The low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities. Water volume controls shall be implemented using the Design Storm Method in §
204-15A or the Simplified Method in §
204-15B. For regulated activity involving less than one acre of impervious coverage that does not require hydrologic routing to design the stormwater facilities, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology, and/or other factors. The Design Storm Method in §
204-15A shall be used for all regulated activity involving greater than one acre of impervious coverage.
A. The Design Storm Method (CG-1 in the BMP Manual) may be used for
any size of regulated activity. This method requires detailed modeling
to achieve the following standards.
(1) The post-development total runoff volume shall not increase for all
storms equal to or less than the two-year twenty-four-hour duration
precipitation.
(2) For modeling purposes:
(a)
Existing (predevelopment), non-forested, pervious areas must
be considered meadow.
(b)
Twenty percent of existing impervious area, when present, shall
be considered meadow in the model for existing conditions.
B. The Simplified Method (CG-2 in the BMP Manual) is independent of
site conditions and may be used for projects involving regulated activities
proposing equal to or less than one acre of impervious coverage and
that do not require design of stormwater storage facilities. When
the Simplified Method is used to address stormwater management needs
of new impervious surfaces, the following design standards shall be
achieved:
(1) Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2) At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow and shall not be
released into the surface waters of the commonwealth. Removal options
for the first one inch of runoff include, but are not necessarily
limited to, reuse and infiltration.
(3) Infiltration facilities shall be designed to accommodate infiltration of as much of the permanently removed runoff as site conditions will allow. If the soils within the project area do not allow for infiltration of the entire first one inch of runoff from new impervious surfaces, other forms of runoff volume control shall be used to achieve the required removal volume. Such measures may include, but are not limited to, vegetated roofs, biorention, and capture-and-reuse systems. In addition, the infiltration alternative authorized in §
204-15C may be employed.
(4) This method is exempt from the requirements of §
204-16, Rate controls.
C. Infiltration alternative. Where infiltration is not possible due to soil characteristics or is not desirable given other characteristics, water quality control may be proposed as an alternative to strict adherence to the volume control standards of §
204-15 of this chapter. Where water quality control is proposed, the following standards shall be achieved.
(1) At a minimum, the following documentation shall be provided to justify
the proposal to reduce the infiltration requirements:
(a)
Description of and justification for field infiltration/permeability
testing with respect to the type of test and test locations.
(b)
An interpretive narrative describing existing soils of the site
and their structure as these relate to the interaction between soils
and water characteristics of the site. In addition to providing soil
and soil profile descriptions, this narrative shall identify depth
to seasonal water tables and depth to bedrock and provide a description
of all subsurface elements (restrictive layers, geology, etc.) that
influence the direction and rate of subsurface water movement.
(c)
A qualitative assessment of the site's contribution to annual
aquifer recharge shall be made, along with the identification of any
restrictions or limitations associated with the use of designed infiltration
facilities.
(d)
The provided documentation must be signed and sealed by a professional
engineer or geologist.
(2) Water quality BMPs shall be implemented on all permanent stormwater
discharges from the proposed project site to achieve pollutant removal
efficiencies in accordance with the Table 204-15.1.
Table 204-15.1 Required Pollutant Removal Efficiencies
for Infiltration Alternatives
|
---|
Pollutant Load
|
Units
|
Required Removal Efficiency (%)
|
---|
Total suspended solids (TSS)
|
Pounds
|
85%
|
Total phosphorus (TP)
|
Pounds
|
85%
|
Total nitrate (NO3)
|
Pounds
|
50%
|
(3) Design guidance from the most current version of the Pennsylvania
Stormwater Best Management Practices Manual, or equivalent resource
as precoordinated with Bonneauville Borough, shall be consulted when
choosing design criteria for water quality BMPs.
Where an applicant proposes to utilize riparian buffers as the
means to meet the requirements of this chapter, said riparian buffers
shall be established and/or maintained in accordance with the BMP
Manual or the publication Riparian Forest Buffer Guidance, published
November 2010, by the Pennsylvania Department of Environmental Protection,
and as may be amended or updated.
Roof drains, sump pumps, and footer drains should discharge
to infiltration or vegetative BMPs and, to the maximum extent practicable,
satisfy the criteria for DIAs. Discharges of each should be conveyed
in such a manner as to not cause water problems for adjoining property
owners.
No person shall modify, remove, fill, landscape, or alter any
SWM BMPs, facilities, areas, or structures in a manner, without the
written approval of Bonneauville Borough, with the exception of necessary
maintenance activities such as mowing.