A.
For all regulated activities, unless preparation of a SWM site plan is specifically exempted in § 257-11:
B.
SWM site plans approved by the municipality, in accordance with § 257-20, shall be on site throughout the duration of the regulated activity.
C.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this chapter, provided that they meet the minimum requirements
of, and do not conflict with, state law including but not limited
to the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
E.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction),
to meet the purposes and requirements of this chapter and to meet
all requirements under Pennsylvania Code Title 25 and the Clean Streams
Law. Various BMPs and their design standards are listed in the Erosion
and Sediment Pollution Control Program Manual (E&S Manual), Commonwealth
of Pennsylvania, Department of Environmental Protection, No. 363-2134-008
(2000), as amended and updated.
F.
Impervious areas.
G.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
to the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this chapter.
H.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property;
(3)
Meet the water quality goals of this chapter by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, natural slopes
over 8%, and existing native vegetation.
(b)
Preserve and maintain trees and woodlands; maintain or extend
riparian buffers and protect existing forested buffer; provide trees
and woodlands adjacent to impervious areas whenever feasible.
(c)
Establish and maintain nonerosive flow conditions in natural
flow pathways.
(d)
Minimize soil disturbance and soil compaction; cover disturbed
areas and replace topsoil to a depth sufficient to achieve vegetated
cover or four inches, whichever is greater; use tracked equipment
for grading when feasible.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas wherever possible.
(4)
To the maximum extent practicable, incorporate the techniques for
low-impact development practices described in the Pennsylvania Stormwater
Best Management Practices Manual (PA BMP Manual).
I.
The design of all facilities over Karst shall include an evaluation
of measures to minimize adverse effects.
J.
Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter.
K.
Storage facilities should completely drain both the volume control
and rate control capacities over a period of time not more than 72
hours from the end of the design storm, or otherwise be treated.
L.
For all regulated activities, SWM BMPs shall be designed, implemented,
operated, and maintained to meet the purposes and requirements of
this chapter and to meet all requirements under Pennsylvania Code
Title 25, the Clean Streams Law,[2] the Storm Water Management Act,[3] and § 257-3 of this chapter.
M.
Various BMPs and their design standards are listed in the PA BMP
Manual.
N.
Materials workmanship and methods. All materials, workmanship, and
methods of work shall comply with the Pennsylvania Department of Transportation
Publication 408 Specifications, as accepted and commonly used by the
municipality, and shall be considered to be incorporated into this
article as if copied in full. In the event a conflict arises between
the requirements of this chapter and the PA DOT Publication 408 Specifications,
the municipality shall resolve the difference, and said opinion shall
be binding.
O.
Supplemental standards and criteria contained in Article IX are hereby incorporated into this chapter to govern the hydrologic and hydraulic design provisions contained herein.
P.
The signature and seal of a registered professional engineer, if
required, must be provided at the time of plan submission.
A.
The following activities are specifically exempt from the plan preparation and submission provisions of this chapter, but remain subject to the requirements in § 257-10, Subsections E through L (and erosion and sedimentation pollution control requirements):
(1)
Regulated activities that create impervious areas smaller in area
than 1,000 square feet and regulated activities that disturb less
than 5,000 square feet are exempt from the peak rate control and the
SWM site plan preparation requirement of this chapter. Refer to the
stormwater management plan (SMP) requirements in Appendix C.[1]
[1]
Editor's Note: Appendix C is included as an attachment to this chapter.
(2)
Regulated activities that create disconnected impervious areas equal
to or greater than 1,000 square feet and less than 5,000 square feet,
and regulated activities that disturb equal to or greater than 5,000
square feet and less than 20,000 square feet without point source
discharge to surface waters, may be exempt from the SWM plan requirements
of this chapter, provided that:
(a)
The regulated activity is disconnected from impervious areas
as specified in Appendix B of this chapter;[2] and
[2]
Editor's Note: Appendix B is included as an attachment to this chapter.
(b)
The regulated activity will not alter or be located within any
existing swale or drainageway.
(c)
Refer to the stormwater management plan (SMP) requirements in
Appendix C.[3]
[3]
Editor's Note: Appendix C is included as an attachment to this chapter.
(3)
Agricultural plowing and tilling are exempt from the rate control
and SWM site plan preparation requirements of this chapter provided
the activities are performed according to the requirements of 25 Pa.
Code Chapter 102, Erosion and Sediment Control.
(4)
Forest management and timber operations are exempt from the rate
control and SWM site plan preparation requirements of this chapter,
provided the activities are performed according to the requirements
of 25 Pa. Code Chapter 102, Erosion and Sediment Control.
(5)
Use of land for gardening for home consumption.
(6)
Agriculture when operated in accordance with an approved conservation
plan.
B.
The municipality shall require an acceptable minor SWM plan, as described in § 257-14P and Appendix C, be submitted, provided that:
(1)
Regulated activities that create impervious areas, if connected to
impervious areas, equal to or greater than 1,000 square feet and less
than 5,000 square feet.
(2)
Regulated activities that disturb equal to or greater than 5,000
square feet and less than 20,000 square feet with point source discharge
to surface waters.
(3)
Refer to the stormwater management plan (SMP) requirements in Appendix
C. A sample minor stormwater management plan can be found in Appendix
D.[4]
[4]
Editor's Note: Such appendixes are included as attachments to this chapter.
D.
The municipality may include permit conditions to specify that regulated
activities maintain a minimum distance between proposed impervious
areas/stormwater management facility outlets and downslope property
line(s).
Water volume controls shall be implemented using the Design
Storm Method in Subsection A or the Simplified Method in Subsection
B below. For regulated activity areas equal or less than one acre
that do not require hydrologic routing to design the stormwater facilities,
this chapter establishes no preference for either methodology; therefore,
the applicant may select either methodology on the basis of economic
considerations, the intrinsic limitations on applicability of the
analytical procedures associated with each methodology, and other
factors.
A.
The Design Storm Method (CG-1 in the PA BMP Manual) is applicable
to any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
Do not increase the postdevelopment total runoff volume for all storms
equal to or less than the two-year, twenty-four-hour duration rainfall.
B.
The Simplified Method (CG-2 in the PA BMP Manual) provided below
is independent of site conditions and should be used if the Design
Storm Method is not followed. This method is not applicable to activities
that disturb greater than one acre, or for projects that require design
of stormwater storage facilities. For new impervious surfaces:
(1)
Stormwater facilities shall be sized to capture at least the first
two inches of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow; i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options include reuse, evaporation, transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases, at least the first one-half inch of the permanently
removed runoff should be infiltrated.
A.
Areas not covered by a release rate map from an approved Act 167
stormwater management plan. Postdevelopment discharge rates shall
not exceed the predevelopment discharge rates for the one-, two-,
five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour
storms. If it is shown that the peak rates of discharge indicated
by the postdevelopment analysis are less than or equal to the peak
rates of discharge indicated by the predevelopment analysis for one-,
two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour,
storms, then the requirements of this section have been met. Otherwise,
the applicant shall provide additional controls as necessary to satisfy
the peak rate of discharge requirement.
B.
Areas covered by a release rate map from an approved Act 167 stormwater
management plan. For the one-, two-, five-, ten-, twenty-five-, fifty-,
and one-hundred-year, storms, the postdevelopment peak discharge rates
will follow the applicable approved release rate maps. For any areas
not shown on the release rate maps, the postdevelopment discharge
rates shall not exceed the predevelopment discharge rates.
All regulated activities shall be conducted in conformance with
the following standards:
A.
After installation of impervious cover, peak discharges for the two-,
five-, ten-, twenty-five-, fifty-, and one-hundred-year frequency
storms from the site shall not exceed the respective peak discharge
performance standards in this chapter.
B.
Stormwater runoff shall be managed so that no downstream increases
in flood damages or impairment of streets and other public facilities
occur. The municipality may require that downstream impacts be evaluated
at critical locations such as dams, tributaries, existing developments,
undersized culverts, and flood-prone areas. The municipality shall
make the final determination with respect to the degree of management
required for any site. The applicant shall evaluate the effects of
the proposed plan on such critical locations by providing computed
water surface elevations (WSEL) for the ten- and one-hundred-year
storms. Methods of computation shall have prior approval of the municipality.
At such downstream critical locations, stormwater management may be
exercised by:
C.
Groundwater recharge. The municipality may impose stormwater quality
measures in accordance with this chapter to protect against ground
or surface water pollution where the type of business or the nature
of the stormwater runoff and soils underlying stormwater management
facilities would constitute a substantial risk of contamination.
D.
In establishing the site conditions for calculating stormwater runoff
prior to development, the following assumptions shall apply:
(1)
Woodland or meadow in good condition shall be used for all undeveloped
areas.
(2)
Average antecedent moisture conditions as defined by the Natural
Resource Conservation Service (NRCS).
(3)
Determining predevelopment peak discharges from Karst geologic areas
apply either:
(a)
Peak adjustment factors in accordance with the USGS Water Resources
Investigations Report 00-4189, Techniques for Estimating Magnitude
and Frequency of Peak Flows for Pennsylvania Streams; or
(b)
Drainage area reductions equal to the area of undrained depressions
or pond factor adjustments in accordance with the Urban Hydrology
for Small Watersheds, Technical Release No. 55 (TR-55, USDA, NRCS).
E.
Hydrologic methods. All plans and designs for stormwater management facilities shall be reviewed by the municipality. Plans for facilities other than storm sewers should determine stormwater peak discharge and stormwater runoff by the use of the PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended. The municipality may permit the use of the Modified Rational Method or other methods for calculation of the storage capacity of a stormwater management facility from drainage areas of 20 acres or less.
(1)
Coefficients.
(a)
Acceptable runoff coefficient values for use in the Rational
Method equation are identified in Appendix E of this chapter.[1] When applying the Rational Method coefficients in Table A-3, "open space" coefficients shall be used for undeveloped, densely vegetated (non-forest) areas instead of "meadow" coefficients. Refer to PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended, for permissible curve numbers.
[1]
Editor's Note: Appendix E is included as an attachment to this chapter.
(b)
The Rational Formula may be used in lieu of the Soil Cover Complex
Method to compute design flows for the sizing of storm sewers, inlets,
and swales.
(2)
Rainfall amounts for the return periods specified shall be determined
using the Precipitation-Frequency Atlas of the United States, Atlas
14, Volume 2 (as amended), U.S. Department of Commerce, National Oceanic
and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland, 20910. Rainfall duration
for hydrograph generation shall be selected for the specified recurrence
intervals on the basis of twice the computed time of concentration
for the given watershed and subwatersheds. In no case shall the duration
be less than 24 hours.
(3)
Time of concentration shall be determined in accordance with the methods presented in PennDOT Drainage Manual, Publication Number 13, DM-2 Chapter 10, as amended.
(4)
In order to reduce stormwater runoff volumes from developed areas
and encourage groundwater recharge, underground basin drains, infiltration
trenches, and cisterns are permitted to which roof leaders may be
connected. These drains consist of stone-filled basins which temporarily
store and release water below ground surface. Plans for such facilities
shall be submitted to the municipality for approval, and the basins
shall be used only in those areas where soils, geologic, and water
table conditions permit.
F.
Stormwater management facilities and related installations shall
be provided:
(1)
To permit unimpeded flow of natural watercourses. Such flow may be
redirected as required, subject to the approval of the Pennsylvania
Department of Environmental Protection.
(2)
To ensure adequate drainage of all low points along the curbline
of streets.
(3)
To intercept stormwater runoff along streets at intervals reasonably related to the extent and grade of the area drained, and to prevent substantial flow of water across intersections or flooded intersections during storms, in accordance with the procedures in the PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended.
(4)
To ensure adequate and unimpeded flow of stormwater under driveways
in, near, or across natural watercourses or drainage swales. Suitable
pipes or other waterways shall be provided as necessary.
(5)
To properly drain stormwater runoff from all land development projects.
All lot and open areas shall be designed to drain to the nearest practical
street or drainage system, existing or proposed, as defined by the
municipality, with no impact on adjoining properties, unless an area
specifically designed for stormwater detention is provided.
G.
Storm sewers and related installations:
(1)
Storm sewers, where required by zoning and land use densities, shall
be placed under or immediately adjacent to the roadway side of the
curb, or as directed by the municipality, when parallel to the street
within the right-of-way.
(2)
When located in undedicated land, they shall be placed within a drainage
easement not less than 20 feet wide as approved by the municipality.
(3)
The use of properly designed, graded, and turfed drainage swales
is encouraged in lieu of storm sewers in commercial and industrial
areas and, where approved by the municipality, in residential areas.
Such swales shall be designed not only to carry the required discharge
without excessive erosion, but also to increase the time of concentration,
reduce the peak discharge and velocity, and permit the water to percolate
into the soil, where appropriate. Criteria related to the use and
design of drainage swales are as follows:
(a)
Criteria.
[1]
Where vegetated drainage swales are used in lieu of or in addition
to storm sewers, they shall be designed to carry the ten-year discharge
without erosion, and also to increase the time of concentration, reduce
the peak discharge and velocity, and permit the water to percolate
into the soil.
[2]
The maximum encroachment of water on the roadway pavement along
roadside swales in cut areas shall not exceed half of a through traffic
lane during a ten-year frequency storm of five-minute duration. Frequent
and/or sustained flooding of the subbase shall be avoided.
[3]
Swales shall be designed in accordance with PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended. Inlets shall be provided to limit the shoulder encroachment and water velocity.
[4]
The side slope for any vegetated drainage channel requiring
mowing of the vegetation shall have a maximum grade of three horizontal
to one vertical on those areas to be mowed.
[5]
Erosion prevention. All drainage swales shall be designed to
prevent the erosion of the bed and bank areas. Suitable temporary
and/or permanent stabilization during vegetative cover establishment
shall be provided to prevent erosion.
[6]
Storm sewers or drainage swales shall discharge to a detention
or retention basin to attenuate the peak rate and volume, respectively
of stormwater runoff, except as provided in the plan.
(4)
Guidelines.
(a)
Deed restrictions may be required on property(ies) containing
drainage swales and/or perennial streams. When required, these deed
restrictions shall specify that no property owner obstruct or alter
any drainage swale or perennial stream identified in the stormwater
management plan.
(b)
The design capacity of storm sewers shall be in accordance with PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended. Storm drainage systems shall be designed without surcharging inlets to provide conveyance of stormwater runoff into a detention basin or similar facility utilized to manage the rate of stormwater runoff. To avoid surcharging inlets, and to ensure that inlets will receive stormwater runoff, the hydraulic grade line at the inlet should be at least six inches below the elevation of the inlet grate. Where site grading will direct stormwater runoff from the one-hundred-year design storm to a detention basin or similar facility utilized to manage the rate of stormwater runoff, then the storm sewer may be designed for the ten-year design storm. Where site grading will not direct stormwater runoff from the one-hundred-year design storm to a detention basin or similar facility utilized to manage the rate of stormwater runoff, then the storm sewer shall be designed for the one-hundred-year design storm. Conveyance of storms to the detention basin, up to and including the one-hundred-year frequency, shall be provided so as not to endanger life or seriously damage property.
(5)
Storm inlet types and inlet assemblies shall conform to the Pennsylvania
Department of Transportation Standards for Roadway Construction as
approved by the municipality.
(a)
Inlets shall, at a minimum, be located at the lowest point of
street intersections to intercept the stormwater before it reaches
pedestrian crossings; or at sag points of vertical curves in the street
alignment which provide a natural point of ponding of surface stormwater.
(b)
Where the municipality deems it necessary because of special
land requirements, special inlets may be approved.
(c)
The interval between inlets collecting stormwater runoff shall be determined in accordance with the PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended.
(d)
In curbed sections, the maximum encroachment of water on the
roadway pavement shall not exceed half of a through traffic lane or
one inch less than the depth of curb during the ten-year design storm
of five-minute duration. Inlets shall be provided to limit the encroachment
of water on the pavement. When inlets are used in a storm system within
the right-of-way limits of a street in lieu of manholes, the spacing
of such inlets shall not exceed the maximum distance of 450 feet.
(6)
Accessible drainage structures shall be located on a continuous storm
sewer system at all vertical dislocations, at all locations where
a transition in storm sewer pipe sizing is required, at all vertical
and horizontal angle points exceeding five degrees, and at all points
of convergence of two or more influent storm sewer mains. The construction
locations of accessible drainage structures shall be as indicated
on the subdivision drainage plan or area drainage plan approved by
the municipality.
(7)
When evidence available to the municipality indicates that existing
storm sewers have sufficient capacity as determined by hydrograph
summation and are accessible, proposed stormwater facilities may connect
to the existing storm sewers so long as the peak rate of discharge
does not exceed the amount permitted by this article.
H.
Bridges and culverts shall have ample waterway opening to carry expected flows, based on the PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended, or as required by the municipality.
I.
Detention or retention basins for the management of stormwater peak
discharges shall meet the following requirements:
(1)
Basins shall be installed prior to or concurrent with any earthmoving
or land disturbances which they will serve. The phasing of their construction
shall be noted in the narrative and on the plan.
(2)
The design of all facilities over limestone formations shall include
measures to prevent groundwater contamination and, where required,
sinkhole formation. Soils used for the construction of basins shall
have moderate to low erodibility factors (i.e., "K" factors of 0.32
or less).
(3)
Energy dissipaters and/or level spreaders shall be installed at points
where pipes or drainageways discharge to or from basins.
(4)
Outlet structures and aprons.
(a)
Outlet structures within detention/retention basins shall incorporate
childproof, nonclogging trash racks or grates over all horizontally
oriented openings. All vertically oriented openings over 12 inches
or larger in any dimension where entry by a child could cause injury
or death shall be covered with childproof, nonclogging trash racks,
except where such openings carry perennial stream flows. Design openings
less than six inches in any dimension shall be covered with a pipe
screen (e.g., Neenah R-7512 or equivalent). Measures to completely
drain detention/retention basins in the event of clogging of the primary
design opening(s) shall be incorporated into the design of basin outlet
structures. Basin outlet pipes shall have a minimum inside diameter
of 15 inches or a cross-sectional area of 176 square inches, except
that pipes under a twenty-five foot or greater fill shall not be less
than 24 inches or a cross-sectional area of 453 square inches, and
shall consist of reinforced concrete.
(b)
Outlet aprons shall be designed and shall extend at a minimum
to the toe of the basin slope. Where spillways will be used to manage
peak discharges in excess of the ten-year storm, such spillways shall
be constructed to withstand the pressures of impounded waters and
convey flows at computed outlet velocities without erosion.
(5)
When the Pennsylvania Department of Environmental Protection requires
facilities to be permitted, the designer shall submit all information
to the PA DEP Regional Office, and obtain all necessary approvals
and permits pursuant to Pennsylvania Code, Title 25, Chapter 105,
Dam Safety and Encroachment Act.
(6)
Downstream analysis:
(a)
Where deemed necessary by the municipality, the applicant shall
submit an analysis of the impacts of detained stormwater flows on
downstream areas within the watershed, established with the concurrence
of the municipality. The analysis shall include hydrologic and hydraulic
calculations necessary to determine the impact of peak discharge modifications
of the proposed development on critical locations such as dams, tributaries,
existing developments, undersized culverts, and flood-prone areas.
(b)
Review and comment of the analysis by the downstream municipality
shall be obtained as deemed necessary.
(7)
Detention basins may be waived by the municipality at sites in close
proximity to larger receiving streams, depending on the hydrology
of the watershed. This is to facilitate drainage prior to main stream
flooding. It shall be incumbent upon the applicant to demonstrate
that no downstream increase in stream flooding or channel erosion
will result in accordance with this article, and that no increases
in peak discharge within the receiving stream will occur as outlined
in this article.
(8)
Multiple use basins. The design and construction of multiple use
stormwater detention facilities are strongly encouraged. In addition
to stormwater management; where appropriate, facilities allow for
recreational uses included: ball fields, play areas, picnic grounds,
etc. Provision for parking facilities within basins and permanent
wet ponds with stormwater management capabilities may also be appropriate.
Prior approval and consultation with the municipality are required
before design. Multiple use basins should be constructed so that potentially
dangerous conditions are not created.
(9)
Multiple development basins. Stormwater management facilities designed
to serve more than one property or development in the same watershed
are encouraged. Staged construction of existing or proposed multiple-use
detention facilities by several developers in conjunction with watershed
development is encouraged. Each applicant shall be responsible for
the incremental increase in stormwater runoff generated by the respective
development and incremental construction improvements necessary for
the overall detention facility. Prior approval and consultation with
the municipality is required before design of such facilities.
(10)
Alternative detention facilities. Alternative stormwater detention
facilities including rooftop, subsurface basins or tanks and in-pipe
detention storage, or other approved alternative designs are permitted
as determined by the municipality.
J.
Calculations; storm drainage system design.
(1)
All calculations shall be submitted to the municipality on computation
sheets acceptable to the reviewer for approval. If the municipality
determines through review and independent computation that the size(s)
of storm pipes or detention basins is insufficient, the municipality
may require the applicant to increase the size(s) of said storm pipes
or detention basins.
(2)
If the storm drainage system design is completed on a computer installation,
sufficient supporting data shall be provided to allow comprehensive
review by municipal officials.
K.
When the elevation of any existing or proposed entrance to a structure,
including windows, is lower than the elevation of the public cartway
serving that site, a drainage plan shall be submitted, reviewed and
approved as part of the zoning permit process for the proposed structure.
L.
The municipality may require that stormwater management facilities
located outside of existing or proposed rights-of-way shall be located
within and accessible by easements as follows:
(1)
Drainage easements.
(a)
Where a tract is traversed by a watercourse, drainageway, channel
or stream, there shall be provided a drainage easement paralleling
the line of such watercourse, drainageway, channel or stream. The
width of the drainage easement will be adequate to preserve the unimpeded
flow of natural drainage in the one-hundred-year floodplain.
(b)
Drainage easements shall provide for maintenance, and for the
purpose of widening, deepening, improving or protecting such drainage
facilities.
(2)
Access easements. Where proposed stormwater management facilities
are not adjacent to proposed or existing public rights-of-way or are
not accessible due to physical constraints, as determined by the municipality,
a twenty-foot wide passable access easement specifying rights of entry
shall be provided. Access easements shall provide for vehicle ingress
and egress on grades of less than 10% for carrying out inspection
or maintenance activities.
(3)
Maintenance easements. A maintenance easement shall be provided which
encompasses the stormwater facility and appurtenances and provides
for access for maintenance purposes. The maintenance easement must
be located at least 20 feet outside of the one-hundred-year surface
elevation and the stormwater facility and appurtenances.
(4)
Easements shall stipulate that no trees, shrubs, structures, excavation,
or fill be placed, and no regrading is to be performed within the
area of the easement without written approval from the municipality.
Upon approval, such landscaping may be placed in maintenance easements,
provided it does not impede access.
(5)
Whenever practicable, easements shall be parallel to width and linked
to property lines of the subdivision.
(6)
All easement agreements shall be recorded with a reference to the
recorded easement indicated on the site plan. The format and content
of the easement agreement shall be reviewed and approved by the municipality.
M.
Sinkhole protection.
(1)
Stormwater from roadways, parking lots, storm sewers, roof drains,
or other concentrated stormwater runoff paths shall not be discharged
directly into sinkholes.
(2)
To protect sensitive Karst areas, the municipality may require basins
to contain an impervious liner. The liner may be of the impervious
membrane type, placed in accordance with the manufacturer's recommendations,
or an approved alternative as approved by the municipality.
N.
Erosion and sedimentation control.
(1)
All plans for erosion and sediment pollution control (E&SPC)
shall meet the requirements of the Clean Streams Law, Act of June
22, 1937, P.L. 1987 as amended, 35 P.S. § 691.1, et.seq.
and 25 Pa. Code § 102.1 et seq., Erosion Control.
(2)
It shall be the responsibility of the applicant to submit the E&SPC
plan, application, and other necessary material to the Conservation
District or DEP Office, as appropriate. A copy of the transmittal
letter shall be provided to the municipality. Comments shall be received
and E&SPC plan approval obtained from the Conservation District
prior to stormwater plan approval.
O.
Minor SWM plan. A minor SWM plan is required per § 257-11B and as outlined in Appendix C.[2] Minor SWM plans shall consist of the following, and are not subject to § 257-12, Volume controls, and § 257-13, Rate controls, of this chapter. Minor plan preparation steps are as follows:
(1)
Prepare a scaled drawing showing key features of the site. The plan
can be developed from a Tax Map, site survey, or other accurate drawing
of the site. The property and boundaries should be accurate in scale.
The plan should include:
(a)
A line showing the limit and location of area(s) that will be
cleared for regulated activities such as buildings, driveways and
lawns.
(b)
The location of all structures, existing and proposed (house,
shed, garage, etc.). Include driveways, parking areas, any other impervious
surfaces, well and septic system locations.
(c)
The location of property boundaries, any streams or wetlands,
and separation distances of structure(s) to any water body or stream.
(d)
The angle/slope of the property in relation to any water body
or stream.
(2)
Calculate the volume of stormwater runoff created by the project.
(a)
Identify the newly created impervious areas. Note on the plan
the area of each proposed structure and impervious surface (paved,
walkways, etc.) and calculate the sum of the areas. For example:
|
20' x 20' shed
|
=
|
400 square feet
| |
|
6' x 60' sidewalk
|
=
|
360 square feet
| |
|
Total impervious area
|
=
|
760 square feet
|
(3)
Calculate the volume of stormwater runoff.
(a)
For minor projects, multiply the total square footage of newly
created total impervious area by (2.85 in./12 in./ft.). For example:
|
760 s.f. x (0.2375ft.) = 180.5 cubic feet
|
|
NOTE:
| |
|---|---|
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2.85 in is the two-year, twenty-four-hour rainfall for Williamsport,
PA, taken from NOAA's Hydrometeorological Design Studies Center
Precipitation Frequency Data Server for Point Precipitation Frequency
Estimates from NOAA Atlas 14.
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(4)
Identify/choose the appropriate stormwater control measures. Size
and place the measures on the project site and add the measures to
the SWM plan.
(a)
The volume of stormwater runoff calculated in Step 3 is now
used to size the stormwater control storage devices. Vegetative controls
and structural measures can be used individually or in combination
to provide the required storage volume. The PA BMP manual identifies
structural and nonstructural control measures that may be used, as
well as instructions to calculate the volume provided by each.
(b)
Please note that all minor stormwater management plans should provide appropriate erosion control measures. Refer to Subsection N above. The PA Erosion and Sediment Pollution Control Program Manual is available for guidance. Please contact the Lycoming County Conservation District for additional information.
(c)
A sample minor stormwater management plan can be found in Appendix
D.[3]
[3]
Editor's Note: Appendix D is included as an attachment to this chapter.
[2]
Editor's Note: Appendix C is included as an attachment to this chapter.
P.
All regulated activities that do not fall under the exemption criteria
referenced herein shall submit a drainage plan to the municipality
for review. These criteria shall apply to the total proposed development
even if development is to take place in stages. Impervious cover shall
include, but not be limited to, any roof, parking or driveway areas
and any new streets and sidewalks. Any areas designed to initially
be gravel or crushed stone shall be considered to be impervious for
the purposes of comparison to the waiver criteria, unless they are
installed and maintained as provided for in the PA BMP Manual.
(1)
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
(2)
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If diffused
flow is proposed to be concentrated and discharged onto adjacent property,
the applicant must document that adequate downstream conveyance facilities
exist to safely transport the concentrated discharge, or otherwise
prove that no erosion, sedimentation, flooding or other harm will
result from the concentrated discharge.
(3)
Where a development site is traversed by watercourses, drainage easements
shall be provided conforming to the line of such watercourses. The
terms of the easement shall prohibit excavation, the placing of fill
or structures, and any alterations that may adversely affect the flow
of stormwater within any portion of the easement. Also, maintenance,
including mowing of vegetation within the easement, shall be required,
except as approved by the appropriate governing authority.
(4)
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by PA DEP through the joint permit application
process, or, where deemed appropriate by PA DEP, through the general
permit process.
(5)
Any stormwater management facilities regulated by this chapter that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by PA DEP through the joint permit application
process, or where deemed appropriate by PA DEP, the general permit
process. When there is a question whether wetlands may be involved,
it is the responsibility of the applicant or his agent to show that
the land in question cannot be classified as wetlands; otherwise,
approval to work in the area must be obtained from PA DEP.
(6)
Any stormwater management facilities regulated by this chapter that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PA DOT).
(7)
Minimization of impervious surfaces and infiltration of stormwater
runoff through seepage beds, infiltration trenches, etc. are encouraged,
where soil conditions permit, to reduce the size or eliminate the
need for detention facilities.
(8)
In order to promote overland flow and infiltration, roof drains should
not discharge directly to streets or storm sewers. Roof drains may
discharge directly to streets or storm sewers when deemed necessary
by the municipality. Under no circumstances shall roof drains discharge
directly to sanitary sewer systems.
