All stormwater management, collection, conveyance, erosion control,
and floodplain considerations shall be accomplished in accordance
with the following provisions:
A.
Prior to the final approval of any subdivision or land development
plan, or the commencement of any regulated activity within the jurisdiction
of this chapter, the developer shall submit a stormwater management
site plan to the Borough for approval.
(1)
When plan applications, whether preliminary or final, are submitted
in sections, a generalized stormwater management site plan for the
entire project site shall be submitted in addition to the detailed
stormwater management site plan for the proposed section. This generalized
plan shall demonstrate how the stormwater of the proposed section
will relate to the entire development. The amount and velocity at
the discharge point of the section shall be included in the data submitted.
If temporary facilities are required for construction of a section,
such facilities shall be included in the submitted plans.
(2)
The type, location and extent of all erosion and sedimentation control measures shall be shown on an erosion and sedimentation pollution control plan that conforms to the requirements of the Soil Erosion and Sedimentation Control Manual of the Pennsylvania Department of Environmental Protection and the Design Standards of § 187-26 of this chapter.
(3)
An ownership and maintenance program shall be submitted, in recordable
form acceptable to the Borough, that clearly sets forth the ownership
and maintenance responsibility of all temporary and permanent stormwater
management facilities and erosion and sedimentation control facilities,
including:
(a)
Description of temporary and permanent maintenance requirements;
(b)
Identification of a responsible individual, corporation, association,
or other entity for ownership and maintenance of both temporary and
permanent stormwater management and erosion and sedimentation control
facilities;
(c)
Provisions for permanent access or maintenance easements for
all existing and proposed physical SWM facilities and BMPs, such as
ponds and infiltration structures, as necessary to implement the operation
and maintenance (O&M) plan. All such agreements shall be duly
recorded in the office of the Recorder of Deeds and shall constitute
a binding permanent covenant upon the property, superior to all liens
of record and not subordinate to any easement or restriction that
would interfere with its provisions and the implementation thereof.
(d)
The intent of these regulations is to provide private ownership
and maintenance of stormwater management and erosion and sedimentation
control facilities. Where the Borough Council accepts dedication of
stormwater management facilities, the Borough Council may require
the developer to establish, at the time of dedication, a maintenance
fund, in an amount determined by the Borough, adequate for the perpetual
care of such facilities.
(4)
A written report shall be submitted that includes the following information:
(a)
Stormwater runoff calculations for both predevelopment and post-development
conditions.
(b)
An erosion and sedimentation pollution control plan narrative
that conforms to the requirements of the Soil Erosion and Sedimentation
Control Manual of the Pennsylvania Department of Environmental Protection
and provides a description of all erosion and sedimentation control
measures, temporary as well as permanent, including the staging of
earthmoving activities, sufficient in detail to clearly indicate their
function.
(c)
A general description of the development site, including a description
of existing natural and hydrologic features and any environmentally
sensitive areas.
(d)
A general description of the overall SWM concept for the project,
including a description of permanent SWM techniques, nonstructural
BMPs to be employed and construction specifications of the materials
to be used for structural SWM facilities.
(e)
For all proposed detention basins and retention basins, except
temporary sedimentation basins, the documentation shall include a
plotting or tabulations of storage volumes with corresponding water
surface elevations and the outflow rates for those water surfaces.
(f)
For all proposed detention basins and retention basins, except
temporary sediment basins, documentation shall set forth the design
hydrograph, the shortcut routing method or a method of equal caliber
acceptable to the Borough Engineer, utilized to determine the function
of the basin.
B.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
C.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be relocated and shall be subject to any
applicable discharge criteria specified in this chapter.
D.
Where a development site is traversed by watercourses other than
permanent streams, a drainage easement shall be provided conforming
substantially to the line of such watercourses. The terms of the easement
shall prohibit excavation, the placing of fill or structures, and
any alterations that may affect adversely the flow of stormwater within
any portion of the easement. Also, maintenance of vegetation within
the easement shall be required.
E.
The PADEP Chapter 105 Rules and Regulations apply to the construction, modification, operation, or maintenance of both existing and proposed water obstructions and encroachments throughout the watershed, including work in wetlands. Inquiries on permit requirements or other concerns shall be addressed to DEP's regional office.
F.
When it can be shown that, due to topographic conditions, natural
drainageways on the development site cannot adequately provide for
drainage, open channels may be constructed conforming substantially
to the line and grade of such natural drainageways. Work within natural
drainageways shall be subject to approval by DEP through the joint
permit application process, or, where deemed appropriate by DEP, through
the general permit process.
G.
If diffused flow is proposed to be concentrated and discharged onto
adjacent property, the applicant must document that adequate downstream
conveyance facilities exist to safely transport the concentrated discharge,
or otherwise prove that no erosion, sedimentation, flooding, or other
harm will result from the concentrated discharge. The applicant must
provide an executed easement for newly concentrated flow across adjacent
properties.
H.
Any stormwater management facilities or any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures, etc.) that are regulated by this chapter, that will be located in or adjacent to waters of the commonwealth (including wetlands), shall be subject to approval by DEP under regulations at 25 Pa. Code Chapter 105 through the joint permit application process, or, where deemed appropriate by DEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the applicant or his agent to show that the land in question cannot be classified as wetlands; otherwise, approval to work in the area must be obtained from DEP.
J.
When stormwater management facilities are proposed within 1,000 feet
of a downstream Borough, the stormwater analysis shall be submitted
to the downstream Borough's Engineer for review and comment.
K.
Roof drains shall not be connected to sanitary or storm sewers. When
it is more advantageous to connect directly to streets or storm sewers,
then the Borough shall permit it on a case-by-case basis.
L.
Any stormwater management facilities regulated by this chapter that
will be located on or discharged onto state highway rights-of-way
shall be subject to approval by PennDOT.
M.
Stormwater management facilities located within or affecting the
floodplain of any watercourse shall comply with the requirements of
the floodplain regulations provided in the Zoning Ordinance or any
future ordinances regulating construction or development within areas
of the Borough subject to flooding.
N.
The minimum floor elevations for all structures that would be affected
by a basin, other temporary impoundments, or open conveyance systems
where ponding may occur shall be two feet above the one-hundred-year
water surface. If basement or underground facilities are proposed,
detailed calculations addressing the effects of the stormwater ponding
on the structure and waterproofing and/or floodproofing design information
shall be provided for review and approval.
O.
Stormwater BMPs shall be encouraged. They shall be located, designed,
and constructed in accordance with the latest technical guidance published
by PADEP, provided they are accompanied by detailed engineering plans
and performance capabilities and supporting site-specific soils, geology,
runoff and groundwater and infiltration rate data to verify proposed
designs. Additional guidance from other sources may be accepted at
the discretion of the Borough Engineer (a preapplication meeting is
suggested).
P.
All existing and natural watercourses, channels, drainage systems,
and areas of surface water concentration shall be maintained in their
existing condition unless an alteration is approved by the appropriate
regulatory agency.
Q.
No outlet structure from a stormwater management facility shall discharge
directly onto a Borough or state roadway.
R.
Infiltration BMPs intended to receive runoff from regulated activities
shall be selected based on suitability of soils and site conditions
and shall be constructed on soils that have the following characteristics:
(1)
A minimum depth of 24 inches between the bottom of the facility and
the limiting zone, unless it is demonstrated to the satisfaction of
the Borough that the selected BMP has design criteria which allow
for a smaller separation.
(2)
A stabilized infiltration rate sufficient to accept the additional
stormwater load and drain completely as determined by field tests
conducted by the applicant's professional designer. The stabilized
infiltration rate is to be determined in the same location and within
the same soil horizon as the bottom of the infiltration facility.
The stabilized infiltration rate is to be determined as specified
in the BMP Manual.
S.
Stormwater discharge points onto an adjacent property shall comply
with the following:
(1)
Stormwater runoff from a project site shall flow directly into a
natural watercourse or into an existing storm sewer system. If neither
of these is available, the applicant shall obtain an easement from
the downstream landowner(s) to allow the site's runoff discharge to
reach a natural watercourse or an existing storm sewer system through
the easement. If an easement is obtained, post-developed flow characteristics
must be similar to or better than the runoff characteristics (spread,
velocity, and peak rate) of the predeveloped flows. The easement from
the downstream property owner(s) shall be to allow for a piped storm
sewer system, an overland flow system, or a combination of the two.
The downstream system design shall conform to the design requirements
of this chapter.
(2)
When the applicant provides verification that the downstream landowner(s)
refuses to grant an easement at reasonable terms in the sole opinion
of the Borough, the site shall be designed such that the discharge
from the applicant's site shall be in a nonerosive, sheet flow condition.
For all design year storms, including the one-hundred-year storm,
runoff from the applicant's site shall flow onto the adjacent property
in a manner similar to the runoff characteristics (spread, velocity,
and peak rate) of the predeveloped flow. The use of level spreaders
is prohibited.
(3)
Stormwater runoff shall not be transferred from one watershed to
another unless the watersheds are subwatersheds of a common watershed
which join together within the perimeter of the property, or both
of the following apply:
T.
Unless an alternate design is submitted to the Borough for review,
and said design is prepared by a licensed (in the Commonwealth of
Pennsylvania) geologist or geotechnical engineer:
(1)
No stormwater facilities shall be placed in, over or within a distance
that will impact the following features:
(2)
The minimum isolation distance from stormwater management facilities
to the listed geologic features shall be as follows:
(3)
Stormwater runoff from any regulated activity shall not be discharged
into sinkholes.
(4)
It shall be the developer's responsibility to verify if the development
is underlain by carbonate geology. The following note shall be attached
to all stormwater management site plans and signed and sealed by the
developer's qualified professional:
"I, __________, certify that the proposed detention basin is/is
not (circle one) underlain by carbonate geology."
(5)
Whenever a stormwater facility will be located in an area underlain by carbonate geology, a geological evaluation of the proposed location by a registered professional geologist shall be conducted to determine susceptibility to sinkhole formation. The evaluation may include the use of impermeable liners to reduce or eliminate the separation distances listed in § 187-25T(2).
U.
All stormwater runoff flowing over the project site shall be considered
in the design of the stormwater management facilities.
V.
The calculated peak rates of runoff for stormwater originating on
the project site must meet one the following conditions, for all watersheds
flowing from the project site:
(1)
Match predevelopment hydrograph. Developers and/or landowners are encouraged to provide infiltration facilities or utilize other techniques which will allow the post-development one-hundred-year hydrograph to match the predevelopment one-hundred-year hydrograph, along all parts of the hydrograph, for the development site. To match the predevelopment hydrograph, the post-development peak rate must be less than or equal to the predevelopment peak rate, and the post-development runoff volume must be less than or equal to the predevelopment volume for the same storm event. A shift in hydrograph peak time of up to five minutes and a rate variation of up to 5% at a given time may be allowable to account for the timing effect of BMPs used to manage the peak rate and runoff volume. This option is most feasible for small subdivisions in areas of noncarbonate geology. Incorporating the volume control requirements as given in § 187-30 can be used as part of this option.
(2)
Where the predevelopment hydrograph cannot be matched, one of the
following shall apply:
(a)
For areas covered by a release rate map from an approved Act
167 plan, the post-development peak discharge rates for the two-,
ten-, twenty-five-, fifty-, and one-hundred-year storm events (a twenty-four-hour
SCS type storm or an IDF Curve Rational Method storm) will follow
the applicable approved release rate maps.
(b)
For areas not covered by a release rate map from an approved
Act 167 plan, post-development runoff from any regulated activity
shall not exceed the peak rates of runoff prior to development for
all design storms (two-, ten-, twenty-five-, fifty-, and one-hundred-year
storm events) except where the post-development hydrograph does not
exceed the predevelopment hydrograph at all points in time for all
design storms.
(3)
Infiltration. Developers and/or landowners are encouraged to provide
infiltration facilities or utilize other techniques which will allow
the post-development hydrograph to match the predevelopment hydrograph,
along all parts of the hydrograph for the site. This option is most
feasible for small subdivisions in areas of noncarbonate geology.
(4)
Developers have the option to propose a regional stormwater management
plan or participate in a regional stormwater management plan developed
by others. A regional stormwater management plan may include off-site
volume and rate control, as appropriate and supported by a detailed
design approved by the Borough. A regional stormwater management plan
must meet all of the volume and rate control standards required by
this chapter for the area defined by the regional stormwater management
plan, but not necessarily for each individual development site. Appropriate
agreements must be established to ensure the requirements of this
chapter and the requirements of the regional stormwater management
plan are met.
W.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity. Staging of earthmoving activities and selection of construction
equipment should consider this protection.
X.
Infiltration BMPs shall not be constructed nor receive runoff from
disturbed areas until the entire contributory drainage area to the
infiltration BMP has achieved final stabilization.
A.
The applicant shall meet requirements as contained in 25 Pa. Code,
Chapters 92 and 102, as required and applicable as follows:
B.
Evidence of any necessary plan or permit approval for earth disturbance
activities from PADEP or the LCCD must be provided to the Borough.
C.
The Borough shall receive simultaneous copies of plans, reports,
applications, and other documents submitted to the LCCD for review.
D.
A copy of the notice of termination for NPDES permits shall be provided
to the Borough once accepted by the LCCD.
E.
A copy of the approved erosion and sediment control plan and any
other permit, as required by PADEP or the LCCD, shall be available
at the project site at all times if required under Chapter 102.
F.
Approval of an erosion and sedimentation control plan by the Borough
shall not be construed as an indication that the plan complies with
the standards of any agency of the commonwealth.
G.
Construction of temporary roadways (e.g., for utility construction,
timber harvesting, etc.) shall comply with all applicable standards
for erosion and sedimentation control and stream crossing regulations
under 25 Pa. Code, Chapters 102 and 105.
H.
The erosion and sedimentation control plan shall be submitted to
the LCCD for approval and shall address the following, as applicable:
(1)
Design of the roadway system, including haul roads, skid roads, landing
areas, trails, and storage and staging areas.
(2)
Runoff control structures (e.g., diversions, culverts, detention
ponds, etc.).
(3)
Stream crossings for both perennial and intermittent streams.
(4)
Access to public roadways, including design of rock construction
entrance for mud and debris control.
(5)
A remediation plan for restoring the disturbed area through regrading,
topsoil placement, reseeding, and other stabilization techniques,
as required.
I.
In accordance with Chapter 102, temporary facilities shall be included
in the submitted plans for a phased section where the following conditions
are met:
Methods shall be selected by the qualified person based on the
individual limitations and suitability of each method for a particular
site. The methods of computation used to determine peak discharge
and runoff shall be:
A.
The Soil-Cover-Complex Method (as set forth in the latest edition
of Urban Hydrology for Small Watersheds, Technical Release No. 55,
as published by NRCS, formerly SCS) may be used for all detention
facilities with a drainage area greater than or equal to 60 acres.
This method is recommended for design of stormwater management facilities
and where stormwater runoff volume must be taken into consideration.
B.
The Rational Method may be used for drainage areas up to 60 acres.
Extreme caution should be used by the qualified person if the watershed
has more than one main drainage channel, if the watershed is divided
so that hydrologic properties are significantly different in one watershed
versus the other, if the time of concentration exceeds 60 minutes,
or if stormwater runoff volume is an important factor. The combination
of Rational Method hydrographs based on timing shall be prohibited.
D.
If the NRCS/SCS Method (also known as the "Soil-Cover-Complex Method")
is used, the design storm volumes to be used in the analysis of peak
rates of discharge shall be obtained from the Precipitation-Frequency
Atlas of the United States, Atlas 14, Volume 2, Version 3.0, United
States Department of Commerce, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 14, United States can
be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/."
[Amended 9-13-2022 by Ord. No. 676]
(1)
Provide the rainfall used for the two-, ten-, twenty-five-, fifty-,
and one-hundred-year, twenty-four-hour storm events. Rainfall values
vary throughout the county depending on location.
(2)
Provide the location (longitude and latitude) or a description of
the location for which the rainfall applies.
(3)
If rainfalls from more than one location are used, provide the methodology
by which the design rainfall was calculated.
E.
If the SCS Method is used, Antecedent Moisture Condition 1 is to
be used in areas of carbonate geology, and Antecedent Moisture Condition
2 is to be used in all other areas. A Type II distribution shall be
used in all areas.
F.
If the Rational Method is used, the NOAA Atlas 14 data (see Subsection D above) shall be used to determine the rainfall intensity in inches per hour based on the information for the five- through sixty-minute duration storm events.
G.
Hydrographs may be obtained from NRCS methods such as TR-55, TR-20,
or from use of the "modified" or "unit hydrograph" rational methods.
If "modified" or "unit hydrograph" rational methods are used, the
ascending leg of the hydrograph shall have a time of three times the
time of concentration (3xTc), and the descending leg shall have a
time of seven times the time of concentration (7xTc) to approximate
an NRCS/SCS Type 2 hydrograph.
I.
Times of concentration shall be based on the following design parameters:
(1)
Sheet flow: The maximum length for each reach of sheet or overland
flow before shallow concentrated or open channel flow develops is
150 feet. Flow lengths greater than 100 feet shall be justified based
on the actual conditions at each development site. Sheet flow may
be determined using the nomograph in Appendix C-4 or Manning's kinematic
solution shown in the Sheet Flow section of Worksheet No. 1 in Appendix
C-5.[2]
[2]
Editor's Note: Appendix C is included as an attachment to
this chapter.
(3)
Open channel flows: At points where sheet and shallow concentrated
flows concentrate in field depressions, swales, gutters, curbs, or
pipe collection systems, the travel times and downstream end of the
development site between these design points shall be based upon Manning's
Equation and/or acceptable engineering design standards as determined
by the Borough Engineer.
J.
For the purpose of calculating predevelopment peak discharges, all
runoff coefficients, both on-site and off-site, shall be based on
actual land use assuming summer or good land conditions. Post-development
runoff coefficients for off-site discharges used to design conveyance
facilities shall be based on actual land use assuming winter or poor
land conditions.
K.
Design of on-site conveyance systems calculations may use the Rational
Method of Q=CIA where Q is the peak discharge of the watershed in
cubic feet per second, C is the coefficient of runoff, I is the intensity
of rainfall in inches per hour, and A is the area of the watershed
in acres; or any other method approved by the Borough.
L.
Runoff calculations shall include a hydrologic and hydraulic analysis
indicating volume and velocities of flow and the grades, sizes, and
capacities of water-carrying structures, sediment basins, and retention
and detention structures and sufficient design information to construct
such facilities. Runoff calculations shall also indicate both predevelopment
and post-development rates for peak discharge of stormwater runoff
from the project site.
M.
Runoff calculations will also be made to ensure that the runoff from
the upstream watershed area can be accommodated by the pipes, drainage
easements, watercourses, etc., on the site.
N.
Peak rate control is not required for off-site runoff. Off-site runoff
may be bypassed around the site, provided all other discharge requirements
are met. If off-site runoff is routed through rate control facilities,
runoff coefficients for off-site discharges used to design those rate
control facilities shall be based on actual land use assuming winter
or poor land conditions.
A.
All storm sewer pipes, grass waterways, open channels, swales, and
other water-carrying facilities that service drainage areas within
the site shall be designed to convey the twenty-five-year storm event
unless, in the opinion of the Borough or Borough Engineer, the character
of development and potential for damage warrant design for the fifty-
or one-hundred-year storm.
B.
Stormwater management facilities that convey off-site water through
the site shall be designed to convey the fifty-year storm event.
C.
All developments shall include provisions that allow for the overland
conveyance and flow of the post-developed one-hundred-year storm event
without damage to public or private property.
D.
Conveyance facilities shall comply with the design criteria in the
following table:
[Amended 9-13-2022 by Ord. No. 676]
|
Conveyance Facility Design Criteria
| ||||||
|---|---|---|---|---|---|---|
|
Location
|
Within Public Street
Ridght-of-Way
|
Outside Public Street Right-Of-Way
| ||||
|
Loading
|
All
|
Vehicular
Loading
|
Nonvehicular
Loading
| |||
|
(1)
|
Pipe design
| |||||
|
(a)
|
Material
|
SLHDPE, RCP
|
PVC, SLHDPE, RCP
|
PVC, SLHDPE, RCP
| ||
|
(b)
|
Slope (minimum)
|
0.5%
|
0.5%
|
0.5%
| ||
|
(c)
|
Cover
|
1 foot to stone subgrade
|
1 foot to stone subgrade
|
1 foot to surface
| ||
|
(d)
|
Diameter (minimum)
|
15 inches
|
15 inches
|
8 inches
| ||
|
(e)
|
Street crossing angle
|
75° to 90°
|
N/A
|
N/A
| ||
|
(f)
|
Access/ maintenance port frequency (maximum)
|
400 feet
|
400 feet
|
600 feet
| ||
|
(2)
|
Inlet design
| |||||
|
(a)
|
Material
|
Concrete
|
Concrete
|
N/A
| ||
|
(b)
|
Grate depression
|
0 inches
|
0 inches
|
0-inch minimum
| ||
|
(3)
|
Manhole design
| |||||
|
(a)
|
Material
|
Concrete
|
Concrete
|
Concrete
| ||
|
(4)
|
Swale design
| |||||
|
(a)
|
Freeboard (minimum)
|
6 inches
|
N/A
|
6 inches
| ||
|
(b)
|
Velocity (maximum)
|
Stability check
|
N/A
|
Stability check
| ||
|
(c)
|
Slope (minimum)
|
1%
|
N/A
|
1%
| ||
|
(d)
|
Side slopes (residential area)
|
4:1 max
|
N/A
|
4:1 max
| ||
|
(e)
|
Side slopes (nonresidential area)
|
4:1 max
|
N/A
|
3:1 max
| ||
|
(f)
|
Bottom width to flow depth ratio (maximum)
|
12:1
|
N/A
|
12:1
| ||
|
(5)
|
Outlet design
| |||||
|
(a)
|
End treatment
|
Headwall/ endwall
|
N/A
|
Headwall/endwall or flared end section
| ||
|
(b)
|
Energy dissipater
|
Required
|
N/A
|
Required
| ||
E.
All storm sewer pipes, culverts, manholes, inlets, endwalls, and
end sections shall be constructed in accordance with Pennsylvania
Department of Transportation, Form 408, as amended by Manheim Borough.
F.
Storm sewer pipes, culverts, manholes, inlets, endwalls, and end
sections proposed for dedication or located along streets shall conform
to the requirements of the Pennsylvania Department of Transportation,
Bureau of Design, Standards for Roadway Construction, Publication
No. 72, in effect and as amended by Manheim Borough at the time the
design is submitted.
G.
The roughness coefficient (Manning "n" values) used for conveyance
pipe capacity calculations shall be determined in accordance with
PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's
specifications.
H.
Endwalls and end sections shall be used where stormwater runoff enters
or leaves the storm sewer horizontally from a natural or man-made
channel.
I.
Inlets shall be placed on both sides of the street at low spots,
at changes in the horizontal or vertical directions of storm sewers,
and at points where the flow in gutters exceeds three inches. Inlets
shall normally be along the curbline at or beyond the curb radius
points. For the purpose of inlet location at corners, the depth of
flow shall be considered for each gutter. At intersections, the depth
of flow for the twenty-five-year storm across the through streets
shall not exceed one inch. Inlets shall be depressed two inches below
the grade of the road-side swale, curbline, or ground surface. An
access/maintenance port may either be an inlet or manhole. Manholes
may be substituted for inlets at locations where inlets are not required
to collect surface runoff.
J.
Material consistency and placement depths for storm sewer pipe backfill
shall be (at a minimum) per all applicable pipe manufacturer's recommendations,
further providing it should be free of large (not exceeding six inches
in any dimension) objectionable or detritus material.
K.
Within the public street right-of-way, the gutter spread based on
the twenty-five-year storm shall be no greater than 1/2 of the travel
lane and have a maximum depth of three inches at the curbline. A parking
lane shall not be considered as part of the travel lane. In the absence
of pavement markings separating a travel lane from the parking lane,
the parking lane shall be assumed to be seven feet wide if parking
is permitted on the street.
L.
Inlets or manholes shall be placed at all points of changes in the
horizontal or vertical directions of conveyance pipes. Curved pipe
sections are prohibited. Roof downspout leaders that are 8 inches
in diameter or less may use pipe fittings (e.g. elbows, wyes, tees,
etc.) at changes in direction.
[Amended 9-13-2022 by Ord. No. 676]
M.
All inlets placed in paved areas shall have heavy-duty, bicycle-safe
grating consistent with PennDOT Publication 72M, latest edition. A
note to this effect shall be added to the SWM site plan or inlet details
therein.
N.
Inlets, junction boxes, or manholes greater than five feet in depth
shall be equipped with nonaluminum ladder rungs and shall be detailed
on the SWM site plan.
O.
Where the connecting pipe has a diameter of 18 inches or greater,
headwalls and endwalls shall be provided with a protective barrier
device to prevent entry of the storm sewer pipe by unauthorized persons.
Such protection devices shall be designed to be removable for cleaning.
P.
Stormwater roof drains and pipes, wherever possible, shall discharge
water to encourage dispersion or infiltration and not into storm sewers
or street gutters.
Q.
All existing and natural watercourses, channels, drainage systems,
and areas of surface water concentration shall be maintained in their
existing condition unless an alteration is approved by the Borough.
R.
In addition to the material requirements in this section, culverts
designed to convey waters of the commonwealth may be constructed with
either a corrugated metal arch or a precast concrete culvert.
S.
Flow velocities from any storm sewer shall not result in a degradation
of the receiving channel.
T.
Energy dissipaters shall be placed at the outlets of all storm sewer
pipes where flow velocities exceed maximum permitted channel velocities.
U.
The capacities of swales shall be computed from the Manning Equation
using the following design parameters: Permissible open channel velocities
and design standards shall be in accordance with good engineering
practice as documented in the Engineering Field Manual for Conservation
Practices, USDA, SCS, or in Design Charts for Open-Channel Flow, Hydraulic
Design Series No. 3, United States Department of Transportation.
(1)
Vegetated swales:
(a)
The first condition shall consider swale stability based upon
a low degree of retardance ("n" = 0.03);
(b)
The second condition shall consider swale capacity based upon
a higher degree of retardance ("n" = 0.05); and
(c)
All vegetated swales shall have a minimum slope of 1% unless
otherwise approved by the Borough Engineer.
[Amended 9-13-2022 by Ord. No. 676]
(2)
The "n" factors to be used for paved or riprap swales or gutters
shall be based upon accepted engineering design practices, as approved
by the Borough Engineer.
[Amended 9-13-2022 by Ord. No. 676]
(3)
All swales shall be designed to maximize infiltration and concentrate
low flows to minimize siltation and meandering, unless geotechnical
conditions do not permit infiltration.
A.
Aboveground storage facilities shall consist of all stormwater facilities
which store, infiltrate/evaporate/transpire, clean or otherwise affect
stormwater runoff and the top of which is exposed to the natural environment.
Aboveground storage facilities shall be located above the finished
ground elevation. Aboveground storage facilities do not include stormwater
management facilities designed for conveyance or cisterns.
B.
Facilities with a facility depth greater than eight feet shall not
be permitted in residential areas.
C.
Aboveground storage facilities shall comply with the design criteria
in the following table:
|
Aboveground Storage Facility Design Criteria
| ||||||
|---|---|---|---|---|---|---|
|
Facility Depth
| ||||||
|
Less Than 2 Feet
|
2 Feet to 8 Feet
|
Greater Than 8 Feet
| ||||
|
(1)
|
Embankment geometry
| |||||
|
(a)
|
Top width (minimum)
|
2 feet
|
5 feet
|
8 feet
| ||
|
(b)
|
Interior side slope (maximum)
|
2:1
|
3:1
|
5:1
| ||
|
(c)
|
Exterior side slope (maximum)
|
2:1
|
3:1
|
3:1
| ||
|
(2)
|
Embankment construction
| |||||
|
(a)
|
Key trench
|
Not required
|
Required
|
Required
| ||
|
(b)
|
Pipe collar
|
Not required
|
Required
|
Required
| ||
|
(c)
|
Compaction density
|
Not required
|
Required
|
Required
| ||
|
(3)
|
Internal construction
| |||||
|
(a)
|
Dewatering feature
|
N/A
|
Required
|
Required
| ||
|
(b)
|
Pretreatment elements
|
Not required*
|
Required
|
Required
| ||
|
(4)
|
Outlet structure
| |||||
|
(a)
|
Pipe size (minimum)
|
6 inches
|
12 inches
|
15 inches
| ||
|
(b)
|
Pipe material
|
SLHDPE, PVC, RCP
|
SLHDPE, RCP
|
RCP
| ||
|
(c)
|
Anticlogging devices
|
Required
|
Required
|
Required
| ||
|
(d)
|
Antivortex design
|
Not required
|
Required
|
Required
| ||
|
(e)
|
Watertight joints in piping?
|
No
|
Yes
|
Yes
| ||
|
(5)
|
Spillway requirements
| |||||
|
(a)
|
Spillway freeboard (minimum)
|
3 inches
|
3 inches
|
6 inches
| ||
|
(b)
|
Width (minimum)
|
Not required
|
10 feet
|
20 feet
| ||
|
(c)
|
Width (maximum)
|
Not required
|
50 feet
|
50 feet
| ||
|
(d)
|
Spillway channel design
|
Not required
|
Required
|
Required
| ||
|
(e)
|
Routing of 100-year storm
|
Permitted
|
Permitted
|
Permitted
| ||
D.
All basins shall be structurally sound and shall be constructed of
sound and durable materials. The completed structure and the foundation
of all basins shall be stable under all probable conditions of operation
and shall be capable of discharging the peak discharge of a post-development
one-hundred-year storm event through the emergency spillway facilities,
in a condition that assumes the primary outlet(s) are blocked, which
will not damage the integrity of the facility or the downstream drainage
areas. Use of the spillway to convey flows greater than the fifty-year
design storm shall be permitted.
E.
An easement shall be provided from the basin spillway outfall to
a natural or artificial watercourse.
F.
The effect on downstream areas if the basin embankment fails shall
be considered in the design of all basins. The basin shall be designed
to minimize the potential damage caused by such failure of the embankment.
G.
The maximum depth of water for basins without restricted access shall
not exceed six feet unless approved by modification by the Borough
Council. Access to basins with a maximum depth of water greater than
six feet shall be restricted by fencing that will discourage access.
H.
Basins without restricted access shall have impoundment areas with
side slopes no greater than five horizontal to one vertical. Access
to basins with steeper side slopes shall be restricted by fencing
that will discourage access.
I.
All detention basins shall include an outlet structure to permit
draining the rate control volume to a completely dry position within
24 hours, exclusive of BMP storage.
J.
All outlet structures and emergency spillways shall include a satisfactory
means of dissipating the energy of flow at its outlet to assure conveyance
of flow without endangering the safety and integrity of the basin
and the downstream drainage area.
K.
An impervious core/key trench, when required, shall consist of a
cutoff trench (below existing grade) and a core trench (above existing
grade). A key trench may not be required wherever it can be shown
that another design feature, such as the use of an impermeable liner,
accomplishes the same purpose. Materials used for the core shall conform
to the Unified Soil Classification GC, SC, CH, or CL and must have
at least 30% passing the No. 200 sieve.
(1)
The dimensions of the core shall provide a minimum trench depth of
two feet below existing grade, minimum width of four feet and side
slope of 1H:1V or flatter.
(2)
The core should extend up both abutments to the ten-year water surface
elevation or six inches below the emergency spillway elevation, whichever
is lower.
(3)
The core shall extend four feet below any pipe penetrations through
the impervious core. The core shall be installed along or parallel
to the center line of the embankment.
(4)
Compaction requirements shall be the same as those for the embankment
to assure maximum density and minimum permeability.
L.
All pipe collars, when required, shall be designed in accordance
with Chapter 7 of the DEP E&S Manual. The material shall consist
of concrete or otherwise nondegradable material around the outfall
barrel and shall be watertight.
M.
When required, embankments shall be compacted by sheepsfoot or pad
roller. The loose lift thickness shall be nine inches or less, depending
on roller size, and the maximum particle size is six inches or less
(2/3 of the lift thickness). Five passes of the compaction equipment
over the entire surface of each lift are required. Embankment compaction
to visible nonmovement is also required.
N.
The embankment fill material shall be taken from an appropriate borrow
area which shall be free of roots, stumps, wood, rubbish, stones greater
than six inches, or frozen or other objectionable materials.
O.
The minimum freeboard shall be provided above the one-hundred-year
design elevation of the water surface at the emergency spillway in
a condition that assumes the primary outlet(s) is(are) blocked.
P.
No outlet structure from a detention basin or swale shall discharge
directly onto any publicly used Borough, state, or private road but
shall discharge into a culvert under or along the road.
Q.
Wherever possible, basins shall have a nonuniform (naturalistic)
shape, rather than a geometric design in the form of a square or rectangle.
R.
The minimum bottom slope of facilities not designed for infiltration
shall be 1%. A flatter slope may be used if an equivalent dewatering
mechanism is provided.
S.
When required, dewatering shall be provided through the use of underdrain,
surface device, or an alternate approved by the Borough Engineer.
If the facility is to be used for infiltration, the dewatering device
should be capable of being disconnected and only be made operational
if the basin is not dewatering within the required time frame.
T.
When required, pretreatment elements shall consist of forebays, or
an alternate approved by the Borough Engineer, to keep silt to a smaller
portion of the facility for ease of maintenance.
[Amended 9-13-2022 by Ord. No. 676]
U.
Within basins designed for infiltration, existing native vegetation
shall be preserved, if possible. For existing unvegetated areas or
for infiltration basins that require excavation, a planting plan shall
be prepared in accordance with this chapter and the BMP Manual which
is designed to promote infiltration.
V.
All discharge control devices with appurtenances shall be made of
reinforced concrete and stainless steel. Bolts/fasteners shall be
stainless steel.
W.
For facilities with a depth less than two feet, no outlet structure
shall be required.
[Amended 9-13-2022 by Ord. No. 676]
The green infrastructure and low impact development practices
provided in the BMP Manual shall be utilized for all regulated activities
wherever possible.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
The post-development total runoff volume shall not increase for all
storms equal to or less than the two-year, twenty-four-hour storm
event.
(2)
For modeling purposes:
(a)
Existing (predevelopment) nonforested pervious areas must be
considered meadow in good condition.
(b)
Twenty percent of existing impervious area, when present, shall
be considered meadow in good condition in the model for existing conditions.
(c)
The maximum loading ratio for volume control facilities in karst
areas shall be 3:1 impervious drainage area to infiltration area and
5:1 total drainage area to infiltration area. The maximum loading
ratio for volume control facilities in non-karst areas shall be 5:1
impervious drainage area to infiltration area and 8:1 total drainage
area to infiltration area. A higher ratio would be acceptable if proper
justification is submitted and approved.
B.
A detailed geologic evaluation of the development site shall be performed
in areas of carbonate geology to determine the design parameters of
recharge facilities. The evaluation shall be performed by a state
licensed/certified professional geologist (PG) and shall, at a minimum,
address soil permeability, depth to bedrock, susceptibility to sinkhole
formation, and subgrade stability.
C.
Any portion of the volume control storage that meets the following
conditions may also be used as rate control storage:
(1)
Volume control storage that depends on infiltration and is designed according to the infiltration standards in § 187-25R.
(2)
The volume control storage which will be used for rate control is
that storage which is available within 24 hours from the end of the
design storm based on the stabilized infiltration rate and/or the
evapotranspiration rate.
D.
Volume control BMPs shall be designed in accordance with the BMP Manual. All applicable worksheets from Chapter 8 of the BMP Manual must be used when establishing volume controls.
E.
Actual field infiltration tests at the location of the proposed elevation
of the stormwater BMPs are required when 5,000 square feet or greater
of new impervious surface is added. Infiltration tests shall be conducted
in accordance with the BMP Manual. The Borough shall be notified 24
hours prior to infiltration tests being conducted as to provide an
opportunity for the Borough to witness the tests.
A.
Subsurface storage facilities shall consist of all stormwater facilities
which store, infiltrate/evaporate/transpire, clean or otherwise affect
stormwater runoff and the top of which is not exposed to the natural
environment. Subsurface facilities shall be located below the finished
ground elevation. Subsurface facilities shall not include stormwater
management facilities designed for conveyance.
B.
Subsurface storage facilities shall comply with the design criteria
in the following table:
|
Subsurface Storage Facility Design Criteria
| |||||
|---|---|---|---|---|---|
|
Facility Type
| |||||
|
Infiltration and Storage
|
Storage Without Infiltration
| ||||
|
(1)
|
Facility geometry
| ||||
|
(a)
|
Depth from surface (maximum)
|
2 feet less than limiting zone
|
N/A
| ||
|
(b)
|
Loading ratio (maximum)
|
Per BMP Manual*
|
N/A
| ||
|
(2)
|
Distribution system requirements
| ||||
|
(a)
|
Pipe size (minimum)
|
4 inches
|
4 inches
| ||
|
(b)
|
Pretreatment
|
Required
|
Required
| ||
|
(c)
|
Loading/balancing
|
Required
|
Not required
| ||
|
(d)
|
Observation/access ports
|
Required
|
Required
| ||
C.
The facility shall be designed to provide a method to eliminate solids,
sediment, and other debris from entering the subsurface facility.
D.
The facility shall be designed to provide a means of evenly balancing
the flow across the surface of the facility to be used for infiltration.
E.
For facilities with the bottom less than five feet below the average
grade of the ground surface, a cleanout shall be an acceptable observation
port. For facilities with the bottom five feet or more below the average
grade of the ground surface, a manhole or other means acceptable to
the Borough shall be provided for access to and monitoring of the
facility. The number of access points shall be sufficient to flush
or otherwise clean out the system.
F.
Distribution system piping shall be PVC, SLHDPE, or RCP.
G.
The stone used for infiltration beds shall be clean-washed, uniformly
graded coarse aggregate (AASHTO No. 3 or equivalent approved by the
Borough). The void ratio for design shall be assumed to be 0.4.
H.
Material consistency and placement depths for backfill shall be (at
a minimum) per all applicable pipe manufacturer's recommendations,
further providing it should be free of large (not exceeding six inches
in any dimension) objectionable or detritus material. Select nonaggregate
material should be indigenous to the surrounding soil material for
nonvehicular areas. Backfill within vehicular areas shall comply with
this section unless otherwise specified in governing municipal road/street
or subdivision and land development ordinances. Furthermore, if the
design concept includes the migration of runoff through the backfill
to reach the infiltration facility, the material shall be well-drained,
free of excess clay or clay-like materials, and generally uniform
in gradation.
I.
Nonwoven geotextiles shall be placed on the sides and top of subsurface
infiltration facilities. No geotextiles shall be placed on the bottom
of subsurface infiltration facilities.
J.
When located under pavement, the top of the subsurface facility shall
be a minimum of three inches below the bottom of pavement subbase.
Where located under vegetative cover, the top of the subsurface facility
shall be a minimum of 12 inches below the surface elevation or as
required to establish vegetation.
K.
Subsurface facilities shall be designed to safely convey and/or bypass
flows from storms exceeding the design storm.
L.
The following principles shall be applied to the design plan and
construction schedule to minimize soil erosion and sedimentation:
