20210507_infiltration_Calcs

Calculations
(Infiltration Pond)
RECEIVED
MAY G 7 20B
LAND QUALITY
MINING PROGRAM

STORM WATER STORAGE - INFILTRATION DEWATERING POND
SCOTTS FARM ROAD MINE
Predominent Soil Type - Craven Series; Sandy Loam at depth (greater than 54-inches)
Permeability averages 2 to 6 in/hr; use 2 in,/hr (ref. NRCS)
Permeability = 0.0000463 ft/sec
HUBERT, NC (NOAA)
RAINFALL
DRAINAGE
RUNOFF
DRAINGE
IMPERVIOUS
IMPERVIOUS
INTENSITY
PEAK
AREA
COEFFICIENT, C
AREA (AC)
AREA (AC)
FRACTION (1A) I (IN/HR), 25-YR
DISCHARGE (CPS)
1
0.35
16.7
0
0.00
8.55
49.97
RETENTION VOLUME REQUIRED PER STORM EVENT
1-IN
2-IN
4-IN
6-IN
8-IN 8S5-IN
VOLUME
DRAINAGE
RUNOFF
DRAINGE
VOLUME
VOLUME
VOLUME
VOLUME
VOLUME VOLUME
PROVIDED
AREA
COEFFICIENT, RV
AREA (AC)
REQUIRED (CF)
REQUIRED (CF) REQUIRED (CF)
REQUIRED (CF)
REQUIRED (CF) REQUIRED (CF)
(CF)
1
0.05
16.7
3,031
6,072
12,124
18,186
24,248 25,915
297,335
NCDENR Stormwater BMP Manual
Simple Method (Schueler,1987)
RV = 0.05 +0.9' IA BASIN VOLUME AVAILABLE
V = 3630. RD • Rv ` A ABOVE NORMAL
GROUNDWATER ELEV. =10.0
INFILTRATION STORM WATER
Permeability of surrounding soils, k
Hydraulic Gradient for Infiltration, I
Surface area for dewatering, A =
(For 8.55-in storm, Elev. =10-S8)
Infiltration Discharge Rate, Q=kiA
Permeability
(ft/sec)
0.0000463
0.0000463 ft/sec
1.0 ft/ft
25,600 sf
CONTOUR
AREA (SF)
AVG. AREA (SF) DEPTH (FT)
VOLUME (CF)
10
41552
44,151 2
88,301
12
46,749
49,488 2
98,976
14
52,227
55,029 2
110,058
16
57,831
TOTAL VOLUME AVAILABLE
297,335
Hydraulic Surface Area Infiltration Rate Volume stored Time to Dewater
Gradient(ft/ft) sf cfs cf Days
1.0 43,059 1.99 25,915 OAS
25-YR, 24-HR STORM EVENT WILL DEWATER IN 2.1 DAYS
INFILTRATION MINE DEWATERING
DETERMINE MAXIMUM ALLOWABLE DAILY PUMPING (ELEV.16)
Maximum allowable storage elevation =16.0 msl
Allowable dewatering time between work days =12 hours (0.5 days)
Permeability of surrounding soils, k = 0.0000463 ft/sec (Craven Series; Sandy Loam)
Hydraulic Gradient for Infiltration, I = 1.0 ft/ft
Surface area for dewatering, A = 57,831 sf
Infiltration Discharge Rate, Q=kiA
Permeability Hydraulic Surface Area Infiltration Rate Volume stored Time to Dewater
(ft/sec) Gradient(ft/ft) sf cfs d Days
0.0000463 1.0 57,831 2.68 115,000 0.50
MAXIMUM ALLOWABLE DAILY DEWATERING TO INFILTRATION BASIN = 115,000 CF
860,200 gal.