[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
This Part 10 is intended to comply with the requirements of
the Pennsylvania "Storm Water Management Act," Act No. 167 of October
4, 1978 (P.L. 864),[1] and its regulations. The purposes of this Part are to
promote the general health, safety, and welfare of the community,
regulate the modification of the natural terrain and alterations of
existing drainage from land disturbance, new subdivisions, and new
land developments in order to control erosion and sedimentation of
soils and preserve stream channels and water quality, as well as provide
for design, construction and maintenance of storm drainage facilities
for controlling stormwater, erosion, and sedimentation and maintaining
the quality of the watersheds within Forward Township.
[1]
Editor's Note: See 32 P.S. § 680.1 et seq.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
The following activities shall be regulated by this Part 10:
A.
Land development.
B.
Subdivision.
C.
Construction of new or additional impervious or semipervious surfaces
(driveways, parking lots, etc.).
D.
Construction of new buildings or additions to existing buildings.
E.
Diversion or piping of any natural or man-made stream channel.
F.
Installation of stormwater management provisions or appurtenances
thereto.
G.
Earth disturbance.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
For the purposes of this Part, certain terms and words used herein shall be interpreted as stated in Part 2 of this chapter.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
The costs of review and inspection by the Engineer for the Township
of the stormwater management system as proposed by the developer shall
be borne by the developer, whether or not the plan is ultimately approved.
The Engineer shall review such changes as the developer may make in
his plan for compliance with the Engineer's recommendations and shall
advise the Board of Supervisors whether the revised plan is in compliance
or not. The Board shall direct the Engineer to inspect a stormwater
management area during its various stages of construction and to point
out to the contractor, the developer and Board any deviations from
the design as approved.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
The owner or developer shall enter into a legal agreement which shall
indemnify and hold the Township harmless from any and all liability
relating to storm drainage collection systems and their discharge
during construction of the system and thereafter. The owner or developer
shall secure, where necessary, in the opinion of the Engineer for
the Township, all off-site easements for storm drainage. In the event
the Township, in its sole discretion, determines that the Township
shall be responsible for maintenance of a retention area, the developer
shall provide permanent access easements to, into, within and around
the retention area. In the event that the Township assumes maintenance,
either through agreement with the developer or because the developer
fails to maintain the area, the developer shall pay to the Township
all costs and expenses necessary to maintain the same, but not less
than $0.50 for each square foot of area to be maintained, which shall
be deposited in an account from which the principal and the interest
shall be used only for the maintenance of the stormwater management
system and no other municipal purpose. The exact square foot unit
price amount shall be determined by the Township when executing the
maintenance agreement when the amount is agreed upon prior to actual
Township maintenance. If maintenance is performed by the Township
as a result of the developer's nonperformance, the Township shall
assess the costs of maintenance based upon actual costs incurred by
the Township, but in an amount not less than the unit price of $0.50
heretofore written.
2.
In the event that the developer should default in regard to the aforementioned
square foot maintenance agreement for whatever cause and it becomes
not feasible for the Township to collect from the developer the minimum
$0.50 per square foot for the area to be maintained, the Township
may lien each property within and served by the development plan for
the individually computed pro rata cost incurred by the Township when
providing maintenance according to this provision.
3.
Where it is the intention of the developer to provide maintenance
and repair of a retention area, the developer shall provide the Township
with a binding legal document pledging and warranting himself to continued
performance, if warranted in the opinion of the Township; the developer
shall furnish the Township with an acceptable bond in an amount not
less than the aforementioned minimum amount to ensure future financial
capability. In addition, there shall be the requirement that the development
plan or subdivision plan, when presented to the Township for approval,
contains the statement that each individual landowner in the development
plan for which a stormwater management control plan is approved, his
heirs, successors or assigns share proportionately in the responsibility
for maintenance and repair of the facility, should the developer fail
to fulfill his obligations as set forth. The statement shall be a
provision of the deed that is issued for each and every individual
lot, parcel or tract within a development plan or subdivision plan
when such development plan is subject to stormwater management control.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
Any delineated wetland areas shall not be drained or flooded
permanently unless the proper permits are obtained from the Pennsylvania
Department of Environmental Protection and the United States Army
Corp of Engineers for such work.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
Storm sewers, culverts, catch basin inlets and related installations
shall be provided to ensure the controlled flow of natural watercourses
and to guarantee the drainage of all low points along the curb or
gutter lines, as well as at intervals related to slope, of all streets
in or adjacent to the plan. Where driveways cross gutter lines, they
shall be designed to allow passage of stormwater along the gutter
line or passage via a pipe below the driveway entrance of sufficient
size to carry the runoff. In no case shall stormwater flowing down
a driveway be permitted to cross a public street.
2.
Catch basin inlets shall be double brick at least eight inches in
thickness, cemented on both sides, or precast concrete meeting at
least the standards of the current edition of PennDOT's specifications
sheet RC-52. Catch basins shall be located no further apart than 400
feet along a single continuous slope. Actual spacing within the minimum
limits specified shall be planned to efficiently intercept proposed
surface flows.
3.
Storm sewers installed shall have a minimum diameter of 15 inches
and a minimum gradient of 1%.
4.
A stormwater drainage system which is adequate to serve the needs
of the proposed subdivision, land development, or mobile home park
shall be constructed for same. All construction shall comply with
this Part, PennDOT specifications, the Pennsylvania Stormwater Management
Act and with the Pennsylvania Department of Environmental Protection
(where construction will affect an existing waterway). Stormwater
drainage plans shall be approved by the County Engineer or his or
her designated representative before construction may commence.
5.
If an adequately sized, existing stormwater drainage system exists
within 500 linear feet of the proposed system, it shall be connected
to same. If a developer cannot connect the proposed system with an
existing system because one does not exist, an existing system is
not adequately sized, or access is unattainable because of ownership,
then storm drainage shall be diverted to an existing natural watercourse
or as permitted by DEP and shall not drain to other property, except
by proper easement in compliance with this Part, and shall not cause
hazard to persons or property.
6.
Drainage ditches or channels may be constructed by the developer,
if approved by the County Engineer or designated representative, to
control surface drainage. Drainage ditches and channels shall have
a minimum gradient of 1% with side slopes no steeper than one vertical
to two horizontal and shall be seeded with an acceptable vegetation,
suitable to prevent erosion.
7.
Roof drains shall be extended to a paved gutter and connected to
a storm sewer system where possible. Where a connection to a system
is not possible, roof drains shall be diverted to an approved drainage
ditch or channel. At no time shall a roof or foundation drain be connected
to a sanitary sewer system.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
In designing the storm drainage system, the developer shall use as
his guide the publication "Urban Hydrology for Small Watersheds" Technical
Release No. 55, United States Department of Agriculture, Soil Conservation
Service, January 1975, as amended. For developments larger than three
acres, the SCS twenty-four-hour Type II rainfall distribution shall
be used for analyzing stormwater runoff control facilities (except
storm runoff collection and conveyance facilites). For development
sites less than three acres, the rational method may be used to determine
peak flows and the modified rational method used for design and routing
of runoff control facilities.
2.
The predevelopment condition of the parcel to be developed, as determined
by the Engineer for the Township, shall be considered the state of
the land surface on the date that the developer entered into an agreement
to purchase the property. If the property has been partially or completely
developed at the time of purchase, the Board of Supervisors may, at
its option, require the new owner, if he proposed to redevelop or
further develop the property, to take remedial action for compliance
with the requirements of this subsection, regardless of the condition
of the surface; the predevelopment design runoff shall not be more
than that generated by a predevelopment land surface condition comparable
to a ground runoff curve number of 75 (see Tables 2-1 and 2-2 of TR
55). The developer may pass through stormwater originating upstream
of his property, but if he elects to control it, bypass devices he
installs shall be capable of handling the ten-year twenty-four-hour
peak flow, and he may trade off, as compensation for such installations,
control measures that would normally be required on his property,
provided the total control system results in equal or better protection
for downstream properties.
3.
The developer shall consult with the Butler County Office of the
Soil Conservation Service before developing his storm drainage plans.
The Township and others reviewing a stormwater control plan will use
discretion in considering unusual conditions, such as drainage from
several basins on the same property under development.
4.
A ten-year storm frequency shall be utilized in designing facilities
serving local, commercial/industrial and marginal accessways and access
roads to multiple business properties. All longitudinal and side drains
and slope pipes for street, road and highway systems will also be
designed considering the ten-year storm frequency. Culvert cross drains
and any other type of drainage facility in an underpass or depressed
roadway section shall be designed utilizing the following storm frequencies:
arterial highways 25 years and collector, local and other streets
10 years. Greater design standards may be required by the Planning
Commission where justified on individual projects.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
The stormwater drainage plan of a subdivision, development plan or
mobile home park shall be designed to assure that, after development,
stormwater does not leave the property at a greater velocity or volume
per second than before development commenced. The ten-year twenty-four-hour
peak flow (3.80 inches of precipitation in 24 hours or as may be subsequently
revised), creating slightly out-of-bank conditions in downstream drainageways,
shall be the maximum release rate condition for water leaving the
property. The maximum storm of record over a twenty-four-hour period
during the preceding 25 years (4.35 inches of precipitation in 24
hours or as may be subsequently revised) shall be the design condition
to be used in developing the storm drainage system. The difference
between the twenty-five-year storm and the ten-year storm shall be
stored on the property for gradual release at the ten-year rate.
2.
The Supervisors reserve the right to require the developer to provide
storage for the difference between the maximum storm of record over
a twenty-four-hour period during the preceding 100 years (5.00 inches
of precipitation in 24 hours or as may be subsequently revised) and
the twenty-five-year storm.
3.
When the area to be developed is composed of more than one watershed,
and discharges from the watersheds do not occur at a common point,
each watershed shall be managed separately so that no uncontrolled
runoff may occur from any major portion of the developed total site.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
The stormwater drainage system of pipes and conduits shall be designed
to transport the stormwater runoff generated by the twenty-five-year
(4.35 inches of precipitation), twenty-four-hour-peak-flow storm.
2.
When tradeoff is utilized as mentioned in § 22-1008 above and storm drains will bypass the stormwater management control facility, pipes and conduits may be designed to transport stormwater runoff generated by a fifteen-year (4.05 inches of precipitation), twenty-four hour peak flow.
3.
All runoff transported over land either by effluent from sewers or
from nonsewered open lands tributary to the retention facilities shall
be conveyed in planned facilities, such as heavily vegetated channels
or otherwise stabilized drainageways, to the stormwater retention
facilities. Facilities, either constructed or natural, shall be designed
to carry the peak flow at nonerosive velocities.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
Retention areas, as required to impede runoff, may be varied in type
and form. Temporary impoundment of stormwaters may be managed by said
storage of water within underground facilities (i.e., as rock fills,
buried conduits, etc.), on flat parking or other surface areas, on
rooftops, in excavated ponds, in embankment ponds (singly or in multiples
thereof), or in any combination of the above. Structural limitations
of impoundment facilities shall be thoroughly reviewed by the developer
and be approved by the appropriate agencies having jurisdiction.
2.
Retention areas shall be designed to meet or exceed the following
minimum standards and the applicable standards of the following referenced
documents:
A.
"Handbook for Earthmoving Activities and Erosion and Sedimentation
Control in Butler County," latest revised edition;
B.
"Soil Conservation Service–Construction Specifications and
Engineering Standards for Embankment Ponds," Technical Guide Section
IV, pages 378-1 to 2378-15, dated May 1977, or the latest revised
edition.
3.
Except where a permanent ponding facility is approved by the Township,
all retention areas shall be designed to be drained completely.
A.
Retention Area as a Parking Lot Facility.
(1)
The low edge of a parking area, curbed or uncurbed, may serve
the purpose of an emergency spillway to pass the overflow from a stormwater
retention area, provided the embankment below the edge is well stabilized
with planting materials and the angle of the slope will not encourage
erosion, in the opinion of the Township and other reviewing agencies.
The maximum depth of water on a parking area used for stormwater management
purposes shall not exceed 12 inches.
B.
Retention Area as an Embankment Reservoir Facility.
(1)
Standards.
(a)
Embankment reservoirs shall be designed to service a drainage
area of not more than 20 acres and have a maximum depth at normal
design pool of no greater than 10 feet. Embankments in this category
shall be known as "Pennsylvania Class III ponds."
(b)
Prior to design or construction, a soil investigation at the
site shall be carried out by the developer. A minimum of two test
borings taken at no greater than 50 feet on center across the site
of the proposed breastwork may be required. Test borings shall, as
a minimum, extend to 10 feet below the level of the case of the impoundment
at the breastwork or five feet into bedrock if bedrock is encountered
within the minimum ten-foot depth. Test hole results will be furnished
as part of project approval documents.
(c)
The minimum top width of the structure shall be six feet. The
minimum elevation at the top of the settled embankment shall be one
foot above the water surface in the reservoir with the emergency spillway,
and the settled top of the impoundment shall be two feet. Initially,
the top of the impoundment shall be constructed 10% higher than the
designed height to allow for the occurrence of possible settlement.
(d)
Fill Material.
1)
Acceptable fill material for embankment construction shall conform
to permitted uses as itemized under Table 3, "Soil Interpretations
for Selected Engineering Uses," as published in the Soil Survey for
Developing Area in Butler County, Pennsylvania, prepared by the United
States Department of Agriculture (USDA), latest revised edition.
2)
In the event that acceptable embankment material is not available
on site, the developer must arrange to provide fill material from
an acceptable source off site. Pre-identification of borrow material
will be required to be furnished by the developer before permits may
be issued by the Township.
(e)
Foundation Preparation. The foundation area for embankment shall
be cleared of all trees, stumps, roots, brush, boulders, sod, topsoil
and debris. All channel banks and sharp breaks shall be sloped to
no steeper than 1:1. The surface of the foundation area will be thoroughly
scarified before placement of the embankment material.
(f)
Fill Placement.
1)
Fill shall be placed in maximum six-inch layers at optimum moisture
content and shall be compacted to 95% original dry density.
2)
The material placed in the fill shall be free of all sod, roots,
frozen soil, stones over six inches in diameter, and other objectionable
material. The placing and spreading of the fill material shall be
started at the lowest point of the foundation, and the fill shall
be brought up in the six-inch horizontal layers.
3)
The distribution and gradation of materials throughout the fill
shall be such that there will be no lenses, pockets, streaks or layers
of material differing substantially in texture or gradation from the
surrounding material. Where it is necessary to use materials of varying
texture and gradation, the more impervious material shall be placed
in the upon stream and center portions of the fill.
(g)
Embankment impoundments shall be constructed with a foundation
cutoff to ensure stability. The cutoff shall extend full length under
the embankment fill at or slightly upstream from the embankment center
line. If deemed necessary after analysis of test boring results, it
shall be extended a sufficient distance beyond the fill to ensure
stability and relative watertightness on the downslope terrain at
the sides. The cutoff trench shall be constructed of relatively impervious
material and shall not be less than three feet in depth and three
feet in width at its base. Side slopes shall be no greater than 1:1.
In all cases, the cutoff shall extend into a relatively impervious
layer of native material.
(h)
Embankment Slopes. The combined upstream and downstream side
slopes of the settled embankment shall not be less than five horizontal
to one vertical with neither slope steeper than 2:1. Slopes must be
designed to be stable in all cases, even if flatter side slopes are
required.
(i)
Emergency Spillway.
1)
An emergency spillway is to be provided to convey large flood
flows safely past earth embankments.
2)
The emergency spillway shall be capable of passing the flow
created by the maximum storm of record over a twenty-four-hour period
during the preceding 100 years. Five inches of precipitation in 24
hours shall be the design condition.
3)
Constructed earth spillways shall be trapezoidal and will be
located in undisturbed or compacted earth. The side slopes shall be
stable for the material in which the spillway is to be constructed.
4)
Earth spillways shall be designed to carry the design peak flow
at nonerosive velocities. Nonerosive velocities for the vegetation
to be established may be determined from Exhibit 7-3, page 7-14, of
the SCS Engineering Field Manual.
(j)
Pipe Conduits–Drains. Pipe conduits under or through the
embankment shall be of minimum Schedule 40 steel pipe, Class III reinforced
concrete pipe or 12-gauge full bituminous coated corrugated metal
pipe. The pipe barrel shall be placed on a firm foundation to the
lines and grades shown on the plans. Selected backfill material shall
be placed around the conduit in four-inch layers. Each layer shall
be thoroughly compacted with hand-operated equipment to a height of
two feet over pipes and other structures before heavy equipment is
operated over them. The invert of the pond drain shall be a minimum
of three feet below the lowest elevation of water impoundment in the
pond. Anti-seep collars shall be installed around the pipe conduit
not greater than 28 feet measured along the length of the pipe. Collars
shall extend a minimum of two feet in all directions at right angles
measured from the face of the pipe. Collars of steel shall be minimum
one-fourth-inch steel plate and shall be welded to the pipe conduit
for the full pipe perimeter. Reinforced concrete collars shall be
minimum 12 inches in thickness. Collars shall be compatible with pipe
materials.
(k)
Pipe Conduit–Inlets. The top of the slotted riser pipe
provided for draining the pond shall be not less than 1/3 the maximum
impoundment depth measured from the bottom of the impoundment. It
shall also be a minimum of four feet above the outfall invert at the
inlet to the pond drain. It shall be fitted with a noncorrosive anti-vortex
device and trash rack. The inlet pipe, where joined to the pipe drain,
shall be firmly anchored to adequate concrete blocking to ensure against
flotation.
(l)
Energy Dissipators. Energy dissipators shall be placed at the
outlet of the pond drain pipe and at the outlet of the emergency spillway
for a minimum distance of 10 feet from the outfalls. Dissipators shall,
as a minimum, be constructed of stone riprap, nominal six-inch diameter.
Width shall be sufficient to control the entire flow between the exit
channel device.
(m)
Seeding.
1)
A protective cover of vegetation shall be established on all
exposed surfaces of the embankment spillway and borrow areas to the
extent practicable under prevailing soil and climatic conditions.
The embankment and spillway shall be fenced where necessary to protect
the vegetation.
2)
Sodding, seeding, liming, fertilizing and mulching shall conform
to the standards for permanent seeding in the Pennsylvania Technical
Guide available in SCS offices, the current Pennsylvania Agronomy
Guide published by Pennsylvania State University, or in the Butler
County Handbook for Earthmoving Activities and Erosion and Sedimentation
Control.
(n)
Visual Resource Design. Ponds in areas of high public visibility
are to receive careful visual design. The underlying criterion for
all visual design is appropriateness. The shape and form of ponds,
excavated material and plantings are to relate visually to their surroundings
and to their function.
C.
Retention Area as an Excavated Pond Facility.
(1)
Side Slopes. Side slopes of excavated ponds shall be such that
they will be stable and shall not be steeper than two horizontal on
one vertical. Where surface water runoff enters the pond in a natural
or excavated channel, the side slope of the pond shall be protected
against erosion by hand-placed stone riprap.
(2)
Emergency Spillway. The crest of the embankment may serve as
the emergency spillway if the back slope (the downstream side) is
six horizontal to one vertical (6:1) or flatter. Otherwise, a spillway
meeting the embankment pond criteria shall be provided.
(3)
Pipe Conduits–Drains and Inlets. All standards shall be
applicable as heretofore written for embankment structures.
(4)
Placement of Excavated Material. The material excavated from
the pond shall be placed in one of the following ways, so that its
weight will not endanger the stability of the pond side slopes and
where it will not be washed back into the pond by rainfall:
(a)
Uniformly spread to a height not exceeding three feet with the
top graded to a continuous slope away from the pond. Maximum grade
shall be two horizontal to one vertical.
(b)
Uniformly placed or shaped reasonably well with side slopes,
assuming a natural angle or repose for the excavated material behind
a berm width equal to the depth of the pond but not less than 12 feet.
(c)
Shaped to a designed form that blends visually with the landscape.
(d)
Used for low embankment and leveling.
(e)
Hauled away.
(5)
Inclusions by Reference. All applicable portions of the written
and referenced standards for embankment ponds shall apply as if herein
written.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
All graded areas associated with stormwater management and development
shall be stabilized with erosion-resisting plantings placed immediately
after the completion of grading. Graded slopes produced by placing
fill earth over the preexisting surface shall be keyed into the original
grade.
2.
Grades of embankments resulting from preparation of building lots
or sites shall not exceed one-foot vertical rise for every two feet
of horizontal run for fill slopes or one-foot vertical rise for every
1.5 feet horizontal run for slopes created by excavating in areas
that have lain dormant for at least two years, except that steeper
slopes may be permitted in areas where, in the opinion of a professional
engineer, as evidenced in a written report, conditions are such as
to allow slopes up to a maximum grade determined by the engineers,
subject to the approval of the Township.
3.
No grading shall occur within five feet of any subdivision or development
plan boundary except as is needed for the entrance of streets or to
grade off land immediately adjacent to a street when establishing
the finished grade street elevation.
4.
All persons, partnerships or corporations intending to excavate,
fill or grade land in the Township shall be required to apply for
a grading permit and shall have a valid grading permit in their possession
prior to the start of any grading work. Prior to the issuance of a
permit, the site shall be subject to the inspection and approval of
the Engineer for the Township. The costs of inspections shall be borne
by the applicant at time of permit issuance. Work shall be undertaken
in conformance with the requirements of this Part and applicable regulations
of Butler County.
[Ord. No. 82-1, 8/15/1982; as amended by Ord. No. 1988-2,
12/13/1988; Ord. No. 2006-1, 6/20/2006]
1.
The Township Supervisors may elect, at their discretion, to forego
stormwater management development plans on a case-by-case basis for
residential development only under the following circumstances:
A.
The developer is an individual lot owner, and the lot to be developed
fronts on an existing public road of record.
B.
The land to be subdivided does not exceed five contiguous lots all
of which front on an existing public road of record, and the subdivision
meets all other subdivision requirements as set forth in the regulations.
Additional contiguous lots in excess of five may be subdivided without
formal stormwater management control facilities with special permission
when, in the opinion of the Township, runoff generated from the proposed
total development will not be in excess of a maximum allowable amount
that will ensure continued adequate protection for downstream developed
and undeveloped lands and waterways.
C.
The land area coverage of any individual lot, when fully developed
according to the plan submitted, does not exceed the following maximum
values: principal structure, 15% of lot area; and driveways, porches,
parking lots and appurtenances, 15% of lot area. The remaining undeveloped
portion of any individual lot shall have a land surface condition
comparable to or less than around runoff curve numbers of 75 (meadowland)
according to Tables 2-1 and 2-2 of Technical Release No. 55, United
States Department of Agriculture, Soil Conservation Service, January
1975, and as amended.
2.
Development as specified under §§22 1001 through 22-1006
above is subject to the following restrictions and ongoing controls:
A.
A subdivider proposing to develop contiguous lots in excess of five
must provide analysis of the watershed upstream which passes through
his development. Exclusion of stormwater management controls may be
considered if the total development does not increase runoff from
that watershed beyond that generated according to the following criteria:
B.
The volume rate of water generated by that watershed shall be computed
for the twenty-five-year storm. Ground cover for the computation shall
be based upon runoff curve number 75. Volume rate shall also be computed
for the post-development runoff curve number based upon the twenty-five-year
storm. When computations indicate a greater runoff for post-development
conditions than was computed for runoff curve number 75, exclusions
of stormwater management development plans will not be considered.
