20230313_Erosion_Control_Evaluation_66-12

ENGINEERING & ENVIRONMENTAL SCIENCE COMPANY
3008 ANDERSON DRIVE,SUITE 102
RALEIGH,NC 27609
[phone]
January 15, 2020 RECEMED
Mr. Alton Williams,Jr.
Prize Management LLC-DBA Sand Ridge Development
P. O. Box 758 LAND QUALITY
Rich Square,NC 27869 MINING PROGRAM
RE: Sand Ridge Mine Modification
Hwy 46
Northampton Co.,NC
Permit Number 66-12
Dear Mr. Williams:
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Following is a discussion and erosion control evaluation for the mine modification at the
Sand Ridge Mine. The accompaning maps reflect this evaluation.
General Sand Ridge Mine Discussion
The Sand Ridge Mine is located on 229.95 acres of land owned by Sand Ridge
Development Association, lac. that is located about '/, mile north of Garysburg, NC in
Northampton County(Figure 1,Attachment A). Access to the site is from HWY 46.
The existing permit allows 31.5 acres disturbed with mining conducted by dredge. The
proposed modification will include 25.27 acres of disturbance (56.27 total acres of I
disturbance). The new disturbance will be at least 50 ft from jurisdictional wetlands as
delineated by Brown's Environmental Group, Inc. and approved by the U. S. Army Corp
of Engineers.
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A trackhoe will primarily be used to excavate the material at a maximum depth of 20 ft.
below ground surface. Excavation will be below the groundwater table but no
dewatering will be necessary for the excavation.
Erosion control will be provided using diversion berms and one (1) sediment basin. As
mining progresses the basin will be enlarged and likely will no longer have stormwater
discharges from the disturbed area. An existing haul road will be used to access the mine
area. No stone surfaced entrance/exit section is provided for the mine since the haul
distance between the plant and Hwy 46 is more than %2 mile. II
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Page 2
Sand Ridge Mine Modification
Upon completion of mining a pond will be formed by the mining, and the land above the
water level will be sloped to 3:1 (H:V) or flatter and will be revegetated. The existing
hall roads will remain in-place. Outside mine area, the haul roads are stable. The roads
are either flush with the adjacent ground or are elevated above the existing ground.
Erosion Control Evaluation
HydroCAD was used to evaluate the run-off volumes and peak flow rates for the 10-year
and 25-year rain events (See Attachment B). Erosion control for the proposed mining
area will consist of one (1) sediment basin with a riser/barrel system with skimmer
attached to the riser pipe. Perimeter berms will be used to divert the stormwater runoff to
the basins. A 25' wide secondary spillway is provided. The basin can pass the 25-year
rain event with one foot of freeboard.
Closure
We appreciate serving you on this project. Please contact us if you have any further
questions.
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Sincerely,
/ 1
T. Patrick Shillington,P. gigot GAR ',,.,
President
a
Attachment A: Figures
Attachment B: Calculations o
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A,f.#achment A: Figures
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Attachment B:Erosion Control Calculations
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Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?laY-36.4..
NOAA Atlas 14,Volume 2,Version 3
Location name:Garysburg,
on North Carolina,USA* �
Latitude:36evatio,Longitude:-77.6699°
Elevation:97.Nb s,
^source:115GS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M Boron,D.bbriin,S.Lin,T.Parsyfuk,MYsi and D.Rky
NOAq National WeaNer service,fiiver Spring.Maryland!
EE_labutar I PE_gtaphLcal I tdao-iLmnalti
PF tabular _
PDS-based point precipitation frequency estimates with 90% confidence intervals(in inches)1 I
Duration�- Average recurrence Interval(years)
�'�-�5 I 10 25 50 __� 100 _ _ 200___ 500 1000__I
0.397 - 0,465 0.537 0.805 0 683 0.745 0.804 0.861 0.833 0.994 l
6-min 0.350.0.453 0.409.0.527) (0.473-0.611)� 0.532-0.687: 0.696-0.77b 0.647-0.843 (0.6960.810, 0.741-0.976) 0.796-1.06 1 0.842-1,13)'
0 834 0.743 0.861 0.968 1.09 1.19 1.28 1.37 1.98 1.57
10-min i(0.559-0.724), 0.655-0.843 0.757-0.978) (0.850-1.10) 0.950-1.24) 1.03-1.34 (1.10.1.45) _(1.18-1.5 (1.20-1.68) (7.33-1.78).
CI15-min 0.792 OS34 1.09 123 1.38 1.50 1.61 1.72 1.86 1.96
(0.69".904) (0.823.1.06) O.B58-1.24) (1.08-1.39 1.2( 1-1,57) 1.31-1.70) (1.90.1.83)_ (1.48-1.05) 1.59-2.11 (1.66-223
30-min I 1.09 1.29 155 L78 2.04 2.26 2.47 2.88 2.98 3.18
(0.958-1.24)I (1.14-1.48)_ (1_38-1.76) (1.56-2.02), (1.78-2.32) (1.97-258) (2.1 1.0) i (231.3.04) 1(252-3.35). (270.3.61)
3-41
60.Min1555_ (7.436284) _(1.7b 2g25) 2:32162_� (2.83.09) (2.66a.47 f2:55.88) (3.24424� (3:2-0.81) (3.83-527�
2-hr 1 58 1.89 235 2.79 9.38 3.88 4 38 4.94 6.73
6.43
h_ �� 24� 8 .. 3� (421-5.61) I (4.648.50) (5.38-7.30).
(1.3B-7 et) _ 1.652.18) (205-288) �r �3C-
&hr 1 68 2.01 2.51 3.00 3.65 4.23 4 86 5. 22 l 6.50 7.38
(1:98-199) 1.75-2.33) (2.1222.90) I (2.59J,45) (314d.20) (3.62Ab 412-5.57) (466.6.33) (5.4&744) (6.10.8.46)
2.01 2.41 3.07 3.59 4.39 5.12 6.90 675 7.89 9.12
6-hr 1.75-232) ' 210.276E (2.61-3,44 3.12�7.11 3.80-5.01 (4.39-5.82) 5.02-6.69 570.764) (6.66.9.04) (7.61-10.3).
12-hr 2.38 2.86 3.58 4.31 b.31 6.22 7.21 832 9.97 11.5
2.10.270) (2525.24) (315-4.05 �'3.784.86).� .63-5_96) .. (5395.98) (8.19-8.08) 70( 6-931) (B_33111)) (eA6128)i
24-hr (2.3.306) 3.077.71 3.94-077) (4.6&5.68 576-7.02) 8.894321 .6e-0o54) (8.78.1.0) (10,4-I3.3 11.7-15A
11 23.20 3.87. .86. '. - 13.3 15.2
2-day 0.
93.3.53 3.54428 4.615.46) kM 647 6.52-7.96) .52-925 8.60.7) (9.7812.3
11.4-14.8 12.8-16.9
3-day 3.41 4.12 6.24 6.19 7.59 879 10.1 11.6 13.7 15.5
(3.16574) (3.604.52) (4.825.74) (5.67-8,77) 6.91-0.30) (7.94-9.61) (9.04.11.1) (10.2-12.7) , (11.&15. (13.3-17.3
_ 15.94 12.0 1413 B3 4.38
077 (518.03) 7.0) (7.3 -8.6 (836 _9) (107-13.1) (124155) (13.8-17.7).74-day I33J -0
7-day7,484 9.03 10.3 1.7 132 104 17.1
933_97) (8. 0 .12) I -9.82) 911. ( 3.6-168) (ib.0.19.0)(47 (534 0. 2) (106-12.8) (118-4.4)
10-0 14
ey4.H6 5.82 7.19 8.32 994 11.3I 2.7 164 182
4.52-525) 5A`I 30) (6.69$78) ,7 -8.99) (9.18-10. (10.3-1 ) 11_5-13. -15.5) (14.517.9 (18.0.20.0
. . . -20.4 224 162 17.9 I
d 8.60 7.87 867 170 12.8
8.9 10-7B) I .8.44) -17)J -13.9) �17 839 (78.&222) (19.91A(8.17A (11 618 9.71 . 6 13.1 15.2 16,9 18.6 20.3 22.7 24.6
30-day -Q,705.70) (SA 10.3) (10.9-124), _(123-14.0)] 14( 2-16.2) (15.7-18.0) I (17219.8) 1._(187278) _(20.7-24.5) (223-26.7)
n45-day 10.3 12.1 14.3 16.1 186 20.3 22 2 24 2 26.8 28.8
9.70-10.9) (it.5-128) 13.5-15.2 15.2-77.0 17.3-19.6) (19.0.21.8 (20723.8 (224258) (24.&28.7 (26.35 I
60-day 1-2 145 17,0 18.9 21.4 23.3 25.3 27.2 29.7 ) (2 31.7
(11.7-13.0) 13( 8-15.3) (16.1-17.8) (17.8-19.9) (20.2-228 (22.0.24.7) (23.7-26.8) (26A-28.9) (27.5J1.8 9.1-34.0),
1 Precpitation frequency(PF)estimates In this table are based on frequency analysis or partial duration series(PDS).
Numbers In parenthesis ere PF estimates at lower and upper bounds of the 90%confidence Interval.The probability that predpitation Irequan�y estimates
(for a given duration and average recurrence,Interval)will be greater than the upper bound(or less than the lower bound)is 5%.Esltmales el upper baundel
are not checked against probable mabmum precipitation(PMP)estimates and may be higher than currently valid PMP values.
Please refer to NO_AA_Atlas 14 document for more IMorrnadon
Back toT2
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3S v 3P
Watershed 3 Basin 3
Subcat Reach on Link Routing Diagram for basin
F�.00-20
{enter your company name here}, Printed 1/14120 20
s/n 07329 0 2017 HydroCAD Soltware Solutions LLC

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basin Type 1124-hr 10 yr Rainfall=5.17" j
Prepared by{enter your company name here} Printed 1/14/2020
HydroCAD®10.00-20 s/n 07329 ©2017 HydroCAD Software Solutions LLC Page 2
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Summary for Subcatchment 3S: Watershed 3
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Runoff -- 95.63 cfs @ 12.14 hrs, Volume= 7.636 af, Depth= 3.63"
Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span=0.00-120.00 hrs, dt=0.05 hrs
Type II 24-hr 10 yr Rainfall=5.17"
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Area (ac) CN Description
24.620 86 Newly graded area, HSG B j
0.650 96 Gravel road, HSG B _ f
25.270 86 Weighted Average
25.270 100.00%Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (fUsec) (cfs)
3.8 100 0.0200 0.43 Sheet Flow,Sheet Fallow n=0.050 P2=3.60" I
17.8 1,071 0.0100 1.00 Shallow Concentrated Flow, Shallow Concent.
Nearly Bare&Untilled Kv= 10.0 fps
21.7 1,171 Total
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basin Type!!24-hr 90 yr Rainfall=5.97"
Prepared by{enter your company name here) Printed 1/14/2020
HydroCAD610.00-20 s/n 07329 ©2017 HydroCAD Software Solutions LLC Page 3
Summary for Pond 3P: Basin 3
Inflow Area= 25.270 ac, 0.00% Impervious, Inflow Depth = 3.63" for 10 yr event
Inflow = 95.63 cfs @ 12.14 hrs, Volume= 7.636 of
Outflow = 10.84 cfs @ 12.94 hrs, Volume= 6.489 af, Atten=89%, Lag=47.8 min
Primary - 10.84 cfs @ 12.94 hrs, Volume= 6.489 of
Routing by Stor-Ind method,Time Span=0.00-120.00 hrs,dt=0.05 hrs
Peak Elev=96.01'@ 12.94.hrs Surf.Area=65,519 sf Storage= 190,596 cf
Plug-Flow detention time= 1,158.8 min calculated for 6.486 of(85%of inflow)
Center-of-Mass det. time= 1,092.7 min ( 1,907.3- 814.6)
Volume Invert Avail.Stora a Storage Descripton
#1 93.00' 256,000 cf Custom Stage Data(Prismatic) Listed below
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
93.00 611000 0 0
94.00 62,500 61,760 61,750
95.00 64,000 63,250 125,000
96.00 65,500 64,750 189,750
97.00 67,000 66,250 256,000
Device Routing, Invert Outlet Devices
#1 Primary 92.00' 18.0" Round 18"CMP Barrel
L=50.0' CMP, projecting, no headwall, Ke=0.900
Inlet/Outlet Invert=92.00'/91.50' S=0.0100'/' Cc=0.900
n=0.025 Corrugated metal, Flow Area= 1.77 sf
#2 Device 1 93.00' 0.230 cfs 4"Skimmer
#3 Device 1 95.00' 24.0" Horiz.24"CMP Riser C=0.600
Limited to weir flow at low heads
#4 Primary 96.00' 25'Secondary Spillway, C=3.27
Offset(feet) 0.00 4.50 29.50 34.00
Height(feet) 1.50 0.00 0.00 1.50
Primary OutFlow Max=10.83 cfs @ 12.94 hrs HW=96.01' (Free Discharge)
=18"CMP Barrel (Barrel Controls 10.71 cfs @ 6.06 fps)
2=4"Skimmer (Passes <0.23 cfs potential flow)
3=24"CMP Riser (Passes< 15.22 cfs potential flow)
4=25'Secondary Spillway (Weir Controls 0.12 cfs @ 0.37 fps)

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basin Type ll 24-hr 25 yr Rainfall=6.49"
Prepared by{enter your company name here) Printed 1/14/2020
HydroCAD®10.00-20 s/n 07329 O 2017 HydroCAD Software Solutions LLC Page 4
Summary for Subcatchment 3S: Watershed 3
Runoff - 125.27 cfs @ 12.14 hrs, Volume= 10.108 af, Depth= 4.80"
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Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span=0.00-120.00 hrs, dt=0.05 hrs
Type 1124-hr 25 yr Rainfall=6.41"
Area ac CN Description
24.620 86 Newly graded area, HSG'B j
0.650 96 Gravel road, HSG B
25.270 86 Weighted Average
25.270 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ftlft) (ftlsec) (cfs)
3.8 100 0.0200 0.43 Sheet Flow, Sheet
Fallow n=0.050 P2=3.60"
17.8 1,071 0.0100 1.00 Shallow Concentrated Flow,Shallow Concent.
Nearly Bare&Untitled Kv= 10.0 fps
21.7 1,171 Total �
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basin Type 1l 24-hr 25 yr Rainfall=6.49"
Prepared by{enter your company name here} Printed 1/14/2020
HydroCADO 10.00-20 s/n 07329 0 2017 HydroCAD Software Solutions LLC Page 5
Summary for Pond 3P: Basin 3
Inflow Area= 25.270 ac, 0.00% Impervious, Inflow Depth= 4.80" for 25 yr event
Inflow - 125.27 cfs @ 12.14 hrs, Volume= 10.108 of
Outflow - 41.83 cfs @ 12.47 hrs, Volume= 8.955 af, Atten=67%, Lag=20.1 min
Primary = 41.83 cfs @ 12.47 hrs, Volume= 8.955 of
Routing by Stor-Ind method, Time Span=0.00-120.00 hrs, dt=0.05 hrs
Peak Elev=96.50'@ 12.47 hrs Surf.Area=66,250 sf Storage=222,859 cf
Plug-Flow detention time= 865.5 min calculated for 8.951 of(89%of inflow)
Center-of-Mass det. time= 811.3 min (1,618.1 -806.7)
Volume Invert Avail.Storage Storage Description
#1 93.00' 256,000 cf Custom Stage Data(Prismatic) Listed below
Elevation Surf.Area lnc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
93.00 61,000 0 0
94.00 62,500 61,750 61,750
95.00 64,000 63,250 125,000
96.00 65,500 64,750 189,750
97.00 67,000 661250 2561000
Device Routing Invert Outlet Devices
#1 Primary 92.00' 18.0" Round 18"CMP Barrel
L=50.0' CMP, projecting, no headwall, Ke=0.900
Inlet/Outlet Invert=92.00'/91.50' S=0.0100'/' Cc=0.900
n=0.025 Corrugated metal, Flow Area= 1.77 sf
#2 Device 1 93.00' 0.230 cfs 4"Skimmer
#3 Device 1 95.00' 24.0" Horiz.24"CLIP Riser C=0.600
Limited to weir flow at low heads
#4 Primary 96.00' 26'Secondary Spillway,C=3.27
Offset (feet) 0.00 4.50 29.50 34.00
Height(feet) 1.50 0.00 0.00 1.50
Primary OutFlow Max=41.51 cfs @ 12.47 hrs, HN=96.50' (Free Discharge)
t2=4"
8"CMP Barrel (Barrel Controls 11.54 cfs @ 6.53 fps)
Skimmer (Passes<0.23 cfs potential flow)
3=24'CMP Riser (Passes <18.51 cfs potential flow)
=25'Secondary Spillway (Weir Controls 29.97 cfs @ 2.16 fps)
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