NONPOINT SOURCE CONTROL GUIDANCE
TD899
.C58t4
CONSTRUCTION ACTIVITIES
OOOB76100
DECEMBER, 1976
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Planning & Standards
Washington, D.C. 20460
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NONPOINT SOURCE POLLUTION CONTROL GUIDANCE
CONSTRUCTION ACTIVITIES
Project Officer
Robert E. Thronson
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
December 1976
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PREFACE
In accordance with EPA's policy, as presented in the "Draft Guidelines
For State and Areawide Water Quality Management Program Development"
February 1976, a clear responsibility has been placed on organizations
developing water quality management plans to establish regulations for
control of nonpoint sources. Where needed, Best Management Practices
such as those presented in this technical guidance document, will be imple-
mented through such regulations. Nonpoint source regulatory guidance
is now being developed by EPA to provide additional assistance to State
and areawide 208 Agencies in their nonpoint source control programs.
This construction nonpoint source pollution control guidance document
is only one of a series designed to provide State and areawide 208 Agencies,
the Federal agencies, and other concerned groups and individuals with
information which will assist them in carrying out their water-quality
planning and implementation responsibilities. It is provided in accordance
with policies and procedures for the "Preparation of Water Quality Management
Plans" (40 CFR, Part 131) which states that "EPA will prepare guidelines
concerning the development of water quality management plans to assist
State and areawide planning agencies in carrying out the provisions of these
regulations". Additional documents to be issued will involve silvicultural
(forestry), mining, agricultural, hydrologic modification and other activities.
The basic guidance information included in this nonpoint source control
document is principally technical in nature and presented in four main
chapters. They include information on the identification and assessment
of existing construction nonpoint source problems; analysis and procedures
needed for selection of controls; descriptions of individual and systems of
Best Management Practices (BMP), with a method for determining their
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effectiveness; and several methods for predicting potential pollution problems
from future construction activities.
Effective control of nonpoint sources of pollution can best be achieved
through proper planning of construction activities, adequate review and
approval of the plans by a responsible management agency, adjustment of
the plans to maximize effectiveness of Best Management Practices prior to
their implementation, monitoring by the management agency for adherence
to the plan, and effective and when required, aggressive enforcement of
compliance to the law. Sixteen states now have direct sediment control laws
which apply to construction activities. Most of them require the submission
of a plan which must be approved prior to initiating construction. The
plans are developed in accordance with criteria, guidelines, specifications,
standards, etc. provided in documents issued by State or local agencies
responsible for sediment control. This nonpoint source pollution control
guidance follows the general format of these documents which were
developed as a result of sediment control laws or ordinances. This is
particularly true of Chapter 3, ''Selected Practices for Control, Construction
Activities".
All existing data indicate that construction activities, when soils and
foundation materials are disturbed and left exposed to erosion by rainfall,
wind, and runoff water, are responsible for causing extraordinary
environmental damages, especially to waterways, lakes, and impoundments.
Off-site damages often are difficult to trace to their source and on-site
damages are not readily apparent until excess quantities of sediment or
other pollutants have been transported from the site in runoff. As a
result, one must conclude that retaining potential pollutants to the site
area is the Best Management Practice. The principal theme throughout
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this guidance document emphasizes pollution prevention rather than
treatment.
Every effort must be taken to keep sediment and other potential
pollutants from leaving the site area. Control of pollution at the source
is the only viable option to mitigate water quality and stream condition
problems. To attempt to control sediment and other nonpoint source
pollutants through water quality standards is not feasible. Even if the
sediment could be traced back to its source, implementation of corrective
measures during the wet season, rather than preventative practices
before, would be difficult, if not impossible. Water quality standards
have a function in the management of a larger watershed, however,
they must form a second line of control behind construction on-site or
source control Best Management Practices.
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CONTENTS
PREFACE ii
INTRODUCTION 0-1
CHAPTER 1 - PROBLEM IDENTIFICATION AND ASSESSMENT
EXISTING PROBLEMS SURFACE WATERS 1-1
Identification of Pollutants 1-1
Assessment of Nonpoint Source Pollution From
Existing and Completed Sites 1-4
References 1-13
CHAPTER 2 - DATA NEEDS AND ANAYLSIS FOR SELECTION OF CONTROLS. 2-1
Precipitation Information 2-1
Wind Data 2-2
Characteristics of Soils and Underlying Geologic Materials 2-3
Ground Water 2-4
Topographic Conditions 2-4
Runoff Determinations 2-5
Selected References 2-7
Other References Used 2-8
CHAPTER 3 - SELECTED PRACTICES FOR CONTROL, CONSTRUCTION
ACTIVITIES 3-1
Erosion and Sediment Control 3-2
Good Housekeeping Practices 3-31
Stormwater Management 3 -34
Systems Approach to Sediment Control 3-40
Selected References 3 -50
Other References Used 3 -52
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CHAPTER 4 - METHODOLOGY FOR ASSESSMENT OF POTENTIAL
POLLUTION PROBLEMS AND THEIR MAGNITUDE 4-1
Pollutants To Be Considered 4-2
Assessing Potential Sediment Losses 4-3
Selected References 4 -21
APPENDIX - BMP STATEMENT _ BEST MANAGEMENT PRACTICES, A-l
CONSTRUCTION NONPOINT SOURCES, WATER POLLUTION. .
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NONPOINT SOURCE POLLUTION CONTROL GUIDANCE
CONSTRUCTION ACTIVITIES
INTRODUCTION
The nonpoint sources of pollution can be separated into categories,
each of which may be further subdivided into subcategories, Man's land-
disturbing construction activities is one of the main categories and, although
management practices presented in this document apply in general to all
types of construction, some subcategories such as dams, power lines,
canals, etc. may require more elaborate measures. As a result, additional,
and more specific BMP guidance may be required.
Advance planning can limit, through management decisions the
generation of conditions which could add materially to the pollution potential
Planning can avoid or limit exposure to potential problems through identi-
fication and allowance for natural hazards such as areas of unstable soils,
limitations imposed by climate and topography; or land capabilities in
terms of soil productivity or vegetative recovery potential
Control of nonpoint source pollution from construction activities should
be considered during the planning stages of a project in order to ensure
that the most effective application of measures is achieved during the actual
construction period. An adequately developed plan should involve preventing
sediment losses; reduction of peak surface runoff; preventing the generation,
accumulation, and runoff of oils, wastewaters, mineral salts, pesticides,
fertilizers, solids, and organic materials from the site area.
Specific instructions as to specific control measures and systems of
measures needed, scheduling and coordination of activities, and the use of
permanent and temporary techniques should be required in contracts between
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owners or developers and the contractors responsible for carrying out
construction activities.
Adequate Planning
Adequate plans for construction nonpoint source pollution control should
be based upon the known soils, topographic, geologic, hydrologic, and other
pertinent factors applicable to the site area. Particular care should be
taken to identify and evaluate possible problems which could result from
the construction of the facilities planned.
Fitting the construction site, or facilities, to the landscape, particularly
with regard to its weaknesses, may prevent potential pollution problems
from arising. The natural ground contours should be followed as closely
as possible and grading minimized. Areas of steep slopes, where high cuts
and fills may be required, should be avoided. Generally, areas adjacent to
natural water courses should be undisturbed. Extreme care should be
used in locating artificial drainageways so that their final gradient and
resultant water discharge velocity will not create additional erosion problems.
Natural protective vegetation should be undisturbed if at all possible.
Steep slopes and areas of credible materials should be avoided or the
exposed soil surfaces protected from the energy of rainfall and runoff
before erosion occurs. If these things cannot be done, runoff of pollutants
will have to be prevented by the development of specific structural or
other control measures.
Effective plans should consider proper scheduling and coordination of
construction activities and the provision of adequate maintenance of control
measures to ensure pollution prevention. The plans should consider the
time of year construction is to occur; extent of grading for surface elevation
changes to be done; amount of ground to be exposed to the elements compared
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to that covered by protective vegetation; quantity of runoff expected to enter
the site from upslope areas; occurrence and characteristics of ground water
underlying the site, and other factors which can create or minimize pollution
problems. A combination of fitting the development to site conditions,
limiting the grading and exposure of bare soils, and applying adequate
control measres and techniques at proper times will prove the most effective
nonpoint source control mechanism.
Early in the planning process, existing construction activities control
requirements, or limitations, imposed by Federal, State, and local agencies
should be determined and followed. Contact should be established with agencies
involved with water development, transportation, pollution control, conservation,
and the like to obtain information regarding prior construction problems they
have had and to obtain guidance with regard to solutions.
Controlling Erosion and Sediment Runoff
Erosion and runoff of sediments can be controlled effectively and
economically by using the following procedures-.
1. Limiting the time of duration that disturbed ground surfaces are
exposed to the energy of rainfall and runoff water.
2. Diverting runoff from upper watershed which would contribute
runoff to areas subject to erosion.
3. Reducing the velocity of the runoff water on all areas subject
to erosion below that necessary to erode the materials.
4. Applying a ground cover sufficient to restrain erosion on that
portion of the disturbed area which further active construction
is not being undertaken.
5. Collecting and detaining runoff from a site in sediment basins
to trap sediment being transported from the site.
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6. Making provision for permanent protection of downstream banks
and channels from the erosive effects of increased velocity and
volume of storm water runoff resulting from, facilities constructed.
7. Limiting the angle for graded slopes and fills to an angle no
greater than that which can be retained by vegetative cover
or other adequate erosion control device or structure.
8. Minimizing the length as well as the angle of graded slopes
to reduce the erosive velocity of runoff water.
Preventing Accumulation and Runoff of Pollutants Other Than Sediments
Practices that prevent transportation of sediments from a site area will
also deter movement of many other pollutants such as oils, pesticides, solid
wastes, metals, etc. from the site area. Pollutants carried in solution
however, will pass through all sediment control defenses. In this case,
proper application of materials and "good house-keeping" activities must
be used to do the job. They will involve such things as optimun dosages
and proper use of pesticides and fertilizers with special attention to not
applying them in excess of quantities required, limiting application only to
points of need, and prohibiting application in periods of weather extremes
such as freezing conditions which render the ground impermeable and
ensure runoff of materials. Washing facilities for equipment should be
located and concentrated at specific points where draining waters can
be collected in impervious holding ponds. Washing of finished surfaces
to remove excess concrete or other chemical residues should be undertaken
only after holding ponds have been provided to catch drainage waters. Waste
quantities of paints, oils, and greases should be collected and transported
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off site for sanitary disposal. Pollution from other waste materials such
as rubber, plastic, or wood building materials; food containers; sanitary
wastes; and miscellaneous solid and liquid materials can be controlled
by the use of adequate disposal facilities and the transport of these materials
from the sites to authorized disposal areas. Anti-litter requirements should
be enforced by regular visual checking of the construction site.
Management of Increased Stormwater Runoff
Stormwater management involves regulating the release of runoff from
a site under construction in order to prevent increased peak flows from
eroding downstream channel areas. Peak flows, caused by changed conditions
during, (and after) construction, may increase tremendously over those which
naturally developed the drainageways. In order to accomodate increased
flows, channels downstream from construction sites will have to increase
their cross-sectional area. This can only be done naturally by erosion;
and sediments resulting from this erosion causes pollution in downstream
areas.
Stormwater management regulates the release of this runoff by temporarily
retarding the flow. This can be done by providing temporary storage facilities
which release the water slowly, increasing the infiltration capacity of soils
and foundation materials by micro-benching or roughing the surface of slopes,
while ensuring that exposed soils are stabilized; adopting site drainage
patterns that increase flow distances and thus inccease time of travel of the
runoff, leaving trees and other vegetated areas in as many areas as possible
to prevent rainfall from rapidly becoming runoff; and other means. Con-
sideration should be made to design Stormwater management facilities into
the completed project to be operational through its estimated life.
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CHAPTER 1
Problem Identification and Assessment,
Existing Problems--Surface Waters
The generation and runoff of pollutants from construction sites are
strongly dependent on the local climatic events such as precipitation, wind,
and overland flow of water resulting from rainfall or snowmelt. As climatic
conditions are dynamic and generally highly variable, the runoff of pollutants
often changes drastically and unpredictably. The nature and quantity of
pollutants leaving a site also depends upon the particular activities being
conducted, extent of disturbed area, soil characteristics in the vicinity,
local topographic and geologic conditions, the number of people and equipment
involved and their impacts on the area, extent of protective vegetative
covering on the site and other factors. Implementation of effective control
measures will involve preventing the generation of pollutants as well as
restricting the runoff of those already generated so that waters are not
affected by these contaminants.
Identification of Pollutants
Sediment resulting from erosion of disturbed soils is one of the principal
pollutants originating from construction activities (Reference No. 1). It
includes solid mineral and organic materials in fragment form which are
transported by runoff water, wind, ice, and the effect of gravity. Chemical
pollutants derived from construction activities originate from inorganic and
organic sources and occur in solid form such as asphalt, boards, fibers,
or metals; or in liquid form such as paints, oils, glues, pesticides, ferti-
lizers, and the like. Biological pollutants include organisms derived from
soils, animal or human orgins. They may be bacteria, fungi, or viruses.
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Sediment includes solid mineral, and organic materials which exert
physical, chemical, and biological effects on receiving water bodies.
Physical damage resulting from excess quantities of sediment deposited
in, or carried in, water includes: reduction of reservoir storage capacity
thus requiring costly dredging or decreasing the life of the project; filling
harbors and navigation channels thereby disrupting their functioning;
increased frequency of flooding through the filling of water courses;
increased turbidity effects and sediment content in waters, and reduced
light penetration thus destroying aquatic plants and organisms; increased
cost of downstream water treatment; damage to fish life; and covering
destruction of organisms on the bottom of streams and other water bodies;
reduction of the velocity and carrying capacity of streams; and impairment
of drainage ditches, culverts, and bridges; altered shape and direction
of stream channels; degradation of water recreational areas; and the
imparting of undesirable taste to water.
Other potential pollutants from construction activities include petroleum
products, pesticides, fertilizers, metals, soil additives, construction
chemicals, and miscellaneous wastes from construction debris. Many
petroleum products impart a persistent odor and taste to water, thus
impairing its use for drinking and contact sports. Oils often have the
ability to block the transfer of air from the atmosphere into water, causing
the suffocation of aquatic plants, organisms, and fish, and other water-
living organisms. Petroleum products often contain quantities of organo-
metallic compounds (nickel, vanadium, lead, iron, arsenic), pesticides,
and other impurities which can be toxic to fish and other organisms and
seriously impair on their use for human consumption.
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The three most commonly used forms of pesticides at construction
sites are herbicides, insecticides, and rodenticides. Unnecessary or
improper application of these pesticides may result in direct water
contamination, indirect pollution by drift or transport off soil surfaces
into water. Pesticides are generally toxic to man and other vertebrate
animals and have strong adverse effects on lower organisms. Persistent
pesticides often accumulate in the environment with magnification of
effects resulting in higher biological organisms which have consumed
contaminated organisms lower in the food chain. The latter problem
is of extreme concern as other forms of life may be destroyed along
with the target pests.
Nitrogen, phosphorous, and potassium are the major plant nutrients
used for the successful establishment of vegetation on disturbed soils
of construction sites. Heavy use of commercial fertilizers result in
movement of these materials to water bodies where they may accelerate
the eutrophication process.
Metals often are transported by sediment particles in runoff water
leaving a construction site. Copper, cobalt, chromium, manganese,
iron, and nickel are at times associated with sediment particles. Some
of these metals are toxic to man. There is limited information on their
precise biological function in animal life. They may be concentrated
in marine organisms such as shellfish and often act synergistically with
other substances to increase their toxicity. This means that the total
effects of the pollutants are greater than the sum of their individual effects.
Soil Additives, commonly used to improve soil characteristics for
construction uses, include lime, fly ash, asphalt, salt (Nad) and calcium
chloride. They may be transported from the site in runoff waters, along
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with sediment. Little work has been done to show the net environmental
effects of soil additives.
Construction chemicals include those used for glueing boards together,
sealing cracks in foundations, solvents for oils and paints, and dying and
cleaning. Construction activities leading to pollution by these materials
involve dumping of excess materials and wash water into streams or storm
sewers, improper handling procedures with the accompanying spills of
materials, and leaky containers being placed in storage. Chemical
material's effects upon the environment depend upon their concentration
and persistence. Many of these materials decompose with their total
effects on water quality unknown.
Miscellaneous wastes include wash from concrete mixers, solid wastes
resulting from trees and shrubs removed during land clearing, wood and
paper materials derived from packaging of building products, food containers
such as paper, aluminum, and metal cans and packets, and sanitary wastes.
The miscellaneous waste products can provide physical damage to stream
systems similar to sediments, they can decompose and creat nutrient or
chemical problems, or even create health hazards. Biological pollutants,
including bacteria, fungi, and viruses from soil, human, and animal origin,
are generally found in or on topsoil layers where they can feed on dead
plants, animals, and other organic materials. The greatest pollution
potential results from those of animal or human origin. They are most
prevalent on construction sites where improper sanitary conditions exist.
Assessment of Nonpoint Source Polluution From Existing and
Completed Sites
Most, if not all, construction activities which involve disturbance of
surface soils or underlying geologic materials result in the generation of
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nonpoint source pollutants. Surface water runoff will transport these
materials from the site unless extreme care is taken to provide control
measures which contain them within the area of development.
It is extremely difficult to assess, with any reasonable accuracy, the
magnitude and extent of future pollutant discharge from the construction
areas. This is due to the fact that the runoff from each construction
site varies tremendously depending on the intensity and duration of
rainfall, and other inclement weather conditions; topography, geology,
and soil types occurring in the area; areal extent of disturbed soil; type
of construction involved; character of vegetative cover; and other
local conditions. The techniques and strategies to be applied are different
from region to region so survey of existing problems at existing sites is
valuable in drawing up plans for controlling such pollution from future
construction sites. Techniques and strategies should be devised to
restrict pollution runoff under anticipated natural and manmade conditions.
The initial step in understanding construction nonpoint source pollution
in an area should involve a survey of all existing and recently completed
construction projects where the ground surface has been disturbed.
Information should be obtained regarding site locations; particularly with
regard to their proximity to water bodies; their surface area, slope, and
geometric configuration; foundation conditions; the duration of construction
activities; and other pertinent factors. A construction site for a linear
facility, such as a highway or pipeline, may cause much greater areawide
pollution problems than a site with a much larger local surface area with
more nearly equal dimensions, such as a shopping center. Construction
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of many dams, recreation facilities, and some power plants do not result
in the disturbance of excessively large areas of the ground surface; however,
they are often on, or extremely near, streams of good quality and so have
a high pollution potential.
Runoff of pollutants other than sediment are even more difficult to
assess than readily visible sediment. Evidence of petroleum products in
runoff may be found in oil sheens on the water or in oil scums on surfaces
downstream from the site. Wastes from solid materials can show up as
debris. Soluble pollutants can be assessed by leaching and analyzing samples
of fine-grained sediments for suspected materials. Toxic materials in
runoff may be apparent by fishkills and evidence of excess nutrients by
algae blooms in water bodies.
An extremely valuable source of information regarding pollution resulting
in areas downstream from existing and completed construction areas is the
local public. Many people, particularly older residents in the area, remember
the condition of the local streams prior to construction and can convey pertinent
information concerning changes which have occured. Areas of prior extreme
sediment deposition, channel erosion, oil spills, fish kills, etc. may be
local >d, and perhaps documented in local papers if dates can be recalled.
Limited research data indicate that up to 70 per cent of the sediment
removed by erosion from a construction site without adequate pollution
control measures is transported from the site by runoff water and deposited
further downstream. Field surveys of existing, or recently completed,
construction sites can provide reliable information that sediment runoff
problems are, or have been, occurring. They should involve estimates, on
site, of the amount of erosion that has occurred and the volume of sediments
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deposited in the site area and immediately downstream. An extremely perti-
nent time to make observations is during a period of intense rainfall when
the processes of erosion and sediment transport and deposition actually are
taking place. At this time erosion and transport of sedimentary materials
can be observed. Deposition of sediments will occur later as runoff velocities
decrease or the runoff waters collect in impoundments at which point
suspended sediments will settle.
Erosion by wind is a significant factor to be considered, particularly
in Western areas of the country where winds may blow continuously and
over long distances with no topographic obstructions. Observations regarding
erosion by this mechanism should be made during and after windstorms when
information on the direction of movement and the location of wind-blown
deposits can be obtained. Materials deposited by the wind can often be
differentiated from water-laid materials by their location with regard to
streams, the uniform grain size of the materials, the angularity of fragments,
and the generally low density of deposits. Water deposits are usually near
the water sources that transported them, generally composed of a mixture
of different sized materials that are more less rounded by the action of water
transport processes, and of much higher density than that of wind blown
sediments.
Erosion of rainfall and runoff occurs as sheet and rill erosion and
gully erosion. Sheet and rill action occurs when water is not concentrated
while gully erosion involves concentrated flows. Estimates of the volume
of sediments derived from gulley erosion can be made from field obser-
vations and measurements. That resulting from sheet and rill erosion,
is less apparent; however, and more difficult to reliably estimate. Gullys,
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where concentrated flow of water has occurred, are readily observed as
they are incised into smooth construction cut and fill slopes. Computations,
using gully dimensions, can provide information on the volume of material
removed by water. If this total volume of material has not been deposited
in the site area where slopes decrease, and runoff water has lost its energy
to transport sediment particles, some of it has been carried further down-
stream to become a pollution load.
To estimate the volume of sediment that has been carried by runoff
into downstream areas from gully erosion in the site area, it is necessary
to determine the approximate volume of this material that has been deposited
on the site itself and subtract it from that eroded from the gully areas.
The deposited materials is apparent as small deltas which generally are
seen at the bottom of cut and fill slopes or wherever runoff velocities
have decreased. Diversion ditches, swales, or depressions also may
be filled with sand-sizes particles and sheets of sediments deposited in
low, flat areas. In some instances, buried survey markers, or other
objects can provide information on the thickness of deposits. The areal
extent of the deposits times their thickness will provide an estimate of
the volume of materials involved. Extreme judgement will be necessary
to define valid thickness measurements in this type of estimate.
The volume of excess sediments deposited downstream from construc-
tion sites can be estimated also in this manner, particularly if information,
such as that provided in photographs, on the condition of the streams prior
to construction are available. Recent contour maps, particularly those
provided by the U. S. Gelogical Survey on a scale of 1:24, 000, may also
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provide pertinent information on the condition of the stream before
construction started. Evidence of excessive sediment loads in the stream
system can be observed where the stream seems to be constricted by
materials in low gradient areas; small pools are filled, or filling, with
deposits; the channel is "braided1 and flowing on a bed of uniformly-sized
material (when it was previously flowing on bedrock); or where massive
sediment deposits cover areas adjacent to and at a higher elevation than the
present stream. A braided stream is one that flows in several dividing and
reuniting channels, similar to the strands of a. braid. This latter evidence
indicates that the stream had an excess sediment load during flood stage
and deposition occurred as the runoff volume decreased and the stream
level dropped. Probably the most reliable measure of the quantity of
sediments that have left a construction area can be obtained by conducting
reservoir sedimentation surveys. If no other construction site, or other
man-induced sediment-generating activity is being conducted in the drainage
basin for the reservoir, measurements of the quantity of sediment deposited
in the reservoir as a result of the construction, are very reliable. A reservoir
deposition survey consists of measuring the areal extent and thickness
of the sediment delta accumulation formed by the deposition of excess
sediment. Some useful information on conducting reservoir and flood
plan studies is presented in Reference No. 2.
The field surveys are intended only to provide information that erosion
is occurring, or has occurred, on construction sites where no sediment
control measures were applied, or were inadequate, and that sediment
runoff is a problem. Estimates of the volume of sediments eroded from
the sites and deposited either in the site area or further downstream should,
not be considered precise or accurate. Even if the quantities of material
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eroded by both sheet and rill and gully processes could be accurately
measured, they would not be equal to the total of materials deposited,
even if the latter can be accurately determined. This is due to the fact
that a volume of some eroded material increases greatly when in a state
of loose deposition. Also, if clays or other fine-grained materials are
present in the volume of eroded sediments they will remain in suspension
in the runoff water and be transported entirely out of the site area.
Chemical and biological runoff from a site during construction can be
difficult to assess after construction has been completed and conditions
have stabilized. Sampling is one way to obtain information on the sediment,
chemical, and biological pollution, being transported by a stream at a
particular location. Existing sampling data may be readily available from
records; however, to compare sediment loads immediately upstream of the
site with those immediately downstream. The difference should be due to
sediment runoff from the construction area. In addition, stream quality
prior to construction when compared to that during and after should indicate
sediment loads contributed by the construction activities. Extraneous
influences on stream regimens should be carefully assessed prior to
evaluation. As the principal sediment loads are transported during flood
flows, it is entirely possible that a sediment load determined in the stream
at the site resulted from an anomalous inflow of materials several miles
upstream and in the past. Landslides often cause this problem and these
sediment loads move downstream as "slugs" to be detected several years
later in downstream areas.
Assessment of sediment runoff resulting from construction sites may
be accomplished by estimating the potential quantity of materials that
can be eroded and transported from each site, assuming no control measures
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have been implemented. The sum of all site estimates should provide a
fairly reliable indication as to the magnitude of pollution in the area and
whether or not it will increase or decrease in the future. Estimates
regarding natural sediment losses from sites prior to construction should
be considered in the assessment as these values must be subtracted from
the total losses estimated above. Only those sediments resulting from the
construction should be considered as the pollution load.
Estimates of sediment resulting from construction and the background,
or natural, sediment losses prior to construction in an area can be obtained
through the use of soil loss equations developed principally by the U. S.
Department of Agriculture (Reference No. 3,4, 5 and 6). Extreme care
must be used, however, in assigning values to particular factors in the
equation involving slopes, soil properties and characteristics of the
construction site, as these conditions often are much different and more
variable than those occurring in farmlands where the soil loss equations
are normally used. In addition, one should be aware that these estimated
losses involve sheet rill erosion only and do not consider how much of
the sediment is transported from the site. Movement of sediment is
extremely complex and quantitative evaluations are difficult due to the
nature of the site variables involved.
Assessment of nonpoint source pollution resulting from ongoing or
completed construction facilities, particularly sediments, should involve
(1) a field examination to determine the materials have been eroded,
and are being eroded from construction sites and that excess quantities
of sediments or other materials are accumulating in channels immediately
downstream and (2) evaluating existing gaging, monitoring, and sampling
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information to establish stormwater runoff quantities and the gross sediment
yield from the sites. Much readily available data on sediment problems
may be obtained from records of local, State, and Federal agencies such
as the Conservation Districts; County Public Works Departments; State
Conservation, Transportation, Water Quality, and Water Development
agencies; and the United States Geological Survey, Bureau of Reclamation,
Soil Conservation Service; Corps of Engineers, and others.
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References
1. "Processes, Procedures and Methods to Control Pollution Resulting
From All Construction Activity", EPA 430/9-73-007, October 1973
2. "SCS National Engineering Handbook - Section 3, Chapter 7"
US DA - SCS, March 1968.
3. "Predicting Rainfall-Eros ion Losses From Cropland East of the
Rocky Mountains", USDA-ARS Agricultural Handbook No. 282, 1965
4. "A Soil Erodibility Nomograph for Farmland and Construction Sites",
Journal of Soil and Water Conservation, Sept-Oct, 1971
5. "Present and Prospective Technology For Predicting Sediment
Yields and Sources", USDA-ARS-S-40, June 1975.
6. "Procedures for Computing Sheet and Rill Erosion on Project
Areas", USDA-SCS, Technical Release No. 51 (Rev. ), Jan. 1975.
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CHAPTER 2
Data Needs and Analysis for Selection of Controls
Precipitation, whether it falls as rain or snow, is the principal source
of all water that moves through a watershed. The characteristics
of the soils and vegetative cover occurring in the area, natural topographic
conditions, and the results of mans alteration of these natural characteristics
have a major effect on the amount of precipitation that actually becomes
runoff water. Precipitation and runoff water are the agents responsible for
the generation and transportation of pollutants from disturbed areas in any
watershed.
As the runoff of nonpoint source pollution from construction sites,
particularly sediment, is strongly dependent on local climatic events such
as the rainfall, wind, and snowmelt, these factors must be considered during
the development of effective Best Management Practices. Additional informa-
tion required includes the rate, velocity, and quantity of runoff; credibility,
chemical, and physical properties of soils and geologic materials at the
site; length, steepness, and roughness of slopes; extent and effectiveness
of protective vegetative cover in the area; and results of man's prior earth-
changing activities. Changes in the drainage system during construction
are of extreme importance. Both the macro-drainage system of the watershed
and the micro-drainage system above, on, and below the site should be
considered.
Precipitation Information
Data on precipitation can be obtained from several sources. Published
data on daily rainfall measured at sta'ndard gages are available principally
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from U. S. Weather Bureau (now the National Weather Service, Department
of Commerce) in monthly issues of "Climatological Data". Other Federal
and State agencies or universities publish rainfall data on an irregular basis,
often in special storm reports or research papers. Unpublished data is
available from various Federal and State agencies as a result of field surveys
following unusually large storms. These surveys obtain measurements of
rainfall caught in buckets, bottles, and similar containers and provide added
detail to rainfall maps developed from standard rain gage data.
To make the information more useful for hydrologic work, the U. S.
Weather Bureau (now the National Weather Service) published analysis of
rainfall data in the fifty States, Puerto Rico, and the Virgin Islands (Reference
Nos. 1 through 4). The western States also are covered by the National
Oceanic and Atmospheric Administrations Precipitation Atlas 2 (Reference
No. 5). Methods for making a more precise analyses of the data is presented
in publications such as the Soil Conservation Service's "National Engineering
Handbook, Section 4 Hydrology", the Bureau of Reclamation's
"Design of Small Dams" and others (References 6 and 7). They provide
essential information for determining, or estimating, the depth of rainfall
to be expected in the area; the intensity, duration and seasonal distribution
of storms with associated probabilities of occurrence; the antecedant conditions
in the drainage, and other factors.
Wind Data
Sediments blowing off areas denuded by construction may be a serious
problem in areas where non-cohesive soils occur, particularly in arid or
semi-arid regions. Data regarding the capacity of the wind to cause erosion,
the prevailing wind directions, and the preponderence of wind erosion forces
in the prevailing directions are presented in U. S. Department of Agriculture
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Handbook No. 346 "Wind Erosion Forces in The LTnited States and Their
Use in Predicting Soil Loss", (Reference No. 8).
Characteristics of Soils and Underlying Geologic Materials
Evaluation of available soils and foundation information is of particular
importance for1 development of Best Management Practices. They include
such factors as the density, permeability, composition, degree of consoli-
dation, and thickness of materials present. Many of these characteristics
are inter-related and all may have an effect on the generation and movement
of pollutants from construction sites. Data on possible ground water bodies
underlying the site are also essential. The depth to this water body and
its quality and direction of movement should be determined. It could possibly
introdxice transporting waters into the site area to carry pollutants into or
from the area to degrade adjacent supplies.
Information regarding the physical characteristics of soils and/or
underlying geologic materials in site areas can be obtained from soil survey
reports published by the U. S. D. A., Soil Conservation Service, in coopera-
tion with other Federal or with State agencies; geologic reports provided
by Federal State and local agencies; from documents available from Univer-
sities or other' institutions of higher learning; and from the agency or company
to do the construction. This information is normally fairly generalized as
it is done on an areawide basis and often for a different purpose than pollution
control. The level of detail of the information in such documents varies
according to the objectives of the work but almost all of them are valuable for
analysis of hazards and potentials and for development of Best Management
Practices.
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Specific soils and foundation information regarding in-place characteristics
can oftea be obtained from engineering project reports, case histories of
prior construction projects, or by sampling the materials at the sites and
evaluating the properties of the materials sampled. In construction sites,
where cuts and fills are common, extreme caution must be used, particularly
with regard to soil eredibilities, to ensure that material characteristics are
determined at the final grade elevation and not at higher elevations where the
material is to be removed or below where it is protected by overlying soils.
Ground Water
Ground water conditions are of critical importance in construction sites
as the inflow of water into a construction site can cause pollution problems.
Movement of runoff, with pollutants into an underlying ground water body can
cause additional problems. Data needed for pollution prevention with regard
to ground water includes depth to the water body, direction of movement, whether
it occurs under confined (artesian) or unconfined (water table) conditions, and
its natural quality. Ground water information may be obtained from U. S.
Geological Survey Water Supply Papers and other technical reports, State
Water development agency reports, from local data obtained regarding studies
of wells in the site area, and other sources.
Topographic Conditions
An evaluation of topographic conditions at a construction site prior to
earth-changing activities, and in adjacent areas, can be made from infor-
mation on existing maps such as the Geological Survey's topographic maps,
the Department of Agriculture's Soil maps, and other maps of this type.
More detailed data on topography and conditions will usually be available
from the site plans prepared by the developers, engineers, and surveyors.
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Data on the length, steepness, and roughness of slopes is important
and may be obtained through actually surveying the site or from interpretation
from the published reports discussed above, as well as from the topographic
maps developed by the U. S. Geologic Survey, Army Map Service, and other
sources.
Runoff Determinations
Water erosion, and resulting soil loss from a site area, is negligable
until runoff actually begins. The quantity and frequency of precipitation
needed to initiate runoff is a function of the interrelationship of many variables
such as the rainfall intensity, temporary surface storage in the area, physical
character of soils or foundation materials, time since prior precipitation
has occurred, location and percentage of the area protected by vegetation,
and steepness and length of slopes at the site.
The combined effect of soils, vegetative cover, man's earth-changing
activities (conservation practices) on the amount of rainfall that actually
becomes runoff from an area can be estimated in several ways. Probably
the most applicable is presented in the Soil Conservation Service's "National
Engineering Handbook, Section 4, Hydrology". It provides information
on estimating runoff through the use of Watershed Curve Numbers. Similar
information is presented in this same Agency's "Engineering Field Manual"
(Refernce No. 9). The State of North Carolina's "Guide for Sediment
Control on Construction Sites (Reference No. 10), and the Bureau of
Reclamation's ''Design of Small Dams'1. The curve numbers (CN's) are
hydrologic "soil-cover" complex numbers and indicate their relative value
as direct runoff producers. The higher the number, the greater the amount
of direct runoff to be expected from a storm.
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Additional information on runoff evaluation is presented in the publications
"Urban Runoff for Small Watersheds" and "Guidelines for Hydrology"
(References 11 and 12). Existing hydrologic data developed for existing
projects in the area, or for other purposes by engineers for developers
or by State or local development agencies also can be useful.
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Selected References
1. U. S. Department of Commerce, Environmental Science Services
Administration, U. S. Weather Bureau. "Rainfall Frequency Atlas
of the United States for Durations from 30 minutes to 24 Hours and
Return Periods from 1 to 100 Years". Technical Paper No. 40, 1963.
2. - - - -"Generalized Estimates of Probable Maximum Precipitation
and Rainfall - Frequency Data for Puerto Rico and Virgin Islands"
Technical Paper No. 42, 1961.
3. - - - - "Rainfall-Frequency Atlas of the Hawaiian Islands for Areas
to 200 Square Miles, Durations to 24 Hours, and Return Periods
from 1 to 100 Years" Technical Paper No. 43, 1962.
4. - - - - "Probable Maximum Precipitation and Rainfall - Frequency
Data for Alaska and Areas to 400 Square Miles, Durations to 24 Hours,
and Return Periods from 1 to 100 Years". Technical Paper No. 47, 1963.
5. National Oceanic and Atmospheric Administration, National Weather
Service. "Precipitation - Frequency Atlas of Western United States",
Atlas No. 2, V.l-11, 1973.
6. U. S. Department of Agriculture, Soil Conservation Service. "National
Engineering Handbook, Section 4, Hydrology", August 1972.
7. U. S. Department of the Interior, Bureau of Reclamation, "Design
of Small Dams", 1974.
8. U. S. Department of Agriculture, Agricultural Research Service,
in cooperation with Kansas Agricultural Experiment Station
"Wind Erosion Forces In The United States and Their Use on
Predicting Soil Loss" Agricultural Handbook No. 346, April 1968.
9. U. S. Departmen of Agriclture, Soil Conservation Service
"Engineering Field Manual For Conservation Practices", 1969.
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2-8-
10. - - - - "Guide For Sediment Control On Construction Sites In
North Carolina", March 1973.
11. "Urban Hydrology For Small Watersheds, Technical Release
No. 55" January 1975
12. American Association of State Highway and Transportation
Officials, Task Force on Hydrology and Hydraulics "Guidelines
for Hydrology" 1973.
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Other References Used
1. National Association of Conservation Districts in cooperation with
the Soil Conservation Service "Suggested Guidelines and Standards
For Erosion and Sediment Control Programs", date unknown.
2. U. S. Department of Agriculture, Soil Conservation Service "A Method
for Estimating Volume and Rate of Runoff in Small Watersheds",
SCS-TP-149, April 1973.
3. - - - - "Procedure for Computing Sheet and Rill Erosion On Project
Areas", Technical Release No. 51, Jan. 1975.
4. - - "Rainfall - Erosion Losses From Cropland East of The
Rocky Mountains, A Guide for Selection of Practices for Soil and
Water Conservation" Agricultural Handbook No. 282, May 1965.
5. U. S. Environmental Protection Agency, Office of Research and
Development and the State of Maryland, Department of Water Resources
"Guidelines For Erosion and Sediment Control Planning and Implementation'
EPA-R2-72-015, August 1972.
6. U. S. Environmental Protection Agency, Office of Water Program
Operations, "Methods For Identifying and Evaluating the Nature and Extent
of Non-Point Sources of Pollutants", EPA-430/9-73-014, October 1973.
7. - - - - "Processes, Procedures, and Methods To Control Pollution
Resulting From All Construction Activity", EPA-430/9-73-007, October
1973.
8. "Comparative Costs of Erosion and Sediment Control, Construction
Activities", EPA-430/9-73-016.
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CHAPTER 3
Selected Practices for Control, Construction Activities
In order to minimize the generation of nonpoint source pollutants resulting
from construction activities and prevent the transport of these materials from
site areas, Best Management Practices must be selected in accordance with
specific natural conditions occurring in the vicinity. They include:
o Physical and chemical characteristics of soils and geologic materials
o Topography
o Intensity, duration, and frequency of precipitation
o Time distribution of annual precipitation
o Prevailing wind direction and velocity
o Expected runoff quantities, peaks, and velocities
o Occurrence and character of ground water
o Density, gradient, and relationships of surface drainage
to the site area
o Climatic conditions for vegetation development
In addition, the selection of BMP should involve a consideration of the
construction activities to be conducted such as the type of construction,
time and duration of each activity, and kinds of equipment to be used.
Sediment is the major pollutant resulting from construction, as a result,
practices for erosion and sediment control are described in the first portion
of this chapter. Other pollutants such as pesticides, nutrients, oils, solid
wastes, and similar materials can be controlled, to a large extent, by sedi-
ment control measures because they cling to sediments in transit. Additional
management practices are needed, however, to make the control more
effective. They are discussed under "Good HouseKeeping Practices".
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Storm water is not a pollutant by itself. Artificially high peak flows,
however, created by impervious surfaces covering the construction area
or by drainage structures which increase the velocity of runoff, will
generally act as generators of pollution by eroding sediments and other
materials from drainage ways and stream channels, particulaly downstream
from the site area. Best Management Practices to control, or manage
storm water runoff are discussed in the section entitled "Storm Water
Management".
Control practices can be designed and installed as temporary or permanent
measures. Temporary measures are those that are used to correct detrimental
conditions that: develop during construction activities, were not predicted
during project design, or are temporarily needed to control erosion or sediment
problems that occur during construction but are not associated with permanent
measures. Permanent measures are those that are intended to remain in
place during the life of the project facilities, and are needed where drainage
characteristics will be permanently stressed by the completed facility.
Erosion and Sediment Control
Erosion and sediment control practices include providing protective
coverings of mulches over bared soils and seeded areas, protecting existing
vegetation or reseeding or replanting exposed surfaces; netting over exposed
surfaces; controlling the erosive and transport energy of runoff water;
and trapping sediments being transported by runoff from the site area.
Many management practices devised for water erosion and sediment-control
purposes also are useful for control of wind-gene rated pollutants. Their
location and orientation for the latter purpose should be designed on the
basis of wind direction and velocity rather than that of surface water flow.
Protecting Exposed Ground Surfaces
Existing natural vegetation should be preserved as much as possible on
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3-3
construction sites, particularly where grading, or soil disturbance is not
necessary. If removal of the vegetation is required, only a necessary mini-
mum of soil should be exposed at any one time. If the duration of exposure is
extensive and erosion probable, vegetation or some other type of protective
covering should be provided and/or sediment control measures installed to
prevent the material from leaving the site. Revegetation should be accomplished
as quickly as possible following completion of the work item. Regardless of
the type of surface covering provided, runoff waters with erosive velocities
should be prevented from entering the area at all times.
1. Vegetation
Establishment of vegetation to protect soil surfaces from
erosion and reduce the runoff of sediments can either be temporary or
permanent. Temporary vegetation should be used to provide control during
construction, or until permanent vegetation develops fully. Permanent
vegetation stabilizes the site following completion of the construction project.
Vegetative soil stabilization should be considered as being an integral part
of, and equal in rank to, mechanical structures for erosion and sediment
control. Prior to initiating grading operations, plans should be made to
preserve as much of the sites existing plant cover as possible. Many times
these areas can serve as filter strips-or buffers to control sediment runoff.
Special care should be taken to protect buffers of natural vegetation along
streams and drainages. Topsoil stripped from the ground surface should
be stockpiled (and protected from erosion) for future replacement on
exposed ground prior to revegetation.
Procedures for establishing vegetation are different in each
area of the U. S. (Reference No's. 1 through 16). They depend upon the climatic,
hydrologic, soil, slope, and other conditions in the specific area and the type
of plants to be used. In general, the site has to be prepared for the seeding
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or installation of plant stock. This involves protecting the surfaces
from erosive effects of rain and runoff, particularly concentrated runoff
on steep slopes, and preparing the seedbed. Soil additives such as lime
and fertilizers should be applied in accordance with needs as determined
by soil tests; recommendations provided by local conservation districts,
farm advisors, Extension Service, Universities, and landscape architects;
or data presented in erosion and sediment control guidebooks, handbooks,
or standards and specifications which cover the site area (Reference
No's 1 through 12, and 16).
Maintenance of established vegetative cover is particularly important
for effective control. Many "domesticated" types of vegetation, particularly
grasses and legumes, need considerable maintenance and can be forced
out by native vegetation if this maintenance is not regular. In many cases,
however, if it provides adequate ground cover and prevent erosion, native
vegetation may be found to be the more desirable product to use.
Figure 1 - Seeding of temporary, fast growing grasses often is most
desirable when final grading cannot be done until a later date.
(Reference No. 17).
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2. Mulches (organic residues)
Mulching consists of applying plant residues, or other
suitable protective materials to the surface of the soil. Organic residues
consist of plant residues, wheat or oat straw, hay, or other materials
such as wood chips, bark, sawdust, and the like. Production of mulch
materials from usable waste products generated during the construction
activities should be encouraged as these materials would otherwise have
to be disposed of elsewhere. Mulches can be used before, during, or
after seeding to aid in the establishment of a vegetative cover or to
prevent erosion and runoff of sediments, reduce soil compaction and
surface crusting, conserve soil moisture, and minimize temperature
changes in ground surfaces. They can also be used without seeding
to temporarily protect exposed and credible soils from erosion and sedi-
ment losses.
Quantities of mulch applied should be based upon the results
desired and the characteristics of the materials used. Smothering of
potential vegetation should be avoided but enough mulch used to prevent
erosion and loss of sediment from the area. Generally, it is applied
with power equipment such as "hydro-mulcher" and anchored to prevent
removal by water or wind. Anchoring is done by "tacking" with asphalt
emulsions, chemical mulches covering with netting, using a serrated
straight disc to punch it into the soil surface, or some other means.
Since the environmental effects on water quality of asphalts and inorganic
chemical mulches are generally unknown, physical binders are preferred.
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Figure 2 - After seeding and fertilizing, the slope was mulched and
covered with netting (Reference No. 16).
3. Pervious Blankets, Nets and Similar Protective Materials
These materials are used to provide protective coverings
in critical areas which are highly susceptible to erosive processes due to
erodible soils, steep slopes or concentrated runoff water. They include
excelsior blankets; fiber glass matting; fiber glass "angel hair" which is
dispensed and spread by compressed air; jute netting; and biodegradable
sheet paper products, with or without reinforcing for strength. Extreme
care should be taken that none of these products contain exotic pollutants
of some sort.
These products are generally used to provide temporary
protection of the underlying soils while a more permanent protective
cover of permanent vegetation is developing. As their cost is generally
higher than mulching, their use is most justifiable where steep slopes
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and erodible soils exist or where runoff water concentrates such as in
swales, waterways, ditches, and the like.
Application of the pervious blankets, nets, and other materials
will depend on the conditions in the area to be protected, characteristics
of the materials to be used, and future activities to be conducted at the site.
The manufacturers of these materials generally provide information appli-
cable for proper installation procedures; and they usually make technical
representatives available for consultation regarding problem conditions.
Being extremely flexible, pervious blankets and nets
generally conform well to irregularities in the ground and restrict movement
of runoff water. Some.method of fastening these materials to the ground,
such as stapling, is usually required. When materials come in rolls,
overlap of adjacent materials is necessary. As a result, the direction
of water flow must be carefully considered prior to installation. In general,
blankets should be installed so that the up-slope layer overlaps the downslope
layer. In swales, or ditches, the material is generally unrolled from
the top of the channel in a downstream direction, with overlaps parallel
to the channel (Figure 3) . On steep cut or fill slopes, the material
is unrolled parallel to the contours with the upslope materials overlapping
the downslope layer. The upper ends of blankets and nets should be
installed in erosion checks to prevent movement of water beneath the
layer and subsequent erosion. Checks involve a technique whereby the
porous mat is installed into a slit trench excavated perpendicular to
the flow of runoff and then contained by backfill. (See Erosion Check,
Figure 14). Information on methods for use in utilizing various types of
flexible channel linings; including vegetation and riprap is presented in
Reference No. 30.
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3-8
Figure 3 - Jute netting being installed (Reference No. 15)
4. Chemicals
Chemicals used for surface soil protection generally function by
infiltrating the ground surfaces and binding particles of soils and other
foundation materials into a coherent mass that resists erosion and reduces
water evaportation losses. In addition, these chemicals may be used as tack
material to bind organic mulch residues into a coherent protective blanket.
Chemical soil binders are used primarily to protect exposed
soils from wind and water erosion during delays in construction activities,
during hot and dry periods after final grading, or until permanent seeding
is possible. As tacks to bind mulch materials, chemicals are more rapid
curing than asphalts. This makes them particularly useful in land develop-
ment projects where tracking of sticky asphalt into homes can create problems.
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Many chemical soil binders can be applied with garden-type
hand sprayers, hydroseeders, or other types of equipment (Reference No.
15). They generally are mixed in a water solution and can be applied
with seed and fertilizer. Numerous dilution ratios and application rates
have been developed by manufacturers of these chemicals for use with
different soil types and textures. In general, the greater the percentage
of water, the deeper the penetration of the solution into the soil and the
weaker the binding strength. The soil characteristics must be evaluated
carefully to determine the proper dilution ratio to achieve adequate depth
of penetration of the material and effective binding strength.
According to their manufacturers, the chemicals used for
surface protection are nontoxic to humans and animals and generally
nonflammable. Additional information is needed, however, to determine
their toxicity with regard to fish and aquatic organisms. Technical repre-
sentatives from the manufacturing firms will provide consultation for
treating specific problem areas.
Controlling The Erosion and Transport Capacity of Runoff Water
Runoff water moves over denuded surfaces of construction sites as sheet
flow or as concentrated flow in rills and gulleys. It is dynamic in that it
has energy to erode as well as transport sediment particles. If the available
energy in the moving water is greater than that required to transport
the sediment it has entrained, erosion of the underlying material will
occur. If the sediment load is greater than the transport capacity under the
existing conditions, deposition will take place and continue until a balance
between energy available and sediment load is achieved. Controlling runoff
water in construction areas is essential to prevent the generation and trans-
port of sediments which can pollute downstream areas.
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Structures, with or without the use of vegetation, have been devised to
reduce or prevent excessive erosion and even to induce sediment deposition,
by preventing runoff water from reaching erosive or transport velocities.
They intercept, divert, and dissipate the energy of runoff; reduce hydraulic
gradients; prevent concentration of flows; retard and filter runoff; and
contain concentrated flows in nonerodible channels.
Structural measures used to accomplish these tasks include diversion
structures such as dikes and ditches, waterways, level spreaders, downdrains,
check dams or flow barriers, filter berms, and inlets; and grade stabilization
structures. These measures can be temporary or permanent. Temporary
control measures are used to correct detrimental conditions in a site
area that develop during construction operations; were not predicted during
project design, or are needed to control erosion and sediment that become
problems during construction but are not associated with permanent
measures. Permanent measures are intended to remain in place during
the life of the project facilities.
A formal design is generally required only for permanent erosion and
sediment control structures. The expected life of the structures, the
estimated maintenance requirements, the potential hazard from failure,
and other factors should be used to determine the design of erosion and
sediment control structures. Rainfall and runoff frequencies, are important
when analyzing the size and desired control characteristics of both temporary
and permanent structures. Minimum capacity for structures should be
that required to control the peak runoff calculated to result from the
selected design storm. For example, a 100 year frequency storm would
not be considered appropriate for the design of a temporary measure intended
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for use only during the short construction life of a small project. This
would be "over designing" and impractical.
1. Dikes, or Berms, and Ditches - Dikes and berms are different
terms used for diversion structures, linear ridges built of compacted earth
or other materials. They may be temporary or permanent. Ditches
and dikes are used conjunctively with one another, or independently, to
intercept and direct runoff, to prevent the concentration of water, reduce
slope lengths so that runoff velocities are reduced, and move water to
stable outlets at nonerosive velocities (See Figures 4 and 5). As the length
of a slope increases, the quantity and velocity of runoff water it collects
increases. The effects of these factors on erosion of materials on the
slope can be controlled through the use of dikes, berms, and ditches
which break up the intensity of the slopes.
The number of structures needed on any construction project
and their size and spacing depend on the land slope, soil types, and
runnoff rate. Runoff from the areas immediately upslope from the project
site must be considered in their design. They should have sufficient
capacity to convey, or store, the peak runoff to be expected from a storm
Area graded for development
Channel to divert woter away
from construction site
Figure 4 - Diversions should also be constructed across graded areas to
shorten slopes and reduce erosion on the sloping areas.
(Reference No. 2)
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«*,jaBi:
,P!^^^^^
jiffaj&?- * *^-4* *%,. sIIiBaiF*1^*''5
-"*"*-'" .iiirt*****^^-'
f
Figure 5 - Small Diversions. If both lip and bed are constructed at zero
grade, these diversions would be level spreaders. (Reference No. 18)
frequency consistent with the hazard deemed acceptable by the control
agency. Most organizations involved with sediment control require these
type of structures to be designed for the peak flow to be expected from
a storm of at least a 10 year frequency and 24 hour duration (See References).
Where structures are to be permanent, and schools, dwellings, or commercial
buildings, etc, are to be protected, the storm frequency period often is
lengthened consistent with the hazards from overtopping or structural failure.
Similarly, if the structures are temporary, with an extremely short expected,
life a shorter frequency may be considered practical for design purposes.
All structures composed of erodible materials should be protected
by establishing a vegetative or other type of cover; and maintenance should be
conducted periodically to ensure that they perform up to design capacities
and are not damaged. This may involve removing sediment accumulations,
repairing eroded or overtopped sections, or even revegetating where needed.
Berms and dikes paralleling natural drainages and streams should be
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3-13
constructed so as to protect the natural qualities of the watercourse from
degradation by runoff from the site. Runoff should be diverted by such
techniques into holding ponds for settling or other water treatment before
discharging into the stream.
2. Level Spreaders - Level spreaders are outlet structures provided
at the downstream end of diversions to dispose of concentrated runoff as
sheet flow at non-erosive velocities into stabilized areas (See Figure No. 6).
They are constructed on undisturbed ground and where the area directly
downslope from the horizontal discharge lip is stabilized by existing vegetation.
Water must not be permitted to concentrate below the discharge area.
f 2:1 or Flatter
l*-Min.1
Undisturbed Soil
Stabilized by
Existing Vegetation
Note: Drawing not to scale.
Figure 7 - Level Spreader (Reference No. 15).
Most authorities do not specify formal design, however,
they suggest the spreader length be determined in accordance with the
estimated discharge from a 10 year storm. The following table presents
information for selecting appropriate spreade lengths.
DESIGNED Q
(CFS)
Up to 10
10 to 20
2O to 30
3O to 40
40 to 5O
MINIMUM LENGTH
("L" IN FEET)
15
20
26
36
44
TABLE 1 (From Reference No. 1)
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3. Downdrains - Downdrains can be of the flexible, or rigid, sectional
type (Figures 7 and 8). They are used to convey storm runoff from the top
Figure 7. Temporary, flexible slope drain. Discharges on gravel energy
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3-15
\V
:.- t-
J
Figure 8 - Sectional Downdrain (Reference No. 18),
of a slope to the bottom without causing erosion. Flexible downdrains, con-
sisting of conduits of heavy-duty fabric or other materials, may be used as
temporary or interim structures to prevent erosion of slopes. Sectional
units also may be for temporary use. They are prefabricated half-round,
or third-round pipe, corrugated metal, concrete, asbestos cement, and
other materials.
Formal design is generally not needed for these temporary
structures, however, they should have sufficient capacity to convey the
maximum quantity of runoff expected during their period of use.
Care must be taken that discharges from these types of structures
do not create additional erosion problems at their downslope ends. Generally
some type of energy dissipator will be required such as riprap, rock rubble
mound, or even a designed structure. The disposal area downstream from the
energy dissipator should be well protected and the surface soil stabilized
by vegetative cover.
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4. Chutes and Flumes - These structures are rigid channels
constructed of concrete, asphalt, or comparable materials and used to
conduct runoff downslope from one elevation to another without causing
erosion. They can be installed as temporary or permanent structures
(See Figure 9 and Reference Nos. 2, 15, and 17).
.,££"* r'
"I?- >«*? #'.
Figure 9 - Temporary flume made of concrete (Reference No. 14).
Chutes and flumes should not be used on slopes steeper than
1. 5:1 (34 degrees) or flatter than 20:1 (3 degrees). The underlying foundation
must be either firm undisturbed material or well-compacted fill. The rigid
lining should be fairly dense, free of voids, and relatively smooth surfaced.
Design criteria for areas in the eastern U. S. are presented in References
No. 1 and 7 for information purposes. Essentially they divide the structures
into two groups, based upon dike height at the structure's entrance, the depth
of flow down the chute, and the length of inlet and outlet sections as follows:
Size Group A
1. The height of the dike at the entrance (H) equals 1. 5 feet.
2. The depth of flow down the chute (d) equals 8 inches.
3. The length of the inlet and outlet sections (.L) equals 5 feet.
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Size Group B
1. The height of the dike at the entrance (H) equals 2 feet.
2. The depth of flow down the chute (d) equals 10 inches.
3. The length of the inlet and outlet sections (L) equals 6 feet.
Each size group has various bottom widths and allowable drainage
areas as shown on the following table:
Bottom Maximum Bottom Maximum
Width, b, Drainage Area Width, b, Drainage Area
Size I/ ft. acres Size I/ ft. acres
A-2
A -4
A-6
A-8
A-10
2
4
6
8
10
5
8
11
14
18
B-4
B-6
B-8
B-10
B-12
4
6
8
10
12
14
20
25
31
36
I/ The size is designated with a letter and a number, such as A-6 which
~~ means a chute or flume in Size Group A with a 6-foot bottom width.
If a minimum of 75% of the drainage area will have a good grass or wood-
land cover throughout the life of the structure, the drainage areas listed
above may be increased by 50%. If a minimum of 75% of the drainage area
will have a good mulch cover throughout the life of the structure, the
drainage areas listed above may be increased by 25%.
These structures in all areas of the country should be designed
based upon runoff flows to be expected at the frequency inteval selected.
Care must be exercised in their construction, as well as their design, as
overtopping by flows, differential settlement of foundation materials, or
opening of construction joints may cause failure.
As in downdrains, chutes and flumes will require some sort
of energy-dissipating device incorporated into their lower, or outlet,
section at the bottom of the slope being protected.
5. Waterways or Outlets These structures are wide, shallow
natural or constructed channels which are shaped, graded, and vegetated
for the purpose of conveying and disposing of excess runoff without causing
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erosion or flooding (See Figure No. 10). Many authorites design them to
accomodate the expected runoff from a storm of selected frequency (generally
a 10 year frequency, 24 hour duration storm) without damaging the channel
or its lining (References 1, 2, 5 and 7). Design may inclixde structural
measures to keep runoff velocities below erosive limits, protective
vegetative coverings, or some type of lining, to prevent erosion. The
success of a waterway depends upon it having a stabilized outlet area.
If this has not been provided, failure could occur, with erosion progressing,
in a headward direction up the waterway.
Figure 11 - Jute Netting Over Straw Mulch in Waterway (Reference No. 15).
6. Grade Stabilization Structures - These structures are provided
to reduce the slope of natural or artificial channels. They prevent concen-
trated runoff from reaching excessive (erosive) velocities and prevent
headward erosion (upward advance) of channels. Generally, they are permanent
and expensive structures and should be used only where vegetative, diversion,
or other types of measures cannot prevent concentrated water from reaching
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high enough velocities to cause erosion. Grade control structures include
check dams, drop structures, and erosion stops.
A. Check dams generally also provide partially-lined channel
sections and overfall structures of concrete, wood, rock, and other
materials. They protect channel surfaces and reduce flow velocities
below that required to-erode (See Figure No. 11). They should be situated
in a fairly straight section of a channel, after careful consideration of site
conditions. Generally, a formal design is required.
""5
Figure 11 - Rock Check Dams (Reference No. 18).
B. Drop, or overfall, structures are made of rock, concrete,
metal or treated wood while pipe-drop facilities are usually constructed
of metal or pre-cast material (See Figures 12 and 13). Suitable inlet and
outlet facilities are normally required for each structure unless foundation
conditions dictate otherwise; and channel protection, through linings or
other means, is essential.
-------
Figure 12 - Box Inlet Grade Control Structure (After Reference No. 13).
- ^ "' **"'"'^'
^^gi^^ a
Figure 13 - Drop Box Structure Combined With Culvert (After Reference No. 13).
C. Erosion checks, or stops, are measures used to prevent
channel erosion through the installation of non-erodible materials, into a.
trench oriented normal to the flow of water (See Figure 14). They can be
installed in channels and swales or on extremely erodible slopes. Depths
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should be below the estimated depth of possible erosion or, to 12 inches.
The check should extend laterally above water surface expected from
design storms for the facility being protected.
SECT.-AA
NO 3CAK
1. Cutaway of fiber glass installation in bottom of trench.
2. Cutaway of fiber glass installation in trench with spoil pile.
3. Trt-.ich with fiber glass erosion check installed.
4. Cap strip of blanketing material over completed erosion check.
Figure 14 - Erosion check (Reference No. 15).
Trapping Sediments
Structures used to trap sediments are developed principally to stop the
movement of materials being transported by runoff water and prevent
them from leaving the site area. They consist of filter berms, sandbag
or straw-bale barriers, filter inlets, culvert risers, sediment detention
basins, and similar facilities. Many other structures and vegetative
measures also act, to a limited extent, as partial sediment traps*
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1. Filter Berms - Filter berms usually consist of pervious
barriers composed of gravel, crushed rock, or similar materials. They
temporarily detain runoff water to allow sediment to deposit and act as a
filters, permitting water to move through them but not the sediment being
transported (See Figure 15). Formal design is not required but pervious
gravelly materials must be sized so that sediments do not pass through the
berm too readily.
Figure 15. Filter berm (Reference No. 18)
2. Sandbag or Straw-Bale Barriers - These temporary structures
may be used independently as control structures or in conjunction with filter
berms. They can act as diversion or detention facilities and used to protect other
structures, such as inlets from sediment, laden flows. Water passes through
straw bales as well as the sand and gravel filter-berm spillways, but the sedimen-
is retained (See Figure 16 and 17).
They are used to detain sediments resulting from small drainage
areas in the order of 1/2 acre in size. The bales must be securely staked and
preferably bound with wire rather than twine. Water must not be allowed to
escape freely under the bales.
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Figure 16 - Semi-pervious barrier of hay bales with more pervious
embankment of sand and gravel for spillway (Reference No. 17)
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3-24
Gutter
~~^ >Storm sewer structure
\*r
Anchor with two stakes
driven into the ground
Figure 17 - Temporary Barrier of Hay Bales to Prevent Sediment-Laden
Water From Entering Storm Sewer (Reference No. 17).
3. Culvert Risers - Culvert risers are upward-extending, often
perforated pipes forming the intake area of culverts. Their purpose is to
pond runoff water temporarily and enable its sediment load to settle
out. Gravel filters may be used around perforated pipe sections. Their
function and design are similar to that for sediment basin outlet works
(principal spillways).
4. Sediment Detention Basins - A sediment detention basin (sometimes
referred to as a debris basin) probably can be considered as the "last line
of defense" in a system of Best Management Practices developed to prevent
runoff of sediments from a construction site. Probably the most expensive
and precisely-designed structures used for sediment control purposes,
they may be installed as temporary structures or as permanent facilities
used to provide storage of water for aesthetic and other useful purposes.
The design used must reflect the intended use of a detention basin.
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Sediment detention basins usually consist of small compacted
earth-fill dams, reservoirs which may be partly excavated to provide em-
bankment materials, uncontrolled outlet pipe (or spillways) and emergency
spillways (See Reference Nos. 14 and 15). This latter spillway is usually
cut into undisturbed materials around the end of the embankment. It is
unlined but vegetated to prevent erosion. Sometimes a lined over-pour
spillway is used over the top of a small dam embankment. The lining of
this latter spillway must be well-designed to prevent lining failure and a
possible dam failure also.
Gravel Cone
Free outlet
Figure 18 - Large, Well-Engineered Sediment Basin Dam. Note Principal
Spillway Pipe with Riser, Gravel Core Filter, and Seepage-path
Cut-off Collars on Outlet (Reference No. 17).
Most existing sediment control guidelines, handbooks, and other
such documents require that detention basins be designed to store 0. 5 inches
of water from the watershed (67 cubic yards/acre) and that they be cleaned
out when storage is decreased, by sediment deposits, to 0. 2 watershed inches
(27 cubic yards/acre) as measured to the crest of the emergency spillway,
or pipe spillway crest if there is no emergency structure. (Reference No's.
2, 4, 7 and 15). In addition, they provide for principal (pipe) spillways to
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Figure 19 - Sediment retention structure - small, less than 1/4 acre
(Reference No. 15).
handle at least 5 inches of runoff from the drainage area in 24 hours and
emergency spillways to pass the peak rurioff from a 10 year 24 hour storm
(less reduction in flow due to pipe spillway). Drainages more than 20 acres
in size generally are designed for a 25 year frequency storm. Maximum
allowable flow velocity in vegetated unlined emergency spillway channels
is 6 feet per second (See Table 1). These design concepts are based on
"rule of thumb" storage capacity for sediments and dam safety. They
certainly are important factors, and must be considered in the design;
however, they do not fully result in the achievement of adequate sediment
detention.
Since the main purpose of a sediment detention basin is to
temporarily detain, or store, runoff water long enough for sediment
particles which are being transported to settle out at their natural settling
rate, this must be the principal factor in the design. Fine-grained materials
such as silts and clays, which settle out at extremely slow velocities, are
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extremely difficult to trap in most of the presently-designed basins. As
a result, considerable effort must be made to design the facilities to trap
materials of these sizes. If it cannot be done, flocculation or some other
technique may be required. Flocculation involves causing the aggregation of
these fine-grained materials through the use of chemical or other materials.
In order to trap sediments of a certain size, a detention basin
must detain runoff water long enough for these materials to settle to the
bottom of the basin naturally. Table 2 gives settling velocities for various
sediment sizes. A detention reservoir should be large enough (in area),
TABLE 2 (From Reference No. 20)
Settling Velocities of Selected Particles
Kind of Material
Coarse sand
Coarse sand
Fine sand
Fine sand
Fine sand
Silt
Coarse clay
Fine clay
Particle Diameter (microns)
1000
200
100
60
40
10
1
0. 1
Settling Velocity (cm/sec)
10. 0
2.1
0.8
0.38
0.21
0.015
0.00015
0.0000015
to enable sediment-laden inflow water to be diffused and dispersed so that it
must move vertically to gain access to the outlet. Design of this outlet is
critical and perforated, easily accessible structures such as that shown in
Figure 18 are not desirable unless sediment is extremely coarse-grained.
This design facilitates "short circuiting" of the flow path and enables currents
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to transport sediment loads directly through the reservoir and into the
outlet facilities without dispersion.
The area of the detention reservoir and its depth are the
critical factors for design purposes. Increases in the surface area of a
correctly designed reservoir will result in decreases in the velocity of the
sediment-laden water as it moves upward and into the pipe outlet, or spillway
(See Figure 20, and Reference No. 20). The area required to trap each
size sediment particle can be determined by the following formula:
A (area in square feet) = Q (pond outflow rate, in cubic feet per second)
V(upflow velocity, in cubic feet per second)
u
If the settling velocity of a particle of given size (V) is greater
s
than V, the velocity of the upward-flowing water, deposition of all particles
u
of.this size and larger will settle to the bottom and be trapped. Smaller-sized
materials will pass through the outlet and spillway and escape. Table 3 presents
minimum reservoir surface area required to trap various sediment sizes.
TABLE 3
Minimum Area for Sediment Detention Basin
To Trap Sediment Particles (1 cubic foot/second outflow)
Kind of
Material
Coarse sand
Coarse sand
Fine sand
Fine sand
Fine sand
Silt
Coarse clay
Fine clay
Particle
Diameter
(microns )
1, 000 (1mm)
200
100
60
40
10
1
0.1
Minimum Area
Required
(sq ft)
3.0
14. 5
38.2
80.0
145.0
2,030.0
203, 000. 0 (4.
20,300, 000.0 (46
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Depth of the reservoir is important to provide storage for
adequate quantities of sediment and still maintain dispersion of inflow and
upward movement into discharge facilities. Detention time should be
determined at the point that sediment storage has reached its maximum and
no "short circuiting" has occurred. In this way the reservoir is designed
for maximum efficiency. Periodic sediment removal will maintain this
storage volume and is required for good operations. Sediments should not
be disposed of in an area where they will create additional pollution problems.
The shape of the reservoir and design of its headwater, or
inlet, area are important in preventing short circuiting of flows. If con-
centrated, high-velocity currents enter the reservoir without being dispersed
and their velocities decreased, they will not only continue transporting
their sediment loads through to the outlet areas but may stir up and erode
deposits that had already been trapped on the reservoir bottom. Multiple
inlets, level spreaders or weirs of some type, and even baffles may be
devised for use in dispersing the inflow and reducing its velocities.
Principal outlets, or spillways, are also important for good
sediment trapping efficiences. Multiple spillway intakes, trough-type
outlets, or even syphon-type structures will prevent concentration of flow
and the accompanying high velocities which may again place sediment back
into transport. A standpipe full of perforations such as that in Figure 18
is a poorly-designed facility because it results in short circuiting. Unless
the gravel envelope is a well-graded filter, sediment will be able to move
through it easily and downstream. If the envelope is clogged, concentration
of flow into the remaining section may occur causing bottom scour and
additional sediment entrainment and loss.
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For outflow rates above one cubic foot per second, the minimum area
shown in Table 3 must be increased equivalently. For example, in
order to trap a coarse sand with a particle size of 200 microns, and
an outflow rate of 3 cubic feet per second, the reservoir area should be
14. 5 square feet x 3 cfs = 43. 5 square feet (See Table 3).
Additional guidance for design, construction, and maintenance
of sediment basins is presented in references listed at the end of this
chapter. It involves principally factors for structural safety, good con-
struction practices, and location and capacity of overflows structures,
not sediment detention capacity. In many states, the larger-sized sediment
detention dams and reservoirs may fall within the jurisdiction of a dam
safety organization. These organizations have mandatory criteria for
minimum spillway capacity, design and construction procedures, seismic
coefficients, and the like.
Good Housekeeping Practices
Good erosion and sediment control, in conjunction with management of
stormwater runoff, will prevent the movement of many pollutants other than
sediments. Those pollutants that are in solution; however, or are carried on
fine-grained sediments, may pass through all sediment control measures and
reach downstream water bodies. Materials, such as pesticides, petro-
chemicals, and fertilizers are nearly impossible to control once they
are present in the runoff water. The only practical control options available
are either to provide expensive water treatment facilities on stormwater
detention basins or preferably to prevent these pollutants from reaching
runoff waters through the use of proper application techniques and "best
housekeeping practices".
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Pesticides
Use of many insecticides, herbicides, and rodenticides is restricted
by Federal, State, or local regulations. In order to limit the possibility of
these materials creating detrimental environmental effects as a result of
construction activities, strict adherence to recommended practices is
required. Application rates should conform to registered label directions,
and application equipment cleaned after use, or properly disposed of
(Reference No's. 21, 22, and 23). All pesticides are listed in issues of
the "EPA Compendium of Registered Pesticides", which can be obtained
from the Superintendant of Documents, U. S. Government Printing Office.
This document provides information on dosage and application rates,
tolerances, formulations, use limitations, and the pests controlled.
Supplements to the Compendium are issued periodically. Similar data
can be obtained from each State's Cooperative Extension Service.
Pesticide storage areas should be protected from the weather and from
public contact. Areas that have been recently treated with particularly
potent pesticides should be clearly marked to warn trespassers or unwary
persons.
Time of pesticide application is of particular importance in preventing
runoff of pesticides from the site area as pesticide losses occur principally
when high-intensity rainfall occurs shortly after application. Also chemicals
should not be applied during periods of weather extremes such as freezing
conditions when the chemicals will not be absorbed, thus assuring their
eventual runoff. Often, more pesticide quantity is contained in solution
in runoff water than attached to sediment particles because the volume
of water that runs off is much greater than the volume of sediment
lost. The concentration of pesticide carried by the sediments is much
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greater, however, and subsequent pollutional impacts may occur when the
sediments are deposited in the bottom of a water body. (See Reference No. 24).
Petrochemicals
Control of petrochemical runoff, such as oils, gasolines, and greases
involves mainly sediment control as these materials adhere to, or coat,
sediment particles. Additional measures include proper collection and
disposal of the waste products, prevention of oil leaks, and proper mainten-
ance of equipment. Used oils and greases and rags and papers impregnated
with this material should be disposed of in proper receptables and kept
out of contact with rainfall or runoff water. Dumping of waste materials
at the construction site should be prohibited. Liquid and solid wastes
should be collected in containers and regularly transported from the site
to sanitary landfills. When machinery is to be maintained, lubricated, or
repaired on site, it can be placed upon a pad of absorbent material to
intercept and contain leaks, spills, or small discharges. Equipment
washing should be undertaken at specified locations and the runoff collected
in holding ponds. In no case should any of these latter operations be
conducted closely adjacent to a stream or water body.
Fertilizers
Inorganic nutrient pollution is derived principally from fertilizers used
to develop adequate vegetation on exposed ground surfaces. Effective
sediment control measures and stormwater management practices as well
as good vegetative cultivation practices are useful for controlling fertilizer
losses. Proper timing of fertilizer applications to avoid bad weather,
harsh seasonal weather extremes, and to pinpoint periods of optimun plant
generation, and provisions for working these and other materials into
the soils at the required depth will do much to minimize runoff of pollutants.
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More efficient use of fertilizers may be achieved, and loss of nutrients
reduced, by applying the required quantity in several rather than one
application. Evaluating essential fertilizer and other additive requirements
from actual soil test in the site area is essential to ensure that only
optimum quantities are applied. This alone should reduce the possibility
of material losses.
Solid Waste
The major mechanism for control of solid wastes such as residues
from trees and shrub generated during land clearing; wood and paper from
packaged supplies; and scrap metals, sanitary wastes, rubber, plastic,
glass fragments, and the like resulting from normal day-to-day operations,
is the provision of adequate and effective disposal facilities. These wastes
should be removed from the site frequently and transported to authorized
and suitable disposal sites. Inert materials which do not leach and cause
groundwater problems may be used effectively to refill borrow pits or
other excavated areas. The same material can be considered for use
in road fills or fills for other facilities. Trees and other vegetation may
be chipped up and used on site areas as inexpensive and convenient mulch
materials. Any solid wastes trapped in sediment detention basins should
be removed as quickly as possible. Adherence to State and local anti-litter
ordinances should be enforced with regard to construction personnel, site
visitors, and others. If no violation of air pollution requirements is
involved, inflammable wastes may be burned. Reference Nos. 25 through
28 will provide information on air and solid waste requirements.
Storm Water Management
Storm water management involves controlling the rate of storm water
runoff from construction sites. It must consider control of storm water
during the life of facilities being constructed as well as during the construction
period itself.
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In past periods, the philosophy for storm water control was to route it
through areas as quickly as possible. Under this concept, areas downstream
from the sites had to accept the brunt of accelerated and increased peak
storm runoff. Flooding, excess channel erosion, and other damaging
effects resulted.
The present concept of storm water management is to reduce and
delay runoff water peak discharges. Management may be achieved by
increasing infiltration in the drainage area to reduce the amount of
precipitation that actually becomes runoff, increasing time of runoff
concentration by accentuating the meandering of drainageways to reduce
gradients and runoff velocities, and providing temporary storage facilities
to release the stored water at controlled rates.
Increasing Infiltration of Runoff
Methods used to increase infiltration of runoff into soils and other
subsurface materials have been used for a number of years in parking
areas. They involve periodic perforation of lawns, development of sub-
surface facilities, and the provision of porous pavement materials. Extreme
infiltration care must be used with regard to the quality of water being
infiltrated as it is possible to create a groundwater pollution problem
with the resolution of a surface water pollution problem.
Periodic perforation of golf course fairways has been used for quite
some time to increase infiltration and aeration. This same process will
help increase infiltration of storm water in vegetated areas of construction
sites. In addition to reducing runoff, the practice should accelerate move-
ment of fertilizers into the subsoil and provide for better vegetative growth.
Infiltration facilities may involve wells or excavations which have been
backfilled with pervious materials. Their purpose is to provide vertical,
highly-pervious conduits through which surface waters can gain access to
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permeable subsurface strata. If these strata contain usable ground water
supplies, the infiltrating water must not be poor enough in quality to degrade
them. These types of infiltration systems have been used in areas of suburban
development and along highways to accommodate excess runoff.
Porous pavements are used principally in parking areas of shopping
centers. They consist of irregularly-shaped aggregate precoated with
asphalt binder. Water can move vertically through this layer into an
underlying lower level of compacted gravels and then, if conditions are
favorable, into underlying natural foundation materials. Favorable
conditions are situations where existing ground water bodies will not
be degraded by infiltration of poor quality runoff. If ground water pollution
is possibly a problem, porous pavement facilities can still be used for
storm water management if designed properly. This design could involve
construction of a clay blanket or some other inpervious material below
the compacted gravel layer. Infiltrating water would then have to slowly
move laterally through the gravel and, after a delayed period of time, be
discharged into a storage basin where it can be treated and released.
Altering Time of Runoff Concentration
This aspect of storm water management should focus on the conservation
and use of existing natural drainageways. Conditions to avoid are long, narrow,
V-shaped channels with steep gradients, as they tend to promote concentration
of flow with accompanying high erosion hazard if the channels are not adequately
lined. The discharge end, where gradients decrease, can create severe
problems with respect to erosion if an effective energy-dissipation structure
is not provided.
To effectively decrease time of runoff concentration, wide, meandering,
vegetated channels with gentle gradients and side slopes are required.
Velocities in major channels of this type should be less than 5 feet per
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second with side slopes of less than 3 to 1. Curves, or bends should be
gentle with radii not less than 100 feet (Reference No. 29). Increasing the
time of concentration by reducing the runoff velocities in channels also acts
to increase infiltration as the runoff has longer contact with the ground
surface. Small check dams can be placed in the vegetated drainage
channels, or swales, to reduce runoff velocities, provide short-term
minor storage, and increase infiltration.
Providing Temporary Surface Storage
Almost all measures used to prevent erosion and sediment losses on
construction sites also function to control the runoff of storm water. Probably
the principal storm water management technique available, however, involves
temporarily storing surface water runoff and releasing it at a predetermined
decreased rate. Consideration of the runoff characteristics in the entire
basin must be made as improper releases of stored water could cause
increased rather than decreased flows in downstream areas. In addition,
in some channels, moderate downstream flows maintained for longer
periods of time may cause more problems than the peak flows themselves.
Storage can be provided on rooftops and in subsurface holding structures
or temporary or permanent surface impoundments. These surface im-
poundments may be in or near drainageways or even constructed in parking
lots or other facilities.
Rooftop storage can be achieved on relatively flat roofs by limiting
the release of precipitation which falls on the roof. Control is through
specially-construe ted roof drains which cause the water to be ponded to
a particular level and release it at a reduced rate (See Figure 21). Flow from
the roof occurs through small holes or slots in the drains. Water released
should be spread, if possible over vegetated areas, to provide for infiltration.
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SCUPPER-
ROOF DRAI
'_ r-, y 77V. - : :' '',''. ' '.: \
H'^ L
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3-39
development concept, can be highly beneficial to a community. They
are generally developed through the construction of a small dam, with
necessary appurtenant structures such as spillway, outlets, and the like,
across a drainageway. The permanent water level of such reservoirs
is designed to be several feet below emergency spillway crest. Reservoir
volume above this elevation accommodates flood storage to attenuate
peak runoff flows. An outlet with a valve should be provided to facilitate
reservoir drainage when repair or maintenance of the structure is required.
Temporary reservoir storage in "dry" impoundments stores water only
during flood events. They are dry during the remainder of the time. These
reservoirs are created by some type of permanent water-detaining
structure or embankment. Outlet facilities, however, are ungated (no valve).
As a result, runoff which enters the reservoir at a high rate is immediately
free to discharge at a pre-designed lesser rate. This reduces peak runoff
to prevent or reduce downstream flooding, channel erosion, and other problems.
Since the same quantity of water must be released, longer periods of moderate
flows will occur in downstream channels. Dry impoundments, or reservoirs,
can be developed in any area that is topographically depressed, whether due
to natural or man-made conditions. Parking lots, tennis courts, playgrounds,
and other areas can be used to provide temporary storage facilities for
runoff if adequate outlet facilities can be installed. (See Figure No. 22).
Figure 22 - Storm Water Detention Storage Structure in Lower Portion
of Parking Lot (Reference No. 14).
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Off-stream impoundment of storm water runoff may be created adjacent
to existing stream channels or drainageways. A diversion embankment is
often used to divert water into a selected area during high flows. When
flood-levels decrease, the diverted water drains back into the main channel
at a decreased rate. Use of side-channel storage areas in flood plain
areas often is an inexpensive way of achieving effective storm water control.
Systems Approach to Sediment Control
Rarely will single erosion or sediment control measures be effective
enough to achieve desired results. Generally, several different measures
are provided as first, second, third, and even more "lines of defense".
This is termed the "systems approach" to sediment control. For example,
on a construction site, the area of exposed soils may be limited. Then
vegetation may be required on all areas which are left exposed more
than a certain length of time. In addition, various structures may be
required to protect the ground surface from rain and runoff water, control
the energy in runoff, and filter or trap sediments being transported. All
of these measures are included within the total system which is devised
to prevent loss of sediments from the site area.
The lack of reliable effectiveness factors hampers the optimization of
erosion and sediment control systems development. The effectiveness of
some individual measures in these systems may be found in published
literature, however, information on the various combinations in the system
is limited. In addition, most effectiveness factors have been developed
for agricultural practices and should not be assumed to be equivalent to
those used on construction sites.
A method to determine the effectiveness of a system of control measures
has been obtained from References 18 and 31, "Comparative Costs of Erosion
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and Sediment Control, Construction Activities", and "An Economic Analysis
of Erosion and Sediment Control Methods for Watersheds Undergoing Urban-
ization". This method involves a comparison of the soil losses from a
construction site without control measures with that from a. site with measures
installed. All other factors in the site area remain the same.
The various individual measures are viewed as cropping-management
(C) and conservation practices (P) factors for reducing soil losses. Thus,
the soil loss (A') from a given construction site having erosion and sediment
control treatments can be computed by the universal soil loss equation:
A' = RLSKCP (1)
If the same construction site was denuded and employed no erosion and
sediment control treatments, the soilless (A") would be:
A" = RLSK (2)
since the factor C_ and P values equal 1. 0. Values for RLSK are equivalent
in Equations (1) and (2) since the same construction site is used for both
equations. The soil retained on the construction site, because erosion
and sediment control treatments were employed, is computed by:
soil retained = A" - A1 (3)
Therefore, the effectiveness percent of the treatments in retaining soil
on the construction site is:
% Effectiveness = A" - A' x 100
IT1"
= RLSK - RLSKCP x 100
RLSK
- (1 - CP) x 100 (4)
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Equation (4) can now be used to compute effectiveness for the various
erosion and sediment control alternatives, providing Factor C and P
values are assigned for the individual treatment comprising a particular
system.
Published Factor C (conservation) values need to be adjusted for
urbanizing areas because stabilized surfaces are disturbed by construction
traffic. Two assumed construction conditions have been considered:
(1) Construction is completed within 18 months following
initial groundbreaking.
(2) When building is started six months after seeding, then
construction is completed within 24 months.
It is further assumed that three months of the 18- or the 24- month
construction periods are consumed by grading operations, and that
construction sites are without surface protection during this time.
Factor C values change with time following surface treatment. For
example, Factor C values for grass decrease from 1. 0 to about 0. 01
between seeding and when the grass is reasonably well established. For
construction sites, Factor C values are assumed altered additionally
by urban development activities.
A typical example of estimating average Factor C value for seed,
fertilizer and straw mulch is as follows, after Reference No. 18:
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Fraction of
Representative Construction
Months
0-3*
3-6
6-18
Factor C Value
1.00
0.35
0.19
Period
3/18
3/18
12/18
Product
0. 167
0.058
0.127
Average Factor C value for 18-month period = 0. 352
^During 0-3 months, Factor C value is 1.0 because the construction
area has no surface stabilizing treatment.
Table 4 lists the average values of Factor C for various surface
stabilizing treatments from (Reference No. 18) and Table 5 lists additional
erosion-reducing values for more specific ground cover.
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TABLE 4
AVERAGE FACTOR C VALUES FOR VARIOUS SURFACE
STABILIZING TREATMENTS ( REFERENCE NO. 18)
Factor C Values for
Treatmemt
Time Elapsed Between
Seeding and Building
None* B Months **
Seed, fertilizer and straw mulch.
Straw disked or treated with asphalt or
chemical straw tack. 0. 35
Seed and fertilizer 0. 64
Chemicals (providing 3 months protection) 0.89
Seed and fertilizer with chemicals
(providing 3 months protection) 0. 52
Chemical (providing 12 months protection) 0. 56
Seed and fertilizer with chemical
(12 months protection) 0.38
0.23
0.54
0.38
* Assumes 18 month construction period.
** Assumes 24 month construction period.
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TABLE 5
EFFECTIVENESS OF GROUND COVER ON EROSION LOSS
AT CONSTRUCTION SITES (REFERENCE NO. 181
Soil Loss Reduction Related to
Bare Surfaces
Kinds of Ground Cover (Percent Effectiveness)
^Seedlings
Permanent Grasses 99
Ryegrass (Perennial) 95
Ryegrass (Annual) 90
Small Grain 95
Millet and Sudangrass 95
Field Bromegrass 97
Grass Sod 99
Hay (2 Tons per Ac) 98
Small Grain Straw (2 Tons per Ac) 98
Corn Residues (4 Tons per Ac) 98
Wood Chips (6 Tons per Ac) 94
** Wood Cellulose Fiber (2-3/4 Tons per Ac) 90
** Fiberglass (1, 000 Lbs per Ac) 95
Asphalt Emulsion (125 Gal per Ac) 98
* Based on full established stand
** Experimental - not fully validated
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Structures used in the various control systems are considered as
requiring Factor P values to describe their efficiency (Reference No. . 31).
These components include small sediment basins, erosion reducing
structures, and downstream sediment basins with or without the use of
chemical flocculants. Diversion structures, grade stabilization measures
and level spreaders are collectively considered as erosion reducing structures.
The practice factor P reflects the runoff and erosion-reducing effects
of structures. The effectiveness of terra'ces and diversions, which reduce
effective slope lengths and runoff concentration should be similar on
construction sites and farmlands (See Reference No. 32).
Small Sediment Basins - The conventional method employs small sediment
basins having inflow (cubic feet per second) to area (square feet) ratios of
0. 03 to 0. 04, with an average trap efficiency of 70 percent. Thus, if the
sediment basin collects sediments coming from only 70 percent of the
construction area then its Factor P value is about (1. 00 - 70%) x 70% = 0. 50.
On the other hand, if it collects sediments from 100 percent of the construction
area then its Factor P value is (1. 00 - 70%) x 100%) = 0. 30 (See Table 6).
Downstream Sediment Basins - The larger size basin constructed down-
stream of the construction site, and having inflow to area ratios of 0. 06
to 0. 07, will have a trap efficiency of 80 percent, thus the corresponding
Factor P value is 0.20. Chemical flocculants may be added to this downstream
basin to cause more efficient settling of incoming sediment. Such chemicals
are assumed to increase the trap efficiency of this basin 90 percent, giving
a Factor P value of 0. 10.
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Erosion-Reducing Structures - Diversion berms, sodded ditches, inter-
ceptor berms, grade stabilization structures and level spreaders are
collectively referred to as one system called "erosion-reducing structures".
The overall effectiveness of erosion reducing structures is estimated at
50 percent. The Factor P value for this normal usage is then 0. 50. For
higher usage, the erosion reducing structures are estimated to be 60 percent
effective, giving a Factor P value of 0. 40 for this case.
Factor P values for these systems are summarized in Table 6 and
discussed below.
In using these Factor P values to estimate effectiveness of the erosion
and sediment control alternatives, it is assumed that 100 percent of the
sediment not caught by the surface stabilization treatments and/or erosion
reducing structures is delivered to the sediment basins.
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TABLE 6
FACTOR P VALUES FOR COMPONENTS OF
EROSION AND SEDIMENT CONTROL SYSTEMS (REFERENCE NO'S 18 and 31)
Factor P
Component Value
Small sediment basin: (0.04 ratio)
Sediment from 70% construction area 0. 50
Sediment from 100% construction area 0. 30
Downstream sediment basin: (0. 06 ratio)
With chemical flocculants 0. 10
Without chemical flocculants 0.20
Erosion reducing structures:
Normal rate usage (165 ft per ac) 0. 50
High rate usage (over 165 ft per ac) 0.40
The effectiveness of various erosion and sediment control systems is
computed and listed in Table 7, using the equation:
Percent Effectiveness = (1 -CP) x 100
Factors C and P are taken from Tables 4 and 6, respectively.
Factor P values are multiplied if a particular erosion and sediment control
alternative has two or more components represented by a Factor P. An
example of this calculation is shown using the conventional method of erosion
and sediment control.
Factor C or
Conventional Method Value
Sediment basin (. 04) 0. 50
Erosion reducing structures (normal) 0. 50
Seed, fertilizer and straw mulch 0. 35
Percent Effectiveness = 1-(0. 35 x 0.50)x 100 = 91.25 percent.
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TABLE 7
PROMISING CONTROL SYSTEM AND EFFECTIVENESS
(AFTER REFERENCE NO. 18)
System Numbers Components Percent Effectiveness
1 Seed, fertilizer, straw mulch. 91
Erosion structures (normal). Sediment
basins (0. 04 ratio, and 70 percent of
area)
2 Same as (1) except chemical (12 months 90
protection) replaces straw.
3 Same as (1) except chemical straw tack 91
replaces asphalt.
4 Seed, fertilizer, straw mulch. Diversion 90
berms. Sediment basins (0.04 ratio, and
100 percent area)
5 Seed, fertilizer, straw mulch. Downstream 93
sediment basin (0. 06 ratio).
6 Seed, fertilizer, chemical (12 months 92
protection). Downstream sediment basin
(0. 06 ratio).
7 Seed, fertilizer, straw mulch. Downstream 96
sediment basin using flocculants.
8 Same as (7) without straw mulch. 94
9 Chemical (12 months protection) sediment 94
basin using flocculants.
10 Same as (9) with seed, fertilizer. 96
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Selected References
1. County of Fairfax, Virginia "Erosion - Sediment Control Handbook"
December, 1974.
2. U. S. Department of Agriculture, Soil Conservation Service "Guide for
Sediment Control on Construction Sites In North Carolina", March 1973.
3. Michigan, Department of Natural Resources "Michigan Soil Erosion
and Sedimentation Control Guidebook", February 1975.
4. Virginia Soil and Water Conservation Commission "Virginia Erosion and
Sediment Control Handbook - Standards, Criteria, and Guidelines",
April 1974
5. Metro Association of Soil and Water Conservation Districts, Anoka,
Carver, Dakota, Hennepin, Scott and Washington Counties, Minnesota
"Urban Erosion Control Handbook", August 1973.
6. Knox Gouty Soil Conservation District, Tennessee "Erosion and
Sediment Control Handbook", July 1973.
7. Maryland Department of Natural Resources, assisted by the U. S.
Department of Agriculture, Soil Conservation Service "Standards and
Specifications for Soil Erosion and Sediment Control in Urbanizing
Areas", November 1969.
8. California State Department of Public Works Division of Highways
"Erosion Control on California Highways", date unknown.
9. New Jersey State Soil Conservation Committee "Standards for Soil
Erosion and Sediment Control in New Jersey", June 1972.
10. University of Minnesota, Department of Horticultural Science, in
Cooperation With The Federal Highway Administration, Minnesota
Highway Department and Minnesota Local Road Research Board
"Development of Ground Covers For Highway Slopes" Final Report,
Investigation No. 615, May 1971.
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11. U. S. Department of Agriculture, Soil Conservation Service
"Handbook For Erosion and Sediment Control In Urbanizing Areas
In Hawaii", March 1972.
12. - - Guidelines For the Control of Erosion and Sediment In
Urban Areas of The Northeast", August 1970.
13. "Engineering Field Manual For Conservation Products", 1969.
14. U. S. Environmental Protection Agency, Office of Air and Water
Programs "Processes, Procedures, and Methods to Control
Pollution From All Construction Activity" EPA-430/9-73-007, Oct. 1973.
15. - - - - ..Office of Research and Monitoring "Guidelines For Erosion and
Sediment Control Planning and Implementation" EPA-R2-72-015, August 1972.
16. - -, Office of Water and Hazardous Materials, "Methods of Quickly
Vegetating Soils of Low Productivity, Construction Activities" EPA-
440/9-75-006, July 1975.
17. - - - -, Office of Water Programs "Control of Sediments Resulting
From Highway Construction and Land Development", September 1971.
18. - - - -, Office of Water Program Operations "Comparative Cost of
Erosion and Sediment Control, Construction Activities", EPA-430/9-
73-016, July 1973.
19. U. S. Department of Transporation, Federal Highway Administration
"Prevention, Control and Abatement of Water Pollution Resulting From
Soil Erosion". Instructional Memorandum 20-3-70, April 1970.
20. American Public Works Association "Practices In Detention of Urban
Stormwater Runoff" Special Report 43 by H. G. Poertner, 1974.
21. U. S. Environmental Protection Agency, "Regulations for the Acceptance
of Certain Pesticides and Recommended Procedures for the Disposal and
Storage of Pesticides and Pesticide Containers" Federal Register Vol. 36,
May 23, 1973.
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Other References Used
Ada Soil Conservation District, Idaho, Assisted by the U. S. D. A.,
Soil Conservation Service and the Soil Conservation Commission, State
of Idaho "Sediment and Erosion Control Guide For The Boise Front-
Urban Area. Part 1 - General" June 1972.
American Association of State Highway and Transportation Officials
"Guidelines For Erosion and Sediment Control In Highway Construction"
1973.
American Association of State Highway Officials "A Guide for Highway
Landscape and Environmental Design", 1970.
Baltimore County, Maryland, assisted by U. S. D.A., Soil Conservation
Service "Sediment Control Manual", June 29, 1970.
Berks County Soil and Water Conservation District, Pennsylvania
"Handbook For Erosion and Sediment Control in Urbanizing Areas".
May 1970.
Georgia State Soil and Water Conservation Committee, In cooperation
with U. S. Department of Agriculture, Soil Conservation Service
"Urban Erosion and Sediment, Damages, Planning For Solutions and
Steps to Effective Control". 1972.
Montgomery County, Maryland, Soil and Water Conservation District
"Erosion and Sediment Control Handbook". June 1970.
National Academy of Sciences, Highway Research Board "Erosion Control
on Highway Construction". 1973.
New Jersey State Soil Conservation Committee "Standards For Soil
Erosion and Sediment Control In New Jersey", June 1972.
Pennsylvania Department of Environmental Resources, assisted by the
U. S. D. A., Soil Conservation Service "Soil Erosion and Sedimentation
Control Manual". January 1974.
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22. - - - - "Certification of Pesticide Applicators" Federal Register, Vol. 39,
No. 197, Part III, October 9, 1974.
23. - - - - Pesticide Programs "Registration, Reregistration, and Classification
Procedures "Federal Register, Vol. 40, No. 129, Part II, July 3, 1975.
24. - - - - and the Department of Agriculture, Agricultural Research Service.
"Control of Water Pollution From Cropland, Volume I", a manual for
Guideline Development, EPA-600/2-75-026a, November 1975.
25. - - "National Primary and Secondary Ambient Air Quality Standards"
Federal Register, Vol. 36, No. 84, April 30, 1971.
26. "Thermal Processing and Land Disposal of Solid Waste" Federal
Register, Vol. 39, No. 148, Aug. 14, 1974.
27. - - - - "Guidelines for The Storage and Collection of Residential,
Commercial, and Institutional Solid Waste", Federal Register, Vol. 41,
No. 31, Feb. 13, 1976.
28. - - "Source Separation For Materials Recovery Guidelines", Federal
Register, Vol. 41, No. 80, April 23, 1976.
29. U. S. Department of the Interior, Office of Water Resources Research
"Approaches to Stormwater Management", by Hiltman Associates, Inc.
Contract No. 14-31-001-9025, Nov. 1973.
30. U. S. Department of Transportation, Federal Highway Administration
"Design of Stable Channels with Flexible Linings" Hydraulic Engineering
Circular No. 15. October 1975.
31. U. S. Department of The Interior, Office of Water Resources Research
"An Economic Analysis of Erosion and Sediment Control Methods For
Watersheds Undergoing Urbanization" By Dow Chemical Corp. Final Report
for contract no. # 14-31-0001-3392. February 15, 1971 - February 14, 1972.
32. National Academy of Sciences, Highway Research Board "Soil Erodibility on
Construction areas", by W. H. Wischmeier and L. D. Meyer-Report 135, 1973
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U. S. Department of Agriculture, Soil Conservation Service
"Environmental Do's and Don'ts on Construction Sites "Miscellaneous
Publication 1291. December 1974.
U.S. Department of Agriculture, Soil Conservtion Service "Sediment
Pollution and Erosion Control Guide For New Jersey". 1970 (Revised
in 1971)
U.S. Department of Agriculture, Soil Conservation Service, Davis,
California "Guides For Erosion and Sediment Control". January 1975.
U. S. Department of Agriculture, Soil Conservation Service, Maryland
"Standards and Specifications for Soil Erosion and Sediment Control
In Developing Areas".
U. S. Department of Agriculture, Soil Conservation Service, Somerset,
New Jersey "Standards and Specifications for Soil Erosion and Sediment
Control In Urbanizing Areas". March 1971.
U. S. Department of Agriculture, Soil Conservation Service, West
Warwick, Rhode Island, "Rhode Island Erosion and Sediment Control
Handbook". 1972.
U. S. Department of Commerce, Bureau of Public Roads, "Design of
Roadside Drainage Channels". 1965.
U. S. Environmental Protection Agency, Alaska Water Laboratory
"Environmental Guidelines for Road Construction In Alaska". August
1971.
U. S. Department of Transporation, Federal Highway Administratiion
"Guidelines for Minimizing Possible Soil Erosion From Highway
Construction". Instructional Memorandum 20-1-71, January 29, 1971.
- - "Stable Channel Design" by J. M. Norman. Preliminary
Subject to Revision. May 1974.
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- - - - "Suggestions For Temporary Erosion and Siltation Control
Measures", February 1973.
University of Minnesota, Department of Horticultural Science,
In Cooperation With U. S. Department of Transporation, Minnesota
Highway Department, and Minnesota Local Road Research Board
"Turf Methods and Materials for Minnesota Highways "Investigation
No. 619, November 1972.
"Vegetation Maintenance Practices, Programs and Equipment
on Minnesota Highways", February 1969.
Virgin Islands Soil and Water Conservation District "Environmental
Protection Handbook", October 1971.
Washtenaw County Soil Conservation District, Michigan, Assisted by
U. S.D. A., Soil Conservation Service, "Standards and Specifications
for Soil Erosion and Sediment Control", January 1970.
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4-1
CHAPTER 4
Methodology for Assessment of
Potential Pollution Problems and Their Magnitude
This chapter will discuss methods that have been developed to predict
approximate magnitude of nonpoint source pollution that could occur if an
area is to be subjected to construction activities in the future and no control
is provided. Methods provide approximations only and should be used only
with extreme caution by professionals that are competent in their use.
Certain areas are so sensitive to environmental change that alternative
locations for the proposed construction activity should be utilized. Potential
problems created by areas where combinations of long, steep slopes highly
unstable soils exist, extremely sensitive or high-quality water bodies
occur immediately downstream, or geologic instability is suspected can be
avoided by providing for less intensive use. These areas can act as buffers
to retain sediment and other pollutants before they reach water bodies.
Construction activities involve a broad range of projects. They maybe
located in, or extend across, areas with drastically different site conditions.
Projects can include land developments which involve construction of housing,
schools, shopping centers, office buildings, and commercial facilities;
transportation and communications networks such as highways, roads, rail-
roads, and bridges; energy facilities which include power plants, dams,
and their appurtenant transmission lines; water development structures
such as dams, aqueducts, canals, and flood-control measures; and recreation
projects including ski facilities, campgrounds, parking and other multiple
use developments. The assessment of potential pollution problems which
may result from these types of projects can involve an entire drainage
area where development seems imminent, and yet no project or development
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4-2
plans have been prepared, or a proposed individual site where complete plans
including information on existing and proposed conditions are readily available
In order to assess the potential of a proposed construction project,
or many projects, in an area to generate nonpoint source pollutants and
release them into downstream areas, all available pertinent information
must be obtained concerning the type of construction activities to be
conducted and the local site conditions. Information on each construction
activity should include whether or not the ground surface is to be disturbed,
the areal extent and nature of materials disturbed, the kind of equipment,
materials, and number of people involved, and the scheduling of events.
Data on site conditions necessary for the assessment of the nonpoint
source pollution potential include information on the proximity of projects
to surface water bodies; surface and subsurface drainage aspects; topo-
graphic, geologic, and soils characteristics, extent of vegetative cover
in the area; and the climatic effects. Chapter 1 provides sources for obtain-
ing this data and emphasizes that the generation and runoff of pollution
from construction sites are strongly dependent on climatic and other
conditions which are dynamic and generally highly variable.
Pollutants To Be Considered
Nonpoint source pollutants resulting from construction activities are
discussed in some detail in Chapter 1; as a result, they will only be summarized
here. Excessive sediment is the principal pollutant with others being chemical
petroleum products, biological materials, pesticides, metals, soil additives
and miscellaneous wastes. Independently, or in combination with one another,
they may have detrimental effects on biota existing in our nation's waters,
the regimen of drainage systems, and water uses.
Sediments are generated by erosion of ground surfaces that have been
disturbed by construction activities and possibly stripped of their protective
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A-6
Solid wastes should be collected at the site and removed for
disposal in authorized disposal areas. Frequent garbage removal
is essential. Often, borrow pits, or excavations can be filled with
inert solid wastes. Such pits should be located away from slopes,
drainages, and ground water recharge areas.
Runoff of construction chemicals resulting from paints, cleaning
solvents, concrete curing compounds, and petroleum products, can
be largely restricted by sediment control measures as many of these
materials are carried by sediment particles. Good "housekeeping"
procedures such as proper disposal of empty containers, prompt
cleanup of accidental spills, and neutralization or deactivation of
excess chemicals and wash waters should minimize runoff of the
remaining materials. Holding ponds should also be used to collect
surface runoff of waters containing these chemicals. Biological
pollutants from human sources can best be controlled by installing and
maintaining portable toilets at construction sites.
Information Sources
Nonpoint source pollution control practices discussed above in
summary form are described in more detail in the following publications:
"Processes, Procedures, and Methods to Control Pollution
Resulting From All Construction Activity" EPA 430/9-73-007,
October 1973.
"Comparative Costs of Erosion and Sediment Control,
Construction Activities" EPA 430/9-73-016, July 1973.
"Guidelines for Erosion and Sediment Control Planning and
Implementation" EPA R2-72-015, August 1972.
Additional data regarding design of structures, specifications for
vegetative practices, instructions for installation of surface pro-
tective coverings, and other useful measures are available in
numerous published standards and specifications, manuals, handbooks,
or guides. They are generally prepared and issued in local areas by
States, Counties, or Conservation Districts, with the assistance of
the U.S. Soil Conservation Service.
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A-5
Basis For Best Management-Practices Development
Best Management Practices for construction are the most practical
and effective measure or combination of measures which, when applied
to the land development or building project, will prevent or reduce the
runoff of pollutants.
Since the amount of pollutant runoff from construction sites depends
on numerous variables such as the type of construction involved, the
quantity and intensity of rainfall, the soil characteristics, etc., it is
recognized that those particular types of control measures that will pre-
vent this runoff must be installed on the site. The proper mix of control
measures must be established on site-specific basis. Whether they are
properly installed and maintained must be checked periodically by on-site
inspection as there is no way that effluent monitoring can accomplish this.
Best Management Practices for construction activities consist of
measures which will prevent the movement of pollutants from construction
sites. While sediment is the principal pollutant resulting from earth-
disturbing construction activities, chemicals, hydrocarbons, solid wastes,
and other materials must also be considered, as well, in selecting techniques
and devising pollution-prevent! on plans for the construction site.
Description of Preventive and Reduction Measures
There are essentially three basic measures for controlling the runoff
of sediment from construction sites. They include (1) preventing erosion
of exposed soil surfaces, (2) restricting the transport of eroded particles,
and (3) trapping sediments being transported. Measures developed for
controlling movement of sediment and other materials by water generally
are useful also for controlling that generated by wind action.
Preventing erosion of exposed soil surfaces is achieved by protecting
these surfaces with such coverings as mulch; sheets of plastic, fiberglass
roving, burlap, rock blankets, or jute netting; temporary growths of fast-
growing grasses; or sod blankets. Mulch consists of hay, straw, wood
chips, bark, or any other suitable protective material. Sheets of plastic
and netting materials are generally used on steep slopes where vegetation
is difficult to establish or erosion rapid. Seeding of temporary fast-
growing grasses is most desirable when final grading cannot be done until
a later date and climatic conditions permit. Sod often is used as a covering
in critical areas susceptible to erosion.
Limiting the areal extent of soils disturbed at any one time is a usable
mechanism for minimizing erosion. It can be achieved by planning and
carrying out the job so that as work progresses existing vegetation is
removed only on the area of soil surface essential to immediate work
activities. Thus, construction activities are completed on each exposed
area and revegetation accomplished as rapidly as feasible.
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A-4
Soil additives are chemicals and materials that are applied to the soil
during construction activities in order to obtain desired soil characteristics.
Often construction activities cover large areas consisting of several
different types of soils. The nature of soils is dependent on the climatic,
topographic and geological conditions. The type of soil additive applied
depends on the objectives of the construction activities. Soils may vary
from one location to another in the amount of water they contain, particle
size distribution (clays, silt, sand and gravel), water infiltration rate,
ability to support heavy structures, and resistance to compaction by con-
struction equipment. Soil additives are used to control the amount of
moisture absorbed by roadway surfaces, to reduce the degree of shrinking
and expanding of clay soils in order to prevent structural damage of
buildings and air field runways, and to increase the firmness of soils.
Several materials are used to obtain desired soil properties. Commonly
used materials include lime, fly ash, asphalt, phosphoric acid, salt, and
calcium chloride. The soil additives carried in runoff from construction
sites alter, and may seriously affect, the quality of receiving waters.
However, little work has been conducted to show the net environmental
effects of these soil additives.
Many other chemicals are used in construction for purposes such as:
binders for pasting boards together, sealants for cracks, applications for
surface treatment, solvents for oils and paints, and dyeing and cleaning
compounds. The amounts of chemicals leaving construction sites as
pollutants have not been established. Poor construction activities that
are liable to contaminate water resources include the following practices:
dumping of excess chemicals and wash water into storm water sewers;
applications of chemicals in bad weather or severe seasonal conditions
such as freezing weather; application of excess quantities of chemicals;
indiscriminate discharging of undiluted or unneutralized chemicals; disregard
for proper handling procedures resulting in major or minor spills at the
construction site; and leaking storage containers and construction equipment.
Miscellaneous pollutants include wash from concrete mixers, acid and
alkaline solutions from exposed soil or rock units high in acid, and alkaline -
forming natural elements. Cuts through coal beds can result in the seepage
of mine acids into streams unless retained in ponds and neutralized before
discharge. Areas with high lime content often increase the alkalinity of
receiving waters unless neutralization procedures are followed.
3. Biological Materials - Biological pollutants from construction
include soil organisms and organisms of human and animal origin. They
include bacteria, fungi, and viruses. The majority of biological pollutants
are found in the topsoil layer where they can feed on dead plants, animals,
birds and other organisms.
The biological pollutants resulting from construction activity indicate
that the greatest pollution potential are of animal and human origin. They
are more prevalent on construction sites where improper sanitary
conditions exist.
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A-3
filling of watercourses thus increasing the frequency of flooding, increasing
turbidity in water and reducing light penetration thus destroying aquatic
plants and organisms, increasing the cost of downstream water treatment,
damaging fish life covering and destroying organisms on the bottom of
streams, reducing the flowing speed and carrying capacity of streams,
and impairing operation of drainage ditches, culverts, and bridges, altering
the shape and direction of stream channels, destroying water recreational
areas, and imparting undesirable taste to water.
2. Chemicals -- The major categories of chemical pollutants
are: petroleum products, pesticides, fertilizers, synthetic materials,
metals, soil additives, construction chemicals, and miscellaneous wastes
from construction.
Some petroleum products impart a persistent odor and taste to water,
impairing its use for drinking water and contact sports. Many oils have
the ability to block the transfer of air from the atmosphere into water,
resulting in the suffocation of aquatic plants, organisms, and fish. Some
petroleum products contain quantities of organo-metallic compounds
(nickel, vanadium, lead, iron, arsenic) and other impurities which can
be toxic to fish and other organisms.
The three most commonly used pesticides at constrution sites are
herbicides, insecticides, and rodenticides. The unnecessary or improper
application of these pesticides may result in direct contamination of water,
or indirect pollution by chemicals clinging or absorbed to sediment or
other solid materials which are transported into water.
Nitrogen and phosphorous are the major plant nutrients used for the
successful establishment of vegetation on disturbed soils of construction
sites. Heavy use, or improper application, of commercial fertilizers
can result in these materials reaching water bodies to accelerate the
eutrophication process.
The construction industry utilizes many different types of synthetic
products. These include structural frames, window panes, wall board,
paints, and many others. Heavy duty construction materials are synthesized
from nondegradable organic materials. They are little affected by biological
or chemical degradation agents, and are usually designed to withstand the
most severe physical conditions. However, they can collect in drainages
and cause blockages which degrade water course capacities.
The concern over metal pollution of water bodies is associated mostly
with the heavy metals (mercury, lead, zinc, silver, cadmium, arsenic,
copper, aluminum, iron, etc. ). Metals are used extensively in construction
activities for structural frames, wiring, ducts, pipes, beams, and many
other uses. Construction vehicles, gasoline, paints, pesticides, fungicides,
and construction chemicals are also potential sources of heavy metals
pollutants. When these latter materials are weathered, decomposed, and
disintegrated by various agents, they utlimately form oxides and salts that
can harm aquatic organisms and impair water quality.
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1. Land Development -- Land Development involves the construction
of housing subdivisions, shopping centers, schools, recreation areas,
and related facilities. The areal extent of the land affected is generally
large although a project may be completed in segments. Topographic
slopes are usually gentle with cut and fill sections relatively minor.
2. Transportation and Communication Networks -- Construction of
transportation and communication facilities involves disturbance of the
land principally in a linear direction. Areas may be quite large but the
width of the disturbed areas is minor compared to their linear extent.
Where they bisect or parallel water courses they are particular problems
especially if located in areas of high relief where slopes may be steep
and rugged. Here the prevention of NFS pollution will be challenging.
Climatic differences are extremely diverse in many of these areas with
torrential rains prevalent in higher altitudes.
3. Water Resource Facilities -- Construction of water resource
facilities involves disturbing the ground surface for installation of dams,
aqueducts and their appurtenant structures. Dams may be located in
relatively steep river valleys or canyons, or in areas of fairly low relief.
Aqueducts have a great linear extent and are generally located along
valley or foothill areas. Climatic differences at these sites may be
extremely variable with intense rainfall occurring in mountain areas.
Dams in higher topographic areas may be underlain by hard, non-
erodible bedrock. Dams and aqueducts in lower areas generally are
located in erodible soils and/or parent materials.
4. Other -- Construction of factories, major office buildings, airports,
power plants, etc., which occur on more restricted surface areas, is
included in this subcategory. Except for airports, the areal extent of these
facilities is generally limited and almost all require extensive subsurface
excavation. They are generally located in areas of fairly low relief with
relatively low cut and fill slopes involved.
Identification of Pollutants
Sediment, resulting from erosion or disturbed soils on construction
sites, is one of the principal pollutants. It includes solid mineral and
organic materials which are transported by runoff water, wind, ice, or
the effect of gravity. Chemical pollutants derived from construction
activities originate from inorganic and organic sources and occur in solid
form such as asphalt, boards, fibers, or metals; or in liquid form such
as paints, oils, glues, pesticides, and fertilizers. Biological pollutants
include organisms resulting from soils, animal, or human origins. They
may be bacteria, fungi, or viruses. High volumes of storm water runoff
due to loss of retention capacity on site can cause large quantities of pollution.
They result from changed conditions due to construction activities.
1. Sediment -- Sediment exerts physical, chemical and biological
effects on the receiving stream and water bodies. Physical damage
resulting from sediment deposition includes: reduction of reservoir storage
capacity, thus requiring costly dredging or decreasing the life of the project,
filling harbors and navigation channels thereby disrupting their functioning,
-------
A-l
BEST MANAGEMENT PRACTICES
CONSTRUCTION NONPOINT SOURCES
WATER POLLUTION
Construction is a broad category covering the alteration and development
of land for differing uses including the installation of structures on the
land. The types of projects within the category generally have two common
characteristics, namely; (1) They involve soil disturbance, resulting in
modification of the physical, chemical, and biological properties of the land;
and (2) They are short-lived in the sense that the "construction phase"
closes when the development and building activities are completed. Stormwater
runoff volumes, however, may be permanently increased as a result of the
project necessitating permanent structures to prevent future stormwa.ters
from generating NFS pollution.
Introduction
This guidance is intended to provide information regarding management
practices for prevention of nonpoint source pollution from construction
activities, and to supplement information regarding control of construction
associated discharges under the provisions of NPDES and Section 404 of
the FWPCA.
Construction activities can result in the development of significant
sources of pollutants which may reach surface or ground waters. About
one million acres of land are being disturbed for construction purposes
each year in the United States. Pollution resulting from these constructionn
areas can be catastrophic in downstream areas, particularly in small
drainages. This statement is intended to provide guidance in the control
of construction nonpoint sources and for the selection of pollution prevention
or reduction measures that are useful both preventing deterioration of water
quality and achieving and maintaining in water quality goals.
Construction nonpoint sources are the land development and building
projects that result in the runoff, seepage or percolation of pollutants to
the surface and ground waters. The runoff of pollutants generated by these
activities is strongly dependent on climatic events such as rainfall or
snowmelt. In general, the runoff is intermittent and does not provide
a continuous discharge.
The nature of the pollutants depends on the particular activities
underway and the condition of surface areas at the time of the rainfall or
snowmelt. Both the nature and amount of pollutants are also dependent
on other factors such as soil types, topography, proximity to drainages
and watercourses, project characteristics, and the number of people and
equipment involved. Appropriate practices can limit or prevent NPS
pollution from occurring.
Description of Construction Activities
There are many types of projects that fall within the construction
category. They generally can be classified into the following sub-categories:
-------
APPENDIX
-------
4-23
19. U. S. Department of the Interior, Geological Survey "Field Methods
For Measurement of Fluvial Sediment" Book 3, Chapter C2 of
Techniques of Water-Resources Investigations of the United States
Geological Survey, 1970.
20. , "Computations Of Fluvial-Sediment Discharge" Book 3,
Chapter C3 of Techniques of Water-Resources Investigations of the
United States Geological Survey 1972.
21. U.S. Department of The Interior, Bureau of Reclamation "Design
of Small Dams" 1974.
22. U.S. Department of Agriculture, Soil Conservation Service " National
Engineering Handbook, Section 3, Sedimentation", April 1971.
23. - - - -, "National Engineering Handbook, Section 4, Hydrology",
August 1972.
24. California Department of Transportation, Office of Transportation
Laboratory "Methods of Measuring Erosion From Road Slope"
Interim Report CA-DOT-TL-7108-6-76-17, January 1976.
25. California Department of Transportation, Office of Transportation
Laboratory "Highway Slope Erosion Transect Surveys"
CA-DOT-TL-7108-4-74-05, March 1974.
26. Colorado State University "Highway Impact On Mountain Streams",
June 1974.
-------
4-22
10. U.S. Environmental Protection Agency, Office of Water Program
Operations "Comparative Costs of Erosion and Sediment Control,
Construction Activities. EPA-430/9-73-016, July 1973.
11. - - - -, Office of Research and Development "Prediction of Subsoil
Erodibility Using Chemical, Mineralogical, and Physical Parameters.
Research Project No. 15030 HIX.
12. U. S. Department of Agriculture, River Basin Planning Staff, Forest
Service, and Soil Conservation Service, in cooperation with the
California Department of Water Resources. "Water, Land and Related
Resources, North Coastal Area of California and Portions of Southern
Oregon - Appendix No. 1 Sediment Yield and Land Treatment" June 1970.
13. State of California, Department of Conservation "Erosion Control
Handbook" under preparation
14. State of California, Division of Highways "Slope Erosion Transects,
Lake Tahoe Basin - Interim Report" July 1971.
15. U.S. Departmment of Agriculture, Soil Conservation Service "National
Engineering Handbook" Section 3, Chapter 7, March 1968.
16. "U.S. Department of the Interior, Geological Survey Effects of Roadway
and Pond Construction On Sediment Yield Near Harrisburg, Pennsylvania"
Open-File Report, August 1971.
17. - - - - "Sediment Movement In An Area of Suburban Highway Construction,
Scotts Run Basin, Fairfax County, Virginia 1961-64" Water Supply Paper
No. 1591-E, 1969.
18. Larry M. Younkin "Effects of Highway Construction On Sediment Loads
In Streams" National Academy of Sciences, Highway Research Board,
Special Report No. 135, 1973.
-------
4-21
Selected References
1. W. H. Wischmeier, C. B. Johnson, andB.V. Cross "A Soil Erodibility
Nomograph For Farmland and Construction Sites", Journal of Soil and
Water Conservation. September - October 1971
2. U.S. Department of Agriculture, Agricultural Research Service "Present
and Prospective Technology for Predicting Sediment Yields and Sources"
ARS-S-40, June 1975.
3. W. H. Wischmeier "Use and Misuse of The Universal Soil Loss Equation"
Journal of Soil and Water Conservation. January - February 1976.
4. U.S. Department of Agriculture, Soil Conservation Service "Procedure
For Computing Sheet and Rill Erosion On Project Areas" Technical
Release No. 51. January 1975.
5. U. S. Water Resources Council, Sedimentation Committee "Proceedings
of The Third Federal Inter-Agency Sedimentation Conference 1976"
Pages 2-13-2-23, March 23-25, 1976.
6. H. P. Guy and D.E. Jones, Jr. "Urban Sedimentation - - - - In
Perspective" Presented at the American Society of Civil Engineer's
National Water Resources meeting, Jan. 24-28, 1972.
7. J. K.H. Ateshian "Estimation of Rainfall Erosion Index" American
Society of Civil Engineers, Journal of The Irrigation and Drainage
Division, September 1974.
8. U. S. Department of Agriculture, Agricultural Research Service "Rainfall-
Erosion Losses From Cropland East of The Rocky Mountains" Agricultural
Handbook No. 282, May 1965.
9. W. H. Wischmeier and L. D. Meyer "Soil Erodibility on Construction Areas"
National Academy of Sciences, Highway Research Board. Special Report No.
135, 1975.
-------
4-20
activities. As a result, to predict the potential pollution from future
construction activities with any degree of accuracy is impractical.
Probably, the most logical way will be to compare the problems that
have occurred in the past with those that may occur in the future. This
will involve determining if pollutants which caused problems in the past
are going to be used in the proposed construction and whether they are
to be used under the same conditions. If no changes are to occur, the
same problem will recur. If no precautions have been made to prevent
spills of petroleum products and other materials; dispose of chemical,
solid, chemical, and biological wastes; and require proper dosage of
fertilizers, pesticides, and other materials as well as disposal of waste
products, pollution will occur in the future as in the past. The magnitude
of this pollution will be directly related to the magnitude of pollution-
generating activities conducted in the past and that to be done in the future.
-------
4-19
during low-flow periods. The sediment concentration is usually computed
as the ratio of the weight of sediment to the weight of the water-sediment
sample and expressed as parts per million or milligrams per liter. The
total quantity of sediment being transported is determined from the sediment-
concentration and water discharge data for a given period of time.
Precipitation data can be obtained through the use of recording and non-
recording gages. Total precipitation, rainfall intensity, duration, etc. can
be determined from the precipitation records or from the sources discussed
in Chapter 2 of this guidance document. Rainfall events with very short
intensities are usually of interest with regard to construction sites but this
data is difficult to obtain.
Information on current and historic construction activities can be obtained
from aerial photographs of the drainage area, records of governmental agencies,
and/or from actual field observations. It should include data on the areal
extent of ground disturbance, scheduling of construction, and other relevant
factors which may influence sediment loads in the streams.
Results of study of sediment discharge from streams may also be trans-
ferred to adjacent areas to predict, or approximate, sediment discharge
from future construction if slopes, soils and geologic conditions, topography,
runoff, and other conditions are similar. If conditions are significantly
different, techniques are available to correlate significant factors and still
make results usable (See Chapter 2 and Reference Nos. 21, 22, and 23).
Assessing Runoff of Pollutants Other Than Sediment
There is little available data on the magnitude of pollution resulting from
petroleum products, pesticides, biological materials, soil additives, mis-
cellaneous wastes, and other potential pollutants used during construction
-------
4-18
These studies generally involve obtaining streamflow, sediment con-
centration, precipitation, and construction activity data on the particular
drainage basin being surveyed. Data from the sampling program should
provide an informational basis for prediction of future events. It should
include instantaneous and average characteristics of sediment movement
as well as the range, variations, and patterns of fluctuations. Present
and future land disturbing activities will determine the optimum distri-
bution of sediment data needed for an area. That portion within the path
of possible land development, or other proposed construction, must re-
ceive more intensive coverage than that of a more stable area.
Streamflow generally is measured continuously with a water-stage recorder
which provides records of the water levels in the stream. These records
are used with discharge measurements, to develop a continuous record
of the stream discharge in cubic feet per second or some other value. The
runoff, which involves the complete regimen of streamflow, may be measured
by the number and characteristics of the rises of streamflow. The quantity
of sediment being moved is directly related to these water level rises. It
involves both suspended and bedload sediment portions. Suspended sediment
is those materials suspended, or carried, in the water and bedload include
the materials that rolls or slides near the streambed. Suspended sediment
loads in streams are computed from measurements obtained with various
types of equipment on a continuous basis, during selected levels of stream-
flow, or at periodic intervals. Bedload quantities may be obtained through
the use of bedload samples or from computations based upon the suspended
loads and sediment size analysis (Reference No. 21). Since the program
involves determining the quantity of sediment moved by the stream it is
desirable to sample at short intervals during high flows and longer intervals
-------
4-17
Sediment discharge records may be available for streams draining small
basins prior to, during, and following construction (Reference Nos. 16, 17,
and 18). Assuming precipitation and runoff conditions are similar during
all periods, the difference in sediment yields will be due to the ground dis-
turbing construction activities. In the absence of useful records, a sampling
program may be developed to provide the needed data. Available data and
analyses may be transferable to adjacent drainages to estimate potential
losses which could occur there due to construction. Care should be used
to ensure that soil, geologic, or other conditions are similar in both areas
or that correlation factors to be used are appropriate.
Sediment yield can be defined as the total sediment outflow from a
drainage basin, measured at a specific location and in a specified period of
time. In general, sediment yield is a function of the storm level, surface
conditions, sheet-flow energy level, rill and stream kinetic energy levels,
and time varying streambed conditions. The greater the flow of runoff from
the basin at any one time, the greater the mass of sediment being trans-
ported at any point on the stream. In-stream effects of each, relatively
small, construction-related source of sediments are often lost in the mass
average statistics of a basin watershed. These sources, however, may be
providing 100% of the sediment pollutant load in a small drainage basin.
Many stream sedimentation studies are conducted by the U.S. Geological
Survey, in cooperation with other Federal agencies and the States. The
results are published for use by concerned organizations. (Reference Nos. 16
and 17). Additional studies are done by other governmental agencies, the
States and local organizations. Information on techniques useful for measur-
ing sediment and computations for discharge is also published (Reference Nos.
19 and 20).
-------
4-16
The survey involves determining volume of sediment in the reservoir
by measuring, from below a bench mark on the dam crest or other
appropriate stable point, the upper surface of the sediment deposit that has
accumulated since: (1) the previous survey or (2) the reservoir was com-
pleted. This can be done by sounding with a line and weight, a sounding pole,
or echo-sounding equipment. The original bottom surface of the reservoir
can be obtained from as-built dam and reservoir plans. If no plans are
available or the lake is natural, the bottom of the reservoir, and sediment
thickness can be determined through the use of a sounding pole, an auger,
or some other piece of probing equipment. If natural materials underlying
the lake bed are of soft consistency, the bottom may be difficult to detect
accurately.
Total weight of the sedimentary material deposited can be computed from
information involving the dry weight of samples obtained at various depths
and the area of the deposits. If historic information is available regarding
construction progress, areas of ground exposed to erosion during specific
times, and the trapping efficiency of the reservoir, approximations of
sediment losses from the sites may be determined. These approximations
also may be transferred to similar areas if conditions are similar or
correlation factors used
Use of Sediment Data From Stream Sampling
Knowledge concerning effects of man-made changes in drainage basins
on the quantity and characteristics of sediment yields in streams is useful
to help predict the approximate changes to occur when future basin changes
are made. This is particularly true of changes caused by construction
activities.
-------
4-15
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4-14
field data. The total sediment quantities estimated to have been deposited
on site areas can be computed similarly. Differences between quantities
eroded and those deposited represent sediment losses from site areas.
This data can then be expanded to cover the entire area under survey.
Results obtained from the field study can be transferred readily to other
areas if slope, soil and other conditions are quite similar. If conditions
are different, correlation factors of some kind may still make results
usable. Correlation between these areas may be facilitated through
the use of factors presented in Table 1, The Yield Approximation Table.
If the data indicate that the area in which field observations were made
to determine sediment losses falls within the same sediment yield classi-
fication as the new area, results are correlatable. Also, if the numerical
scores fall within 25 points of one another, correlation is valid.
Another very appropriate method is to make sediment-loss approxima-
tions from an area where construction has been conducted by determining
quantities of sediment deposited in reservoirs and lakes downstream from
sites and apply them to future construction site losses, or relate them to
other areas. Sediment detention or debris basins can also provide much
data on sediment quantities that have been lost from sites. Procedures
for conducting reservoir deposition surveys are presented in Reference
No. 15. They essentially involve determining the volume and weight of
sediment that has accumulated in a reservoir during a specific period of
time. Depending on the survey frequency, annual or even monthly sediment
rates may be determined. Naturally-occurring sediment deposition rates
may be estimated if a determination can be made as to when construction in
the area under study was initiated and sediment deposition increased drastic-
ally
-------
4-13
used to plot areas of exposed ground where erosion is occurring due
to prior construction. Lengths of exposed surfaces of road cuts, fills,
or other sample reaches can be measured in the field by car odometer,
pacing, or some other technique and the average heights of cuts and
fills and widths of other areas estimated (Reference Nos., 12, 13 and
14). Average slope angles can be determined by using, a Brunton-type
compass. On some cut slopes, where the surface configuration may
be highly irregular due to extremely variable or concentrated erosion,
protrusion of hard, massive rock, or other reason, the angle can be
classified as variable (Reference No. 13 and 14). The data should all
be recorded for subsequent computations.
Assessment surveys should be made periodically to determine annual
erosion rates and sediment losses, or if possible, monthly rates. Indicators
to be used for estimating erosion include the depth, width, length, and
number of rills and gullies on cuts, fills, and bare road surfaces; the
extent that the toes of slopes have moved back from the edges of roads
and ditches (particularly where locally erodible streaks may occur); the
length of roots now extending from cut slopes, and other factors. Volumes
of eroded material deposited where slopes terminate can be estimated also
as they may be apparent as small deltas, filled drain ditches and sediment
traps, or obstructed culvert intakes. Sediment quantities also may be noted
where vegetative strips have acted to filter out or cause deposition of the
materials. Records of sediment deposits removed by maintenance crews
should be reviewed to provide additional data on losses arid a quick check
of quantities at disposal sites may give an indication of annual amounts.
Annual, or even monthly quantities of sediment eroded from each area;
from all areas with similar slope and other characteristics, and from total
miles of the entire surveyed area can be computed and totaled from the
-------
4-12
greater increases in sediment yield result and the use of data from
Figure 5 on slopes steeper than 20% (5:1) would only be speculative and
is not recommended (Reference No. 9).
The last two factors in the Universal Soil Loss Equation, C and P,
represent the cropping and structural control practice factors. The C
factor involves vegetative and other practices for controlling ground
surfaces which have been disturbed by construction from the erosive
action of rainfall and runoff. The P factor concerns structural measures
used to control runoff water and prevent transport of sediments. Both
factors have a value of 1 for determining potential sediment losses in a
disturbed area where no effective control measures have been installed
(See Page 95, Reference No. 10).
It must be emphasized again that soil losses determined with the use
of the soil loss equation must be considered to be the best available rough
estimate and not precise data. The equation has been derived empirically
and involves experimental error as well as possible estimation error due
to the effects of unmeasured variables (Reference No. 3).
Transferring Results From Field Observations
Field observations can be used to estimate quantities of sediment
which are being eroded from ground surfaces exposed by construction
activities in the past and still left unprotected by vegetation or other
control measures. Data from these observations may be transferred
to adjacent areas to permit estimating sediment losses which could result from
construction activities. Again, extreme care must be used to ensure
that soil, geologic, topographic, and other conditions are similar in both
sites or that correlation factors used are appropriate.
For example, if sediment losses from existing roads are to be
estimated, a map of suitable scale (1"=2, 000 feet or less) should be
-------
4-11
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US (feet/75)°-6
Extrapolated beyond the range of
the data. Use only as speculative
estimates.
200
1*00
800
600
Slope Length
1000
1200
1600
(Feet)
FIGURE 5 - Slope-Effect Chart for Slopes and Lengths Exceeding
Those in Figure 4 (Reference No. 4)
Construction site slopes usually are developed into shorter and steeper
runoff units than those under which the USLE was developed. As a result,
greater quantities of runoff occur at higher velocities. This is particularly
true in highway and other "heavy " construction projects. Significantly
-------
4-10
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-------
4-9
It should be realized that the R Factor is the long-term average
yearly total of the erosive potential of rainfall in the area. R, being a
climatic factor, is extremely variable during a short period of time;
and the erosion potential, and thus sediment yield, for an area may be
several times as great during one season of the year than during another.
If construction is completed during the period of low potential, sediment
losses will be minimized, assuming other factors are equal.
Highly variable conditions for given months must also be considered
as well as the seasonal variations. During some years, very small rains
may occur during one month, resulting in a portion of the normal sediment
yield, whereas in other years, the same month may have several storms,
one or more of which may produce more than the expected annual sediment
yield.
The slope-length factor (L) and slope gradient (S) usually, for con-
venience, are combined into a single factor, LS (Reference No. 4). The
LS factor for gradients up to 20% and slope lengths to 800 feet, can be
obtained from the Slope-Effect Chart, Figure 4. For slope lengths greater
than 800 feet and gradients greater than 20%, data are extrapolated and
may be used as speculative estimates from Figure 5. The computed soil
loss obtained using such LS values from Figure 5 will require adjustment
based on judgment.
-------
4-8
and on Pages 2-13 through 2-23 of Reference 5. Figure 3 presents a map
of the western States with erosion index values contoured. Erosion index
values for areas farther to the east are provided in Handbook 282. Values
may be selected from the map for use in the Universal Soil Loss Equation.
ita
*>*
He*
110"
Figure 3 - Average Annual Rainfall Erosion Index (Reference No. 5)
In Western U. S.
-------
4-7
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SOIL ERODIBILITY FACTOR, K
Figure 2 - Nomograph for Estimating the Erodibility Factor, K, of Subsoils
with high clay content, very low permeability, blocky or massive
structure and containing amorphous iron and aluminum hydrous
oxides (Reference No. 11).
Information on R, the rainfall factor, is presented in the U. S. D. A. -A. R. S.
Agricultural Handbook No. 282 (Reference No. 8) for States east of the Rocky
Mountains and in U. S. D. A. -SCS Technical Release No. 51 (Reference No. 4)
for areas in the western U. S. Many State Soil Conservation offices have
developed R factor maps that are detailed for local conditions. Another
method for obtaining R values, also referred to as the erosion index, in
western States is presented in Reference No. 7
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4-6
There are severe limitations in the use of this credibility nomograph,
particularly with materials which have no organic matter and a fairly
high clay content. This has been recognized by some researchers, and
work is being conducted to obtain erodibility information on these types
of materials. Figure 2 presents a nomograph for estimating erodibility
of clayey soils of low permeability if the gradation of the material, percent
amorphous iron and aluminum hydrous oxides, and percent extractable
silica are known. The theory behind this nomograph is that amorphous
iron and aluminum oxides and silica are the primary binding agents in
subsoils much as organic matter is the-prime binding agent in surface
(or agricultural) soils. Studies are still underway regarding this type
of evaluation as the parameters required for the nomograph of Figure 2
are not usually available from existing soil analyses and cannot be esti-
mated readily. Procedures for testing samples of subsurface materials
may be developed in the near future to obtain this needed data.
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4-5
Factors developed for use in this equation were established empirically
and must be used with care and judgment. They were devised initially for
farmland and erosion of agricultural soils. In most construction sites,
these soils which usually contain organic matter, are generally removed
and the underlying purely-mineral foundation materials exposed, excavated,
transported elsewhere, and remolded by large earthmoving equipment to
produce a final grade for the project facilities. As a result, K, the soil
erodibility factor must be revised to make it appropriate for use in con-
struction sites. This has been done to some extent in Reference No. 1,
which presents a nomograph to derive erodibility if the percent silt, sand,
and organic content, structure, and permeability of soil (or other foundation
materials) can be ascertained (See Figure 1).
PROCEDURE- *IUi looniprlitK d»w. eMer sc«l« at left *mt proceed to points representing
U* soil's 1 i*nd (O.IO-Z.O OB), 1 organic Mtter, structure, »nd p«nwibit1ty, jn th«t sequeoct.
lnt*rpoljU b«tve*n plotted curves. The dotted line 1llustrite« procedure for > soil luvtnq:
t1«-vfl iS«, *WM* St.
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4-4
Approximations regarding potential sediment losses from construction
sites can be made in several ways. One method is to use adaptions of the
Universal Soil-Loss Equation in which soil credibility factors have been
determined from test information involving soil particle sizes, structure,
permeability and other characteristics (Reference No. 1 through 5).
Another is to transfer results from field observations of sediment losses in
similar areas to the site under study and estimate differences. Still another
method is to evaluate case histories of sediment losses determined by sampling
runoff immediately downstream from sites during their construction period
and relating them to the proposed site area. In all cases, extreme care
should be used. Factors involved in equations or derived from other areas
or studies are extremely variable and subject to judgment; as a result,
only experienced personnel should be engaged in evaluating soil losses.
Sheet Erosion Approximation Using Soil Loss Equations
Approximations regarding potential sediment losses from construction
sites can be made through the use of soil loss equations such as those
developed and used by the U. S. Department of Agriculture (Reference No. 1
through 5 for this Chapter and References at end of Chapter 2). The
complete Universal Equation is:
A=RKLSCP
A-is the computed average annual soil loss in tons/acre
R-is the rainfall factor, designed to account for storm energy
and intensity in a normal year (also termed erosion index).
K-is the soil erodibility factor, expressing the sediment loss
from a specific soil on a unit plot 72. 6 feet long with a 9%
slope adjusted for rainfall.
L-is the slope-length factor, the ratio of soil loss from a specific
slope to that from a 72. 6-foot slope of simiular characteristics.
S- is the slope steepness factor relating soil loss from a specific
slope to that from a 9% slope.
C-is the cropping management factor, a ratio of soil loss from a
site protected by mulch or vegetative measures to that from a site that
has been disturbed and left bare to erosive forces.
P-is the structural-control factor, a ratio of soil loss from a site with
with fully-installed structural control measures to that of one without.
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4-3
vegetative cover. Other pollutants result from materials that have been
brought in to the site and used for construction purposes, occur naturally
in the area, or are adsorbed to soil particles. These materials may be
used to implement construction requirements, altered or combined with
other materials to produce a third product, disposed of, or even accidently
spilled in the site area. If site conditions are not considered carefully,
any of these materials can be transported from the site area by runoff
water, wind, gravity, or some other mechanism and become water pollutants.
Assessing Potential Sediment Losses
Construction activities which involve disturbance of surface soils or
underlying foundation materials will generally cause the generation of
quantities of sediment that are greatly in excess of those resulting under
natural conditions. Surface runoff and other transportation agents will
carry these materials from the site areas to become pollutants unless
effective sediment control measures are installed to prevent their move-
ment. If no control is provided, it will not be necessary to determine
whether soil losses will occur, but only to determine their magnitude.
The initial step in assessing potential sediment pollution to be expected
from future construction projects should involve a consideration of the
type of facilities to be constructed, the location of these proposed facilities;
areal extent, depth, and type of ground disturbance or grading to be
accomplished; proposed or estimated changes in the existing surface
and ground water drainage systems; and other pertinent factors. For
a proposed site, the project plans prepared by a design engineers may
provide much of this information. In an area where development
is imminent but no project plans are available, only estimates can be made
regarding what land changes will definitely occur and their extent.
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