SW3230303_Supplement-EZ Form_20230803

SUPPLEMENT-EZ COVER PAGE
FORMS LOADED
PROJECT INFORMATION
1 Project Name Twelve Mile Creek WRF 9.0 MGD Expansion
2 Project Area(ac) 53.24
3 Coastal Wetland Area(ac) 0
4 Surface Water Area(ac) 3.246
5 Is this project High or Low Density? Low
6 Does this project use an off-site SCM? No
COMPLIANCE WITH 02H.1003(4)
7 Width of vegetated setbacks provided(feet) 30
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
10 Is streambank stabilization proposed on this project? No
NUMBER AND TYPE OF SCMs:
11 Infiltration System 0
12 Bioretention Cell 0
13 Wet Pond 0
14 Stormwater Wetland 0
15 Permeable Pavement 0
16 Sand Filter 0
17 Rainwater Harvesting(RWH) 0
18 Green Roof 0
19 Level Spreader-Filter Strip(LS-FS) 0
20 Disconnected Impervious Surface(DIS) 0
21 Treatment Swale 0
22 Dry Pond 0
23 StormFilter 0
24 Silva Cell 0
25 Bayfilter 0
26 Filterra 0
FORMS LOADED I
DESIGNER CERTIFICATION
27 Name and Title: Michael Parker P.E.
28 Organization: Hazen&Sawyer
29 Street address: 9101 Southern Pine Boulevard,Suite 250
30 City,State,Zip: Charlotte,North Carolina,28273
31 Phone number(s): [phone]
32 Email: [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.
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Seal Date

DRAINAGE AREAS
1 Is this a high density project? No
2 If so,number of drainage areas/SCMs 0
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 LD 1 I
4 Type of SCM Dispersed flow Dispersed flow_
5 Total drainage area(sq ft) 2319134 sf 2319134 sf _
6 Onsite drainage area(sq ft) 2319134 sf 2319134 sf
7 Offsite drainage area(sq ft) n/a n/a
8 Total BUA in project(sq ft) 347620 sf 347620 sf
New BUA on subdivided lots(subject to
9 permitting)(sq ft) n/a n/a
New BUA not on subdivided lots(subject to
10 permitting)(sf) 102190 sf 102190 sf
11 Offsite BUA(sq ft) n/a n/a
12 Breakdown of new BUA not on subdivided lots:
-Parking(sq ft) sf sf
-Sidewalk(sq ft) 8320 sf 8320 sf
-Roof(sq ft) 31300 sf 31300 sf
-Roadway(sq ft) _ 62570 sf 62570 sf
-Future(sq ft) _ sf sf
-Other,please specify in the comment box
below(sq ft) sf sf
New infiltrating permeable pavement on
13 subdivided lots(sq ft) sf sf
New infiltrating permeable pavement not on
14 subdivided lots(sq ft) sf sf
Existing BUA that will remain(not subject to
15 permitting)(sq ft) _ 245430 sf 245430 sf
16 Existing BUA that is already permitted(sq ft) _ sf sf
17 Existing BUA that will be removed(sq ft)
18 Percent BUA 15% 15%
19 Design storm(inches) 7.6 in 7.6 in
20 Design volume of SCM(cu ft) n/a n/a
21 Calculation method for design volume n/a n/a
rDITIONAL INFORMATION
Please use this space to provide any additional information about the
22 drainage area(s):
The 12 Mile Creek WRF property boundary is less than 0.001%of the total
contributing drainage area according to StreamStats(Appendix D).Due to
the significant difference,offsite drainage was not considered in the BUA
table(Drawing C6).Percent BUA includes all BUA that will be on site after

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) n/a
5 Maximum velocity in the vegetated conveyances during the 10-year storm?
6 Are curb outlet swales proposed? No
7 Maximum longitudinal slope of curb outlet swale(s)(%) n/a
8 Bottom width of curb outlet swale(s)(feet) n/a
9 Maximum side slope of curb outlet swale(s)(H:V) n/a
10 Minimum length of curb outlet swale(s)(feet) n/a
11 Are treatment swales used instead of curb outlet swales? No
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:
This site has a preexisting storm system that is required for conveyance under roadways.The protective measures taken under
the project were to minimize impact to the existing stormwater design and provide aditional outfall protection with riprap in areas
where imperviousness in a storm systems catchbasin were made.
Drainage Pervious
Swale BUA Q Slope Van,w Vam„i Flow depth
# Area area
(ac) (cfs) (%) (fps) (fps) (ft)
(ac) (ac)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
2