[Ord. 2125, 7/14/2014; as amended by Ord. No. 2217, 9/12/2022]
The green infrastructure and low-impact development practices
provided in the BMP Manual shall be utilized for all regulated activities
to the maximum extent practicable. Water volume controls shall be
implemented using the Design Storm Method in Subsection A or the Simplified
Method in Subsection B below. For regulated activity areas equal to
or less than one acre that do not require hydrologic routing to design
the stormwater facilities, this Part establishes no preference for
either methodology; therefore, 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 other factors.
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. Do not increase the post-development total runoff volume for all
storms equal to or less than the two-year, twenty-four-hour duration
precipitation.
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.
B. The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and should be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities greater than one acre or for projects that require design
of stormwater storage facilities. For new impervious surfaces:
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, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options include reuse, evaporation, transpiration, and infiltration.
3. Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed runoff should be infiltrated.
4. This method is exempt from the requirements of § 224, Rate
Controls.
[Ord. 2125, 7/14/2014; as amended by Ord. No. 2217, 9/12/2022]
For areas not covered by a release rate map from an approved
Act 167 Stormwater Management Plan, post-development discharge rates
shall not exceed the predevelopment discharge rates for the one-,
two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour
storms. If it is shown that the peak rates of discharge indicated
by the post-development analysis are less than or equal to the peak
rates of discharge indicated by the predevelopment analysis for one-,
two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour
storms, then the requirements of this section have been met. Otherwise,
the applicant shall provide additional controls as necessary to satisfy
the peak rate of discharge requirement.