20070932 Ver 1_Reports_20110301

G? o? 3a
Indirect and Cumulative Impact
Water Quality Study Report
NC 43 Connector
From NC 55 to US 17
Craven County, North Carolina
State Project No. 8.2231201
TIP No. R-44633
Prepared for:
North Carolina Department of Transportation
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Prepared by:
Baker Engineering, Inc.
8000 Regency Parkway, Suite 200
Cary, North Carolina 27518
March 2011
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Table of Contents
Executive Summary ...................................................................................................................... 5
1 Introduction .......................................................................................................................... .. 8
1.1 Background .............................................................................................................................. ....8
1.2 Project Overview and Study Area Description ......................................................................... ..10
2 Existing Water Quality Conditions ..................................................................................... 11
2.1 Neuse River Basin Water Quality Background ........................................................................ .. 11
2.2 Neuse River Basin Water Quality Initiatives ........................................................................... ..11
2.3 Development Considerations ................................................................................................... ..12
2.4 Stormwater Management ......................................................................................................... ..16
3 Land Use Forecasts ............................................................................................................... 18
3.1 Updates to the No Build Scenario ............................................................................................ ..18
3.2 Updates to the Build Scenario Land Use Forecast ................................................................... ..22
4 Watershed Modeling Approach .......................................................................................... 28
' 4.1 Objectives and Model Selection ............................................................................................... ..28
4.2 The GWLF Model .................................................................................................................... ..29
5 GWLF Model Development ................................................................................................. 31
5.1 Drainage Areas Delineation ..................::................................................................................. ..31
5.2 Scenario Comparisons .............................................................................................................. ..31
5.3 Surface Water Hydrology ......................................................................................................... ..34
5.4 Groundwater Hydrology .......................................................................................................... ..37
5.5 Erosion and Sediment Transport .............................................................................................. ..38
5.6 Nutrient Loading ................; ................................................................................................... ..40
5.7 Consideration of Existing Ehvironmental Regulations ............................................................ ..42
5.8 Model Implementation .....................................':.................................................................... ..44
6' Model Results and Discussion ............................................................................................. 44
6.1 Hydrology ................................................................................................................................. .44
6.2 Pollutant Loading Results ........................................................................................................ ..45
6.3 Nitrogen Loading to the Neuse River Estuary ........................................................................:. ..49
7 Stream Erosion Risk Analysis ............................................................................................. 50
7.1 Method ...................................................................................................................................... .50
7.2 Results ....................................................................................................................................... .50
8 Conclusions ............................................................................................................................ 53
9 References ..............................................................................................................................55
NC 43 Connector March 2011
ICI Water Quality Report
Tables
Table 2.3.1 Permit Holders for Groundwater Withdrawals in Craven County.
Table 3.1.1 Land Use Categories and Estimated Percent Impervious Cover
Table 3.1.2 Maximum Percent Impervious for New Hanover County
Table 3.1.2 NCDOT Population Growth Estimates
Table 3.1.3 Updated Population Growth Estimates
Table 3.1.4 Revised Build Scenario Population Forecasts
Table 3.2.1 Revised Build Scenario Household Forecasts
Table 3.2.2 NCDOT Population Growth Estimates
Table 5.2.1 Projected Changes in Land Use No Build versus Build in Study Area
Table 5.2.2 Projected Changes in Land Use No Build versus Build in Study Area Watersheds
Table 5.2.3 Land Use Categories and Estimated Imperviousness
Table 5.3.1 Surface Water Hydrology Input Parameters
Table 5.3.2 Curve Numbers for Land Use and Soil Hydrologic Groups
Table 5.4.1 Groundwater Input Parameters
Table 5.5.1 Rural Sediment Transport Input Parameters
Table 5.5.2 Cover and Management Practice Factors
Table 5.6.1 Nutrient Loading Input Parameters
Table 5.6.2 Nutrient Runoff and Buildup Rates for Existing Land Uses
Table 6.1.1 11-Year Total Nitrogen Loads (Mg) for all Drainage Areas
Table 6.1.2 11-Year Total Phosphorus Loads (Mg) for all Drainage Areas
Table 6.1.3 I 1-Year Total Sediment (TSS) Loads (Mg) for all Drainage Areas
Table 6.3.1 Project Area Nitrogen Loading Percentage as Percentage of Nitrogen Loading in
Estuary
Table 7.2.1 Storm Flow Volumes (m3) for the 1-Year, 24-Hour Storm
Table 7.2.2 Storm Flow Volumes (m3) for the 5-Year, 24-Hour Storm
Table 7.2.3 Storm Flow Volumes (m3) for the 10-Year, 24-Hour Storm
Charts
Chart 6. 1.1 Eleven-Year Nitrogen Loads for all Drainages
Chart 6.1.2 Eleven-Year Phosphorus Loads for all Drainages
Chart 6.1.3 Eleven-Year TSS Loads for all Drainages
Chart 7.2.1 Runoff Predictions for 1-Year, 24-Hour Storm Using SCS Curve Number Method
Chart 7.2.2 Runoff Predictions for 5-Year, 24-Hour Storm Using SCS Curve Number Method
Chart 7.2.3 Runoff Predictions for 10-Year, 24-Hour Storm Using SCS Curve Number
Method
NC 43 Connector March 2011
ICI Water Quality Report
Figures
Figure 1.1.1 Project Vicinity Map
Figure 3.1.1 CAMA Plan Future Development Zones
Figure 3.1.2 No Build Land Use Scenario
Figure 3.1.3 Craven 30 North Conceptual Development Plan
Figure 3.1.4 Build Land Use Scenarios
Figure 4.2.1 Schematic of GWLF Model Processes
Figure 5.1.1 Model Subwatersheds
Figure 6.1.1 Mean Monthly Water Balance for the Rocky Run Subwatershed (No Build
Scenario)
Appendices
Appendix A. Model Input Data
Appendix B. Modeled Drainage Area Land Use
NC 43 Connector March 2011
ICI Water Quality Report
Executive Summary
The North Carolina Department of Transportation (NCDOT) has proposed the construction of an
extension of NC 43 from NC 55 to US 17 west of New Bern in Craven County. This project is
referred to as the NC 43 Connector and is proposed as a four-lane, median-divided, partial
control of access facility on a new location. The approximate length of the project is 4.5 miles
(7.2 kilometers). The proposed project is included in the North Carolina Transportation
Improvement Program (TIP) as project R-4463.
An Indirect and Cumulative Impacts (ICI) Assessment was developed in January 2005 to provide
comprehensive information on the potential long-term, induced impacts of the proposed project
(NCDOT, 2005). In response to NC Division of Water Quality (NCDWQ) comments on the ICI
Assessment and in preparation for an Individual Section 401 Water Quality Certification, a water
quality modeling analysis was conducted to quantify the project's ICIs on water resources. This
analysis was completed by Stantec Consulting Services in February 2006 (NCDOT, 2006).
The 2006 ICI included a Build-Enhanced scenario based on measures proposed by the City of
New Bern, including re-zoning residential areas south of US 70 to cluster developments. Cluster
development is designed to protect environmentally sensitive areas by maximizing undisturbed
open space and by creating small lots. In addition, a one hundred foot buffer was added around
all delineated wetlands, a five hundred foot conservation area in the southwestern section of the
study area was created, and a fifty-foot buffer was added to the drainage canal in the Greenbriar
community located in the southeastern section of the study area.
NCDWQ has requested an update to the 2006 Stantec ICI study because, by August 2010, it was
apparent that the measures in the Build-Enhanced scenario were not being implemented
(NCDENR, 2010a). Additionally, Weyerhaeuser Corporation is planning a mixed-use
development within the project study area and requested three additional access points on the
connector. To account for this and any other forecast modifications to the land use changes
between 2006 and 2010, NCDOT requested that Michael Baker Engineering, Inc. (Baker), revisit
the land use forecasts for the Build and No Build scenarios, and re-run the models to quantify the
indirect and cumulative impacts (ICIs) of the project on water resources. Again, the focus of the
analysis are the potential increases in stormwater runoff and nonpoint source loads of nitrogen,
phosphorus, and sediment resulting from future development scenarios associated with the
facility.
Baker updated the Build and No Build land use forecasts as part of this study. NCDOT provided
a geographic information system (GIS) shapefile of the previous land use projections developed
by Stantec and these projections were used as a starting point for developing the updated land
use models. The City of New Bem Planning Department provided GIS shapefiles of current
zoning and planned land use areas based on the New Bern Regional Land Use Plan adopted in
2000 (hereafter referred to as the "CAMA Plan" for its compliance with the Coastal Area
Management Act). Weyerhaeuser also provided the most recent conceptual plan for its proposed
Craven 30 North development. These resources, along with discussions with local planners,
were the basis for determining the relevance of previous assumptions and what, if any, changes
NC 43 Connector March 2011
ICI Water Quality Report
were needed to account for new developments, changed development expectations, and new
population projections.
The modeling analysis simulated potential increases in nonpoint source loads of nitrogen,
phosphorus, and sediment given future land use scenarios with or without the NC 43 Connector.
The Generalized Watershed Loading Function (GWLF) model (Haith and Shoemaker, 1987;
Haith et al., 1992) was chosen to simulate pollutant loading. Additionally, storm event runoff
was evaluated using the Soil Conservation Service (SCS) Curve Number Method (SCS, 1986) to
assess the risk of stream channel erosion. A discussion of the modeling approach for this project
is summarized in Chapter 4.
GWLF model input files were developed to analyze the impacts on water quality from land use
changes associated with the NC 43 Connector. This analysis projects nutrient load increases in
the Build Scenario beyond the No Build Scenario of 1.6 percent for total phosphorus and 2.6
percent for total nitrogen over nearly 14,000 acres in the modeled subwatersheds. These results
assume that the Neuse River Nutrient Sensitive Waters Management Rules ("Neuse Rules") will
be implemented and that nutrient offset payments will be used only in a portion of cases (except
in the Neuse subwatershed, where offset payments were assumed for all new development). The
projected land use changes have less effect on storm runoff, where there is expected to be a 1.2
to 3.1 percent less runoff under the Build Scenario (than the No Build scenario) based on an
analysis using the SCS Curve Number Method. Total suspended solids (TSS) declined in many
drainage areas as a result of the Coastal Stormwater Rule, which requires an 85 percent reduction
in TSS loading on all new development with greater than 24 percent impervious cover. In all
subwatersheds combined, TSS loading is 3.6 percent less in the Build scenario than the No Build
scenario. Whether the TSS reductions are realized is dependent upon enforcement of the
regulation. Assessing the effectiveness and enforcement of the regulation is outside of the scope
of this study.
The subwatersheds that had the highest increases in total nitrogen loading between the Build and
No Build scenarios are Hayward Creek (5.9 percent), Deep Branch (4.8 percent), and Rocky Run
(4.3 percent). The remaining subwatersheds had differences of 3 percent or less. The higher
total nitrogen loading in Hayward Creek was the result of less than 10 hectares being developed
as commercial land (Build) instead of medium high density residential land (No Build). In Deep
Branch, the higher nitrogen load was due to a 143-hectare difference in high density residential
(Build) versus medium high density residential (No Build). This was also the case in Rocky Run
where approximately 150 hectares were assumed to be high density residential in the Build
scenario and medium high density residential in the No Build scenario.
The nutrient loading increases beyond the existing land use may cause some eutrophication of
the local streams. The differences between the Build and No Build are relatively small, though
greater eutrophication could occur in the Build scenario in some instances. This would entail
increased vegetative growth, both in the water column as algae and on the substrate as
periphyton, and more dynamic dissolved oxygen levels. Dissolved oxygen would be higher
during photosynthesis and lower as algae die or respire at night. In-stream monitoring may be
conducted to observe algal growth and dissolved oxygen levels.
NC 43 Connector March 2011
ICI Water Quality Report
In terms of potential cumulative effects, the loading from the subwatersheds in this study over
the 11 year model runs are predicted to contribute 11.3 Mg (2.6 percent) more total nitrogen and
1.4 Mg (1.6 percent) more total phosphorus under the Build scenario than the No Build scenario.
These differences are equivalent to 2.8 kg/day of total nitrogen (112.2 kg/day versus 109.4
kg/day) and 0.35 kg/day of total phosphorus (21.7 kg/day versus 21.3 kg/day). The total
nitrogen delivered to the estuary from the project subwatersheds is roughly 1.3 percent of the
total maximum daily load (TMDL) to the Neuse River estuary, or 8,388 kg/day (see Section 6.3).
The nitrogen load difference between the Build and the No Build appears to be inconsequential,
but the increase in load from either scenario above existing conditions from may have an effect
on estuarine water quality.
To summarize, localized water quality impacts to smaller streams in the project area area (e.g.,
Hayward Creek, Deep Branch, and Rocky Run), such as eutrophication, may occur if R-4463 is
constructed and the projected development occurs. However, similar changes in water quality in
the Neuse River estuary do not appear to be likely because the incremental increase in nutrient
loading between the Build and the No Build Scenarios (2.6 percent) is relatively small.
NC 43 Connector March 2011
ICI Water Quality Report
Introduction
1.1 Background
The North Carolina Department of Transportation (NCDOT) has proposed the construction of an
extension of NC 43 from NC 55 to US 17 west of New Bern in Craven County. This project is
referred to as the NC 43 Connector and is proposed as a four-lane, median-divided, partial
control of access facility on a new location. The approximate length of the project is 4.5 miles
(7.2 kilometers). The proposed project is included in the North Carolina Transportation
Improvement Program (TIP) as project R-4463. Figure 1.1.1 shows the vicinity of the proposed
project.
Full movement intersections are proposed between the NC 43/NC55 and US 17. An interchange
is proposed with US 70. Four access points are included in the design: two between US 17 and
US 70 and two between US 70 and NC 43/55 (one of these being the intersection at Bosch
Boulevard). Weyerhaeuser Corporation has requested three additional access points to serve a
mixed-use development that is being considered.
The purpose of and need for this project is based on the economic development of Craven
County and on projected traffic volumes. A new connection between US 17, NC 43, and the
proposed US 17 Bypass (TIP Project No. R-2301 A & B) would help promote economic
development in Craven County by providing a transportation infrastructure capable of
accommodating future development, which would result in job creation. The proposed
connector would provide a more direct route for truck traffic to access US 70 from the north,
which would reduce truck traffic on Glenburnie Road between NC 43/55 and US 70.
An Indirect and Cumulative Impacts (ICI) Assessment was developed in January 2005 to provide
comprehensive information on the potential long-term, induced impacts of the proposed project
(NCDOT, 2005). In response to NC Division of Water Quality (NCDWQ) comments on the ICI
Assessment and in preparation for an Individual Section 401 Water Quality Certification, a water
quality modeling analysis was conducted to quantify the project's ICIs on water resources. This
analysis was completed by Stantec Consulting Services in February 2006 (NCDOT, 2006).
NCDWQ has requested an update to the 2006 Stantec ICI study because, by August 2010, it was
apparent that the measures in the Build-Enhanced scenario assumed in the original study would
not be implemented (NCDENR, 2010a). Additionally, Weyerhaeuser Corporation is planning a
mixed-use development within the project study area and requested three additional access points
on the connector. To account for this and any other forecast modifications to the land use
changes between 2006 and 2010, NCDOT requested that Michael Baker Engineering, Inc.
(Baker), revisit the land use forecasts for the Build and No Build scenarios, and re-run the
models to quantify the indirect and cumulative impacts (ICIs) of the project on water resources.
Again, the focus of the analysis are the potential increases in stormwater runoff and nonpoint
source loads of nitrogen, phosphorus, and sediment resulting from future development scenarios
associated with the facility.
NC 43 Connector March 2011 Page 18
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NC 43 Connector March 2011 Page 19
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In accordance with the National Environmental Policy Act (NEPA) of 1969, as amended, an
assessment of indirect and cumulative effects (ICES) was conducted for the project (NCDOT,
2005). The Council for Environmental Quality (CEQ) defines direct, indirect, and cumulative
impacts as follows:
Direct effects are caused by the action and occur at the same time and place. (40 CFR §
1508.8)
• Indirect effects are caused by the action and are later in time or farther removed in
distance, but are still reasonably foreseeable. Indirect effects may include growth
inducing effects and other effects related to induced changes in the pattern of land use,
population density or growth rate, and related effects on air and water and other natural
systems, including ecosystems. (40 CFR § 1508.8)
• Cumulative impact is the impact on the environment, which results from the incremental
impact of the action when added to other past, present, and reasonably foreseeable future
actions regardless of what agency (Federal or non-Federal) or person undertakes such
other actions. Cumulative impacts can result from individually minor but collectively
significant actions taking place over a period of time. (40 CFR § 1508.7)
Section 401 of the Clean Water Act (CWA) of 1972, as amended, requires each state to certify
that state water quality standards will not be violated for activities that either involve issuance of
a federal permit or license or require discharges to Waters of the United States. Prior to the
issuance of a Section 404 permit from the US Army Corps of Engineers (USACE) for the NC 43
Connector, NCDOT is required submit a permit application to NCDWQ to obtain the 401 Water
Quality Certification. For this reason, it is necessary to demonstrate that the NC 43 Connector
project will not result in downstream water quality violations [15a NCAC 2H .506(c)(4)].
1.2 Project Overview and Study Area Description
The purpose of this water quality study is to quantify the impacts of changes in land use
associated with the proposed construction of the NC 43 Connector. The focus of the analysis
was on the potential increases in stormwater runoff and nonpoint source loads of nitrogen,
phosphorus, and sediment resulting from various future development scenarios associated with
the roadway. For the purposes of this study, the water quality study area (study area) is the same
as that used in the 2006 Stantec ICI. This includes seven subwatersheds covering 54 km' (21
miz). The model study area contains portions of Craven County, as well as the following
municipalities: New Bern, Trent Woods, and River Bend.
The modeling analysis simulated potential increases in nonpoint source loads of nitrogen,
phosphorous and sediment resulting from various future development scenarios associated with
the roadway. The Generalized Watershed Loading Function (GWLF) (Haith and Shoemaker,
1987; Haith et al., 1992) model was selected for simulation purposes. An additional parameter,
storm event runoff, was evaluated using a separate assessment tool, the Soil Conservation
Service (SCS) Curve Number Method (SCS, 1986), to assess the risk of downstream channel
erosion. The modeling tools were used to quantify the impacts of various development scenarios
associated with the roadway.
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A particular focus in the analysis was the potential increase in predicted pollutant loads to the
adjacent Neuse and Trent Rivers, which have been designated as impaired for chlorophyll a, an
indicator of algal growth, by the NC Department of Environment and Natural Resources
(NCDENR).
2 Existing Water Quality Conditions
2.1 Neuse River Basin Water Quality Background
Water quality has long been an issue in the Neuse River estuary. Based on data from Cooper
(2000), sediment rates in the Neuse River estuary have increased by more than 300 percent in the
past 50 years. There have also been increases in nutrient, metal, and sulfur flux. Cooper states
that in the past 30 to 50 years, land use changes associated with industrial activity, increasing
population, and other development has resulted in marked changes in diatom and pollen
assemblages. Recent assemblages had higher abundances of small planktonic species most
commonly associated with high nutrient waters and exhibit relatively low species richness and _
diversity as compared to older (pre-1950) samples.
The most recent Neuse River Basinwide Water Quality Plan (NCDWQ, 2009), stated that
euthrophication was noted as a water quality concern in the late 1970s. At that time, NCDWQ
began investigations of nuisance algal blooms. These investigations determined that the blooms
were associated with high nutrient concentrations in the Neuse River estuary. In 1988, NCDWQ
revised the classification of the Neuse River estuary, adding a Nutrient Sensitive Waters (NSW)
designation.
In 1993, the Neuse River Basinwide Water Quality Plan noted the problems associated with high
nutrient levels in the basin south of New Bem. Since 1994, the Neuse River estuary has been on
North Carolina's 303(d) list of impaired waters due to high chlorophyll a levels. Extensive fish
kills were reported in the Neuse River estuary in 1995.
2.2 Neuse River Basin Water Quality Initiatives
In 1996, the NC Senate Select Committee on River Quality and Fish Kills sponsored a workshop
to examine potential mitigation measures for the nutrient issues associated with the Neuse River
estuary. The committee reached consensus that a 30 percent reduction in total nitrogen entering
the estuary would reduce the extent and duration of algal blooms.
2.2.1 Neuse River Management Strategy
The North Carolina Environmental Management Commission (EMC) approved the Neuse
Nutrient Strategy in 1998. This set of rules were phased in by 2003 and included the Neuse
Riparian Buffer Protection Strategy, as well as measures for wastewater, stormwater, and
agricultural discharges, and measures for nutrient management goals and nutrient offset
payments. NCDWQ is responsible for administering and enforcing these rules. For the
complete strategy, please refer to httn://h2o.enr.state.nc.us/nps/neuse.htm.
NC 43 Connector March 2011 Page I 1 I
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2.2.2 Neuse River Estuarv TMDL
A Total Maximum Daily Load (TMDL) was developed in a two-stage process and approved
by the US Environmental Protection Agency (USEPA) in 2002 to reduce nitrogen levels in
the estuary. A TMDL is the maximum amount of a pollutant that a waterbody can receive
and still meet its designated uses. For the complete Neuse River Estuary TMDL, please refer
to NCDENR 2001.
2.2.3 Recent Water Quality Trends
Based on the 2006 sampling reported in the 2009 Neuse River Basinwide Water Quality
Plan, the goal of a 30 percent reduction in nitrogen loading has yet to be achieved. Water
quality data has yet to show a distinct improvement in nutrient levels, so NCDWQ has stated
that they will continue to evaluate the limitations of the current strategy and seek to identify
measures that could provide positive impacts to the system.
2.3 Development Considerations
There are several aspects of the project area which will have an effect on development in the ICI
project area. These considerations are summarized below.
2.3.1 Surface Water Resources
The project is located within Neuse River Hydrologic Unit 03020204. This subbasin
includes Caswell Branch, Deep Branch, Hayward Creek, Rocky Run, Trent River, Wilson
Creek, and associated unnamed tributaries (UTs), all of which eventually that flow into the
Neuse River estuary. There is also an extensive drainage ditch system.
NCDWQ classifies Caswell Branch, Deep Branch, Hayward Creek, Hayward Creek, the
Neuse River estuary, Rocky Run, and Wilson Creek as Class C, NSW, Swamp Waters (Sw),
best suited for aquatic life survival and propagation, fishing, wildlife, secondary recreation,
and agriculture. Trent River is listed as Class SB, NS, Sw. None of the waters are listed for
a shellfishing use.
Trent River from the mouth of Brice Creek to the Neuse River is included on the North
Carolina 303(d) list of impaired waters for high levels of chlorophyll a. South of the Trent
River, the Neuse River Estuary is also listed for chlorophyll a and high levels of copper
(NCDWQ, 2010b).
2.3.2 Wetland Resources
While most of the project study area is designated as wetlands, based on the US Fish and
Wildlife Service (USFWS) National Wetland Inventory (NWI) (1994) and NC Division of
Coastal Management (NCDCM 1999) mapping, the majority of these wetlands were
converted to either agricultural or other uses. As stated previously there is an extensive
drainage network in the study area. In addition to the NWI data, information from a wetlands
inventory conducted in 2008 on behalf of Weyerhaeuser Real Estate Company was also
included in the project analysis (Weyerhaeuser, on file with USACE, 2009). Based on the
NC 43 Connector March 2011 Page 12
ICI Water Quality Report
ICI and the 2006 Water Quality Analysis Report (NCDOT, 2005, 2006, respectively), most
of the jurisdictional wetlands are located in the southern portion of the project study area,
where ditching is less prevalent. Typically, wetlands in the project study area are pocosins
and headwater systems, which act as natural detention and infiltration areas. Many of these
wetlands are terrestrially isolated from other surface waters, which makes them important
habitat for amphibians.
2.3.3 Groundwater Resources
Stratigraphy in the project study area consists of layers of permeable (aquifer) and
impermeable (aquiclude) units. The most important aquifers are the surficial aquifer, the
Castle Hayne formation aquifer, and the Cretaceous Black Creek and Peedee formations.
The surficial aquifer is, as the name suggests, the unconfined, saturated portion of the upper
layer of sediments. The Castle Hayne aquifer is an Oligocene/Paleocene limestone formation
that underlies the eastern half of the Coastal Plain. Recharge to the Castle Hayne aquifer is
rather slow, as most recharge is captured by the surficial aquifer or moves laterally to
streams. Approximately 3 cm (1 inch) per year reaches the, Castle Hayne (Giese et al., 1997).
The Peedee formation of the Late Cretaceous age consists of dark clays mixed with fine to
medium grained sands with a few thin limestone inclusions. The Black Creek formation of
the Late Cretaceous age also consists of dark clays and sands and is not hydrologically
distinguishable from the overlying Peedee formation (LeGrand, 1960).
According to the US Geological Survey (USGS), the water table in the project study area has
been steadily dropping over the last 30 years. This has been attributed to groundwater
withdrawals, which have exceeded the rate of recharge for the surficial and Cretaceous
aquifers. Permit holders allowed to withdraw groundwater for use in Craven County are
shown in Table 2.3.1.
Table 2.3.1
Permit Holders for Groundwater Withdrawals in Craven County
Permitted`
Groundwater Approved
Permit Withdrawal Base Rate
Permittee No. Rate MGD MG Type
°
Aquifer*
Industrial,
Public
We erhauserNRCompany CU1013 3 Supply Tch
Public
City of Havelock CU1029 2.8 Supply Tch
Public
US Marine Corps, Cherry Point CU1060 8 Supply Tch
Public
CWS Systems, Inc., Fairfield Harbour CU1087 1.05 Supply Tch

White Rick Fish Farm, Inc. CU1090 0.448 A uaculture Tch
Public
Town of Vanceboro CU1097 0.412 Supply Tch
Public
First Craven Sanitary District CU1105 1.476 Supply Tch
Vanguard Farms, Inc. CU 1106 3 A uaculture Tch
NC 43 Connector March 2011 Page 113
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Permitted
Groundwater Approved
vj Permit Withdrawals Base Rate
Permittee" No. Rate GD G Type A uifer*
Coastal Plains Catfish CU1108 0.518 A uaculture Tch
Craven Pond, Inc. CUI 112 1.008 A uaculture Tch
Mine
Carolina Stone, LLC Grifton Mine CU1024 3 Dewaterin S
Mine
Parson Mine CU1028 1.26 Dewaterin S
Smith Farm of Vanceboro LLC CU3008 0.792 A uaculture Tch
Morris Fish Farm, LLC CU3009 0.763 A uaculture Tch
Mine
W.O. White Mine CU3017 5.184 Dewaterin S
Martin Marietta Materials, Inc. Mine
Clarks Quarry) CU3033 16 Dewaterin S, Tch
Public
Town of River Bend CU3052 1 Supply Tcb
Craven County Wood Energy, L.P. CU3055 1.8 Industrial Tch
Fish and Chicks, Inc. CU3063 0.36 A uaculture K pd
Public Kbc, Kucf,
City of New Bern CU3071 5.5 1,549.84 Supply Tch
Spring Hoe Fisheries CU3087 0.36 A uaculture Tch
Public Kbc, Kucf,
Craven County Water CU3108 0.734 952.791 Supply K pd
Mine
W.O. White, LLC J.C. Holton Pit CU3129 2.88 Dewaterin S
Mine
RJ Bushho in , Inc., Mine No.2 CU3131 2.88 Dewaterin S
Irrigation,
Carolina Creek LLC CU3140 0.72 Golf Course S, Tch
Mine
Cieszko Const. Co. White Hall Pit CU3143 1.44 Dewaterin S
Carolina Stone, LLC (Ft.Bamwell Mine
Mine CU3152 1.44 Dewaterin S, Tch
Irrigation,
Emerald Golf Course CU3155 0.75 Golf Course Tch
Mine
NCDOT R-3403 A CU4019 Dewaterin S
R. J. Bushhogging, Inc., (Willis Neck Mine
Mine 1 CU3167 1.44 Dewaterin S, Tch

Irrigation,
Tabema Country Club CU3168 0.378 Golf Course Tch
Irrigation,
River Bend Country Club CU3179 0.331 Golf Course Tch
Source: NCDENR Division of Water Resources, 2009
' - Aquifer Types - S=Surficial, Tch=Castle Hayne, Kbc=Black Creek, Kpd=Peedee, Kucf=Upper Cape Fear
MGD = Million Gallons per Day MGY - Million Gallons per Year
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2.3.4 Soils
Based on the Craven County Soil Survey (US Department of Agriculture [USDA], 1989), the
soils the predominant soils in the study area are listed as Bayboro, Craven, or Pantego.
Pantego soils, and several other soils in the project study area are hydric soils. According to
the soil survey, hydric soils have severe development limitations due to their low
permeability and strength. In addition, the majority of the soils in the project study area are
classified as prime, unique, or statewide important farmlands, and the Pantego soils are listed
as prime farmland if drained.
2.3.5 Protected Species
In accordance with provisions of the Endangered Species Act (ESA) of 1973, the project
study area was evaluated for threatened and endangered species habitat. Six species are
listed as endangered (E) or threatened (T) for Craven County: sensitive joint-vetch
(Aeschynomene virginica) T, rough-leaved loosestrife (Lysimachia asperulaefolia) E,
leatherback sea turtle (Dermochelys coriacea) E, West Indian manatee (Trichechus manatus)
E, red-cockaded woodpecker (Picoides borealis), and American alligator (Alligator
mississippiensis) T (USFWS, December 2010). Also, the bald eagle (Haliaeetus
leucocephalus) is listed in the study area and is protected by the Bald and Golden Eagle
Protection Act. The American alligator is listed as "Threatened Due to Similar Appearance"
[T(S/A)] to provide protection to the American crocodile (Crocodylus aeutus), but is not
protected under Section 7 of the ESA. The project study area does not contain suitable
habitat for any of these protected species (NCDOT, 2005). There are 18 Federal Species of
Concern (FSCs) listed for Craven County (USFS, 2010). The North Carolina Natural
Heritage Program (NCNHP) lists an additional species, coastal goldenrod (solidago
villosicarpa) (NCNHP, 2010). There is suitable habitat for several FSCs. The project study
area may also host a population of black bear (Ursus americanus).
2.3.6 Fishery Resources
The Trent River and its tributaries may provide habitat for anadromous fish including river
herring (Alosa pseudoharengus), striped bass (Morone saxatilis), and American shad (Alosa
sapidissima). The NC Division of Marine Fisheries (NCDMF) stated that there are no known
anadromous fish spawning areas or nursery areas within Hayward Creek or the adjacent areas
of the Trent River (NCDMF, 2003). Bachelor Creek is an important spawning area for river
herring and there is a river herring nursery area at the convergence of Bachelor Creek and the
Neuse River. The Trent River also contains habitat suitable for estuarine species such as spot
(Leiostomus xanthurus), croaker (Micropogonias undulatus), and Atlantic menhaden
(Brevoortia tyrannus). These species are also important for their commercial and recreational
value (NCDOT, 2006).
Areas of the Trent River have submerged aquatic vegetation (SAV), which provides valuable
fish habitat, especially during the larval and juvenile development stages of development.
SAV also provides habitat for crab and shrimp species. Downstream of the confluence of the
Trent River with the Neuse River there is a large area of submerged aquatic vegetation
(SAV), composed primarily of wild celery (Vallisneria americana) (NCDMF, 2005).
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2.3.7 Natural Areas
The NCDCM has classified areas in and around the Trent River as "public trust waters" and
"estuarine waters" Areas of Environmental Concern (AECs) as specified in the City of New
Bern's Draft CAMA Land Use Plan (City of New Bern, 2010a). These waters are within the
watersheds of the Rocky Run, Hayward Creek, and Wilson Creek. Mitchell Island, located
south of the project study area, is an estuarine island protected as an Estuarine AEC.
The Croatan National Forest is south of the project study area, bound on its north side by the
Trent River. The National Forest and the project study area are along the Atlantic Flyway for
migratory birds; the project study area may provide migratory habitat.
2.3.8 Infrastructure
The project study area is bounded to the north by NC 55 and NC 43/55, and to the south by
US 17. Other highways included the proposed US 17 Bypass and US 70, which roughly
bisects the project study area. The undeveloped portions of the project study area, which are
currently managed forests areas, are served by a system of logging roads. An active railroad
and two large power lines also traverse the project study area.
Water service from the City of New Bern is currently supplied to the Greenbrier community
and to properties along NC 55, NC 43, Glenburnie Road, and US 17. Sewer service from the
City is available in Greenbrier and along NC 55, NC 43, Glenbumie Road, and US 17,
although sewer lines on US 17 do not extend as far west as the water lines along US 17
(NCDOT, 2006).
2.3.9 Other Development Considerations
The majority of land to the north, east, and south of the project study area has been
developed as moderate to high developed by residential and commercial properties, mostly
within the jurisdiction of the City of New Bern and the Town of Trent Woods. Most of the
land within the project study area is within the extraterritorial jurisdiction of the City of New
Bern and, as stated previously, is currently managed forestry acreage. Most of the area west
of the project study area is undeveloped. As the proposed US 17 Bypass would be access
controlled, it would not encourage additional development within the project study area.
According to the USEPA, the seven-acre Amital Spinning property along Bosch Boulevard is
an archived Superfund site (Superfund ID NCD981928088, also known as the TEX-Fl
Industries site). The site was originally listed for organic contaminants in groundwater and
was removed from the list of Active Superfund sites in 2003. It is anticipated that any
development in this area would require the assessments and potential removal of
contaminated soils.
2.4 Stormwater Management
Although the City of New Bern is not a community subject to the new National Pollutant
Discharge Elimination System (NPDES) Phase II Stormwater Rules, the City is subject to the
NC 43 Connector March 2011 Page 1 16
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stormwater rules contained within the Neuse River NSW Management Strategy discussed in
Section 2.2.1 and the Coastal Stormwater Rule. Both sets of rules seek to lessen the impact that
future development will have on water quality.
The Neuse stormwater rules require the development of stormwater management plans for each
of the 15 largest local governments within the basin. The local government stormwater plans
must be consistent with the overall 30 percent nitrogen reduction goal of the Neuse River NSW
Management Strategy (City of New Bern, 2010b) and the City's Stormwater Management
Manual (City of New Bern, 2007). The Stormwater Management Manual requires that anyone
proposing new developments within a 50-foot riparian buffer around all intermittent and
perennial streams and other water bodies and anyone proposing new development that will result
in disturbance of greater than one-half acre of land must obtain a Stormwater Permit. A
Stormwater Permit "requires each development to meet a nitrogen export performance standard
of less than or equal to 3.6 pounds total nitrogen (TN) per acre per year (#/ac/yr). Where that
standard cannot be reasonably achieved, there are provisions for variance and mitigation offsets."
The City also requires that all new development control water runoff so that there is no net
increase in the peak discharge from the predevelopment conditions for either the 1-year, 24-hour
storm or the 10-year, 24-hour storm. Variances may be granted for various reasons including
limits on impervious area.
The North Carolina EMC adopted the Coastal Stormwater Rule (15A NCAC 02H .1005) in
January 2008. Included in the amendments are requirements for developments with more than
24 percent impervious cover to control the first one and a half inches of rainfall and to reduce
post-development average annual total suspended solids (TSS) loading by 85 percent. The latter
has important implications to the model results of this study, which are discussed in Section
5.8.2.
The City of New Bern requires that that 50-foot wide riparian buffers be maintained on all sides
of intermittent and perennial streams, ponds, lakes, and estuaries in the City and its
extraterritorial jurisdiction (City of New Bern, 2007).
The State Stormwater Management Program was established in 1988 under the authority of the
EMC and North Carolina General Statute 143-214.7. This program, codified in 15A NCAC
2H.1000, affects development activities that require either a Erosion and Sediment Control Plan
(for disturbances of one or more acres) or a CAMA major permit within 20 coastal counties,
which include Craven. The program also applies to development draining to Outstanding
Resource Waters (ORW) or High Quality Waters (HQW).
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3 Land Use Forecasts
3.1 Updates to the No Build Scenario
The February 2006 ICI and Water Quality Analysis Report (NCDOT, 2006) was based on the
implementation of a "Build-Enhanced Scenario," which included designation of new
conservation areas and expanded buffers around wetlands to be implemented by the City of New
Bern. While City planners have attempted to implement these recommendations during
development review, they have not been formally incorporated into development regulations.
Therefore, the Build-Enhanced Scenario is not expected to be fully implemented. Therefore, for
this study, future development was based on existing criteria. Also, a substantial new
development, Craven 30 North, has been proposed within the study area. These changes, and
others, were used to update the land use scenarios.
NCDOT provided a geographic information system (GIS) shapefile of the previous land use
projections developed by Stantec and these projections were used as a starting point for
developing the updated land use models. The City of New Bern Planning Department provided
GIS shapefiles of current zoning and planned land use areas based on the New Bern Regional
Land Use Plan adopted in 2000 (called the CAMA Plan as it was developed to comply with the
Coastal Area Management Act). Weyerhaeuser also provided the most recent conceptual plan
for its proposed Craven 30 North development. These resources, along with discussions with
local planners, were the basis for determining the relevance of previous assumptions and what, if
any, changes were needed to account for new developments, changed development expectations
and new population projections.
Land use categories used were the same as those used in the Water Quality Study. For reference,
Table 4.2.1 from the NCDOT 2006 Study is reproduced as Table 3. 1.1 below:
Table 3.1.1
Land Use Categories and Estimated Percent Impervious Cover
LAND USE NAME GWLF CODE PERCENT IMPERVIOUS
Residential - Very Low Density
(2+ acres per dwelling unit) RVL 8
Residential - Low Density
(1.5-2 acres per d.u.) RLL 14
Residential - Medium Low Density
(I-1.5 acres per d.u.) RML 18
Residential - Medium High Density
(0.5-1 acres per d.u.) RMH 23
Residential - High Density
(0.25-0.5 acres per d.u.) RHH 29
Residential - Multifamily/Very High Density
(0.25 acres per d.u.) RVH 50
Office/Institutional/Light Industrial OFF 70
Commercial/Heavy Industrial COM 85
Paved Road with Right of Way ROAD 85
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LAND USE NAME GWLF CODE PERCENT IMPERVIOUS
Urban Green Space/Golf Course UGR 0
Row Crop ROW 0
Forest FOR 0
Wetlands WET 0
Water W AT N/A
Source: NCDOT, 2006
3.1.1 Revised No Build Scenario Population Data
The 2006 No Build Land Use model used Census Bureau population forecasts and statistical
analysis of population trends to develop population forecasts for the study area (NCDOT,
2006). Table 3.1.2 includes the population forecasts used in the 2006 report plus additional
calculated percentages in italics.
Table 3.1.2
NCDOT 2006 Population Growth Estimates
Po ulation "71 IPerceut Change

2000

010
1

020 ' 4,

2030 2000-

2010 2010-

2020 2020-

2030
No Build
Stud Area 4,659 5,496 6,350 7,208 18.0% 15.5% 13.5%
New Bern 23,111 32,517 46,207 63,442 40.7% 42.1% 37.3%
Craven County 91,523 97,513 102,080 105,070 6.5% 4.7% 2.9%
New Bern as % o Craven 25.3% 33.3% 45.3% 60.4%
Stud Area as % o Craven 5.1% 5.6% 6.2% 6.9% "
Build Scenario
Stud Area 4,659 5,496 9,430 14,523 18.0% 71.6% 54.0%
New Bern 23,111 32,517 50,142 73,937 40.7% 54.2% 47.5%
Craven Count 91,523 97,513 106,015 114,213 6.5% 8.7% 7.7%
No Build to Build Increase
Stud Area 0 0 3,080 7,315
New Bern 0 0 3,935 10.495
Craven County 0 0 3,935 9,143
No Build to Build Percent Increase
Stud Area 0.0% 0.0% 48.5% 101.5%
New Bern 0.0% 0.0% 8.5% 165%
Craven County 0.0% 0.0% 3.9% 8.7%
Source: NCDOT, 2006
The most recent available population forecasts from the NC Office of State Budget and
Management (September 2010) project that population increases in Craven County will be
greater than the 2005 forecasts. The 2005-generated forecast of 2030 population in Craven
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County was 105,070. The 2010 Craven County forecast, however, shows a 2030 population
of 116,835. This increase requires changes in the No Build residential land use. To account
for this additional population, the NCDOT 2006 population forecasts were analyzed to
determine the ratio of study area population to Craven County population. The resulting
ratio was applied to the new, higher population estimates to develop a new No Build
population forecast. Based on the additional calculations in Table 3.1.2, the study area
population is predicted to be 6.9 percent of the Craven County population in 2030. Table
3.1.3 shows the updated No Build population projections, developed by applying the ratio
factors from Table 3. 1.1 to the updated population forecast for Craven County.
Table 3.1.3
Updated Population Growth Estimates
Population Percent Chan e
2000 2010 2020 2030 2000-2010 2010-2020 2020-2030
New No Build Prqiections
Craven Count 91,523 101,052 108,942 116,835 10.4% 7.8% 7.2%
New Bern 23,111 33,697 49,313 70,546 45.8% 46.3% 43.1%
Stud Area 4,659 5,695 6,777 8,015 22.2% 19.0% 18.3%
source: Baker 2011
Table 3.1.4 shows the impact of this higher population on households. Applying the same
household factors from Table 3.1.2 of the ICI report, indicates that the increased population will
require an additional 447 households in the Study Area, representing an 11.2 percent increase
over the NCDOT 2006 No Build forecast.
Table 3.1.4
Population Growth Estimated Increase

Household
Type

% of All
Households
Persons
Per '
Household 2030 No
Build
(NCDOT,
2006
Revised
2030 No
Build

ifference

Percent
Difference
Single Person 32.4% 1.00 2,335 2,597 262 11.2%
Family 63.5% 2.98 1,536 1,708 172 11.2%
Other 4.1% 2.59 114 127 13 11.3%
Total 100.0% 3,985 4,432 447 11.2%
Source: Baker2011
Therefore, the No Build Land Use Scenario must be updated to account for the additional 447
households resulting from the increase in forecasted growth. Based on discussions with the City
of New Bern Planning Department, planned land use, zoning and the expectations for growth and
development patterns have not changed substantially since 2005, indicating that the overall
pattern of development in the NCDOT 2006 Land Use model is reasonably accurate. Thus, the
only change needed is to address the increased number of households. Planners with the City
indicated that most new development is expected to occur in the Urban Transition zones
documented in the CAMA Plan as seen in Figure 3.1.1.
NC 43 Connector March 2011 Page 1 20
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O
Neuse River ?•
Deep
Rocky Run
0
o
}t'i Wilson Creek ? ` ?.
v
Utto

17 " kz ?
=R
J•
CAMA Plan Figure 3.1.1
Future Development Zones CAMA Plan
Developed C3Subwatershed Future Development
urban Transition Zones
Limited Transition "?"'POL
Nwru
E. vraonmtNr
Rural UNIT
- Conservation o o.s t
D
Miles
Figure 3. 1.1 CAMA Plan Future Development Zones
NC 43 Connector March 2011 Page 121
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Regulations for the Limited Transition and Rural Zones are expected to maintain 4 units per acre
maximum density. The most logical area remaining for substantial increase in density to
accommodate these households was the area within the Urban Transition Zone along US 17 in
the Hayward Creek and Unnamed Tributary (UT) to Wilson Creek Subwatersheds. Residential
densities in this vicinity were increased to accommodate the increase in households.
Specifically, about 220 acres of land categorized as Residential Medium to High was changed to
Residential High or Residential Very High to accommodate the projected additional households.
In addition, to incorporate the most recent data, the wetlands delineated by a 2008 survey on
behalf of Weyerhaeuser Real Estate Company were identified in the No Build Scenario as any
development of that site will be required to either protect the wetlands or incorporate measures to
mitigate any wetland loss.
After the initial forecasting was completed, two adjustments were made to the land use forecast.
First, the power line easements that run through the study area were specifically added to the
forecasted land use under both scenarios. The changes associated with this addition were fairly
minimal since the overall area of the easements is relatively small compared to the overall study
area. Second, planners with the City of New Bern indicated that a recent lease agreement had
been developed by Martin Marietta to expand the quarry operations in the northern portion of the
study area. The approximately 636-acre tract was thus altered under both the Build and No
Build Scenarios to indicate that the land would be used for mining operations. The resulting
2030 No Build Land Use is shown in Figure 3.1.2. Since there was little remaining area for
increased residential density to accommodate the land uses originally forecasted for this area, it
was assumed that those future land uses would shift to areas outside the study area. For this
reason, the population and households resulting from the land use model would be lower than
that forecast in Tables 3.1.3 and 3.1.4.
3.2 Updates to the Build Scenario Land Use Forecast
Similar to the No Build Scenario update, but with one exception, planned land use, zoning and
the expectations for growth and development patterns have not changed substantially since 2005
with the exception of the expansion of quarry operations in the northern portion of the study area
and the Craven 30 North development. Thus, the overall pattern of development in the Stantec
Land Use model is reasonably accurate once these two changes were addressed. The recently
proposed Craven 30 North development requested by Weyerhaeuser would include retail, office,
industrial and residential development mostly in the northeast quadrant of the proposed US
70/NC 43 interchange. The current development plan, shown in Figure 3.1.3, is still conceptual
but the illustrative plan was provided by Weyerhaeuser to provide a basis for updating the Build
Scenario.
The illustrative plan was converted into the same land use categories shown in Table 3.1
below:
Table 3. 1.1 and the new planned uses replaced the previously forecast uses in the 2006 report.
This resulted in approximately 150 fewer acres of Commercial and Office/Institutional/ Light
Industrial uses and about 120 more acres of residential development. Also, about 40 acres of
residential land use was increased in density based on the Craven 30 North proposal. Overall,
changes made to the Build Scenario to account for the Craven 30 North proposal resulted in
NC 43 Connector March 2011 Page 1 22
ICI Water Quality Report
increases in the forecasted residential development and decreases in the forecast non-residential
development.
NC 43 Connector March 2011 Page 1 23
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N 5\ ?
43
f \
r,
ell Bra 70
1
U'?. T V _ r. ,' 3
' Nadse Riva. 't?"
c ? v +
E?ra'Deep,"" ch
55
o
WE
y
9
i
'ry Ut to
Ro un ni WI C s -
xr a
17 "?
rent t
Land Use [] Residential Very High Figure 3.1.2
Forest Residential High No Build
Row Crop Residential Medium High Land Use Scenario
Ef] urban Green Space Residential Medium Low
rr] Commercial Residential Low
xrroi-vnrw
rrl Office/Institutional/Light Industrial Residential Very Low
NaN?
E?J N9RONMEW
Mine U xr F
L.l
F'j Wetland ? o 0.5 t
Subwatershed ?
Water W Miles
Figure 3.1.2 No Build Land Use Scenario
NC 43 Connector March 2011 Page 1 24
ICI Water Quality Report

Figure 3.1.3 Craven 30 North Conceptual Development Plan
NC 43 Connector March 2011 Page 25
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In addition to updating the Build Scenario to include the Craven 30 North development,
residential density was increased to account for the increased population forecast outlined in the
No Build section. This update was accomplished by applying the No Build to Build percent
increase in population calculated in 3.1.2 from NCDOT's 2006 forecast and applying the same
growth factors to the new No Build forecast in Table 3.1.3. The resulting Build Scenario
population forecast is shown in Table 3.2.1 and Figure 3.1.4.
Table 3.2.1
Revised Build Scenario Population Forecasts
Population Percent Chan e
2000 2010 2020 2030 2000-2010 2010-2020 2020-2030
Craven County 91,523 101,052 113,142 127,002 10.4% 12.0% 12.3%
New Bern 23,111 33,697 53,513 82,216 45.8% 58.8% 53.6%
Stud Area 4,659 5,695 10,064 16,149 22.2% 76.7% 60.5%
Source: Baker 2011
Converting these population forecasts to household forecasts was accomplished by the same
method outlined for Table 3.1.4. The resulting household forecast, shown in 3.2.2, indicates that
an additional 899 households, an 11.2 percent increase, will be required to accommodate the
additional population.
Table 3.2.2
Revised Build Scenario Household Forecast
Household
Type
=Percent Persons Per
Households 2030 Build
NcoOT zoos Updated
2030 Build
Difference %
Difference
Single Person 32.4% 1.00 4,705 5,232 527 11.2%
Family 63.5% 2.98 3,095 3,441 346 112%
Other 4.1% 2.59 230 256 26 11.2%
Total 100.0% 8,030 8,929 899 11.2%
Source: Baker 2011
About one-third of the acreage required to meet this increase in households is accounted for in
additional acres and increased densities of residential development in the Craven 30 North plan.
The remainder was added to the Build Scenario by increasing residential densities along the
eastern side of NC 43 south of US 70. Due to the changes required to incorporate the expanded
quarry operations of Martin Marrietta and the lack of substantial areas to shift expected
development, it is anticipated that some of the forecast development would be shifted outside the
project study area. For this reason, similar to the No Build Scenario, the population and
households resulting from the land use projections shown in Figure 3.2.1 would be lower than
that forecast in Tables 3.2.1 and 3.2.2.
NC 43 Connector March 2011 Page 1 26
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Craven

Land Use , Residential Very High Figure 3.1.4
Forest rri Residential High Build
Row Crop Residential Medium High Land Use Scenario
F'I Urban Green Space
j
Residential Medium Low
Commercial Residential Low
'

Office/Institutional/Light Industrial
Residential Very Low vi
mr.rou
Nnnr

Road
?
Mine EN "RO-NmENT
UNIT
Wetland 0 0.5 1
?
i Water ?
W Subwatershed Miles
Figure 3.1.4 Build Land Use Scenario
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Watershed Modeling Approach
4.1 Objectives and Model Selection
The objective of this modeling analysis is to quantify future pollutant loading as a result of
potential land use changes induced by the construction of the NC 43 Connector. The analysis
does not consider pollutant loading from existing conditions; instead, it quantifies the relative
changes between predicted future land use scenarios if the NC 43 Connector is constructed or not
constructed.
The two future land use scenarios, the Build and No Build Scenarios, were updated from the
2005 ICE as part of this study (Section 3). The updated land use forecasts were incorporated in
the model input files (Appendices A and B).
The water quality pollutants of interest in this study were TN, total phosphorus (TP), total
suspended solids (TSS), and storm event runoff volume. The modeling addresses nutrient
loading because the primary waterbody impairments in the area are low dissolved oxygen
concentrations, which can result from excessive nutrient loading. Nutrient loading was modeled
on a small watershed scale in order to assess impacts to local streams as a result of indirect and
cumulative development from the extension construction. TSS was also modeled because it is a
pollutant common to all watersheds and streams, and new development may cause additional
erosion. Storm event runoff was modeled because it is a primary cause of stream channel
erosion. This study did not analyze fecal coliform loading because there are no impairments due
to that pollutant and there are no waters designated for shellfish harvesting within the study area.
The GWLF model (Haith and Shoemaker, 1987; Haith et al., 1992) version 2.0 was chosen to
simulate long-term pollutant loading from 16 drainage areas within the ICE study area. The
modeled drainage areas contained all of the tax parcels predicted to have different land uses in
the Build and No Build scenarios. The same drainage areas were used when estimating storm
event runoff with the SCS Curve Number Method.
The GWLF model provides a simplified simulation of precipitation-driven runoff and sediment
delivery. Runoff, groundwater movement, and solids loading can then be used to estimate
dissolved and particulate nutrient delivery to the stream network, based on concentrations in
runoff, groundwater, and soil. The model is a well-accepted tool for estimating seasonal loads
from smaller watersheds (NCDENR, 2007). The model can account for point sources and septic
systems; however, none are located in the modeled areas. Based on its features, GWLF provides
a basis to estimate nutrient and sediment loading as a result of the two land use scenarios for the
NC 43 Connector.
GWLF falls in the mid-range of watershed model complexity. There are more detailed
mechanistic models, such as Hydrologic Simulation Program - Fortran (Bicknell et al., 1985)
and simpler empirical models, such as GIS Pollutant Load (PLOAD) (USEPA, 2001). GWLF is
useful for assessment with or without calibration. This study included more formal hydrologic
calibration using observed data from a nearby USGS gage. However, a similar water quality
monitoring station was not available. Therefore, calibration of the pollutant loading estimates
was not possible. Nevertheless, export from specific land uses was adjusted based on empirical
NC 43 Connector March 2011 Page 1 28
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evidence, and overall loading was compared with long-term observational averages from local
monitoring data.
4.2 The GWLF Model
The section provides an overview of the GWLF model, largely derived from the GWLF manual
(Haith et al., 1992). GWLF includes dissolved and sediment-bound nitrogen and phosphorus in
streamflow from urban and rural runoff, groundwater, and point sources. The model is
illustrated in Figure 4.2.1.
Rural nutrient loading is transported via runoff and eroded soil. Each rural land use (e.g.,
cropland, pasture, forest) is considered to be uniform in soil type, based on an area-weighted
composite of the soil hydrologic groups. Dissolved nutrient loads are calculated for each land
use by multiplying the predicted runoff by dissolved concentrations associated with a given land
use. GWLF estimates surface runoff using the SCS Curve Number Equation (SCS, 1986).
Sediment-bound nutrient loading is calculated by multiplying monthly sediment yield by average
sediment nutrient concentrations. Erosion is estimated using the Universal Soil Loss Equation
(USLE), which includes factors for slope length and angle, soil erosivity, and cropping and
management practices. The sediment yield is the product of erosion and sediment delivery ratio.
Urban nutrient loading is assumed to be entirely sediment-bound. It is modeled using
exponential buildup and washoff functions. Septic systems are classified by four types, one
working and three failing (ponding, short-circuiting, and direct discharge). Nutrient loading
from septic systems is calculated by estimating the daily per capita load from each type of
system and the number of people in the watershed served by each type.
The model uses daily time steps for water balance calculations. The water balance divides
precipitation inputs into streamflow (sum of surface and groundwater runoff),
evapotranspiration, and groundwater deep seepage. Daily evapotranspiration is determined by
the product of a vegetation cover factor and potential evapotranspiration, which is based on
temperature, time of year, and water vapor pressure in the soil profile.
Daily water balances are calculated for unsaturated and shallow saturated zones. Infiltration is
equal to precipitation minus runoff and evapotranspiration.
Daily temperature, precipitation, land use, transport parameters and nutrient concentrations are
required as inputs. Transport parameters for each runoff source (e.g., parcel) include areas,
runoff curve numbers, and USLE factors. Watershed transport parameters are groundwater
recession, seepage coefficients, and available water capacity in the unsaturated zone.
NC 43 Connector March 2011 Page 1 29
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Precipitation Evapotranspiration
Erosion
(USLE)
Land Surface - SCS Curve
Number Simulation
Unsaturated Zone
Shallow Saturated Zone
Deep Seepage
Loss
Runoff
Septic System Loads
Particulate
Nutrients
Dissolved Nutrients
Groundwater
(Shallow)
Loading to
Stream
Figure 4.2.1 Schematic of GWLF Model Processes (from NCDOT, 2006)
The GWLF model provides output for the following variables:
• Monthly Streamflow
• Monthly Watershed Erosion and Sediment Yield
• Monthly TN and TP Loading
• Annual Erosion from Each Land Use
• Annual and Monthly Nitrogen and Phosphorus Loads from Each Land Use
• Monthly Precipitation and Evapotranspiration
• Monthly Groundwater Discharge to Streamflow
• Monthly Watershed Runoff
• Monthly Dissolved Nitrogen and Phosphorus Loads in Streamflow
• Annual Dissolved Nitrogen and Phosphorus Loads from Septic Systems.
NC 43 Connector March 2011 Page 1 30
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5 GWLF Model Development
Descriptions of model development, data sources, parameter inputs, and assumptions for the NC
43 Connector project are provided in the following sections. The transport and nutrient input
files for all drainage areas and scenarios are shown in Appendix A.
The bulk of the model development was initially done by Stantec in 2006 (NCDOT, 2006).
Much of that work was left unchanged. Changes to the original assumptions and inputs are
specifically noted in the following sections.
5.1 Drainage Areas Delineation
The study area was delineated into seven subwatersheds ranging from 1.63 to 12.07 km' (0.63 to
4.66 mil) using a hydrology modeling extension developed for ArcGIS (ESRI, 2005). A 6-meter
(20-foot) digital elevation model (DEM), a raster grid of regularly spaced elevation values
derived from recent Light Detecting and Ranging (LIDAR) data and obtained from NCDOT
(2005), was used to develop drainage areas. Field reconnaissance to verify flow paths and
directions of drainage aided in refining the delineation. The size of each subwatershed in square
miles is shown in Figure 5.1.1.
5.2 Scenario Comparisons
Commercial, industrial, roadway, and residential land uses in the Build scenario are expected to
increase as compared to the No Build scenario. The development is expected to occur primarily
in the vicinity of the proposed facility. Table 5.2.1 shows the overall projected land use changes
expected within the project study area. Residential Medium High Density (RMH) is much
higher in the No Build scenario (95 percent) while Residential Multifamily Very High Density
(RVH) much more present in the Build scenario (47 percent).
Table 5.2.2 shows projected changes in land use from the No Build to the Build scenarios for the
subwatersheds in the project study area. While no land use differences are forecast to take place
in the Caswell Branch subwatershed, there are forecast differences in all other project study area
subwatersheds.
Table 5.2.1
Proiected Chanties in Land Use No Build versus Build in Study Area
No Build. Land Use hectares Build Land Use hectares
Types
COM 324.42 408.25
COMe 320.53 321.57
FOR 796.90 808.55
MINE 257.85 257.85
OFF 168.18 188.92
OFFe 128.90 128.61
RHH 896.18 1,025.20
RHHe 458.97 457.63
RLL 10.52 10.52
NC 43 Connector March 2011 Page 31
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No Build Land Use hectares Build Land Use hectares
RLLe 9.06 9.06
RMH 472.47 23.07
RMHe 76.30 76.30
RML 26.43 26.43
ROAD 305.36 364.51
ROW 29.43 29.43
RVH 291.11 428.14
RVHe 74.31 74.31
RVL 17.37 17.37
RVLe 0.38 0.38
UGR 429.65 444.69
WAT 316.18 316.18
WET 108.39 101.91
Grand
Total 5,514.72 5,514.72
Source: Baker 2011
Table 5.2.2
Projected Changes in Land Use No Build versus Build for Stud Area Subwatersheds
Caswell
Branch Deep
Branch Hayward
Creek Neuse River Rocky Run UT Wilson
Creek Wilson
"Creek
Types No Build/
Build No Build/
Build No Build/
Build No Build/
Build No Build/
Build No Build/
Build No Build/
Build
COM 57.73/57.73 21.24123.30 5.79/15.53 142.12/174.14 1.94/1.94 37.45/47.07 54.03/84.43
COMe 8.11/8.11 46.24/46.24 6.20/7.54 80.38/80.08 4.45/4.45 25.77/25.77 149.37/149.37
FOR 35.45/35.45 255.17/255.17 -/- 411.66 506.27/506.27 -/- -/-
MINE 125.23/125.23 119.00/119.00 -/- 13.62/13.62 -/- -/- -/-
OFF 0.28/0.28 118.31/118.31 14.47/14.47 22.59/43.34 6.47/6.47 1.68/1.68 4.38/438
OFFe -/- 3.33/3.33 0.01/0.01 46.31/46.01 5.57/5.57 0.19/0.19 73.50/73.50
RHH -/- 0/140.93 57.74/57.20 254.64/133.85 64.86/218.56 249.30/238.65 269.64/263.02
RHHe -/- -/- 1.34/0 99.05/99.05 0/0 106.11/106.10 252.47/252.47
RLL 10.41/10.41 0.07/0.07 -/- 0.04/0.04 -/- -/- -/-
RLLe 7.70/7.70 1.33/1.33 -/- 0.03/0.03 -/- -/- -/-
RMH 1.35/135 145.33/2.34 11.75/2.55 3.64/3.64 166.71/13.01 50.60/0.17 93.08/0
RMHe 1.55/1.55 -/- 10.26/10.26 4.67/4.67 58.72/58.72 1.10/1.10 -/-
RML -/- -/- -/- -/- 26.43/26.43 -/- -/-
ROAD 11.82/11.82 41.83/41.83 6.12/6.12 62.18/95.22 14.69/14.69 43.58/57.54 125.13/137.28
ROW 1.70/1.70 0.40/0.40 -/- -/- 27.32/27.32 -/- -/-
RVH 97.89/97.89 -/- -/- 133.34/150.12 -/- 45.41/83.90 14.46/96.23
RVHe 4.76/4.76 -/- -/- 38.84/38.84 -/- 19.02/19.02 11.69/11.69
RVL -/- -/- 17.37/17.37 -/- -/- -/- -/-
RVLe -/- 0.12/0.12 0.26/0.26 -/- -/- -/- -/-
UGR 127.7 20.59/20.59 4.98/4.98 46.61/59.27 49.35/49.35 28.39/28.39 151.90/154.28
WAT 127.84/127.84 - 3.42/3.42 -/- 178.55/178.55 -/- 18.08/18.08 0.07/0.07
WET -/- 6.67/6.67 25.87/25.87 25.18/19.67 0.3 42.02/41.04 8.35/8.35
Grand
To[al 607.87 783.06 162.15 1,151.8 933.08 668.6 1,208.07
Source: Baker 2011
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F
Caswell Bronco ,
2.3 mi' i .rf
?? 1 5
./ w
h N e-River,
4. mi
55
New Bern
Wilson Creek
Wilson 4.7 rrii"''

Co
Study Area C31Model Subwatemhed Figure 5.1.1
Proposed NC 43 Connector '-N* County Line Model
?- Roads New Bern ETJ Subwatersheds
/`- Railroads
Waterbody LL`? rnnG
ww((
' T
`

•J?-- Streams "RoNm
rrrr
ff
U .N .Nti IT
0 1 2
0
Miles
Figure 5. 1.1 Model Subwatersheds
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5.2.1 Model Imperviousness
The land use categories and percent impervious cover used in the model were derived from
the ICE assessment (NCDOT, 2006). Impervious cover affects the quantity and timing of
runoff, and consequently, the level of pollutant loading. The land use categories and average
percent impervious areas match those used in the SCS TR-55 Manual (SCS, 1986). The
categories and their percent imperviousness are presented in Table 5.2.3.
Table 5.2.3
Land Use Categories and Estimated Imperviousness
Land Use Name GWLF
Code Percent
Impervious
Residential - Very Low Density
2+ acres per dwelling unit RVL 8
Residential - Low Density
1.5-2 acres per d.u. RLL 14
Residential - Medium Low Density
1-1.5 acres per d.u. RML 18
Residential - Medium High Density
0.5-1 acres per d.u. RMH 23
Residential - High Density
0.25-0.5 acres per d.u. RHH 29
Residential - Multifamily/Very High Density
0.25 acres per d.u. RVH 50
Office/Institutional/Li ht Industrial OFF 70
Commercial/Heavy Industrial COM 85
Paved Road with Right of Way** ROAD 85
Urban Green Space/Golf Course UGR 0
Row Crop ROW 0
Forest FOR 0
Wetlands WET 0
5.3 Surface Water Hydrology
Table 5.3.1 summarizes the surface water inputs and assumed values used in the GWLF
modeling analysis. More detail on the individual parameters is provided in the following
sections.
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Table 5.3.1
Surface Water Hydrology Input Parameters
Input Description., . Unit Baseline Comments/ - Reference,
Parameter Value Literature Ran e .
Precipitation Daily rainfall cm Annual 1 I years of data Data from
Min = 96.5 (1998-2009) used Craven
Max = 183.7 for simulation and County
Mean = 129.4 assumed to be Airport
uniform for the (KEWN) and
study area COOP Station
316108, State
Climate
Office of NC
Evapotranspir- Cover none Values range Rural land uses: Huth et al.
ation (ET) Cover coefficient from 1.0 for default values (1992)
for estimating forest to 0.15 for derived based on
ET high intensity land use. Urban land
urban category uses: one minus
COMM impervious fraction
Antecedent Soil Moisture for up cm 0 Unknown and Haith et al.
Moisture to five days therefore assumed in (1992)
Conditions prior to initial accordance with
step manual to be zero
Runoff Curve Parameter for none Ranges from 63 Site dependant SCS (1986)
Numbers converting to 98 in the based on soil type
mass rainfall to current study and land use
mass runoff
5.3.1 Precipitation
Daily rainfall records from two stations, located one kilometer apart and 4.8 kilometers from
the study area were obtained from the North Carolina State Climate Office: Craven County
Airport (KEWN) and COOP Station 316108 (Figure 4.1.1). Baker added precipitation from
COOP Station 316108 from 4/1/05 to 4/1/09 to the previous seven-year time series
assembled in NCDOT, 2006. Thus, rainfall data for an 11-year period were used for this
study. NCDOT 2006 stated that data from station KEWN for the period 4/1/98 - 3/31/99 was
appended to data from station 316108 for the period 4/1/99 - 3/31/05. Missing values in the
time series from station 316108 were filled in using either values from KEWN or the average
for that month.
The mean rainfall over the 11-year period is 7 percent below the long-term average (139 cm)
at station 316108, indicating that the model simulation period includes representative, though
slightly dry, hydrologic conditions for the area. Rainfall was assumed uniform throughout the
study area.
5.3.2 Evapotranspiration Cover Coefficients
Precipitation that is returned to the atmosphere by evapotranspiration (ET) is a function of
temperature and vegetative cover. Rural land use coefficients were set according to values
provided in the GWLF manual (Haith et al., 1992). The ET cover coefficients were area-
NC 43 Connector March 2011 Page 1 35
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weighted by land use and specific to each drainage area. Per the GWLF manual, urban
coefficients were set equal to one minus the impervious fraction. The portion of deciduous
trees was not known, so vegetation was assumed to grow year round. Cropland was the only
land use that had different dormant and growing season coefficients.
5.3.3 Antecedent Soil Moisture Conditions
Antecedent soil moisture conditions are a function of rainfall levels up to five days prior to
the day on which modeling begins. Antecedent soil moisture conditions were unknown and
were assumed to be zero as per guidance provided in the GWLF manual (Haith et al., 1992).
5.3.4 Runoff Curve Numbers
The portion of rainfall that becomes runoff in GWLF depends on the SCS Curve Number.
The curve numbers were taken from the TR-55 Manual (SCS, 1986) and are based on soil
hydrologic group and percent impervious cover. Soil hydrologic groups were determined
using the detailed Soil Survey Geographic (SSURGO) database (USDA-NRCS, Brunswick
County and New Hanover County htty://www.netic.nres.usda.gov/products/datasets/ssurgoo-
Hydrologic response units (HRU) were derived by combining land use categories with soil
hydrologic groups. Each HRU was assigned a curve number based the TR-55 Manual (SCS,
1986) and interpolations where needed. Table 4.3.2 displays the curve numbers based on
land use and soil group in this study. The HRUs were area-weighted to derive one number
per land use in each drainage area.
Table 5.3.2
Curve Numbers for Land Use and Soil Hydrologic Groups
Land Use Land Use Group Group Group Group Group
Name Code A B C D, B&D
Residential - Very RVL 44 64 76 82 73
Low Density
Residential - Low

Density RLL 47 66 77 83 75
Residential -
Medium Low RML 50 67 78 84 76
Density
Residential -
Medium High RMH 53 69 80 84 77
Density
Residential - High
PHH 57 72 81 86 79
Density
Residential-Very
High Density RVH 68 .79 86 89 84
Office/Light
Industrial OFF 80 87 91 93 90
Commercial/Heavy
COM 89 92 94 95 94
Industrial
Paved Road with
Right of Way ROAD 83 89 92 93 91
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Land Use
Name Land Use
Code Group
A Group
B Group
C Group'
D Group
B&D
Urban Greenspace UGR 49 69 79 84 77
Row Crop ROW 67 78 85 89 84
Forest FOR 33 57 71 78 68
Wetlands WET 45 66 77 83 75
Water WAT 98 98 98 98 98
Source: NCDOT, 2006
5.4 Groundwater Hydrology
A summary of assumptions and values for the groundwater input parameters is provided in Table
5.4.1. Further discussion on the parameters is provided below.
5.4.1 Recession Coefficient
The rate at which groundwater is discharged to stream channels in the model is governed by
the recession coefficient. No flow data were available within the study area, so an empirical
equation developed by Lee et al. (1999) was used. The authors developed the following
equation for the recession coefficient using GWLF model calibrations and regression
analyses on numerous watersheds:
R = 0.045 + 1.13 * (0.306 + DA)"'
Where DA = drainage area in km2
Recession coefficients were calculated for each of the 16 drainage areas. Results ranged in
value from 0.14 to 0.63.
5.4.2 Seepage Coefficient
GWLF controls the portion of rainfall lost to deep aquifers using the seepage coefficient.
The manual states that no standard technique is available for estimating this rate and
recommends that it be determined by model calibration. In eastern North Carolina, 2.5 to 5
cm per year typically infiltrates through to deep groundwater aquifers, representing about
two to three percent of the water balance (Evans et al., 2000). The seepage coefficient was
set to a value (0.005) that produced a two percent loss to deep groundwater.
5.4.3 Available Soil Water Capacity
The amount of water available to be held in the soil profile, or available water capacity
(AWC), is dependent on the soil porosity and texture, among other variables. Volumetric
AWC estimates were obtained from the SSURGO database and area-weighted according to
the soil types in each drainage area. Values for the seven subwatersheds ranged from 12.9 to
19.0 cm. These values assumed a 100-cm rooting depth according to the GWLF manual.
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5.4.4 Initial Unsaturated and Saturated Storage
The GWLF manual recommends values for 10 and 0 cm for initial unsaturated and saturated
storage, respectively, when these values are uncertain, as was the case in this study.
Table 5.4.1
Groundwater Input Parameters
Input Parameter Description Unit Baseline Comments/ Reference
Value Literature Range
Basellow Recession Groundwater Day' Drainage area- Lee et al.
Coefficient (r) seepage rate Min = 0.14 dependent and (1999)
Max = 0.63 calculated by Lee et al.
Mean = 0.24
1999
Seepage (s) Deep seepage Day' Site dependant; Goal Haith et al.
coefficient to generate 2% deep (1992); Evans
0.005 seepage over the et al. (2000)
simulation period
Available Soil Interstitial cm Min = 12.9 Determined from Haith et al.
Water Capacity storage Max = 19.0 SSURGO soils data (1992)
Mean = 16.2
Initial Unsaturated Initial amount cm GWLF Manual Haith et al.
Storage of water stored Default (1992)
in the 10
unsaturated
zone
Initial Saturated Initial amount cm GWLF Manual Haith et al.
Storage of water stored 0 Default (1992)
in the
saturated zone
5.5 Erosion and Sediment Transport
Table 5.5.1 summarizes erosion and sediment transport inputs and assumed values used in the
GWLF modeling analysis. More detail on the individual parameters is provided in the following
sections.
Sediment loss in GWLF is simulated through application of the USLE, which uses four input
factors: K for soil erodibility; LS for length-slope factor; C for cover factor; and P for
management practice factor.
5.5.1 Soil Erodibility Factor
The soil erodibility factor, K, is the propensity of a soil to erode when it is struck by water.
K values were obtained from the SSURGO database and were area-weighted by rural land
use type in each modeled drainage areas. For the four soil groups distributed within the
study area, the K factors ranged from 0.15 to 0.32.
5.5.2 Length-Slope Factor
The length-slope factor is the average slope length (L) that travels from the highest flow path
within a drainage area to the point at which it reaches concentrated flow multiplied by the
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slope (S), which represents the effect of slope steepness for each soil type. Higher slopes
increase erosion risk for a given soil type.
LS factors for this modeling analysis were generated in NCDOT, 2006 using GIS spatial
analysis using the USLE Sediment Tool included in the USEPA Watershed Characterization
System (Tetra Tech, 2000). Area-weighted values ranged from 0.13 to 1.4, with the high
values associated with the quarries.
Table 5.5.1
r7nrel Codimnnt Trnnsnnrt inmrt Parameters
Input Parameter Description Unit Baseline Comments/ Reference
Value- Literature
Range
Rainfall Erosivity Kinetic energy MJ-Mm/ha Min = 0.16 Rainfall Haith et al.
(R) of rainfall (cool season) erosivity; (1992) for
Max=0.28 varies Wilmington,
(warm season, seasonally NC
A r-Oct
Soil Erodibihty Soil erosion none Area-weighted Derived from SSURGO soils
Factor (K) potential Min = 0.15 soils GIS data data for the
Max = 0.32 (function of study area
soil texture
and porosity)
Length-Slope Sediment none Varies by Derived from USEPA
Factor (LS) transport subwatershed DEM as a Watershed
potential based function of Characterization
on topography slope and System (Tetra
overland Tech,2000)
runoff
Sediment Delivery Portion of none Varies by Empirically- BasinSim
Ratio (SDR) eroded subwatershed derived Utility
sediment that relationship (Dai et al.,
is transported 2000)
to receiving
waters
5.5.3 Cover (C) and Management Practice (P) Factors
Soil erosion is also affected by the type of cover vegetation (C) (e.g., soybeans or forest) and
the practice by which soil erosion is managed (P) (e.g., no support practice or planting on
contours). Cover and management factors for non-agricultural land uses in this study are
from the GWLF manual (Haith et al., 1992). With limited cropland acreage in the modeled
drainage area and uncertainty about the type of crops grown and the erosion-control practices
employed, it was assumed that the cropland C was 0.1 and P was 0.6. Factors for cropland
were estimated from the North Carolina Revised USLE Manual (USDA, 1995; NCDOT,
2006). The P factor is equivalent to using contour plowing and C is indicative of a
moderately productive rotation of corn, wheat, and hay (Stewart et al., 1975; Haith et al.,
1992). Cover and management factors for non-agricultural land uses in this study are from
Haith et al. (1992). The C factor selected for forested land was 0.001, which indicates a tree
canopy of 75 to 100 percent.
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Table 5.5.2
Cover and Management Practice Factors
Land Use Name Cover Factor Management Practice Factor
Residential - Very Low Density 0.0100 1.000
Barren Land 0.5000 1.000
Wetlands 0.0020 1.000
Forest 0.0020 1.000
Row Crop 0.0940 0.600
Urban Grass 0.0065 1.000
5.5.4 Sediment Delivery Ratio
The sediment delivery ratio in GWLF accounts for the portion of erosion that is delivered to
the stream network from the edge of field, with the balance trapped in the watershed. The
BasinSim version of GWLF, used by in NCDOT 2006 included a software utility that
calculates the sediment delivery ratio on the basis of the drainage area of the subwatershed
being simulated. Sediment delivery ratios in the study ranged from 0.212 to 0.318.
5.5.5 Sedimentation from Urban Land Uses
For urban land uses, the GWLF model calculates particle loads associated with particulate
nutrients without calculating sediment load. For the present study, sediment from urban
sources was modeled using the same accumulation and washoff functions from the model
substituting sediment accumulation rates for particulate nutrient accumulation rates. This
procedure follows Schneidermann et al. (2002).
Suspended solids accumulation rates.were estimated from Kuo et al. (1988) as presented in
the GWLF manual (Haith et al., 1992). One rate was set for each urban land use by
interpolating between the estimates for pervious and impervious surfaces. Rates for
residential land uses ranged from 1.8 to 3.7 kg/ha/day, with values increasing with
imperviousness. Rates for nonresidential land uses including commercial and institutional
categories were 2.2 to 2.5 kg/ha/day, respectively.
The accumulation rate (1.8 kg/ha/day) for roads was determined in NCDOT 2006 by
iteratively running the Wilson Creek No Build Scenario, adjusting the rates until the model
predicted an export rate of 185 kg/ha/yr. The target export is based on the average of the
North Carolina value from the Federal Highway Administration (FHWA) (1990) and
regional event mean concentration values in USEPA (2001).
5.6 Nutrient Loading
A summary of assumptions and values for the nutrient input parameters is provided in Table
5.6.1. Further discussion on the parameters is provided below.
5.6.1 Solid Phase Nutrients
Loading of nutrients attached to sediment particles is governed in the model by soil nutrient
concentrations multiplied by an enrichment ratio. The soil nutrient concentrations in the
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model inns were set at 1,400 mg/kg and 352 mg/kg for nitrogen and phosphorus,
respectively. These parameter estimates were derived from guidance in the GWLF manual
(Haith, 1992) and regional soil nutrient concentration observations (Parker et al., 1946; Mills
et al., 1985).
5.6.2 Groundwater Nutrient Concentrations
Values for nutrient concentrations in groundwater discharge to the stream network were
based on work by Spruill et al. (1998). This study monitored groundwater concentrations in
the Albemarle-Pamlico Drainage Basin and included sample statistics for the outer Coastal
Plain. The resulting median values used for this study were 0.42 and 0.04 mg/l for nitrogen
and phosphorus, respectively.
Table 5.6.1
Nutrient Loadin Input Parameters
Input Par"ameter iDescription- Unit =e ° a rBaseline - + Comments/, 'Reference
Value „Literature
`Ran 'e tt ei:
Solid Phase Nutrient Loadin
Nutrient Total nitrogen mg/kg 1,400 Varies Haith et al.
Concentration in concentration regionally and (1992);
Sediment from by site; 500- Mills et al.
Rural Sources 900 based on (1985)
literature;
multiplied by .
a mid range
enrichment
values of 2.0
Total mg/kg 352 Varies Haith et al.
phosphorus regionally and (1992);
concentration by site; less Mills et al.
than or equal (1985)
' to 400; multi-
plied by P2O1
conversion
factor (0.44),
enrichment
ratio of 2.0
Dissolved Nutrient in Groundwater
Nutrient Total nitrogen ml/L 0.42 Median value Spruill et al.
Concentration concentration for the inner (1998)
Coastal Plain '
Total mUL 0.04 Median value Spruill et al.
phosphorus for the inner (1998)
concentration Coastal Plain
5.6.3 Runoff Concentrations and Accumulation Rates
GWLF uses accumulation (buildup) and washof£ functions to predict nutrient loads from
urban land uses and runoff concentrations to predict nutrient loads from rural land uses. For
modeling purposes in this study, all residential land uses were considered to be urban. The
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accumulation rates and runoff concentrations used in this study are presented in Table 5.6.2.
The selected values were based on those used in the Jordan Lake TMDL watershed model
(TetraTech, 2003), with some adjustments. These rates are significantly higher than the
GWLF default values; however, they were based on event mean concentrations from Line et
al. (2002), CH2M Hill (2000), Greensboro (2003), and USEPA (1983). Those rates were
found to be in agreement with export coefficients reported in the literature (CDM, 1989;
Hartigan et al., 1983; USEPA, 1983; Beaulac and Reckhow, 1982; and, Frink, 1991). The
Jordan Lake values appear to be more appropriate given that they are largely based on North
Carolina monitoring data.
Table 5.6.2
Nutrient Runoff and Buildup Rates for Existing Land Uses
Runoff Concentrations
Rural Land Uses - Dissolved N m L Dissolved P m
Pasture 2.770 0.250
Row Crop 2.770 0.250
Forest 0.190 0.006
Wetlands 0.190 0.006
Barren 0.190 0.006
Urban Greens ace 0.200 0.0065
Residential - Very Low Density 0.230 0.007
Mass Buildu Rates
Urban Land Uses N Buildup k a/da P Buildup k ha/da
Residential - Low Density 0.214 0.040
Residential - Medium Low Density 0.242 0.040
Residential - Medium High Density 0.242 0.040
Residential - High Density 0.219 0.037
Residential- Very High Density 0.201 0.033
Office/Li ht Industrial 0.158 0.025
Commercial/Heavy Industrial 0.191 0.029
Roadways 0.052 0.006
Quarry 0.055 0.005
Buildup rates for roadways were assigned by running the model iteratively to produce the
loading rates for nitrogen and phosphorus of 5.5 kg/ha/yr and 0.7 kg/ha/yr, respectively (FHWA,
1990; USEPA, 2001). Urban greenspace land uses were assigned values between very low
density residential and forest land uses.
An important assumption of the analysis was that the study area would be served by the existing
wastewater treatment plant of the City of New Bern (Avery, personal communication, 2005). As
a result, no inputs for septic tanks were included in the GWLF modeling analysis. Also, there
are no permitted point sources of pollutant load located within the study area.
5.7 Consideration of Existing Environmental Regulations
5.7.1 Neuse River Nutrient Sensitive Waters Management Rules
The Neuse NSW stormwater management program imposes a 4.0 kg/ha/yr (3.6 pounds per
acre per year or lb/ac/yr) nitrogen loading limit on new development. Nitrogen loads from
NC 43 Connector March 2011 Page 1 42
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new developments that exceed this performance standard may be offset by payment of a fee
to the Ecosystem Enhancement Program provided, however, that no new residential
development can exceed 6.7 kg/ha/yr (6.0 lb/ac/yr) and no new nonresidential development
can exceed 11.2 kg/ha/yr(10.0 lb/ac/yr).
Since most existing development within the study area occurred before 1998, all existing
development was assigned loading rates shown in Table 5.6.2. Rates for future residential
and nonresidential development were determined using the iterative process described in
section 5.5.5, targeting TN export rates of 6.5 and 4.4 kg/ha/yr for nonresidential and
residential land uses, respectively. These export rates are based on an approximation of the
percent of the time that land developers in New Bern choose to use the payment offset
provision in the regulations rather than implementing best management practices to achieve
the loading limits. Meadows (2006) suggests that use of the offset provision occurs 15 and
50 percent of the time for residential and commercial development, respectively. Weighted
build-up rates were determined accordingly. These rates were applied to all subwatersheds
with the exception of the Neuse subwatershed. In the Neuse subwatershed, where the Craven
30 development is proposed, loading rates equivalent to the maximum allowed under the
Neuse Rules were assumed. Weyerhaeuser Corporation, which is developing the Craven 30
project, has expressed their intention of using the maximum offset payment permitted. The
modeled rates assume a worst-case scenario that the offset payments will not result in
implementation of stormwater best management practices within the project study area.
Reductions in nitrogen loading will be accompanied by reductions in TP and TSS (NCDWQ,
2004 and 2005). A concomitant reduction of 30 percent in both constituents is assumed and
implemented in the model simulations. However, further TSS reductions are predicted based
on the Coastal Stormwater Rule described below. The Coastal Stormwater Rule TSS
reductions took precedence where it applied.
An additional feature of the Neuse rules requires no net increase in peak flow leaving a
newly developed site compared to predevelopment conditions for the one-year, 24-hour
storm. This feature was not explicitly incorporated into the model simulation for two
reasons. Since most BMPs convert little runoff to infiltration, mitigating peak flows will
have little impact on long-term runoff rates or volumes. In addition, BMPs for water quality
provide some control of peak flow, so some of this required control is considered implicitly.
In all three land use scenarios, a 50-foot buffer on all perennial and intermittent streams
identified on the USGS-based stream coverage was classified as urban greenspace.
5.7.2 Coastal Stormwater Rule
As explained in Section 2.1.3, the Coastal Stormwater Rule passed in January 2008 requires
control of the first one and a half inches of rainfall and removal of 85 percent of the annual
TSS load from new developments with more than 24 percent impervious cover.
Control of the first one and a half inches of rainfall was factored into this study because the
rule is meant to detain runoff to mitigate peak stream flow. The SCS Curve Number Method
NC 43 Connector March 2011 Page 1 43
ICI Water Quality Report
(see Section 6), which estimates total runoff, was altered to reduce precipitation by 1.5 inches
where the CAMA rules applied.
The 85 percent TSS removal requirement of this regulation was incorporated into the
modeling analysis by reducing the sediment accumulation rate on land uses with assumed
impervious cover greater than 24 percent. This applies to commercial, industrial, and high-
and very high- density residential land uses. The TSS removal requirement was applied by
multiplying the accumulation rates for these land uses by 0.15. This assumes that nearly all
TSS is transported in the first 1.5 inches of rainfall. Over the course of the 1 I-year
precipitation record used for this study, only 2 percent of the days had more than 1.5 inches
of rain. Furthermore, it seems reasonable to expect nearly all of the accumulated TSS to be
washed off the landscape with this amount of rain.
5.8 Model Implementation
Individual model runs were conducted for the Build and No Build scenarios in the seven
subwatersheds using the input files for transport, nutrients, and sediment. The model input files
are provided in Appendix A. The same weather file was used in all model runs.
6 Model Results and Discussion
6.1 Hydrology
The GWLF hydrology inputsfrom the 2006 Stantec ICI study were used for this analysis because
the hydrologic calibration was accepted by NCDWQ. Components of the hydrologic cycle
illustrated in Figure 4.2.1 include precipitation, evapotranspiration, runoff, and deep groundwater
seepage. In eastern North Carolina, rainfall typically ranges from 112 to 152 cm (44-60 in).
Evapotranspiration (ET), runoff (surface and subsurface) and deep groundwater outflow range
from 81 to 102 cm (32-40 in), 30 to 51 cm (12-20 in), and 3 to 5 cm (1-2 in), respectively (Evans
et al., 2000).
A comprehensive study of hydrology of forested lands in eastern North Carolina found that
annual outflow or runoff from forested sites ranged from 17 to 45 percent of rainfall (Chescheir
et al., 2003). Runoff from the most undeveloped subwatershed in the model simulations, Rocky
Run, comprised 39 percent of the water balance over the simulation period for the No-Build
Scenario. ET comprised 59 percent of the water balance, lower than the typical range of 67 to 73
percent cited by Evans et al. (2000). The lower percentage of ET is likely due to the greater
amount of development compared to the typical mass balance described in Evans et al. (2000).
Urbanization is accompanied by a decrease in vegetation available to produce evapotranspiration
as well as a greater proportion of surface runoff (versus subsurface runoff in shallow
groundwater). For the study area as a whole, ET and runoff were 46 and 53 percent of total
rainfall for the No Build Scenario.
The seasonal change in hydrologic conditions in the Rocky Run subwatershed is shown in Figure
5.1.1. As expected, evapotranspiration decreases in winter due to lower temperatures and
dormant vegetation resulting in a higher proportion of runoff.
NC 43 Connector March 2011 Page 44
ICI Water Quality Report
20
18
16
14
12
E 10
8
6
4
2
0
---k-Precipitation (cm)
-e-Evapotranspiration (cm)
-* Subsurface Runoff (cm)
* Surface Runoff (cm)
*Total Runoff (cm)
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
Figure 6. 1.1 Mean Monthly Water Balance for the Rocky Run Subwatershed (No Build Scenario,
from NCDOT, 2006)
6.2 Pollutant Loading Results
The model was run for seven subwatersheds for the Build and No Build scenarios and produced
loading predictions for total nitrogen, total phosphorus, and sediment. The annual loads from
each drainage area and for each pollutant were summed over the 11-year modeling period. The
results are shown in Tables 6.1.2, 6.1.3, and 6.1.4; and Charts 2, 3, and 4.
Table 6.1.2
11_Vnar Tntal Nitrnorn Lnads (Mgl for all Drainage Areas
Subwatershed No Build Alternative Build Alternative ; Percent Change over,
No Build
Caswell Branch 32.3 32.3 0%
Dee Branch 52.3 54.8 4.8%
Hayward Creek 10.2 10.8 5.9%
Neuse River 123.2 126.4 2.6%
Rock Run 34.9 36.4 4.3%
L FT to Wilson Creek 50.5 52.5 3.0%
Wilson Creek 135.9 137.9 1.5%
TOTAL 4393 450.6 2.6%
NC 43 Connector March 2011 Page 45
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Chart 6.1.1
11-Year Total Nitrogen Loads for all Subwatersheds
160

140

c 120

0
~
100
V
80
a
60
c
c 40
o
E 20
a 0
Caswell Deep Hayward Neuse Rocky Run UT to Wilson
Branch Branch Creek River Wilson Creek -
Creek,
¦ No-Build Alternative ¦ Build Alternative
Table 6.1.3
NC 43 Connector March 2011 Page 46
ICI Water Quality Report
Chart 6.1.2
Table 6.1.4
11-Year Total Sediment (TSS) Loads (Ma) for all Drainage Areas
Subwatershed

Caswell Branch No Build Alternative

514.7 Build Alternative

514.7 Percent Change over
No Build
0%
Dee Branch 621.9 520.3 -16.3%
Hayward Creek 130.5 130.7 0.2%
Neuse River 1139.8 1187.8 4.2%
Rock Run 743.6 646.0 -13.1%
UT to Wilson Creek 480.9 455.4 -5.3%
Wilson Creek 1635.2 1629.2 -0.4%
TOTAL 5266.6 5084.1 -3.6%
NC 43 Connector March 2011 Page 147
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Chart 6.1.3
11-Year Total Sediment Loads for all Subwatersheds
1800

1600

0 1400,
-
1200

v 1000

800

= 600

400

E 200
0
Caswell Deep Hayward Neuse Rocky Run UT to Wilson
Branch Branch Creek River Wilson Creek
Creek
- 0 No-Build Alternative ¦ Build Alternative
This analysis projects slight nutrient load increases in the Build Scenario beyond the No Build
Scenario of 1 to 3 percent over nearly 14,000 acres in the modeled drainage areas. TN loading
increased by 2.6 percent, while TP loading increased by 1.6 percent. The nutrient load increases
are the result of land uses with somewhat higher impervious cover in the Build Scenario than the
No Build Scenario (see Appendix B for projected land use differences).
The subwatersheds that had the highest differences in total nitrogen loading between the Build
and No Build scenarios are Hayward Creek (5.9 percent), Deep Branch (4.8 percent), and Rocky
Run (4.3 percent). The remaining subwatersheds had differences of 3 percent or less. The
higher total nitrogen loading in Hayward Creek was the result of less than 10 hectares being
developed as commercial land (Build) instead of medium high density residential land (No
Build). In Deep Branch, the higher nitrogen load was due to a 143-hectare difference in high
density residential (Build) versus medium-high density residential (No Build). This was also the
case in Rocky Run where approximately 150 hectares were assumed to be high density
residential in the Build scenario and medium-high density residential in the No Build scenario.
Developed land has higher nutrient loading than less developed land (i.e., lower impervious
cover percentages) because there are more nutrient sources (e.g., pets, vehicles, lawn fertilizer)
and more direct delivery (i.e., less infiltration, more runoff). Sediment (TSS), however, declined
in several drainage areas as a result of the Coastal Stormwater Rule requiring an 85 percent
reduction in TSS loading on all new development with greater than 24 percent impervious cover.
Cumulative sediment loading decreased by 3.6 percent in the Build Scenario compared to the No
Build Scenario.
NC 43 Connector March 2011 Page 1 48
ICI Water Quality Report
As a result of the Coastal Stormwater Rule requirements (see Section 5.8.2), model predictions
show reductions in TSS loading compared to slight increases in nutrient loading. Whether these
reductions are realized is dependent upon enforcement of the regulations. Assessing the
effectiveness and enforcement of the regulation is outside of the scope of this study. Any
practices used to decrease TSS loading would likely also reduce nutrient loading, particularly
phosphorus since it is frequently sediment-bound.
6.3 Nitrogen Loading to the Neuse River Estuary
Given concerns about water quality in the Neuse River estuary, it is important to consider how
the predicted increase in nitrogen loading predicted by the GWLF model compares to the
cumulative nutrient loading to the Neuse River estuary. Total nitrogen is the limiting nutrient to
algal growth in the estuary and is subject to an EPA-approved Total Maximum Daily Load
(TMDL). The TMDL for total nitrogen is 8,388 kilograms per day (6.75 million pounds per
year) (NCDENR, 2001). The ICI model results in Mg over an 11-year period were converted to
kg per day and compared to the estuary inputs. Table 6.3.1 shows the results.
Table 6.3.1
Proiect Area Nitrogen Loading as a Percentage of Nitrogen Load
Scenario TN units
Build 450.6 M
No Build 439.3 M

Build 112.2 k d
No Build 109.4 k d
ONIMIE W
R

Build
1.338 .
% of TMDL to estuary
No Build 1.304 % of TMDL to estuary
ing to Estuary
The loading from the ICI study area amounts to roughly 1.3 percent of the loading to the estuary.
The nitrogen load difference between the Build and the No Build (2.6 percent) appears to be
inconsequential in terms of estuarine water quality, but the increase in load from either scenario
above existing conditions from may have an effect on estuarine water quality.
NC 43 Connector March 2011 Page 1 49
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7 Stream Erosion Risk Analysis
Land development adds impervious cover to a watershed, which increases the volume and
decreases the delivery time to the stream network. As a result, high stream flow events increase
in frequency and magnitude, which results in stream channel erosion. To assess the potential for
stream channel erosion as a result of constructing the NC 43 Connector, an analysis using the
SCS Curve Number Method was performed (SCS, 1986). The method and results are outlined
below.
7.1 Method
The Curve Number Method estimates drainage area-wide runoff following a rainfall event. The
approach uses three equations. First, runoff retention is approximated for each land use using:
Su = (1,000/CNu) - 10
Where S„ = retention on land use u and CNu = curve number for land use u.
The curve numbers used for this analysis are the same as those shown in Table 4.3.2.
The runoff contributed by each land use in a drainage area is estimated using:
Qu = (P - 0.2*Su)z / (P + 0.8*Su)
Where Qu = flow volume contributed by land use u and P = rainfall.
The total flow volume for each drainage area is estimated by summing Qu for each land use.
Three storm events were used in the analysis: the 24-hour storm occurring with a frequency of
one, five, and ten years. The rainfall totals for these storms are 3.49, 5.49, and 6.54 inches,
respectively. Which storm has the greatest potential for channel erosion depends on whether a
floodplain bench is present and, if so, the elevation of the bench. In general, however, higher
precipitation results in greater channel erosion potential.
This exercise factored the requirement of the CAMA stormwater management rules requiring the
control of the first 1.5 inches of rainfall for new developments with more than 24 percent
impervious area. Though eventually nearly all of this runoff would enter the stream network, the
peak flows, which typically have the biggest effect on channel erosion, would be reduced.
Therefore, the SCS estimate for total runoff was altered slightly by reducing precipitation by 1.5
inches in the calculations.
7.2 Results
The Curve Number Method was applied to the seven subwatersheds for both the Build and the
No Build scenarios. The results for the 1-year (Table 7.2.1, Chart 5), 5-year (Table 7.2.2, Chart
6), and 10-year (Table 7.2.3, Chart 7) storm events show that the Build scenario would decrease
runoff volume by 1 to 3 percent depending on whether the 1-, 5-, or 10-yr 24-hour storm is
NC 43 Connector March 2011 Page 50
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considered. The Build scenario has 3 percent less runoff volume than the No Build Scenario for
the 1-year storm; 1.5 percent less for the 5-year storm; and 1 percent less than the 10-year storm.
The 1-year storm is frequently the event that stormwater BMPs are designed to control since it
happens more frequently and will flush a high percentage of pollutants from the landscape into
the stream network.
Table 7.2.1
Storm Flow Volumes (m3) for the 1-Year. 24-Hour Storm (1 acre-foot=1233.5 m})
W60alerstiedJ N6jBuild Altternatrve .:Build Alternative P,eicenttClian e:over NolBiiild
Caswell 49,653 49,653 0.0%
Dee 53,431 46,426 -13.1%
Ha and 7,414 7,513 1.3%
Neuse 82,918 87,541 5.6%
Rock 52,347 45,788 -12.5%
UT Wilson .31,080 30,839 -0.8%
Wilson 79,758 77,747 -2.5%
Total 356,600 345,506 -3.1%
Chart 7.2.1
Runoff Predictions for 1-Year 24-Hour Storm using SCS
Curve Number Method
100,000
80,000
a
.Du 60,000
3
40,000
zt:
0 20,000
3
iiAi I
Caswell Deep Hayward Neuse Rocky UT Wilson Wilson
¦ No-Build Alternative ¦ Build Alternative
NC 43 Connector March 2011 Page 151
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Table 7.2.2
Storm Flow Volumes m3 for the for the 5-Year, 24-Hour Storm 1 acre-foot=1233.5 m3)
kSubwat6rshedW 4NoiBuildiAlternative ,?BuildrAlternative? iPercentiChan a?over4No)Buildii
Caswell 95,915 95,915 0.0%
Dee 109,634 101,454 -7.5%
Hayward 18,065 18,354 1.6%
Neuse 168,989 174,694 3.4%
Rock 114,371 106,412 -7.0%
UT Wilson 74,705 75,011 0.4%
Wilson 165,861 164,119 -1.1%
Total 747,540 735,958 -1.5%
Chart 7.2.2
200,000
N
L
160,000
v
120,000
80,000
c
o 40,000
c
0
0
Runoff Predictions for S-Year 24-Hour Storm using SCS
Curve Number Method
Caswell Deep Hayward Neuse Rocky UT Wilson Wilson
¦ No-Build Alternative ¦ Build Alternative
Table 7.2.3
Storm Flow Volumes m3 for the for the 10-Year, 24-Hour Storm 1 acre-foot=1233.5 m3)
hSubwateistied fNoBoildYklte WrtJfgeiI OBuild$Alte'ruativej OPe"r&iASChan "T} ,VirA&Buil&
Caswell 121,112 121,112 0.0%
Dee 140,822 132,361 -6.0%
Hayward 24,229 24,592 1.5%
Neuse 216,369 222,343 2.8%
Rock 149,726 141,442 -5.5%
UT Wilson 99,933 100,447 0.5%
Wilson 213,981 212,366 0.8%
Total 966,172 954,663 -1.2%
NC 43 Connector March 2011 Page 1 52
ICI Water Quality Report
Chart 7.2.3
Runoff Predictions for 10-Year 24-Hour Storm using SCS
Curve Number Method
250,000
a
Y
? 200,000
150,000
3
300,000
O 50,000
C
3
0
Caswell Deep Hayward Neuse Rocky UT Wilson Wilson
¦ No-Build Alternative ¦ Build Alternative _
8 Conclusions
The GWLF model was applied to analyze the impacts on water quality from land use changes
predicted to occur with the construction of the NC 43 Connector (TIP Project No. R-4463). This
analysis projects nutrient load increases in the Build Scenario beyond the No Build Scenario of
1.6 percent for phosphorus and 2.6 percent for nitrogen over 13,627 acres in the modeled
drainage areas. The nutrient load increases are the result of more urbanized land uses (i.e.,
higher impervious percentages) in the Build scenario compared to the No Build scenario (see
Table 5.2.2 and Appendix B). These land use changes have less effect on storm runoff, where 1
to 3 percent less runoff is expected in the Build Scenario as a result of the Coastal Stormwater
Rule requirements for control of the first 1.5 inches of rainfall on developments with 24 percent
impervious cover or higher. Similarly, sediment (TSS) declined in many drainage areas as a
result of the Coastal Stormwater Rule requirement of an 85 percent reduction in TSS loading
from all new development with greater than 24 percent impervious cover. In all drainage areas
combined, TSS loading was 3.6 percent lower in the Build scenario than the No Build one. J>
Nutrient accumulation rates are subject to the Neuse Rules and were treated accordingly in
the modeling (see Section 5.7.1). Since most existing development within the study area
occurred before 1998, all existing development was assigned loading rates shown in Table
5.6.2. Rates for future residential and nonresidential development were determined using
the iterative process described in Section 5.5.5 targeting TN export rates of 6.5 and 4.4
kg/ha/yr for nonresidential and residential land uses, respectively. These export rates are
based on an approximation of the percent of the time that land developers in New Bern
choose to use the payment offset provision in the regulations rather than implementing best
management practices to achieve the loading limits. Meadows (2006) suggests that use of
the offset provision occurs 15 and 50 percent of the time for residential and commercial
development, respectively. These rates were applied to land use in all subwatersheds with
the exception of the Neuse subwatershed. In the Neuse subwatershed, where the Craven 30
NC 43 Connector March 2011 Page 1 53
ICI Water Quality Report
development is proposed, loading rates equivalent to the maximum allowed under the Neuse
Rules were assumed. Weyerhaeuser Corporation, which is developing the Craven 30 project,
has expressed their intention of using the maximum offset payment permitted. The modeled
rates assume a worst-case scenario that the offset payments will not result in implementation
of stormwater best management practices within the project study area.
Reductions in nitrogen loading will be accompanied by reductions in TP and TSS (NCDWQ,
2004 and 2005). A concomitant reduction of 30 percent in both constituents was assumed and
implemented in the model simulations. However, the Coastal Stormwater Rule TSS reductions
took precedence where it applied since that reduction is 85 percent.
The subwatersheds that had the highest differences in total nitrogen loading between the Build
and No Build scenarios are Hayward Creek (5.9 percent), Deep Branch (4.8 percent), and Rocky
Run (4.3 percent). The remaining subwatersheds had differences of 3 percent or less. The
higher total nitrogen loading in Hayward Creek was the result of less than 10 hectares being
developed as commercial land (Build) instead of medium high density residential land (No
Build). In Deep Branch, the higher nitrogen load was due to a 143-hectare difference in high
density residential (Build) versus medium high density residential (No Build). This was also the
case in Rocky Run where approximately 150 hectares were assumed to be high density
residential in the Build scenario and medium high density residential in the No Build scenario.
The nutrient loading increases beyond the existing land use may cause some eutrophication of
the local streams. The differences between the Build and No Build are relatively small, though
greater eutrophication could occur in the Build scenario in some instances. This would entail
increased vegetative growth, both in the water column as algae and on the substrate as
periphyton, and more dynamic dissolved oxygen levels. Dissolved oxygen would be higher
during photosynthesis and lower as algae die or respire at night. In-stream monitoring may be
conducted to observe algal growth and dissolved oxygen levels.
In terms of potential cumulative effects, the loading from the subwatersheds in this study over
the 11-year model runs are predicted to contribute 11.3 Mg (2.6 percent) more total nitrogen and
1.4 Mg (1.6 percent) more total phosphorus under the Build scenario than the No Build scenario.
These differences are equivalent to 2.81 kg/day of total nitrogen and 0.35 kg/day of total
phosphorus from the entire study area. The total nitrogen delivered to the estuary from the
project subwatersheds is roughly 1.3 percent of the TMDL to the Neuse River estuary, or 8,388
kg/day (see Section 6.3). The nitrogen load difference between the Build and the No Build
appears to be inconsequential, but the increase in load from either scenario above existing
conditions from may have an effect on estuarine water quality.
To summarize, localized water quality impacts to smaller streams in the project area (e.g.,
Hayward Creek, Deep Branch, and Rocky Run), such as eutrophication, may occur if R-4463 is
constructed and the projected development occurs. However, similar changes in water quality in
the Neuse River estuary do not appear to be likely because the incremental increase in nutrient
loading between the Build and the No Build Scenarios (2.6 percent) is relatively small.
NC 43 Connector March 2011 Page 54
ICI Water Quality Report
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r Road Mine
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Roads Office/Institutional/Light Industrial Land Use Scenario
Railroads Residential Very High Density ICI Water Quality Study - NC 43 Connector
County Boundary Clustered Residential Very High Density TIP No R 4463, Craven County, NC
Streams Residential High Density
Water Bodies Clustered Residential High Density North Carolina
Department of Transportation
_ Wetland Residential Medium High Density
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Row Crop Residential Low Density
Golf Course Residential Very Low Density
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Road Mine
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