20240314_ADI_Reply

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ENGINEERING & ENVIRONMENTAL SCIENCE COMPANY
3008 ANDERSON DRIVE,SUITE 102
RALEIGH,NC 27609
[phone]
LETTER OF TRANSMITTAL
Date: March 8,2024
To: NCDEQ-DEMLR
1612 Mail Service Center
Raleigh,NC 27699-1612
From: T. Patrick Shillington,P.E.
Engineering and Environmental Science Company (E2S)
3008 Anderson Dr., Suite 102
Raleigh,NC 27609
Subject: Brickhaven Mine#2 Tract B (Mining Permit# 19-08)
Mining Permit Modification
Chatham County
Submitted are two (2) copies of the revised mine maps, specifications, and evaluation for
the above referenced project. The revisions were based on the comments from NCDEQ-
DEMLR in a letter dated September 15, 2023. The letter also included comments from
the Raleigh Regional Office.The following are responses to the review comments.
NCDEO-DEMLR Central Office
1. Please clearly identify and label on the mine map all pit boundaries and limits of
excavation. The reclamation map only shows excavated ponds on the area south of the
Progress Energy Easement.
The limits of disturbance for the life of the mine are shown on Sheet 1, 2, 3, and 6.
Anticipated ponds that will remain north of the power lines are shown on Sheet 6.
2. Please clearly identify and label on the mine map the haul road that will be utilized to
access the newly proposed mining areas north of the Progress Energy Easement.
Sheets 1, 2, and 3 show the newly proposed haul road to the mine area north of the
power line. The haul road continues from an existing haul road for the existing mine
area south of the Progress Energy Easement.
3. Please clearly identify and label on the mine map any wells located within 500' of the
mine excavation.
Water supply wells within 500 ft. of the mine excavation are shown on Sheet 1.

NCDEQ-DEMLR Raleigh Regional Office
1. There is a break in the soil berm on the northern boundary of the site west of Basin#1.
It appears that a soil berm, undisturbed buffer, or other erosion and sediment control
measures are needed in this area to address potential future development of the adjacent
tract to the north.
The berm was not added because surface water runoff is from off-site towards the
mine area. However, from the wetland moving east, the berm was extended about
200 ft.to ensure no direct off-site runoff.
2. Diversion ditches and/or berms are needed to positively direct runoff to well-defined
points of discharge to the sediment basins. Discharge into all skimmer basins should enter
before the baffle cell farthest from the skimmer outlet(inlet zone).
The diversion berms direct the stormwater to the farthest point of the basin from
the primary and secondary outlets. For Basin 2, 4, 5, 6, 7, 8, 11, and 12, berms were
added to ensure that the stormwater is appropriately directed into the basins.
3. The basin inflow must discharge into the basin in a manner to prevent erosion. It is
standard practice to provide a stable conveyance from diversions into basins (e.g., rip rap
lined channel, slope drain, tarp, etc.) This practice should be implemented and indicated
for all basins.Provide additional construction details as needed.
Where the ground is cut and sloped downward into the basin, laminated plastic
lining or an impermeable geotextile fabric will be installed (See Detail on Sheet 5).
4. The sediment basins are shown directly abutting the soil berms along the boundaries of
the site. Provide adequate space between the sediment basins and the soil berms to
prevent sloughing from berms directly into basins and for installation and maintenance
access.
This is a mine with large sediment basins. Track hoes are always available for
removing the sediment from the basins.The sediment removal is normally started at
the upstream end of the basin, and working towards the primary and secondary
outlet structures.
5. The project narrative states that lakes will be formed after mining is complete as part
of the reclamation plan. However, the area being added to the permit (north of the of the
power line easement) shows no permanent lakes/ponds on the proposed Reclamation Plan
(Sheet 6 of 6). Please include details regarding which (if any) sediment basins will be
converted to lakes/ponds at reclamation and which basins will be removed and stabilized.
Include proposed final grades for reclamation phase.
The formed lakes are shown on Sheet 6.
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6. It appears that the topographic contours on the provided mine maps are simply 2-foot
LIDAR contours rather than being representative of actual site conditions. If this is the
case, it will greatly impact sediment basin and other aspects of design. This should be
confirmed with the designer and actual surveys conducted as needed to support design.
The 5-foot contours shown on the maps are relatively accurate for a mine site. Our
company, before the start of construction of the basins, surveys and stakes the
basins as required by General Shale.
7. Sediment basin design:
a. Delineate and label all watersheds on plan sheets consistent with nomenclature
provided in supporting calculations. Indicate flow paths upon which the travel
times are based.
The watershed/drainage area limits, as well as the flow paths for the time of
concentrations for each of the proposed basins are provided on Sheet 1.
b. The design calculations for the sediment basins appear to be based upon a 10-
year return period storm. Provide design calculations for peak discharge rate for
the 25-year storm event. Provide NOAA rainfall data for design storm events
used.
The routing of the 25-year rain event was provided in the calculations. The
basins can pass the 25 year rain event with at least 1 ft. of freeboard. The
NOAA rainfall data for the design storm was not originally provided,but has
been added to the submitted report.
c. Provide drawdown calculations supporting the figures in table (Sheet 5 of 6)
based on a 2 to 5 day detention time. Due to this mine's predominant soil types
and history of turbid discharge, it is strongly recommended that a minimum of 3
days detention time is utilized.
The draw down times, basin volumes, and skimmer flow rates are provided
in the calculations and on Sheet 5. The newly proposed basins (Basins 1
through 12) that had detention times of less than 48 hours have been revised
with smaller skimmer orifices. The draw down time ranges between 60.7 and
106.4 hours
d. Sheet flow travel time: Provide justification for using surface roughness
(Manning's n) value for fallow ground (n=0.05) which refers to agricultural land
rather n=0.011 for bare soil which better represents historical and typical mine
site conditions.
We feel the Manning's coefficient of 0.05 reflects the conditions of the
exposed surface. The surface is excavated and is rough. No smooth surfaces
are exposed,except at the haul roads.
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e. Shallow concentrated flow travel time: Based upon an independent check of the
designer's calculations,the input velocities used to calculate shallow concentrated
flow component of travel time generally appear low. The designer should provide
his design calculations and justification for each of his velocity inputs. This
component of the design is critical because it will result in under-designed
sediment basins.
The velocity factor (Kv) values used for the shallow concentrated flow
segment of the Time of Concentration calculations were taken from the
USDA Natural Resources Conservation Service (MRCS) National
Engineering Handbook (NEH-4), for a surface described as "Nearly Bare &
Untilled".
f. Proposed sediment basin risers are to be corrugated metal pipes(CMP).A detail
is needed to show how the proposed PVC inlet pipe(to which the skimmer will be
connected) is to be constructed/installed securely to the round CMP to prevent
structural issues and leakage/bypass.
Details for the skimmer connection to the CMP risers are provided on Sheet
5. A note has been added describing the required welded stub-out connection
to the riser, with a threaded coupler that can be attached to the skimmer
arm.
g. Provide anti-flotation calculations and anti-flotation block dimensions. How
will riser be secured to block?
Anti-flotation block dimensions are provided on Sheet 5. A note has been
added to embed the CMP riser pipe to the bottom of the 4'x4'xl' concrete
anti-flotation block.
h. The skimmer detail (Sheet 5 of 6) indicates only a 4-inch Faircloth skimmer.
The basin design table indicates skimmers of various sizes. Revise detail to
reconcile this issue.
Details for a 2-inch,2.5 inch,and 3-inch Faircloth skimmer have been added
to Sheet 5.
i. Add note to skimmer detail emphasizing that the appropriately-sized orifice
plate must be installed at time of construction per manufacturer/supplier guidance.
A note has been added to Sheet 5.
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8. The plan states that a 25-foot buffer will be maintained along the power easement.
Operating Condition#9 states that a 40-foot undisturbed buffer(with adjacent excavation
side slopes maintained at a minimum of#:1 slopes shall be maintained around all the
Progress Energy Powerline right-of-way. Unless this Operating Condition is to be
revised, a 40-foot buffer on each side of the Progress Energy Easement should be
provided. The note in the plan should be revised from 25-feet to meet the 40-foot
requirement, as well as a symbol included in the legend for this buffer.
The 40' undisturbed buffer in this Operating Condition refers to the power poles
located within the easement. The 40' undisturbed buffer was from the powerline
tower foundations and mining was conducted in the easement. Since the 1990's, this
practiced has stopped. A 25 ft. undisturbed buffer is provided along the easement,
and results in mine excavation being further from the powerline tower foundations.
The only disturbance within the easement will be the proposed haul road leading
from the existing mine area to the newly proposed mining area.
9. Existing haul roads are shown outside of the mining permit boundaries on the
southwestern section of the site and encroaching into wetlands and the Progress Energy
Easement. Further, there are no new haul roads shown for the project to access the
northern section of the site. Please show all haul roads that will be used to access the site
and ensure they are located within the mining permit boundary and do not encroach on
any buffered areas.
The off-site road near the southwest corner are remnants of the haul roads used
when General Shale owned the adjacent property.The portion of the road that is on
the mine property have been vegetated and are not used.
10. Show all existing/proposed culverts under proposed haul roads and include
stormwater calculations designed based on a 25-year storm event for culverts under haul
roads and construction entrances.
The haul roads are through the high points of the site and no culverts are proposed.
11. According to aerial imagery, it appears there is an access point on the northeastern
corner of the site. Please label all access points and haul roads that will be used to access
the site and designate construction entrances to prevent off-site tracking of sediments.For
the purposes of safety and access control, any points of ingress to the mine that will not
be used regularly should be provided with lockable gates or otherwise obstructed to
prevent unauthorized access.
This road is pre-existing, and will not be used by the mining operation to access the
new mine area.
12. Note the latitude and longitude of the perimeter corners of the mining site on the
plans so they can be field verified during inspections.
The latitude and longitude of the perimeter corners are provided on Sheet 1.
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13. Include a note on the plans that all affected area boundaries shall be permanently
marked at the site on 100-foot intervals unless the line of sight allows for larger spacing
intervals. Further, Operating Condition #5 will need to be updated to reflect new total
acreage.
This note has been added to Sheets 1 and 3.
14. Include a note on the plans that existing vegetated or vegetated earthen berms shall be
maintained between the mine and public thoroughfares to screen the operation from the
public.Mining Permit: Operating Condition#8.
This note has been added to Sheets 1 and 3.
15. There are two ponds/basins shown on the plans on the southwest corner of the site
that are located outside of the mining permit boundary. Clarify if these are proposed for
use as sediment or stormwater detention basins or otherwise involved in the mine
operation. Please note, all such measures must be within the mine permit boundaries.
Extend proposed permit limits or relocate measures.
These basins are no longer present and have been filled. They have been removed
from the plans and are not part of the mining operations.
16. The extents of the various undisturbed/unexcavated buffers are unclear as depicted.
Please improve map symbology and notes to clarify. Include any additional symbols for
the undisturbed/unexcavated buffer zones on the legend on the appropriate plan sheets.
The buffers have been re-labeled for clarity. For the new mining area, 25-foot
undisturbed buffers are provided along the Property Lines and the Progress Energy
Easement. 50-foot undisturbed buffers are provided along wetlands and streams.
17. Provide design calculations for planned channels and diversion ditches. Provide
identifiers on plan to corresponding calculations. Provide liners/matting to aid the
stabilization when the runoff velocity will exceed 2 ft/sec on bare earth during the 2-year
rainfall event that produces the peak runoff. The product(s) selected must have a
permissible shear stress that exceeds the shear stress of the design runoff event. If
liners/matting is to be installed, provide a plan detail, construction specifications, and
maintenance requirements.
No channels or diversion ditches are proposed.
18. Include a note on the plans that existing vegetation or vegetated earthen berms shall
be maintained between the mine and public throughfares wherever practical to screen the
operation from the public. This maintenance requirement is not included on the plans.
This note has been added to Sheets 1 and 3.
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19. The soil berm appears to vary in width along the boundary of the site. There is a soil
berm cross section detail on Sheet 4 that shows a range of dimensions of the proposed
berm. Provide notes or otherwise clearly depict the proposed width and height of each
berm section and vegetation details for stabilization after construction. Berm footprint
should be shown to scale in plan view to ensure there is sufficient room for construction
and access for mowing/maintenance.
All proposed earthen diversion berms are to be 3 ft. high, except at the basin
embankment locations. The heights of the berms at the basin embankment locations
are provided on Sheet 5. The heights of the berms at the embankments range from
5.5 to 7 ft.high.A note conveying this information is provided on Sheets 1 and 3.
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