20061085 Ver 2_Stormwater Info_20061116

~ DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
ENGINEERING LAND PLANNING • SURVEYING
6415 Old Plank Road, High Point, NC 27265
[phone] • Fax [phone] • www.dmp-inc.com
Cynthia Van Der Wiele
NCDWQ Wetlands Unit/Express Review Program
2321 Crabtree Blvd
Suite 250
Raleigh, NC 27604
November 15, 2006
RE: Elementary School G
DMP Job No. E3938
DWQ EXP No. 06-1085
Dear Ms. Van Der Wiele,
Thank you for your review of the storm water management plan for Elementary School G. Per the letter dated
November 7, 2006 enclosed is 1 copy of the revised plan sheets in accordance with the comments with 2 copies
being forward to Mr. Barry Love in the Mooresville Regional Office. The comments are listed below with our
response in italics.
A.) You have subdivided your project site into nine drainage areas. Three of these areas
meet the criteria for requiring engineered storm water management- Basins 1,3, and 4. You have not
provided storm water management for Basin No. 4. This will be required.
A bio retention area for Basin No. 4 has been provided. Sizing calculations are enclosed
B.) Grassed swales provide only 35%TSS removal; you are required by the conditions of the General
Water Quality Certification to provide storm water BMP's that removes at least 85%TSS. Please redesign
the storm water management plan for Basin No. 1.
The grass swale has been replaced with a bio retention area. Sizing calculations are
enclosed.
C.) The fore bay for Wet Detention Pond for Basin No. 3 is extremely oversized. This does not provide
additional water quality benefits. Please redesign your pond.
The pond has been redesigned to include the required littoral shelf and the
sediment fore bay has been redesigned to be more adequate for the pond.
D.) Please provide a planting plan for the littoral shelves of the wet detention ponds. Please refer to the
NC DENR 1999 Storm water Best Management Practices Manual for design guidance.
A planting plan for the littoral shelves is included.
If you have any additional comments or questions about the plans please do not hesitate to give me or Eddie
MacEldowney a call.
I look forward to hearing from you.
~~~aa~
D
CC: File
Barry Love (MRO) r ~~'' `'~~;
' Q<'thli'lfdiEr:
Don Dixon (UCPS)
Sincerely,
Davis-Martin-Powell and Associates
Ja G ffey, E

Bioretention Sizing (#1 Basin #1)
Watershed Size
4.37 acres
Percent Connected Impervious
31.T
Water Quality Storm
1 in
For Disconnected/Composite Area
Soil Type CN
0 A 49
1 B 69
0 C 79
0 D 84
69` Selected Curve Number
Hate: Select Soil Group with "1"
First Flush Runoff
1.1 Q ac-in equation: based off SCS CN Method. No Composite CN
Average Depth
9 in
Surface Area
0.12 ac equation: Volume /Depth
5335 sf
Fill Soil Choice
Nitrogen Removal -Sandy Loam
K= 1 in/hr Soil Type: 12% Fines (Silt+Clay), 82-85% Sand, 3-Ei% Organic
Other Pollutant Removal -Loamy Sand
K= 2 in/hr Soil Type: 8% Fines (Silt+Clay), 86-90% Sand, 2-4% Organic
K= 2 in/hr
Underdrains
Minimum Flow
equation: Q = 2.3E-5 * K * A
0.25 cfs
Factor of Safety (range between 2 and 10)
4
Design Flow
Note to User:
Yellow Cells Require User Input
Blue Dells Have Been Previously Determined
Pink Cells are Calculations within this Spreadsheet
Breakdown of Runoff
Connected Imperv RO 0.79 in 1.10 ac-in
Composite RO (the rest) 0.00 in 0.01 ac-in

0.98 cfs
Manning's Roughness Coefficient
0.011 smooth wall
0.015 corrugated wall
:0.011. ; n
Internal Slope (recommended minimum 0.5%)
05`
Pipe(s) Diameter(s)
7:91: inches
equation: D = 16 * (Q * n * s^0.5)^(3/8)
# of 4"diam. # of 6" diam. calculations assume n=0.011
Underdrains Underdrains
7 3
Note: A minimum of 2 underdrains recommended
Equivalent Pipe Diameters
D= (in) No. of 4" diam
5.13 2
5.95 3
6.66 4
7.22 5
7.75 6
8.2 7
D= (in) No of 6" diam
7.84 2
9.11 3
10.13 4

Bioretention Sizing (#2 Basin #4)
Watershed Size
1.2 acres
Percent Connected Impervious
37.8'
Water Quality Storm
1 in
For Disconnected/Composite Area
Soil Type CN
0; A 49
1 B 69
0 C 79
0 D 84
69 Selected Curve Number
note: Select Soil Group with "1"
First Flush Runoff
0.36 ac-in equation: based off SCS CN Method. No Composite CN
Average Depth
_9 in
Surface Area
0.04 ac equation: Volume /Depth
1744 sf
Fill Soil Choice
Nitrogen Removal -Sandy Loam
K=1 in/hr Soil Type: 12% Fines (Silt+Clay), 82-85% Sand, 3-6% Organic
Other Pollutant Removal -Loamy Sand
K= 2 in/hr Soil Type: 8% Fines (Silt+Clay), 86-90% Sand, 2-4% Organic
K= ' - 2 in/hr
Underdrains
Minimum Flow
equation: Q = 2.3E-5 " K * A
Q.08 cfs
Factor of Safety (range between 2 and 10)
4
Design Flow
Note to User:
Yellow Cells Require User Input
Blue Gells Have Been Previously Determined
Pink Cells are Calculations within this Spreadsheet
Breakdown of Runoff
Connected Imperv RO 0.79 in 0.36 ac-in
Composite RO (the rest) 0.00 in 0.00 ac-in

0.32 cfs
Manning's Roughness Coefficient
0.011 smooth wall
0.015 corrugated wall
0.011', n
Internal Slope (recommended minimum 0.5%)
0.5
Pipe(s) Diameter(s)
5.2fl inches
equation: D = 16 " (Q " n ' s^0.5)^(3/8)
# of 4" diam. # of 6" diam. calculations assume n=0.011
Underdrains Underdrains
3 2
Note: A minimum of 2 underdrains recommended
Equivalent Pipe Diameters
D= (in) No. of 4"diam D= (in) No of 6" diam
5.13 2 7.84 2
5.95 3 9.11 3
6.66 4 10.13 4
7.22 5
7.75 6
8.2 7

wetpond.xls
PERMANENT WET DETENTION POND DESIGN
-;
i

PROJECT: ! School G INDEX NO:
CHECKED BY: etm
LOCATION: DATE:
REVISED: 11-15-06 JNG

SITE DATA
TOTAL SITE AREA = 5.32 acres WATERSHED =
PROPOSED BUILT UPON AREA = 4.08 acres CLASSIFICATION : WS -
FUTURE BUILT UPON AREA = 0.00 acres
TOTAL ON-SITE BUILT UPON AREA = 4.08 acres
PERCENT BUILT-UPON = 76.69% (GWANVCA) _
ON-SITE DRAINAGE AREA TO POND = 5.32 acres MAX. OFF-SITE B.U.% _
OFF-SITE DRAINAGE AREA TO POND = 0.00 acres
TOTAL WATERSHED AREA TO POND = 5.32 acres
DISTURBED AREA = 5.32 acres
TEM P. SED. STOR. USED (Y/N Y

DESIGN DATA
TEMPORARY SEDIMENT STORAGE 0.5 acre-inch per disturbed acre
PERMANENT SEDIMENT STORAGE 0.125 acre-in per total drainage area
PERMANENT WATER QUALITY
COMPOSITE B.U. % = 76.69 percent
_ DEPTH (minimum 3 feet) 3.0 feet
SA/DA (Figure 5.6-2) 3.2 percent
TEMPORARY WATER QUALITY 1.0 Inch rainfall to be controlled

PRINCIPAL SPILLWAY
TYPE X corrugated aluminum
reinforced concrete
DESIGN STORM 10 ,year
RAINFALL INTENSITY 5.32 inches per hour
RUNOFF COEFFICIENT 0.7

EMERGENCY SPILLWAY
TYPE X grass lined
rip-rap lined
DESIGN STORM 100 year
RAINFALL INTENSITY 8.15 inches per hour
RUNOFF COEFFICIENT 0.7

POND DATA ~
ELEV. @ BOT. OF POND = 675 i SURFACE AREA = 2518 SF
ELEV.@ BOT. OF PSS = 675 ~ SURFACE AREA = 2518 SF
ELEV. @ BOT. OF PWQ = 677 ~ SURFACE AREA = 4221 SF
ELEV. @ BOT. OF TWQ = 680 SURFACE AREA = 9697 SF
ELEV. @ TOP. OF TWQ = 681.5 SURFACE AREA = 14968 SF
EL EV_ @ EMER_
SPILLWAY = T683 _ ~____ _
_____ _
ELEV. @ TOP OF DAM
= 1685 ~
__ ___ _ _
INVERT OF BARREL = ________
909 _________ _______
~
Page 1

wetpond.xls
ELEV. @ BOT. OF POND=1675.00 SURFACE AREA =2518 Square Feet ~
ELEV. C~ BOT. OF TWQ = 680.00 SURFACE AREA = 9697 Square Feet
I I ALLOW 75% OF BASIN VOLUME TO WQ ORIFICE =1 22903 Cubic Feetl
OKI
14
ELEV. @ BOT. OF PSS =1675.00 ~ SURFACE AREA =12518 Square Feet ~
ELEV. (c~ BOT. OF PWQ = 677.00 ! SURFACE AREA = 4221 Square Feet
VOLUME PROVIDED =
741
NORMAL POOL ELEVATION = 680.00
SURFACE AREA PROVIDED = 9697 Square Feet
Rv=~ 0.740 in/ink
VOLUME REQUIRED = 14295 Cubic Feed
ELEV. @ BOT. OF TWQ = 680.00 SURFACE AREA =19697 Square Feet
ELEV. @ TOP OF TWQ = 681.50 SURFACE AREA = 14968 Square Feet
i ~
~ VOLUME PROVIDED = 18499 Cubic Feet
OK
Page 2

wetpond.xls

PRINCIPAL SPILLWAY

DESIGN STORM PEAK FLOW = 19.8 CFS
HEAD ABOVE TOP OF RISER = ; i 1.50
ELEVATION AT TOP OF RISER = ~ I 681.50

BARREL: ELEV. OF BARREL INV. = 909
TRY BARREL DIA. = 24.00 in. dia. h = -227
ORIFICE EQUATION i Q =i #NUM! #NUM!

RISER: RISER(AREA) =1.5 TIMES BARREL(AREA)
TRY RISER DIA. = 36 in. dia.
WEIR EQUATION Q =; 57.7 CFS OK

ORIFICE EQUATION Q= 41.7 CFS OK

ORIFICE CONTROLS

WATER QUALITY RELEASE HOLE

ELEV. @ BOT. OF WATER QUALITY REL EASE HOLE = 680.00
MAXIMUM RELEASE RATE = i 4 Days
MINIMUM RELEASE RATE = 6 Days
MAXIMUM HOLE SIZE = 0.014273539 1.62 in. dia.
MINIMUM HOLE SIZE = 0.009515693 1.32 in. dia.

EMERGENCY SPILLWAY

ELEV. @EMER. SPILLWAY = , 683
DESIGN STORM PEAK FLOW = 30.4 CFS
FLOW THROUGH EMER. SPILLWAY = 10.5 CFS
HEAD ABOVE TOP OF RISER = 1
BOTTOM WIDTH = 3.51

FLOTATION OF RISER

ELEV. @ TOP OF RISER = 681.50
ELEV. @ BOT. OF PSS = 675.00
H = 6.50 ft
AREA OF RISER = 7.1 SF
VOLUME OF RISER = 45.9 Cubic Feet

AREA OF BARREL = ; 3.1 SF
EXPOSED LENGTH = 10.00 ft
VOLUME OF BARREL = ' 31.4 Cubic Feet

WEIGHT OF WATER DISPLACED = 4827.37 Ib
FACTOR OF SAFETY (10%) 5310.11 Ib

VOLUME OF CONCRETE ANCHOR = , 35.4 Cubic Feet
Page 3

i

Wet Detention Pond ~
Volume Worksheet

Sediment Forebay 20% of permanent sed iment storage 1340.274 cf

EI Area Av. Area Volume Sum Volume

675 517.67
652.15 652.15
676 786.63 652.15
945.065 945.065
677 1103.5 1597.215

Sediment storage in forebay is 23.8% of perm anent sedi ment storag e

i

Overall Volume

EI Area Av. Area Volume Sum Volum e

675 2518.13
2924.995 2924.995
676 3331.86 2924.995
3776.375 3776.375
677 4220.89 6701.37
4701.495 4701.495
678 5182.1 11402.87
6245.74 6245.74
679 7309.38 17648.61 !
8503.04 8503.04
680 9696.7 26151.65
11953.05 11953.05
681 14209.4 38104.7
14947.63 14947.63
682 15685.86 53052.33
I 16452.37 16452.37
683 17218.88 69504.7'
17218.88 1 I

10 Year Storm
PROJECT__: _ School G _ JOB NUMBER: E-3698
10-Year
O 22.01 D 24 AREA 3.14 EMERGENCY S PILLWAY
TP 19.4806 BARREL INVERT UP 675 ELEVATION 683.5
dT 4 Cw 3.33 BARREL INVERT OR LENGTH 25
Ks 2392.410083 L 160 DOWNSTREAM W.L. 674 C FACTOR 3
b 1.49 36 N FACTOR 0.027
N 1 STARTING LEVEL 680 Ke 1
Cd 0.59 SPILLWAY LEVEL 681.5
SPILLWAY AREA 7.07 SPILLWAY LENGTH 9.42
1
INFLOW STORAGE STAGE HEADWATER ORIFICE WEIR HYD. GRADE TOTAL EMERGENCY
_ _ _ _ _
TIME CFS CFS FT _
FLOW FLOW FLOW FLOW FLOW SPILLWAY

0.0 0.00 0 680.00 0.00 0.00 0.00 0.00 0.00 0
1.9 0.54 63 680.09 33.53 0.00 0.00 19.99 0.00 0
2.9 1.20 133 680.14 33.72 0.00 0.00 20.08 0.00 0
3.9 2.10 256 680.22 33.97 0.00 0.00 20.21 0.00 0
4.9 3.22 444 680.32 34.30 0.00 0.00 20.37 0.00 0
5.8 4.54 709 680.44 34.68 0.00 0.00 20.56 0.00 0
6.8 6.01 1060 680.58 35.11 0.00 0.00 20.78 0.00 0
7.8 7.60 1505 680.73 35.59 0.00. 0.00 21.02 0.00 0
8.8 9.28 2047 680.90 36.11 0.00 0.00 21.28 0.00 0
9.7 11.00 2691 681.08 36.67 0.00 0.00 21.56 0.00 0
10.7 12.73 3434 681.28 37.24 0.00 0.00 21.85 0.00 0
11.7 14.40 4276 681.48 37.84 0.00 0.00 22.15 0.00 0
12.7 16.00 5211 681.69 38.45 14.54 2.57 22.46 2.57 0
13.6 17.47 6082 681.87 38.98 20.46 7.17 22.73 7.17 0
14.6 18.79 6761 682.01 39.37 23.95 11.49 22.93 11.49 0
15.6 19.91 7253 682.11 39.64 26.13 14.92 23.07 14.92 0
16.6 20.81 7597 682.18 39.83 27.53 17.44 23.16 17.44 0
17.5 21.47 7833 682.22 39.95 28.43 19.22 23.23 19.22 0
18.5 21.87 7988 682.25 40.03 29.01 20.41 23.27 20.41 0
19.5 22.01 8081 682.27 40.08 29.35 21.14 23.30 21.14 0
20.5 21.87 8124 682.28 40.10 29.50 21.47 23.31 21.47 0
21.4 21.47 8124 682.28 40.10 29.50 21.47 23.31 21.47 0
22.4 20.81 8086 682.27 40.08 29.36 21.17 23.30 21.17 0
23.4 19.91 8012 682.26 40.05 29.09 20.60 23.28 20.60 0
24.4 18.79 7906 682.24 39.99 28.71 19.78 23.25 19.78 0
25.3 17.63 7780 682.21 39.92 28.23 18.82 23.21 18.82 0
26.3 16.52 7645 682.19 39.85 27.72 17.80 23.18 17.80 0
27.3 15.48 7509 682.16 39.78 27.18 16.79 23.14 16.79 0
28.2 14.50 7376 682.13 39.71 26.64 15.81 23.10 15.81 0
29.2 13.59 7246 682.11 39.64 26.10 14.87 23.07 14.87 0
30.2 12.73 7121 682.08 39.57 25.57 13.98 23.03 13.98 0
31.2 11.93 7002 682.06 39.50 25.05 13.14 23.00 13.14 0
32.1 11.18 6887 682.04 39.44 24.53 12.35 22.97 12.35 0
33.1 10.48 6778 682.02 39.38 24.03 11.60 22.94 11.60 0
34.1 9.82 6673 681.99 39.32 23.54 10.90 22.91 10.90 0
35.1 9.20 6574 681.97 39.26 23.05 10.25 22.88 10.25 0
36.0 8.62 6479 681.96 39.21 22.58 9.63 22.85 9.63 0
Page 1

10 Year Storm

INTENSITY 5.91 SCS CURVE
NO. 81 _ ___

C" FACTOR
0.7 __
Weighted C -See
Below _
PRECIP DEPTH
3.64

----- - DRAINAGE AREA 5.32 T 19.48062221
-_-
O 22.00884

_ _ ___ S Z ___
CONTOUR CONTOUR INCR ACCUM __ _ _
__ _ ___ AREA VOLUME VOLUME STAGE In S In Z Zest
675 2518.13 0 0 0
676 3331.86 2924.995 2924.995 1 7.9810 0.0000 2.0771
677 4220.89 3776.375 6701.37 2 8.8101 0.6931 2.1759
678 5182.1 4701.495 11402.865 3 9.3416 1.0986 2.86
679 7309.38 6245.74 17648.605 4 9.7784 1.3863 3.84
680 9696.7 8503 26152 5 10.1717 1.6094 5.00

Ks 2392.410083 __
b 1.49

Area "C" C*A
4.96 0.22 1.0912

6.04
0.6
3.624 _
-
- -- -- _ 11 4.7152

Wei hted C 0.4

Page 2

100 year Storm
PR_OJECT:_ _ _School G__ _ JOB NUMBER: E-3698
100-Year
O 30.35 D 24 AREA 3.14 EMERGENCYS PILLWAY
TP 25.2045 BARREL INVERT UP 675 ELEVATION 682.5
dT 4 Cw 3.33 BARREL INVERT O R LENGTH 25
Ks 2392.41008 L 160 DOWNSTREAM W. L. 674 C FACTOR 3
b 1.49 36 N FACTOR 0.027
N 1 STARTING LEVEL 680 Ke 1
Cd 0.59 SPILLWAY LEVEL 681.5
SPILLWAY AREA 7.07 SPILLWAY LENG TH 9.42
1
INFLOW STORAGE STAGE HEADWATER ORIFICE WEIR HYD. GRADE TOTAL EMERGENCY
TIME CFS CFS FT FLOW _
FLOW FLOW FLOW FLOW SPILLWAY

0.0 0.00 0 680.00 0.00 0.00 0.00 0.00 0.00 0
2.5 0.74 112 680.13 33.67 0.00 0.00 20.05 0.00 0
3.8 1.65 237 680.21 33.94 0.00 0.00 20.19 0.00 0
5.0 2.90 457 680.33 34.32 0.00 0.00 20.38 0.00 0
6.3 4.44 793 680.48 34.79 0.00 0.00 20.62 0.00 0
7.6 6.26 1266 680.65 35.34 0.00 0.00 20.89 0.00 0
8.8 8.29 1892 680.85 35.97 0.00 0.00 21.21 0.00 0
10.1 10.49 2685 881.08 36.66 0.00 0.00 21.56 0.00 0
11.3 12.80 3653 681.33 37.40 0.00 0.00 21.93 0.00 0
12.6 15.18 4800 681.60 38.19 10.47 0.96 22.33 0.96 0
13.9 17.55 6055 681.87 38.96 20.31 7.00 22.72 7.00 0
15.1 19.86 7027 682.06 39.52 25.16 13.32 23.01 13.32 0
16.4 22.06 7689 682.19 39.88 27.88 18.13 23.19 18.13 0
17.6 24.10 8140 682.28 40.11 29.56 21.59 23.31 21.59 0
18.9 25.91 8466 682.34 40.28 30.69 24.18 23.40 23.40 0
20.2 27.45 8773 682.40 40.44 31.71 26.67 23.48 23.48 0
21.4 28.70 9167 682.47 40.63 32.98 29.94 23.58 23.58 0
22.7 29.61 9623 682.55 40.85 34.33 33.82 23.69 23.70 0
23.9 30.16 10112 682.64 41.09 35.71 38.08 23.81 23.91 0
25.2 30.35 10600 682.72 41.32 37.02 42.42 23.93 24.34 0
26.5 30.16 11040 682.80 41.52 38.14 48.41 24.03 25.03 1
27.7 29.61 11386 682.86 41.67 39.00 49.60 24.11 25.82 2
29.0 28.70 11604 882.89 41.77 39.52 51.62 24.16 26.45 2
30.2 27.45 11679 682.91 41.80 39.70 52.33 24.18 28.70 3
31.5 25.91 11619 682.90 41.78 39.56 51.77 24.16 26.50 2
32.8 24.31 11453 682.87 41.70 39.16 50.22 24.13 26.00 2
34.0 22.78 11209 682.83 41.59 38.57 47.97 24.07 25.38 1
35.3 21.34 10904 682.78 41.46 37.80 45.17 24.00 24.78 1
36.5 20.00 10542 682.71 41.29 36.87 41.90 23.91 24.28 0
37.8 18.74 10124 882.64 41.09 35.74 38.18 23.81 23.92 0
39.1 17.56 9643 682.56 40.86 34.38 33.99 23.70 23.70 0
40.3 16.46 9095 682.46 40.60 32.74 29.34 23.56 23.58 0
41.6 15.42 8480 682.34 40.29 30.74 24.29 23.40 23.40 0
42.8 14.45 7803 682.22 39.94 28.32 18.99 23.22 18.99 0
44.1 13.54 7391 682.14 39.72 26.70 15.92 23.11 15.92 0
45.4 12.69 7147 682.09 39.58 25.68 14.16 23.04 14.18 0
46.6 11.89 6975 682.05 39.49 24.93 12.95 22.99 12.95 0
47.9 11.14 6838 682.03 39.41 24.31 12.01 22.95 12.01 0
49.1 10.44 6719 682.00 39.34 23.75 11.21 22.92 11.21 0
50.4 9.78 6611 681.98 39.28 23.24 10.49 22.89 10.49 0
51.7 9.17 6511 681.96 39.23 22.74 9.84 22.86 9.84 0
52.9 8.59 6417 681.94 39.17 22.27 9.23 22.83 9.23 0
54.2 8.05 6327 681.92 39.12 21.80 8.67 22.80 8.67 0
55.4 7.54 6243 681.91 39.07 21.35 8.14 22.78 8.14 0
56.7 7.07 6162 681.89 39.02 20.91 7.64 22.76 7.64 0
58.0 6.62 6085 681.87 38.98 20.48 7.18 22.73 7.18 0
59.2 6.21 6011 681.86 38.94 20.05 6.74 22.71 8.74 0
60.5 5.82 5941 681.84 38.89 19.64 6.34 22.69 6.34 0
Page 1

100 year Storm

-- - - --- -
INTENSrfY 8.15 SCS CURVE NO. 81

_
C" FACTOR
0.7 Weighted C -See
Below
PRECIP DEPTH
5.3
DRAINAGE AR EA 5.32 T 25.2045408
_____ O 30.3506

S Z

CONTOUR__
CONTOUR
INCR
ACCUM __
__ ___
AREA VOLUME VOLUME _
STAGE In S In Z Zest
675 2518.13 0 0 0
676 3331.86 2924.995 2924.995 1 7.9810 0.0000 2.0771
677 4220.89 3776.375 6701.37 2 8.8101 0.6931 2.1759
678 5182.1 4701.495 11402.865 3 _
9.3416 1.0986 2.86
679 7309.38 6245.74 17648.605 4 _
9.7784 1.3863 3.84
680 9696.7 8503 26152 5 10.1717 1.6094 5.00

Ks 2392.410083
__ _.__ b 1.49

Area "C" C'A
4.96 0.22 1.0912
6.04 0.6 3.624

11 4.7152

Wei hted C 0.4

Page 2

r