SW5230901_Design Calculations_20240404

WET POND SIZING DATE
4/4/2024 •• •.�
PROJECT NAME PROJECT NO TIMMONS GROUP
NCNG CB BOM Yard 42324 °°""°'°"""`°""°"'°""
LOCATION BY
Stem,NC Jake Lewis
POND A
Drainage Area,(DA)= 8.10 ac
Impervious Area c=0.95 4.47 ac
Pervious Area c= 0.30 3.63 ac
Cc= 0.66
CN=
Permanent Water Quality Pool
% Impervious= 55.1
Permanent Pool Design Depth= 3.00 ft
SA/DA Ratio= 1.94 (from Tbl. 1.1)
Required Surface Area= 6,858 sf
Permanent Pool Volume Req.= 20,574 cf
Temporary Water Quality Pool
Design Storm Rainfall 1.00 in (Typically 1-in)
Runoff Coeff.(Rv=0.05+0.009(%Imperv.))= 0.55 in/in
Required Volume(design rainfall)(Rv)(DA)= 16,056.94 cf
Surface Area Provided:
Permanent Pool Max.Depth= 4.00 ft
Area of Pond Bottom(Above PSS)= 6,884 sf (EL=452.0)
Area Bottom of Shelf= 9,361 sf (EL=457.0)
Area of Permanent Pool= 10,466 sf (EL=457.5)
Area Top of Shelf= 11,489 sf (EL=458.0)
Perm.Pool Volume Provided= 33,300 cf > 20,574 OK
Avg.Perm.Pool Depth Provided(Eq.3). 3.18 ft > 3.00 OK
Surface Area at 1"Storage Volume= 16,122 sf (EL=1203.1)
1"Storage Volume Provided= 22,159 cf > 16,057 OK
Percent of Full Size 138%
Temp.Storage Depth above Dewatering Hole= 1.50 ft
Diameter of Dewatering Hole= 2.00 in
Detention(Draw-Down)Time = 3.6 days (2-5 days Required)
T days=(Temp.Storage Vol Req/(0.6*A*(2`g*(h))^1/2)`86400
(where h=one third temp.storage depth measured to centroid of orifice)
Max Drawdow Rate= 0.13 cfs
Permanent Pool Volume= 33,300 cf > 20,574 OK
Forebay Volume Required= 4,995 cf
Forebay Volume Provided= 5,127 cf
15.4% OK
Table 1.1
SA/DA Ratios 85%TSS efficiency
Permanent Pool Depth(ft)
%Impervious 3.0 4.0 5.0 6.0
10 0.51 0.43 0.37 0.30
20 0.84 0.69 0.61 0.51
30 1.17 0.94 0.84 0.72
40 1.51 1.24 1.09 0.91
50 1.79 1.51 1.31 1.13
60 2.09 1.77 1.49 1.31
70 2.51 2.09 1.80 1.56
80 2.92 2.41 2.07 1.82
90 3.25 2.64 2.31 2.04
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DATE
POND A
Main Pool Permanent Pool Volume
Stage(ft) Elevation Area(sf) Storage(cf)
Top of Sed.Stor.in Main Pond
-4.00 452.50 6,884
-3.50 453.00 7,218 3,525
-2.50 454.00 7,907 11,088
-1.50 455.00 8,621 19,352
-0.50 456.00 9,361 28,343 Inside of Shelf Elev.
0.00 456.50 10,466 33,300 Normal Pool Elev.
0.50 457.00 11,489 38,788 Outside of Shelf Elev.
Forebay Volume
Stage(ft) Elevation Area(sf) Storage(cf)
-4.00 452.50 644 0 Top of Sed.Stor.in Forebay
-3.50 453.00 770 354
-2.50 454.00 1,058 1,268
-1.50 455.00 1,390 2,492
-0.50 456.00 1,765 4,069
0.00 456.50 2,467 5,127 Normal Pool Elev.
Total Pond Stage/Storage Detail
Stage(ft) Elevation Area(sf) Storage(cf)
0.00 456.5 12,926 0 Normal Pool Elev.
0.50 457 14,489 6853.8175
Water Quality Elevation
1.50 458 16,122 22159.3175
2.50 459 17,815 39127.8175
3.50 460 20,414 58242.3175
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Project Information Complete this sheet if required by your reviewing authority.
Contact them for any questions. Grey boxes/text are optional.
SNAPv4.2.0 LOCATION
Project Name(optional): NCNG Camp Butner BOM Yard Parcel ID(optional): 86900128714
Submission Date(optional): 4/5/2024 date Nutrient Management Watershed: Falls Lake menu
Local Jurisdiction/Reviewing Agency: Stem menu Subwatershed: Upper_Falls menu
Project Latitude Coordinates(optional): 36°11'38.4"N N Phosphorus Delivery Zone: Neuse- Upper 03020201 menu
Project Longitude Coordinates(optional): 78°47'25.6"W W Nitrogen Delivery Zone: Falls- Upper menu
PROJECT DETAILS
Development Land Use Type: Industrial menu Disturbed Area: 466,435 ft2
Part of Common Development Plan? .no yin Project Activity: Redevelopment menu
Designated Downtown Area? no yin Project Drains to SA Waters? no yin
Public Linear Road/Sidewalk Project? .no yin Pre-Project Land Use: forest menu
Project Owner Type: State non-NCDOT menu Project Description(optional):
STORMWATER DETAILS
(Falls ONLY)Onsite Reduction%Req. 30% % Project Uses LID/Runoff Volume Match? no yin
Existing BUA/Development Onsite? yes yin Local Gov't nutrient req's same as State? yes yin
Local Gov't cutoff date for Existing BUA: 12/01/2006 date Project Drains to Regional SCM? no yin
Nitrogen Export Rate Target: .2.20 lb/ac/yr Total Nitrogen Offset Credits Needed: 0.0 lb/yr
Phosphorus Export Rate Target: 0.33 lb/ac/yr Total Phosphorus Offset Credits Needed: 0.0 lb/yr

SNAP v4.2.0
Project Area and Offsite Land Cover Characteristics Precipitation Oxford
Station:
Copy ' Paste VALUES ONLY for Best Results Click here to scroll down to error messages on this sheet.
—
PROJECT AREA LAND COVERS TN EMC (mg/L) TP EMC (mg/L) Pre-Project Area (ft2) Post-Project Area (ft2) Change pre-to-post(ft2)
1
Roof 1.18 0.11 0
Roadway 1.64 0.34 0
Parking/Driveway/Sidewalk 1.42 0.18 57,710 225,400 167,690
Protected Forest 0.97 0.03 587,650 587,650 0
Managed Pervious/Landscaping 2.48 1.07 400,786 220,170 -180,616
Offsite or Existing Roof 1.18 0.11 0
Offsite or Existing Roadway 1.64 0.34 0
Offsite or Existing Parking/Driveway/Sidevin 1.42 0.18 0
Offsite Protected Forest 0.97 0.03 0
Offsite Managed Pervious I 2.48 1.07 0
CUSTOM LAND COVER 1 0
CUSTOM LAND COVER 2 0
CUSTOM LAND COVER 3 0
LAND TAKEN UP BY SCM 1.18 0.11 12,926 12,926
Total (Regulated & UnReg)Area 1,046,146.00 1,046,146.00
Project (Regulated)Area 1,046,146.00 1,046,146.00

SCM Characteristics
Stormwater Control Measure (SCM) Characteristics Click here to go to
Copy ft Paste VALUES ONLY SCM101's Land Cover Data
SNAP v4.2.0
for Best Results
Catchment ID 1 1 1
Drains to Drains to
SCM ID 101 102 103
7 Type of SCM Wet Pond
rHydrologic soil group at SCM location C
' SCM Description
ftDesign Storm Size(inches/24hrs) 1.00
■ Percent of Full Size 138%
Annual Effluent 79% 0% 0%
Annual Overflow 7% 0% 0%
I. %Annual ET/Infiltrated 14% 0% 0%
ElCustom%Annual Effluent A
r� Custom%Annual Overflow
rCustom%Annual ET/Infiltrated 1
l SCM Effluent TP EMC(mg/L) 0.13 0.00 0.00
III SCM Effluent TN EMC(mg/L) 0.86 0.00 0.00
■ Custom Effluent TP EMC
1.1 Custom Effluent TN EMC
r SCM Land Cover TP EMC(mg/L) 0.11 0.00 0.00
L SCM Land Cover TN EMC(mg/L) 1.18 0.00 0.00
r'This SCM Drains to Numbered SCM 0 0 0
Catchment Routing Catchments Draining to Catchments Draining to Catchments Draining to
SCM 101 SCM 102 SCM 103
Catchment 1
Catchment 2
Catchment 3
Catchment 4
Catchment 5
Catchment 6
Error Check-Missing SCM Area:

SCM Characteristics
Error Check-Min/Max Size:
II— Error Check-Hydrology:
Error Check-Missing SCM Info:
Error Check-Drainage Data w/o SCM:
Error Checks-SCM Type:
- SCM ID: 101 102 103
TArea Draining Directly to Area Draining Directly to Area Draining Directly to
SCM Drainage Area Land Covers SCM 101 (ft2) SCM 102 (ft2) SCM 103 (ft2)
Roof
Roadway
Parking/Driveway/Sidewalk 194,512
Protected Forest 17,650
Managed Pervious/Landscaping 127,848
Offsite or Existing Roof
Offsite or Existing Roadway
Offsite or Existing Parking/Driveway/Sidewalk
Offsite Protected Forest
Offsite Managed Pervious
CUSTOM LAND COVER 1
CUSTOM LAND COVER 2
CUSTOM LAND COVER 3
LAND TAKEN UP BY SCM 12,926
TOTAL AREA DRAINING TO SCM (ft2): 352,936 0 0
CATCHMENT AREA(ft2): 352,936

SCM Characteristics
Error Check-Min/Max Size:
Error Check-Hydrology:
Error Check-Missing SCM Info:
Error Check-Drainage Data w/o SCM:
IIIError Checks-SCM Type:
SCM ID:
Allowable Total Land Use
Total Land Use Area Post-Project Untreated
SCM Drainage Area Land Covers z Area to be Treated Based z
Treated By All SCMs(ft ) z Land Area (ft2)
on Post-Project Areas(ft2)
..roof 0 0 0
Roadway 0 0 0
Parking/Driveway/Sidewalk I 194,512 225,400 30,888
Protected Forest 17,650 587,650 570,000
Managed Pervious/Landscaping I 127,848 220,170 92,322
Offsite or Existing Roof 0 0 0
Offsite or Existing Roadway 0 0 0
Offsite or Existing Parking/Driveway/Sidew 0 0 0
Offsite Protected Forest 0 0 0
Offsite Managed Pervious 0 0 0
CUSTOM LAND COVER 1 0 0 0
CUSTOM LAND COVER 2 0 0 0
CUSTOM LAND COVER 3 0 0 0
LAND TAKEN UP BY SCM 12,926 12,926 0
TOTAL AREA DRAINING TO SCM (ft2): 352,936 1,046,146 693,210
CATCHMENT AREA(ft2):

Nutrient Export Summary
Landcover Et SCM Data Review
Errors/Advisories
Avg Annual precip(in) = 44.46
Total (Regulated+
1,046,146
Unregulated)Area (ftZ)=
Project(Regulated)
1,046,146
Area (ftZ) =
Net BUA(Project Area
2 167,690 Net BUA indicates new development or expansion.
BUA only ft )_
Custom Landcovers are
present:
no
Total Nitrogen Export Target
52.84
Scaled to Project Area (lb/yr):
Total Area Total Area Project Area
Project Area
(Onsite+ Post-Project Post-Project
Nutrient Export Summary (Onsite Only)
Offsite) before before
Pre-Project
Pre-Project Treatment Treatment
Area (All Landcover Types) (acres) 24.0162 24.0162 24.0162 - 24.0162
Percent Built-Upon Area (BUA)(%) 6% 6% 22% 22%
Built-Upon Area(BUA) (sqft) 57,710 57,710 225,400 225,400
Annual Runoff Volume(ft3/yr) 347,609 347,609 891,802 891,802
Annual Runoff%Change 157% _ 157%
Total Runoff Change(cuft/yr) 544,193 544,193
Total Nitrogen EMC(mg/L) 1.50 1.50 1.40 1.40
Total Nitrogen Load Leaving Site(Ib/yr) _ 32.49 32.49 _ 78.11 78.11
Total Nitrogen Loading Rate(Ib/ac/yr) _ 1.35 1.35 3.25 3.25
Total Nitrogen%Change Pre-to-Post 140% 140%
Total Nitrogen Change(Ib/yr) Pre-to-Post 45.61 45.61
Total Phosphorus EMC(mg/L) 0.31 0.31 0.20 7- 0.20
Total Phosphorus Load Leaving Site(Ib/yr) 6.70 6.70 10.96 10.96
Total Phosphorus Loading Rate(Ib/ac/yr) 0.28 0.28 0.46 0.46
Total Phosphorus%Change Pre-to-Post 63% -E_ 63%
Total Phosphorus Change (Ib/yr)Pre-to-Post 4.25 4.25
SCM/Catchment Summary
1

SCM ID and Type Volume TN Reduction TP Reduction TN Out I TP Out
Reduction(%) (%) (%) (Ibs/ac/yr) (Ibs/ac/yr)
I
Catchment 1 14.01% I 45.97% ‘ 42.60% 4.09 0.61
101:Wet Pond 14.01% 45.97% 42.60% 4.09 0.61
102:NA 0.00% 0.00% 0.00% 0.00 0.00
103:NA 0.00% 0.00% 0.00% 0.00 0.00
Catchment 2 0.00% 0.00% _ 0.00% 0.00 0.00
201:NA 0.00% 0.00% 0.00% 0.00 0.00
202:NA 0.00% 0.00% _ 0.00% 0.00 0.00
203:NA 0.00% 0.00% 0.00% 0.00 0.00
Catchment 3 0.00% 0.00% 0.00% 0.00 0.00
301:NA 0.00% 0.00% 0.00% 0.00 0.00
302:NA 0.00% 0.00% 0.00% 0.00 0.00
303:NA 0.00% 0.00% 0.00% 0.00 0.00
Catchment 4 0.00% 0.00% _ 0.00% 0.00 0.00
401:NA 0.00% 0.00% 0.00% 0.00 0.00
402:NA 0.00% 0.00% _ 0.00% 0.00 0.00
403:NA 0.00% 0.00% 0.00% 0.00 0.00
Catchment 5 0.00% 0.00% 0.00% 0.00 0.00
501:NA 0.00% 0.00% 0.00% 0.00 0.00
502:NA 0.00% 0.00% 0.00% 0.00 0.00
503:NA 0.00% 0.00% 0.00% 0.00 0.00
Catchment 6 0.00% 0.00% _ 0.00% 0.00 0.00
601:NA 0.00% 0.00% 0.00% 0.00 0.00
602:NA 0.00% 0.00% _ 0.00% 0.00 0.00
603:NA 0.00% 0.00% 0.00% 0.00 0.00
1

SNAP v4.2.0
Errors/Advisories
SCM Area (ft2) = 12,926
SCM Treated Area (ft2) = 352,936
Catchment Routing: No errors
Treating Runoff from
Existing BUA or Offsite:
no
Disturbed Area (ft2) = 466,435
Total Phosphorus Export Target
7.93
Scaled to Project Area (Ib/yr):
Total Area Project Area Total Area Project Area
Total Area Project Area
Post-Project Post-Project Post-Project Post-Project
Post-Project Post-Project
SCM-Treated SCM-Treated Untreated Untreated
after Treatment after Treatment
Area Only Area Only Areas Areas
24.0162 24.0162 8.1023 8.1023 15.9139 15.9139
22% I 22% 55% 55% 4% I 4%
225,400 225,400 194,512 194,512 30,888 _ 30,888
796,069 796,069 587,797 587,797 208,272 208,272
129% _ 129%
448,459 448,459
1.01 1.01 0.90 0.90 1.29 1.29
49.93 I 49.93 33.12 33.12 16.82 -t 16.82
2.08 2.08 4.09 4.09 1.06 1.06
54% 54%
17.44 I 17.44
0.15 0.15 0.14 0.14 0.18 0.18
7.27 7.27 - 4.97 4.97 2.31 2.31
0.30 0.30 0.61 0.61 0.14 0.14
8% 8%
0.57 0.57 ===
1

Falls Lake ONLY: Onsite Reduction Compliance Check
Nitrogen Phosphorus
Onsite%Reduction Requirement 30% 30%
Export Target Scaled to Area (Ib/yr) 52.84 7.93
Export Load Post-Project Before Treatment 78.11 10.96
Total Reduction Need (Ib/yr) 25.27 3.03
Onsite Reduction Need (Ib/yr) 7.58 0.91
Onsite Export Target(Ib/yr) 60.42 8.83
Project Area Post-Project After Treatment 49.93 7.27
1