BWD1stResponseforMoreInfoReq

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Venture IV Building
September 20, 2018
Ms. Karen Higgins, Supervisor
NCDWR, 401 & Buffer Permitting Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: Buffalo Water District
Project No. 1 — 2017-18 Hydraulic Improvements
401 and Riparian Buffer Permitting
Project ID No.: DWR #18-0901
Dear Ms, Higgins:
E N G I N E E R S
5URVEY0RS
P L A N N E R S
M&C 0358-0138(40)
On behalf of the Buffalo Water District, we are submitting the requested additional
information for the subject project (DWR Project ID No. 18-0901) for your review and
approval.
• You have proposed crossings of streams via Open -Cut Method. Please provide
details as to why each crossing could not be completed using the HDD method
or a conventional bore to avoid impacts to the stream channels.
Response: The location of the Neuse River crossing was chosen as it is parallel to
an existing water main located 20 feet to the north, consolidating temporary and
permanent impacts to the River and surrounding properties and terrain.
Construction of this pipeline through a trenchless method was investigated,
however, geotechnical analysis of soil boring data taken in this location indicated
an elevation of existing groundwater table at the same location of the proposed
water main, submerging the proposed water line in groundwater. Raising the
water main to an elevation above the groundwater table would place the main
within the riverbed. Lowering the water main to an elevation below the
groundwater table would become too costly to construct.
1 730 Varsity Drive
Based on the elevation of the groundwater, it was deemed not feasible to install
Raleigh, NC 27606 the water line through a trenchless installation. Installation via the horizontal
directional drill method is not feasible, as groundwater will either flood or
collapse the pilot hole which is created prior to drilling and pulling the new
91 9.233.8091 water main. Soils are also more prone to "frack-out" of drilling fluids, causing
risk to surface waters, wetlands, and other surrounding environmental features.
Fax 919.233,8031
www.mckimcreed.com
\ � RAL]NFOl \ cad \ 0358 \ 0138\ 90-Permit\45-DIM, DEH, DC7C, etc \ 401404 Permitting 2018.09.XX Higgins Response Letter.doc

Ms. Karen Higgins
September 20, 2018
Page 2
Installation via the conventional jack and bore method is also not feasible due to
groundwater flooding the jack and bore tunneling operation.
Groundwater flooding concerns also present a problem in other stream crossing
locations south and east of the Neuse River crossing. At smaller stream locations
where groundwater presents less of a concern, open -cut was chosen versus jack
and bore as it is a significantly more economical option where the stream
crossings are smaller in nature. Open -cut was also chosen versus HDD both for
economical reasons, as well as to avoid the need to introduce material transition
couplings between the more flexible pipe that is stalled in traditional HDD (IE:
HDPE or fusible PVC) and the more rigid ductile iron pipe. Introducing these
additional couplings typically creates future maintenance problems where pipe
material degrades over the long term.
• Please clarify if the proposed crossings will be constructed by working in the dry
for each open -cut crossing proposed.
Response: It is anticipated that the General Contractor will elect to utilize a
temporary cofferdam system, such as Portadam, to isolate a portion of the River
or stream crossing at a time allowing the River or stream to continue to flow
around the area of construction. Standard details for working in the dry at the
Neuse River and other stream crossings are shown on the Drawings, including
temporary coffer dams and/or temporary pump around systems. Ultimate
selection of damming of the River and streams, as well as specific pump sizes
and redundancy, will be at the discretion of the General Contractor as part of
their means and methods to construct the proposed design.
• Please provide an explanation of the details showing how coffer dams/pumps,
turbidity curtains, or other sediment barriers will be installed where the open -cut
method will be utilized to cross stream and/or wetland complexes and
demonstrate how the integrity of the coffer dams will preserved in high
volume/velocity streams like the Neuse River. The Division has concerns over
the effectiveness of the construction methodology proposed in high
volume/velocity streams.
Response: Details of temporary dams/pumps, curtains, and other sediment
barriers are contained in the Drawings. These details were approved by the
NCDWR for use on other projects of similar scope, where large pipelines within
similar disturbance limits were installed via the open -cut method across
wetlands and streams in Wake, Durham, Johnston Counties, as well as the Neuse
River in Johnston and Wake Counties. Devices contained in these details were
effectively installed by General Contractors on these projects.
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