunting Creek From Little Hunting Creek to a point 1.1
miles upstream of Davie County SR 1147 12-108-16-(0.5)b WS-III 31.1
Second Creek From Withrow Creek to Beaverdam Creek 12-108-21b C 3.4
South Deep
Creek
From a point 0.6 mile upstream of Yadkin
County SR 1710 to Deep Creek 12-84-2-(5.5) WS-IV 2.8
South Yadkin
River
From a point 1.0 mile upstream of Davie
County SR 1159 to N.C. Hwy. 801 12-108-(14.5) WS-IV 9.5
South Yadkin
River
From mouth of Fourth Creek to Yadkin
River 12-108-(19.5)b C 5.3
Third Creek From SR 2359 to SR 1970 12-108-20-4b C 22.1

Section 303(d) of the Clean Water Act (CWA) requires States to develop a list of waterbodies
that do not meet water quality standards. The list, referred to as the 303(d) list, is submitted
biennially to the U.S. Environment Protection Agency (USEPA) for review and approval. The

2
303(d) process requires that a Total Maximum Daily Load (TMDL) be developed for each of the
waters appearing on the 303(d) list.

The objective of a TMDL is to allocate allowable pollutant loads to known sources so that
actions may be taken to restore the water to its intended uses (USEPA, 1991). Generally, the
primary components of a TMDL, as identified by USEPA (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.

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

Assimilative Capacity. Estimation of level of pollutant reduction needed to achieve water
quality goal. The level of pollution should be characterized for the water body, 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 waste load allocation portion of the TMDL accounts for the loads associated
with point sources, including NPDES stormwater. Similarly, the load allocation portion of the
TMDL accounts for the loads associated with nonpoint sources.

Margin of Safety. The margin of safety addresses uncertainties associated with pollutant loads,
modeling techniques, and data collection. Per EPA (2000a), 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. Once EPA approves a
TMDL, the water body is moved off the 303(d) list. Waterbodies remain impaired until
compliance with water quality standards is achieved.

3
1.2 Water Quality Target: North Carolina Standards and Classifications

The North Carolina fresh water quality standard for turbidity (15A NCAC 02B. 0211) states:

The turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units
(NTU) in streams not designated as trout waters and 10 NTU in stream, lakes or
reservoirs designated as trout water; for lakes and reservoirs not designated as trout
waters, the turbidity shall not exceed 25 NTU; if turbidity exceeds these levels due to
natural background conditions, the existing turbidity level cannot be increased.
Compliance with this turbidity standard can be met when land management activities
employ Best Management Practices (BMPs) recommended by the Designated Nonpoint
Source Agency. BMPs must be in full compliance with all specifications governing the
proper design, installation, operation and maintenance of such BMPs.

1.3 Watershed Description

The impaired waterbodies are located in the Yadkin-Pee Dee River Basin. Watersheds of the
impaired waterbodies were delineated using USGS -12 digit HUCs. Location maps for the
impaired waterbodies are shown in the following Figures.

Land Cover

The land cover dataset used for this project was created by the NC Center for Geographic
Information and Analysis (CGIA) for the upper portion of the Yadkin River Basin, including the
entire High Rock Lake watershed. Data are derived from Landsat 5 imagery from 2006 and
2007. The methodology used to create this dataset was based on that used to create the 2001
National Land Cover Database (NLCD). Land cover distribution maps of the watersheds are
shown in the following figures, and a comparison is shown in Figure 1.20. A detailed land cover
distribution by square miles and percent area are shown for each impaired watershed in
Appendix A.

Figure 1.21 shows the land cover distribution adjacent to streams. These data were derived by
using GIS to select only land cover grid cells that were intersected by a 1:24000 stream
segment.

4

Figure 1.2 Abbotts Creek Watershed

5

Figure 1.3 Land cover distribution in the Abbotts Creek watershed

6

Figure 1.4 Ararat River watershed

7

Figure 1.5 Land cover distribution in the Ararat River watershed

8

Figure 1.6 Hunting Creek watershed

9

Figure 1.7 Land cover distribution in the Hunting Creek watershed

10

Figure 1.8 Second Creek watershed

11

Figure 1.9 Land cover distribution in the Second Creek watershed

12

Figure 1.10 South Deep Creek watershed

13

Figure 1.11 Land cover distribution in the South Deep Creek watershed

14

Figure 1.12 South Yadkin River watershed

15

Figure 1.13 Land cover distribution in the South Yadkin River watershed

16

Figure 1.14 Third Creek watershed

17

Figure 1.15 Land cover distribution in the Third Creek watershed

18

Figure 1.16 Land cover distribution in the impaired watersheds

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Abbots
Creek
Ararat
River
Hunting
Creek
Second
Creek
South
Deep
Creek
South
Yadkin
Third
Creek
Developed, High
Intensity
Developed, Medium
Intensity
Developed, Low
Intensity
Developed, Open
Space
Barren Land
Cultivated Crops
Pasture/Hay
Grassland/Herbaceous
Scrub/Shrub
Deciduous Forest
Mixed Forest
Evergreen Forest
Emergent Herbaceous
Wetland
Woody Wetlands

19

Figure 1.17 Land cover adjacent to streams in the impaired watersheds
1.4 Water Quality Monitoring

Turbidity and total suspended solids (TSS) data collected monthly at DWQ Ambient Monitoring
Stations and one Yadkin Pee Dee River Basin Association were used for the TMDLs. The data
period used for the TMDLs was from 2000 through 2009. The data used for the 2010 303(d) list
assessment are summarized in Table 1.2. Detailed data used in this study is included in
Appendix B.

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Abbots
Creek
Ararat River Hunting
Creek
Second
Creek
South Deep
Creek
South
Yadkin
River
Third Creek
Developed, High
Intensity
Developed, Medium
Intensity
Developed, Low
Intensity
Developed, Open
Space
Barren Land
Cultivated Crops
Pasture/Hay
Grassland/Herbaceous
Shrub/Scrub
Deciduous Forest
Mixed Forest
Evergreen Forest
Herbaceous Wetlands
Woody Wetlands
Open Water

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Table 1.2 Summary of 2010 turbidity assessment (data from 2004-2008)
Waterbody Assessment Unit Station
Number
of
Samples
Number
Exceeding
Standard
Exceeding
Percentage
Abbotts Creek 12-119-(6)a Q5930000 77 8 10.4
Ararat River 12-72-(18) Q1950000 36 5 13.9
Ararat River 12-72-(4.5)b Q1780000 71 8 11.3
Hunting Creek 12-108-16-(0.5)b Q3484000 59 6 10.2
Second Creek 12-108-21b Q4120000 58 7 12.1
South Deep Creek 12-84-2-(5.5) Q2135000 60 7 11.7
South Yadkin River 12-108-(14.5) Q3460000 77 9 11.7
South Yadkin River 12-108-(19.5)b Q3970000 60 7 11.7
Third Creek 12-108-20-4b Q3934500 58 8 13.8

2.0 General Source Assessment

Turbidity is a measure of the cloudiness of water. In a waterbody, the cloudiness can be
increased due to silt and clay from watershed and stream erosion, organic detritus from
streams and wastewater, and phytoplankton growth. In this study, turbidity is measured in
Nephelometric Turbidity Units (NTU), which is significantly correlated with total suspended
solid (TSS) in this watershed. The relationship between turbidity and TSS is discussed below.

2.1 Nonpoint Sources of Turbidity

Potential sources of turbidity from nonpoint sources are forests, agricultural lands, land
disturbance, urban runoff, and stream channel erosion. Surface runoff is the main carrier of
sediments from forests and agricultural land. Normally, runoff flowing through undisturbed
forest carries insignificant amounts of sediments. Runoff flowing through agricultural land can
carry a substantial amount of sediments, depending on erodibility of soils, types of agricultural
practices, crop type and density, rainfall intensity, and existence and type of agricultural BMPs.

Urbanization also increases the amount of sediment transported to receiving waters.
Impervious urban landscapes like roads, bridges, parking lots, and buildings prevent rainwater
from percolating into the ground. In impervious areas, rainwater remains above the land
surface, gathers sediments and solid materials, and runs off in large amounts.

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2.2 Point Sources of Turbidity

Point sources are distinguished from nonpoint sources in that they discharge directly into
streams at discrete points. Point sources of turbidity consist primarily of industries, wastewater
treatment plants, and Municipal Separate Storm Sewer Systems (MS4). Municipal storm sewer
systems can quickly channel urban runoff from roads and other impervious surfaces. When it
leaves the system and empties into a stream, large volumes of quickly flowing runoff erode
stream banks, damage streamside vegetation, and widen stream channels. The amount of
sediment depends on erodibility of soils, types of surfaces, vegetation, rainfall intensity, and
existence and type of BMPs. DWQ implements the Clean Water Act National Pollutant
Discharge Elimination System (NPDES) permit program to control water pollution due to point
sources. Individual homes that are connected to a municipal system, use a septic system, or do
not have a surface discharge do not need an NPDES permit; however, industrial, municipal, and
other facilities must obtain permits if their discharges go directly to surface waters.

NPDES-Regulated Municipal and Industrial Wastewater Treatment Facilities

Discharges from wastewater treatment facilities may contribute sediment to receiving waters
as total suspended solids (TSS) and/or turbidity. Municipal and industrial treatment plants are
assigned enforceable TSS limits to protect water quality. Notices of violation and civil penalties
are examples of enforcement tools DWQ uses in order to bring non-compliant facilities into
compliance.

NPDES Stormwater Permits

Most stormwater permittees are subject to TSS benchmarks. Relatively few permittees are
required by the stormwater permits to monitor or address turbidity per se. Generally,
permitted facilities are required to develop a stormwater pollution prevention plan, and
conduct qualitative and/or quantative monitoring at stormwater outfalls. Monitoring
parameters and monitoring frequency are selected for each site, or each industry group, based
on DWQ’s assessment of the stormwater runoff pollution risks posed by the particular
industrial activities under consideration.

Municipal Separate Storm Sewer System (MS4)

EPA requires NPDES permitted stormwater to be placed in the waste load allocation (WLA) of a
TMDL (Wayland, 2002). In 1990, EPA promulgated rules establishing Phase I of the NPDES
stormwater program. The Phase I program for Municipal Separate Storm Sewer System (MS4)
requires operators of medium and large MS4s, which generally serve populations of 100,000 or
greater, to implement a stormwater management program as a means to control polluted
discharges from these MS4s. Phase II of the program expanded permit requirements to
construction disturbing an acre or more and smaller communities (< 100,000 population) and
public entities that own or operate an MS4.

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3.0 Abbotts Creek Impairment
3.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

NPDES Wastewater Permits:

There are three facilities that discharge wastewater continuously to Abbotts Creek and
tributaries under the NPDES program (Table 3.1). In general, facilities are permitted to
discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are
shown in Figure 1.2.

Table 3.1 NPDES Wastewater Dischargers in the Abbotts Creek Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended Solids
Monthly Average Limit
NC0028037 Lexington WTP #1 & 2 467,000 30 mg/L
NC0034452 Willow Creek WWTP 80,000 30 mg/L
NC0051713 Lakeview Mobile Home Park 15,000 30 mg/L

MS4 and Individual Stormwater Permits:

Duracell holds an individual stormwater permit (NCS000310) and discharges into Abbotts
Creek. The North Carolina Department of Transportation holds a statewide MS4 stormwater
permit (NCS000250).
3.2 Technical Approach

Because the magnitude of turbidity in a water body is associated with flow, a load duration
approach is adopted for this study. This approach is used to estimate pollutant loads under
different flow conditions (high flow, transition flow, typical flow, and low flow ) to identify
source types, specify assimilative capacity of a stream, and to estimate magnitude of load
reduction required to meet the water quality standard. The methodology used to develop a
load duration curve is based on Cleland (2002).

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3.2.1 Endpoint for Turbidity
As discussed in Section 2.1, turbidity is a measure of cloudiness and is reported in
Nephelometric Turbidity Units (NTU). Therefore, turbidity is not measured in terms of
concentrations and cannot be directly converted into loadings required for developing a load
duration curve. For this reason, total suspended solid (TSS) was selected as the measure for this
study.

In order to determine the relationship between TSS and turbidity in Abbotts Creek, a regression
equation between the two parameters was developed using the observed data collected from
February 2000 through December 2009 at ambient station Q5930000 on Abbotts Creek. The
relationship is shown in Equation 3.1. The coefficient of determination (R-Square) between the
two parameters was 0.88, indicating a strong linear relationship between the two parameters.
The R2 value is the percentage of the total variation in turbidity that is explained or accounted
for by the fitted regression (TSS).

y = 0.8499x - 0.6076 R² = 0.8782 (3.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 42 mg/L.
3.2.2 Methodology
The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Abbotts Creek because of the availability of long-term
data. It is also an efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002). The
required load reduction was determined based on water quality monitoring and stream flow
data from January 2000 through December 2009.
3.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 3.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.

Figure 3.1 Flow Duration Curve for

Daily flow data were used from USGS
the DWQ water quality monitoring
3.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values alo
by the pollutant concentrations and the appropriate conversion factors.
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality num
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high
mixture of point and non-point sources may cause exceedances during

Existing TSS loads to Abbotts Creek
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.
Flow Duration Curve for Abbotts Creek at DWQ Station Q5930000
used from USGS Abbotts Creek gauging station 02121500,
water quality monitoring station.
A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
ny values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely cause
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
point sources may cause exceedances during normal flows.
Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.
24

, co-located with
ng the flow duration curve
As shown in Figure 3.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
ny values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
event runoff. A
normal flows.
were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

25

Figure 3.2 Load Duration Curve for Abbotts Creek at DWQ station Q5930000

The assimilative capacity was exceeded primarily during high-flows (< 10% of flow exceedance)
and transitional-flows (10% –30% flow exceedance) in Abbotts Creek. There was no
exceedance during typical-flows (30% - 90% flow exceedance) and low-flows (>90% flow
exceedance). High loads during high and transitional flows suggest that the sources of turbidity
could be storm runoff and/or bank erosion. During the high flow periods, runoff would carry a
substantial amount of sediments and solid materials from impermeable as well as permeable
land surfaces. Bank erosion may be another result of high and transitional flows. Bank erosion
occurs when high volume and velocity runoff exceeds the resistance of the lateral (side) soil
material.

TSS load under typical flows stayed under the turbidity standard of 50 NTU (42 mg/L TSS) in
Abbotts Creek. The power curve fitted to the average TSS loads under different flow conditions
in figure 3.2 clearly shows that the TSS loads did not exceed the allowable load except during
high flow periods (<10% flow exceeded). The loads during highest flow periods are considered
unmanageable and hence are excluded in the TMDL estimation in this study.
3.5 TMDL

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
0.0
0.1
1.0
10.0
100.0
1000.0
10000.0
0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0%
To
t
a
l

S
u
s
p
e
n
d
e
d

S
o
l
i
d
s

(
t
o
n
s
/
d
a
y
)
Percent Flow Exceeded
Total Suspended Solids Load Duration Curve
Existing Load Summer Existing Load
Allowable Load Power (Existing Load)

26
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
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 3.2.

∑∑++=MOSLAsWLAsTMDL (3.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for turbidity. The systematic procedures adopted to estimate TMDLs are
described below.
3.6 Margin of Safety (MOS)

Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
3.7 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the standard (estimated as 42 mg TSS/L) were identified within the
10th to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is
not included in the TMDL calculation to allow cases of extreme drought or flood to be excluded.

A power curve equation for the data points violating the water quality criterion was estimated.
The equation is presented in Equation 3.2.

y = 2.1577x-1.803 R² = 0.6434
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

To present the TMDLs as a single value, the existing load was calculated from the power curve
equation as the average of the load violations occurring between 10 and 90 percent flow
exceedances. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the power curve based on the exceedances are shown in Figure 3.3.

The necessary percent reduction was calculated by taking the difference between the average
of the power curve load estimates and the average of the allowable load estimates. At each

27
recurrence interval between 10 and 90 (again using recurrence intervals in multiples of 5), the
equation of the power curve was used to estimate the existing load. The allowable load was
then calculated in a similar fashion by substituting the allowable load curve. The estimated
values are given in Appendix C.

Figure 3.3 Load duration curve allowable TSS load and existing total TSS load in Abbotts Creek
3.8 TMDL Allocation

3.8.1 Waste Load Allocation (WLA)
Three wastewater treatment plants (WWTP) plus Duracell and the NC Department of
Transportation hold NPDES permits in the Abbotts Creek Watershed. The wastewater load
contributions are shown in Table 3.2

Table 3.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly max in
mg/L)
Load
(tons/day)
% of Average
Ambient
Station Load
Lexington WTP #1 & 2 NC0028037 467,000 30 0.0530 0.25
Willow Creek WWTP NC0034452 80,000 30 0.0091 0.04
Lakeview Mobile Home Park NC0051713 15,000 30 0.0017 0.01

In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged
reaches the ambient station with no settling. Based on facility permit limits of flow and the
y = 2.1577x-1.803
R² = 0.6434
1.0
10.0
100.0
1000.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow ExceededAllowable load with MOS Existing Load Violation
Power (Existing Load Violation)

28
monthly average permit limits for TSS, the combined WWTP load contributes less than 1% of
the average load at DWQ station Q5930000 based on data from years 2000 through 2009. The
limit of 30 mg/l is less than the equivalent concentration necessary to meet the turbidity
standard (50 NTU ≈ 42 mg/l). In addition, as discussed previously, violations of the turbidity
standard did not occur during low flows when continuous dischargers’ contributions would be
greatest. These WWTPs do not represent a significant load to Abbotts Creek; therefore it was
concluded that the WWTPs are adequately regulated under existing permits and the waste load
allocations in this TMDL were calculated at the existing permit limits. In addition, when
individual industrial stormwater permittees are in compliance with their permits, they are
assumed to be adequately regulated; therefore, no reduction in TSS loading is required.

NCDOT was considered a significant contributor, and was assigned a percent reduction identical
to the nonpoint source reduction. The NCDOT is currently in compliance with their NPDES
stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and other impervious areas, data
are not available (n/a) to calculate a WLA for the stormwater permittees as a load.

The wasteload allocation and required reductions for NPDES permittees in the Abbotts Creek
watershed are shown in Table 3.3.

Table 3.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Lexington WTP #1 & 2 0.0530 0.0530 0%
Willow Creek WWTP 0.0091 0.0091 0%
Lakeview Mobile Home
Park 0.0017 0.0017 0%
Duracell - Stormwater N/A N/A 0%
NCDOT - Stormwater N/A N/A 57%

3.8.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS from point and
nonpoint sources are presented in Table 3.4. The estimated percent reductions needed from
NPDES stormwater and nonpoint sources is 57%, as shown in Table 3.5.

Table 3.4 Estimated TMDL and load allocation for TSS (tons/day) for Abbotts Creek
Pollutant Water Body Existing Load WLA LA Explicit
MOS TMDL
TSS Abbotts
Creek 21.30 0.064 9.236 10% 9.30
Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10%

29
Table 3.5 Estimated reduction by source for TSS (tons/day) for Abbotts Creek
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) 0.064 N/A 21.24
Allocation (tons/day) 0.064 N/A 9.236
Percent Reduction 0% 57% 57%
3.8.3 Critical Conditions and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because the allocation
applies to all seasons. In the load duration curves, the mark inside a square box indicates
pollutant load during the summer period.

According to the load duration curve (Figure 3.2), the greatest frequency of exceedances of
turbidity occurred during high-flow periods. The result shows that wet weather is the critical
period for turbidity in Abbotts Creek.

4.0 Ararat River Impairment
4.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

NPDES Wastewater Permits

There are two facilities that discharge wastewater continuously to the Ararat River and
tributaries under the NPDES program (Table 4.1). In general, facilities are permitted to
discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are
shown in Figure 1.4.

30

Table 4.1 NPDES Wastewater Dischargers in the Ararat River Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended
Solids Monthly
Average Limit
NC0026646 Pilot Mountain WWTP 1,500,000 30 mg/L
NC0068365 Pilot Mountain WTP No Flow Limit 30 mg/L

MS4 and Individual Stormwater Permits

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the Ararat River
watershed.
4.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

In order to determine the relationship between TSS and turbidity in the Ararat River, a
regression equation between the two parameters was developed using the observed data
collected from February 2000 through December 2009 at ambient station, Q1780000, on the
Ararat River. The relationship is shown in Equation 4.1. The coefficient of determination (R-
Square) between the two parameters was 0.92, showing a strong relationship between the two
parameters. The R2 value is the percentage of the total variation in turbidity that is explained or
accounted for by the fitted regression (TSS).

y = 0.0128x2 - 0.3967x + 11.084 R² = 0.9251 (4.1)
Where, Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 23 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for the Ararat River because of the availability of long-
term data. It is also an efficient method to calculate a percent load reduction from nonpoint
sources. The methodology used to develop the load duration curve was based on Cleland
(2002). The required load reduction was determined based on water quality monitoring and
stream flow data from January 2000 through December 2009.

4.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of recor
are used. The flow duration curve, shown in Figure
and flow regimes during which the exceedances of the pollutants occurred.

Figure 4.1 Flow Duration Curve for

Daily flow data were used from USGS Ararat River gauging station 02
the DWQ water quality monitoring
4.4 Load Duration Curve

A load duration curve is developed by multiplying the
by the pollutant concentrations and the appropriate conversion factors.
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
y 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of recor
are used. The flow duration curve, shown in Figure 4.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.
Flow Duration Curve for the Ararat River at DWQ Station Q1780000
Daily flow data were used from USGS Ararat River gauging station 02113850, co
water quality monitoring station.
A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown
allowable and existing loads are plotted against the flow recurrence interval. The allowable
ter quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
31
Development of a flow duration curve is the first step of the load duration approach. A flow
distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
y 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
, was used to determine the seasonality

113850, co-located with
flow values along the flow duration curve
As shown in Figure 4.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow

conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high
mixture of point and non-point sources may cause exce

Existing TSS loads to the Ararat River were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capaci
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.

Figure 4.2 Load Duration Curve for

For the Ararat River, the standard
conditions. Few exceedances during
watershed may not be a significan
high and transitional flows suggest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
thunderstorms would increase runoff.
sediments and solid materials from impermeable as we
erosion may be another result of high and transitional flows.
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
point sources may cause exceedances during normal flows.
Existing TSS loads to the Ararat River were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

Load Duration Curve for the Ararat River at DWQ station Q1780000
standard violations occurred mostly during typical to high flow
conditions. Few exceedances during low-flow conditions suggest that point sources in the
watershed may not be a significant source of TSS in this watershed. The higher
high and transitional flows suggest that the sources of turbidity could be from storm runoff
In addition most of the exceedances occurred during summer when
d increase runoff. Stormwater runoff would carry a substantial amount of
sediments and solid materials from impermeable as well as permeable land surfaces
erosion may be another result of high and transitional flows. Bank erosion occurs when high
32
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
re likely caused by
continuous or point source discharges, which are generally diluted during storm events.
event runoff. A
edances during normal flows.
Existing TSS loads to the Ararat River were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

to high flow
conditions suggest that point sources in the
loads during
high and transitional flows suggest that the sources of turbidity could be from storm runoff
In addition most of the exceedances occurred during summer when
runoff would carry a substantial amount of
ll as permeable land surfaces. Bank
Bank erosion occurs when high

33
volume and velocity runoff exceeds the resistance of the lateral (side) soil material. The loads
during high flow period are considered unmanageable and hence are excluded from the TMDL
estimation in this study.
4.5 TMDL

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 wasteload allocations (WLAs), nonpoint source load
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 4.2.

∑∑++=MOSLAsWLAsTMDL (4.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

4.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
4.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the estimated standard (23 mg TSS/L) were identified within the 10th
to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is not
included in the TMDL calculation to allow cases of extreme drought or flood to be excluded.

An exponential curve equation for the data points violating the water quality criterion was
estimated. The equation is presented in Equation 4.3.

y = 95.357e-2.93x R² = 0.7667 (4.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

34

To present the TMDLs as a single value, the existing load was calculated from the exponential
curve equation as the average of the load violations occurring between 10% and 90% flow
exceedances. The average load was calculated by using percent flow exceedances in multiples
of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the exponential curve based on the exceedances are shown in Figure 4.3.

The necessary percent reduction was calculated by taking the difference between the average
of the exponential curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 10 and 90 (again using recurrence intervals in
multiples of 5), the equation of the exponential curve was used to estimate the existing load.
The allowable load was then calculated in a similar fashion by substituting the allowable load
curve. The estimated values are given in Appendix C.

Figure 4.3 Load duration curve allowable TSS load and existing total TSS load violation in the
Ararat River
4.7 TMDL Allocation

4.7.1 Waste Load Allocation (WLA)
Two wastewater treatment plants (WWTP) plus the NC Department of Transportation hold
NPDES permits in the Ararat River Watershed. The wastewater load contributions are shown in
Table 4.2
y = 95.357e-2.93x
R² = 0.7667
1.0
10.0
100.0
1000.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing Load Violation
Expon. (Existing Load Violation)

35

Table 4.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly max in
mg/L)
Load
(tons/day)
% of Average
Ambient Station
Load
Pilot Mountain
WWTP NC0026646 1,500,000 30.00 0.17 0.60
Pilot Mountain WTP NC0068365 No Flow Limit 30.00 N/A N/A

The Pilot Mountain WTP does not have a flow limit, therefore a load will not be calculated for
this facility. In order to estimate contributions from the WWTPs, it was assumed that all TSS
discharged reaches the ambient station with no settling. Based on facility permit limits of flow
and the monthly average permit limits for TSS, the combined WWTP load contributes less than
1% of the average load at DWQ station Q1780000 based on data from years 2000 through
2009. It appears that these WWTPs do not present a significant load to the Ararat River.
Therefore it was assumed that the WWTPs are adequately regulated under existing permits and
the waste load allocations in this TMDL were calculated at the existing permit limits.

The NCDOT was considered a significant contributor, and was assigned a percent reduction
identical to the nonpoint source reduction. The NCDOT is currently in compliance with their
NPDES stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and highways, data are not
available (n/a) to calculate a WLA for the NCDOT as a load.

The waste load allocation and required reductions for NPDES permittees in the Ararat River
watershed are shown in Table 4.3.

Table 4.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Pilot Mountain WWTP 0.17 0.17 0%
Pilot Mountain WTP N/A N/A N/A
NCDOT - Stormwater N/A N/A 54%

4.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and
nonpoint sources are presented in Table 4.4. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 54%, as shown in Table 4.5.

36
Table 4.4 Estimated TMDL and load allocation for TSS (tons/day) for the Ararat River
Pollutant Water Body Existing Load
(tons/day) WLA LA MOS TMDL
TSS Ararat River 28.20 0.170 12.830 Explicit
10% 13.00
Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10%

Table 4.5 Estimated reduction by source for TSS (tons/day) for the Ararat River
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) 0.170 N/A 28.03
Allocation (tons/day) 0.170 N/A 12.83
Percent Reduction 0% 54% 54%
4.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.

The greatest frequency of exceedances of turbidity occurred during normal to high flow
periods. The result shows that wet weather under the high-flow period is the critical period for
turbidity in the Ararat River.

5.0 Hunting Creek
5.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

37

NPDES Wastewater Permits:

There are no NPDES wastewater dischargers in the Hunting Creek Watershed.

MS4 and Individual Stormwater Permits:

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the Hunting Creek Watershed.
5.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

In order to determine the relationship between TSS and turbidity in Hunting Creek, a regression
equation between the two parameters was developed using the observed data collected from
February 2000 through December 2009 at ambient station, Q3484000, on Hunting Creek. The
relationship is shown in Equation 5.1. The coefficient of determination (R-Square) between the
two parameters was 0.91, showing a strong relationship between the two parameters. The R2
value is the percentage of the total variation in turbidity that is explained or accounted for by
the fitted regression (TSS).

y = 0.7125x + 1.5044 R² = 0.9055 (5.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 37 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Hunting Creek because of the availability of long- term
data. It is also an efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002).The
required load reduction was determined based on water quality monitoring and stream flow
data from January 2000 through December 2009.

5.3 Flow Duration Curve

Development of a flow duration curve is the first step of the loa
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were eq
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure
and flow regimes during which the exceedances of the pollutants occurred.

Figure 5.1 Flow Duration Curve for Hunting Creek at DWQ Station Q3484000

Daily flow data were used from USGS Hunting Creek gauging station 02118500, co
the DWQ water quality monitoring
5.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors.
allowable and existing loads are plotted against
load is based on the water quality numerical
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
ng stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 5.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.
Flow Duration Curve for Hunting Creek at DWQ Station Q3484000
Daily flow data were used from USGS Hunting Creek gauging station 02118500, co
water quality monitoring station.
A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
s the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
38
d duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
ualed or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
ng stations. Accuracy of the curve increases when longer periods of record
, was used to determine the seasonality

Daily flow data were used from USGS Hunting Creek gauging station 02118500, co-located with
A load duration curve is developed by multiplying the flow values along the flow duration curve
As shown in Figure 5.2,
the flow recurrence interval. The allowable
, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
s the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during

which exceedances occur. Exceedances that occur during low
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high
mixture of point and non-point sources may cause exceedances during normal flows.

Existing TSS loads to Hunting Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and conve
daily loading values. The assimilative capacities of the
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.

Figure 5.2 Load Duration Curve for Hunting Creek at DWQ station Q3484000

For Hunting Creek, the standard
higher loads during high and transitional flows sugg
from storm runoff and/or bank erosion. Stormwater runoff would carry a substantial amount of
sediments and solid materials from impermeable as we
erosion may be another result of
volume and velocity runoff exceeds the resistance of the lateral (side) soil material.
during high flow period are considered unmanageable and
estimation in this study.
ch exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-e
point sources may cause exceedances during normal flows.
Existing TSS loads to Hunting Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

Load Duration Curve for Hunting Creek at DWQ station Q3484000
violations occurred during typical to high flow conditions.
higher loads during high and transitional flows suggest that the sources of turbidity could be
from storm runoff and/or bank erosion. Stormwater runoff would carry a substantial amount of
sediments and solid materials from impermeable as well as permeable land surfaces.
erosion may be another result of high and transitional flows. Bank erosion occurs when high
volume and velocity runoff exceeds the resistance of the lateral (side) soil material.
during high flow period are considered unmanageable and hence are excluded from
39
flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
event runoff. A
point sources may cause exceedances during normal flows.
Existing TSS loads to Hunting Creek were determined by multiplying the observed TSS
rting the result to
were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

typical to high flow conditions. The
est that the sources of turbidity could be
from storm runoff and/or bank erosion. Stormwater runoff would carry a substantial amount of
ll as permeable land surfaces. Bank
Bank erosion occurs when high
volume and velocity runoff exceeds the resistance of the lateral (side) soil material. The loads
hence are excluded from the TMDL

40
5.5 TMDL

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 wasteload allocations (WLAs), nonpoint source load
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 5.2.

∑∑++=MOSLAsWLAsTMDL (5.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

5.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
5.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the estimated standard (37 mg TSS/L) were identified within the 10th
to 95th percentile flow recurrence range. Typically the remaining flow recurrence range is not
included in the TMDL calculation to allow cases of extreme drought or flood to be excluded.

A power curve equation for the data points violating the water quality criterion was estimated.
The equation is presented in Equation 5.3.

y = 13.001x-0.598 R² = 0.4097 (5.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

To present the TMDLs as a single value, the existing load was calculated from the power curve
equation as the average of the load violations occurring between 10% and 90% flow
exceedances. The average load was calculated by using percent flow exceedances in multiples

41
of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the power curve based on the exceedances are shown in Figure 5.3.

The necessary percent reduction was calculated by taking the difference between the average
of the power curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 10 and 90 (again using recurrence intervals in
multiples of 5), the equation of the exponential curve was used to estimate the existing load.
The allowable load was then calculated in a similar fashion by substituting the allowable load
curve. The estimated values are given in Appendix C.

Figure 5.3 Load duration curve allowable TSS load and existing total TSS load violation in
Hunting Creek
5.7 TMDL Allocation
5.7.1 Waste Load Allocation (WLA)
The NCDOT is the only NPDES permitted entity in the Hunting Creek Watershed. The NCDOT
was considered a significant contributor, and was assigned a percent reduction identical to the
nonpoint source reduction. The NCDOT is currently in compliance with their NPDES stormwater
permit, and will continue to implement measures required by the permit (NCS000250). Because
of the nature of drainage from roads and highways, data are not available (n/a) to calculate a
WLA for the NCDOT as a load.

The reduction required for the NCDOT in the Hunting Creek watershed is shown in Table 5.1.
y = 13.001x-0.598
R² = 0.4097
1.0
10.0
100.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing load violation Power (Existing load violation)

42

Table 5.1 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
NCDOT - Stormwater N/A N/A 52%

5.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and
nonpoint sources are presented in Table 5.2. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 52%, as shown in Table 5.3.

Table 5.2 Estimated TMDL and load allocation for TSS (tons/day) for Hunting Creek
Pollutant Water Body
Existing
Load
(tons/day)
WLA LA MOS TMDL
TSS Hunting
Creek 23.40 0.000 11.200 Explicit
10% 11.20
Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10%

Table 5.3 Estimated reduction by source for TSS (tons/day) for Hunting Creek
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) N/A N/A 23.40
Allocation (tons/day) N/A N/A 11.2
Percent Reduction N/A 52% 52%
5.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.

The exceedances of turbidity occurred during normal to high flow periods. The result shows
that wet weather under high-flow period is the critical period for turbidity in Hunting Creek.

43
6.0 Second Creek

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.
6.1 Source Assessment

NPDES Wastewater Permits

There are five facilities that discharge wastewater continuously to Second Creek and tributaries
under the NPDES program (Table 6.1). In general, facilities are permitted to discharge a monthly
average TSS concentration up to 30 mg/L. Locations of dischargers are shown in Figure 1.8.

Table 6.1 NPDES Wastewater Dischargers in the Second Creek Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended Solids
Monthly Average Limit
NC0004944 Performance Fibers Operations, Inc. 2,305,000 120 lbs/day
NC0028941 Pine Valley Subdivision WWTP 25,000 30 mg/L
NC0034959 West Rowan High School 10,000 30 mg/L
NC0075523 RDH Tire & Retread No flow limit 32 lbs/day
NC0078361 Second Creek WWTP 30,000 30 mg/L

MS4 and Individual Stormwater Permits

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the Second Creek
Watershed.

6.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

44

In order to determine the relationship between TSS and turbidity in Second Creek, a regression
equation between the two parameters was developed using the observed data collected from
February 2000 through December 2009 at ambient station, Q4120000, on Second Creek. The
relationship is shown in Equation 7.1. The coefficient of determination (R-Square) between the
two parameters was 0.98, showing a strong relationship between the two parameters. The R2
value is the percentage of the total variation in turbidity that is explained or accounted for by
the fitted regression (TSS).

y = 0.8078x - 2.9658 R² = 0.9795 (6.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 37 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Second Creek because of the availability of long-term
data. It is also an efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002). The
required load reduction was determined based on water quality monitoring and stream flow
data from January 2000 through December 2009.
6.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 6.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.

45

Figure 6.1 Flow Duration Curve for Second Creek at DWQ Station Q4120000

Daily flow data were used from USGS Second Creek gauging station 02120780, co-located with
the DWQ water quality monitoring station.
6.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown in Figure 6.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
mixture of point and non-point sources may cause exceedances during normal flows.

Existing TSS loads to Second Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.
1
10
100
1000
10000
0.
0
0
5
%
0.
0
1
0
%
0.
1
0
0
%
1.
0
0
0
%
5.
0
0
0
%
10
.
0
0
0
%
15
.
0
0
0
%
20
.
0
0
0
%
25
.
0
0
0
%
30
.
0
0
0
%
35
.
0
0
0
%
40
.
0
0
0
%
45
.
0
0
0
%
50
.
0
0
0
%
55
.
0
0
0
%
60
.
0
0
0
%
65
.
0
0
0
%
70
.
0
0
0
%
75
.
0
0
0
%
80
.
0
0
0
%
85
.
0
0
0
%
90
.
0
0
0
%
95
.
0
0
0
%
99
.
0
0
0
%
10
0
.
0
0
0
%
Fl
o
w

(
c
f
s
)
Percent Flow Exceeded

6.2 Load Duration Curve for Second Creek at DWQ station Q

For Second Creek, the standard violations occurred mostly during typical to high flow
conditions. Few exceedances during
watershed may not be a significant source of TSS in this watershed.
high and transitional flows suggest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
thunderstorms would increase runoff. Stormwater runoff wo
sediments and solid materials from impermeable as we
erosion may be another result of high and transitional flows.
volume and velocity runoff exceeds the re
during high flow period are cons
estimation in this study.
6.5 TMDL

Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant t
assimilated by the receiving water body while achieving water quality standards. A TMDL can
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (M
uncertainty concerning the relationship between effluent limitations and water quality. This
definition can be expressed by equation 6
Load Duration Curve for Second Creek at DWQ station Q4120000
violations occurred mostly during typical to high flow
conditions. Few exceedances during low-flow conditions suggest that point sources in the
watershed may not be a significant source of TSS in this watershed. The higher loads during
high and transitional flows suggest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
would increase runoff. Stormwater runoff would carry a substantial amount of
sediments and solid materials from impermeable as well as permeable land surfaces.
erosion may be another result of high and transitional flows. Bank erosion occurs when high
volume and velocity runoff exceeds the resistance of the lateral (side) soil material.
during high flow period are considered unmanageable and hence are excluded in the TMDL
Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant t
assimilated by the receiving water body while achieving water quality standards. A TMDL can
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
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
can be expressed by equation 6.2.
46

violations occurred mostly during typical to high flow
conditions suggest that point sources in the
higher loads during
high and transitional flows suggest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
uld carry a substantial amount of
ll as permeable land surfaces. Bank
Bank erosion occurs when high
sistance of the lateral (side) soil material. The loads
excluded in the TMDL
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 wasteload allocations (WLAs), nonpoint source load
OS), which takes into account any
uncertainty concerning the relationship between effluent limitations and water quality. This

47

∑∑++=MOSLAsWLAsTMDL (6.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

6.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
6.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the estimated standard (estimated as 37 mg TSS/L) were identified
within the 10th to 90th percentile flow recurrence range. Typically the remaining flow
recurrence range is not included in the TMDL calculation to allow cases of extreme drought or
flood to be excluded.

A power curve equation for the data points violating the water quality criterion was estimated.
The equation is presented in Equation 6.3.

y = 1.2969x-2.598 R² = 1 (6.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

Typically, to present the TMDLs as a single value, the existing load is calculated from the power
curve equation as the average of the load violations occurring when the flow exceeded at a
frequency greater than 10 percent and less than 90 percent. However, only two data points
exceeded the allowable load in the TMLD calculation which occurred in the 50 to 70 percent
flow exceedance. Therefore only the 50-70 percent flow exceedance range was used in the
TMDL calculation and reduction needed. Additionally, the average load was calculated by
using percent flow exceedances in multiples of 5 percent. The allowable loadings for each
exceedance were calculated from the TMDL target value, which includes the 10 percent MOS.
The target curve based on the allowable load and the power curve based on the exceedances
are shown in Figure 6.3.

48

The necessary percent reduction was calculated by taking the difference between the average
of the power curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 50 to 70 (again using recurrence intervals in
multiples of 5), the equation of the exponential curve was used to estimate the existing load.
The allowable load was then calculated in a similar fashion by substituting the allowable load
curve. The estimated values are given in Appendix C.

Figure 6.3 Load duration curve allowable TSS load and existing total TSS load violation in
Second Creek
6.7 TMDL Allocation

6.7.1 Waste Load Allocation (WLA)
Five wastewater treatment plants (WWTP) plus the NC Department of Transportation hold
NPDES permits in the Second Creek Watershed. The wastewater load contributions are shown
in Table 6.2.

y = 1.2969x-2.598
R² = 1
0.1
1.0
10.0
100.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing Load Violation Power (Existing Load Violation)

49
Table 6.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit
Limit
(monthly
max)
Load
(tons/day)
% of
Average
Ambient
Station
Load
Performance Fibers
Operations, Inc. NC0004944 2,305,000 120 lbs/day 0.05 1.05
Pine Valley Subdivision WWTP NC0028941 25,000 30 mg/L 0.00 0.05
West Rowan High School NC0034959 10,000 30 mg/L 0.00 0.02
RDH Tire & Retread NC0075523 No flow
limit 32 lbs/day 0.01 0.28
Second Creek WWTP NC0078361 30,000 30 mg/L 0.003 0.07

In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged
reaches the ambient station with no settling. Based on facility permit limits of flow and the
monthly average permit limits for TSS, the combined WWTP load contributes 1.6% of the
average load at DWQ station Q4120000 based on data from years 2000 through 2009. It
appears that these WWTPs do not present a significant load to Second Creek. Therefore it was
concluded that the WWTPs are adequately regulated under existing permits and the waste load
allocations in this TMDL were calculated at the existing permit limits.

The NCDOT was considered a significant contributor, and was assigned a percent reduction
identical to the nonpoint source reduction. The NCDOT is currently in compliance with their
NPDES stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and highways, data are not
available (n/a) to calculate a WLA for the NCDOT as a load.

The waste load allocation and required reductions for NPDES permittees in Second Creek
watershed are shown in Table 6.3.

Table 6.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Performance Fibers Operations,
Inc. 0.05 0.05 0%
Pine Valley Subdivision WWTP 0.00 0.00 0%
West Rowan High School 0.00 0.00 0%
RDH Tire & Retread 0.01 0.01 0%
Second Creek WWTP 0.01 0.01 0%
NCDOT - Stormwater N/A N/A 41%

50
6.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and
nonpoint sources are presented in Table 6.4. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 41%, as shown in Table 6.5.

Table 6.4 Estimated TMDL and load allocation for TSS (tons/day) for Second Creek
6.5
Pollutant
Water
Body
Existing Load
(tons/day) WLA LA MOS TMDL
TSS Second
Creek 5.20 0.17 2.977 Explicit 10% 3.10
Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10%

Table 6.5 Estimated reduction by source for TSS (tons/day) for Second Creek
NPDES
Wastewater
WLA
NPDES
Stormwater WLA LA
Existing Load (tons/day) 0.170 N/A 5.03
Allocation (tons/day) 0.170 N/A 2.977
Percent Reduction 0% 41% 41%

6.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.
The exceedances of turbidity occurred during normal to high flow periods. The result shows
that wet weather under high-flow period is the critical period for turbidity in Second Creek.

7.0 South Deep Creek
7.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

51
NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

NPDES Wastewater Permits

There are three facilities that discharge wastewater continuously to South Deep Creek and
tributaries under the NPDES program (Table 7.1). In general, facilities are permitted to
discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are
shown in Figure 1.10.

Table 7.1 NPDES Wastewater Dischargers in the South Deep Creek Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended Solids
Monthly Average Limit
NC0029599 Courtney Elementary School
WWTP 5,000 30 mg/L
NC0070459 Starmount High School WWTP 26,000 30 mg/L
NC0079260 Yadkinville WTP No Permit
Limit 30 mg/L

MS4 and Individual Stormwater Permits

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the South Deep Creek
Watershed.
7.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

The ambient monitoring station on South Deep Creek (Q2135000) does not monitor TSS. In
order to determine the relationship between TSS and turbidity in South Deep Creek, a
regression equation between TSS and NTU is used from the other combined ambient stations
used for the waterbodies in this TMDL. These stations include Q5930000, Q3484000,
Q2600000, Q2720000, Q4120000, and Q3934500 using observed data from February 2000
through December 2009. The combined relationship is shown in Equation 7.1. The coefficient of
determination (R-Square) between the two parameters was 0.92, showing a strong relationship
between the two parameters. The R2 value is the percentage of the total variation in turbidity
that is explained or accounted for by the fitted regression (TSS).

52

y = -0.0002x2 + 1.1917x - 4.665 R² = 0.9249 (7.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 54 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for the South Deep Creek because of the availability of
long- term data. It is also an efficient method to calculate a percent load reduction from
nonpoint sources. The methodology used to develop the load duration curve was based on
Cleland (2002).The required load reduction was determined based on water quality monitoring
and stream flow data from January 2000 through April 2010.
7.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 7.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.

53

Figure 7.1 Flow Duration Curve for South Deep Creek at DWQ Station Q21350000

The South Deep Creek watershed does not have a USGS flow gage. Daily flow data were used
from USGS gage on Hunting Creek (02118500), which is located adjacent to the south of South
Deep Creek. The South Deep Watershed area is 80 square miles while the Hunting Creek water
area is 155 square miles. A drainage area ratio between the two watersheds was used to
estimate the flow on South Deep Creek.
7.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown in Figure 7.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
mixture of point and non-point sources may cause exceedances during normal flows.

Existing TSS loads to South Deep Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
1
10
100
1000
10000
0.
0
0
5
%
0.
0
1
0
%
0.
1
0
0
%
1.
0
0
0
%
5.
0
0
0
%
10
.
0
0
0
%
15
.
0
0
0
%
20
.
0
0
0
%
25
.
0
0
0
%
30
.
0
0
0
%
35
.
0
0
0
%
40
.
0
0
0
%
45
.
0
0
0
%
50
.
0
0
0
%
55
.
0
0
0
%
60
.
0
0
0
%
65
.
0
0
0
%
70
.
0
0
0
%
75
.
0
0
0
%
80
.
0
0
0
%
85
.
0
0
0
%
90
.
0
0
0
%
95
.
0
0
0
%
99
.
0
0
0
%
10
0
.
0
0
0
%
Fl
o
w

(
c
f
s
)
Percent Flow Exceeded

daily loading values. The assimilat
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.

Figure 7.2 Load Duration Curve for South Deep Creek at DWQ station Q2135000

For South Deep Creek, the standard
Few exceedances during low-flow
not be a significant source of TSS in this watershed.
transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank
erosion. Stormwater runoff would carry a substantial amount of sediments and solid materia
from impermeable as well as permeable land surfaces
high and transitional flows. Bank erosion occurs when high volume and velocity runoff exceeds
the resistance of the lateral (side) soil material.
considered unmanageable and hence are
7.5 TMDL

Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be
assimilated by the receiving water body while achi
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

Curve for South Deep Creek at DWQ station Q2135000
standard violations occurred during typical to high flow conditions.
flow conditions suggest that point sources in the watershed may
ant source of TSS in this watershed. The higher loads during high and
transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank
erosion. Stormwater runoff would carry a substantial amount of sediments and solid materia
ll as permeable land surfaces. Bank erosion may be another result of
Bank erosion occurs when high volume and velocity runoff exceeds
the resistance of the lateral (side) soil material. The loads during high flow period are
idered unmanageable and hence are excluded in the TMDL estimation in this study.
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 wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
54
were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full

Curve for South Deep Creek at DWQ station Q2135000
violations occurred during typical to high flow conditions.
conditions suggest that point sources in the watershed may
The higher loads during high and
transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank
erosion. Stormwater runoff would carry a substantial amount of sediments and solid materials
. Bank erosion may be another result of
Bank erosion occurs when high volume and velocity runoff exceeds
g high flow period are
excluded in the TMDL estimation in this study.
Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be
eving water quality standards. A TMDL can
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any

55
uncertainty concerning the relationship between effluent limitations and water quality. This
definition can be expressed by equation 8.2.

∑∑++=MOSLAsWLAsTMDL (8.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

7.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study, the
MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
7.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the estimated standard (estimated as 54 mg TSS/L) were identified
within the 10th to 90th percentile flow recurrence range. Typically the remaining flow
recurrence range is not included in the TMDL calculation to allow cases of extreme drought or
flood to be excluded.

An exponential curve equation for the data points violating the water quality criterion was
estimated. The equation is presented in Equation 7.3.

y = 34.556e-1.645x R² = 0.2386 (7.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

To present the TMDLs as a single value, the existing load was calculated from the exponential
curve equation as the average of the load violations occurring between 10% and 90% flow
exceedances. The average load was calculated by using percent flow exceedances in multiples
of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the exponential curve based on the exceedances are shown in Figure 7.3.

56
The necessary percent reduction was calculated by taking the difference between the average
of the exponential curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 10 and 90 (again using recurrence intervals in
multiples of 5), the equation of the exponential curve was used to estimate the existing load.
The allowable load was then calculated in a similar fashion by substituting the allowable load
curve. The estimated values are given in Appendix C.

Figure 7.3 Load duration curve allowable TSS load and existing total TSS load violation in South
Deep Creek

The power line representing the exceeding TSS loads in Figure 7.3 has a lower R-Square value
due to presence of an observation that is numerically distant from the rest of the loads.
7.7 TMDL Allocation

7.7.1 Waste Load Allocation (WLA)
Three wastewater treatment plants (WWTP) plus the NC Department of Transportation hold
NPDES permits in the South Deep Creek Watershed. The wastewater load contributions are
shown in Table 7.2

y = 34.556e-1.645x
R² = 0.2386
1.0
10.0
100.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing Load Violation Expon. (Existing Load Violation)

57
Table 7.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly max
in mg/L)
Load
(tons/day)
% of Average
Ambient
Station Load
Courtney Elementary
School WWTP NC0029599 5,000 30 0.0006 0.003
Starmount High School
WWTP NC0070459 26,000 30 0.0030 0.018
Yadkinville WTP NC0079260 No Permit Limit 30 N/A N/A

The Yadkinville WTP does not have a flow limit, therefore a load will not be calculated for this
facility. In order to estimate contributions from the WWTPs, it was assumed that all TSS
discharged reaches the ambient station with no settling. Based on facility permit limits of flow
and the monthly average permit limits for TSS, the combined WWTP load contributes less than
1% of the average load at DWQ station Q2135000 based on data from years 2000 through
2009. It appears that these WWTPs do not present a significant load to South Deep Creek.
Therefore it was concluded that the WWTPs are adequately regulated under existing permits
and the waste load allocations in this TMDL were calculated at the existing permit limits.

The NCDOT was considered a significant contributor, and was assigned a percent reduction
identical to the nonpoint source reduction. The NCDOT is currently in compliance with their
NPDES stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and highways, data are not
available (n/a) to calculate a WLA for the NCDOT as a load.

The waste load allocation and required reductions for NPDES permittees in the South Deep
Creek watershed are shown in Table 7.3.

Table 7.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Courtney Elementary
School WWTP 0.0006 0.0006 0%
Starmount High School
WWTP 0.0030 0.0030 0%
Yadkinville WTP N/A N/A N/A
NCDOT - Stormwater N/A N/A 48%

7.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and
nonpoint sources are presented in Table 7.4. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 48%, as shown in Table 7.5.

58

Table 7.4 Estimated TMDL and load allocation for TSS (tons/day) for South Deep Creek
Pollutant Water Body Existing Load
(tons/day) WLA LA MOS TMDL
TSS South Deep
Creek 16.40 0.003 8.497 Explicit
10% 8.50

Table 7.5 Estimated reduction by source for TSS (tons/day) for South Deep Creek
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) 0.003 N/A 16.40
Allocation (tons/day) 0.003 N/A 8.497
Percent Reduction 0% 48% 48%

7.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.

The exceedances of turbidity occurred during normal to high flow periods. The result shows
that wet weather under high-flow period is the critical period for turbidity in South Deep Creek.

8.0 South Yadkin River
8.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.

59
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

NPDES Wastewater Permits

There are six facilities that discharge wastewater continuously to the South Yadkin River and
tributaries under the NPDES program (Table 8.1). In general, facilities are permitted to
discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are
shown in Figure 1.12.

Table 8.1 NPDES Wastewater Dischargers in the South Yadkin River Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended Solids
Monthly Average Limit
NC0004898 Turnersburg Plant 10,000 30 mg/L
NC0024872 Cooleemee WWTP 1,500,000 30 mg/L
NC0028606 I-77 Rest Area Iredell County 18,000 30 mg/L
NC0037371 North Iredell High School 12,500 30 mg/L
NC0076333 Statesville Auto Auction WWTP 25,000 30 mg/L
NC0085120 Iredell Distribution Center WWTP 16,000 30 mg/L

MS4 and Individual Stormwater Permits

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the South Yadkin River
Watershed.
8.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

In order to determine the relationship between TSS and turbidity in the South Yadkin River, a
regression equation between the two parameters was developed using the observed data
collected from January 2000 through December 2009 at ambient station Q3460000
on the South Yadkin River. The relationship is shown in Equation 8.1. The coefficient of
determination (R-Square) between the two parameters was 0.88, showing a strong relationship
between the two parameters. The R2 value is the percentage of the total variation in turbidity
that is explained or accounted for by the fitted regression (TSS).

60
y = 1.104x - 1.8288 R² = 0.88 (8.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 53 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for the South Yadkin River because of the availability of
long- term data. It is also an efficient method to calculate a percent load reduction from
nonpoint sources. The methodology used to develop the load duration curve was based on
Cleland (2002).The required load reduction was determined based on water quality monitoring
and stream flow data from January 2000 through December 2009.
8.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 8.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.

61

Figure 8.1 Flow Duration Curve for the South Yadkin River at DWQ Station Q3460000

Daily flow data were used from USGS South Yadkin River gauging station 02118000, co-located
with the DWQ water quality monitoring station.
8.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown in Figure 8.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
mixture of point and non-point sources may cause exceedances during normal flows.

Existing TSS loads to the South Yadkin River were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.
1
10
100
1000
10000
100000
0.
0
0
5
%
0.
0
1
0
%
0.
1
0
0
%
1.
0
0
0
%
5.
0
0
0
%
10
.
0
0
0
%
15
.
0
0
0
%
20
.
0
0
0
%
25
.
0
0
0
%
30
.
0
0
0
%
35
.
0
0
0
%
40
.
0
0
0
%
45
.
0
0
0
%
50
.
0
0
0
%
55
.
0
0
0
%
60
.
0
0
0
%
65
.
0
0
0
%
70
.
0
0
0
%
75
.
0
0
0
%
80
.
0
0
0
%
85
.
0
0
0
%
90
.
0
0
0
%
95
.
0
0
0
%
99
.
0
0
0
%
10
0
.
0
0
0
%
Fl
o
w

(
c
f
s
)
Percent Flow Exceeded

Figure 8.2 Load Duration Curve for the South Yadkin River at DWQ station Q3460000

For the South Yadkin River, the standard
conditions. Few exceedances during
watershed may not be a significant source of TSS in this watershed.
high and transitional flows suggest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
thunderstorms would increase runoff. Stormwater runoff would carry a substantial amount of
sediments and solid materials from impermeable as we
erosion may be another result of high and transitional flows.
volume and velocity runoff exceeds the resistance of the lateral (side) soil material.
during high flow period are cons
estimation in this study.
8.5 TMDL

Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be
assimilated by the receiving water body
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
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 8
Load Duration Curve for the South Yadkin River at DWQ station Q3460000
standard violations occurred during typical to high flow
conditions. Few exceedances during low-flow conditions suggest that point sources in the
watershed may not be a significant source of TSS in this watershed. The higher loads during
gest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
would increase runoff. Stormwater runoff would carry a substantial amount of
id materials from impermeable as well as permeable land surfaces.
erosion may be another result of high and transitional flows. Bank erosion occurs when high
volume and velocity runoff exceeds the resistance of the lateral (side) soil material.
during high flow period are considered unmanageable and hence are excluded in the TMDL
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 wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
rning the relationship between effluent limitations and water quality. This
can be expressed by equation 8.2.
62

Load Duration Curve for the South Yadkin River at DWQ station Q3460000
ations occurred during typical to high flow
conditions suggest that point sources in the
The higher loads during
gest that the sources of turbidity could be from storm runoff
and/or bank erosion. In addition most of the exceedances occurred during summer when
would increase runoff. Stormwater runoff would carry a substantial amount of
ll as permeable land surfaces. Bank
Bank erosion occurs when high
volume and velocity runoff exceeds the resistance of the lateral (side) soil material. The loads
excluded in the TMDL
Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be
while achieving water quality standards. A TMDL can
be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
rning the relationship between effluent limitations and water quality. This

63

∑∑++=MOSLAsWLAsTMDL (8.2)

The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

8.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.
8.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the standard (estimated as 53 mg TSS/L) were identified within the
10th to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is
not included in the TMDL calculation to allow cases of extreme drought or flood to be excluded.

A power curve equation for the data points violating the water quality criterion was estimated.
The equation is presented in Equation 8.3.

y = 31.051x-0.5 R² = 0.2229 (8.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

To present the TMDLs as a single value, the existing load was calculated from the power curve
equation as the average of the load violations occurring between 10% and 90% flow
exceedances. The average load was calculated by using percent flow exceedances in multiples
of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the power curve based on the exceedances are shown in Figure 8.3.

The necessary percent reduction was calculated by taking the difference between the average
of the power curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 10 and 90 (again using recurrence intervals in
multiples of 5), the equation of the power curve was used to estimate the existing load. The

64
allowable load was then calculated in a similar fashion by substituting the allowable load curve.
The estimated values are given in Appendix C.

Figure 8.3 Load duration curve allowable TSS load and existing total TSS load violation in the
South Yadkin River

The power line representing the exceeding TSS loads in Figure 8.3 has a lower R-Square value
due to presence of an observation that is numerically distant from the rest of the loads.
8.7 TMDL Allocation
8.7.1 Waste Load Allocation (WLA)
Six wastewater treatment plants (WWTP) plus the NC Department of Transportation hold
NPDES permits in the South Yadkin River Watershed. The wastewater load contributions are
shown in Table 8.2.

Table 8.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly
max in mg/L)
Load
(tons/day)
% of Average
Ambient
Station Load
Turnersburg Plant NC0004898 10,000 30 0.0011 0.002
Cooleemee WWTP NC0024872 1,500,000 30 0.1703 0.339
I-77 Rest Area Iredell County NC0028606 18,000 30 0.0020 0.004
North Iredell High School NC0037371 12,500 30 0.0014 0.003
Statesville Auto Auction WWTP NC0076333 25,000 30 0.0028 0.006
y = 31.051x-0.5
R² = 0.2229
1.0
10.0
100.0
1000.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing load violation Power (Existing load violation)

65
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly
max in mg/L)
Load
(tons/day)
% of Average
Ambient
Station Load
Iredell Distribution Center
WWTP NC0085120 16,000 30 0.0018 0.004

In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged
reaches the ambient station with no settling. Based on facility permit limits of flow and the
monthly average permit limits for TSS, the combined WWTP load contributes less than 1% of
the average load at DWQ station Q3460000 based on data from years 2000 through 2009. It
appears that these WWTPs do not present a significant load to the South Yadkin River.
Therefore it was concluded that the WWTPs are adequately regulated under existing permits
and the waste load allocations in this TMDL were calculated at the existing permit limits.

The NCDOT was considered a significant contributor, and was assigned a percent reduction
identical to the nonpoint source reduction. The NCDOT is currently in compliance with their
NPDES stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and highways, data are not
available (n/a) to calculate a WLA for the NCDOT as a load.

The waste load allocation and required reductions for NPDES permittees in the South Yadkin
River watershed are shown in Table 8.3.

Table 8.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Turnersburg Plant 0.0011 0.0011 0%
Cooleemee WWTP 0.1703 0.1703 0%
I-77 Rest Area Iredell County 0.0020 0.0020 0%
North Iredell High School 0.0014 0.0014 0%
Statesville Auto Auction WWTP 0.0028 0.0028 0%
Iredell Distribution Center WWTP 0.0018 0.0018 0%
NCDOT - Stormwater N/A N/A 50%

8.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS from point and
nonpoint sources are presented in Table 8.4. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 50%, as shown in Table 8.5.

66
Table 8.4 Estimated TMDL and load allocation for TSS (tons/day) for the South Yadkin River
Pollutant Water Body Existing Load
(tons/day) WLA LA MOS TMDL
TSS South Yadkin
River 50.20 0.179 25.221 Explicit
10% 25.40

Table 8.5 Estimated reduction by source for TSS (tons/day) for the South Yadkin River
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) 0.179 N/A 50.02
Allocation (tons/day) 0.179 N/A 25.221
Percent Reduction 0% 50% 50%

8.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.

The exceedances of turbidity occurred during normal to high flow periods. The result shows
that wet weather under high-flow period is the critical period for turbidity in the South Yadkin
River.

9.0 Third Creek
9.1 Source Assessment

Nonpoint Sources

Potential sources of turbidity from nonpoint sources are described in section 2.1

Point Sources

NPDES wastewater and stormwater permittees upstream of an ambient monitoring site that is
not impaired (not intersected by the impaired waterbody) are not subject to the TMDL.
Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an
unimpaired ambient monitoring site are subject to the TMDL and are discussed below.

67
NPDES Wastewater Permits

There are four facilities that discharge wastewater continuously to Third Creek and tributaries
under the NPDES program (Table 9.1). In general, facilities are permitted to discharge a monthly
average TSS concentration up to 30 mg/L. Locations of dischargers are shown in Figure 1.14.

Table 9.1 NPDES Wastewater Dischargers in the Third Creek Watershed
Permit
Number Facility Name Permit Flow
(gpd)
Total Suspended Solids
Monthly Average Limit
NC0020591 Third Creek WWTP 4,000,000 30 mg/L
NC0023191 Seven Cedars Mobile Home Park WWTP 10,000 30 mg/L
NC0045471 Barium Springs Home WWTP 30,000 30 mg/L
NC0049867 Cleveland WWTP 270,000 30 mg/L

MS4 and Individual Stormwater Permits

The NCDOT (NCS000250) is the only MS4 stormwater permitted entity in the Third Creek
Watershed.
9.2 Technical Approach

Endpoint for Turbidity

Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not
measured in terms of concentrations and cannot be directly converted into loadings required
for developing a load duration curve. For this reason, TSS was selected as the measure for this
study.

In order to determine the relationship between TSS and turbidity in Third Creek, a regression
equation between the two parameters was developed using the observed data collected from
January 2000 through December 2009 at ambient station, Q3934500, on Third Creek. The
relationship is shown in Equation 9.1. The coefficient of determination (R-Square) between the
two parameters was 0.97, showing a strong relationship between the two parameters. The R2
value is the percentage of the total variation in turbidity that is explained or accounted for by
the fitted regression (TSS).

y = 1.2711x - 2.0421 R² = 0.9783 (9.1)
Where Y = TSS in mg/l and X = turbidity in NTU.

The corresponding TSS value at the turbidity standard of 50 NTU is 62 mg/L.

Methodology

The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Third Creek because of the availability of long
data. It is also an efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002).
required load reduction was determined based on water quality monitoring and str
data from January 2000 through December 2009.
9.3 Flow Duration Curve

Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest,
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, sh
and flow regimes during which the exceedances of the pollutants occurred.

Figure 9.1 Flow Duration Curve for the Third Creek at DWQ Station Q393450

The Third Creek watershed does not have a USGS flow gage. Daily flow data were used from
USGS gage on Second Creek (02120780), which is located adjacent to the south of Third Creek.
The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Third Creek because of the availability of long
efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002).
required load reduction was determined based on water quality monitoring and str
data from January 2000 through December 2009.
Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
are used. The flow duration curve, shown in Figure 9.1, was used to determine the seasonality
and flow regimes during which the exceedances of the pollutants occurred.
Flow Duration Curve for the Third Creek at DWQ Station Q3934500
The Third Creek watershed does not have a USGS flow gage. Daily flow data were used from
USGS gage on Second Creek (02120780), which is located adjacent to the south of Third Creek.
68
The load duration curve method is intended to be a simple method to calculate pollutant
reductions. This method was chosen for Third Creek because of the availability of long- term
efficient method to calculate a percent load reduction from nonpoint sources.
The methodology used to develop the load duration curve was based on Cleland (2002).The
required load reduction was determined based on water quality monitoring and stream flow
Development of a flow duration curve is the first step of the load duration approach. A flow
duration curve employs a cumulative frequency distribution of measured daily stream flow over
the period of record. The curve relates flow values measured at the monitoring station for the
percent of time the flow values were equaled or exceeded. Flows are ranked from lowest,
which are exceeded less than 1
percent of the time. Reliability of the flow duration curve depends on the period of record
available at monitoring stations. Accuracy of the curve increases when longer periods of record
, was used to determine the seasonality

The Third Creek watershed does not have a USGS flow gage. Daily flow data were used from
USGS gage on Second Creek (02120780), which is located adjacent to the south of Third Creek.

69
The Third Creek Watershed area is 100 square miles while the Second Creek water area is 114
square miles. A drainage area ratio between the two watersheds was used to estimate the flow
on Third Creek.
9.4 Load Duration Curve

A load duration curve is developed by multiplying the flow values along the flow duration curve
by the pollutant concentrations and the appropriate conversion factors. As shown in Figure 9.2,
allowable and existing loads are plotted against the flow recurrence interval. The allowable
load is based on the water quality numerical standard, margin of safety, and flow duration
curve. The target line is represented by the line drawn through the allowable load data points
and hence, it determines the assimilative capacity of a stream or river under different flow
conditions. Any values above the line are exceeded loads and the values below the line are
acceptable loads. Therefore, a load duration curve can help define the flow regime during
which exceedances occur. Exceedances that occur during low-flow events are likely caused by
continuous or point source discharges, which are generally diluted during storm events.
Exceedances that occur during high-flow events are generally driven by storm-event runoff. A
mixture of point and non-point sources may cause exceedances during normal flows.

Existing TSS loads to the Third Creek were determined by multiplying the observed TSS
concentration by the flow observed on the date of observation and converting the result to
daily loading values. The assimilative capacities of the waterbodies were determined by
multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full
range of measured flow values.

Figure 9.2 Load Duration Curve for the Third Creek at DWQ station Q3934500

For Third Creek, the standard violations occurred during typical to high flow conditions. Few
exceedances during low-flow conditions suggest that point sources in the watershed may not
be a significant source of TSS in this watershed.
flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion.
Stormwater runoff would carry a substantial amount of sediments and solid materials from
impermeable as well as permeable land surfaces
and transitional flows. Bank erosion occurs when high volume and velocity runoff exceeds the
resistance of the lateral (side) soil material.
unmanageable and hence are excluded in the TMDL estimation in this study.
9.5 TMDL

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 wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
uncertainty concerning the relationship between effluent limitations and water quality.
definition can be expressed by equation 9

∑ ∑+=LAsWLAsTMDL

Load Duration Curve for the Third Creek at DWQ station Q3934500
violations occurred during typical to high flow conditions. Few
conditions suggest that point sources in the watershed may not
be a significant source of TSS in this watershed. The higher loads during high and transitional
flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion.
Stormwater runoff would carry a substantial amount of sediments and solid materials from
ll as permeable land surfaces. Bank erosion may be another result of high
Bank erosion occurs when high volume and velocity runoff exceeds the
resistance of the lateral (side) soil material. The loads during high flow period are cons
excluded in the TMDL estimation in this study.
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
e sum of all point source wasteload allocations (WLAs), nonpoint source load
allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any
uncertainty concerning the relationship between effluent limitations and water quality.
can be expressed by equation 9.2.
+MOSLAs
70

violations occurred during typical to high flow conditions. Few
conditions suggest that point sources in the watershed may not
igh and transitional
flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion.
Stormwater runoff would carry a substantial amount of sediments and solid materials from
erosion may be another result of high
Bank erosion occurs when high volume and velocity runoff exceeds the
The loads during high flow period are considered
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
e sum of all point source wasteload allocations (WLAs), nonpoint source load
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
(9.2)

71
The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in
order to implement control measures and to achieve water quality standards. The Code of
Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass
per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are
expressed as tons per day. TMDLs represent the maximum one-day load the river can
assimilate and maintain the water quality criterion. Load duration curve approach was utilized
to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are
described below.

9.5.1 Margin of Safety (MOS)
Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the
simulated relationship between the pollutants and the water quality standard. In this study,
the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent
lower than the water quality target for turbidity.

9.6 Target Reduction

To determine the amount of turbidity reduction necessary to comply with the water quality
standard, exceedances of the estimated standard (62 mg TSS/L) were identified within the 10th
to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is not
included in the TMDL calculation to allow cases of extreme drought or flood to be excluded.

A power curve equation for the data points violating the water quality criterion was estimated.
The equation is presented in Equation 9.3.

y = 6.17x-0.753 R² = 0.794 (9.3)
Where, Y = TSS (tons/day) and X = Percent Flow Exceeded.

To present the TMDLs as a single value, the existing load was calculated from the power curve
equation as the average of the load violations occurring between 10% and 90% flow
exceedances. The average load was calculated by using percent flow exceedances in multiples
of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL
target value, which includes the 10 percent MOS. The target curve based on the allowable load
and the power curve based on the exceedances are shown in Figure 9.3.

The necessary percent reduction was calculated by taking the difference between the average
of the power curve load estimates and the average of the allowable load estimates. For
example, at each recurrence interval between 10 and 90 (again using recurrence intervals in
multiples of 5), the equation of the power curve was used to estimate the existing load. The
allowable load was then calculated in a similar fashion by substituting the allowable load curve.
The estimated values are given in Appendix C.

72

Figure 9.3 Load duration curve allowable TSS load and existing total TSS load violation in Third
Creek
9.7 TMDL Allocation

9.7.1 Waste Load Allocation (WLA)
Four wastewater treatment plants (WWTP) plus the NC Department of Transportation hold
NPDES permits in the Third Creek Watershed. The wastewater load contributions are shown in
Table 9.2

Table 9.2 Existing NPDES WW Load Contributions
Facility Name Permit
Number
Flow
(gpd)
Permit Limit
(monthly max
in mg/L)
Load
(tons/day)
% of Average
Ambient
Station Load
Third Creek WWTP NC0020591 4,000,000 30 0.4542 3.415
Seven Cedars Mobile Home Park
WWTP NC0023191 10,000 30 0.0011 0.009
Barium Springs Home WWTP NC0045471 30,000 30 0.0034 0.026
Cleveland WWTP NC0049867 270,000 30 0.0307 0.231

In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged
reaches the ambient station with no settling. Based on facility permit limits of flow and the
monthly average permit limits for TSS, the combined WWTP load contributes approximately
3.7% of the average load at DWQ station Q3934500 based on data from years 2000 through
y = 6.17x-0.753
R² = 0.794
1.0
10.0
100.0
10% 20% 30% 40% 50% 60% 70% 80% 90%
TS
S

(
t
o
n
e
s
/
d
a
y
)
Percent Flow Exceeded
Allowable load with MOS Existing Load Violation Power (Existing Load Violation)

73
2009. It appears that these WWTPs do not present a significant load to the Third Creek.
Therefore it was concluded that the WWTPs are adequately regulated under existing permits
and the waste load allocations in this TMDL were calculated at the existing permit limits.

The NCDOT was considered a significant contributor, and was assigned a percent reduction
identical to the nonpoint source reduction. The NCDOT is currently in compliance with their
NPDES stormwater permit, and will continue to implement measures required by the permit
(NCS000250). Because of the nature of drainage from roads and highways, data are not
available (n/a) to calculate a WLA for the NCDOT as a load.

The waste load allocation and required reductions for NPDES permittees in the Third Creek
watershed are shown in Table 9.3.

Table 9.3 NPDES waste load allocations and required reductions
NPDES Permittee Permitted Load
(tons/day) WLA (tons/day) Percent Reduction
Required
Third Creek WWTP 0.4542 0.4542 0%
Seven Cedars Mobile
Home Park WWTP 0.0011 0.0011 0%
Barium Springs Home
WWTP 0.0034 0.0034 0%
Cleveland WWTP 0.0307 0.0307 0%
NCDOT - Stormwater N/A N/A 50%

9.7.2 Load Allocation (LA)
All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and
forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and
nonpoint sources are presented in Table 9.4. The estimated percent reduction needed from
NPDES stormwater and nonpoint sources is 50%, as shown in Table 9.5.

Table 9.4 Estimated TMDL and load allocation for TSS (tons/day) for Third Creek
Pollutant Water Body Existing Load
(tons/day) WLA LA MOS TMDL
TSS Third Creek 13.30 0.489 6.411 Explicit
10% 6.90
Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10%

74

Table 9.5 Estimated reduction by source for TSS (tons/day) for Third Creek
NPDES
Wastewater
WLA
NPDES
Stormwater
WLA
LA
Existing Load (tons/day) 0.489 N/A 12.81
Allocation (tons/day) 0.489 N/A 6.41
Percent Reduction 0% 50% 50%
9.7.3 Critical Condition and Seasonal Variation
Critical conditions are considered in the load duration curve analysis by using an extended
period of stream flow and water quality data, and by examining the flows (percent flow
exceeded) where the existing loads exceed the target.

Seasonal variation is considered in the development of the TMDLs, because allocation applies
to all seasons. In the load duration curves, the mark inside a square box indicates pollutant
load during the summer period.

The exceedances of turbidity occurred during normal to high flow periods. The result shows
that wet weather under high-flow period is the critical period for turbidity in Third Creek.

10.0 Summary and Future Implementation

This report presents the development of the Total Maximum Daily Loads (TMDL) for nine
waterbodies in the Yadkin Pee-Dee River Basin.

Available water quality data were reviewed to determine the critical periods and the sources
that lead to exceedances of the standard. The necessary percent reduction to meet the TMDL
requirement was then calculated by taking a difference between the average of the curve load
estimates and the average of the allowable load estimates. The summary of the results is as
follows:

• Abbots Creek: A 57% reduction in nonpoint source and NPDES stormwater
contributions of TSS is required in order to meet the water quality standard.

• Ararat River: A 54% reduction in nonpoint source and NPDES stormwater contributions
of TSS is required in order to meet the water quality standard.

• Hunting Creek: A 52% reduction in nonpoint source and NPDES stormwater
contributions of TSS is required in order to meet the water quality standard in.

75
• Second Creek: A 41% reduction in nonpoint source and NPDES stormwater
contributions of TSS is required in order to meet the water quality standard.

• South Deep Creek: A 48% reduction in nonpoint source and NPDES stormwater
contributions of TSS is required in order to meet the water quality standard.

• South Yadkin River: A 50% reduction in nonpoint source and NPDES stormwater
contributions of TSS is required in order to meet the water quality standard. This
reduction may be achieved in part through the reductions required for Hunting Creek,
Third Creek and Second Creek.

• Third Creek: A 50% reduction in nonpoint source and NPDES stormwater contributions
of TSS is required in order to meet the water quality standard.

10.1 TMDL Implementation

This TMDL does not include an implementation plan. This section is intended to provide some
initial assistance for implementing this TMDL.

Reduction of turbidity in these watersheds will result from reduced overland and stormwater
runoff, and improved land management. Landowners, stakeholder groups, local governments,
and agencies are encouraged to utilize all available funding sources for water quality
improvement projects within the watershed. The following programs provide technical and
financial resources for reducing non-point source pollution:

• The North Carolina Soil and Water Conservation Service
• The Natural Resources Conservation Service
• Clean Water Act Section 319 Nonpoint source pollution control grant
• North Carolina Clean Water Management Trust Fund
• 205(j) Water Quality Management Planning Grant

11.0 Public Participation

This TMDL was public noticed through the DWQ Modeling and TMDL unit website, through the
Modeling and TMDL unit listserv, through the DWQ events calendar, and through the Water
Resources Research Institute (WRRI) listserv of North Carolina State University. The
announcement is provided in Appendix D. The TMDL was also available from DWQ’s website at
http://portal.ncdenr.org/web/wq/ps/mtu/tmdl/tmdls during the comment period. The public
comment period lasted from July 26 – August 25, 2011. NCDWQ received comments from
seven entities. A summary of their comments and DWQ’s response is provided in Appendix E.

76

12.0 References

Cleland, B.R. 2002. TMDL Development from the “Bottom Up” – Part II: Using load duration
curves to connect the pieces. Proceedings from the WEF National TMDL Science and Policy
2002 Conference.

U.S. Environmental Protection Agency (USEPA). 1991. Guidance for Water Quality-Based
Decisions: The TMDL Process. Assessment and Watershed Protection Division, Washington, DC.

U.S. Environmental Protection Agency (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.

U.S. Environmental Protection Agency (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).

Wayland, R. November 22, 2002. Memorandum from Rober Wayland of the U. S.
Environmental Protection Agency to Water Division Directors. Subject: Establishing TMDL
Waste Load Allocation for stormwater sources and NPDES permit requirements based on those
allocations.

77

Appendix A: Land Cover Data in Square Miles and Percent Area for the Impaired Watersheds
Description
Third
Creek
Abbots
Creek
Ararat
River
Hunting
Creek
Second
Creek
South
Yadkin
S. Deep
Creek
Barren Land 0.4 0% 0.5 0% 0.4 0% 0.0 0% 0.2 0% 1.1 0% 1.1 0%
Cultivated Crops 3.1 3% 3.6 2% 3.6 1% 2.9 2% 5.9 4% 21.8 2% 21.8 2%
Deciduous Forest 17.8 18% 38.4 19% 117.0 37% 48.7 32% 20.4 14% 200.5 22% 200.5 22%
Developed, High Intensity 1.3 1% 3.7 2% 2.2 1% 0.4 0% 0.6 0% 6.1 1% 6.1 1%
Developed, Low Intensity 8.7 9% 28.0 14% 23.6 8% 6.2 4% 9.3 7% 56.9 6% 56.9 6%
Developed, Medium Intensity 2.4 2% 6.3 3% 3.3 1% 0.6 0% 1.4 1% 9.7 1% 9.7 1%
Developed, Open Space 12.1 12% 28.0 14% 21.2 7% 5.9 4% 12.7 9% 68.6 8% 68.6 8%
Emergent Herbaceous
Wetland 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0%
Evergreen Forest 11.1 11% 25.8 13% 45.3 14% 17.8 12% 17.6 12% 105.5 12% 105.5 12%
Grassland/Herbaceous 0.3 0% 0.4 0% 0.7 0% 0.5 0% 0.2 0% 2.8 0% 2.8 0%
Mixed Forest 5.1 5% 5.8 3% 6.6 2% 9.7 6% 6.7 5% 52.4 6% 52.4 6%
Open Water 0.4 0% 1.8 1% 1.1 0% 0.5 0% 0.6 0% 3.0 0% 3.0 0%
Pasture/Hay 36.8 37% 53.3 27% 85.1 27% 55.9 37% 64.4 46% 368.8 41% 368.8 41%
Scrub/Shrub 0.6 1% 1.1 1% 3.3 1% 0.8 1% 0.4 0% 4.7 1% 4.7 1%
Woody Wetlands 0.7 1% 1.6 1% 0.1 0% 0.8 1% 1.0 1% 4.4 0% 4.4 0%
Total SQMI 101 198 313 151 141 906 906

78

Appendix B. Water Quality Data Used for TMDL Development

79

Abbotts Creek DWQ Station Q5930000 and USGS station 02121500
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
2/28/2000 94 22.00 14 5.56 7/27/2005 23 24.00 32 1.48
3/6/2000 67 11.00 8.5 1.98 8/8/2005 30 30.00 29 2.42
4/27/2000 86 8.00 16 1.85 8/23/2005 29 25.00 24 1.95
5/15/2000 42 11.00 12 1.24 9/22/2005 18 12.00 11 0.58
6/19/2000 32 14.00 9.7 1.21 10/18/2005 27 9.20 13 0.67
7/18/2000 14 12.14 15 0.46 10/27/2005 22 4.00 4.8 0.24
8/21/2000 14 13.84 17 0.52 11/16/2005 27 16.00 7.5 1.16
9/11/2000 16 9.00 9 0.39 11/28/2005 111 5.80 7.6 1.73
10/19/2000 16 3.90 5.3 0.17 12/13/2005 138 7.50 19 2.78
11/27/2000 41 18.94 23 2.09 1/3/2006 586 101.00 110 159.21
12/13/2000 17 3.00 3.2 0.14 1/17/2006 219 26.00 22 15.32
4/24/2001 56 10.00 8 1.51 2/2/2006 89 5.20 12 1.24
5/16/2001 21 5.51 7.2 0.31 2/16/2006 97 6.00 12 1.57
6/11/2001 16 28.00 26 1.21 3/1/2006 81 5.50 7.4 1.20
7/23/2001 11 10.44 13 0.31 3/16/2006 69 4.20 7.4 0.78
8/13/2001 25 41.89 50 2.82 3/29/2006 69 4.00 6.4 0.74
9/12/2001 9.8 8.00 9.5 0.21 4/11/2006 64 5.80 9.4 1.00
10/16/2001 21 3.56 4.9 0.20 4/24/2006 86 19.00 18 4.40
11/14/2001 11 4.32 5.8 0.13 5/18/2006 49 24.00 20 3.16
12/13/2001 27 18.00 37 1.31 5/31/2006 21 13.00 14 0.73
1/16/2002 19 17.24 21 0.88 6/14/2006 226 52.00 65 31.61
2/12/2002 72 6.53 8.4 1.27 6/26/2006 81 24.89 30 5.42
4/30/2002 15 8.74 11 0.35 7/11/2006 51 27.00 21 3.70
5/30/2002 12 11.29 14 0.36 7/26/2006 106 28.00 25 7.98
6/25/2002 6.8 6.00 10 0.11 8/7/2006 40 25.00 28 2.69
7/18/2002 8.2 16.39 20 0.36 8/24/2006 21 14.00 17 0.79
8/14/2002 5 4.66 6.2 0.06 9/11/2006 37 19.00 22 1.89
9/23/2002 21 30.00 32 1.69 10/16/2006 24 2.37 3.5 0.15
10/17/2002 1430 41.89 50 161.13 11/7/2006 61 6.11 7.9 1.00
11/20/2002 235 29.99 36 18.96 12/18/2006 58 4.20 18 0.66
12/18/2002 189 40.00 24 20.34 1/22/2007 453 80.13 95 97.65
1/22/2003 76 18.09 22 3.70 2/7/2007 97 12.99 16 3.39
2/20/2003 223 16.39 20 9.83 3/20/2007 159 20.00 25 8.55
3/24/2003 278 34.00 80 25.43 4/19/2007 260 33.39 40 23.35
4/8/2003 1910 54.64 65 280.71 5/16/2007 47 14.69 18 1.86
5/29/2003 217 19.79 24 11.55 6/12/2007 175 154.00 210 72.50
6/26/2003 76 20.00 18 4.09 7/9/2007 18 13.84 17 0.67
7/17/2003 80 18.09 22 3.89 8/23/2007 28 15.54 19 1.17
8/14/2003 186 80.13 95 40.09 9/19/2007 10 12.00 24 0.32
9/15/2003 74 17.00 16 3.38 10/16/2007 15 7.38 9.4 0.30
10/15/2003 110 36.79 44 10.89 10/29/2007 38 12.14 15 1.24
11/1/2003 76 11.29 14 2.31 12/10/2007 15 2.28 3.4 0.09
12/8/2003 70 4.00 7.7 0.75 1/24/2008 67 6.87 8.8 1.24
1/7/2004 84 7.89 10 1.78 2/11/2008 69 9.59 12 1.78
2/3/2004 346 63.13 75 58.76 3/17/2008 228 22.00 22 13.49
3/4/2004 256 18.00 26 12.40 4/10/2008 196 16.00 18 8.44
4/6/2004 86 6.87 8.8 1.59 5/15/2008 53 11.00 11 1.57
5/20/2004 52 14.69 18 2.05 6/10/2008 21 8.50 10 0.48
6/28/2004 174 220.00 170 102.97 7/9/2008 23 22.00 29 1.36
7/28/2004 353 75.88 90 72.06 8/7/2008 8.9 14.00 18 0.34
8/24/2004 25 11.29 14 0.76 9/9/2008 18 11.00 15 0.53
9/16/2004 52 9.00 7.2 1.26 10/13/2008 24 2.88 4.1 0.19
10/7/2004 85 12.99 16 2.97 11/12/2008 21 1.60 2.6 0.09
11/8/2004 57 5.60 7.3 0.86 12/4/2008 63 6.96 8.9 1.18
12/7/2004 92 4.00 6.9 0.99 1/8/2009 1530 40.00 75 164.63
1/11/2005 80 14.69 18 3.16 2/3/2009 108 6.20 17 1.80
2/21/2005 105 11.29 14 3.19 3/5/2009 335 20.00 26 18.02
3/10/2005 169 17.00 21 7.73 4/15/2009 226 18.00 17 10.94
3/30/2005 540 42.00 50 61.01 5/14/2009 101 24.00 20 6.52
4/12/2005 149 17.24 21 6.91 6/25/2009 34 22.00 22 2.01
4/21/2005 95 8.50 12 2.17 7/22/2009 31 16.00 16 1.33
5/16/2005 71 9.80 8.6 1.87 8/24/2009 42 26.00 34 2.94
5/23/2005 72 17.00 32 3.29 9/16/2009 13 12.00 15 0.42
6/14/2005 109 23.00 22 6.74 10/13/2009 35 6.20 7.8 0.58
6/28/2005 156 160.00 210 67.14 11/16/2009 260 13.00 35 9.09
7/13/2005 48 26.00 27 3.36 12/7/2009 199 9.20 25 4.92

80
Ararat River DWQ Station Q1780000 and USGS station 02113850
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
01/05/2000 173 11.00 8.2 5.12 07/06/2005 264 72.00 150 51.13
02/03/2000 183 2.00 10 0.98 07/14/2005 399 106.00 120 113.77
03/07/2000 180 4.00 4 1.94 07/26/2005 244 13.00 13 8.53
04/04/2000 427 54.00 28 62.03 08/11/2005 211 13.00 8.9 7.38
05/10/2000 184 13.00 6.5 6.43 08/25/2005 160 7.20 8.6 3.10
06/07/2000 185 45.00 45 22.39 09/22/2005 128 22.00 33 7.58
07/19/2000 74 4.00 3.4 0.80 10/17/2005 194 5.00 6.2 2.61
08/14/2000 84 7.00 10 1.58 10/25/2005 179 2.80 2.9 1.35
09/13/2000 96 11.00 7.9 2.84 11/15/2005 171 10.52 1.5 4.84
10/11/2000 87 10.11 2.7 2.37 11/29/2005 1070 308.00 140 886.52
11/14/2000 111 10.21 2.4 3.05 12/14/2005 245 10.21 2.4 6.73
12/27/2000 97 11.00 5.8 2.87 01/04/2006 341 6.80 9.1 6.24
01/10/2001 89 9.70 4 2.32 01/12/2006 414 37.00 55 41.21
02/13/2001 119 10.38 1.9 3.32 01/31/2006 260 7.20 5.8 5.04
04/23/2001 132 10.34 2 3.67 02/13/2006 227 10.24 2.3 6.25
05/07/2001 91 9.39 5.1 2.30 02/27/2006 191 10.52 1.5 5.40
06/13/2001 93 14.00 10 3.50 03/30/2006 170 4.50 3.6 2.06
08/16/2001 129 8.27 11 2.87 04/27/2006 328 39.38 65 34.74
09/10/2001 92 4.00 3.7 0.99 05/30/2006 140 8.77 7.8 3.30
10/10/2001 74 10.21 2.4 2.03 06/15/2006 109 17.00 15 4.98
11/13/2001 83 8.40 10 1.87 07/17/2006 256 8.09 13 5.57
12/06/2001 85 8.17 12 1.87 08/10/2006 199 9.70 27 5.19
01/14/2002 116 8.98 6.8 2.80 09/13/2006 520 82.00 71 114.70
02/20/2002 151 9.95 3.2 4.04 10/12/2006 186 9.53 4.6 4.77
03/07/2002 167 3.00 3.5 1.35 11/16/2006 2970 3664.90 550 29279.98
04/11/2002 205 8.75 7.9 4.82 12/05/2006 255 3.00 3 2.06
05/14/2002 251 53.33 75 36.01 01/18/2007 371 9.32 5.4 9.30
06/12/2002 69 9.12 6.2 1.69 02/19/2007 293 9.53 4.6 7.51
07/09/2002 53 8.67 8.3 1.24 03/07/2007 412 13.00 14 14.41
08/01/2002 63 8.98 6.8 1.52 04/26/2007 288 10.04 2.9 7.78
09/09/2002 30 4.00 6 0.32 05/09/2007 238 9.59 4.4 6.14
10/01/2002 121 9.47 4.8 3.08 06/19/2007 165 8.50 6.7 3.77
11/14/2002 355 9.70 27 9.27 07/16/2007 145 8.87 7.3 3.46
12/09/2002 193 2.50 4 1.30 08/08/2007 104 9.07 6.4 2.54
02/04/2003 240 8.01 15 5.17 09/10/2007 80 9.02 6.6 1.94
03/12/2003 290 9.56 4.5 7.46 10/10/2007 102 9.98 3.1 2.74
04/24/2003 466 8.73 8 10.94 10/31/2007 222 9.14 6.1 5.46
05/19/2003 387 8.65 8.4 9.01 11/27/2007 169 10.14 2.6 4.61
06/04/2003 739 170.00 140 337.94 01/10/2008 186 10.34 2 5.17
07/09/2003 583 8.04 14 12.61 02/19/2008 196 9.88 3.4 5.21
08/12/2003 798 15.08 39 32.37 03/06/2008 204 9.37 5.2 5.14
09/04/2003 1210 810.00 260 2636.47 04/14/2008 216 9.29 5.5 5.40
10/13/2003 298 9.85 3.5 7.90 05/12/2008 300 10.34 29 8.35
11/19/2003 1510 11.93 33 48.47 06/19/2008 92 8.93 7 2.21
12/02/2003 381 4.00 5.5 4.10 07/16/2008 97 8.01 15 2.09
01/08/2004 340 10.07 2.8 9.21 08/18/2008 46 8.01 15 0.99
02/19/2004 331 8.83 7.5 7.86 09/24/2008 61 9.67 4.1 1.59
03/22/2004 260 3.00 3 2.10 10/22/2008 85 10.27 2.2 2.35
04/21/2004 284 8.43 9.8 6.44 11/18/2008 122 10.11 2.7 3.32
05/12/2004 222 8.04 14 4.80 12/18/2008 195 8.27 20 4.34
06/10/2004 222 33.00 35 19.71 01/27/2009 149 9.76 3.8 3.91
07/26/2004 196 8.49 9.4 4.47 02/04/2009 137 10.04 2.9 3.70
08/23/2004 181 8.46 9.6 4.12 03/30/2009 275 8.8 5.3 6.51
09/29/2004 925 76.00 40 189.11 04/28/2009 177 9.28935 5.5 4.42
10/12/2004 283 9.02 6.6 6.87 05/07/2009 805 313.565 170 679.01
11/03/2004 236 9.91 3.3 6.29 06/29/2009 243 9.14042 6.1 5.97
12/16/2004 309 2.50 4.2 2.08 07/13/2009 197 8.039 14 4.26
01/06/2005 279 9.34 5.3 7.01 08/31/2009 152 9.4475 4.9 3.86
02/23/2005 311 8.93 7 7.47 09/09/2009 188 16 23 8.09
03/08/2005 394 10.00 3.2 10.60 10/01/2009 152 9.4205 5 3.85
03/29/2005 931 60.00 65 150.26 11/05/2009 200 10.1391 2.6 5.45
04/07/2005 386 16.00 10 16.61 12/08/2009 299 9.61486 4.3 7.73
04/27/2005 334 8.00 5.7 7.19
05/10/2005 255 4.00 3.4 2.74
06/02/2005 313 41.00 8.2 34.52
06/15/2005 254 52.00 35 35.53

81
Hunting Creek DWQ Station Q3484000 and USGS station 02118500
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
1/4/2000 97 9.00 6.3 2.35 1/9/2006 152 5.14 5.1 2.10
2/14/2000 345 110.00 130 102.09 2/1/2006 156 3.20 4 1.34
3/14/2000 95 5.78 6 1.48 3/2/2006 131 8.42 9.7 2.97
4/19/2000 264 31.00 23 22.01 4/5/2006 111 8.63 10 2.58
5/16/2000 89 6.00 8.5 1.44 5/4/2006 93 15.00 5.4 3.75
6/15/2000 63 8.00 7.9 1.36 6/8/2006 62 10.05 12 1.68
7/17/2000 56 5.00 9 0.75 7/5/2006 66 20.03 26 3.56
8/6/2000 45 8.00 9 0.97 8/2/2006 55 6.50 6.7 0.96
9/5/2000 115 33.57 45 10.38 9/7/2006 76 11.48 14 2.35
10/16/2000 52 3.21 2.4 0.45 10/11/2006 58 5.14 5.1 0.80
11/16/2000 58 3.07 2.2 0.48 11/6/2006 82 2.50 1.6 0.55
12/6/2000 64 3.29 2.5 0.57 12/5/2006 102 4.00 3.5 1.10
1/8/2001 64 3.50 2.8 0.60 1/8/2007 1130 136.88 190 416.07
2/5/2001 64 2.00 2.5 0.34 2/7/2007 128 3.50 3.3 1.21
4/19/2001 100 5.42 5.5 1.46 3/8/2007 198 9.34 11 4.98
5/10/2001 71 5.00 4.3 0.95 4/3/2007 144 4.00 3.5 1.55
6/11/2001 56 5.49 5.6 0.83 5/2/2007 131 4.50 3.8 1.59
7/9/2001 87 28.58 38 6.69 6/6/2007 90 9.34 11 2.26
8/14/2001 125 42.00 50 14.12 7/5/2007 62 9.34 11 1.56
9/10/2001 39 5.07 5 0.53 8/8/2007 45 4.64 4.4 0.56
10/3/2001 33 6.14 6.5 0.54 9/6/2007 24 5.14 5.1 0.33
11/8/2001 40 4.71 4.5 0.51 10/2/2007 43 3.78 3.2 0.44
12/4/2001 43 3.29 2.5 0.38 11/1/2007 81 4.64 4.4 1.01
1/10/2002 67 4.64 4.4 0.84 12/4/2007 59 2.29 1.1 0.36
2/13/2002 107 5.07 5 1.46 1/3/2008 126 4.57 4.3 1.55
3/12/2002 88 3.86 3.3 0.91 2/5/2008 369 45.00 85 44.67
4/8/2002 91 4.28 3.9 1.05 3/5/2008 155 11.48 14 4.79
5/14/2002 116 94.00 160 29.33 4/1/2008 125 5.14 5.1 1.73
6/10/2002 33 7.13 7.9 0.63 5/5/2008 91 13.00 17 3.18
7/8/2002 16 7.35 8.2 0.32 6/2/2008 58 9.34 11 1.46
8/27/2002 14 4.00 6.9 0.15 7/1/2008 46 14.33 18 1.77
9/18/2002 27 16.47 21 1.20 8/5/2008 30 8.20 14 0.66
10/16/2002 227 27.15 36 16.58 9/2/2008 50 7.13 7.9 0.96
11/13/2002 385 78.00 75 80.78 10/2/2008 74 12.19 15 2.43
12/18/2002 152 9.34 11 3.82 11/3/2008 55 2.93 2 0.43
1/29/2003 105 4.43 4.1 1.25 12/1/2008 107 4.92 4.8 1.42
2/20/2003 173 7.00 9 3.26 1/6/2009 103 17.18 22 4.76
3/20/2003 6600 286.50 400 5086.60 2/2/2009 80 3.71 3.1 0.80
4/7/2003 400 51.38 70 55.28 3/3/2009 279 27.15 36 20.38
5/7/2003 386 12.90 16 13.40 4/1/2009 153 6.99 7.7 2.88
6/9/2003 2450 87.00 120 573.40 5/4/2009 103 12.00 10 3.32
7/1/2003 403 115.50 160 125.21 6/2/2009 233 22.88 30 14.34
8/13/2003 288 32.00 29 24.79 7/6/2009 132 6.78 7.4 2.41
9/10/2003 205 8.63 10 4.76 8/3/2009 104 11.00 12 3.08
10/6/2003 159 5.07 5 2.17 9/2/2009 106 10.77 13 3.07
11/3/2003 159 4.07 3.6 1.74 10/1/2009 83 5.78 6 1.29
12/1/2003 167 3.86 3.3 1.73 11/2/2009 332 47.00 45 41.97
1/7/2004 148 5.85 6.1 2.33 12/1/2009 150 4.35 4 1.76
2/3/2004 438 310.00 120 365.25
3/1/2004 198 4.50 4.2 2.40
4/13/2004 561 158.25 220 238.82
5/3/2004 165 10.00 10 4.44
6/2/2004 107 13.62 17 3.92
7/8/2004 90 15.04 19 3.64
8/4/2004 80 14.00 19 3.01
9/9/2004 748 58.50 80 117.72
10/6/2004 149 9.34 11 3.74
11/1/2004 130 4.00 3.2 1.40
12/2/2004 219 12.19 15 7.18
1/4/2005 175 4.78 4.6 2.25
2/14/2005 158 7.00 4.9 2.98
3/3/2005 239 5.00 4.9 3.21
4/4/2005 253 15.04 19 10.24
5/4/2005 162 6.00 4.5 2.61
6/6/2005 135 11.48 14 4.17
7/6/2005 206 69.19 95 38.34
8/3/2005 131 11.00 10 3.88
10/4/2005 59 7.63 8.6 1.21
11/2/2005 88 3.20 3.1 0.76
12/5/2005 202 17.18 22 9.33

82

Second Creek DWQ Station Q4120000 and USGS station 02120780
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
02/15/2000 165 55.00 65 24.41 01/09/2006 93 14.00 18 3.50
03/13/2000 47 5.00 9.4 0.63 02/02/2006 78 8.34 14 1.75
04/17/2000 93 29.00 22 7.25 03/06/2006 71 6.73 12 1.28
05/15/2000 28 12.00 9.4 0.90 04/06/2006 61 15.00 13 2.46
06/07/2000 20 17.00 14 0.91 05/08/2006 68 19.65 28 3.59
07/24/2000 27 50.00 50 3.63 06/08/2006 29 4.95 9.8 0.39
08/15/2000 8 22.00 12 0.47 07/06/2006 47 64.00 70 8.09
09/12/2000 7.6 6.73 12 0.14 08/09/2006 22 29.35 40 1.74
10/05/2000 7.9 7.00 5.8 0.15 09/07/2006 20 5.92 11 0.32
11/06/2000 13 0.02 3.7 0.00 10/11/2006 16 4.20 6.7 0.18
12/11/2000 17 1.32 5.3 0.06 11/06/2006 29 0.51 4.3 0.04
01/17/2001 18 4.00 5.8 0.19 12/05/2006 53 5.92 11 0.84
02/12/2001 30 3.42 7.9 0.28 01/09/2007 318 58.00 90 49.61
05/23/2001 22 29.35 40 1.74 02/07/2007 68 5.92 11 1.08
06/25/2001 10 12.38 19 0.33 03/08/2007 140 22.08 31 8.31
07/25/2001 7.7 13.00 13 0.27 04/03/2007 63 16.00 8.7 2.71
08/13/2001 12 7.54 13 0.24 05/02/2007 55 4.63 9.4 0.68
09/13/2001 4.5 3.50 8 0.04 06/06/2007 25 8.34 14 0.56
10/09/2001 6.9 6.00 3.5 0.11 07/09/2007 15 22.00 24 0.89
11/28/2001 9.2 9.15 15 0.23 08/09/2007 2.7 2.20 6.4 0.02
12/27/2001 20 1.96 6.1 0.11 09/06/2007 1.8 10.77 17 0.05
01/23/2002 533 1500.00 1800 2150.66 10/02/2007 1.2 19.00 15 0.06
02/27/2002 24 0.99 4.9 0.06 11/01/2007 4.1 2.12 6.3 0.02
03/20/2002 51 12.38 19 1.70 12/04/2007 8.6 2.50 3.1 0.06
04/24/2002 15 5.00 7.7 0.20 01/08/2008 21 2.37 6.6 0.13
05/23/2002 9.7 7.54 13 0.20 02/05/2008 41 5.92 11 0.65
06/17/2002 3.7 6.73 12 0.07 03/05/2008 270 166.67 210 121.05
07/30/2002 3.1 10.00 15 0.08 04/07/2008 166 35.00 45 15.63
08/26/2002 1.7 5.11 10 0.02 05/06/2008 46 12.00 13 1.48
09/16/2002 3.8 15.61 23 0.16 06/03/2008 22 7.50 10 0.44
10/23/2002 12 4.00 10 0.13 07/07/2008 24 24.00 50 1.55
11/19/2002 96 17.23 25 4.45 08/06/2008 7.9 5.11 10 0.11
12/16/2002 120 16.42 24 5.30 09/03/2008 28 9.20 11 0.69
01/27/2003 44 16.00 24 1.89 10/06/2008 26 2.04 6.2 0.14
02/20/2003 111 14.81 22 4.42 11/04/2008 27 1.64 5.7 0.12
03/17/2003 325 57.62 75 50.37 12/02/2008 63 13.00 29 2.20
04/07/2003 800 160.00 450 344.32 01/20/2009 60 9.50 12 1.53
05/06/2003 680 223.22 280 408.31 02/03/2009 54 8.00 15 1.16
06/19/2003 282 57.62 75 43.71 03/10/2009 86 16.00 19 3.70
07/01/2003 79 9.15 15 1.94 04/16/2009 130 27.00 27 9.44
08/18/2003 90 19.65 28 4.76 05/14/2009 52 13.00 14 1.82
09/08/2003 92 9.96 16 2.46 06/03/2009 37 23.00 23 2.29
10/07/2003 62 8.00 10 1.33 07/07/2009 30 11.00 14 0.89
11/03/2003 61 2.20 6.4 0.36 08/11/2009 14 4.95 9.8 0.19
12/01/2003 59 2.28 6.5 0.36 09/09/2009 21 4.79 9.6 0.27
01/07/2004 61 8.00 13 1.31 10/13/2009 39 10.00 15 1.05
02/03/2004 193 93.97 120 48.79 11/30/2009 78 8.00 11 1.68
03/08/2004 86 9.15 15 2.12 12/29/2009 162 28.00 40 12.20
04/14/2004 270 43.00 60 31.23
05/04/2004 90 21.27 30 5.15
06/02/2004 35 9.96 16 0.94
07/08/2004 27 18.00 13 1.31
08/04/2004 22 12.38 19 0.73
09/09/2004 301 57.62 75 46.65
11/01/2004 56 0.91 4.8 0.14
12/02/2004 96 7.54 13 1.95
01/04/2005 68 10.00 12 1.83
02/14/2005 74 3.82 8.4 0.76
03/03/2005 129 14.00 21 4.86
04/05/2005 105 30.00 28 8.47
05/04/2005 64 8.34 14 1.44
06/07/2005 126 14.81 22 5.02
07/07/2005 52 32.00 40 4.48
08/04/2005 38 16.42 24 1.68
10/05/2005 14 6.80 8.9 0.26
11/02/2005 35 1.23 5.2 0.12
12/06/2005 358 93.97 120 90.50

83
South Deep Creek DWQ Stations Averaged (see text) and USGS station 02118500
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
01/11/2000 173.4 269.82 240 125.87 10/17/2005 56.774 13.17 15 2.01
02/02/2000 61.42 19.09 20 3.15 11/14/2005 44.387 0.46 4.3 0.05
03/03/2000 51.61 10.20 12.5 1.42 12/12/2005 72.774 8.42 11 1.65
04/12/2000 65.55 29.61 28.9 5.22 01/23/2006 102.71 60.27 55 16.65
05/08/2000 58.32 52.54 48.4 8.24 02/20/2006 73.806 11.98 14 2.38
06/12/2000 34.58 28.31 27.8 2.63 03/13/2006 63.484 5.21 8.3 0.89
07/10/2000 32 56.53 51.8 4.87 04/10/2006 57.806 3.79 7.1 0.59
08/15/2000 22.19 22.87 23.2 1.37 05/08/2006 70.194 19.09 20 3.60
09/28/2000 51.61 75.10 67.7 10.43 06/12/2006 56.774 135.46 120 20.69
10/30/2000 28.39 1.09 4.83 0.08 07/17/2006 26.839 21.46 22 1.55
11/21/2000 31.48 0.93 4.7 0.08 08/14/2006 43.355 13.17 15 1.54
12/20/2000 40.77 4.86 8 0.53 09/11/2006 40.258 100.97 90 10.93
01/09/2001 33.03 0.69 4.5 0.06 10/16/2006 28.903 9.61 12 0.75
02/19/2001 42.84 17.91 19 2.06 11/13/2006 68.645 10.79 13 1.99
03/28/2001 58.32 0.57 4.4 0.09 12/11/2006 49.032 10.79 13 1.42
04/23/2001 48.52 4.26 3.7 0.56 01/22/2007 110.45 60.27 55 17.91
05/18/2001 46.45 4.86 8 0.61 02/12/2007 59.871 9.61 12 1.55
06/13/2001 27.87 7.23 10 0.54 03/12/2007 84.129 42.68 40 9.66
07/16/2001 20.65 10.79 13 0.60 04/16/2007 289.03 180.89 160 140.64
08/06/2001 24.77 4.26 7.5 0.28 05/07/2007 68.129 11.98 14 2.20
09/10/2001 20.13 8.42 11 0.46 06/11/2007 36.129 19.09 20 1.86
10/08/2001 14.97 4.74 7.9 0.19 07/09/2007 29.935 43.86 41 3.53
11/12/2001 20.65 3.57 3.1 0.20 08/27/2007 13.935 34.44 33 1.29
12/03/2001 23.23 3.92 3.4 0.24 09/10/2007 11.871 32.09 31 1.02
01/14/2002 30.45 2.83 6.3 0.23 10/08/2007 21.677 13.17 15 0.77
02/11/2002 65.55 6.52 9.4 1.15 11/12/2007 32.516 13.17 15 1.15
03/04/2002 65.55 16.72 18 2.95 12/10/2007 31.484 7.23 10 0.61
04/08/2002 46.97 1.05 4.8 0.13 01/14/2008 41.29 10.79 13 1.20
05/06/2002 34.06 7.23 10 0.66 02/18/2008 55.226 14.35 16 2.13
06/10/2002 17.03 10.79 13 0.49 03/10/2008 88.774 21.46 22 5.12
07/08/2002 8.258 16.72 18 0.37 04/21/2008 71.742 8.42 11 1.62
08/05/2002 6.194 8.42 11 0.14 05/05/2008 46.968 7.23 10 0.91
09/23/2002 13.94 6.04 9 0.23 06/09/2008 22.71 20.27 21 1.24
10/07/2002 11.87 4.50 7.7 0.14 07/14/2008 42.839 35.62 34 4.10
11/04/2002 30.97 4.50 7.7 0.37 08/11/2008 10.323 36.80 35 1.02
12/02/2002 36.65 8.42 11 0.83 09/08/2008 16.516 13.17 15 0.59
01/06/2003 80 34.44 33 7.41 10/06/2008 24.774 9.61 12 0.64
02/10/2003 61.94 7.23 10 1.20 11/03/2008 28.387 1.05 4.8 0.08
03/17/2003 330.3 106.74 95 94.85 12/08/2008 34.065 2.83 6.3 0.26
04/07/2003 206.5 100.97 90 56.07 01/26/2009 40.258 10.79 13 1.17
05/12/2003 128.5 14.35 16 4.96 02/16/2009 36.129 5.21 8.3 0.51
06/09/2003 1265 336.99 302 1146.29 03/16/2009 208 135.46 120 75.79
07/14/2003 151.2 41.51 39 16.89 04/20/2009 72.774 19.09 20 3.74
08/25/2003 105.3 17.91 19 5.07 05/04/2009 53.161 541.19 500 77.39
09/22/2003 85.68 14.35 16 3.31 06/08/2009 178.06 124.00 110 59.40
10/27/2003 121.3 6.76 9.6 2.21 07/13/2009 58.323 22.64 23 3.55
11/17/2003 79.48 7.11 9.9 1.52 08/10/2009 42.323 17.91 19 2.04
12/08/2003 89.29 7.23 10 1.74 09/14/2009 40.774 13.17 15 1.44
01/12/2004 76.39 4.97 8.1 1.02 10/19/2009 44.903 7.23 10 0.87
02/09/2004 163.6 135.46 120 59.62 11/16/2009 107.35 66.12 60 19.09
03/08/2004 90.84 21.46 22 5.24 12/14/2009 205.94 124.00 110 68.69
04/05/2004 85.16 14.35 16 3.29
05/10/2004 72.77 22.64 23 4.43
06/07/2004 55.74 26.18 26 3.93
07/12/2004 50.06 28.55 28 3.84
08/09/2004 30.45 20.27 21 1.66
09/20/2004 67.61 27.37 27 4.98
10/25/2004 69.68 14.35 16 2.69
11/15/2004 108.9 34.44 33 10.09
12/13/2004 142.5 54.42 50 20.85
01/24/2005 91.87 39.15 37 9.68
02/14/2005 81.55 19.09 20 4.19
03/14/2005 95.48 10.79 13 2.77
04/11/2005 102.7 20.27 21 5.60
05/09/2005 76.39 13.17 15 2.71
06/13/2005 74.84 35.62 34 7.17
07/11/2005 124.4 158.25 140 52.95
08/15/2005 59.87 15.54 17 2.50
09/19/2005 34.06 13.17 15 1.21

84
South Yadkin River DWQ Station Q3460000 and USGS station 02118000
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
01/03/2000 128 7.00 6.4 2.41 08/08/2005 189 70.00 75 35.59
02/01/2000 258 13.00 20 9.02 08/23/2005 162 34.00 32 14.82
03/01/2000 181 13.00 17 6.33 09/22/2005 82 17.00 13 3.75
04/06/2000 399 71.00 50 76.21 10/18/2005 151 16.00 17 6.50
05/01/2000 377 84.00 40 85.19 10/27/2005 120 6.20 6.2 2.00
07/05/2000 72 11.42 12 2.21 11/16/2005 124 6.00 5.5 2.00
08/09/2000 97 33.50 32 8.74 11/28/2005 150 3.20 4.1 1.29
09/06/2000 109 53.37 50 15.65 12/13/2005 228 5.20 8.1 3.19
10/12/2000 62 6.01 7.1 1.00 01/03/2006 1080 318.00 310 923.85
11/14/2000 89 4.35 5.6 1.04 01/17/2006 455 24.00 45 29.37
12/20/2000 132 18.04 18 6.41 02/02/2006 244 14.00 14 9.19
01/24/2001 180 10.32 11 4.99 02/16/2006 229 7.50 5.9 4.62
02/20/2001 145 11.00 18 4.29 03/02/2006 206 14.00 12 7.76
04/30/2001 115 8.33 9.2 2.58 03/16/2006 186 14.00 14 7.00
05/30/2001 99 31.00 15 8.26 03/29/2006 191 8.80 8.7 4.52
06/26/2001 208 97.53 90 54.57 04/11/2006 183 15.00 18 7.38
07/25/2001 56 19.15 19 2.88 04/25/2006 203 50.00 45 27.30
08/27/2001 38 20.00 17 2.04 05/18/2006 150 26.00 24 10.49
09/25/2001 140 53.37 50 20.10 05/31/2006 105 29.00 27 8.19
10/11/2001 25 7.89 8.8 0.53 06/14/2006 155 52.00 24 21.68
11/15/2001 61 9.21 10 1.51 06/26/2006 106 34.00 19 9.69
12/10/2001 68 13.63 14 2.49 07/11/2006 101 24.00 22 6.52
01/07/2002 135 36.81 35 13.37 07/26/2006 119 35.00 55 11.20
02/12/2002 182 12.00 17 5.87 08/07/2006 73 11.00 13 2.16
03/21/2002 222 33.50 32 20.01 08/24/2006 108 48.00 60 13.94
04/30/2002 77 16.94 17 3.51 09/28/2006 90 16.94 17 4.10
05/30/2002 57 19.00 24 2.91 10/16/2006 78 7.11 8.1 1.49
06/13/2002 27 35.71 34 2.59 11/07/2006 152 2.15 3.6 0.88
07/17/2002 27 24.67 24 1.79 12/19/2006 154 6.20 7.1 2.57
08/14/2002 3 8.00 13 0.06 01/24/2007 291 18.04 18 14.12
09/16/2002 23 41.23 39 2.55 02/20/2007 226 7.00 10 4.26
10/09/2002 25 11.42 12 0.77 03/21/2007 315 31.29 30 26.51
11/07/2002 179 24.00 28 11.56 04/19/2007 324 37.92 36 33.05
12/10/2002 252 8.22 9.1 5.57 05/22/2007 133 20.00 23 7.16
01/14/2003 145 6.89 7.9 2.69 06/26/2007 131 274.17 250 96.62
02/03/2003 154 6.00 7.5 2.49 07/25/2007 147 75.45 70 29.84
03/13/2003 262 15.84 16 11.16 09/04/2007 33 18.00 19 1.60
04/08/2003 906 108.57 100 264.60 09/13/2007 23 35.71 34 2.21
06/11/2003 1030 119.61 110 331.41 10/30/2007 115 18.04 18 5.58
07/01/2003 350 35.71 34 33.62 11/26/2007 94 2.81 4.2 0.71
08/04/2003 512 51.00 34 70.24 12/19/2007 106 3.91 5.2 1.12
09/25/2003 252 33.50 32 22.71 01/30/2008 117 4.24 5.5 1.34
10/20/2003 198 8.33 9.2 4.44 02/20/2008 170 9.21 10 4.21
11/24/2003 253 12.00 9.9 8.17 03/19/2008 197 13.63 14 7.22
12/09/2003 229 7.89 8.8 4.86 04/17/2008 194 26.00 25 13.57
01/14/2004 215 3.69 5 2.13 05/13/2008 135 24.00 22 8.72
02/11/2004 448 37.00 30 44.59 06/12/2008 61 24.00 25 3.94
03/10/2004 252 8.33 9.2 5.65 07/10/2008 90 44.00 45 10.65
04/22/2004 261 24.67 24 17.32 08/07/2008 40 24.00 32 2.58
06/01/2004 169 43.00 27 19.55 09/10/2008 246 222 120 146.91
06/30/2004 151 27.98 27 11.36 10/09/2008 92 14 20 3.46
07/20/2004 122 42.33 40 13.89 11/12/2008 84 5.016 6.2 1.13
08/24/2004 99 22.00 20 5.86 12/08/2008 105 2.5872 4 0.73
09/14/2004 189 39.02 37 19.84 01/28/2009 172 11.4192 12 5.28
10/06/2004 200 31.29 30 16.83 02/05/2009 146 7.1136 8.1 2.79
11/23/2004 204 12.52 13 6.87 03/10/2009 265 32 29 22.81
12/01/2004 269 20.25 20 14.65 04/15/2009 369 38 32 37.72
01/04/2005 227 3.58 4.9 2.19 05/26/2009 668 166 170 298.29
02/14/2005 231 10.00 6.9 6.21 06/11/2009 667 120 100 215.31
03/10/2005 284 13.00 6.8 9.93 07/22/2009 184 35 60 17.32
03/31/2005 650 68.00 90 118.90 08/27/2009 154 34 45 14.08
04/12/2005 293 36.81 35 29.01 09/21/2009 197 44 45 23.32
04/25/2005 275 20.00 14 14.80 10/05/2009 146 20 23 7.85
05/05/2005 229 26.00 13 16.02 11/16/2009 438 46 45 54.20
06/02/2005 235 62.00 55 39.19 12/21/2009 431 17 24 19.71
06/16/2005 170 23.00 40 10.52
06/28/2005 133 48.00 45 17.17
07/13/2005 237 58.00 45 36.98
07/27/2005 131 28.00 34 9.87

85
Third Creek DWQ Station Q3934500 and drainage area ratio estimated flow from
USGS station 02120780
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
Sample
Date
Flow
(cfs)
TSS
(mg/L)
Turbidity
(NTU)
TSS Load
(tons/day)
02/15/2000 144.7 110.00 110 42.83 07/07/2005 45.614 22.00 21 2.70
03/13/2000 41.23 9.00 10 1.00 08/04/2005 33.333 31.01 26 2.78
04/17/2000 81.58 51.00 23 11.19 10/05/2005 12.281 7.50 11 0.25
05/15/2000 24.56 17.00 9.3 1.12 11/02/2005 30.702 10.16 9.6 0.84
06/07/2000 17.54 29.00 17 1.37 12/06/2005 314.04 150.49 120 127.13
07/24/2000 23.68 36.00 27 2.29 01/09/2006 81.579 22.00 25 4.83
08/15/2000 7.018 11.00 9.4 0.21 02/02/2006 68.421 18.30 16 3.37
09/12/2000 6.667 2.15 3.3 0.04 03/06/2006 62.281 9.02 8.7 1.51
10/05/2000 6.93 6.00 7.6 0.11 04/06/2006 53.509 16.00 16 2.30
11/06/2000 11.4 1.90 3.1 0.06 05/08/2006 59.649 93.29 75 14.97
12/11/2000 14.91 5.08 5.6 0.20 06/08/2006 25.439 37.36 31 2.56
01/17/2001 15.79 6.00 7.2 0.25 07/06/2006 41.228 55.00 45 6.10
02/12/2001 26.32 8.64 8.4 0.61 08/09/2006 19.298 38.63 32 2.01
04/17/2001 37.72 10.00 9.5 1.01 09/07/2006 17.544 28.46 24 1.34
05/23/2001 19.3 13.21 12 0.69 10/11/2006 14.035 7.00 9.3 0.26
06/25/2001 8.772 31.01 26 0.73 11/06/2006 25.439 4.57 5.2 0.31
07/25/2001 6.754 11.00 12 0.20 12/05/2006 46.491 11.94 11 1.49
08/13/2001 10.53 8.25 8.1 0.23 01/09/2007 278.95 61.00 150 45.77
09/13/2001 3.947 5.08 5.6 0.05 02/07/2007 59.649 13.21 12 2.12
10/09/2001 6.053 2.50 2.6 0.04 03/08/2007 122.81 47.53 39 15.70
11/28/2001 8.07 8.13 8 0.18 04/03/2007 55.263 20.00 15 2.97
12/27/2001 17.54 11.94 11 0.56 05/02/2007 48.246 18.30 16 2.37
01/23/2002 467.5 1100.00 850 1383.46 06/06/2007 21.93 28.46 24 1.68
02/27/2002 21.05 9.52 9.1 0.54 07/09/2007 13.158 32.00 24 1.13
03/20/2002 44.74 34.82 29 4.19 08/08/2007 3.6842 13.21 12 0.13
04/24/2002 13.16 17.00 23 0.60 09/06/2007 1.5789 7.36 7.4 0.03
05/23/2002 8.509 14.48 13 0.33 10/02/2007 1.0526 12.00 12 0.03
06/17/2002 3.246 14.48 13 0.13 11/01/2007 3.5965 14.48 13 0.14
07/30/2002 2.719 8.00 13 0.06 12/04/2007 7.5439 4.19 4.9 0.08
08/26/2002 1.491 10.67 10 0.04 01/08/2008 18.421 9.00 12 0.45
09/16/2002 3.333 52.62 43 0.47 02/05/2008 35.965 23.38 20 2.26
10/23/2002 10.53 7.00 16 0.20 03/05/2008 236.84 226.76 180 144.47
11/19/2002 84.21 74.22 60 16.81 04/01/2008 56.14 19.00 20 2.87
12/16/2002 105.3 112.36 90 31.81 05/06/2008 40.351 28.46 24 3.09
01/27/2003 38.6 9.00 10 0.93 06/02/2008 17.544 22.11 19 1.04
02/20/2003 97.37 23.38 20 6.12 07/01/2008 8.7719 40.00 50 0.94
03/17/2003 285.1 118.71 95 91.04 08/05/2008 7.5439 22.11 19 0.45
04/07/2003 701.8 350.00 260 660.70 09/02/2008 28.07 29.74 25 2.25
05/08/2003 262.3 61.51 50 43.40 10/02/2008 32.456 13.00 17 1.13
06/19/2003 247.4 201.33 160 133.97 11/03/2008 22.807 5.08 5.6 0.31
07/16/2003 62.28 31.01 26 5.19 12/01/2008 121.93 67.87 55 22.26
08/21/2003 64.91 31.01 26 5.41 01/06/2009 193.86 327.00 300 170.52
09/08/2003 80.7 29.74 25 6.46 02/02/2009 42.982 18.30 16 2.12
10/06/2003 53.51 13.00 10 1.87 03/03/2009 291.23 188.62 150 147.77
11/03/2003 53.51 9.14 8.8 1.32 04/01/2009 97.368 28.00 26 7.33
12/01/2003 51.75 15.75 14 2.19 05/04/2009 47.368 13.21 12 1.68
01/07/2004 53.51 11.00 14 1.58 06/02/2009 35.088 80.58 65 7.61
02/03/2004 169.3 188.62 150 85.90 07/06/2009 27.193 14.00 16 1.02
03/08/2004 75.44 14.48 13 2.94 08/04/2009 16.667 24.65 21 1.11
04/14/2004 236.8 190.00 150 121.05 09/02/2009 42.105 125.07 100 14.17
05/04/2004 78.95 36.09 30 7.66 10/01/2009 26.316 12.00 14 0.85
06/02/2004 30.7 29.74 25 2.46 11/02/2009 241.23 201.33 160 130.65
07/08/2004 23.68 21.00 13 1.34 12/01/2009 70.175 17.02 15 3.21
08/04/2004 19.3 32.28 27 1.68
09/09/2004 264 137.78 110 97.86
11/02/2004 49.12 7.75 7.7 1.02
12/02/2004 84.21 19.57 17 4.43
01/04/2005 59.65 12.00 13 1.93
02/14/2005 64.91 8.51 8.3 1.49
03/03/2005 113.2 34.82 29 10.60
04/05/2005 92.11 36.00 37 8.92
05/04/2005 56.14 17.02 15 2.57
06/07/2005 110.5 33.55 28 9.97

86
Appendix C. Load Reduction Estimations

Estimation of Load Reduction Required for TSS for Abbotts Creek at
Station Q5930000.

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding
Load
(tons/day)
10.000% 30.38 137.09
15.000% 22.01 65.99
20.000% 17.54 39.29
25.000% 14.60 26.27
30.000% 12.27 18.91
35.000% 10.24 14.32
40.000% 8.92 11.26
45.000% 7.91 9.10
50.000% 7.00 7.53
55.000% 5.98 6.34
60.000% 5.07 5.42
65.000% 4.16 4.69
70.000% 3.45 4.10
75.000% 2.84 3.62
80.000% 2.23 3.23
85.000% 1.83 2.89
90.000% 1.52 2.61
Average 9.3 21.3
Load Reduction = 56%

87
Estimation of Load Reduction Required for TSS for the Ararat River at
Station Q1780000.
% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding Load
(tons/day)
10.00% 25.99 71.14
15.00% 22.28 61.44
20.00% 19.94 53.07
25.00% 18.08 45.84
30.00% 16.43 39.59
35.00% 15.08 34.20
40.00% 13.78 29.54
45.00% 12.43 25.51
50.00% 11.55 22.03
55.00% 10.73 19.03
60.00% 10.00 16.44
65.00% 9.32 14.20
70.00% 8.65 12.26
75.00% 7.97 10.59
80.00% 7.17 9.15
85.00% 6.16 7.90
90.00% 5.20 6.83
Average 12.98589 28.16262
Load Reduction = 54%

88
Estimation of Load Reduction Required for TSS for Hunting Creek at
Station Q3484000.

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding Load
(tons/day)
10.00% 24.27 51.52
15.00% 19.87 40.43
20.00% 17.31 34.04
25.00% 15.46 29.79
30.00% 14.20 26.71
35.00% 13.13 24.36
40.00% 11.79 22.49
45.00% 10.88 20.96
50.00% 10.07 19.68
55.00% 9.17 18.59
60.00% 8.36 17.65
65.00% 7.73 16.82
70.00% 6.92 16.09
75.00% 6.20 15.44
80.00% 5.57 14.86
85.00% 5.03 14.33
90.00% 4.14 13.85
Average 11.18 23.39
Load Reduction Needed = 52%

89

Estimation of Load Reduction Required for TSS for Second Creek at
Station Q2600000. Only two data points exceeded the allowable load in the TMLD calculation
which occurred in the 50 to 70 percent flow exceedance. Therefore only the 50-70 percent flow
exceedance range was used in the TMDL calculation and reduction needed.

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding
Load
(tons/day)
10.00% 12.99 513.93
15.00% 10.15 179.23
20.00% 8.69 84.88
25.00% 7.59 47.54
30.00% 6.68 29.60
35.00% 5.94 19.83
40.00% 5.40 14.02
45.00% 4.79 10.32
50.00% 4.21 7.85
55.00% 3.57 6.13
60.00% 3.11 4.89
65.00% 2.56 3.97
70.00% 2.29 3.28
75.00% 1.83 2.74
80.00% 1.46 2.32
85.00% 1.10 1.98
90.00% 0.74 1.71
Average 3.15 5.22
Load Reduction Needed = 40%

90
Estimation of load reduction required for TSS for South Deep Creek using average TSS values
from DWQ water quality monitoring stations. These stations include Q5930000, Q3484000,
Q2600000, Q2720000, Q4120000, and Q3934500.

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding
Load
(tons/day)
10.00% 18.37 29.31
15.00% 15.03 27.00
20.00% 13.10 24.87
25.00% 11.70 22.90
30.00% 10.75 21.10
35.00% 9.93 19.43
40.00% 8.93 17.90
45.00% 8.23 16.48
50.00% 7.62 15.18
55.00% 6.94 13.98
60.00% 6.33 12.88
65.00% 5.85 11.86
70.00% 5.24 10.93
75.00% 4.69 10.06
80.00% 4.22 9.27
85.00% 3.81 8.54
90.00% 3.13 7.86
Average 8.46 16.44
Load Reduction Needed = 49%

91

Estimation of Load Reduction Required for TSS for the South Yadkin River at DWQ
Station Q3460000

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding
Load
(tons/day)
10.00% 58.9 98.19
15.00% 46.9 80.17
20.00% 39.5 69.43
25.00% 34.8 62.10
30.00% 31.9 56.69
35.00% 29.4 52.49
40.00% 27.0 49.10
45.00% 25.2 46.29
50.00% 23.0 43.91
55.00% 20.9 41.87
60.00% 19.2 40.09
65.00% 17.3 38.51
70.00% 15.2 37.11
75.00% 13.2 35.85
80.00% 11.5 34.72
85.00% 10.2 33.68
90.00% 8.0 32.73
Average 25.42 50.17
Load Reduction Needed = 49%

92

Estimation of Load Reduction Required for TSS for Third Creek at DWQ
Station Q3934500

% Flow
Exceedance
Allowable
Load
(tons/day
Estimated
Exceeding
Load
(tons/day)
10.00% 18.43 34.94
15.00% 14.41 25.74
20.00% 12.33 20.73
25.00% 10.77 17.52
30.00% 9.47 15.28
35.00% 8.44 13.60
40.00% 7.66 12.30
45.00% 6.79 11.26
50.00% 5.97 10.40
55.00% 5.06 9.68
60.00% 4.41 9.06
65.00% 3.63 8.53
70.00% 3.24 8.07
75.00% 2.60 7.66
80.00% 2.08 7.30
85.00% 1.56 6.97
90.00% 1.05 6.68
Average 6.94 13.28
Load Reduction Needed = 48%

Appendix D: Public Notification of TMDL for

93
Appendix D: Public Notification of TMDL for Yadkin River Basin Turbidity TMDLSYadkin River Basin Turbidity TMDLS

94
App endix E: Public Comments

2011 Yadkin River Basin Turbidity TMDLs
Public Comment Response Summary

The comments received for this TMDL were based on the public comment version which included
assessment units for Muddy Creek and the Yadkin River. These two waterbodies were not included in
the final TMDL presented here in order to allow time to meet with and explain the TMDL process to the
MS4 permittees that would be impacted by these TMDLs. However, the comments received regarding
Muddy Creek and the Yadkin River were left in the response summary and are addressed below.
Comments were received from:
• Piedmont Triad Regional Council (PTRC)
• Town of Lewisville
• Salisbury-Rowan Utilities
• Winston-Salem
• Village of Clemmons
• North Carolina Department of Transportation (NCDOT)
• North Carolina Conservation Network

1) PTRC:

Response: Each TMDL has a Load Allocation, Wasteload Allocation and Margin of Safety. The TMDL
Load Allocations show the reductions needed from nonpoint sources. The TMDL does not suggest that
the wasteload allocations alone will achieve water quality standard attainment. Reductions for the
identified jurisdictions are identical to the reductions for nonpoint sources.
2) PTRC , Town of Lewisville, Winston-Salem, Village of Clemmons:

The commenters mentioned that the Village of Clemmons and the Town of Lewisville have only
been NPDES Phase II communities since 2005, and Winston-Salem since 2001. The commenters
suggested that the DWQ acknowledge new stormwater ordinances and development regulations in
this time period and the impacts of these requirements on the receiving streams have not had time
to be assessed. Further, the need for additional expenses to mitigate stormwater sources of water
quality pollutants is not readily apparent.

Response: The data used in the TMDL was from years 2000-2009. Implementation of the TMDL will
not necessarily incur additional significant costs to the affected NPDES permit holders. The DWQ
Stormwater Permitting Unit will consider recent improvements and determine further permit
requirements in the next permit renewal.
3) PTRC , Town of Lewisville, Village of Clemmons:

Response: The implementation timeline will depend on your water quality recovery plan that you will
submit as required under your stormwater permit. We expect the fulfillment of your water quality
recovery plan to take several permit cycles. Because this TMDL can be implemented along with various
existing permit requirements, and it only requires reductions in the named TMDL subwatersheds, it is not
expected to trigger sprawl outside of MS4 jurisdictions.
4) PTRC, Town of Lewisville, Winston-Salem:

The commenters acknowledged that a TMDL Load Allocation has no regulatory authority to require
a reduction from nonpoint sources. However, the commenters requested a clearer representation
of the presence of animal and forestry operations and communities enrolled in cost-share programs
to manage runoff. The commenters also requested greater acknowledgement that rural land uses
are contributing to the impairment.
Response: General sources of nonpoint source pollution are described in section 2.1. The TMDL shows
land cover for each watershed as well as land cover adjacent to streams for each watershed, including
the distribution of agricultural lands (pasture/hay and crop). Further source assessment, including how
land is managed, will be useful for TMDL implementation. Reductions in both point and nonpoint sources
of turbidity are needed to meet water quality standards as stated in section 12. Reductions for the
identified jurisdictions are identical to the reductions for nonpoint sources.
5) PTRC, Town of Lewisville:

Response: The jurisdictions are encouraged to conduct additional monitoring to gain further knowledge
of the watersheds’ pollution sources. In addition, DWQ indeed uses data from various outside sources;
municipalities interested in collecting data to be used for use support assessment should contact DWQ.
Please review this website on data sources and how to submit data
http://portal.ncdenr.org/web/wq/ps/mtu/assessment#4.
6) PTRC, Town of Lewisville, Winston-Salem:

Response: This is not a correlation between wet weather and TSS. The equation of this line was used to
determine the target reduction as describe in section 6.6. Figure 6.2 shows that no exceedances occurred
during low flow events. The R2 of 0.23 for Muddy Creek refers to strength of the linear relationship
between the calculated existing load exceedances in Figure 6.3. This response also addresses similar
comments for the Yadkin River.
7) PTRC and Winston-Salem:

Response: The Salem Creek TMDL targeted Fecal Coliform. If the retrofits to reduce fecal coliform were
targeted at stormwater, and also achieved a reduction in turbidity, this can be reflected in your water
quality recovery program for your stormwater permit and count towards compliance with this TMDL.
8) PTRC:

Response: Ambient station Q2040000 was used to develop the TMDL for both impaired segments of the
Yadkin River for several reasons. One reason is that it is co-located with a USGS gage, which is ideal to
develop the load duration curve. Second, the correlation of Turbidity vs. TSS for the lower ambient
monitoring site, Q2180000, has an R2 of 0.579, which is less than the TSS vs turbidity R2 value of 0.88 for
the ambient station (Q2040000) used in the TMDL. Finally, the turbidity data comparison between the
two stations show that the data is comparable with median NTU values for Q2040000 and Q2180000 at
16 and 18 respectively for years 2000-2009. The change in reductions between the two stations would
likely be insignificant, and uncertainty would be higher due to estimating flow and using the lower TSS vs
NTU correlation from site Q2180000.
9) PTRC, Town of Lewisville:

Response: Perhaps the commenters are referring to South Deep Creek. Reductions in South Deep
Creek alone are not expected to attain the turbidity standard in the Yadkin River. Your water quality
recovery program can reflect your implementation and monitoring timeline.

10) Town of Lewisville:

Response: Reductions required in the TMDL for NPDES stormwater permittees will be implemented
through the stormwater permit, in the form of a water quality recovery program submitted to DWQ by
each permittee. This plan will outline how each permittee will improve water quality. Implementation of
the TMDL will not necessarily incur additional significant costs to the affected NPDES permit holders. An
implementation section has been added to the TMDL to clarify responsibilities of MS4 permittees.
11) Town of Lewisville:

Response: Your water quality recovery program will describe how the Town will implement the TMDL.
The monitoring you propose (see Comment 5) can assist with source identification and tracking of
reductions.
12) Salisbury-Rowan Utilities:

Response: Thank you. We have made these corrections in the text.
13) Winston-Salem:

Response: These TMDLs were developed to address localized turbidity impairments in the High Rock
Lake watershed. A separate analysis will be conducted to determine how to address the turbidity
impairment in High Rock Lake. Winston-Salem is represented on the High Rock Lake nutrient TAC.

14) Winston-Salem:

Response: This TMDL approach estimates TSS reduction for any flow exceeded between 10% and 90%.
Therefore, we developed Figure 6.3 to show the relationship between percent flow exceeded and daily
TSS load to estimate an averaged TSS reduction for the flow exceedance between 10% to 90%. Any
method used would require some percent reduction in turbidity. Implementation of this TMDL will
involve adaptive management, with the ultimate measure of success attainment of the standard
instream.
15) Village of Clemmons:

Response: The Load Allocation reported in the TMDL sets a limit, or “allowance,” for turbidity originating
from nonpoint sources. An implementation plan is not included in this TMDL. Local governments and
other stakeholders are encouraged to design and carry out implementation plans. The monitoring
proposed in Comment 5 could assist with source identification and tracking of reductions. Your water
quality recovery program can describe how you will differentiate contributions from the Village of
Clemmons from other sources.
16) Village of Clemmons:

Response: Sand dredging operations are not permitted to exceed the turbidity standard of 50 NTU in
Muddy Creek. Sand dredging operations are permitted under general permit NCG520000. Please call the
DWQ Winston-Salem Regional Office at 336-771-5000 if you observe a sand dredging operation causing
excess turbidity in Muddy Creek.
17) Village of Clemmons:

Response: DWQ acknowledges that some soil types can make it more difficult to control erosion and
turbidity. However Muddy Creek has met the turbidity standard in previous years. Muddy Creek was
just added to the 303d list in 2010.

18) Village of Clemmons -

Response: It is currently difficult to quantify a justifiable load from stormwater outfalls within each
municipality without monitoring those outfalls. However, MS4 permittees cannot be ignored when
addressing a turbidity impairment, especially during wet weather events. The Village has not been
“singled out.” Nonpoint sources outside your jurisdiction have been assigned a load allocation. The
monitoring proposed in Comment 5 could assist with source identification and tracking of reductions.
Your water quality recovery program can describe how you will differentiate contributions from the
Village of Clemmons from other sources.

19) Part 1 – NCDOT:

Response: NPDES discharges not subject to the TMDLs are identified in the report by the description
in the text (as repeated above). Water quality stations refer to Ambient Monitoring Sites as shown in
the watershed maps in section 1.3 of the report. We have changed the term “water quality station”
to “ambient monitoring site” in the text. Therefore an ambient monitoring site that is not impaired is
shown on the watershed maps not falling within the 12 assessment units described in table 1.1 (also
shown in red on the watershed maps in section 1.3). We would be happy to assist you with
identifying areas of interest to you that are subject to the TMDL.

Part 2 - Comment Continued from 19 – Part 1

Response: The paragraph above has been revised for clarification in the text as follows: “NPDES
wastewater and stormwater permittees upstream of an Ambient Monitoring Site that is not
impaired (not intersected by the impaired waterbody) are not subject to the TMDL. Permittees that
discharge directly to, or upstream of the impairment, yet still downstream of an unimpaired ambient
monitoring site are subject to the TMDL and are discussed below.”

20) NCDOT:

Response: DWQ is open to new ideas or methods to calculate wasteload allocations for DOT
stormwater in TMDLs. It is possible for a permittee to be in compliance with its current permit, yet
need to make further reductions to achieve water quality standards instream.

21) Part 1 – NCDOT:

Response: The dashed line in the load duration curve figures represents the best fit for the entire
data set. As shown in Table 1.2 in the text, 11 to 14 percent of the data has exceeded the turbidity
standard. This is why the majority of the dashed lines in the load duration curve figures are below
the allowable load line. The load duration curve methodology uses only the points exceeding the
allowable load to provide a formula to estimate the exceeding load at a variety of flow ranges. This
also enables data points that fall in ranges of extreme flow or drought conditions to be excluded
from the TMDL calculation.

Part 2 – Continued from above

Response: Seasonality is included in the TMDL by using a long term 10 years of data for the TMDLs.
This allows for a variety of flow conditions and seasonal variation to be captured in the data.

Part-3 Continued from above

Response: The equation from the best-fit line from the exceeding loads is used to calculated load
exceedances across multiple flow ranges that are not represented by actual data points. This is a
good method to estimate or model reductions needed across multiple flow ranges. An alternative
method would be to take the TSS value from the highest exceeding point between the 90th and 10th
percentile flow exceedance range and reduce it to the TSS standard. Any method used would require
some percent reduction in turbidity. Implementation of this TMDL will involve adaptive
management, with the ultimate measure of success attainment of the standard instream.

Part 4 – Continued from above

Response: The load duration curve methodology uses only the points exceeding the allowable load to
provide a formula, in this case 20th to 50th percentile, to estimate the exceeding load at a flow ranges
from 10th to the 90th percentile.

22) NCDOT:
Response: The 51% reduction shown in Appendix C is the overall reduction needed based on the TMDL of
21.6 tons/day TSS. However, because NPDES WW discharges are not required to make a reduction, the
reductions shown in the TMDL text are based on that of the load allocation only which does not include
the wasteload allocation of 5.462 tons/day TSS.
23) NCDOT:

Response: The turbidity and TSS data used in the TMDL can be found in Appendix B.

24) Part 1 NCDOT:

Response: The South Yadkin River watershed is a large drainage area (906 sqmi) and contains other
impaired streams included in this TMDL. Each stream received a unique TMDL. Reductions achieved
from the impaired streams upstream of the South Yadkin River impairment will also count as
reductions for the South Yadkin River TMDL. There is a 3.25 mile stretch of the South Yadkin River
that is currently not impaired located between Aus 12-108-(14.5) and 12-108-(19.5)b. Two small
unnamed tributaries flow in from the northeast to the South Yadkin River in this stretch; this
approximately 7.75 square mile area is not a large intervening drainage area. This 3.5 mile stretch is
within the watershed draining to the impaired waters, and not above an unimpaired Ambient
Monitoring Site, thus is subject to the TMDL.

Part 2 – Continued from above

Response: The South Yadkin River watershed is a large drainage area (906 sqmi) and contains other
impaired streams included in this TMDL. Each stream received a unique TMDL. Reductions achieved
from the impaired streams upstream of the South Yadkin River impairment will also count as
reductions for the South Yadkin River TMDL. Ambient monitoring station Q3970000 was not used to
calculate the TMDL for the lower impaired section (12-108-(19.5)b because there is no flow gage
located with that station. Second, the correlation of Turbidity vs. TSS has an R2 of 0.552, which is less
than the TSS vs NTU R2 value of 0.88 for the upstream ambient station (Q3460000) used in the TMDL.
Finally, the turbidity data comparison between the two stations shows that the data is comparable
with median NTU values for Q3460000 and Q3970000 both at 22 for years 2000-2009. The change in
reductions between the two stations would likely be insignificant, and uncertainty would be high due
to estimating flow and using the lower TSS vs NTU correlation from site Q3970000.

25) NCDOT :

Response: Ambient station Q2040000 was used to develop the TMDL for both impaired segments of
the Yadkin River for several reasons. One reason is that it is co-located with a USGS gage used to
develop the load duration curve. Second, the correlation of Turbidity vs. TSS for the lower ambient
monitoring site, Q2180000, has an R2 of 0.579, which is less than the TSS vs NTU R2 value of 0.88 for
the ambient station (Q2040000) used in the TMDL. Finally, the turbidity data comparison between
the two stations show that the data is comparable with median NTU values for Q2040000 and
Q2180000 at 16 and 18 respectively for years 2000-2009. The change in reductions between the two
stations would likely be insignificant, and uncertainty would be high due to estimating flow and
using the lower TSS vs NTU correlation from site Q2180000. Reductions achieved through the South
Deep Creek TMDL will count towards reductions in both assessment units of the Yadkin River TMDL.

26) NCDOT :

Response: DWQ did not use data from ambient station Q1950000 because data collection at this
station was discontinued in 2006.
27) North Carolina Conservation Network:

Response: The highest 10% flows were excluded from the TMDL calculation to address extreme flows
and this has been the general practice for most TMDLS developed using the LDC method so far. As
the commenter suggested, if high flows are commonly occurring in an area a different
implementation strategy can be employed to address these high flows. It should be noted that the
load duration flow interval serves as an indicator of the hydrologic condition. Even though
implementation is not a required element of the TMDL, the use of duration curve zones (e.g., high
flow, moist, mid-range, dry, and low flow) presented in the TMDL provide useful information to direct
potential implementation actions that most effectively address water quality concerns for various
flow conditions.

28) North Carolina Conservation Network:

Response: An implementation section has been added to the TMDL explaining how the TMDL will be
implemented through NPDES stormwater permits. Addressing nonpoint sources of turbidity beyond
regulatory authority requires the will and cooperation among the community to voluntarily adjust
land management practices and to use incentive programs listed in Section 12.1 of the report. An
implementation plan, although very useful, is not required in a TMDL.

29) North Carolina Conservation Network:

Response: DWQ agrees high volume and resulting stream bank erosion is likely to contribute a
significant portion of turbidity and that using volume as a surrogate parameter would be useful for
turbidity TMDLs. DWQ is open to discussing the use of flow, or other innovative approaches for
future TMDLs.

30) North Carolina Conservation Network:

Response: DWQ agrees that volume from upstream locations will contribute to stream bank erosion
in the impaired sections. However this TMDL is not intended to address flow. The paragraph
mentioned above has been changed in the text in response to comment 19-Part 2. DWQ is open to
discussing the use of flow, or other innovative approaches for future TMDLs.

31) North Carolina Conservation Network:

Response: DWQ believes that a TMDL is not the best tool to address stormwater from construction
sites due to the relative short time period in which sites are actually under construction and
vulnerable to erosion. DWQ does not require on-site monitoring of stormwater runoff for
construction sites and the uncertainty would be very high to estimate a load from construction sites
with varying BMPs if DWQ were to base loading on construction stormwater runoff studies alone.