A.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 188-14:
(1)
Preparation and implementation of an approved SWM site plan is required.
(2)
No regulated activities shall commence until:
(a)
The municipality issues written approval of an SWM site plan,
which demonstrates compliance with the requirements of this chapter;
and
(b)
The applicant has received a letter of adequacy or approval
for the erosion and sediment control plan review by the municipality
and the Conservation District (if required) and has received all other
local, state and federal permit approvals required for the project
involving the regulated activity.
B.
Neither submission of an SWM site plan under the provisions herein
nor compliance with the provisions of this chapter shall relieve any
person from responsibility for damage to any person or property otherwise
imposed by law.
C.
SWM site plans approved by the municipality, in accordance with § 188-29, shall be on site throughout the duration of the regulated activity.
D.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this chapter, provided that such alternative measures meet the
minimum requirements of, and do not conflict with, state law including,
but not limited to, the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
E.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law.[2] Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual[3]), No. 363-2134-008, as amended and updated.
F.
Impervious areas:
(1)
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages.
(2)
For development taking place in stages, the entire development plan
shall be used in determining compliance with this chapter.
(3)
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 188-15 and the peak rate controls of § 188-18 do not need to be retrofitted for existing impervious areas that are not being altered by the proposed regulated activity.
G.
Stormwater flows onto adjacent property shall not be created, increased,
relocated, or otherwise altered without written notification to the
adjacent property owner(s). Such stormwater flows shall be subject
to the requirements of this chapter.
H.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property.
(2)
Meet the water quality goals of this chapter by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(3)
Incorporate methods described in the Pennsylvania Stormwater Best
Management Practices Manual (PA BMP Manual[4]). If methods other than green infrastructure and LID methods
are proposed to achieve the volume and rate controls required under
this chapter, the SWM site plan must include a detailed justification
demonstrating that the use of LID and green infrastructure is not
practicable.
I.
For areas underlain by Karst or carbonate geology that may be susceptible
to the formation of sinkholes and other Karst features, the location,
type, and design of infiltration BMPs shall be based on a site evaluation
conducted by a qualified licensed professional and based on the PA
BMP Manual (as amended) or other design guidance acceptable to the
Municipal Engineer.
J.
Infiltration BMPs should 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 chapter.
K.
Normally dry, open top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
L.
The design of all BMPs and conveyances shall incorporate sound engineering
principles and practices in a manner that does not aggravate existing
stormwater problems as identified by the municipality. The municipality
reserves the right to disapprove any design that would result in construction
in an area affected by existing stormwater problem(s) or continuation
of an existing stormwater problem(s).
M.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the latest version of the Precipitation-Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 14[5] can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
N.
P.
Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 188-15, 188-16, 188-17 and 188-18). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.
Q.
Existing wetlands, either on the site or on an adjacent property,
shall not be used to meet the minimum design requirements for stormwater
management or stormwater runoff quality treatment. Stormwater discharges
to existing wetlands shall not degrade the quality or hydrologic integrity
of the wetland.
R.
Hotspots runoff controls. Specific structural or pollution prevention
practices may be required, as determined to be necessary by the Municipal
Engineer, to pretreat runoff from hotspots prior to infiltration.
Following is a list of examples of hotspots:
(1)
Vehicle salvage yards and recycling facilities;
(2)
Vehicle fueling stations;
(3)
Vehicle service and maintenance facilities;
(4)
Vehicle and equipment cleaning facilities;
(5)
Fleet storage areas (bus, truck, etc.);
(6)
Industrial sites based on Standard Industrial Classification Codes;
(7)
Marinas (service and maintenance areas);
(8)
Outdoor liquid container storage;
(9)
Outdoor loading/unloading facilities;
(10)
Public works storage areas;
(11)
Facilities that generate or store hazardous materials;
(12)
Commercial container nursery;
(13)
Contaminated sites/brownfields;
(14)
Other land uses and activities as designated by the municipality.
S.
Additional water quality requirements. The municipality may require
additional stormwater control measures for stormwater discharges to
special management areas including, but not limited to:
(1)
Water bodies listed as "impaired" by PADEP.
(2)
Any water body or watershed with an approved total maximum daily
load (TMDL).
(3)
Areas of known existing flooding problems.
(4)
Critical areas with sensitive resources (e.g., state-designated special
protection waters, cold water fisheries, carbonate geology or other
groundwater recharge areas that may be highly vulnerable to contamination,
drainage areas to water supply reservoirs, etc.).
T.
All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with Chapter 117 of the New Freedom Borough Code of Ordinances, more specifically known as the "New Freedom Borough Floodplain Management Ordinance," and shall be designed to maintain the flood-carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.
A.
General exemptions. Regulated activities that involve less than 500 square feet of proposed impervious surfaces and less than or equal to 5,000 square feet of earth disturbance or are listed in Subsection G are exempt from those (and only those) requirements of this chapter that are included in the sections and articles listed in Table 188-14.1. Exemptions are for the items noted in Table 188-14.1 only and shall not relieve the landowner from other applicable requirements of this chapter. Exemption shall not relieve the applicant from implementing such measures as are necessary to protect health, safety and welfare, property, and water quality.
[Amended 6-12-2023 by Ord. No. 2023-3]
B.
Agricultural activity is exempt from the SWM site plan preparation
requirements of this chapter provided the activities are performed
according to the requirements of 25 Pa. Code Chapter 102.
C.
Forest management and timber operations are exempt from the SWM site
plan preparation requirements of this chapter provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
E.
The municipality may deny or revoke any exemption or modified requirements
pursuant to this section at any time for any project that the municipality
believes may pose a threat to public health and safety or the environment.
F.
Requirements for exempt activities.
[Amended 6-12-2023 by Ord. No. 2023-3]
(1)
An exemption from any requirement of this chapter shall not relieve
the applicant from implementing all other applicable requirements
of this chapter or from implementing such measures as are necessary
to protect public health, safety, and welfare, property and water
quality.
(2)
An exemption shall not relieve the applicant from complying with
the requirements for state-designated special protection waters designated
by PADEP as high quality (HQ) or exceptional value (EV) waters, or
any other current or future state or municipal water quality protection
requirements.
(3)
An exemption under this chapter shall not relieve the applicant from
complying with all other applicable municipal ordinances or regulations.
(4)
Any applicant desiring exemption from design, plan submission, and
plan processing requirements shall complete an application for exemption
in the form available at the Municipality's office and pay any applicable
filing fee.
|
Table 188-14.1
Thresholds for Regulated Activities Exempt from Chapter Provisions
| |||
|---|---|---|---|
|
Ordinance Article/Section
|
Activities Listed In § 188-14G
|
Less Than 500 Square Feet of Proposed Impervious Surfaces and
Less Than 5,000 Square Feet of Proposed Earth Disturbance
|
Greater Than 500 Square Feet of Proposed Impervious Surfaces
or Greater Than 5,000 Square Feet of Proposed Earth Disturbance
|
|
Article I
|
Not exempt
|
Not exempt
|
Not exempt
|
|
Article II
|
Not exempt
|
Not exempt
|
Not exempt
|
|
Not exempt
|
Not exempt
|
Not exempt
| |
|
Exempt
|
Exempt
|
Not exempt
| |
|
Article IV
|
Exempt
|
Exempt
|
Not exempt
|
|
Article V
|
Exempt
|
Exempt
|
Not exempt
|
|
Article VI
|
Exempt
|
Exempt
|
Not exempt
|
|
Article VII
|
Not exempt
|
Not exempt
|
Not exempt
|
|
Article VIII
|
Not exempt
|
Not exempt
|
Not exempt
|
|
Other erosion, sediment and pollution control requirements
|
Must comply with Title 25, Chapter 102 of the Pa. Code and other
applicable state and municipal codes, including the Clean Streams
Law
| ||
G.
Exemptions for specific activities. The following specific regulated activities are exempt from the requirements of §§ 188-13, 188-15, 188-16, 188-17, 188-18, 188-19 and 188-20, and Article IV, Article V, and Article VI of this chapter (as shown in Table 188-14.1), unless otherwise noted below. All other conveyance and system design standards established by the municipality in other codes or ordinances shall be required, and all other provisions of this chapter shall apply.
(1)
Emergency exemption. Emergency maintenance work performed for the
protection of public health, safety and welfare. This exemption is
limited to repair of an existing stormwater management facility; upgrades,
additions or other improvements are not exempt. A written description
of the scope and extent of any emergency work performed shall be submitted
to the municipality within two business days of the commencement of
the activity. A detailed plan shall be submitted no later than 30
calendar days following commencement of the activity. If the municipality
finds that the work is not an emergency, then the work shall cease
immediately and the requirements of this chapter shall be addressed
as applicable.
(2)
Maintenance. Any maintenance to an existing stormwater management
facility, BMP or conveyance made in accordance with plans and specifications
approved by the Municipal Engineer or municipality.
(3)
Existing landscaping. Use of land for maintenance, replacement or
enhancement of existing landscaping.
(4)
Gardening. Use of land for gardening for home consumption.
(5)
Agricultural related activities.
(a)
Agricultural activities (as defined in Article II), when performed in accordance with the requirements of 25 Pa. Code Chapter 102.
(b)
High tunnel if:
[1]
The high tunnel or its flooring does not result in an impervious
surface exceeding 25% of all structures located on the landowner's
total contiguous land area under common ownership; and
[2]
The high tunnel meets one of the following:
[a]
The high tunnel is located at least 100 feet from
any perennial stream or watercourse, public road or neighboring property
line.
[b]
The high tunnel is located at least 35 feet from
any perennial stream or watercourse, public road or neighboring property
line and located on land with a slope not greater than 7%.
(6)
Forest management. Forest management operations, which are consistent with a sound forest management plan as filed with the municipality and which comply with the Pennsylvania Department of Environmental Protection's management practices contained in its publication "Soil Erosion and Sedimentation Control Guidelines for Forestry" (as amended or replaced by subsequent guidance). Such operations are required to have an erosion and sedimentation control plan, which meets the requirements of 25 Pa. Code Chapter 102 and meets the erosion and sediment control standards of § 188-15 of this chapter.
(7)
Maintenance of existing gravel and paved surfaces. Replacement of existing gravel and paved surfaces shall meet the erosion and sediment control requirements of 25 Pa. Code Chapter 102 and § 188-13E of this chapter, and is exempt from all other requirements of this chapter listed in § 188-14G above. Resurfacing of existing gravel and paved surfaces is also exempt from the requirements of this chapter listed above. Paving of existing gravel surfaces is exempt from the requirements of this chapter listed above. Construction of new or additional impervious surfaces shall comply with all requirements of this chapter as indicated in Table 188-14.1.
(8)
Municipal roadway shoulder improvements. Shoulder improvements conducted
within the existing roadway cross section of municipal-owned roadways,
unless an NPDES permit is required, in which case the proposed work
must comply with all requirements of this chapter.
(9)
In-place replacement of residential dwelling unit. The replacement
in the exact footprint of an existing one- or two-family dwelling
unit.
(10)
In-place replacement, repair, or maintenance of residential
impervious surfaces. The replacement of existing residential patios,
decks, driveways, pools, garages, and/or sidewalks that are accessory
to an existing one- or two-family dwelling unit in the exact footprint
of the existing impervious surface.
H.
Modified requirements for small projects.
(1)
Regulated activities that involve both of the following: 1) 500 to
2,000 square feet of proposed impervious surfaces and 2) less than
5,000 square feet of proposed earth disturbance may apply the modified
requirements presented in the "Simplified Approach to Stormwater Management
for Small Projects" (Simplified Approach) (Appendix A[2]) to comply with the requirements of §§ 188-13, 188-15, 188-16, 188-17, 188-18, 188-19 and 188-20, and Article IV, Article V, and Article VI of this chapter (as shown in Table 188-14.2). The applicant shall first contact New Freedom Borough: to confirm that the proposed project is eligible for use of the Simplified Approach and is not otherwise exempt from these chapter provisions; to determine what components of the proposed project are to be considered as impervious surfaces; and to determine if other known site or local conditions exist that may preclude the use of any techniques included in the Simplified Approach. Appendix A includes instructions and procedures for preparation, submittal, review and approval of documents required when using the Simplified Approach and shall be adhered to by the applicant. All other provisions of this chapter shall apply.
[Amended 6-12-2023 by Ord. No. 2023-3]
|
Table 188-14.2
Thresholds for Regulated Activities That Are Eligible for "Modified"
Requirements for the Provisions of This Chapter That Are Listed Below
| |
|---|---|
|
Chapter Article/Section
|
Activities Listed in § 188-14H
|
|
Article I
|
All provisions apply
|
|
Article II
|
All provisions apply
|
|
All provisions apply
| |
|
Exempt if modified requirements of § 188-14H are applied
| |
|
Article IV
|
Exempt if modified requirements of § 188-14H are applied
|
|
Article V
|
Exempt if modified requirements of § 188-14H are applied
|
|
Article VI
|
Exempt if modified requirements of § 188-14H are applied
|
|
Article VII
|
Exempt if modified requirements of § 188-14H are applied
|
|
Article VIII
|
All provisions apply
|
|
Other erosion, sediment and pollution control requirements
|
Must comply with Title 25, Chapter 102 of the Pa. Code and other
applicable state and municipal codes, including the Clean Streams
Law
|
|
Notes:
|
|
Modified requirements" - Regulated activities listed within the subsections of this chapter noted in Table 188-14.2 are eligible for exemption only from the indicated sections and subsections of this chapter and only if the modified requirements of § 188-14H are met to the satisfaction of the municipality; all other provisions of this chapter apply.
|
[2]
Editor's Note: Appendix A is included as an attachment to this chapter.
To control postconstruction stormwater impacts from regulated
activities and meet state water quality requirements, BMPs shall be
provided in the site design that replicate predevelopment stormwater
infiltration and runoff conditions, such that postconstruction stormwater
discharges do not degrade the physical, chemical, or biological characteristics
of the receiving waters. The green infrastructure and low-impact development
(LID) practices provided in the PA BMP Manual, as well as the guidance
on green infrastructure LID and conservation design (CD) provided
in Appendix D,[1] shall be utilized for all regulated activities wherever
possible. The applicant shall comply with the following water quality
and runoff volume requirements for all regulated activities, including
all new development and redevelopment activities:
A.
The postconstruction total runoff volume shall not exceed the predevelopment
total runoff volume for all storms equal to or less than the two-year,
twenty-four-hour duration precipitation (design storm) or a minimum
of 1.5 inches of runoff from all regulated impervious surfaces shall
be managed, whichever volume to be managed is greater. The water quality
and runoff volume to be managed shall consist of any runoff volume
generated by the proposed regulated activity over and above the predevelopment
total runoff volume and shall be captured and permanently retained
or infiltrated on the site. Permanent retention options may include,
but are not limited to, reuse, evaporation, transpiration, and infiltration.
B.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 188-19D of this chapter.
C.
The design of the stormwater management facility outlet shall provide
for protection from clogging and unwanted sedimentation.
D.
BMPs that moderate the temperature of stormwater shall be used to
protect the temperature of receiving waters.
E.
Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 188-16. The infiltration volume required under § 188-16 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.
F.
Runoff from the disturbed area shall be treated for water quality
prior to entering existing waterways or water bodies. If a stormwater
management practice does not provide water quality treatment, then
water quality BMPs shall be utilized to provide pretreatment prior
to the runoff entering the stormwater management practice.
G.
The municipality may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 188-13S.
H.
When the regulated activity contains or is divided by multiple drainage
areas, the water quality and runoff volume shall be separately addressed
for each drainage area.
I.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
J.
Areas located outside of the site (i.e., areas outside of the regulated
activity) may be excluded from the calculation of the water quality
and runoff volume requirements.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
Providing for infiltration consistent with the natural hydrologic
regime is required to compensate for the reduction in the recharge
that occurs when the ground surface is disturbed or impervious surface
is created or expanded. The applicant shall achieve the following
infiltration requirements:
A.
For regulated activities involving either new development or redevelopment, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 188-15. If the runoff volume required by § 188-15 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) may be used to manage this volume with approval from the Municipal Engineer. If the requirements of any subsection of § 188-16 cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Municipal Engineer why the required infiltration volume controls cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated; however in all cases at least the first 0.5 inch of runoff volume shall be infiltrated.
B.
A waiver from § 188-16 shall be considered by the municipality only if a minimum of at least 0.5 inch infiltration requirement cannot be physically accomplished on the site.
C.
If site conditions preclude capture of runoff from portions of the
impervious surfaces, the infiltration volume for the remaining area
shall be increased by an equivalent amount to offset the loss.
D.
When a project contains or is divided by multiple watersheds, the
infiltration volume shall be separately addressed for each watershed.
E.
Existing impervious surfaces located in areas outside of the site
(i.e., outside of the regulated activity) may be excluded from the
calculation of the required infiltration volume.
F.
A detailed soils evaluation of the site shall be conducted by a qualified
professional and at a minimum shall address soil permeability, depth
to bedrock, and subgrade stability. The general process for designing
the infiltration BMP shall be conducted by a qualified licensed professional
and shall be consistent with the PA BMP Manual (as amended) (or other
guidance acceptable to the Municipal Engineer) and in general shall:
(1)
Analyze hydrologic soil groups as well as natural and man-made features
within the site to determine general areas of suitability for infiltration
practices. In areas where development on fill material is under consideration,
conduct geotechnical investigations of subgrade stability; infiltration
may not be ruled out without conducting these tests.
(2)
Provide field tests such as double ring infiltrometer or other hydraulic
conductivity tests (at the elevation of the proposed infiltration
surface) to determine the appropriate hydraulic conductivity rate.
Standard septic/sewage percolation tests are not acceptable for design
purposes.
(3)
Design the infiltration facility for the required retention (infiltration)
volume based on field-determined infiltration capacity (and apply
safety factor as per applicable design guidelines) at the elevation
of the proposed infiltration surface.
(4)
On-lot infiltration features are encouraged; however, it shall be
demonstrated to the Municipal Engineer that the soils are conducive
to infiltration on the identified lots.
G.
Infiltration BMPs 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 BMP and the
top of the limiting zone. Additional depth may be required in areas
underlain by Karst or carbonate geology.
(2)
An infiltration rate sufficient to accept the additional stormwater
volume and drain completely as determined by field tests conducted
by the applicant.
(3)
The infiltration facility shall completely drain the retention (infiltration)
volume within three days (72 hours) from the end of the design storm.
H.
All infiltration practices shall:
(1)
Be set back at least 25 feet from all buildings and features with
subgrade elements (e.g., basements, foundation walls, etc.), unless
otherwise approved by the Municipal Engineer;
(2)
For any infiltration practice that collects runoff from shared or
multiple features and that is located within 50 feet of a building
or feature with subgrade elements (e.g., basements, foundation walls,
etc.), the bottom elevation shall be set below the elevation of the
subgrade element.
I.
Infiltration facilities shall, to the maximum extent practicable,
be located to avoid introducing contaminants to groundwater:
(1)
When a hotspot is located in the area draining to a proposed infiltration
facility, an evaluation of the potential of groundwater contamination
from the proposed infiltration facility shall be performed, including
a hydrogeologic investigation (if necessary) by a qualified licensed
professional to determine what, if any, pretreatment or additional
design considerations are needed to protect groundwater quality.
(2)
When located within a "wellhead protection area" of a public water
supply well, infiltration practices shall be in conformance with the
applicable approved source water protection assessment or source water
protection plan.
(3)
The applicant shall provide appropriate safeguards against groundwater
contamination for land uses that may cause groundwater contamination
should there be a mishap or spill.
J.
During site construction, all infiltration practice components shall
be protected from compaction due to heavy equipment operation or storage
of fill or construction material. Infiltration areas shall also be
protected from sedimentation. Areas that are accidentally compacted
or graded shall be remediated to restore soil composition and porosity.
Adequate documentation to this effect shall be submitted to the Municipal
Engineer for review. All areas designated for infiltration shall not
receive runoff until the contributory drainage area has achieved final
stabilization.
K.
Where sediment transport in the stormwater runoff is anticipated
to reach the infiltration system, appropriate permanent measures to
prevent or collect sediment shall be installed prior to discharge
to the infiltration system.
L.
Where roof drains are designed to discharge to infiltration practices,
they shall have appropriate measures to prevent clogging by unwanted
debris (for example, silt, leaves and vegetation). Such measures shall
include but are not limited to leaf traps, gutter guards and cleanouts.
M.
All infiltration practices shall have appropriate positive overflow
controls.
N.
No sand, salt or other particulate matter may be applied to a porous
surface material for winter ice conditions.
O.
The following procedures and materials shall be required during the
construction of all subsurface facilities:
(1)
Excavation for the infiltration facility shall be performed with
equipment that will not compact the bottom of the seepage bed/trench
or like facility.
(2)
The bottom of the bed and/or trench shall be scarified prior to the
placement of aggregate.
(3)
Only clean aggregate with documented porosity, free of fines, shall
be allowed.
(4)
The tops, bottoms and sides of all seepage beds, trenches, or like
facilities shall be covered with drainage fabric. Fabric shall be
nonwoven fabric acceptable to the Municipal Engineer.
(5)
Stormwater shall be distributed throughout the entire seepage bed/trench
or like facility and provisions for the collection of debris shall
be provided in all facilities.
For regulated activities involving new development with one
or more acres of earth disturbance, the applicant shall comply with
the following stream channel protection requirements to minimize stream
channel erosion and associated water quality impacts to the receiving
waters:
A.
The peak flow rate of the postconstruction two-year, twenty-four-hour
design storm shall be reduced to the predevelopment peak flow rate
of the one-year, twenty-four-hour duration precipitation, using the
SCS Type II distribution.
B.
To the maximum extent practicable, and unless otherwise approved
by the Municipal Engineer, the postconstruction one-year, twenty-four-hour
storm flow shall be detained for a minimum of 24 hours and a maximum
not to exceed 72 hours from a point in time when the maximum volume
of water from the one-year, twenty-four-hour storm is stored in a
proposed BMP (i.e., when the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the orifice is at the invert of the proposed
BMP).
C.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 188-19D of this chapter.
D.
The minimum orifice size in the outlet structure to the BMP shall
be three inches in diameter unless otherwise approved by the Municipal
Engineer, and a trash rack shall be installed to prevent clogging.
For sites with small drainage areas contributing to the BMP that do
not provide enough runoff volume to allow a twenty-four-hour attenuation
with the three-inch orifice, the calculations shall be submitted showing
this condition.
E.
When the calculated orifice size is below three inches, gravel filters
(or other methods) are recommended to discharge low-flow rates subject
to the Municipal Engineer's satisfaction. When filters are utilized,
maintenance provisions shall be provided to ensure filters meet the
design function.
F.
All proposed stormwater management facilities shall make use of measures
to extend the flow path and increase the travel time of flows in the
facility.
G.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate control shall be separately addressed for
each drainage area.
The applicant shall comply with the following peak flow rate
control requirements for all regulated activities including those
that involve new development and redevelopment.
A.
Postconstruction peak flow rates from any regulated activity shall
not exceed the predevelopment peak flow rates as shown for each of
the design storms specified in Table 188-18.1.
|
Table 188-18.1
Peak Rate Control Standards
(Peak Flow Rate of the Postconstruction Design Storm Shall Be
Reduced to the Peak Flow Rate of the Corresponding Predevelopment
Design Storm Shown in the Table)
| ||
|---|---|---|
|
Postconstruction Design Storm Frequency (24-Hour Duration)
|
Predevelopment Design Storm
| |
|
New Development Regulated Activities
|
Redevelopment Regulated Activities
| |
|
2-Year
|
1-Year
|
2-Year
|
|
5-Year
|
5-Year
|
5-Year
|
|
10-Year
|
10-Year
|
10-Year
|
|
25-Year
|
25-Year
|
25-Year
|
|
50-Year
|
50-Year
|
50-Year
|
|
100-Year
|
100-Year
|
100-Year
|
B.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 188-19D of this chapter.
C.
For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total proposed impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table § 188-18.1, using the redevelopment ground cover assumptions presented in § 188-19D. This design criterion for redevelopment is only permitted with approval of Municipal Engineer. It shall result in no measurable impact on downstream properties.
D.
Only the area of the proposed regulated activity shall be subject
to the peak flow rate control standards of this chapter. Undisturbed
areas for which the discharge point has not changed are not subject
to the peak flow rate control standards.
E.
Areas located outside of the site (i.e., areas outside of the regulated
activity) that drain through a proposed site are not subject to peak
flow rate control requirements. Drainage facilities located on the
site shall be designed to safely convey flows from outside of the
site through the site.
F.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate controls shall be separately addressed for
each drainage area.
G.
The effect of structural and nonstructural stormwater management
practices implemented as part of the overall site design may be taken
into consideration when calculating total storage volume and peak
flow rates.
A.
Stormwater runoff from all regulated activity sites with a drainage
area of greater than five acres shall be calculated using a generally
accepted calculation technique(s) that is based on the NRCS Soil Cover
Complex Method. Table 188-19.1 summarizes acceptable computation methods.
The method selected for use shall be based on the individual limitations
and suitability of each method for a particular site. The use of the
Rational Method to estimate peak discharges for drainage areas greater
than five acres shall be permitted only upon approval by the Municipal
Engineer.
|
Table 188-19.1
Acceptable Computation Methodologies for SWM Site Plan
| ||
|---|---|---|
|
Method
|
Developed by
|
Applicability
|
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
|
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans where limitations described
in TR-55 are met
|
|
HEC-1/HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
|
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites up to five acres, or as approved by the municipality
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
|
B.
All calculations using the Soil Cover Complex Method shall use the
appropriate design rainfall depths for the various return period storms
consistent with this chapter. Rainfall depths used shall be obtained
from NOAA Atlas 14 values consistent with a partial duration series.
When stormwater calculations are performed for routing procedures
or infiltration, water quality and runoff volume functions, the duration
of rainfall shall be 24 hours.
C.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration (duration) and
storm events with rainfall intensities obtained from NOAA Atlas 14
partial duration series estimates, or the latest version of the PennDOT
Drainage Manual (PDM Publication 584). Times of concentration shall
be calculated based on the methodology recommended in the respective
model used. Times of concentration for channel and pipe flow shall
be computed using Manning's equation.
D.
The applicant shall utilize the following ground cover assumptions
for all predevelopment water quality and runoff volume, infiltration
volume and peak flow rate calculations:
(1)
For regulated activities involving new development, the following
ground cover assumptions shall be used:
(2)
For regulated activities involving redevelopment, the following ground
cover assumptions shall be used:
(a)
For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."
(b)
For areas that are not woods or not impervious surfaces, predevelopment
calculations shall assume ground cover of "meadow."
(c)
For areas that are impervious surfaces, predevelopment calculations
shall assume at least 20% of the existing impervious surface area
to be disturbed as "meadow" ground cover.
(3)
The applicant shall determine which stormwater standards apply to
the proposed regulated activity as follows:
(a)
Stormwater standards for new development shall apply to all
proposed regulated activities that involve only new development activities
as defined in this chapter.
(b)
Stormwater standards for redevelopment shall apply to all proposed
regulated activities that involve only redevelopment activities as
defined in this chapter.
(c)
At the discretion of the Municipal Engineer, regulated activities
that involve a combination of both new development and redevelopment
activities, as defined in this chapter, may either:
[1]
Apply the stormwater standards (redevelopment or new development)
that are associated with the activity that involves the greatest amount
of land area; or
[2]
Apply the redevelopment and new development stormwater standards
to the corresponding redevelopment and new development portions of
the proposed regulated activity.
E.
Runoff curve numbers (CN) for both predevelopment and proposed (postconstruction)
conditions to be used in the Soil Cover Complex Method shall be obtained
from Table C-1 in Appendix B[1] of this chapter.
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
F.
Runoff coefficients (C) for both predevelopment and proposed (postconstruction)
conditions for use in the Rational Method shall be obtained from Table
F-2 in Appendix B[2] of this chapter.
[2]
Editor's Note: Appendix B is included as an attachment to this chapter.
G.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
H.
Hydraulic computations to determine the capacity of pipes, culverts,
and storm sewers shall be consistent with methods and computations
contained in the Federal Highway Administration Hydraulic Design Series
Number 5 (Publication No. FHWA-NHI-01-020 HDS No. 5, as amended).
Hydraulic computations to determine the capacity of open channels
shall be consistent with methods and computations contained in the
Federal Highway Administration Hydraulic Engineering Circular Number
15 (Publication No. FHWA-NHI-05-114 HEC 15, as amended). Values for
Manning's roughness coefficient (n) shall be consistent with Table
3-1 in Appendix B[3] of this chapter.
[3]
Editor's Note: Appendix B is included as an attachment to this chapter.
A.
Any stormwater basin required or regulated by this chapter designed
to store runoff and requiring a berm or earthen embankment shall be
designed to provide an emergency spillway to safely convey flow up
to and including the 100-year proposed conditions. The height of embankment
shall provide a minimum 1.0 foot of freeboard above the maximum pool
elevation computed when the facility functions for the 100-year proposed
conditions inflow. Should any BMP require a dam safety permit under
Pa. Code Chapter 105 regulations, the facility shall be designed in
accordance with and meet the regulations of Pa. Code Chapter 105 concerning
dam safety. Pa. Code Chapter 105 may require the safe conveyance of
storms larger than 100-year event.
B.
Any drainage conveyance facility and/or channel not governed by Pa.
Code Chapter 105 regulations shall be designed to convey, without
damage to the drainage facility or roadway, runoff from the twenty-five-year
storm event. Larger storm events (fifty-year and 100-year storms)
shall also be safely conveyed in the direction of natural flow without
creating additional damage to any drainage facilities, nearby structures,
or roadways.
C.
Conveyance facilities to or exiting from stormwater management facilities
(i.e., detention basins) shall be designed to convey the design flow
to or from the facility.
D.
Roadway crossings or structures located within designated floodplain
areas shall be able to convey runoff from a 100-year design storm
consistent with Federal Emergency Management Agency National Flood
Insurance Program — Floodplain Management Requirements.
E.
Any stormwater management facility located within a PennDOT right-of-way
shall comply with PennDOT minimum design standards and permit submission
and approval requirements.
F.
Adequate erosion protection and energy dissipation shall be provided
along all open channels and at all points of discharge. Design methods
shall be consistent with the Federal Highway Administration Hydraulic
Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as
amended) and the PADEP Erosion and Sediment Pollution Control Program
Manual (Publication No. 363-2134-008, as amended), or other design
guidance acceptable to the Municipal Engineer.
A.
In order to protect and improve water quality, a riparian buffer
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian buffer. Riparian buffer
easement agreements shall be submitted to the municipality's Solicitor
for review and approval prior to recording.
B.
Except as required by Pa. Code Chapter 102, the riparian buffer easement
shall be measured to be the greater of the limit of the 100-year floodplain
or a minimum of 35 feet from the top of the stream bank (on each side).
C.
Minimum management requirements for riparian buffers.
(1)
Existing native vegetation shall be protected and maintained within
the riparian buffer easement.
(2)
Whenever practicable invasive vegetation shall be actively removed
and the riparian buffer easement shall be planted with native trees,
shrubs and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
D.
The riparian buffer easement shall be enforceable by the municipality
and shall be recorded in the appropriate County Recorder of Deeds
office, so that it shall run with the land and shall limit the use
of the property located therein. The easement shall allow for the
continued private ownership and shall count toward the minimum lot
area as required by zoning, unless otherwise specified in the municipal
Zoning Ordinance.[1]
E.
Any permitted use within the riparian buffer easement shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
G.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
The following permit or other regulatory requirements may apply
to certain regulated activities and shall be met prior to (or as a
condition of) final approval by the municipality of the SWM site plan
and prior to commencement of any regulated activities, as applicable:
A.
All regulated activities subject to permit or regulatory requirements
by PADEP under regulations at Title 25 Pennsylvania Code Chapter 102,
or erosion and sediment control requirements of the municipality.
B.
Work within natural drainageways subject to permit by PADEP under
Title 25 Pennsylvania Code Chapter 105.
C.
Any BMP or conveyance that would be located in or adjacent to surface
waters of the commonwealth, including wetlands, subject to permit
by PADEP under Title 25 Pennsylvania Code Chapter 105.
D.
Any BMP or conveyance that would be located on or discharge to a
state highway right-of-way, or require access to or from a state highway
and be subject to approval by PennDOT.
E.
Culverts, bridges, storm sewers, or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by PADEP under Title 25 Pennsylvania
Code Chapter 105.
To control postconstruction stormwater impacts from regulated
activities and meet state water quality requirements, BMPs shall be
provided in the site design that replicate predevelopment stormwater
infiltration and runoff conditions, such that postconstruction stormwater
discharges do not degrade the physical, chemical, or biological characteristics
of the receiving waters. The green infrastructure and low-impact development
(LID) practices provided in the PA BMP Manual, as well as the guidance
on green infrastructure LID and conservation design (CD) provided
in Appendix D,[1] shall be utilized for all regulated activities wherever
possible. The applicant shall comply with the following water quality
and runoff volume requirements for all regulated activities, including
all new development and redevelopment activities:
A.
The postconstruction total runoff volume shall not exceed the predevelopment
total runoff volume for all storms equal to or less than the two-year,
twenty-four-hour duration precipitation (design storm) or a minimum
of 1.5 inches of runoff from all regulated impervious surfaces shall
be managed, whichever volume to be managed is greater. The water quality
and runoff volume to be managed shall consist of any runoff volume
generated by the proposed regulated activity over and above the predevelopment
total runoff volume and shall be captured and permanently retained
or infiltrated on the site. Permanent retention options may include,
but are not limited to, reuse, evaporation, transpiration, and infiltration.
B.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 188-19D of this chapter.
C.
The design of the stormwater management facility outlet shall provide
for protection from clogging and unwanted sedimentation.
D.
BMPs that moderate the temperature of stormwater shall be used to
protect the temperature of receiving waters.
E.
Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 188-15. The infiltration volume required under § 188-15 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.
F.
Runoff from the disturbed area shall be treated for water quality
prior to entering existing waterways or water bodies. If a stormwater
management practice does not provide water quality treatment, then
water quality BMPs shall be utilized to provide pretreatment prior
to the runoff entering the stormwater management practice.
G.
The municipality may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 188-13R.
H.
When the regulated activity contains or is divided by multiple drainage
areas, the water quality and runoff volume shall be separately addressed
for each drainage area.
I.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
J.
Areas located outside of the site (i.e., areas outside of the regulated
activity) may be excluded from the calculation of the water quality
and runoff volume requirements.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
