Township of Scott, PA Design Standards and Criteria

Post-development peak discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty- and one-hundred-year recurrence interval design storms from project sites that are not within the Susquehanna River Tributaries Watershed (as delineated on Plates B-1 and B-2 in Appendix B[1] of this chapter) shall not exceed the respective predevelopment peak discharge rates.

Editor's Note: Appendix B is an attachment to this chapter.

Post-development peak discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty- and one-hundred-year recurrence interval design storms from project sites (or portion of project sites) that are within the Susquehanna River Tributaries Watershed (as delineated on Plates B-1 and B-2 in Appendix B of this chapter) shall be subject to the allowable release rates that are tabulated in Tables C-1 and C-2 in Appendix C of this chapter.[2]

[2]

Editor's Note: Appendix B and Appendix C are attachments to this chapter.

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 recurrence interval design storms. Methods of computation shall have prior approval of the Municipal Engineer. At such downstream critical locations, stormwater management may be exercised by:

Providing off-site improvements to downstream conveyances in order to contain flow increases.

Providing downstream drainage easements with sufficient widths to contain the flood limits.

Stormwater management plans for all regulated activities must include infiltration and stormwater quality BMPs. For regulated activities that do not require an NPDES construction permit, the design of infiltration and stormwater quality BMPs shall be in accordance with Appendix A, Section IV, of this chapter.[3] Otherwise, the design of infiltration and stormwater quality BMPs shall be in accordance with the NPDES construction permit.

[3]

Editor's Note: Appendix A is an attachment to this chapter.

In establishing the watershed conditions for calculating stormwater runoff prior to development, the following assumptions shall apply:

Woodland (in good condition) or meadow shall be used for all undeveloped areas.

Average antecedent moisture conditions as defined by the Natural Resource Conservation Service shall be used for all areas.

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.

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, USDA, NRCS) and Technical Release No. 20 (TR-20, USDA, NRCS), with specific attention given to antecedent moisture conditions, flood routing, and peak discharge specifications included therein, and in the National Engineering Handbook, Part 630 - Hydrology (USDA, NRCS, current edition). 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.

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 and A-2 of Appendix A of this chapter.[4] 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 and undisturbed, densely vegetated (nonforest) areas instead of "meadow" coefficients.

[4]

Editor's Note: Appendix A is an attachment to this chapter.

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 the Pennsylvania Department of Environmental Protection may be used to design the waterway areas of bridges.

Design rainfall amounts for the specified recurrence intervals shall be determined using the Precipitation-Frequency Atlas of the United States (NOAA Atlas 14, Volume 2). Rainfall duration for the design of stormwater detention basins shall not be less than 24 hours, unless waived in writing by the municipality and its Engineer. All hydrologic computations utilizing the Soil-Cover-Complex Method shall use a rainfall duration of not less than 24 hours, unless waived in writing by the municipality and its Engineer. Rainfall distribution shall be SCS Type II, unless waived in writing by the municipality and its Engineer.

Time of concentration shall be determined in accordance with methods presented in Chapter 15 of the National Engineering Handbook, Part 630 - Hydrology (USDA, NRCS, current edition).

Stormwater management facilities and related installations shall be provided:

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;

To ensure adequate drainage of all low points along the curbline of streets;

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 (PennDOT), Chapter 10;

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;

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.

Storm sewers and related installations.

Placement.

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.

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.

(c)

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, of this chapter.[5]

[5]

Editor's Note: Appendix A is an attachment to this chapter.

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 recurrence interval 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 recurrence interval design storm. Where site grading will not direct stormwater runoff from the one-hundred-year recurrence interval 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 recurrence interval design storm. Conveyance of storms to the detention basin, up to and including the one-hundred-year recurrence interval design storm, shall be provided so as not to endanger life or seriously damage property.

Storm inlet types and inlet assemblies shall conform to the Standards for Roadway Construction, Publication 72M (PennDOT) and the following criteria:

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.

Where the municipality and its Engineer deem 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 Design Manual Part 2 - Highway Design, Publication 13M (PennDOT), Chapter 10, Section 5, "Capacity of Waterway Areas," or Urban Drainage Design Manual (HEC-22, US DOT, FHA).

(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 recurrence interval design storm. 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).

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.

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 § 118-14A of this article.

Bridges and culverts shall have ample waterway to carry expected flows, based on the following minimum design storms: ten-year recurrence interval for driveways; twenty-five-year recurrence interval for local streets; fifty-year recurrence interval for collector streets; and one-hundred-year recurrence interval for arterials; or as otherwise required by the municipality and its Engineer. Bridge and/or culvert construction shall be in accordance with Pennsylvania Department of Transportation specifications.

The design criteria contained in this article are intended for use in conjunction with the (Pennsylvania Code Title 25) Chapter 105 Regulations of the Pennsylvania Department of Environmental Protection, entitled "Water Obstructions and Encroachments." All information and regulations contained in Chapter 105 shall be considered to be incorporated into this article 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 25 Pa. Code § 105.161 for bridge and culvert designs.) In the event any question or conflict arises between this article and the PA DEP Chapter 105 Regulations, the design criteria contained in the PA DEP regulations shall govern.

Refer to Appendix A, Section II, of this chapter for additional design criteria.[6]

[6]

Editor's Note: Appendix A is an attachment to this chapter.

Detention or retention basins for the management of stormwater peak discharges shall meet the following requirements:

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.

The design of all facilities over limestone formations shall include measures designed by a professional geologist 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).

Energy dissipaters and/or level spreaders shall be installed at points where pipes or drainageways discharge to or from basins.

Outlets.

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.

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 recurrence interval design storm, such spillways shall be constructed to withstand the pressures of impounded waters and convey flows at computed outlet velocities without erosion.

(c)

Stormwater facilities shall be designed to release their total volume within the following maximum time periods:

Roofs and parking lots: 24 hours.

[2]

Detention basin: 48 hours.

[3]

Infiltration facilities: 72 hours.

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.

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.

Review and comment of the analysis by the engineer of a downstream municipality shall be obtained as deemed necessary by Scott Township.

(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 § 118-14N(6) of this article, and that no increases in peak discharge within the receiving stream will occur, as outlined under § 118-14A of this article.

(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 rooftop 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, are encouraged.

(11)

Specific criteria related to the design of detention basins is contained in Appendix A, Section III, of this chapter.[7]

[7]

Editor's Note: Appendix A is an attachment to this chapter.

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.

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.

Natural drainageways shall be utilized to the maximum extent possible in carrying stormwater runoff, provided such use remains consistent with the purpose of this chapter specified in Article I, § 118-4.

Stormwater management facilities located outside of an existing or proposed public right-of-way shall be located within and accessible by easements as follows:

Drainage easements. 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 regulatory floodplain, in accordance with computed top widths for water surface elevations determined under § 118-14A of this article. Drainage easements shall provide for maintenance, and for the purpose of widening, deepening, improving, or protecting such drainage facilities.

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.

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.

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.

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.

§ 118-15 Sinkhole protection.

Stormwater from roadways, parking lots, storm sewers, roof drains or other concentrated stormwater runoff paths shall not be discharged directly into sinkholes.

The municipality and its Engineer may require the diversion of runoff away from a sinkhole or the planting and perpetual maintenance of a dense filter path of suitable vegetative material in such manner and location to disperse and slow runoff to a sheet flow condition and to promote, to the maximum extent practical, the filtration of impurities. The design of any required diversion and/or filter path shall be submitted to the municipality and its Engineer for review and approval.

The municipality and its Engineer may require a hydrogeologic assessment by a professional geologist of the risk of increased sinkhole activity due to any regulated activity(ies).

As required by the municipality and its Engineer, sinkholes shall be posted by permanent notices that are clearly visible at the sinkhole prohibiting any disposal of refuse, rubbish, hazardous wastes, organic matter and soil and prohibiting stormwater discharges listed in Article III, § 118-15A, into the sinkhole. Upon the recommendation of a professional geologist, clean rock may be permitted in the sinkhole to prevent the disposal of refuse, rubbish, hazardous wastes, organic matter and soil into the sinkhole.

To reduce the risk of increased sinkhole activity, the municipality and its Engineer may require basins to contain an impervious liner. The design of any recommended/required impervious liner shall be prepared by a professional geologist.

§ 118-16 Erosion and sediment control.

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.

The Columbia 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 Columbia 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.

§ 118-17 Ownership; operation and maintenance.

Each stormwater management plan shall contain provisions which clearly set forth the ownership responsibilities of all permanent stormwater management and erosion and sediment pollution control facilities, including the following items:

Description of ownership and maintenance requirements.

Establishment of suitable easements for access to all facilities in accordance with § 118-14L of this article.

Identification of the responsible party for ownership and maintenance of both temporary and permanent stormwater management and erosion and sediment pollution control facilities.

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, operation and maintenance shall be the responsibility of a homeowners' association or similar entity. A description of the facility or system and the terms of the required operation and 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 Columbia 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.

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, operation 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.

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.

§ 118-18 Additional general criteria.

All materials, workmanship and methods of work shall comply with the current edition of PennDOT 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 article and the current edition of the PennDOT Publication 408 Specifications, the Municipal Engineer shall resolve the difference, and his/her opinion shall be binding.

At the completion of the project and as a prerequisite for the release of any financial security and/or issuance of an occupancy permit, the responsible party shall:

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.

Provide a set of approved stormwater management plan record drawings showing all approved revisions and elevations and inverts to all manholes, inlets, pipes and stormwater management facilities.

The municipality may inspect stormwater management facilities to ensure that such stormwater management facilities are being operated and maintained as designed. These inspections should 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 may also inspect stormwater management facilities after any storm event.

If the municipality determines at any time that any permanent stormwater management facility has been eliminated, altered or improperly operated or maintained, the municipality will notify the party (or parties) responsible for stormwater management facility operation and maintenance that required corrective measures must be implemented and will provide said party (or parties) with a specific time frame to implement the required corrective measures. If such action is not undertaken by the party (or parties) responsible for stormwater management facility operation and maintenance, the municipality may cause the work to be done and back-charge all costs to the party (or parties) responsible for stormwater management facility operation and maintenance in accordance with Article IV of this chapter.

Supplemental minimum standards and criteria contained in the technical reference materials listed in Appendix D of this chapter are hereby incorporated into this chapter to govern the hydrologic and hydraulic design provisions contained herein.[1]

Editor's Note: Appendix Dis an attachment to this chapter.

§ 118-19 Prohibited and authorized discharges.

All regulated activities shall prohibit the discharges that appear in Section I of Appendix E of this chapter. The prohibited discharges that appear in Section I of Appendix E of this chapter shall be listed on the stormwater management plan drawing(s).[1]