SWM facilities shall comply with the below standards as applicable
to the proposed facility:
A. Infiltration facilities shall be required unless subsurface conditions prevent the use of infiltration BMPs, in which case §
158-304B below shall be followed. Infiltration facilities:
1. Shall be spread out, made as shallow as practicable, and located
to maximize use of natural on-site infiltration features while still
meeting the other requirements of this ordinance.
2. Must have soil permeability greater than or equal to 0.5 inch/hour
and less than or equal to 12 inches per hour.
3. Shall be protected from disturbance and compaction.
4. Shall be set back by the following distances:
a.
For all SWM permits: 100 feet from water supply wells.
b.
For major SWM permits: 15 feet downgradient or 100 feet upgradient
from building foundations.
c.
For minor SWM permits: 15 feet downgradient or 40 feet upgradient
from building foundations.
d.
For major SWM permits: 50 feet from septic system drainfields.
e.
For minor SWM permits: 25 feet from septic system drainfields.
f.
For major SWM permits: if the above neighboring features are
not present, 100 feet from property lines unless evidence is provided
that the above setbacks can be maintained for existing or potential
wells, foundations, and drainfields on neighboring properties.
g.
For major SWM permits: 50 feet from a geologic contact with
carbonate bedrock unless a carbonate assessment report is done and
shows either the absence of special geologic features within 50 feet
of the proposed infiltration area or provides recommendations on the
means of acceptability for infiltration.
5. Infiltration for stormwater management is encourage where soils and
geology permit, consistent with the provisions or this ordinance and,
where appropriate, the Recommendation Chart for Infiltration Stormwater
Management BMPs in Carbonate Bedrock in Appendix D.
B. All SWM facilities shall be set back a minimum of 15 feet from a
property line or public right-of-way as measured from the nearest
point of the facility that may provide water storage.
C. Runoff not being treated by infiltration shall utilize two SWM BMPs
in series ("treatment train"), including but not limited to bioretention
facilities, capture/reuse, constructed wetlands, dry extended detention
ponds, stormwater filters, vegetated buffers/filter strips, vegetated
roofs, vegetated swales, water quality inlets, and/or wet detention
ponds. The second BMP shall be a vegetated buffer, filter strip, bioretention
facility, vegetated swale, or other BMP that provides a thermal benefit
to surface waters.
D. Low-flow channels are prohibited.
E. Trash racks shall be provided for all orifices equivalent to 12 inches
or smaller in diameter. Additionally, all basin inflow and outflow
structures shall be designed with trash racks over the outflows where
practicable.
F. Anti-seep collars shall be provided on all outflow culverts in accordance
with the methodology in the E&S Manual. An increase in seepage
length of 15% must be used in accordance with the requirements for
permanent anti-seep collars.
G. Embankment/berm tops shall not be planted with vegetation greater
than three feet in mature height. Only vegetation that is tolerant
to the conditions of embankment planting (for example, lack of water
retainage in the soil) may be utilized. When this requirement is in
conflict with other ordinances or regulations (for example, landscape
buffer plantings), this requirement shall preside for the purposes
of public safety and protection.
H. Embankment/berm side slopes shall be no steeper than 3:1.
I. Embankment/berm soils shall have low erodibility factors as per the
E&S Manual and be identified on the SWM site plan.
J. If a major SWM permit is required, all embankments/berms shall meet
Subsection J.1 through 4. If a minor SWM permit is required, embankments/berms
greater than or equal to three feet in height shall:
1. Have a cross-sectional top width of at least five feet.
2. Have emergency spillways capable of providing nonerosive release
of the post-development 100-year design storm. The emergency spillway
shall provide a minimum one foot of freeboard below the top of berm
elevation, convey the entire 100-year design storm at a maximum depth
of one foot over the spillway, and may not be utilized as an outflow
for design storms up to and including the 100-year storm.
3. Have cutoff/key trenches of impervious material.
4. The primary outflow structure must be designed to pass all design
storms (up to and including the 100-year event) without discharging
through the emergency spillway.
K. All facilities shall drain over a period of time not less than 24
hours and not more than 72 hours from the end of the facility's
inflow hydrograph unless, at the sole discretion of the Municipal
Engineer, the BMP is specifically designed to function with differing
time frames (for example, wet ponds, constructed wetlands, etc.).
L. Maximum water depth in any open SWM facility shall be no greater
than six feet when functioning through the primary outlet structure.
M. The 100-year water surface elevation within any SWM facility shall
provide a minimum of 1.0 foot of freeboard below the invert of the
emergency spillway. For facilities that do not utilize an emergency
spillway, this freeboard shall be provided to the top of the storage
facility (i.e., top of berm, top of stone pit, etc.).
N. A minimum four-foot-high, galvanized or vinyl-clad chain-link metal
fence, or any material and fence design acceptable to the municipality,
with a self-closing and self-latching gate with a minimum opening
of 10 feet shall be provided around stormwater management facilities
if any of the following conditions are present:
1. When deemed a public safety hazard at the sole discretion of the
municipality.
2. The maximum depth of water in the basin after a ten- or twenty-five-year
storm is greater than 30 inches.
3. The basin is intended to hold water for periods of longer than three
hours after the storm subsides.
4. The basin is to be dedicated to the municipality.
5. Fencing of a detention basin may be waived by the municipality upon
the recommendation of the Municipal Engineer if the nearest residential
zoning district, school, existing dwelling or recreation facility
is at least 1,500 feet away in walking distance from the basin.
O. Floodplains:
1. Facilities and their points of discharge shall not be located within
the 1% flood event (100-year floodplain) as determined by FEMA, HEC-RAS,
or similar analysis. If no floodplain is defined, the floodplain is
assumed to extend 50 feet from the top of stream bank in both directions.
2. Facility bottom elevations must be greater than 1% (100-year) floodplain
elevations. If no floodplain is defined, the floodplain is assumed
to extend 50 feet from the top of stream bank in both directions.
3. Novel approaches to stormwater management that require placement within the floodplain, including but not limited to floodplain restorations, may be exempted from the requirements in §
158-304O.1 and 2 above at the sole discretion of the Municipal Engineer.
4. Properties that are entirely or majority constrained by floodplains may be exempted from the requirements in §
158-304O.1 and 2 above at the sole discretion of the Municipal Engineer.
P. SWM facility bottom elevations:
1. Shall be located at least two feet above any bedrock.
2. For major SWM permits, shall be located at least three feet above
the seasonal high water table.
3. Shall be located above any other soil limiting zone.
Q. The type, location, and number of landscaping and planting specification
shall be provided for all stormwater management facilities and be
specific for each type of facility.
R. Stormwater management facilities excavated to carbonate rock must
either be fitted with an impervious clay liner, or if infiltration
is determined to be an acceptable practice, over-excavated four feet
and refilled with a suitable material mix. Suitable backfill material
is subject to approval from the Municipal Engineer.
S. The minimum circular orifice diameter for controlling discharge rates
from detention facilities shall be three inches.
T. Aeration devices may be required for retention basins, dependent
upon the quality of influent and retention time.
U. Within areas containing soils identified by the Soil Conservation
Service to be sinkhole prone, permanent detention basins shall be
lined with a material which after installation attains a maximum permeability
rate as determined by the Township's Geotechnical Engineer or Township
Engineer.
Conveyance facilities shall:
A. Safely convey the twenty-five-year design storm without erosion or
hazard utilizing Manning's equation.
B. Be prohibited from connecting to or discharging into existing downstream
conveyance or storage systems, whether man-made or natural, without
verification of the adequacy of downstream hydraulic capacity.
C. In the case of storm sewers:
1. Completely contain flows with no surface discharges.
2. Be constructed with watertight joints. If conveyance facilities are
proposed that require watertight joints, provide a note as listed
in § 158-401a.X.7.
3. Be designed and constructed without "knocking out" any inlet or structure
corners. If inlets or structures are proposed, provide a note as listed
in § 158-401a.X.8 below.
4. Have inlets, manholes, or similar structures at all horizontal and/or
vertical directional changes. Tee joints, elbows, wyes, and similar
structures are prohibited. No run of pipe shall exceed 400 feet in
length without appropriate measures to allow cleanout.
5. Include double inlets set 0.2 foot below the final paving elevation
on both sides of the low point of a curbed street.
6. Not have inlets placed in front of or within three feet of a driveway.
7. Not have inlets spaced more than 600 feet apart.
8. Not have manholes spaced more than 600 feet apart without an inlet
in between.
9. Have all upstream pipe crown elevations be greater than or equal
to all downstream pipe crown elevations.
10.
Have flow velocities greater than or equal to 2.5 feet per second.
11.
Have slopes greater than or equal to 0.5%.
12.
Have a minimum pipe size of 15 inches in diameter.
13.
Have a minimum two-inch drop between the lowest inlet pipe invert
elevation and the outlet pipe invert elevation within inlets.
14.
All inlets in paved areas shall have heavy-duty bicycle-safe
grating consistent with PennDOT Publication 72M. If inlets or structures
are proposed, provide a note as listed in § 158-401a.X.16
below.
15.
Inlets, junction boxes, or manholes greater than five feet in
depth shall be equipped with ladder rungs and shall be detailed on
the SWM site plan.
16.
Inlets shall not have a sump condition in the bottom unless
designed as a water quality BMP, and shall have flow channels installed.
17.
Provide the note listed in § 158-401a.X.18 stating
concrete top units and grade adjustment rings shall be set in a bed
of full mortar according to Publication 408.
18.
Pavement base drain shall be provided at all low points in cut
areas, toe of slope areas, and other areas dictated by proven engineering
principles and design judgments. All base drains shall be in accordance
with PennDOT Publication 408.
D. In the case of gutters:
1. Not allow flow to encroach into adjacent roadway lanes more than
1/2 of the lane width, exceed three inches in depth, or exceed 1.5
inches in depth across driveways.
2. Not allow flow to cross intersections or street center lines.
3. Have a minimum slope of 1%.
E. In the case of swales:
1. Provide six inches of freeboard to the top of the swale.
2. Have a minimum slope of 1%.
3. Have side slopes no steeper than 3:1.
4. Be designed for stability using velocity (slopes less than 10%) or
shear (all slopes) criteria.
5. Multiply velocities or shear stresses by the following factors when
swale bends occur:
a.
1.75: when the bend is 30° to 60°.
b.
2.00: when the bend is 60° to 90°.
c.
2.5: when the bend is 90° or greater.
6. Be designed for both temporary and permanent conditions.
F. In the case of culverts, bridges, and other conveyance facilities
that convey surface drainage across or under streets or other vehicular
passageways (excluding driveways and access drives), whether public
or private:
1. Safely convey the 100-year design storm without erosion or hazard utilizing Manning's equation. This shall replace the requirement listed in §
158-305A above.
The following criteria shall apply to any use of property that
meets the definition of "hotspot." Noncommercial accessory uses incidental
to residential uses shall not be considered hotspot uses.
A. All hotspot uses (as determined by the municipality on a case-by-case basis based upon the definition in Article
II of this ordinance) shall include a stormwater pollution and prevention plan as part of the O&M plan. The stormwater pollution and prevention plan (SWPP) shall implement regular pavement sweeping, practice proper salt storage, maintain an on-site spill kit with oil booms, perform regular visual inspection of the site and SWM facilities, and report to the municipality every two years on the implementation and use of this plan.
1. The following are typical hotspot land uses and acceptable pretreatment
method(s):
Hotspot Land Use
|
Pretreatment Method(s)
|
---|
Vehicle maintenance and repair facilities including auto parts
stores
|
•
|
Water quality inlets
|
•
|
Use of drip pans and/or dry sweep material under vehicles/equipment
|
•
|
Use of absorbent devices to reduce liquid releases
|
•
|
Spill prevention and response program
|
Vehicle fueling stations
|
•
|
Water quality inlets
|
•
|
Spill prevention and response program
|
Storage areas for public works
|
•
|
Water quality inlets
|
•
|
Use of drip pans and/or dry sweep material under vehicles/equipment
|
•
|
Use of absorbent devices to reduce liquid releases
|
•
|
Spill prevention and response program
|
•
|
Diversion of stormwater away from potential contamination areas
|
Outdoor storage of liquids
|
•
|
Spill prevention and response program
|
Commercial nursery operations
|
•
|
Vegetated swales/filter strips
|
•
|
Constructed wetlands
|
•
|
Stormwater collection and reuse
|
Other hotspot uses
|
•
|
As determined for acceptability by the Municipal Engineer
|
Other NPDES-regulated facilities
|
•
|
As required by the site's NPDES permit
|
B. All hotspot uses shall utilize a "treatment train" that treats any
and all required stormwater management volumes in a series of at least
two water quality SWM BMPs before surface discharge.
C. Infiltration of runoff from hotspot uses will only be allowed after
the runoff has been treated by one or more SWM BMPs, not including
the infiltration BMP itself, designed to treat the quality of stormwater
runoff based upon the pollutants expected at the hotspot use.