7A-1. General Information
In an effort to
protect the nation’s waters from pollution, the Environmental Protection Agency
(EPA) has developed a system of regulations, under the Clean Water Act,
entitled the National Pollutant Discharge Elimination System (NPDES). These regulations require the owner of a site
to obtain a permit prior to construction, and ensure that proper steps are
taken during construction to help prevent erosion and prevent sediment from leaving
construction sites.
The purpose of
this chapter is to explain the erosion and sedimentation process, and describe
methods that may be used to protect natural resources by reducing both. In addition, the steps required to comply
with the EPA’s NPDES regulatory requirements will be explained.
Approximately 40%
of the nation’s waterways have been identified as impaired, meaning that they
do not meet the water quality standards for their intended use. In Iowa,
the most common reason for a waterway to be designated as impaired is due to
high levels of suspended sediment. One
of the main sources of suspended sediment found in waterways is construction
site stormwater runoff.
Sediment in
runoff from construction sites is a direct result of the erosion created when
the site is stripped of its stabilizing vegetation. According to the U.S. Environmental
Protection Agency (EPA), sediment rates in stormwater runoff from construction
sites are typically 10 to 20 times greater than for agricultural lands. In urban areas, stormwater runoff is quickly
intercepted by the storm sewer and does not have a chance to travel over
vegetated areas where suspended sediment can be removed. The sediment in this runoff eventually
reaches streams, ponds, lakes, and rivers.
High levels of suspended sediment can quickly form large silt deposits,
filling in these waterways.
Silt deposits can
cause damage to public and private property.
Silt deposits often flow onto adjacent property, causing damage; flow
onto public streets, creating mud and dust; and clog storm sewers and
ditches. The financial impact caused by
this sediment is substantial. Waterways
must be dredged to remove the deposits, streets swept, ditches and storm sewers
cleaned, and property damaged by sediment must be repaired or replaced. While the financial impacts are significant,
the loss of natural resources is just as important.
High levels of
sediment in storm runoff can destroy an ecosystem. Sediment is often contaminated with other
pollutants such as phosphorous, nitrates, pesticides, and heavy metals. In high enough concentrations, these
pollutants become poisonous. In
addition, the suspended sediment filters out sunlight, killing off aquatic
vegetation. Many species of animals
depend on this vegetation for habitat and nourishment. If enough vegetation is destroyed, the levels
of dissolved oxygen in the water can drop to levels where aquatic wildlife
cannot survive. Waterfowl and other
animals, dependent on the fish and vegetation for sustenance, may die or leave
the area.
Aggregate: Crushed rock or gravel screened to different
sizes for various uses in construction projects.
Annual plant: A plant that completes its life cycle and dies
in one year or less.
Apron: A floor or lining to protect a surface from
erosion. Normally at the inlet or outlet of a storm conduit.
Berm: A raised area that breaks the continuity of a
slope.
Best Management Practices: Schedules of activities, prohibitions of
practices, maintenance procedures, and other management practices to prevent or
reduce the pollution of waters of the United States. BMPs also include treatment requirements,
operating procedures, and practices to control plant site runoff, spillage or
leaks, sludge or waste disposal, or drainage from raw material storage.
Channel: A stream that conveys continuous or
intermittent water; a ditch or channel excavated for the flow of water.
Channel stabilization: Erosion prevention and stabilization of
velocity distribution in a channel using jetties, drops, revetments,
vegetation, and other measures.
Clay (soils): (1) A mineral soil separate consisting of
particles less than 6.6x10-6 ft (0.002 mm) in equivalent
diameter. (2) A soil textural
class. (3) A fine-grained soil that has
a high plasticity index in relation to the liquid limits.
Clean Water Act (CWA): The Federal Water Pollution Control Act.
Clod: A compact, coherent mass of soil ranging in
size from 2 to 5 inches and much larger, produced artificially, usually by
digging, etc., especially when these operations are performed on soils that are
either too wet or too dry for normal soil movement.
Code of Federal Regulations
(CFR): A codification of the final
rules published daily in the Federal Register.
Title 40 of the CFR contains the environmental regulations.
Compaction: The process by which the soil grains are
rearranged to decrease void space and bring the grains into closer contact with
one another and thereby increase the weight of solid material per cubic foot.
Contour: An imaginary line on the surface of the ground
connecting points of the same elevation.
Cover: (1) Vegetation or other material providing
protection. (2) Ground and soils: any
vegetation producing a protective mat on or just above the soil surface. (3) Stream: generally trees, large shrubs,
grasses, and forbs that shade and otherwise protect the stream from erosion,
temperature elevation, or sloughing of banks.
(4) Vegetation: all plants of all sizes and species found on an area, regardless
of whether they have forage or other value.
(5) Artificial: any material (natural or synthetic) that is spread or
rolled out over the ground to protect the surface from erosion.
Detention basin (pond): A structure barrier built to divert part or
all of the runoff water from a land area and to release the water under a
controlled condition.
Drainage: The removal of excess surface water or
groundwater from a land area.
Erosion: (1) The wearing away of the land surface by
running water, wind, ice, or other geological agents, including such processes
as gravitational creep. (2) Detachment
and movement of soil or rock fragments by water, wind, ice, or gravity.
Filter strip: Strip of vegetation above ponds, diversion
structures, or other elements to retard flow of runoff water and thereby reduce
sediment flow.
Final stabilization: Period when all soil-disturbing activities at
the site have been completed and a uniform perennial vegetative cover with a
density of 70% for the area has been established, or equivalent stabilization
measures have been employed.
Gabion: A rectangular or cylindrical wire mesh cage
filled with rock and used as a protecting apron, revetment, retaining wall,
etc., against erosion.
General Permit: An NPDES permit issued under 40 CFR 122.28
that authorizes a category of discharges under the CWA within a geographical
area. A general permit is not
specifically tailored for an individual discharger.
Grade: (1) The slope of a road, channel, or natural
ground, or any surface prepared for the support of construction such as
paving. (2) To finish the surface of a
roadbed, top of embankment, or bottom of excavation.
Grass: A member of the botanical family Gramineae
characterized by blade-like leaves arranged on the culm or stem in two ranks.
Grassed channel (waterway): A natural or constructed waterway, usually
broad and shallow, covered with erosion-resistant grasses, used to conduct
surface water from land.
Ground cover: Grasses or other plants grown to keep soil
from being blown or washed away.
Gully: A channel or miniature valley cut by
concentrated runoff, through which water commonly flows only during and
immediately after heavy rains, or during the melting of snow. The gullies may be branching or linear,
rather long, narrow, and of uniform width.
The difference between a gully and rill is the depth. A gully is sufficiently deep that it would
not be obliterated by tillage operations.
A rill of lesser depth can be smoothed by regular tillage
equipment.
Infiltration: The gradual downward flow of water from the
surface through soil to ground water and water table reservoirs.
Large construction activity:
As defined in 40 CFR 122.26(b)(14)(x), a large
construction activity includes clearing, grading, and excavating, resulting in
a land disturbance that will disturb five acres or more of land, or will
disturb fewer than five acres of total land area, but is part of a larger
common plan of development or sale that will ultimately disturb five acres or
more. Large construction activity does
not include routine maintenance that is performed to maintain the original line
and grade, hydraulic capacity, or original purpose of the site.
Legume: A member of the
Leguminosae family, one of the most important and widely distributed plant
families. Leaves are alternate, have
stipples, and are usually compound. Most
legumes are nitrogen-fixing plants.
Loess: Soil material transported and deposited by
wind and consisting predominantly of silt-sized particles.
Mulch: A natural or artificial layer of plant residue,
or other materials such as straw, leaves, bark, sand, or gravel on the soil
surface, to protect the soil and plant roots from the effects of raindrops,
soil crusting, freezing, evaporation, etc.
Municipal Separate Storm
Sewer System (MS4): A conveyance
or system of conveyances (including roads with drainage systems, municipal
streets, catch basins, curbs, gutters, ditches, man-made channels, or storm
drains) meeting the following criteria:
a.
Owned and operated by a state, city, town, borough,
county, parish, district, association, or other public body (created by or
pursuant to state law) having jurisdiction over disposal of sewage, industrial
wastes, stormwater, or other wastes, including special districts under state
law such as a sewer district, flood control district or drainage district, or
similar entity, or an Indian tribe or an authorized Indian tribal organization,
or a designated and approved management agency under section 208 of the Clean
Water Act (CWA) that discharges to waters of the United States.
b.
Designed or used for collecting or conveying
stormwater
c.
Which is not a combined sewer
d.
Which is not part of a publicly owned treatment
works (POTW)
National Pollutant Discharge
Elimination System (NPDES): National program
under Section 402 of the Clean Water Act for regulation of discharges of
pollutants from point sources to waters of the United States. Discharges are
illegal unless authorized by an NPDES permit.
Nurse crop: Seeding of a short-life crop with a permanent
species to aid in erosion control until the permanent species are established.
Organic matter: Decomposition products of plant and animal
materials, such as litter, leaves, and manure.
Perennial plant: A plant that normally lives three years or
longer.
Permeability, soil: The quality of a soil horizon that enables
water or air to move through it. The
permeability of a soil may be limited by the presence of one nearly impermeable
horizon even though the others are permeable.
Permitting authority: The United States EPA, a Regional
Administrator of the EPA, or an authorized representative. Under the Clean
Water Act, most states are authorized to implement the NPDES permit program.
pH: A measure of hydrogen ion concentration. Values range from 0 to 14; a pH of 7.0 is
neutral. All pH values below 7.0 are
acidic, and all above 7.0 are alkalinic.
Planting season: The period of the year when planting or
transplanting is considered advisable from the standpoint of successful
establishment.
Point source: Any discernible, confined, and discrete
conveyance, including but not limited to, any pipe, ditch, channel, tunnel,
conduit, well, discrete fissure, container, rolling stock concentrated animal
feeding operation (CAFO), landfill leachate collection system, vessel, or other
floating craft from which pollutants are or may be discharged. This term does
not include return flows from irrigated agriculture or agricultural stormwater
runoff.
Pollutant: Dredged spoil, solid waste, incinerator
residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical
wastes, biological materials, radioactive materials (except those regulated
under the Atomic Energy Act of 1954, as amended (42 U.S.C. 2011 et seq.)),
heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial,
municipal, and agricultural waste discharged into water.
Receiving water: The "Water of the United States" as defined in
40 CFR 122.2 into which the regulated stormwater discharges.
Revetment: Facing of
riprap, or other material, either permanent or temporary, placed along the edge
of a stream to stabilize the bank and protect it from the erosive action of the
stream.
Riprap: Broken rock,
cobbles, or boulders placed as revetment on earth surfaces such as the face of
a dam or the bank of a stream, for the protection against the action of water
or waves.
Runoff: That portion of the precipitation on a
drainage area that is discharged from the area.
Includes surface runoff and groundwater runoff.
Section 401 Certification: A requirement of Section 401(a) of the Clean
Water Act that all federally issued permits be certified by the state in which
the discharge occurs. The state certifies that the proposed permit will comply
with state water quality standards and other state requirements.
Sediment: Solid material, both mineral and organic,
that is in suspension, is being transported, or has been moved from its site of
origin by air, water, gravity, or ice.
Seed: The fertilized and ripened ovule of a seed
plant that is capable, under suitable conditions, of independently developing
into a plant similar to the one that produced it.
Seedbed: The soil prepared by natural or artificial
means to promote the germination of seed and the growth of seedlings.
Small construction activity:
Clearing, grading, and excavating resulting in
a land disturbance that will disturb one acre or more and fewer than five acres
of total land area, but is part of a larger common plan of development or sale
that will ultimately disturb five or fewer acres. Small construction activity
does not include routine maintenance that is performed to maintain the original
line and grade, hydraulic capacity, or original purpose of the site.
Sod: A closely knit ground cover growth, primarily
of grasses, held together by its roots.
Soil amendment: Any material, such as compost, lime, gypsum,
sawdust, or synthetic conditioner that is worked into the soil to make it more
productive. This term is used most
commonly for added materials other than fertilizer.
Soil horizon: A layer of soil, approximately parallel to
the soil surface, with distinct characteristics produced by soil-forming
processes.
Soil structure: The combination or arrangement of primary soil
particles into secondary particles or units.
The secondary particles are characterized by size, shape, and degree of
distinctness into classes, types, and grades.
Stormwater: Storm runoff, snow melt runoff, and surface
runoff and drainage.
Stormwater discharge related
activities: Activities that cause,
contribute to, or result in stormwater point source pollutant discharges,
including excavation, site development, grading, and other surface disturbance
activities; and measures to control stormwater, including the siting,
construction, and operation of BMPs to control, reduce, or prevent stormwater
pollution.
Stubble: The base portion of plants remaining after
the top portion has been harvested.
Tacking: The process of binding mulch fibers together
by adding a sprayed chemical compound.
Topsoil: The unconsolidated earthy material that
exists in its natural state and is or can be made favorable to the growth of
desirable vegetation. Usually the
A-horizon of soils with developed profiles.
Vegetation: Plants in general or all plant life in the
area.
Waters of the United States: All waters that are currently used, were used
in the past, or may be susceptible to use in interstate or foreign commerce,
including all waters subject to the ebb and flow of the tide. Waters of the United States
include all interstate waters and intrastate lakes, rivers, streams (including
intermittent streams), mudflats, sand flats, wetlands, sloughs, prairie
potholes, wet meadows, playa lakes, or natural ponds.
Weed: An undesired uncultivated plant.
Wetlands: Areas that are inundated or saturated by
surface or groundwater at a frequency and duration sufficient to support, and
that under normal circumstances do support, a prevalence of vegetation
typically adapted for life in saturated soil conditions. Wetlands generally
include swamps, marshes, bogs, and similar areas.