methodol ogi es
- The project plan shall specify permanent stormwater BMPs to be implemented, operated
and maintained to meet legal water quality, rate and volume requirements. Ifmethods other
than low impact development (LID) and green infrastructure methods are proposed to
achieve the volume and rate controls required under this ordinance, the SWM Site Plan
must include a detailed justification demonstrating that the use of LID and green
infrastructure is not practicable.
- In order to protect and maintain water quality, additional stormwater runoff created by the
development project must be captured, stored and treated. In addition, post construction
stormwater infiltration of runoff must replicate preconstruction infiltration of runoff to the
maximum extent possible with the exception of hot spots. As a minimum, this shall be a
volume of additional runoff generated by a 2-year, 24 hour storm. Preferred BMP's for a
hot spot include storm inlet filters, proprietary stormwater quality devices, underground
detention tanks, detention ponds with forebays, tree planting, green roof. Permeable
pavement, infiltration BMP's, and rain gardens are not recommended for hotspots.
- In addition to the provisions set forth in paragraphs A. through c., inclusive, as set forth
above, all regulated development activities within the [Municipality] shall be designed,
implemented, operated and maintained to meet the purposes of this Ordinance, through
these two elements:
- Erosion and sediment control during the earth disturbance activities (e.g., during
- Water quality, rate and volume protection measures after completion of earth
disturbance activities (e.g., post-construction stormwater management), including
operations and maintenance.
- No regulated development activities within Bolivar Borough shall commence until the
requirements of this Ordinance are met.
- All best management practices (BMPs) used to meet the requirements of this Ordinance
shall conform to the State water quality requirements, and any more stringent requirements
as determined by Bolivar Borough.
- LID and green infrastructure techniques described in the P A DEP Stormwater BMP Manual
2006 or most current edition are encouraged.
§30B. Watershed Standards
- The stormwater management performance standards in this Ordinance are intended to
implement the provisions, standards and criteria contained in the Pennsylvania Stormwater
Management Act (Act 167), 32 P.S. §680.1 et seq. If there is any discrepancy between the
provisions of this Ordinance and the provisions, standards and criteria of the Act, or if a
storm water management plan is subsequently approved and adopted by the appropriate
governmental agency or body, then the provisions, standards and criteria of the current
watershed plan shall govern.
- Management of stormwater runoff is key objective of25 Pa.Code, Chapter 93, of the DEP Regulations, because runoff can change the physical, chemical and biological integrity of waterbodies thereby impacting rate, volume and water quality.
- The project plan shall describe how these rate, volume and water quality protection
requirements will be met. Infiltration BMPs shall be evaluated and utilized to the maximum
extent possible to manage the net change in stormwater runoff generated so that post
construction discharges do not degrade the physical, chemical or biological characteristics
of the receiving waters. These BMPs may be used to satisfy all or part of the requirements
found within this Ordinance.
- Refer to the Stormwater Performance Districts outlined in Appendix A, and the
Westmoreland County Integrated Water Resources Plan (IWRP) at
www.westmorelandstormwater.org. The project plan shall describe how the proposed
project will address performance standards, impairments, and pollutant loading found in the
IWRP. For areas not covered by a stormwater performance district, the release rate shall be
80% of the pre-development peak flow as set by the municipality.
§309. Design Criteria for Stormwater Management Facilities and BMPs.
A. General Criteria.
- Applicants may select runoff control techniques, or a combination of techniques,
which are most suitable to control stormwater runoff from the development site.
Refer to the Acceptable Computation Methodologies table of this ordinance. All
controls must be subject to approval of the Bolivar Borough engineer and the WCD.
The [Municipality] engineer may request specific information on design and/or
operating features of the proposed stormwater controls in order to determine their
suitability and adequacy in terms of the standards of this Ordinance.
- If the proposed development site is located in an impaired water shed according to
Category 4 of the P A Integrated Water Quality Monitoring and Assessm ent Report,
or in a watershed with a TMDL according to Category 5 of the same Report, the
applicant shall identify the source and cause of impairment and shall propose, if
required or applicable the use ofBMPs to mitigate any impacts to the waters.
- The applicant should consider the effect of the proposed stormwater management
techniques on any special soil conditions or geological hazards which may exist on
the development site. In the event such conditions are identified on the site, the
Bolivar Borough engineer may require in depth studies by a competent geotechnical
engineer. Not all stormwater control methods may be advisable or allowable at a
particular development site.
- The applicant shall consider the effect of the proposed stormwater management
techniques on existing stream impairments and pollutant loading. Refer to the
Westmoreland County Integrated Water Resources Plan (IWRP) at
- The applicant shall consider existing conditions on the site for the prior [five] years
to determine prevailing land use and impervious cover, and shall consider 20% of
existing impervious cover as meadow for pre-existing conditions on redevelopment
- The stormwater management practices to be used in developing a stormwater management plan for a particular site shall be selected according to the following order of preference:
a. Site planning for locating proposed buildings, impervious areas and grading which minimizes disruption of the natural site characteristics especially utilizing low impact development techniques.
- Minimization of impervious areas and promotion of retentive grading.
- Implementation of non-structural measures (refer to the PA DEP
Stormwater BMP Manual 2006 or current edition).
d. Implementation of innovative / green infrastructure structural measures (refer to the PA DEP Stormwater BMP Manual 2006 or current edition).
e. Stormwater detention/retention structures.
- Any BMP which is a dam, culvert, stream obstruction or encroachment or outfall
as defined in 25 Pa.Code, Chapter 105, shall be designed according to the
requirements in those regulations.
- Drainage easements shall be provided for all stormwater conveyance and BMPs
serving multiple properties and not located within a public right of way. Easements
shall include ingress and egress to a public right of way, and shall be recorded at
the County with the final plan. Terms of easement shall prohibit excavation or
placement of fill or structures and any alteration that may adversely affect the flow
of stormwater within any portion of the easement.
- No person shall install, create, modify, remove, fill, landscape or otherwise alter
or place any structure, soil, rock, material or vegetation in or on, or otherwise
adversely affect, any stormwater management facility or any area within a
stormwater easement without the written approval of the Bolivar Borough.
- Persons engaged in land development activities shall provide the required [financial
security, O&M Agreements] to the [municipality] as outlined in the Appendix B.
B. Criteria for Stormwater Management Facilities and BMPs.
- If stormwater management facilities and BMPs are utilized for the development
site, the facility(s) shall be designed such that post-development peak runoff rates
from the developed site are controlled to those rates defined by a Stormwater
Management Performance District for the 100 year storm frequencies. Rainfall
data shall be obtained from NOAA Atlas 14 or other source as approved by the
- All stormwater management facilities and BMPs shall be equipped with
outlet/overflow structures to provide rate discharge control for the designated storm
frequencies. Provision shall also be made to safely pass the entire post-development
100-year storm without breaching or otherwise damaging the facilities, downstream
or neighboring properties.
- Release of stormwater flow from a development site must be to an existing
stormwater conveyance or easement whether natural or man-made. Calculations
and information shall be presented as to the ownership, responsible party, capacity,
and stability of such conveyance. Release of 'sheet flow' as from a level spreader,
will be permitted on a case-by-case basis as approved by the municipality and
- All stormwater management facilities and BMPs shall be designed to control volume and water quality as defined by the Stormwater Management Performance District. Refer to Appendix A.
- Shared stormwater management facilities and BMPs, which provide control of
runoff for more than one development site within a single subarea may be
considered and are encouraged. Such facilities shall meet the criteria contained in
this Section. In addition, runoff from the development sites involved shall be
conveyed to the facility in a manner that avoids adverse impacts (such as flooding
or erosion) to channels and properties located between the development site and the
shared storage facilities.
- Where stormwater management facilities and BMPs will be utilized, multiple use
facilities, such as wetlands, lakes, ballfields or similar recreational/open space uses
are encouraged wherever feasible, subject to the approval of the [Municipality].
- Other considerations which shall be incorporated into the design of the stormwater
management facilities and BMPs include:
- Inflow and outflow structures shall be designed and installed to prevent
erosion and embankments, cuts, fills and bottoms of impoundment type
structures should be protected from soil erosion.
- Control and removal of debris both in the storage structure and in inlet or
outlet devices shall be a design consideration.
- Inflow and outflow structures, pumping stations and other structures shall
be designed and protected, using safety benches, trash racks, energy
dissipaters and other means to minimize safety hazards.
- Access may be restricted as specified by [the provisions for fencing
swimming pools] as found in the municipality Zoning Ordinance, and in
appropriate instances such restriction of access may include fencing in a
minimum height of 6 feet
- Interior slopes of storage ponds shall not exceed a ratio of three to one
horizontal to vertical dimension with a combination of interior and exterior
slopes not exceeding five. Steeper slopes may be approved by the
municipality engineer if documented to be stable by a geotechnical analysis.
f Landscaping shall be provided for the facility which stabilizes disturbed
areas and preserves the natural and beneficial values of the surrounding
- Facility shall be located to facilitate maintenance, considering the frequency
and type of equipment that will be required.
- Underground detention / retention / infiltration facilities shall be equipped
with open grate inlet or manhole access to facilitate visual inspections.
C. Criteria for Collection/Conveyance Facilities.
- All stormwater runoff collection or conveyance facilities, whether storm sewers or
other open or closed channels, shall be designed 'in accordance with the following
- All building sites shall use measures to provide drainage away from and
around the structure in order to prevent any potential flooding damage as
much as practical. Such measures shall include grading the surrounding
lawn or pavement area so that it slopes away from the structure by a minimum of 5% slope over a minimum distance of 10 feet; raising the floor of the structure so that it is a minimum of 6 inches above the predominate surrounding land elevation and above the designated floodplain elevation for those located within a floodplain; eliminating or waterproofing penetrations thru the structure's walls or foundation; constructing berms, curbs, or swales to divert surface water around the structure; arranging roof and area drains to carry water away from the structure.
- Developers proposing a land development or subdivision shall arrange
internal drainage within the subdivision so that surface water is safely
directed and channeled away from all structures within and adjacent to the
- Developers shall provide to all persons constructing a structure within a land
development site, standards including drawings and specifications to ensure
that those persons adhere to the general site plans and storm water
management plans for the development. Persons constructing a structure
within a land development site shall submit to the municipal engineer and
WCD drawings, calculations, and other information to show how they will
meet the stormwater management requirements of the development site.
- Lots located on the high side or low side of streets shall extend roof, trench
and area drains to a stable vegetated area, natural watercourse, the curb or
gutter line of roadway or storm collection/conveyance/control system (if
applicable) in accordance with the approved stormwater management plan
for the development site.
- For all building sites and lots, the inclusion ofrain barrels, rain gardens,
drywells and other strategies for infiltration of roof runoff close to its source
- Collection/conveyance facilities should not be installed parallel and less
than 10 feet from the top or bottom of an embankment, greater than or equal
to 15 feet height to avoid the possibility of failing or causing the
embankment to fail, unless documented to be stable by a geotechnical
- All collection/conveyance facilities shall be designed to convey the 100year
storm peak flow rate from the contributing drainage area and to carry it to
the nearest suitable outlet such as a stormwater control facility, curbed
street, storm sewer or natural watercourse.
- Where drainage swales or open channels are used, they shall be suitably
lined to prevent erosion and designed to avoid erosive velocities.
- Wherever storm sewers are proposed to be utilized, they shall comply with the
following additional criteria.;
- Where practical, designed to traverse under seeded and planted areas. If
constructed within 10 feet of road paving, walks or other surfaced areas,
drains shall have a narrow trench and maximum compaction of backfill to
prevent settlement of the superimposed surface or development.