20181192 Ver 1_C540_ICE_Memo_3_1117_20180122

Memorandum on Water Quality Modeling
Methodology and Results
(Quantitative ICE Assessment Memo #3)
For
Complete 540 — Triangle Expressway Southeast Extension
�_.
� ;� .
:,�o�����
�. 54p
"t��� . �,., .,, �.� _ ._s.., ...v..,
Wake and Johnston Counties, North Carolina
STI P Nos. R-2721, R-2828, R-2829
Prepared for:
Prepared By:
Michael Baker Engineering
I N T E R W AT I 0 N A L
November 2017

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table of Contents
1. Introduction ..........................................................................................................................................1
2. Water Quality Study Area ..................................................................................................................... 3
2.1 Water Quality Study Area Definition ..................................................................................................3
2.2 Water Resources .................................................................................................................................7
3. Impervious Surface Results .................................................................................................................12
4. Water Quality Analysis Approach .......................................................................................................17
4.1 MapShed Description ........................................................................................................................17
4.1.1 GWLF History and Application ...................................................................................................17
4.1.2 Estimation of Copper Loads .......................................................................................................19
4.2 Input Parameters ..............................................................................................................................20
4.2.1 Land Use and Land Cover ...........................................................................................................20
4.2.3 Soils ............................................................................................................................................ 24
4.2.4 Curve Numbers ..........................................................................................................................24
4.2.5 Streams ...................................................................................................................................... 24
4.2.6 Weather Stations ....................................................................................................................... 24
4.2.7 Point Sources .............................................................................................................................26
4.2.8 Surface Elevation .......................................................................................................................27
4.2.9 Basins ......................................................................................................................................... 27
4.2.10 Best Management Practice (BMP) Implementation ................................................................27
4.3 Model Calibration .............................................................................................................................28
5. Results and Discussion ........................................................................................................................31
5.1 2010 Scenario .................................................................................................................................... 32
5.2 2040 No-Build Scenario .....................................................................................................................33
5.3 2040 Build Scenario ...........................................................................................................................33
5.4 Results Tables ....................................................................................................................................36
6. Conclusions ......................................................................................................................................... 54
7. References .......................................................................................................................................... 56
AppendixA: Maps ..................................................................................................................................... A-1
Appendix B: Model Parameters and Notes ................................................................................................B-1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
List of Figures
Figure 1: Watersheds and Impaired Streams in the Water Quality Study Area ...........................................4
Figure 2: Water Quality Study Area Compared to FLUSA .............................................................................5
Figure 3: Change in Percent Impervious from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build
Scenarios for Model Runs 1 and 2 .................................................................................................16
Figure 4: Monthly average temperature and precipitation for Raleigh Airport Station over a 30-year
period............................................................................................................................................. 26
Figure 5: Comparison of Monthly Simulated and Observed Flow at the Outlet of Swift Creek Watershed
between January 2009 and December 2015 for Model Run 1 Calibration ...................................29
Figure 6: Comparison of Monthly Simulated and Observed Flow at the Outlet of Swift Creek Watershed
between January 2009 and December 2015 for Model Run 2 Calibration ...................................30
Figure 7: Comparison of Average Monthly Simulated and Average Monthly Observed Flow at the Outlet
of Swift Creek Watershed between January 2009 and December 2015 for Model Run 1
Calibration...................................................................................................................................... 30
Figure 8: Comparison of Average Monthly Simulated and Average Monthly Observed Flow at the Outlet
of Swift Creek Watershed between January 2009 and December 2015 for Model Run 2
Calibration...................................................................................................................................... 31
Figure 9: Change in Streamflow from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios
forModel Runs 1 and 2 ..................................................................................................................39
Figure 10: Change in Runoff from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
ModelRuns 1 and 2 .......................................................................................................................42
Figure 11: Change in TSS from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
ModelRuns 1 and 2 .......................................................................................................................45
Figure 12: Change in TN from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
ModelRuns 1 and 2 .......................................................................................................................48
Figure 13: Change in TP from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
ModelRuns 1 and 2 .......................................................................................................................51
Figure 14: Change in Copper from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
ModelRuns 1 and 2 .......................................................................................................................54
List of Tables
Table 1: Land Use Scenarios Considered in the Quantitative Water Quality Analysis ................................. 2
Table 2: Percent Impervious Coverage by Land Cover Type Used in Model Runs 1 and 2 ...........................3
Table 3: Water Quality Study Area Hydrologic Unit Codes (HUCs) ...............................................................6
Table 4: Hydrologic Unit Codes (HUCs) Excluded from the Water Quality Study Area ................................6
Table 5: NC Department of Environmental Quality Classifications for Water Quality Study Area Streams 7
Table 6: Water Quality Study Area Streams on North Carolina 2014 303(d) List and Listing Year ............10
Table 7: Upper-Limit Impervious Surface Results for Model Run 1 of the 2010, 2040 No-Build, and 2040
BuildScenarios ............................................................................................................................................14
Table 8: Low-Limit Impervious Surface Estimates for Model Run 2 of the 2010, 2040 No-Build, and 2040
BuildScenarios ............................................................................................................................................15
Table 9: Water Quality Study Area Summary Results for Impervious Surface ...........................................17
Table 10: Average Sediment Copper Concentrations by County ................................................................20

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 11: Model Inputs and Data Sources Used .........................................................................................20
Table 12: Description of Land Cover Categories Used in the GWLF-E Model .............................................21
Table 13: Mapping of Quantitative ICE Place Type Codes to GWLF-E Land Cover Categories ...................23
Table 14: Curve Number Values for Land Use Soil Hydrologic Group Combinations .................................25
Table 15: Point Sources Located within the Water Quality Study Area .....................................................26
Table 16: Water Quality Study Area Riparian Buffer Widths ......................................................................28
Table 17: Information about the Swift Creek Gauge Station near Clayton, NC ..........................................29
Table 18: Percent Change from the 2040 No-Build Scenario to the 2040 Build Scenario for the Water
QualityStudy Area as a Whole ....................................................................................................................34
Table 19: Standard Error of Pollutants as Modeled ....................................................................................35
Table 20: Percent Change in Modeled Parameters between the 2040 Build and 2040 No-Build Scenarios
in the Lower Swift Creek Watersheds .........................................................................................................35
Table 21: Comparison of the Upper-Limit Annual Streamflow Results for 2010, 2040 No-Build, and 2040
Build Scenarios Under Model Run 1 ...........................................................................................................37
Table 22: Comparison of Lower-Limit Annual Streamflow Results for 2010, 2040 No-Build, and 2040
Build Scenarios under Model Run 2 ............................................................................................................38
Table 23: Comparison of Upper-Limit Annual Runoff Results of the 2010, 2040 No-Build, and 2040 Build
ScenariosUnder Model Run 1 ....................................................................................................................40
Table 24: Comparison of Lower-Limit Annual Runoff Results of the 2010, 2040 No-Build, and 2040 Build
Scenariosunder Model Run 2 .....................................................................................................................41
Table 25: Comparison of Upper Limit Annual Total Suspended Sediment (TSS) Results for 2010, 2040 No-
Build, and 2040 Build Scenarios under Model Run 1 ..................................................................................43
Table 26: Comparison of Lower Limit Annual Total Suspended Sediment (TSS) Results for 2010, 2040 No-
Build, and 2040 Build Scenarios under Model Run 2 ..................................................................................44
Table 27: Comparison of Upper Limit Annual Total Nitrogen (TN) Results for 2010, 2040 No-Build, and
2040 Build Scenarios under Model Run 1 ...................................................................................................46
Table 28: Comparison of Lower Limit Annual Total Nitrogen (TN) Results for 2010 Condition, 2040 No-
Build, and 2040 Build Scenarios under Model Run 2 ..................................................................................47
Table 29: Comparison of Upper Limit Annual Total Phosphorus (TP) Results for 2010, 2040 No-Build, and
2040 Build Scenarios under Model Run 1 ...................................................................................................49
Table 30: Comparison of Lower Limit Annual Total Phosphorus (TP) Results for 2010, 2040 No-Build, and
2040 Build Scenarios under Model Run 2 ...................................................................................................50
Table 31: Comparison of Upper Limit Annual Copper (Cu) Results for 2010 Condition, 2040 No-Build, and
2040 Build Scenarios under Model Run 1 ...................................................................................................52
Table 32: Comparison of Lower Limit Annual Copper (Cu) Results for 2010, 2040 No-Build, and 2040
Build Scenarios under Model Run 2 ............................................................................................................53
Appendix A: Maps
Appendix B: Model Parameters and Notes
�

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
1. Introduction
The North Carolina Department of Transportation (NCDOT) and the Federal Highway Administration
(FHWA) propose building a new, controlled-access highway from NC 55 Bypass in Apex to US 64/US 264
Bypass (I-495) in Knightdale, a distance of approximately 28 miles. The project, known as Complete 540
—Triangle Expressway Southeast Extension, is proposed as a toll facility.
Through the National Environmental Policy Act (NEPA) process, NCDOT previously completed a
Qualitative Indirect and Cumulative Effects (ICE) Report (H.W. Lochner, Inc., 2014) and a summary of the
results are included in the Draft Environmental Impact Statement (DEIS), which was published in
November 2015 (H.W. Lochner, Inc., 2015). The Quantitative ICE is under development to support the
Final Environmental Impact Statement (FEIS), and the project team has developed a serious of technical
memoranda to summarize the procedures, decisions, and results related to this analysis.
Quantitative ICE Memo #1 (Michael Baker Engineering, 2017a) documented the NCDOT and FHWA
determination that the CommunityViz model from the Imagine 2040 regional land use planning initiative
would be a reasonable and appropriate tool to develop land use scenarios for this project. NCDOT and
FHWA came to this conclusion in large part because the CommunityViz model has already been
calibrated to regional conditions and has been applied to regionally approved transportation plans.
Quantitative ICE Memo #2 (Michael Baker Engineering, 2017b) outlined the methodology used in this
analysis to forecast land use changes between the base year (2010) and year 2040 and summarized the
results of the land use scenarios developed for the Quantitative ICE. The outputs of the forecasting and
modeling documented in this memo were used for the Quantitative Indirect and Cumulative Effects (ICE)
Assessment and Water Quality Indirect and Cumulative Impacts (ICI) Assessment discussed in this Memo
#3. The methodology described in Memo #2 is based on information collected from regional and local
planners who are most familiar with the Future Land Use Study Area (FLUSA), land use forecasting and
socioeconomic data approved for use in long-range transportation planning, and a review of recent
literature on land use changes associated with construction of transportation infrastructure.
The purpose of this Memo #3 is to describe the methodology and results of the Water Quality ICI,
including the inputs and methods used in the water quality modeling. Results are presented, but a more
complete discussion of the ICI for water quality and endangered species is included in Indirect and
Cumulative Effects Memorandum - Quantitative ICE Memo #4 (Michael Baker Engineering, 2017c). The
ICI combines the data collected and CommunityViz model output from Quantitative ICE Memo #2 with a
watershed model to estimate the water quality impacts that may occur as indirect and cumulative
effects from planned and anticipated development in the FLUSA with and without the construction of
the proposed facility.
This analysis is a critical component of the Quantitative ICE analysis, as documented in ICE Memo #4,
due in part to requests from resource agencies during coordination to focus on water quality and
endangered species in indirect and cumulative effect analysis. The dwarf wedgemussel (Alasmidonta
heterodon) is the endangered species of primary concern to this analysis as known populations and
suitable habitat for this species are found along Swift Creek within the FLUSA. On April 5, 2017, the
USFWS proposed threatened species status for the yellow lance (Elliptio lanceolate; 82 FR 16559). The
historical range, habitat, and stressors overlap for both species; therefore, this analysis will assess
effects to the dwarf wedgemussel and will also apply to the yellow lance.

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
The water quality analysis used a watershed model, Generalized Watershed Loading Function —
Enhanced (GWLF-E), to estimate the annual streamflow, runoff, and annual overland contaminant
loadings of total nitrogen (TN), total phosphorus (TP), total suspended sediment (TSS), and copper for
the three land use scenarios examined as part of the Quantitative ICE Assessment. These three
scenarios, described in Table 1, are the 2010 Condition (2010), 2040 No-Build Land Use (2040 No-Build),
and 2040 Preferred Alternative Build Land Use (2040 Build) scenarios. The ICE Memos #1 and #2 provide
a full explanation of the development of the land use scenarios and the conversion from land use to land
cover, which is the basis for water quality modeling. Comparison of the streamflow, runoff, and
contaminant loadings projected for the 2040 No-Build and 2040 Build scenarios provides an indication of
the project's potential Water Quality ICI.
Table 1: Land Use Scenarios Considered in the Quantitative Water Quality Analysis
Full Name of Land Use Abbreviated Name Definition
Scenario
2010 2010 Land use conditions existing in 2010
2040 No-Build Land Use 2040 No-Build Forecast land use for the year 2040 without
construction of the project
2040 Preferred Alternative 2040 Build Forecasted land use for the year 2040 with
Build Land Use construction of the Preferred Alternative
The GWLF-E model was run twice for each scenario to estimate a range of likely indirect and cumulative
impacts to the water quality study area. For both model runs, the process described in Quantitative ICE
Memo #2 was used to estimate land cover in the water quality study area. The first, more-conservative
model run used the land cover results and the GWLF-E defaults to convert land cover results to an
"upper limit" of percent impervious coverage for each HUC in the study area. The second model run
used the observed percent impervious coverage by land cover type in the Baseline condition to estimate
the "lower limit" of impervious coverage for the 2010, 2040 No-Build, and 2040 Build scenarios. The
percent impervious coverage estimates by land use category developed for use in the second model run
provide a closer approximation of regulatory limits that currently apply in much of the FLUSA, including
open space regulations and impervious surface limits, as discussed in Section 2 of ICE Memo #4.
This approach could produce some under-estimation of impervious surface percentages; therefore,
Model Run 2 provides a low-end-of-range estimate, and Model Run 1 provides a high-end-of-range
estimate. It should be noted that the percent impervious coverages for both model runs under the 2010
scenario are theoretical estimates calculated from the GWLF-E defaults (Model Run 1) or from an
average of observed percent impervious by land cover type observed in the FLUSA (Model Run 2). Table
2 shows the percent impervious coverage by land cover type used in each model run. With one
exception, the observed impervious surface ratios are lower than the default values from the model for
each land use type. The one exception is Low Density Mixed Urban land cover category, which accounts
for a very small amount (approximately 4 percent) of the land cover in the FLUSA.
2

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 2: Percent Impervious Coverage by Land Cover Type Used in Model Runs 1 and 2
Land Use Land Cover Category
Code
2 Low Density Mixed Urban
3 High Density Mixed Urban
17 Low Density Residential
18 Medium Density Residential
19 High Density Residential
20 Medium Density Mixed Urban
2. Water Quality Study Area
Percent Impervious
Model Run 1
GWLF-E Defaults
Upper Limit
15
87
15
52
87
52
Model Run 2
Observed Baseline
Lower Limit
18
29
9
12
33
25
�
The following sub-sections describe the selection of the water quality study area, its definition, and the
conditions of the study area.
2.1 Water Quality Study Area Definition
The FLUSA for the ICE analysis was selected in cooperation with NCDOT, FHWA, and other federal and
state regulatory and resource agencies. The FLUSA encompasses an approximately 450-square mile area
south and east of Raleigh, NC, including parts of Wake, Johnston, and Harnett counties.
The water quality study area used for this analysis was slightly modified from the FLUSA for modeling
purposes. The study area was created by selecting the 12-digit Hydrologic Unit Code (HUC) watersheds
within the original FLUSA boundary (See Figure 1). For those watersheds where the natural boundary
extended beyond the original FLUSA boundary, the area of analysis for the purpose of this study was
limited to just the watershed area within the original FLUSA. Two of the 12-digit HUCs were subdivided
to provide data for the endangered species analysis. Seven HUCs or portions of HUCs along the fringes
of the FLUSA were excluded from the water quality study area because such small areas of these
watersheds were located within the FLUSA that modeling data for these areas would present data
quality concerns. The final water quality study area (Figure 2) consisted of about 430 square miles. Table
3 displays a list of the twenty-one HUC watersheds in the water quality study area, and Table 4 shows
the seven HUCs, or portions thereof, excluded from the study area. The subdivided White Oak Creek
(030202011003) and Little Creek watersheds appear twice (ID #22 and #23) in the data results tables at
the end of this document. In the water quality and related discussions, the subdivided White Oak Creek
(030202011003 — Neuse River Basin) and Little Creek (030202011005 — Neuse River Basin) watersheds
are referred to with (Upper) and (Lower) modifiers in text and table references, and the White Oak
Creek watershed in the Cape Fear Basin (030300040102) is also referred to with the modifier (Cape Fear
Basin) to provide clarity (see Table 3). Note that HUCs beginning with 0302 are in the Neuse River basin
and those beginning with 0303 are in the Cape Fear River Basin.
3

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 1: Watersheds and lmpaired Streams in the Water Quality Study Area
4
�omplete 540
Water Quality
Studv ?�rea
�
Water Resources �
Impaired Stieams
Legend
� FLUSA Boundary
� River Basins
�— 3�3(d) Ir�paired Streams
Streams
Major Highways
��� Proposed 540
• Water Trea�ment Facilities
D 3 6
I i I i I
Miles
INTERNATIQNAL

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 2: Water Quality Study Area Compared to FLUSA
Complete 540
Water Quality
St�c�v Watersheds
�
� FLUS�=�
Legend
� River Basins
�--
� J—� Gounties
�' Existing Highways
,s�°���� Pro�osed 540
�j Study Watershed Area
� FWSA
�� E
0 3 6
I i I i I
Miles
INTERNATIONAL

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 3: Water Quality Study Area Hydrologic Unit Codes (HUCs)
12-digit HUCl Watershed Name
030202011003 White Oak Creek
030300040106 Avents Creek-Cape Fear River2
030300040502 Hector Creek-Cape Fear River
030202011202 Camp Branch-Black Creek
030300040501 Neills Creek
030202011201 Little Black Creek-Black Creek
030300040103 Buckhorn Creek
030202010903 Lower Middle Creek
030202011007 Reed Branch-Swift Creek
030202011006 Piney Grove Cemetery-Swift Creek
030202010902 Middle Middle Creek
030300040102 White Oak Creek (Cape Fear Basin)
030202011005 Little Creek
030202010901 Upper Middle Creek
030202011004 Mahlers Creek-Swift Creek
030202011002 Lake Benson-Swift Creek
030202011001 Lake Wheeler-Swift Creek
030202011101 Walnut CreekZ
030202011103 Poplar Creek-Neuse River
030202011102 Marks Creek
030202010804 Lower Crabtree Creek
1 HUCS beginning with 0302 are in the Neuse River basin and those
beginning with 0303 are in the Cape Fear River Basin.
Z Small portions of this HUC were excluded from the water quality study
area because these portions were small and spatially separated from the
rest of the HUC modeled during this study.
Table 4: Hydrologic Unit Codes (HUCs) Excluded from the Water Quality Study Area
12-digit HUCl Watershed Name
030202010705 Mango Creek-Neuse River
030202011101 Walnut Creekz
030202011104 Mill Creek-Neuse River
030202011105 Buffalo Creek-Neuse River
030202011203 Holts Lake-Black Creek
030300060101 Upper Black River
030300040106 Avents Creek-Cape Fear River2
1 HUCS beginning with 0302 are in the Neuse River basin and those
beginning with 0303 are in the Cape Fear River Basin.
Z The portions of this HUC excluded from the water quality study area were
small and spatially separated from the rest of the HUC modeled during this
study.
0

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
2.2 Water Resources
The majority of the water quality study area is located in the Neuse River watershed. A small portion of
the western study area is within the Cape Fear River watershed. Named creeks in the water quality
study area include Swift Creek, Middle Creek, Walnut Creek, Crabtree Creek, Buckhorn Creek, and Black
Creek. Water quality classifications for study area streams are shown in Table 5.
Table 5: NC Department of Environmental Quality Classifications for Water Quality Study Area Streams
Classification Name
Index
18-13-(1) Avents Creek
18-15-(0.4) Hector Creek
18-15-(0.7) Hector Creek
18-16-(0.3)
18-16-(0.7)
18-16-1-(1)
18-16-1-(2)
18-7-(1)
18-7-(3)
18-7-5
18-7-5-1
18-7-5.5
18-7-6
18-7-6-1
18-7-6-1-1
18-7-7
27-(22.5)
Neills Creek (Neals
Creek)
Neills Creek (Neals
Creek)
Kenneth Creek
Kenneth Creek
Buckhorn Creek
Buckhorn Creek
(Harris Lake)
Cary Branch
Norris Branch
Utley Creek
White Oak Creek
Big Branch
Little Branch
Little White Oak
Creek
Neuse River
27-(36) Neuse River
27-(38.5) Neuse River
27-(41.7)
27-33-(10)
27-33-22
27-34-(4)
Neuse River
Crabtree Creek
Carolina Lake
Walnut Creek
Description
From source to a point 1.3 miles upstream of Harnett
County SR 1418 (River Rd.)
From source to a point 1.1 miles upstream of Harnett
County SR 1415 (Rawls Church Rd.)
From a point 1.1 miles upstream of Harnett County SR
1414 to Cape Fear River
From source to a point 0.3 mile upstream of Wake-
Harnett County Line
From a point 0.3 mile upstream of Wake-Harnett
County Line to Cape Fear River
From source to Wake-Harnett County Line
From Wake-Harnett County Line to Neills Creek
From source to Norfolk Southern Railroad
From backwaters of Harris Lake to dam at Harris Lake
From source to Harris Lake, Buckhorn Creek
From source to Cary Branch
From source to Harris Lake, Buckhorn Creek
From source to Harris Lake, Buckhorn Creek
From source to White Oak Creek
From source to Big Branch
From source to Harris Lake, Buckhorn Creek
From Town of Wake Forest proposed water supply
intake to mouth of Beddingfield Creek
From mouth of Beddingfield Creek to a point 0.2 mile
downstream of Johnston County SR 1700 (Covered
Bridge Rd.)
From a point 0.2 mile downstream of Johnston County
SR 1700 to a point 1.4 mile downstream ofJohnston
County SR 1908 (Fire Department Rd.)
From City of Smithfield water supply intake to a point
1.4 miles downstream of Gar Gut
From mouth of Richlands Creek to Neuse River
Entire lake and connecting stream to Crabtree Creek
From dam at Lake Raleigh to Neuse River
7
Classificationl
C; HQW
C; HQW
WS-IV; HQW
C
WS-IV
C
WS-IV
C
WS-V
C
C
C
C
C
C
C
C; NSW
WS-V; NSW
WS-IV; NSW
WS-V; NSW
C; NSW
C; NSW
C; NSW

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Classification
Index
27-34-11
27-34-11-1
27-34-11-2
27-35
27-37
27-38
27-43-(1)
27-43-(5.5)
27-43-(8)
27-43-10
27-43-11
27-43-12
27-43-13
27-43-14
27-43-15-(1)
27-43-15-(2)
27-43-15-(4)
27-43-15-10
27-43-15-10-
1
27-43-15-10-
2
27-43-15-10-
2-1
27-43-15-11
27-43-15-12
27-43-15-13
27-43-15-14
27-43-15-15
27-43-15-16
27-43-15-3
27-43-15-4.5
27-43-15-5
27-43-15-6
27-43-15-7
Name
Big Branch
Poplar Branch
Little Arm Branch
Poplar Creek
Beddingfield Creek
Marks Creek (Lake
Myra)
Swift Creek (Lake
Wheeler)
Swift Creek (Lake
Benson)
Swift Creek
Neal Branch
White Oak Creek
(Austin Pond)
Little Creek
Cooper Branch
Reedy Branch (Little
Branch)
Middle Creek
Middle Creek
(Sunset Lake)
Middle Creek
Little Creek
Juniper Creek
Guffy Branch
Ditch Branch
Buffalo Branch
Mill Branch
Beaverdam Branch
Cow Branch
Shop Branch
Steep Hill Branch
Basal Creek [(Bass
Lake, (Mills Pond)]
Rocky Branch
Camp Branch
Bells Lake
Mills Branch
Description
From source to Walnut Creek
From source to Big Branch
From source to Big Branch
From source to Neuse River
From source to Neuse River
From source to Neuse River
From source to a point 0.6 mile upstream of Wake
County SR 1006 (Old Stage Rd.)
From a point 0.6 mile upstream of Wake County SR
1006 (Old Stage Rd.) to dam at Lake Benson
From dam at Lake Benson to Neuse River
From source to Swift Creek
From source to Swift Creek
From source to Swift Creek
From source to Swift Creek
From source to Swift Creek
Classificationl
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
WS-III; NSW
WS-I I I;
NSW,CA
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
From source to backwaters of Sunset Lake C; NSW
From backwaters of Sunset Lake to dam at Sunset Lake B; NSW
From dam at Sunset Lake to Swift Creek
From source to Middle Creek
From source to Little Creek
From source to Little Creek
From source to Guffy Branch
From source to Middle Creek
From source to Middle Creek
From source to Middle Creek
From source to Middle Creek
From source to Middle Creek
From source to Middle Creek
From source to Sunset Lake, Middle Creek
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
C; NSW
6; NSW
From source to Middle Creek C; NSW
From source to Middle Creek C; NSW
Entire lake and connecting stream to Middle Creek C; NSW
From source to Middle Creek C; NSW
0

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Classification
Index
27-43-15-8-
(1)
27-43-15-8-
(2)
27-43-15-9
27-43-2.2
27-43-2.5
27-43-2.8
27-43-3
27-43-3.5
27-43-4
27-43-4.5
27-43-5-(1)
27-43-5-(1.5)
27-43-5-(2)
27-43-6-(1)
27-43-6-(2)
27-43-7-(1)
27-43-7-(2)
Name
Terrible Creek
(Johnsons Pond)
Terrible Creek
Panther Branch
MacGregor powns
Lake
Regency Park Lake
Long Branch
Lynn Branch
(Meadows Creek)
(Lochmere Lake)
Speight Branch
Woodys Lake
Dutchmans Branch
Unnamed Tributary
to Swift Creek
(Silver Lake)
Unnamed Tributary
to Swift Creek
(Yates Mill Pond)
Unnamed Tributary
to Swift Creek
Buck Branch
Buck Branch
Reedy Branch
Reedy Branch
Description
From source to dam at Johnsons Pond
From dam at Johnsons Pond to Middle Creek
From source to Middle Creek
Entire lake and connecting stream to Swift Creek
Entire lake and connecting stream to Swift Creek
From source to Swift Creek
From source to Swift Creek
From source to Swift Creek
Entire lake and connecting stream to Swift Creek
From source to Swift Creek
From source to dam at Silver Lake
From dam at Silver Lake to a point 0.5 mile upstream
of mouth
From a point 0.5 mile upstream of mouth to Swift
Creek
From source to a point 0.6 mile upstream of mouth
From a point 0.6 mile upstream of mouth to Lake
Benson, Swift Creek
From source to a point 0.5 mile upstream of mouth
From a point 0.5 mile upstream of mouth to Lake
Benson, Swift Creek
Classificationl
B; NSW
C; NSW
C; NSW
WS-III; NSW
WS-III; NSW
WS-III; NSW
WS-III; NSW
WS-III; NSW
WS-III; NSW
WS-III; NSW
WS-III,B; NSW
WS-III; NSW
WS-I I I;
NSW,CA
WS-III; NSW
WS-III;
NSW,CA
WS-III; NSW
WS-III;
NSW,CA
27-43-9 Mahlers Creek From source to Swift Creek C; NSW
27-45-(1) Black Creek (Partins From source to dam at Panther Lake B; NSW
Pond, Panther Lake)
27-45-(2) Black Creek From dam at Panther Lake to mouth of Sassarixa Creek C; NSW
27-45-3 Little Black Creek From source to Black Creek C; NSW
27-45-4 Hooks Branch From source to Black Creek C; NSW
27-45-6 Camp Branch From source to Blacl< Creek C; NSW
18 - Primary Recreation, Fresh Water, C- Aquatic Life, Secondary Recreation, Fresh Water; CA - Critical Area; HQW -
High Quality Waters; NSW - Nutrient Sensitive Waters; WS-111- Water Supply 111- Moderately Developed; WS-IV -
Water Supply IV- Highly Developed; WS-V - Water Supply V- Upstream
NC Department of Environmental Quality (NCDEQ) Division of Water Resources (DWR) maintains a list of
waters classified as impaired under Section 303(d) of the Clean Water Act. The list of 303(d) impaired
waterbodies identifies each impaired waterway and the contaminant(s) causing its impairment. Table 6,
below, shows water quality study area waterways that are included in the current (2014) 303(d) list.
0

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 6: Water Quality Study Area Streams on North Carolina 2014 303(d) List and Listing Year
Watershed Name
Neills Creek
Impaired Stream or Water
Body
Neills Creek (from source
to a point 0.3 mile
upstream of Wake-Harnett
County line)
Neills Creek (from a point
0.3 mile upstream of
Wake-Harnett County line
to SR 1441 [East Williams
St.])
Kenneth Creek (from
Wake-Harnett County line
to Neills Creek)
Poplar Creek- Neuse River (from Crabtree
Neuse River Creek to SR 2555 [Auburn
Knightdale Road])
Lower Crabtree
Creek
Walnut Creek
Lake Benson-Swift
Creek
Neuse River2 (from mouth
of Beddingfield Creek to a
point 0.2 mile downstream
of Johnston County SR
1700 [Covered Bridge Rd.])
Neuse RiverZ (from a point
0.2 mile downstream of
Johnston County SR 1700
[Covered Bridge Rd.] to
point 1.4 mile downstream
of Johnston County SR
1908 [Fire Dept. Rd])
Beddingfield Creek (from
its source to Neuse River)
Crabtree Creek (from 2.75
miles upstream of Neuse
River to Neuse River)
Walnut Creek (from an
unnamed tributary [UT] 0.6
miles west of I-440 to
Neuse River)
Swift Creek (from Lake
Wheeler Dam to a point
0.6 mile upstream of Wake
Impaired Reasons (Year)
Benthos Poor (2006)
Benthos Poor (2006)
Benthos Fair (1998)1
pH (2012)1
Dissolved Oxygen (2014)
Copper (2008)1
Polychlorinated biphenyl (PCB)
Fish Tissue Advisory (2010)
Copper(2008)
Zinc (2008)
Copper (2012)
Benthos Fair (2014)
PCB Fish Tissue Advisory (2008)
Copper (2008)1
PCB Fish Tissue Advisory (2010)
10
Benthos Poor (2008)
Likely Origin
Non-point
source
Non-point
source
Non-point
source
Non-point and
point sources
Non-point
source
Non-point and
point sources
Non-point and
point sources
Non-point
source
Non-point
source
Non-point
source

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Watershed Name
Piney Grove
Cemetery-Swift
Creek
Impaired Stream or Water
Body
County SR 1006 [Old Stage
Rd.])
Swift Creek (from a point
0.6 mile upstream of Wake
County SR 1006 [Old Stage
Rd.] to the backwaters of
Lake Benson)
UT to Swift Creek (from its
source to Lake Benson)
Swift Creek (from dam at
Lake Benson to Little
Creek)
Impaired Reasons (Year)
BenthosPoor(2008)
Benthos Fair (2014)
Benthos Fair (2012)
Mahlers Creek- Swift Creek (from dam at Benthos Fair (2012)
Swift Creek Lake Benson to Little
Creek)
Little Creek Little Creek (from source to Benthos Fair (1998)
(Upper) Swift Creek)
Little Creek Little Creek (from its Benthos Fair (1998)
(Lower) source to Swift Creek)
Upper Middle Terrible Creek (from
Creek Johnsons Pond to Middle
Creek)
Middle Creek (from 0.8
mile south of US 1 to UT on
west side of creek 3.0 miles
downstream)
Middle Creek (from UT on
west side of creek 3.0 miles
downstream to backwaters
of Sunset Lake)
Middle Creek (from dam at
Sunset Lake to small
impoundment upstream of
US 401)
1 Impaired reason proposed for delisting in 2016.
z Segment proposed for delisting in 2016.
Benthos Fair (2012)
Benthos Fair (2008)
Benthos Fair (2012)
Fish Community Poor (2014)
Likely Origin
Non-point
source
Non-point
source
Non-point and
point sources
Non-point and
point sources
Non-point and
point sources
Non-point and
point sources
Non-point and
point sources
Point source
Non-point and
point sources
Non-point and
point sources
The Neuse River has been affected for decades by human activity, including construction of
impoundments, discharge from water and wastewater treatment plants, runoff from agricultural
activities, and runoff from development (NC WRC, 2015; Harned, 1980). The remainder of the FLUSA is
11

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
in the Cape Fear River basin. Common human-induced water quality issues in the Cape Fear Basin
include sedimentation, invasive species, eutrophication (elevated nutrient levels that lead to algal
blooms), and impoundments (NC WRC, 2015).
In 1998, the Neuse River Buffer Rules were enacted to reduce nitrogen inputs to the Neuse River (15A
NCAC 02B.0233). These regulations include requiring property owners to protect 50-foot riparian buffers
along the river and its tributaries, limiting point source pollution and stormwater runoff in new
developments. The 50-foot buffers are not uniform and consist of two zones: 30 feet of undisturbed
"forest" vegetation nearest the stream and 20 feet of herbaceous or woody vegetation to provide
filtration of pollutants further from the stream. The Wake County Board of Commissioners adopted the
Swift Creek Land Management Plan in 1990, further protecting the water supply watershed in the upper
Swift Creek. This plan was adopted by local jurisdictions and identifies how each jurisdiction proposes to
promote development while maintaining the water quality in the basin. Some communities have
additional, more restrictive buffer requirements for perennial and intermittent streams. Importantly,
Wake County has a 100-foot buffer requirement on perennial streams (comprised of two 50-foot zones,
comparable in vegetation to the two zones on the Neuse River buffers), and Johnston County has a 100-
foot buffer requirement specifically on perennial streams within the Swift Creek watershed.
3. Impervious Surface Results
The impervious surface coverage is estimated from the land cover forecasts discussed in Memo #2 and
used in the water quality modeling. Table 7 shows the Model Run 1 impervious surface estimates for all
three scenarios for the water quality study area and all the watersheds therein. Table 8 shows the
Model Run 2 impervious surface estimates for all three scenarios for the water quality study area and all
the watersheds therein. Figure 3 presents a graphic comparison of the difference in estimated percent
impervious coverage by water quality study area and HUC between the 2010 and future scenarios for
each model run. Throughout this memo, to avoid confusion, Model Run 1 results are presented in
purple and Model Run 2 results are presented in green. The results can only be compared within each
model run and not across the model runs. As explained in Section 4, comparisons across model runs are
not valid because of the differences in each model run's calibration.
In the water quality study area, estimated impervious surface coverage increases by 12 percent using
the Model Run 1 estimation methodology and by 3 percent using Model Run 2 methodology from the
2010 to 2040 No-Build scenarios. Between the 2010 and 2040 Build scenarios, the estimated percent
impervious increases by 13 percent for Model Run 1 and by 3 percent for Model Run 2. From the 2040
No-Build to 2040 Build scenarios, estimated impervious surface coverage increases by one percent or
less for the entire water quality study area for both model runs. These figures and the corresponding
acreage amounts for the Water Quality Study Area are shown in Table 9. In acres, the difference in
estimated impervious surface between 2010 and the 2040 No Build scenario is over 32,000 acres and
the difference from the 2040 No-Build to the 2040 Build scenario is 3,400 acres in Model Run 1. For
Model Run 2, these figures are 8,800 acres from 2010 to the 2040 No-Build Scenario, and 500 acres for
the difference between 2040 No-Build and 2040 Build scenarios.
Most watersheds see an increase in impervious surface from the 2010 to 2040 No-Build scenarios, as is
consistent with growth projections for the area in most watersheds, with a relatively small incremental
increase from the 2040 No-Build to 2040 Build scenarios. Impervious surface coverage is projected to
12

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
increase by one percent or less from the 2040 No-Build to the 2040 Build scenarios in most watersheds
for Model Run 1 and by less than one percent in all watersheds for Model Run 2. In Model Run 1, three
percent increases in impervious surface coverage were estimated between the 2040 No-Build to 2040
Build scenarios in Middle Middle Creek, Poplar Creek-Neuse River, and White Oak Creek (Upper). In
addition, the estimation method for Model Run 1 projected a 6 percent increase in the Mahlers Creek-
Swift Creek watershed from the 2040 No-Build to 2040 Build scenarios. Projected increases in estimated
percent impervious coverage were less than one percent in these watersheds for Model Run 2.
Some watersheds show a decrease in estimated impervious surface coverage from the 2040 No-Build to
2040 Build scenarios. These reductions are likely due to changes in the types of development and
associated density assigned to the parcels in these watersheds. This finding is consistent with the
qualitative ICE documentation provided in the DEIS. Development associated with the 2040 No-Build
scenario is influenced more by the existing (and projected) roadway network (without Complete 540) as
compared to the 2040 Build scenario. As explained in Quantitative ICE Memo 1, the CommunityViz
model accounts for this influence by utilizing customized inputs for attractiveness factors to forecast
future land use.
Four watersheds are of concern with respect to habitat for the endangered dwarf wedgemussel (and
yellow lance mussel):
• White Oak Creek (Lower)
• Piney Grove Cemetery-Swift Creek
• Mahlers Creek-Swift Creek
• Little Creek (Lower)
Impervious surface coverage increases in these areas from the 2040 No-Build scenario to the 2040 Build
scenario are 1 percent or less, with the exception of the Mahlers Creek-Swift Creek watershed for Model
Run 1. Although this watershed has the largest increase among those in the study area, it is only six
percent for Model Run 1, and the estimated percent increase for Model Run 2 is less than one percent.
13

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 7: Upper-Limit Impervious Surface Results for Model Run 1 of the 2010, 2040 No-Build, and 2040
euild Scenarios
Water- Name
shed
ID
I Water Quality Study Area I
1 I White Oak Creek (Lower) I
2 Avents Creek-Cape Fear
I River
3 Hector Creek-Cape Fear
River
4 Camp Branch-Black Creek �
5 Neills Creek
6 Little Black Creek-Black
Creek
7 Buckhorn Creek
8 Lower Middle Creek
9 Reed Branch-Swift Creek �
10 Piney Grove Cemetery-
I Swift Creek
11 Middle Middle Creek
12 White Oak Creek (Cape
Fear Basin)
2010
(�)
2040
No-Build
1i)
14 I 26
10 I 28
4 5
5 7
6 7
16 33
9 22
12 29
8 � 13
12 21
7 12
16 28
14 20
Difference 2040
between Build
Zoso (i)
and
2040
No-Build1
��)
12 27
18 i 29
<1 5
2 I 7
<1 7
18 33
13 23
17 30
5 14
10 � 22
5 13
12 31
6 20
Difference
between
2010
and
2040
Build1
(�)
13
20
<1
Difference
between
2040
No-Build
and
2040 Build1
(�)
1
1
<1
3 <1
<1 <1
18 <1
15 1
18 <1
6 1
10 � <1
6 <1
15 3
6 <1
13 I Little Creek (Lower) I 9 I 22 I 13 I 22 I 13 <1
14 Upper Middle Creek 22 39 17 39 18 <1
15 Mahlers Creek-Swift Creek 14 29 15 34 21 6
16 Lake Benson-Swift Creek 19 26 7 26 7 <1
17 Lake Wheeler-Swift Creek 21 24 3 24 3 <1
18 Walnut Creek 21 38 17 38 17 <1
19 Poplar Creek-Neuse River 11 27 16 30 20 3
20 Marks Creek 7 25 I 18 26 18 <1
21 Lower Crabtree Creek 39 40 2 40 2 <1
22 White Oak Creek (Upper) 20 38 18 40 21 3
23 Little Creek (Upper) 25 38 13 38 14 <1
1 Note: all results are rounded and, as such, may not appear to add/subtract correctly. For example, 1.4% rounds to
1%, while 1.7% rounds to 2%, but the difference between them, 0.3%, would be shown as <1. Note that all figures
use the watershed acreage as the denominator and are mathematically comparable (i.e., the difference between
the 2040 No-Build and 2040 Build scenarios is the mathematical difference between each scenario's percentage
result, as opposed to a relative percentage change from the 2040 No-Build result).
14

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 8: Low-Limit Impervious Surface Estimates for Model Run 2 of the 2010, 2040 No-Build, and 2040
euild Scenarios
Water- Name 2010 2040 Difference 2040 Difference Difference
shed (%) No-Build between Build between between
ID (%) 2010 (%) 2010 2040
and and No-Build
2040 2040 and
No-Buildl Build1 2040 Build1
��) (�) ��)
Water Quality Study Area 5 8 3 9 3 <1
1 White Oak Creek (Lower) 4 9 5 9 5 <1
2 Avents Creek-Cape Fear 2 2 <1 2 <1 <1
River
3 Hector Creek-Cape Fear 2 3 <1 3 <1 <1
River
4 Camp Branch-Black Creek 3 4 <1 4 <1 <1
5 Neills Creek 5 10 4 10 4 <1
6 Little Black Creek-Black 3 6 3 7 4 <1
Creek
7 Buckhorn Creek 4 8 4 8 4 <1
8 Lower Middle Creek 3 5 1 5 2 <1
9 Reed Branch-Swift Creek 4 7 2 7 3 <1
10 Piney Grove Cemetery- 4 5 1 5 1 <1
Swift Creek
11 Middle Middle Creek 5 8 3 9 4 <1
12 White Oak Creek (Cape 5 7 2 7 2 <1
Fear Basin)
13 Little Creek (Lower) 4 7 3 7 3 <1
14 Upper Middle Creek 7 11 4 11 4 <1
15 Mahlers Creek-Swift Creek 5 10 5 11 5 <1
16 Lake Benson-Swift Creek 7 10 3 10 3 <1
17 Lake Wheeler-Swift Creek 9 10 1 10 1 <1
18 Walnut Creek 7 12 4 12 4 <1
19 Poplar Creek-Neuse River 4 8 5 9 5 <1
20 Marks Creek 2 7 5 7 5 <1
21 Lower Crabtree Creek 15 16 <1 16 <1 <1
22 White Oak Creek (Upper) 7 13 6 14 6 <1
23 Little Creek (Upper) 9 12 3 12 3 <1
1 Note: all results are rounded and, as such, may not appearto add/subtract correctly. For example, 1.4% rounds to
1%, while 1.7% rounds to 2%, but the difference between them, 0.3%, would be shown as <1. Note that all figures
use the watershed acreage as the denominator and are mathematically comparable (i.e., the difference between
the 2040 No-Build and 2040 Build scenarios is the mathematical difference between each scenario's percentage
result, as opposed to a relative percentage change from the 2040 No-Build result).
15

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 3: Change in Percent Impervious from 2010 to 2040 No-euild Scenarios and 2010 to 2040 euild
Scenarios for Model Runs 1 and 2
Change in Estimated Impervious SurFace (%)
0 5 10 15 20 25
Water Quality Study Area
�
White Oak Creek (Lowerj
�
Avents Creek-Cape Fear River �
Hector Creek-Cape Fear River �
CampBranch-BlackCreek �
Nei Ils Creek
� I
Little Black Creek-Black Creek
�
Buckhorn Creek
�
Lower Middle Creek
I
Reed Branch-Swift Creek
�
Piney Grove Cemetery-Swift Creek
�
Middle Middle Creek
�
White Oak Creek (Cape Fear Basinj
�
Little Creek (Lowerj
Upper Middle Creek
�
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
�
Lake Wheeler-Swift Creek �
Walnut Creek
�
Poplar Creek-Neuse River
�
Marks Creek
�
Lower Crahtree Creek �
White Oak Creek (Upper]
Little Creek (Upperj
❑ 2010 to 2040 No-Build (Model Run 1) � 2010 to 2040 Build (Model Run 1)
❑ Z010 to 2040 No-Build (Model Run 2) d 2010 to Z040 Build (Model Run Z)
16

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 9: Water Quality Study Area Summary Results for Impervious Surface
Model Run and Units 2010 2040 Difference 2040 Difference Difference
No-Build between Build between between
2010 2010 2040
and and No-Build
2040 2040 Build1 and
No-Build1 2040 Build1
Model Run 1- percentage 14 26 12 27 13 1
Model Run 1- Acres 38,600 72,000 32,100 75,400 35,500 3,400
Model Run 2- percentage 5 8 3 9 3 <1
Model Run 2- Acres 14,600 23,400 8,800 23,900 9,300 500
The Water Quality Study Area (as shown in Figure 2) includes approximately 275,800 acres. The acreages above are based on
detailed impervious surface calculations and are not a product of the rounded percentages shown.
4. Water Quality Analysis Approach
This section outlines the methodology used to quantify the project's potential water quality effects. The
MapShed watershed modeling suite employed in the analysis is discussed in detail. The procedures used
to develop model input parameters, special model considerations, and model calibration are also
presented.
4.1 MapShed Description
MapShed is a customized Geographic Information System (GIS) interface developed in MapWindow, an
open-source GIS platform, to create input data for the GWLF-E watershed model. The watershed
simulation tools used in MapShed are based on the unenhanced GWLF and Runoff Quality from
Development Sites (RUNQUAL) models originally developed by Dr. Douglas Haith and colleagues at
Cornell University, as described in Section 4.1.1, below. Routines associated with both models, originally
written in QuickBasic, were converted to Visual Basic by Evans et al. (2002) and enhanced with
additional functionality to facilitate their use in MapShed. In MapShed, the functionality provided by
these two models has been further enhanced and combined into a new model called GWLF-E. MapShed
provides an interface to select and modify various GIS datasets, creates GWLF-E input files, provides
interfaces to modify the GWLF-E model input files, runs the model, and provides interfaces to display
the outputs from the model.
4.1.1 GWLF History and Application
The core watershed simulation model for the MapShed software application is the unenhanced GWLF
model developed by Haith and Shoemaker (1987). The GWLF model simulates runoff, sediment, and
nutrient (nitrogen [N] and phosphorus [P]) loads from a watershed based on various source areas (e.g.,
agricultural, forested, and developed land). It also has algorithms for calculating septic system loads and
allows for the inclusion of point source discharge data. This continuous simulation model uses daily time
steps for weather data and water-balance calculations. Monthly calculations are made for sediment and
nutrient loads based on the daily water balance accumulated to monthly values.
17

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
GWLF is a combined distributed/lumped parameter watershed model. For surface loading, it allows
multiple land use/land cover inputs, but assumes each area is homogenous regarding the attributes
considered by the model. The model does not spatially distribute the source areas, but simply
aggregates the loads from each source area into a watershed total; in other words, there is no spatial
routing. For sub-surface loading, the model acts as a lumped parameter model using a water-balance
approach. No distinctly separate areas are considered for sub-surface flow contributions. Daily water
balances are computed for unsaturated and saturated sub-surface zones, where infiltration is computed
as the difference between precipitation and snowmelt minus surface runoff and evapotranspiration.
The Natural Resources Conservation Service (NRCS) Curve Number (CN) approach is used to simulate
surface runoff within the GWLF model. The CN is an empirical parameter that can be used to estimate
the potential maximum soil moisture retention and thereby predict the direct runoff from a rainfall.
Erosion and sediment yield are estimated using monthly erosion calculations based on the Universal Soil
Loss Equation (USLE) algorithm, monthly rainfall-runoff coefficients, and monthly soil erosion values for
each source area. The soil erosion calculation uses the following variables: soil loss erosion (K), the
length slope factor (LS), the vegetation cover factor (C), and daily weather inputs (temperature and
conservation practices factor, or P in KLSCP). These variables, known collectively as KLSCP, are used in
calculations and can be thought to depict the susceptibility of soil to erosion. A sediment-delivery ratio is
calculated from the watershed size and a transport capacity (based on average daily runoff) and then
applied to the calculated erosion to determine sediment yield for each source area. Surface nutrient
losses are determined by applying dissolved nitrogen and phosphorus coefficients to surface runoff and
applying sediment coefficients to the yield portion for each agricultural source area. The dissolved
nitrogen and phosphorus coefficient values are default values in the model, derived from national-level
studies. Point source discharges, manured areas, and septic systems can also be considered to
contribute to dissolved losses and are specified in terms of kilograms per month. The CN approach uses
an exponential accumulation and wash-off function to calculate the urban nutrient loadings. Sub-surface
losses are calculated using dissolved nitrogen and phosphorus coefficients for shallow groundwater
contributions to stream nutrient loads, and the sub-surface sub-model only considers a single, lumped-
parameter contributing area. Evapotranspiration is determined using daily weather data and a cover
factor dependent upon land use/land cover type. Finally, a water balance is performed daily using
supplied or computed precipitation, snowmelt, initial unsaturated zone storage, maximum available
zone storage, and evapotranspiration values.
In GWLF-E, transport-related data define the necessary parameters for each source area as well as
global parameters (e.g., initial storage, sediment delivery ratio) that apply to all source areas. Nutrient
data specifies the various loading parameters for the different source areas. The weather file
(weather.dat) contains daily average temperature and total precipitation values for the simulation time
period.
Since its initial incorporation into the ArcView interface of GWLF (AVGWLF), the GWLF model has been
revised to include routines and functions not found in the original model. These include the streambank
erosion routine, the simulation of water withdrawals from surface and ground water sources, and more
comprehensive watershed modeling capabilities, such as loads from farm animals and a new pathogen-
load estimation routine. Another significant change has been an improvement in the simulation of
hydrology and loads from urban areas. These new functions are based on the RUNQUAL model
developed by Haith (1993) at Cornell University. The model input structure used by RUNQUAL is very
18

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
similar to GWLF, which greatly facilitated implementation of these new functions within the GWLF-E
model used in MapShed.
As with older versions of GWLF, the new urban routines derived from RUNQUAL and included in GWLF-E
provide for continuous daily simulation of surface runoff and contaminant loads from developed land
within a given watershed. In contrast to the original GWLF, flows and loads in GWLF-E are calculated
from both the pervious and impervious fractions associated with each land use/land cover category. The
contaminated runoff may also be routed through various urban Best Management Practices (BMPs) to
simulate reductions that may occur prior to being discharged at the watershed outlet. These routines in
GWLF-E are adapted from the urban runoff component of the original GWLF model (Haith and
Shoemaker, 1987). Runoff volumes are calculated from procedures given in the US Soil Conservation
Service's Technical Release 55 (1986). Contaminant loads are based on exponential accumulation and
wash-off functions similar to those used in the Storm Water Management Model (SWMM) (Huber and
Dickinson, 1988) and Storage, Treatment, Overflow Runoff Model (STORM) (USACE, 1977). The pervious
and impervious fractions of each land use type are modeled separately, and runoff and contaminant
loads from the various surfaces are calculated daily and aggregated monthly in the model output. With
the RUNQUAL-derived routines in GWLF-E, it is assumed that the area being simulated is small enough
that travel times are on the order of one day or less.
As mentioned above, the RUNQUAL-derived routines in GWLF-E allow the user to consider the potential
effects of BMPs on contaminated runoff. Three basic types of BMPs can be modeled using GWLF-E —
detention basins, infiltration/retention facilities, and vegetated filter strips (buffers). Detention basins
may be dry or wet (sometimes referred to as extended dry basins and wet ponds, respectively).
Infiltration facilities are trenches, basins, and/or porous areas designed to allow specific volumes of
runoff water to drain to underlying groundwater rather than directly to streams via overland flow. Filter
(or buffer) strips are grassed or forested areas through which runoff passes as sheet (un-channelized)
flow. In the original version of RUNQUAL, all runoff is routed through the BMPs. In GWLF-E, the user can
specify the extent to which the three BMPs are implemented within any given watershed. If the
practices are used in combination, runoff is routed through them in the following order:
infiltration/retention, filter strips, and detention basins.
Finally, another significant revision that has been included in MapShed and GWLF-E is the ability to
simulate the transport and attenuation of contaminant loads from multiple sub-watersheds within a
larger watershed. In this case, loads are attenuated (i.e., reduced) using a combination of daily loss rates
for contaminants and travel times based on the distances of each sub-watershed to the larger
watershed outlet. This new functionality allows for better identification of contaminant "hot-spots"
within the larger watershed, as well as better evaluation of the potential load-reduction effects of
various contaminant mitigation activities in different geographic locations.
4.1.2 Estimation of Copper Loads
Copper loads are of concern in the study area because several studies have indicated that freshwater
mussels, including the federally endangered dwarf wedgemussel and the proposed threatened yellow
lance, are sensitive to copper and ammonia during their early life stages (Jacobson et al., 1993; Jacobson
et al., 1997; Milam et al., 2005; Wang et al., 2007a; Wang et al., 2007b). The GWLF-E models TN, which
includes ammonia. The model does not have the capability to directly model copper loads from the land
use categories; however, the model does have the capability to model sediment loading by land use
19

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
category. For this analysis, the watershed loading of copper was estimated based on modeled sediment
loading and average copper levels in sediment for each county. This approach is based on TMDL studies
in which copper was a modeled pollutant (KDHE, 2006; MapTech, Inc., 2004). The average sediment
copper concentrations for each county were obtained from HealthGrove (2016) and are available in
Table 10.
Table 10: Average Sediment Copper Concentrations by County
County Concentration (ppm)
Wake County 8.870
Johnston County 6.921
Harnett County 7.266
4.2 Input Parameters
GIS data layers were used as inputs by MapShed to derive spatially aggregated input parameters for the
GWLF-E model. Additionally, important non-spatial data were required by the model. Sources for these
data are listed in Table 11. The sections below describe the use of each dataset.
Table 11: Model Inputs and Data Sources Used
Dataset
Study Area Land Use
National Hydrography Dataset
Weather Station Locations and Data
Digital Elevation Model
2004 Public Sewer Systems — Current
Service Areas Municipal Boundaries
Streamflow Data
Hydrologic Unit Code (HUC) Boundaries
Soil Survey Geographic (SSURGO)
Database
Point Source Dischargers Location and
Discharges
Data Source
Michael Baker Engineering, Inc. and U.S.
Geological Survey (USGS)
USGS
National Oceanic and Atmospheric
Administration (NOAA)
USGS
North Carolina Department of Water
Resources (NCDWR)
USGS
Natural Resources Conservation Service
(NRCS) Watershed Boundary Dataset/USGS
N RCS
NCDWR, U.S. Environmental Protection
Agency (USEPA) Discharge Monitoring Report
(DMR)
4.2.1 Land Use and Land Cover
Study area land use datasets for the Baseline Condition, 2040 No-Build, and 2040 Build scenarios were
developed as part of the ICE analysis for this project. The development of these datasets is detailed in
Memorandum on Land Use Scenario Methodology and Results (Quantitative ICE Assessment Memo #2J.
The memorandum explains the methodology for developing the datasets, assigning the 29 land use
classifications (Place Types), and converting the model outputs into land cover results. For the purposes
of this water quality study, each of the Place Types defined for the Quantitative ICE analysis (Memo #2)
20

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
were assigned to the land cover categories compatible with the GWLF-E model requirements (see Tables
12 and 13).
Table 12: Description of Land Cover Categories Used in the GWLF-E Model
GWLF-E Land
Cover
Categories
Water
Hay/Pasture
Description
Open water
Cover crops similar to "Row Crops" category with lower runoff and generally lower
surface erosion, but similar nutrient loading characteristics.
Row Crops Cover crops similar to "Hay/Pasture" category with higher runoff and generally
higher surface erosion, but similar nutrient loading characteristics.
Coniferous Wooded areas dominated by non-deciduous species. GWLF-E treats all forested
Forest
Mixed Forest
Deciduous
Forest
Woody
Wetland
Emergent
Wetland
Quarries
Transitional
Turfgrass/
Golf
Low Density
Residential
areas similarly with regard to runoff, erosion, and nutrient loading.
Wooded areas with a mixture of deciduous and coniferous species. GWLF-E treats all
forested areas similarly with regard to runoff, erosion, and nutrient loading.
Wooded areas dominated by deciduous species. GWLF-E treats all forested areas
similarly with regard to runoff, erosion, and nutrient loading.
Wetlands dominated by woody vegetation, but treated the same as Emergent
Wetland by GWLF-E.
Wetlands dominated by herbaceous vegetation, but treated the same as Woody
Wetland by GWLF-E.
Quarries and transitional areas are grouped together in one category since both
areas are treated as "non-vegetated, disturbed" areas within GWLF-E.
Quarries and transitional areas are grouped together in one category since both
areas are treated as "non-vegetated, disturbed" areas within GWLF-E.
Highly-maintained, intensively-fertilized areas such as golf courses or sod farms.
Areas with a mixture of constructed materials, with vegetation mostly in the form of
lawn grasses, shrubs and/or trees. Impervious surfaces account for less than 30
percent of the total cover. These areas most commonly include large-lot, single-
family housing units.
Medium Areas with a mixture of constructed materials, with vegetation mostly in the form of
Density lawn grasses, shrubs and/or trees. Impervious surfaces account for 30 to 75 percent
Residential of the total cover. These areas commonly include low and medium density housing
in suburban or smaller urban areas.
High Density Areas with a mixture of constructed materials, with vegetation mostly in the form of
Residential lawn grasses, shrubs and/or trees. Impervious surfaces account for greater than 75
percent of the total cover. These areas most commonly include small-lot housing or
row houses. Some commercial uses, usually converted residences, may be present,
Low Density
Mixed
but represent less than 20 percent of the total area.
Areas with a mixture of constructed materials, with vegetation mostly in the form of
lawn grasses, shrubs and/or trees. Impervious surfaces account for less than 30
percent of the total cover. These areas commonly include schools, hospitals,
commercial areas and industrial parks with extensive, surrounding open land.
21

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
GWLF-E Land
Cover
Categories
Description
Medium Areas with a mixture of constructed materials, with vegetation mostly in the form of
Density lawn grasses, shrubs and/or trees. Impervious surfaces account for 30 to 75 percent
Mixed of the total cover. These areas are typically found in smaller cities and suburban
locations.
High Density Areas with a mixture of constructed materials, with vegetation mostly in the form of
Mixed lawn grasses, shrubs and/or trees. Impervious surfaces account for greater than 75
percent of the total cover. These areas are typically high-intensity
commercial/industrial/institutional zones in large and small urban areas. They may
include some dense residential development, which should not exceed 20 percent of
the total area.
22

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 13: Mapping of Quantitative ICE Place Type Codes to GWLF-E Land Cover Categories
Place Type Place GWLF-E Land Cover Category
Type Code
Light Industrial Center LIC Low Density Mixed Urban
Health Care Campus HCC Low Density Mixed Urban
University Campus UC Low Density Mixed Urban
Urban Neighborhood UN High Density Mixed Urban
Suburban Commercial Center SCC High Density Mixed Urban
Suburban Hotel SH High Density Mixed Urban
Suburban Office Center SOC High Density Mixed Urban
Regional Employment Center REC High Density Mixed Urban
Heavy Industrial Center HIC High Density Mixed Urban
Transit-Oriented Development TOD High Density Mixed Urban
Metropolitan Center MC High Density Mixed Urban
Airport AIR High Density Mixed Urban �
Working Farm WF Cropland
Rural Living RL Low Density Residential
Large-Lot, Residential Neighborhood LLRN Low Density Residential
Mobile Home Community MHC Low Density Residential
Rural Cross Roads RCR Low Density Residential
Small-Lot, Residential Neighborhood SLRN Medium Density Residential i
Shade Tree Residential Neighborhood STRN Medium Density Residential I
Mixed Residential Neighborhood MXR Medium Density Residential
Multifamily Residential Neighborhood MFRN High Density Residential
High-Rise Residential HRR High Density Residential
Neighborhood Commercial Center NCC Medium Density Mixed Urban
Mixed-Use Center MUC High Density Mixed Urban �
Mixed-Use Neighborhood MUN Medium Density Mixed Urban
Village Center VC Medium Density Mixed Urban
Town Center TC Medium Density Mixed Urban
Civic & Institutional Facilities CIV Medium Density Mixed Urban
Parks and Open Space POS Varies1
Z Underlying NLCD inputs were used to determine the Land Use Category
Because the Place Types focus on developed land uses, some lands within the water quality study area
were not categorized in the Quantitative ICE (see quantitative discussion of these differences by
scenario in ICE Memo #4). National Land Cover Database (NLCD) data were used to fill in these gaps in
the ICE dataset. The additional NLCD land cover types included in the modeling are Water, Coniferous
Forest, Mixed Forest, and Deciduous Forest.
23

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
4.2.3 Soils
Spatial and tabular Soil Survey Geographic (SSURGO) database soil information for Johnston, Wake, and
Harnett counties was downloaded from NRCS. The average available water-holding capacity, soil
erodibility factor (KF), and dominant hydrologic soil group were calculated for each soil map unit and
joined to the appropriate GWLF-E soil feature class. SSURGO stores the available water storage as
centimeters (cm) of water in its map unit components root zone layers table (chorizon table). The
weighted average available water-holding capacity of all the soil components were calculated and
assigned to each soil feature. Similarly, the weighted average of the KF value corresponding to the top
soil layer for all components of the map unit was calculated and assigned to each feature as the
representative KF value. For each map unit, the soil hydrologic group (stored in SSURGO component
table) was assigned based on the value corresponding to the dominant soil component for each soil map
unit.
4.2.4 Curve Numbers
MapShed automatically calculates CNs based on land use class and hydrologic soil group information in
the soil data to simulate surface runoff in the GWLF-E model. The CNs used for each of the GWLF-E land
use categories are presented in Table 14. The CNs were the same for both model runs.
4.2.5 Streams
The stream network was obtained from the National Hydrography Dataset (NHD) (USGS, 2016a) by
extracting and merging the high-resolution NHD flow lines for the 8 digit-HUCs Upper Neuse (03020201)
and Upper Cape Fear (03030004). The merged streams were used with MapShed.
4.2.6 Weather Stations
General climate conditions for the study area can be characterized using data from meteorological
observations made by the Raleigh Airport National Climatic Data Center station
(GHCND:USW00013722). This station is in the Upper Neuse Watershed approximately three miles north
of the water quality study area. Average annual precipitation at this station is 46.58 inches, and the
average annual daily temperature is 60.8°F. The highest average daily temperature of 89°F occurs in July
while the lowest average daily temperature of 32°F occurs in January, as obtained from the 1961-1990
climate normals (U.S. Climate Data, 2017). Figure 4 provides a summary of rainfall and climate data for
the Raleigh Airport Station based on the same period.
24

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 14: Curve Number Values for Land Use Soil Hydrologic Group Combinations
Land Use Category CN for Soil Hydrologic Group
A1 BZ C3 D4
Water 98 98 98 98
Low Density Mixed Urban 745/926 74/92 74/92 74/92
High Density Mixed Urban 795/986 79/98 79/98 79/98
Hay/Pasture 43 63 75 81
Cropland 64 75 82 85
Forest 37 60 73 80
Mixed Forest 37 60 73 80
Deciduous Forest 37 60 73 80
Wetland 69 80 87 90
Emergent Wetland 72 82 87 89
Disturbed 76 85 89 91
Sandy Areas 20 20 20 20
Turf/Golf 30 58 71 78
Low Density Residential 745/926 74/92 74/92 74/92
Medium Density Residential 745/926 74/92 74/92 74/92
High Density Residential 745/926 74/92 74/92 74/92
Medium Density Mixed Urban 79s/986 79/98 79/98 79/98
Open land 43 63 75 81
Bare Rock 98 98 98 98
1 Soils in this group have low runoff potential when thoroughly wet. Water is transmitted freely through the soil. Group A soils
typically have less than 10 percent clay and more than 90 percent sand or gravel and have gravel or sand textures.
2 Soils in this group have moderately low runoff potential when thoroughly wet. Water transmission through the soil is
unimpeded. Group B soils typically have between 10 percent and 20 percent clay and 50 percent to 90 percent sand and have
loamy sand or sandy loam textures.
3 Soils in this group have moderately high runoff potential when thoroughly wet. Water transmission through the soil is
somewhat restricted. Group C soils typically have between 20 percent and 40 percent clay and less than 50 percent sand and
have loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures.
4 Soils in this group have high runoff potential when thoroughly wet. Water movement through the soil is restricted or very
restricted. Group D soils typically have greater than 40 percent clay, have less than 50 percent sand, and have clayey textures.
5 CN for pervious portion
6 CN of impervious portion
25

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 4: Monthly average temperature and precipitation for Raleigh Airport Station over a 30-year
period
ioo
90
�
� 80
a,
� 70
a�
Y 60
ca
�
Q 50
a�i 40
F—
aao 30
�a
L
; zo
a
�o
0
�
ti
r
1an Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
Precipitation (Inch) f High (F) � Low (F)
5
Cl1.�
4 �
3.5 �
0
�
3 �
�a
2.5 �
Z a`
N
�
1.5 L
v
i a'
0.5
0
In addition to the Raleigh Airport station, data from two other stations were also used in the study as
these stations are closer to some of the water quality study area watersheds. The location of weather
stations with daily temperature (maximum and minimum) and precipitation records for the period 2000
to 2008 were retrieved from NOAA. Weather data from the Raleigh Airport NC (GHCND:USW00013722),
Smithfield NC (GHCND:USC00317994), and Raleigh State University NC (GHCND:USC00317079) stations
were formatted for use by MapShed.
4.2.7 Point Sources
Locations of facilities within the study area with National Pollutant Discharge Elimination System
(NPDES) permits were obtained from NCDEQ. These facilities include large municipal wastewater
treatment plants (WWTPs) and are listed in Table 15. The 2016 annual nitrogen and phosphorus loading
rates (annual discharges) from each point source was obtained from the USEPA DMR data and used for
all scenarios modeled.
Table 15: Point Sources Located within the Water Quality Study Area
NPDES Permit Number
NC0025453
NC0029033
NC0063096
NC0063096
NC0064050
NC0065102
NC0066516
Facility Name
Little Creek WWTP
City of Raleigh Public Utilities
Holly Springs WWTP
Holly Springs WWTP
Apex Water Reclamation Facility
Town of Cary - South Cary WWTP
Terrible Creek WWTP
26

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Cropland land use is the major contributor of TN to the study area. However, a number of point sources
in the study area also contribute TN. These are the Neuse River WWTP in Poplar Creek-Neuse River
watershed; Terrible Creek WWTP, South WWTP, and Middle Creek WWTP in Upper Middle Creek
watershed; Little Creek WWTP in Little Creek watershed (Upper); and Holly Springs WWTP in White Oak
Creek (Cape Fear Basin) watershed. Based on the 2016 data, the Neuse River WWTP facility contributes
more TN to the study area than the other point sources. The only point source that contributed
phosphorus was the Holly Springs WWTP located in the White Oak Creek (Cape Fear Basin) watershed.
4.2.8 Surface Elevation
Topography and relief data were obtained from the USGS National Data Set at a resolution of
approximately 10 meters. The region is characterized by low, rolling hills ranging in elevation from 70 to
500 feet above sea level. The slope ranges between 0 degrees and 60 degrees.
4.2.9 Basins
Drainage basins were defined based on the 12-digit HUCs collaboratively developed by USGS and NRCS.
Out of the 23 watersheds within the water quality study area, some are partial areas of the selected 12-
digit HUCs. The White Oak Creek (030202011003 — Neuse River Basin) and Little Creek (030202011005 —
Neuse River Basin) 12-digit HUCs were subdivided to provide data for the endangered species analysis
(See Table 3).
4.2.10 Best Management Practice (BMP) Implementation
GWLF-E can include contaminant reductions based on various BMPs including riparian buffers in rural
and urban areas. The model requires inputting the total length of buffered streams in rural areas.
Reduction efficiency coefficients are assigned for each contaminant - nitrogen, phosphorus, and
overland sediment. These coefficients estimate reductions in runoff-bound contaminant levels due to
riparian buffers in rural areas. By accommodating only a single reduction efficiency coefficient per
contaminant in rural areas, GWLF-E, in effect, simulates a single buffer width. In urban areas, the
reduction efficiency coefficient is calculated by the model from the amount of the stream network with
a buffer and a buffer width value for the urban area. The reduction efficiency coefficients applied to the
runoff are hardwired into the model and not available for editing. GWLF-E also does not consider
variable buffer widths within a single watershed.
To calculate the reduction efficiency coefficient in urban areas, GWLF-E requires information about the
amount of the stream network with a riparian buffer and an average buffer width value. This
information was derived by delineating and characterizing buffers throughout the study area based on
the buffer regulations in the various planning jurisdictions in the study area (Wake County, 2016;
Johnston County, 2016; Johnston County Dept. of Utilities, 2008). Using GIS, the stream network
represented by the NHD flowlines was buffered based on the applicable buffer requirements for each
waterbody type and jurisdiction (Table 16). The resulting buffer layer establishes the extent and width of
regulated buffer zones in the study area. Note that the model uses a weighted average buffer for each
watershed; therefore, minor differences in buffer width assumptions do not readily affect the model
resu Its.
27

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 16: Water Quality Study Area Riparian euffer Widths
Jurisdiction
Wake County
Swift Creek Watershed
(Johnston portion)
Neuse River and Cape
Fear River Watershed
Wake County
Wake County
Criterion
Perennial Watercourse
Perennial Watercourse
Perennial and intermittent streams
Non-Perennial/Non-intermittent
Watercourse, 25+acre-stream
drainage area
Non-Perennial/Non-intermittent
Watercourse, 5 to 25 acre — stream
drainage area
Source: Wake County, 2016; Johnston County Dept. of Utilities, 2008
� 1/ � �[�[�1f1.�7'�.Ti%Ti1
Width (feet)1
100
100
50
50
30
Although the GWLF-E model was originally developed for use in ungauged watersheds, calibration is
routinely performed to ensure that hydrology is being simulated accurately. This process minimizes
errors in sediment simulations due to potential errors in hydrology-related parameters. The model's
parameters are assigned based on available soils, land use, and topographic data. During calibration,
adjustments are made to parameters including the recession constant, the monthly evapotranspiration
cover coefficients, and the seepage coefficient.
In order to conduct the hydrology calibration for this analysis, a GWLF-E model was set up for the Swift
Creek watershed for the January 2009 to December 2015 time period. The GWLF-E model-simulated
streamflow was compared to the observed data available for the USGS station 208773375 (Swift Creek
at SR 1555 [Barber Mill Rd.] near Clayton, NC) (USGS, 2016d). Additional information about this gauge
station is available in Table 17. The calibration involved adjusting the model parameters to obtain an
acceptable match between GWLF-E monthly simulated streamflow and the observed monthly
streamflow. Other hydrologic components were calculated including baseflow, seasonal streamflow,
and total annual streamflow.
Simulated and observed monthly flows for the model calibration are compared in Figure S for Model
Run 1 and in Figure 6 for Model Run 2. Figures 7 and 8 show the average simulated and observed
monthly flows aggregated by month for Model Runs 1 and 2, respectively. A visual inspection of the
results indicates that the GWLF-E model was able to adequately predict the observed values. The root
mean square error between simulated and observed monthly values was 1.58 percent for Model Run 1
and 1.45 percent for Model Run 2. In addition, the Nash-Sutcliffe Efficiency (N-S) value was calculated to
be 0.43 for Model Run 1 and 0.52 for Model Run 2. These values suggest that the model was able to
predict the observed values well, as shown in Figures 7 and 8, which compare the average monthly
simulated flow and the average monthly observed flow at the USGS gauge for each month of the year.
N-S values range between one and negative infinity. The closer N-S is to one (exact match), the better
the model fit. An N-S value that is lower than zero indicates that the mean value of the observed time
series is a better predictor than the model. A value of 0.4 or higher for N-S indicates a reasonably well-
28

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
calibrated model for use in predicting annual averages. In particular, the error in the model as calibrated
appears to result primarily from differences in the predicted level of variation, as shown in Figures 5 and
6, but the directional fit is very good, as shown in Figures 5 through 8. In other words, the model tracks
rise and fall based on the precipitation levels well, is not as effective at predicting the precise degree of
highs and lows, and tracks average conditions very well. Since the model is only used to predict
averages, not extremes, this level of calibration appears suitable for use in this study.
Table 17: Information about the Swift Creek Gauge Station near Clayton, NC
Gauge Station
Stream
Location
Observation Record (month/year)
Calibration Period
208773375
Swift Creek
SR 1555 (Barber Mill Rd.) near Clayton, NC
10/2008 - current
2009 - 2015
Figure 5: Comparison of Monthly Simulated and Observed Flow at the Outlet of Swift Creek Watershed
between January 2009 and December 2015 for Model Run 1 Calibration
12
10
s 8
.+
c
0
E
� 6
E
U
3
o q
�
2
0
� Precipitation (cm)
�USGS --GWLF
29

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 6: Comparison of Monthly Simulated and Observed Flow at the Outlet of Swift Creek Watershed
between January 2009 and December 2015 for Model Run 2 Calibration
12.0
10.0
8,0
r
0
E
E 6.0
u
3
0
LL 4,0
2.0
Precipitation�cm) �—USGS —M—GWLF
0,00 ' '•-• `3 . .. •
mmm rnrnrn000000.����.�.�N NNNNNmmmmmmaaaaaa����n�n�n
0 0 0 0 0 o N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
C � � � O. ? C � � � O. ? C � � = O. ? C � � = O. ? C � � � Q ? C � � � Q ? C � � � O. ?
��� ��Z �����Z m����Z m ����Z m����Z m����Z�o����Z
Month-Year
0.00
10,00
20,00
30,00 E
u
c
40,00 y°-,
+�
50.00 •a
v
�
60.00 a
�
c
70,00 °
�
80,00
90,00
100,00
Figure 7: Comparison of Average Monthly Simulated and Average Monthly Observed Flow at the Outlet
of Swift Creek Watershed between January 2009 and December 2015 for Model Run 1 Calibration
5.00
4.50
E 4.00
v
3 3.50
0
� 3.00
oa
� 2.50
v
c�o 2.00
T
� 1.50
c
� 1.00
0.50
0.00
USGS Flow (cm) GWLF Flow (cm)
I I �
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
30

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 8: Comparison of Average Monthly Simulated and Average Monthly Observed Flow at the Outlet
of Swift Creek Watershed between January 2009 and December 2015 for Model Run 2 Calibration
4, 5
E
—"- 3. 5
3
0 3
w
ao
`� 2, 5
v
�
�, Z
L
0 1,5
�
�
�
0.5
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
—115G5 Flow (cm) —GWLF Flow (cm)
5. Results and Discussion
The GWLF-E model was run twice for each of the three Quantitative ICE scenarios — 2010, 2040 No-
Build, and 2040 Build (as explained in the Introduction section of this memo). The input parameters
remained constant for each of the modeled scenarios and, with the exception of impervious surface
coverage, for each model run. Simulations were conducted using data for the period between 2009 and
2015 to establish the 2010 scenario as well to analyze the changes in 2040 No-Build and 2040 Build
scenarios. The results from each model run represent the average condition of the watershed over a
period of time for each scenario. This provides a more accurate representation of overall watershed
conditions than considering only a single year because it includes periods of dry, wet, and medium flow
regimes. The results of the GWLF-E model runs for each scenario are reported in the Tables 21 through
32. In addition, the figures in Appendix A correspond to the annual average of the model results.
Streamflow, runoff, and loading rates of the contaminants (TN, TP, TSS, and copper) vary as land use
patterns change within a study area. In both of the 2040 scenarios, increased impervious surface
coverage, due to additional development relative to the 2010 scenario, resulted in increased runoff.
These results are expected as increased urbanization occurs. Contaminant loads are anticipated to
increase as undeveloped and unmanaged land is converted to residential, commercial, or industrial use.
Nutrient export loads from commercial and industrial parcels are significantly higher than from forest
lands. However, some changes to more urbanized land uses can result in lower contaminant loads. For
example, the conversion of agricultural lands to other land uses may reduce nutrient loads, depending
on the type of development. The change from "undeveloped, but managed" land use categories to
31

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
"developed" land use categories can result in decreased contaminant loads, but increases in runoff,
which can alter in-stream habitat.
The results of the water quality analysis are discussed individually for the three modeled land use
scenarios and for each model run. Tables 21 through 32 compare the streamflow and contaminant loads
among the three scenarios for each model run. Sections 5.1 through 5.4 describe the results in more
detail. Maps of the analysis results are presented in Appendix A.
NOTE: When reviewing the water quality comparison tables or the following summary text, please keep
in mind that the percent change calculated between the 2010 and the 2040 No-euild scenarios and
between the 2010 and the 2040 Build scenarios both use the same denominator (the 2010 scenairo)
while the 2040 euild to 2040 No-Build percentage change uses the 2040 No-euild scenario as the
denominator. Therefore, the 2010 to 2040 No-Build percent change cannot be simply subtracted from
the 2010 to z040 Build percent change to get the z040 Build to 2040 No-Build percent change, as these
ratios have different denominators. In addition, all results are rounded and, as such, may not appear to
add/subtract correctly. For example, 1.4% rounds to 1% while 1.7% rounds to 2% but the difference
between them, 0.3% would be shown as <1.
All watershed models are simplified representations of real world conditions. GWLF-E is one of the
mid-range models widely used for watershed hydrology, sediment, and nutrients. As per the normal
procedure with this model, calibration for hydrology was conducted. In this case, the period from
January 2000 to December 2015 was used, based on regional weather data. Typically, other calibrations
are not required for this type of model, as comparative analyses would have a consistent model error
that is expected to affect the study scenarios equally. The GWLF-E has been widely accepted as an
appropriate tool for watershed-scale assessments and has been used in previous studies for NCDOT
projects.
A key qualification about this water quality analysis is that it was not conducted to predict the specific
amount of contaminants delivered at the outlet of each modeled catchment. Rather, the goal of the
analysis was to determine the magnitude of the change in streamflow and contaminant loading
between the 2040 No-Build and 2040 Build scenarios. This change indicates the trend of water quality
over time in each catchment and in the water quality study area as a whole. In addition, the analysis
only considered riparian buffers as a BMP. No other site-specific BMPs, such as bioretention basins,
stormwater ponds, grass swales, etc., are accounted for in the results. Consequently, both runs of the
watershed model likely over-estimate contaminant loadings from areas with treated stormwater and
can be considered a conservative estimate. In reality, substantial reductions in contaminant loadings
could be attained as future development takes place, if existing BMP regulations are enforced and BMPs
are constructed and properly maintained. This topic is discussed in greater detail in ICE Memo #4.
5.1 2010 Scenario
The 2010 scenario corresponds to the Baseline (2010) land uses within the water quality study area. The
watersheds with the highest streamflow and runoff quantities for both model runs are Lower Crabtree
Creek, Little Creek (Upper), Lake Wheeler-Swift Creek, White Oak Creek (Upper), and Walnut Creek. This
is expected as the percentages of urban land uses are higher in these watersheds than in the others.
Urban land uses account for over 70 percent of the land in the Lower Crabtree and Lake Wheeler-Swift
Creek watersheds. For both model runs, Upper Middle Creek has the highest TSS unit area load
32

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
(sediment loadings in metric tons per acre per year [MT/ac/year]) followed by Lake Wheeler-Swift
Creek. Since the copper load is calculated from the sediment load, these same watersheds have the
highest copper unit area loads as well.
Of the 23 watersheds, the Poplar Creek-Neuse River watershed contributes the largest share of TN
based on either model run and contributes greater than three times more TN than any other modeled
watershed. The Little Creek (Upper) watershed is the second largest contributor in both model runs.
The unit area contribution of TP is higher for Hay/Pasture, Turf/Golf, and Cropland land use categories
than for other uses. The Avents Creek-Cape Fear River, Neills Creek, Little Black Creek-Black Creek, and
Upper Middle Creek watersheds show highest unit area load of TP in the study area for both runs.
5.2 2040 No-Build Scenario
As shown in Tables 21 and 22, the GWLF-E model projected comparable streamflow values for the
watersheds when comparing 2010 and 2040 No-Build scenarios for both model runs. The largest
increase for Model Run 1 was only 13%, and Model Run 2 projected most watersheds would either not
have a streamflow increase or would have a slight streamflow reduction in the 2040 No-Build scenario
as compared to the 2010 scenario.
Runoff from the Marks Creek, Poplar Creek-Neuse River, White Oak Creek (Upper), and White Oak Creek
(Lower) watersheds increased from the 2010 scenario to the 2040 No-Build scenario for both model
runs. These modeled increases are expected as the No-Build Scenario assumes increases in urban land
use and percent impervious in these watersheds relative to the 2010 scenario.
The largest percent increases in the TSS loads and copper loads from the 2010 to the 2040 No-Build
scenarios were projected in the Marks Creek, Poplar Creek-Neuse River, Mahlers Creek-Swift Creek, and
White Oak Creek (Upper) watersheds for both model runs.
Marks Creek, Poplar Creek-Neuse River, Mahlers Creek-Swift Creek, White Oak Creek (Upper), and
Walnut Creek watersheds showed greater increases in TP loads between the 2010 and 2040 No-Build
scenarios than the other watersheds in the study area. The TP loads in these watersheds from the 2010
to 2040 No-Build scenarios increased 48 to 81 percent in Model Run 1 and 35 to 66 percent in Model
Run 2. Upper Middle Creek, Marks Creek, Mahlers Creek-Swift Creek, White Oak Creek (Upper), Lake
Benson-Swift Creek, and Walnut Creek watersheds showed the greatest watershed percent increases
from the 2010 scenario in TN loading with increases of 9 to 23 percent in Model Run 1 and 5 to 12
percent in Model Run 2.
5.3 2040 Build Scenario
The land cover condition captured by the 2040 Build scenario is different from the 2040 No-Build
scenario in that it assumes construction of the project and its anticipated indirect land use effects. The
2040 Build scenario adds approximately 8,000 acres of Medium Density Residential, 730 acres of Low
Density Mixed Urban, and 300 acres of High Density Mixed Urban development. However, this scenario
also includes about 7,700 fewer acres of Low Density Residential Area in the water quality study area as
compared to the 2040 No-Build scenario. The decrease in acres of projected Low Density Residential
land cover results from displacement or replacement by the proposed roadway, commercial or
industrial development near interchanges, or Medium Density Residential development in the 2040
Build scenario.
33

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
The changes in development density, along with the location of those changes, drive the differences in
streamflow, runoff, and contaminant loading in the 2040 Build scenario as compared to the 2040
No-Build scenario. Areas with large increases in the highest density development are projected to
experience the largest increases in streamflow, runoff, and contaminant loading. To some extent, an
increase in the highest density land use is offset by decreases in lower density development. The effect
of runoff on contaminant loading is determined by whether the increase occurred in a rural or urban
portion of the catchment because urban nutrient loads are influenced by the buildup/wash-off
processes and not directly tied to sediment loads.
The watersheds with the highest increase in TSS and copper loading for the 2040 Build scenario
compared to the 2040 No-Build scenario for both model runs are Piney Grove Cemetery-Swift Creek,
Middle Middle Creek, Little Black Creek-Black Creek, and Lower Middle Creek. The highest percent
increase in TN loads for the 2040 Build scenario compared to the 2040 No-Build are the Mahlers Creek-
Swift Creek, White Oak Creek (Upper), and Middle Middle Creek for Model Run 1. The percent change in
TN loads to all watersheds was less than one percent between the 2040 No-Build and 2040 Build
scenarios for Model Run 2. The highest percent increase in TP load for the 2040 Build scenario compared
to the 2040 No-Build scenario in both model runs were projected in Mahlers Creek-Swift Creek and
Middle Middle Creek watersheds.
Overall for the water quality study area, Model Run 1 projects that the streamflow would increase by <1
percent and runoff would increase by 2 percent under the 2040 Build scenario as compared to the 2040
No-Build scenario. Similarly, the TSS, TN, TP, and copper loads would increase by <1 percent. Model Run
2 projects that all parameters would increase by <1 percent for the water quality study area as a whole
(Table 18). With the exception of streamflow and runoff projected in Model Run 1, these increases, as
well as the maximum observed increase between the 2040 Build and 2040 No-Build scenarios, were
observed to be within the standard error of each pollutant as modeled (see Table 19). For Model Run 1,
the maximum change in streamflow and runoff exceeded the standard error. Results within the
standard error cannot be distinguished from a random occurrence.
Table 18: Percent Change from the 2040 No-Build Scenario to the 2040 Build Scenario for the Water
Quality Study Area as a Whole
Modeled Parameter
Streamflow
Runoff
TSS
TN
TP
Copper
Percent Change from 2040 No-Build to 2040
Build
Model Run 1
GWLF-E Defaults
Upper Limit
34
Model Run 2
Observed Baseline
lower Limit
<1
<1
<1
<1
<1
<1 �

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 19: Standard Error of Pollutants as Modeled
Parameter Value
TSS (MT/ac/year)
TN (kg/ac/year)
TP (kg/ac/year)
Streamflow (cm)
Runoff (cm)
Copper (g/yr/ac)
Model
Run 1
0.24
0.34
0.01
0.36
0.55
0.22
Model
Run 2
0.25
0.34
0.01
0.18
0.25
0.23
Maximum Change
(2040 Build — 2040 No-Build)
Model Run 1 Model Run 2
0.17
0.05
0.01
0.72
1.12
0.15
0.14
0.01
<0.01
0.07
0.14
0.12
In the four watersheds of concern for the dwarf wedgemussel, increases from the 2040 No-Build
scenario to 2040 Build scenario are presented in Table 20, including totals for weighted average
increases in these watersheds combined. The weighted average changes are projected to be 1 and less
than one percent for streamflow and 7 and 2 percent for runoff in Model Runs 1 and 2, respectively. For
TSS, TN, and copper loads, the weighted average increases are 2 percent for Model Run 1 and less than
one percent for Model Run 2. Weight average TP loads are projected to be 5 percent for Model Run 1
and 1 percent for Model Run 2. Water quality conditions and results by watershed are discussed in
greater detail in the Indirect and Cumulative Effect discussion of ICE Memo #4. The ICE Memo #4 also
provides more information about the stormwater management regulations that will serve to reduce the
effects of development in these watersheds beyond that reflected in the model results.
Table 20: Percent Change in Modeled Parameters between the 2040 Build and 2040 No-Build Scenarios
in the Lower Swift Creek Watersheds
Watershed
Mahlers Creek-Swift
Creek
Piney Grove Cemetery-
Swift Creek
White Oak Creek
(Lower)
Little Creek (Lower)
Weighted Average
Increase
� Model Run 1
z Model Run 2
Percent Change
Streamflow Runoff TSS TN TP Copper
MR11 MR22 MR1 MR2 MR1 MR2 MR1 MR2 MR1 I MR2 MR1 MR2
2 <1 10 2 2 <1 3 �<1 7 I 2 2 <1
<1 <1 4
<1 <1 2
<1 <1 <1
1 <1 7
35
2 4
1 1
<1 <1
2 2
3 <1 <1 2
<1 <1 I <1 2
<1 <1 <1 1
<1 2 , <1 5
1 4 3
1 1 <1
<1 <1 <1
1 2 <1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
5.4 Results Tables
The water quality analysis results are compared in the series of tables in this section (Tables 21-32). Each
table presents the results of a single experimental parameter for the 23 watersheds composing the
water quality study area. The watersheds of concern for the dwarf wedgemussel are outlined in orange.
The percent difference between the 2040 No-Build and 2040 Build scenario results are reported in the
right-most column of the tables, with the heading "2040 Build — 2040 No-Build". The values in this
column quantify the potential water quality effect of the proposed project as measured by this analysis.
Figures 9 through 14 graphically display the modeling results by watershed against the standard error
(black bar) for each parameter. The change in value of each modeled parameter is displayed in purple
(Model Run 1) or green (Model Run 2). The black standard error bar graphically represents the amount
of change in the value of each modeled parameter that cannot be distinguished from a random
occurrence. The graphics in Appendix A present the level of pollutants for each watershed through the
thematic mapping. The differences between the 2010 and 2040 No-Build scenarios and the 2040 No-
Build and 2040 Build scenarios are presented through labeling.
36

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 21: Comparison of the Upper-Limit Annual Streamflow Results for 2010, 2040 No-Build, and 2040 euild Scenarios Under Model Run 1
Watershed
ID
Name
HUC I 2010 Streamflow (cm/yr)1
1 I White Oak Creek (Lower) 030202011003 25.42
2 Avents Creek-Cape Fear River � 030300040106 � 24.99
3 Hector Creek-Cape Fear River 030300040502 24.24
4 Camp Branch-Black Creek 030202011202 25.02
5 Neills Creek 030300040501 26.55
6 Little Black Creek-Black Creek 030202011201 25.47
7 I Buckhorn Creek 030300040103 25.56
8 Lower Middle Creek 030202010903 25.41
9 Reed Branch-Swift Creek 030202011007 I 26.33
10 Piney Grove Cemetery-Swift Creek 030202011006 24.95
11 Middle Middle Creek 030202010902 26.23
12 White Oak Creek (Cape Fear Basin) 030300040102 26.10
13 Little Creek (Lower) 030202011005 25.09
14 Upper Middle Creek 030202010901 27,27
15 Mahlers Creek-Swift Creek 030202011004 26.15
16 � Lake Benson-Swift Creek 030202011002 27,p2
17 I Lake Wheeler-Swift Creek 030202011001 27,g2
18 Walnut Creek 030202011101 I 27.30
19 Poplar Creek-Neuse River 030202011103 24.86
20 Marks Creek 030202011102 24.30
21 I Lower Crabtree Creek 030202010804 32.11
22 White Oak Creek (Upper) 030202011003 27,49
23 Little Creek (Upper) 030202011005 28,73
1Centimeters of streamflow generated over the catchment area per year
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: �(future scenario - 2010 scenarioJ x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ X 100]/2040 No-Build
2040 No-Build
Streamflow (cm/yr)1 Change2
28.51 3.09
25.14 0.15
24.57 0.33
25.15 0.13
29.20 2.65
27.21 1.74
28.20 2.64
26.13 0.72
27.74 1.41
25.66 0.71
28.03 1.80
27.34 1.24
26.88 1.79
30.15 2.88
28.86 2.71
28.78 1.76
28.66 0.84
30.28 2.98
27.74 2.88
27.12 2.82
32.64 0.53
31.18 3.69
31.03 2.30
37
2040 Build
� % Change3 Streamflow (cm/yr)1 ChangeZ
12 28.67 � 3.25
<1 25.14 0.15
1 24.58 0.34
<1 25.14 0.12
10 29.20 2.65
7 27.36 1.89
10 28.29 2.73
3 26.28 0.87
5 27.81 1.48
3 25.79 0.84
7 28.40 2.17
5 27.35 1.25
7 26.90 1.81
11 30.23 2.96
10 29.58 3.43
7 28.74 1.72
3 28.66 0.84
11 30.30 3.00
12 28.13 3.27
12 27.23 2.93
2 32.64 � 0.53
13 31.53 4.04
8 31.14 2.41
% Change3
13
<1
1
<1
10
7
11
3
6
3
8
5
7
11
13
6
3
11
13
12
2
15
8
2040 Build - 2040 No-Build
% Change'
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
1
<1
<1
<1
2
<1
<1
<1
1
<1
<1
1
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 22: Comparison of Lower-Limit Annual Streamflow Results for 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 2
Watershed Name HUC 2010 Streamflow (cm/yr)1 2040 No-Build 2040 Build 2040 Build - 2040 No-Build
ID Streamflow (cm/yr)1 Change2 % Change3 Streamflow (cm/yr)1 ChangeZ % Change3 % Change
1 White Oak Creek (Lower) 030202011003 2g,18 28.13 -0.05 <1 28.18 0.00 <1 <1
2 Avents Creek-Cape Fear River 030300040106 27.06 � 27.07 � 0.01 � <1 � 27.06 0.00 <1 <1
3 Hector Creek-Cape Fear River 030300040502 26.29 26.29 0.00 <1 26.29 0.00 <1 <1
4 Camp Branch-Black Creek 030202011202 27.07 27.07 0.00 <1 27.07 0.00 <1 <1
5 Neills Creek 030300040501 2g.25 28.25 0.00 <1 28.25 0.00 <1 <1
6 Little Black Creek-Black Creek 030202011201 27,58 27.51 -0.07 <1 27.58 0.00 <1 <1
7 Buckhorn Creek 030300040103 27,g2 27.81 -0.01 <1 27.82 0.00 <1 <1
8 Lower Middle Creek 030202010903 27.40 27.38 -0.02 <1 27.40 0.00 <1 <1
9 Reed Branch-Swift Creek 030202011007 27,g0 27.79 -0.01 <1 27.80 0.00 <1 <1
� 10 Piney Grove Cemetery-Swift Creek 030202011006 _ 27,12 I_ 27.06 I -0.06 I <1 I._ 27.12 _ 0.00 <1 I <1
11 Middle Middle Creek 030202010902 27,90 27.84 -0.06 <1 27.90 0.00 <1 <1
12 White Oak Creek (Cape Fear Basin) 030300040102 27.32 27.32 0.00 <1 27.32 0.00 <1 <1
13 Little Creek (Lower) 030202011005 27.41 27.41 0.00 <1 27.41 0.00 <1 <1
14 Upper Middle Creek 030202010901 28.64 28.62 -0.02 <1 28.64 0.00 <1 <1
15 Mahlers Creek-Swift Creek 030202011004 2g,52 28.46 -0.06 <1 28.52 0.00 <1 <1
16 Lake Benson-Swift Creek 030202011002 28.45 28.46 0.01 <1 28.45 0.00 <1 <1
17 Lake Wheeler-Swift Creek 030202011001 2g.52 28.52 0.00 <1 28.52 0.00 <1 <1
18 Walnut Creek 030202011101 28.65 28.65 0.00 <1 28.65 0.00 <1 <1
19 Poplar Creek-Neuse River 030202011103 27.68 27.67 -0.01 <1 27.68 0.00 <1 <1
20 Marks Creek 030202011102 27.29 27.27 -0.02 <1 27.29 0.00 <1 <1
21 Lower Crabtree Creek 030202010804 29.95 29.94 -0.01 <1 29.95 0.00 <1 <1
22 White Oak Creek (Upper) 030202011003 29,36 29.30 -0.06 <1 29.36 0.00 <1 <1
23 Little Creek (Upper) 030202011005 29.15 29.13 -0.02 <1 29.15 0.00 <1 <1
1Centimeters of streamflow generated over the catchment area per year
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
38

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 9: Change in Streamflow from 2010 to 2040 No-Build Scenarios and 2010 to 2040 euild Scenarios
for Model Runs 1 and 2
Change in Streamflow (cm)
-0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4,00 4.50
White Oak Creek (Lower)
Avents Creek-Cape Fear River
HectorCreek-Cape Fear River
Camp Branch-Black Creek
Neills Creek
Little Black Creek-Black Creek
Buckhorn Creek
Lower Middle Creek
Reed Branch-Swift Creek
Piney Grove Cemetery-Swift Creek
Middle Middle Creek
White Oak Creek [Cape Fear Basin)
Little Creek (Lower)
Upper Middle Creek
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
Lake Wheeler-Swift Creek
Walnut Creek
Poplar Creek-Neuse River
Marks Creek
Lower Crahtree Creek
White Oak Creek (Upper)
Little Creek (Upper)
❑ 2010 to 2040 No-Build (Model Run 1) ■ 2010 to 2040 Build (Model Run 1)
❑ 2010 to 2040 No-Build (Model Run 2) � 2010 to 2040 Build (Model Run 2)
39

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 23: Comparison of Upper-Limit Annual Runoff Results of the 2010, 2040 No-Build, and 2040 Build Scenarios Under Model Run 1
Watershed Name HUC 2010 Runoff � 2040 No-Build � 2040 Build
ID (cm/yr)1 Runoff (cm/yr)1 Change2 % Change3 Runoff (cm/yr)1 ChangeZ % Change3
1 White Oak Creek (Lower) I 030202011003 I 5.99 10.69 4.70 78 10.91 4.92 82
2 Avents Creek-Cape Fear River 030300040106 5.36 5.58 0.22 4 5.58 0.22 4
3 Hector Creek-Cape Fear River 030300040502 4.14 4.70 i 0.56 i 14 i 4.71 i 0.57 i 14
4 Camp Branch-Black Creek 030202011202 5.42 5.62 0.20 4 5.58 0.16 3
5 Neills Creek 030300040501 7.77 11.71 3.94 51 11.72 3.95 51
6 Little Black Creek-Black Creek 030202011201 6.10 8.73 2.63 43 8.97 2.87 47
7 Buckhorn Creek 030300040103 6.23 10.21 3.98 64 10.33 4.10 66
8 Lower Middle Creek 030202010903 6.01 7.10 1.09 18 7.32 1.31 22
� 9 Reed Branch-Swift Creek 030202011007 7.42 � 9.54 � 2.12 � 29 � 9.68 � 2.26 � 30
10 Piney Grove Cemetery-Swift Creek 030202011006 5.28 6.33 1.05 20 6.57 1.29 24
11 Middle Middle Creek 030202010902 I 7.27 9.93 2.66 37 10.47 3.20 44
12 � White Oak Creek (Cape Fear Basin) I 030300040102 7.03 8.93 1.90 27 8.97 1.94 28
13 Little Creek (Lower) 030202011005 I 5.51 I 8.24 I 2.73 I 50 8.25 2.74 I 50
14 � Upper Middle Creek � 030202010901 8.80 13.09 4.29 49 13.21 4.41 50
15 I Mahlers Creek-Swift Creek 030202011004 , 7.11 11.14 4.03 57 12.26 5.15 72
16 Lake Benson-Swift Creek 030202011002 8.41 11.02 2.61 31 10.99 2.58 31
17 Lake Wheeler-Swift Creek 030202011001 9.62 10.84 1.22 13 10.84 1.22 13
18 Walnut Creek 030202011101 8.86 13.32 4.46 50 13.34 4.48 51
19 Poplar Creek-Neuse River 030202011103 5.13 9.49 4.36 85 10.08 4.95 96
20 Marks Creek 030202011102 4.27 8.57 4.30 101 8.71 4.44 104
21 Lower Crabtree Creek 030202010804 16.12 16.88 0.76 5 16.89 0.77 5
22 White Oak Creek (Upper) 030202011003 9.15 14.61 5.46 60 15.15 6.00 66
23 Little Creek (Upper) 030202011005 11.02 14.47 3.45 31 14.61 3.59 33
�Centimeters of runoff generated over the catchment area per year
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
'Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100J/2040 No-Build
40
� 2040 Build - 2040 No-Build
% Change4
2
<1
i <1
<1
<1
3
1
3
� 1 �
4
5
<1
I <1
<1
10

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 24: Comparison of Lower-Limit Annual Runoff Results of the 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 2
Watershed Name HUC 2010 Runoff 2040 No-Build 2040 Build
ID (cm/yr)1 Runoff (cm/yr)1 ChangeZ % Change3 Runoff (cm/yr)1 ChangeZ
1 White Oak Creek (Lower) 030202011003 4.74 6.71 1.97 42 6.81 2.07
2 Avents Creek-Cape Fear River 030300040106 i 5.01 � 5.06 _II 0.05 I <1 � 5.06 � 0.05 �
3 Hector Creek-Cape Fear River 030300040502 3.49 3.75 0.26 -{ 7 3.74 � 0.25
4 Camp Branch-Black Creek 030202011202 4.96 5.05 0.09 2 5.05 0.09
5 Neills Creek 030300040501 5.54 6.90 1.36 25 6.90 1.36
6 Little Black Creek-Black Creek 030202011201 5.02 5.79 0.77 15 5.85 0.83
7 Buckhorn Creek 030300040103 4.56 6.18 1.62 36 6.21 1.65
8 Lower Middle Creek 030202010903 5.14 5.54 0.40 8 5.60 0.46
9 Reed Branch-Swift Creek 030202011007 5.62 6.27 0.65 12 6.27 0.65
� 10 Piney Grove Cemetery-Swift Creek 030202011006 4.63 I 5.02 _ I 0.39 _I 8 I_ 5.13 _ I 0.50 I
11 Middle Middle Creek 030202010902 5.32 6.28 0.96 18 6.37 1.05
12 White Oak Creek (Cape Fear Basin) 030300040102 4.45 5.40 0.95 21 5.43 0.98
13 Little Creek (Lower) 030202011005 4.62 5.58 0.96 21 5.59 0.97
14 Upper Middle Creek 030202010901 5.82 7.48 1.66 29 7.53 1.71
15 Mahlers Creek-Swift Creek 030202011004 5.27 7.20 1.93 37 7.34 2.07
16 Lake Benson-Swift Creek 030202011002 5.71 7.25 � 1.54 27 7.23 � 1.52
17 Lake Wheeler-Swift Creek 030202011001 6.56 7.35 0.79 12 7.36 0.80
18 Walnut Creek 030202011101 5.52 7.56 2.04 37 7.56 2.04
19 Poplar Creek-Neuse River 030202011103 3.82 5.96 2.14 56 5.98 2.16
20 Marks Creek 030202011102 3.38 5.32 1.94 57 5.39 2.01
21 Lower Crabtree Creek 030202010804 9.12 9.64 0.52 6 9.65 0.53
22 White Oak Creek (Upper) 030202011003 5.83 8.59 2.76 47 8.65 2.82
23 Little Creek (Upper) 030202011005 7.00 8.35 1.35 19 8.39 1.39
1Centimeters of runoff generated over the catchment area per year
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
41
% Change3
44
<1
7
2
25
17
36
9
12
11
20
22
21
29
39
27
12
37
57
59
6
48
20
2040 Build - 2040 No-Build
% Change4
1
� <1
<1
<1
<1
1
<1
1
<1
I 2
1
<1
<1
<1
2
<1
<1
<1
<1
1
<1
<1
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 10: Change in Runoff from 2010 to 2040 No-euild Scenarios and 2010 to 2040 euild Scenarios for
Model Runs 1 and 2
Change in Runoff {cmj
-1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
White Oak Creek (Lowerj
Avents Creek-Cape Fear River
Hedor Creek-Cape Fear River
Cam p Branch-Black Creek
Neills Creek
Little Black Creek-Black Creek
Buckhorn Creek
Lower Middle Creek
Reed Bra nch-Swift Creek
Piney Grove Cemetery-Swift Creek
Middle Middle Creek
White Oak Creek (Cape Fear Basin]
Little Creek (Lowerj
Upper Middle Creek
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
Lake Wheeler-Swift Creek
Walnut Creek
Poplar Creek-Neuse River
Marks Creek
Lower Crabtree Creek
White Oak Creek (Upperj
Little Creek (Upperj
�
_�
❑ 2010 to 2040 No-Build (Model Run 1) ■ 2010 to 2040 Bu ild [Model Run 1]
❑ 2010 to 2040 No-Build (Model Run 2) � 2010 to 2040 Bu ild [Model Run 2]
42

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 25: Comparison of Upper Limit Annual Total Suspended Sediment (TSS) Results for 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 1
Watershed Name HUC 2010 TSS � 2040 No-Build �
ID (MT/yr/ac)1 TSS (MT/yr/ac)1 Change2 % Change3 TSS (MT/yr/ac)1
1 White Oak Creek (Lower) 030202011003 0.08 0.11 0.03 38 0.11
2 Avents Creek-Cape Fear River 030300040106 0.15 0.15 0.00 1 0.15
3 Hector Creek-Cape Fear River 030300040502 0.11 0.13 0.02 20 0.13
4 Camp Branch-Black Creek 030202011202 0.16 0.16 0.00 2 0.16
5 Neills Creek 030300040501 0.34 0.57 0.23 67 0.57
6 Little Black Creek-Black Creek 030202011201 0.27 0.43 0.17 62 0.45
7 Buckhorn Creek 030300040103 0.19 0.34 0.15 77 0.35
8 Lower Middle Creek 030202010903 0.33 0.43 0.10 30 0.44
� 9 Reed Branch-Swift Creek 030202011007 0.17 0.23 � 0.06 38 � 0.24 �
10 Piney Grove Cemetery-Swift Creek 030202011006 0.20 0.24 0.04 20 0.24
11 Middle Middle Creek 030202010902 0.32 0.49 0.17 55 0.51
12 � White Oak Creek (Cape Fear Basin) 03030004010�- 0.16 0.26 0.09 56 0.26
13 Little Creek (Lower) 030202011005 � 0.11 I 0.14 I 0.03 I 27 I 0.14 I
14 � Upper Middle Creek 030202010901 0.54 0.88 0.34 63 0.88
15 I Mahlers Creek-Swift Creek 030202011004 0.26 0.50 0.24 94 0.51
16 Lake Benson-Swift Creek 030202011002 0.36 0.54 0.18 50 0.54
17 Lake Wheeler-Swift Creek 030202011001 0.41 0.49 0.08 20 0.49
18 Walnut Creek 030202011101 0.21 0.38 0.17 79 0.38
19 Poplar Creek-Neuse River 030202011103 0.24 0.54 0.30 123 0.54
20 Marks Creek 030202011102 0.07 0.16 0.10 144 0.17
21 Lower Crabtree Creek 030202010804 0.09 0.10 0.01 8 0.10
22 White Oak Creek (Upper) 030202011003 0.19 0.36 0.17 86 0.36
23 Little Creek (Upper) 030202011005 0.22 0.29 0.07 32 0.29
�Metric tons per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
'Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100J/2040 No-Build
43
2040 Build
Change2
0.03
0.00
0.02 �
0.00
0.23
0.18
0.15
0.11
0.07 �
0.05
0.19
0.09
0.03 I
0.34
0.25
0.18
0.08
0.17
0.30
0.10
0.01
0.17
0.07
% Change3
40
1
18
2
67
68
79
34
41
24
60
57
28
63
97
49
20
79
124
150
8
88
33
2040 Build - 2040 No-Build �
% Change°
1
<1
<1
<1
<1
3
1
3
2 �
4
3
<1
<1
<1
2
<1
<1
<1
<1
2
<1
1
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 26: Comparison of Lower Limit Annual Total Suspended Sediment (TSSJ Results for 2010, 2040 No-euild, and 2040 euild Scenarios under Model Run 2
Watershed Name HUC 2010 TSS 2040 No-Build 2040 Build
ID (MT/yr/ac)1 TSS (MT/yr/ac)1 ChangeZ % Change3 TSS (MT/yr/ac)1 ChangeZ
1 White Oak Creek (Lower) 030202011003 0.08 0.10 0.02 26 0.10 0.02
2 Avents Creek-Cape Fear River 030300040106 0.15 I 0.15 � 0.00 �_ <1 � 0.15 � 0.00 �
3 Hector Creek-Cape Fear River 030300040502 0.12 � 0.14 0.02 19 0.14 0.02
4 Camp Branch-Black Creek 030202011202 0.16 0.16 0.00 2 0.16 0.00
5 Neills Creek 030300040501 0.34 0.55 0.21 61 0.55 0.21
6 Little Black Creek-Black Creek 030202011201 0.27 0.43 0.16 58 0.44 0.17
7 Buckhorn Creek 030300040103 0.19 0.33 0.14 71 0.33 0.14
8 Lower Middle Creek 030202010903 0.34 0.44 0.10 29 0.45 0.11
9 Reed Branch-Swift Creek 030202011007 0.17 0.23 0.06 34 0.23 0.06
� 10 Piney Grove Cemetery-Swift Creek 030202011006 _ 0.20 0.24 I. 0.04 �_ 18 _I._ 0.25 _I 0.04 I
11 Middle Middle Creek 030202010902 0.32 0.48 0.16 51 0.49 0.17
12 White Oak Creek (Cape Fear Basin) 030300040102 0.16 0.25 0.09 54 0.25 0.09
13 Little Creek (Lower) 030202011005 0.11 0.13 0.02 21 0.13 0.02
14 Upper Middle Creek 030202010901 0.54 �. 0.84 0.31 57 0.85 0.31
15 Mahlers Creek-Swift Creek 030202011004 0.26 0.49 0.23 88 0.48 0.23
16 Lake Benson-Swift Creek 030202011002 0.36 I 0.53 0.17 � 47 0.53 0.17
17 Lake Wheeler-Swift Creek 030202011001 0.41 0.49 0.08 19 0.49 0.08
18 Walnut Creek 030202011101 0.20 0.35 0.15 72 0.35 0.15
19 Poplar Creek-Neuse River 030202011103 0.25 0.53 0.28 115 0.52 0.28
20 Marks Creek 030202011102 0.07 0.15 0.09 132 0.16 0.09
21 Lower Crabtree Creek 030202010804 0.08 0.09 0.01 8 0.09 0.01
22 White Oak Creek (Upper) 030202011003 0.19 0.34 0.15 78 0.34 0.15
23 Little Creek (Upper) 030202011005 0.21 0.27 0.06 28 0.27 0.06
1Metric tons per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
44
2040 Build - 2040 No-Build
% Change3 % Change'
27 <1
<1 <1
18 <1
2 <1
60 <1
62 3
72 <1
32 3
37 2
22 _. 3
55 3
55 <1
21 <1
57 <1
87 <1
47 <1
19 <1
72 <1
113 <1
137 2
8 <1
79 <1
28 <1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 11: Change in TSS from 2010 to 2040 No-Build Scenarios and 2010 to 2040 euild Scenarios for
Model Runs 1 and 2
-o.os
White Oak Creek (Lower]
A�ents Creek-Cape Fear River
Hedor Creek-Cape Fear River
Camp Branch-BlackCreek
Neills Creek
Little Black Creek-Black Creek
Buckhorn Creek
Lower Middle Creek
Reed Branch-Swift Creek
Piney Grove Cemetery-Swift Creek
Middle Middle Creek
White Oak Creek (Cape Fear Basinj
Little Creek (Lowerj
Upper Middle Creek
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
Lake Wheeler-Swift Creek
Walnut Creek
Poplar Creek-Neuse River
Marks Creek
Change in Annual Total Suspended Sediment Loads (MT/yr/ac)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0.40
Lower Crabtree Creek
WhiteOakCreek(Upperj
Little Creek (Upperj
❑ 2010 to 2040 No-Build (Model Run lj � 2010 to 2040 Bu ild (Model Run 1)
❑ 2010 to 2040 No-Build (Model Run 2j � 2010 to 2040 Bu ild (Model Run 2)
45

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 27: Comparison of Upper Limit Annual Total Nitrogen (TN) Results for 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 1
Watershed I Name I HUC I 2010 TN (kg/yr/ac)1
ID I I I
1 I White Oak Creek (Lower) I 030202011003 I 1.61
2 Avents Creek-Cape Fear River 030300040106 I 2.27
3 Hector Creek-Cape Fear River 030300040502 1.31
4 Camp Branch-Black Creek 030202011202 2.37
5 Neills Creek 030300040501 1.85
6 Little Black Creek-Black Creek 030202011201 1.91
7 I Buckhorn Creek 030300040103 1.56
8 Lower Middle Creek 030202010903 1.87
9 Reed Branch-Swift Creek 030202011007 1.55
10 Piney Grove Cemetery-Swift Creek 030202011006 1.87
11 Middle Middle Creek 030202010902 1.62
12 White Oak Creek (Cape Fear Basin) 030300040102 1.35
13 Little Creek (Lower) 030202011005 1.78
14 I Upper Middle Creek 030202010901 2.41
15 I Mahlers Creek-Swift Creek 030202011004 1.43
16 I Lake Benson-Swift Creek 030202011002 1.48
17 Lake Wheeler-Swift Creek I 030202011001 1.94
18 Walnut Creek 030202011101 1.02
19 Poplar Creek-Neuse River 030202011103 9.15
20 Marks Creek 030202011102 0.86
21 Lower Crabtree Creek 030202010804 1.14
22 White Oak Creek (Upper) 030202011003 1.33
23 Little Creek (Upper) 030202011005 2.86
1Kilograms per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
TN (kg/yr/ac)1
1.72
2.28
1.31
2.37
1.95
1.97
1.65
1.94
1.64
1.91
1.71
1.46
1.81
2.64
1.63
1.61
2.00
1.26
9.42
1.05
1.15
1.54
2.91
2040 No-Build
ChangeZ
0.11
0.01
0.00
0.00
46
0.09
0.07
0.09
0.04
0.10
0.11
0.03
0.23
0.20
0.13
0.05
0.24
0.27
0.19
0.01
0.20
0.05
� % Change3 I
I 7 I
<1
<1
<1
6
3
6
4
6
2
6
8
2
10
14
9
3
23
3
21
1
15
2
TN (kg/yr/ac)1
1.72
2.28
1.32
2.37
1.95
1.97
1.65
1.95
1.65
1.92
1.74
1.46
1.82
2.65
1.68
1.61
2.00
1.26
9.45
1.06
1.15
1.56
2.91
2040 Build
ChangeZ
0.11
0.01
0.01
0.00
0.10
0.06
0.08
0.08
� 0.10
0.04
0.13
0.12
0.03
0.23
I 0.25
0.13
0.05
0.24
0.30
0.19
0.01
0.23
0.05
% Change3
7
<1
<1
<1
6
3
5
4
6
2
8
9
2
10
18
8
3
23
3
22
1
17
2
2040 Build - 2040 No-Build
% Change4
I <1
<1
<1
<1
<1
<1
<1
<1
<1
<1
2
<1
<1
<1
3
<1
<1
<1
<1
<1
<1
2
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 28: Comparison of Lower Limit Annual Total Nitrogen (TN) Results for 2010 Condition, 2040 No-Build, and 2040 Build Scenarios under Model Run 2
Watershed Name HUC 2010 TN (kg/yr/ac)1 2040 No-Build
ID TN (kg/yr/ac)1 ChangeZ % Change3 TN (kg/yr/ac)1
1 White Oak Creek (Lower) 030202011003 1.63 1.61 -0.02 <1 1.61
2 Avents Creek-Cape Fear River 030300040106 2.40 � 2.40 � 0.00 � <1 � 2.40
3 Hector Creek-Cape Fear River 030300040502 1.36 1.35 -0.01 <1 1.36
4 Camp Branch-Black Creek 030202011202 2.47 2.47 0.00 <1 2.47
5 Neills Creek 030300040501 1.88 1.88 0.00 <1 1.88
6 Little Black Creek-Black Creek 030202011201 1.99 1.96 -0.02 <1 1.96
7 Buckhorn Creek 030300040103 1.59 1.58 -0.01 <1 1.57
8 Lower Middle Creek 030202010903 1.92 1.96 0.04 2 1.97
9 Reed Branch-Swift Creek 030202011007 1.56 1.59 0.03 2 1.59
� 10 Piney Grove Cemetery-Swift Creek 030202011006 1.93 _._ 1.93 _I 0.00 I <1 I 1.93
11 Middle Middle Creek 030202010902 1.61 1.63 0.02 1 1.64
12 White Oak Creek (Cape Fear Basin) 030300040102 1.27 1.34 0.07 5 1.34
13 Little Creek (Lower) 030202011005 1.83 1.78 -0.05 <1 1.79
14 Upper Middle Creek 030202010901 2.36 2.48 0.11 5 2.48
15 Mahlers Creek-Swift Creek _ 030202011004 1.41 1.51 0.10 7 1.52
16 Lake Benson-Swift Creek 030202011002 1.43 1.51 0.08 6 � 1.51
17 Lake Wheeler-Swift Creek 030202011001 1.88 1.92 0.04 2 1.92
18 Walnut Creek 030202011101 0.91 1.02 0.11 12 1.02
19 Poplar Creek-Neuse River 030202011103 9.14 9.29 0.15 2 9.29
20 Marks Creek 030202011102 0.87 0.92 0.05 6 0.92
21 Lower Crabtree Creek 030202010804 0.96 0.97 0.01 <1 0.97
22 White Oak Creek (Upper) 030202011003 1.25 1.34 0.08 7 1.34
23 Little Creek (Upper) 030202011005 2.83 2.81 -0.02 <1 2.81
1Kilograms per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenarioJ x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
47
2040 Build
Change2
-0.02
0.00
0.00
0.00
0.00
-0.03
-0.02
0.04
0.03
0.00
0.02
0.07
-0.05
0.12
. 0.10
. 0.08
0.04
0.11
0.15
0.05
0.01
0.09
-0.02
2040 Build - 2040 No-Build
% Change3 % Change4
<1 i <1
<1 <1 i
<1 <1
<1 <1
<1 <1
<1 <1
<1 <1
2 <1
2 <1
_ <1 I <1
2 <1
5 <1
<1 <1
5 <1
7 <1
� 6 <1
2 <1
13 <1
2 <1
6 <1
<1 <1
7 <1
<1 <1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 12: Change in TN from 2010 to 2040 No-Build Scenarios and 2010 to 2040 Build Scenarios for
Model Runs 1 and 2
Change in Total Nitrogen Loads (kg/yr/ac)
-0.40 -0.20 0.00 0.20 0.40 0.60
White Oak Creek (Lower] �
Avents Creek-Cape Fear Ri�er
Hedor Creek-Cape Fear River �
i
Camp Branch-Black Creek
Neills Creek �
Little Black Creek-Black Creek '
�
Buckhorn Creek
�
LowerMiddleCreek � �'
I
Reed Branch-Swift Creek �
Piney Grove Cemetery-Swift Creek �
Middle Middle Creek � '
� �.
� �
White Oak Creek (Cape Fear Basin]
Little Creek (Lowerj
Upper Middle Creek �
Mahlers Creek-Swift Creek ' � i �
� i
Lake Benson-Swift Creek �
Lake Wheeler-Swift Creek
Walnut Creek �
� � .
Poplar Creek-Neuse River � �
�
Marks Creek
�
Lower Crahtree Creek �
WhiteOakCreek(Upper] � '
, �i ,
�
Little Creek (Upperj
❑ 2010 to 2040 No-Build (Model Run 1) ■ 2010 to 2040 Bu ild [Model Run 1)
❑ 2010 to 2040 No-Build (Model Run 2) � 2010 to 2040 Bu ild (Model Run 2)
48

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 29: Comparison of Upper Limit Annual Total Phosphorus (TP) Results for 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 1
Watershed I Name I HUC I 2010 TP (kg/yr/ac)1
ID I I I
1 White Oak Creek (Lower) I 030202011003 0.06
2 Avents Creek-Cape Fear River 030300040106 0.14
3 Hector Creek-Cape Fear River 030300040502 0.06
4 Camp Branch-Black Creek I 030202011202 0.10
5 Neills Creek I 030300040501 0.13
6 Little Black Creek-Black Creek 030202011201 0.13
7 Buckhorn Creek 030300040103 0.09
8 � Lower Middle Creek 030202010903 0.10
9 Reed Branch-Swift Creek 030202011007 I 0.09
10 Piney Grove Cemetery-Swift Creek 030202011006 0.08
11 Middle Middle Creek 030202010902 0.10
12 White Oak Creek (Cape Fear Basin) 030300040102 0.12
13 Little Creek (Lower) 030202011005 0.07
14 Upper Middle Creek 030202010901 0.13
15 Mahlers Creek-Swift Creek 030202011004 0.08
16 Lake Benson-Swift Creek 030202011002 0.09
17 I Lake Wheeler-Swift Creek 030202011001 0.09
18 Walnut Creek 030202011101 0.07
19 Poplar Creek-Neuse River 030202011103 0.07
20 Marks Creek 030202011102 0.04
21 Lower Crabtree Creek I 030202010804 I 0.06
22 White Oak Creek (Upper) 030202011003 0.08
23 Little Creek (Upper) 030202011005 0.10
1Kilograms per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenarioJ x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
TP (kg/yr/ac)1
0.07
0.14
0.06
0.10
0.16
0.15
0.12
0.12
0.10
0.09
0.13
0.14
0.07
0.18
0.12
0.12
0.10
0.11
0.12
0.07
0.07
0.11
0.11
2040 No-Build
Change2
0.01
0.00
0.00
0.00
0.03
0.02
0.02
0.02
0.02
0.01
0.02
0.02
0.00
0.05
0.04
0.03
0.01
0.04
0.05
0.03
0.00
0.04
0.01
49
% Change3
25
<1
2
<1
24
14
23
16
20
9
23
17
5
42
54
30
13
58
81
69
3
48
12
TP (kg/yr/ac)1
0.07
0.14
0.06
0.10
0.16
0.15
0.12
0.12
0.10
0.09
0.13
0.14
0.07
0.18
0.13
0.12
0.10
0.11
0.13
0.07
0.07
0.12
0.11
2040 Build
Change2
0.02
0.00
0.00
0.00
0.03
0.02
0.02
0.02
0.02
0.01
0.03
0.02
0.00
0.05
0.05
0.03
0.01
0.04
0.06
0.03
0.00
0.04
0.01
% Change3
27
<1
4
<1
23
15
23
19
21
11
28
17
7
43
65
30
13
59
88
73
4
54
13
2040 Build - 2040 No-Build
� % Change'
2
<1
2
<1
<1
1
<1
2
1
2
4
<1
1
<1
7
<1
<1
<1
4
2
<1
4
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 30: Comparison of Lower Limit Annual Total Phosphorus (TPJ Results for 2010, 2040 No-Build, and 2040 euild Scenarios under Model Run 2
Watershed Name HUC 2010 TP (kg/yr/ac)1 2040 No-Build 2040 Build 2040 Build - 2040 No-Build
ID TP (kg/yr/ac)1 Change2 % Change3 TP (kg/yr/ac)1 Change2 % Change3 % Change'
1 White Oak Creek (Lower) 030202011003 0.05 0.05 0.00 <1 0.05 0.00 <1 1
2 Avents Creek-Cape Fear River 030300040106 0.14 0.14 � 0.00 I <1 � 0.14 � 0.00 <1 I <1 i
3 Hector Creek-Cape Fear River 030300040502 0.06 0.06 0.00 I <1 0.06 0.00 <1 2
4 Camp Branch-Black Creek 030202011202 0.10 0.10 0.00 <1 0.10 0.00 <1 <1
5 Neills Creek 030300040501 0.12 0.14 0.02 13 0.14 0.02 12 <1
6 Little Black Creek-Black Creek 030202011201 0.12 0.13 0.01 5 0.13 0.01 5 <1
7 Buckhorn Creek 030300040103 0.09 0.10 0.01 9 0.09 0.01 8 <1
8 Lower Middle Creek 030202010903 0.10 0.11 0.01 13 0.12 0.01 14 2
9 Reed Branch-Swift Creek 030202011007 0.08 0.09 0.01 11 0.09 0.01 11 <1
� 10 Piney Grove Cemetery-Swift Creek 030202011006 0.08 I_ 0.08 _I_ 0.00 I._ 4 _I._ 0.08 I. 0.00 I 5 � 1 �
11 Middle Middle Creek 030202010902 0.09 0.11 0.01 14 0.11 0.02 17 2
12 White Oak Creek (Cape Fear Basin) 030300040102 0.11 0.12 0.01 14 0.12 0.01 14 <1
13 Little Creek (Lower) 030202011005 0.06 0.06 -0.01 <1 0.06 -0.01 <1 <1
14 Upper Middle Creek 030202010901 0.11 0.15 0.04 32 0.15 0.04 33 <1
15 Mahlers Creek-Swift Creek 030202011004 0.07 0.10 0.03 42 0.10 0.03 44 2
16 Lake Benson-Swift Creek 030202011002 0.08 0.10 0.02 28 0.10 0.02 27 � <1
17 Lake Wheeler-Swift Creek 030202011001 0.08 0.09 0.01 12 0.09 0.01 13 <1
18 Walnut Creek 030202011101 0.05 0.08 0.03 48 0.08 0.03 48 <1
19 Poplar Creek-Neuse River 030202011103 0.06 0.10 0.04 66 0.10 0.04 66 <1
20 Marks Creek 030202011102 0.04 0.05 0.01 36 0.05 0.01 38 2
21 Lower Crabtree Creek 030202010804 0.04 0.04 0.00 4 0.04 0.00 4 <1
22 White Oak Creek (Upper) 030202011003 0.06 0.08 0.02 35 0.08 0.02 37 1
23 Little Creel< (Upper) 030202011005 0.08 0.08 0.00 2 0.08 0.00 3 <1
1Kilograms per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenarioJ x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
50

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 13: Change in TP from 2010 to 2040 No-Build Scenarios and 2010 to 2040 euild Scenarios for
Model Runs 1 and 2
Change in Total Phosphorus Loads {kg/yr/acj
-0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
White Oak Creek (Lower)
�F �
Avents Creek-Cape FearRi�er �� I
HectorCreek-Cape Fear Ri�er � �
� ��
� ��
Camp Branch-Black Creek ��
Neills Creek
Little Black Creek-Black Creek
Buckhorn Creek
Lower Middle Creek
Reed Branch-Swift Creek
Piney Grove Cemetery-Swift Creek
Middle Middle Creek
White Oak Creek (Cape Fear Basin)
Little Creek (Lower)
Upper Middle Creek
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
Lake Wheeler-Swift Creek
Walnut Creek
Poplar Creek-N euse River
Marks Creek
Lower Cra btree Creek
White Oak Creek (Upper)
Little Creek (Upper)
❑ 2010 to 2040 No-Build (Model Run 1) � 2010 to 2040 Build (Model Run 1)
❑ 2010 to 2040 No-Build (Model Run 2) � 2010 to 2040 Build (Model Run 2)
51

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 31: Comparison of Upper Limit Annual Copper (CuJ Results for 2010 Condition, 2040 No-Build, and 2040 Build Scenarios under Model Run 1
Watershed I Name I HUC I 2010 Cu
ID I I I (g/Yr/ac) �
1 I White Oak Creek (Lower) I 030202011003 I 0.70
2 � Avents Creek-Cape Fear River � 030300040106 1.09
3 Hector Creek-Cape Fear River 030300040502 I 0.82
4 Camp Branch-Black Creek 030202011202 1.09
5 Neills Creek 030300040501 3.05
6 Little Black Creek-Black Creek 030202011201 2.36
7 Buckhorn Creek � 030300040103 I 1.71
8 Lower Middle Creek 030202010903 2.26
9 Reed Branch-Swift Creek 030202011007 1.17
10 Piney Grove Cemetery-Swift Creek 030202011006 1.36
11 Middle Middle Creek 030202010902 2.80
12 White Oak Creek (Cape Fear Basin) 030300040102 1.45
13 Little Creek (Lower) 030202011005 0.74
14 Upper Middle Creek 030202010901 4.79
15 Mahlers Creek-Swift Creek I 030202011004 � 2.27
16 Lake Benson-Swift Creek � 030202011002 I 3.22
17 Lake Wheeler-Swift Creek 030202011001 3.66
18 Walnut Creek I 030202011101 1.87
19 Poplar Creek-Neuse River 030202011103 2.14
20 I Marks Creek 030202011102 0.60
21 � Lower Crabtree Creek 030202010804 0.82
22 White Oak Creek (Upper) 030202011003 1.72
23 Little Creek (Upper) 030202011005 1.96
1Grams per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: �(future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
I �u (g/Yr/ac)�
0.96
1.10
0.98
1.12
5.10
3.84
3.03
2.95
I 1.61
1.63
4.34
2.26
0.94
7.81
4.41
4.81
4.37
3.34
4.77
1.46
0.89
3.19
2.59
2040 No-Build
ChangeZ
0.27
0.01
0.16
0.02
52
2.05
1.47
1.32
0.69
0.44
0.27
1.54
0.82
0.20
3.01
2.14
1.59
0.72
1.47
2.63
0.86
0.07
1.47
0.63
% Change3
38
1
20
2
67
62
77
30
38
20
55
56
27
63
94
50
20
79
123
144
8
86
32
Cu (g/yr/ac)1 I
0.97
1.11 �
0.97
1.11
5.08
3.97
3.06
3.04
1.65
1.69
4.49
2.27
0.94
7.83
4.48
4.80
4.38
3.35
4.79
1.50
0.89
3.24
2.60
2040 Build
Change2
0.28
0.01
0.15
0.02
2.03
1.35
0.78
0.48
0.33
1.68
0.83
0.20
3.04
2.21
1.58
0.72
1.48
2.65
0.90
0.07
1.52
0.64
% Change3
40
1
18
- 2 -
67
68
79
34
41
24
60
57
28
63
97
49
20
79
124
150
8
88
33
2040 Build - 2040 No-Build
% Change4
1
<1
<1
<1
1
3
2
4
3
<1
<1
<1
2
<1
<1
<1
<1
2
<1
1
<1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Table 32: Comparison of Lower Limit Annual Copper (CuJ Results for 2010, 2040 No-Build, and 2040 Build Scenarios under Model Run 2
Watershed Name HUC 2010 Cu 2040 No-Build 2040 Build
ID (g/yr/ac)1 Cu (g/yr/ac)1 ChangeZ % Change3 Cu (g/yr/ac)1 Change2
1 White Oak Creek (Lower) 030202011003 0.69 0.86 0.18 26 0.87 0.18
2 Avents Creek-Cape Fear River 030300040106 1.10 II 1.11 � 0.01 <1 � 1.11 0.01
3 Hector Creek-Cape Fear River 030300040502 0.84 1.00 0.16 19 0.98 0.15
4 Camp Branch-Black Creek 030202011202 1.12 1.14 0.02 2 1.14 0.02
5 Neills Creek 030300040501 3.06 4.92 1.86 61 4.90 1.84
6 Little Black Creek-Black Creek 030202011201 2.41 3.79 1.38 58 3.91 1.51
7 Buckhorn Creek 030300040103 1.71 2.92 1.21 71 2.95 1.24
8 Lower Middle Creek 030202010903 2.34 3.02 0.68 29 3.09 0.75
9 Reed Branch-Swift Creek 030202011007 1.17 1.56 0.39 34 1.60 0.43
� 10 Piney Grove Cemetery-Swift Creek 030202011006 _ 1.40 1.66 I, 0.25 I_ 18 I.. 1J1 0.31
11 Middle Middle Creek 030202010902 2.82 4.24 1.43 51 4.35 1.54
12 White Oak Creek (Cape Fear Basin) 030300040102 1.44 2.21 0.78 54 2.22 0.78
13 Little Creek (Lower) 030202011005 0.74 0.89 0.15 21 0.89 0.16
14 Upper Middle Creek 030202010901 _ 4.78 �_ 7.49 2.71 57 7.51 2.72
15 Mahlers Creek-Swift Creek 030202011004 2.29 4.31 2.01 88 4.29 2.00
16 Lake Benson-Swift Creek 030202011002 3.21 I 4.74 1.52 47 4J3 1.51
17 Lake Wheeler-Swift Creek 030202011001 3.65 4.34 0.69 19 4.35 0.70
18 Walnut Creek 030202011101 1.81 3.11 1.30 72 3.12 1.31
19 Poplar Creek-Neuse River 030202011103 2.18 4.69 2.51 115 4.65 2.47
20 Marks Creek 030202011102 0.59 1.36 0.78 132 1.39 0.81
21 Lower Crabtree Creek 030202010804 0.72 0.78 0.06 8 0.77 0.06
22 White Oak Creek (Upper) 030202011003 1.68 2.98 1.31 78 2.99 1.32
23 Little Creek (Upper) 030202011005 1.89 2.42 0.53 28 2.43 0.53
1Grams per year per acre
ZDifference between future scenario and 2010: future scenario - 2010 scenario
3Percent difference between future scenario and 2010 scenario: ((future scenario - 2010 scenario) x 100]/2010 scenario
4Percent difference between 2040 Build and 2040 No-Build: ((2040 Build - 2040 No-BuildJ x 100]/2040 No-Build
53
2040 Build - 2040 No-Build
% Change3 % Change4
27 i <1
<1 <1
18 <1
2 <1
60 <1
62 3
72 <1
32 3
37 2
_ 22 I 3
55 3
55 <1
21 <1
,_ 57 <1
87 <1
47 <1
19 <1
72 <1
113 <1
137 2
8 <1
79 <1
28 <1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Figure 14: Change in Copper from 2010 to 2040 No-Build Scenarios and 2010 to 2040 euild Scenarios for
Model Runs 1 and 2
Change in Total Copper Loads (g/yr/acj
-0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50
White Oak Creek (Lower]
Avents Creek-Cape Fear River
Hedor Creek-Cape Fear River
Camp Branch-Black Creek
Neills Creek
Little Black Creek-Black Creek
Buckhorn Creek
Lower Middle Creek
Reed Branch-Swift Creek
Piney Grove Cemetery-Swift Creek
Middle Middle Creek
White Oak Creek (Cape Fear Basinj
Little Creek (Lowerj
Upper Middle Creek
Mahlers Creek-Swift Creek
Lake Benson-Swift Creek
Lake Wheeler-Swift Creek
Walnut Creek
Poplar Creek-Neuse River
Marks Creek
Lower Crabtree Creek
WhiteOakCreek(Upperj
Little Creek (Upperj
❑ 2010 to 2040 No-Build (Model Run 1j � 2010 to 2040 Bu ild (Model Run 1)
❑ 2010 to 2040 No-Build (Model Run 2] 0 2010 to 2040 Bu ild (Model Run 2)
54

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
6. Conclusions
The water quality analysis was performed by constructing watershed models for portions of twenty-one
12-digit HUCs within the water quality study area, using the MapShed/GWLF-E modeling tool (note - two
of the 12-digit HUCs were subdivided to provide data for the endangered species analysis). Model
estimates of annual streamflow, runoff, and annual overland contaminant loadings of TN, TP, TSS, and
copper loads produced from the three land use scenarios — 2010, 2040 No-Build, and 2040 Build were
reviewed and compared to assess the project effects. Differences in streamflow and contaminant
loadings exhibited between the 2040 scenarios would be attributable to the proposed project.
Impervious surface estimations were also derived from the land use analysis. The majority of the total
changes in impervious surface in the water quality study area from 2010 to 2040 are projected to occur
for either the 2040 No-Build scenario or the 2040 Build scenario. The changes in impervious surface
coverage from the 2040 No-Build scenario to the 2040 Build Scenario range from less than one percent
to six percent, with an overall average of one percent or less. The largest changes occur in the Mahlers
Creek-Swift Creek, White Oak (Upper), Poplar Creek-Neuse River, and Middle Middle Creek watersheds
under the more conservative model run.
Overall for the water quality study area, Model Run 1 projects that the streamflow would increase by <1
percent and runoff would increase by 2 percent under the 2040 Build scenario as compared to the 2040
No-Build scenario. Similarly, the TSS, TN, TP, and copper loads would increase <1 percent, <1 percent, 1
percent, and <1 percent, respectively. For Model Run 1, the maximum change in streamflow and runoff
exceeded the standard error (See Table 19).
Model Run 2 projects the following for the water quality study area as a whole: the streamflow would
increase by <1 percent and runoff would increase by <1 percent under the 2040 Build scenario as
compared to the 2040 No-Build scenario; similarly, the TSS, TN, TP, and copper loads would each
increase by <1 percent. These increases, as well as the maximum observed increase between the 2040
Build and 2040 No-Build scenarios, were observed to be within the standard error of each pollutant as
modeled (see Table 19).
Table 20 shows the weighted average changes are projected to be 1 and less than one percent for
streamflow and 7 and 2 percent for runoff in Model Runs 1 and 2, respectively. For TSS, TN, and copper
loads, the weighted average increases are 2 percent for Model Run 1 and less than one percent for
Model Run 2. Weight average TP loads are projected to be 5 percent for Model Run 1 and 1 percent for
Model Run 2. Water quality conditions and results by watershed are discussed in greater detail in the
Cumulative Effects discussion of ICE Memo #4.
A key qualification about this water quality analysis is that it only considered riparian buffers as a BMP.
No other site-specific BMPs, such as bioretention basins, stormwater ponds, grass swales, etc., are
accounted for in the results. Consequently, the watershed model likely over-estimates contaminant
loadings from areas with treated stormwater. In reality, substantial reductions in contaminant loadings
could be attained as future development takes place, if existing BMP regulations are enforced and BMPs
are constructed and properly maintained. This topic is discussed in greater detail in ICE Memo #4.
55

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
7. References
ASCE Task Committee on Definition of Criteria for Evaluation of Watershed Models of the Watershed
Management Committee, Irrigation and Drainage Division. 1993. Criteria for evaluation of
watershed models. lournal of Irrigation and Drainage Engineering 119(3).
Evans, B.M., D.W. Lehning, K.J. Corradini, G.W. Petersen, E. Nizeyimana, J.M. Hamlett, P.D. Robillard,
and R.L. Day. 2002. A comprehensive GIS-based modeling approach for predicting nutrient loads
in watersheds. Journal of Spatial Hydrology 2(2).
Evans, B.M., and K.J. Corradini. 2012. MapShed, Version 1.1: Users Guide. Pennsylvania State University,
Penn State Institutes of Energy and the Environment, University Park, PA.
Haith, D.A. 1993. RUNQUAL: Runoff Quality from Development Sites: Users Manual. Cornell University,
Department of Agricultural and Biological Engineering, Ithaca, NY.
Haith, D.A., and L.L. Shoemaker. 1987. Generalized watershed loading functions for stream flow
nutrients. Water Resources Bulletin 23(3):471-478.
Haith, D.A., R. Mandel, and R.S. Wu. 1992. GWLF: Generalized Watershed Loading Functions User's
Manual. Version 2.0. Cornell University, Department of Agricultural and Biological Engineering,
Ithaca, NY.
Harned, D.A. 1980. Water Quality of the Neuse River, North Carolina — Variability, Pollution Loads, and
Long-Term Trends. WRI 80-36. Raleigh, NC.
HealthGrove. 2016. Research Environmental Health Statistics. Online information. Available at:
http://environmental-health.healthgrove.com/ (Accessed December 2016).
Huber, W.C., and R.E. Dickinson. 1988. Storm Water Management Model, Version 4: User's Manual.
EPA/600/3-88-001a. U.S. Environmental Protection Agency, Athens, GA.
H.W. Lochner, Inc. 2014. Indirect and Cumulative Effects Report. STIP No: R-2721, R-2828, and R-2829.
Prepared for NCDOT, Raleigh, NC.
H.W. Lochner, Inc. 2015. Draft EnvironmentallmpactStatement-Complete 540 Triangle Expressway
Southeast Extension. STIP No: R-2721, R-2828, and R-2829. FHWA-EIS-15-02-D. Prepared for
NCDOT, Raleigh, NC.
Jacobson, P.J., J.L. Farris, D.S. Cherry, and R.J. Neves. 1993. Juvenile freshwater mussel
(Bivalvia:Unionidae) responses to acute toxicity testing with copper. Environmental Toxicology
and Chemistry 12(5):879-833.
Jacobson, P.J., R.J. Neves, D.S. Cherry, and J.L. Farris. 1997. Sensitivity of glochidial stages of freshwater
mussels (Bivalvia: Unionidae) to copper. Environmental Toxicology and Chemistry 16(11):2384—
2392.
Johnston County. 2016. Neuse River Regulations. Online information. Available at:
https://www.johnstonnc.com/mainpage.cfm?category_level_id=718&content_id=1111
(Accessed October 2016).
Johnston County Department of Utilities. 2008. lohnston County Stormwater Design Manual. Smithfield,
NC.
56

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
KDHE (Kansas Department of Health and Environment). 2006. Neosho Basin Total Maximum Daily Load,
Water Body/Assessment Unit: Eagle Creek, Water Quality Impairment: Copper. Topeka, KS.
MapTech, Inc. 2004. Fecal Bacteria and General Standard Total Maximum Daily Load Development for
Peak Creek. Prepared for Virginia Department of Environmental Quality, Richmond, VA.
Michael Baker Engineering. 2017a. Memorandum on Local Jurisdiction Outreach and Methodology
Updates (Quantitative ICEAssessment Memo #1). Prepared for NCDOT, Raleigh, NC.
Michael Baker Engineering. 2017b. Memorandum on Land Use Scenario Methodology and Results
(Quantitative ICEAssessment Memo #2). Prepared for NCDOT, Raleigh, NC.
Michael Baker Engineering. 2017c. Memorandum on Indirect and Cumulative Effects (Quantitative ICE
Assessment Memo #4J. Prepared for NCDOT, Raleigh, NC.
Milam, C.D., J.L. Farris, F.J. Dwyer, and D.K. Hardesty. 2005. Acute toxicity of six freshwater mussel
species (glochidia) to six chemicals: Implications for daphnids and Utterbackia imbecillis as
surrogates for protection of freshwater mussels (Unionidae). Archives of Environmental
Contamination and Toxicology 48(2):166-173.
Nash, J.E., and J.V. Sutcliffe. 1970. River flow forecasting through conceptual models: Part 1— A
discussion of principles. Journal of Hydrology 10(3): 282-290.
NC WRC (Wildlife Resources Commission). 2015. 2015 North Carolina Wildlife Action Plan. Raleigh, NC.
NOAA (National Oceanic and Atmospheric Administration). 2016. National Climate Data Center. Online
information. Available at: http://www.ncdc.noaa.gov/oa/climate/stationlocator.html (Accessed
October 2016).
NRCS (Natural Resource Conservation Service). 2016. Web SoilSurvey. Online information. Available at:
https://websoilsurvey.sc.egov.usda.gov/App/HomePa�e.htm (Accessed October 2016).
USACE (U.S. Army Corps of Engineers). 1977. Generalized Computer Program 723-58-L7520: Storage,
Treatment, Overflow, Runoff Model 'STORM' Users Manual. Hydrologic Engineering Center,
Davis, CA.
U.S. Climate Data. 2017. U.S. Climate Data: Temperature — Precipitation — Sunshine — Snowfall: Raleigh,
North Carolina. Online information. Available at:
http://www.usclimatedata.com/climate/raleigh/north-carolina/united-states/usnc0558
(Accessed February 2017)
USEPA (U.S. Environmental Protection Agency). 2017. Discharge Monitoring Report (DMR) Pollutant
Loading Tool. Online information. Available at: https://cfpub.epa.gov/dmr/adv_search.cfm
(Accessed January 2017).
U.S. Soil Conservation Service. 1986. Urban Hydrology forSmall Watersheds. Technical Release No. 55
(2nd edition). U.S. Department of Agriculture, Washington, DC.
USGS (U.S. Geological Survey). 2016a. National Hydrography Dataset Viewer. Online information.
Available at: https://viewer.nationalmap.gov/basic/ (Accessed March 2016).
USGS (U.S. Geological Survey). 2016b. The National Map — Elevation. Online information. Available at:
https://nationalmap.�ov/elevation.html (Accessed February 2016).
57

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
USGS (U.S. Geological Survey). 2016c. National Water Information System: Help System. Online
information. Available at: https://help.waterdata.us�s.�ov/faq/about-tab-delimited-output
(Accessed February 2016).
USGS (U.S. Geological Survey). 2016d. National Water Information System: Web Interface. Online
information. Available at:
https://waterdata.us�s.�ov/nwis/uv/?site no=0208773375&a�ency cd=USGS (Accessed
February 2016).
Wake County. 1990. Swift Creek Land Management Plan. Raleigh, NC.
Wake County. 2016. Wake County WaterSupply Watershed euffers. Online information. Available at:
http://www.wakegov.com/planning/maps/Documents/watershedregulations.pdf (Accessed
October 2016)
Wang, N., C.G. Ingersoll, I.E. Greer, D.K. Hardesty, C.D. Ivey, J.L. Kunz, W.G. Brumbaugh, F.J. Dwyer, A.D.
Robers, T. Augspurger, C.M. Kane, R.J. Neves, and M.C. Barnhart. 2007a. Assessing contaminant
sensitivity of early life stages of freshwater mussels (Unionidae): Acute toxicity testing of copper,
ammonia, and chlorine to glochidia and juveniles of freshwater mussels (Unionidae).
Environmental Toxicology and Chemistry 26(10):2036-2047.
Wang, N., C.G. Ingersoll, I.E. Greer, D.K. Hardesty, C.D. Ivey, J.L. Kunz, W.G. Brumbaugh, F.J. Dwyer, A.D.
Robers, T. Augspurger, C.M. Kane, R.J. Neves, and M.C. Barnhart. 2007b. Assessing contaminant
sensitivity of early life stages of freshwater mussels (Unionidae): Chronic toxicity testing of
copper and ammonia to juvenile freshwater mussels (Unionidae). Environmental Toxicology and
Chemistry 26(10):2048-2056.
58

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Appendix A: Maps
A-1

Complete 540
Z�Iater Quality
Study Area
Catchments &
�Xlater Resources
Legend
� FLUSA Boundary
�— i
� ;`,-� Counties
� River Basin
�� Major Highways
.�
�`�r � Proposed 540
Streams
N
W�E
S
0 3 6
Miles
I N T E R N AT I 0 N A L

Complete 540 Water Quality
Percent Impervious for Three Modeled Scenarios
2010 (Model Run 1)
2010 (Model Run 2)
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
2040 Build (Model Run 1)
Percent Change - From 2040 No-Build to 2040 Build
2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build
N
W E
S
5 0
Miles
Percent Impervious
(Model Run 1)
�4.03%-9.83%
�9.84%-1585%
� 15.86% -24.99%
-25%-31.25%
- 31.26% -40.49%
Legend
��� � Proposed 540
�River Basin
Boundary
Percent Impervious
(Model Run 2)
�4.03%-9.83%
a9.84%-15.85%
ai5.86, _ 24.99,
-25%-31.25%
- 31.26% -40.49%
I N T E R H AT I 0 H A L

Complete 540 Water Quality
Streamflow for Three Modeled Scenarios
2010 (Model Run 1)
2010 (Model Run 2)
I
� i
��
Cape Fear
River Basin
N eu se
River Basin
B
�
�
_ �
��
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
5
<� °io .
<1%
�
�1% <1%
'��� y� �' �
� <1 % <1 %
l y,. <1%
\ _�—
�� �� _' <, �ro
�� �
<1 "/o `
Cape Fear `�-�, _�'�
River Basin
N eu se
� � River Basin
<� °io
�
� ,
��
�
�� <1 % �... .
f
���
<1% <�%
<1 % �
_�a�`sil`.�! ��� <1%
<1 % <1 %
�
<1 %
<�%
�'<1% -_ _.
_: �._
2040 Build (Model Run 1) 2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build Percent Change - From 2040 No-Build to 2040 Build
� �.<1%��. � '<1%'
��
� <1 % -
�
Z \�� �io
I
<� �/ �
�
� <1 %
Cape Fear �_,
River Basin
N
W E
S
0
�
Miles
5
<1%
� Neuse
<i^�o River Basin
Streamflow (cm)
(Model Run 1)
� 24.24 - 25.47
� 25.48 - 26.55
� 26.56-27.52
� 27.83 - 29.58
� 29.59-32.64
�
�
<1% <1%
<1 % � <1 %
,
<1%
�
i
0
�� a�r � <1 /o
� <1% '
Cape Fear �-_,_i�
River Basin
Legend Streamflow (cm)
(Model Run 2)
�6� � Proposed 540 � z4za-25.4�
� 25.48-26.55
�River Basin � z6.56- 27.82
Boundary
- 27.83-29.58
- 29.59 - 32.64
<1 °/a
<1 %
N eu se
�l� ���o River Basin
{� " ' -
� '
�� <
�� <� io
f
<1 %� <'� %
<1 % ,_.. <1 %
<1 %
<1%
�j
<1 %
�1% - ` - „
I N T E R H AT I 0 H A L

Complete 540 Water Quality
Runoff for Three Modeled Scenarios
2010 (Model Run 1)
2010 (Model Run 2)
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
2040 Build (Model Run 1)
Percent Change - From 2040 No-Build to 2040 Build
2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build
N
W E
S
5 0
Miles
Runoff (cm)
(Model Run 1)
� 3.74 - 6.10
� 6.11 - 7.77
� 7.75 - 9.93
� 9.94 - 12.26
� 1227- 16.89
Legend
�6� � Proposed 540
�River Basin
Boundary
Runoff (cm)
(Model Run 2)
� 3.74 - 6.10
� 6.11 - 7.77
� 7.78 - 9.93
- 9.94 - 12.26
- 12.27- 16.89
I N T E R H AT I 0 H A L

Complete 540 Water Quality
Annual Total Suspended Sediment (TSS) Loads for Three Modeled Scenarios
2010 (Model Run 1)
Cape Fear
River Basin
2010 (Model Run 2)
N eu se
River Basin
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
N eu se
�32°�o River Basin
$ o/ � u �
Cape Fear
River Basin
_���'-�`�, sa%
y �E�-
� o/ `�-��! ��
19%
58%
'� ._�„�-,
2%
��
��' 115%; .
aa�io 2a°io
2 s ia z ��io I�
�e
,8�,0 � � �,
34%
2040 Build (Model Run 1) 2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build Percent Change - From 2040 No-Build to 2040 Build
N eu se
�, River Basin
5
N
W E
s
0
�
Miles
5
TSS Loads (MT/yr/ac)
(Model Run 1)
O 0.07 - 0.14
O 0.15 - 0.21
� 0.22 - 0.32
- 0.33 - 0.45
� 0.46 - 0.88
<1% �`,:., <1%
<1 %
�,
<1 °/', <1 °i
� 3°/a! ..,� 2%
<1%
Cape Fear
River Basin
Legend TSS Loads (MT/yr/ac)
(Model Run 2)
�6� � Proposed 540 � 0.07 -o.t47
O 0.15 - 0.21
�River Basin � o.zz - o.3z
Boundary
- 0.33 - 0.45
- 0.46 - 0.88
3 °/a;,
<1 %
I N T E R H AT I 0 H A L

Complete 540 Water Quality
Total Nitrogen (TN) Loads for Three Modeled Scenarios
2010 (Model Run 1) 2010 (Model Run 2)
N eu se
River Basin
_`�. �
e ' . �� ( �
w
�`���
ie
r" � _.
;.l � � -v _ � -- _. ''�, .� - �t�..•�,%` `_'��f' �``� `�rF
s�'r'_
� ��,,
Cape Fear Cape Fear
River Basin River Basin
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
N eu se N eu se
21°io River Basin sa�o River Basin
1% t <1%--. „ 'u
l� SI
��
8%
�" 6%
,� f
<1 %
� �x4
<1%
Cape Fear �
River Basin
rJ%
<1
2% 6%
�y��'�-�`� _,
�6Sp�_
��
5%
�
� ti
� - ._
1%
� ��
12% �. !� 2�/
<1%
�
�1 a�o �-'-� <1 % �.
� <� % ' , _-`I - e. _.
� �_i
Cape Fear `-_�, �'�
River Basin
2040 Build (Model Run 1) 2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build Percent Change - From 2040 No-Build to 2040 Build
N eu se
����o River Basin
5
N
W E
s
0
I
Miles
5
TN Loads (kg/yr/ac)
(Model Run 1)
O 0.86 - 1.35
O 1.36 - 1.74
� 1.75 - 2.00
- 2.01 - 2.91
- 2.92 - 9.45
<1 %
<1
<1
��� <1 % � <1 %
} _ _ t
<1% _' <1%
.� f �t �r �� �
� 9
�'`�<1 % <1 %
yG��� �� .. � <�% l
L�E�e� ���•.�, l
� � ._ 7
<1% ��-�'.�__ 21% _<1%
�-
�� o�o _i� �t"�,._ <1 °/ 1
� !
� <1%
_� —
<1 %
<�^/° � —.- --,
Cape Fear __
River Basin
Legend TN Loads (kg/yr/ac)
(Model Run 2)
�o� � Proposed 540 � 0.86 - 1.35
� 1.36 - 1.74
�River Basin � 1.75 - 2.00
Boundary
_ 2.01 - 2.91
_ 2.92 - 9.45
<1 °/a
<1 %
<1% .;,_ �.
I N T E R H AT I 0 H A L

Cape Fear
River Basin
Complete 540 Water Quality
Total Phosphorus (TP) Loads for Three Modeled Scenarios
2010 (Model Run 1)
N eu se
2010 (Model Run 2)
N eu se
River Basin
Cape Fear
River Basin
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
�
N eu se
3s°io River Basin
4% � S
��I` `Y1 �.
48% ;� 66%
12%
t
1"
_ ��\4yG��� :
� 140/ 32°/
9 °/a
28°/
i
' �, 5%
��, 13%
� <� %
Cape Fear �
River Basin
14%
2040 Build (Model Run 1) 2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build Percent Change - From 2040 No-Build to 2040 Build
N eu se
� _ �Zo�o River Basin
5
N
W E
s
0
I
Miles
5
TP Loads (kg/yr/ac)
(Model Run 1)
O 0.04 - 0.07
O 0.08 - 0.09
� 0.10 - 0.11
- 0.12 - 0.14
� 0.15 - 0.18
�� <, o/
. ��
Z��yC��=—
�
� <1% <1%
� �
<1 %
`
��.
<1 °/d. <1 %
2%
Cape Fear
River Basin
Legend TP Loads (kg/yr/ac)
(Model Run 2)
�6� � Proposed 540 � 0.04 - 0.07
� 0.08 - 0.09
�River Basin � 0.10 - 0.11
Boundary
_ 0.12 - 0.14
_ 0.14 - 0.18
I N T E R H AT I 0 H A L

Complete 540 Water Quality
Copper (Cu) Loads for Three Modeled Scenarios
2010 (Model Run 1)
Cape Fear
River Basin
2010 (Model Run 2)
N eu se
River Basin
2040 No-Build (Model Run 1) 2040 No-Build (Model Run 2)
Percent Change - from 2010 to 2040 No-Build Percent Change - from 2010 to 2040 No-Build
N eu se
�32°�o River Basin
$ o/ � u �
Cape Fear
River Basin
_���'-�`�, sa%
y �E�"��_
� o/ `s--��! �d'
19%
58% ' �'�
2%
2040 Build (Model Run 1) 2040 Build (Model Run 2)
Percent Change - From 2040 No-Build to 2040 Build Percent Change - From 2040 No-Build to 2040 Build
5
N
W E
s
0
I
Miles
5
Cu Loads (g/yr/ac)
(Model Run 1)
� 0.60 - 1.17
O 1.18 - 1.96
� 1.97 - 2.80
- 2.81 - 3.97
- 3.98 - 7.83
Legend
�6� � Proposed 540
�River Basin
Boundary
Cu Loads (g/yr/ac)
(Model Run 2)
� 0.60 - 1.17
� 1.18 - 1.96
0 1.97 - 2.80
_ 2.81 - 3.97
_ 3.98 - 7.83
I N T E R H AT I 0 H A L

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Appendix B: Model Parameters and Notes
Parameter Upper Lower Units
Recession coefficient (Model 0.32 0.32 Unitless
Run 1)
Recession coefficient (Model 0.14 0.14 Unitless
Run 2)
Seepage coefficient (Model 0.56 0.56 Unitless
Run 1)
Seepage coefficient (Model 0.2 0.2 Unitless
Run 1)
Sediment lateral erosion 0.00649 0.00117 Unitless
factor for streambank erosion
Sediment adjustment factor 1 1 Unitless
Streams in agricultural areas 37.97 0 Km
Streams in agricultural areas 35.31 0 Km
with vegetated buffers
Streams in urban areas 229.2 3.9 Km
Fraction of streams in urban 0.49 0.08 Unitless
areas with vegetated buffers
Vegetated buffer strips BMP 0.41 0.41 Unitless
Nitrogen load efficiency
Vegetated buffer strips BMP 0.4 0.4 Unitless
Phosphorus load efficiency
Vegetated buffer strip width 22.99 15.14 m
Vegetated buffer strips BMP 0.53 0.53 Unitless
sediment load efficiency
Group Remarks
3 Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area.
3 Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area.
3 Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area.
3 Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area.
2 MAPSHED supplied. Varies by watershed based on input GIS
layers.
1 Default constant supplied by MAPSHED.
2 MAPSHED supplied. Varies by watershed based on input GIS
layers.
3 Calculated. Varies by watershed based on stream GIS layer and
calculated buffer intactness.
2 MAPSHED supplied. Varies by watershed based on input GIS
layers.
3 Optional parameter with no default. Calculated in order to
model BMPs. Varies by watershed based on stream GIS layer
and calculated buffer intactness.
3 Default constant supplied by MAPSHED.
3 Default constant supplied by MAPSHED.
3 Optional parameter with no default. Calculated in order to
model BMPs. Varies by watershed based on stream GIS layer
and calculated buffer intactness.
3 Default constant supplied by MAPSHED.
B-1

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Parameter Upper Lower Units Group Remarks I
Curve number for impervious 98 92 Unitless 3 Calibrated value. Modified MAPSHED defaults by using area �
fractions weighted curve numbers based on land use and soils to better
reflect observed streamflows in the study area. I
Curve number for pervious 82 58 Unitless 3 Calibrated value. Modified MAPSHED defaults by using area
fractions weighted curve numbers based on land use and soils to better
reflect observed streamflows in the study area.
Nitrogen accumulation on 0.11 0.045 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
impervious surfaces layers.
Nitrogen accumulation on 0.045 0.012 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
pervious surfaces layers.
Nitrogen dissolved fraction 0.33 0.28 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
layers. �
Phosphorus accumulation on 0.0112 0.0045 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
impervious surfaces layers.
Phosphorus accumulation on 0.0078 0.0016 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS �
pervious surfaces layers.
Phosphorus dissolved fraction 0.4 0.37 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
layers.
Dissolved nitrogen runoff 2.9 0.012 mg/L 2 MAPSHED supplied default. Varies by land use and watershed �
coefficient based on input GIS layers.
Dissolved phosphorus runoff 0.1856 0.002 mg/L 2 MAPSHED supplied. Varies by land use and watershed based on
coefficient input GIS layers including soil test phosphorus.
Manure nitrogen runoff 2.44 2.44 mg/L 1 Default constant supplied by MAPSHED.
coefficient �
Manure phosphorus runoff 0.38 0.38 mg/L 1 Default constant supplied by MAPSHED.
coefficient
Groundwater nitrogen 0.77 0.77 mg/L 1 Default constant provided by MAPSHED
content ,
Groundwater phosphorus 0.01 0.01 mg/L 1 Default constant provided by MAPSHED
content
Tile drainage nitrogen content 15 15 mg/L 1 Default constant supplied by MAPSHED.
B-2

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Parameter Upper Lower Units Group Remarks I
Tile drainage phosphorus 0.1 0.1 mg/L 1 Default constant supplied by MAPSHED.
content
Per capita tank effluent — 12 12 g/d 1 Default constant supplied by MAPSHED. �
nitrogen
Per capita tank effluent — 2.5
phosphorus
Growing season nitrogen 1.6
uptake
Growing season phosphorus 0.4
uptake
Sediment nitrogen content 2000
Sediment phosphorus content 562
Percentage bank fraction for 0.25
nitrogen
Percentage bank fraction for 0.25
phosphorus
Septic system populations 268
Point source discharge 0
K= soil erodibility factor 0.248
LS = slope length factor * 1.6
slope steepness factor
C = cover-management factor 0.42
P= support practice factor 0.45
Evapotranspiration (ET) cover 0.98
coefficient
Daylight 14.4
Growing season TRUE
2.5
1.6
0.4
2000
562
0.25
0.25
268
0
0.17
0.545
0.001
0.1
0.13
9.6
FALSE
g/d
g/d
g/d
mg/Kg
mg/Kg
Unitless
Unitless
people
MGD
Unitless
Unitless
Unitless
Unitless
Unitless
hours
Boolean
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
1 Default constant supplied by MAPSHED.
2 MAPSHED supplied default.
1 MAPSHED supplied default.
2 MAPSHED supplied default. Varies by land use and watershed
based on input GIS layers.
2 MAPSHED supplied default. Varies by land use and watershed
based on input GIS layers.
2 MAPSHED supplied default. Varies by land use based on input
GIS layers.
2 MAPSHED supplied default. Varies by land use and watershed
based on input GIS layers.
3 Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area.
2 MAPSHED supplied. Varies by month.
3 Required parameter with no default. Used May - September
growing season.
B-3

Parameter
Erosion coefficient
Stream extraction
Ground extraction
Initial unsaturated storage
Initial saturated storage
Unsaturated available water
Initial snow
Sediment delivery ratio
Tile drain ratio
Tile drain density
TSS EMC
Open land nitrogen EMC
Open land phosphorus EMC
Ground water(subsurface)
nitrogen
Ground water (subsurface)
phosphorus
Soil nitrogen
Soil phosphorus
Lateral erosion factor for
streambank erosion
ET adjustment percentage
Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Upper Lower Units Group Remarks
0.28 0.18 Unitless 1 Default value provided by GWLF. Varies by month.
0 0 cubic 1 Default constant supplied by MAPSHED.
meters/
month
0 0 cubic
meters/
month
10 10 cm
0 0 cm
18.403 10.68 cm
0 0 cm
0.083 0.083 Unitless
0.5 0.5 Unitless
0 0 Unitless
110 60 mg/L
1.5 1.5 mg/L
0.12 0.12 mg/L
1 1 mg/L
0.01 0.01 mg/L
50 50 ppm
100 100 ppm
0.00535 0.00299 Unitless
3.1 0.9 Unitless
1
1
1
2
1
2
1
1
2
1
1
1
1
1
1
2
3
B-4
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
MAPSHED supplied. Varies by watershed bas�u .,�� ���Nu� ���
layers.
Default constant supplied by MAPSHED.
MAPSHED supplied based on the watershed size.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
MAPSHED supplied. Varies by land use based on input GIS
layers.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
Default constant supplied by MAPSHED.
MAPSHED supplied. Varies by watershed based on input GIS
layers.
Calibrated value. Modified from MAPSHED default to better
reflect observed streamflows in the study area

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Parameter Upper Lower Units Group Remarks
Point source nitrogen loads 196997 0 Kg 3 Calculated based on NPDES data. Varies by watershed based on
input GIS layers.
Point source phosphorus loads 868 0 Kg 3 Calculated based on NPDES data. Varies by watershed based on
input GIS layers.
Combined sewer overflows - 35 35 mg/L 1 Default constant supplied by MAPSHED.
nitrogen I
Combined sewer overflows - 10 10 mg/L 1 Default constant supplied by MAPSHED.
phosphorus
Critical rainfall 1 1 cm/day 1 Default constant supplied by MAPSHED.
Dissolved phosphorus runoff 0.752 0.002 mg/L 2 MAPSHED supplied. Varies by land use and watershed based on
coefficient input GIS layers including soil test phosphorus.
High intensity urban nitrogen 0.101 0.101 Kg/ha/d 1 Default constant supplied by MAPSHED.
runoff coefficient
Low intensity urban nitrogen 0.12 0.12 Kg/ha/d 1 Default constant supplied by MAPSHED.
runoff coefficient
High intensity urban 0.011 0.011 Kg/ha/d 1 Default constant supplied by MAPSHED. I
phosphorus runoff coefficient I
Low intensity urban 0.002 0.002 Kg/ha/d 1 Default constant supplied by MAPSHED.
phosphorus runoff coefficient
Ground water nitrogen 1 1 mg/L 1 Default constant provided by MAPSHED
content
Ground water phosphorus 0.01 0.01 mg/L 1 Default constant provided by MAPSHED
content
Per capita tank effluent - 12 12 g/d 1 Default constant supplied by MAPSHED.
nitrogen
Per capita tank effluent - 2.5 2.5 g/d 1 Default constant supplied by MAPSHED.
phosphorus �
Growing season Phosphorus 2.5 2.5 g/d 1 Default constant supplied by MAPSHED.
uptake
Sediment nitrogen content 3000 3000 mg/Kg 1 Default constant supplied by MAPSHED.
Sediment phosphorus content 6143 474 mg/Kg 2 Default constant supplied by MAPSHED. Varies by watershed
based on GIS including soil test phosphorus.
B-S

Complete 540 - Triangle Expressway Southeast Extension Project Water Quality Analysis
November 2017
Parameter Upper Lower Units Group Remarks
Septic system populations 4386 0 people 2 MAPSHED supplied default. Varies by watershed based on input
GIS layers.
Point source nitrogen loads 6379.9 0 Kg 2 MAPSHED supplied default. Varies by watershed based on input
GIS layers.
Point source phosphorus loads 652.3 0 Kg 2 MAPSHED supplied default. Varies by watershed based on input
GIS layers.
Point source discharge 1.2 0 MGD 2 MAPSHED supplied default. Varies by watershed based on input
GIS layers.
Curve number 91 59 Unitless 3 Modified MAPSHED defaults by using area weighted curve
numbers based on land use and soils. I
Vegetated buffer strips BMP 0.51 0.3 Unitless 3 Modified default value to fit NC standards from the NCDWQ �
Nitrogen load efficiency stormwater manual. �
Vegetated buffer strips BMP 0.51 0.3 Unitless 3 Modified default value to fit NC standards from the NCDWQ
Phosphorus load efficiency stormwater manual.
Vegetated buffer strips BMP 0.9775 0.85 Unitless 3 Modified default value to fit NC standards from the NCDWQ I
sediment load efficiency stormwater manual. I
Nitrogen accumulation on 0.101 0.045 Kg/Ha/day 2 MAPSHED supplied. Varies by land use based on input GIS
impervious surfaces layers.
Point source nitrogen loads 196997 0 Kg 2 MAPSHED supplied. Varies by watershed based on input GIS �
layers.
Point source phosphorus loads 868 0 Kg 2 MAPSHED supplied. Varies by watershed based on input GIS
layers.
Point source discharge 0 0 MGD 2 MAPSHED supplied. Varies by watershed based on input GIS I
layers. I
�