BWD2ndResponseforMoreInfoReq

46 �MCKIM&CREED ENGINEERS
SURVEYORS
P L A N N E R S
October 12, 2018 M&C 0358-0138(40)
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:
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 based on receipt of your October 1, 2018 letter.
On September 10, 2018, the Division requested more information regarding the
details of the coffer dams, turbidity curtains and/or sediment barriers to be used
in the construction sequence of the stream crossings. The Division needs to
ensure the project will be constructed in the dry and the proposed structures will
not fail when pressurized by the high velocity / volume of rivers like the Neuse.
In your response, you stated:
It is anticipated that the General Contractor will elect to utilize a temporary coffer dam
system, such as Portadam... and 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.
Venture IV Building The Division needs specific design criteria and certainty about construction
methodology to fully evaluate potential impacts on water resources. Please
1 7 3 0 Varsity Drive provide specific construction design and sequence information.
R o I e i g h, NC 27606 Response: The project specifications direct the Contractor to work in the dry and
monitor surrounding and upstream weather conditions for potential heavy
precipitation events. Should the weather forecast predict that heavy rain events
919.233.8091 at or greater than a 50-year storm have the potential to impact the construction
work proposed within the Neuse River, the Contractor will be responsible for
Fox 91 9.233.803 1 backfilling all trenching operations and removing all materials and equipment,
www,mckimcreed.com
S:\0358\0338\40LPermit\45-DEM, DEH, DOT, etc\901404 Pernvtting\2018.10.12 Higgins Response Letter.doc

Ms. Karen Higgins
October 12, 2018
Page 2
including the cofferdam system, within 24 hours prior to the rain event.
Contractor abandonment will be confined to areas within the Neuse River's
Riparian Buffer.
In addition, prior to installation of the proposed cofferdam and pump -around
system, the Contractor will be responsible for submitting their proposed system
for review and acceptance by the Engineer. No installation shall occur until after
a thorough review has occurred, and acceptance of the cofferdam system has
been issued. The specific cofferdam design is proprietary in nature, the
Contractor will be responsible for providing a system that is designed to
accommodate all site conditions.
The construction drawings detailing the Stream crossing layout (EC-12) show
spoil piles on either side of the stream. How will the spoil be dewatered? Will
any of the spoil be placed back into the stream (bed/bank, etc)?
Response: The spoil piles will be encompassed by silt fence with silt fence relief
outlets installed at the low point(s) to allow accumulated water to be filtered and
discharged down gradient. Native materials will be used as trench backfill for
the river banks, less the top 30" of fill which will consist of class 2 riprap as
indicated on the Drawings. Trench backfill for the pipe installed below the river
bed will consist of washed stone and 30" of Class 2 riprap, except native riverbed
materials will be utilized as the top 24" to 36" of fill in river, as indicated on the
Drawings. All excess spoils will be removed from the site by the Contractor.
If you have any questions, please feel free to contact me at [phone] or by email at
[e-mail].
Sincerely,
McKIM & CREED, Inc.
Adam Paukovich, PE
Project Manager
cc: Rick Hester, PE, Wilson's Mills Water District
Chandra Farmer, PE, Wilson's Mills Water District
Jason Steele, EEE Consulting, Inc
McKIM&CREED

Ms. Karen Higgins
September 20, 2018
Page 3
Ultimately, 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
stream and Neuse River crossings are shown on the Drawings, including
temporary coffer dams and/or temporary pump around systems. Temporary silt
bag details are shown on the Drawings; however, sediment barriers will be at the
discretion of the General Contractor as part of their means and methods to
construct the proposed design.
Construction documents will provide for open -cut of the Neuse River starting on
or about December 1, the driest month of the year. Based on the Geotechnical
data acquired, it is estimated that the River crossing will take 6 to 8 weeks from
top -of -bank to top -of -bank. Approximately half of the River would be
temporarily dammed for 3 to 4 weeks to allow for excavation and pipe
installation; then the other half of the River would be dammed for an additional
3 to 4 weeks to complete this crossing.
• Please provide construction drawings, including construction sequencing for the
Neuse River crossing.
Response: Construction drawings of the Neuse River crossing, including
construction sequencing, are attached.
If you have any questions, please feel free to contact me at [phone] or by email at
,[e-mail].
Sincerely,
McKIM & CREED, Inc.
Adam Paukovich, PE
Project Manager
Enclosures
cc: Rick Hester, PE, Wilson's Mills Water District
Chandra Farmer, PE, Wilson's Mills Water District
Jason Steele, EEE Consulting, Inc
yr MCK M&CREED

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