A.
All land development within the Borough shall be designed, implemented,
operated and maintained to meet the purposes of this chapter through
these two elements:
B.
No approval of any subdivision or land development plans, or issuance of any building or occupancy permit, or the commencement of any earth disturbance at a project site within the Borough shall proceed until the requirements of this chapter are met, including approval of a project plan under § 230-17 and a permit under PADEP regulations, where applicable.
F.
Techniques described in Appendix E (Low-Impact Development) of this
chapter are encouraged because they reduce the costs of complying
with the requirements of this chapter and the state water quality
requirements.[1]
[1]
Editor's Note: Appendix E and other appendixes referenced
in this chapter are on file in the Borough office.
The following permit requirements apply to certain land development
activities and must be met prior to municipal approval of subdivision
approval or land development plans or issuance of building or occupancy
permits, where applicable:
A.
All earth disturbance activities subject to standards and possible
permit requirements by PADEP under regulations at 25 Pa. Code Chapter
102.
B.
Work within natural drainageways subject to permit by PADEP under
25 Pa. Code Chapter 105.
C.
Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by PADEP under 25 Pa. Code Chapter 105.
D.
Any stormwater management facility that would be located on a state
highway right-of-way subject to approval by the Pennsylvania Department
of Transportation (PennDOT).
E.
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by PADEP under 25 Pa. Code
Chapter 105.
A.
Any person conducting any land development activities in the Borough
involving earth disturbance of 5,000 square feet or greater shall
submit and obtain approval from the Borough of a project plan meeting
the requirements of this chapter prior to commencing the activity.
B.
The project plan shall describe the BMPs for erosion and sediment
control and the post-construction BMPs for water quality protection.
D.
The requirements in this section apply to the total land development
project, even if it is to take place in stages.
E.
All redevelopment projects shall evaluate the feasibility of reducing
site impervious area by at least 20%. Where project site conditions
prevent the reduction of impervious area, then stormwater BMPs shall
be evaluated to provide qualitative controls for at least 20% of the
site's impervious area.
A.
Earth disturbance activities of 5,000 square feet or greater require
design, implementation and maintenance of erosion and sediment control
BMPs that control erosion and prevent sediment pollution during the
earth disturbance activities.
B.
The BMPs shall be identified in a plan and a permit, if applicable,
as required by PADEP regulations at 25 Pa. Code Chapter 102.
C.
The local county conservation districts are frequently delegated
the authority to issue permits and other approvals by PADEP. Evidence
of any necessary permits for the earth disturbance activities from
the appropriate PADEP regional office or the local county conservation
district office, if delegated by DEP, must be provided to the Borough.
D.
A copy of the erosion and sediment control plan and any required
permit under 25 Pa. Code Chapter 102 shall be available at the project
site at all times.
A.
The project plan shall specify permanent stormwater BMPs to be implemented,
operated and maintained to meet legal water quality requirements.
Because water quality requirements vary depending on the uses of the
water bodies in the watershed, a framework methodology is provided
here.
B.
In order to protect and maintain water quality, additional stormwater
runoff created by the development project must be captured, stored
and treated. In addition, post-construction stormwater infiltration
of runoff must replicate preconstruction infiltration of runoff to
the maximum extent possible; in high quality and exceptional value
watersheds special requirements may apply.
C.
The volume of additional stormwater runoff to be captured, stored
and treated is called the "water quality volume" ("WQv").
(1)
The formula for determining WQv is:
|
WQv = [(P)(Rv)(A)]/12]
|
|
Where:
| ||||
|---|---|---|---|---|
|
P
|
=
|
Rainfall depth in inches, using the "90% storm" — the
volume of rainfall for 90% of the storm events which produce runoff
in the watershed annually (e.g., 1.0 inches) (see Appendix A)
| ||
|
A
|
=
|
Project area in acres
| ||
|
Rv
|
=
|
Volumetric runoff coefficient [0.05 + 0.009(I)], where I is
the impervious surface percentage (impervious area ÷ total
project area) X 100%
| ||
(2)
In special protection watersheds, as described in 25 Pa. Code Chapter
93, this volume may be required to remain on site through infiltration
and other methods to protect water quality. Guidance can be obtained
from PADEP.
(3)
Runoff treatment BMPs must be employed where necessary to ensure
the water quality requirements are met.
D.
Water temperature is a particular concern in high quality and exceptional
value watersheds. Temperature-sensitive BMPs and stormwater conveyance
systems are to be used and designed with storage pool areas and supply
outflow channels and should be shaded with trees. Vegetation shall
be planted within the facilities, provided that capacity for volumes
and rate control as required by this chapter is maintained.
(1)
At a minimum, the southern half on pond shorelines shall be planted
with shade or canopy trees within 10 feet of the pond shoreline.
(2)
In conjunction with this requirement, the maximum slope allowed on
the berm area to be planted is 10 to 1. This will lessen the destabilization
of berm soils due to root growth.
(3)
A long-term maintenance schedule and management plan for the thermal
control BMPs is to be established and recorded for all development
project sites.
E.
The applicant may, subject to approval of the Borough, use any of
the following stormwater credits, described in the following table,
in computing the required water quality volume:
|
Stormwater Credit
|
Description
| |
|---|---|---|
|
Natural area conservation
|
Conservation of natural areas such as forest, wetlands, or other
sensitive areas in a protected easement thereby retaining their predevelopment
hydrologic and water quality characteristics. Using this credit, a
designer may subtract conservation areas from total site area when
computing the required water quality volume.
| |
|
Disconnection of rooftop runoff
|
Credit is given when rooftop runoff is disconnected and then
directed over a pervious area where it may either infiltrate into
the soil or filter over it. Credit is typically obtained by grading
the site to promote overland flow or by providing bioretention on
single-family residential lots. If a rooftop area is adequately disconnected,
the impervious area may be deducted from the total impervious cover.
| |
|
Disconnection of nonrooftop runoff
|
Credit is given for practices that disconnect surface impervious
cover by directing it to pervious areas where it is either infiltrated
or filtered though the soil. As with rooftop runoff, the impervious
area may be deducted from the total impervious cover thereby reducing
the required water quality volume.
| |
|
Stream buffer
|
Credit is given when a stream buffer effectively treats stormwater
runoff. Effective treatment constitutes capturing runoff from pervious
and impervious areas adjacent to the buffer and treating the runoff
through overland flow across a grass or forested area. Areas treated
in this manner may be deducted from total site area.
| |
|
Grass channel (open section roads)
|
Credit may be given when open grass channels are used to reduce
the volume of runoff and pollutants during smaller storms. If designed
according to appropriate criteria, these channels may meet water quality
criteria for certain types of residential development.
| |
|
Environmentally sensitive rural development
|
Credit is given when a group of environmental site design techniques
are applied to low-density or rural residential development. This
credit eliminates the need for structural practices to address water
quality volume. See Appendix E.[1]
|
[1]
Editor's Note: Appendix E and the other appendixes referenced
in this chapter are on file in the Borough office.
F.
The volume and rate of any stormwater discharges allows under this
chapter must be managed to prevent the physical degradation of receiving
waters, such as by stream bank scour and erosion. If a detention facility
is proposed which is part of the BMPs approved for the project, the
facility(ies) must be designed to provide for a twenty-four-hour extended
detention of the one-year, twenty-four-hour storm event (i.e., the
stormwater runoff will be released over a minimum 24 hours for the
one-year, twenty-four-hour storm event).
A.
Prevention of stormwater runoff is the key objective of Chapter 93
of the DEP regulations, because runoff can change the physical, chemical
and biological integrity of water bodies thereby impacting water quality.
B.
The project plan shall describe how these water quality protection requirements will be met. Infiltration BMPs shall be evaluated and utilized to the maximum extent possible to manage the net change in stormwater runoff generated so that post-construction discharges do not degrade the physical, chemical or biological characteristics of the receiving waters. These BMPs may be used to satisfy all or part of the requirements in § 230-13.
C.
Post-construction stormwater infiltration of runoff shall replicate
preconstruction infiltration of runoff to the maximum extent possible.
In high quality and exceptional value watersheds, special requirements
may apply. Guidance is available from PADEP.
D.
In calculating the volume of runoff that can be infiltrated at a
site, the following methodology shall be used:
(1)
Methodology.
|
Rev = [(S)(Rv)(A)]/12
|
|
Where:
| ||||||
|
Rev
|
=
|
Recharge volume (acre-feet)
| ||||
|
S
|
=
|
Soil specific recharge factor (inches)
| ||||
|
A
|
=
|
Site area contributing to the recharge facility (acres)
| ||||
|
Rv
|
=
|
Volumetric runoff coefficient, Rv = 0.05
+ 0.009 (I),
| ||||
|
Where:
| ||||||
|
I
|
= percent impervious area; and
| |||||
|
S
|
shall be obtained based upon hydrologic soil group based upon
the table below.
| |||||
|
Hydrologic Soil Group
|
Soil Specific Recharge Factor (S)
| |
|---|---|---|
|
A
|
0.38
| |
|
B
|
0.25
| |
|
C
|
0.13
| |
|
D
|
0.06
|
|
If more than one hydrologic soil group (HSG) is present at a
site, a composite recharge volume shall be computed based upon the
proportion of total site area within each HSG.
|
(2)
In selecting the appropriate infiltration BMPs, the applicant shall
consider the following:
(3)
A detailed soils evaluation of the project site shall be performed
to determine the suitability of infiltration BMPs. The evaluation
shall be performed by a qualified professional and, at a minimum,
address soil permeability, depth to bedrock, susceptibility to sinkhole
formation, and subgrade stability. The general process for designing
the infiltration BMP shall be:
(a)
Analyze hydrologic soil groups as well as natural and man-made
features within the watershed to determine general areas of suitability
for infiltration BMPs.
(b)
Provide field testing data to determine appropriate percolation
rate and/or hydraulic conductivity.
(c)
Design infiltration BMPs for required stormwater volume based
on field-determined capacity at the level of the proposed infiltration
surface.
(4)
Soil characteristics. Subject to the specific considerations in Subsection D(7) below:
(a)
Infiltration BMPs are particularly appropriate in hydrologic
soil groups A and B, as described in the Natural Resources Conservation
Service Manual TR-55.
(b)
Low-erodibility factors ("K" factors) are preferred for the
construction of basins.
(c)
There must be a minimum depth of 48 inches between the bottom
of any facility and the seasonal high-water table and/or bedrock (limiting
zones), except for infiltration BMPs receiving only roof runoff, which
shall be placed in soils having a minimum depth of 24 inches between
the bottom of the facility and the limiting zone.
(d)
There must be an infiltration and/or percolation rate sufficient
to accept the additional stormwater load and to drain completely,
as determined by field tests.
(e)
Infiltration BMPs shall be located a minimum of 10 feet away
from the foundation wall of any building.
(f)
The infiltration system shall have positive overflow controls
to prevent storage within one foot of the finished surface or grade.
(g)
Infiltration rates shall not be used in computing the storage
volume of the infiltration system.
(h)
Surface inflows shall be designed to prevent direct discharge
of sediment into the infiltration system.
(5)
The recharge volume provided at the site shall be directed to the
most permeable HSG available, except where other considerations apply,
such as in limestone geology.
(6)
Any infiltration BMP shall be capable of completely infiltrating
the impounded water within 48 hours.
(7)
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas, such as:
(a)
Strip mines;
(b)
Where salt or chloride may be applied in deicing and other winter
applications, causing groundwater pollution since soils do little
to filter this pollutant; and
(c)
Limestone areas:
[1]
Whenever a basin will be located in an area underlain by limestone,
a geological evaluation of the proposed location shall be conducted
to determine susceptibility to sinkhole formations.
[2]
The design of all BMPs over limestone formations shall include
measures to prevent groundwater contamination and, where necessary,
sinkhole formation.
[3]
It shall be the applicant's responsibility to verify whether
the site is underlain by limestone.
[4]
The following note shall be attached to all drainage plans and
signed and sealed by the applicant's licensed engineer/surveyor/landscape/architect/geologist
if a detention facility is proposed: "I certify that the proposed
facility is/is not underlain by limestone."
(8)
During the period of land disturbance, runoff shall be controlled
prior to entering any proposed infiltration area, areas proposed for
infiltration BMPs shall be protected from sedimentation and compaction
during the construction phase, so as to maintain their maximum infiltration
capacity.
(9)
Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
received final stabilization.
A.
Applicants may select a combination of runoff control techniques
which are most suitable to control stormwater runoff from the site.
All controls shall be subject to approval of the Borough Engineer.
The Borough Engineer may request specific information on design and/or
operating features of the proposed stormwater controls in order to
determine their suitability and adequacy in terms of the standards
of this section.
B.
The applicant shall consider the effect of the proposed stormwater
management techniques on any special soil conditions or geological
hazards which may exist on the development site. In the event such
conditions are identified on the site, the Borough Engineer may require
in-depth studies by a competent geotechnical engineer.
C.
The stormwater management BMPs shall be selected according to the
following order of preference:
(1)
Site planning for locating proposed buildings, impervious areas and
grading which minimizes disruption of the natural site characteristics.
(2)
Minimization of impervious areas and promotion of retentive grading.
(3)
Implementation of innovative nonstructural measures.
(4)
Infiltration of runoff on site.
(5)
Flow attenuation by use of open vegetated swales and natural depressions
(6)
Stormwater detention/retention structures.
D.
Any BMP which is a dam, culvert, stream enclosure or outfall, as
defined in 25 Pa. Code Chapter 105, shall be designed according to
the requirements in those regulations.
E.
Any stormwater BMP which does not constitute a dam under 25 Pa. Code
Chapter 105 and is designed to store runoff and requiring a berm or
earthen embankment (i.e., detention basin) shall be designed to satisfy
the following:
(1)
Berms and earthen embankments shall be designed to provide an emergency
spillway to handle flow up to and including the one-hundred-year post-development
conditions.
(2)
Berms and earthen embankments shall be designed to provide a minimum
one foot of freeboard above the maximum pool elevation computed when
the facility functions for the one-hundred-year post-development inflow.
(3)
Water obstructions shall convey runoff from the twenty-five-year
design storm with a minimum of one foot of freeboard measured below
the lowest point along the top of the roadway without damage to the
drainage structure or the roadway.
(4)
Roadway crossings located within designated floodplain areas must
be able to convey runoff from a one-hundred-year design storm.
(6)
Adequate erosion and sediment control protection shall be provided
along all open channels, and at all points of discharge.
A.
Stormwater runoff from all development and post-development sites
shall be calculated using either the Rational Method or a Soil Cover
Complex Methodology.
B.
Any stormwater runoff calculations involving areas greater than 200
acres, including on- and off-site areas, shall use a generally accepted
calculation technique that is based on the NRCS Soil Cover Complex
Method. Table III-1 below summarizes acceptable computation methods.
All methods will be selected by the design professional based on the
individual limitations and suitability of each method for a particular
site. These assumptions shall be used in runoff calculations:
(1)
Average antecedent moisture conditions.
(2)
Type II distribution storm.
(3)
Meadow in good condition shall be used in predevelopment runoff calculations
for all areas of existing cultivation.
(4)
All areas other than cultivation shall use the land cover condition
which existed during the past 10 consecutive years.
(5)
All areas to be disturbed during construction and subsequently returned
to open space will be assumed to be reduced one hydrologic group category
level for post-development runoff.
(6)
If the initial condition of the site is undeveloped land, the land
use shall be considered as "meadow" unless the natural land cover
is proven to generate lower curve numbers or Rational "C" value, such
as forested lands.
C.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms presented in Table D-1 in Appendix
D of this chapter.[1] If a hydrologic computer model such as TR-20, PSRM or
HEC-HMS is used for stormwater runoff calculations, then the duration
of rainfall shall be 24 hours. The Natural Resources Conservation
Service's "S" curve shown in Figure D-1, Appendix D, of this chapter
shall be used for the rainfall distribution.
[1]
Editor's Note: Appendix D and the other appendixes referenced
in this chapter are on file in the Borough office.
D.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration for overland flow
and return periods from the design storm curves from Pennsylvania
Department of Transportation Design Rainfall Curves (1986) (Figure
B-2). Times of concentration for overland flow shall be calculated
using the methodology presented in Chapter 3 of Urban Hydrology for
Small Watersheds, NRCS, TR-55 (as amended or replaced from time to
time by NRCS). Times of concentration for channel and pipe flow shall
be computed using Manning's Equation.
G.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations, and to determine the capacity of
open channels, pipes and storm sewers. Values for Manning's roughness
coefficient (n) shall be consistent with Table B-4 in Appendix B of
the chapter.[4]
[4]
Editor's Note: Appendix B and the other appendixes referenced
in this chapter are on file in the Borough office.
H.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
I.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method. For drainage areas greater than 20 acres in size, the design
storm hydrograph shall be computed using a calculation method that
produces a full hydrograph. The Borough may approve the use of any
generally accepted full hydrograph approximation technique which shall
use a total runoff volume that is consistent with the volume from
a method that produces a full hydrograph.
J.
The Borough may require that computed existing runoff rates be reconciled
with field observations and conditions. If the design professional
can substantiate through actual physical calibration that more appropriate
runoff and time-of-concentration values should be utilized at a particular
site, then appropriate variations may be made upon review and recommendations
of the Borough Engineer. Calibration shall require detailed gauge
and rainfall data for the particular site in question.
|
Table III-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 model's limitations
| |
|
HEC-1
|
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 200 acres
| |
|
Other methods
|
Various
|
As approved by the Borough Engineer
| |
