20230817_ESC

G2,
ENGINEERING & ENVIRONMENTAL SCIENCE COMPANY
3008 ANDERSON DRIVE,SUITE 102
RALEIGH,NC 27609
[phone] -
August 10, 2023
Mr. David Miller
Hammill Construction Company, Inc.
5051 St. Stephens Church Road
Gold Hill,NC 28071
RE: Stormwater Basin IEvaluation
Kluttz Mine Modification (13-02)
11703 Sansbury Rd.
Mt. Pleasant,NC
Permit No. 13-02
Dear Mr. Miller:
The following evaluation is for Stormwater Basin 1 at the Kluttz Mine.
For this evaluation, the additional approximately 6 acres of new disturbance, plus the area
draining to Basin 2 was included.
Attached are the calculations. The evaluation indicates that the 10 year rain event will
not reach the top of the riser pipe, and the 25-year rain is about 0.12 ft. above the riser
pipe. More than 3 ft. of freeboard is available.
Please contact me if you have any questions.
Sincerely,
Patrick Shillin on, P. \,Q�oFf10w�•.;
President
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Watershed 1 Basin
SUbCat Reach A
Link Routing Diagram for Basin#1
Prepared by E2S
HydroCAD®10.00-26 s/n 07329 0 2020 HydroCAD Software Solutions LLC

Basin #1 Type 11 24-hr 2 yr Rainfall=3.48"
Prepared by E2S
HydroCAD®10.00-26 s/n 07329 ©2020 HydroCAD Software Solutions LLC Page 2
Summary for Subcatchment IS: Watershed 1
Runoff = 114.56 cfs @ 12.47 hrs, Volume= 15.570 af, Depth= 1.29"
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 2 yr Rainfall=3.48"
Area (ac) CN Description
34.700 91 Fallow, bare soil, HSG C
110.400 70 Woods, Good, HSG C
145.100 75 Weighted Average
145.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
29.3 100 0.0330 0.06 Sheet Flow,
Woods: Dense underbrush n= 0.800 P2=3.48"
1.6 460 0.0840 4.67 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
15.0 3,009 0.0430 3.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
45.9 3,569 Total

Basin #1 Type //24-hr 2 yr Rainfall=3.48"
Prepared by E2S
HydroCADO 10.00-26 s/n 07329 ©2020 HydroCAD Software Solutions LLC Pa-ge 3
Summary for Pond 2P: Basin
Inflow Area = 145.100 ac, 0.00% Impervious, Inflow Depth = 1.29" for 2 yr event
Inflow = 114.56 cfs @ 12.47 hrs, Volume= 15.570 of
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag=0.0 min
Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 of
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 597.46' @ 26.65 hrs Surf.Area= 8.036 ac Storage= 15.570 of
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 596.00' 69.355 of Custom Stage Data(Prismatic)Listed below
Elevation Surf.Area Inc.Store Cum.Store
(feet) (acres) (acre-feet) (acre-feet
596.00 5.890 0.000 0.000
602.50 15.450 69.355 69.355
Device Routing Invert Outlet Devices
#1 Primary 596.00' 18.0" Round Culvert
L=40.0' CMP, square edge headwall, Ke= 0.500
Inlet/Outlet Invert= 596.00'/595.48' S= 0.0130'/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 1.77 sf
#2 Device 1 599.60' 18.0" Horiz. 18" Riser C= 0.600 Limited to weir flow at low heads
Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=596.00' (Free Discharge)
L1=Culvert ( Controls 0.00 cfs)
L2=18 Riser ( Controls 0.00 cfs)

Basin #1 Type !!24-hr 90 yr Rainfall=5.06"
Prepared by E2S
HydroCADO 10.00-26 s/n 07329 ©2020 HydroCAD Software Solutions LLC Page 4
Summary for Subcatchment 1 S: Watershed 1
Runoff = 231.86 cfs @ 12.45 hrs, Volume= 30.205 af, Depth= 2.50"
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=5.06"
Area (ac) CN Description
34.700 91 Fallow, bare soil, HSG C
110.400 70 Woods, Good, HSG C
145.100 75 Weighted Average
145.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
29.3 100 0.0330 0.06 Sheet Flow,
Woods: Dense underbrush n= 0.800 P2=3.48"
1.6 460 0.0840 4.67 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
15.0 3,009 0.0430 3.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
45.9 3,569 Total

Basin #1 Type ii 24-hr 10 yr Rainfali=5.06"
Prepared by E2S
HydroCAD@ 10.00-26 s/n 07329 @ 2020 HydroCAD Software Solutions LLC Page 5
Summary for Pond 2P: Basin
Inflow Area = 145.100 ac, 0.00% Impervious, Inflow Depth = 2.50" for 10 yr event
Inflow = 231.86 cfs @ 12.45 hrs, Volume= 30.205 of
Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 100%, Lag= 0.0 min
Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 of
Routing by Stor-Ind method, Time Span=0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 598.83' @ 26.65 hrs Surf.Area= 10.054 ac Storage=30.205 of
Plug-Flow detention time= (not calculated: initial storage exceeds outflow)
Center-of-Mass det. time= (not calculated: no outflow)
Volume Invert Avail.Storage Storage Description
#1 596.00' 69.355 of Custom Stage Data(Prismatic)Listed below
Elevation Surf.Area Inc.Store Cum.Store
(feet) (acres) (acre-feet) (acre-feet)
596.00 5.890 0.000 0.000
602.50 15.450 69.355 69.355
Device Routing Invert Outlet Devices
#1 Primary 596.00' 18.0" Round Culvert
L= 40.0' CMP, square edge headwall, Ke= 0.500
Inlet/Outlet Invert= 596.00'/595.48' S= 0.0130 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 1.77 sf
#2 Device 1 599.60' 18.0" Horiz. 18" Riser C= 0.600 Limited to weir flow at low heads
Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=596.00' (Free Discharge)
L1=Culvert ( Controls 0.00 cfs)
L2=18 Riser ( Controls 0.00 cfs)

Basin #1 Type 11 24-hr 25 yr Rainfall=6.01"
Prepared by E2S
HydroCAD®10.00-26 s/n 07329 ©2020 HydroCAD Software Solutions LLC Page 6
Summary for Subcatchment IS: Watershed 1
Runoff = 307.90 cfs @ 12.44 hrs, Volume= 39.789 af, Depth= 3.29"
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 25 yr Rainfall=6.01"
Area (ac) CN Description
34.700 91 Fallow, bare soil, HSG C
110.400 70 Woods, Good, HSG C
145.100 75 Weighted Average
145.100 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
29.3 100 0.0330 0.06 Sheet Flow,
Woods: Dense underbrush n=0.800 P2= 3.48"
1.6 460 0.0840 4.67 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
15.0 3,009 0.0430 3.34 Shallow Concentrated Flow,
Unpaved Kv= 16.1 fps
45.9 3,569 Total

A
Basin #1 Type /l 24-hr 25 yr Rainfall=6.01
Prepared by E2S
HydroCADO 10.00-26 s/n 07329 ©2020 HydroCAD Software Solutions LLC Page 7
Summary for Pond 2P: Basin
Inflow Area = 145.100 ac, 0.00% Impervious, Inflow Depth = 3.29" for 25 yr event
Inflow = 307.90 cfs @ 12.44 hrs, Volume= 39.789 of
Outflow = 0.66 cfs @ 25.23 hrs, Volume= 1.277 af, Atten= 100%, Lag=767.1 min
Primary = 0.66 cfs @ 25.23 hrs, Volume= 1.277 of
Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs
Peak Elev= 599.72' @ 25.23 hrs Surf.Area= 11.362 ac Storage= 39.699 of
Plug-Flow detention time= 2,269.7 min calculated for 1.276 of(3% of inflow)
Center-of-Mass det. time= 2,045.9 min (2,906.1 -860.2 )
Volume Invert Avail.Storage Storage Description
#1 596.00' 69.355 of Custom Stage Data(Prismatic)Listed below
Elevation Surf.Area Inc.Store Cum.Store
(feet) (acres) (acre-feet) (acre-feet
596.00 5.890 0.000 0.000
602.50 15.450 69.355 69.355
Device Routing Invert Outlet Devices
#1 Primary 596.00' 18.0" Round Culvert
L= 40.0' CMP, square edge headwall, Ke= 0.500
Inlet/Outlet Invert= 596.00'/595.48' S= 0.0130 '/' Cc= 0.900
n= 0.025 Corrugated metal, Flow Area= 1.77 sf
#2 Device 1 599.60' 18.0" Horiz. 18" Riser C= 0.600 Limited to weir flow at low heads
Primary OutFlow Max=0.65 cfs @ 25.23 hrs HW=599.72' (Free Discharge)
t-1=Culvert (Passes 0.65 cfs of 11.45 cfs potential flow)
'L2=18 Riser (Weir Controls 0.65 cfs @ 1.14 fps)