SW4210901_Stormwater Narrative_20211117

Kernodle Landing Phase 2 Project Narrative
A residential site -development is proposed within the County of Alamance on Gerringer Mill Rd.
The proposed site layout is shown on the construction drawings prepared by Stoltzfus Engineering, Inc.
(SE►). The proposed major subdivision contains 40.122 acres of total area. The project is a 30-lot
residential subdivision. The project is owned and developed by Gerringer Mill Road, LLC.
An existing portion of Terry Smith Trail runs through the site. This driveway will remain
throughout construction to provide access to the property directly adjacent to the Phase 2 southern
border. The ex. gravel drive will not be removed until access has been provided through the site by
proposed Terry Smith Trail construction, as seen on the site plans. The site qualifies for low density
standards of development as detailed in the North Carolina Administrative Code.
The site contains 40.122 Ac. of drainage. Runoff from the site will drain to Haw River primarily
through a series of roadside ditches. Storm water pipes have been added where necessary to facilitate
drainage per NCDOT requirements. The project site is not located in a designated water supply
watershed.
Project Summary & Impervious Area Allocation:
Total Property Area: 40.122 AC. (1,747,714 SF)
Total Surface Water Area: 0.550 (23,958 SF)
Total Project Area: 39.572 Ac. (1,723,756 SF)
Area of Existing Built -Upon Area Prior to Phase 2 Stormwater Requirements=17,299 SF
Existing area includes gravel portion of Terry Smith trail prior to development.
15,766 SF will be replaced with pavement, 1,533 will remain as gravel.
Proposed On -site Building/Lots = 367,216 SF (Based on lot allocation, see chart)
Proposed On -site Streets=42,333 SF (Additional Impervious Area above existing)
Total New BUA = 409,549 SF
Toal BUA in Proposed Condition = 411,082 SF
Total BUA in Existing Condition = 17,299 SF
Net Increase in BUA = 393,783 SF
Total BUA % = 393,783 SF/(1,723,756 SF—17,299 SF) = 23.1%

Kernodle Landing, Phase 2
Alamance County
Impervious Area Lot Allocation
Lot Number
Lot Area (SF)
% Total Area
Allowable
BUA/Lot le
29
30,777
1.93 %
7,070
30
30,000
1.88%
7,000
31
32,737
2.05%
7,520
32
30,000
1.88%
7,000
33
36,192
2.26%
8,314
34
30,003
1.88%
7,000
35
30,000
1.88%
7,000
36
30,000
1.88%
7,000
37
31,543
1.97%
7,246
38
31,172
1.95%
7,161
39
30,817
1.93 %
7,079
40
36,928
2.31%
8,483
41
53,595
3.35%
12,312
42
349,480
21.86%
79,742
44
38,956
2.44%
8,949
45
34,091
2.13 %
7,832
46
39,245
2.46%
9,015
47
36,064
2.26%
8,285
48
34,670
2.17%
7,965
49
34,800
2.18%
7,994
50
34,800
2.18%
7,994
51
35,360
2.21%
8,123
52
31,870
1.99%
7,321
53
35,750
2.24%
8,213
54
184,977
11.57%
42,493
55
116,547
7.29%
26,773
56
58,636
3.67%
13,470
96
32,745
2.05%
7,522
97
32,885
2.06%
7,554
98
33,893
2.12%
7,786
Totals 1,598,534 100.00% 367,216
BUA = Built -Upon Area

v�JL&
NOAA Atlas 14, Volume 2, Version 3
Location name: Elon, North Carolina, USA*
"
Latitude: 36.153°, Longitude:-79.41390
Elevation: 565.53 ft**
' source: ESRI Maps
** source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. ParzOok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
/� Ac'(- Z
PF tabular
11 PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1 il
Average
recurrence interval (years)
Duration
I I
10
25
50
100
200
500
1000
4.62
5.48 6.40
6.97
7.61
7.99
8.33
8--w
8.82
8.95
5-min
4.21-5.05)
(5.02-6.01) (5.83-7.00
(6.36-7.62 }
6.90-8.30)
7.22-8.72)
(7.50-9.10)
(7.69-9.38)jl
(7.84-9.65)
1 (7.88-9.79)
3.69
4.39 5.12
5.57
6.07
6.37
6.62
6.80
6.98
7.05
10-min
3.374.04)
4.01-4.81) 11 (4.67-5.60)
1 (5.09-6.10)
1 (5.50-6.61)
5.75-6.95)
1 (5.96-7.23)
1 (6.10-7.44
(6.20-7.63
(6.21-7.71)
3.08
3.68 4.32
4.70
5.12
5.37
5.58
5.72
5.85
5.90
15-min
(2.80-3.36)
3.364.03) (3.944.72)
(4.29-5.14)
4.65-5.59)
(4.86-5.86)
(5.02-6.09)
(5.13-6.26)
1 (5.20-6.40)
1 (5.20-6.45)
30-min
1 92-i2 30)
2. 2 27 8) 2.80 3735)
(3.131 3172
3.444.14)
3.664 42)
3.854.67
(3.99 4587
4. 4 5609
4.215823)
1.31
1.59 1.97
2.22
2.53
2.74
2.94
3.12
3.34
3.49
60-min
1.20-1.44)
1.46-1.75) 1 (1.79-2.15)
(2.02-2.42)
1 (2.29-2.76)
1 (2.48-2.99)
1 (2.65-3.21)
(2.80-3.42
(2.97-3.65
(3.07-3.81)
6.774
0.938 1.17
7.33
1.54
1.69
1.84
1.98
2.15
2.28
2-hr
(0.710-0.844)
(0.860-1.02) 1 (1.07-1.27)
1 (1.21-1.45)
1 (1.39-1.67)
1 (1.53-1.84)
1 (1.65-1.99)
1 (1.76-2.15)
1.90-2.34)
1 (1.99-2.48)
0.552
0.670 0.832
0.952
7.10
1.21
1.32
7.42
1.55
1.65
3-hr
(0.508-0.600)
0.616-0.729) (0.766-0.904)
(0.873-1.03)
L1.00-1.19)
1.10-1.31)L(l.19-1.43)jl
(1.27-1.54)
1.37-1.68)
( 1.44- 78)
0.337
0.407
0.580 7F
0.6797F0.755
0.831
0.907
1.01
1.08
6-hr
.5O6-7F
0.312-0.367)
(0.377-0.443) (0.467-0.550)
(0.534-0.629)
1(0.620-0.734
0.684-0.815)
(0.747-0.896)
0.806-0.978
0.883-1.09)
0.937-1-17)
0.200
0.241 0.301
0.348
0.413
0.464
1 F 0.517
0.572
0.648
0.7 77
12-hr
(0.184-0.218)
(0.223-0.264) (0.277-0.328)
(0.319-0.379)
(0.375-0.447)
(0.418-0.501)
(0.461-0.556)
(0.504-0.614)
(0.560-0.695
-0.759) 0.601
0.207
0.245
0.275
0.306
0.338
0.383
0.418
[24-hr]F-5-.11-9-7-6.-14-3-JF0.179
(0.110-0.128)
0.133-0.154) (0.166-0.192)
(0.192-0.222)
(0.226-0.263)
0.253-0.296)
(0.280-0.330)
(0.309-0.366)
(0.347-0.415)
(0.377-0.454)
0.069
0.083 0.103
0.118
0.138
0.154
0.171
0.187
0.210
0.228
2-day
0.065-0.074
0.078-0.089) (0.096-0.111)
1(0.110-0.127)
1(0.129-0.149)
0.143-0.166)
(0.157-0.184)
(0.172-0.203)
(0.191-0.228)
L(0.207-0.248)
0.049
0.059 7 F 0.072
0. 883
0.097 7
F-O.-I08
0.120
0.132
0.148
0.161
3-day
(0.046-0.052)
(0.055-0.063) (0.067-0.078)
(0.077-0.089)
(0.090-0.104)
1(0.100-0.117)
(0.110-0.129)
1(0.121-0.143)
(0.135-0.161)
(0.146-0.175)
0.038
F 0.046 7 F 0.057
0.065
0.077 7
F 0.085
F 0.095
0.104
0.117
0.127
4-day
(0.036-0.041)
(0.043-0.050) (0.053-0.061)I
(0.061-0.070)
1(0.071-0.082)
(0.079-0.092)
(0.087-0.102)
(0.095-0.112)
(0.106-0.127)
(0.115-0.138)
7-day (0024-0 027)1(0028-0 032) (0034-0 039 0039-0 044 0.045-0 052) (0. 50-0 058) (0.055-0 064) (0060-0 070) 0.06 -0 079) 007 -0 086
10ilay 00019-0 021) (0022-0 025) (0027---0 031)1(0030-0 035)1(0035-0.040) 0039-0 044) (0.042-0.049) (0046-0 054)1(0051---0 060 0055-0 065)
[20-dayF-0.0-13-JF0.016 0.019 0.021 0.024 0.027 0.029 0.032 0.035 0.038
0.013-0.014) (0.015-0.017) (0.018-0.020) (0.020-0.022) (0.023-0.026) (0.025-0.028) (0.027-0.031) (0.029-0.034) (0.032-0.038) (0.035-0.041)
3o-day 0.0110-0 012} (00012-0 014) (0. 01 -0 016 (0. 016-0 018 0.018-0 020) 0009-0.022) (0.0210-0 024 (0.02 -0 025 (0. 24-0 028 0.026-0 030)
45-day 0009-0 010) 000100-0011) (0.012-0 013 (0.001 -0014) LO115-0 016) 00016--0 018) (0001 -0 019) (00018-0 020 0.019-0 022 0. 20-0 023
60-day 0.008 0.010 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018
(0.008-0.009) (0.009-0.010) (0.011-0.012j (0.011-0.013) (0.013-0.014) (0.013-0.015) (0.014-0.016) (0.015-0.017)I (0.016-0.018) 0.017-0.019)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
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PF graphical