United States
Environmental Protection
Agency
Industrial Environmental Researi
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S7-81-117 Aug. 1981
Project Summary
Use of a Vegetative Filter
Zone to Control Fine-Grained
Sediments from Surface Mines
Steve C. Albrecht and Billy J. Barfield
The objective of this study was "to
demonstrate the effectiveness of a
vegetative filter zone in trapping fine-
grained sediments from surface mining
operations." The area selected for
study was located in Whitley County,
Kentucky, directly below an active
surface mining operation. The out-
slope above the filter was the primary
drainage area monitored during this
study.
This project was initiated for the
specific purpose of conducting a field
test on vegetation as a viable sediment
trapping medium. From the onset, the
project was wholly designed for a field
evaluation under typical mining con-
ditions. The filter area was constructed
directly below an abandoned surface
mine bench, on typical soil types
found in mined areas of Eastern
Kentucky. The outslope located above
the filter was the primary area, from
which sediment-laden drainage was
to be diverted to the inlet monitoring
station. Sediment-laden water samples
were collected at the inlet flume for
comparison with samples collected at
the outlet flume to permit evaluation
of the sediment removal capability of
the vegetative filter.
Results of the monitoring efforts
revealed that a dramatic reduction in
sediment load was achieved by
vegetative filtration for particle sizes
larger than clay. Based on the results
of this study, it was concluded that
vegetative filters are an effective
control for reducing the quantity of
sediment transported into surface
streams and rivers from disturbed
mined lands.
This Project,Summary was devel-
oped by EPA's Industrial Environmen-
tal Research Laboratory. Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The coal regions of the United States
are richly endowed with abundant
mineral resources. The surface mining
of these valuable resources results in a
major disturbance of the land. This
disturbance interrupts a natural balance
between soils and geologic formations
established over many years. When
highly erodible surface material is
broken up, a natural pollutant, sediment,
is introduced into rivers and streams.
Surface mining operations often serve
to accelerate the amount of sediment
introduced into the environment. The
resulting sedimentation can adversely
affect local and surrounding ecosystems.
Various structures such as ponds,
rock dams, silt fences, as well as other
devices can be used to control sediment
on surface mining operations. This
report addresses the usefulness of one
particular type of sediment control
structure, the vegetative filter zone.
The objective of this study was to
demonstrate under actual field condi-
tions Jhe technical, economic, and
environmental feasibility of using a
cultivated vegetative filter zone to assist
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in controlling fine-grained sediments
originating from surface mining opera-
tions. Project evaluation criteria focused
on the sediment trapping efficiency of
the filter, the suitability of selected types
of vegetation for use within the filter
zone, the filter's usefulness in improving
water quality, and its cost feasibility.
Description of Results
The filter was constructed in the late
spring of 1979. The flow was diverted
away from the filter area while vegeta-
tion was being established. Flow was
diverted into the filter in the late fall of
1979 and-monitoring equipment in-
stalled. During the months of January
and February, the monitoring equipment
was removed to prevent freeze damage.
During that period, storms were hand-
sampled whenever possible. Monitoring
equipment was reinstalled in the spring
of 1980, and monitoring continued until
November, 1980. During the monitoring
period, several storms of sufficient
magnitude occurred to cause runoff and
flow through the filter. One storm, with
a duration equal to two hours, had a
return period of over 100 years. The
data from these storms are summarized
below. Details of filter construction,
operation, sampling, analyses, and
suggestions for design and use of
vegetative filters are presented in the
full report.
Storm of January 11. 1980 - An
unusually warm period in January
brought rains and runoff at the filter
site. All equipment and records had
been removed for the winter but the
flow was hand sampled for a thirty
minute period for sediment concentra-
tion only. The storm did not generate
massive amo.unts of sediment; the peak
concentration was only 6,750 mg/l.
Outflow concentrations were typically
500 to 600 mg/l, with the exception of
one sample that was 1600 mg/l.
Ninety-two percent of the sediment was
trapped in the filter area, indicating that
the filter was performing well.
Storm of April 3, 1980 - On April 3,
1980, a complete data set was taken by
hand sampling the inflows and outlf lows
and by measuring flow depths in the H-
flumes with point gauges. The sediment
concentrations are shown in Figures 1
and 2. The peak inflow and outflow rates
were 0.11 and 0.03 cfs (3.11 and .85
I/sec) respectively, indicating a signifi-
cant attenuation of the flow rate, due
primarily to infiltration. The infiltration
volume was 54 percent of the inflow
volume.
100,000
10,000
1,000
I
§
tb
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1
-Q
is
c
100
90
80
70
60
50
40
30
20
10
i r
Inflow
Outflow
I J I 1 Mil I I I I II III I I i ll I I
0.001
0.005 0.07
0.05 0.1
Grain Size (mm)
0.5
10
j Clay | Silt
Fine Sand
Medium
Sand
Coarse Sand
Gravel
Figure 2. Aggregate size distribution of sediment for storm on April 3, 1980.
outflow rates were 0.070 and 0.047 cfs
(1.98 and 1.33 I/sec). Infiltration
accounted for 35 percent of the inflow.
Peak and average inflow concentrations
were 3788 and 1420 mg/l. The trap
efficiency, although flows were low, fell
to 97.1 percent.
Storm of August 29, 1980 - The storm
of August 29 was sampled by automatic
equipment. The ink pens for the water
stage recorders did not work properly,
therefore only the concentrations can
be calculated from the data. The
trapping efficiency of the vegetation
was only 78.3 percent during this test,
which was the lowest value for the filter
to that date. By this time, however,
considerable deposition has occurred
throughout the filter. The aggregate size
distribution of the eroded sediment was
such that 99 percent of the sediment
was silt size or larger, indicating the
filter continued to provide good trapping.
Storm of September 3, 1980 - The
storm of September 3, 1980, was
monitored by automatic equipment.
According to the rainfall charts, over 9.0
cm of rain fell. This represents an
intensity which has a return period of
over 100 years. An inspection of the site
after the storm indicated that massive
amounts of sediment had washed in
during the storm, plugging the stilling
wells and partially plugging the inlet to
the pumping sampler. Sediment had
also deposited in the middle of the filter
with numerous boulders, four inches
(10.2 cm) in diameter, washed as far as
40 feet (12.2m) into the plot.
Approximately 20 percent of the filter
was completely inundated where sedi-
ment, in large amounts, deposited in the
vegetation.
Summary
In summary, the vegetation (fescue)
worked well as a filter for most of the
year. The storms evaluated are sum-
marized in Table 1. The 100+ year storm
which occurred on September 3, 1980,
caused significant deposition in the
filter. Subsequent tests showed a
decrease in trapping efficiency. The
trapping efficiency in storms early in the
monitoring period were very high, (95-
100 percent), but toward the end of the
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Table 1 . Summary of Storms Sampled
Peak Peak
Date of Storm
January 1 1, 1980
April3, 1980
April 1 1. 1980
May 17, 1980
May 24, 1980
July 10,1980
August 29, 198O
September 3, 1980*
October 18, 19803
Test 1
Test 2
Test 3
Inflow
Rate
I/sec.
—
2.1
4.8
1.1
—
12.7
—
1.9
4.24
4.02
4.13
Outflow
Rate
I/sec.
—
.85
.36
.34
—
1.33
—
—
1.36
1.93
2.91
Volume
Inflow
—
2,745
8,093
3,623
—
2,575
—
—
—
—
—
Volume
Outflow
—
1,245
1,670
538
—
1,669
—
—
—
—
• —
Percent
Infiltrated
%
54.6
73.3
85.2
—
35.7
—
—
—
—
—
Peak
Inflow
Cone.
mg/l
8,939
71,000
6,380
30,148
67,200
62,487
30,200
24.900
28,692
22,636
24,030
Peak
Mass
Mass
Percent
Outflow Sediment Sediment Sediment
Cone.
mg/l
1.607
2.400
240
4.651
911
3.788
5,600
5.900
3,180
2,324
2,460
Inflow
Kg
85.00
39
54
—
447
—
—
—
—
—
Outflow
Kg
.35
.6
1.6
—
5
—
—
—
—
—
Trapped
%
92.5
>99
>99
97.1
98.3
>99
78.3
70.4
—
—
—
Total
Rainfall
cm
2.2
2.6
2.8
4.1
3.8
1.2
2.3
9.0
—
—
—
1 Not all storms were sampled since new equipment completely malfunctioned.
2 Numbers probably suspect due to the magnitude of the event. Equipment failure resulted.
3 Runoff and sediment generated by spraying water from a water truck onto a disturbed area.
period trapping efficiencies had de-
creased to approximately 75 percent.
The size distribution of the eroded
sediment was such that most of the
aggregates and primacy particles were
silt size or larger.
Conclusions
Conclusions drawn from this study are
as follows:
1. By vegetative filtration, 70 to 99
percent of all fine-grained sedi-
ments can be removed. This range
does not include clays held in
suspension and it was determined
from all data recorded during
storm events.
2. Vegetative filter areas can normally
be constructed using equipment
found on most surface mining
operations.
3. Vegetation used in the filter are
subjected to high stress conditions.
Response to this stress was excel-
lent despite acid inflow into the
area. Based upon the results of
this study, the vegetative trapping
medium can adapt to severe
environmental conditions with
very little difficulty.
4. The Kentucky Grass Filter Model
was found to be excellent in
predicting trapping efficiencies.
given parameters of the individual
storm events.
The trapping efficiency in storms
early in the monitoring period
were very high (95-100 percent),
but toward the end of the period,
trapping efficiencies had decreased
to approximately 75 percent.
Steve C. Albrecht is with Hittman Associates, Inc., Lexington, KY 40504, and
Billy J. Barfield is with the University of Kentucky, Lexington, KY 40506.
Edward R. Bates is the EPA Project Officer (see below).
The complete report, entitled "Use of a Vegetative Filter Zone to Control Fine-
Grained Sediments from Surface Mines," (Order No. PB 81-226 110, Cost:
$14.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•fa US GOVERNMENT PRINTING OFFICE, 1981 —757-012/7312
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