Specific terms. Other terms or words used in this chapter are defined
as follows:
AASHTO
American Association of State Highway and Transportation
Officials.
ACCD
Allegheny County Conservation District.
ACCELERATED EROSION
The removal of the surface of the land through the combined
action of human activities and natural processes at a rate greater
than would occur because of the natural process alone.
ACHD
Allegheny County Health Department.
ACT 167
The Stormwater Management Act (Act of October 4, 1978, P.L.
864 No. 167; 32 P.S. §§ 680.1 through 680.17, as amended).
ACT 167 PLAN (or WATERSHED PLAN)
The plan for managing stormwater runoff throughout a designated
watershed adopted by Allegheny County as required by the Pennsylvania
Storm Water Management Act (Act 167).
AGRICULTURAL ACTIVITY
The work of producing crops, including tillage, land clearing,
plowing, disking, harrowing, planting, harvesting crops, or pasturing
and raising of livestock and installation of conservation measures.
Construction of new buildings or impervious area is not considered
an agricultural activity.
APPLICANT
A landowner, developer, or person, as hereinafter defined,
including heirs, successors, and assigns, who has filed an application
to the Municipality for approval to engage in any regulated activity
at a project site in the Municipality.
APPLICATION
Every application, whether preliminary or final, required
to be filed and approved prior to start of construction or development
for the approval of a subdivision plat or plan, or for the approval
of a development plan.
ATTENUATE
To reduce the magnitude of the flow rate by increasing the
time it takes to release a specified volume of runoff (for example
the one year, twenty-four-hour storm event). "Attenuation" is a method
of reducing the peak flow rates for post-development compared to the
peak flow rates in predevelopment.
BASE FLOW
Portion of stream discharge derived from groundwater; the
sustained discharge that does not result from direct runoff or from
water diversions, reservoir releases, piped discharges, or other human
activities.
BEST MANAGEMENT PRACTICE (BMP)
Activities, facilities, designs, measures, or procedures
used to manage stormwater impacts from regulated activities, to meet
state water quality requirements, to promote groundwater recharge,
and to otherwise meet the purposes of this chapter. Stormwater BMPs
are commonly grouped into one of two broad categories or measures:
structural or nonstructural. In this chapter, "nonstructural" BMPs
or measures refer to operational and/or behavior-related practices
that attempt to minimize the contact of pollutants with stormwater
runoff, whereas "structural" BMPs or measures are those that consist
of a physical device or practice that is installed to capture and
treat stormwater runoff. Structural BMPs include, but are not limited
to, a wide variety of practices and devices, from large-scale retention
ponds and constructed wetlands to small-scale underground treatment
systems, infiltration facilities, filter strips, low-impact design,
bioretention, wet ponds, permeable paving, grassed swales, riparian
or forested buffers, sand filters, detention basins, and manufactured
devices. Structural stormwater BMPs are permanent appurtenances to
the project site.
CFS
Cubic feet per second.
CHANNEL
A perceptible natural or artificial waterway which periodically
or continuously contains moving water or which forms a connecting
link between two bodies of water. It has a defined bed and banks which
confine the water.
CONSERVATION DESIGN
A series of holistic land development design practices that
maximize protection of key land and environmental resources, preserve
significant concentrations of open space and greenways, evaluate and
maintain site hydrology, and ensure flexibility in development design
to meet community needs for complementary and aesthetically pleasing
development. Conservation design encompasses the following objectives:
conservation/enhancement of natural resources, wildlife habitat, biodiversity
corridors and greenways (interconnected open space); minimization
of environmental impact resulting from a change in land use (minimum
disturbance, minimum maintenance); maintenance of a balanced water
budget by making use of site characteristics and infiltration; incorporation
of unique natural, scenic and historic site features into the configuration
of the development; preservation of the integral characteristics of
the site as viewed from adjoining roads; and reduction in maintenance
required for stormwater management practices. Such objectives can
be met on a site through an integrated development process that respects
natural site conditions and attempts, to the maximum extent possible,
to replicate or improve the natural hydrology of a site.
CONSERVATION DISTRICT
A conservation district, as defined in Section 3(c) of the
Conservation District Law [3 P.S. § 851(c)], which has the
authority under a delegation agreement executed with PADEP to administer
and enforce all or a portion of the erosion and sediment control program
in this commonwealth.
DEMOLITION
The intentional act of substantially pulling down, destroying,
dismantling, defacing, removing or razing a building or structure,
or commencing the work of a total, substantial, or partial destruction
with the intent of completing the same. Demolition includes, but is
not limited to: removal of one or more exterior wall(s) or partition(s)
of a building or separately leased portions of a multitenant building,
gutting of a building's interior to the point where exterior features
(windows, doors, roof, etc.) or the building's structural framework
is impacted, removal of more than 50% of a structure's overall gross
square footage as determined by the Municipal Building Official, the
lifting and relocating of a building on its existing site or to another
site.
DEP
The Pennsylvania Department of Environmental Protection.
DESIGN STORM
The magnitude and temporal distribution of precipitation
from a storm event measured in probability of occurrence (e.g., a
five-year storm) and duration (e.g., 24 hours), used in the design
and evaluation of stormwater management systems.
DESIGNATED PLAN REVIEWER
A qualified professional, as defined herein, or organization
such as the Allegheny County Conservation District that has been designated
by the Municipality to be the reviewer of SWM site plans for the Municipality,
and shall be understood to be the reviewer where indicated as the
Municipality within this chapter.
DETENTION BASIN
An impoundment designed to collect and retard stormwater
runoff by temporarily storing the runoff and releasing it at a predetermined
rate. Detention basins are designed to drain completely shortly after
any given rainfall event and are essentially dry until the next rainfall
event.
DETENTION or TO DETAIN
The prevention of, or to prevent, the discharge, directly
or indirectly, of a given volume of stormwater runoff into surface
waters by temporary storage.
DETENTION VOLUME
The volume of runoff that is captured and released into the
waters of the commonwealth at a controlled rate.
DEVELOPER
Any landowner, agent of such landowner, or tenant with the
permission of the landowner, who makes or causes to be made a subdivision
of land or a land development.
DEVELOPMENT
See "earth-disturbance activity." This term includes redevelopment.
DISCHARGE
To release of water from a project, site, aquifer, drainage
basin or other point of interest (verb); the rate and volume of flow
of water such as in a stream, generally expressed in cubic feet per
second (volume per unit of time) (noun).
DISTURBED AREA
An unstabilized land area where an earth disturbance is occurring
or has occurred.
DRAINAGE AREA
That land area contributing runoff to a single point and
that is enclosed by a ridgeline, or the area served or drained by
a sewer or watercourse.
DRAINAGE SYSTEM
All facilities and natural features used for the movement
of stormwater through and from a drainage area, including, but not
limited to, any and all of the following: conduits, pipes and appurtenant
features; channels, ditches, flumes, culverts, streets, swales, gutters,
as well as all watercourses, water bodies and wetlands.
EARTH-DISTURBANCE ACTIVITY
A construction or other human activity which disturbs the
surface of the land, including land clearing and grubbing, grading,
excavations, embankments, land development, agricultural plowing or
tilling, operation of heavy animal use areas, timber harvesting activities,
road maintenance activities, oil and gas activities, well drilling,
mineral extraction, and the moving, depositing, stockpiling, or storing
of soil, rock or earth materials.
EASEMENT
Authorization by a property owner for the use by another,
and for a specific purpose, of any designated part of his property.
EPA
United States Environmental Protection Agency.
EROSION
The detachment and movement of soil or rock fragments, or
the wearing away of the surface of the land by wind, water, ice, or
gravity.
EXISTING CONDITION
The dominant land cover during the five-year period immediately
preceding a proposed regulated activity, unless previous activities
have been performed without required municipal approvals, in which
case the Municipality reserves the right to designate existing conditions
as that which existed prior to the nonpermitted alterations.
FEMA
Federal Emergency Management Agency.
FHWA
United States Department of Transportation Federal Highway
Administration.
FLOODPLAIN
A relatively flat or low land area which is subject to inundation
from the rapid accumulation of surface waters; including Floodway
Districts, Flood-Fringe Districts, and General Floodplain Districts.
Also includes areas that comprise Group 13 soils, as listed in Appendix
A of the Pennsylvania DEP Technical Manual for Sewage Enforcement
Officers (as amended or replaced from time to time by DEP).
FLOODWAY
The channel of a watercourse and portions of the adjoining
floodplain which are reasonably required to carry and discharge the
100-year-frequency flood. The boundary of the floodway shall be as
delineated on maps and studies prepared by the Federal Emergency Management
Agency (FEMA). In areas where no FEMA maps and studies have defined
the floodway, the assumed floodway boundary shall be 50 feet, as measured
from the top of the bank of the stream.
FOREST MANAGEMENT
Planning and activities necessary for the management of forestland.
These include timber inventory and preparation of forest management
plans, silvicultural treatment, cutting budgets, logging road design
and construction, timber harvesting, site preparation and reforestation.
FREEBOARD
The vertical distance from the water surface to the top of
a channel. In an emergency spillway, "freeboard" is the difference
between the elevation of the design flow in the emergency spillway
(usually the 100-year peak elevation) and the top elevation of the
settled basin embankment (that is, top of berm).
GREEN INFRASTRUCTURE
Systems and practices that use or mimic natural processes
to infiltrate, evapotranspire, or reuse stormwater on the site where
it is generated.
GROUNDWATER
Water that occurs in the subsurface and fills or saturates
the porous openings, fractures, and fissures of underground soils
and rock units.
HOT SPOTS
An area where land use or activities generate highly contaminated
runoff, with concentrations of pollutants in excess of those typically
found in stormwater.
HYDROGRAPH
A graph of discharge versus time for a selected point in
the drainage system.
HYDROLOGIC SOIL GROUP (HSG)
Infiltration rates of soils vary widely and are affected
by subsurface permeability as well as surface intake rates. Soils
are classified into four HSGs (A, B, C, and D) according to their
minimum infiltration rate, which is obtained for bare soil after prolonged
wetting. The Natural Resources Conservation Service (NRCS) of the
US Department of Agriculture defines the four groups and provides
a list of most of the soils in the United States and their group classification.
The soils in the area of the development site may be identified from
a soil survey report that can be obtained from local NRCS offices
or conservation district offices. Soils become less pervious as the
HSG varies from A to D.
HYDROLOGY
The study of the properties, distribution, circulation and
effects of water on the Earth's surface, soil and atmosphere.
IMPERVIOUS SURFACE
A surface (area) which has been compacted or covered with
a layer of material so that it prevents the infiltration of water
into the ground. Impervious surfaces (areas) shall include semipervious
surfaces such as compacted clayey soils, as well as most conventionally
surfaced streets, roofs, sidewalks, parking lots, and other similar
surfaces. "Net increase of impervious surface" refers to the difference
between the existing impervious coverage and the total impervious
surface proposed.
INFILTRATION
Movement of surface water into the soil, where it is absorbed
by plant roots, evaporated into the atmosphere, or percolates downward
to recharge groundwater.
INTENSITY
The depth of accumulated rainfall per unit of time.
INTERMITTENT STREAM
A defined channel in which surface water is absent during
a portion of the year, as groundwater levels drop below the channel
bottom.
INVASIVE SPECIES
DCNR defines "invasive plants" as those species that are
not native to the state, grow aggressively, and spread and displace
native vegetation. (See http://www.dcnr.state.pa.us/cs/groups/public/documents/document/dcnr_010314.pdf
for a list of invasive species.)
LAND DEVELOPMENT
Any of the following:
(1)
The improvement of one lot or two or more contiguous lots, tracts,
or parcels of land for any purpose involving:
(a)
A group of two or more residential or nonresidential buildings,
whether proposed initially or cumulatively, or a single nonresidential
building on a lot or lots regardless of the number of occupants or
tenure; or
(b)
The division or allocation of land or space, whether initially
or cumulatively, between or among two or more existing or prospective
occupants by means of or for the purpose of streets, common areas,
leaseholds, condominiums, building groups, or other features; or
(c)
Development in accordance with Section 503(1.1) of the PA Municipalities
Planning Code.
(2)
A subdivision of land. (See "subdivision.")
(3)
Land development shall not include:
(a)
The conversion of an existing single-family detached dwelling
or single-family semidetached dwelling into not more than three residential
units, unless such units are intended to be a condominium;
(b)
The addition of an accessory building, including farm buildings,
on a lot or lots subordinate to an existing principal building; or
(c)
The addition or conversion of buildings or rides within the
confines of an enterprise which would be considered an amusement park.
For purposes of this subsection, an "amusement park" is defined as
a tract or area used principally as a location for permanent amusement
structures or rides. This exclusion shall not apply to newly acquired
acreage by an amusement park until initial plans for the expanded
area have been approved.
LEVEL SPREADER
A low earthen berm constructed perpendicular to the direction
of slope and extending across the width of the slope for the purpose
of intercepting surface runoff and spreading it behind the berm to
enhance infiltration and reduce erosion and runoff from the slope.
The purpose of a level spreader is to prevent concentrated, erosive
flows from occurring and to spread out stormwater runoff uniformly
over the ground as sheet flow.
LOADING
The total amount (generally measured in pounds or kilograms
per acre per year) of material (sediment, nutrients, oxygen-demanding
material, or other chemicals or compounds) brought into a lake, stream
or water body by inflowing streams, runoff, direct discharge through
pipes, groundwater, the air (aerial or atmospheric deposition) and
other sources over a specific period of time (often annually).
LOW-IMPACT DEVELOPMENT (LID)
Site design approaches and small-scale stormwater management
practices that promote the use of natural systems for infiltration,
evapotranspiration, and reuse of rainwater. LID can be applied to
new development, urban retrofits, and revitalization projects. LID
utilizes design techniques that infiltrate, filter, evaporate, and
store runoff close to its source. Rather than rely on costly large-scale
conveyance and treatment systems, LID addresses stormwater through
a variety of small, cost-effective landscape features located on-site.
MAINTENANCE
The action taken to restore or preserve the as-built functional
design of any facility or system.
MS4
Municipal separate storm sewer system.
MUNICIPALITY
Municipality of Monroeville, a Home Rule Charter Municipality,
Allegheny County, Pennsylvania.
NATIVE VEGETATION
Plant species that have historically grown in Pennsylvania
and are not invasive species as defined herein.
NEW DEVELOPMENT
Any activity regulated by this chapter that is not considered
a redevelopment as defined in this chapter.
NOAA
National Oceanic and Atmospheric Administration.
NONSTRUCTURAL STORMWATER MANAGEMENT PRACTICES
Passive, site-design approaches or regulatory approaches
that positively impact water quality and reduce or minimize the generation
of stormwater runoff without requiring the construction of specific
or discrete stormwater management control structures.
NPDES
National Pollutant Discharge Elimination System, the federal
government's system for issuance of permits under the Clean Water
Act, which is delegated to PADEP in Pennsylvania.
NRCS
Natural Resources Conservation Service.
OPEN VEGETATED CHANNEL
Also known as "swales," "grass channels," and "biofilters."
These vegetated channels are used for the conveyance, retention, infiltration
and filtration of stormwater runoff.
OUTFALL
"Point source," as described in 40 CFR 122.2, at the point
where the Municipality's storm sewer system discharges to surface
waters of this commonwealth.
PADEP
Pennsylvania Department of Environmental Protection.
PEAK DISCHARGE
The maximum rate of stormwater runoff from a specific storm
event.
PENNDOT
Pennsylvania Department of Transportation.
PERCOLATION RATE
The rate of movement of water under hydrostatic pressure
through interstices of rock or soil. For stormwater analysis, it is
typically measured as a distance per unit of time (e.g., inches per
hour).
PERSON
An individual, partnership, public or private association
or corporation, or a governmental unit, public utility, or other legal
entity whatsoever which is recognized by law as the subject of rights
and duties.
POINT SOURCE
Any discernible, confined and discrete conveyance, including,
but not limited to, any pipe, ditch, channel, tunnel, or conduit from
which stormwater is or may be discharged, as defined in state regulations
at 25 Pa. Code Chapter 92.1.
PREDEVELOPMENT ASSUMPTION
The ground cover assumption used when analyzing the stormwater
runoff characteristics of a drainage area prior to the proposed development.
PROJECT SITE
The specific area of land where any regulated activities
in the Municipality are planned, conducted, or maintained.
QUALIFIED PROFESSIONAL
Any person licensed by the Pennsylvania Department of State
or otherwise qualified under Pennsylvania law to perform the work
required by this chapter.
RATE
Volume per unit of time.
RECEIVING WATERS
Any water bodies, watercourses or wetlands into which surface
waters flow.
RECHARGE
The replenishment of groundwater through the infiltration
of rainfall, other surface waters, or land application of water or
treated wastewater.
REDEVELOPMENT
An existing, developed property and/or a graded, altered
and compacted site (as of or after the date of adoption of this chapter)
that is proposed for reconstruction involving the demolition or partial
demolition of the property.
REGULATED ACTIVITIES
Any earth disturbances or any activities that involve the
alteration or development of land in a manner that may affect post-construction
stormwater runoff, as specified in this chapter.
RELEASE RATE DISTRICT
A watershed or portion of a watershed for which a release
rate has been established by an adopted Act 167 stormwater management
plan.
RELEASE RATE PERCENTAGE
The percentage of predevelopment peak rate of runoff from
a watershed subarea (as delineated in the Act 167 watershed plan),
which defines the allowable post-development peak discharge from any
development site in that subarea.
RETENTION or TO RETAIN
The prevention of direct discharge of stormwater runoff into
receiving waters or water bodies by temporary or permanent containment
in a pond or depression; examples include systems which discharge
by percolation to groundwater, exfiltration, and/or evaporation processes
and which generally have residence times of less than three days.
RETENTION BASIN
An impoundment designed to collect and retard stormwater
runoff by temporarily storing the runoff and releasing it at a predetermined
rate. Retention basins may also be designed to permanently retain
additional stormwater runoff. Retention basins are designed to retain
a permanent pool of water during dry weather.
RETENTION VOLUME/REMOVED RUNOFF
The volume of runoff that is captured and not released directly
into the surface waters of this commonwealth during or after a storm
event.
RETURN PERIOD
The average interval, in years, within which a storm event
of a given magnitude can be expected to occur one time. For example,
the twenty-five-year return period rainfall would be expected to occur
on average once every 25 years.
RIPARIAN
Pertaining to anything connected with or immediately adjacent
to the banks of a stream or other body of water.
RIPARIAN BUFFER
An area of land adjacent to a body of water and managed to
maintain the integrity of stream channels and shorelines to reduce
the impact of upland sources of pollution by trapping, filtering and
converting sediments, nutrients and other chemicals, and supply food,
cover and thermal protection to fish and other wildlife.
SCS
Soil Conservation Service.
SEDIMENT
Fragmented material that originated from weathering rocks
and decomposing organic material that is transported by, suspended
in, and eventually deposited in the streambed.
SEDIMENTATION
Occurs when sediment particles that have been suspended within
flowing water are deposited on the stream bottom or floodplain.
SEMIPERVIOUS SURFACE
A surface consisting of gravel, limestone, or other aggregate.
See "impervious surface" definition.
SEPARATE STORM SEWER SYSTEM
A conveyance or system of conveyance, including roads with
drainage systems, municipal streets, catch basins, curbs, gutters,
ditches, man-made channels, or storm sewers, primarily used for collecting
and conveying stormwater runoff.
SHEET FLOW
A flow process associated with broad, shallow water movement
on sloping ground surfaces that is not channelized or concentrated.
SLAMM
Source Loading and Management Model. This model is based
on small storm hydrology and pollutant runoff from urban land uses.
Pollutant sources are identified and both structural and nonstructural
stormwater practices can be accounted for in the model.
STATE WATER QUALITY REQUIREMENTS
The regulatory requirements to protect, maintain, reclaim,
and restore water quality under Pennsylvania Code Title 25 and the
Clean Streams Law.
STORM EVENT
The storm of a specific duration, intensity, and frequency.
STORMWATER or RUNOFF
The flow of water overland and/or in water bodies that results
from and occurs during and immediately following a rainfall event
or snow or ice melt.
STORMWATER MANAGEMENT FACILITY
Any structure, natural or man-made, that, due to its condition,
design, or construction, conveys, stores, or otherwise affects stormwater
runoff. Typical stormwater management facilities include, but are
not limited to: detention and retention basins, open channels, storm
sewers, pipes, and infiltration facilities.
STORMWATER MANAGEMENT PLAN
The approved detailed analysis, design, and drawings of the
stormwater management system required for all construction.
STORMWATER MANAGEMENT PRACTICES
The designed and/or constructed features which infiltrate,
treat, collect, convey, channel, store, inhibit, or divert the movement
of stormwater; such practices include structural and nonstructural
practices.
STREAM
A channel or conveyance of surface water having a defined
bed and banks, whether natural or artificial, with perennial or intermittent
flow.
STRUCTURE
Any man-made object having an ascertainable stationary location
on or in land or water, whether or not affixed to the land, including,
in addition to buildings, billboards, carports, porches, and other
building features, but not including sidewalks and driveways.
SUBAREA (SUBBASIN)
A portion of the watershed (basin) that has similar hydrological
characteristics and drains to a common point.
SUBDIVISION
The division or redivision of a lot, tract, or parcel of
land by any means into two or more lots, tracts, parcels, or other
divisions of land, including changes in existing lot lines, for the
purpose, whether immediate or future, of lease, partition by the court
for distribution to heirs or devisees, transfer of ownership, or building,
or lot development; provided, however, that the subdivision by lease
of land for agricultural purposes into parcels of more than 10 acres,
not involving any new street or easements of access or any residential
dwelling, shall be exempted.
SUBGRADE
The top elevation of graded and compacted earth underlying
roadway pavement.
SWALE
An artificial or natural waterway which may contain contiguous
areas of standing or flowing water only following a rainfall event,
or is planted with or has stabilized vegetation suitable for soil
stabilization, stormwater treatment, and nutrient uptake, or is designed
to take into account the soil erodibility, soil percolation, slope,
slope length, and contributing drainage area so as to prevent erosion
and reduce the pollutant concentration of any discharge.
SWMM
Stormwater Management Model. EPA developed this model for
analyzing stormwater quantity and quality associated with runoff from
urban areas. Both single-event and continuous simulation can be performed
on catchments having storm sewers, or combined sewers and natural
drainage, for prediction of flows, stages and pollutant concentrations.
USDA
United States Department of Agriculture.
WATER BODY
Any natural or artificial pond, lake, reservoir, or other
area which ordinarily or intermittently contains water and which has
a discernible shoreline and receives surface water flow.
WATER TABLE
The uppermost level of saturation of pore space or fractures
by subsurface water in an aquifer. "Seasonal high-water table" refers
to a water table that rises and falls with the seasons due either
to natural or man-made causes.
WATERCOURSE
A channel or conveyance of surface water having defined bed
and banks, whether natural or artificial, with perennial or intermittent
flow.
WATERS OF THE COMMONWEALTH
Any and all rivers, streams, creeks, rivulets, impoundments,
ditches, watercourses, storm sewers, lakes, dammed water, wetlands,
ponds, springs, and all other bodies or channels of conveyance of
surface and underground water, or parts thereof, whether natural or
artificial, within or on the boundaries of this commonwealth.
WATERSHED
All land and water within the confines of a drainage basin.
WETLAND
Any area defined as a wetland by the Federal Manual for Identifying
and Delineating Jurisdictional Wetlands.