Vehicle fueling stations
| |
Industrial manufacturing sites*
| |
Salvage yards
| |
Recycling centers
| |
Hazardous material storage areas*
| |
Interstate highways
|
*
|
The Township Engineer will determine if a development is a Sensitive
Development on a case-by-case basis. The Pennsylvania DEP wellhead
protection contaminant source list shall be used as a guide in these
determinations. Industrial manufacturing site and hazardous material
storage areas must provide NPDES SIC codes.
|
Drainage Area Size
(acres)
|
Model
| |
---|---|---|
Up to 100
|
NRCS's TR-55 or TR-20
| |
Over 100
|
NRCS's TR-20 or HEC-1 (HEC-HMS)
|
Return Period
|
Minimum Discharge
| |
---|---|---|
1-year
|
Qpmin = 0.018 (DA) + 0.2
| |
2-year
|
Qpmin = 0.03 (DA) + 0.4
| |
10-year
|
Qpmin = 0.09 (DA) + 1.0
|
Where:
| ||||
DA
|
=
|
the drainage area in acres
| ||
Qpmin
|
=
|
minimum allowable peak runoff rate in cfs
|
Size
|
Model
| |
---|---|---|
Up to 200 acres
|
Rational Method
| |
Between 200 acres and 1.5 square miles
|
HEC-1
PSRM
TR-20
| |
Over 1.5 square miles
|
PSU-IV with the carbonate adjustment factor at the discretion
of the Township Engineer
| |
Other methods as approved by the Township Engineer such as SWMM,
SWIRM-ROUTE, etc.
|
All impervious areas
|
C = 0.95
| |
All pervious areas
|
C = 0.30
|
"This project is located within a source water protection area
for the (insert name of water provider). Blasting should be used as
a last resort method of rock excavation. If blasting techniques are
to be employed, the contractor shall provide the Township and the
water provider with information supporting the use of blasting techniques
along with copies of blasting permits."
|
WQdepth = 0.25 + (0.012)2.9(0.044(SIA))
| |
WQv = WQdepth(A)/12
|
Where:
| ||||
WQv
|
=
|
water quality volume in acre-feet
| ||
WQdepth
|
=
|
depth in inches that must be captured for impervious areas
| ||
SIA
|
=
|
percent of site impervious area (all paved areas and roof with
asphalt-based roofs)
| ||
A
|
=
|
total of all paved areas and asphalt-based roofs on site in
acres
|
WQdepth = the larger of 0.5 inches or
0.25 + (0.012)2.9(0.044(SIA))
| |
WQv = WQdepth(A)/12
|
Where:
| ||||
WQv
|
=
|
water quality volume in acre-feet
| ||
WQdepth
|
=
|
depth in inches that must be captured for impervious areas
| ||
SIA
|
=
|
percent of site impervious area (all paved areas and roof with
asphalt-based roofs)
| ||
A
|
=
|
total of all paved areas and asphalt-based roofs on site in
acres
|
Nonstructural Technique
|
Water Quality Credit
| |
---|---|---|
Drainageway protection (DWP)
|
Subtract drainageway protection areas from impervious site area
in WQv computation
| |
Natural area conservation (NAC)
|
Subtract conserved natural areas from impervious site area in
WQv computation
| |
Filter/buffer area
|
Subtract impervious areas discharged over pervious areas from
impervious site area in WQv computation
|
IAc = WIA LIA
|
Where:
| ||||
IAc
|
=
|
Impervious area recharge credit (L2)
| ||
LIA
|
=
|
Length of impervious area measured perpendicular to the sheet
flow direction (L)
| ||
WIA
|
=
|
Width of impervious area (L). Maximum width permitted for credit
is the smaller of 100 feet or twice the width of the vegetated filter
strip
|