A.
The applicant shall meet requirements as contained in 25 PA Code,
Chapters 92 and 102 as required and applicable as follows:
B.
Evidence of any necessary plan or permit approval for Earth Disturbance
activities from PADEP or the McKean County Conservation District must
be provided to the municipality.
C.
A copy of the approved erosion and sediment control plan and any other permit, as required by PADEP or the McKean County Conservation District, shall be available at the project site at all times if required under Chapter 102.
D.
Construction of temporary roadways (e.g., for utility construction, timber harvesting, etc.) shall comply with all applicable standards for erosion and sedimentation control and stream crossing regulations under 25 PA Code, Chapters 102 and 105. The erosion and sedimentation control plan shall be submitted to the McKean County Conservation District for approval and shall address the following, as applicable:
(1)
Design of the roadway system, including haul roads, skid roads, landing
areas, trails, and storage and staging areas.
(2)
Runoff control structures (e.g., diversions, culverts, detention
ponds, etc.).
(3)
Stream crossings for both perennial and intermittent streams.
(4)
Access to public roadways, including design of rock construction
entrance for mud and debris control.
(5)
A remediation plan for restoring the disturbed area through re-grading,
topsoil placement, reseeding, and other stabilization techniques,
as required.
E.
Additional erosion and sedimentation control design standards and
criteria that must be applied where infiltration BMPs are proposed
include the following:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase, as to maintain their
maximum infiltration capacity.
(2)
Infiltration BMPs shall be protected from receiving sediment-laden
runoff.
(3)
The source of protection for infiltration BMPs shall be identified
(i.e. orange construction fence surrounding the perimeter of the BMP).
F.
McKean County description.
(1)
There are about 120 frost-free days during the year in McKean County.
Annual precipitation varies throughout the county but is about 42
inches of which about 21 inches drains out of the county. Several
weather records are held by McKean County including the world record
for a four-and-a-half-hour rainfall of 30.8 inches on July 18, 1942,
Smethport (NOAA) and National Record of 34.5 inches July 17-18, in
Smethport. The average annual snowfall amounts up to 90 inches a year.
(2)
Rainfall.
(a)
Figures 3.1 and 3.2 show the rainfall statistics for McKean
County. The average rainfall, shown in Figure 3.1 portrays the amount
of precipitation throughout each year since November 1934. Although
there can be significant variation in the annual rainfall total (between
32 and 61 inches). While this variation can have a significant impact
on water supply and vegetative growth, it is the quantity of rain
in a relatively short time period (one-hour, six-hour, twenty-four-hour,
forty-eight-hour) that receives the focus of most stormwater regulations.
(b)
Figure 3.2 show the annual maximum rainfall events recorded
over the same time period graphed and the NOAA Atlas 14 values for
the two-year and 100-year storm events, derived using partial series
data. The annual maximum rainfall for a station is constructed by
extracting the highest precipitation amount for a particular duration
in each successive year of record. A partial duration series is a
listing of period of record greatest observed precipitation depths
for a given duration at a station, regardless of how many occurred
in the same year. Thus, a partial data series accounts for various
storms that may occur in a single year.
(c)
Historical focus on the annual maximum rainfall and the larger
magnitude, low-frequency storm events as done in previous stormwater
planning efforts throughout Pennsylvania has lead to neglect of 1)
the majority of storm events that are smaller than the annual maximum
and their subsequent value to the landscape in terms of volume and
water quality and 2) the fact that inclusion of every storm may increase
the twenty-four-hour rainfall total typically used in design.
(d)
The majority of rainfall volume in McKean County comes from
storms low magnitudes. Only 10% of the daily rainfall values between
1934 and 2009 exceeded 0.7 inch, which is below any design standards
currently being used in the county. Thus, any stormwater policy should
incorporate provisions such as water quality, infiltration, or retention
BMPs that account for these small events. It is important to acknowledge
that many of these smaller rainfall events lead to larger runoff events
as they may be saturating the soils prior to a larger storm or occurring
within a short time period that still overwhelm existing conveyance
facilities.
(e)
For the gage shown in Figure 3.1 and 3.2, the NOAA Atlas twenty-four-hour,
two-year storm event total of 2.48 inches was exceeded 93 times in
75 years of data. When analyzing only the annual maximum series, the
NOAA Atlas twenty-four-hour, two-year storm was exceeded only 27 times.
Thus, viewing only the annual maximum series neglects a substantial
number of significant historical rainfall events. The implication
for stormwater policy in McKean County is that best management practices
should incorporate the NOAA Atlas 14, partial duration data series
to ensure the best available data is being used for design purposes.
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