MRO Comments for Piedmont Lithium 20240131

MRO Comments for Piedmont Lithium Response to ADI#3
The Mooresville Regional Office has the following comments concerning the Erosion and
Sediment Control portion of the referenced application:
1) Sheet OOG-005: The NCGO10000 references omit one of the zeros to the right of the"1". This
comment is provided so that the reference can be corrected to avoid confusion in the future.
2) Sheet OOG-005: ST228 is undersized. It appears to have been designed using 325 square
feet/cfs rather than 435 square feet/cfs. This sediment trap should be sized as required by the
NC Erosion and Sediment Control Planning and Design Manual requirements.
3) Sheet OOG-006: The required surface area for SK33 is shown incorrectly in the table. The
correct"required surface area"should be 10,010 square feet,not 1010 square feet. This comment
is provided so that the number can be corrected to avoid confusion in the future. The basin was
sized correctly, and this error is typographic.
4) Sheet 01 CP-001:
a. The drainage area of SK248 is incorrect for the initial phase of the project. It appears that
most of the drainage area shown for SK243 will drain to SK248. This skimmer basin should
be sized for the maximum drainage area that it will see during the project.
b. Silt fence is needed along the eastern limit of disturbance north of S13201.
5) Sheet 01CP-B005: SB-205 is slightly too shallow. Sediment basins should have at least 2
feet of elevation difference between the bottom of the basin and the riser crest or weir. This
basin slightly misses this requirement.
6) Sheet 01CP-0008: SB-209 is 0.5 ft too shallow. Sediment basins should have at least 2
feet of elevation difference between the bottom of the basin and the riser crest or weir. This
basin does not meet this requirement.
7) General Comment: We cannot locate a table or drawing that directly compares the provided
surface area elevation, the emergency spillway elevation, and the top of berm, for the skimmer
basins and sediment traps. This information can be found for the Sediment Basins on the basin
details, but this information does not appear readily available for the skimmer basins and
sediment traps.
8) Question: How will the vegetated bank area beneath the arch culverts be stabilized? This should
be specified in the plan, as the vegetation beneath arch culverts typically dies due to lack of
sunlight.