20150539 Ver 1_Parkview (2)_20150820

PNTA Environmental Consultants
34 Castlewood Drive
Clayton, NC 27520
(919) 624 -8825
June 25, 2015 .
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NC DWQ, WBSCP Unit
1650 Mail Service Center
Raleigh; NC 27699 -1650
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Re: Revised Pre - Construction Notification Cover Letter for Parkview Subdivision
' City Road, Clayton, NC 27520
PIN #: 165912 -97 -7376
Dear Sir/Madam:
Please find attached the revised cover letter for the PCN submitted on May 22, 2015, plans, and
supporting documentation for the Parkview Subdivision, a proposed residential subdivision
located in Clayton, North Carolina. There are three impact areas — Impact Area B -1, Impact Area
B -2, and Impact Area B -3. Impact Area B -1 consists of removing an existing culvert and
installing a larger culvert required to construct a Town of Clayton standard road to serve the first
phase of the subdivision consisting of 42 single - family lots located on a 32.24 acre tract. Impact
area B -1 is proposed to have stream impacts authorized under a NWP 29 and riparian buffer
impacts. Impact Areas B -2 and B -3 are proposed to have riparian buffer impacts only.
Description of Stream Impacts (Impact Area B -1):
The existing 22 LF 18" RCP culvert is located on the south (upstream) side of a constructed farm
pond located on the eastern portion of the site. There is an additional 1 foot of stream impact
associated with fill on the inlet side of the existing culvert used as inlet protection. The total
existing stream impact is 23 LF. A dirt/gravel farm path currently crosses the stream at this
location. The proposed improvements include replacing the existing culvert with a longer and
larger RCP pipe that will be sized to adequately convey at minimum the 25 -year, 24 -hour storm
event as required by the Town of Clayton's roadway. design construction standards. The length of
the pipe will be approximately 63 linear feet with headwalls at both the inlet and outlet of the
pipe. An additional 10 feet of riprap is proposed at the outlet of the culvert to prevent scouring
for a total proposed impact of 73 linear feet. The net increase in stream impact for this crossing is
50 LF (73 LF Proposed — 23 LF Existing).
Description of Riparian Buffer Impacts:
Impact Area B -1:
There is currently 1,646 ft' of existing Zone 1 impact and 547 ft" Of Zone 2 impact associated
with the existing farm path crossing at the culvert. This summary does not include the existing
riparian buffer impacts associated with the farm path around the pond. Other than the impacts
associated with a level spreader bypass pipe (see Impact Area B -2 below) no additional riparian
buffer impacts are proposed around the pond. The proposed subdivision road will use the same
alignment as the farm path crossing, but will have a larger footprint and increased buffer impacts

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associated with the increased roadway width, sidewalk, and right -of -way. The total proposed
new buffer impacts for the roadway include 3,636 ft' in Zone 1 and 2,395 ft'- in Zone 2.
Impact Area B -2:
The riparian buffer impacts for this area are all associated with the high flow bypass pipe and
riprap dissipater pad. There are proposed 450 ft'-Zone I and 266 ft' Zone 2 impacts.
Impact Area B -3:
The riparian buffer impacts for this area are all associated with the high flow bypass channel lined
with riprap and geotextile fabric. There are proposed 546 WZone I and 285 ft'- Zone 2 impacts.
Stormwater and Diffuse Flow
The proposed development is subject to the Nutrient Sensitive Waters (NSW) stormwater
regulations administered by Johnston County. The farm pond water elevation is currently
controlled by a 34 LF 18" vitrified clay pipe (VCP) outlet. This outlet will be replaced with an
engineered riser structure so that the pond can be used to attenuate the additional runoff
associated with the proposed impervious surfaces of the subdivision. The Town of Clayton has
an intergovern mental agreement with Johnston County for stormwater review and approval for
new developments. Full construction plans, stormwater calculations, and nutrient calculations
will be sent to Johnston County concurrently with this PCN for approval. Diffuse flow of
stormwater discharges will be achieved by the use of flow splitter boxes, pre- formed scour holes,
and level spreaders.
Impact Area B -2 will have a double splitter box which divides the expected flow generated from
the 1" per hour storm event into two equal flows of approximately I CFS each. Each of the low
flow outlets will be piped using 6" CPP to proposed pre - formed scour holes. All flows higher
than the I" per hour storm will flow through a 24" high flow bypass RCP. The high flow bypass
pipe will discharge via a flared end section into a dissipater pad prior to flowing into the existing
pond.
Impact Area B -3 will meet the diffuse flow requirement by the use of a splitter box manhole and
a standard 40 ft. long level spreader used to treat 0.77 CFS expected from the I" per hour storm
event. Higher flows will be directed into a 24" RCP that outlets into a riprap w/ geotextile fabric
lined channel that will discharge into Sam's Branch.
If any additional information is needed, please advise.
Sincerely,
Jamie Guerrero, PE, CPSWQ
PNTA Environmental Consultants