Dr. Mark Boster 5 August 2, 1979

This retained generality of the probabilistic analysis because the
incorporation of a range of cycle times avoids the need to have site-
specific data on the available pond area which affects the cycle time.

To evaluate the probabilities of multiple storm occurrences, it was
assumed that the occurrence of a storm having a return period equal
to N-years within a given time period of L~years is governed by the
Poisson's probability distribution given by:

-hL n
Pr(n) = e 7 QL)”

n

where
1
a N
n = number of occurrences of the storm event.

The encounter probability of any such storm during a specified mine life
can then be calculated following a procedure as outlined by Borgman. (1)
Similarly, the probability of such storms occurring within a given cycle
time can also be calculated. The combined probability of these two
storm events occurring within a given cycle period can then be cal-
culated using the laws of probability.

For the probabilistic analysis it was assumed that the combined prob-
ability for two storms could be determined from the joint probabilities
of two independent events. There is reason to believe that two storms
are not independent such that the probability of a second storm within a
period of N-days from the first would require a conditional probability
based on the first storm occurring. A Markov process could be used to
approximate such a probability, but sufficient data are not available on
conditional probabilities to render the results meaningful. The approach
used for determining combined probabilities in this study is believed to
overestimate the joint probability because the probability of the second
storm occurring within N-days was computed for any N-day period and not
necessarily for the exact N-day period following the first storm. This
probability will be larger than for a second storm occurring within
exactly N-days of the first storm.

Because additional volume requirements affect costs and also determine
the amount of overflow (volume in excess of pond capacity) and there are
numerous possible combinations of storm events, a decision theory
approach was used to perform a risk-benefit analysis of any additional
volume requirements. This approach is based on forming a decision tree

() orgman, L. E., August 1963, "Risk Criteria," ASCE, WW 3.

NP APOLONILS.


TABLE A-8. SEDIMENT POND WV-2A (10 yr. storm)

PERMANENT POUL CAPACITY 2 4.46 ACRE@FT
DEAD STURAGE = 0,0 ACRE@FT
STORM RUNOFF VOLUME = 23,90 ACRESFT
STURM VILUME DISCHARGED a 19,39 ACRE@FT
POND VOLUME AT PEAK STAGE = 22,83 ACRE@FT
PEAK STAGE a 15,45 FT

PEAK INFLOW RATE g 117,46 crs
PEAK DISCHARGE RATE 2 5,15 cFKS

PEAK INFLUW SEDIMENT CONCENTRATION 2 [e1s4,6 MG/L]
PEAK EFFLUENT SEDIMENT CUNCENTRATIUN = [456.4 MG/L]

STORM AVERAGE EFFLUENT CONCENTRATION = 202.6 MG/L
AVERAGE EFFLUENT SEDIMENT CUNCENTRATIUN & 166,5 MG/L
BASIN TRAP EFFICIENCY = 93,72 *

DETENTION TIME UF FLOW WITH SEDIMENT = 33,56 HRS

OETENTIUN TIME FROM HYDROGRAPH CENTERS &

OETENTION TIME INCLUDING STURED FLUW a 30,86 HRS

SEDIMENT LOAD a 85,00 TONS
yy


ACRE-FEET OF STORAGE

ACRE-FEET OF STORAGE

100 —
80

60 Z|

pt
40 7 WV-4A,
WV-3A 77 WV-1A

20 of

°

20 30 40 50 60 70

THOUSANDS OF DOLLARS

Figure 5. Cost curve for ponds at location A.

20

WV-3B

WV-1B) 4

15

10

KY-1. “S| y
WV-4B x

ee

10 20 30 40 50
THOUSANDS OF DOLLARS

Figure 6. Cost curve for ponds at location B.

28



wom

ae
ya’,
3}

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
\ ta WASHINGTON, DC 20460

ae pps

The Environmental Protection Agency is evaluating the following reports
as part of its reconsideration of the catastrophic precipitation exen-
tions to effluent guidelines limitations and new source performance
standards for coal mining point source discharges of water pollution.
See 44 Fed. Reg. 39391 (July 6, 1979).

The Agency is distributing this report to interested members of the
public for review and comment. All comments should be submitted in
writing to:

B. M. Jarrett

Effluent Guidelines Division (WH-552)
Environmental Protection Agency

401 M Street, S.W.

Washington, D.C. 20460

All comments must be postmarked no later than October 1, 1979.

a Su AGENCY


TABLE A-10. (continued)

PERMANENT POOL CAPACITY

DEAD

STURAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CUNCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATIUN

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

OETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD

48

4,37 ACRE®FT
0,0 ACRE®FT
7,97 ACRE®FT
3,59 ACRE@FT

11,00 ACRESFT
18,64 fT
87,17 CFS
1,13 CFs
6406246 MG/L
3342.5 MG/L
2429,4 MG/L
1119,5 MG/L
96,15 x
81,24 HRS
39,70 HRS
71,34 HRS
308,00 TONS

he


-29-

flocculating agents provide an economic solution to meeting water qual~
ity goals even on large surface mine areas. On three watersheds near
Centralia, Washington, water quality was maintained within the new Fed-
eral limits for an estimated cost of $10/acre-ft of runoff. Suppliers
of chemical agents indicate that they are now being used widely through

the U.S.

Multiple Basins

Frequently several basins in series are used instead of a single
basin. In Eastern states this practice is common because of the diffi-
culty of locating large structures on the small steeply sloping water~
sheds found in these areas. Large operators may have over 50 basins
within their permit area. In general water quality from the lower basin
is good but one of the problems with this type of practice is that the
upper basins quickly become filled and the deposited sediment tends to
be washed out of the basin at a later time (often after active mining
has ccased). Under the new legislation most of these ponds will re-
quire cleaning and eventually will be removed completely. How this
may be accomplished is beyond the scope of this paper and appears a
difficult question. Design for multiple basins can perhaps be best de-

termined through routing with a simulation method such as DEPOSITS.

SUMMARY
Predictive equations have been presented for estimating basin trap
efficiency and peak effluent sediment concentrations. All the predic-

tive equations were generated from use of the DEPOSITS model. This


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(Qj-910e) e8e103s quauewiag = § az0uy

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SdVOT LNSWIGHS ONINIWWGLAC YOd ALVE AVEd
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TABLE A-4. (coritinued)

PERMANENT POOL CAPACITY

DEAD STURAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK OISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLUW

SEDIMENT LOAD
39

co

6.33 ACRE@FT

0,0 ACRE®FT
21,59 ACRE@FT
12,32 ACRESFT
24,75 ACRE@FT
15,95 FT
99,93 CFS
3,10 cFs

22634,9 MG/L

1280,9 MG/L

732,9

491,8

95,83

80,19

140.76

74,96

294,00

MG/L

MG/L

&

HRS

HRS]
Reg

fONS


-23-

In this case the volume of base flow is included in the runoff volume
Q, andtd is the average detention time of the entire event including
the base flow condition. toe is still the duration of the design storm
event. The coefficient of determination for this equation is 0.91, and

all the variables are again significant at the 99.5% confidence level.

PEAK EFFLUENT SEDIMENT DISCHARGE

In developing equations to estimate peak outflow concentrations, it
was felt that these concentrations would be closely correlated to the
basin trap efficiency and the peak inflow concentration. If an equation
could be developed based upon these two variables, an estimate could be
made of the peak outflow concentration which is independent of the meth-
ods adopted in this study, Trap efficiency may either be determined
through regression equations for the particular area or through use of
methods outlined earlier. Peak inflow concentration may also be esti-~
mated by equations based upon actual field monitoring or through use of

equation 5.

Dry Basin

288 data points were used and the following equation developed:
= *O34 5% 1.2 +21 *  _ pkey +2) 13
Cour 70-0114 PZ? POO (td/t.Y (P5q - ey (13)

where C, is the peak effluent sediment concentration (mg/2). The co-

ut
efficient of determination R, is equal to 0.96 and all variable are sig-
nificant at the 99.5% confidence level. The equation, however, is diffi-

cult to use, as a good estimate is required of the particle size distri-

bution at the peak flow rate.


Peak Effluent Sediment Concentration

Peak sediment concentration contained in the flow being discharged
from the pond as determined by the model.

Storm Average Effluent Concentration

Average concentration of the sediment in the effluent measured from
the initial discharge of sediment until the end of the simulation period
(does not include clear water discharged by the precipitation event).

Average Effluent Sediment Concentration

Average sediment concentration contained in the effluent during the
entire simulation period (including the period before any sediment is
discharged). Clear previously stored flow which might be discharged has
been included in the determination of this average.

Basin Trap Efficiency

The percentage of the sediment inflow which has remained in the
pond at the end of the discharge event. It should be noted that most of the
fine colloidal particles will have remained in suspension in the perman-
nent pool and may well be discharged during the next storm event.

Detention Time of Flow with Sediment

This definition gives a volume weighted average detention time of
the design storm event. Credit is given for previously stored flow being
discharged initially and also for part of the design flow remaining in the
permanent pool following the event. This definition will give the longest
theoretical detention time of the three presented.

Detention Time From Hydrograph Centers

This definition of detention time gives the detention time between
the centers of the inflow and outflow hydrographs, which conforms to the
definition contained in OSM regulations. Occasionally, the computer
simulation will end before the end of the discharge event. When this
occurs, the reported detention time will be underestimated. In all cases,
however, the simulation period included tie peak effluent TSS concentration.

Detention Time Including :

red Flow

This deftnition gives a volume weighted detention time based on the
time between the hydrograph centers but also gives credit for some of the
flow remaining in the permanent pool.

Sediment Load

The sediment load is the amount of sediment entering the basin
during the design event, derived from MUSLE.

2)


TABLE A-21. SEDIMENT POND KY-1B (5yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION T2ME OF FLOW WITH SEDIMENT

OETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD

64

1,50 ACRE@FT
0,0 ACRE@FT
2,20 ACRE@FT
0,70 ACRE@FT
2,95 ACRE@FT
9.92 fT
31,39 crs
0,81 CFS
2602.2 MG/L
1564,5 MG/L
$19,2 MG/L
97.91 x
91671 HRS
84,59 HRS
71,00 TONS


¥=95 (VOp)>8 K (LSC) P
Y - sediment load (tons)

(vapy56 - runoff energy factor, see Table 1 for V, volume
(acre-feet) and Qp, peak runoff rate (cfs)

K = soil erodibility (0.28 for PA-1, 0.3 for all other
sizes)
LSC - composite length - steepness - cover-management factor,

see Table 3 for LS values and Table 4 for C values

P ~ support practice (1.0)

* Maximum tons/acre of 16.9 equivalent to 0.056 inches of soil loss
over entire watershed.

STORM HYDROGRAPH COMPUTATION

The inflow hydrographs for the 2-year, 5-year, and 10-year 24-hour
storm events were determined using the Watershed Storm Hydrograph (WASH)
model as developed by the University of Kentucky, Department of Agricultural
Engineering. 12 The WASH model is based upon the procedures for developing
runoff rates and volumes currently used by the SCS for small watersheds,
which are generally adequate for surface mined areas. In order to verify
the WASH hydrograph model, each watershed hydrograph was also calcnlated
using a computer model entitled the Penn State Urban Runoff Mode1.13 For
eaeh hydrograph generated, a correlation between peak flows generated by the
two models was within ten percent. For use of the WASH model in hydrograph
generation, the following watershed parameters need to be determined:

1) The watershed drainage area in acres,

2) The average watershed slope,

3) The watershed flow length in feet,

4) The design storm duration in hours,

5) The design storm rainfall in inches, and

6) The composite curve number for the watershed (CN value).

For each of the eleven sediment ponds modelled, the watershed
drainage area, average watershed slope, and flow length were determined from
a USGS quadrangle map of the area. For location A, it was assumed the en-
tire drainage area above the pond contributed to pond inflow. For location
B, it was assumed that diversion ditches were constructed above the dis-
turbed area to limit the contributing drainage area to the active mining
area, regraded area, valley fill, and virgin land adjacent to the pond

14

fe


ADDENDUM B


The modified tniversal sc.i loss equation (MUSLE} was used to
determine the total seviment load to tne pond. The DEPOSITS modei computes
the inflow sedimentgraph (tire vs sediment concentration) by making the
inflow sediment concentration proportional to the square of the incremental
water inflow volume. This method was compared to a more sophisticated
approach developed by W1iliams which used an instantaneous unit sediment-
@raph applied to ar. optimized unit hydrcgraph to predict sediment concen-
trations.! When Williams hydrograph and sediment yield cata were evaluated
using DEPOSITS sedimentgraph analysis, the result was found to closely
approximate the measured data and Williams simulation if tne sediment load
is lagged two time increments before the hydrograph values. This showed
that the DEPOSITS analysis can give a good approximation of sediment inflow
concentration with an optimized hydrograph and sediment load. The ijag time
of sediment load to hydrograph is site-specific, therefore, no lag was used
in the study's simulation because site-specific information was not
available.

A particle size distribution covering the size range of particles
from coarse sand to clay particles, as depicted in Figure 4, was used and
held constant for each performance simulation. This distribution assumes a
more uniform concentration over a wider size vange than was actually mea-
sured on grab samples taken at the six sites during moderate precipitation
events because of the potential scour velocity and carrying capacity of run
off associated with more severe storm events. Ideally, one would collect
site-specific data concerning particle size distribution (and the other
factors discussed above). Such an undertaking would, however, require con-
siderable resources. Moreover, particle size distribution will vary not
only from one site to the next, but also at the same site under different
storm conditions, and during the same storm event. The choice of a
"typical" particle size distribution was arbitrary but consistent with ob-
served values and with those in the literature. All assumptions were con-
servative with respect to pond performance.

A summary table of results from the computer simulations is
included in the appendix. A bricf description of the factors addressed in
the summary table follows:

Permanent Pool Capacity

This term refers to the volume below the stage of the lowest
dewatering device and is equal to the sediment storage.

Dead Storage

The volume of the permanent pool that is bypassed at the beginning
of discharge from the pond. The variable DEAD may also be used to account


= 30-

simulation model has been outlined in several publications and has not
been described here. Several revisions have been made to the program
and further information may be obtained by contacting the authors.

. It appears that trap efficiencies greater than 90% will be re-
quired if water quality standards are to be obtained. If the runoff
into the basin contains more than 20% finer than 20 microns, it is un-
likely that water quality standards will be achieved unless flocculat-
ing agents are used or storage in excess of 24 hours is possible.

Basin storage may be increased through partial dewatering between
storm events. It should be noted however that the permanent pool acts
as a stilling basin and if the basins are dewatered to a shallow depth,
considerable turbulence and resuspension of deposited sediment will
occur during the next storm event. Trickle spillways may prove to be
a viable alternative to drop inlet risers but have not been evaluated
in this study. In this paper little attention has been paid to the
surface area requirement of one square foot for each 50 gallons of flow
per day as sizing of most basins under this criteria is not possible.
For an inflow event of 8 acre~ft, for example, a surface area of 1.25
acres would be required. In Eastern Kentucky two or three basins on a
75 acre watershed would be required as surface areas on single basins

seldom exceed one acre and are usually much smaller than this.

RECOMMENDATIONS
Although several predictive equations have been developed for esti-
mating basin performance it is recommended that where possible mine op-

erators conduct field research and utilize simulation models such as


TABLE A-20. (continued)

PERMANENT POOL CAPACITY = 1,50 ACRE®FT
DEAD STORAGE 2 0,0 ACREwFT
STORM RUNOFF VULUME « 3,62 ACRE*FT
STURM VOLUME DISCHARGED s 2.12 ACRE®FT
POND VOLUME AT PEAK STAGE = 4,53 ACRE@FT
PEAK STAGE ® 13,19 FT

PEAK INFLOW RATE z 44,66 crs
PEAK DISCHARGE RATE . 2 0,49 crs
PEAK INFLOW SEDIMENT CONCENTRATION = [roaso.7 G/U
PEAK EFFLUENT SEDIMENT CONCENTRATIUN s 559.7 MG/L
STURM AVERAGE EFFLUENT CONCENTRATIUN . 323.5 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION = 194,8 MG/L
BASIN TRAP EFFICIENCY 2 95,75 x
DETENTION TIME OF FLOW WITH SEDIMENT : 69,57 HRS

DETENTION TIME FROM HYDROGGRAPH CENTERS

DETENTION TIME INCLUDING STURED FLUW s 59,80 HRS

SEDIMENT LOAD s 22,00 TONS
63


TABLE A-6. SEDIMENT POND WV-1B (10 yr. storm)

PERMANENT POOL CAPACITY 2: 6,42 ACREOFT
DEAD STORAGE s 0,0 ACRE@FT
STORM RUNOFF VOLUME = 11,23 ACRE@FT
STORM VOLUME DISCHARGED a 4,81 ACRE@FT
POND VOLUME AT PEAK STAGE 2 14,96 ACRESFT
PEAK STAGE ® 21,48 FT
PEAK INFLOW RATE 2 148,66 CFS
PEAK DISCHARGE RATE s 2,31 CFS
PEAK INFLOW SEDIMENT CONCENTRATION = |125316,0 MG/L
PEAK EFFLUENT SEDIMENT CONCENTRATION a 7994,5 MG/L
STORM AVERAGE EFFLUENT CONCENTRATIUN z 5398,3 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION 3 2392.6 MG/L
BASIN TRAP EFFICIENCY 2 95,90 *
OETENTION TIME OF FLOW WITH SEDIMENT = $1,512 HRS
DETENTION TIME FROM HYDROGRAPH CENTERS 2 26,29 HRS
DETENTION TIME INCLUDING STORED FLUK a 45,05 HRS
SEDIMENT LUAOD 2 861,00 TONS

4Y


78-434-81

Boe 2. RAWing

Se
BES [Ea] 79 |nuwoce

CHECKED BY

[7-25-79] APPROVED

ey

‘OnawnT MEL,

Mine Life:

oe

Cycle Tine:
4 days

LEVEL SECOND STORM (R) at
First Storm(N) Te) Pr(i,t)
es Pr(1,2)
Pr(1,5)
Pr(R=10) Pr(1,10)
Pr(2,1)
Pr(2,2)
Pr(2,5)
Pr(2,10)

Pr(5,1)

Pr(5,2)

Pr(3,5)

Pr(5,10)

Pr(10,1)

Pr(10,2)

Pr(10,5)

Pr(10,10)

EXPECTED
OVERFLOW
E(NR)

Pr(W,R)

FQ

E(N,R)
E(1,2)

(1,5)

£(1,10) Ry

£(2,1)

RR

£(2,2)

£(2,5)

E(2,10) Egax (Lid)

25,1)
2(5,2)
£(5,5)

(5,10)

(19,0)
£(10,2)

(10,5)

£10, 10)
Emax (Lyd) = £ E(N,R)

Probabitity of a N-YR storm
followed by 2 R-YR storm with
mine Life L years and cycle
time d days = Pr(N) Pr(R)

Expected overflow due to
occurrence of a N-¥R storm
followed by a R-YR storm
within cycle time of d days
and mine Life of L years
= Pr(NJR)IRy * Rp - Vol

Run-off volume of the firet
storm having @ ceturn period
of N-Yeare

Run-off volume of the second
atorm having @ return period
of R-Years

Volume of storage pond

Maximum expected overflow for
4 pond of capacity Vg, mine
Life of L Years and cycle
time of d days

FIGURE 38
DECISION TREE CONCEPT
USED TO DERIVE MAXIMUM

EXPECTED OVERFLOW

PREEARED FOR

- § DEPARTMENT CF THE INTERIOR



-1U-

factors and will vary throughout the storm event. Detachment and trans-
port of sediment is very dependent on the following factors:

Rainfall intensity

Depth of runoff on the watershed

Watershed topography

Onsite control practices

Soil particle characteristics

Hydraulic characteristics of the watershed

Ground cover on the watershed

Rausch and Heinemann (1975) found that the percent finer for a

given particle size may be related to the storm peak runoff rate by

the equation:

M

Pg = CCay,) (3)

where Pg is the percent finer for a particular particle size d, and Gin
is the peak inflow rate to a reservoir. The coefficient C will vary with
the particle diameter and each watershed. The coefficient M will vary
from watershed to watershed. For Callahan Reservoir in Missouri, M had

a value of 0.33. Callahan reservoir is located on a 3600 acre agricul-
tural watershed, In this study a value of 0.3 was used for M and the

equation

Pe = (a,/a? Py (4)

where Pg is the percent finer for a given particle size measured at a
flow rate qy (cfs) and q is the runoff rate (cfs), at any given time
during the storm event. In all the regression equations developed dur-
ing this study, the percent finer Py* has been related to the peak run-

off rate nt


‘spuod juewjpes Apnjs jo uojeco7 *} eunbig

=
AM
wa ~~ we
\ eure ww 4
Vv i]
. b-va ol
VINVATASNNAS



FOREWORD

When energy and material resources are extracted, processed,
converted, and used, the related pollutional impacts on our environment
and even on our health often require that new and increasingly more
efficient pollution control methods be used. The Industrial Environmental
Research Laboratory - Cincinnati (IERL-Ci) assists in developing and
demonstrating new and improved methodologies that will meet these needs
both efficiently and economically.

This study attempts to define the ability of best practicable
technology in the design of surface mine sedimentation basins to meet the
current effluent limitations for suspended solids. This subject has been
under study by the Resource Extraction and Handling Division of the
Industrial Environmental Research Laboratory which may be contacted for
futher information.

David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati


AREA
OVERLAND
FLOW LENGTH
SLOPE-LENGTH
Ya A/F)

Figure 2. Determination of slope-length
for modified USLE.

Once these values are derived, the LS factor can be determined for
each area according to the SCS graph. Table 2 summarizes the LS values
computed for each site.

TABLE 2 - SUMMARY OF TOPOGRAPHIC FACTOR (LS)
FOR MODIFIED USLE

LS
Area Virgin land Active pit Regraded Valley fill
PA-1 - 0.57 1.9 -
KY-1(A) 5.5 0.64 4.6 1.4
KY-1(B) 4.6 0.64 4.6 14
wv-1(A) 13.0 0.57 7.5 2.3
WV-1(B) 5.7 0.57 7.5 2.3
WV-1(C) 5.7 0.57 7.5 2.3
WV-2(A) 6.5 0.50 2.6 2.1
WV-?(B) 1.5 0.50 2.6 2.1
WV-3(A) S21 0.53 5.0 2.6
WV-3(B) 5.7 0.53 5.0 2.6
WV-4(A) 28.0 0.57 10.0 -
WV-4(B) 28.0 0.57 10.0 -



=2h-

vosin with a Permanent Pool

Base flow following the storm event will not usually affect the
peak outflow concentration as the peak will normally occur during the
runoff event for the design storm. Because of 'flooding' of one of
the basins only 258 data values were used in the analysis for the per-
manent pool condition. A much simpler equation than that for the dry

basin was obtained:

c = 0.11 (100.0 - EY" c, +78 (q

00142
out sy) (4)

out

The R* value for this equation is 0.96 and again all the variables are
significant at the 99.5% confidence level. Using estimates of E from
equations 11 or 12 and estimates of Cin calculated with equation 5,
values of Cout calculated with equation 14 had an R? value of 0.86.

This is more typical of the correlation that might be expected if knowl-
edge of the actual basin trap efficiency and peak inflow concentrations
is not available.

For most small basins the ratio Gout Fin will probably vary between

will therefore vary between

0.2 - 0.8. The term 0.11 (qy./a,,) 7°"?

0.J1 - 0.14 and equation 14 may be approximated by the equation:

= F094 0.75
Sout = 0-23(100 ~ E) Cy (15)

A graphical solution to equation 15 is presented in Figure 4A. Estimates
of the peak inflow concentrated (c,)> based upon equation 5, may be ob-
tained from Figure 4B, An example of how the figures may be used is
shown. In the example, a 24-hour storm event has a peak runoff rate of

1000 cfs and 0.5 tons/acre of sediment is delivered to the detention


-15-

c. Condition b. followed by a base flow event of 1 or 2 cfs
for 48 hours following the storm event.

Unless a dewatering drawdown device is used, a permanent pool will be
formed in basins with a drop inlet riser. Basins are frequently de-
signed based on condition "a", although in fact conditions similar to
“b" or "c" actually occur. The following assumptions were made in the
study:

1. The effects of turbulence ur short circuiting in the basin
were not significant.

2. No flocculation occurred within the basin.

3. Inflow sediment concentrations are proportional to the in-
flow rate.

4. A winter or spring water viscosity of 0.015 cm*/sec.
5. Sediment delivery proportional to 95(Qxqin)?*.

6. Particle size variation with storm intensity could be repre-
sented by equation 4.

Five different basin geometries were considered, together with four
different riser configurations. Table 3 describes the combination of
basin sizes, riser configurations and storm events used to generate the
data for the regression analysis. The 6 particle size distributions
shown in Figure 1 were used for each combination illustrated in Table 3.
It was assumed that the distributions had all been determined at a flow
rate of 20 cfs. Basins A, B and C are all typical of sediment basins
found on Eastern surface mines and are based on actual basin geometries.
Basins D and E represent the larger size basins that might be found in
Western states, large agricultural watersheds and urban basins. All

basins are in general smaller than the size basin that might be required


ttttuent Guidelines Division

Environmental Provection WHS5S2 EPA 440/1-79/200
Agency + Washington, DC 20460 August 1979
Water and Waste Management c.])

DRAFT

EVALUATION OF
PERFORMANCE CAPABILITY

OF SURFACE MINE
‘SEDIMENT BASINS


TABLE A-18. SEDIMENT POND WV-4B (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD

STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STURM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLUW

SEDIMENT LOAD

59

1.98 ACRESFT
0,0 AGRE@FT
3,62 ACRE@FT
1.68 ACRE@FT
4,73 ACRE@FT
12,52 FT
51.64 cS
0,72 crs
165327,4 MG/L

5660.4 MG/L
2818,8 MG/L
96,40 x
78.61 HRS
28,93 HRS
7,23 HRS
372,00 TONS


TABLE A-2. (continued)

PERMANENT POUL CAPACITY = 2.93 ACRESFT
DEAD STORAGE . 9.0 ACRE*FT
STORM RUNOFF VOLUME . 5,16 ACRESFT
STURM VOLUME DISCHARGED a 1,98 ACRE@FT
POND VOLUME AT PEAK STAGE s 7.13 ACRE*FT
PEAK STAGE 2 6,78 FT

PEAK INFLOW RATE a 61,69 crs
PEAK DISCHARGE RATE . 0,78 cFs
PEAK INFLOW SEDIMENT CONCENTRATION = [Se295.6 MG/L]
PEAK EFFLUENT SEDIMENT CONCENTRATION = = [4811.6 MG/L
STURM AVERAGE EFFLUENT CONCENTRATION = 115te1 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION # a816% ~~ MGV
BASIN TRAP EFFICIENCY = 98,18
DETENTION TIME OF FLOW WITH SEDIMENT . 94,08 HRS

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW 2 84,26 HRS

SEDIMENT LOAD s 170,00 TONS
36


DISCLAIMER

This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names of commercial products constitute
endorsement or recommendation for use.

"8 Age

‘Seney

ii


TABLE A-17. SEDIMENT POND WV-4B (Syr. storrn)

PERMANENT POOL CAPACITY

DEAD

STORAGE

STURM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STURM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CUNCENTRATION

BASIN TRAP EFFICIENCY

OETENTION TIME UF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD

1,94 ACRESFT
0,0 ACRE®FT
2,72 ACRESFT
0,77 ACRE@FT
3,86 ACRE@FT
11,43 Fy
38,77 CFS
0,72 CFS
159768,7 MG/L
ea74.4 MG/L
5127,0 MG/L
1525,1 MG/L
98,01 x
72,90 HRS

67,51

270,00

HRS

TONS


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gL OOnL 0'On t L L dt a
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LL Oost 0°0€ i?) €L 8 2 a
9S 0002 o°oL 0 £1 g SLE v n-AM
gL O0SL o'st Se of 6 ol a
19 000€ o'le Se of 6 9EL Vv €-AM
gL 000€ oOveL gt €2 9 0s @
gS 000€ L°0L eb €2 9 Len v em AK
gL 00z2 ole 92 92 6 89 ct
09 0009 9°8L gz 92 6 one v br AM
gL OOLL o's 0 (44 ol ze Price L-¥d
(NO) (35) "a38ueT (g) ‘edots (sedoe )
‘ou aAano MOTS paysuezem ITI ASTTeEA pepeaday 3td eaTqOy eoue
aqtTsoduog oTTNeupAY eseuaay (sauoe) Baue pequnystg esgeuteig gUOTPEDOT puog

SOILSIUSLOVUVHO GHHSUSLYM “9 aTavl


Table 2 — continued

100-Year, 6-Hour Stonm

Watershed

Curve Volume
Area Slope Number Rainfall Runoff Peak Rate Runoff
(acres) (%) CN (inches) (inches) (cfs) (acre-ft)
500 5 60 2.0 05 9.6 2.1
3.0 29 49.6 12.4
4.0 68 116.2 28.3
70 2.0 23 39.6 9.6
3.0 70 131.9 29.2
4.0 1.30 260.7 54.2
80 2.0 56 131.0 23.3
3.0 1.25 316.9 52.8
4.0 2.04 537.2 85.0
500 10 60 2.0 05 11.4 21
3.0 229 56.1 12.1
4.0 -68 142.0 28.3
70 2.0 24 44.8 10.0
3.0 71 159.7 29.6
4.0 1.32 321.4 55.0
80 2.0 56 178.1 23.3
3.0 1.25 436.7 52.8
4.0 2.04 740.3 85.0
1000 5 60 2.0 05 13.0 4.2
3.0 229 104.2 24.2
4.0 68 278.0 $6.7
70 2.0 -23 142.1 19.2
3.0 70 482.4 $8.3
4.0 1.30 983.9 108.3
80 2.0 0.56 611.4 46.7
3.0 1.25 1403.1 104.2
4.0 2.04 2322.2 170.0
1000 10 60 2.0 .05 19.0 4.2
3.0 29 99.1 24.2
4.0 -68 232.4 56.7
70 2.0 223 79.3 19.2
3.0 70 203.7 58.3
4.0 1.30 521.3 108.3
80 2.0 56 261.9 46.7
3.0 1.25 633.8 104.2
4.0 1074.5 170.0



= 0 #74 y0.3 94 177
Coy 63577(Y ,/a) (q;,) toe (5)

where Ci is the peak inflow concentration (mg/2), Yq is sediment de-
livery to the basin for the storm event (tons), a is the watershed
area (acres), Gin is the peak runoff rate (cfs), and tee is the storm
duration (hours). The coefficient of determination for the equation is
R? = 0,97. The conditions for which equation 5 was developed are out-
lined in the next section. All the variables are significant at the
99% confidence level and 288 data points were used in the analysis.

In developing equation 5, C, was determined by making the inflow-

in
ing sediment concentration proportional to the inflowing runoff rate.
Thus by knowing the runoff hydrograph and the total sediment yield,

Yq, the inflowing sediment concentration at any time can be determined.

The concentration corresponding to the peak runoff rate is cow

SIMULATION STUDY CHARACTERISTICS

An attempt was made in this study to develop predictive equations
which might be employed by the mine design engineer to estimate basin
trap efficiency and peak effluent sediment concentrations. It was felt
that effluent standards could probably not be met with a perforated riser
and, as they are no longer required by law, only drop inlet risers were
evaluated,

The following flow conditions were evaluated:

a. Dry basin prior to the storm event.

b. Permanent pool below the riser crest prior to the design storm
event.


SECTION 4
METHODOLOGY OF POND EVALUATION

Six mine sites with eleven sedimentation ponds located throughout
the Appalachian coal fields were evaluated relative to sediment removal
performance. The Appalachian region was selected because in this area,
topographic constraints may render treatment of storm runoff most
difficult; therefore, it provides a worst-case for analysis. Five of the
sites were evaluated with ponds at two locations on the drainageway. The
first location, "A", refers to the pond's present location downstream from
the disturbed area. The second location, "B", refers to a position
adjacent to the disturbed area, which consists of the active mine, valley
fill and regraded areas. One sediment pond, PA-1, was evaluated at only
one location, adjacent to the disturbed area, as this is the pond's present
location,

In order to perform the evaluation of pond performance, a three
step approach was employed. First, the gross erosion in tons from the
watershed tributary to the pond was computed for the 2-year, 5-year, and
10-year 24-hour storm events for each of the sediment pond locations, A and
B. Second, the inflow hydrograph for each sediment pond was computed for
the 2-year, 5-year, and 10-year 24-hour storm events. Finally, the
performance of each sediment pond was evaluated using the DEPOSITS computer
program to model sediment removal efficiency.

All ponds were designed to meet OSM design criteria. These cri-
teria include a sediment storage capacity of 0.1 acre-feet for each acre of
disturbed area and a detention time (time between hydrograph centers) of a
minimum of 24 hours for the runoff from a 10-year 24-hour storm.

SEDIMENT YIELD COMPUTATIONS

The phenomena of soil erosion from rainfall and its delivery to a
stream system are very complex occurrences that are difficult to estimate
accurately. The most widely used and accepted method of estimating sediment
yield is the Universal Soil Loss Equation (USLE), developed by the U.S.
Department of Agriculture's (USDA) Agricultural Research Service, in
cooperation with Purdue University. The empirical equation was developed
utilizing more than 10,000 plot-years of basic runoff and soil loss data
primarily from agricultural lands. Additional data have lead to refinement
of USLE parameters and expansion of data to include non-agricultural lands,
especially construction sites .3


Dr. Mark Boster 10 August 2, 1979

©@ The probability of a multiple storm event is
significantly less than the probability of
having a l0-year, 24-hour storm.
Very truly yours,

Satyananda Chakrabarti

Donald E.

SC/DES:asm
Enclosures

DAPPOLONIA


THE DESIGN OF SEDIMENT BASINS?

A. D. Ward,? C. T. Haan? and B, J. Barfield?

ABSTRACT
Passage of Public Law 95-87 has placed several new restrictions on

the design of surface mine sediment basins. It created much contro-
versy as to the required sizing of the sediment basins, and adequate
design methods are not available for estimating basin performance and
effluent sediment concentrations. This paper presents guidelines as
to how the hydrologic parameters affecting sediment basin desigtvamay
be quantified and contains predictive equations for estimating basin
trap efficiency and peak effluent sediment concentrations. Multiple
regression analysis techniques were employed with data generated by

the WASH hydrograph computer program and by the DEPOSITS

1. The work reported in this paper was supported in part by funds pro-
vided by the Office of Water Research and Technology, United States
Department of Interior, as authorized under the Water Resources Act
of 1964, in part by the Kentucky Institute for Mines and Minerals
Research and in part by the Kentucky Agricultural Experiment Station
and is published with the approval of the Director of the Station
as Journal Article No. 78-2-94.

2. Research Associate, Agricultural Engineering Department, University
of Kentucky, Lexington, Kentucky.

3. Professor, Agricultural Engineering Department, University of
Kentucky, Lexington, Kentucky.

Acknowledgements: The authors would like to acknowledge the assistance
of D. L. Rausch, H. G. Heinemann and the USDA Watershed Research Office
in Coiumbia, Missouri, for providing access to data collected on Callahan
Reservoir. Results of verification studies using the DEPOSITS model on
this data will be published late in 1978.


*Aouo ots sq deay vo oury uofqwojied jo iazsqA *E vanBry

(SHH) SWIL NOILN3SL30 39Ve3AV

3I o at ral or 3 9 > oO
‘ ‘ s ‘ roe v e t rs | i U y°
4
A0
“2lvy MOISNI AXV3ad LV
Q3YNSV3AW 3Z1IS 3B1DILuVd Viv 4
7 a
>
0
“00m
: n
xs | n
x 1 3
ie
mr
z=
WOZ> 2SE AG> BS) 709 ~
aa
HO2>%0b 1S>%S 7 ~
%O02 WS>%S i
102 > ‘%b os
oOo -
“00!

BWIL NOILNAL3I0 HLIM JONVHOD AONSIOISSR dval


1) Inflow hydrograph,

2) Viscosity of the storm water,

3) Stage-area curve for the basin,

4) Stage-discharge curve for the basin,

5) Stage-discharge distribution curve,

6) Degree of dead storage or short circuiting,

7) Sediment inflow graph or total load,

8) Particle size distribution and specific
gravity of the suspended sediment.

The inflow hydrograph to each sediment pend for each of the three storms
evaluated was generated by using the WASH hydrograph model. The viscosity
of the water used in the evaluation was .012 cm2 /sec at 56°F. This value
represents viscosity at a typical winter temperature. The stage area curve
for each sediment basin location, A and B, was determined from a topographic
map. The stage discharge curve for each basin modelled was based upon four
objectives:

1) provide 0.1 acre foot of sediment storage for
each acre of disturbed area in the watershed
(in accordance with OSM minimum requirements) ,

2) provide a system of constant discharge rate with
surface withdrawal from the elevation of the
permanent pool to the crest of the principal
spillway through the use of a floating weir or
similar device,

3) provide a minimum theoretical detention time
of 24 hours for the runoff from a 10-year 24-
hour storm event (in accordance with OSM re-
quirements), and

4) provide a detention time in excess of 24 hours for
the runoff from a 10-year 24-hour storm event to
determine the effect of longer detention times on
peak effluent suspended solids.

Complete surface withdrawal was used in the pond modelling for the stage-
discharge-distribution curve. For the evaluation of the sediment ponds in
question, it was assumed that each pond tud uo dead storage (volume of pond
not used for sediment removal) and did not exhibit short circuiting (flowing
directly from inlet to outlet). ‘*-s, the results represent the pond's
performance at its peak sediment removal efficiency.

17

7


19 IDRAWING 39. .
NUMSER 78-334-A ||

Se &
mF

CHECKED BY

L

ME
7-24-79] APPROVED BY

DRAWN
BY

DEPTH, FEET

50

40

w
°o

'
fe}

F
| 4210 % 10> mm —
l
° 4 8 12 16 20
TIME , DAYS
4=DIAMETER OF PARTICLE
FIGURE |

DEPTH OF FALL OF PARTICLES
THROUGH WATER VERSUS TIME

PREPARED FOR

U.S. DEPARTMENT OF THE INTERIOR
OFFICE OF SURFACE MINING

DAPPOLONIA



TABLE A-12. SEDIMENT POND WV-3A (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTIUN TIME FROM HYDROGRAPH CENTERS

OETENTIUN TIME INCLUDING STORED FLOW

SEDIMENT LOAD
50

6,37 ACRE@FT
0,0 ACRE@FT
13,00 ACRESFT
6,42 ACRE@FT
15,62 ACRE*FT
13,30 FT
119,08 crs
4,01 crs
41310,3 MG/L

2301.5 MG/L

1456,9 MG/L
753,4 MG/L
95,84 z
78,90 HRS
70,81 HRS

306,00 TONS


TABLES

IDEN DILON!


FIGURES

DAPPOLON TL


-19-

than 5 microns at the peak inflow rate. The equation is dimensionless,
and units other than those indicated may be used, The equation explains
93% of the variation in the trap efficiency and all the variables are
significant at the 99.5% confidence level. Values for P50 and Pe may be
estimated using equation 4. The volume weighted average detention time
is given by:

n n
td = £ Agdt,/ AQ, (10)
isl jel +

where At; is the detention time of each plug of flow as shown in Figure

2. AQ; is the volume of each plug i, and n is the number of plugs.

Basin with a Permanent Pool

In this study no Sediment was associated with the water contained
in the permanent pool. Sediment was partitioned to the design storm
event as in the case of the dry basin. Normally the permanent pool
would contain a suspended sediment load but the purpose of this study
was to evaluate the effect of a permanent pool on the design criteria.

The following equation was developed:

E = 89.2 + 25.4(S/Q) + 1.77(P3p - Ps) (td/t..) ay

~ 1.23¢q oe /4yy)” Po)

The equation is very similar to equation 9 for a dry basin except that
the permanent storage S is more significant and the last term of the
equation will be larger as the peak outflow rate Gout is increased if

a permanent pool exists. The equation explains 90% of the variation

in the trap efficiency and again all the variables are significant at


of the amount of erosion occurring for a single storm may be obtained
with equation 1 but this knowledge is only of value if accurate esti-

mates of the delivery ratio to the downstream sediment basin can be

obtained.

Delivery Ratio

Williams (1977) suggests that estimates of delivery ratios may be
obtained by dividing predicted average annual values of sediment yield
by sheet erosion. Average annual sheet erosion can be determined through
the use of the Universal Soil Loss Equation (USLE). In a study on Little
Elm Creek basin, Williams developed a predictive equation for delivery

ratio of the form:
a 7,,\b c
DR = k (DA)* (2L)” (cn) (2)

where DR is the delivery ratio, DA is the drainage area, ZL is the relief-
length ratio, and CN is the curve number. The coefficients k, a, b and c
would need to be determined for the given location. Predictive equations
of this nature were developed for 15 Texas basins, and good estimates of
downstream sediment delivery were obtained. It appears that in large
surface mine areas, determination of a predictive equation of this nature

would be of considerable importance to the mine engineers.

Particle Size Distribution
Although the particle size gradation of soil found on a disturbed
area may be fairly uniform, the distribution of coarse and fine material

being transported downstream to a sediment basin will depend on many


3
4
z 0.18 T
s :
be {
@o
i

Q ws

26 0.16

z

§2

\e-

c.

iS lee O14 —

EE

ic

‘yl > \

iw a O12

rt Ss

~ a ~

ale °

Pars a

4 |

sl2 a 0.10

ab =

5 8
lh a MINE LIFE =I0 YRS.
1S & 0.08 f+ +
Oa 3 MINE LIFE=5 YRS.

z

zy ta

5° 5 / |

—— w O06]
a MINE LIFE =2YRS,
iy}

MINE LIFE =!1YR.
0.04

0.02 |

10 12 14 16 18 2.0
DESIGN VOLUME RATIO (Vg / Vg!)
FIGURE 5
MINE 3
NOTES: EXPECTED OVERFLOW
DESIGN VOLUME
|. Vg = DESIGN VOLUME OF POND PREPARED FOR

FOR MULTIPLE EVENTS.

U.S DEPARTMENT OF THE INTERIOR
2. Vg°= DESIGN VOLUME FOR 10-YEAR OFFICE OF SURFACE MINING

STORM.

oe
3. COST RATIO = DESIGN VOLUME RATIO. DAPPOLONIA

GPO o4ges23


TABLE A-4. SEDIMENT POND WV-1A (15 yr. storm)

PERMANENT POOL CAPACITY

DEAD

STORAGE

STORM RUNOFF VOLUME

STURM VOLUME DISCHARGED

POUND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RAVE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLUNW

SEDIMENT LOAD

38

CONCENTRATIUN

6,353 ACRE@FT
0,9 ACRE@FT
21,59 ACRE@FT
15,00 ACREOFT
22,95 ACRE@FT
15,34 aT
99,93 Ces
6,44 crs
22654,9 MG/L

[is95.6 MG/L]

824,66

587,9

94,26

57.58

26,08

52,20

294,00

MG/L

MG/L

%

HRS

RKS

HRS

TONS


TABLE A-14. (continued)

PERMANENT POOL CAPACITY a 6.42 ACRE FT
DEAD STURAGE s 0,0 ACREOFT
STURM RUNOFF VOLUME 2 22,56 ACRE@FT
STORM VOLUME DISCHARGED s Seid ACRE@FT
PUND VOLUME AT PEAK STAGE e 15,93 ACRE@FT
PEAK STAGE = 22,17 eT
PEAK INFLOW RATE = 153,03 CFS
PEAK DISCHARGE RATE od 1,63 crs

PEAK INFLOW SEDIMENT CONCENTRATION = [rezoe,4 MG/L]
PEAK EFFLUENT SEDIMENT CONCENTRATION =

STORM AVERAGE EFFLUENT CONCENTRATION =  3032,0 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATIUN 2 1398.6 MG/L
BASIN TRAP EFFICIENCY = 96,07 %

DETENTION TIME OF FLOW WITH SEDIMENT s 78,76 HRS
DETENTION TIME FROM HYSROGRAPH CENTERS = 3 (40,59 ARS]
DETENTION TIME INCLUDING STCRED Fuus ” 68,87 HRS

SEDIMENT LOAD

#

349,00 TONS


TABLE A-8. (continued)

PERMANENT POOL CAPACITY s

DEAD STURAGE

STURM RUNOFF VOLUME

STORM VULUME DISCHARGED 5
POND VULUME AT PEAK STAGE s
PEAK STAGE ®

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION s
PEAK EFFLUENT SEDIMENT CONCENTRATIUN =
STORM AVERAGE EFFLUENT CONCENTRATION 5

AVERAGE EFFLUENT SEDIMENT CUNCENTRATION

BASIN TRAP EFFICIENCY w

DETENTION TIME OF FLOW WITH SEDIMENT a

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTIUN TIME INCLUDING STORED FLUW =

SEDIMENT LUAD

45

23,90

19,39

24,54

15.77

117,46

3,43

6184.6

397.9

172.6

141,8

94,65

52,14

ACREOFT

ACRE@FT-

ACRE@FT

ACRE@FT

ACRE@FT

FT

CFs

MG/L

MG/L

MG/L

MG/L

%

HRS

47,48

85,00

HRS

TONS


TABLE A-5. SEDIMENT POND WV-1B (5 yr. storm)

PERMANENT PUQL CAPACITY 2 6.42. ACRESFT
DEAD STORAGE s 0,0 ACRE*FT
STORM RUNOFF VOLUME 2 8,47 ACRE@FT
STORM VOLUME DISCHARGED ® 2.05 ACRE*FT
POND VOLUME AT PEAK STAGE a 12,30 ACRE*FT
PEAK STAGE 8 19,52 FT
PEAK INFLOW RATE 2 112,13 crs
PEAK DISCHARGE RATE = 2.31 crs

PEAK INFLUW SEDIMENT CONCENTRATION 100058,5 MG/L

PEAK EFFLUENT SEDIMENT CONCENTRATION = & 16696,4 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION s 4013.9 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION ®& 1015,8 MG/L
BASIN TRAP EFFICIENCY 2 97,85 x
DETENTIUN TIME OF FLOW WITH SEDIMENT 2 44,11 HRS!
DETENTION TIME FROM HYDROGRAPH CENTERS s 19,18 HRS
DETENTION TIME INCLUDING STORED FLOW . 40,30 HRS
SEDIMENT LOAD s $20,00 TONS

4O


EVALUATION OF PERFORMANCE CAPABILITY
OF SURFACE MINE SEDIMENT BASINS

By:
Charles E. Ettinger
and
Joseph E. Lichty

SKELLYanc LOY
2601 North Front Street
Harrisburg, Pennsylvania 17110

Contract Number 68-03-2677

Project Officer:
Roger C. Wilmoth
Resource Extraction and Handling Division
Industrial Environmental Research Laboratory

on hee nor

.

a byarbom, Street
Performed for:
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
Office of Research and Development
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

Cincinnati, Qhio 45268


TABLE A-19. SEDIMENT POND KY-1A (5 yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION
PEAK EFFLUENT SEDIMENT CONCENTRATION
STORM AVERAGE EFFLUENT CONCENTRATION
AVERAGE EFFLUENT SEDIMENT CONCENTRATION
BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT
DETENTION TIME FROM HYDROGRAPH CENTERS
DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD
61

1,50 ACRE@FT
0,0 ACRE@FT
2.41 ACRE@FT
0,92 ACRE@FT
3,09 ACRE@FT
10,20 FT
27,51 crs
0,74 CFS

[1070.5 MG/L]

59000 MG/L
47006 MG/L
186,6 MG/L
95,79 x
33,30 HRS
28,93 HRS
14,00 TONS


-31-

DEPOSITS and WASH. The costs of studies with such programs is low and
computer access in most areas can be obtained easily.

The objectives of the new legislation appear sound. The wording
of the law makes it sufficiently flexible that compliance by mine op-
erators is feasible in most areas. Much of the terminology used in the
law however needs defining and parts of the legislation need amending.
Sizing of basins is based upon several conflicting criteria. I1f basins
are designed to comply with all the requirements of the new legislation,
the hydrologic balance on most watersheds will be severely affected, as
large impoundments will be required to satisfy water quality standards.
The long term effects of using chemical agents needs to be studied.
Compliance with the 70 mg/% water quality standard appears difficult.
The price will be high and the long term benefits dubious. It is doubt-
ful that sediment ponds will provide the solution to better downstream

water quality over the long term.

REFERENCES

Brune, G. M. 1953, Trap Efficiency of Reservoirs. Trans. American
Geophysical Union 34(3):407-418.

Curtis, D. C. 1976. A Deterministic Urban Storm Water and Sediment
Discharge Model, Proc. National Symposium on Urban Hydrology and
Sediment Control, University of Kentucky, Lexington, Kentucky.
July 27-29,

Environmental Protection Agency. 1976. Erosion and Sediment Control.
Surface Mining in the Eastern U.S., EPA-625/3-76-006.

Graf, W. ul. 1971. Hydraulics of Sediment Transport. McGraw-Hill,
New York.
Haan, C. T. 1970. A Dimensionless Nydrograph Equation. Unpublished

Paper, Agricultural Engineering Department, University of Kentucky,
Lexington, Kentucky.


TABLE 1

DESIGN PARAMETERS OF THE
THREE REPRESENTATIVE SURFACE MINES

Design Parameters Mine #1 Mine #2 Mine #3
Effective Drainage Area (acres) ‘)) 80 650 80
Disturbed Area (acres) 20 425 40
10-YR, 24-HR Precipitation (inches) 4.37 > 4.3 3.8

Run-off (inches) 1.904 1.904 1.528
5-YR, 24-HR Precipitation (inches) 3.8 3.8 3.3
Run-off (inches) 1.528 1.528 1.173
2-YR, 24-HR Precipitation (inches) 2.9 2.9 2.55
Run-off (inches) 0.898 0.898 0.681
1-YR, 24-HR Precipitation (inches) 2.6 2.6 2.15
Run-off (inches) 0.712 0.712 0.461
TSS in Runoff (mg/£) 2100 2100 360
Percentage Passing for 70 mg/£ 3.3 3.3 20
Minimum Particle Size (mm) 1.3 x 1073|1.3 x 10°} 8 x 10°

(1) Effective drainage area accounts for runoff which is diverted and
not allowed to enter the sedimentation pond.

IDI IPOLONI


TABLE A-22. (continued)

PERMANENT POOL CAPACITY 2 1,50 ACRE®FT
DEAD STURAGE 2 0,0 ACRESFT
STORM RUNOFF VOLUME a 2,92 ACRE@FT
STORM VOLUME DISCHARGED . i,t ACRE@FT
POND VOLUME AT PEAK STAGE 2 3.93 ACRE®FT
PEAK STAGE 3 12,24 FT

PEAK INFLOW RATE s 41,47 crs
PEAK DISCHARGE RATE = 0.39 crs
PEAK INFLOW SEDIMENT CUNCENTRATION = [53648,1 MG/L
PEAK EFFLUENT SEDIMENT CONCENTRATION . 2374,5 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION = 150646 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION ©& 665.5 MG/L
BASIN TRAP EFFICIENCY 2 97,66 x
DETENTION TIME OF FLOW WITH SEDIMENT 2 95,71 HRS

DETENTION TIME FROM HYDROGRAPH CENTERS &

OETENTIUN TIME INCLUDING STORED FLOW 2 65,73 HRS

SEDIMENT LUAD a 97,00 TONS
66


1) Equipment production rates were calculated from the "Cater-
pillar Performance Handbook"16

2) Labor costs were computed from UMW/BCOA 1979 rates. '7

3) All construction was assumed to be performed by the operator 18
with typical mining equipment.

4) Pipe costs and installation was taken from "1979 Dodge Guide
to Public Works and Heavy Construction Costs".

5) Ali construction materials were available from the site.
6) Access roads to the sites were not included in the costs.

7) Sediment removai was not anticip2ted with the yeilds predicted
and the storage volume used in the designs.

8) All costs are in 1979 dollars with no inflation factor for
reclamation costs.

Table 9 is a summary of costs for sediment pond construction, ana
reclamation for the represeiitative pond location and sizes. The acre-feet
of storage available at the respective embankment elevations for each pond
is also tabulated. Figures 5 and 6 present graphs of available storage
versus total cost for sediment ponds constructed at locations A and B.
Table 11 is a summary of the estimated construction costs derived from
Figures 5 and 6 for the ponds used in the study.

TABLE 9. ESTIMATE Of KMBANKMENT SEDIMENT POND COSTS

Embankment Storage Cost ($)
Site height (ft)  (ac-ft)  Construction* Reclamation Total
A 20 20.0 25100 10600 35700
25 48.0 37800 15000 52800
30 86.0 53500 19200 72700
B 15 2.75 10800 2800 13600

20 15200 3400 18600
25 21300 4900 26200
30 37700 7100 44800

* Includes materials

TABLE 10. ESTIMATE OF EXUxVATED SEDIMENT POND COST

Storage Cost ($)
Size (ft) sss fac-ft) Construction Reclamation Total
200x200x 10 10.1 16200 7500 23700



TABLE 11. SUMMARY OF ESTIMATED COST FOR STUDY PONDS

Storage Cost
Pond (ae-ft) ($)
PA-1 10.1 23,700
WV-1A 29.0 42,000
WV-~1B 18.0 37,000
Wv-2A 51.3 54,000
WV-2B 13.1 27,000
WV-3A 21.1 38 ,000
WV~3B 18.4 38,000
WV-4A 42.7 51,000
WV-4B 5.9 17,000
KY-1A 6.4 18,000
KY-1B ay 16,000

29


TABLE A-20. SEDIMENT POND KY-1A (1G yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIEICY

OETENTION TIME OF FLOW WITH SEOIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STOREQ FLOW

SEOIMENT LOAD

1,50 ACRE@FT
0,0 ACRE@FT
3,62 ACRE@FT
2,12 ACRESFT
4,28 ACRECFT
12,68 FT
44,66 CFS
0,74 crs
10430.7 MG/L
o46,5 MG/L
390,5 MG/L
235.1 MG/L
94,88 x
44,ag HRS



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TABLE A-13. SEDIMENT POND WV-3B (5 yr. storm)

PERMANENT POOL CAPACITY

DEAD STURAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION
PEAK EFFLUENT SEDIMENT CONCENTRATION
STORM AVERAGE EFFLUENT CONCENTRATION
AVERAGE EFFLUENT SEDIMENT CONCENTRATION
BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT
DETENTION TIME FROM HYOROGRAPH CENTERS
DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD
52

6,42 ACRESFT
0.0 ACRE@FT
8,72 ACREmFT
2.30 ACRE@FT
12,44 ACRE“FT
19,62 FT
115,43 CFS
2,38 CFs
73273,6 MG/L
4980.0 MG/L
3127.0 MG/L
865,5 MG/L
97,51 x
42,52 HRS

38,54

392,00

HRS

TONS


Dr. Mark Boster 6 August 2, 1979

of all combinations of the storm events considered and evaluating the
potential overflow for varying pond sizes which are greater than that
required to hold the 10-year storm. Using this technique, the utility
of a given decision and possible outcomes was taken to be the expected
value of overflow for a given pond size. Expected value from any given
event is defined as the quantity of overflow times the probability of
the overflow occurring. It is noted that expected overflow is a measure
of utility for decision making and has no physical significance once any
particular event occurs. Summed over all possible outcomes, the expected
overflow represents the most probable amount of overflow. The physical
significance of additional pond capacity is designated by the ratio of
the total design volume to the 10-year-storm volume where this ratio is
always greater than or equal to 1.0.

For estimating the increased costs associated with large pond sizes, the
methods used for the OSM cost impact study for the Regulatory Analysis
were followed. In the absence of site-specific information relative to
topography and general mine layout, the cost estimate was found to be
essentially directly proportional to volume. Site~specific consideration
could, of course, lead to significant variations compared with this
methodology on a case-by-case basis. Because the costs are essentially
directly proportional to pond capacity, the ratio of total design volume
to the 10-year-storm volume is also the ratio of cost for the larger
volume compared to cost for the pond designed to hold the 10-year storm.
This is true whether the increased pond capacity is provided as a single
larger pond or as two separate ponds. Consequently, the determination
of expected overflow as a function of increased pond size is also a
measure of the cost effectiveness of providing additional pond capacity
for multiple storm events.

Knowing the combined probability, the expected overflow for. any combina-~
tion of two storms is given by:

E (N, R) = Pr (N, R) * (Ry + RR ~ VQ)
where

E (N, R) = Expected overflow due to two storms
having return periods N- and R-years,
respectively, occurring within a speci-
fied cycle time and mine life;

Pr (N, R) = Combined probability of occurrence
of two storms within a given cycle
time and mine life having return
periods N- and R~years, respectively;

YUP IX DLONILA


TABLE A-15. SEDIMENT POND WV-4A (5 yr. storm)

PERMANENT POOL CAPACITY

OEAD STURAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDRUGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEOIMENT LUAD

41,93 ACRE*FT
0.0 ACRE@FT
10,77 ACRE®FT
8.83 ACRE@FT
8,97 ACRE@FT
11,12 FT
42,29 crs
3,87 crs
15103,8 MG/L
1236.1 MG/L
507,7 MG/L
420.9 MG/L
93,52 x
24,47 HRS

23,31

94,00

HRS

TONS


-21-

the 99.5% level. When developing the design criteria, sediment con-
tained in the permanent pool prior to the design event should be allocated
to the base flow or storm events prior to the event being evaluated. The
volume of flow stored in the basin should be included in the routing of

the storm event through the basin.

Basin with a Permanent Pool and Base Flow

If no flow is considered following the design event, a portion of
the design storm equivalent in volume to the permanent storage of the
basin will remain in the basin. Frequently this remaining volume will
contain a very high suspended sedima@t load. If a flow condition occurs
within a few days of the storm event much of this suspended load will be
discharged from the basin. For a perforated riser there is normally
discharge from the basin most of the time except in very dry periods.
Even with a drop inlet riser there is usually flow between storm events
due to pumping from mine areas or due to the fact that most basins are
located on small streams and creeks. The amount and rate of the base
flow following a storm event will determine how much additional sedi-
ment discharge will occur. In this studya base flow of 1 cfs for 48
hours was simulated for basins A, B and C and a flow rate of 2 cfs for
48 hours on basins D and E. Exerat for basin D which has a permanent
storage of nce.rly 16 acre-feet, the base flow replaced all or most of
the storm flow previously stored in the basins.

The following predictive equation was obtained:

= * pk

E = 93.1 + 27.6(S/Q) + 0.046(P5, - PS) (td/t..) a2)

_ * 0.3
1.4 Poy (Que / 45)


The settleable solids (settleable matter)! test requires that
water samples be placed in an Imhoff Cone and undergo a one hour period of
quiescent settling. Based upon Stoke's Law, assuming a water temperature
of 10° c and a particle density of 2.65 g/cm » all particles greater than
.012 mm should settle during the test. Referring to Table 8, it can be
seen that in all cases that particles greater than .005 mm were removed.
Therefore, under the conditions modelled, all settleable solids should be
removed by ponds designed to meet OSM criteria.

SEDIMENT POND CONSTRUCTION COST ANALYSIS

A cost analysis of embankment type sediment pond construction was
performed for two topographical conditions, simulating sites A and B. The
topography at site A represented a location downstream of the disturbed area
where a U-shaped valley and moderate slopes occur. Site B represents a
V-shaped valley with steep side slopes, typical of the topography found
immediately below mine areas in Appalachia.

To generate cost curves for sites A and B, three sizes of ponds
were costed for site A and four sizes were costed for site B. A third site,
representing a totally excavated pond for PA-1, was analyzed adjacent to the
disturbed area of a modified area mine.

The sediment pond cost analyses for the representative sites
included both construction and reclamation of the ponds.

The construction phase consisted of move-in and erection of
equipment, clearing and grubbing, topsoil removal and storage, drill bench
construction, drilling and blasting, excavation, embankment placement and
grading, pipe placement, spillway construction and material costs. Recla-
mation included removal of the embankment, removal of spillway structures,
final grading to contour, topsoil replacement and revegetation.

Since the site for PA-1 was a totally excavated pond, drill bench
construction and drilling and blasting operations were excluded.

For each of the eight representative ponds, material handling
requirements and equipment production rates were determined for each
operation involved. From this, operation times (in hours) were determined
for both equipment and labor. The hourly cost for equipment ownership and
depreciation, labor, and equipment operation were applied to the operation
times to arrive at a cost for each operation.

Presented below are the o.-.'all methods and assumptions entered
into this cost analysis:

25


Cuidelines as to how these parameters may be estimated are pre-
sented in this paper. Clarificationon some sections of the law have
been attempted,and several amendments have been made since passage of
the law in 1977. The 24-hour detention period restriction has been
relaxed provided mine operators can demonstrate that basins will satis-
fy the quality standards of 70 mg/2% during storm events and 35 mg/2 aver-
age during 30 consecutive discharge days. It appears that some of the
regulations pertaining to spillway discharge rates need to be revised.
A 25-year, 24-hour precipitation event will usually have a higher peak
runoff rate than a 100-year, 6-hour event. A 25-year, 6-hour event, how-
ever, will produce peak rates lower than those already provided for by
the 10-year, 24-hour design event. In fact, the peak rates from the 10-
year, 24-hour event will be very similar to the peak rates produced
from a 100-year, 6-hour event on many watersheds.

In addition to providing guidelines on how to quantify the water—
shed hydrologic parameters that might occur on surface mine areas, pre-
dictive equations ure presented for estimating peak effluent sediment
concentrations and basin trap efficiency. Care should be taken in us-
ing these equations as all the data were generated by the DEPOSITS
model (Ward, Haan and Barfield, 1977a). The model does not adequately
account for basins in which there is considerable turbulence, short
circuiting or resuspension of deposited sediment. The coefficient of
determination for all the equations that are presented is greater than
0.9 but, unless great care is taken in estimating the parameters used

in each cquation, poor estimates of actual basin performance may be obtained.



The use of the DEPOSITS model requires the input of certain
specific information pertinent to the evaluation of sediment pond effi-
ciency, such as:

1. inflow hydrograph of storm event under study,

2. amount of sediment delivered to the pond during
the storm event,

3. characteristics of the sediment, and
4. physical characteristics of the sediment pond.

Each of these factors -- and hence the determination of sediment pond
performance during various storm events -- is inherently site-specific.

The DEPOSITS model will determine sediment removal efficiencies for given
erosion and sediment delivery to a sediment pond under a given storm con-
dition. The methodology used to compute input to the model is delineated in
subsequent sections of this study.

Expected TSS effluent concentrations are reported for each of the
six mines under different conditions relating to: (1) proximity of the pond
to the disturbed area (active pit, regraded area, and valley fill); (2)
detention times, and (3) return frequency of storm events. The sediment
ponds were modelled at two locations at each mine. The first location, A,
is the actual position of the pond as it exists at the mine site. In most
cases, the pond is located a substantial distance downstream from the
disturbed area where construction of a large structure is less restricted by
severe topographic constraints. At this location the pond also collects
runoff from undisturbed areas of the watershed.

The second location, B, was selected as close to the disturbed area
as possible to minimize the storage requirement. This location was selected
based on familiarity with site~specifiec conditions. In four out of six
cases, this was immediately adjacent to the toe of a valley fill. When
modelling location B, it was assumed that undisturbed drainage from above
the mining area was diverted around the sediment pond.

The eleven sediment ponds were modelled to determine pond per-
formance for detention times (time between hydrograph centers) of 24 hours
and greater (up to 45 hours) for the runoff from a 10-year 24-hour storm
event. As a final determination of pond removal efficiency, each sediment
pond was modelled for pond performance during the passage of a 2-year and
5-year, 24-hour storm event. In all cases under study, the ponds were
designed in accordance with design criteria established by the Office of
Surface Mining (OSM).

In addition, this study includes an analysis of the costs for con-
struction, maintenance and reclamation of each sediment pond, the results of
which are detailed in the study results section.


-20-

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11

TABLES

Determination of Estimated Runoff Volume
and Peak Rate for Determining Sediment Loads

Summary of Topographic Factor (LS) for
Modified USLE . 2... 2 ee ee ee eee

Cover and Management Factors (C) for
each Land Cover Type... . 1... ee eee

Summary of Sediment Loads Using Modified USLE
Watershed Composite Curve Numbers ......
Watershed Characteristics ........4..
Summary of Simulated Sediment Pond Performance
Particle Size Distribution of Pond Effluent .
Estimate of Embankment Sediment Pond Costs . .
Estimate of Excavated Sediment Pond Cost .. .

Summary of Estimated Cost for Study Ponds ..

vii

11

12
13
15
23
24
26
27
27
29


TABLE A-16. SEDIMENT POND WV-4A (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD STURAGE

STORM RUNUFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDRUGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LUAD

1.93

9,0

17,89

15,77

17,09

13,90

94,78

2,58

ACRESFT
ACRESFT
ACRESFT
ACRE@FT
ACRE®FT
FT

crs

CFS

17118,7 MG/L

1174.4 MG/L
435,48 MG/L
390.7 MG/L
94,4 x
49,62 HRS
39,50 HRS
47,61 HRS

167,00 TONS


-16-

to provide a 24-hour detention time for a 10-year, 24-hour storm event.
The feasibility of placing large size basins on most Eastern surface

mines is remote.

BASIN TRAP EFFICIENCY
Conventionally, basin trap efficiency has been estimated either through
use of an empirical curve developed by Brune (1953) or by a method adopted
by the EPA (1976). Brune's curve are based upon large reservoir data and
give poor estimates of small basin performance. The EPA method, if used
carefully, may give reasonable estimates of basin performance for steady

flow conditions. The following equations describe the method:
A= Q,/V, (6)

where A is the basin size in m?, Qa is the overflow rate through the
pond (m3/sec) and V, is the critical settling velocity m/sec. The EPA
recommend that the desired basin size be multiplied by 1.2 to account
for non-ideal settling. Vg may be calculated for a particular particle

size by using Stoke's Law:
ve = (g/18u) (S - D bp? (7)

where g is the acceleration of gravity (981 cm/sec”), yu is the kinematic
viscosity of a fluid (cm*/sec?) and D is the particle diameter (cm). Qo
is frequently determined in two ways:

1. Qo 2 volume inflow/storm duration (8)

= Q/tey where Q and tee are converted to the appropriate units.


TABLE A-18. (continued)

PERMANENT POOL CAPACITY

DEAD STURAGE

STURM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEOIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD

60

1.94 ACRE@FT
0,0 ACREWFT
3,62 ACRE@FT
1,60 ACRE@FT
4,96 ACRESFT
12,80 FT
51,64 crs
0,48 CFS
165327,4 MG/L!
4955,8 MG/L
2321,9 MG/L
97,09 x
92,26 HRS
42,57 HRS
61,85 HRS
372,00 TONS


Table 1. Rainfall and Runoff for 10-Year, 24-Hour Rainstoms.

10-Year, 24-Hour Stonn

Watershed Curve Volume
“Area Slope Number Rainfall Runoff Peak Rate Runoff
(acres) (%) CN (inches) (inches) (cfs) (acre-ft)

75 15 60 4.0 0.77 29 4.8
5.0 1.32 59 8.3
6.0 1.94 95 12.1
70 4.0 1.35 83 8.4
5.0 2.06 133 12.9
6.0 2.84 187 17.8
80 4.0 2.06 169 12.9
5.0 2.92 241 18.3
6.0 3.82 314 23.9
75 30 60 4.0 0.77 37 48
5.0 1.32 74 8.3
6.0 1.94 118 12.1
70 4.0 1.35 104 8.4
5.0 2.06 165 12.9
6.0 2.84 231 17.8
80 4.0 2.06 169 12.9
. 5.0 2.92 241 18.3
6.0 3.82 314 23.9
200 15 60 4.0 0.77 56 12.8
5.0 1,32 113 22.0
6.0 1.94 183 32.3
70 4.0 1.35 149 22.5
5.0 2.06 242 34.
6.0 2.84 344 47.3
80 4.0 2.06 368 34,3
5.0 2.92 525 48.7
6.0 3.82 688 63.7
200 30 60 4.0 0.77 78 12.8
0 1.32 159 22.0
6.0 1.94 255 32.3
70 4.0 1.35 221 22.5
5.0 2.06 355 34.3
6.0 2.84 500 47.3
80 4.0 2.06 452 34.3
5.0 2.92 643 48.7
6.0 839 63.7



Dr. Mark Boster 4 August 2, 1979

and neglecting the effects of the time of inflow and outflow require-
ments. Site-specific conditions of topography, mining operations, pond
location and geometry, influent rate and location and discharge rate
must all be considered in an actual situation to judge the ability to
meet given influent limitation by sedimentation alone. Also, detailed
fluid dynamic considerations relative to mixing and induced turbulence
will affect the theoretical efficiency of a sedimentation pond. Rig-
orous treatment of all of these parameters are beyond the scope of this
study. Thus, the area requirements shown in Figure 2 may be considered
as the minimum requirements for the respective sites.

If the volume of runoff from a multiple storm event leads to additional
pond volume, it has been assumed that the additional volume would be
provided in a second pond so that influx from the second storm would
not mix with it until at least some time has been allowed for sedimenta-
tion of the additional water to minimize the effect of mixing on sedi-
mentation that had already taken place in the basic pond. Thus, any
overflow of pond capacity resulting from a second storm has been assumed
to occur in the second pond providing additional storage so as not to
mix with water already partially treated. The effect of this assumption
on costs is no different than if a single pond is used because total
cost is basically proportional to total storage volume without detailed
knowledge of site-specific conditions. The basic pond volume was con-
sidered to be that required to hold the 10-year, 24-hour storm in
accordance with OSM regulations plus 0.1 acre-foot of sediment storage.

Multiple Storm Events

A probabilistic approach was used to evaluate the effects of a multiple
storm scenario. It was decided that a maximum combination of two storms
having return periods as specified below, occurring within a specified
cycle time, would be considered. More storms can, of course, be postu-
lated and may even occur. However, the probabilities of more than two
storms occurring within the cycle times are sufficiently small to be
considered too remote for consideration. The methods used can, however,
be applied to any number of storms desired.

Four storm return periods were used in the analysis. They are:

One-year, 24-hour storm (1-year storm),
Two-year, 24-hour storm (2-year storm),
Five-year, 24-hour storm (5-year storm),
Ten-year, 24-hour storm (10--year storm).

Because the probability of occurrence of two storms within a given cycle
time is also dependent on the life of the surface mining project, the
mine life was used in the analysis. Four different mine lives, respec—
tively spanning 1, 2, 5 and 10 years, were considered in the analysis.

DAPPOLONIA


Dr. Mark Boster 8 August 2, 1979

"Probability of Occurrence Points
None 0
Insignificant 1-4
Unlikely 5-9
Likely 10-14
Occurred is"

This appears to state that the larger the storm event for which a pond
is designed such that the probability of the event is considered, the
lesser the penalty in case of a violation. However, because no prob-
ability values are given and there is no event with a probability of
zero, there will always be a penalty if a pond capacity is exceeded.
This makes it difficult to decide on a design criteria in view of
probabilities calculated above. This is important because Figures 4
and 5 show that the incremental cost for additional capacity becomes very
large compared with incremental benefits as measured by the decreased
expectéd overflow once the pond reaches a certain size. In other words,
the cost/benefit ratio increases greatly as the design is based on
events with smaller and smaller probabilities.

Because there is always a probability of having a pond overflow from
multiple storm events and the total suspended solids in the overflow
will not meet the effluent limitations, there is no basis for selecting
a pond size which, even theoretically, will treat all runoff from every
possible single or multiple storm event. For the case of single storm
events, this fact has been recognized in the regulations by the release
from the effluent limitations if a 10-year, 24-hour storm or greater
occurs. However, for the case of multiple storms leading to overflow
from the second storm before the required retention time is complete
for the first storm, there is no release from the effluent limitations.

On a practical basis, an operator is faced with deciding how large a
sedimentation pond should be, recognizing that no matter how large he
makes it, he must always accept a risk of exceeding the capacity due
to multiple storm events even though that risk is small and becomes
smaller as the pond capacity increases. If a risk-benefit approach is
used to select pond capacity, Figures 4 and 5 can provide guidance. For
a 20 percent increase in capacity (WQ/Vqt® = 1.2), there is a signifi-
cant reduction in risk of overflow. From a 20 percent increase to a
40 percent increase, there is a lesser but still significant reduction
in risk of overflow. Beyond a 40 percent increase, the risk reduction
diminishes greatly from the same incremental costs. On the basis of
Figures 4 and 5, it would appear that the optimum risk-benefit decision
would be to increase pond capacity about 30 to 40 percent.

Based on optimizing the risk-benefit, the increased costs for designing
for a multiple storm event are approximately 30 to 40 percent higher

than the costs for a pond designed to meet existing regulations for the
10-year, 24-hour storm. To maintain the same treatment cycle time for

ID2AUPLOILON LE


13.

we

15.

16.

17.

U.S. Weather Bureau. 1960. Rainfall Frequency Atlas for the United
States, Technical Paper No. 40.

Ward, A., Haan T. and Tapp, J. 1979. The Deposits Sedimentation Pond
Design Manual. Institute for Mining Minerals Research, Kentucky Center
for Energy Research Laboratory, University of Kentucky, Lexington,
Kentucky.

Williams, J.R. 1975. Sediment-Yield Prediction with Universal Soil
Loss Equation Using Runoff Energy Factor. Present and Prospective
Technology for Predicting Sediment Yield and Sources. In: Proceedings
of the Sediment Yield Workshop, ARS-S-40, U.S. Department of Agricul-
ture Sedimentation Laboratory, Oxford, Mississippi. 244-252 pp.

Williams, J.R. 1978. A Sedimentgraph Model Based on an Instantaneous
Unit Sedimentgraph. Water Resources Research, Vol. 14, No. 4, August
1978. 659-664 pp.

Wischmeier, W.H., and Smith, D.D. 1978. Predicting Rainfall Erosion

Losses - a Guide to Conservation Planning. U.S. Department of Agricul-
ture, Agriculture Handbook No. 537.

33


—

78-334 -Al5

"A DRAWING

Be [NUMBER

Aus 2

a

CHECKED BY
8 - 1-79] APPROVED BY | es

ck

DRAWN
BY

550pe—= 55

500f- 50 sp ———
|
|
450R- 45 ae ie - —
400f- 40 ap sa—t --4
6
a « |_—-MINE MODEL |
@ 3507-9 35 — -
& Ss Dyn = 1.3 x 1073 mm
4 ° TSS= 2100 mg/I
N 300fF-230
w s
z n
=
= 250;-2 25 MINE MODEL 2
w = Duin = 13 x1073 mm
< q TSS=2100 mg/l
a
Z 200}-& 20
& 2
2
co}
1I50F-% 15
MINE MODEL 3
100k 10 —Dwin = 8x 1073mm 4
TSS = 360 mg/!
50F— 5 t—
es
oh} o —
ie) 4 8 12 16 20 24
RETENTION TIME (DAYS)
FIGURE 2
MINES.|, 2, & 3
THEORETICAL AREA REQUIREMENTS
NOTE: FOR RUN-OFF RETENTION
—S OF A I0-YEAR STORM
Dwin = MINIMUM PARTICLE SIZE TO BE PREPARED FOR
REMOVED TO OBTAIN 35 mg/Ii TSS IN
EFFLUENT FOR IDEAL CONDITIONS. U.S. DEPARTMENT OF THE INTERIOR

OFFICE OF SURFACE MINING

DAPPOLONIA



TABLE 2

Combined Probabilities, Pr (N, R),
of Two Storms Occurring Within
a Given Cycle Time and Mine Life

Mine BE vieat Seorm cf Second Scorn Pr (N, R) for cycle time = _
ure N-years Reyears 2 days 10 days
. 1 0.344 x 1072 0.169 x 107)
2 0.173 x 10? 0.854 x 107
2 5 0.692 x 1079 0.344 x 1072
10 0.346 x 107? 0.173 x 107?
1 0.214 x 107? 0.105 x 107?
2 2 0.108 x 1072 0.532 x 107?
5 0.431 x 107? 0.214 x 107?
, 10 0.215 x 107? 0.108 x 1072
1 0.988 x 107? 0.483 x 1072 |
5 2 0.495 x 107? 0.245 x 107?
5 0.198 x 107? 0.988 x 10°?
10 0.993 x 107% 0.495 x 107?
0.519 x 107? 0.254 x 107?
10 2 0.260 x 107? 0.129 x 107?
(0,095)* 5 0.106 x 1079 0.519 x 107?
10 0.523 x 1074 0.260 x 107?
1 0.471 x 107? 0.230 x 107+
1 2 0.236 x 1072 0.117 x 107)
5 0.947 x 10> 0.471 x 1072
10 0.474 x 107? 0.236 x 1077
1 0.364 x 1072 0.169 x 107?
2 2 0.173 x 107? 0.854 x 107?
5 0.692 x 1079 0.344 x 107?
> 10 0.346 x 107? 0.173 x 107?
1 0.180 x 107? 0.879 x 10°?
5 2 0.901 x 107? 0.645 x 107?
. 5 0.361 x 107? 0.180 x 1072
10 0.182 x 207? 0.901 x 107?
1 0.988 x 1079 0.483 x 107?
10 2 0.495 x 107? 0.245 x 107?
(0.191)* 3 3
5 0.198 x 10 0.988 x 10
10 0.993 x 107 0.495 x 1079

* Munbere in parentheses are the probability of having a 10-year, 24-hour storm within the mine
Mfe.

DVPIPOLON ILA


-17-

2. Qo is equal to the peak inflow rate qin (in the appropriate
units.

If the particle size distribution of the inflowing sediment is
estimated at or near the peak inflow rate, the second method may give a
good estimate of the actual basin performance. Several predictive equa-
tions have been developed by Ward, Haan and Barfield (1977). These equa-
tions are shown in Table 4. The equations are fairly difficult to use
and care should be taken to read the original publication. In this study
dimensionless equations have been developed based upon the simulation
conditions described earlier. No ‘bad’ points were removed from the
analysis. Several basins however were 'flooded' by the design event
and no data points were generated for this condition. Flooding occurred

when. the peak discharge of the outlet riser was exceeded - indicating

flow through the emergency spillway.

Dry Basin

Based on 288 sets of data the following regression equation was

developed:

E = 92.5 + 13.2(S/Q) + 1.9(P5q - Ps) (td/t..) (9)
~ L4G / agg)? ? Py")

where E is the trap efficiency (4%), S is the basin capacity up to the
riser crest (acre-ft), Q is the inflow volume (acre-ft), td is the volume

welghted average detention time (hrs), t is the storm duration (hrs),

st

q is the peak outflow rate (cfs), Vin the peak inflow rate (cfs), Poo

out

the % finer than 20 microns at the peak inflow rate and PS the % finer


Because the USLE was initially developed to account for yearly
sediment yields from agricultural lands, modifications of this formula are
advisable to compute sediment delivery to coal mine sediment ponds during
specific storm events. From analysis of runoff and soil loss from small
single-cropped watersheds, Williams developed a Modified Universal Soil Loss
Equation (MUSLE) that eliminated the need for sediment delivery techniques
by replacing the rainfall energy factor (R) with a runoff gperey factor that
is a function of the volume and peak rate of storm runoff. This runoff
energy factor also allows the MUSLE to be used to estimate sediment yield
from various storm events. This modified USLE is used in this study to
estimate the total sediment delivered to the sedimentation ponds for various
rainfall events.

It is recognized that the USLE, even with the modifications dis-
cussed below, is not a perfect predictive tool regarding sediment delivery
to coal mine sediment ponds; it is believed that the equation will over-
estimate the amount of sediment delivered to a sediment pond. However, this
formula is the best available, in the absence of detailed site-specific
data. A recent study by Miller and Veon prepared for Pennsylvania Depart-
ment of Transportation showed that MUSLE had the best correlation (r2 =
0.84) and smallest error of all sediment yield models tested for over 200
highway construction sites. 5 This type of construction may closely corre-
spond to the situation encountered at surface mines.

Soil Loss Equation
The modified USLE developed by Williams utilizing the runoff energy
concept for sediment yield and delivery is shown by the following relation-
ship:
Y= 95 (vap)-56 — K(LS)¢P
where,

Y is the total sediment delivered from the watershed (tons)

(VQp).56 is the runoff energy factor consisting of V, the
runoff volume (acre-feet) and Qp, the runoff peak (cfs)

K is the soil erodibility factor

LS is the slope length-steepness factor
C is the cover and management factor

P is the support practice factor

A discussion of the methodology and assumptions used to determine
these parameters follows.


Dr. Mark Boster 9 August 2, 1979

the larger pond, the same depth would have to be maintained. Thus, the
areas shown on Figure 2 as a function of retention time for treating
the 10-year storm would have to be increased by 30 to 40 percent. Site-
specific considerations may render it impossible to provide such addi-
tional area if the pond to hold the 10-year storm has been designed for
maximum available area.

Conclusions

Based on the assumption that runoff from multiple storm events can be
treated by sedimentation alone, the following conclusions have been
reached:

@ It is impossible to design a pond which guaran-
tees that there is no possibility that its
capacity will be exceeded by some storm scenario.
When overflow occurs from a multiple storm event
which leads to greater runoff than for the 10-year
storm, the effluent limitations will not be met.
While some mixing will occur which would tend to
reduce the TSS from the influent TSS, it is doubt-
ful that such a reduction would ever be sufficient
to meet the effluent limitations for the overflow.
The amount of overflow is determined by the total
precipitation and is not equal to the expected
overflow but is proportional to expected overflow.

@ Increasing pond size to retain runoff from
multiple storm events obeys a law of diminishing
returns. As the pond size increases in order
to reduce the expected overflow, large incremen-—
tal cost increases are anticipated for decreas-
ing increments of protection. Figures 4 and 5
may be used to judge the point at which cost
increases compared with decreased overflows
became excessive. This would appear to be in
the range of an additional 30 to 40 percent
capacity.

@ Without regulations which recognize the prob-
ability of extreme events in terms of numerical
values, there is no event for which the prob-
ability is zero so that a penalty would always
be levied for multiple storm events even if a
10-year storm does not occur. This makes inter-
pretation of a design criteria difficult or
impractical.

DAP IPODIEON ILA


ABSTRACT

This document presents findings of a study to determine the ef-
fectiveness of surface mine sedimentation basins in sediment removal
during the occurrence of a variety of rare storm events. Through the use
of simulation techniques, a series of six sedimentation basins were
studied to determine their performance during the experience of three
discrete precipitation events, the 2-year, 5-year, and 10-year twenty-four
hour storms. This report details findings, conclusions, and recommenda-
tions relative to a surface mine sediment basin's ability to meet the
current effluent guidelines for suspended solids removal.

This report was submitted in partial fulfillment of Contract No.
68-03-2677 by Skelly and Loy under the sponsorship of the U.S. Environ-
mental Protection Agency. This report covers the period June 20, 1979 to
July 27, 1979, and work was completed as of August 3, 1979.

iv -


800

600
=
~
a
E
5 400
fo}
°
=98 %
200 £:8
£*99 %
: 70 mg/h
Be —
0 rl \ \ rj | \ ! 1 ! 1
oO 2000 - 4000 6000 8000 10000

| iq (mg 7)
Figure 4a. Estimation of Peak Outflow Concentration.

2.0 |

STORM DURATION | Ss .
-~ r 24 HRS ° e
ws | 9 )
ra & &
Sousb | * v
N os
wn
2 L.
fs)
e
o FOF
Ns
uv
>
05+ —~——4 -—
fe) n 1 4
ro) 2000 4000 6000 8000 10000

Cin (mg/2)

Figure 4b. Determination of Peak Inflow Concentration,


TABLE 8. PARTICLE SIZE DISTRIBUTION OF POND EFFLUENT

Pond Precipitation event Detention Percent of particles finer
frequency @ 24-hr time (hrs) -001mm 002mm =. .005mm
PA-1 10yr 25.0 83.9 100.0 100.0
10yr 38.0 97.0 100.0 100.0
5yr 20.8 96.4 100.0 100.0
WV-1A 10yr 26.0 47.9 90.3 100.0
10yr 40.7 61.9 99.5 100.0
5yr 25.7 58.7 99.0 100.0
WV-1B 10yr 36.3 52.8 98.1 100.0
10yr 40.6 63.4 100.0 100.0
5Syr 19.2 51.9 93.7 100.0
WV-2A 10yr 24.7 45.5 88.1 100.0
Wyr 38.6 53.4 95.6 100.0
Syr 13.9 443 87.6 100.0
WV-2B 1Oyr 25.7 52.1 97.3 100.0
1Oyr 39.7 62.4 100.0 100.0
Syr 18.7 53.1 96.4 100.0
WV-3A 10yr 26.3 61.2 99.7 100.0
10yr 45.8 92.1 100.0 100.0
5yr 26.3 80.0 100.0 100.0
WV-3B 10yr 26.3 48.8 93.5 100.0
10yr 40.6 57.5 99.8 100.0
5yr 19.0 50.5 92.6 100.0
WV-4A 10yr 25.7 448 85.6 100.0
1Oyr 39.5 52.2 92.8 100.0
5yr 15.4 43.5 84.5 100.0
WV-4B 10yr 28.9 64.1 100.0 100.0
yr 42.6 76.7 100.0 100.0
Syr 21.6 66.5 100.0 100.0
KY-1A yr 26.3 53.8 98.3 100.0
10yr 411 64.9 100.0 100.0
5yr 16.2 55.7 99.8 100.0
KY-1B 10yr 24.0 60.7 99.3 100.0
1Oyr 41.5 80.3 100.0 100.0
5Syr 27.4 72.5 100.0 100.0

26


with a slope of 30% and during mining the composite curve number for the
watershed is 60. The watershed has a drainage area of 75 acres. A 36
inch diameter drop inlet riser is to be placed in the basin with the
crest of the riser at an elevation of 12 feet above the bed of the basin.

From Table 2 it can be seen that the principal spillway and emer-
gency spillway must handle a peak runoff rate of 104 cfs for the 100-year,
6 hour event. The peak for the 10-year, 24-hour event is 75 cfs and 8.3
acre-ft of runoff is produced. If it is assumed that active mining dis-
turbs about 5 acres, then nearly 9.3 acre-ft of storage below the riser
crest would be required to provide a 24-hour detention time (8.3 + 0.2 x 5).
When the inflow hydrograph is estimated and the flow routed through the
basin, the peak outflow rate is estimated to be 36 cfs and the average
detention time a little over 10 hours. If we assume that field monitor-
ing on the watershed indicates that at a flow rate of 50 cfs, 8% of the
particles are finer than 5 microns and 24% are finer than 20 microns, it
is possible to make an evaluation of the basin performance.

Using equation 4, P,* = (50/75)? (8), therefore P,* = 7.1 and sim-
ilarly Poy* = 21.2. From Table 3 the permanent storage S = 3.4 acre-ft.
The volume of runoff is determined from Table 1 and by assuming base flow

cquivalent to the dead storage
Q = 8.3 + 3.4 = 11.7 acre-ft

Then by using equation 12, an estimate can be made of the trap

efficiency.


IDAAPIPOION ILA

August 2, 1979

Project No. 78-334-D

Dr. Mark Boster

Office of Surface Mining

Branch of Environmental Services
Department of the Interior
Washington, DC 20240

Letter Report
Task 8

Evaluation of Sedimentation Pond Design
Relative to Capacity and Effluent Discharge

Dear Dr. Boster:

D'Appolonia Consulting Engineers, Inc. (D'Appolonia) is pleased to
submit this report on the evaluation of sedimentation pond design
criteria relative to capacity and effluent discharge. The objective of
this evaluation was to assess the impact of multiple storm occurrences
on the design requirements for the sedimentation ponds for surface mine
facilities. The study has been performed by evaluating the capacity
requirements of the three representative surface mines in the Northern
and Southern Appalachian regions which were used for the study of cost
impacts for discretionary alternatives for the Regulations Analysis.
Table 1 describes these mines relative to data required for sedimentation
pond design.

Sedimentation Pond Design Requirements

Paragraph 816.42 of the Office of Surface Mining (OSM) Reclamation and
Enforcement regulations specifies effluent limitations of total sus—
pended solids (TSS) for discharges from sedimentation ponds. Broadly,
the regulation specifies a maximum TSS discharge of 70 mg/2 and an
average discharge of 35 mg/£ measured over a period of 30 consecutive
days.

Additionally, Paragraph 816.42 of the OSM regulations also has a pro-
vision which releases the operator from meeting the effluent limitations
if a 10-year, 24-hour (10-yr storm) or larger storm event has occurred.
However, the effluent criteria must be met if a 9.9-year storm (10 -yr
storm) having rainfall characteristics which are basically the same as
that of a 10-year storm, occurs. Furthermore, even if a storage equal
to the total runoff of a 10-year storm is provided for the sedimentation

10 DUFF ROAD, PITTSBURGH, PA 15235 TELEPHONE 412/243-3200

BECKIEY, WV Cte STE
WILMINGTON

N CHIC AGG, DENVER CO HOUSTON, TX LAGUNA N.GUEL, CA
JM SEOUL, KONA TERERAN IRAN

Betiet oS,



13.

1h,

16.

17.

18.

Aron, G., Laktos, J., and Stom, L.E. 1979. Penn State Urban Runoff
Model - User's Manual ~ Jan. 1979 Edition. The Pennsylvania State
University, University Park, Pennsylvania.

Williams, J.R. 1978. A Sedimentgraph Model Based on an Instantaneous
Unit Sedimentgraph. Water Resources Research, Vol. 14, No. 4, August
1978. 659-664 pp.

American Public Health Association, Standard Methods for the Examina-
tion of Water and Wastewater, Fourteenth Edition, 1975.

Caterpillar Tractor Co. Caterpillar Performance Handbook, 8th Edition,
Peoria, Illinois : Caterpillar Tractor Co., 1977.

United Mine Workers of America and Bituminous Coal Operator's Asso~
ciation Wage Agreement of 1978 (Three Year Contract).

Dodge Building Cost Services, 1979 Dodge Guide for Estimating Public
Works Construction Cost, Annual Edition No. 11 : McGraw-Hill
Information Systems Company, New York, New York.

31


DRAINAGE

DRAINAGE
BOUNDARY -

POND B

y SEDIMENTATION POND 8B

SEDIMENTATION

LEGEND

ACTIVE PIT
SJ REGRADED
(C[] ‘VALLEY FILL
([] vircIN LAND

Figure 3. Generalized map of mine sites.

16


Dr. Mark Boster 7 August 2, 1979

Ry = Runoff volume of the storm having return
period of N-years;

RR = Runoff volume of the storm having return
period of R-years; and

Yq = Storage capacity of the pond.
Typical values of Pr (N, R) are given in Table 2 for mine lives of 1, 2,
5, and 10 years for 2-day and 10-day cycle times. The probability of
having a 10-year storm within the life of the mine is also shown in Table 2
for comparison. The results indicate that the probability of a multiple
storm event is always lower than a single 10-year storm event during
the mine life.

Figures 3A and 3B show the decision tree which was constructed for all
possible combinations of storms considered in the analysis for a given
cycle time. The maximum expectation of the overflow for a given cycle
time is obtained by summing the respective expected overflows for all
possible storm combinations.

The process was repeated for all cycle times considered in the analysis,
i.e., 2-, 5-, 10-, 15- and 20-day cycles. The maximum expectation of
overflow for all cycle times was then obtained by summing respective
maximum expected overflows for each specified cycle time.

The analysis was then repeated for increased storage capacities (VQ) of

the pond and the maximum expected overflow (VoP) for all cycle times

was evaluated. The results of these analyses were then normalized by

dividing the maximum expected overflow (VoP) by the storage capacity

We 5 and by dividing the storage capacity (VQ ) by the storage capacity

0) required to store one 10-year storm. one variation of (V, ‘oP/VQ)

sy (VQ /VQ 10) is shown in Figure 4 for Mines 1 and 2 and in Figure 5 for

Mine 3° for the four different mine lives, respectively.

Figures 4 and 5 show that the probability of an overflow never goes to
zero regardless of how large the pond may be. This results from the

fact that there is always a probability, however small, of a multiple
storm scenario which would exceed the capacity of any pond. Thus, it is
impossible to design a pond which absolutely guarantees that the capac-
ity will never be exceeded. While the wording is unclear, it appears
that Paragraph 845.13 of the OSM regulations does recognize this fact in
that penalty points for violatio:. are assigned based on a qualitative
assessment of probabilities of event occurrence. Specifically, Paragraph
845.13 states:

“The office shall assign up to 15 points based on

the probability of the occurrence of the event which
a violated standard is designed to prevent. Points
shall be assessed according to the following schedule:

1ID2UPIPOLON IL


10.

We

12.

REFERENCES

iH “Federdl Register 2586 (January 12, 1979) and 44 Federal Register
19193 (April 2, 1979). This provision has been temporarily suspended
in part. #4 Federal Register 39391.

Ward, A., Haan T. and Tapp, J. 1979. The Deposits Sedimentation Pond
Design Manual. Institute for Mining Minerals Research, Kentucky Center
for Energy Research Laboratory, University of Kentucky, Lexington,
Kentucky.

Wischmeier, W.H., and Smith, D.D. 1978. Predicting Rainfall Erosion
-Losses ~ a Guide to Conservation Planning. U.S. Department of Agricul-
ture, Agriculture Handbook No. 537.

Williams, J.R. 1975. Sediment-Yield Prediction with Universal Soil
Loss Equation Using Runoff Energy Factor. Present and Prospective
Technology for Predicting Sediment Yield and Sources. In: Proceedings
of the Sediment Yield Workshop, ARS-S-40. U.S. Department of Agricul-
ture Sedimentation Laboratory, Oxford, Mississippi. 244-252 pp.

Miller, A.C. and Veon, W. 1979. Sediment Prediction from Pennsylvania
Highway Construction Sites. Pennsylvania Department of Transportation,
Harrisburg, Pennsylvania. In Print.

Soil Conservation Service. 1975. Urban Hydrology for Small
Watersheds. U.S. Department of Agriculture, Technical Release No. 55.

Kent, K.M. 1973. A Method for Estimating Volume and Rate of Runoff in
Small Watersheds. U.S. Department of Agriculture, Soil Conservation
Service, Technical Paper No. 149.

U.S. Weather Bureau. 1960. Rainfall Frequency Atlas for the United
States, Technical Paper No. 40.

Miller, A.C. and Veon, W. 1977. Soil Properties that Affect Erosion.
Transportation Research Record #642,

Wischmeier and Smith. op. cit.

ibid. ‘

Ward, Haan, and Tapp. op. cit.

30


Table 2. Rainfall and Runoff for 100-Year, 6-Hour Rainstors.

100-Year, 6-Hour Storm

Watershed Curve Volume

Area Slope Number Rainfall Runotf Peak Rate Runoir
1)

(acres) (%) CN (inches) (inches) (cfs) (acl

75 15 60 4.0 76 43.8

438

5.0 1.30 83.3 8.1

6.0 1.91 130.4 11.0

70 4.0 1.33 112.9 8.3
5.0 2.03 179.1 12.7

6.0 2.80 252.6 17.5

80 4.0 2.04 233.0 12.6
5.0 2.89 332.6 18.1

6.0 3.78 435.1 236

75 30 60 4.0 76 54.9 oma
5.0 1.30 104.0 8.1

6.0 1.91 161.9 1.9

70 4.0 1.33 147.5 8.5
35.0 2.03 230.6 12.7

6.0 2.80 319.7 7.5

80 4.0 2.04 233.0 12.8
5.0 2.89 18.1

6.0 3.78 23.6

200 15 60 4.0 716 12.6
5.0 1.30 21.6

6.0 1.91 31.7

70 4.0 1.33 22.1
5.0 2.03 33.9

6.0 2.80 46.7

80 4.0 2.04 341
5.0 2.89 483

6.0 3.78 62.0

200 30 60 4.0 +76 2.8
5.0 1,30 21.6

6.0 1.91 31.7

70 4.0 1.33 22.1
5.0 2.03 33.9

6.0 2.80 46.7

80 4.0 2.04 34.1
S86 2.89 48.3

6.0 3.78 62.9



IDRAWING

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DESIGN VOLUME RATIO (Vg / Vg!)
FIGURE 4
MINES | AND 2
NOTES: EXPECTED OVERFLOW
v:

DESIGN VOLUME
PREPARED FOR

U.S DEPARTMENT OF THE INTERIO
OFFICE OF SURFACE MINING

DAPPOLONIA



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pond, no consideration has been included in the regulations for the case
in which a combination of lesser storms may occur such that their com-
bined runoff would exceed the capacity of the pond. It is theoretically
possible to postulate storm scenarios which would not individually equal
the 10-year storm but collectively could result in greater runoff which
would then require treatment to meet the effluent limitations. The
objective of this evaluation was to study whether the costs to design
for these scenarios would be greater than for the 10-year storm for
which effluent limitations do not have to be met.

It is important to note that this study was based on the assumption that
storm runoff could be treated by sedimentation to remove suspended
particles. It is emphasized that this assumption does not imply that
such treatment is either possible or practical on a site-specific basis.
The study was directed at the potential impact of multiple storm occur-
rences on sedimentation pond capacities and not on specific design
methods to meet effluent requirements.

Theoretical Design Basis

Runoff treatment to theoretically meet a given effluent criteria by
sedimentation alone depends on the following five factors:

e@ Runoff volume which is determined by rainfall from a
storm event,

©@ Total suspended solids (TSS) in the runoff which is a
function of site-specific conditions including the
mining operation,

@ Particle size distribution of the TSS which determines
the minimum particle size which must be settled out and
is dependent on site-specific conditions and mining
operations, .

@ Length of time for which runoff is stored depends upon
pond area and depth that can be practically realized
at a specific site and the minimum particle size to be
removed to meet the effluent limitations, and

@ Settling velocity which depends upon the minimum particle
size that must be removed, as given by Stoke's Law.

Runoff volume is a function of the storm event and the effective drainage
area for a site-specific sedimentation pond. The effective drainage arca

may be less than the total drainage area for a given site because diver-
sion ditches may be used to divert influent from above a mining area so

IDO NPP DILONTLA


inflow Sed imentgraph

The sediment concentrations associated with a storm hydrograph will
vary depending on the same factors as affected sediment yield, sediment
delivery and particle size distribution. Usually the inflow sediment-
graph will have a similar shape as the inflow hydrograph, with a peak
at about the same time as the peak runoff rate. On some watersheds the
peak may preceed that of the inflow hydrograph (Graf, 1971). Through
field monitoring on a particular watershed, an estimate of the relation-
ship between the runoff rate and sediment concentrations can be made.
If knowledge on this relationship is unavailable, the sediment concen-
trations may be assumed proportional to the flow rate. Based on studies
by Rendon-Herrero (1974) and Curtis (1976), it appears that this assump-
tion will give reasonable estimates for small, moderately sloping water-

sheds.

Peak Inflow Sediment Concentration

Mine engineers are required to design sediment basins to meet ef-
fluent water quality standards. It was felt that peak effluent sediment
concentrations would be closely correlated with basin trap efficiency
and peak inflow sediment concentrations. Inflow sediment concentrations
for a given watershed might be estimited by developing predictive equa-
tions based on field sampling for several storms of different intensity.
An attempt was made in this study to correlate peak inflow sediment con-
centrations to the design storm characteristics and its associated sedi-

ment delivery to the basin. The following equation was developed:


TABLE A-9. SEDIMENT POND WV-2B (5 yr. storm)

PERMANENT POUL CAPACITY 2 4,37 ACRE@FT
DEAD STORAGE 8 0,0 ACRE@FT
STORM RUNOFF VOLUME Ld 6,01 ACKESFT
STORM VOLUME DISCHARGED s 1,64 ACRECFT
POND VULUME AT PEAK STAGE 2 8,59 ACRE#FT
PEAK STAGE s 16,53 FT

PEAK INFLOW RATE 2 64,91 CFS
PEAK DISCHARGE RATE = 1,70 CFS

PEAK INFLOW SEDIMENT CONCENTRATION

62541,9 MG/L

PEAK EFFLUENT SEDIMENT CONCENTRATION = 3638,3 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION 2 2453,3 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION = 687.6 MG/L
BASIN TRAP EFFICIENCY 2 97,55 x

DETENTION TIME OF FLOW WITH SEDIMENT = 43,94 HRS
DETENTION TIME FROM HYDROGRAPH CENTERS = 18.71 HRS
DETENTIUN TIME INCLUDING STURED FLOW x 39,87 HRS
SEDIMENT LUAD = 223,00 TUNS

46


TABLE A-7. SEDIMENT POND WV-2A (5 yr. storm)

PERMANENT POOL CAPACITY

DEAD STURAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATIUN

BASIN TRAP EFFICIENCY

DETENTION TYME OF FLOW WITH SEDIMENT

DETENTION TIME FROM WYOROGRAPH CENTERS

DETENTIUN TIME INCLUDING STORED FLOW

SEDIMENT LG&D
43

4,48

0.0

44,90

10,40

14,01

12,80

58,51

5,15

(5702.7 MG/L]

ACRE@FT

ACRESFT

ACRE@FT

ACRE@FT

ACRE@FT

FY

CFS

crs

427,8 MG/L

212,6

151.4

93.99

22,80

13,91

20,05

50,00

MG/L
MG/L
%
HRS

HRS|

HRS

TONS


SECTION 5
RESULTS OF STUDY

For each of the study mine sites, two sediment pond locations were
evaluated for sediment removal performance under three different conditions
of rainfall. In addition, the ten-year 24-hour storm condition was mod-
elled using a minimum detention time of twenty-four hours and a higher de-
tention time, usually greater than thirty-six hours. These varying condi-
tions of rainfall and detention times resulted in forty-four separate simu-
lations. The watershed characteristics used in the simulation are listed
in Table 6.

SIMULATION RESULTS

The results of the pond performance simulation are listed in Table
7. The Table itemizes the detention time, concentration of peak influent
suspended solids and concentration of peak effluent suspended solids for
each of the eleven sediment ponds modelled during the inflow from a 5-year
and 10-year 24-hour precipitation event. The results from the 2-year
Precipitation event are not included in this summary because the computer
model simulated 100% trap efficiency for the total runoff. Because of the
plug flow concept, the model assumes that the runoff from the 2-year storm
event merely displaces the standing pool of clear water. In an actual
field situation, the pre-storm contents of the permanent pool which will be
discharged prior to storm discharge will contain an unknown amount of
colloidal material contributing to suspended solids in the effluent.

The results presented in Table 7 indicate that none of the
sediment ponds meets the daily maximum effluent limitations for suspended
solids, 70 mg/l. The effluent particle size distribution for each of the
simulations shows that all particles greater than .005 mm were removed from
suspension under all scenarios for all ponds. The simulation which has the
least detention time (WV-2A - 5 year storm, 13.9 hours), showed that 87.6%
of the particles less than .002 mm remained in solution. The simulation
which has the greatest detention time (WV-3A - 10 year storm, in excess of
45 hours) showed that 92.1% of particles less than .001 mm remained. These
two pieces of data indicate the dramatic effect of particle size on sedi-
ment removal performance. The simulation with a detention time in excess
of 45 hours still showed a peak effluent suspended solids concentration of
1362 mg/l], clearly in violation of the effluent guidelines.

22


SECTION 1
INTRODUCTION

The Environmental Protection Agency (EPA) has promulgated effluent
limitations guidelines and new source performance standards for point source
discharges of water pollution in the coal mining industry. Both regulations
limit the concentration of total suspended solids (TSS) which may be dis-
charged from coal mine sediment ponds to a 24-hour maximum value of 70
mg/l. The regulations also recognize, however, that relief from the efflu-
ent limitations, including TSS, is appropriate in the event of severe storms
which overwhelm properly designed, constructed, and maintained sediment
ponds. Accordingly, the regulations provide that:

"Upon satisfactory demonstration by the discharger, any
overflow, increase in volume of a discharge, or discharge
from a by-pass system, resulting from a 10-year 24-hour
or larger precipitation event or from a snow melt of
equivalent volume, from facilities designed, constructed,
and maintained to contain or treat the volume of water
from a 10-year 24-hour precipitation event, shall not be
subject to (the otherwise applicable effluent require-
ments)".1

It is the purpose of this study to provide EPA with an assessment
of the expected sediment removal efficiency of eleven sediment ponds at six
representative Appalachian coal mines under the two-year, five-year and ten-
year 24 hour precipitation events. A description of each mine site is
contained in Section 5 of this report. They are located as follows:
southwestern Pennsylvania (PA-1); northeastern West Virginia (WV-3); central
West Virginia (WV-2); southwestern West Virginia (WV-1) and (WV-4); and
southeastern Kentucky (KY-1) (See Figure 1).

The effectiveness of these ponds' sediment removal during various
storm events has been determined through the use of a state of the art com-
puter modelling technique, developed by the University of Kentucky, Depart-
ment of Agricultural Engineering, known as the "DEPOSITS" (Deposition Per-
formance of Sediment in Trap Structures) model.2 A computer modelling
technique to evaluate performance of sediment ponds was selected because
determination of actual sediment pond efficiency based on field data
obtained during a severe storm event is a difficult if not impossible task.
To obtain empirical data concerning sediment pond performance in a 10-year
24-hour storm event, by definition one would have to remain on-site for
years to obtain the desired effluent samples, and the costs of such a
monitoring program would far outweigh the benefits.


DRAWING

2 [7G NUMBER

78-334-Al2y

CHECKED BY

PROVED BY

MEL

7-25-79 [AP

DRAWN

BY

E

MAXIMUM EXPECTED

OVERFLOW
Cycle time 2 da See
y YS Figure Emax (L,2)
3B
Cycle time 5 days See
Figure Enax (1,5)
3B
: . . See
Mine Life - Cycle time 10 days .
L Years Figure Enax (L,10)
3B
Cycle time 15 days See .
2 Figure Emax (L,15)
3B
Cycle time 20 days See
Figure Emax (L,20)
3B

max (L,d) = Maximum expected over!tow for
a pond of capacity Vo, mine
life L years and cycle time of
d days.

Enax (L) = Maximum expected overflow for

a pond of capacity Va and mine
life L years.

Emax (L) = 2Emax (L,d)

FIGURE 3A

DECISION TREE CONCEPT
USED TO DERIVE MAXIMUM
EXPECTED OVERFLOW

PREPARED FOR

US DEPARTMENT OF THE INTERIOR
OFFICE OF SURFACE MINING

DAPPOLONIA



ACKNOWLEDGMENT

The cooperation and assistance of the following individuals is
gratefully acknowledged: Mr. Ron Hill; Mr. Gene Harris; Mr. Roger Wilmoth;
of the IERL-~Ci; USEPA, Mr. Matt Jarrett, EGD-USEPA, Mr. Barry Neuman, Office
of General Counsel - USEPA, Mr. Jose Del Rio, OSM, and Mr. Harry Kohlmann,
Hydrotechnic Corporation. We would also like to thank Dr. Arthur Miller of
the Pennsylvania State University for his assistance during the project.

viii


Sediment Yield Application

A standard procedure was used in this analysis for estimating
sediment yields from each site for the 2-year, 5-year, and 10-year
recurrence interval storms. The procedure used the following steps:

1) Compute the runoff volume and peak rate of runoff
from the watershed during the 2, 5 and 10-year storm
events.

2) Compute or assume a soil erodibility (K).
3) Determine LS values for each land cover at the site.

4) Multiply the LS values by the designated C factors
to compute a LSC for each land cover.

5) Weight the LSC values based on the percent of watershed
area of each land cover to compute a composite LSC for
the watershed.

6) Compute the sediment yield in tons using the modified
USLE.

The results of this analysis are summarized in Table 4.

Sediment load for WV-4 (B) pond site resulted from the highest
calculated soil loss. The 16.9 tons of sediment per acre during the 10 year
event equates to a loss of 56 thousandths of an inch of soil from the entire
watershed. Although this is a small volume, it can cause very high
suspended solids concentrations in the receiving stream, as will be shown
later when the results of the DEPOSITS model are presented.

TABLE 4 ~ SUMMARY OF SEDIMENT LOADS USING MODIFIED USLE

Composite Sediment load (tons)
Area LSC. 2-Year 5-Year 10-Year
PA-1 0.26 50 124 170
KY-1(A) 0.12 3 14 22
KY-1(B) 0.31 28 71 97
WV-1(A) 0.13 32 180 294
WV-1(B) 0.52 253 520 861
WV-1(C) 0.28 8: 194 260
WV-2(A) 0.05 8 50 85
WV-2(B) 0.41 89 223 308
WV-3(A) O.e4 59 202 306
WV-3(B) 0.45 158 392 539
WV-4(A) 0.10 1 gy 167
WV-4(B) 0.74 105 270 372"

13


TABLE A-10. SEDIMENT POND WV-2B (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATIUN

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME UF FLUW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

OETENTIUN TIME INCLUDING STORED FLUW

SEDIMENT LOAD

AT

4.37

10,46

16,23

87,17

1,70

4062.6

3897,7

2934,6

1552,4

95,34

54,37

25,70

47,90

308,00

ACRE@FT

ACRE SET

ACKESFT

ACRESFT

ACRE OFT

FT

MG/L

MG/L

MG/L

MG/L

x

HRS

HRS

ARS

TONS


10.

11.

12.

BIBLIOGRAPHY

American Public Health Association, Standard Methods for the Examina-
tion of Water and Wastewater, Fourteenth Edition, 1975.

Aron, G., Laktos, J., and Stom, L.E. 1979. Penn State Urban Runoff
Model - User's Manual - Jan. 1979 Edition. The Pennsylvania State
University, University Park, Pennsylvania.

Caterpillar Tractor Co. Caterpillar Performance Handbook, 8th Edition,
Peoria, Illinois : Caterpillar Tractor Co., 1977.

Clyde, Calven G., et. al. 1978. Manual of Erosion Control Principles
and Practices During Highway Construction. Utah Water Research
Laboratory, Utah State University, Logan, Utah. UWRL/H-78102.

Dodge Building Cost Services, 1979 Dodge Guide for Estimating Public
Works Construction Cost, Annual Edition No. 11 : McGraw-Hill
Information Systems Company, New York, New York.

44 Federal Register 2586 (January 12, 1979) and 44 Federal Register
19193 (April 2, 1979). This provision has been temporarily suspended
in part. 44 Federal Register 39391.

Haan, C.T. and B.J. Barfield, 1978. Hydrology and Sedimentology of
Surface Mined Lands, Office of Continuing Education and Extension,
College of Engineering, University of Kentucky, Lexington, Kentucky
4O546.

Kent, K.M. 1973. A Method for Estimating Volume and Rate of Runoff in
Small Watersheds. U.S. Department of Agriculture, Soil Conservation
Service, Technical Paper No. 149.

Miller, A.C. and Veon, W. 1979. Sediment Prediction from Pennsylvania
Highway Construction Sites. Pennsylvania Department of Transportation,
Harrisburg, Pennsylvania. In Print.

Miller, A.C. and Veon, W. 1977. Soil Properties that Affect Erosion.
Transportation Research Record #642.

Soil Conservation Service. 1975. Urban Hydrology for Small
Watersheds. U.S. Department of Agriculture, Technical Release No. 55.

United Mine Workers of America and Bituminous Coal Operator's Asso-
ciation Wage Agreement of 1978 (Three Year Contract).

32


Runoff Energy

The runoff energy factor proposed by Williams is directly propor-
tional to runoff volume multiplied by the peak rate of runoff and provides a
mechanism for estimating both sediment yield and delivery ratio. The ex-
ponent of 0.56 may vary between watersheds and can be used for calibration
if actual data is available. However, Williams found this value to be

accurate for a wide range of watersheds, therefore, this same value was used
for computation in this study.

The DEPOSITS model uses a subroutine, (WASH), to compute runoff
volumes and peaks, and an estimate of these values was therefore needed to
determine sediment load on the pond (also an input variable to DEPOSITS).
Since WASH uses a Soil Conservation Service runoff curve number to simulate
runoff, a similar approach was used to compute the values used in the MUSLE.
The techniques that were used are documented in USDA Technical Release No.
55 "Urban Hydrology for Small Watersheds" 6 and SCS Technical Paper No. 149
"A Method for Estimating Volume and Rate of Runoff in Small Watersheds" 7
These publications contain a series of tables and graphs to determine runoff
peaks and volumes using runoff curve numbers, watershed slope, and rainfall
total. The land cover and soil type are used to select the runoff curve
number (CN), which is used to determine runoff volume, and is used with the
watershed slope to determine peak runoff rate.

Site-specific soil information was only available for the Pennsyl-
vania site, and it was found to be predominantly B soils. Therefore, to
select the CN for the four general types of land cover encountered in mine
watersheds, this study assumed that all soils are hydrologic soil type B,
characterized by moderate infiltration capacity when thoroughly wetted.
CN's for the four land cover types with B soils were determined to be:

virgin land - 55
active pit - 84
regraded - 75
valley fill - 85

The total rainfall for 2-year, 5-year, and 10-year 24-hour events
was determined to be 2.25, 3.40, and 4.00 inches respectively, using data
presented in Technical Paper No. 40 "Rainfall Frequency Atlas for the u.s."8
The composite CN for each site and runoff for each storm are summarized in
Table 1. It should be noted that in some cases, especially during the
2-year precipitation events, that simulated runoff volumes from areas
tributary to larger areas exceed the volumes computed for the larger areas.
While this phenomenon can occur in certain geologic conditions, it is
recognized that this will probably not be true at these mine sites. This
anomally is because of certain inherent assumptions selected about initial
abstractions and watershed storage based on composite CNs. The values are
still considered to be good approximations for use in the sediment yield
computations and were used as calculated.


CONTENTS

Foreword . 6. 6 6 6 ee ee ee ee ee
Abstract . 1. 6 1 6 ee ee ee ee ee

Figures 2... 1 we ee ee ee te

Tables 6 1 we ee ee ee ee ee
Acknowledgment .  . 2... ee ee ee ewe
1. Introduction ..... 1...
2. Conclusions Foe ee ee ee ee
3. Recommendations .........
4, Methodology of Pond Evaluation .

Sediment Yield Computations
Storm Hydrograph Computation .

Sedimentation Pond Performance

5. Results of Study ........

Simulation Results ....

Sediment Pond Construction Cost Analysis .
References... . - ee ee eee ee ee
Bibliography... 2. 1 ee ee ee ee
Appendix . 2... 1 ee ee ee ee eee

Model .

Page
iii

iv
vi
vii

viii

Anne

14

22
22
25

30
32
34


TABLE A-2. SEDIMENT POND PA-1 (10 yr. storm)

PERMANENT POOL CAPACITY = 2,93 ACRE SFT
DEAD STORAGE 2 0.0 ACRE@FT
STORM RUNOFF VOLUME = 5,16 ACRE@FT
STORM VOLUME DISCHARGED 3 2,22 ACREAFT
POND VOLUME AT PEAK STAGE * 6,68 ACRE@FT
PEAK STAGE s 6,38 FT

PEAK INFLOW RATE 2 61,69 crs
PEAK DISCHARGE RATE = 1,31 CFS

PEAK INFLOW SEDIMENT CONCENTRATION x S4295,6 MG/L

PEAK EFFLUENT SEDIMENT CONCENTRATION = 2312,3 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION = 1424,8 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION # 635.7 MG/L
BASIN TRAP EFFICIENCY 2 97,48 2
DETENTION TIME UF FLOW WITH SEDIMENT = 82,27 HRS
DETENTIUN TIME FROM HYDROGRAPH CENTERS ® 25,04 HRS
DETENTION TIME INCLUDING STORED FLOW = 7$,07 HRS
SEDIMENT LOAD 2 170,00 TONS

w
on


TABLE A-16. (continued)

PERMANENT POUL CAPACITY z 1,93 ACRE#FT
DEAD STORAGE = 0,0 ACRE@FT
STORM RUNOFF VOLUME 2 17,89 ACRE@FT
STORM VULUME O1SCHARGED a 15,94 ACRESFT
POND VOLUME AT PEAK STAGE . 15,83 ACRE®FT
PEAK STAGE s 13,47 FT
PEAK INFLOW RATE 2 94,75 CFS
PEAK DISCHARGE RATE = 3,87 crs
PEAK INFLOW SEDIMENT CONCENTRATION = = (i7118,7 MG/L
PEAK EFFLUENT SEDIMENT CONCENTRATION = 1336.7 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION a 503.4 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION & 451,8 MG/L

: BASIN TRAP EFFICIENCY 2 93,47 %

DETENTION TIME OF FLOW WITH SEDIMENT ® 31,96 HRS
DETENTION TIME ©RG HYDROGRAPH CENTERS 2 25.69 HRS]

: DETENTION TIME INCLUDING STORED FLUW 2 31,32 HRS

SEDIMENT LOAD 2 167,00 TONS

‘ 51


-28~

E = 93.1 + 27.6(3.4/12.7) + 0.046(21.2 - 7.1)(10.5/24)
= 1.4(21.2) (36/75)°3 |

when evaluated E = 77.6%.(DEPOSITS estimate 78.5%). If these values
are substituted into equation 14 it is determined that the peak in-
flow concentrations may not exceed 95 mg/& if the effluent standard
of 70 mg/2 is to be maintained. If this value is then substituted in-
to equation 5 an estimate of the maximum permissible sediment delivery
to the basin may be obtained. For this storm event only 0.054 tons of
sediment may be delivered to the basin. Clearly onsite measures will
have to be very effective, flocculation must be induced through use of
chemical agents or a series of basins must be employed. If it was
possible to obtain a trap efficiency of 95% with the same basin and
flow characteristics, the permissible sediment delivery would be in-
creased to 0.68 tons and the permissible peak inflow concentration would

be 630 mg/%.

ALTERNATIVE WATERSHED PRACTICES

Chemical Flocculating Agents

The use of chemical flocculating agents is beginning to see more
widespread use. Flocculation occurs due to the electrokinetic potential
of the soil particles. It may either be induced through the use of chem-
ical flocculating agents or may occur naturally by the collision of rap-
idly settling particles with slower particles. In the past, polymer
electrolytes and several other chemical agents have been widely used

in water treatment facilities. McCarthy (1977) however indicates that


TABLE 11. SUMMARY OF ESTIMATED COST FOR STUDY PONDS

Storage Cost
Pond (ac-ft) ($)
PA-1 10.1 23,700
WV-1A 29.0 42,000
WV-1B 18.0 37,000
Wv-2A 51.3 54,000
WV-2B 13.1 27,000
WV-3A 21.1 38 ,000
WV-3B 18.4 38,000
WV-4A 42.7 51,000
WV-4B 5.9 17,000
KY-1A 6.4 18,000
KY-1B ay 16,000

29


SECTION 2
CONCLUSIONS

The results of the computer modelling indicate that all eleven
pond designs were unable to meet the maximum 24-hour TSS limitations
during the five-year and ten-year 24-hour precipitation events.

The performance of surface mine sedimentation basins depends upon
several factors including:

1. hydrologic and hydraulic characteristics
of the watershed in question;

2. physical characteristics of the sediment
delivered to the pond; and

3. geometry of the sediment pond

As evidenced by this study, one of the most important factors in sediment
‘pond performance is the particle size distribution of the influent sedi-
ment. The study showed that under all conditions particle sizes greater
than .005 mm were removed, therefore, if the influent contains more than
70 mg/l of particles less than this size, the effluent TSS concentrations
will theoretically exceed the limitations under the five and ten-year
storm events in the absence of chemical treatment.


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24



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1) pl sy deen
(Le corel

PAPER NO

THE DESIGN OF SEDIMENT BASINS

A.D. Ward, Research Associate
C. 7. Haan, Professor
B. J. Barfield, Professor
Agricultural Engineering Department
University of Kentucky
Lexington, Kentuchy 40506

For presentation at the 1978 Summer Meeting
AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS

Utah State University
Logan, Utah
June 27-30, 1978

SUMMARY:

Public Law 95-87 has placed several new restrictions on the surface
mining industry. This paper addresses procedures that can be used
to meet the requirements concerning sediment detention basins as
set forth in the new law,

American Society of Agricultural Engineers
St. Joseph, Michigan 49085

Papers presented betore ASAL meetings are considered to be the p operty of the Society
In general, the Society reserves the right of first pubhcation of such papers. in compete
form However it has no ctyecton 19 pubheanion an condensed fore, with cHedit to the
Socwty and the author Permssion to publish a paper in full may te feacestea trom ASAE
PO Brox 410, St Joseph Michigan 49085,

The Society is not rescans.t for stelements or ofmons advanced ir Hapers oF d SCUSs'OrS,
atts meennags Papers - vat been subjected to the review process Dy ASAE edtorat
comnunees, therefore « bbe consiauied as retereed



-6-

Table 1 ~ continued

10-Year, 24-iJour Storm

Watershed Curve Volume

Area Slope Number Rainfall Runoff Peak Rate Runoff
(acres) (Rh) CN (inches) (inches) (cfs) (acre-ft)
500 5 60 2.0 06 3 2.5

3.0 33 26 14.0

4.0 77 72 32.1

70 2.0 224 : 2) 10.1

3.0 72 87. 30.1

4.0 1.34 186 56.0

80 2.0 56 91 23.7

3.0 1.26 233 $2.7

4.0 2.06 395 85.8

500 10 60 2.0 06 3 2.5
3.0 33 29 14.0

4.0 77 89 32.1

70 2.0 24 24 10.1

3.0 72 107 30.1

4.0 1.34 231 56.0

80 2.0 56 126 23.7

3.0 1.26 323 $2.7

4.0 2.06 549 85.8

1000 10 60 2.0 -06 6 5.1
3.0 33 53 28.1

4.0 17° 145 64.2

70 2.0 24 43 20.2

3.0 72 178 60.2

4.0 1.34 372 112.1

80 2.0 56 183 47.4

2.0 1.26 466 105.3

4.0 2.06 795 171.9

1000 5 60 2.0 95 26 4.8
3.0 32 154 27.2

4.0 74 380 62.4

5 70 2.0 wad 130 20.2
24) .72 440 60.0

ay 1.44 867 111.8

5 80 25 So 431 47.4
20 } 20 103) 105.3

uO 2.06 1731 171.9



SECTION 3
RECOMMENDATIONS

Based on the results of this study, the following recommenda-
tions are presented:

1,

The EPA should allow an exemption from the
maximum allowable effluent standards for
suspended solids (70 mg/l) during any pre-
cipitation event for sediment ponds designed,
constructed, and maintained in accordance with
OSM design criteria. However, as part of this
exemption, the EPA should consider limiting dis-
charges of settleable solids during precipitation
events.

Further study is recommended to determine if the
70 mg/l total suspended solids limitation can be
achieved for any precipitation event without
chemical treatment.


Copies of this document are also available
from the American Society of Agricultural
Engineers, P.0. Box 410, St. Joseph, MI 49085


TABLE A-22. SEDIMENT POND KY-1B (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD

STORAGE

STORM RUNOFF VOLUME

STORM VULUME DISCHARGED

POND

PEAK

PEAK

PEAK

PEAK

PEAK

VOLUME AT PEAK STAGE

STAGE

INFLOW RATE

DISCHARGE RATE

INFLOW SEDIMENT CONCENTRATION

EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEPIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME, INCLUDING STORED FLOW

SEDIMENT LOAD

65

1,50 ACRE*FT
0,0 ACRE=FT
2,92 ACRESFT
1,40 ACRE*FT
3,57 ACRE*FT
11,39 FT
41,47 crs
0,83 crs
53608,1 MG/L
3331.1 MG/L
2013.9 MG/L
1006,6 MG/L
96,04 x
77,01 HRS
23,98 HRS
70,08 HRS
97,00 TONS


TABLE A-11. SEDIMENT POND WV-3A (5 yr. storm)

PERMANENT POOL CAPACITY

DEAD STURAGE

STORM RUNOFF VOLUME

STORM VULUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD
Ng

6.37 ACRE®FT
0,0 ACRE®FT
9.02 ACRE®FT
2,50 ACRESFT
12,73 ACRESFT
12,34 FT
17,65 ck
2,76 crs
1588.2 MG/L
1191.8 MG/L
351.0 MG/L
97,99 %
99,16 HRS
90,69 HRS
202,00 TONS


=32-

Haan, C. T. 1976. Urban Runoff Hydrographs ~ Basic Principles, Mini-

Course, National Symposium on Urban Hydrology, Hydraulics and
Sediment Control, University of Kentucky, Lexington, Kentucky.

McCarthy, R. E. 1977. Erosion and Sediment Control for Coal Surface

Mine Areas. National Symposium on Soil Erosion and Sedimentation
by Water, Chicago, Illinois.

Mynear, D. K. and C. T. Haan. 1978. Systems Analysis of Urban Storm

Water Detention Basins. ASAE Paper 78-2069 presented at 1978 Summer
Meeting, American Society of Agricultural Engineers, Logan, Utah,
June 27-30.

Rausch, D. L. and H. G. Heinemann. 1975. Controlling Reservoir Trap

Efficiency. Transactions American Society of Agricultural
Engineers 5:1105~1113.

Rendon-Herrero, 0. 1974. Estimation of Wash Load Produced on Certain

Soil

Soil

U.S.

Ward

Ward

Small Watersheds. Proc. American Society of Civil Engineers 100(HY7):
835-848,

Conservation Service. 1972. A Method for Estimating Volume and
Rate of Runoff in Small Watersheds. 5CS-TP-149, U.S. Department
of Agriculture, SCS, Washington, D.C.

Conservation Service. 1972. Hydrology. Section 4, National Engineer-
ing Handbook, U.S. Department of Agriculture, Washington, D.C.

Weather Bureau. 1963. Rainfall Frequency Atlas of the United
States. Technical Paper 40, U.S. Department of Commerce, Washington,
D.C.

» A. D., C. T. Haan and B, J. Barfield. 1977a,. Simulation of the

Sedimentology of Sediment Bssins. Technical Report 103, University
of Kentucky Water Resources Institute, Lexington, Kentucky.

» A. D., C. T. Haan and B. J. Barfield. 1977b. Prediction of

Sediment Basin Performance. Paper presented at 1977 Winter Meeting
American Society of Agricultural Engineers, Chicago, Illinois.

Williams, J. R. 1975. Sediment-Yield Prediction with Universal Equa-

tion using Runoff Energy Factor. Present and Prospective Technology
for Predicting Sediment Yield and Sources. Proceedings of the
Sediment-Yield Workshop, USDA Sedimentation Laboratory, Oxford,
Mississippi. ARS-S-40, pp. 224-252.

Williams, J. R. 1977. Sediment Delivery Ratios Determined with Sedi-

ment and Runoff Models. Proceedings of the Paris Symposium on
Erosion and Solid Matter Transport in Inland Waters, Paris, France.


basin. ror the water quality standard of 70 mg/2 to be met, a trap

efficiency of 99% will be required.

- DISCUSSION

It can be seen from tables 1 and 2 that even for small, shallow
sloping watersheds a minimum basin capacity of over 5 acre-ft will be
required to provide a volume weighted average detention time of 24
hours. This is because, for a 24-hour detention time, the basin must
essentially store the entire runoff volume. Most basins in the East-
ern U.S. are fairly small (1-10 acre-ft) and will in general provide
an average detention time less than 12 hours. In Figure 3 curves have
been drawn which relate trap efficiency with detention time and the
particle size distribution at the peak runoff rate. For clarity the
data points have been omitted but there was much scatter in the points.
It appears however that if the percent finer than 20 microns is greater
than 30 percent, trap efficiencies will not exceed 80% in basins which
provide a detention time of less than 12 hours for the 10-year, 24-
hour design event. Figure 3 was developed based on the data generated
for a basin with a permanent pool at the riser crest and base flow follow-

ing the design storm event.

Design Example

The use of the equations described in this paper can perhaps be
best illustrated by an example. Assume it is desired to evaluate the
suitability of basin B to control sediment discharge for a design storm

of S inches of rainfall in 24 hours. The basin is located on a watershed


Sail Brodibili

‘Soil erodibility is a term that applies to the capacity of a par-
‘tkeular soil to erode under fallow conditions. The value of "K" has been
debermined for 23 major soil groups in the United States under natural
wantitions on the basis of data collected since 1930 and this data has been
extrapolated to other soil types by using soil characteristics such as
pereent silt and fines, percent sand, percent organic material, soil

stnucture, and permeability. Nearly all soils will fall into a range of K
from 0.1 to 0.7.

Although information required to determine K at particular sites is
often available through the Soil Conservation Service (SCS), none of the
counties in which the six ponds are located have published soil surveys.
However, the area around PA-1 could be located on a General Soils Map for
Pennsylvania and K values for the B and C horizons of the soil associations
averages 0.28. Additionally, published national soil erodibility index maps
showed that soils throughout the locations in West Virginia and Kentucky
possess medium erodibility (K ranging from 0.24-0.32). Based on this
information and data determined for the Pennsylvania site,a K value of 0.3
was used. Miller and Veon found that for highway construction sites in

Pennsylvania K did not vary greatly between the construction subsoils and
the B and C horizons.

Topography

The length and steepness of the land slope have major impacts on
the rate of soil erosion during a rainfall event. In past research efforts,
‘the slope-length (L) and slope-steepness (S) have been evaluated separately,
but for field application, the two have been combined into a single
topographic factor (LS). The SCS has developed a graph to determine LS as a
function of the slope-length and steepness.1

Slope length is the distance from the point of origin of overland
flow to the point where either the slope gradient decreases enough that
deposition begins, or the runoff enters the drainage network. For this
analysis it was assumed that each component of the watershed area being
considered was a rectangle having a length equal to the overland flow length
and a slope-length equal to half the width, which is determined by dividing
the area by the overland flow length. The area and overland flow length
were determined from maps. This concept is illustrated by Figure 2.

The slope-steepness or gradient was determined by measuring the
average gradient from the topographic maps for the virgin and regraded
areas. The active pit and valley fill areas, however, will not have these
characteristics because they drastically change the natural conditions.
Both of these areas will be flatter than the surrounding terrain over the
greatest portion of their area. For these areas an average gradient of 5%
was assumed for active pits and 10% for valley fills.

10


ADDENDUM A


10.

m1,

12.

4 Pederal Register 2586 (January 12, 1979) and 44 Federal Register
19193 (April 2, 1979). This provision has been temporarily suspended
in part. U4 Federal Register 39391.

M@erd, &., Haan T. and Tapp, J. 1979. The Deposits Sedimentation Pond
Design Manual. Institute for Mining Minerals Research, Kentucky Center
‘fer Energy Research Laboratory, University of Kentucky, Lexington,
Kentucky .

Wischmeier, W.H., and Smith, D.D. 1978. Predicting Rainfall Erosion
Losses — a Guide to Conservation Planning. U.S. Department of Agricul-
ture, Agriculture Handbook No. 537.

Williams, J.R. 1975. Sediment-Yield Prediction with Universal Soil
‘Loss Equation Using Runoff Energy Factor. Present and Prospective
Technology for Predicting Sediment Yield and Sources. In: Proceedings
of the Sediment Yield Workshop, ARS-S-40, U.S. Department of Agricul-
ture Sedimentation Laboratory, Oxford, Mississippi. 244-252 pp.

Miller, A.C. and Veon, W. 1979. Sediment Prediction from Pennsylvania
Highway Construction Sites. Pennsylvania Department of Transportation,
Harrisburg, Pennsylvania. In Print.

Soil Conservation Service. 1975. Urban Hydrology for Small
Watersheds. U.S. Department of Agriculture, Technical Release No. 55.

Kent, K.M. 1973. A Method for Estimating Volume and Rate of Runoff in
Small Watersheds. U.S. Department of Agriculture, Soil Conservation
Service, Technical Paper No. 149.

U.S. Weather Bureau. 1960. Rainfall Frequency Atlas for the United
States, Technical Paper No. 40.

Miller, A.C. and Veon, W. 1977. Soil Properties that Affect Erosion.
Transportation Research Record #642.

Wischmeier and Smith. op. cit.

ibid.

Ward, Haan, and Tapp. op. cit.

30


TABLE 2

(Continued)
Return Period Return Period
Mine of First Storm] of Second Storm Pr (Ny R) for eycle time =
Life
Neyears R-years 2 days 10 days
-2 “1
| 1 0.541 x 10 0.265 x 10
1 2 0.271 x 107? 0.134 x 107!
5 0.109 x 107? 0.541 x 1077
10 0.544 x 107? 0.271 x 107?
1 0.500 x 107? 0.245 x 107?
2 2 0.251 x 1077 0.124 x 107!
5 0.100 x 107? 0.500 x 107?
10 0.503 x 107? 0.251 x 1074
5
1 0.344 x 107? 0.169 x 10”
5 2 0.173 x 10°? 0.854 x 107°
5 0.692 x 10°? 0.344 x 107?
10 0.346 x 107? 0.173 x 107?
1 0.214 x 10°? 0.105 x
10 2 0.108 x 107? 0.532 x
(0.393)* 3
5 0.432 x 10 0.214 x
10 0.215 x 10°? 0.108 x
~2 =I
1 0.545 x 10 0.267 x 10
1 2 0.273 x 1072 0.135 x 107!
5 0.109 x 207? 0.545 x 107"
10 0.548 x 107? 0.273 x 10°?
1 0.541 x 10°? 0.265 x 107?
2 2 0.271 x 10°? 0.134 x 107)
5 0.109 x 107? 0.541 x 107?
10 0.544 x 1079 0.271 x 107?
10
1 0.471 x 10°? 0.230 x 107!
5 2 0.236 x 1077 0.117 x 107?
5 0.947 x 107? 0.471 x 107?
10 0.474 x 107? 0.236 x 107?
-2 =
rT 0.344 x 10 0.169 x 10
10 2 0.173 x 107? 0.854
(0.632) ae *
5 0.692 x 10 0.344 x
10 0.340 x 107? 0.175 «
4s DD ry:
ILM UP



simulation model. The DEPOSITS model has been tested in simulation
studies. on several actual basins and appears to give a good estimate
of basin performance. It also gave a good estimate of the performance
of Callahan Reservoir during a 60-day period in 1973. A new version
of the model allows for variation in the particle size distribution
with runoff rate, and in this paper criteria are presented which ac-
count. for basins with a permanent pool and also considers base flow

conditions following a design storm event.

INTRODUCTION
Although the new surface mine legislation imposes many new re-
strictions on mining operators, perhaps the most controversial and dif-
ficult provision to comply with is contained in section 715.17 (e) of
Public Law 95-87. In part this section says:

Sedimentation ponds must provide at least a 24-hour detention
time and a surface area of at least 1 square foot for each

50 gallons per day of inflow for runoff entering the pond(s)
that results from a 10-year, 24-hour precipitation event.

.-. An additional sediment storage volume must be provided

equal to 0.2 acre-feet for each acre of disturbed area with-

in the upstream drainage area... Spillway systems shall be
provided to safely discharge the peak runoff from a precipita-
tion event with a 25-year recurrence interval, or larger event
as specified by the regulatory authority ... An appropriate com-
bination of principal and emergency spillways shall be provided
to safely discharge the runoff resulting from a 100-year, 6-
hour precipitation event, or larger event as specified by the
regulatory authority. ... All ponds shall be removed ... unless
the regulatory authority approves retention of the ponds ...

The terminology used in this section is not clearly defined and sizing
of the basin, determination of peak flow rates, detention times, and

estimation of runoff volumes is open to many interpretations.

ory


for a partial reduction in permanent pool storage due to sediment deposi-
tions. In this case it was assumed that the pond was new or recently
cleaned of sediment and thus the full sediment storage volume was available.
In addition, it was assumed that the pond had no dead storage. This assump-
tion is on the conservative side for this study because, in actuality as
much as 50% of the pond volume may be dead storage.

Storm Runoff Volume

The volume of runoff from the design storm event as computed by the
WASH model.

Storm Volume Discharged

The volume of the design storm runoff which has been discharged
during the simulation period -- that is, either 24 hours or longer if a
greater detention time has been modelled. It should be remembered that if
the basin has a permanent pool, previously stored flow will be discharged
initially and part of the design storm flow will remain in the basin. This
study assumed a permanent pool of 0.1 acre-foot per acre of disturbed land
(sediment storage volume).

Pond Volume at Peak Stage

The capacity of the pond at the peak stage reached during the
routing of the design event by the computer model.

Peak Stage

The highest water surface elevation reached during the routing of
the design event as determined by the model.

Peak Inflow Rate

Peak inflow rate of storm runoff into the pond, as determined by
WASH.

Peak Discharge Rate
Peak discharge rate from the pond during the routing of the design

event. In this study, a constant. discharge rate was assumed since a
floating discharge structure was used.

Peak Inflow Sediment Concentration

Peak sediment concentration entering the pond, based upon total
sediment delivered to the pond as determined by MUSLE.

20


TABLE A-1. SEDIMENT POND PA-1 (5 yr. storm)

PERMANENT POOL CAPACITY 5 2,93 ACRE@FT
DEAD STURAGE = 9,0 ACRESFT
STORM RUNOFF VOLUME = 3,89 ACRE#FT
STORM VOLUME DISCHARGED 2 0.96 ACRE@FT
POND VOLUME AT PEAK STAGE 2 5.50 ACRE OFT
PEAK STAGE = 5.36 Fy

PEAK INFLOW RATE = 46,36 crs
PEAK DISCHARGE RATE , = i.31 CES

PEAK INFLOW SEDIMENT CUNCENTRATION

52315,7 MG/L

PEAK EFFLUENT SEDIMENT CONCENTRATION 2 1729,3 MG/L
STORM AVERAGE EFFLUENT CONCENTRATION = 994.4 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION = 256.9 MG/L
BASIN TRAP EFFICIENCY 2 98,96 *
DETENTION TIME OF FLOW WITH SEDIMENT = 94,02 HRS
OETENTION TIME FROM HYDROGRAPH CENTERS 3 20,83 HRS
DETENTION TIME INCLUDING STORED FLOW = 87,60 HRS
SEDIMENT LOAD e 124,00 TONS

34


Dr. Mark Boster 3 August 2, 1979

that it does not reach either the disturbed area or the sedimentation
pond. Table 1 shows the effective drainage area for each of the repre-
sentative mine models used for the OSM cost impact analysis referred to
previously. The maximum rainfall associated with 24-hour storms having
return periods of 1, 2, 5, and 10 years are also shown in Table 1. Fora
multiple storm event, the total runoff is the sum of that given by each
individual storm considered.

The total suspended solids (TSS) in the storm runoff in conjunction with
the particle-size distribution of the TSS determines the amount of the
TSS which must be removed by sedimentation to meet a given effluent
limitation and the minimum particle size which must be removed. The
lower the effluent limitation which must be satisfied, the greater the
percentage of total suspended solids which must be removed. This per-
centage then determines the percent fines passing which can be used
with the particle-size distribution to determine minimum particle size.
In general, lower effluent limitations lead to smaller particles to be
removed fz..i suspension. Table 1 shows typical values of TSS and mini-
mum particle size for each of the three model mines assumed in the
analyses.

The retention time required to remove a given particle size from suspen~
sion 1s determined by the settling velocity from Stoke's Law and the
depth over which sedimentation must occur. Because the settling velocity
is a function of particle size and the retention time is determined by
the pond area and depth for a constant volume, there is no single reten-
tion time associated with a required pond volume. This parameter may be
chosen by the designer through appropriate adjustments of pond area and
depth for a given minimum particle size. However, for multiple storm
events, the retention time adds an additional variable in that as the
retention time following an initial storm increases, the probability of
having a second storm also increases. Figure 1 shows a plot of retention
time versus depth for various minimum particle sizes.

For the drainage areas, total suspended solids, minimum particle sizes,
and disturbed areas for each of the three model mines shown in Table 1,
Figure 2 shows the variation of required area with retention time. For
simplicity in this study, the parameter "cycle time" has been used where:

Cycle time = time of runoff + retention time
+ discharge time.

Thus, cycle time represents that period during which treated water is in
the pond and s..;sceptible to the influx from a second storm. The differ-
ence between xvetention time and cycle time is a function of the site-
specific design, including influent and effluent rates, but is taken to
represent the length of time required for treatment.

Figure 2, therefore, may be considered to represent the area requirements

as a function of cycle time based on theoretically treating the water by
retaining it for a time based on pond depth and minimum particle size

IDENUPPOLON IL


TABLE A-3. SEDIMENT POND WV-1A (5 yr. storm)

PERMANENT POUL CAPACITY = 6.33 ACRE@FT
po DEAD STURAGE 2 0,0 ACRE@FT
STURM RUNUFF VOLUME ® 13,86 ACRESFT
|
: STORM VULUME DISCHARGED 2 1,32 ACRE@FT
: POND VOLUME AT PEAK STAGE 3 16,31 ACRE®FT
|
PEAK STAGE 2 13,57 FT

PEAK INFLUW RATE r 53.99 CFS

PEAK DISCHARGE RATE 2 4,45 crs

PEAK INFLOW SEDIMENT CUNCENTRATION

[2i002.6 MG/L]
PEAK EFFLUENT SEDIMENT CUNCENTRATION 2 [r239.3 MG/L]

STORM AVERAGE EFFLUENT CUNCENTRATIUN 2 740,47 MG/L
AVERAGE EFFLUENT SEDIMENT CONCENTRATION a 405,9 MG/L
BASIN TRAP EFFICIENCY 2 95,91 %

DETENTION TIME OF FLOW WITH SE IMENT 2 74,95 HRS
DETENTION TIME *KOM AYDROGRAPH CENTERS = 25,72 HRS]
DETENTION TIME INCLUDING STORED FLOW 2 67,10 HRS
SEDIMENT LOAD 2 180,00 TONS

37


TABLE A-14. SEDIMENT POND WV-3B (10 yr. storm)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STORM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME OF FLOW WITH SEDIMENT

DETENTION TIME FROM HYOROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD
53

6,42 ACRE*FT
0,0 ACRE®FT
11,56 ACRESFT
5,13 ACRESFT
15,18 ACRE@FT
21,65 FT
153,03 CFS
2,38 crs
76208,4 MG/L
5259.1 MG/L
3600.7 MG/L
1660,8 MG/L
95,34 x
52,83 HRS

46,35 HRS

539,00 TONS


TABLE A-12. (continued)

PERMANENT POOL CAPACITY

DEAD STORAGE

STORM RUNOFF VOLUME

STURM VOLUME DISCHARGED

POND VOLUME AT PEAK STAGE

PEAK STAGE

PEAK INFLOW RATE

PEAK DISCHARGE RATE

PEAK INFLOW SEDIMENT CONCENTRATION

PEAK EFFLUENT SEDIMENT CONCENTRATION

STORM AVERAGE EFFLUENT CONCENTRATION

AVERAGE EFFLUENT SEDIMENT CONCENTRATION

BASIN TRAP EFFICIENCY

DETENTION TIME UF FLOW WITH SEDIMENT

DETENTION TIME FROM HYDROGRAPH CENTERS

DETENTION TIME INCLUDING STORED FLOW

SEDIMENT LOAD

6.37 ACRE®FT
0,0 ACRE*FT
13,00 ACRE®FT
2,88 ACRE*FT
17,76 ACRE*FT
14,02 FT
119,08 crs
1,48 crs
41310,5 MG/L
1362.1 MG/L
1051,2 MG/L
340,68 MG/L
96,66 x
108,49 HRS
a5,77 HRS
99,90 HRS
306,00 TONS


Humber

na ww & w N

FIGURES

Page
Location of Study Sediment Ponds .........-+24.-. 2
Determination of Slope-length for Modified USLE...... 1
Generalized Map of Mine Sites. .........-- rn)
Particle Size Distribution of Influent ....... eee 19
Cost Curve For Ponds at Location A ...... 2.20 ee 28
Cost Curve For Ponds at LocationB ...... ++ ee ee 28

vi


WATERSHED HYDROLOGY

The procedures for developing runoff rates and volumes currently
used by the SCS for small watersheds should prove adequate for surface
mined areas (Soil Conservation Service, 1972). Care must be exercised
in determining curve numbers (CN) for the disturbed portions of mined
watersheds since the exposed spoil and soil may bear little resemblance
to the original soil. The WASH hydrograph model was used to generate
expected peak runoff rates and volumes for a variety of conditions. The
results of these simulations are shown in Tables 1 and 2, The WASH pro-
gram is a modified version of the HYDRO simulation model (Mynear and
Haan, 1978) and allows for the simulation of storm hydrographs for a
storm duration of 1-24 hours. The model is essentially based on SCS

procedures and a copy may be obtained from the authors.

SEDIMENT PRODUCTION & YIELD

Sediment Yield
Determination of the rate of sediment production for a given storm

event is difficult and perhaps the best method which is available is

MUSLE (Williams, 1975):
Ye 95 (Qxq, °° FK LS C P (1)

where Y is the sediment yield for an individual storm (tons), Q is the
runoff volume (acre-feet), Ga is the peak runoff rate (cfs),K is soil
erodibility factor, LS the slope-steepness factor, C is the crop manage-

ment factor, and P is the erosion control practice factor. Good estimates


(Figure 3). For all sites, the design storm duration in each case was 24
hours. The design storm rainfall was 2.25 inches for the 2-year storm, 3.4
inches for the 5-year storm, and 4.0 inches for the 10-year storm event. A
composite (CN) curve number was computed for each drainage area based upon
the acreage of active pit, regraded area, valley fill, and virgin land
within the watershed. The composite curve numbers for the watersheds of
each sediment pond are listed in Table 5.

Table 5. WATERSHED COMPOSITE CURVE NUMBERS

Mine site Sediment pond location
A B
PA-1 78
WV-1A 60 78
WV-2A 58 78
WV-3A 67 78
WV-4A 56 77
KY-1A 63 78

The WASH computer program generates the storm hydrograph, the volume of run-
off, and the peak runoff rate for the watershed under study. These results
are then used in the computer model to determine sediment pond performance.

SEDIMENTATION POND PERFORMANCE MODEL.

To evaluate che performance of the sediment ponds under various
conditions, this study used the "DEPOSITS" model. DEPOSITS describes the
sediment transport and deposition process in a reservoir as a function of
the basin geometry, inflow hydrograph, the inflow sedimentgraph, the sedi-
ment characteristics, the outlet spillway design, and the hydraulic behavior
of the flow within basin. The DEPOSITS model has been evaluated on data
from eleven different ponds and reservoirs and explained over 90% of the
variation in trap efficiency of tnese basins. It is considered to be a
state of the art modei for estimating sediment pond trap efficiency (per-
centage of sediment in inflow to the pond which was settled out of solution
in the pond) and effiuent quality.

In the moceiliag of t.« flow within the basin, the DEPOSITS model
uses a plug fiow concept. Piiy fiow assumes no wixing between plugs and
routes the flow on a first-in first-cut tasis. Settling of the sediment
within the basin ts calculated by Stoke’s Law of Settling and particles are
considered trapped when they reo uhe bed of the reservoir. The model
subdivides each plug into foii law to account for the variation in
sediment concentraLion with depth. The DEPOSITS model requires the

following information regarding sediment: ani flow characteristics and the
physical characteristics of the jond:



TABLE A-6. (continued)

PERMANENT POUL CAPACITY 2
DEAD STURAGE 2
STORM RUNOFF YULUME s
STORM VOLUME DISCHARGED ®
PUND VOLUME AT PEAK STAGE 2
PEAK STAGE s
PEAK INFLOW RATE z
PEAK DISCHARGE RATE .
PEAK INFLOW SEDIMENT CONCENTRATION 2
PEAK EFFLUENT SEDIMENT CONCENTRATION 2
STORM AVERAGE EFFLUENT CONCENTRATIUN 2

AVERAGE EFFLUENT SEDIMENT CONCENTRATION &

BASIN TRAP EFFICIENCY =

DETENTION TIME OF FLOW WITH SEDIMENT 2

DETENTION TIME FROM HYDROGRAPH CENTERS 5

DETENTION TIME INCLUDING STORED FLOW «

SEDIMENT LUAD ®

6.42 ACRE@FT
0,0 ACRE@FT
11,23 ACRE@FT
4,81 ACRESFT
15,68 ACRE®FT
22,02 FT
148,66 CFs
1,54 CFS
125316.0 MG/L
6777.47 MG/L
44605,2 MG/L
1978.6 MG/L
96,61 %
79.73 HRS
40,56 HRS]
69.86 HRS
361,00 TONS


TECHNICAL REPORT DATA
{Please read Instructions on the reverse before completing)

1 REPORT NO. 3. RECIPIENT'S ACCESSION NO.

TtOS

4. TITLE AND SUBTITLE 5. REPORT DATE

EVALUATION OF PERFORMANCE CAPABILITY OF SURFACE | August 3, 1979 TIOS
MINE SEDIMENT BASINS 6. PERFORMING ORGANIZATION CODE

7 AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO.

Charles E. Ettinger, Joseph E. Lichty

‘9. PERFORMING ORGANIZATION NAME AND ADDRESS

Skelly and Loy
2601 North Front Street 11, CONTRACT/GRANT NO.
Harrisburg, Pennsylvania 17110 68-03-2677

10. PROGRAM ELEMENT NO.

12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF HEPORT AND PERIOD COVERED

Industrial Environmental Research Laboratory Final_6/20-8/3/79
Office of Research and Development 14. SPONSORING AGENCY CODE
U.S. Environmental Protection Agency

15. SUPPLEMENTARY NOTES,

rt
16, ABSTRACT

This document presents findings of a study to determine the effectiveness of surface
mine sedimentation basins in sediment removal during the occurrence of a variety of rare storm
events. Through the use of simulation techniques, a series of six sedimentation basins were
studied to determine their performance during the experience of three discrete precipitation
events, the 2-year, 5-year, and 10-year twenty four hour storms. This report details
findings, conclusions, and recommendations relative to a surface mine sediment basin's ability
to meet the current effluent guidelines for suspended solids removal.

This report was submitted in partial fulfillment of Contract No. 68-03-2677 by Skelly
and Loy under the sponsorship of the U.S. Environmental Protection Agency. This report
covers the period June 20, 1979 to July 27, 1979, and work was completed as of August 3,
1979.

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS b. SGENTIFIERS/OPEN ENCED TERMS: c. COSATI Fleld/Group

Sedimentation Ponds

18. DISTRIBUTION STATEMENT —— Vis Seeuait  C

S (This Report) 2°. BD. OF PAGES
‘

Ann

22. PRICE

Release to Public

i
i

eee reer


Cover and Management

The cover and management factor (C) in the USLE is the ratio of soil
loss from land under specific conditions to the corresponding loss from
clean-tilled, continuous fallow. The factor measures the combined effect of
all the interrelated cover and management variables.

A large number of C values are presented in Agriculture Handbook No.
537,11 and one must select the situation that most closely fits field
conditions. This study utilizes a C factor for each of the four cover

types, and the same values are used at all pond site locations for each
cover type.

Virgin lands were assumed to be undisturbed forest land with 70
percent of the area covered by canopy and 85 percent covered by duff
(leaves, branches, and other organic matter covering the forest floor) at
least 2 inches deep (C=0.002). The active pit area was considered to be
construction slopes with no mulch cover, which would yield a C of 1.0.

The area was, however, also assumed to be 30-percent impervious nonerodible
rock so a C=0.7 was used. Valley fill areas were also assumed to be equiv-
alent to construction sites using straw mulch at 1.0 tons per acre

(C=0.20). Regraded areas were assumed to be partially revegetated with no
appreciable canopy but with approximately 50-percent cover (C=0.10). The
following table summarizes the C factors assumed for each land cover type at
each of the mine site locations.

TABLE 3 - COVER AND MANAGEMENT FACTORS (C)
FOR EACH LAND COVER TYPE

Land cover c
Virgin land 0.002
Active pit 0.7
Valley fill 0.20
Regraded area 0.10

Support Practice

The support practice factor (P) in the USLE is used to show the
effects of specific soil loss prevention practices. These support
practices, which are generally used in agricultural applications, include
contouring, contour listing, contour strip-cropping, and controlled row
ridge planting. Since they are not practiced in mine development and
reclamation, a P value of 1.0 was assumed for this analysis.

12