[Ord. 2004-2, 4/5/2004]
1.
All regulated activities (including subdivision and land development
activities) involving an increase in impervious cover (i.e., reduction
in permeability), shall be conducted in conformance with the following
standards:
A.
After installation of impervious cover, peak discharges for the one-,
ten-, twenty-five-, and one-hundred-year frequency storms from the
project site shall not exceed the respective predevelopment peak discharges.
Stormwater runoff shall be managed so that no downstream increases
in flood damages or impairment of streets and other public facilities
occur. The Municipal Engineer may require that downstream impacts
be evaluated at critical locations such as dams, tributaries, existing
developments, undersized culverts, and flood-prone areas. The municipality
and its Engineer shall make the final determination with respect to
the degree of management required for any site. The applicant/developer
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 Municipal Engineer. At such downstream critical locations,
stormwater management may be exercised by:
B.
The municipality and its Engineer may impose stormwater quality measures
in accordance with Appendix A, Section IV,[1] of 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.
[1]
Editor's Note: Said appendix is included as an attachment
to this chapter.
C.
In establishing the watershed 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 shall be used for all areas.
(3)
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)
procedure shall be applied in determining predevelopment peak discharges
from karst geologic areas.
D.
Hydrologic Methods. All plans and designs for stormwater management
facilities shall be reviewed by the Municipal Engineer. Plans for
facilities other than storm sewers should determine stormwater peak
discharge and stormwater runoff by the use of the Soil Cover Complex
Method as set forth in Technical Release No. 55 (TR-55) and Technical
Release No. 20 (TR-20), with specific attention given to antecedent
moisture conditions, flood routing, and peak discharge specifications
included therein, and in the National Engineering Handbook, Section
4, both by United States Department of Agriculture, Natural Resource
Conservation Service. The Municipal Engineer 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)
Acceptable runoff coefficient values for use in the Rational
Method equation, and permissible curve numbers for TR-55 and TR-20
are identified in Tables A-1 through A-2 of Appendix A, Section I,[2] of this chapter. When applying the Rational Method coefficients
in Table A-2, "open space" coefficients shall be used for all predevelopment
pervious areas, and for all undeveloped, densely vegetated (non-forest)
areas instead of "meadow" coefficients.
[2]
Editor's Note: Said appendix is included as an attachment
to this chapter.
(2)
The Rational Method may be used in lieu of the Soil Cover Complex
Method to compute design flows for the sizing of storm sewers, inlets,
and swales. Methods approved by the Pennsylvania Department of Transportation
and/or Department of Environmental Protection may be used to design
the waterway areas of bridges.
(3)
Rainfall amounts for the return periods specified shall be determined
using the Pennsylvania Department of Transportation Intensity Duration
Frequency Curves (PDT-IDF) presented in Figure A-1 of Appendix A,
Section I,[3] of this chapter. Rainfall duration for the design of stormwater
detention basins shall be 24 hours, unless waived in writing by the
municipality and its Engineer.
[3]
Editor's Note: Said appendix is included as an attachment
to this chapter.
(4)
Time of concentration shall be determined in accordance with
the method presented in TR-55.
(5)
In order to reduce stormwater runoff volumes from developed
areas, and in order to encourage groundwater recharge, underground
basin drains, infiltration trenches, and cisterns are permitted to
which roof leaders may be connected. These drains may 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. Performance criteria
which govern the location, design, construction, and maintenance of
these infiltration facilities are contained in Appendix A, Section
IV,[4] of this chapter. Suggested guidelines are contained in
Standards and Specifications for Infiltration Practices (MD DNR).
At a minimum, these infiltration facilities shall be designed to temporarily
store a volume of runoff from a two-year, twenty-four-hour design
storm.
[4]
Editor's Note: Said appendix is included as an attachment
to this chapter.
E.
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 and the municipality.
(2)
To insure 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 contained in the Design Manual Part 2 - Highway Design, Publication 13M (PA DOT), Chapter 10.
(4)
To insure 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 project sites.
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
Municipal Engineer, with no impact on adjoining properties, unless
an area specifically designed for stormwater detention is provided.
F.
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 and its Engineer,
when parallel to the street within the right-of-way.
(a)
When located in undedicated land, they shall be placed within
a drainage easement not less than 20 feet wide, as approved by the
Municipal Engineer.
(b)
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 Municipal Engineer, 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 contained in
Appendix A, Section II,[5] of this chapter.
[5]
Editor's Note: Said appendix is included as an attachment
to this chapter.
(2)
The design capacity of storm sewers shall be in accordance with
Urban Drainage Design Manual, Hydraulic Engineering Circular Number
22 (US DOT, FHA). 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.
(3)
Storm inlet types and inlet assemblies shall conform to the
Pennsylvania Department of Transportation Standards for Roadway Construction,
and the following criteria:
(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 and its Engineer deem it necessary because
of special land requirements, special inlets may be approved.
(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.
(e)
The design of storm inlets shall be in accordance with Drainage
of Highway Pavements, Hydraulic Engineering Circular Number 12, (US
DOT, FHA).
(4)
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 5°, and at all
points of convergence of two or more influent storm sewers.
(5)
When evidence available to the municipality and its Engineer indicates that existing storm sewers have sufficient capacity, as determined by hydrograph summation, and where such existing storm sewers are accessible, proposed stormwater facilities may connect to these existing storm sewers as long as the peak rate of discharge does not exceed the amount permitted by § 23-301, Subsection 1A, of this Part.
G.
Bridges and culverts shall have ample waterway to carry expected
flows, based on the following minimum storm frequencies: ten-year
for driveways; twenty-five-year for local streets; fifty-year for
collector streets; and one-hundred-year for arterials; or as otherwise
required by the municipality and its Engineer. Bridge and/or culvert
construction shall be in accordance with the Pennsylvania Department
of Transportation specifications.
(1)
The design criteria contained in this Part are intended for
use in conjunction with the Chapter 105 Regulations of PA DEP entitled,
"Water Obstructions and Encroachments."[6] All information and regulations contained in Chapter 105
shall be considered to be incorporated into this Part as if reproduced
in full. A PA DEP permit in accordance with Chapter 105 shall be required
for any obstruction or encroachment in regulated waters of the commonwealth,
prior to the approval of the stormwater plan. All areas of the municipality
shall be classified as rural, suburban, or urban, as determined by
the municipality and its Engineer. (See PA DEP Section 105.161 for
bridge and culvert designs.[7]) In the event any question or conflict arises between
this Part and the PA DEP Chapter 105 Regulations, the design criteria
contained in the PA DEP regulations shall govern.
H.
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.
Generally, outlet pipes designed to carry the predevelopment, one-year
storm flow will be permitted to discharge to a stream with only an
energy dissipater; discharges to drainage swales shall be dissipated
with a level spreader, or piped to an acceptable point of discharge.
(4)
Outlet structures within stormwater detention 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 stormwater detention 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 25 feet or greater fill shall not be less
than 24 inches (or a cross-sectional area of 453 square inches), and
shall be reinforced concrete pipe.
(a)
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 and its Engineer,
the applicant/developer shall submit an analysis of the impacts of
detained stormwater flows on downstream areas within the watershed.
The analysis shall include hydrologic and hydraulic calculations necessary
to determine the impact of peak discharge modifications on critical
locations such as dams, tributaries, existing developments, undersized
culverts, and flood-prone areas.
(b)
Review and comment of the analysis by the Engineer of a downstream
municipality shall be obtained as deemed necessary.
(7)
Detention basins may be waived by the municipality and its Engineer at sites in close proximity to large receiving streams, depending on the hydrology of the watershed. It shall be incumbent upon the applicant/developer to demonstrate that no downstream increase in stream flooding or channel erosion will result, in accordance with § 23-301, Subsection 1H(6), of this Part, and that no increases in peak discharge within the receiving stream will occur, as outlined under§ 23-301, Subsection 1A, of this Part.
(8)
Multiple-Use Basins. The design and construction of multiple-use
stormwater detention facilities are strongly encouraged. In addition
to stormwater management, multiple-use basins, where appropriate,
allow for recreational uses including ball fields, play areas, picnic
grounds, etc. Provisions for parking facilities within basins and
permanent wet ponds with stormwater management capabilities may also
be appropriate. Prior approval and consultation with the municipality
and its Engineer 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 applicants/developers
within the watershed development is encouraged. Each applicant/developer
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 and its Engineer is required
before design of such facilities.
(10)
Alternative Detention Facilities. Alternative stormwater detention
facilities including roof top storage, subsurface basins or tanks
and in-pipe detention storage, or other approved alternative designs
that may be permitted by the municipality and its Engineer.
I.
All calculations shall be submitted to the Municipal Engineer on
computation sheets for approval. If the Municipal Engineer determines
through review and independent computation that the size(s) of storm
pipes or detention basins is insufficient, the municipality and its
Engineer may require the applicant/developer to increase the size(s)
of said storm pipes or detention basins. If the storm drainage system
design is completed using computer software, sufficient supporting
data shall be provided to allow comprehensive review by the municipality
and its Engineer.
J.
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 grading plan shall be submitted to the municipality
for review and approval as part of the zoning permit process for the
proposed structure.
K.
Natural drainageways shall be utilized to the maximum extent possible
in carrying stormwater runoff.
L.
Stormwater management facilities located outside of an existing or
proposed public right-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, a drainage easement shall be provided that parallels the line of such watercourse, drainageway, channel, or stream. The width of the drainage easement shall be adequate to preserve the unimpeded flow of natural drainage in the one-hundred-year floodplain, in accordance with computed top widths for water surface elevations determined under § 23-301, Subsection 1A, of this Part.
(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
will not be adjacent to an existing or proposed public right-of-way,
or where they will not be accessible due to physical constraints,
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 stormwater facility and
its appurtenances.
(4)
Easements shall stipulate that no trees, shrubs, structures,
excavation, or fill be placed, and no regrading be performed within
the area of the easement without written approval from the municipality
upon review by the Municipal Engineer. Upon approval of the Municipal
Engineer, such landscaping may be placed in maintenance easements,
provided it does not impede access.
(5)
Whenever practicable, easements shall be parallel with, and
linked to property lines.
(6)
All easement agreements shall be recorded with a reference to
the recorded easement indicated on the stormwater management plan.
The format and content of the easement agreement shall be reviewed
and approved by the Municipal Engineer and the Solicitor.
[Ord. 2004-2, 4/5/2004]
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 and its Engineer
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
and its Engineer.
[Ord. 2004-2, 4/5/2004]
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 and Sediment Control.
2.
The Northumberland County Conservation District has been delegated
the authority by the Pennsylvania Department of Environmental Protection
to administer the Erosion and Sediment Pollution Control Program in
Northumberland County. It shall be the responsibility of the applicant/developer
to submit the E&SPC plan, application, and other necessary material
to the Conservation District. 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
management plan approval.
[Ord. 2004-2, 4/5/2004]
1.
Each stormwater management plan shall contain provisions which clearly
set forth the ownership and maintenance responsibility of all permanent
stormwater management, and erosion and sediment pollution control
facilities, including the following items:
A.
Description of maintenance requirements.
B.
Establishment of suitable easements for access to all facilities by public officials, in accordance with § 23-301, Subsection 1L, of this Part.
C.
Identification of the responsible party or entity for ownership and
maintenance of both temporary and permanent stormwater management,
and erosion and sediment pollution control facilities.
(1)
Stormwater facilities within subdivisions may be part of an
individual lot (or lots) where the respective lot owner (or owners)
will own the facility; however, maintenance shall be the responsibility
of a homeowner's association, or similar entity. A description
of the facility or system, and the terms of the required maintenance
shall appear on the stormwater management plan drawing(s), and shall
be incorporated into the deed to the property. All stormwater management
plan drawings shall be recorded with the approved subdivision plan
among the deed records of Northumberland County, Pennsylvania. In
addition, the approved subdivision plan, and any deed written from
said plan for a lot or lots that will contain stormwater management
facilities shall contain a condition stating that it shall be mandatory
for the owner (or owners) of said lot (or lots) to be members of said
homeowners' association.
(2)
For stormwater management facilities that are proposed as part
of a site development plan, the applicant/developer will be required
to execute a developer agreement and a maintenance agreement with
the municipality for the construction and continued maintenance of
the facilities prior to approval of the final subdivision or land
development plan. Access for inspection by the municipality of all
such facilities deemed critical to the public welfare at any reasonable
time shall be provided.
(3)
In the event the above priorities cannot be achieved, or where
it is required, the facilities may be dedicated to the municipality
in accordance with this chapter. As a condition of municipal acceptance
of said facilities, the applicant/developer shall provide 15% of the
cost of improvements, in the form of a maintenance bond, as estimated
by the applicant's/developer's registered professional,
and approved by the Municipal Engineer, to cover contingency maintenance
costs for 18 months from the date that dedication of the stormwater
management facilities is accepted by the municipality. The fifteen-percent
bond shall be based on the construction costs of the stormwater management
facilities that will be offered for dedication to the municipality.
[Ord. 2004-2, 4/5/2004]
1.
Compliance with the provisions of this chapter shall be in accordance
with the following additional general criteria:
A.
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 Part as if copied in full. In the event
a conflict arises between the requirements of this Part and the PA
DOT Publication 408 Specifications, the Municipal Engineer shall resolve
the difference, and his/her opinion shall be binding.
B.
At the completion of the project, and as a prerequisite for the release
of the guarantee or issuance of an occupancy permit, the owner(s)
or his representative shall:
(1)
Provide a certification of completion from a registered professional
engineer or professional land surveyor verifying that all permanent
facilities have been constructed according to the plans and specifications
and approved revisions thereto.
(2)
Provide a set of approved stormwater management plan drawings
showing all approved revisions, and elevations and inverts to all
manholes, inlets, pipes, and stormwater management facilities.
C.
The municipality shall inspect stormwater management facilities to
ensure proper functioning of such stormwater management facilities.
These inspections shall occur at least once annually for five years
after the installation of said stormwater management facilities, and
then at least once every three years thereafter. The municipality
shall also inspect stormwater management facilities after a one-hundred-year
or greater storm event.
D.
If the municipality determines at any time that any permanent stormwater management facility has been eliminated, altered, or improperly maintained, the municipality shall advise the responsible party (or parties) of the required corrective measures, and shall provide said responsible party (or parties) with a specific time frame to implement the required corrective measures. If such action is not undertaken by the responsible party (or parties), the municipality may cause the work to be done and backcharge all costs to the responsible party (or parties), in accordance with Part 4 of this chapter.
E.
Supplemental standards and criteria contained in the technical reference
materials listed in Appendix B[1] of this chapter are hereby incorporated into this chapter
to govern the hydrologic and hydraulic design provisions contained
herein.
[1]
Editor's Note: Said appendix is included as an attachment
to this chapter.
