20161220 Ver 2_I-5000 NCDOT Response to NCDWR and USACE Site 1 Concerns 2019-09-16 (2)_20190916

STATE OF NORTH CAROLINA
DEPARTMENT OF TRANSPORTATION
ROY COOPER JAMES H. TROGDON, III
GOVERNOR SECRETARY
September 16, 2019
U.S. Army Corps of Engineers
Asheville Regulatory Field Office
151 Patton Avenue, Room 208
Asheville, NC 28801-5006
N.C. Division of Water Quality
Mooresville Regional Office
610 East Center Ave, Suite 301
Mooresville NC 28115
ATTN: Mr. Steven Kichefski, NCDOT Regulatory Coordinator
Ms. Donna Hood, NCDWR Regulatory Coordinator
Subject: Response to Additional Information Requests for the Construction of Permit Site 1, TIP
I-5000 (Interchange Improvements at I-40 and US 321, Gaston County).
NCDOT is in receipt of requests for additional information from the US Army Corps of Engineers and NC
Division of Water Quality for the above -referenced project. This update/response is provided as a formal
response to the sediment accumulation in the culvert extensions at Permit Site 1, pursuant to the email
communication sent by Ms. Donna Hood on March 27, 2019, and Mr. Steve Kichefski dated April 1, 2019.
The questions in these emails have been copied to this document below. Multiple -part questions were
divided to ensure each question or comment is addressed.
DWR Email from Ms. Donna Hood dated March 27, 2019:
Based on some preliminary findings of on -site personnel a few months ago, there is bedrock in the
stream, the width of the stream, and it is at a higher elevation than the bottom of the culvert. 2 feet
higher. This is of great consequence because it will prevent the stream from flushing the sand that
currently fills the culvert, even when Rankin Lake Road bridge is removed. This will not meet the
CLOMAR and houses/properties upstream will be flooded. Current conditions during rain events are
already showing impacts by how much water cannot get through the culvert during storm events. The
current situation also will not meet 401 permit conditions. 6 feet of sand would have to be dug out of
the stream channel to install the benches. This is also the area of the stream that was going to show a
postconstruction uplift.
Apparently bedrock location was not investigated during the site assessment for the merger and
permitting processes. Bill, if you know of anything done and I am remembering incorrectly, please
help us out.
In-depth bedrock and stream modeling was not conducted in the design process for this project.
Subsequently, detailed bedrock and 2-D hydraulic modeling was conducted. NCDOT intends to increase the
usage of hydraulic modeling to improve the selection, sizing, and locations of hydraulic structures in the
future.
Mailing Address:
NC DEPARTMENT OF TRANSPORTATION
ENVIRONMENTAL ANALYSIS UNIT
1598 MAIL SERVICE CENTER
RALEIGH NC 27699-1598
Telephone: [phone]
Customer Service: 1-877-368-4968
Website: www.ncdot.gov
Location:
1000 BIRCH RIDGE DRIVE
RALEIGH NC 27610

There were conversations on site several months ago about this problem and it is my understanding
that the Division did not move forward with further investigations. Larry and Eric, if I am wrong
about that please advise because we are now in a bit of a time crunch to address the problem before fill
slopes encroach too much on stream access in some areas. It is also my understanding that Div. 12 has
surveyors available to help, as they did with the postconstruction site assessment of the wetland at the
Buffalo Shoals bridge.
NCDOT Hydraulics moved forward with further investigations of the modeling of this system to identify if
the current plan, and/or additional methods that could help improve the situation.
To move forward there needs to be a thorough investigation of bedrock depths down the length of the
stream channel past the Rankin Lake Road bridge. Survey information gathered by the contractor
indicates that break point in the channel, where the elevation begins to be lower than the bottom of the
culvert, is after the bridge.
This request for additional thorough investigations is underway, as exampled by the recent project update
and modeling meeting on August 22, 2019. Refining the recommendations made at the August 22, 2019
meeting to practicable, clearly defined actions, is underway.
Please be advised that bedrock depths cannot be determined by sticking a grade rod on top of the sand
in the thalweg of the stream, a probe rod must be used. Once we have more stream information, we
can move forward with how to correct the problem and modify the permit.
The above comment is noted and acknowledged. The previous response also applies to this comment: This
request for additional thorough investigations is underway, as exampled by the recent project update and
modeling meeting on August 22, 2019. Refining the recommendations made at the August 22, 2019 meeting
to practicable, clearly defined actions, is underway.
Eric or Tyler, if either of you could please share the preliminary bedrock grade information already
gathered by the contractor, it would be greatly appreciated.
Detailed bedrock information has been obtained and used in the hydraulic modeling.
I look forward to solving this problem. Bill, I am on I-485 today but will be available Thursday
afternoon if you would like to talk about this for more clarification.
USACE/Steve Kichefski questions, dated April 1, 2019:
1) What level of sediment in the culverts was submitted when obtaining the CLOMR for the National
Flood Insurance Program and do you still anticipate they are correct?
The modeling that was used for the approved MOA, NCDOT, NCFMP and Kimley-Horn agreed was the
best modeling representation at the time, was to simulate an average sediment depth through the existing
culvert barrels based on 2013 surveyed upstream and downstream levels.
This equated to levels of 3.05' in the left barrel, 2.97' in the center barrel, and 3.53' in the right barrel
(looking downstream). The original proposed conditions scenario assumed that after clean -out of material at
the culvert exit and removal of Rankin Lake Rd, the average of the upstream and downstream sediment
depths would be 3 ft, and this was represented in the model.
Updated models have been prepared to specifically account for varying sediment levels within the culvert.
1-5000 Additional Information Response 9/16/2019 Page 2 of 4

This is an improvement in representing conditions, as the previously used sediment averaging method
overestimated slopes through the culvert (0.009 ft/ft versus 0.004 ft/ft based on the existing sediment
gradient through the culvert) and shows approximately 1 ft more sediment depth within the culvert on the
upstream end and approximately 2 ft less sediment on the downstream end than was documented by 2013
survey.
Field verification of current sediment levels up and downstream of the culvert is underway and will be
compared to the 2013 survey and adjusted in the updated modeling.
NCFMP assessment of impacts for the proposed improvements was based on a comparison against current
conditions (sediment within the culvert).
Even assuming no change in sediment levels after removal of Rankin Lake Rd, the removal of the bridge
itself was shown to reduce base flood levels and therefore represent no associated increases in base flood
levels as compared to current conditions.
Accumulated sediment inside culvert structures is not a calculated factor when obtaining the CLOMR for the
National Flood Insurance Program. The sediment in the culverts pose no hazard to upstream insured
structures.
2) Are there additional obstructions between the Rankin Lake Road Bridge and Site 1 that would
prevent the sediment from flushing as proposed? Provide the contractor and any additional Div12
surveys for verification on this reach of stream.
There are no additional obstructions between the Rankin Lake Road Bridge and Site 1 that would prevent
sediment from flushing as proposed.
Were the original surveys done in a manor sufficient to determine the elevation or are additional
investigation needed in this area to ensure the stream elevations originally proposed?
The original 2013 topographic survey and the Stream Aggradation Investigation referenced above included
sufficient information. Field investigation data collected this month will be compared against this data to
detect any significant variations.
3) Do you still anticipate completion of Site 1 and Site 5 as permitted?
Yes. However, based on the additional stream modeling, efforts beyond the removal of the Rankin Lake
Road bridge may be recommend, such as the increase in height of the sills in the culvert. It is advised that
we observe the stream's response to the removal of the Rankin Lake Road bridge before seeking permit
modifications for additional activities.
If three feet of sediment are expected to remain in the culverts how will the culvert benching be
constructed at a two foot depth and how will the base flow of the stream be directed into just one pipe
instead of spread out across all three culverts?
Pursuant to the responses received at the August 22, 2019 update and modeling results meeting, NCDOT will
construct the benches regardless of the sediment levels, even though the ultimate goal will be to create a
situation where sediment will move through the culverts, so the benches will function to allow base flow to
flow through one barrel.
1-5000 Additional Information Response 9/16/2019 Page 3 of 4

4) What is the current timetable for of the completion of construction around Rankin Lake Road
Bridge, including its removal and the channel alterations in this area?
It will likely be the first quarter of 2020 before the Rankin bridge can be removed.
While surveying the 24" water line, it has been located two -feet behind the US 321 curb, but 20 feet deep.
Therefore, temporary shoring will be required to tie in the new water line, thus necessitating the need to keep
the current active water line along Rankin Road.
Do you have concerns regarding the current culvert capacity as mentioned above during this
timeframe?
There are no concerns regarding the current culvert capacity during this timeframe.
5) How deep is the utility line crossing the creek near Rankin Lake Road and will it have sufficient
cover if the channel sediment is flushed as proposed?
A survey was conducted after our August 22 meeting that identified the 24" water line to be at an elevation
of 695'. This will leave sufficient cover for the channel sediment to be flushed as proposed.
Will its elevation affect the flushing of the sediment in this area as proposed?
Modeled velocities do not appear to be significantly greater after the Rankin Lake Road bridge is removed to
flush a significant depth of sediment that would result in a situation that the utility would conflict or cause an
impediment to the stream.
Pursuant to the August 22 update and modeling results meeting, NCDOT is continuing to refine the
recommendations to determine the practicable and appropriate actions that may exist to improve the situation
at Site 1. It is anticipated that NCDOT will reconvene the Agencies to review the recommendations once
they are determined and refined.
Please feel free to contact Michael Turchy at [phone] or [e-mail] for additional
questions or concerns.
Sincerely,
4#1ke,v.t/tAxi
1/41(Pll
hlip S. Harris III, P.E., C.P.M.
Environmental Analysis Unit Head
cc:
Mr. Stephen Morgan, P.E., Hydraulics
Mr. Larry Carpenter, P.E., Division 12 Construction Engineer
Ms. Trish Beam, Division 12 Environmental Officer
1-5000 Additional Information Response 9/16/2019 Page 4 of 4