RMFDraftResponse_20190512

rrrRMF Engineering
Reliability ncy.Integnty.
May 12, 2019
Paul Wojoski
401 & Buffer Permitting Branch
Division of Water Resources
Department of Environmental Quality
RE: Request for Additional Information — Draft Responses
ECM 1A High Temperature Hot Water (HTHW) Distribution System Replacement
DWR: 19-0392
Durham County
Mr. Wojoski,
Please see below draft responses to the additional information request. A conference call is set up for
May 13, 2019 at 2PM to discuss these responses. Afterwards, RMF will adjust responses as necessary
and upload the information through the edoc/deq.nc/gov/Forms/Supplemental-Information-Form.
1. Part of the proposed High Temperature Hot Water (HTHW) Supply and Return Line is to be
constructed in an existing easement. Please show the location and width of this easement.
Do buffer impacts presently exist for the current easement and associated utilities?
���✓ RMF Draft Response: The current easement above the existing HTHW and CHW utility
.RI/ corridor is approximately 100' wide and defined by the tree line. Our understanding is that
this is not a formal documented easement, but it is a maintenance corridor that was
established when the lines were installed and has been maintained ever since that time as
part of a formal maintenance plan. The existing corridor does cross several of the streams
shown on the Durham County Soil Survey, but our understanding is that the existing corridor
existed prior to the implementation of the buffers rules, and that there is no documented
buffer impacts associated with the existing utilities.
2. Please provide plan and profile exhibits and information showing how the coffer dams and
pump around will be installed where the open -cut method will be utilized to cross streams.
RMF Response: The design intent was for the contractor to install a long enough section of
temporary stream piping/culvert for them to bypass both the utility trench and access road.
All of the stream crossings other than S-4 are intermittent and appear to only have flow
after rain events during the late summer and fall (when the project is expected to be
constructed) and it is expected that a pump around will only be required for the S-4 crossing
and stabilization. Is it acceptable to only provide the plan and profile for that pump around,
or is it desired to also show a plan and profile for the other stream crossings also in the
event that the contractor needs to install one while setting up or taking down the
temporary culvert?

rrrRMF Engineering
Reliability Efficiency, Integrity.
Sheet C-503 shows four (4) temporary stream crossings, and sheet C-502 shows one (1)
temporary crossing (reference Sheet C-507 for construction details). Please revise the four
(4) temporary crossings to show the impact as open cut utility installation with pump
around. Please update impacts tables as necessary.
RMF Response: It is desired for all of the crossings to remain temporary culverts if that is
acceptable to NCDEQ. The access road that crosses these streams will need to remain open
for the duration of the project as the contractor will need it to access the Central Utility
Plant for mechanical and controls upgrades. It is preferred to establish the temporary
culverts at the beginning of the project and stabilize the crossings instead of having four
pump around setups that must be up and running with temporary generators and
constantly maintained for several months. We believe that the temporary culverts will
reduce the risk of a pump failing in the middle of the night and runoff washing out part of a
trench or the access road. After further review, we intend to provide the below additional
information to the stream crossing detail:
• Show the utility trench crossing the temporary culvert parallel to the access
road, not just the access road.
• Add another cross section along the temporary culvert
• Specific pipe sizing for each crossing (sized for the 2-year storm)
• Requirements for installing a temporary pump around during installation and
removal of the temporary culverts
• Additional restoration details for restoring the streams back to existing
conditions after temporary culvert removal.
Please confirm if it is acceptable to keep the temporary culvert detail (revised with the
above information) for the all stream crossings except for the stream stabilization which
will require a pump around. An additional detail will be provided for the pump around
associated with S-4. After the approach for these crossings is coordinated, we will update
the impact tables as needed.
Impact S5 on the pre -construction notification (PCN) and Sheet C-509 shows proposed
stream bank stabilization.
a. Please revise your impact tables to show this work as permanent impact.
RMF Response: Impact tables will be updated to show this work as permanent impact.
b. What is the drainage area of this stream?
RMF Response: Approximately 42 acres.
c. The Division has concerns with the large quantity of rock proposed as toe protection
and concrete ballasts as footers for the log steps. Using soil geolifts with wood footers
(such as willow/dogwood) is a preferred method of toe protection. Also a design that
considers riffles with 2-3 alternating rock/log step pools (2-3 depending on
slope/drainage area) is preferable. Please contact the Division to discuss design.

rrrRMF Engineering
Reliability. Efii -ry. Integrity.
RMF Response: We are happy to adjust our stabilization detail based on your
suggestions. Could the Division provide some additional details/examples of the geolifts
with wood footers that they have used in the past with success? If possible, we would
prefer to keep all log steps because there will be quite a few trees required to be
removed where the new utility corridor turns north through the woods. The goal was tc
reuse as many of these trees on site as possible. To stabilize the headcut, we need to
drop approximately 5' across 100' of stream. We currently show ten log drops with 6"
of drop each.
5. Please revise your exhibits to show the permanent buffer impacts in one color and the
temporary buffer impacts in a different color. As presented, the boundaries of the
permanent and temporary impacts are unclear.
RMF Response: Boundaries will be updated and exhibits resubmitted.
Sincerely,
RMF Engineering, Inc.
Matthew Boatwright, PE
Project Engineer