20001432 Ver 1_Stormwater Info_20080806

Desc: US 421 -NC 87 (Sanford Bypass) from West of SR 1400 to West of US 1-15-501
Hydraulics Project Manager: W. Herbert Turner, Jr., PE Ko & Associates, PC
Galen Cail, PE NCDOT Hydraulics Unit
I 81 �W� r. Y�1560
TO i��gmen o the S' nfbe& Bypass,,, US -4 1,7,,
The "' , "t �`f a
, ject,,inVolve8:��the,,con'-stru
NC, .$7, from West,bVSR 1400 tip' of,,,:US:",l �l5-501.' Th'b",o'Vbrall:, length ,,,Qf,:, the , proj ct i
appr
_Qxirnately� 3'.76�,milb8',: The', prop,Qsed,rQadway is o 4ourAane, dividdd'frooway section, with
dc,p I , - 1, 1 � location: n:,Jn , addition, :,the ,,projeot includes � one, half-clover ,��,:r,
pressed grass -median on'�hew 0
inteTc, hango"at SR, 1400 [ US 42
The project is located in the Cape Fear River Basin in which buffer rules currently have not
been adopted. The project crosses nine jurisdiction_. ,streaMs!a nd,J,mpac ts,five,,wetland, s it
es,
bhp proposed project 'contains the, relocation and .,OxtohsiorE ,'& one existing Qrpssing of
U,nripmpd:, , Tributary , io,,Patterson ,, qrpek,,pne pw, ,crossigg of. Buffalo Creek and sevep
p
6ross,ing,q, of Unnamed Tributaries to: Buffalo, Creek. Both, Patterson and Buffalo Creeks are
direct tributaries to the Deep River.
r fi "I'll "V I i6j ` 6 bd project`
Th6re',,Iare �' ive wetlond',gitb8 theit'Will,bd'it'6066t'�e"'d'b' " h' 'prop s Wetland impacts
have been kept to a minimum by the proposed roadway alignment and footprint and by avoid
ditching through wetlands. Fill slope of 2:1 have been utilized at four of the five sites.
Pattbit6h' Creek ,and the Deep River are classified as water,sppply source, W&[V! A review of
the Environmental Assessment and Environmental Sensitivity Maps indicates that the study
area is not located within '/2 mile of the critical area of this water supply source. Based on the
Division of Environmental Management (DEM) Classifications of the impacted streams,;,11,]13ig",
Buffalo Crbbk']s listed=owl the 303'(d) list for ih4paieOd,),,stream§',,,'t The creek is impaired due jo,--,,;
biological data from urban runoff and storm sbWe-r&,I
Table I below is a listing of these streams, wetlands, and the proposed crossing structure.
The project drainage system consists of cross pipes, grated inlets with associated pipe
systems, tail ditches, and roadway and lateral stormwater ditches and grass swales.
Stormwater Management Plan
Page 1 of 5

..... . . .
Table 1: Stream Crossings and Wetland Locations
Non-jurisdictional ephemeral channel
Intermittent Stream - No Mitigation Required
UT Unnamed Tributary
R-2417AA
Stormwater Management Plan
Page 2 of 5
DEM
Site
Location
Stream Name
Classification
Drainage
Proposed Structure
No.
(Wetland)
or Wetland
Area
Rating
-L-
1
22+30126+80
(Wetland)
21
---
(LT)
-L-
UT to Patterson
42" CMP Extension
2**
33+00133+65
Creek /
WS-IV 133
73 Ac.
&
(LT/RT)
(Wetland)
54" RCP Suppl.
-L-
3
35+20/36+30
(Wetland)
26
(RT)
4
-L-52+08(LT/
Big Buffalo
C
19.4 sq.
Dual, Single-Span,
RT)
Creek
mi.
Bridges
5
-L-87+90
UT1 to Big
C
31.7 Ac.
54" RCP
(LT/RT)
Buffalo Creek
1-
-L-105+20(LT/
"QT�tq Big',
7=-" _H1
C
130 Ac.
RT)
f 3 - ff reew
101
6**
-L-120+20(LT)
UT2 to Big
C
4.3 Ac.
36" RCP for Low
Buffalo Creek
Flow Conveyance
6
-L-120+57
UT3 to Big
C
110 Ac.
8' x 6'RCBC
(LT/RT)
Buffalo Creek
-L-142+67
UT4 to Big
C
90 Ac.
R C 8 0
(LT/RT)
Buffalo Creek
-L-
8
153+50/160+00
(Wetland)
24
---
54" RCP
(RT)
-L-177+29
UT5 to Big
9
Buffalo Creek/
C / 57
330 Ac.
(2) 9'x 7'RCBC
(LT/RT)
(Wetland)
9**
-L-178+82(LT)
UT6 to ig
Buffalo CrBeek
C
37 Ac,
54" RCP
-L-
10
194+60/196+10
P-2, Pond
(LT/RT)
C
6.8 Ac.
36" RCP
10**
-L-195+65(LT)
UT7 to Big
Buffalo Creek
Non-jurisdictional ephemeral channel
Intermittent Stream - No Mitigation Required
UT Unnamed Tributary
R-2417AA
Stormwater Management Plan
Page 2 of 5

BEST MANAGEMENT PRACTICES (BMP's)
The primary goal of Best Management Practices (BMP) is to prevent degradation of the states
surface waters by the location, construction and operation of the highway system. BMP's are
activities, practices and procedures taken to prevent or reduce stormwater pollution. The
BMP's and measures that have been used on this project to reduce stormwater impacts are
grassed swales, preformed scour holes, riprap outlet protection and energy dissipaters, and
submergence of box and pipe culverts below stream beds. Discharge from highway drainage
systems has been outleted, where practical, into lateral ditches or preformed scour holes to
promote filtration of discharge prior to entering the stream. The proposed grassed ditches and
channel banks will have side slopes no steeper than 3:1. The use of riprap has been limited
to pipe outlets, channel banks, and steep ditches to reduce soil erosion. In addition, fill slopes
of 2 :1 have been used in stream and wetland areas, where practical, to minimize impacts.
The BMP's and measures that have been used on this project for the roadside drainage
are as follows:
GRASSED SWALES
Grassed swales have been utilized, where feasible, along the entire project in the median and
roadside drainage swales. Grass swale summary tables are included within Appendix A. The
grass swale summary tables indicate whether the grass swale provides treatment for the
discharge.
PREFORMED SCOUR HOLES
Preformed Scour Holes have been utilized at the following locations in an effort to diffuse the
concentrated flow from the storm drainage system into sheet flow:
Sheet
RDWY
Station
Side
Sheet
RDWY
Station
Side
6
-L-
29 +25
LT
12
-L-
126 +50
RT
6
-L-
31+50
RT
13
-L-
131+00
RT
6
-RPC-
14 +55
RT
14
-L-
152 +00
RT
7
-L-
62 +20
RT
15
-L-
156 +50
RT
10
-L-
100 +50
RT
16
-L-
177 +00
RT
11
-L-
105 +49
RT
21
-Y-
44 +50
LT
DRY DETENTION BASIN
Dry Detention Basin with 1.0 Ac -ft of treatment volume has been proposed inside Ramp B
(plan sheet 6) in an effort to provide treatment for the stormwater discharge. The basin will be
designed to capture the 1 -inch storm and allow it to drawdown over a period of 2 to 5 days.
The dry detention basin is used in conjunction with grass swales within the interchange area to
increase the treatment efficiency.
R- 2417AA
Stormwater Management Plan
Page 3 of 5

The BIVIP's and measures that have been used on this project for the jurisdictional
stream crossings are as follows:
Site 2 — UT to Patterson Creek (Sta 33+00 - 33+65 -L-)
The proposed work at this location involves the relocation of the existing channel on the
outside of Ramp B, extension of existing 42" CMP and installation of supplemental 54 :
ura "c
steel / concrete pipe. f_r,,
,,,,o,,Ah'e' re ocaff6h'--' t hainbel,design ,1s; NOT �Otiliz'6"d 00,10
..topography ,,,end .,,''-jurjqoiqt geometry is
The existing channel geomet
maintained, and permanent rock checks will be utilized to damped design flow
velocities. ,,T,,h,, 9T,buried,abelow ,, propq
eo b d, pro i I e.,
However, the culverts will be installed to match crowns at the inlet and outlet to allow for
a low flow channel through the 54" RCP. The base flow barrel will provide a continuum
of water depth and channel width. The riprap for outlet protection will be placed on
banks only and will not be placed in streambed.
Site 4 - Big Buffalo Creek (Sta 52+08 -L-)
The proposed work at this location involves the construction of -L- and dual, single-
span, bridges on new location. The bridges are also designed so that no deck drains
discharge directly into the surface waters. Roadway grass swales drain and treat runoff
on the west side of the proposed bridges prior to collection into the storm drainage
system, is discharged directly into,,Blig: Buffalo
Greek -,ihll the 'No'rthw'ost'g66di°'6�n"t,, On the east side, the' §torrn,draIn8ge in cut sections
is treated in roadway grass swales prior to collection. The storm drainage in fill sections
is collected and discharged to a lateral grass swale in the northeast quadrant.
Site 5 — UT1 to Big Buffalo Creek (Sta 87+90 -L-)
The proposed work at this location involves the placement of a 54" RCP for the
jurisdictional stream crossing. The culvert will be buried I foot below the natural
streambed. The riprap for outlet protection will be placed on banks only and will not be
placed in streambed. The crossing will accommodate the natural stream channel with
minimum disruption to the ecosystem and values unique to the floodplain
Site 6 — UT2 to Big Buffalo Creek (Sta 120+20 -L-)
The proposed work at this location involves the placement of 36" RCP for low flow
conveyance of the intermittent jurisdictional stream. The culvert will be buried 0.6 feet
below the natural streambed. The riprap for outlet protection will be placed on banks
only and will not be placed in streambed.
Site 6 — UT3 to Big Buffalo Creek (Sta 120+57 -L-)
The proposed work at this location involves the placement of a single barrel RCBC for
the jurisdictional stream crossing. The culvert will be buried I foot below the natural
streambed. The riprap for outlet protection will be placed on banks only and will not be
placed in streambed. The crossing will accommodate the natural stream channel with
minimum disruption to the ecosystem and values unique to the floodplain.
R-2417AA
Stormwater Management Plan
Page 4 of 5

Site 7 — UT4 to Big Buffalo Creek (Sta 142+67 -L-)
The proposed work at this location involves the placement of a single barrel RCBC. for
the jurisdictional stream crossing. The culvert will be buried 1 foot below the natural
streambed. The riprap for outlet protection will be placed on banks only and will not be
placed in streambed. The crossing will accommodate the natural stream channel with
minimum disruption to the ecosystem and values unique to the floodplain.
Site 9 — UT5 to Big Buffalo Creek (Sta 177+29 -L-)
The proposed work at this location involves the placement of a two barrel RCBC for the
jurisdictional stream crossing. Sill ri ""the""" Western barrel on the Up8troa end will be',
�3 eel e' barrel: ' The base flow barrel will provide a
to,, restrict the b88eJloW,Ab,the';east"rn,
continuum of water depth and channel width without substantial modifications of
velocity. The culvert will be buried 1 foot below the natural streambed. The riprap for
outlet protection will be placed on banks only and will not be placed in streambed. The
crossing will accommodate the natural stream channel with minimum disruption to the
ecosystem and values unique to the floodplain.
Site 9 — UT6 to Big Buffalo Creek (Sta 178+82 -L-)
The proposed work at this location involves the placement of a 54" RCP for the
jurisdictional stream crossing. The culvert will be buried 1 foot below the natural
streambed. The riprap for outlet protection will be placed on banks only and will not be
placed in streambed. The crossing will accommodate the natural stream channel with
minimum disruption to the ecosystem and values unique to the floodplain.
Site 10 — Pond (Sta 194+601196+10 -L-) and UT7 to Big Buffalo Creek (Sta 195+65-L-)
T ,;pro osect 'vsierk dt',thisJoqa is n s,,
involve - ,remQ
val of the the placement of
c"ulvert will be buried 0.6 feet below
36" RCP for the jurisdictional stream crossing. rh6'
rr the natural streambed. The riprap for outlet protection will be placed on banks only and
will not be placed in streambed.
R-2417AA
Stormwater Management Plan
Page 5 of 5