*In areas not covered by a stormwater performance district,
an 80% release rate or less is recommended as a standard. This is
to apply a "factor of safety" to stormwater calculations; to account
for the many variables in site design and stormwater management; and
to avoid a land development project inadvertently increasing runoff
and causing harm downstream.
|
Regulated Development Activity Table
| |||
---|---|---|---|
SWM Plan Requirement
|
New Impervious Area for New and Redevelopment
|
Disturbed Area*
|
Next Steps
|
Exempt
|
Less than 1,000 square feet
|
Less than 1 acre
|
Comply with exemption section of this chapter
|
Waivers; modifications; demonstrated equivalency
|
Less than 1/2 acre, subject to municipal approval
|
Less than 1 acre
|
Comply with waivers; modifications; demonstrated equivalency
section of this chapter
|
Small project (per definition), refer to Appendix C[1]
|
1,000 square feet to 3,000 square feet
|
3,000 square feet to 5,000 square feet
|
Submit small project site plan complete with all attachments
|
Stormwater management plan meeting the ordinance requirements
|
Greater than 3,000 square feet and if waiver/modification/demonstrated
equivalence criteria are not met
|
Greater than 5,000 square feet
|
Consult a qualified professional
|
Note:
| |
*
|
The above table is only applicable for projects with earth disturbance
less than one acre and that have not had cumulative impacts, within
five years preceding the permit application date, that are in excess
of the square foot limits.
|
Acceptable Computation Methodologies for Stormwater Management
Plans
| ||
---|---|---|
Method
|
Developed By
|
Applicability
|
Win TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
Win TR-55 (or commercial computer package based on TR-55 ie.
VT/PSUHM
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
|
HEC-1, HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
PennDOT 584 (based on rational method)
|
PennDOT
|
Applicable under standards established by PennDOT; not to be
used for runoff volume and pond sizing computations
|
EFH2
|
USDA NRCS
|
Applicable in agricultural areas subject to the program limits
|
SWMM
|
EPA
|
Applicable in urban and suburban areas subject to limits established
by EPA
|
PA DEP BMP Manual 2006
|
PA DEP
|
Applicable under standards established by PA DEP
|
Other methods
|
Varies
|
Other methodologies approved by the Township
|