SW5240202_Stormwater Narrative_20240723

SUPPLEMENT-EZ COVER PAGE
FORMS LOADED
PROJECT INFORMATION
1 Project Name WRENN VILLAS _
2 Project Area(ac) 33.31
3 Coastal Wetland Area(ac) 0 .
4 Surface Water Area(ac) 21,598
5 Is this project High or Low Density? _ Both High and Low Density
6 Does this project use an off-site SCM? Yes
COMPLIANCE WITH 02H.1003(4)
7 Width of vegetated setbacks provided(feet) I 50
8 Will the vegetated setback remain vegetated? _ Yes
9 If BUA is proposed in the setback,does it meet NCAC 02H.1003(4)(c-d)? N/A
70 7 Is streambank stabilization proposed on this project? No
NUMBER AND TYPE OF SCMs:
11 Infiltration System _
12 Bioretention Cell
13 Wet Pond - 1
14 Stormwater Wetland
15 Permeable Pavement _ —
16 Sand Filter
17 Rainwater Harvesting(RWH)
18 Green Roof
19 Level Spreader-Filter Strip(LS-FS)
20 Disconnected Impervious Surface(DIS)
21 Treatment Swale
22 Dry Pond
23 StormFilter _.
24 Silva Cell
25 Bayfilter
26 Filterra
FORMS LOADED
DESIGNER CERTIFICATION
27 I Name and Title: John R Wadsworth,PE-Project Engineer
28 Organization: Timmons Group
29 Street address: 5410 Trinity Road,Ste 102
30 City,State,Zip: Raleigh,NC 27607
31 Phone number(s): r919-866-4516
32 Email: I [e-mail]
Certification Statement-
I certify,under penalty of law that this Supplement-EZ form and all supporting information were prepared under my direction or supervision;that the
information provided in the form is,to the best of my knowledge and belief,true,accurate,and complete;and that the engineering plans,specifications,
operation and maintenance agreements and other supporting information are consistent with the information provided here.
Designer
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OFF-SITE SCM
THE DRAINAGE AREA
1 Drainage area number for this project 1
2 Master permit number 5240201
3 Drainage area number from the master permit 1
4 Lot or outparcel number Wrenn Farms
5 BUA allocated by Master Permit 29185 sf
INFORMATION ABOUT THE OFF-SITE SCM
6 Type of off-site SCM Wet Pond
7 Available treatment capacity in the off-site SCM (cu ft) 260192 cf
8 Have deed restrictions limiting the BUA on the site been recorded? No
9 Has an Engineer's Certification for the off-site SCM been submitted to DEQ? No
10 Are there any Notices of Violation for the off-site system? No
11 Has the off-site SCM been maintained in accordance with its O&M Plan? Yes
12 Will the collection system be maintained in its design state and kept clean? Yes
ADDITIONAL INFORMATION
13 Please use this space to provide any additional information about the off-site SCM(s):

DRAINAGE AREAS
1 Is this a high density project? Yes
2 If so,number of drainage areas/SCMs 1
3 Does this project have low density areas? Yes
4 If so,number of low density drainage areas 1
Is all/part of this project subject to previous rule
5 versions? No
FORMS LOADED
DRAINAGE AREA INFORMATION Entire Site 1 LD 1
4 Type of SCM Wet Pond
5 Total drainage area(sq ft) 2,541,423 887,556 144993
6 Onsite drainage area(sq ft) 1003684 887556 116128
7 Offsite drainage area(sq ft) 1051512 0 _ 28864
8 Total BUA in project(sq ft) 506099 sf 465933 sf 40166 sf
New BUA on subdivided lots(subject to permitting)
9 (sq ft) 304300 sf 304300 sf sf
New BUA not on subdivided lots(subject to
10 permitting)(sf) 181583 sf 161633 sf 19950 sf
11 Offsite BUA(sq ft) 738231 sf 8602 sf
12 Breakdown of new BUA not on subdivided lots:
-Parking(sq ft) 17000 sf 17000 sf
-Sidewalk(sq ft) 48440 sf 39090 sf 9350 sf
-Roof(sq ft)
-Roadway(sq ft) 116143 sf 105543 sf 10600 sf
-Future(sq ft)
-Other,please specify in the comment box
below(sq ft)
New infiltrating permeable pavement on
13 subdivided lots(sq ft) N/A N/A N/A
New infiltrating permeable pavement not on
14 subdivided lots(sq ft) N/A N/A N/A
Existing BUA that will remain(not subject to
15 permitting)(sq ft) 11614 sf N/A 11614 sf
16 Existing BUA that is already permitted(sq ft) N/A N/A N/A
17 Existing BUA that will be removed(sq ft) N/A N/A _ N/A
18 Percent BUA 50% 52% 14%
19 Design storm(inches) 1.0 in N/A
20 Design volume of SCM(cu ft) 76372 cf N/A
21 Calculation method for design volume Simple Method N/A
ADDITIONAL INFORMATION
Please use this space to provide any additional information about the
22 drainage area(s):
All the offsite BUA is bypassing the SCM.Drainage area 1 drains to the SCM.
Drainage area LD1 drains to POI 2.A small portion of this project,29,185 sf
(considered 100%BUA),drains an offsite in Wrenn Farms to the east.

WET POND
1 Drainage area number 1 I
2 Minimum required treatment volume(Cu ft) 38644 cf
GENERAL MDC FROM 02H.1050
3 Is the SCM sized to treat the SW from all surfaces at build-out? Yes
4 Is the SCM located away from contaminated soils? Yes
5 What are the side slopes of the SCM(H:V)? 3:1
6 Does the SCM have retaining walls,gabion walls or other engineered No
side slopes?
7 Are the inlets,outlets,and receiving stream protected from erosion(10- Yes
year storm)? _
8 Is there an overflow or bypass for inflow volume in excess of the Yes
design volume?
9 What is the method for dewatering the SCM for maintenance? - Pump(preferred)_
10 If applicable,will the SCM be cleaned out after construction? Yes
11 Does the maintenance access comply with General MDC(8)? Yes
12 Does the drainage easement comply with General MDC(9)? Yes
13 If the SCM is on a single family lot,does(will?)the plat comply with N/A
General MDC(10)?
14 Is there an O&M Agreement that complies with General MDC(11)? Yes
15 Is there an O&M Plan that complies with General MDC(12)? Yes _
16 Does the SCM follow the device specific MDC? Yes
17 Was the SCM designed by an NC licensed professional? Yes
WET POND MDC FROM 02H.1053
_ 18 Sizing method used SA/DA
_ 19 Has a stage/storage table been provided in the calculations? Yes _
20 Elevation of the excavated main pool depth(bottom of sediment 405.00
removal)(fmsl)
21 Elevation of the main pool bottom(top of sediment removal)(fmsl) 406.00
22 Elevation of the bottom of the vegetated shelf(fmsl) 410.00
23 Elevation of the permanent pool(fmsl) 410.00
24 Elevation of the top of the vegetated shelf(fmsl) 411.00
25 Elevation of the temporary pool(fmsl) 411.66
26 Surface area of the main permanent pool(square feet) 17398
27 Volume of the main permanent pool(cubic feet) 55914 cf
28 Average depth of the main pool(feet) 3.00 ft
29 Average depth equation used Equation 3
30 If using equation 3,main pool perimeter(feet) 596.0 ft
31 If using equation 3,width of submerged veg.shelf(feet) .0 ft _
32 Volume of the forebay(cubic feet) 9117 cf _
33 Is this 15-20%of the volume in the main pool? Yes
34 Clean-out depth for forebay(inches) 48 in
35 Design volume of SCM(cu ft) 76372 cf
36 Is the outlet an orifice or a weir? Orifice
37 If orifice,orifice diameter(inches) 2.75 in _
38 If weir,weir height(inches)
39 If weir,weir length(inches)
40 Drawdown time for the temporary pool(days) 3.2 _
41 Are the inlet(s)and outlet located in a manner that avoids short- Yes
circuiting?
42 Are berms or baffles provided to improve the flow path? No
43 Depth of forebay at entrance(inches) 48 in _
44 Depth of forebay at exit(inches) 54 in
45 Does water flow out of the forebay in a non-erosive manner? Yes
46 Width of the vegetated shelf(feet) 6 ft
47 Slope of vegetated shelf(H:V) _ 6:1
48 Does the orifice drawdown from below the top surface of the No
permanent pool?
Does the pond minimize impacts to the receiving channel from the 1-
49 Yes
yr,24-hr storm?
50 Are fountains proposed?(If Y,please provide documentation that No
MDC(9)is met.)
51 Is a trash rack or other device provided to protect the outlet system? Yes
52 Are the dam and embankment planted in non-clumping turf grass? Yes
53 Species of turf that will be used on the dam and embankment Bermuda
54 Has a planting plan been provided for the vegetated shelf? Yes
ADDITIONAL INFORMATION
55 Please use this space to provide any additional information about the
wet pond(s):
2

LOW DENSITY
DESIGN REQUIREMENTS FOR LOW DENSITY PROJECTS FROM 02H.1003
1 Is project below density thresholds set forth in the applicable stormwater rule? Yes
2 Does project maximize dispersed flow and minimize channelization of flow? Yes
3 Has the use of piping been minimized per.1003(2)(c)? Yes
4 Side slopes of the vegetated conveyances(H:V) 3:1
5 Maximum velocity in the vegetated conveyances during the 10-year storm? 4.7
6 Are curb outlet swales proposed? No
7 Maximum longitudinal slope of curb outlet swale(s)(%)
8 Bottom width of curb outlet swale(s)(feet)
9 Maximum side slope of curb outlet swale(s)(H:V)
10 Minimum length of curb outlet swale(s)(feet)
11 Are treatment swales used instead of curb outlet swales?
12 Is stormwater released at the edge of the setback as dispersed flow? Yes
13 Have stormwater outlets been designed to prevent downslope erosion? Yes
14 Are variations to rule.1003 proposed? No
ADDITIONAL INFORMATION
15 Please use this space to provide any additional information about this low density project:
Stormwater runoff will be conveyed with the use of a roadside swale and RCP pipes.Runoff will outlet at non-erosive velocities.
Calculcations pipes are provided in the stormwater impact analysis.
Drainage Pervious
Swale Area BUA area C Q Slope Vanaw V,ct,,,i Flow depth
# (ac) (ac) area (cfs) (%) (fps) (fps) (ft)
1 1.74 0.44 1.30 0.65 8.17 2.50 9.42 4.70 0.76
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