"I, (signature of consultant and date), hereby certify that
there are no wetlands on the subject property, the proposed project
will not impact off-site wetlands, and wetland permits are not required
from the state or federal government."
|
NOTE: For further description of those and other
methods, see the Pennsylvania Stormwater Best Management Practices
Manual.
|
Table 611.1
Exemption Criteria
| |||
---|---|---|---|
Parcel Size*
(acres)
|
Minimum Separation Distance
(feet)
|
Maximum Additional Impervious Area — Since The Date
of Adoption of This Chapter
(square feet)
| |
0.5
|
10
|
2,700
| |
1.0
|
50
|
4,600
| |
1.5
|
100
|
6,200
| |
2.0
|
125
|
7,600
| |
2.5
|
150
|
9,000
| |
3.0
|
175
|
10,300
| |
3.5
|
200
|
11,500
| |
4.0
|
225
|
12,700
| |
4.5
|
250
|
13,800
| |
5.0
|
275
|
15,000
| |
>5.0
|
300
|
15,000
|
*
|
NOTE: Parcel size to be rounded to the nearest
half-acre for the purpose of utilizing Table 611.1.
|
Time of Concentration = Tc = [(Tlag/.6) * 60] (minutes)
|
Where:
| ||||
Tlag
|
=
|
Lag time (hours)
| ||
L
|
=
|
Hydraulic length of watershed (feet)
| ||
Y
|
=
|
Average overland slope of watershed (percent)
| ||
S
|
=
|
Maximum retention in watershed as defined by:
| ||
S
|
=
|
[(1,000/CN) - 10]
| ||
CN
|
=
|
SCS curve number for watershed as defined by the SCS Loss Method
|
Table 614.1 — Acceptable Computation Methodologies
for Stormwater Management Plans
| |||
---|---|---|---|
Method*
|
Method Developed By
|
Applicability
| |
TR-20 or Commercial Package Based on TR-20
|
USDA — NRCS
|
When use of full model is desirable or necessary
| |
TR-55 Or Commercial Package Based on TR-55
|
USDA — NRCS
|
Applicable for plans within the models limitations
| |
HEC — HMS
|
U.S. Army Corps of Engineers
|
When full model is desirable or necessary
| |
PSRM
|
Penn State University
|
When full model is desirable or necessary
| |
Rational Method or Commercial Package based on Rational Method
|
Emil Kuiching (1889)
|
For sites less than 20 acres
| |
Other Methods
|
Various
|
As approved by the Municipal Engineer
|
*
|
NOTE: Successors to the above methods are also
acceptable. These successors include Win TR55 for TR-55 and Win TR20
for TR-20.
|
Rev = [(S)(Rv)(A)] / 12
| ||||
Where:
| ||||
Rev
|
=
|
Groundwater Recharge Volume (ac-ft)
| ||
S
|
=
|
Soil Specific Recharge Factor
| ||
Rv
|
=
|
0.05 + 0.009(I)
| ||
I
|
=
|
Percent Impervious Cover (i.e., use I = 20 when there is 20%
impervious cover)
| ||
A
|
=
|
Site area (acres)
|
Rev=(S)(Ai)
| ||||
Where:
| ||||
Rev
|
=
|
Groundwater Recharge Volume (ac-ft)
| ||
S
|
=
|
Soil Specific Recharge Factor
| ||
Ai
|
=
|
Measured impervious cover (acres)
|
Hydrologic Soil Group
|
Soil Specific Recharge Factor
(S)
| |
---|---|---|
A
|
0.39
| |
B
|
0.26
| |
C
|
0.14
| |
D
|
0.07
|
WQv = [(P)(Rv)(A)]
/ 12
| ||||
Where:
| ||||
WQv
|
=
|
Water Quality Volume (ac-ft)
| ||
P
|
=
|
1.1 inches of rainfall
| ||
Rv
|
=
|
0.05 + 0.009(I)
| ||
I
|
=
|
Percent Impervious Cover (i.e., use I = 20 when there is 20%
impervious cover)
| ||
A
|
=
|
Site Area (acres)
|