20051920 Ver 2_Stormwater Info_20080306

Estes Deem ..
EnVirOnmental Design & Consulting
February 29, 2008
Ms. Annette M. Lucas
North Carolina Department of
Environment and Natural Resources
Division of Water Quality
2321 Crabtree Boulevard
Suite 250
Raleigh, NC 27604
Reference: DWQ EXP No. 05-1920
Marvin Ridge Middle School & High School
(New middle and High School B, Crane Rd, Waxhaw, NC)
Union County, NC
Dear Ms. Lucas,
k[9@[99WR B
MAR 6 2008
DENR . WATER QUAUTY
WETLANDS AND STORMWATER 6RANC'
Since our meeting with you on December 10, 2007, we have completed a thorough review of the
possible alternatives for meeting the water quality requirements for the three central drainage
areas at the referenced project site. These drainage areas are referred to as DA 2, DA 2a, and
DA 3 in the enclosed plans and calculations.
Our review included an extensive investigation of the site conditions, including the existing
topography, soils, utilities, current land use, buffers, boundaries & easements, construction cost
and maintenance cost. Several stormwater management alternatives were evaluated, including
bio -retention, porous pavement/ infiltration and re -engineered wet ponds.
Our analysis indicates that re-engineering the two existing ponds and creating a third wet pond
will be the most effective way to satisfy the water quality requirements for these drainage areas.
We have prepared the enclosed preliminary plans for these wet ponds for your review.
These three wet ponds were designed to meet the requirements of Chapter 10 of the NCDENR
Stormwater BMP Manual (December 2007 revisions). Each wet pond incorporates a 10 -foot
wide vegetated shelf and forebays that comprise approximately 20% of the permanent pond
volume. The details of the outlet structures have not been developed yet.
• P.O. Box 79133 Charlotte, N.C. 28271-7050 • Phone [phone] Fax [phone] •

The wet ponds for DA 2 and DA 2a have been designed for 90% TSS removal, since the site
constraints do not allow for a vegetated filter strip in these locations. The wet pond for DA 3
was designed for 85% TSS removal, and includes provisions for a 30 -foot wide vegetated filter
strip for the discharge.
Before we finalize the design and details for these three wet ponds, we ask that you review the
enclosed preliminary plans and calculations and confirm your agreement with this solution. We
will then finalize the plans and submit them formally for your approval.
Should questions arise during your review of these preliminary plans, please give me a call.
ely
Christopher J. Estes, RLA
President
Enclosures
cc: Debbie Green, Union County Public Schools
Eddie MacEldowney, Davis -Martin -Powell & Associates
P.O. Box 79133 Charlotte, N.C. 28271-7050 • Phone [phone] Fax [phone] •

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Marvin Ridge Schools
WET POND MODIFICATIONS
DRAINAGE AREA PROPERTIES
Drainage Area 2a
Gross Area: 284,204.4
Pervious-, 137,629.7
Grass 137,629.7
Impervious: 146,574.7
Drainage Area 3
6.52 acres
3.16 acres 48.4% pervious
3.36 acres 51.6% impervious
Gross Area:
29
:CM
Drainage Area 2
1,007,589.8
23.13 acres 61.4% pervious
Gross Area.
783,491.5
17.99 acres
Parking
624,856.4
14.34
Field
158,635.1
3.64
Pervious:
323,667.4
7.43 acres 41.3% pervious
Grass
165,032.3
3.79
Field
158,635.1
3.64
Impervious:
459,824.1
10.56 acres 58.7% impervious
Drainage Area 2a
Gross Area: 284,204.4
Pervious-, 137,629.7
Grass 137,629.7
Impervious: 146,574.7
Drainage Area 3
6.52 acres
3.16 acres 48.4% pervious
3.36 acres 51.6% impervious
Gross Area:
1,641,483.9
37.68 acres
Pervious:
1,007,589.8
23.13 acres 61.4% pervious
Grass
995,983.6
22.86
Gravel Drive
11,606.2
0.27
Imoervious:
633,894.1
14.55 acres 38.6% impervious
Estes Desi Inc,
Marvin Ridge - Drainage
212711008
Page 9

Marvin Ridge Schools
WET POND REQUIREMENTS
Drainage Area 2:
Permanent WQ Pool Volume
Use 574.5 Perm Pond Elev, deduct 1ft for sediment storage
Table 10-3: SADA = Ratio for 90% TSS Removal
For 58.7% Impery & Avg D = 4.16
Ratio = 0.0278
Required Surface Area: SA = DA x Ratio
783,491.5 SF x 0.0278 = 21.780.5 SF Reqd
Required WQ Volume =
SA x Avg Depth = WQ Vol: = 90,561.1 CF Reqd
Temoorary Storaae Volume
Simple Method (3.3.1) Control 1"Rainfall (Rd = 1'9
Required Volume, V = 3630 x Rd x (Rv=0.05 + 0.9x1a) x A
Impervious %: la = 58.7%
Runoff Factor. Rv = 0.5782
Required Temporary Storage Volume:
V = 37.751.4 CF Reqd
Forebay Volume
Approx 20% of WQ Vol
Approx Forebay Volume
Marvin Ridge - Requirements
= 18.112.2 CF Reqd
FTr�T.Zi:�I:i
Design: 21,977 SF Elev=573
Design:
Design
Design
Estes Design Inc.
_.. __. Camuflu y w
Env.ipmwntuf Daspn 3
91,373 CF
53,844 CF Elev =575
17,868 CF 19.6%
Page 1

Marvin Ridge Schools
WET POND REQUIREMENTS
Drainage Area 2a:
Permanent I Volume
Use 573.0 Perm Pond Elev, deduct 1ft for sediment storage
Table 10-3: SADA = Ratio for 900/6 TSS Removal
For 51.6% Impery & Avg D = 3.17
Ratio = 0.0299
Required Surface Area: SA = DA x Ratio
284,204.4 SF x 0.0299 = 8,491.2 SF Reqd
Required WQ Volume =
SA x Avg Depth = WQ Vol: = 26,879.4 CF Reqd
Temporary Storage Volume
Simple Method (3.3.1) Control 1"Rainfall (Rd = V)
Required Volume, V = 3630 x Rd x (Rv=0.05 + 0.9xla) x A
Impervious W la = 51.6%
Runoff Factor: Rv = 0.5142
Required Temporary Storage Volume:
V = 12.177.3 CF Reqd
Forebay Volume
Approx 20% of WQ Vol
Approx Forebay Volume:
Marvin Ridge - Requirements
5,375.9 CF Reqd
Estes Oesi n Inc,
227/2008
Design: 10,739 SF E/ev =573
Design: 33,995 CF
Design: 2'7,978 CF Elev=575
Design: 5,221 CF 18.3%
Page 2

Marvin Ridge Schools
WET POND REQUIREMENTS
Drainage Area 3:
Permanent WQ Pool Volume
Use 572.0 Perm Pond Elev, deduct 1 f for sediment storage
Table 10-3: SA/DA = Ratio for 85% TSS Removal
For 38.6% Impery & Avg D = 3.20
Ratio = 0.0151
Required Surface Area: SA = DA x Ratio
1,641,483.9 SF x 0.0151 = 24.765.3 SF Reqd
Required WQ Volume =
SA x Avg Depth = WQ Vol: = 79,164.8 CF Reqd
Temporary Storage Volume
Simple Method (3.3.1) Control I" Rainfall (Rd= 1'7
Required Volume, V = 3630 x Rd x (Rv=0.05 + 0.9x1a) x A
Impervious %: la - 38.6%
Runoff Factor: Rv = 0.3976
Required Temporary Storage Volume:
V = 54.381.6 CF Reqd
Forebay Volume
Approx 20% of WQ Vol
Approx Forebay Volume
Marvin Ridge - Requirements
= 15.833.0 CF Reqd
Estes Design Inc.
CmrNv+�wmWOra�nkCo+w.uWg _...;'
2127/2008
Design: 25,457 SF Elev =572
Design: 81,376 CF
Design: 62.282 CF Elev=574
Design: 15,264 CF 18.8%
Page 3

Marvin Ridge High School
WATER RETENTION POND PLANS
POND 2 - 90% TSS REMOVAL
POND 2.FOREBAY
Surf Area
Incremental
SaFt
SaFt
CUFt
562.0
835
566.0
563.0
1,254
1,045
564.0
2,189
1,722
565.0
3,621
2,905
566.0
5,014
4,318
567.0
6,562
5,788
568.0
8,296
7,429
569.0
10,209
9,253
570.0
12,458
11,334
571.0
14,752
13,605
572.0
17,216
15,984
572.5
18,488
8,926
573.0
21,977
10,116
573.5
25,632
11,902
574.0
27,151
13,196
575.0
30,341
28,746
576.0
33,442
31,892
POND 2.FOREBAY
Marvin Ridge - Pond Plans
2%27/2008
Cumulative
Surf Area
CuFt
SaFt
564.0
333
565.0
586
566.0
872
567.0
1,190
568.0
1,565
569.0
1,981
570.0
2,589
571.0
3,117
572.0
3,673
572.5
3,965
573.0
4,257
573.5
4,563
Marvin Ridge - Pond Plans
2%27/2008
Cumulative
Avg Depth Temp Storage
CuFt
Ft CuFt
< bottom of pond
< allow 1 ft for sediment
1,722
4,627
8,944
14,732
22,161
31,414
42,747
56,352
72,336
81,262
91,378
4.18 < Permanent Pond Elev
103,280
11,902
116,476
25,098
145,222
53,844 < Temporary Storage
177,114
85,736 < 1 ft Freeboard
Incremental Cumulative Avg Depth
CUR QUE1 Ft
< bottom of foriebay
460 460
729 1,189
1,031 2,220
1,378 3,597
1,773 5,370
2,285 7,655
2,853 10,508
3,395 13,903
1,910 15,813
2,056 17,868 19.6% < Permanent Pond Elev
2,205 20,073
Estes LOBI n Inc,
E���er om.pn a Co+m.uiung ..
Page 1

Marvin Ridge High School
WATER RETENTION POND PLANS
POND 2a - 90°x6 TSS REMOVAL
POND 2a. FOREBAY
Avg Depth Temp Storage
Ft CuFt
3.17
< bottom of pond
< remove 1 ft for sediment
< Permanent Pond Efev
5,962
12,764
27,976 < Temporary Storage
45,397 < 1 ft Freeboard
Surf Area
Incremental
Cumulative
SaFt
CuFt
CuFt
565.0
685
< bottom of forebay
566.0
1,176
931
634
567.0
2,081
1,629
1,629
568.0
2,957
2,519
4,148
569.0
3,970
3,464
7,611
570.0
5,122
4,546
12,157
571.0
6,411
5,767
17,924
572.0
7,837
7,124
25,048
572.5
8,607
4,111
29,158
573.0
10,739
4,836
33,995
573.5
13,109
5,962
39,957
574.0
14,098
6,802
46,758
575.0
16,326
15,212
61,970
576.0
18,517
17,422
79,392
POND 2a. FOREBAY
Avg Depth Temp Storage
Ft CuFt
3.17
< bottom of pond
< remove 1 ft for sediment
< Permanent Pond Efev
5,962
12,764
27,976 < Temporary Storage
45,397 < 1 ft Freeboard
Estes Qesi n llnc,
Marvin Ridge - Pond Plans
Page 2
Surf Area
Incremental
Cumulative Avg Depth
,SaFt
QF�
CuFtFt
568.0
514
< bottom of forebay
569.0
753
634
634
570.0
1,037
895
1,529
571.0
1,364
1,201
2,729
572.0
1,735
1,550
4,279
572.5
1,943
919
5,198
573.0
2,150
1,023
6,221 18.3% < Permanent Pond Elev
573.5
2,380
1,132
7,353
574.0
2,609
1,247
8,601
Estes Qesi n llnc,
Marvin Ridge - Pond Plans
Page 2

Marvin Ridge High School
WATER RETENTION POND PLANS
POND 3 - 85% TSS REMOVAL
POND 3.FOREBAY
Cumulative Avg Depth Temp Storage
CuFt Ft CuFt
10,945
24,335
40,314
59,082
69,575
81,376
95,120
110,345
143,658
180,791
3.20
2/27/2008
< bottom of pond
< remove 1 ft for sediment
< Permanent Pond Elev
13,744
28,969
62,282 < Temporary Storage
99,415 < 1 ft Freeboard
Surf Area
Incremental
Cumulative Avg Depth
SaFt
CuFt
566.0
6,414
567.0
567.0
9,759
8,087
568.0
12,131
10,945
569.0
14,648
13,390
570.0
17,310
15,979
571.0
20,226
18,768
571.5
21,748
10,493
572.0
25,457
11,801
572.5
29,520
13,744
573.0
31,378
15,225
574.0
35,249
33,314
575.0
39,017
37,133
POND 3.FOREBAY
Cumulative Avg Depth Temp Storage
CuFt Ft CuFt
10,945
24,335
40,314
59,082
69,575
81,376
95,120
110,345
143,658
180,791
3.20
2/27/2008
< bottom of pond
< remove 1 ft for sediment
< Permanent Pond Elev
13,744
28,969
62,282 < Temporary Storage
99,415 < 1 ft Freeboard
Estes Desion Inc,
Emaunmrtn4J 6as'gn � GxwuW+q
Marvin Ridge - Pond Plans
Page 3
Surf Area
Incremental
Cumulative Avg Depth
SgFt
,C�Ft
QuFt Ft
567.0
1,568
< bottom of pond
568.0
2,083
1,826
1,826
569.0
2,664
2,374
4,199
570.0
3,310
2,987
7,186
571.0
4,022
3,666
10,852
571.5
4,412
2,108
12,960
572.0
4,801
2,303
15,264 18.8% < Permanent Pond Elev
572.5
5,366
2,542
17,805
573.0
5,931
2,824
20,630
574.0
7,173
6,552
27,182
Estes Desion Inc,
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Marvin Ridge - Pond Plans
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