[Ord. 7-2005, 7/13/2005]
The following principles of subdivision and land development,
general requirements and minimum standards of design shall be observed
by the applicant in all instances.
A. All portions of a tract being subdivided shall be taken up in lots,
streets, public lands or other proposed uses so that remnants and
landlocked areas shall not be created.
B. Whenever possible, applicants shall preserve mature trees and vegetation,
waterways, scenic points, historic resources and other community assets
and landmarks.
C. Subdivisions and land developments should be laid out so as to avoid
the necessity for excessive cut or fill unless specifically warranted
by terrain or location.
D. Applicants shall observe the ultimate rights-of-way for contiguous existing streets as prescribed by the Official Street Map for the Borough. Additional portions of the right-of-way for such streets shall be offered to the Borough at the time the subdivision or land development when recommended by the Planning Commission. Applicable building setback lines, as defined by the Borough Zoning Ordinance of current adoption [Chapter
27], shall be delineated as measured from the street line or ultimate right-of-way.
E. The standards of design in this Chapter will be used to judge the
adequacy of subdivision and land development proposals. The standards
included in these regulations are minimum design requirements. The
Borough Council reserves the right in any case to request that development
features exceed these standards if conditions so warrant.
F. The Borough Council may modify or adjust the standards to permit
reasonable utilization of property while securing substantial conformance
with the objectives of the regulations.
[Ord. 7-2005, 7/13/2005]
In accordance with the Borough Code, all new streets and widened
portions of all existing rights-of-way intended for public use shall
be dedicated to the Borough subject to final acceptance based on compliance
with the following requirements.
A. Street System.
(1)
Conformance with Adopted Plans. The proposed street pattern
shall conform to existing streets, to any Borough Official Street
Map, and to such county and state road and highway plans as have been
duly adopted by said agencies.
(2)
Arrangement. Streets shall be arranged in regular manner which
is consistent with the Borough's existing grid pattern and planned
streets, and located so as to allow proper development of surrounding
properties.
(3)
Where, in the opinion of Borough Council, it is desirable to
provide for street access to adjoining property, streets shall be
extended by dedication to the boundary of such property.
(4)
Conformity with Topography. Streets shall be adjusted to the
contour of the land so as to produce usable lots and streets of reasonable
grade, alignment and drainage.
(5)
Grading. The street shall be graded to the full width of the
right-of-way and provision made for slopes beyond the right-of-way
in conformance with Borough specifications.
(6)
Provisions of Streets for Future Development. Access shall be
given to all lots and portions of the tract in the subdivision and
to adjacent unsubdivided territory. Streets giving such access shall
be improved to the limits of the subdivisions. Remnants, reserve strips
and landlocked areas shall not be created.
(7)
New Streets. New streets shall be designed to continue existing
streets at the right-of-way and cartway width recommended by this
Chapter.
(8)
Dead-End Streets. Dead-end streets are prohibited, unless designed
as culs-de-sac or designed for access exclusively to neighboring tracts.
(9)
Street Names. Continuations of existing streets shall be known
by the same name. Names for new streets shall not duplicate or closely
resemble names of existing streets. All street names are subject to
the approval of Borough Council.
(10)
Design. The design of all new streets and extensions of existing
streets shall be reviewed and approved by the Borough Engineer.
B. Street Alignment.
(1)
Sight Distance. For all streets, a sight distance of 200 feet
should be maintained. Sight distance should be measured at the center
line of the street and at a driver's eye height of four feet.
(2)
Street Grades.
(a)
There shall be a minimum grade of at least 1% on all streets.
(b)
Grades in excess of 5% shall be avoided where possible, and
no grade shall exceed 10% without approval of Borough Council. The
grade shall be measured along the center line.
(c)
All streets shall be graded to the grades shown on the street
profile and cross section plan submitted and approved with the preliminary
plan of subdivision or land development. They shall be inspected and
checked for accuracy by the Borough Engineer.
C. Right-of-Way Width, Paving Width and Curbing.
(1)
Street. The minimum widths of the right-of-way and the paving,
and the requirements for curbing, shall not be less than those of
an existing street of which the new street is to be a continuation,
nor less than the following:
|
Type of Street
|
Right-of-Way
(feet)
|
Paving Width
(feet)
|
Curbing
|
---|
|
Primary arterial
|
80
|
50
|
Required
|
|
Collector
|
60
|
40
|
Required
|
|
Residential
|
50
|
30
|
Required
|
|
Cul-de-sac
|
50
|
30
|
Required
|
(2)
Additional widths may be required by the Borough:
(a)
Where necessary for public safety and convenience.
(b)
For parking in commercial or industrial areas.
(c)
Where older streets do not provide the proper width and additional
dedication is necessary.
(3)
Minimum right-of-way width for development along existing streets
shall correspond with the Official Street Map.
(4)
The area between an existing right-of-way line and the ultimate
right-of-way line should be offered for dedication to the Borough
when land is subdivided or developed along an existing right-of-way.
(5)
Splitter islands, refuge medians, channelization and other traffic
calming devices may be required in any area where traffic volumes
warrant their use for pedestrian and vehicular safety, and may be
permitted in any area at the discretion of the Borough Council. Such
devices on state roads must meet or exceed the requirements of the
Pennsylvania Department of Transportation Traffic Calming Manual.
(6)
A cul-de-sac will not be approved when a through street is practicable.
The developer or subdivider shall have the burden of showing the impracticability
of the through street in order to justify a cul-de-sac. A cul-de-sac
shall not be more than 500 feet in length except in cases approved
by Borough Council where conditions of the land so warrant the increase
in length. A cul-de-sac shall have a right-of-way of 50 feet and shall
have a circular turnaround with a minimum right-of-way radius of 50
feet and an outer paving radius of 40 feet.
(7)
Where it is proposed that a street be constructed to an abutting
property line with the intention that such a street will be extended
onto the property at a future date, a temporary circular turnabout
shall be built, wholly within the right-of-way. The right-of-way whether
permanent or temporary shall have a minimum radius of 50 feet, and
the cartway of the turnabout shall have a radius of 40 feet.
(8)
No fences, landscaping, expect for street shade trees, walls,
plantings or other obstructions shall be located or be permitted within
the right-of-way except for ground covers such as grass, ivy, crown-vetch,
or horizontally spreading shrubs less than one-foot high, or retaining
walls necessitated by street widening and constructed by the authority
having jurisdiction over the street.
D. Street Intersections.
(1)
Number of Intersections. No more than two streets shall cross
at the same point. When existing streets intersect at odd angles,
or have more than four approaches, the subdivider, developer or builder
shall be required to make corrective changes to eliminate the odd
angle or reduce the number of approaches to the intersection by curving
the lesser street.
(2)
Minimum Angle of Intersection. The minimum angle of intersections
shall be 90°.
(3)
Sight Distance. Proper sight lines should be maintained at all
intersections of streets. There shall be measured along the center
line a minimum clear sight triangle of 75 feet from the point of intersection.
No building, trees, hedge, shrubbery or other obstruction whatsoever
will be permitted in this area. Any obstruction to sight shall be
removed at the time a building or structure is erected, whichever
shall first occur.
(4)
Maximum Grade. Maximum grade within any intersection shall not
exceed 1% and approaches to an intersection shall follow a straight
horizontal course for 100 feet.
(5)
Approach Grades. All approaches to an intersection shall not
exceed 3% for a distance of 50 feet measured from the nearest right-of-way
line of the intersecting street.
(6)
Curbline Radii at Street Intersections. In an effort to limit
speeding and reduce the pedestrian crossing distance, the maximum
curbline radius of any street intersection shall be 15 feet.
E. Street Paving. All street paving must conform to the Conshohocken
Borough Construction Details and be approved by the Borough Engineer
prior to acceptance by Borough Council. All construction must be in
conformance with PennDOT Publication 408, latest edition.
[Ord. 7-2005, 7/13/2005]
Except where a structure was obviously built to house more than
one family, but where heretofore that structure and the surrounding
property was held in single and separate ownership, and further where
such a subdivision is proposed for the purpose of separating such
a structure into two or more ownership parcels, no subdivision or
land development will be approved with the property line extending
through any portion of any existing structure.
A. If structure(s) is to remain:
(1)
In residential zoning districts of the Borough, the lot and
lot dimensions of the newly created lot containing the structure(s)
must be consistent with the height and bulk of the structure, even
if this requires a lot area and/or dimensions exceeding the minimum
zoning requirement for that district.
(2)
In cases where the principal building use has not been as a dwelling, its conversion to a dwelling shall comply with all of the requirements of the Borough Zoning Ordinance [Chapter
27] and the Building Code [Chapter
5].
B. If existing structure(s) is to be removed: Subdivision or land development approval will be issued upon the condition of the expeditious removal of existing structures in complete conformity to all other Borough procedural requirements. In commercial and industrial areas, plots of land that have been cleared, as well as the existing vacant portions of such lands, should be developed in conformity with the long-range needs of the area to the extent possible and all developmental requirements embodied in the Building Code [Chapter
5] and zoning regulations shall be adhered to.
C. If existing structure is to be replaced or is to be added on to:
Demolition plans and/or construction plans must be detailed as part
of the subdivision or land development plan review and subsequent
plan approval will be conditional upon compliance with said proposed
details. Renovation work to the remaining portion of a structure following
partial demolition must be completed promptly and expeditiously.
[Ord. 7-2005, 7/13/2005; as amended by Ord. 9-2008, 12/17/2008;
and by Ord. No. 11-2022, 7/20/2022]
The applicant shall provide stormwater management in accordance with the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances, and as follows:
1. Purpose.
A. The objective of stormwater management is to prevent or mitigate
the adverse impacts related to the conveyance of excessive rates and
volumes of stormwater runoff. Further, the objectives of stormwater
management propose to maintain, as nearly as possible, natural runoff
flow characteristics, either by augmenting the infiltration process
or by temporarily storing stormwater for release at controlled rates
of discharge and/or intercepting runoff to reduce accelerated erosion
and sedimentation.
B. Applicants shall construct and/or install stormwater management facilities,
on site and off site, as necessary to meet the stormwater management
design and criteria provided by these and other Borough of Conshohocken
requirements and to:
(1)
Permit unimpeded flow of natural watercourses.
(2)
Ensure adequate drainage of all low points along the lines of
streets.
(3)
Intercept stormwater runoff along streets at intervals related
to the extent and grade of the area drained.
(4)
Provide positive drainage away from on-site sewage disposal
and structures.
(5)
Remove surface water from the bottom of vertical grades, lead
water from springs, and avoid excessive use of cross-gutters at street
intersections and elsewhere.
(6)
Ensure that the peak volume and rate of discharge from the development
site is no greater than prior to development.
(7)
Prevent erosion damage by controlling the rate and velocity
of runoff discharge to watercourses, avoid increasing the occurrence
of streambank overflow, and satisfactorily carry off, detain or retain,
and control the rate of release of stormwater.
(8)
Preserve bridges, culverts, and similar structures by suppressing
the new peak discharges created by new alteration or development of
land.
2. Applicability.
A. All regulated activities and all activities that may affect stormwater runoff are subject to regulation by this section and the requirements of the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances, which is included in these regulations by reference. Activities subject to these regulations include:
(3)
All sites of 0.5 acre or more.
(5)
Construction of new or additional impervious surfaces.
(6)
Construction of new buildings or additions to existing buildings.
(9)
Diversion or piping of any natural or man-made stream channel.
(10)
Installation of stormwater systems or appurtenances thereto.
(11)
Alteration of the natural hydrologic regime.
(12)
Nonstructural and structural stormwater management best management
practices (BMPs) or appurtenances thereto.
B. Stormwater management design and criteria such as stormwater runoff peak volume and rate requirements, runoff calculation methodology, stormwater management plan requirements, operations and maintenance requirements, storm sewer system design, stormwater BMP design, etc., shall be as described in this section and the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances.
C. The standards contained in this section shall apply as minimum design
standards; however, federal, state, and other Borough of Conshohocken
regulations may impose additional standards subject to their jurisdiction.
The more stringent requirements of this section, federal, state, and
other Borough of Conshohocken regulations shall apply to any activity
which requires compliance. Permits and approvals issued pursuant to
this section do not relieve the applicant of the responsibility to
secure required permits or approvals for activities regulated by any
other applicable code, rule, act or ordinance. Additional studies
and higher levels of control than the minimum provided in these and
other requirements may be required by Borough Council to ensure adequate
protection to life and property.
D. Earth disturbance activities and associated stormwater management
controls are also regulated under existing state law and implementing
regulations. This section shall operate in conjunction with those
parallel requirements; the requirements of this section shall be no
less restrictive in meeting the purposes of this section than state
law.
E. No associated construction activities within the Borough of Conshohocken
shall commence until the requirements of this section and all other
applicable stormwater management criteria are met.
F. All best management practices (BMPs) used to meet the requirements
of federal, state, and Borough of Conshohocken regulations shall conform
to the state water quality requirements and any more stringent requirements
as set forth by the Borough.
G. Retention of Existing Watercourses and Natural Drainage Features.
(1)
If an applicant concentrates dispersed stormwater flow or redirects
stormwater flow to exit at another location on the property, the applicant
is responsible for constructing an adequate stormwater conveyance
system on the adjacent property and on all downstream properties until
a natural outfall is reached. The natural outfall shall have sufficient
capacity to receive the stormwater without deterioration of the facility
and without adversely impacting property in the watershed. This natural
outfall may be a river, creek or other drainage facility so designated
by the Borough of Conshohocken for the proposed system.
(2)
Whenever a watercourse, stream or intermittent stream is located
within a site, it shall remain open in its natural state and location
and shall not be piped.
(3)
No stormwater runoff or natural drainage shall be so diverted
as to overload existing drainage systems (including existing stormwater
management facilities) or create flooding.
(4)
Borough Council may require an applicant to provide a permanent
easement along any watercourse located within or along the boundary
of any property subject to the regulations of this section. The purpose
of any such easement shall be for the maintenance of the channel of
any watercourse; and the terms of the easement shall prohibit excavation,
the placing of fill or structures and any alterations which may adversely
affect the watercourse. The applicant will retain the easement until
such time as one of the following is accomplished:
(a)
The easement is offered for dedication by the applicant and
accepted by the Borough of Conshohocken.
(b)
If an easement acceptable to the Borough is established, the
maintenance shall then be the responsibility of the individual lot
owners over whose property the easement passes. For land developments,
the maintenance shall then be the responsibility of the owner.
(c)
A homeowners' association or other approved legal entity,
approved by the Borough of Conshohocken, assumes responsibility for
the maintenance of the development, including the retention of the
watercourse easement.
3. Site Drainage Plan Requirements. The following site drainage plan
materials shall be submitted to the municipality in a format that
is clear, concise, legible, neat and well organized; otherwise, the
site drainage plan shall not be accepted for review and shall be returned
to the applicant:
A. General:
(1)
Provide a narrative including a description of the project,
erosion and sedimentation control, stormwater control for both during
and after construction, operation and maintenance requirements for
each facility with the responsible party, and expected project schedules.
(2)
If the subdivision or land development is to be developed in
stages, provide a general drainage plan for the entire subdivision
or land development with the first stage, and appropriate development
stages for the drainage system shall be indicated, in accordance with
Pennsylvania Department of Environmental Protection's Rules and
Regulations, Title 25, Chapter 102, as last revised.
(3)
Proof of required permits or approvals under applicable state
or federal regulations, including but not limited to PennDOT, Montgomery
County Conservation District, PADEP NPDES permit for stormwater discharges
from construction activities, and other PADEP permits.
B. Plans and Calculations:
(3)
Total acreage of the parcel(s) and area to be disturbed.
(4)
Existing and proposed two-foot contours, based on established
elevations or the U.S.G.S. datum, and all bodies of water, physical
features, underground utilities, proposed changes to land surface
and vegetative cover, areas to be cut and filled, and as required
by subdivision and land development regulations.
(5)
Pre- and postdevelopment mapping of all drainage areas (for
each point of interest, inlet, roof drain, etc.), watershed areas,
and floodplains in which the project is located.
(6)
Complete hydrologic and hydraulic computations for all storm
sewer and stormwater management techniques, facilities, and BMPs.
(7)
Complete drainage systems, including storage facilities where
required and identification of all existing drainage features which
are to be incorporated in the design.
(8)
Identification and delineation of all soil classifications with
the site, based on the Official Soil Survey provided by the U.S. Department
of Agriculture, Natural Resources Conservation Service, Web Soil Survey
(http://websoilsurvey.nrcs.usda.gov/), or a signed and sealed report
from a qualified professional licensed in the Commonwealth of Pennsylvania.
(9)
Identification of all infiltration test and soil boring locations.
(10)
Stormwater management facilities and BMPs, and appurtenances
with related details, calculations, assumptions, criteria used in
design.
(11)
Existing and proposed rights-of-way and easements, including
provisions for permanent access or maintenance easements for all physical
SWM BMPs as necessary to implement the operation and maintenance (O&M)
requirements.
4. Storm Sewer System Design. Storm sewer systems shall be required
to be constructed by the applicant in any area from which the surface
or subsurface drainage could impair public safety or cause physical
damage to adjacent lands or public property. The system shall be designed
to collect water at the bottom of all vertical grades, immediately
upgrade of all street intersections, and other areas where excessive
flow may occur. The system shall lead water from springs and avoid
excessive use of cross-gutters at street intersections and elsewhere.
A. All storm sewer system design shall be based on gravity flow using
the rational formula:
Q
|
=
|
Discharge/rate of flow in cubic feet per second.
|
C
|
=
|
Runoff coefficient.
|
I
|
=
|
Intensity of rainfall in inches per hour.
|
A
|
=
|
Watershed area in acres.
|
(1)
Runoff coefficients (C) for both existing and proposed conditions
for use in the Rational Method shall be consistent with Table 1 in
Appendix A of the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, at the Borough's Code of Ordinances.
(2)
The intensity of the storm shall be based on the 100-year frequency
storm with the inlet time of concentration equal to the storm duration
for any given point. The elevation of the hydraulic gradient at any
point in the storm sewer system shall be below the surface of the
ground during the 100-year storm event.
(3)
The rainfall data shall be obtained from the latest version
of the National Oceanic and Atmospheric Administration (NOAA) Atlas
14, rain data corresponding to the Conshohocken station for the precipitation
intensity using the upper bound of the ninety-percent confidence interval
for the various return period storms. If a hydrologic computer model
is used for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours. This data may also be directly retrieved from the
NOAA Atlas 14 website: http://hdsc.nws.noaa.gov/hdsc/pfds/orb/pa pfd
s.html.
(4)
A minimum five-minute time of concentration shall be used. Where
supported by the drainage area and related plans and calculations,
longer times of concentration for channel and pipe flow may be computed
using Manning's equation and utilizing roughness coefficients
consistent with Table 2 in Appendix A of the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances.
B. Storm Sewer Pipe.
(1)
The minimum slope of any pipe shall be 0.5%.
(2)
The minimum allowable pipe size is 18 inches. Where pipe cover
is restricted, equivalent elliptical pipe may be used in lieu of circular
pipe.
(3)
All storm sewer pipes shall be reinforced concrete pipe, smooth
lined high-density polyethylene, or other pipe material as may be
approved by the Borough Engineer.
(4)
Storm sewer pipes shall have a minimum cover of 24 inches. Greater
cover shall be provided where recommended by the pipe manufacturer.
(5)
Backflow preventers shall be provided where necessary to prevent
backwater from a watercourse from flowing into the storm sewer system.
C. Inlets and Manholes.
(1)
Inlets, manholes, and related tops, covers, grates, and frames
shall conform to Pennsylvania Department of Transportation specifications.
The type to be used shall depend on the particular application.
(2)
Sufficient inlets shall be located and constructed so as to
collect all of the flow in the contributory drainage area. Spread
of runoff in gutters shall not exceed eight feet in width or 1/2 of
the travel lane, whichever is lesser, during a ten-year storm event.
Calculations of inlet capacities shall be in accordance with Pennsylvania
Department of Transportation guidelines.
(3)
The gutter of all inlets shall be set not less than two inches,
nor more than four inches, below the gutter grade. The surface of
the paving adjacent to the inlets shall be constructed to blend into
the lowered gutter grade at the inlet in such a manner that sudden
drop-off or dip at the inlet will not be created.
(4)
Where surface water is collected from two directions at one
street corner, inlets shall be placed at or near the tangent points
of both ends of the radius. The use of an inlet in the radius shall
not be allowed.
(5)
Abrupt changes in direction or slope of storm sewer pipe shall
be avoided. An inlet or manhole shall be provided at all points where
there is a horizontal deflection, change in grade, transition in pipe
size, and convergence of two or more influent pipes.
(6)
The spacing of inlets and manholes shall not exceed a maximum
distance of 400 feet along any one continuous line. Inlets shall be
provided in lieu of manholes where they will serve a useful purpose.
D. Drainage Channels and Swales.
(1)
The design standards for drainage channels and swales shall
follow the PADEP Erosion and Sediment Pollution Control Manual, latest
edition (PA E&S Manual) as a minimum guide.
(2)
All drainage channels and swales shall be designed to carry
the peak flow from the 100-year design storm with a minimum six inches
of freeboard.
(3)
All drainage channels and swales shall be designed to prevent
erosion of the channel bed and bank areas and provide suitable stabilization
to prevent erosion. The maximum permissible flow velocity shall not
exceed those outlined in Table 6.4 Maximum Permissible Velocities
(ft/sec) of Channels Lined with Vegetation and its additional notes
of the PA E&S Manual.
(4)
Design shall be based on the Manning equation and utilize roughness
coefficients consistent with Table 2 in Appendix A of the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances.
(5)
Drainage channels and swales shall be designed to conform, wherever
possible, to the adjacent average ground conditions. This means that
the channel or swale should not be projecting excessively above the
surrounding ground or placed excessively below the surrounding ground.
(6)
Drainage channels and swales shall have a maximum side slope
of three horizontal to one vertical and shall have adequate slope
protection as required by the Borough Engineer.
(7)
No open watercourses shall be permitted within the rights-of-way
of any street or alley.
E. Endwalls. Endwalls conforming to Pennsylvania Department of Transportation
specifications shall be installed on all influent and effluent pipes.
F. Bridges and Culverts. Single opening culverts are desirable. The
design of all bridges and culverts shall be such as to minimize the
probability of debris accumulation. Bridges and culverts shall be
designed to meet current Pennsylvania Department of Transportation
standards to support expected loads and carry the peak flow from a
100-year design storm. They shall be constructed for the full width
of the right-of-way.
G. Roof Drains and Sump Pumps.
(1)
Roof drains and sump pumps shall discharge to a stormwater BMP
wherever feasible. Where it is more advantageous to connect to streets
or sewers, connections may be permitted on a case-by-case basis as
determined by the Borough.
(2)
Roof drain and sump pump pipes shall not discharge water over
a sidewalk but shall extend under the sidewalk to the gutter.
(3)
A solid lid cleanout shall be provided for all roof drains and
sump pumps, located within the lot between the contributing building
or structure and the right-of-way.
5. Stormwater BMP Design. Whenever an increase in runoff volume and/or rate would occur as the result of regulated activities, the applicant will be required to provide permanent stormwater management BMPs to attain zero increase in runoff and address the requirements of this section, the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances, and any other requirements of the Borough of Conshohocken, except as may otherwise be exempted.
A. Storage Requirements.
(1)
The storage requirements of all stormwater BMPs shall be computed in accordance with the requirements of the Borough of Conshohocken Stormwater Management Ordinance, codified at Chapter
19, Stormwater Management, of the Borough's Code of Ordinances, and must be submitted to the Borough Engineer for review and, when required, to the Montgomery County Conservation District, Pennsylvania Department of Environmental Protection, the Pennsylvania Department of Transportation, and/or other agencies.
(2)
The volume of storage provided shall be no less than the total
additional volume of runoff due to regulated activities based on a
100-year frequency twenty-four-hour duration storm. Except in the
case where 1,000 square feet or less of impervious area is being added
to the site, an additional storage allowance of 218 cubic feet must
be provided to compensate for sediment accumulation.
(3)
In addition to the permanent storage facilities, the applicant
must provide adequate erosion and sedimentation control measures in
accordance with the Pennsylvania Clean Stream Act, and Pennsylvania Department of Environmental Protection
Rules and Regulations, Title 25, Chapter 102, as last revised.
(4)
The design of any stormwater storage facility shall be verified
by routing the design storm hydrographs using the Storage-Indication
Method. A storage versus elevation versus discharge curve shall be
included, along with a routing of the postdevelopment 100-year storm.
(5)
The maximum 100-year water surface elevation associated with
each BMP shall be calculated and shown to be contained within the
provided storage volume of the BMP.
(6)
All aboveground storage areas must be located outside of the
100-year floodplain. All underground storage areas must be located
a minimum of 24 inches above the groundwater and seasonal high water
table elevations.
(7)
All stormwater BMPs shall be designed with an overflow or spillway
which safely permits the passing of runoff greater than that occurring
during the postdevelopment 100-year design storm in a nonerosive manner.
The overflow or spillway shall be set above the maximum proposed ponding
depth for the 100-year storm.
(8)
All stormwater BMPs shall be designed to completely dewater
the stored water volume within 72 hours from the end of the design
storm, with the exception that an underground Managed Release Concept
BMP shall dewater within seven days from the end of the design storm
and other longer dewatering times as permitted by the Pennsylvania
Stormwater Best Management Practices Manual, December 2006, as amended
(PA BMP Manual) for non-open-air BMPs.
B. BMPs which may be used to meet the applicable standards are described
in this section and the volume peak rate reduction by infiltration
BMPs, volume peak rate reduction BMPs, and the nonstructural BMP credits
sections from the PA BMP Manual. Any selected BMP must meet or exceed
these standards and shall incorporate sound and accepted engineering
principles and practices.
(1)
No more than 25% of volume reduction may be met through nonstructural
BMP credits. In order to permit utilization of the volume reduction
credit, a completed copy of the related checklist from the PA BMP
Manual must be provided to demonstrate that the selected nonstructural
BMP is applicable to the project.
(2)
An impermeable liner is required where the possibility of groundwater
contamination exists. A detailed hydrogeologic investigation may be
required.
C. Design Criteria for Infiltration BMPs. Infiltration BMPs shall be
designed in accordance with the design criteria and specifications
in the PA BMP Manual and shall meet the following minimum requirements:
(1)
A detailed infiltration testing and soils evaluation of the
project site shall be performed by the applicant to determine and
support the suitability of all infiltration BMPs. The evaluation shall
meet the following requirements:
(a)
The evaluation shall be performed by a qualified professional
and, at a minimum, address soil permeability, hydrologic soil groups,
depth to limiting zones, karst/susceptibility to sinkhole formation,
subgrade stability, and natural and man-made features within the site
to determine general areas of suitability for infiltration practices.
(b)
Provide field tests, such as double-ring infiltrometer or hydraulic
conductivity tests, at the level of the proposed infiltration surface
(bottom surface of the infiltration facility) to determine the appropriate
hydraulic conductivity rate. Percolation tests will not be accepted
for infiltration BMP design purposes.
(c)
A minimum depth of 24 inches shall be provided between the bottom
of an infiltration BMP and the top of bedrock, seasonal high water
table, groundwater, or other limiting zone.
(d)
An infiltration rate sufficient to accept the additional stormwater
load and dewater completely as determined by field tests. A minimum
infiltration rate of 0.2 inch/hour is required and then a minimum
safety factor of two should be applied for design purposes (e.g.,
for soil which measured 0.4 inch/hour, the BMP design should use 0.2
inch/hour). Greater safety factors may be required by the Borough
Engineer based on the site conditions.
(e)
Design the infiltration structure based on field-determined
capacity at the level of the proposed infiltration surface and based
on the applied safety factor.
(2)
The maximum side slopes of an aboveground infiltration BMP shall
be three horizontal to one vertical. Every effort should be made to
blend aboveground storage areas into the natural topography of its
surroundings.
(3)
Infiltration BMPs shall have a bottom slope of no greater than
1% but shall preferably have a level bottom.
(4)
The infiltration system shall have positive overflow controls
to prevent storage within one foot of the finished surface elevation
above the facility.
(5)
Surface inflows shall be designed to prevent direct discharge
of sediment into the infiltration system.
(6)
A minimum of 10 feet of undisturbed fill or compacted impermeable
material shall separate the foundation wall of any building and an
infiltration BMP.
(7)
A minimum of 50 feet of undisturbed fill or compacted impermeable
material shall separate water supply wells and an infiltration BMP.
(8)
A minimum of 50 feet shall separate a septic system disposal
area and an infiltration BMP unless specific circumstances allow for
a reduced separation distance.
D. Design Criteria for Underground BMPs. Underground BMPs shall be designed
in accordance with the design criteria and specifications in the PA
BMP Manual and shall meet the following the minimum requirements:
(1)
Underground BMPs shall have a bottom slope of no greater than
1% but shall preferably have a level bottom.
(2)
At a minimum, the top and sides of the underground BMP shall
be wrapped in a nonwoven geotextile which provides separation between
the storage volume and the surrounding materials. Providing nonwoven
geotextile on the bottom of the underground BMP is optional and shall
be determined by a qualified professional based on site conditions.
Where required due to the possibility of groundwater contamination,
an impermeable liner will be accepted in place of the nonwoven geotextile.
(3)
A minimum of one foot of cover shall be provided, measured from
the top of the system to the finished surface elevation.
(4)
Storage within the aggregate, soil, or other material above
and surrounding the underground BMP shall not be considered in the
calculation of the underground BMP storage volume.
(5)
Maintenance access to permit long-term operation and maintenance
shall be incorporated into the design.
(6)
Where an underdrain is provided, a separate maintenance cleanout
and minimum six-inch-deep stone envelope wrapped in geotextile shall
be provided.
E. Design Criteria for Bioretention BMPs. Bioretention BMPs, including
rain gardens, shall be designed in accordance with the design criteria
and specifications in the PA BMP Manual and shall meet the following
the minimum requirements:
(1)
All concentrated discharges directed to a bioretention facility
shall be conveyed through a pretreatment filter strip. The filter
strip shall be designed to reduce the incoming velocities and to filter
out coarser sediment particles. Examples of pretreatment filter strips
include sand or gravel diaphragms, grass swales, sand filters, stone
check dams, etc.
(2)
All bioretention facilities shall incorporate a mix of trees,
shrubs, and/or herbaceous plants. Plant species shall be native and
selected based on the ability to tolerate stresses such as pollutants,
variable soil moisture, and ponding fluctuations.
(3)
A minimum planting soil bed depth of two feet for herbaceous
plants and three feet for trees and shrubs shall be provided. Planting
soil shall be capable of supporting healthy vegetative cover.
(4)
All bioretention facilities shall incorporate an organic mulch
layer. The organic mulch layer shall be standard landscape style,
single or double, shredded hardwood mulch or chips. The mulch layer
shall be well-aged, uniform in color, and free of other materials
such as weed seed, soil roots, etc. The mulch layer shall be applied
to maximum depth of three inches. Grass clippings shall not be used
as mulch material.
(5)
The maximum side slopes of bioretention BMPs shall be three
horizontal to one vertical.
(6)
A minimum grade of 2% shall be maintained for areas of sheet
flow. For channel flow, a minimum grade of 1% shall be maintained.
For bioretention facilities relying on infiltration for drainage,
rather than sheet or channel flow, a level bottom is permitted.
(7)
Bioretention facilities with an aboveground ponding depth greater than 2.5 feet during any postdevelopment design storm, or as directed by the Borough Engineer based on the storage volume, shall be designed in accordance with the requirements of §
22-410, Subsection
5F.
F. Design Criteria for Aboveground Basins. Aboveground basin BMPs shall
be designed in accordance with the design criteria and specifications
in the PA BMP Manual and shall meet the following the minimum requirements:
(1)
Whenever possible, the side slopes and basin shape shall conform
to the natural topography. When such design is impractical, the construction
of the basin shall utilize slopes as flat as possible to blend the
structure into the terrain. The maximum side slopes of the earthen
basin embankments shall be three horizontal to one vertical.
(2)
A minimum grade of 2% shall be maintained for areas of sheet
flow. For channel flow, a minimum grade of 1% shall be maintained.
For basins relying on infiltration for drainage, rather than sheet
or channel flow, a level bottom is permitted.
(3)
The top or toe of any slope shall be located a minimum of five
feet from any property line.
(4)
A minimum ten-foot-wide flat area shall be provided at the top
of the basin berm.
(5)
The maximum permitted aboveground ponding depth during any postdevelopment
design storm is five feet.
(6)
If permanent ponds are used, the applicant shall demonstrate
that such ponds are designed to protect the public health and safety.
(7)
All aboveground basins shall be provided with a primary outlet
and emergency spillway.
(8)
A cutoff trench shall be provided along the center line of any
dam or earth fill embankments. The trench shall have a bottom width
of not less than four feet, but adequate to allow use of equipment
necessary to obtain proper compaction. Side slopes of the cutoff trench
shall be no steeper than 1:1 ratio. The trench shall be filled with
successive thin layers of relatively impervious material, each layer
being thoroughly compacted.
(9)
All basin embankments shall be placed in lifts not to exceed
eight inches in thickness and each lift shall be compacted to a minimum
of 95% of modified proctor density as established by ASTM D-1557.
Prior to proceeding to the next lift, the compaction shall be checked
by a soils engineer hired by the applicant. Compaction tests shall
be run on the leading and trailing edge of the berm along with the
top of the berm. Verification of required compaction shall be submitted
to the Borough prior to utilization of any aboveground basin for stormwater
management.
G. Primary Spillway/Outlet Pipes.
(1)
The sizing of the outlet pipe shall be based on the postconstruction
100-year storm without utilizing the emergency spillway.
(2)
The pipe barrel and riser shall be solidly attached and placed
on a firm foundation. The fill material around the primary spillway
shall be placed in four-inch lifts and compacted to at least the same
density as the adjacent embankment.
(3)
All outlet pipes through a basin berm shall be reinforced concrete
pipe with watertight joints.
(4)
Anti-seep collars shall be installed around the pipe barrel
within the normal saturation zone of the basin berms and shall be
poured in place.
(a)
The anti-seep collars and their connections to the pipe barrel
shall be watertight.
(b)
The anti-seep collars shall extend a minimum of two feet beyond
the outside of the principal pipe barrel.
(c)
The maximum spacing between the collars shall be 14 times the
minimum projection of the collar measured perpendicular to the pipe.
(d)
A minimum of two anti-seep collars shall be installed on each
outlet pipe.
(5)
All outlet pipes shall have endwalls and energy dissipating
devices (riprap, end sills, etc.) designed in accordance with the
Pennsylvania Department of Environmental Protection's Erosion
and Sediment Pollution Control Program Manual No. 363-2134-008, as
amended and updated (PA E&S Manual).
H. Emergency Spillways.
(1)
The minimum capacity of the emergency spillway shall be the
peak flow rate into the BMP from the postdevelopment 100-year design
storm. In no case shall the emergency spillway be utilized in the
design routing of the postdevelopment 100-year storm.
(2)
Whenever possible, the emergency spillway shall be constructed
on undisturbed ground. The emergency spillway shall not discharge
over earthen fill and/or easily eroded material. Emergency spillways
constructed on undisturbed ground may be constructed of reinforced
vegetated earth with supporting calculations. All other spillways
shall be constructed of concrete, riprap, concrete checkerblocks,
or similar materials approved by the Borough Engineer.
(3)
All emergency spillways shall be constructed to protect against
erosion. The construction material of the emergency spillways shall
extend along the upstream and downstream berm embankment slopes. The
upstream edge of the emergency spillway shall be a minimum of three
feet below the spillway crest elevation. The downstream slope of the
spillway shall, at a minimum, extend to the toe of the berm embankment.
(4)
The minimum freeboard through any emergency spillway shall be
one foot; "freeboard" is defined as the difference between the design
flow elevation through the spillway and the elevation of the top of
the BMP or berm. Six inches, minimum, is required between the postconstruction
100-year water surface elevation in a basin and the emergency spillway
crest. The minimum depth of an emergency spillway shall be two feet.
I. Sediment basins and sediment traps for sediment control during construction
shall be designed in accordance with the PA E&S Manual.
[Ord. 7-2005, 7/13/2005]
All development proposed within a flood-prone areas shall be
subject to the Borough Floodplain Conservation Ordinance.
[Ord. 7-2005, 7/13/2005]
All land developments shall include open space and outdoor recreational
areas for site employees and visitors. These facilities may include
one or more of the following:
A. Landscaped walkways and pathways.
B. Landscaped plazas, civic spaces, sitting areas.
D. Public access to preserved natural features areas, including large
trees, groves, waterways, scenic areas, historical buildings or areas,
and other amenity areas.
[Ord. 7-2005, 7/13/2005]
All land developments, especially those along the Schuylkill
River Trail, shall include provisions that encourage the use of bicycles.
These facilities may include one or more of the following:
C. Employee showers and changing rooms.
[Ord. 7-2005, 7/13/2005]
All subdivisions and land development proposals shall be required
to indicate the closest public transit route. When a public transit
route operates directly adjoining a subdivision or land development,
appropriate transit stop and shelter shall be provided. When a subdivision
or land development encompasses an exiting transit stop, said facility
shall also be upgraded. Transit stops shall include, at a minimum,
a shelter or enclosure, seating and route maps and schedule information.