20180134 Ver 2_Lake Tahoma IP DEQ additional information 6.8.2023_20230608

CLearWaLer
An EnviroScience Company g
ClearWater Environmental Consultants, Inc.
www.cwenv.com
June 8, 2023
Ms. Sue Homewood
NC Division of Water Resources
401 & Buffer Permitting Branch
1611 Mail Service Center
Raleigh, North Carolina, 27699-1611
Sue.Homewood(a)-ncdenr.gov
RE: Response to DEQ Comments
Lake Tahoma Dredge Project Individual Permit Application
McDowell County, North Carolina
SAW-1997-02095
Dear Ms. Homewood,
Regarding Lake Tahoma, Inc.'s Individual Permit application for the Lake Tahoma Dredge Project,
ClearWater, an EnviroScience Company (ClearWater) provides the following information in response
to DWR's request letter dated May 12, 2023.
DWR 1. The application states that the justification for the dredging material to be placed in treatment
cells in Orchard Meadow is that the hydraulic dredging method requires adjacent disposal. It is unclear
if the dredge material from the mechanical dredging to occur behind the cofferdams within Buck Creek
and Little Buck Creek is also proposed to be disposed in the Orchard Meadow Treatment Cells.
Further avoidance and minimization of secondary impacts to Orchard Creek and Lake Tahoma are
possible by minimizing the use of the treatment cells in Orchard Meadow and continuing to use prior
disposal areas for areas that are mechanically dredged.
Response:
The disposal area for the Buck Creek cofferdam, Miller Farm, is only a temporary site where
material is temporarily stored for processing and sale to the public. Miller Farm was used for
disposal because the field adjacent to Buck Creek is too small for long term storage. This site
is also approximately two miles south, which increases the overall cost of the project for trucks
traveling back and forth.
The disposal area for the Little Buck Creek cofferdam was permitted for 3,000 yds3 (SAW-
1997-02095). Continued mechanical dredging from behind the cofferdam will use this site for
disposal until full. This is a small area and it is expected that 3,000 to 5,000 additional yds3
could be stored there in the future; this small storage area does not have enough volume to
reduce the size and need for storage at the Orchard Meadows site.
DWR 2. The project application states "At the mouth of Orchard Creek with Lake Tahoma, a Type 3,
double floating silt curtain turbidity barrier will be placed approximately 80 feet into the lake to prevent
any silt created by dredging discharge or construction operations from flushing into the lake
(Attachment A). The curtain will be elevated above the lake bottom more than two feet." It appears
you expect elevated turbidity within Orchard Creek as a result of dewatering discharge and are
proposing to use Orchard Creek(WS-11,B;HQW) as a treatment zone for the dredge slurry discharge.

The dredge slurry must be adequately treated prior to discharge into Orchard Creek to ensure that all
water quality standards for WS-11; 8; HQW are met at the discharge point. Please provide a proposed
dewatering plan and/or return water treatment plan that will not cause a violation of the water quality
standard for turbidity in Orchard Creek, which is 50 NTU in accordance with 15A NCAC 028.0211(21).
Response:
The applicant doesn't expect to use Orchard Creek as a treatment zone, the floating silt curtain
is just an added precaution. The applicant is using the two-chamber sediment basin as required
by DWR under NWP 16, which we expect would be the appropriate NWP if this was not an
Individual Permit application due to previous permits. The applicant is willing to remove the silt
curtain if DWR prefers.
No turbidity issues are expected from dredging activities and disposal in the storage cells. The
cells will have protective measures that include phase separation dikes, riser outlets
surrounded by rock filter, rock protected culvert outlets that dissipate discharge, and a 25-foot
stream buffer.
The dewatering plan would be as follows:
• For cells 1 to 6, dredged material would be pumped into each cell up to a 2-foot
freeboard from the cell's containment crest. For cells 7 and 8, dredged material would
be pumped to the height of the phase separation dike (10 feet).
• Cell performance would be monitored during dredging disposal and the discharge
moved as needed to manage spoils accumulation.
• For cells 7 and 8, the phase separator dike would be raised in 10-foot increments to
accommodate new material.
• Once a cell is full, the hydro-dredge pipe would be moved to discharge material into a
new cell.
• Dredge material would be allowed to dry through ground infiltration, evaporation, and
flow-through.
• Once a cell is full and dry, the remaining freeboard would be filled in with dry sediment
from adjacent cells, the top of the containment cell would be graded to achieve positive
drainage, and the cell vegetated for permanent stabilization.
DWR 3. The applicant is proposing to hydraulically dredge the lake (i.e., excavate "in the wet'). The
application states that turbidity impacts are not expected to go below the dam, however, the water
quality standard for turbidity in Lake Tahoma (WS-11, 8; Tr, HQW) is 10 NTU in accordance with 15A
NCAC 02B .0211(21). The remaining area of the lake should not be used as a treatment zone for any
turbidity created during dredging activities. Please provide a hydraulic dredge plan that includes a
turbidity curtain proposed around the dredge area during all dredging operations to prevent turbidity
outside the immediate work area.
Response:
Hydraulic dredging involves the suction of silt, sediment and debris from the bottom of the lake
into the disposal tube; it should not cause movement of material away from the suction head.
Therefore, we do not expect dredging activities to exceed turbidity standards in Orchard,
Creek, Lake Tahoma, or downstream of the dam; and installing a turbidity curtain around the
lake dredge area would not be practical.
To prevent backflush of silt each time hydro-dredging activities stop, the suction head would
be lifted off the lake bottom to pump only water through the pipe and flush any remaining
material into an Orchard Meadow containment cell.

DWR 4. The application states that a temporary stream crossing is necessary to construct Cell 8 but
will be removed and reinstalled when Cell 8 is needed. Please explain why construction of Cell 8 is
necessary prior to the time it is required. Please explain how long the temporary crossing is proposed
to be in place during construction.
Response:
Cell 8 would be the last storage cell used for discharge material and will not be constructed
until needed. The construction sequence will be revised so the access road culvert and cell 8
are constructed simultaneously. The access road culvert would only be in place as long as
required to fill the cell with dredge material and complete the dewatering closure steps
described in Response #1 above.
Using a bridge instead of a culvert was not considered a viable alternative due to the bridge's
higher cost. A bridge would also be a permanent feature to the landscape whereas the culvert
would be temporary and allow the landscape and stream to recover to current conditions.
Removing cell 8 from the project design was also not considered a practical alternative. The
current Orchard Meadow discharge site design accommodates the estimated volume of lake
sediments found during the 2020 bathymetric survey as well as anticipated dredging over the
permit period.
The applicant believes the information submitted in this letter addresses the comments provided by
DWR. Should you have any further questions or comments, please contact me anytime at
[e-mail] or 828-698-9800. Thank you.
Sincerely,
Eric Romaniszyn
Senior Scientist
Copy issued:
Amanda Jones - US Army Corps of Engineers
Stephanie Goss - NC Department of Environmental Quality
Joey Winston - NC Department of Environmental Quality
Andrea Leslie - NC Wildlife Resources Commission
Paul Coughlin - President, Lake Tahoma, Inc.
Robert Cottam — Porus, LLC
Clement Riddle - ClearWater, an EnviroScience Company