NCCU Student Center - NCCU Stormwater Calculations

CALYX'"
ENGINEERS + CONSULTANTS
NCCU Student Center
Stormwater Impact Analysis
Fayetteville Street
Durham, NC
CALYX Project 2017032.00
September 10, 2018
Revised December 4, 2018
Revised March 15, 2018
6750 Tryon Road, Cary, NC 27518 P:919.836.4800 F:919.851.1918 CALYXengineers.com

CALYX"
ENGINEERS + CONSULTANTS
TABLE OF CONTENTS
• ENGINEER'S CERTIFICATION
• NARRATIVE
• MAPS AND EXHIBITS
o USGS QUAD MAP
o DURHAM COUNTY SOILS MAP
o FIRM PANEL
o CITY OF DURHAM AERIAL PHOTO — 1994
o CITY OF DURHAM AERIAL PHOTO - 1999
o CITY OF DURHAM AERIAL PHOTO — 2006
o LAND USE MAP 1997
o LAND USE MAP 2001
o LAND USE MAP POST -DEVELOPMENT
o LAND USE MAP FOR SCM
• PRE -POST PEAK FLOW ANALYSIS
o DRAINAGE AREA MAPS
o HYDRAFLOW HYDROGRAPHS
• JORDAN/FALLS LAKE STORMWATER NUTRIENT LOAD ACCOUNTING TOOL
• CITY OF DURHAM NUTRIENT REPORTING FORM
• SAND FILTER CALCULATIONS

LX.
KNGINEERS + CONSULTANTS
ENGINEERS CERTIFICATION:
The calculations presented in this manual were performed by me or under my direct supervisory
control, witnessed by my seal, date, and original signature.
C
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/y ...............
AN A
Jonathan A. Allen
NC PE License No.: 25497
CALYX Engineers & Consultants, Inc.
6750 Tryon Road
Cary, North Carolina 27518
[phone]
[e-mail]
6750 Tryon Road, Cary, NC 27518 P:919.836A800 F:919.851,1918 CALYXenqmcerc cow

CALYX"
ENGINEERS + CONSULTANTS
NARRATIVE
SITE INFORMATION
North Carolina Central University is proposing a new student center building on Fayetteville
Street in Durham, NC. The existing parcel (PIN 0830-05-08-0647) is 7.14 acres and is owned
by the State of North Carolina. There are 10 smaller residential parcels to the south that will be
combined with the parcel above. The total project site is approximately 4.55 acres. The
property is located within the Jordan Lake Watershed. As a State-owned property, stormwater
management will be reviewed by both the State (water quality requirements) and the City of
Durham (water quantity requirements).
The existing site features a parking lot on the north portion and residential housing on the south
portion. A baseline date of April 23, 1997 was used for water quantity and December 31, 2001
was used for water quality. The impervious area only increased from 2.68 acres in 1997 to 2.80
acres in 2001. The site is divided by a ridge in the middle and drains to the north west and
north east corners. The report shows that the post -development peak flow does not increase
for the 1-, 2-, 10-year, and 100-year, 24-hour storm events for both drainage areas. An
underground sand filter will provide treatment for water quality and an underground detention
system will ensure the water quantity requirements are met.
The site contains one main soil type, WwC — White Store. This soil type has been determined
to be in hydrologic group "D" per the Durham County soil report. The project is not located in a
floodplain per FIRM map # 3720082000L dated October 19, 2018.
METHODOLOGY
TR-55 methodology was used to perform stormwater routing. TR-55 can compute peak
discharges by creating hydrographs using the following information: 24-hour rainfall, rainfall
distribution (I, IA II, III), CN, Tc, Tt, and the drainage area. The method is also used to estimate
storage volume for detention basins. Hydraflow Hydrographs is the software used in this report
to model the drainage basin and the detention system. The time of concentration was assumed
to be 6 minutes since the site has a large amount of impervious area and is a relatively small
site.
6750 Tryon Road, Cary, NC 27518 P:919.836.4800 F:919.851.1918 CALYXengineers.com

4CALYX
ENGINEERS + CONSULTANTS
Pre vs Post Drainage Area 1
Site Condition
Storm Event (cfs)
1-year (cfs)
2-year (cfs)
10-year (cfs)
100-year (cfs)
Pre -development
5.41
6.57
10.24
15.45
Post -development
3.67
4.53
7.33
11.31
Pre vs Post Drainage Area 2
Site Condition
Storm Event (cfs)
1-year (cfs)
2-year (cfs)
10-year (cfs)
100-year (cfs)
Pre -development
9.98
12.11
18.88
28.49
Post -development
12.37
14.75
22.27
32.96
Post -development
w/detention
9.89
11.56
18.21
27.33
Conclusion: The new building for North Carolina Central University on Fayetteville Street will
receive stormwater treatment for water quality and water quantity using an underground sand
filter and underground detention system. The peak flow rates will decrease for the 1-, 2-, 10-,
and 100-year, 24-hour storm events.
6750 Tryon Road, Cary, NC 27518 P:919.836.4800 F:919.851.1918 CALYXengineers.com

CALYX"'
ENGINEERS + CONSULTANTS
MAPS AND EXHIBITS
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CITY OF D U RHAM
REPORTING FORM
CALYX"'
ENGINEERS + CONSULTANTS
OF NUTRIENT
6750 Tryon Road, Cary, INC 27518 P:919.836.4800 F:919.851.1918 CALYXengineers.com

DURHAM
18
-CITY OF t ED+CINE
CITY OF DURHAM Neuse, Falls Lake and Jordan Lake Developer Nutrient Reporting Form
Not required if the project is exempt from pollutant standards per Section 70-739 of the City Code
Please complete and submit the following information to the City of Durham Stormwater Services to
characterize your project and assess the need to purchase nutrient offsets. See the
City of Durham Stormwater Standards. For nutrient offset information, see nutrient offset info
PROJECT INFORMATION
Applicant Name :
CALYX Engineers + Consultants
Prepared by:
Will Mowery
Project Name (& Previous name, if applicable):
NCCU Student Center
Site Plan #:
Project Address (if available): Street: City/Town: County:
Fayetteville Street, Durham
Date: (mo/d/yr)
9/7/2018
Project
Locat'n:
Lat: (dec. degrees)
Long: (dec. degrees)
PIN/PID #s:
10830-05-08-0647
Is this Redevelopment?
I 0 Yes ❑ No
Development Type (Please check all that apply)
Impervious Cover (%) Pre -Construction:
61.6
❑ Commercial ❑ Duplex Residential
❑ Industrial ❑ Single -Family Residential
❑ Institutional ❑ Multi -Family Residential
Mixed Use
Impervious Cover (%) Post -Construction:
63.3
WATERSHED INFORMATION (see Jordan map or Falls Lake map)
❑ Upper Falls Basin, 12-digit Watershed ID:
❑ Neuse/Outside of Falls Basin, 03020201 03020201
❑ Jordan Lake (Upper New Hope) 6-digit Small
Watershed ID:
Jordan Lake Delivery Factors (%)
Nitrogen
Phosphorus
Site Factor:
Site Factor:
100.00
100.00
Neuse/Falls Lake Delivery Factors: There are no delivery factors, so the Delivery Factor = 1.
DURHAM STORMWATER PERFORMANCE STANDARDS FOR DEVELOPMENT COMPLIANCE ALTERNATIVE
Nutrient loading limits and on -site treatment minimum (Sections 70-740(a) and Sections 70-741(a))
Off -site treatment threshold (%):
N:
1 0
P:
1 0
Required on -site reduction achieved?
N:
YES
P:
YES
NUTRIENT OFFSET REQUEST (Must meet the offsite thresholds — see above)
Nitrogen Loading / Offset Needs (For the Jordan, Falls, and Neuse/Outside of Falls Watershed areas)
(A)
(B)
(C)
(D)
(E)
(F)
(G)
(H)
(1) (Where
Applicable)
(J)
Untreated
Loading
Rate
(Ibs/ac/yr)
Treated
Loading
Rate
(Ibs/ac/yr)
Load Rate
Target
(Ibs/ac/yr)
Reduction
Needed
(lbs/ac/yr)
(from Compi.
Worksheet)
Project Size
(square feet)
Offset
Duration
(yrs)
Site Delivery
Factor
State Buy Down
Amount Delivered
(Ibs)
D ` E ` F ` G
Additional
5% if bank
not in City
limits (Ibs)
Total Delivered
(Ibs)
H + I
8.37
8.00
2.20
5.80
198,082
30
1.00
791.24
791.24
Phosphorus Loading / Offset Needs (For the Jordan and Falls Watershed areas)
(A)
(B)
(C)
(D)
(E)
(F)
(G)
(H)
(1) (Where
Applicable)
(J)
Untreated
Loading
Rate
(Ibs/ac/yr)
Treated
Loading
Rate
(Ibs/ac/yr)
Load Rate
Target
(Ibs/ac/yr)
Reduction
Needed
(lbs/ac/yr)
(from Compi.
Worksheet)
Project Size
(square feet)
Offset
Duration
(yrs)
Site Delivery
Factor
State Buy Down
Amount Delivered
(Ibs)
D ` E ` F ` G
Additional
5% if bank
not in City
limits (Ibs)
Total Delivered
(Ibs)
H + 1
2.93
2.75
0.82
1.93
198,082
30
1.00
263.29
13.16
276.46
Responsible
Professional Engineer's Name:
I
PE #:
Staff Name:
I
Staff e-mail:
I
Phone #:
January 9, 2018 Version

CALYX"'
FNGINFERS + CONSULTANTS
JORDAN/FALLS LAKE STORMWATER
NUTRIENT LOAD ACCOUNTING
TOOL
6750 Tryon Road, Cary, NC 27518 P:919.836.4800 F:919.851.1918 CALYXengineers.com

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JCALYX
ENGINEERS + CONSULTANTS
SAND FILTER CALCULATIONS

NCCU STUDENT UNION
DA #1
AREA
IMP. AREA
GRASS AREA
(SF)
(SF)
(SF)
15802
14052
1750
TOTAL (SF)
15802
14052
1750
TOTAL (ACRES)
0.36
0.32
0.04
DRAINAGE BASIN - TREATMENT AREA
DRAINAGE BASIN = 0.36 Acres
IMPERVIOUS = 0.32 Acres
PERVIOUS = 0.04 Acres
P= 1 inch
WATER QUALITY VOLUME CALCULATION
IA = 0.89
R = 0.85
WQV = 1,111
WQVAdj= 833
NCCU STUDENT UNION SAND FILTER
IA = Impervious Fraction
R = 0.05 + .9 * Impervious fraction
WQV=3630*P*R *A
SURFACE AREA REQUIREMENT - FILTER BED AND SEDIMENTATION BASIN SURFACE AREA
MAXIMUM HEAD ON THE SANDFILTER
h MaxFilter = WQV Adj / (As + Af) h m_F;ner = Maximum Head on the Sand Filter (ft)
h MaxFllter = Choose o Value for hM,,er so that the following equation holds true: hr -Fnrer = WQVAdil(A, +Af)
A, = Surface Area of the Sedimentation Basin (ft')
A f = Surface Area of the Sand Filter Bed (ft`)
hA = hMaxFilter / 2 h A = Average Head (ft)
hA = 2.0 FT
SEDIMENTATION BASIN SURFACE AREA
A, = [240 * R * AD] * RD A, = Minimum Surface Area of the Sedimentation Basin
Rv = 0.85 R v = Volumetric Runoff Coefficient (unitless)
AD = 0.36 A o = Drainage Area (Acres)
Rv = 1 R v = Design Rainfall Depth (inches)
A,= 73.44 SO. FT
SAND FILTER BED SURFACE AREA
Af = (WQV*dF)/(k*t*(hA + dF)) A f = Minimum Surface Area of the Sand Filter
k = 3.50 FT/DAY k = coefficient of permeability for the sand filter bed = 3.5 (ft/day)

dF = 1.5 FT
t = 1.66 DAYS
Af = 81.94 SQ FT
SAND FILTER
MINIMUM SAND FILTER DESIGN REQUIREMENTS
hMaxFilter = 4.0 FT
As = 73.44 SQ FT
Af = 81.94 SQ FT
SAND FILTER DIMENSIONS
hMaxFilter = 4.0 FT
As = 105.00 SQ FT
Af = 105.00 SQ FT
ENSURE WATER QUALITY VOLUME IS CONTAINED
WQVAdj = 833 CF
[Af +Aj * [hMaxFilterl >= WQVAdj
d F = Depth of the Sand Filter Bed (ft) = 1.5 ft minimum
t = time requried to drain the WQV through the sand filter bed -maximum 40 hours = 1.67 days
h A = Average Head (ft)
840 CF >= 833 CF OK