Appendix B.0_Response_DEMLR_comments

Piedmont Lithium Carolinas, Inc. I Response to Additional Information Request (dated January 14, 2022)
Appendix B: Response to Mooresville Regional Office Comments
PIEDAA'0NT
LITHIUM
Appendix B:
Mooresville
Comments
Response to
Regional Office

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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
Comments on Carolina Lithium Project by MRO Staff
January 14, 2022
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 areneeded to properly show overland flows. Provide sheets as
necessary.
Drawings have been reformatted and broken down into grids with overlapping sections to ensure
continuity of drawings. Overall large scale drawings for sitewide views provided at 1" = 600' with
detailed sections provided with scales ranging from 1" = 1 00'to 1" = 20' as needed to see the detail.
A Legend Sheet is included for ease of identification of the drawings.
2. 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.
Streams and water bodies are shown on the plans. 30 foot top of stream bank buffers are included
on drawings as represented by description in the legend. Jurisdictional waters approved to be
disturbed under the 401/404 are shown per the Legend on the applicable design sheets. Non -impact
areas are labeled on applicable design sheets as well.
3. 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.
Drawings have been included for each map section with drawings referencing pre -construction
(phase 1), during construction (phase 2), and reclamation of each section.
Each basin has been provided its own unique ID number. Skimmers have been added to basins
with their design details included on the basin detail sheets.
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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
4. It is recommended that the project follow the NCG01 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.
Drawings have been designed to follow the NCG01 design guidelines as referenced.
5. 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.
Design calculations can be found on OOG-005, OOG-006, 01 CP-A001, 01 CP-A002, 01 CP-B001,
01 CP-B002, 02CO-005-009, and sediment basin detail sheets.
6. 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.
Adequate diversion berms to divert overland flow into basins or sediment traps are included on the
design sheets. Slope drains or rip rap inlets are included to convey run-off into basins.
7. 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 behandled adequately by the proposed diversion ditches directing flow
towards basins. Clarify intent as necessary.
Flumes carrying stormwater drainage into the applicable sediment basin or outlet protection into the
basin will be constructed to ensure a non -erodible path for the stormwater is provided for entrance
to the erosion and sediment control structure. The flow paths have been designed to function during
field conditions. Slope drains or rip rap inlets are included to convey run-off into basins.
8. 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.
This basin is now shown on Sheet OOCO-E006. Sediment Basin No. 9 has been revised to better
store sediment volume throughout the structure per agency guidance.
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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
9. 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 sb 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.
Basins are designed for the maximum drainage area throughout all phases. Drainage area
delineation maps for pre- and post -construction are included with this response.
At this time, we do not have details for utility routes to buildings. Utility routings to the overall site are
shown based on our current understanding of future connection locations from the utility provider.
The erosion control plans account for disturbance caused by routing utilities to site buildings. Once
finalized any necessary modifications will be communicated accordingly to the agency.
All drainage systems are shown and identified on the plans. The provided legend can assist with
finding the system and location within the package.
10.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 comers of the
crossing along with diversion ditches. All stream crossings need to be labeled on the
plans to show Iocation.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 401/404permits.
Jurisdictional waters approved to be disturbed under the 401/404 are now labeled on the applicable
design sheets located on Sheet 02CO-001 and associated Insets. Stream buffers are shown on all
applicable design sheets and properly noted on the legend. Also, non -impact areas are clearly
labeled on the Site / Mine Map Additional information pertaining to the construction of Stream
Crossing No. 1, Stream Crossing No. 2, and the Whitesides Road Crossing can be found on Sheets
OOCO-G010, OOCO-G011, OOCO-K004, OOCO-K005, OOCO-L004, and OOCO-L005.
For the Conversion Plant, there are no 401/404 stream impacts, as noted on plan sheets 01CP-
B007, 01 CP-B008, 01 CP-B009, 01 CP-0009, 01 CP-0010, AND 01 CP-0011. Allowable buffer
impacts are shown in accordance with the most recent Gaston County UDO.
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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
11. 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.
Detailed information can be found on Sheets OOG-005 and OOG-006.
12.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.
All symbols/lines are now shown on the Legend Sheet.
13.Please identify measures that have already been installed, and those measures that
are proposed.
No measures are currently installed for the site. One existing bridge on Hephzibah Church Road will
be upgraded for heavy equipment usage. This existing bridge is labeled on the applicable
sheets. Proposed measures are located within this package.
14. Please provide sequentially phased construction and provide very detailed
sequencing such that the extent and duration of the land -disturbing activity is
minimized.
Proposed construction sequence is now included on the Sheets OOG-005 and OOG-006
15. Modification of the baffle configuration is necessary to achieve the desired volume
betweenbaffles, 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.
Baffle configuration has been designed to achieve desired volume between baffles, allow necessary
maintenance, and allow for longest water path for entering flow. Baffles are shown on the map and
on the Legend Sheet.
16.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.
Detailed information, including manufacturer specific calculations can be found on Sheets OOG-005,
OOG-006, and sediment basin detail sheets.
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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
17. 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.
Slope drains or rip rap inlets are included to convey run-off into basins and traps and shown on detail
sheets.
18. 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 workarea. Pump must be an adequate size to accomplish the pump around.
A pump around system as shown on Sheet OOG-012 will be implemented for in -stream culvert
construction. No pump around system is necessary for Stream Crossing No. 1, Stream Crossing No.
2, Stream Crossing No. 3, or Stream Crossing No. 4.
19.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 asminimize the potential for damage to the silt fence
during fill slope construction.
Silt fence will be installed a minimum of 10 feet off of the proposed toe of slope.
20.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.
All construction entrances are shown on plans and legend. Each entrance is designed with a
minimum of 100' length.
21. Significant plans revisions will be necessary before this plan can be recommended for
permit issuance.
Plans have been revised based on comments noted above.
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Piedmont Lithium Carolinas, Inc. I I Response to DEMLR Additional Information Request
Appendix B Response to DEMLR Mooresville Regional Office Comments
All drainage calculations can be found as Attachments to this document.
Attachment 1 — Concentrator Plant Drainage Calculations
Attachment 2 — Conversion Plant Drainage Calculations
Attachment 3 — Full Package of all detailed Drawings
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