20100425 Ver 2_More Info Received_20100903 (2)

LITTLE & LITTLE .
1 September 2010
DWQ # 10-0425, Ver. 2
Wake County
Mr. Ian McMillan ?
NC DENR DWQ ILB l? (2
Wetlands and Stormwater Branch,
401 Oversight/Express Permitting Unit ?- - S 2010
1650 Mail Service Center DEW-WATER QUALITr
Raleigh, NC 27699-1650 VA>' ANDS TW.4,WATER 0RANCH
SUBJECT: Stream Restoration Project - N4 Cluster, NCSU Centennial Campus
North Creek/Lake Raleigh/Ut to Walnut Creek (030402, 27-34-(3.5), B, NSW)
Dear Ian:
We received your request for more information dated August 30, 2010 and offer the following
responses to your questions.
1) A clay stream bed with pools and riffles will be constructed within the impervious liner and is
intended to convey and contain the water flow and act as a natural stream. The purpose of
the impervious liner in the stream bed is to serve as an extra layer of protection to keep the
stream flow at the surface and ensure that the stream channel does not cut down through
the fill to its previous level. According to our geotechnical consultant and the soils report, the
existing on-site soils that will be used for filling the stream valley are not of sufficient
structural quality to provide a reliable seal under the stream without the liner. Imported clay
soil will be used for the stream bed above the liner, but it is not feasible to use imported soil
for all the fill.
The liner is designed to be deep enough to hold moisture and provide sanctuary for stream
organisms during droughty periods. It will rise to the stream bed elevation at intervals under
the rock vanes, so that any subsurface water flow within the liner is forced to the surface.
The existing stream base flow appears to come almost entirely from ground water springs in
the eastern end of the site which feed the segment of stream that will remain undisturbed.
We measured 3.3 gal./min. flow where that stream segment discharges through the pipe
that will be removed. We were unable to measure flow at the other end of the stream
segment where it enters the existing pipe under Main Campus Drive, but the stream does
not appear to increase much, if at all, in volume or size from one end to the other, and we
have not observed any ground flow from the sides.
The design intent is to intercept the flow from the existing stream at the east end of the
project, providing a concrete pad and sill at this point to channel it into the new stream and
prevent it from flowing below the new stream channel.
2) The fill slopes shown in the buffer zones 1 & 2 near the northwest comer of the Hunt Parking
Deck are part of the stream restoration project, not the Hunt Parking Deck. That project is
almost complete and has been constructed without grading or filling in the buffer. The
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1 September 2010
DWQ # 10-0425, Ver. 2
Wake County
Page 2
existing topography shown on the stream restoration plans represents the topography that
either exists now or will exist when the parking deck is complete.
The proposed contours are all part of the stream restoration project. The proposed fill
slopes near the northwest comer of the parking deck are for the purpose of reducing the
steepness of the existing slopes in this area for better vegetation stability, as well as to
accommodate a future greenway and minimize future disturbance to the NRB vegetation
installed with the stream restoration project.
3) The main purpose for the stream restoration project is to create a less entrenched stream
with access to a wider floodplain and more gradual slopes beyond the floodplain. The
grading and fill in Zone 1 are for the purpose of raising the stream channel to a higher
elevation in order to achieve this goal. Therefore the proposed contours in Zone 1 are
different from the existing ones. The ground and stream will be higher and flatter.
4) Attached is a detail showing the means we propose to achieve diffuse flow at the proposed
junction box pipe extension.
Please contact me if you have further questions about this project.
Since ely,
J. Mack Little, RLA, FASLA, LEED AP
LITTLE & LITTLE
Copy: Jamie Shem
Michael Harwood
Rachel Miller
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