EPA 440/9-76-026
Methods To Control
Fine-Grained
Sediments
Resulting From
Construction Activity
December 1976
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Planning and Standards
Washington, D.C. 20460
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This report is issued under Section 304(e)(2)(C) of Public Law
92-500. This Section provides:
"The Administrator, after consultation with appropriate Federal
and State agencies and other interested persons, shall issue to
appropriate Federal agencies, the States, water pollution con-
trol agencies, and agencies designated under Section 208 of
this Act, within one year after the effective date of this sub-
section (and from time to time thereafter) information includ-
ing...(2) processes, procedures, and methods to control pollu-
tion resulting from -
(C) all construction activity, including runoff from the
facilities resulting from such construction;..."
This publication is the third in a series issued under Section
304(e)(2)(C) of Public Law 92-500 concerning the control of water
pollution from construction activity. The first report, "Processes,
Procedures and Methods to Control Pollution From All Construction
Activity", was issued in October 1973 (Publication No. EPA-430/9-73-007),
The second was entitled "Methods of Quickly Vegetating Soils of Low
Productivity, Construction Activities (Publication No. EPA-440/9-75-006).
It was published in July, 1975.
This document was prepared for use by planners, engineers, resource
managers, and others who may become involved in programs to effectively
provide for sediment control. Standard erosion and sediment control
measures are usually effective for preventing the runoff of the total
sediment load. The effectiveness of these standard techniques; however,
has been found to be relatively poor with regard to preventing the
runoff of the fine-grained fractions, such as the silts and clays.
The objective of this study was to research practical, cost-
effective methods which would help to reduce specifically the fine-
grained sediment pollution derived from construction activities. The
prime consideration during this study was the use or adaptation of
existing technology, as described in the current literature or data,
to the fine-grained sediment pollution problem.
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EPA-440/9-7
Methods To Control
Fine-Grained Sediments
Resulting From
Construction Activity
December 1976
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Planning and Standards
Washington, D.C. 20460
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METHODS TO CONTROL FINE-GRAINED
SEDIMENTS RESULTING FROM
CONSTRUCTION ACTIVITY
Project Officer
Robert Thronson
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Planning and Standards
Washington, D.C. 20460
November 1976
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TABLE OF CONTENTS
Page
List of Figures Hi
List of Tables iv
Acknowledgements u
Sections
I Summary 1
II Introduction 3
III Conclusions 6
IV Recommendations 8
V Erosion Control Measures 10
VI Sediment Control Techniques 24
VII Removal and Disposal of Sediment
From Detention Ponds 58
VIII References £8
Appendix Some Post-Sediment Pond Equipment 73
Manufacturers
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LIST OF FIGURES
No. Page
1 Ideal Settling Velocity for a Sphere
(10°C Water) 28
2 Siphon Arrangement in Riser Pipe 35
3 Flocculant Addition in Two-Pond System 37
4 Basic Concept of Use of Post-Sediment Pond
Equipment 43
5 Cross Section of Typical Vertical Leaf
Vacuum Filter 45
6 Simplified Operation of a Typical Pressure
Filter or Strainer 47
7 Basic Operation of a Hydrocyclone 49
8 Principle of Operation of an Inclined
Tube Settler 51
9 Cross Section of Centrifugal Concentrator 52
lOa Arrangement for Crane-Operated Scraper 60
lOb Alternate Arrangement for Crane-Operated
Scraper 60
11 Settling Tank - Vacuum Filtration Technique
for Dewatering Fine-Grained Sediment 65
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LIST OF TABLES
No. Page
1 Runoff Control Methods 14
2 Relative Effectiveness of Erosion Control
Treatments (Using Check Plot as 100) 16
3 Relative Effectiveness of Mulch Treatments
on an Earth Cut With a 3:1 Slope 18
4 Relative Effectiveness of Mulch Treatments
of an Earth Fill With a 2:1 Slope 19
5 Soil Particle Size in Runoff from Test
Plots Mulched with Wheat Residue on a
2.3% Slope 21
6 Average Soil Particle Size Distribution in
Runoff from a Highway Construction Site 22
7 Minimum Sediment Pond Area Requirements
for Selected Particles for a .0283 m3/sec
1 (cfs) Outflow 29
8 Short Circuiting for Settling Tanks 32
9 Effectiveness of Two-Pond and Chemical
Addition System, Centralia Mine 40
10 Post-Sediment Pond Equipment Costs and
Removal Efficiencies 54
11 Costs and Removal Efficiencies of Most
Feasible Post-Sediment Pond Equipment 56
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ACKNOWLEDGEMENTS
This document was prepared for the Environmental
Protection Agency by Hittman Associates, Inc. of Columbia,
Maryland. Principal authors were Mr. Michael A. Nawrocki,
Program Manager, and Mr. James M. Pietrzak, Associate
Engineer. Project Officer for the Environmental Protection
Agency was Mr. Robert Thronson, Hydrologist with the Non-
point Source Branch.
The U.S. Environmental Protection Agency has reviewed this
report and approved its publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency.
v
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SECTION I
SUMMARY
The following course of action is offered for increasing
the amount of fine-grained sediment which is retained on a
construction site. The discussion summarizes the most
promising control alternatives. Utilization of a specific
technique, or combination of techniques, depends upon the
degree of fine-grained sediment control required and the
characteristics of the soils present at the site.
For pre-sediment pond control of fine-grained sediment,
or when the installation of a sediment pond is not feasible
because of site constraints, plastic filter cloth fences
appear to be very effective for controlling fine-grained
sediment. Where sediment detention ponds are to be pro-
vided and no plastic filter cloth fence is used, two ponds
in series should be installed since efficiency measurements
on these systems indicate that they are more efficient than
a single pond of the same overall surface area. In de-
signing the pond(s) the following should be considered:
1. The performance of a preconstruction site survey
and analysis which includes the type and grain
size distribution of the soils. This will
provide for the accurate sizing of the pond
system according to anticipated flow rates
and the characteristics of the soils in the
site area.
2. Provision of baffles or compartments within
the sediment pond(s).
3. Ensure that the length-to-width ratio of
the pond be kept on the order of 5 to 1.
4. The use, where feasible, of very wide in-
flow and outflow structures.
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5. Provision, where wide inflows are not possible
to obtain, of energy dissipators to decrease
the flow velocity.
6. The use, where space is available only for a
standard riser pipe, of risers which have
improved fine-grained sediment retention
capability. These include siphon-drawdown
or plastic filter cloth wrapped units.
Additional fine-grained sediment control can be achieved
through the addition of chemical flocculants. For this,
a two pond system is recommended, with the chemical being
added into the outflow from the first pond.
There is also some available water treatment equipment
which can be used at the outlet structure of a sediment
pond to achieve fine-grained sediment removal.
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SECTION II
INTRODUCTION
Background
The implementation of an effective erosion and sediment
control plan based on current standards can prevent much
of the potential sediment p-ollution generated on a construc-
tion site. Standard erosion and sediment control measures
are usually effective in preventing runoff of the total
sediment load. However, the effectiveness of these stan-
dard techniques has been found to be relatively poor as far
as the prevention of the runoff of the fine-grained frac-
tion of the sediment, i.e., silt and clay is concerned.
The objective of this study, therefore, was to research
practical, cost-effective methods which would help to re-
duce specifically the fine-grained sediment pollution de-
rived from construction activities. The prime consideration
during this study was the use or adaptation of existing
technology, as described in the current literature or data,
to the fine-grained sediment pollution problem.
For the purpose of this study, fine-grained sediment, or
silt and clay, is defined according to the Unified Soil
Classification System. This classification includes as silt
and clay any particles 74 microns or less in diameter, i.e.,
those passing through a No. 200 U.S. Standard Sieve. There-
fore, the methods investigated during the course of this
study focused primarily on controlling particles in this
size range.
The term soils, when used in this report, includes those
natural aggregates of mineral grains, or other materials,
that can be separated by such gentle mechanical means as
agitation in water. Sediment refers to the individual
particles of material which have been eroded from their
original locations, transported, and deposited by runoff
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waters. In-place soil materials may consist of a great
range of individual particles varying from fine clays to
boulders. Others may be fairly uniform such as sands,
gravels, or clays. In most construction site areas, the
sediment most subject to erosion and causing pollution
problems consists of from clay to coarse sand-sized
materials. Silts and clays are considered to be the fine-
grained portions discussed in this report.
Study Methodology
Methods for the control of fine-grained sediment can be
grouped into four general categories. These categories
closely follow the lines along which a standard erosion
and sediment control plan is im-pl emented, since it was
found that the control of fine-grained sediment can best
be achieved by modification and expansion of a standard
erosion and sediment control plan designed in accordance
with good current practice. Thus, the methods investi-
gated during this study were grouped so as to show how
utilization of these techniques can complement and improve
the fine-grained sediment removal ability of a standard
erosion and sediment control plan.
The first category consists of standard erosion control
techniques which are used on construction sites and which
may tend to reduce the production of fine-grained sedi-
ment on the'site. Proper planning of construction activi-
ties as well as various runoff control and surface soil
stabilization techniques which are used in an effort to
keep the soil in place on a construction site are included
in this category.
The second category or line of defense involves the use of
adequate sediment control measures. They include sediment
traps, sediment filters and buffers, and detention basins
or sediment ponds to retain the fine-grained sediment on
site. Modification of and addition to original sediment
and erosion control plan designs is, in most cases, neces-
sary to specifically improve the retention of fine-grained
sediments.
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Use of post-depositional (post-sediment pond) devices and
techniques comprises the third fine-grained sediment con-
trol line of defense. It involves the installation of
mechanical separation devices, which are capable of re-
moving fine-grained particles from water, at the overflow
structure of the sediment retention basins.
The final aspect of the control technology is the removal
and disposal of the fine-grained sediment from detention
ponds and post-depositional devices. It includes the re-
emoval, dewatering, drying, and, possibly, the utilization
of the sedimentary materials.
This study, therefore, concentrated on identifying and
assessing the applicability, practicality, effectivcra::
and economics of techniques in the four above categories
which could be used to control fine-grained sediments
resulting from construction activities.
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SECTION III
CONCLUSIONS
1. The overall control of fine-grained sediments can best
be achieved through the modification and expansion of
a standard erosion and sediment control plan.
2. Standard erosion control measures such as mulches,
chemical binders, etc., which are designed to keep
the sediment in place, are most effective on coarse-
grained particles. Some fine-grained sediment control
is also achieved, however, through use of these
methods.
3. Fences constructed of plastic filter cloth appear to
be one of. the most effective fine-grained sediment
control devices. These fences can be used around the
periphery of a construction site to contain most of
the fine-grained sediment before it enters a sediment
pond, or when the installation of a sediment pond is
not feasible.
4. Conventionally-designed sediment detention ponds need
to be modified to achieve removal of more of the fine-
grained sediments. Pond characteristics which can
be modified to achieve more effective fine-grained
sediment control include the installation of baffles
or compartments within the pond, provision of a more
effective pond length-to-width ratio, use of very
wide inflow and outflow wiers, redesign of outfalls,
and the installation, of energy dissipators in the
pond intake area.
5. Multiple sediment detention ponds in series appear to
have a greater settling efficiency than a single large
pond of equivalent surface area.
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6. Chemical coagulants and flocculants used in conjunc-
tion with a multiple pond system can achieve good
control of fine-grained sediments.
7. There is some available equipment which can be used
at the outlet structure of a sediment pond to achieve
further fine-grained sediment removal. Of this equip-
ment, hydrocyclones appear to be the most cost-effec-
tive for the widest variety of situations.
8. The most feasible equipment for removing sediment
from sediment ponds include standard draglines, crane-
operated scrapers, conventional front-end loaders,
and, for larger ponds, hydraulic dredges.
9. Scarification or reworking of sediment, either after
it has been removed from a pond or after the pond has
been drained, is an effective method of dewatering the
sediment. Placement of sediment removed from ponds
on drying beds which consist of underdrains with layers
of sand and/or gravel on top has also been shown to
be effective in dewatering in some cases.
10. Ultimate disposal or reuse of fine-grained sediments
removed from sediment ponds depends upon the local
economics of transporting the sediment to the place
where it will be used. Agricultural and some landfill
uses appear to offer the best alternatives for reuse.
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SECTION IV
RECOMMENDATIONS
For Fine-Grained Sediment Control
1. Continue to use standard erosion control techniques
on construction sites. They effect some fine-grained
sediment control but, more importantly, they keep the
coarser-grained particles in place, thus making it
possible to design downstream sediment control devices
to specifically and more efficiently remove the fine-
grained sediments from the water.
2. Utilize plastic filter cloth fences for sediment
control wherever possible.
3. Include the following factors in the design and con-
struction of sediment ponds to achieve more efficient
detention of fine-grained particles:
a. Adequate pond surface area based on settling
theory and the individual site characteristics.
b. Baffles or compartments within the pond.
c. A pond length-to-width ratio of approximately
5 to 1 .
d. Very wide inflow and outflow wiers where
feasible.
e. Energy dissipators to slow the flow prior to
entering the pond.
8
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f. Riser pipes redesigned to achieve more fine-
grained sediment removal. Examples of such
redesigns include the siphon drawdown type
or the riser wrapped in plastic filter cloth.
4. Use chemi'cal flocculants in conjunction with a two-
pond system, with the flocculant being added after
runoff flows through the first pond.
For Research Needs
1. Determine the exact effect of recommended sediment
pond modifications on efficiencies. In-field evalua-
tions of each of the above recommended modifications
need to be.performed. The modifications should be
evaluated both singly and in combination with other
modifications.
2. Encourage the conduct of field trials of the various
pieces of post-depositional equipment which have been
identified as being most feasible. Practical trials
are needed to determine their range of applicability
and costs in comparison to other fine-grained sediment
control measures.
3. Perform additional economic and technical field evalu-
ations using multiple sediment ponds in conjunction
with flocculant additions.
4. Conduct studies to determine if flocculants used in
standard water treatment practices are toxic under any
anticipated conditions.
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SECTION V
EROSION CONTROL MEASURES
Basic Concepts
The first consideration in the control of sediment on a
construction site is to keep as much of the soil in place
as possible. This is accomplished through the use of
good on-site erosion control techniques. Within the past
few years, many advancements have been made in the field
of erosion control on construction sites. They include
application of techniques which can be grouped into three
general areas of control:
t Good construction planning to include staging
of construction whenever possible in order to
minimize the area of land disturbed at any
given time
Runoff control through planned stormwater
drainage and management
Utilization of a combination of vegetative,
mulching, and other stabilization measures to
shield and stabilize the surface soils.
These control techniques were developed to retain most of
the overall soil materials on the site, not specifically
for fine-grained sediment control.
In order to determine the effect that standard erosion
control techniques have on the production of fine-grained
sediment, a literature review was performed. In addition,
representatives of agencies actually responsible for imple-
menting erosion and sediment control programs were con-
tacted for their opinions on this matter. The prevailing
opinion among these agencies was that although little
definitive data is available concerning the effectiveness
10
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of these presently existing methods specifically for fine-
grained sediment control, use of these standard practices
will still effect some reduction in the amount of fine-
grained sediment leaving a construction site.
There are some available data, however, which cover various
aspects of the effectiveness of the standard erosion con-
trol techniques in preventing fine-grained sediment runoff.
Therefore, this section will present brief descriptions
of the commonly-used erosion control techniques and pro-
vide guidelines for their applicability and probable cost
effectiveness in controlling fine-grained sediment.
Erosion Control Techniques
Construction Planning
Land development plans which take into consideration the
climate, topography, soils, existing vegetative cover, and
natural drainage systems of both the proposed construction
site and its neighboring areas will provide an insight
into fine-grained sediment control. Since the amount of
this material generated on a site depends primarily upon
the composition of the soils present at the site and the
site runoff factors, information on these parameters is
invaluable during the initial site planning phase. Climato-
logical data is readily available for most proposed construe
tion sites from the National Weather Service. Information
on soils at the site is similarly available from many
Federal and State Departments of Agriculture, Geology, and
Mining; universities; and others. Topography and natural
drainage system surveys, performed utilizing both maps and
actual field inspection,wi11 help to identify problem areas.
Field surveys of the existing vegetation are needed to
identify critical areas or places where natural buffer
strips can be left for erosion control. These natural
buffer strips can decrease the velocity of runoff and trap
sediment, thus retaining it on site.
Reduction in both the area of disturbed land and the amount
of time it is left bare also will help to reduce the amount
of fine-grained sediment in runoff leaving the site. Basi-
cally, this technique requires that the amount of bare
soil exposed to erosive processes at any one time be mini-
mized by proper staging or phasing of the construction.
For example, a large development might be able to be con-
structed in phases whereby a number of small areas are
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constructed and stabilized in sequence rather than exposing
the entire area to construction activity at the. same time.
This might require more comprehensive planning and sched-
uling of the various construction phases if the overall
project schedule is to be maintained.
Plans for the retardation of runoff waters during construc-
tion must also be implemented effectively if control of
silt and clay is to be achieved. These plans should pro-
vide for effective control of increased runoff caused by
changes in soil horizons and surface conditions both during
and after development.
Runoff Control
The control of runoff is perhaps the most important means
of reducing or preventing soil erosion. Along with the
impact of falling raindrops, runoff is a major cause of
soil erosion. The rate of runoff, that is both the quan-
tity and velocity of the surface flow, is directly related
to the rate of erosion. Physical factors having the
greatest effect on both the amount and velocity of runoff
are: soil infiltration rate, surface roughness, slope
steepness, and slope length. These factors can be con-
trolled to a certain degree, thus reducing overall soil
loss and, in turn, possibly reducing the amount of fine-
grained sediment which must be controlled while being
transported by runoff water. This requires that slopes
and drainage systems be properly designed and that both
temporary and permanent runoff control practices be em-
ployed during and after completion of construction.
Runoff control involves three major considerations:
Decreasing the amount of total runoff
Limiting the land surface area over which
the runoff flows
t Proper handling and disposal of concen-
trated flows.
When the amount of runoff generated on a site is reduced,
the potential for erosion is correspondingly reduced. Sur-
face roughening and loosening are two means of doing this.
Scarification and "tracking" (i.e., movement of a cleated
dozer up and down a slope) often are used as means of
protecting the slope and increasing infiltration. Care
must be taken to insure that an equipment operator under-
stands that the surface materials must be roughened in a
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manner that impedes flow rather than channelizing it and
causing it to concentrate.
Contour benching and furrowing are two methods of runoff
control which have been utilized to a great extent in
agricultural practice to reduce soil erosion. They can
also be effectively applied on many construction sites.
The interception of runoff before it reaches highly-erod-
ible, exposed surface areas, or before it accumulates to
a critical concentration, and diverting it to a stabilized
disposal area is another means of reducing soil erosion.
This is accomplished with the use of diversion structures
such as ditches, dikes, and terraces. The principal goal
of interception and diversion is to control the velocity of
the runoff and protect critical areas of the construction
site.
Once the runoff becomes concentrated, grade control struc-
tures may be required to prevent gully erosion or stream
channel degradation. These structures prevent excessive
erosion by reducing velocities in watercourses or by pro-
viding lined channel sections or structures that can with-
stand high flow velocities. They include downdrains used
to channel concentrated runoff down credible slopes, check
dams or weirs which reduce the flow gradient and physically
impede channel degradation, channel linings which shield
the channel from erosion, energy dissipators to slow and
impede the runoff, and level spreaders which spread the
flow.
Table 1 presents the most commonly used runoff control
methods and their functions as related to erosion prevention
Surface Soil Protection
Another general type of erosion control procedure used
during construction consists of minimizing the period of
time that a graded area is exposed by promptly providing
surface protection upon completion of the grading activity.
This requires the use of short term forms of protection
while the long term forms of stabilization are becoming
established.
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Table 1
Control Method
Selective Grading
and Shaping
Vegetative Buffer
Strips
Roughened Surface
Benches
Diversion Structures
Grade Control Structures
Grassed Waterways
Level Spreader
RUNOFF CONTROL METHODS
Functions
Reduces critical slope lengths
and gradients, thus slowing
runoff.
Slows runoff velocity, thus
filtering sediment from runoff.
Reduces volume of runoff by
increasing surface ponding.
Reduces velocity while increasing
infiltration rates. Collects
sediment and holds water.
Reduces runoff velocites by de-
creasing effective slope lengths.
Retains some sediment. Provides
access to slopes for revegeta-
t i o n.
Collects and directs water from
vulnerable areas to prepared
drainageways and so reduces
erosion potential.
Slows velocity of flow, reducing
erosive capacity. Usually per-
manent .
Grass tends to filter sediment
and slow runoff and so stabilizes
drainageways.
Collects channel or pipe flow
and converts it to sheet flow.
Increases deposition.
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Short term forms of surface protection include the use of
chemical emulsions to bind the soil particles into a more
erosion resistant mass; the use of various matting materials
such as jute, wood excelsior, paper, etc.; and the utiliza-
tion of straw, hay, woodchips and other relatively low-cost
mulch materials to shield the soil surface from the action
of raindrop splash and runoff. Fast-growing annual and
perennial plant materials which both shield and bind the
soil can also be used in conjunction with the mulch while
the hearty, perennial plant materials such as grasses,
forbs, and shrubs which will be used for permanent stabi-
lization and landscaping become firmly established.
Effectiveness
Relative Effectiveness of Techniques
Some important comparisons have been made between the use
of different types of mulches, varying mulch application
rates, and other erosion control techniques. Although
these comparisons were not specifically related to fine-
grained sediment control, they are important in that con-
trol of overall soil erosion is expected to result in
the control of some of the fine-grained sediment. In addi-
tion, good on-site erosion control, even if effective
primarily for the control of the coarse-grained soil parti-
cles, can increase the effectiveness of downstream sedi-
ment control devices which are designed primarily for fine-
grained sediment control by reducing their need for main-
tenance due to the accumulation of coarse-grained sediment.
Table 2 presents comparisons of the relative effectiveness,
on a fairly fine-grained soil, of various erosion control
measures normally used on construction sites. The compari-
sons in Table 2 were made based on data from experimental
test plots on gently sloping land. As can be seen from
Table 2, the amount of erosion generated on a site varies
widely when different standard erosion control techniques
are applied. In general, though, it can be seen that as the
application rate of a given mulch or soil binding technique
increases, the amount of erosion generated decreases. There
is a point, however, where the economics of the overall
sediment and erosion control plan come into play. At this
point, it is less expensive to provide downstream sediment
control, instead of increasing the application rate in order
to hold more soil in place. Thus, mulch or chemical treat-
ment rates should be developed on the basis of the cost-
effectiveness of the overall erosion and sediment control
plan.
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Table 2. RELATIVE EFFECTIVENESS OF EROSION CONTROL
TREATMENTS (USING CHECK PLOT AS 100) (REF. 1, 2, 3)
ireatment
Fiberglass and asphalt
emulsion
Asphalt emulsion
Prairie hay and asphalt
emulsion
Prairie hay and asphalt
emulsion
Fiberglass
Woodchlps
Uoodchlps
Wood cellulose fiber
(as a slurry)
Asphalt emulsion
Wheat straw (disk-packed,
cross-slope)
Prairie hay (disk-packed,
cross-slope)
Prairie hay
Prairie hay and
asphalt emulsion
Asphalt emulsion
Resinous soil binder
Prairie hay (disk-packed,
cross-slope)
Wheat straw (disk-packed,
cross-slope)
Sawdust (disked In with
tandem disk)
Asphalt emulsion
Prairie hay (disk-packed,
cross-slope)
Elastomerlc emulsion
Woodchlps
"Resinous soil binder
Emuls1f1able latex
Sawdust (disked In with
tandem .disk)
Check (Untreated)
Wheat straw (disk-packed,
cross-slope)
Check (disk-packed; cross-slqpe)
Woodchlps
Prairie hay (disk-packed,
downslope)
Check (disk-packed.
downslope)
Application Rate
per hectare
1,123 kg & 1,406 1
11,234 1
1,123 kg 4 11,234 1
1,123 kg & 1,406 1
1,123 kg
13,473 kg
20,209 kg
3,930 kg
5,617 1
2245 kg
2,245 kg
1,123 kg
561 kg & 1406 1
2,808 1
11,234 1
1,123 kg
1,123 kg
5.08-cm depth
1,406 1
561 kg
341 1
2,727 kg
5£17 1
303 1
2.54-cm depth
0
561 kg
0
£245 kg
1,123 kg
per acre
1,000 Ib & 150 gal
1,200 gal
1,000 Ib & 1,200 gal
1,000 Ib & 150 gal
1,000 Ib
12,000 Ib
18,000 Ib
4500 Ib
600 gal
2J300 Ib
2,000 Ib
WOO Ib
500 Ib & 150 gal
300 gal
1,200 gal
1,000 Ib
1,000 Ib
2-1n.depth
150 gal
500 Ib
90 gal
6000 Ib
600 gal
80 gal
l-1n.depth
0
500 Ib
0
2000 Ib
1,000 Ib
Relative
Erosion8
1.4
1.9
3.0
5.3
5.3
6.2
6.4
10.0
14.0
14.6
17.4
20.4
21.0
27.5
28.4
Z9.7
47.0
60.6
64.6
65.5
68.9
69.8
86.5
94.6
94.8
100.0
124.3
124.8
194.5
195.7
545.0
Average of three etorme replicated twice for eaoh treatment. All treatments compared
to an untreated check plot, Sharpsburg silty olay, St alope, Lincoln, Nebraska
(rated at 100.). All plots were similarly prepared by planing and smoothing.
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Table 2 only presents data on the relative effectiveness
of erosion control treatments on gently sloping land.
It is virtually impossible, however, that all construction
activities would occur on flat or gently sloping land.
Tables 3 and 4, therefore, present the relative effectiveness
of some erosion control techniques which would normally
be used on more steeply sloping land. Table 3 presents
the results of experiments on a cut slope at a 3:1 slope
in a relatively fine-grained soil, and Table 4 presents
the results of experiments on a 2:1 fill slope in a
similar soil. These two tables show that the relative
effectiveness of a given erosion control method depends
on a number of factors, including the surface characteris-
tics (i.e., cut or fill, etc.), the steepness of slope upon
which it is applied, and other factors. This emphasizes
the importance of adequate site investigations and precon-
struction planning before an overall erosion and sediment
control plan is adopted.
Although most erosion control techniques will provide sub-
stantial protection to a bare soil, there are data which
indicate that some control techniques may not be as effec-
tive as previously thought. Meyer, Wischmeier, and Daniel
(Ref. 4) performed an experiment in which six different
erosion control treatments were imposed on an area denuded
by a bucket Voader and a bulldozer. The treatments were:
scalped only (no further treatment), scarified to a depth
of 5.08 to 10.16 cm (2 to 4 in.), mulched with 2.24 metric
tons per hectare (1 ton/acre), covered with 10.16 cm (4 in.)
of topsoil, covered with 0.61 m (2 ft) of loose subsoil
fill, and covered with 0.61 m (2 ft) of compacted subsoil
fill. They found no significant difference at the 95
percent confidence level between the scalped only, scarified,
and compact fill treatments for all tests. This included
tests on dry to very wet soil, all of which showed that
scarification did not significantly reduce erosion on the
test plots. This conclusion is also supported by the data
presented in Table 2. Plots that were disk-packed, cross-
slope (similar to cross-slope scarification) showed greater
erosion than the untreated check plot.
Light applications of straw, hay, and woodchip mulches
(i.e., applications less than normally recommended) were
also found to be relatively ineffective in preventing
erosion according to the data presented in Table 2.
17
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Table 3.
RELATIVE EFFECTIVENESS OF MULCH TREATMENTS ON AN EARTH CUT
WITH A 3:1 SLOPE (REF. 1)
00
Mulch Treatment
Jute netting
Wood excelsior mat
Fiberglass & asphalt
emulsion
Woodchips & asphalt
emulsion
Prairie hay &
asphalt emulsion
Asphalt emulsion
Coarse ground corncobs
& asphalt emulsion
Prairie hay anchored
with paper net
Fiberglass
Wood cellulose (as a
slurry) & asphalt
emulsi on
Wood cellulose (as a
siurry)
Kraft paper netting
Emulsifiable latex
Application Rate
per hectare
1,123 kg & 1,406 1
13,473 kg & 1,406 1
2^45 kg & 1,406 1
11,234 1
11,227 kg & 1,406 1
2^45 kg
1,123 kg
1,123 kg & 1,406 1
1,123 kg
1,406 1
per acre
1,000 Ib & 150 gal
12,000 Ib & 150 gal
2,000 Ib & 150 gal
1,200 gal
10,000 Ib & 150 gal
2JOOQ Ib
1,000 Ib
1,000 Ib & 150 gal
1,000 Ib
150 gal
Relative
Erosi
100
110
140
230
250
250
450
790
790
850
1,290
2,070
2,540
Total evasion from three simulated rainstorms replicated twice for each treatment.
All treatments compared to jute netting (rated at 100) and are in silty clay,
Nebraska.
-------
Table 4.
RELATIVE EFFECTIVENESS OF MULCH TREATMENTS ON AN EARTH FILL
WITH A 2:1 SLOPE (REF. 1)
Mulch Treatment
Asphalt emulsion
Woodchips & asphalt
emulsion
Jute netting
Prairie hay & asphalt
emulsion
Wood excelsior mat
Coarse ground corncobs &
asphalt emulsion
Wood cellulose (Brand A)
(as a slurry)
Fiberglass & asphalt
emulsion
Wood excelsior
Wood cellulose (Brand B)
Wood excelsior & wood
eellulose
Application Rate
per hectare
11,234 1
13,473 kg & 1,406 1
2^45 kg & 1,406 1
11,227 kg & 1,406 1
1,572 kg
1,123 kg & 1,406 1
4,491 kg
1,572 kg
393 kg & 1,179 kg
per acre
1,200 gal
12,000 Ib & 150 gal
2£OQ Ib & 150 gal
10,000 Ib & 150 gal
1,400 Ib
1,000 Ib & 150 gal
4,000 Ib
1,400 Ib
350 Ib & 1,050 Ib
Re!ative
Erosion3
16
28
100
104
159
234
310
345
391
811
1,500
^Total erosion for three simulated rainstorms replicated twice for each treatment.
All treatments compared to jute netting (rated at 100) and are in silty clay,
Wahoo, Nebraska.
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Fine-Grained Sediment Control
In the investigation of the effectiveness of erosion con-
trol techniques, a number of research studies have found
that the percentage of fine-grained material in the runoff
from a site is greater than the percentage of fine-grained
material in the original in-place soil (Ref. 1, 7, 8).
This was true even with the application of standard erosion
control techniques. Tables 5 and 6 illustrate this point.
Thus, standard erosion control practices are not only more
effective on coarse-grained sediment, but they also reduce
the total amount of sediment generated.
Analysis of these two tables shows a definite shift toward
more fine-grained sediment in runoff following land dis-
turbance. As more of the coarse-grained fraction is re-
tained on site by control measures, the percentage of fine-
grained sediment in runoff increases. The data indicates
that standard erosion control techniques tested are more
efficient in retaining coarse-grained particles on site than
they are in retaining the fine-grained ones. The main
function of these standard erosion control techniques, then,
is to effect some retention of fine-grained particles but
mainly to retain the coarse-grained soil particles on the
site so that the downstream sediment control devices can
more efficiently control the fine-grained particles.
Utilization Recommendations
When applied as recommended, the standard erosion control
techniques show an ability to hold some of the fine-grained
soil particles in place. However, they have a much greater
efficiency in controlling coarse-grained particles.
More effective fine-grained sediment control can be achieved
at a fairly high cost either by utilizing some of the more
effective erosion control techniques shown in Tables 2, 3,
and 4 or by increasing the application quantities of the
various mulches. In an overall erosion and sediment control
program, however, the most cost-effective means of con-
trolling the fine-grained portion of the sediment would be
to first use good, sound erosion control techniques to keep
the majority of the coarse-grained soil particles and some
of the fine-grained ones in place, and then utilize sediment
ponds, other downstream sediment control measures, and post-
depositional devices to prevent the fine-grained materials
from leaving the construction site. When the coarse-grained
soil particles are kept in place, downstream sediment
20
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Table 5. SOIL PARTICLE SIZE IN RUNOFF FROM TEST PLOTS MULCHED
WITH WHEAT RESIDUE ON A 2.3% SLOPE (REF. 1)
Average Erosion
(kg/ha) (tons/acre)
4339 1.94
2074
830
285
Soil In
1.04
0.42
0.14
place
Runoff
(cm)
4.06
5.08
2.90
2.77
Percent Soil Particle Diameter
>50J/
coarse silt
31.5
33.4
25.9
47.4
68.5
50-20/f
medium silt
23.5
17.7
9.1
8.6
18.5
20-5A*
fine silt
19.7
19.5
25.3
15.9
6.8
5-2/*
coarse clay
9.3
8.1
8.1
5.1
1.2
<2 microns
fine clay
16.0
21.3
31.6
23.0
5.0
-------
Table 6. AVERAGE SOIL PARTICLE SIZE DISTRIBUTION IN RUNOFF
FROM A HIGHWAY CONSTRUCTION SITE (REF. 7, 8)
TO
Condition
Average suspended solids
in 4 streams before
construction
Average suspended solids
in 4 streams during
construction
Average suspended solids
in runoff leaving the
construction area
Topsoil at site
Exposed subsoil at site
Percent Soil Particle Diameter
2000-62/J . 62-4/u
(medium sand-si It) silt to clay
7 53
30
27
42
40
42
35
cjj
40
69
70
16
25
-------
control measures will function more efficiently and retain
more of the fine-grained particles. Also,,they will re-
quire less maintenance in the form of periodic clean out.
23
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SECTION VI
SEDIMENT CONTROL TECHNIQUES
Types of Control
Even with the best on-site erosion control plan, some sedi-
ment can be expected to be generated due to the nature of
the construction activities being conducted. Soils are
constantly being disturbed and their characteristics changed,
These activities constantly produce loose, bare soils so
that it is almost impossible to prevent sediment movement
from the site without adequate sediment control measures.
To control the sediment resulting from erosion, various
standard practices are used to contain or trap the sediment
and thus prevent it from leaving the construction site.
These practices can be divided into three general types:
pre-sediment pond techniques such as small check dams to
contain a portion of the sediment near its point of origin,
filter barriers which remove the suspended sediment before
it enters a drainageway, and buffer strips which detain
sediment being transported by sheet flow; sediment ponds,
which are impoundment structures constructed to detain
runoff long enough to remove additional sediment from the
runoff by the action of gravitational settling; and post-
sediment pond devices which remove additional fine-grained
sediments from the water leaving the sediment pond.
Pre-Sediment Pond Techniques
Sediment traps or filters are small, often temporary struc-
tures used at various points within the construction area to
detain runoff for very short periods of time and trap
heavier sediment particles. Examples of such structures
include pits dug along ditches and other areas where runoff
is concentrated, low gravel dikes placed across graded
24
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roadways or in drainage ditch&s, and straw bale barriers
placed at the base of slopes and in drainage ditches.
The effectiveness of sediment traps consisting of gravel
dikes and straw bales depends upon the relationship be-
tween the size distribution of the sediment and the void
spaces in the devices which detain sediment but pass the
water. Reed (Ref. 8) measured the effectiveness of check
dams (traps) used on a highway construction site. He
found that the rock dams and straw bales had trapped the
sand, some silt, but little clay. His measurements, given
previously in Table 6, showed that three percent of the
sediment in the runoff was greater than 62/y (medium sand-
silt) in diameter, 27 percent was between 62 and 4j* (silt
to clay), and the remainder, 70 percent,'was less than ty
microns in diameter (clay). Due to the size distribution
of the particles in the runoff from his measured construc-
tion site, he found that the check dams were less than ten
percent effective, that is, a minimum of 90 percent of the
material reaching these check dams passed through them.
Therefore, the main use of check dams appears to be to trap
coarse-grained sediment.
Other filtering techniques include preservation of natural
vegetative buffers or the installation of new vegetative
buffers downslope of an exposed area. The installation or
preservation of relatively flat vegetated buffer areas at
the base of steep slopes is an effective means of detaining
sediment being transported in sheet flow.
One recent innovation which appears to be a very effective
fine-grained sediment control technique is the use of fences
built of plastic filter fabric. These barriers have been
successfully used on construction sites in both North
Carolina and Virginia. On a highway construction site in
Virginia, the filter barrier removed 99.6 percent of the
total sediment in the runoff (Ref. 9).
Plastic filter fabric fences usually consist of wooden posts
spaced approximately 3.0 m (10 ft) apart with large-hole
wire (hog wire) fencing fastened to the posts. The filter
fabric, approximately 0.91 m (3 ft) high is then fastened
to the wire fence. On the upstream side of the fence, the
fabric is anchored into a ditch which is then backfilled in
order to keep the runoff from flowing under the fence.
Plastic filter fabric will last from 9 to 18 months in such
usage. Burlap could also be used, but it deteriorates more
rapidly.
25
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Most filter material will transmit water at a rate of
about 10~2 cm/sec, which would be equivalent to the sett-
ling rate of an approximately 8-micron diameter particle
(Ref. 10, 11). Thus, these fabrics would be very good for
retaining fine-grained sediment since particles larger
than this size can be expected to settle out of suspension
behind the fabric filter fence.
Material costs for plastic filter fences range from $1.08
to $11.50 per square meter ($0.10-$1.10/sq ft), installed.
About 55 percent of the total installed cost is labor, 15
percent is the filter fabric, and 30 percent of the cost
is due to other materials required to make the fence (Ref.
9).
Sediment Ponds
Conventional Design
One of the conventional methods of controlling the sediment
in the runoff from a construction site is through the con-
struction of a sediment retention basin at a point which
intercepts the surface runoff. These sediment basins are
not designed to achieve any set effluent water quality cri-
terion or to remove any given percentage of the sediment in
the inflow. Rather, the size of the basin is usually
determined by utilizing a rule-of-thumb on the volume of
the basin required based on the area of land disturbed.
For example, the State of Maryland, following criteria
developed by the U.S. Soil Conservation Service, requires
that the sediment basin site should be designed to provide
adequate sediment storage for not less than 127 cubic meters
per hectare (0.5 acre-inch per acre) of disturbed land
(Ref. 12).
Sediment basins designed by these rules-of-thumb are gene-
rally very effective in trapping the coarse-grained fraction
of the sediment in the runoff. In order to retain the fine-
grained sediment, however, conventionally-designed sediment
basins must be redesigned to improve their effectiveness.
26
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Theoretical Design Requirements
Ideal Settling of Particles
Within a detention pond, the removal of sediment from run-
off water is accomplished through settling of the particles
to the bottom of the pond. For the settling of discrete
particles in a suspension of low solids concentration,
termed free or ideal settling, three flow regimes have been
identified according to classical settling theory. The
governing equation for the settling velocity within each
flow regime is (Ref. 13):
Stokes1 Law:
u = _g (S.
Re
-------
u
OJ
vt
u
u
o
"a*
0)
CO
10
3 -
10
2 .
10
10
-1-
10
-2-
10
-3.
10
Newton's Law
Transition Region
Stokes' Law
10"4 10"3 10"2 10
Particle Diameter, cm
-1
FIGURE 1. Ideal Settling Velocity for a Sphere
(10°C Water)
10
28
-------
Specific gravity and anticipated grain size
of the incoming solids
t Anticipated pond water temperature.
In the design of sediment ponds to provide for the deposi-
tion of sediments, the ratio of the pond outflow to the
surface area of the pond, Qo/A, is termed the overflow
velocity, Vo. therefore:
Vo = Qo/A (4)
Based on the above relationship, it can be shown that if
the critical settling velocity of any size sediment particle
is greater than the overflow velocity, that particle and
all larger than it will settle out. Increasing the area of
the pond, therefore, would decrease the overflow velocity.
This means that the critical settling velocity for the
largest size particle to be settled would also decrease.
Thus, at a given overflow velocity, increasing the pond
surface area would effect the settling of smaller particles
within the pond.
There is a limit of practicality, however, on how large
a pond surface area can be provided in order to induce the
settlement of fine-grained particles. As can be seen from
Table 7, the pond area required to settle fine-grained
particles increases rapidly as the particle size to be
settled decreases.
Table 7. MINIMUM SEDIMENT POND AREA REQUIREMENTS
FOR SELECTED PARTICLES FOR A .0283 m3/sec. (1 cfs)
OUTFLOW (Ref. 14)
Particle Diameter Minimum Area Required
(microns) fn2 ft?
60 (fine sand) 7.43 80
40 (fine sand) 13.5 145
10 (silt) 189 2030 (0.046 acres)
1 (coarse clay) 18,900 203,000 (4.6 acres)
0.1 (fine clay) 1,890,000 20,300,000 (466 acres)
29
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Factors Affecting Ideal Settling
In any sediment pond, it is unlikely that purely ideal
settling conditions will be met. Factors which disturb
these conditions and thus alter the pond area required
(as calculated using ideal settling theory) include:
Shape of the suspended particles
Water turbulence
Bottom scouring of deposited sediment
Short circuiting, i.e., when the runoff water
travels through the pond in less time than the
calculated detention period
Nonuniform deposition of materials
Entrance and exit effects
t Specific gravity and velocity of the inflow.
In most cases, the effects of the above factors would be
to increase the required pond surface area over that cal-
culated by ideal settling theory. Therefore, these
significant factors affecting particle settling should be
considered in the design of the sediment pond.
Particle Shape
The ideal settling equations (Equations 1, 2, and 3) were
derived assuming a spherical particle and, for each of the
three flow regions, the drag coefficient for a sphere be-
comes an approximate unique function of the Reynolds num-
ber. However, suspended sediment particles in water are
hardly ever spherical. Drag coefficients for spheres,
cylinders, and disks differ significantly at high Reynolds
numbers (>1000). At low Reynolds numbers (^10), the
settling velocities of rod-like and disk-like particles
are, respectively, 78 percent and 73 percent of the velocity
of an equal-volume spherical particle (Ref. 15).
Turbulence
The horizontal velocity through a sediment pond also affects
the particles which have settling velocities roughly
equivalent to the overflow velocity. This is called the
-------
turbulence effect, even though it occurs with flows at low
Reynolds numbers in the laminar flow range.
The net result of turbulence is to prohibit the settling of
certain particle sizes, which are carried out with the over-
flow instead of settling. An expression which can be used
to compute the removal ratio of any size particle with
turbulence present has been developed (Ref. 16). This re-
moval ratio is defined as the fraction of particles of a
given size that would be settled in a detention pond with
turbulence present. Thus, a removal ratio of 1.0 would
mean that all particles larger than or equal to the given
size would be settled even with turbulence present. This
removal ratio is a function of the flow velocity per unit
of surface area in the settling zone.
Scouring
Scour velocity is defined as the horizontal channel velo-
city required to start in motion particles of size D, and
is given by the equation (Ref. 16):
vc =
where:
vc - scour velocity, cm/sec
B = "stickiness" factor, 0.04 for unigranular
sand and 0.06 for cohesive, interlocking
material (Ref. 17)
F = Darcy-Weisbach friction factor, usually 0.02
to 0.03, depending on the surface over which
flow is taking place (Ref. 17)
and the other parameters are as previously defined in Equa-
tions 1 through 3. In sediment detention ponds, the hori-
zontal velocity through the pond should be kept less than
the scour velocity so that settled smal1.particles are not
scoured from the bottom of the pond. The theoretical scour
velocity is seen to be independent of the dimensions of the
pond.
31
-------
Short Circuiting
The effects of short circuiting are emphasized by mixing
of the materials within the pond, high inlet velocities,
and density currents. Experiments have been performed on
settling tanks of various shapes to determine the influence
which the tank shape has on the settling of particles.
Table 8 presents the results of these experiments (Ref. 16),
A higher short circuiting factor in Table 8 indicates that
short circuiting is more of a problem.
Table 8. SHORT CIRCUITING FOR SETTLING TANKS
Short-Circuiting
Type of Tank Factor (f\
Ideal dispersion tank
Radial-flow circular 1.2
Wide rectangular (length=2.4xwidth) 1.08
Narrow rectangular (length=17xwidth) 1.11
Baffled mixing chamber (length=528xwidth) 1.01
Ideal basin 1.0
2
The surface area (A, in m ) of a pond can be increased
to approximately account for short circuiting as follows
A =F_ V. (6)
where:
V = critical settling velocity, m/sec
Q = flow, m/sec
Methods for Improving Pond Efficiency
It has been shown that the pond surface area required to
remove fine-grained sediments often will become prohibi-
tively large at the flow rates anticipated on many con-
struction sites. Therefore, it is necessary to use tech-
niques which increase sediment pond efficiency, that is,
provide for the settling of fine-grained materials with
less pond surface area than that specified by theoretical
analysis.
32
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Use of Internal Baffles and Design of Pond
Configuration
Recently, research on sediment ponds in conjunction with
lignite mines in Poland has yielded insights into improve-
ment in efficiency. The use of baffles within ponds has
shown promise. Baffles increase the
-------
sediment pond retains water to the riser top. Although
this is effective in terms of fine-grained sediment con-
trol, it might be unacceptable from a safety standpoint.
Another device for improving sediment pond efficiency
through improved outflow design involves a siphon arrange-
ment in a nonperforated riser pipe. This is illustrated in
Figure 2. As shown, the intake for the siphon pipe, lo-
cated at the approximate elevation of the desired cleanout
level of the pond, would help in implementing cleanout
procedures when the required sediment storage capacity has
been reached by providing a readily visible reference point.
If the pond is not cleaned when the sediment reaches the
bottom of the siphon pipe, the pond will not drain between
storm events.
Use of a very wide overflow wier instead of a standard riser
pipe has also been shown to be effective in increasing pond
efficiency (Ref. 18, 19). Using this device, outflow velo-
cities in the wier intake area are decreased, thus ensuring
that fine-grained particles are not carried out with the
overflow.
The use of sand wiers or filter dams at sediment basin
outflows may be useful for filtering-out fine sediment.
They are currently being investigated by the U.S. Army
Engineer Waterways Experiment Station in connection with
dredged material containment areas.
Use of Multiple Sediment Ponds
In a number of cases, two or more sediment ponds in series
have been used to increase the detention of fine-grained
materials, instead of one larger basin covering the same
area. Applications of the value of this technique have been
studied for both the surface coal mining and dredging in-
dustries. Data has shown that multiple sediment ponds in
series are more efficient, i.e., they remove finer particles
than a single, larger pond of the same total surface area is
predicted to (Ref. 20, 21). The multiple basin concept is
similar to that of a compartmentalized, larger sediment
basin. Thus, higher removal efficiencies can be expected
from both multiple sediment basins and a compartmentalized,
larger basin.
34
-------
10 cm (4") pipe
\
Trash rack/
antivortex -
device
Riser
Flow
0.64 cm (1/4")
'hole at
sediment
cleanout
level
_Sediment
cleanout level
'Elevation of top of
conduit
FIGURE 2. Siphon Arrangement in Riser Pipe (Ref. 20).
35
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Use of Flocculants
Basic Concept
Flocculants are chemicals or other materials used to induce
fine-grained sediments to flocculate or aggregate into
small clumps. This increases their rate of settling.
Figure 3 illustrates the use of two sediment ponds when
chemical addition is used to enhance the settling of fine-
grained sediment. The first pond is designed to settle
coarse-grained sediment. Flocculants are added to the
outflow from the first pond. In this way, the chemicals
would be used for the finer-grained materials in the most
effective and economical manner. The required flocculant
dosage increases with increasing concentrations of sedi-
ment to be flocculated. Thus, by settling the coarse-
grained particles prior to the addition of a flocculant, a
more cost-effective dosage can be determined.
Types of Flocculants
Commonly used flocculants include (Ref. 22):
Metal Salts
Aluminum sulfate
Ferrous sulfate
Ferric chloride
Metal Hydroxides
Aluminum hydroxides
Calcium hydroxide
Synthetic Polymers or Polyelectrolytes
An ionic
Cat ionic
Nonionic
Selection of Flocculant and Dosage
The selection of the proper flocculant and the proper dosage
required are important parameters in the process of floccu-
lation. These selections depend upon the characteristics of
the solution and the specific material to be flocculated.
There is no accurate theoretical method or rule-of-thumb
for selection of a flocculant and its dosage. However, a
36
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FLOCCULANT ADDITION
AND MIXING
FINE-GRAINED
SEDIMENT POND
INFLOW
CO
COARSE-GRAINED
SEDIMENT POND
FINAL
EFFLUENT
FIGURE 3. Flocculant Addition in Two-Pond System.
-------
rough estimate of the amount of flocculant required can be
determined through use of a standard laboratory jar test or
by measurement of the zeta-potential or electric charge of
the suspended sediment with a meter. The optimum dosage for
best results will, of course, have to be adjusted to suit
the existing field conditions. Polymer flocculants are
usually used in small doses, on the order of a few mg/1 .
Possible Environmental Impacts of the Use
77? Pn 1 vmpr«;
of Polymers
Research has been performed to identify some of the possible
hazards of the use of polymers of various chemical composi-
tions. Acrylamide and acrylonitrile polymers are among
those approved for use as flocculant aids in treatment for
potable water. However, these may become hazardous to
animals and man if contaminated with their own chemical
monomers (Ref. 23). While this is considered to be an
unlikely occurrence in standard water treatment practice,
there is reason for the exercise of caution where these
polymers are to be used as sediment coagulants in sediment
ponds located on construction sites. For example, approxi-
mately 1.9xl06 liters (500,000 gal) per day of sediment-
laden runoff waters may have to be treated from time-to-time
with about 9 kg (20 Ib). . of these polymers. From time-to-
time the mixture of sediment and polymer must be removed
from sediment basins and disposed of in designated landfills,
by mixing with surface soils, or some other technique.
Under these conditions, the opportunity is great for inter-
action to occur between the polymer and various microorga-
nisms, not only in the sediment pond, but also when the
sediment-polymer mixture is disposed of. No definitive
information is known relative to the rate of biodegradation
of the acrylamide and acrylonitride polymers by soil micro-
organisms. Nor is there any known information with respect
to the phytotoxicity or toxicology of such potential de-
gradation products. But, the need for caution in the use of
these polymers is underlined not only by the fact that their
monomers are neurotoxic, but also because of limited know-
ledge concerning the biodegradation products and their
potential effects on plants, animals, and man.
Carboxymethylcellulose (CMC) and polymers of ethylene oxide
are also used as flocculants in water treatment practices.
Carboxymethylcellulose is reported to be physiologically
inert on oral ingestion by animals and man (Ref. 24).
However, under the conditions of use in construction site
sediment ponds, there is need for the exercise of caution
with respect to overall environmental concerns, because
38
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some of the chemical and enzymatic reactions involving CMC
produce compounds which are soluble in water. These com-
pounds can subsequently cause water quality degradation.
Both the low and high molecular weight polymers of ethylene
oxide possess a Very low order of toxicity to animals and
man. However, they are subject to oxidation by direct
combination with oxygen (as in air) at ordinary temperatures,
and because of this, various antioxidants such as phenolic
materials, sulfur, and phenothiazine, at concentrations of
0.01 to 0.1 percent, are used with ethylene oxide to alle-
viate this tendency (Ref. 25). The exact pollution poten-
tial of these antioxidants under construction site condi-
tions is not known, although all of the above antioxidants
have some toxic effects (Ref. 26).
Practical Experience
Systems which feed chemical flocculants to enhance the
settling characteristics of suspended sediments in water
have been installed at a number of sediment pond sites. For
the most part, these systems have proven effective. Fol-
lowing are brief discussions of some of the better known
examples of this type of treatment alternative. These
examples point out some of the major considerations which
must be taken into account during the use of this control
technique.
Lake Needwood, Maryland
A chemical flocculation system is currently being used to
treat sediment-laden water above Lake Needwood, a multiple
use lake in Montgomery County, Maryland. The system was
installed along the stream channel upstream of a 1.2-hectare
(3-acre) forebay to the lake. The forebay, which was
constructed for detention of the flocculated suspended
solids, is periodically dredged to remove the settled solids.
In this way, the large majority of the suspended solids are
removed before they reach the lake proper, further down-
stream.
The drainage area to the lake is 31.3 km2 (12.1 mi2) and the
design inflow ranges from a baseflow of about 0.11 m3/sec
(4 cfs) to 7.1 m3/sec (250 cfs), a storm which occurs on the
average of once every five years (Ref. 27, 28). Flocculant
addition, which is added to the inflow in proportion to the
flow, begins when the flow reaches 0.57 m3/sec (20 cfs).
39
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Enough flocculant is added for the stream to contain about
5 ppm. Inflow water quality to date has ranged from 15 to
over 20,000 ppm of suspended solids (Ref. 27, 29).
Since the system was installed in 1967, the forebay-chemical
flocculant system has removed from 90 to 95 percent of the
suspended solids (Ref. 27, 28). It was found that approxi-
mately 240 meters (800 ft) of flow along the stream channel
was needed to thoroughly mix the chemical. Removal of
accumulated sediment from the forebay by dredging is done
approximately once every two years. No adverse ecological
consequences have been observed as a result of the opera-
tion. Annual chemical costs have been $3600 per year, which
equates to about $1.14 per hectare of drainage area ($0.46
per acre) (Ref. 30).
Centralia, Washington
Another application of chemical flocculants to help remove
suspended solids, in this instance in a two-pond system, is
being used for sediment control from a surface mining site
near Centralia, Washington. The first pond is used to
settle out the coarse-grained sediment. A coagulant is
added to the overflow from the first pond. Fins and angle-
iron obstructions on the first pond outflow cause turbulence,
which promotes rapid mixing of the chemical. The flocculant
is metered into the stream according to the flow rate
in order to consistently maintain a 5 ppm concentration in
the stream. Flow rates averaged in the 0.38 to 0.63 m3/sec
(13 to 22 cfs) range. Table 9 summarizes the effectiveness
of this system of flocculation.
Table 9. EFFECTIVENESS OF TWO-POND AND
CHEMICAL ADDITION SYSTEM, CENTRALIA MINE (Ref. 31)
Location
Inflow to first pond
First pond overflow
(at chemical addi-
tion station)
Second pond overflow
Volume Percent
Solids
1.5-2.0
0.4-0.7
Turbidity
(JTU)
1000+
85-120
4-15
Suspended Solids
rcg/1
10,000-15,000
120-130
Data not available
40
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Poland
Good suspended solids removal efficiencies, using chemical
flocculants in sediment ponds, have also been achieved at
coal strip mining sites in Poland. Effluents of 20 mg/1
have been obtained with the use of chemical flocculants in
conjunction with sediment ponds designed according to pre-
viously discussed criteria. Thorough mixing of the chemi-
cal with the inflow waters was essential. It was provided
by a long, open channel between the chemical addition sta-
tion and the sediment pond, where turbulent mixing took
place (Ref. 18, 19).
Economics
Prices for liquid polyelectrolytes range between approxi-
mately $0.20 and $0.25 per kg ($0.45-$0.55 per Ib) depend-
ing upon the manufacturer and the quantity purchased.
Liquid polyelectrolytes are ready to be added directly
into the flow and need not be mixed beforehand. Dry
polymer, which can be mixed with water at the construction
site before addition to the stream, costs in the range
of $0.70 to $0.90 per kg ($1.50 to $2.00 per Ib) in concen-
trated form. Since it must be diluted for use, however, it
results in a lower unit cost than the liquid polyelectro-
lytes.
Experimental Techniques
Laboratory experiments have shown that the use of gamma
radiation considerably accelerates the settling of solids
out of a suspension. The exact mechanism which causes this
accelerated settling was not reported. However, under
laboratory conditions, radiation doses in the range of 500-
1000 k Rad caused a two to three times increase in the
settling rate, and a significant decrease in oxygen con-
sumption, color, and turbidity of the water. The effects of
the radiation treatment appeared to be greater in suspen-
sions of greater electrokinetic potential and which had a
high percentage of fine-grained material.
Despite positive results achieved under laboratory condi-
tions, this method is not expected' to be used on a practical
level. This is due to the high cost of the technique and
the uncertainties of the duration of the radiation effects
on the water (Ref. 18).
41
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Post-Sediment Pond Techniques
Description
In many cases, outflow from a sediment pond may still con-
tain too much sediment even though the pond design was
modified specifically to increase removal of fine-grained
sediment. In other cases, the economics may not justify
the use of chemical additives or revised sediment basins in
order to achieve even greater removal of fine-grained sedi-
ment. Therefore, this section presents alternative or
additional ways to remove fine-grained sediment from the
water. Basically, they involve the use of standard sus-
pended solids removal or separation equipment at the out-
flow of sediment ponds. Figure 4 presents the basic con-
cept of this system.
Suspended solids removal equipment which is used in waste-
water treatment, sand and gravel processing, and by various
manufacturing industries was studied for applicability to
this problem. Basic parameters which were assumed for
equipment sizing and performance purposes are on Figure 4.
They include an inflow of about 0.063 m3/sec (1000 gpm) with
a suspended solids content of 500-1000 mg/1, consisting
mainly of fine-grained sediment. The equipment also has
to have the ability to remove particles less than 74 microns
in diameter (silts and clays), have relatively low main-
tenance requirements, and require a minimum of auxiliary
equipment such as pumps, motors, etc. Another basic con-
sideration was the portability of the equipment. Emphasis
was placed on portability so that the equipment could be
used again by a contractor on other construction sites.
Feasible Equipment Types
After an intensive literature review and interviews with
equipment manufacturers' representatives, the following
types of equipment were selected as being feasible for
removing silt and clay in a post-sediment pond role on
construction sites:
Vacuum filters
Upflow filters
Tubular pressure filters or strainers
Microscreens
Hydrocyclones
Separator screens
42
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Emergency Overflow
SEDIMENT
POND
Flow -5 .063 m /sec
(1000 gpm)
POST-DEPOSITIONAL
EQUIPMENT
500-1000 mg/1
Suspended Solids
(Consisting of
Silts and Clays)
co
Sludge
Silt and Clay
Dewatering Pond
-^Outflow
FIGURE 4. Basic Concept of Use of Post-Sediment Pond Equipment.
-------
Gravity settlers (inclined tube settlers)
0 Centrifugal concentrators
Two-stage separators
Vacuum Filters
The vacuum filter is similar to the more widely known
pressure filter. The principal difference is that with
a vacuum filter, filtration is performed in an open tank
where the elements can be easily inspected. The pump of
a vacuum filter is located on the discharge side, thus it is
used to pump water away from the filter after it is filtered
The elements of a vacuum filter can be either of the cylin-
drical or the vertical leaf type.
A vertical leaf type vacuum filter is shown in Figure 5.
Suspended material is caught and retained on the filter
element. In the cylindrical or rotary type vacuum filter,
a drum which is covered with the filter media revolves in a
tank filled with the slurry to be filtered.
The filter elements of either type of equipment can be
coated with a substance such as diatomaceous earth or other
precoat material so that particles much finer than the
openings in the filter element can be retained. Vacuum
filters operate at low differential pressures, on the order
of 0.42 to 0.70 kg/cm2 (6-10 psi). When a precoat substance
is utilized on a vacuum filter, particles down to about one
micron in diameter can be removed and very clean effluents
result. Influent slurries, however, usually must be
limited to less than a one percent solids concentration.
The vacuum filter can be cleaned by either hosing, internal
sluicing, or air bump backwashing.
Upflow Filters
The upflow filter incorporates four sediment removal tech-
niques, resulting in an overall effective method of water
clarification. Basically, it involves the filtration of
water in an upward direction through progressively finer
filter media. This traps solids throughout the entire
filter column. Gravity also plays a role in the upflow
filter since the larger solids tend to settle out of the
liquid being filtered as it works its way up through the
media. Prevention of the movement of the filter materials
is accomplished by the use of restrictive screens and grids.
Polyelectrolytes can be added to the sediment-laden in-
fluent for further solids removal by the filter.
44
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Outflow
Sediment- > Baffle
Laden Inflow
Filter Element
FIGURE 5. Cross Section of Typical Vertical
Leaf Vacuum Filter.
45
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Tubular Pressure Filters or Strainers
This unit consists of a vertical pressure vessel containing
tubular filter elements. As shown in Figure 6, sediment-
laden waterj under pressure, enters the filter element chamber
where the filter tubes or cartridges are housed. It is
forced through the walls of the filter cartridges, with the
clarified water flowing into the hollow cores of the car-
tridges and then being removed from the filter. Periodi-
cally, the particles are washed from the walls of the car-
tridges and discharged from the filter through a bottom
drain. This cleansing action, termed backwashing, is
accomplished by reversing the pressure in the filter and
applying it from inside the cartridges toward the outside,
thus knocking the particles off. The filters can also be
equipped with disposable 'cartridges, which are replaced
instead of backwashed when they become clogged.
Common materials which filter cartridges or tubes are con-
structed of include cemented sand grains, stainless steel
screening, cellulose, and glass. The size of sediment
particles to^be removed by a filter depends upon the size
of the void 'spaces in the material used in the cartridges.
Sizes of particles removed range from a few hundred microns
(sand) for some tubes made of stainless steel screening, to
less than one micron (clays) for some special application
cartridges. Filtering capacities per unit area of filter
material decrease as the size of sediment particles removed
decreases.
Filter elements can usually be precoated with a filter aid
to remove a higher percentage of the sediments. When a
filter aid is used, retention of particles down to a few
tenths of a micron in diameter is possible.
These types of filters can be set up to be operated in the
manual, remote manual, or fully automatic mode.
Microscreens
A microscreen consists of a rotating drum with a fine screen
around its periphery. Feed water enters the interior of
the drum through the open end and passes radially through
the screen with deposition of solids on the inner surface of
the screen. At the top of the drum, pressure jets of
effluent water are directed onto the screen to remove the
deposited solids. A portion of the backwash water penetrates
the screen and dislodges solids which are captured in a
waste hopper and removed through the hollow axle of the
unit.
46
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Clean Water
Outflow
Back-flush Sediment
Filter Tubes
or Cartridges
Sediment-Laden Inflow
FIGURE 6. Simplified Operation of a Typical Pressure
Filter or Strainer.
47
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Hydrocyclones
A hydrocyclone uses centrifugal force to cause incoming
fluid and sediment particles to accelerate rapidly and
uniformly in an open conical section. Maximum centrifugal
force is reached at a bottom orifice where rejected material
is discharged. Clarified effluent is discharged from the
top of the cone. Figure 7 shows the basic operation of a
hydrocyclone cone.
Hydrocyclones are simple, efficient, and low cost devices
for removal of sediment solids from sediment-laden water.
There are no moving parts, and the removal of particles as
fine as five to ten microns in diameter (silts and clays)
can be accomplished. Incoming waters containing up to 16
percent solids can be treated.
Hydrocyclone cones come in a variety of sizes and a number
of them can be grouped together in banks to obtain virtually
any desired flow rate. The most common sizes which would
be applicable to construction sites have top diameters which
range from 5 to 30.5 cm (2 to 12 in.) in diameter. Gene-
rally, the smaller the cone size, the finer the particle
size that can be removed at a given differential pressure
(the difference between incoming and outgoing pressures),
albeit at a smaller flow rate. Normally, hydrocyclones
operate at pressure differentials between 0.7 and 4.2 kg/cm2
(10-60 psi).
Separator Screens
This category of suspended solids removal equipment com-
prises a wide variety of vibrating screens. The screens
normally consist of rectangular or circular structures
supporting wire mesh screens. Water is introduced directly
onto the screen surface. Solids are detained on the
surface while the screened water exits downward through the
screen. Trapped solids are vibrated to the outer periphery
of the screen element for disposal.
Screens are available to remove a wide range of particle
sizes. Particle sizes removed by these screens ranges from
a few hundred microns in diameter (sand) to somewhat less
than 50 microns. Sediment removal rate decreases, of course,
with decreasing size of particle removed.
48
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Sediment-Laden
Inflow
Vortex
Outflow of
Water
Discharged Sediments
FIGURE 7. Basic Operation of a Hydrocyclone
49
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Gravity or Inclined Tube Settlers
The principle of operation of the inclined tube settler is
illustrated in Figure 8. Water entering from the bottom of
the tube and flowing up the tube at velocity Vf contains
particles having a settling velocity, Vs. The resultant
velocity vector, vr, tends to move the particles toward the
tube wall where they become entrapped in a layer of particles
previously settled. The steep inclination of the tubes
causes the sludge to counterflow along the side of the tubes
after it accumulates. It then falls into a sediment storage
sump below the tube assembly. The inclined tube settler
configuration also requires influent and effluent chambers
to distribute the flow to the tubes and to collect it after
clarification.
Inclined tube settlers are manufactured with tubes having
various geometrically-shaped cross sections. Systems em-
ploying flocculation with inclined tube settlers are capable
of removing particles less than 10 microns in diameter
(fine sand). They are usually used to clarity influent
waters which have under 1000 mg/1 of suspended solids.
Typical flow rates through inclined tube settlers are on the
order of 8.5 to 14.2 1iters/min/m2 (3 to 5 gpm/ft2}. The
number of tubes may be increased to provide treatment for
virtually any flow rate desired.
There is limited operating data available on gravity sett-
lers which is applicable to construction site installations,
however, most installations have produced satisfactory
performance. Problems with buildup of slime growth, which
may constrict shallow passages, have been reported, conse-
quently, periodic cleaning may be required. In view of
this factor, an allowance for accessibility to the settling
units should be incorporated into the design of inclined
tube facilities.
Centrifugal Concentrators
The centrifugal concentrator utilizes a high flow rate and a
fine-mesh centrifugal screen to remove suspended solids from
the sediment-laden inflow (Figure 9). The incoming fluid
enters the unit from the bottom. The flow travels upward
through the center of the unit (inside the screen) and onto
distributors which direct the flow against the inner top
surface of the rotating screen. Suspended sediment is
caught in the screen and washed down the inside. The com-
bination of the screen's rotational velocity and the impinge-
ment velocity of the inflowing water results in removal of
50
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Single Inclined Tube
maximum
where:
v.
s L cos 0
L
0
d
= flow velocity through the tube
= resultant velocity vector
= settling velocity of a particle
a length of the tube
= inclination angle
= diameter of the tube
(Simple Theory)
FIGURE 8. Principle of Operation of an Inclined
Tube Settler (Ref. 22).
51
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tn
no
Rejected
Sediment
Rotating
Cylindrical
Screen
.-,« ,. . x.,.v.-tv;-
Inflow
FIGURE 9. Cross Section of Centrifugal Concentrator.
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particles smaller than the screen mesh openings. These
centrifugal units can remove particles down to around 40 or
50 microns in diameter (silts).
Two-Stage Separators
This equipment is similar to conventional hydrocyclones.
However, instead of the standard cone shape, the walls of
the separator are cylindrical. Therefore, flow velocities
decrease as solids are spun through orifices in the center
rather than increase as in standard hydrocyclones.
The flow enters the separator at a high velocity. Solid
matter is spun through tangential openings in the inner
shell and settles to the bottom of the separator where it is
discharged. After the sediment" has been removed, the water
exits at the top of the separator. Removals of up to 98
percent of all solids greater than 44 microns (silt) have
been reported for this piece of equipment.
Cost-Effectiveness
Table 10 presents a summary of the capital costs and rela-
tive effectiveness of the various pieces of post-sediment
pond equipment identified above. Included are capital cost
per unit of flow, anticipated smallest diameter particle
removed, design flow rates of the equipment, and the ancil-
lary equipment, supplies, power, and facility requirements.
The table provides a compilation of the data received from a
number of manufacturers of the equipment. Hence, the unit
capital costs show quite a variance for some of the pieces
of equipment. The smallest particle size removed also
varies somewhat, depending upon the manufacturer. The
actual cost to a contractor will vary depending upon the
exact specifications of the equipment. For example, whether
or not such things as automatic solids unloading, automatic
backflushing, totally automatic operation, and the required
feed pump are specified will have a, bearing on the total
investment which must be made. Table 10 is provided as a
general guide to the relative costs and sediment particle
sizes removed by the various pieces of equipment. Specific
site characteristics and the amount of fine-grained sediment
either removed by sediment ponds or retained on site by
other techniques will determine whether or not the use of
post-sedimentation equipment is necessary and, if it is
necessary, what type of equipment would be the most effec-
tive for a specific construction site. The particle size of
53
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Table 10. POST-SEDIMENT POND EQUIPMENT COSTS AND REMOVAL EFFICIENCIES
Equipment Type
Unit Capital Cost (1975),
$/Hter/min
($/gpm)
Approximate
Smallest Particle
Removed
en
Vacuum Filter
Vertical Leaf,
Diatomaceous Earth
Filter Coat
Rotary Drum
with Precoat
Upflow Filters
Tubular Pressure
Filters or
Strainers
Microscreens
Hydrocyclones
Separator Screens
Gravity or Inclined
Tube Settlers
Centrifugal
Concentrator
Two-Stage Separator
71 (270)
528 (2000)
21-25 (80-95)
5-13 (20-50)
17-23 (63-88)
1-3 (4-10)
3-17 (10-63)
31-48 (127-182)
16 (60)
3-9 (10-35)
1 (fine clay)
1 (fine clay)
2-10 (clay-silt)
30 (silt)
20-40 (silt)
10-20 (silt)
45-50 (silt)
1-10 (clay-silt)
44 (silt)
44 (silt)
Design Flow,
liters/min
(gpin)
1100 (300)
160 (40)
3780 (1000)
3780 (1000)
2650-3290 (700-870)
3780-4160 (1000-1100)
190-1900 (50-500)
470-2400 (120-920)
1890 (500)
1510-4540 (400-1600)
Remarks
Requires centrifugal pump and electricity.
The system is self-contained and skid-mounted.
Clean water for initial filling ind washdovm
must be available. A simple equipment shelter
is required.
Requires two pumps and electricity. Precoat
material not included in price. Uses about
1450 kg (3200 Ib) of precoat each 24 hr of
operation.
Feed pump required. Can be skid-mounted.
Polyelectrolyte costs not included.
Pump required. Incoming solids limited to
about 1000 mg/1. Includes automatic backflush.
Requires electric power supply, leveled pad,
wash water supply and pumps. Cost includes
pump and controls.
Includes all valves, gauges, supports, headers,
and piping. Requires feed pump. Skid-mounted.
Electrical power required. Cost includes screen
motor. Site requirements include a level base,
and a possible support frame for the feed unit.
Requires Influent pump. Particle size removed
assumes flocculant addition. Unit 1s fully
assembled and ready to install.
Cost Includes feed pumps and electrical controls.
No special foundation or enclosure required.
Influent range = 2000-3000mg/l suspended solids.
Requires electrical power.
Feed pump required. Rated to remove 981 of
particles of specified size.
-------
the fine-grained sediment which must be removed to meet a
specific effluent water quality is, of course, one of the
basic considerations.
The applicable post-sediment pond equipment identified in
Table 10 were further analyzed to determine which pieces of
equipment have the highest applicability to construction
site conditions. The equipment parameters which were most
important in this analysis included the ability to process
at least 3780 liters/min (1000 gpm) with suspended solids
contents of not less than about 1000 mg/1 at a cost which is
not prohibitive. For example, many of the pieces of equip-
ment consist of individual units which process a given flow.
The number of units on line can therefore, theoretically, be
increased to handle any specified flow. However, in many
cases the cost of such multiple units quickly becomes pro-
hibitive.
Table 11 summarizes the initial costs of the most feasible
post-sediment pond equipment. The equipment is grouped
according to smallest particle size which each type is
capable of removing.
Data presented in Table 11 indicates that as the particle
size which is desired to be removed decreases, the equip-
ment cost generally increases. The notable exception to
this is the use of hydrocyclones. Hydrocyclones are re-
ported to be capable of removing a large percentage of fine-
grained sediment particles at a reasonable cost. Therefore,
they would probably be the most useful for fine-grained
sediment control in the widest variety of situations.
The investment which one is willing to make in the purchase
of post-sediment pond equipment is dependent upon the se-
verity of the fine-grained sediment problem and the total
cost of the construction. In some instances, removal of
particles less than ten microns in diameter may be required.
If total project costs and anticipated future usage justi-
fies the investment, the use of upflow filters, or gravity
or inclined tube settlers as post-sediment pond devices is
indicated.
In summary, then, if the use of post-sediment pond equipment
is indicated, hydrocyclones appear to be able to provide
the broadest range of protection against fine-grained
sediment pollution at the most reasonable cost. If the
removal of particles smaller than ten microns in diameter
is required, upflow filters or gravity (inclined tube)
55
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Table 11. COSTS AND REMOVAL EFFICIENCIES OF
MOST FEASIBLE POST-SEDIMENT POND EQUIPMENT
Smallest Diameter Approximate Average
Particle Removed (,/*) Equipment Type Initial Cost ($)*
l-iot (clay-silt) Upflow filters 95,000
Gravity (inclined 110,000
tube) settlers
10-20 (silt) Hydrocyclones 7,000
20-30 (silt) Tubular pressure 50,000
filters/strainers
30-50 (silt) Two-stage separator 20,000
*
Based on a design inflow of 3780 liters/min (1000 gpm)
Twith the addition of a chemical flocculant.
5,6
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settlers with the addition of chemical flocculants would
probably be the most efficient at the most reasonable equip-
ment cost. It is recommended, of course, that the decision
to purchase post-sediment pond equipment also take into
account the need for the equipment on future construction
sites.
57
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SECTION VII
REMOVAL AND DISPOSAL OF SEDIMENT FROM DETENTION PONDS
Removal
When a sediment pond becomes filled, its efficiency for
removing sediment decreases. Removal of the sediments
accumulated in ponds should, therefore, be done on a
periodic basis at any construction site in order to keep the
ponds functioning at their maximum efficiency. There are a
number of means by which this can be accomplished. The
various alternatives are discussed below. The feasibility
of utilizing a specific method at a specific site will
depend upon site constraints such as the size of the sedi-
ment basin, equipment availability, and time constraints.
Conventional Draglines
One of the commonly used methods of cleaning ponds involves
the use of a crane with a dragline bucket attached. The
crane is located on the bank of the pond. Through rapid
rotation of the boom, the bucket is thrown into the pond
and then hauled in as it scrapes, from the bottom, a load
of sediments. The entrapped material is either piled in
windrows along the bank of the pond or loaded directly onto
trucks.
The reach of a dragline is usually limited to about 18
meters (60 ft) from the crane. A longer reach can be
achieved if a long boom is used; however, this practice
results in less efficient use of the bucket. In addition,
the long boom can present difficulties in transporting the
dragline equipment to the pond site. Thus, the cost per
yard removed by a dragline with a conventional boom usually
is significantly lower than one with an extra long boom.
Sediment removal with a conventional dragline is, therefore,
limited to removing the material from ponds up to 36 meters
(120 ft) wide, or from the edges of larger ponds. Since the
58
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dragline is positioned on the edge of a sediment pond, it
can be used to clean ponds with bottoms that are too soft to
support other types of cleaning equipment which must enter
the pond, after it is drained, to remove the sediment.
The cost of c-leaning a sediment pond by dragline is about
$3.20 per cubic meter ($2.50/yd3) removed (Ref. 32).
Front-End Loaders
Standard front-end loaders are often used to enter a pond
and remove the accumulated sediment. A pond must first be
drained prior to cleaning operations to allow enough time
for some sediment dewatering and drying to take place.
Then, the front-end loader enters the pond and removes the
sediment.
This method of sediment removal is less expensive than use
of a convertional dragline. However, two important con-
siderations will limit its use:
t The pond must be drained and dewatered before-
hand. Thus, use of the pond for sediment
retention is lost for a longer period of time
than with a conventional dragline operation.
Specific site and/or pond bottom characteristics
may preclude use of this method if the front-end
loader cannot enter the pond at all.
Crane-Operated Scrapers
Sediment removal by this equipment -involves basically a
variation of the conventional dragline approach. This equip-
ment, however, increases the effective reach of a crane to
over 300 meters (1000 ft).
Figure 10 shows two different approaches for the use of
crane-operated scrapers. Several manufacturers produce
scrapers which are compatible with them. Basically, as
shown in the figure, the scrapers are hauled in by cranes
or winches, but are returned by a cable attached to a "dead
man", or support mechanism, located on the bank of the
pond, some distance away. As the scraper is being hauled
in, it functions in the same manner as a conventional drag-
line bucket in that it scrapes the bottom and accumulates a
load of sediment which it transport toward the crane. The
sediment is piled along the .side of the pond for subsequent
59
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Guide Block
Load Cable
Track Cable
i1 Deadman"
Support
FIGURE lOa. Arrangement for Crane-Operated Scraper.
Boom Support
Guide Block
Load Cable
Track Cable
Level
Scraper
.Bulldozer
Support
FIGURE lOb. Alternate Arrangement for Crane-Operated Scraper.
60
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removal by front-end loader and truck. Larger scrapers
can be used and greater mobility achieved by using a boom
support for the crane and a bulldozer for the tail anchor,
as shown in Figure 10 b. Like the conventional dragline,
they can be used where pond bottoms are too soft to provide
a firm foundation for other types of equipment.
Costs for sediment removal are roughly equivalent to those
of a conventional dragline, because the economics inherent
in the longer reach of the scraper roughly offset the addi-
tional initial set up costs and possible additional spoil
handling costs.
Hydraulic Dredges
Small hydraulic dredges are available which can be used to
clean sediment ponds. Usually, these dredges are equipped
with mechanical augers or cutter teeth which loosen the
sediment. Sediment is then pumped into a submerged intake
pipe attached to or directly behind the auger or cutter
teeth. Discharge from the dredge pump is directed to a
spoils area for subsequent dewatering. Resuspension of
the sediment in the pond is kept to a minimum during the
dredging activity since water is continually being drawn
into the intake pipe. Some hydraulic dredges are even
equipped with shields over the intake pipe to further reduce
suspended sediment movement.
One difficulty connected with this method of sediment
removal is the problem of the proper disposal of the large
quantities of water pumped along with the sediment. Since
the solids content of the dredged slurry is sometimes less
than 10 percent by weight, adequate containment basins must
be provided to dewater, dry, and otherwise handle the
dredged material.
Generally, cleaning of a sediment pond by hydraulic dredging
becomes more economically feasible as the size of a pond
increases. In addition, it must contain water of sufficient
depth to float the dredge throughout the sediment-removal
operation. Therefore, hydraulic dredging is most likely a
feasible alternative for sediment removal in ponds with an
area of 0.4 hectare (1 acre) or larger and located across a
drainageway which has a constant inflow. Small hydraulic
dredges which could be used to clean sediment ponds have a
minimum pumping rate of about 0.09 m3/sec (1500 gpm).
Thus, a pond will require at least that amount of inflow to
keep them afloat unless discharge water is decanted and
recycled after flowing through the containment basin.
61
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Dewatering and Drying Techniques
Once sediment has been removed from a sediment pond, it must
be dewatered and/or dried before it can be properly disposed
of or reused. If the sediment is removed by equipment other
than a hydraulic dredge, much less water is included; as a
result, it is much easier to dewater further. If it was
removed via hydraulic dredging, up to 90 percent of it by
weight could be water, thus causing a more time-consuming
dewatering process. Presented here are techniques and
alternatives which appear promising for use in the dewatering
and drying of fine-grained sediments after they have been
removed from a sediment pond.
Use of Drying Beds
With this technique, sediment that is removed from a sedi-
ment pond is placed in a drying bed which has a sand/gravel
la.yer at the bottom. It results in downward drainage of
water and consequent dewatering of the material. The sand/
gravel layer is connected to an underdrain system which
carries the water away from the .sediment. One drawback to
the use of this technique involves the clogging of the
sand/gravel layer by the fine-grained sediment.
Some success has been reported on the use of this technique
as an aid in dewatering fine-grained sediment which was
removed from a pond by a crane-operated scraper.. In one
study, the use of gravity drainage beds did increase the
dewatering rate of fine-grained sediment which was removed
from a pond, as compared to simply dumping the removed
sediment into a confined disposal area (Ref. 32).
Rehandling of Deposits
Simple rehandling of fine-grained sediment removed from
ponds is presently being used by the sand and gravel pro-
cessing industry as a means of drying and dewatering it
before truck transport (Ref. 33). The settled sediment is
removed with a crane and dumped into an adjacent contain-
ment area. Later, this containment area is cleaned again
by the crane. By this time, enough water has drained from
the slurry so that it can be cast directly onto the ground,
without the need for confining dikes, for further drying.
When sufficiently dry, the fine-grained sediment is loaded
onto trucks with a front-end loader, and transported off the
site.
62
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The main disadvantages of this operation involve the rela-
tively large amount of area required and the relatively
long drying period. Sufficient time and area must be pro-
vided for dewatering and handling the material. As an aid
to dewatering, a gravel filter layer and underdrain system
could be used. This could decrease the dewatering times
required between handling operations.
Reworking of Deposits
Reworking the top portions of fine-grained sediment deposits
which have either been removed from a sediment pond, or
remain in the pond after the pond has been drained, has
proven to be effective in increasing the dewatering rate.
When the surface has been reworked, the water which is
brought to the surface evaporates.
Experiments performed on sediment removed from a pond by a
crane-operated scraper showed that surface scarification was
effective in aiding the immediate drying of the sediment to
a depth of approximately 0.3 meter (1 ft) (Ref. 32). The
scarification was found to be most effective on the finer-
grained materials.
Field trials have been conducted in which a conventional
tracked vehicle was used to continually agitate the surface
of a containment basin which was filled with sediment de-
posited via a hydraulic dredge. Consolidation and dewatering
was obtained in a much shorter period of time than if the
material was allowed to dewater naturally (Ref. 34). The
use of a twin helical screw amphibious vehicle to produce
continual surface roughening of deposited sediment in order
to enhance drying has also been successfully demonstrated
(Ref. 35).
Other Techniques
The following dewatering and drying techniques which may
be applicable to the fine-grained sediment problem have been
identified. They have not been field tested on a large
scale and thus are not readily available for immediate
application on construction sites.
63
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Thickening Followed by Vacuum Filtration
A potentially useful concept for the dewatering of fine-
grained sediment which has been investigated for possible
use in the restoration of the clay spoil ponds in the sand
and gravel processing industry is shown in Figure 11 (Ref.
33). This method consists of the use of a standard sett-
ling tank such as those used in the wastewater treatment
industry followed by a rotating drum vacuum filter.
3
An experimental system was designed to process 0.12 m /sec
(1950 gpm) of a clay slurry which was to be removed by
pumping from the bottom of a pond. This technique shows
promise as a means for dewatering fine-grained sediment,
as no cranes would be necessary to handle the silt, clay,
and water mixture and the use of trucks would be reduced.
The cost of such a system, however, is estimated to be over
$100,000. Full scale prototype operations are planned
to further refine this technique.
Centrifugation
Centrifuges mechanically dewater sediment through the use
of centrifugal force. This technique has long been used for
the dewatering of sewage sludges, and standard mechanical
centrifuges are available. At present, the most commonly-
used centrifuge for sludge dewatering is the solid bowl
centrifuge. It provides fairly good dewatering and produces
solids concentrations of the discharged solids-in the range
of 15 to 35 percent by weight. The use of centrifuges for
dewatering fine-grained sediment deposits is relatively
expensive, and thus their practical use on construction
sites is probably limited.
Mechanically Drying and Heating of Materials
Large mechanical dryers and heaters, used for a variety of
drying tasks in the chemical and mineral processing indus-
tries, may be used for sediment dewatering purposes. A
common type of dryer is the rotary dryer, in which heat
is supplied to a large, continuously-rotating drum. The
rotating dryer shell exposes the wet surfaces of the sedi-
ment particles to the drying media as they are conveyed at
a controlled rate through the dryer. The applicability of
this technique to the drying of fine-grained sediment re-
moved from ponds would be limited by the availability of
sufficient fuel and power for heating. In addition, capi-
tal, operation, and maintenance costs are much higher for
this technique than for other standard methods of dewatering
or drying.
64
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Clean Water
I
Water and
Fine-Grained
Sediment
Settling Tank
Silt
/
/
/
X
Optional Tank
Truck Transport
Off Site
Clay
X
X
X
Water, Silt,
& Clay
yv-QQ O. Q, -y\
Silt
Rotary Drum Vacuum Filters Clay
Water
FIGURE 11. Settling Tank - Vacuum Filtration Technique
for Dewatering Fine-Grained Sediment.
65
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Capillary Enhancement
Experiments conducted in the past have shown that vertical
capillary wicks have the potential for removing water from
subsurface zones of dredged material fills, promoting the
formation of a surface crust, and increasing the evapora-
tion rate from the material. Further laboratory evaluations
are planned if an initial state-of-the-art assessment proves
the practicability of the technique (Ref. 36).
Reuse of Sediments
The disposal of fine-grained sediments after they have been
removed from a sediment pond and sufficiently dewatered has
always been a problem. If space is available, spreading in
another area and stabilizing through the establishment of a
vegetative cover offers perhaps the most practical solution.
Some research has been performed on the utilization of fine-
grained sediments for a variety of other purposes. Some
promising results have been obtained regarding the use of
dredged sediments for a variety of agricultural purposes
such as turf farming and the rehabilitation of eroded and
depleted soils. For example, the following utilization
procedures were found usable for disposing of sediments
which are continuously being removed from the Delaware River
and Bay (Ref. 37) during maintenance dredging operations:
The application of sediments to light sandy
soils to improve their agricultural potential
at rates of 450 to 670 metric tons per
hectare (200-300 tons/acre).
0 The application of sediments also to heavier
soils without reducing their agricultural
potential.
The additions of sediments to beach sands
for establishing vegetative cover.
During another study, the feasibility of enhancing dredged
sediments in order to acquire a material with improved
characteristics for the growing of grass was investigated.
Several low cost and readily available materials were tested
for their effectiveness as conditioners for sediment which
had been removed from a sediment pond. They include
66
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digested sewage sludge, fly ash, woodchips, crushed dolo-
mite, and 10-10-10 fertilizer. Good grass germination and
growth were achieved on a number of plots (Ref. 32).
The use of fine-grained sediments as fill material for
engineering purposes has often been proposed. The ideal
material for this use would probably be clean sand, how-
ever, both coarse- and fine-grained sediments have been
used (Ref. 38). For most engineering uses, fine-grained
sediments will have to be blended with coarser-grained
sediment in order to obtain material with acceptable
physical characteristics such as shear strength, cohesion,
permeability, and plasticity.
Some research has been performed on the utilization of the
fine-grained sediments, particularly the clays, for the
manufacture of bricks (Ref. 39). The results indicate that
although technologically feasible processes can be deve-
loped, the immediate commercial feasibility of the clay
utilization is limited because of the variability in the
quality of the clays obtained.
Overall, the determination as to what possible reuse will
be made of the fine-grained sediments removed from a sedi-
ment pond will depend upon what alternatives are available
in the immediate vicinity of the construction site. A
variety of agricultural uses appear to be feasible, but
their ultimate use would depend upon the cost of trans-
porting the sediments from the construction site to the
point of use. Generally, there is always some need for
fill material in the general area surrounding a construction
site. Again, the economics of transporting the sediment to
its point of need, the physical characteristics of the sedi-
ment, and the proposed use of the fill would dictate whether
or not this is a feasible alternative.
67
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SECTION.VIM
REFERENCES
1. Swanson, Norn's P., "Advances in Water Erosion
Control in the Great Plains," Conservation
Tillage in the Great Plains. Great Plain Agri-
cultural Council Publication No. 32, 1968,
pp. 37-46.
2. . Swanson, Norris P., and A.R. Dedrick, "Protecting
Soil Surface Against Water Erosion with Organic
Mulches," presented at the Annual Meeting of the
American Society of Agronomy, Oct. 31-Nov. 5, 1965,
Columbus, Ohio.
3. Swanson, N.P., A.R. Dedrick, H.E. Weakly, and H.R.
Haise, "Evaluation of Mulches for Water-Erosion
Control," Transactions of the ASAE.1965. pp. 438-
440.
4. Meyer, L.D., W.H. Wischmeier, and W.H. Daniel,
"Erosion, Runoff and Revegetation of Denuded
Construction Sites," Transactions of the ASAE,
Vol. 14, No. 1, 1971, pp. 138-141.
5. U.S. Environmental Protection Agency, Comparative
Costs of Erosion and Sediment Control, Construction
Activities, Document No. EPA-430/9-73-016,
July 1973, 205 pp.
6. The Dow Chemical Company, An Economic Analysis
Of Erosion and Sediment Control Methods for
Watersheds Undergoing Urbanization, Report No.
C-1677, for U.S. Dept. of the Interior, OWRT,
Feb. 14, 1972, 181 pp.
68
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7. Weber, William G., Jr., and L.A. Reed, "Sediment
Runoff During Highway Construction", Civi1
Engineering. Vol. 46, No. 3, March 1976, pp. 76-79.
8. Reed, Lloyd A., "Controlling Sediment from Con-
struction Areas," Third Symposium on Surface
Mining and Reclamation, Vol. II, NCA/BCR Coal
Conference and Expo II, Oct. 21-23, 1975, pp. 48-57
9. Dallaire, Gene, "Filter Fabrics: Bright Future in
Road and Highway Construction," Civil Engineering,
Vol. 46, No. 5, May 1976, pp.61-65.
10. Seemel, Richard N., "Plastic Filter Fabrics
Challenging the Conventional Granular Filter,"
Civil Engineering. Vol. 46, No. 3, March 1976,
pp. 57-59.
11. Steel, Ernest W., Water Supply and Sewerage,
Mc-Graw Hill Book Company, Inc., New York, 1960,
655 pp.
12. Soil Conservation Service, Standards and Specifi-
cations for Soil Erosion and Sediment Control in
Urbanizing Areas, U.S. Department of Agriculture,
1969.
13. Weber, W.J., Jr., Physicochemical Processes for
Water Quality Control. Wiley-Interscience, New
York, 1972.
14. Poertner, Herbert G., Practices in Detention of
Urban Stormwater Runoff, American Public Works
Association, Special Report No. 43, June 1974,
231 pp.
15. Fair, G.M., J.C. Geyer, and D.A. Okun, Water and
Wastewater Engineering, John Wiley & Sons, New
York, N.Y., 1971.
16. Camp, T.R., "Sedimentation and the Design of
Settling Tanks," Transactions of the American
Society of Civil Engineers. Vol. Ill, 1946,
pp. 895-958.
17. Clark, B.J., and M.A. Ungersma, eds.., Wastewater
Engineering: Collection, Treatment, Disposal,
Metcalf & Eddy, Inc., McGraw-Hill, New York,
N.Y., 1972.
69
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18. Janiak, Henryk, "Purification of Waters from
Strip Lignite Mines," Environmental Protection of
Open-Pit Coal Mines in Poland. Central Research
and Design Institute for Open-Pit Mining,
Wroclaw, Poland, April 1976.
19. Janiak, Henryk, personal communication, May 20, 1976.
20. Kathuria, D. Vir, M.A. Nawrocki, and B.C. Becker,
Effectiveness of Surface Mine Sedimentation Ponds,
IERL-CIN-019, EPA Contract No. 68-03-2139,
Dec. 1975, 101 pp. (in press).
21. U.S. Army Engineer Waterways Experiment Station,
"Field Evaluation of the Performance of Silt Re-
moval Basins," Dredged Material Research, Mis-
cellaneous Paper D-75-12, December 1975, pp. 4-6.
22. Mallory, Charles W., and M.A. Nawrocki, Containment
Area Facility Concepts for Dredged Material Separa-
tion. Drying, and Rehandling, U.S. Army Engineer
Waterways Experiment Station, Contract Report
D-74-6, October 1974, 236 pp.
23.
Encyclopedia of Polymer Science and Technology,
Volume 1, John Wiley and Sons, Inc., 1964.
24. Encyclopedia of Polymer Science and Technology,
Volume 3, John Wiley and Sons, Inc., 1964.
25. Encyclopedia of Polymer Science and Technology,
Volume 6, John Wiley and Sons, Inc., 1964.
26. U.S. Department of Health, Education, and Welfare,
National Institute for Occupational Safety and
Health, Registry of Toxic Effects of Chemical
Substances, 1975 Edition, June 1975, 1296 pp.
27. Katzer, Melvin F., and J.W. Pollack, "Clarifying
Muddy Waters is Possible with Automatic System,"
Environmental Science and Technology, Vol. 2,
No. 5, May 1968, pp. 341-351.
/.
28. Young, Robert L., "Above Lake Needwood," TRENDS
In Parks and Recreation, January/February 1970,
pp. 17-20.
70
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29. Katzer, Melvin F., "In Situ Treatment of Rivers
and Streams," presented at 1969 ASME/Aj£hE Stream
Pollution Abatement Conference, June 10-12, 1969,
Rutgers University, New Brunswick, N.J.
30. Dorsey, Ronald E., "A Report on Lake Dredging
and Sediment Control in the Upper Rock Creek
Watershed," The Maryland-National Capital Park
and Planning Commission, October 15, 1973.
31. McCarthy, Richard E., "Surface Mine Siltation
Control," Mining Congress Journal. June 1973,
pp. 30-35.
32. State of Maryland Water Resources Administration,
and B.C. Becker, D.B. Emerson, M.A. Nawrocki,
Joint Construction Sediment Control Project,
U.S. Environmental Protection Agency Document
No. EPA-660/2-73-035, April 1974, 167 pp.
33. Groom, F., "Vacuum Filtration-An Alternative
to the Use of Large Settling Ponds in Sand and
Gravel Production," NSGA Circular No. 117,
National Sand and Gravel Association, Silver
Spring, Md., July 1972.
34. Garbe, Carl W., D.D. Smith, and S. Amerasinghe,
Demonstration of Methodology for Dredged Material
Reclamation and Drainage. U.S. Army Engineer
Waterways Experiment Station Contract Report
D-74-5, September 1974, 71 pp.
35. U.jS. Army Engineer Waterways Experiment Station,
"RJUC Field Trials," Dredged Material Research.
Miscellaneous Paper D-75-10, October 1975,
pp. 2-3.
36. U.S. Army Engineer Waterways Experiment Station,
"DMRP Research Initiated," Dredged Material
Research. Miscellaneous Paper D-75-10, October
1975, pp. 4-5.
37. Toth, S.J., and B. Gold, Agricultural Value of
Dredged Sediments-Final Report. U.S. Army Corps
of Engineers, Philadelphia District, Philadelphia,
Pa., January 1970, 24 pp.
71
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38. Murphy, W.L., and T.W. Zeigler, Practices and
Problems in the Confinement of Dredged Materials
in Corps of Engineers Projects, working draft,
U.S. Army Engineer Waterways Experiment Station,
Vicksburg, Miss., August 1973.
39. Heller, H.L., and E. Thelen, "Building Materials
from Dredge Spoil," Technical Report F-C3069,
U.S. Army Corps of Engineers, Philadelphia
District, Philadelphia, Pa., January 1970, 10 pp,
72
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APPENDIX
SOME POST-SEDIMENT POND EQUIPMENT MANUFACTURERS
Included below is an alphabetical listing of some manu-
facturers of the post-sediment pond equipment which was
selected as being feasible for fine-grained sediment con-
trol and removal. Detailed performance and other data
is available from them.
Ametek
Process Equipment Division
East Moline, Illinois 61244
C.E. Bauer
The Bauer Bros. Co.
Springfield, Ohio 45501
BIF
A Unit of General Signal
West Warwicke, R.I. 02893
Crane Co.
Cochrane Environmental Systmes
800 3rd Avenue
P.O. Box 191
King of Prussia, PA 19406
Croll-Reynolds Engineering Co., Inc.
1122 Main Street
Stamford, CN 06902
The De Laval Separator Company
Poughkeepsie, NY 12602
DEMCO Incorporated
845 S.E. 29th Street
Oklahoma City, OK
Dorr-Oliver, Inc.
2051 W. Main Street
Stamford, CN 06904
Envirex, A Rexnord Company
Water Quality Control Sales Office
10380 Drummond Road
Philadelphia, PA 19154
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Eriez Magnetics
Asbury Road at Airport
Erie, PA 16512
Johns-Manville
Filtration & Minerals Division
Greenwood Plaza
Denver, CO 80217
Laval Separator Corp.
1899 N. Helm Street
P.O. Box 6119
Fresno, CA 93727
Parkson Corp.
5601 N.E. 14th Avenue
Ft. Lauderdale, FL 33334
Roberts-Boze, Inc.
2611 Sharon Street
Kenner, LA 70062
Rotex, Inc.
1230 Knowlton Street
Cincinnati, OH 45223
Serfilco
Division of Service Filtration Corporation
1415 Wankegan Road
Northbrook, IL 60062
Sweco, Inc.
6033 E. Bandini Blvd.
P.O. Box 4151
Los Angeles, CA 90051
Zurn Industries, Inc.
Water and Waste Treatment Div.
Erie, PA 16518
74
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TECHNICAL REPORT DATA
(Please read Inslnictions on the reverse before completing)
. REPORT NO.
EPA 440/9-76-026
3. RECIPIENT'S ACCESSI ON>NO.
4. TITLE AND SUBTITLE
"Methods To Control Fine-grained Sediments Resulting
From Construction Activity"
5. REPORT DATE
12/15/76
6. PERFORMING ORGANIZATION CODE
(Approval Date)
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Michael Nawrocki and James Pietrzak
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Hittman Associates, Inc.
Columbia, Maryland 21045
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-01-3260
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Water Planning and Standards
Washington, D.C., 20460
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This publication is the third in a series issued under Section 304(3)(2)(C)
of Public Law 92-500 concerning the control of water pollution from construction
activity. It was prepared for use by planners, engineers, resource managers,
and others who may become involved in programs to effectively provide for
sediment control. Standard erosion and sediment control measures are usually
effective for preventing the runoff of the total sediment load. The effectiveness
of these standard techniques; however, has been found to be relatively poor
with regard to preventing the runoff of the fine-grained fractions, such as the
silts and clays.
The objective of this study was to research practical, cost-effective methods
which would help to reduce specifically the fine-grained sediment pollution
derived from construction activities. The prime consideration during this study
was the use or adaptation of existing technology, as described in the current
literature or data, to the fine-grained sediment pollution problem.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Sediment Control, Pollution Abatement
Soil Erosion, Water Erosion, Construction
Sediment Control
Water Pollution
Water Erosion
1312, 0807,
0203, 0201,
1308
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
75
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
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