MCDEP fecal TMDL final

Fecal Coliform Total Maximum Daily Load for the
Irwin, McAlpine, Little Sugar and Sugar Creek Watersheds,
Mecklenburg County
Final
February 2002
Catawba River Basin
Prepared by:
Mecklenburg County Department NC Department of Environment and
of Environmental Protection Natural Resources
Water Quality Section Division of Water Quality
700 North Tryon Street Water Quality Section – Planning Branch
Charlotte, NC 28202 1617 Mail Service Center
[phone] Raleigh, NC 27699-1617
[phone]
NORTH CAROLINA INDEX OF TMDL SUBMITTAL
303(D) LIST INFORMATION
Basin Catawba
303(d) Listed Waters Name of Stream Description Class Index #Miles
Irwin Creek From source to Sugar Creek C 11-137-1 11.8
Sugar Creek From SR1156 Mecklenburg,
to Hwy 51
C 11-137b 11.9
Sugar Creek From NC Hwy 51 to NC/SC
state line
C 11-137c 1.2
Little Sugar Creek From source to Archdale Rd C 11-137-8a 11.8
Little Sugar Creek From Archdale Rd to NC 51 C 11-137-8b 5.3
Little Sugar Creek From NC 51 to state line C 11-137-8c 3.6
McAlpine Creek From source to SR 3356
(Sardis Rd)
C 11-137-9a 8.3
McAlpine Creek From SR 3356 to NC 51 C 11-137-9b 6.3
McAlpine Creek From NC 51 to NC 521 C 11-137-9c 4.7
McAlpine Creek From NC Hwy 521 to NC/SC
state line
C 11-137-9d 1.1
8 Digit Cataloging
Unit(s)
03050103
Area of Impairment 69.3 stream miles
WQS Violated Fecal coliform bacteria
Pollutant of Concern Fecal coliform bacteria
Sources of Impairment Point and nonpoint
PUBLIC NOTICE INFORMATION
Form(s) of Public Notification A stakeholders group consisting of environmental groups, local
utilities, and area residents was formed at the onset of the TMDL.
This group met several times during TMDL development and
reviewed the TMDL before formal public notice. Notification of
the public review draft was accomplished through the internet and
by fliers mailed to the basinwide mailing list for Mecklenburg
County and the City of Charlotte. The public comment period for
the TMDL was open from April 30, 2001 until May 31, 2001.
Did notification contain specific
mention of TMDL proposal?
Yes
Were comments received from the
public?
No
Was a responsiveness summary
prepared?
N/A
TMDL INFORMATION
Critical conditions Site-specific critical conditions occurred during periods of low stream flow
coinciding with high fecal coliform loads from both the SSOs and the WWTPs
Seasonality All seasons addressed
Development tools Watershed model, BASINS Versions
NORTH CAROLINA INDEX OF TMDL SUBMITTAL
Page 2 of 2
Supporting documents “Fecal Coliform Total Maximum Daily Load for the Irwin, McAlpine, Little
Sugar, and Sugar Creek Watersheds, Mecklenburg County” and references listed in
report
TMDL(s)Waterbody TMDL (cfu/100mL)
Sugar Creek 8.4x1012
Little Sugar Creek 9.4x1012
McAlpine Creek downstream of Sardis Road 1.1x1013
McAlpine Creek upstream of Sardis Road 6.8x1012
Loadings Sugar Creek watershed:
Point sources 7.4x1012 col/100mL (63% reduction)
Nonpoint sources 8.9x1011 col/100mL (58% reduction)
Little Sugar Creek watershed:
Point sources 6.7x1012 col/100mL (43% reduction)
Nonpoint sources 2.6x1012 col/100mL (19% reduction)
McAlpine Creek watershed (downstream):
Point sources 7.8x1012 col/100mL (70% reduction)
Nonpoint sources 3.2x1012 col/100mL (28% reduction)
McAlpine Creek watershed (upstream):
Point sources 7.8x1012 col/100mL (32% reduction)
Nonpoint sources 5.9x1011 col/100mL (68% reduction)
Margin of Safety Implicit
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
Table of Contents
1 INTRODUCTION.....................................................................................................1
1.1 Background ........................................................................................................1
1.2 Watershed Description........................................................................................2
1.3 Water Quality Monitoring Programs ...................................................................2
1.4 Water Quality Target..........................................................................................4
2 SOURCE ASSESSMENT.........................................................................................5
2.1 Point Source Assessment ....................................................................................5
2.2 Non-Point Source Asssessment...........................................................................9
3 MODELING APPROACH AND RESULTS...........................................................19
3.1 Model Framework Selection .............................................................................19
3.2 Model Setup .....................................................................................................20
3.3 Fecal Coliform Source Representation ..............................................................22
3.4 Model Calibration.............................................................................................23
3.5 Critical Conditions............................................................................................30
3.6 Model Results...................................................................................................31
4 ALLOCATION.......................................................................................................40
4.1 Total Maximum Daily Load .............................................................................40
4.2 Waste Load Allocations (Point sources)............................................................41
4.3 Load Allocations (Non-Point sources)..............................................................43
4.4 Seasonal Variation............................................................................................48
4.5 Margin of Safety...............................................................................................48
5 RECOMMENDATIONS.........................................................................................50
6 PUBLIC PARTICIPATION....................................................................................51
REFERENCES .............................................................................................................52
APPENDIX 1. USGS AND DWQ MONITORING DATA
APPENDIX 2. IMPLEMENTATION STRATEGY OUTINE
APPENDIX 3. LAND USE
APPENDIX 4. WWTP FLOWS AND FECAL COLIFORM CONCENTRATIONS
APPENDIX 5. SSO DATABASE
APPENDIX 6. RESULTS OF TMDL FIELD STUDY OF STORM DRAINS
APPENDIX 7. GROUNDWATER CONCENTRATION DATA
APPENDIX 8. MODEL SELECTION CRITERIA
APPENDIX 9. PUBLIC PARTICIPATION
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 1
1 INTRODUCTION
North Carolina’s 2000 303(d) list was approved by EPA Region IV on May 15th, 2001. The 2000 list
identified ten stream segments, totaling 66.0 miles, in the Sugar, Little Sugar, and McAlpine Creek
watersheds, as impaired due to elevated fecal coliform concentrations. The objective of this study is
to develop a fecal coliform TMDL using a watershed approach for Irwin, Sugar, Little Sugar, and
McAlpine Creeks. This TMDL encompasses all the stream segments listed in the 2000 303(d) list for
these watersheds.
Table 1. Impaired stream segments listed in NC’s draft 2000 303(d) list as Partially Supporting due
to fecal coliform contamination.
In response to the high level of interest in this TMDL from local government officials and concerned
citizens, a stakeholder group was formed in 1999. The stakeholder group, lead by the Mecklenburg
County Department of Environmental Protection (MCDEP) and the NC Division of Water Quality
(DWQ), took a very active role in every stage of the TMDL development process. MCDEP has a
well developed and respected water quality management program and was able to take the lead role in
both the source assessment and model development.
1.1 Background
Section 303(d) of the Clean Water Act (CWA) requires states to develop a list of waters not meeting
water quality standards or which have impaired uses. This list, referred to as the 303(d) list, is
submitted biennially to the U.S. Environmental Protection Agency (EPA) for review. The 303(d)
process requires that a Total Maximum Daily Load (TMDL) be developed for each of the waters
appearing on Part I of 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 (EPA
1991). Generally, the primary components of a TMDL, as identified by EPA (1991, 2000) and the
Federal Advisory Committee (FACA 1998), are as follows:
Target identification or selection of pollutant(s) and end-point(s) for consideration. The pollutant
and end-point are generally associated with measurable water quality related characteristics that
indicate compliance with water quality standards. North Carolina indicates known pollutants on
the 303(d) list.
Source assessment. All sources that contribute to the impairment should be identified and loads
quantified, where sufficient data exist.
Stream Use Support Index No.Location Impaired Stream Miles
Irwin Creek 11-137-1 From source to Sugar Creek 11.8
Little Sugar Creek 11-137-8a From source to Archdale Rd 11.8
Little Sugar Creek 11-137-8b From Archdale Rd to NC 51 5.3
Little Sugar Creek 11-137-8c From NC 51 to state line 3.6
McAlpine Creek 11-137-9a From source to SR 3356, (Sardis Rd)8.3
McAlpine Creek 11-137-9b From SR 3356 to NC 51 6.3
McAlpine Creek 11-137-9c From NC 51 to NC 521 4.7
McAlpine Creek 11-137-9d From NC Hwy 521 to NC/SC stateline 1.1
Sugar Creek 11-137b From SR 1156 Mecklenburg, to HWY 51 11.9
Sugar Creek 11-137c From Hwy 51 to NC/SC border 1.2
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 2
Assimilative capacity estimation or level of pollutant reduction needed to achieve water quality goal.
The level of pollution should be characterized for the waterbody, highlighting how current
conditions deviate from the target end-point. Generally, this component is identified through
water quality modeling.
Allocation of pollutant loads. Allocating pollutant control responsibility to the sources of
impairment. The wasteload allocation portion of the TMDL accounts for the loads associated with
existing and future point sources. Similarly, the load allocation portion of the TMDL accounts
for the loads associated with existing and future nonpoint sources, stormwater, and natural
background.
Margin of safety. The margin of safety addresses uncertainties associated with pollutant loads,
modeling techniques, and data collection. Per EPA (2000), the margin of safety may be
expressed explicitly as unallocated assimilative capacity or implicitly due to conservative
assumptions.
Seasonal variation. The TMDL should consider seasonal variation in the pollutant loads and end-
point. Variability can arise due to stream flows, temperatures, and exceptional events (e.g.,
droughts, hurricanes).
Section 303(d) of the CWA and the Water Quality Planning and Management regulation (USEPA
2000a) require EPA to review all TMDLs for approval or disapproval. Once EPA approves a TMDL,
the waterbody may be moved to Part III of the 303(d) list. Waterbodies remain on Part III of the list
until compliance with water quality standards is achieved. Where conditions are not appropriate for
the development of a TMDL, management strategies may still result in the restoration of water
quality.
The goal of the TMDL program is to restore uses to water bodies. Thus the implementation of
bacterial controls will be necessary to restore uses in these creeks. Although an implementation plan
is not included in this TMDL, reduction strategies are needed. The involvement of local governments
and agencies will be needed in order to develop implementation plans. The MCDEP and affected
groups began developing the implementation plan during public review of the TMDL.
1.2 Watershed Description
The Sugar, Little Sugar and McAlpine Creek watersheds are all located within Mecklenburg County,
North Carolina. The headwaters of each watershed originates in Mecklenburg County and all three
creeks flow into the State of South Carolina. In South Carolina, Little Sugar and McAlpine Creeks
are tributary to Sugar Creek. Figure 1 shows the location of the three TMDL watersheds within
Mecklenburg County.
Each compliance point utilized for this TMDL is associated with ambient monitoring that occurs in
the watersheds. Water quality and quantity data is collected at multiple locations within these three
watersheds by different agencies. For the purposes of assessing TMDL compliance the DWQ stations
were used. There are five DWQ ambient monitoring stations within the Sugar, Little Sugar, and
McAlpine Creek watersheds. These locations are noted on Figure 1. Other monitoring is discussed
below.
1.3 Water Quality Monitoring Programs
The MCDEP, DWQ, Charlotte Mecklenburg Utilities (CMU), USGS, and South Carolina Department
of Health and Environmental Control (DHEC) collect ambient data in the Sugar, Little Sugar, and
McAlpine Creek watersheds at regular intervals. However, CMU analyses do not include fecal
coliform bacteria. DWQ maintains five ambient monitoring locations in the Sugar, Little Sugar, and
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 4
McAlpine Creek watersheds. MCDEP maintains over 15 monitoring locations and DHEC maintains
three within North Carolina. A list of USGS flow gauges, DWQ ambient stations, and data
summaries is presented in Appendix 1.
1.4 Water Quality Target
All TMDLs include the establishment of in-stream numeric endpoints, or targets, used to evaluate the
attainment of water quality goals and designated use criteria. The target represents the restoration
objective to be achieved by implementation of load reductions specified by the TMDL. For the
TMDLs presented in this document, the fecal coliform 30-day geometric mean of 200 c.f.u./100 mL
is applicable, as referenced in NC’s water quality standard for fecal coliform in Class C waters (15A
NCAC 2B .0211 (3)(e)).
Secondary recreation is the designated use being addressed in this TMDL. Secondary recreation is
defined in NC’s standards (15A NCAC 2B .0202 (57)) as including “wading, boating, other uses not
involving human body contact with water, and activities involving human body contact with water
where such activities take place on an infrequent, unorganized, or incidental basis.” MCDEP officials
believe that the streams addressed in this document are used for secondary recreation by the local
residents predominantly during warm temperature, non-storm conditions. High stream flow activities
such as white water kayaking are not known to take place on a frequent and organized basis in these
predominantly urban streams. Hence, MCDEP and DWQ have focused the source assessment and
TMDL allocation on those sources and conditions, which represent the highest risk to human health
during the times of highest recreational use by the public.
For calibration purposes fecal coliform contributions delivered to the streams via stormwater runoff
from unidentified sources were estimated and included in the model. However, loadings from
unidentified, stormwater delivered sources were not included as part of the target evaluation and no
load allocation was assigned to these sources which could not be identified.
Four compliance points have been established for these TMDLs, representing every DWQ ambient
monitoring station location in the affected watersheds. Compliance points are physical locations
within a watershed that are used to monitor water quality conditions and assess progress on the
TMDL.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 5
2 SOURCE ASSESSMENT
In an urban setting such as Mecklenburg County, potential sources of fecal coliform in a water body
are numerous and often time transient. For the purpose of this report, the sources of fecal coliform
have been divided into two broad categories; point sources and non-point sources. Point sources can
be defined as sources, either constant or time transient, which occur at a fixed location in a watershed.
Non-point sources are generally accepted to be diffuse sources not entering a water body at a specific
location. Examples of point sources are wastewater treatment plants (WWTP) and documented
sanitary sewer overflows. Examples of non-point sources are stormwater runoff, dry weather flow
from storm drains and groundwater.
The source assessment presented in this document represents the best estimation of the sources of
fecal coliform in the TMDL watersheds at this time. Additional investigation into the sources and
distribution of sources of fecal coliform is critical to achieving the water quality target. Therefore, it
is expected that, in the future, the source assessment will be modified to reflect additional data.
Specifically, seasonal changes and the variation between watersheds needs to be better understood.
Specific investigations and program enhancements are presented in the Implementation Strategy
(Appendix 1).
2.1 Point Source Assessment
All documented point source dischargers were included in the source assessment. Actual discharge
values for fecal coliform concentration and effluent flow rate were used throughout the TMDL. In
the absence of direct measurements, permit limit values were used. This was critical for model
calibration because National Pollutant Discharge Elimination System (NPDES) Permitted dischargers
contribute the vast majority of flow in the TMDL watersheds during dry periods. Furthermore, it was
assumed that discharges recorded during 1999 are typical and effectively estimate future conditions.
However, many of the discharges recorded during 1999 were well below permit limits and increases
in discharges are likely.
2.1.1. NPDES Permitted Dischargers
Tables 2, 3 and 4 present the breakdown of permitted NPDES point source dischargers in the Little
Sugar Creek, McAlpine Creek and Sugar Creek Watersheds respectively. Figure 2 is a map of the
TMDL Watersheds showing the locations of the permitted point source dischargers. Appendix 3
presents the daily flow rates and fecal coliform loadings for the McAlpine Creek WWTP, Sugar
Creek WWTP and Irwin Creek WWTP.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 6
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 7
Table 2: NPDES Permitted Dischargers in Little Sugar Creek Watershed
Facility ID Address Sub-
Watershed
ID
NPDES ID Flow Rate
(cfs)
Fecal Coliform
Loading
(cfu/hour)
Nations Bank 525 N Tryon St 003 NCG510398 0*-
Nations Bank
Housing
401 N Tryon St 003 NCG510277 0.003*
(none)
Three First Union
Center
301 S Tryon St 003 NC0086207 0.008*
(0.029 mgd)
-
Weyerhaeuser Inc.201 E 28th St 003 NC0084298 0.0072
(0.0072 mgd)
-
BP Store #24768 7214 The Plaza 006 NCG510242 0 -
Tommy’s
Automotive
6000 The Plaza 006 NCG510387 0*-
Celanese Acetate 2300 Archdale Dr 008 NC0084301 0.1152 -
Sugar Creek WWTP 5301 Closeburn Rd 008 NC0024937 Daily*
(20 mgd)
Daily*
(200/100 ml mo
ave
400/100 ml
weekly ave.)
Note: * indicates measured values
cfs = cubic feet per second (ft3/sec)
permit limits shown in parentheses
Table 3: NPDES Permitted Dischargers in McAlpine Creek Watershed
Facility ID Address Sub-
Watershed
ID
NPDES ID Flow Rate
(cfs)
Fecal Coliform
Loading
(cfu/hour)
Circle K #8382 9201 Lawyers Road 001 NCG510200 0.0001*
(none)
-
Forest Ridge
WWTP
1076 Kalewood Dr 002 NC0029181 0.138*
(0.15 mgd)
4.2E+05*
(200/100 ml mo
ave
400/100 ml daily
max)
Mint Hill Festival
Shopping Center
6908 Matthews-
Minthill Road
007 NC0063789 0.031*
(0.035 mgd)
3.4E+05*
(200/100 ml mo
ave
400/100 ml daily
max)
Amoco #57 4475 Randolph
Road
003 NC0085286 0.0144
(0.0144 mgd)
McAlpine Creek
WWTP
12701 Lancaster
Hwy
006 NC0024970 Daily*
(48 mgd)
Daily*
(200/100 ml mo
ave
400/100 ml
weekly ave.)
Note: * indicates measured values
permit limits shown in parentheses
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 8
Table 4: NPDES Permitted Dischargers in Sugar Creek Watershed
Facility ID Address Sub-
Watershed
ID
NPDES ID Flow Rate
(cfs)
Fecal Coliform
Loading
(cfu/hour)
Carillon Building 227 W Trade St 003 NC0085731 0.003*
(0.0316 mgd)
-
Cousins Real Estate 800 W Trade St 003 NC0086517 0.05
(0.05 mgd)
-
Franklin Water
Treatment Plant
5200 Brookshire
Blvd
004 NC0084549 1.36
(none)
-
Quick Mart 2501 Freedom
Drive
004 NCG510284 0 -
Weyerhaeuser Paper
Company
5419 Hovis Road 004 NC0084298 0.0072 (0.0072
mgd)
-
Irwin Creek WWTP 4000 Westmont 005 NC0024945 Daily* (15
mgd)
Daily*
(200/100 ml mo
ave
400/100 ml
weekly ave.)
Terrell Properties 3000 South Blvd 005 NC0085391 0.0007* (0.004
mgd)
-
Industrial Piping,
Inc
800 Culp Rd 006 NC0056669 0.003*1.2E+05*
(200/100 ml mo
ave
400/100 ml daily
max)
National Welders
Supply Company,
Inc.
5305 Old Dowd
Road
010 NC0079758 0.0143 (0.0143
mgd)
-
Charlotte Douglas
International Airport
5501 Josh
Birmingham Pky
011 NC0083887 0.01* (none)-
Hertz 6521 Old Dowd
Road
011 NC0084000 0*-
Note: * indicates measured values
permit limits shown in parentheses
2.1.2 Sanitary Sewer Overflows
Charlotte Mecklenburg Utilities (CMU) sanitary sewers serve all of the Sugar Creek, Little Sugar
Creek and McAlpine Creek Watersheds. However, there are three private NPDES facilities with
permit limits for fecal coliform in the TMDL watersheds (Tables 2 and 3). Data is not available for
un-permitted overflows from the collection systems of these three private facilities. CMU maintains
the Sanitary Sewer Overflow Database (SSO Database) system, which is a computerized database of
all un-permitted discharges from their collection system. The database includes the location, date and
time the discharge started and stopped, whether or not the discharge reached a surface water body,
estimated discharge volume and additional data not pertinent to this report. Using this information,
all documented un-permitted discharges from CMU’s collection system were geocoded using a GIS
system. The resulting GIS coverage was then subdivided by sub-watershed for inclusion in the water
quality model. A fecal coliform concentration in sewage of 6.4 x 106 cfu/100 ml was used to
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 9
calculate loading values (Center for Watershed Protection, 1999). It is important to note that the SSO
Database system may not accurately document the start of an unpermitted discharge because the start
time recorded is the moment CMU is first contacted about the discharge (Gallaher, 2001). Processed
SSO Database system data for each of the TMDL watersheds is included with this report in Appendix
4. Note, complete SSO Database system data was only available from July, 1998 through June, 2000.
Figure 3 depicts the location of each CMU overflow included in this study.
2.2 Non-Point Source Assessment
Non-point sources of fecal coliform are generally attributed to stormwater runoff, however, for the
purpose of this report, widely distributed point sources were included in the non-point source
category. Examples of widely distributed point sources are failing septic systems and dry weather
flow from storm drains. Additionally, impacts from sanitary sewer exfiltration and wildlife were
investigated.
2.2.1 Stormwater Runoff
Typically, assessment of the contribution of stormwater runoff is based upon estimations of wildlife,
agricultural operations and typical accumulation rates on built up (urban) areas. However, for this
report, build-up and wash off rates for each land-use in the TMDL watersheds were calculated from
local in-stream stormwater samples collected by the United States Geological Survey (USGS) from
December 1993 to September 1997 (Bales et. Al, 1999). The in-stream samples were collected
seasonally (four sampling events per year) from relatively uniform land-uses. Each TMDL land-use
was paired with a sample site draining a similar land-use as presented in Bales et. Al., 1999 (Note:
calculations were based upon raw data obtained from USGS and summarized in Bales (et. Al., 1999)).
Table 5 presents the build-up and maximum accumulation levels used in this study.
Table 5: Rate of Accumulation and Maximum Storage of Fecal Coliform by Land-Use
TMDL Land-Use Dominant Land-Use
from Bales et. Al.,
1999
Rate of
Accumulation of
Fecal Coliform
(count per acre per
day)
Maximum Storage
of Fecal Coliform
(count per acre)
Heavy Residential/
Institutional
Institutional & High
Density Residential
9.04 x 109 1.9 x 1010
Light Residential Woods/Brush & Low
Density Residential
6.86 x 109 1.44 x 1010
Heavy Industrial Heavy Industrial 2.68 x 109 5.63 x 109
Heavy Commercial Heavy Industrial 2.68 x 109 5.63 x 109
Light Commercial/
Light Industrial
Light Industrial &
Light Commercial
3.2 x 1010 6.72 x 1010
Woods/Brush Woods/Brush & Very
Low Density
Residential
5.48 x 109 1.15 x 1010
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 10
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 11
2.2.2 Failing Septic Systems
Failing septic systems have been cited in many TMDLs as a significant contributor of fecal coliform
to water bodies (Tennessee Department of Environment and Conservation, Division of Water
Pollution Control, Watershed Management Section, 2000). Previous studies have used failure rate
values ranging from 4% to 50% of all septic systems. The Mecklenburg County Health Department
has estimated the local septic system failure rate to be 1%, (Daniel, 2000). The Health Department
cited the following reasons for this estimate (Daniel, 2000):
· In general, Mecklenburg County soils are highly conducive to septic system operation;
· Areas where soil types are not conducive to septic system operation have been excluded from
septic system use and existing systems in these areas have been targeted for integration to the
CMU sanitary sewer system; and,
· Mecklenburg County has been a leader in enacting septic system regulation in North Carolina,
which has prevented the installation of sub-standard systems.
Many stakeholders, including Charlotte Mecklenburg Utilities, have questioned the validity of a 1%
failure rate for septic systems. Personal observations and anecdotal evidence appear to indicate a
much higher value. However, no documentation of a local investigation to establish a more accurate
or reproducible value exists. Because of the lack of direct evidence to refute the 1% value cited by
the Health Department, that value has been adopted for the TMDLs presented in this document.
Discussion of additional investigation into the failure rate of septic systems in Mecklenburg County
will be presented in the Implementation Strategy (Appendix 1).
No direct accounting of the number of septic systems in use in the TMDL watersheds was available.
Estimates of the possible number of septic systems were completed through analysis of Mecklenburg
County Finance Department data. Essentially, a listing of all built upon parcels of land meeting the
following criteria was provided:
· Parcels receiving water bills but no sewer bills. It was inferred that these parcels are likely to be
using a septic system. Residences and businesses using small package systems not operated by
CMU were omitted from the list; and,
· Parcels receiving no water bills or sewer bills but that were built upon. It was inferred that these
parcels are likely to be using a septic system. Residences and businesses using small package
systems not operated by CMU were omitted from the list.
The pared down list meeting the above criteria was then geocoded using a GIS system and subdivided
by TMDL sub-watershed. An estimated 2.8 individuals were served by each septic system (Daniel,
2000), an estimated flow rate per person of 70 gallons per individual per day (Horsely and Witten,
1996) and an estimated fecal coliform concentration of 10,000 c.f.u./100 ml (Horsely and Whitten,
1996) were used to calculate the loading and flow rates. Tables 6, 7 and 8 present the septic system
information used in the water quality model by sub-watershed in the Sugar Creek, Little Sugar Creek
and McAlpine Creek Watersheds respectively.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 12
Table 6: Septic System Loading and Flow for Sugar Creek Watershed
Sub-
Watershed
Number
of
Septic
Systems
Individua
ls per
System
Individuals
Served
Failure
Rate
(%)
FC
Concentration
in effluent
(c.f.u./100 ml)
FC Load
(cfu/hour)
Flow
(cfs)
001 717 2.8 2007.6 1 10000 2.2E+07 0.0022
002 392 2.8 1097.6 1 10000 1.2E+07 0.0012
003 325 2.8 910 1 10000 1.0E+07 0.0010
004 1117 2.8 3127.6 1 10000 3.4E+06 0.0034
005 426 2.8 1192.8 1 10000 1.3E+06 0.0013
006 43 2.8 120.4 1 10000 1.3E+06 0.0001
007 172 2.8 481.6 1 10000 5.3E+06 0.0005
008 26 2.8 72.8 1 10000 8.0E+05 0.0001
009 520 2.8 1456 1 10000 1.6E+07 0.0016
010 426 2.8 1192.8 1 10000 1.3E+07 0.0013
011 169 2.8 473.2 1 10000 5.2E+06 0.0005
Table 7: Septic System Loading and Flow for Little Sugar Creek Watershed
Sub-
Watershed
Number
of
Septic
Systems
Individua
ls per
System
Individuals
Served
Failure
Rate
(%)
FC
Concentration
in effluent
(c.f.u./100 ml)
FC Load
(cfu/hour)
Flow
(cfs)
001 381 2.8 1066.8 1 10000 1.1E+07 0.0012
002 313 2.8 876.4 1 10000 9.6E+06 0.0009
003 545 2.8 1526 1 10000 1.6E+07 0.0017
004 480 2.8 1344 1 10000 1.4E+07 0.0015
005 388 2.8 1086.4 1 10000 1.1E+07 0.0012
006 271 2.8 758.8 1 10000 8.3E+06 0.0008
009 105 2.8 294 1 10000 3.2E+06 0.0003
008 64 2.8 179.2 1 10000 1.9E+06 0.0002
Table 8: Septic System Loading and Flow for Little Sugar Creek Watershed
Sub-
Watershed
Number
of
Septic
Systems
Individuals
per System
Individuals
Served
Failure
Rate
(%)
FC
Concentration
in effluent
(c.f.u./100 ml)
FC Load
(cfu/hour)
Flow
(cfs)
003 168 2.8 470.4 1 10000 1.2E+08 0.0005
006 709 2.8 1985.2 1 10000 5.2E+08 0.0021
007 344 2.8 963.2 1 10000 2.5E+08 0.0010
008 809 2.8 2265.2 1 10000 6.0E+08 0.0025
009 255 2.8 714 1 10000 1.8E+08 0.0008
010 263 2.8 736.4 1 10000 1.9E+08 0.0008
012 373 2.8 1044.4 1 10000 2.7E+08 0.0011
013 786 2.8 2200.8 1 10000 5.8E+08 0.0024
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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2.2.3 Dry Weather Flow from Storm Drains
Dry weather flow from storm drains has been the subject of multiple investigations in Mecklenburg
County. Initially, an accounting of the storm drain outfalls for the City of Charlotte, which comprises
most of the TMDL watersheds, was completed in 1991 (Ogden Environmental & Engineering
Services, 1991). This study included the production of a system-wide outfall coverage for use with
GIS systems. Additionally, 500 screening points were selected for a field investigation to document
the presence of dry weather flow. Of the 500 sites visited, 201 (40.2 %) were found to have dry
weather flow. Follow-up activities were completed by the MCDEP from December 1995 to October
1997 at 231 of the outfalls identified as having the potential for dry weather flow pollution (MCDEP,
1998). The follow-up study did not include an assessment of fecal coliform. In order to assess the
fecal coliform loading from the storm drain system for the TMDLs, an additional study was
completed by MCDEP from June 2000 to October 2000. For the TMDL study, 168 outfalls were
randomly selected from the GIS outfall coverage produced in 1991 for screening of flow and fecal
coliform. For the TMDL study, dry weather flow was defined as flow occurring after a minimum of
72 hours without rain. Of the 168 outfalls visited during the TMDL study 165 were located and 33
(19.6%) were found to have dry weather flow. Possible reasons for the reduction in dry weather flow
from the 1991 study (40.2 %) to the 2000 study (19.6 %) are ongoing investigation of dry weather
sources of pollution and different definitions of dry weather flow. Figure 4 shows the locations of the
outfalls evaluated during the TMDL study and the distribution of the outfalls for the entire storm
drain system. Based upon the data collected from the 33 outfalls that had dry weather flow, a flow
rate of 0.0146 cfs and a fecal coliform loading rate of 22,925,015 c.f.u./hour were calculated. Results
of the TMDL study are presented in Appendix 5. Note in Appendix 5, that some outfalls have dry
weather flow but no flow rate or fecal coliform concentration. These outfalls were inaccessible for
sample collection or flow measurement, however dry weather flow was observed. For development
of the TMDL, it was assumed that the results of the TMDL study were representative of the entire
storm drain system in the TMDL watersheds. Using a GIS system and the system-wide outfall
coverage, the total number of outfalls in each of the sub-watersheds in the TMDL watersheds was
determined. Overall flow and fecal coliform loading rates were then calculated for each sub-
watershed using the total number of outfalls per sub-watershed and the results of TMDL study.
Tables 9, 10 and 11 present the results of the TMDL study for the Sugar Creek, Little Sugar Creek
and McAlpine Creek watersheds respectively.
Table 9: Dry Weather Flow and Fecal Coliform Loading for Sugar Creek
Sub-Watershed
ID
# of Outfalls # Outfalls
w/Dry Weather
Flow
Dry Weather
FC Loading
(cfu/hour)
Dry Weather
Flow-Rate (cfs)
001 48 9.3 2.1 x 109 0.1359
002 10 1.9 4.4 x 107 0.0283
003 72 14.0 3.2 x 108 0.2038
004 134 26.0 5.9 x 108 0.3793
005 91 17.7 4.0 x 108 0.2576
006 0 0.0 0 0.0000
007 57 11.1 2.5 x 108 0.1614
008 13 2.5 5.7 x 107 0.0368
009 50 9.7 2.2 x 108 0.1415
010 64 12.4 2.8 x 108 0.1812
011 4 0.8 1.7 x 107 0.0113
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Table 10: Dry Weather Flow and Fecal Coliform Loading for Little Sugar Creek
Sub-Watershed
ID
# of Outfalls # Outfalls
w/Dry Weather
Flow
Dry Weather
FC Loading
(cfu/hour)
Dry Weather
Flow Rate (cfs)
001 105 20.5 4.4 x 108 1.5312
002 146 28.5 6.1 x 108 2.1291
003 125 24.4 5.2 x 108 1.8228
004 202 39.4 8.5 x 108 2.9457
005 147 28.7 6.1 x 107 2.1436
006 120 23.4 5.0 x 108 1.7499
009 96 18.7 4.0 x 108 1.3999
008 38 7.4 1.6 x 108 0.5541
Table 11: Dry Weather Flow and Fecal Coliform Loading for McAlpine Creek
Sub-Watershed
ID
# of Outfalls # Outfalls
w/Dry Weather
Flow
Dry Weather
FC Loading
(cfu/hour)
Dry Weather
Flow-Rate (cfs)
001 226 44.3 1.0 x 109 0.6460
002 2 0.4 8.9 x 106 0.0057
003 13 2.5 5.8 x 107 0.0372
006 1 0.2 4.5 x 106 0.0029
007 127 24.9 5.7 x 108 0.3630
008 6 1.2 2.6 x 107 0.0171
009 103 20.2 4.6 x 108 0.2944
010 132 25.9 5.9 x 108 0.3773
012 32 6.3 1.4 x 108 0.0915
013 157 30.8 7.0 x 108 0.4487
2.2.4 Wildlife
Typically, for TMDL purposes, wildlife are accounted for in the calculation of build-up and wash-off
rates, which are then incorporated into a water quality model. For the purpose of this report, build-up
and wash-off rates were developed from direct sampling by land-use and therefore, no direct
assessment of wildlife contributions to fecal coliform concentration in stormwater runoff was
conducted. Excluding the contribution of wildlife to build-up and wash-off rates, the only remaining
pathway of inputting fecal coliform contributions from wildlife to a water body is through direct
application. Examples of wildlife meeting this criterion in the TMDL watersheds, which are largely
urban, are geese (Branta canadensis), ducks (Anas platyrhynchos) and beavers (Castor canadensis).
Estimates of the population of these species were provided by the Mecklenburg County Park and
Recreation Department using anecdotal knowledge of the species and informal surveys (Seriff, 2001).
All species counts were assumed to be adults. No significant populations of livestock exist in these
watersheds and were excluded from the study. Table 12 presents population estimates by TMDL
watershed for geese, ducks and beavers.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Table 12: Wildlife Population Estimates by TMDL Watershed
Species Percentage of
time in direct
contact with
creeks
Fecal Production
Rate
(count/animal/day)
Sugar Creek
(total
population)
Little Sugar
Creek
(total
population)
McAlpine
Creek
(total
population)
Geese 0%4.9 x 1010 40 150 200
Ducks 10%2.43 x 109 20 50 100
Beaver 25%2.5 x 108 0 0 10
Fecal production rates obtained from Tetra Tech, Inc. (2001).
Percentage of time in direct contact with active water obtained from Serriff (2001).
To determine the total fecal coliform loading from wildlife, a total load for each TMDL sub-
watershed was determined using species population, fecal production rates and typical species
behavior. For the purposes of this study, fecal coliform contributions from wildlife will occur
through direct application; therefore, wildlife contact must occur with a moving stream or a pond or
wetland, which flows directly to a stream. Ducks and beavers spend a significant percentage of their
time in direct contact with moving water; however, their fecal production rates are very low. Geese
have the highest fecal production rate; however, they have minimal direct contact with the TMDL
creeks, which are typically narrow, shallow and have a wide tree overhang, which is unsuitable
habitat for geese. However, geese are frequently in direct contact with ponds and wetlands, which are
often times hydraulically connected to the TMDL creeks during the wet winter months and
disconnected during the dryer summer months. For the purposes of this study, 1%, 10% and 25% of
the fecal coliform load from geese, ducks and beavers respectively was input to the creek. Tables 13,
14 and 15 present the fecal coliform loading for the Sugar Creek, Little Sugar Creek and McAlpine
Creek Watersheds respectively.
Table 13: Fecal Coliform Loading from Wildlife for Sugar Creek
Sub-
Watershed
ID
FC Loading
from Geese
(cfu/hour)
FC loading
from Ducks
(cfu/hour)
FC Loading
from Beavers
(cfu/hour)
Total Wildlife
FC Load
(cfu/hour)
Notes
009 8.17 E+08 2.03E+08 0 1.02E+09
Geese Not
Contributing in
Summer Months
Table 14: Fecal Coliform Loading from Wildlife for Little Sugar Creek
Sub-
Watershed
ID
FC
Loading
from Geese
(cfu/hour)
FC loading
from Ducks
(cfu/hour)
FC Loading
from Beavers
(cfu/hour)
Total Wildlife
FC Load
(cfu/hour)
Notes
002 1.53E+09 2.53E+08 0 1.78E+09
Geese
contributing year
round
008 1.53E+09 2.53E+08 0 1.78E+09
Geese
contributing year
round
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Table 15: Fecal Coliform Loading from Wildlife for McAlpine Creek
Sub-
Watershed
ID
FC
Loading
from
Geese
(cfu/hour)
FC loading
from Ducks
(cfu/hour)
FC Loading
from
Beavers
(cfu/hour)
Total Wildlife
FC Load
(cfu/hour)
Notes
012 1.53E+11 3.04E+09 1.04E+08 1.56E+11
Geese
contributing
year round
008 0 1.01E+09 0 1.01E+09
001 0 5.06E+08 0 5.06E+08
002 0 5.06E+08 0 5.06E+08
010
5.10E+10
1.01E+09 0 5.21E+10
Geese
contributing
year round
007 0 1.01E+09 0 1.01E+09
009 8.17E+10 0 0 8.17E+10
Geese not
contributing in
summer
months
003 5.10E+10 0 0 5.10E+10
Geese
contributing
year round
013 2.04E+10 1.01E+09 0 2.14E+10
Geese
contributing
year round
006 5.10E+10 2.03E+09 0 5.31E+10
Geese
contributing
year round
2.2.5 Exfiltration from Sanitary Sewer Pipes
In the North Carolina Piedmont Physiographic Province, groundwater flows to the creek except
during runoff events. This provides the possibility for surface water impact from groundwater during
times of moderate to low flow. A previously unstudied possible source of fecal coliform in
Mecklenburg County surface waters is the leaking or exfiltration of untreated sewage from sanitary
sewer pipes to groundwater, which may then flow to surface water. In an effort to investigate this
possible source, 18 shallow groundwater monitoring wells were installed at 9 locations throughout
Mecklenburg County (MCDEP, 2000(a)). The sites were selected by CMU and MCDEP to represent
all line sizes, construction material and construction techniques present in the CMU collection
system. At each of the 9 sites a minimum of 1 well was installed between the sewer line and the
creek and 1 well was installed upgradient of the sewer line. One groundwater sample was collected
and groundwater elevations calculated at each of the 18 monitoring wells weekly from November 13,
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 18
2000 to December 27, 2000 (MCDEP, 2000(b)). At 5 of the sites the sewer line was below the water
table, therefore making exfiltration highly unlikely. None of the samples collected at these 5 sites
contained measurable concentrations of fecal coliform in either the upgradient or downgradient well.
At the remaining 4 sites, the sewer line was above the water table, making exfiltration from the sewer
pipe hydraulically possible. At these sites fecal coliform was detected in 3 out of 4 downgradient
wells. None of the samples collected from the upgradient wells at these 4 sites contained measurable
concentrations of fecal coliform. Measured concentrations in the downgradient wells at these sites
ranged from a minimum of <10 c.f.u./100 ml to a maximum of 1700 c.f.u./100 ml. In order to
establish a representative groundwater concentration for use in the water quality models, an average
of all sampling data was calculated. This resulted in an average fecal coliform concentration in
groundwater of 58 c.f.u./100 ml, which was input to the water quality model as a constant
groundwater concentration. The fecal coliform sampling data and analysis is included as Appendix 6.
It is important to note that failing septic systems may discharge to groundwater, which may also flow
to surface water, however discharges from failing septic systems have been assessed as a separate
source (See Section 2.2.2 above). It is important to note that the investigation of exfiltration from
sanitary sewer pipes was extremely limited. It is likely that the conclusions presented in this
document will be modified as additional data becomes available.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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3 MODELING APPROACH AND RESULTS
Water quality modeling is an integral part of any TMDL developed for an environmental pollutant.
Establishing the relationship between in-stream water quality and source loadings with a water quality
model is a critical component of TMDL development. Similarly, water quality models have the
ability to support regulatory decisions and the development of implementation strategies.
3.1 Model Framework Selection
In response to the expected increase in water quality modeling due to the TMDL process, the United
States Environmental Protection Agency (USEPA) developed a document entitled “Compendium of
Tools for Watershed Assessment and TMDL Development” (Shoemaker et. Al., 1997). This
document was intended to serve as a guide to model selection, however it does not endorse the use of
a particular model for any pollutant or setting. Model selection is left up to the organization
developing a TMDL and often the most important selection criterion is familiarity. Because of the
lack of firm guidance, the Technical Subcommittee of the TMDL Stakeholders Group developed a
model selection process whereby each model under consideration was carefully assessed based on
fixed criteria. Likewise, future modeling considerations were taken into account such that experience
and similar aspects could be built upon for future modeling projects. The remainder of this section
discusses the rational for model selection.
For the purpose of the TMDL, the top six ranked models in each category in Shoemaker et. Al. (1997)
were selected for evaluation. The models included the following:
Simple Models:
1. Simple Method
2. Watershed Management Model
Moderately Complex Models:
3. SLAMM
4. P8-UCM
Complex Models:
5. NPSM/HSPF
6. SWMM
The following criteria were used to compare the models:
?Ease of Use;
?Defensibility (and/or acceptability);
?Accuracy;
?Available Sources;
?Baseflow/Stormflow;
?User Interface;
?Tools;
?Support;
?Data Requirements;
?Dynamic (or Steady State);
?Other notable points.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 20
Using these criteria a model selection matrix was prepared and is included with this document as
Appendix 7.
With the exception of P8-UCM, all of the models reviewed were capable of modeling fecal coliform
in surface water. An important factor to be considered was the ability of the model to accurately
represent baseflow conditions. Accurate baseflow simulation was important because the TMDL
includes dry weather conditions. Additionally, the model needed to be able to accurately simulate
both point and non-point sources of fecal coliform. Furthermore, the time transient quality of point
sources, such as WWTP effluent and SSOs, warranted the use of a continuous simulation model.
Based upon the aforementioned criteria, NPSM/HSPF was selected for use in preparation of the Fecal
Coliform TMDLs for the Sugar Creek, Little Sugar Creek and McAlpine Creek watersheds. HSPF is
a spatially distributed, lumped parameter, continuous simulation model used to model water quality
conditions in watersheds and river basins. HSPF calculates non-point source loadings of selected
pollutants for specified land use categories in a watershed; represents subsequent pollutant runoff
response to hydrologic influences, such as precipitation; simulates point sources as constant or
variable flow and load; and simulates flow and pollutant routing through a stream network.
3.2 Model Setup
Figures 5 shows the sub-watershed delineations for the Sugar Creek, Little Sugar Creek and
McAlpine Creek Watersheds. Sub-watershed delineation was based upon factors such as the
presence of USGS gaging station, presence of a water quality monitoring site, presence of a
NCDENR compliance point, confluence of major stream segments and presence of major point
source dischargers. Sub-watershed delineation, stream cross section geometry, slope and length were
determined using Mecklenburg County’s version of the Watershed Information System, which is a
GIS based application that allows the manipulation of digital elevation data for modeling
applications. Locally developed land use data (based upon individual land parcels) was simplified
and used for model preparation. Table 16 shows the land uses used in the TMDL models along with
percent imperviousness. Percent imperviousness by TMDL land-use was determined by intersecting
the TMDL land-use GIS coverage with an impervious surface GIS coverage. Appendix 2 presents
the distribution of land use by sub watershed for the Sugar Creek, Little Sugar Creek and McAlpine
Creek watershed respectively. Also included in Appendix 2 are maps showing the distribution of
land use in the Sugar Creek, Little Sugar Creek and McAlpine Creek Watersheds. With the exception
of rainfall, all weather data was adopted from the Charlotte Douglas International Airport (WBAN
13881). Rainfall data was adopted from USGS rainfall gages located in each watershed. USGS
station numbers 351331080525945, 351553080562645 and 02146600 were used for the Sugar Creek,
Little Sugar Creek and McAlpine Creek Watersheds respectively.
Table 16. Percent Impervious by Land-Use for TMDL Water Quality Models
Land Use in TMDL Models Percent Impervious
Heavy Commercial 77.2
Heavy Industrial 38.5
Light Commercial/Light
Industrial
49.2
Woods/Brush 7.4
Heavy Residential 32.5
Light Residential 19.6
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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3.3 Fecal Coliform Source Representation
Both point and non-point sources of fecal coliform are represented in the water quality model.
Certain non-point source categories are not associated with land loading processes and are
represented as direct, in-stream source contributions in the model. These include failing septic
systems, dry weather flow from the storm drain system, wildlife in streams and sanitary sewer
overflows. Land loading non-point sources are represented as indirect contributions to the stream
through build-up and wash-off processes (see Section 2.2.1 above). The following sections describe
the assumptions used for the various sources described in Section 2.0.
3.3.1 NPDES Discharges
There are 8, 5 and 11 NPDES point source dischargers in the Little Sugar, McAlpine and Sugar Creek
Watersheds respectively. With the exception of the CMU WWTPs, all NPDES dischargers were
represented in the model as constant (do not vary with time) sources of both flow and fecal coliform.
CMU WWTPs were represented as variable sources in the model with a flow and fecal coliform
loading rate for each day during the simulation period. CMU’s self-monitoring data was used to
calculate the loading and flow values. The data used to prepare the CMU WWTP variable source
input files is included as Appendix 3.
3.3.2 Sanitary Sewer Overflows
Sanitary sewer overflows were represented in the water quality models as time variable point sources.
The geocoded sanitary sewer overflow data from CMU’s SSO database was transformed into an
hourly loading file appropriate for NPSM/HSPF. In other words, an individual loading value was
developed for each hour an overflow occurred in each sub-watershed. The loading values were
calculated as described in Section 2.1.2.
3.3.3 Urban Development
Fecal coliform loading from urban areas was represented in the model as both pervious and
impervious surfaces. Typically, urban loading rates are adjusted as a primary calibration parameter in
the water quality model. However, for the water quality models developed for the TMDL watersheds
discussed in this report, loading values were determined through local focused land-use sampling.
Therefore, it was assumed that the values calculated were representative of both pervious and
impervious urban loading in Mecklenburg County and were not altered in the model to better fit
observed data. The values used in the model are presented in Section 2.2.1 above.
3.3.4 Dry Weather Flow
Fecal coliform loading values from dry weather flow were input to the water quality models as
continuous point sources by sub-watershed. The fecal coliform loading rates are presented in Section
2.2.3 above.
3.3.5 Failing Septic Systems
Fecal coliform loading values from failing septic systems were input to the water quality models as
continuous point sources by sub-watershed. The fecal coliform loading rates are presented in Section
2.2.2 above.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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3.3.6 Wildlife
Fecal coliform loading values from wildlife is represented in water quality simulations as described in
section 2.2.4 above. Approximate counts of each wildlife species by sub-watershed were used to
determine the fecal loading rates. The loading rates were input to the model as continuous point
sources by sub-watershed.
3.3.7 Exfiltration from Sanitary Sewer Pipes
Fecal coliform loading rates contributed by exfiltration from sanitary sewer pipes were input to the
water quality models as a constant groundwater concentration of 58 c.f.u./100 ml (see Section 2.2.5
above)
3.4 Model Calibration
Calibration of a dynamic loading model involves both hydrologic and water quality components. The
model must be calibrated to accurately represent hydrologic response in the watershed before
reasonable water quality simulations can be performed. The hydrologic calibration involves
comparison of simulated stream-flows to observed stream-flow data from stream gaging stations in
the watershed. Simulated stream-flows are generated by the model using both meteorological data
and the physical characteristics of the watershed. Typically, certain model parameters are altered
until a reasonable match is developed between simulated and observed stream flow. Similar
techniques are used to calibrate the water quality portion of the model.
A complete stream-flow data set for the Sugar Creek, Little Sugar Creek and McAlpine Creek
Watersheds was only available from July 1998 – June 2000. In order to obtain the best possible
hydrologic calibration and representation of pollutant loads, all model simulations were limited to this
time frame. Although the data set was limited to July 1998 – June 2000, all model runs were started
on January 01, 1998 to allow the model to stabilize.
All model inputs, calibration and validation information, and full model results are discussed in the
full modeling report, which is presented in Appendix 8. A condensed presentation of the hydrologic
calibration data is included as Tables 17, 18, 19, 20 and 21 for the Sugar Creek, Irwin Creek, Little
Sugar Creek, McAlpine Creek Downstream of Sardis Road and McAlpine Creek Upstream of Sardis
Road respectively. Much of the difference presented in Tables 17, 18, 19, 20 and 21 may be
attributable to the use of a single rain gage in each of the TMDL watersheds. Although the rain gages
used were located in each TMDL watershed, a significant variation in rainfall distribution has been
reported within each watershed (Sarver et. al., 1999). Figures 6, 7, 8, 9 and 10 are plots of the
hydrology calibration for Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek
Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road respectively. Figures 11,
12, 13, 14 and 15 are plots of the water quality calibration for Sugar Creek, Irwin Creek, Little Sugar
Creek, McAlpine Creek Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road
respectively.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 24
Table 17: Basic Hydrology Calibration Data for Sugar Creek
Parameter Goal Observed Simulated Difference
Total of Highest 10% of
flows 15%8730 9930 12.1%
Total of Lowest 50% of
flows 10%5597 5515 1.5%
Observed Summer flow
volume 30%4484 4555 1.6%
Observed Fall flow
volume 30%4091 5617 27.2%
Observed Winter flow
volume 30%8959 9180 2.4%
Observed Spring Flow
volume 30%5575 5391 3.4%
Observed Total Volume 10%23109 24744 6.6%
Note: Goal was adopted from HSPEXP.
Note: Units in cfs
Table 18: Basic Hydrology Calibration Data for Irwin Creek
Parameter Goal Observed Simulated Difference
Total of Highest 10% of
flows 15%4788 5132 6.7%
Total of Lowest 50% of
flows 10%1961 1770 10.8%
Observed Summer flow
volume 30%2428 2307 5.3%
Observed Fall flow
volume 30%1871 1819 2.8%
Observed Winter flow
volume 30%1809 2288 21%
Observed Spring Flow
volume 30%3862 4206 8.2%
Observed Total Volume 10%9970 10620 6.1%
Table 19: Basic Hydrology Calibration Data for Little Sugar Creek
Parameter Goal Observed Simulated Difference
Total of Highest 10% of
flows 15%12187 10634 14.6%
Total of Lowest 50% of
flows 10%6024 6267 3.9%
Observed Summer flow
volume 30%5602 5299 5.7%
Observed Fall flow
volume 30%4548 5676 19.9%
Observed Winter flow
volume 30%9919 10334 4.0%
Observed Spring Flow
volume 30%5584 6010 7.1%
Observed Total Volume 10%25653 27320 6.1%
Note: Goal was adopted from HSPEXP.
Note: Units in cfs
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
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Table 20: Basic Hydrology Calibration Data for McAlpine Creek Downstream of Sardis Road
Parameter Goal Observed Simulated Difference
Total of Highest 10% of
flows 15%17086 16864 1.3%
Total of Lowest 50% of
flows 10%2366 2603 9.1%
Observed Summer flow
volume 30%3027 3329 9.0%
Observed Fall flow
volume 30%2978 4242 29.8%
Observed Winter flow
volume 30%2936 4213 30.3%
Observed Spring Flow
volume 30%4810 4847 0.7%
Observed Total Volume 10%25692 26365 2.6%
Note: Goal was adopted from HSPEXP.
Note: Units in cfs
Table 21: Basic Hydrology Calibration Data for McAlpine Creek Upstream of Sardis Road
Parameter Goal Observed Simulated Difference
Total of Highest 10% of
flows 15%4616 5003 7.7%
Total of Lowest 50% of
flows 10%974 1119 13.0%
Observed Summer flow
volume 30%2000 2023 1.2%
Observed Fall flow
volume 30%1341 1462 8.3%
Observed Winter flow
volume 30%1363 1817 25.0%
Observed Spring Flow
volume 30%5512 7739 28.8%
Observed Total Volume 10%10216 13042 21.7%
Note: Goal was adopted from HSPEXP.
Note: Units in cfs
In order to assess the status of the hydraulic calibration of the models the goals presented in Table 17,
18, 19, 20 and 21 were adopted from HSPEXP (USGS, 1994). Similarly, for water quality
calibration, model parameters (primarily the first order decay coefficient) were adjusted until the
closest match of simulated and observed concentrations were made. The closeness of the match was
evaluated using the sum of the squares of the differences between simulated and observed values.
The models were evaluated by sources outside MCDEP for reasonableness, completeness and basis in
reality. As a result of the outside evaluation, improvements to the model were suggested and adopted.
3.5 Critical Conditions
Fecal coliform contributions to Sugar Creek, Little Sugar Creek and McAlpine Creek may be
attributed to both point and non-point sources. Critical conditions for waters impaired by non-point
sources generally occur during periods of wet weather, whereas those impaired by point sources
generally occur during dry periods. Among the categories of non-point sources are sources that
continuously discharge directly to the water body. Examples include failing septic systems, dry
weather flow from storm drains and wildlife. It is important to note that the TMDLs discussed in this
document do not include stormwater runoff as an allocation category.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 31
The critical conditions for fecal coliform impairment in Sugar Creek, Little Sugar Creek and
McAlpine Creek are extended periods of dry weather. Typically, these conditions occur during the
summer (June through September) when the minimum stream-flow is available for dilution.
However, critical conditions may occur at practically any time because of the highly dynamic and
time transient quality of both SSO loads and WWTP effluent loads. Therefore, the 30-day geometric
mean of the fecal coliform concentrations produced by the water quality models were used to
determine the critical conditions (in other words, flow was not the only consideration). It is important
to note that the critical low-flow, dry weather conditions occur during periods when there is not
washoff of fecal coliform from the land surface.
3.6 MODEL RESULTS
3.6.1 Existing Conditions
Exclusive of stormwater runoff, model results indicate that the primary sources of fecal coliform
contamination in the Little Sugar, Sugar and McAlpine Creek Watersheds are point sources and direct
input non-point sources (failing septic systems etc.).
3.6.2 Critical Conditions
Results of the year-long water quality simulation of the 30-day geometric mean concentration for
existing conditions at the outlet of the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek
Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road Watersheds are shown in
Figures 16, 17, 18, 19 and 20 respectively. Critical conditions for each watershed occurred during
periods of low stream flow coinciding with high fecal coliform loads from both the SSOs and the
WWTPs. The date of maximum exceedance, according to the model simulation, is the time period
preceding and including the highest simulated exceedance of the 30-day geometric mean standard.
Achieving the water quality criteria for this period ensures that water quality criteria will be achieved
for the remainder of the modeling period. The highest 30-day geometric mean for each watershed is
listed in Table 22.
Table 22: Critical Condition for the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek
Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road Watersheds.
Watershed Date of Predicted
Maximum
Exceedance
Value of Predicted Maximum
Exceedance (30 day geomean FC
Concentration [c.f.u./100 ml])
Sugar Creek 06/28/1999 365.24
Irwin Creek 06/28/1999 362.09
Little Sugar Creek 12/21/1999 297.34
McAlpine Creek
Downstream of Sardis
Road
08/17/1999 284.43
McAlpine Creek
Upstream of Sardis
Road
09/12/1999 883.20
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 32
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 33
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 34
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 35
Tables 23, 24, 25, 26 and 27 present the contribution of each of the source categories to the date of
maximum exceedance listed in Table 22. Figures 21, 22, 23, 24 and 25 graphically display the fecal
coliform load by source category during these times for the Sugar Creek, Irwin Creek, Little Sugar
Creek and McAlpine Creek Downstream of Sardis Road and McAlpine Creek Upstream of Sardis
Road Watersheds respectively.
Table 23: Loading Values by Source Category for the Date of Maximum Exceedance in the Sugar
Creek Watershed (05/29/1999 – 06/27/1999).
Source Category Source Sub-Category FC Load (c.f.u./30 days)
Point Source WWTP 3.8 x 1012
Sanitary Sewer Overflows 1.6 x 1013
Non-Point Source Wildlife 1.5 x 1011
Failing Septic Systems 1.0 x 1011
Dry Weather Flow from
Storm Drain System
1.8 x 1012
Sewer Exfiltration 1.0 x 1011
All Sources 2.0 x 1013
Table 24: Loading Values by Source Category for the Date of Maximum Exceedance in the Irwin
Creek Watershed (05/29/1999 – 06/27/1999).
Source Category Source Sub-Category FC Load (c.f.u./30 days)
Point Source WWTP 5.6 x 1012
Sanitary Sewer Overflows 1.2 x 1013
Non-Point Source Wildlife -
Failing Septic Systems 1.0 x 1011
Dry Weather Flow from
Storm Drain System
1.7 x 1012
Sewer Exfiltration 1.5 x 1011
All Sources 1.9 x 1013
Table 25: Loading Values by Source Category for the Date of Maximum Exceedance in the Little
Sugar Creek Watershed (11/21/1999 – 12/20/1999).
Source Category Source Sub-Category FC Load (c.f.u./30 days)
Point Source WWTP 3.2 x 1012
Sanitary Sewer Overflows 8.6 x 1012
Non-Point Source Wildlife 1.9 x 1012
Failing Septic Systems 3.1 x 1010
Dry Weather Flow from
Storm Drain System
1.7 x 1011
Sewer Exfiltration 3.9 x 1011
All Sources 1.6 x 1013
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 36
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 37
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 38
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 39
Table 26: Loading Values by Source Category for the Date of Maximum Exceedance in the
McAlpine Creek Watershed Downstream of Sardis Road (07/18/1999 – 08/16/1999).
Source Category Source Sub-Category FC Load (c.f.u./30 days)
Point Source WWTP 1.6 x 1013
Sanitary Sewer Overflows 9.8 x 1012
Non-Point Source Wildlife 2.3 x 1012
Failing Septic Systems 5.7 x 1010
Dry Weather Flow from
Storm Drain System
1.3 x 1012
Sewer Exfiltration 8.0 x 1011
All Sources 3.2 x 1013
Table 27: Loading Values by Source Category for the Date of Maximum Exceedance in the
McAlpine Creek Watershed Upstream of Sardis Road (07/18/1999 – 08/16/1999).
Source Category Source Sub-Category FC Load (c.f.u./30 days)
Point Source WWTP -
Sanitary Sewer Overflows 1.2 x 1013
Non-Point Source Wildlife 6.2 x 1010
Failing Septic Systems 4.9 x 109
Dry Weather Flow from
Storm Drain System
9.2 x 1011
Sewer Exfiltration 8.8 x 1011
All Sources 1.4 x 1013
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 40
4 ALLOCATION
4.1 Total Maximum Daily Load
The TMDL process quantifies the amount of a pollutant that can be assimilated by a water body,
identifies the sources of the pollutant, and recommends regulatory or other actions to be taken to
achieve compliance with applicable water quality standards based on the relationship between
pollution sources and in-stream water quality conditions. A TMDL can be expressed as the sum of all
point source loads (Waste Load Allocations [WLAs]), non-point source loads (Load Allocations
[LA]), and an appropriate margin of safety (MOS), which takes into account any lack of knowledge
concerning the relationship between the effluent limitations and water quality:
å å ++=MOSLAsWLAsTMDL
The objective of a TMDL is to allocate loads among all of the known pollutant sources throughout a
watershed so that appropriate control measures can be implemented and water quality standards
achieved. 40 CFR § 130.2 (I) states that TMDLs can be expressed in terms of mass per time, toxicity,
or other appropriate measure. For fecal coliform, TMDLs are expressed as counts per 30 days to be
consistent with the water quality standard. Therefore, the TMDL represents the maximum fecal
coliform load that can be assimilated by the stream during the critical 30 day period while
maintaining the fecal coliform water quality standard of the geometric mean of 200 c.f.u./100 ml over
30 days.
The total maximum daily load of fecal coliform was determined by adding the WLA and LA. The
MOS was implicitly included in the TMDL analysis through conservative model inputs and
assumptions and does not factor directly in the TMDL equation as shown above. The TMDLs for the
Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek Downstream of Sardis Road and
McAlpine Creek Upstream of Sardis Road Watersheds are listed in Table 28. Also included in Table
28 are the number of exceedances of 400 c.f.u./100 ml predicted by the model for calendar year 1999.
Note that daily average fecal coliform concentrations were used to produce these counts.
Table 28: TMDLs for the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek
Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road Watersheds
Watershed Predicted Critical
Condition
Predicted TMDL
(c.f.u./30 days)
Number of exceedances
of 400/100 ml during
1999 (% in parentheses)
Sugar Creek 07/01/1999*8.4 x 1012 26 (7%)
Irwin Creek 06/30/1999**7.7 x 1012 49 (13%)
Little Sugar Creek 12/21/1999 9.4 x 1012 15 (4%)
McAlpine Creek
Downstream of Sardis
Road
09/06/1999**1.1x 1013 25 (7%)
McAlpine Creek
Upstream of Sardis
Road
09/06/1999***6.8 x 1012 22 (6%)
*Note: after SSO sources were reduced in the water quality model, the date of maximum exceedance moved from
06/28/1999 to 07/02/1999.
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 41
*Note: after SSO sources were reduced in the water quality model, the date of maximum exceedance moved from
06/28/1999 to 07/30/1999.
***Note: after SSO sources were reduced in the water quality model, the date of maximum exceedance moved from
08/17/1999 to 09/06/1999.
****Note: after SSO sources were reduced in the water quality model, the date of maximum exceedance moved from
09/12/1999 to 09/06/1999.
4.2 Waste Load Allocations (Point Sources)
The WLA for the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek Downstream of
Sardis Road and McAlpine Creek Upstream of Sardis Road Watershed is presented in Tables 29, 30,
31, 32 and 33 respectively. The same information is presented graphically in Figures 21, 22, 23, 24
and 25. In all three watersheds, the sum of the fecal coliform load from point sources vastly
outweighs the load from non-point sources during the critical conditions. Therefore, reductions to the
point sources would have the greatest impact on the in-stream fecal coliform concentration. The
reduction strategy for the point sources is as follows:
NPDES Permitted Dischargers: For calculation of the TMDL, the NPDES permitted dischargers
were held to a maximum fecal coliform concentration in their effluent of 1000 c.f.u./100 ml. The
original WWTP time variable input files for the model were altered to reflect these changes and then
re-input to the model.
Sanitary Sewer Overflows: For calculation of the TMDL, the occurrence of overflows was cut by
33.3 %, 25%, 25% and 33% in the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek
Downstream of Sardis Road and McAlpine Creek Upstream of Sardis Road respectively..
Additionally, the remaining SSOs were limited to a maximum of 3 hours of flow. The original SSO
time variable input files for the model were altered to reflect these changes and then re-input to the
model.
Table 29: In Stream Fecal Coliform Load Reductions for the Sugar Creek Watershed (05/30/1999 –
06/28/1999).
Source Category Source Sub-
Category
Original FC
Load (c.f.u./30
days)
FC Load after
Reduction
(c.f.u./30 days)
Reduction
Point Source (WLA)WWTP 3.8 x 1012 3.5 x 1012 7.2 %
Sanitary Sewer
Overflows
1.6 x 1013 3.9 x 1012 75.7%
Non-Point Source
(LA)
Wildlife 1.5 x 1011 1.5 x 1011 0 %
Failing Septic
Systems
1.0 x 1011 3.8 x 1010 61.7%
Dry Weather Flow
from Storm Drain
System
1.8 x 1012 7.0 x 1011 61.7 %
Sewer Exfiltration 1.0 x 1011 8.5 x 109 91.6 %
All Sources
(TMDL)
2.0 x 1013 8.4 x 1012 59.2 %
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 42
Table 30: In Stream Fecal Coliform Load Reductions for the Irwin Creek Watershed (05/30/1999 –
06/28/1999).
Source Category Source Sub-
Category
Original FC
Load (c.f.u./30
days)
FC Load after
Reduction
(c.f.u./30 days)
Reduction
Point Source (WLA)WWTP 5.6 x 1012 5.4 x 1012 3.6 %
Sanitary Sewer
Overflows
1.2 x 1013 1.6 x 1012 86.7%
Non-Point Source
(LA)
Wildlife ---
Failing Septic
Systems
1.0 x 1011 4.0 x 1010 60.0%
Dry Weather Flow
from Storm Drain
System
1.7 x 1012 6.8 x 1011 60.0 %
Sewer Exfiltration 1.5 x 1011 1.3 x 1010 91.3 %
All Sources
(TMDL)
1.9 x 1013 7.8 x 1012 58.9 %
Table 31: In-Stream Fecal Coliform Load Reductions for the Little Sugar Creek Watershed
(11/21/1999 – 12/20/1999).
Source Category Source Sub-
Category
Original FC
Load (c.f.u./30
days)
FC Load after
reduction
(c.f.u./30 days)
Reduction
Point Source (WLA)WWTP 3.2 x 1012 2.7 x 1012 16.7%
Sanitary Sewer
Overflows
8.6 x 1012 4.0 x 1012 53.2 %
Non-Point Source
(LA)
Wildlife 1.9 x 1012 1.9 x 1012 0 %
Failing Septic
Systems
3.1 x 1010 1.2 x 1010 60 %
Dry Weather Flow
from Storm Drain
System
1.7 x 1011 6.8 x 1010 60 %
Sewer Exfiltration 3.9 x 1011 4.4 x 1010 88.7 %
All Sources
(TMDL)
1.6 x 1013 9.4 x 1012 40.9 %
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 43
Table 32: In-Stream Fecal Coliform Load Reductions for the McAlpine Creek Watershed
Downstream of Sardis Road (08/07/1999 – 09/05/1999).
Source Category Source Sub-
Category
Original FC
Load (c.f.u./30
days)
FC Load after
Reduction
(c.f.u./30 days)
Reduction
Point Source (WLA)WWTP 1.6 x 1013 5.7 x 1012 64.0 %
Sanitary Sewer
Overflows
9.8 x 1012 2.1 x 1012 78.2 %
Non-Point Source
(LA)
Wildlife 2.3 x 1012 2.3 x 1012 0 %
Failing Septic
Systems
5.7 x 1010 3.5 x 1010 38.1%
Dry Weather Flow
from Storm Drain
System
1.3 x 1012 7.7 x 1011 39.7%
Sewer Exfiltration 8.0 x 1011 8.7 x 1010 89.1 %
All Sources
(TMDL)
3.2 x 1013 1.1 x 1013 65.8 %
Table 33: In-Stream Fecal Coliform Load Reductions for the McAlpine Creek Watershed Upstream
of Sardis Road(08/07/1999 – 09/05/1999).
Source Category Source Sub-
Category
Original FC
Load
(c.f.u./30
days)
FC Load after
reduction
(c.f.u./30 days)
Reduction
Point Source (WLA)WWTP ---
Sanitary Sewer
Overflows
1.2 x 1013 7.8 x 1012 32.6 %
Non-Point Source
(LA)
Wildlife 6.2 x 1010 6.2 x 1010 0 %
Failing Septic
Systems
4.9 x 109 2.4 x 109 50.7 %
Dry Weather Flow
from Storm Drain
System
9.2 x 1011 4.2 x 1011 53.8 %
Sewer Exfiltration 8.8 x 1011 1.1 x 1011 87.7 %
All Sources
(TMDL)
1.4 x 1013 6.8 x 1012 52.1 %
4.3 Load Allocations (Non-Point Sources)
The LA for the Sugar Creek, Irwin Creek, Little Sugar Creek and McAlpine Creek Watershed is
presented in Tables 29, 30, 31, 32 and 33 respectively. Modeling results indicate much less impact
from non-point sources in the TMDL watersheds than from point sources. Therefore, large
reductions in non-point source loads have lesser impact than reductions in point source loads. The
reduction strategy for the non-point sources is as follows:
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 44
Wildlife: For calculation of the TMDL, no reductions in fecal coliform loading from wildlife were
included.
Failing Septic Systems: For calculation of the TMDL, estimated fecal coliform loads from failing
septic systems were reduced by 60% in the Sugar Creek, Irwin Creek and Little Sugar Creek
Watershed, 40% in the McAlpine Creek Watershed Downstream of Sardis Road and 80% in the
McAlpine Creek Watershed Upstream of Sardis Road. The original constant input files for the model
were altered to reflect this load reduction.
Dry Weather Flow from Storm Drains: For calculation of the TMDL, estimated fecal coliform loads
from dry weather flow from storm drains were reduced by 60% in the Sugar Creek, Irwin Creek and
Little Sugar Creek Watersheds, 40% in the McAlpine Creek Watershed Downstream of Sardis Road
and 80% in the McAlpine Creek Watershed Upstream of Sardis Road. The original constant input
files for the model were altered to reflect this load reduction.
Exfiltration from Sanitary Sewer Pipes: For calculation of the TMDL, estimated groundwater and
interflow concentrations in the model were reduced to 5 c.f.u./100 ml.
Tables 34, 35, 36, 37 and 38 present example reduction strategies that were used to calculate the
TMDLs in the Sugar Creek, Irwin Creek, Little Sugar Creek, McAlpine Creek downstream of Sardis
Road and McAlpine Creek Upstream of Sardis Road respectively. The reductions presented in this
table represent calculated reductions based entirely upon the source assessment. It is highly likely
that once implementation begins, this matrix will change to reflect additional data. The tables are
presented for comparison purposes only.
Table 34: Example Source Reduction Strategy for the Sugar Creek Watershed
Source
Category
Original Source
Distribution
Example Reduction
Scenario
Example Source
Distribution
WWTP No Daily Max Max 1000 c.f.u./100
ml conc. In effluent
NA
SSOs 86 SSOs; 371 hour
duration
33% Reduction and 3
hour duration
57 SSOs; 165 hour
duration
Wildlife 40 Geese
20 Ducks
NA 40 Geese
20 Ducks
Septic Sytems 43.3 Failing Septic
Systems
60% Reduction 17.3 Failing Septic
Systems
Dry Weather
Flow
105.4 Outfalls with
Dry Weather Flow
60% Reduction 42.2 Outfalls with Dry
Weather Flow
Sewer
Exfiltration
58 c.f.u./100 ml in
Ground Water
5 c.f.u./100 ml in
Ground Water
NA
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 45
Table 35: Example Source Reduction Strategy for the Irwin Creek Watershed
Source
Category
Original Source
Distribution
Example Reduction
Scenario
Example Source
Distribution
WWTP No Daily Max Max 1000 c.f.u./100
ml conc. In effluent
NA
SSOs 55 SSOs; 228 hour
duration
33% Reduction and 3
hour duration
36 SSOs; 103 hour
duration
Wildlife NA NA NA
Septic
Systems
29.7 Failing Septic
Systems
60% Reduction 11.9 Failing Septic
Systems
Dry Weather
Flow
68.9 Outfalls with Dry
Weather Flow
60% Reduction 27.6 Outfalls with Dry
Weather Flow
Sewer
Exfiltration
58 c.f.u./100 ml in
Ground Water
5 c.f.u./100 ml in
Ground Water
NA
Table 36: Example Source Reduction Strategy for the Little Sugar Creek Watershed
Source
Category
Original Source
Distribution
Example Reduction
Scenario
Example Source
Distribution
WWTP No Daily Max Max 1000 c.f.u./100
ml conc. In effluent
NA
SSOs 93 SSOs; 443 hour
duration
25% Reduction and 3
hour duration
69 SSOs; 206 hour
duration
Wildlife 150 Geese
50 Ducks
NA 150 Geese
50 Ducks
Septic
Systems
25.5 Failing Septic
Systems
60% Reduction 10.2 Failing Septic
Systems
Dry Weather
Flow
191.1 Outfalls with
Dry Weather Flow
60% Reduction 76.4 Outfalls with Dry
Weather Flow
Sewer
Exfiltration
58 c.f.u./100 ml in
Ground Water
5 c.f.u./100 ml in
Ground Water
NA
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 46
Table 37: Example Source Reduction Strategy for the McAlpine Creek Watershed Downstream of
Sardis Road
Source
Category
Original Source
Distribution
Example Reduction
Scenario
Example Source
Distribution
WWTP No Daily Max Max 1000 c.f.u./100
ml conc. In effluent
NA
SSOs 39 SSOs; 195 hour
duration
25% Reduction and 3
hour duration
31 SSOs; 93 hour
duration
Wildlife 160 Geese
90 Ducks
10 Beavers
NA 160 Geese
90 Ducks
10 Beavers
Septic Sytems 34.5 Failing Septic
Systems
40% Reduction 20.7 Failing Septic
Systems
Dry Weather
Flow
91.7 Outfalls with Dry
Weather Flow
40% Reduction 55.02 Outfalls with
Dry Weather Flow
Sewer
Exfiltration
58 c.f.u./100 ml in
Ground Water
5 c.f.u./100 ml in
Ground Water
NA
Table 38: Example Source Reduction Strategy for the McAlpine Creek Watershed Upstream of
Sardis Road
Source
Category
Original Source
Distribution
Example Reduction
Scenario
Example Source
Distribution
WWTP No WWTP --
SSOs 40 SSOs; 206 hour
duration
33% Reduction and 3
hour duration
21 SSOs; 39 hour
duration
Wildlife 40 Geese
10 Ducks
NA 40 Geese
10 Ducks
Septic Sytems 2.5 Failing Septic
Systems
80% Reduction 0.5 Failing Septic
Systems
Dry Weather
Flow
64.9 Outfalls with Dry
Weather Flow
80% Reduction in
Sub-watershed 001 &
002; 85% in 009
11.9 Outfalls with Dry
Weather Flow
Sewer
Exfiltration
58 c.f.u./100 ml in
Ground Water
5 c.f.u./100 ml in
Ground Water
NA
The data included in Tables 34, 35, 36, 37 and 38 is presented graphically in Figure 26.
Table 39 presents a matrix of reduction strategies that were evaluate prior to arrival at the strategy
discussed above.
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SourceCategory Original SourceDistribution Reduction Scenario Example SourceDistribution
WWTP No daily max Max 1000 cfu/100mL ineffluent NA
SSOs 93 SSOs, 443 hourduration 25% Reduction and 3-hour duration 69 SSOs, 206 hourduration
Wildlife 150 Geese50 Ducks NA 150 Geese50 Ducks
Septic Systems 25.5 Failing Septic System 60% Reduction 10.2 Failing SepticSystems
Dry WeatherFlow 191.1 Outfalls with DryWeather Flow 60% Reduction 76.4 Outfalls with DryWeather Flow
Sewer Exfiltration 58 cfu/100mL in GroundWater 5 cfu/100mL in GroundWater NA
Source
Category
Original Source
Distribution
Reduction Scenario Example Source
Distribution
WWTP No daily max Max 1000 cfu/100mL ineffluent NA
SSOs 39 SSOs, 195 hour duration 25% Reduction and 3-
hour duration
31 SSOs, 93 hour
duration
Wildlife 160 Geese
90 Ducks10 Beavers
NA 160 Geese
90 Ducks10 Beavers
Septic Systems 34.5 Failing Septic System 40% Reduction 120.7 Failing Septic
Systems
Dry WeatherFlow 91.7 Outfalls with DryWeather Flow 40% Reduction 55.0 Outfalls with DryWeather Flow
Sewer Exfiltration 58 cfu/100mL in GroundWater 5 cfu/100mL in GroundWater NA
SourceCategory Original SourceDistribution Reduction Scenario Example SourceDistribution
WWTP No daily max Max 1000 cfu/100mL ineffluent NA
SSOs 86 SSOs, 371 hourduration 33% Reduction and 3-hour duration 57 SSOs, 165 hourduration
Wildlife 40 Geese20 Ducks NA 40 Geese20 Ducks
Septic Systems 43.3 Failing SepticSystem 60% Reduction 17.3 Failing SepticSystems
Dry Weather Flow 105.4 Outfalls with DryWeather Flow 60% Reduction 42.2 Outfalls with DryWeather Flow
SewerExfiltration 58 cfu/100mL in GroundWater 5 cfu/100mL in GroundWater NA
Source
Category
Original Source
Distribution
Reduction Scenario Example Source
Distribution
WWTP No WWTP
SSOs 40 SSOs, 206 hourduration 33% Reduction and 3-hour duration 21 SSOs, 39 hourduration
Wildlife 40 Geese10 Ducks NA 40 Geese10 Ducks
Septic Systems 2.5 Failing Septic System 80% Reduction 0.5 Failing SepticSystems
Dry Weather Flow 69.4 Outfalls with DryWeather Flow 80% Reduction 11.9 Outfalls with DryWeather Flow
Sewer Exfiltration 58 cfu/100mL in GroundWater 5 cfu/100mL inGround Water NA
Irwin, McAlpine, Little Sugar, and Sugar Creeks Fecal Coliform TMDL
page 48
Table 39: Reduction Strategies Used during the Allocation Process
Strategy WWTP SSOs Wildlife Septic Dry
Weather
Flow
Sewer
Exfiltration
1 No Red.50%, 3
hour Limit
No Red 90%90%58 c.f.u/100 ml
to 5 c.f.u./100
ml
2 No Red 50%, 3
hour Limit
No Red 90%90%58 c.f.u/100 ml
to 5 c.f.u./100
ml
3 1000
cfu/100ml
daily max
50%, 3
hour Limit
No Red.90%90%58 c.f.u/100 ml
to 5 c.f.u./100
ml
4 1000
cfu/100ml
daily max
33%, 3
hour Limit
10%60%60%58 c.f.u/100 ml
to 5 c.f.u./100
ml
5 1000
cfu/100ml
daily max
33%, 3
hour Limit
20%60%60%58 c.f.u/100 ml
to 5 c.f.u./100
ml
6 1000
cfu/100ml
daily max
25%, 3
hour Limit
10%60%60%58 c.f.u/100 ml
to 5 c.f.u./100
ml
7 1000
cfu/100ml
daily max
25%, 3
hour Limit
No Red.60%60%58 c.f.u/100 ml
to 5 c.f.u./100
ml
8 1500
cfu/100ml
daily max
25%, 3
hour Limit
No Red.40%40%58 c.f.u/100 ml
to 5 c.f.u./100
ml
9 1000
cfu/100ml
daily max
33%, 3
hour Limit
No Red.80%80%58 c.f.u/100 ml
to 5 c.f.u./100
ml
10 1000
cfu/100ml
daily max
33%, 3
hour Limit
No Red.60%60%58 c.f.u/100 ml
to 5 c.f.u./100
ml
Note: All percentages are in reduction (90% indicates 90% reduction not 90% remaining); No Red. = No Reduction
4.4 Seasonal Variation
Seasonal variation is accounted for in the dynamic water quality model by simulations covering a full
calendar year.
4.5 Margin of Safety
The MOS is a required component of TMDL development. There are two basic methods for
incorporating the MOS: 1) implicitly incorporate the MOS using conservative model assumptions to
develop allocations, or 2) explicitly specify a portion of the total TMDL as the MOS and use the
remainder for allocations. For Sugar Creek, Little Sugar Creek and McAlpine Creek Fecal Coliform
TMDLs, the MOS was both implicitly and explicitly incorporated into the modeling analysis by use
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of conservative model assumptions and a water quality target of 180 c.f.u./100 ml. This was
accomplished by selection of conservative model input parameters and incorporation of the critical
period based on the results of a full year simulation. Similarly, the explicit margin of safety was
included in an attempt to account for possible inaccuracies in the source assessment.
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5 RECOMMENDATIONS
Implementation of the TMDL can be accomplished cooperatively by the Mecklenburg County
Department of Environmental Protection, Charlotte Mecklenburg Utilities and Charlotte Mecklenburg
Storm Water Services. Local coordination, oversight and reporting for the TMDL should be the
responsibility of the Mecklenburg County Department of Environmental Protection. Each of the three
programs have currently funded efforts dedicated to reducing fecal coliform levels in Charlotte’s streams
and these efforts can be augmented to fulfill the requirements of the TMDL Implementation Strategy.
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6 PUBLIC PARTICIPATION
The TMDL for Little Sugar, Sugar and McAlpine Creeks was developed from an interactive
stakeholder process involving a group of thirteen (13) individuals representing diverse community
interests from the following organizations:
Mecklenburg County Department of Environmental Protection - 2 representatives
Charlotte Mecklenburg Utilities - 1 representative
Charlotte Mecklenburg Storm Water Services - 2 representatives
Sierra Club - 1 representative
Catawba River Keeper - 1 representative
N.C. Department of Environment and Natural Resources - 1 representative
S.C. Department of Health and Environmental Control - 1 representative
University of North Carolina at Charlotte - 1 representative
Building Development Commission - 1 representative
Community Resident - 2 representatives
The Mecklenburg County Department of Environmental Protection led the stakeholder process and
worked to provide stakeholders with the facts and information necessary to make informed decisions and
to ensure that ample opportunities were available for stakeholder input and involvement throughout the
process. The stakeholder group met on seven (7) different occasions between December 2, 1999 and
April 3, 2001. Stakeholder involvement included input into the development of the source assessment
strategy, model selection and field data collection methodology. The stakeholders were also given the
opportunity to review and comment on two (2) separate drafts of the TMDL document. Each comment
was carefully considered by staff of the Mecklenburg County Department of Environmental Protection
and the TMDL was revised accordingly. As a result of this process, the stakeholder group has indicated a
high degree of confidence that the TMDL will achieve the desired result of meeting North Carolina’s
fecal coliform standard for class C waters.
The draft TMDL was publicly noticed on April 30, 2001. Public notice was achieved by posting the
TMDL to the DWQ web site, sending a notice to multiple electronic mailing lists, and mailing hardcopies
of the notice to interested citizens. Interested citizens were identified using the Planning Branch Catawba
River Basin mailing list for Mecklenburg County and the City of Charlotte. A public comment period
was through May 31, 2001. Written comments were not received from the public as a result of this
review. A copy of the notice is included in Appendix 9.
It is the intent of the Mecklenburg County Department of Environmental Protection to conduct the TMDL
implementation phase using continued community involvement and stakeholder input. The stakeholder
group will continue to meet to finalize the Implementation Strategy for the TMDL. Community
involvement in this process will be expanded by conducting public education and input sessions.
Following the completion of the Implementation Strategy, stakeholder involvement will continue to
provide oversight throughout the implementation phase of the TMDL.
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