Comments Addressed-Response Document- NCDEMLR 7-23-19 2019 PAS

Comments Addressed- Response Document-
7-23-19 Paul Stimpson, PE
COMMENTS FOR ALAMANCE AGGREGATES,
LLC
PLAN RECEIVED BY WSRO ON 6/7/2019
1. Sediment skimmer basins must be designed for the 25-year storm. As submitted, the
sediment skimmer basins have been designed for the 10-year storm. Please revise. All
Skimmer basins have been resized for a 25 year storm (1=8.02 in/hr)
2 Auxiliary spillways for sediment skimmer basins may not be shown within fill material for each
basin. The majority of the spillways are now in the cut areas. Skimmer 6, 7, 11, 22, and 25 all
have spillways in fill material because the skimmer outlet pipe had constraints (stream buffer,
property line, etc.) which required the bottom elevation to be raised, resulting in a basin that is
in fill.
3. Please provide match lines on sheets C301A through C301F. Match lines added to drawing.
4. Final plans submitted for review may not be stamped "Preliminary - Not for Construction". The
not for construction note has been removed.
5. A detailed construction sequence must be sown on sheet C301B for the installation of the
proposed 24' arch span culvert and the proposed retaining wall. The construction sequence
must include sediment controls for areas adjacent to the stream during the culvert
placement and retaining wall construction. Also, particular attention must be given to
maintain the stream buffers for the maximum duration possible during culvert placement.
Construction drawings must also show fill placement on either side of the stream as the road
fill retaining walls are brought to final grade. Construction sequence added along with
additional erosion control measures. Additionally, all backfill for the wall and roadway will be
clean washed stone for the entire length of walls.
6. No sediment control measures have been shown for the proposed fence clearing around
the perimeter of the property. Please provide acceptable sediment control measures for
these areas. Added silt fence on the down -slope side of security fencing
7. Please note the following comments addressing permanent ditch placement and stabilization:
a. All proposed ditches must be assigned a specific number (i.e., #1, #2, #3, etc.)
corresponding to the design calculations. In addition, a schedule must be provided on the
detail sheets of the plans showing each proposed ditch and methods for stabilization
Design calculations have been numbered; also, added ditch numbers and a stabilization
schedule to sheet C 301A and C402
The following proposed permanent ditches may not be constructed as shown with
temporary diversions shown within the ditch line: (1) FES #1 to 6+50, (2) FES #2 to 6+50,
(3)
7+00 to 14+00 (West), (4) 8+50 to 14+00 (East), (5) Access road (East side) 14+00 to
stream buffer, (6) Access road (West side) 14+00 to stream buffer, (7) Access road (East
side) 17+50 to 20+00, (8) Access road (West side) stream buffer to 20+00. Removed the
temporary diversions and relocated the skimmer basins so that the ditches flow into the
temporary skimmer basins
c. An adequate sediment control measure must be placed at the outlet of the access
road ditch (East side) stations 18+50 to stream buffer. Skimmer basin intercepts all
flow from ditch
d. An adequate sediment control measure must be placed at the outlet of the ditch from

the outlet of sediment skimmer basin #8 to the stream buffer. Note: the drainage for
this ditch is 4.86 acres, which would necessitate the use of sediment skimmer basin.
Outlet ditch will only have flow during events in which skimmer 8 utilizes the emergency
spillway.
e. An adequate sediment control measure must be placed at the outlet of the ditch from the
outlet of sediment skimmer basin #11 to the stream buffer. Note: the drainage for this
ditch is 3.S8 acres, which would necessitate the use of sediment skimmer basin. Ditch has
been removed and skimmer 11 has been shifted and upsized.
f. Adequate sediment control measures are needed at the outlets of ditches discharging
toward Clark Road. In addition, a rock check dam will need to be placed in the ditch along
Clark Road below the outlet of FES#2. Skimmers now intercept all flow from ditches. Also a
check dam was added downstream of FES 2
g. Ditches adjacent to sediment skimmer basins #4, #5, #6, and #7 are required to
discharge into the sediment skimmer basins. As shown, discharges are routed around
the basins. Relocated Skimmers to intercept all upslope ditch flows
8. No adequate sediment control measures have been shown below the fill slope north east of
proposed sediment skimmer basin #7. In addition, proposed fill in this area is shown within
the proposed temporary diversion berm, which is not acceptable. Changed grading in area,
which eliminated the need for additional sediment control measures.
9. It appears that permanent storm water control measures will be needed within the
proposed plant areas located west of the proposed pit excavation. In addition, the
temporary diversion berms that have been shown will not function properly on fill material
and cannot be properly maintained throughout the grading process. Per our phone
conversation on 7/15/19, no permanent storm water measures will be necessary as the site
will be permanently stabilized after construction activities. Sheet flow will be provided in a
stable manner through the preserved stream buffers.
10. Proposed baffles within sediment skimmer basins must be located such that runoff entering
each basin will be filtered through three baffles. Please reevaluate baffle place placement
and the temporary diversion berm configuration such that this requirement may be
properly addressed. Baffles were reevaluated and moved to ensure flow through three
baffles is possible; please see sheet C 302.
11. It appears that sediment skimmer basin #13 could be relocated further to the east (back
uphill) so that additional areas below the basin would not have to be cleared. In addition, the
temporary diversion berms leading to sediment skimmer basin #13 may not be shown
directing site runoff over constructed fill slopes. Basin 13 has been moved uphill; a
temporary slope drain with temporary diversions at the top of the slope have been added
12. Please provide reasoning to support the clearing of additional areas as noted below:
a. Areas below the proposed temporary diversions around sediment skimmer basin #23.
It is all within the mine area
b. Areas around sediment skimmer basin #25. Within the Mine area
c. Areas shown as being graded below sediment basin #1. Clearing is necessary for fence
installation, basin installation, pipe installation and spillway installation. Additional
cleared area is also needed for access and maintenance of skimmer.
d. Areas around sediment skimmer basin#2. Construction for temporary diversions,
skimmer basin, silt fence, security fence, and access for maintenance.
e. Areas around sediment skimmer basin#3. Construction for temporary diversions,
skimmer basin, silt fence, security fence, and access for maintenance.
f. Areas around sediment skimmer basin#12. Construction for temporary diversions,
skimmer basin, silt fence, security fence, and access for maintenance.

g. Areas around sediment skimmer basin#14. Construction for temporary diversions,
skimmer basin, silt fence, security fence, 8' berm and access for maintenance.
h. Areas around sediment skimmer basin #15, also ensure that discharge from FES#4
is directed into skimmer basin #15. Construction for temporary diversions,
skimmer basin, silt fence, security fence, 8' berm and access for maintenance.
Areas around sediment skimmer basin#26. Within the Mine area
j. Areas around sediment skimmer basin#27. Within the Mine area
k. Areas around sediment skimmer basin #24 (Note: clearing has been shown through
the 50' undisturbed buffer below sediment skimmer basin #24). The Owner has
changed the mining limits. Clearing will not occur within the 50' stream buffer.
13. Provide sediment control measures for the perimeter fence installation through the
50' undisturbed buffer zone shown on sheet C3O1E. Fence to clear span the
jurisdictional area.
14. On sheet C3O1E, sufficient sediment control measures must be shown on the south side of
the processing area (east of sediment skimmer basin #12). The temporary diversion berm
that has been shown will not function as intended because it will not have positive drainage
toward sediment skimmer basin #12. Also, areas have been shown graded such that they will
be directed into the 50' undisturbed buffer zone, which is not acceptable. Added an
additional skimmer basin and modified temporary diversions.
15. At numerous locations on the plan the disturbed limits have encroached into the proposed
50' buffer zone. Please amend the plans to show no encroachments into the 50' buffer zone.
Due to weight of plotted lines it appears that it crosses the into the 50' buffer. After closer
review all contours tie out just outside of 50' buffer. Additional notes on C301 have been
added to instruct contractors to stay out of 50' stream buffer
16. No sediment control measures have been provided for the "emergency access road". It
appears that this area will need to be disturbed to have proper drainage for vehicle access.
Access road will not be graded or altered other than the addition of 8" ABC stone.
17. An acceptable sediment control measure is needed below the north side of the proposed 8' tall
berm shown on sheet C3O1E. The proposed check dam is not an acceptable sediment
control measure. Existing Contours are sloping towards the stream buffer. The drainage
area is minimal; therefore, the stone outlets and sediment fence will suffice in this
particular location per our phone conversation on 7/15/19.
18. Acceptable sediment control measures must be shown below the construction of proposed
tailings pond #2. Silt fence shown below this measure is not an acceptable sediment control
measure. In addition, basin construction is encroaching into the 50' undisturbed buffer zone.
Tailing pond #2 has been relocated and re -graded
19. Additional silt fence outlets must be shown below the 8' proposed berm on sheet C3O1C.
added additional stone outlets
20. A number of the temporary berms shown on the plan do not appear to be "temporary"
structures. Any "temporary" diversion berms used for permanent storm water conveyance
must be accompanied by design calculations and construction details. All diversions shown
on the plan are temporary. Once construction activities are complete the berms are to be
removed and the site stabilized to ensure sheet flow across site into stream buffers
21. Provide elevations for the temporary diversion berm upstream of FES#9 to show that the
diversion will actually direct runoff into skimmer basin #8 and not through the pipe inlet at
FES#9. Should this not be the case, calculations for skimmer basin #22 will need to be revised
for the additional drainage area. Skimmer #22 was upsized to accommodate the additional
drainage area

22. No sediment control measures have been shown west of the temporary diversion directing
runoff into skimmer basin #10. Only a perimeter security fence has been shown below the
basin. Added additional silt fence. We appreciate your assistance to date with this project.
If any additional items, beyond these comments are noted, hopefully, we can obtain an
approval with modifications. Respectfully submitted and Thank you, Paul Stimpson, PE