20211006_DEMLR_MRO_Piedmont_Comments

Comments on Carolina Lithium Project by MRO staff.
Gaston County
36-35
1. The scale 1" = 200 feet on the plans are very difficult to see existing and proposed overland
flows. Overview sheets are needed to see the entire project, however, smaller scale plans are
needed to properly show overland flows. Provide sheets as necessary.
2. The overview sheets are showing areas to be developed, however, smaller scale plans have
not been provided for these locations (e.g. concentrate plant, solar farm, etc.).
3. Ensure plans show existing and proposed topo contours on all sheets. In addition, ensure
contours are labeled on all sheets.
4. All streams and water bodies need to be clearly shown on the plans. Adequate undisturbed
stream buffers must be provided. Provide a legend to denote stream buffer on plans. All
land disturbance and proposed measures must be relocated out of the required stream buffers.
All 401/404 impact areas and non -impact areas needs to be clearly indented on the plans.
5. Basins must be designed for the maximum drainage area throughout all phases of
construction. Provide drainage area delineation maps for pre & post construction for sizing of
basins. Emergency spillways need to be located on natural ground. The principle spillway
systems need to be located away from emergency spillways. Basins throughout entire project
need to have a specific ID number. Basins need to have skimmers for dewatering and plans
need to show skimmers in basins & construction details. Cross-section details for basins
need to show the minimum required crest width. Ensure skimmer basins have baffles.
Basins should be located within the existing natural drainage channels and/or below proposed
fill slopes. Basins should not be located on fill slopes. It is unclear why some basins have
two barrel pipes being shown. It is recommended that one large sized pipe be provided for
the barrel pipes instead of the double -barrel pipes.
6. It is recommended that the project follow the NCGO1 design guidelines. The drainage area of
proposed sediment traps has to be less than 1.0 acre. Skimmer basins are required for
drainage areas of 1.0 acre or more. All proposed sediment traps need to have a specific ID
number.
7. Provide design calculations for all proposed sediment traps and basins. Ensure stage storage
data is provided. In addition, ensure the required surface area is provided at proper
elevations.
8. Adequate diversion berms need to divert all overland flow into basins. Ensure diversion
berms have positive drainage and enter upper reaches of basin. Provide adequately sized
slope drains to convey run-off into basins.

9. The intent and purpose of the proposed "Flumes" into basins are unclear. It appears some
flumes and ditches have ninety -degree bends to divert water into basins. It is unclear how
these can properly function during field conditions. Make sure flow from the flumes can be
handled adequately by the proposed diversion ditches directing flow towards basins. Clarify
intent as necessary.
10. The proposed Sediment Basin #9 (Sheet 17 of 34) does not appear that it will function as
intended. Suggest expanding basin width as necessary to allow basin to properly function.
11. Adequate measures have not been provided below all proposed disturbed areas and/or
throughout all phases of construction. Adequate perimeter measures must be provided.
Diversion berms need to be provided along the outer perimeter of site to adequately sized
skimmer basins. Phase 1 erosion control plans need to show existing conditions with
adequate proposed measures below all disturbed areas. Phase 2 plans need to show proposed
site development improvements, including proposed topo contours, with adequate measures
located below all disturbed areas. It may be necessary to provide more phasing on such a
large site. All proposed utilities to buildings must be shown on the plans. All proposed
storm drainage systems need to be shown and identified on the plans.
12. Adequate measures must be provided throughout all phases of the proposed permanent
stream crossings (e.g. pre & post construction). In addition, all stream work must be
conducted "In the Dry." Provide adequate construction sequence and details as necessary.
Typically, adequately sized basins will be needed at all four corners of the crossing along
with diversion ditches. All stream crossings need to be labeled on the plans to show location.
Ensure to provide a specific stream crossing ID number. It is unclear how proposed arch
culvert for Stream Crossing #2 (Sheet 13 of 18) will be installed. Ensure wall foundation
locations are shown on the plans. Will the arch culvert have a bend without relocating
stream channel? Make sure the proposed stream impacts are covered in your 401/404
permits.
13. Provide sizes and pipe material for proposed culverts on the plans. Ensure all design
calculations are provided for sizing culverts. Provide legend to identify pipes. Ensure all
proposed storm drainage systems are clearly shown and identified on the plans.
14. Need to clearly identify all temporary and permanent outfalls. The outfall numbering system
should match the industrial storm water permit map.
15. Should they apply for a NCG02 Storm water permit for mining or should an individual storm
water permit be required for the chemical plant?

16. Please provide locations for the concrete washout station with measures. These should not
be located within 50 feet of any storm drain, basin, or stream.
17. Make sure the legend specified all symbols/lines shown on the plan. A legend for erosion and
sedimentation control measures and their corresponding symbols or line -types has not been
provided on the plan or not very clear.
18. Please identify measures that have already been installed, and those measures that are
proposed.
19. Please provide sequentially phased construction and provide very detailed sequencing such
that the extent and duration of the land -disturbing activity is minimized.
20. Modification of the baffle configuration is necessary to achieve the desired volume between
baffles, to allow the longest water path for settling and to allow access for maintenance.
Show the baffle placement on the plans indicative of field conditions.
21. Please specify the skimmer size, orifice diameter, and barrel diameter on the plans. Different
branded skimmers have different design and operational parameters. Please specify the
skimmer manufacturer on the plans. Please also provide manufacturer -specific calculations,
if not yet provided. Any alternate skimmer must have calculations submitted and approved
prior to installation.
22. Permanent/Temporary slope drains should be provided where temporary diversions discharge
into sediment basins or traps with a slope height greater than seven feet. Diversions should be
installed to the slope drains to prevent sheet flow over sediment basin slopes greater than 7
feet.
23. When operating a pump around system the water shall be flow in the work area must be
pumped around the work area and discharged in a stable manner downstream of the work
area. Pump must be an adequate size to accomplish the pump around.
24. Silt fencing below fill slopes should be installed a minimum of 10 feet off the proposed toe
of the slope. This will allow room for sediment storage and maintenance access, as well as
minimize the potential for damage to the silt fence during fill slope construction.
25. A construction entrance should be provided on the plans where construction traffic will
access a paved surface. For the construction entrance, provide turning radius sufficient to
accommodate large trucks. A minimum length of 100' must be provided for the construction
entrance/exit.
26. Rip rap aprons should not be placed on the fill material. It should be extended far enough to
reach a stable section of the channel. Ensure that the apron has zero grade
27. Provide E&SC measures for the solar farm or label as future development, no land
disturbance for this phase.

28. Significant plans revisions will be necessary before this plan can be recommended for permit
issuance.