06_Stormwater Performance Criteria, Design Standards, and Procedures (Aug 20, 2010)

THE UNIVERSITY Department of Facilities Services
Of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
University of North Carolina at Chapel Hill
Stormwater Performance Criteria,
Design Standards, and Procedures
August 20, 2010 Version
2013 Design Guidelines 1 I P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
ft at CHAPEL HILL
About the this Document
The UNC-CH Stormwater Performance Criteria,Design Standards, and Procedures are maintained by the UNC
Stormwater Engineer in Energy Services,Water,Wastewater and Stormwater. Stormwater personnel in Energy
Services,Environment,Health and Safety,Grounds,and Facilities Planning have contributed directly and indirectly
to this document.
UNC-CH Stormwater guidelines resided in the University's Design and Construction Guidelines until the first
release as a separate document in May 2010.
Performance criteria address regulatory requirements from NCDENR,Town of Chapel Hill,and the University's
NPDES MS4 Phase II Permit. Design Standards reflect operation and maintenance conditions and draw on the
standards from other agencies.
Document Revision History
Version Summary of Revisions Lead Staff Reviewers
6/1/2010 First release of SW Guidelines as a Hoyt/Bingham ES-Holton
separate document EHS-Keeney,Myers
Grounds-Rigsbee
8/11/2010 Formatting;Reference to 2004 Plan Hoyt
8/20/2010 Info about redundant systems to prevent Holton/Hoyt
building flooding
2013 Design Guidelines 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
Table of Contents
I. Stormwater Management Performance Criteria 7
A. UNC Policy to Implement Jordan Lake Rules 8
B. Summary of Water Quality Requirements—TSS and Nutrients 8
C. Summary of Quantity Requirements—Peak Discharge and Volume 9
II. Stormwater Management Design Standards 10
A. NCDENR Stormwater BMP Manual and Amendments 10
B. Town of Chapel Hill Design Manual and Town Policies 10
C. UNC Amendments to the NCDENR Stormwater BMP Manual 10
1. Maintenance Considerations for All BMPs 10
2. All BMPs Designed for Infiltration 10
3. Bioretention 10
4. All Underground BMPs 11
5. Cisterns 11
6. Proprietary Water Quality BMPs 12
7. Permeable Pavement 12
8. Green Roofs 12
9. Ponds/Wetlands 12
III. Storm Drainage System Performance Criteria 13
A. Piped Flow 13
1. Design Storm 14
2. Extents of Analysis 14
3. Boundary Conditions 14
4. Pipe Size 15
5. Acceptable Analysis Methods 15
B. Inlet Analysis 15
C. Open Channel Flow 15
D. Overland Flow 16
IV. Storm Drainage System Design Standards 17
A. Existing Storm Drains 17
B. Storm Drain Location 17
C. Storm Drain Structures and Markings 17
D. Acceptable Storm Drain Materials 19
V. Design and Construction Procedures 20
A. Programming 20
B. Schematic Design 20
1. Plans 20
2. Preliminary Stormwater Management Report 20
3. Infiltration Test Results for any Proposed Infiltration BMPs 21
C. Design Development Submittal 21
1. Plans 21
2. Stormwater Management Report 21
3. Specifications 22
4. Calculations for Storm Drainage System 22
5. BMP Operation and Maintenance Plan 22
D. Construction Documents Submittal 22
E. During Construction 22
1. Submittals 22
2013 Design Guidelines 2 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
2. Design Engineer Responsibilities 23
3. UNC Inspection 23
F. Prior to Project Closeout 23
1. Video of Pipe and Structure Condition 23
2. Project Walk Through 23
G. Project Closeout 23
1. As-built Plans 23
2. Revised Calculations 23
3. Revised Operations and Maintenance Manuals 24
VI. Buffers,Wetlands,Streams,and Floodplains 25
A. Buffers 25
1. Jordan Lake Buffer Rules
2. Town of Chapel Hill RCD
3. Other
B. Wetlands and Waterways
C. Floodplains
Appendix A—Example Narrative 26
Appendix B—Sample Tables 27
Appendix C—0I-4 Stormwater Management Performance Standards
Map 1—Stormwater Performance Criteria Jurisdictions
Map 2—NCDOT,Town of Chapel Hill,and UNC-maintained Roads on UNC Main Campus
Map 3—NCDOT,Town of Chapel Hill,and UNC-maintained Roads at Friday Center
Map 4—NCDOT,Town of Chapel Hill,and UNC-maintained Roads at Carolina North
Map 5—UNC Drainage Areas
2013 Design Guidelines 3 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
ft at CHAPEL HILL
Stormwater Performance Criteria,Design Standards,and Procedures
Designers beginning a project at UNC that involves any land disturbance should contact the UNC Stormwater
Engineer and review the requirements in this document.
The following related UNC documents are also available:
• Department of Facilities Planning and Construction Design Guidelines
Erosion and Sediment Control Guidelines(Chapter 3)
http://www.fac.unc.edu/PlansPolicies/DesignGuidelines
• Illicit Discharge Detection and Elimination Policy
http:Hehs.unc.edu/environmental/stormwater/docs/discharge nolicy_pdf
• 2010 Stormwater Capital Improvement Plan
This document will be released in Fall 2010. This document presents conceptual designs for structural
repairs,flooding improvements,and water quality retrofits.
• 2004 Stormwater Plan
The 2004 Stormwater Plan effort guided the UNC stormwater program in the 2000's and is useful in
understanding the University's general philosophy regarding low impact development and stormwater
management.
Design guidance from the 2004 Stormwater Plan has been replaced by this document. Capital
Improvement Projects listed and described in the 2004 Stormwater Plan have either been completed or
included in the 2010 Stormwater Capital Improvement Plan.
2013 Design Guidelines 6 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
I. Stormwater Management Performance Criteria
Stormwater Management performance criteria establish the design objectives for Stormwater BMPs.
All projects at UNC,including those that do not increase the impervious area,are required to meet the University
policy on implementation of the Jordan Lake Rules,which are further explained below.
Additionally,each project must meet the water quality,peak discharge,and volume reduction requirements that
apply to in that jurisdiction. The applicable regulations are listed in Table I-1 below and the requirements are
compared in Tables I-2 and I-3. Map 1 shows the areas where specific requirements apply. Additional State
requirements apply to projects that impact wetlands,streams,stream buffers,or floodplains.
Table I-1—Stormwater Manage ent Performance Criteria by Jurisdiction
If your Project is located in.... Then the following stormwater management performance criteria will
apply...
Town of Chapel Hill— • Stormwater Management Performance Standards for Development and
Central Campus vicinity Redevelopment in the Office/Institutional-4(0I-4)Zoning District,
(see map) Adopted July 2,2001 (see Appendix C)
0I-4 Zoning • UNC Policy to Implement Jordan Lake Rules
Town of Chapel Hill—Carolina . Carolina North Development Agreement, Article 5.6 Stormwater
North(see map) U-1 Zoning Management
http://www.ci.chapel-
hill.nc.us/Modules/ShowDocument.aspx?documentid=4284
• UNC Policy to Implement Jordan Lake Rules
Town of Chapel Hill—other • Town of Chapel Hill Land Use Management Ordinance,
Appendix A,Section 5.4.6. General Performance Criteria for Stormwater
Management.
hqp://www.townofchgpelhill.orv,/index.aspx?page=1222
• UNC Policy to Implement Jordan Lake Rules
Town of Carrboro . Town of Carrboro's Land Use Ordinance
hqp://www.ci.carrboro.nc.us/pzi/PDFs/LUO/A-rt-xvi.12d
• UNC Policy to Implement Jordan Lake Rules
Unincorporated Orange County • State Stormwater Program
or Chatham County http://h2o.enr.state.nc.us/su/bmp_forms.htm
• UNC Policy to Implement Jordan Lake Rules
Other Locations • State Stormwater Program and other watershed based state requirements.
2013 Design Guidelines 7 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
A. UNC Policy to Implement Jordan Lake Rules
The UNC Policy to Implement Jordan Lake Rules will be met by every UNC project that creates land disturbance.
In addition to implementing the new development and re-development rules as stated in 15A NCAC 02B .0271,the
University will meet the existing development requirements of the Jordan Lake Rules by requiring additional
treatment at redevelopment sites.
B. Summary of Water Quality Requirements
All stormwater management performance criteria listed above require an 85%reduction in Total Suspended Solids
(TSS). The nutrient requirements listed below reflect UNC Policy to Implement the Jordan Lake Rules.
Table I-2—Water Quality Performance Criteria
I your project is... The water uality performance criteria are...
85% TSS Nutrient Loading Rate: Percentage Nutrient
Removal 2.2 lb/ac/yr TN and Load Reduction:
0.82 lb/ac/yr TP 35%TN and 5%TP
New Development x x
(Greenfield,no existing impervious)
Re-development with no increase in x x
Impervious Cover
Re-Development with increase in x x* x*
Impervious Cover
*In these situations, the designer can choose to meet either the Percentage Load Reduction OR the Loading Rate
Target.
85%TSS Removal—Post-construction stormwater treatment shall remove 85%of TSS for the volume of
stormwatcr runoff resulting from the first 1"of precipitation. This requirement is in place across
jurisdictions. There may be exceptions for sites in unincorporated Orange or Chatham Counties that meet
the State definition for Low Density Development and do not meet require Diffuse Flow Plans.Treatment
shall be designed according to the design standards listed in the subsequent section.
Nutrient Loading Rate—The nutrient loading rate,was applied to State entities under 15A NCAC 02B
.0271. For new development,the site must export not more than 2.2 lb/ac/yr of Total Nitrogen(TN)and
0.82 lb/ac/yr Total Phosphorus(TP). Designers must use the calculation method approved by the State
DWQ. As of the publishing of these guidelines,the Tar Pam Piedmont Worksheet is the approved method
and can be downloaded here:
hlW://h2o.enr.state.nc.us/nps/documents/N-PCalcsheetPiedProtected 10-04.xls
Percentage Nutrient Load Reduction—The requirement also comes from 15A NCAC 02B .0271 and is
further defined by the University Policy to Implement the Jordan Lake Rules. The post-construction
nutrient exports will be compared to the baseline(December 31,2001)nutrient exports for that site. A
35%reduction of TN and 5%reduction of TP must be demonstrated based on the calculation method
approved by the State DWQ.As of the publishing of these guidelines,the Tar Pam Piedmont Worksheet is
the approved method. The University has calculated the 2001 baseline and can assist designers in locating
this information for their site.
2013 Design Guidelines 8 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I N A Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
C. Summary of Quantity Requirements—Peak Discharge and Volume
The following table summarizes the volume and peak discharge control requirements for the various applicable
performance criteria. A project designed to provide 2-year volume control and 1,2,5, 10,25,and 50 year peak
discharge control would meet or exceed the requirements from all the applicable criteria.
At some sites the quantity control requirements will be evaluated at one point. For sites where runoff discharges to
multiple outlets from the UNC property,analysis must be conducted for each outlet. For example,if a site partly
discharges to Battle Branch and partly to the Town of Chapel Hill storm drainage system along Franklin Street,at
least two design points are required.
Table I-3 Volume and Peak Discharge Control Performance Criteria
Volume Peak Discharge Control
Control
2- r 1- r 2- r 5- r 10-yr 25-yr 50-yr
0I-4 Performance x x x x X
Standards
Carolina North x x x x x x
Development Agreement
Town of Chapel Hill x x x x
Land Use Management
Ordinance
Town of Carrboro x x x x x
Land Use Ordinance
State Stormwater Program
Volume Control—The Town of Chapel Hill requires that the post-construction runoff volume for the 2-
year,24-hour storm does not exceed the existing condition runoff volume. The calculations will be based
on the SCS(MRCS)Methodology.
Peak Discharge Control—Post-construction peak discharge(rate)for the required 24-hour design storms
shall not exceed the existing conditions peak discharge(rate). The calculations must be based on a method
acceptable to the Town and UNC.
2013 Design Guidelines 9 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
II. Stormwater Management Design Standards
All stormwater management practices constructed at UNC must follow the NCDENR Best Management Practices
Manual,as amended by the DENR,the Town of Chapel Hill,and UNC. BMPs shown in the NCDENR manual are
acceptable unless otherwise noted.
A. NCDENR Stormwater Best Management Practices Manual and Amendments
The manual,supplements,and BMP forms can be found here:
http://portal.ncdenr.org/wcb/wq/ws/su/bmp-manual
The University expects stormwater designers to be familiar with this manual and its supplements.
B. Town of Chapel Hill Design Manual and Town Policies
The manual can be found here: http://www.townofchgpelhill.org/index.amx?NID=254
The UNC Stormwater Engineer will review current Town policies with the designer during schematic design.
C. UNC Amendments to the NCDENR Stormwater BMP Manual
The following amendments to the NCDENR manual are to be used for designs on UNC property:
1. Maintenance Considerations for All BMPs
• As the owner of the BMPs,UNC will review for maintenance and operation considerations as well as
regulatory compliance. The UNC Stormwater Engineer may require changes to the design to improve
safety,provide maintenance access,or control maintenance costs.
• All BMPs require access by maintenance personnel to all areas of the BMP.
• Access paths to inlets,outlets,and access maholes must be accessible by tractor towing a trailer with
maintenance equipment.
• Forebays must be accessible by a backhoe or mini-excavator.
• See Underground BMPs for additional requirements.
2. All BMPs Designed for Infiltration
Infiltration BMPs may include underground infiltration vaults,permeable pavement, or bioretention.
• An in situ infiltration testing report shall be submitted to the University Stormwater Engineer. This
testing shall follow the testing requirements given on page 16-7 of the DENR Manual(Section 16.3.5
In-Situ Soil Requirements).
• The potential impact of infiltration BMPs on existing or proposed utilities and structures in the area
shall be considered. Analysis by a geotechnical or structural engineer may be required.
3. Bioretention
• Choking stone shall be used in lieu of geotextile between the soil media and the drainage stone. This is
the alternate given on page 12-12 of the DENR Manual.
• An upturned elbow shall be included where the underdrain enters the overflow structure. See NCSU
Stormwater Group recommendations.
• Flows higher than the design storm shall bypass the bioretention area. If this is not possible,the
bioretention must be designed to safely convey a 100-year,24-hour storm.
• Soil testing of the bioretention media must be included in the construction specifications.
• Soil tests for the bioretention media must be submitted to the UNC Stormwater Engineer.
2013 Design Guidelines 10 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
• Bioretention variations may be acceptable if designed appropriately for the site. The following are
examples,but others may be suitable.
o Tree pits
o Planter boxes
o Behind retaining walls
o Step pools
• Bioretention areas shall require underdrains unless the infiltration requirements are met.
• Bioretention cells can be contained in impermeable liner where infiltration is undesirable.
4. All Underground BMPs and Underground Stormwater Vaults
Underground BMPs and vaults include underground infiltration vaults, underground cisterns and
detention, and underground water quality devices.
• A dewatering device shall be provided. The control for the dewatering shall be accessible when the
facility is full.
• A staff gauge shall be permanently affixed to the inside of the BMP such that it is visible from the
surface.
• An access manhole shall be provided to every chamber of the underground BMP,at every inlet and
outlet,and at opposite ends of structures 15 feet or longer.
• All areas of the BMP shall be within 50 feet of an access manhole to facilitate the use of a tripod and
winch for confined space entry.
• Access manholes shall be accessible to UNC's pump trailer which is towed by a tractor.
• Access manholes shall be located outside of roadway travel lanes and driveways.
• Access manholes shall have at least one small diameter opening(approx.2")so that the lids can be
opened with a metal hook. This opening shall be in addition to the standard notches on the side of the
manhole lid.
• Each access point shall have steps to the bottom of the deepest elevation.
o The first step shall be located 2'below the top of the structure.
o Steps shall be placed at uniform intervals of either 12"or 15"on center.
o Steps shall follow NCDOT Standard Drawing 840.66"Drainage Structure Steps".
• If an access manhole is over 5 feet deep,a minimum of 15 feet of vertical clearance over the manhole
shall be provided. This clearance will allow a tripod and winch to be set up for confined space entry,
and also allow the vacuum truck's arm to be positioned properly for BMP cleaning.
• If an access manhole is over 5 feet deep,the interior diameter shall be 4 feet or greater. If over 10 feet
deep,the interior diameter shall be 5 feet or greater. An eccentric cone may be used to transition from
the manhole frame to a riser section of 4 feet or greater.
• All manhole lids or hatches shall be pre-cast with the following labels:
o "Storm"
o "Entry Permit Required"or"Confined Space Entry"
o "Dump no Waste! Drains to Jordan Lake"
5. Cisterns
• Only year-round demand shall be considered to meet the stormwater performance criteria.
• The cistern may be designed with additional capacity for seasonal irrigation use.
• Cisterns may be designed to provide peak discharge control.
• Pre-treatment must be provided to remove trash,debris and sediment prior to flow entering the cistern.
This pre-treatment shall be sized to allow an average of at least six months between clean outs.
2013 Design Guidelines 11 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
6. Proprietary Water Quality BMPs
• If a designer proposes the use of a proprietary BMP to meet water quality requirements,documentation
of an independently verified pollutant removal rate shall be provided to the UNC Stormwatcr Engineer
during schematic design.
• Proprietary Water Quality BMP shop drawings shall be reviewed by the design engineer and the UNC
Stormwater Engineer during construction.
• The following are examples of acceptable independent verification agencies:
o NJCAT
o Washington State
o State of Massachusetts
7. Permeable Pavement
• Permeable pavement is acceptable only when used in applications accessible by the University street
sweeper. The installation must be in a drive lane or a series of at least 8 continuous parking spaces.
• Pervious areas adjacent to permeable pavement shall not drain onto the pervious pavement.
• Drainage area to the permeable pavement must be stabilized prior to installation.
• For permeable asphalt or concrete,the design engineer or designer's representative must be on-site full
time when the concrete or asphalt is poured.
• Construction or landscaping materials containing fines may not be stockpiled on permeable pavement.
8. Green Roofs
• Plans must show the actual footprint of the green roof,considering set backs from walls and
equipment.
• If the green roof is a proprietary product,information of the components,including drainage layers,
soil mix,and depth must be submitted.
• The design engineer should consult the UNC Grounds Department regarding green roof plants which
have been successful on the UNC Campus.
• Access for maintenance and OSHA safety requirements must be incorporated into the design.
9. Ponds/Wetlands
• No additional requirements at this time.
2013 Design Guidelines 12 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
!-I Air at CHAPEL HILL
III. Storm Drainage System Performance Criteria
The purpose of the UNC drainage performance criteria is to safely convey flows through University property
without causing flooding of buildings,roadways,pedestrian routes,or other facilities.
A. Piped Flow
Due to the extensive network of storm drainage piping maintained by the University on central campus,the
University performance criteria are more specific and stringent than those for isolated building sites as presented by
the State Construction Office or the Towns of Chapel Hill or Carrboro.
Site designs shall not subject any buildings to flooding at any time. This includes buildings downstream of the
development site. The 100-year,24-hour storm will be used to assess flooding.
1. Design Storm
a. The State Construction Office requires any site without an overland emergency flow route to design for
the 24-hour, 100-year storm. See page 5 at the following link:
htlp://www.nc-sco.com/documents/guidelines/SitePrep2.pdf
An emergency flow route is a path for water to flow over the surface if the pipe capacity is exceeded.
An emergency flow route may not be impeded by a building,embankment,or hill.
When a pipe passes under a building,no overland emergency flow route is available. Any pipes
passing under a building(s)must be sized for the 100-year design storm.
b. Many roads on UNC property are maintained by NCDOT or the Town of Chapel Hill. Pipes under
these roads must meet the following design standards:
• NCDOT—see Table 4-3 at the following link:
http://www.ncdot.or /g doh/preconstruct/highway/hydro/g10399webNI_hydrology.html#tab43
• Town of Chapel Hill—see Section 2.6.1 at the following link
http://www.ci.chapel-hill.nc.us/Modules/ShowDoc ument.aspx?documentid=2645
c. Select design storms for piped flow on UNC property using the tables below. Flow for the design storm
must be conveyed within the pipe. There shall be no surcharging in the drainage system for the
applicable design storm.
Any site meeting more than one condition shall use the largest of the required design storms.
2013 Design Guidelines 13 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
Table III-1 NCDOT Roads
If the pipe is.... Design Storm
WITHOUT overland emergency flow route 100-year
Downstream of pipes under a NCDOT-maintained interstate,US or NC 50-year
highway,or major secondary road
Downstream of pipes under a NCDOT-maintained secondary road 25-year
Table III-2 Town of Chapel Hill Roads
If the pipe is.... Design Storm
WITHOUT overland emergency flow route 100-year
Downstream of pipes under a Town-maintained arterial or collector 25-year
Under or downstream of pipes under a Town-maintained local road 10 year
Table III-3 Other Areas on UNC Property
If the pipe is.... Design Storm
WITHOUT overland emergency flow route 100-year
Drainage area greater than 25 acres 50-year
Drainage area less than 25 acres,but greater than 3 acres 25 year
Drainage area less than 3 acres 10 year
d. The 100-yr,24hr design storm shall be evaluated to determine flooding conditions.The 100-yr storm
shall not cause flooding of any buildings or basements and shall be safely conveyed downstream via an
overland emergency flow route.
If a non-gravity flow(pumping)design is proposed,the design team must meet with the UNC
Stormwater Engineer and project team during the schematic design phase to discuss. In preparation for
this meeting,the design team shall document the gravity solutions considered and shall evaluate the
impacts to infrastructure and building interiors if the proposed pumps fail. The design will provide
redundancy in the electrical and mechanical systems. The pump-failure impact analysis and redundancy
measures shall be submitted for review in each design phase.
2. Extents of Analysis
Analyze storm drainage system for the appropriate design storm(s)from the site to one of the following
downstream points:
• An open channel.
• Storm drainage system in the public ROW.
• University storm drainage system designed for the 50-year storm.
• Other point determined by the UNC Stormwater Engineer.
3. Boundary Conditions
• Tailwater conditions/depth shall be determined from the downstream conditions.
• If the discharge location(s)from the project site are located within 200 ft of a pipe of 42"in diameter
or larger,the tailwater condition should be verified by the University Stormwater Engineer.
• The maximum water surface elevation of the receiving stream(if higher than the water surface in the
outfall)or the water surface elevation in the junction used for tie into the existing storm drainage
system for the design condition(see Table 1)shall be considered as the downstream hydraulic control.
• Additional boundary conditions explanation will be added in subsequent version of this document.
2013 Design Guidelines 14 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
4. Pipe Size
• A minimum pipe diameter of 15"will be used for conveyance pipes.
• A minimum pipe diameter of 6"will be used for roof drains and underdrains.
5. Acceptable Analysis Methods
• Hydraulic grade line calculations and plots shall be submitted.
• If the hydraulic grade line is not contained within the pipe,the energy grade line must also be plotted.
• Additional information on analysis methods will be added in subsequent version.
B. Inlet Analysis
Inlets located within NCDOT or Town of Chapel Hill roadways must follow the design standards of those
agencies.
• Town of Chapel Hill Design Manual—Section 2.6.2
http://www.ci.chal2el-hill.nc.us/Modules/ShowDocument.aspx?documentid=2645
• NCDOT Storm Drainage System Design Guidelines
http://www.ncdot.orWdoh/preconstruct/highwgylydro/g10399web/IX stormdraina eg html
Inlets located on University property shall be designed as follows:
1. Inlet Openings
• Inlets shall be hydraulically designed to capture 100%of the flow from the 10 year storm.
• Inlets located in landscape low point or a roadway/driveway sag shall compensate debris blockage by
providing twice the computed opening.
• Inlets on a slope or grade do not need this factor of safety if spread limits are met.
2. Spread
• Spread limits for roads and driveways shall follow Town of Chapel Hill Design Manual Section
2.6.2.
• Flow spread must leave at least 36"free of water in sidewalks,pathways,plazas,courtyards,or
other walking surfaces.
C. Open Channel Flow
1. Lining and Velocity
Channels should be designed for non-erosive conveyance. Calculate the velocity of the channel at the 10-
year design storm and compare that velocity to literature values for channel lining types.
2. Capacity
Select design storms for open channel flow on UNC property using the tables below. Any site meeting
more than condition shall use the largest of the required design storms.
Table III-4 Open Channels Downstream of NCDOT Roads
If the channel is.... Design Storm
Downstream of a pipe under a NCDOT-maintained interstate,US 50-year
or NC highway, or major secondary road
Downstream of a pipe under a NCDOT-maintained secondary 25-year
road
2013 Design Guidelines 15 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
Table III-S Open Channels Downstream of Town of Chapel Hill Roads
If the channel is.... Design Storm
Downstream of a pipe under a Town maintained arterial or collector 25-year
Downstream of a pipe under a Town maintained local road 10 year
Table III-6 Open Channels on UNC Property
If the channel serves.... Design Storm
Drainage area greater than 25 acres 100-year
Drainage area less than 25 acres,but greater than 3 acres 25 year
Drainage area less than 3 acres 10 year
D. Overland Flow
• All runoff from the site must be non-erosive.
• Maintain existing topography and undisturbed soils where possible.
• Slopes shall not exceed 3:1.
• Provide positive surface drainage away from buildings. The suggested minimum slopes are 2.5%for
unpaved areas, 1%for paved areas.
2013 Design Guidelines 16 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
IV. Storm Drainage System Design Standards
A. Existing Storm Drainage System
Sites with existing storm drain pipes and structures within the limit of disturbance of a project shall do one of the
following:
• Remove or replace all storm drains and structures,especially terra cotta storm drains.
• Demonstrate the good condition of the storm drain pipes and structures to remain.
The University has assessed all storm drain pipes 48"and larger and a limited number of smaller storm drain pipes.
Contact the UNC Stormwater Engineer to determine if the project site has been assessed. If the site has not been
assessed,the lines shall be videoed and evaluated by the design engineer. The video and design engineer's
recommendation shall be submitted to the UNC Stormwater Engineer for review.
B. Storm Drain Pipe Location
• Storm drain pipes shall be accessible for future maintenance including excavation. An accessible
corridor shall be centered on the pipe alignment and its minimum width shall be calculated as the
greater of the following:
o 20 feet
o {[10 feet]+ [the pipe diameter or total pipe width for multiple pipes]+ [2*invert depth]},
rounded up to the nearest 5 feet.
• New storm drain pipes shall not be located under buildings or within a 1 to 1 slope from a building
foundation.
• Storm drain pipes at redevelopment sites shall be relocated outside building footprints. Consult with
the UNC Stormwater Engineer during schematic design if this is infeasible.
• Storm drain pipes should not be located under athletic or recreation fields. Consult with the UNC
Stormwater Engineer during schematic design if this is infeasible.
C. Storm Drainage Structures
Note: For Stormwater vaults larger than typical manholes, the design standards on pages 11-12 `All Underground
BMPs and Underground Stormwater Vaults"also apply.
1. Location
• Storm drain pipes shall have surface-accessible structures at every junction and every change in slope,
direction,and pipe size.
• The maximum distance between structures shall be 250 feet.
• When feasible,inlets should be located in landscaped areas rather than pedestrian paths. This allows
for ponding outside the walkways and provides better ADA access.
• Inlets in landscaped areas shall be placed so that flow is captured before it reaches roads or major
walkways,and so that no concentrated flow crosses over a pathway.
• Inlets in roads,driveways,or parking lots on a continuous grade shall be spaced to limit the spread of
stormwater onto the pavement. Inlets shall be placed at intersections and at low points in the gutter
grade. Inlets should be placed upstream of pedestrian crossings
2. Loading
All structures must be traffic rated,with a minimum of H2O loading. Exceptions may be
considered for structures within bioretention areas.
2013 Design Guidelines 17 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
3. Details
• Designers may use Standard Details from NCDOT or the Town of Chapel Hill,with modifications to
reflect the UNC Standards.
o NCDOT Drainage Structure Standard Drawings
hlW://www.ncdot.or /g doh/preconstruct/ps/std draw/06en,glish/08/
o Town of Chapel Hill Storm Drainage Standard Details
hlW://www.ci.chgpel-hill.nc.us/index.aMx?j2aae=466
4. Interior Dimensions
• Interior dimensions shall provide access for maintenance,with greater dimensions as depth increases.
• Inside dimension for storm drainage structures shall be based on standard details from NCDOT or the
Town of Chapel Hill. However,no structure shall be less than 3'by 2'.
5. Grates and Lids
• All storm drain structures shall have a removable grate or manhole cover.
• Access manholes and grates,shall have at least one small diameter opening(approx.2")so that the lids
can be opened with a metal hook. This opening shall be in addition to the standard notches on the side
of the manhole lid.
• All grates and lids located in sidewalks,pathways,plazas,courtyards,or other walking surfaces shall
meet the current version of the Americans with Disability Act Accessible Guidelines(ADAAG)and
the current edition of the North Carolina Building Code and their referenced standards.
• Designers shall replace existing non-compliant grates within the construction limits with grates
meeting the above guidelines and standards. The designer must evaluate the drainage area and grate
inlet capacity to ensure storm drainage performance criteria are met by the proposed conversion. In the
calculations,structures outside the construction limits should be considered to have compliant grates
regardless of their current status. If needed,add additional structures to compensate for capacity
reduction. Calculations for the proposed changes shall be submitted to the UNC Stormwater Engineer
for review.
• Grates in roads and driveways shall be placed with the long dimension of the opening perpendicular to
the route of travel. This safety consideration for bicyclists prevents wheels from being caught in
grates.
6. Marking
• All manholes lids,grates,hoods,and covers installed or replaced shall be permanently labeled with the
message"Dump no Waste! Drains to Jordan Lake".
• All stormwater manhole lids shall be permanently labeled with the following additional labels:
o "Storm","Stormwater",or"Storm Drain"
o "Entry Permit Required"or"Confined Space Entry"
• If stormwater manhole lids within the construction limits are mislabeled as sanitary sewers or other
utilities,the lids shall be replaced as part of the project.
• Structures located in a Town or NCDOT right-of-way shall follow the Town of Chapel Hill Standard
Details for markings.
• Structures located on University Property shall NOT be marked"Town of Chapel Hill"but should
otherwise follow the Town Standard Details for markings.
7. Steps
• All structures deeper than 3.5' shall have steps to the deepest elevation.
• The first step shall be located 2'below the top of the structure.
• Steps shall be placed at uniform intervals of either 12"or 15"on center.
• Steps shall follow NCDOT Standard Drawing 840.66"Drainage Structure Steps".
2013 Design Guidelines 18 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
8. Vertical Clearance
If an access manhole is over 5 feet deep,a minimum of 15 feet of vertical clearance over the manhole shall
be provided. This clearance will allow a tripod and winch to be set up for confined space entry,and also
allow the vacuum truck's arm to be positioned properly for inlet cleaning.
D. Acceptable Storm Drain Materials
All pipes must be traffic rated. Regardless of location, pipes may be subjected to heavy vehicle loading; therefore,
pipe material shall meet manufacturer's minimum specifications for this load. Acceptable pipe materials are:
1. Conveyance Pipes 12"and greater:
• Reinforced Concrete Pipe(RCP)—Class III or higher
2. Conveyance Pipes 10"and smaller:
• Ductile Iron Pipe(DIP)
• Polyvinyl Chloride Pipe(PVC)Schedule 40 or SDR 26 or better
3. Underdrains
• Perforated Polyvinyl Chloride(PVC)Schedule 40 or SDR 26 or better
Flexible HDPE drain line is not allowed for storm drainage piping,or subsurface(foundation drainage)piping.
E. Illicit Discharge Prevention
1. Illicit Discharge Detection and Elimination Policy
Designers shall review the University's policy to avoid introducing illicit discharges to the storm drainage
system.
http:Hehs.unc.edu/environmental/stormwater/docs/discharge nolicy_pdf
2. Dumpsters
Dumpster leakage or wash off is not allowed to drain to the storm system. Dumpsters shall drain to the
sanitary sewer. The site shall be graded so that only the area beneath the dumpster discharges to the
sanitary sewer. Clearly mark the drain as a sanitary sewer drain. Pre-treatment such as oil water
separators may be required for dumpster pads with trash compactors or other equipment. Dumpster sites
shall be reviewed with the University and OWASA.
2013 Design Guidelines 19 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
!-I Air at CHAPEL HILL
V. Design and Construction Procedures
A. Programming
The designer meets with the UNC Stormwater Engineer to review the stormwater performance criteria,
standards,and procedures.
B. Schematic Design
The following items shall be submitted to the UNC Stormwater Engineer for the Schematic Design Review.
Both electronic(PDF)and hard copies shall be submitted.
1. Plans
The following plan sheets shall be submitted with the indicated items clearly shown:
• Existing Condition Plan
0 50'Jordan Lake buffer
o Town of Chapel Hill RCD buffer
o Floodplains
o Streams
o Wetlands
o Significant Natural Heritage Areas(NC Natural Heritage Program)
o Existing Contours
o Existing storm drain pipes and structures with location,size,and invert elevations
o Existing storm drain pipe schedule
o Existing BMPs,with their location,size,and type
o Construction limits
• Demolition plan
o Any storm drain or BMP being removed or abandoned
• Proposed Site Plan
0 50'Jordan Lake buffer
o Town of Chapel Hill RCD buffer
o Flood plains
o Streams
o Wetlands
o Significant Natural Heritage Areas(NC Natural Heritage Program)
o Existing Contours
o Proposed Contours
o Proposed storm drain pipes, structures,and channels with location, size,and invert elevations
o Existing storm drainage infrastructure to remain
o Proposed BMPs,with their location,size,and type
o Proposed other utilities and existing utilities to remain
o Construction limits
2. Preliminary Stormwater Management Report
The report shall include the following:
• Short narrative(see Appendix A)
o Address the manner in which applicable stormwater management requirements will be met
o Types of BMPs proposed
o Any changes to the storm drainage system
• Drainage Area map
o Drainage area(s)shall cover the entirety of the project limits
o A drainage area shall be defined for each pipe,channel,or other point where concentrated
flow exits the project limits
2013 Design Guidelines 20 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
o Drainage areas entering the site from upstream areas shall be delineated and given separate
designations.
o All design points shall be clearly shown and labeled
o All drainage areas shall be clearly labeled
• Table with existing and proposed land cover
• Tar Pamlico worksheets for nutrient removal
• Preliminary calculations for BMP sizes
3. In-Situ Infiltration Test Results for any Proposed Infiltration BMPs
C. Design Development Submittal
The following items shall be submitted to the UNC Stormwater Engineer for the Design Development Review.
Both electronic(PDF)and hard copies shall be submitted.
1. Plans
The following plan sheets shall be submitted with the indicated items clearly shown:
• Existing Conditions Plan
o Same components as schematic design
• Demolition Plan
o Same components as schematic design
• Proposed Storm Plan
o Same components as schematic design,with the following additions:
o Proposed pipe schedule
o Any proposed phasing of the project shall be clearly shown
• Storm Drain Profile Sheets
• Stormwater Detail Sheets
o Storm Drainage System Details
o BMP Details in plan,cross section,and profile views
o BMP invert,weir,and orifice elevations
• Any landscape or architectural drawings related to BMPs(e.g.green roofs or planter boxes)shall be
submitted along with the above items for review by the UNC Stormwater Engineer
• Existing and proposed land cover shall be included in the stormwater report,or shown VERY clearly
on the plans.
2. Stormwater Management Report
The report shall include the following:
• Narrative
o Same components as schematic design
o Table summarizing the drainage areas,including label and acreage(see Appendix B for
example)
o Summary of each BMP,and its drainage area(see Appendix B for example)
o Water Quality Table(see Appendix B for example)
o Peak Discharge Table(see Appendix B for example)
o Volume Table(see Appendix B for example)
o Address the ways in which the Jordan Lake rules are satisfied
• Drainage Area map(same components as schematic,updated with any new relevant information)
• Table with existing and proposed land cover(updated with any new relevant information)
• Tar Pamlico worksheets for nutrient removal
• Hydrology and Hydraulics calculations
o Curve number calculations
2013 Design Guidelines 21 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
171 Arat CHAPEL HILL
o Time of concentration calculations
o Water quality volume calculations
o If project is in the Town of Chapel Hill,include 2 year volume reduction calculations
o Peak discharge calculations,with input and output files
o If multiple drainage areas are in a project area,use proper hydrology and hydraulic routing
methods
o Existing conditions modeling shall include existing de facto detention(e.g. storage behind a
culvert in a roadway embankment and low points in the landscape)
o For detention structures and ponds/wetlands,include the following:
■ Stage/storage discharge curves
■ Summary of outlets and elevations
o For infiltration BMPs,include the infiltration calculations
o For cisterns,include the following:
■ Demand projection calculations
■ Include input/output from the NCSU rainwater harvester model
3. Specifications
Specifications for all BMP components shall be submitted and include:
• Soil testing for bioretention and soil specifications
• Permeable pavement specifications
• Green roof media specifications
4. Calculations for Storm Drainage System
• Calculations will be submitted for each proposed storm drainage pipe,inlet,and channel.
• Submitted calculations will follow the performance critieria in this document.
5. BMP Operation and Maintenance Plan
• The stormwater designer should use the procedures from the NCDENR BMP Operation and
Maintenance forms as a starting point and adapt them to be site specific. The University's NPDES
permit requires maintenance of all BMPs,so the agreement portion of the form should be deleted. The
forms can be found here:
htII2://portal.ncdenr.ory/web/wq/ws/su/bmp-manual
• Non-standard and complex BMPs will require more detailed information.
• Proprietary BMPs shall submit product-specific operation and maintenance plans.
• BMPs with mechanical and electrical components,such as cisterns,shall submit preventative
maintenance requirements for these components.
D. Construction Documents Submittal
All Design Development submittal documents and plans shall be updated and submitted to the UNC
Stormwater Engineer for the Construction Documents Review. Both electronic(PDF)and hard copies shall be
submitted.
E. During Construction
1. Submittals
• Shop drawings
• Manufacturer's Operation and Maintenance information for any proprietary BMPs
2013 Design Guidelines 22 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
• Material test results for any permeable pavement
• Source of stone used for any underground storage or detention
2. Design Engineer Responsibilities
• The design engineer shall oversee BMP installation at critical points and sign off on the as-builts.
3. UNC Inspection
• The contractor and UNC Construction Manager shall notify the UNC Stormwater Engineer when a
BMP is ready to begin construction so UNC can observe the installation.
F. Prior to Project Closeout
1. Video of Pipe and Structure Condition
• The project team shall submit video of the pipes and structures that is filmed near the end of
construction. The appropriate timing of the video work will be project dependent,so the project team
should coordinate the timing with UNC stormwater staff.
• The video shall include:
o All storm drainage structures
o All chambers and joints in an underground stormwater management vault
o All existing storm drainage pipes 8"and larger that remained in place during construction.
o All new storm drainage pipes 8"and larger
• The video segments shall be labeled using the structure labeling used in the construction documents.
• The purpose of this video is to demonstrate that pipes and structures:
o Were installed correctly
o Remain in good condition
o Are free of debris and soil
• If the video depicts improper installation, structural deficiencies,or the presence of debris or other
blockages,the project team shall either:
o Correct the problem then submit a follow-up video.
o Demonstrate that the condition was pre-existing with video submitted to UNC during the
design phase.
2. Project Walk-Through
• The project team shall include the UNC Stormwater Engineer in the walk through(s)for all aspects of
the project relating to stormwater,including:
o Grading
o Stormwater BMPs
o Storm Drainage System(Pipes, Structures,Channels)
G. Project Closeout
1. As-built Plans
• As-builts shall be submitted to the UNC Stormwater Engineer.
• As-builts must include updated pipe schedules to reflect any changes made during construction.
• PDF and AutoCAD version of the as-builts shall be submitted.
2. Revised Calculations
• If any changes made during construction impact BMP performance,revised calculations shall be
submitted to the UNC Stormwater Engineer.
2013 Design Guidelines 23 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
3. Revised Operations and Maintenance Plans
• If any changes were made to BMPs during construction,revised operation and maintenance plans shall
be submitted to the UNC Stormwater Engineer.
• 1 copy of the Operation and Maintenance Manuals for any mechanical or electrical equipment in the
stormwater system shall be submitted to the UNC Stormwater Engineer. This is in addition to other
copies required by the University.
2013 Design Guidelines 24 P a g e

THE UNIVERSITY Department of Facilities Services
Of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
ft at CHAPEL HILL
VI. Buffers,Wetlands,Streams,and Floodplains
• Content to be added at future date.
2013 Design Guidelines 25 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Air at CHAPEL HILL
Appendix A—Example Narrative
A short narrative needs to accompany the stormwater calculations. This can be less than 1 page. This is
needed to help explain the calculations and how the stormwater requirements are being met. It will help clear
up questions before they are asked. It needs to address the following:
Existing Conditions
• The project area used for the hydrologic and hydraulic calculations is acres,which is shown
on (e.g.Map 1,or Sheet XXX as the Limit of Construction)
• The existing land cover is (e.g.landscaped areas over,brick walkways, ...). The
existing land cover is shown on (e.g. Sheet XXX)and summarized in Table X below.
• Under existing conditions runoff leaves the project area by
(e.g. "a 24"storm drain located south of the road"or"sheet flow to the Road right-of-way"
or"roof drains that tie into the 12"located ")
Proposed Conditions
• The proposed project will remove acres of (land cover)and replace this area with
(e.g.The proposed acre building addition will remove acres of landscaped area,
acres of concrete patio,and....)
• The proposed land cover is shown on
• The net change in impervious cover is
• Under proposed conditions,runoff will leave the project area by (e.g. new xx"storm
drains will convey flow from x new structure to )
Stormwater Requirements
• The water quality volume for the site was calculated to be (cubic feet or acre-feet). OR
Water quality volume was not calculated for this site because
• A (BMP)was designed to provide (units)water quality volume.
• Address peak discharge and volume—change(increase,decrease)and how requirements will be
met
2013 Design Guidelines 26 1 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RQ L I NA Stormwater Performance Criteria,Design Standards,and Procedures
fl Airat CHAPEL HILL
Appendix B—Sample Tables
Project Land Cover Summary
Existing Land Proposed Land Cover Change from Existing to
Cover(sf) (sf) Proposed(sf)
Impervious Area
Landscaped Area
Turf Area
Wooded Area
Summary of Project Drainage Areas
Project Drainage Area ID Subwatershed or Sub-basin Drainage Area(sf)
A
B
C
D
Curve Number Summary
Include TR-55 Worksheet 2 or equivalent for each drainage area
BMP Summary
BMP ID Type Project Drainage Area ID BMP Drainage Area(sf)
if different than Project Drainage Area
1 e.g.Bioretention
2
3
Water Quality Summary
Volume Provided(cf)
Volume Required for TSS Removal(cf) BMP 1 BMP 2 BMP 3 Total
2013 Design Guidelines 27 P a g e

THE UNIVERSITY Department of Facilities Services
of NORTH C A RO L I NA Stormwater Performance Criteria,Design Standards,and Procedures
ft at CHAPEL HILL
Volume Summary
2-yr Runoff Volume(cf) Volume Reduction Provided(cf)
Post- Post-
Drainage Pre- Development Development
Area ID Development without BMP with BMP BMP 1 BMP 2 BMP 3
A
B
C
D
Peak Discharge Rate Summary
Drainage Area ID (This table to be repeated for each drainage area)
Peak Discharge Rate(cfs)
1-yr 2-yr 10-yr 25-yr 50-yr
Pre-Development
Post-Development without BMP
Post-Development with BMP
2013 Design Guidelines 28 1 P a g e