City of Scranton, PA Article V Stormwater Management Standards

§ 405-23 General requirements.

A. For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 405-24:

(1) Preparation and implementation of an approved SWM site plan is required.

(2) No regulated activities shall commence until the City of Scranton issues written approval of an SWM site plan, which demonstrates compliance with the requirements of this Part 3.

B. SWM site plans approved by the City of Scranton, in accordance with § 405-33, shall be on site throughout the duration of the regulated activity.

C. The City of Scranton may, after consultation with the DEP, approve measures for meeting the state water quality requirements other than those in this Part 3, provided that they meet the minimum requirements of, and do not conflict with, state law, including but not limited to the Clean Streams Law.

D. 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 Part 3 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.

E. Impervious areas.

(1) The measurement of impervious areas shall include all of the impervious areas in the total proposed development even if development is to take place in stages.

(2) For development taking place in stages, the entire development plan must be used in determining conformance with this Part 3.

(3) For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this Part 3; except the volume controls in § 405-25 and the peak rate controls of § 405-26 do not need to be retrofitted to existing impervious area.

F. Stormwater flows onto adjacent property shall not be created, increased, relocated, or otherwise altered without written notification to the adjacent property owner(s). Such stormwater flows shall be subject to the requirements of this Part 3.

G. All regulated activities shall include such measures as necessary to:

(1) Protect health, safety, and property;

(2) Meet state water quality requirements as defined in Article IV;

(3) Meet the water quality goals of this Part 3 by implementing measures to:

(a) Minimize disturbance to floodplains, wetlands, woodlands, areas of steep slopes and existing native vegetation.

(b) Preserve and maintain trees and woodlands; maintain or extend riparian buffers and protect existing forested buffer; and 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 adequate vegetated cover; 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).¹

H. The design of all facilities over karst shall include an evaluation of measures to minimize adverse effects.

I. 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 Part 3.

J. 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.

K. For all regulated activities, SWM BMPs shall be designed, implemented, operated, and maintained to meet the purposes and requirements of this Part 3 and to meet all requirements under Pennsylvania Code Title 25, the Clean Streams Law, the Storm Water Management Act, and § 405-15 of this Part 3.

L. Various BMPs and their design standards are listed in the PA BMP Manual.¹

M. 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 City of Scranton, and shall be considered to be incorporated into this Part 3 as if copied in full. In the event a conflict arises between the requirements of this Part 3 and the PADOT Publication 408 specifications, the City of Scranton shall resolve the difference, and said opinion shall be binding.

N. Supplemental standards and criteria contained in Article XI are hereby incorporated into this Part 3 to govern the hydrologic and hydraulic design provisions contained herein.

O. The signature and seal of a registered professional engineer, if required, must be provided at the time of plan submission.

§ 405-24 Exemptions.

A. The following activities are specifically exempt from the plan preparation and submission provisions of this Part 3 but remain subject to the requirements in § 405-23E through L of this Part 3 (and erosion and sedimentation pollution control requirements):

(1) Regulated activities that create impervious areas smaller in area than 5,000 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 requirements of this Part 3. Refer to the stormwater management plan (SMP) requirements in Appendix B.[1]

[1] Editor's Note: Appendix B is attached to this chapter.

(2) Agricultural plowing and tilling are exempt from the rate control and SWM site plan preparation requirements of this Part 3, provided that the activities are performed according to the requirements of 25 Pa. Code Chapter 102, Erosion and Sediment Control.

(3) Forest management and timber operations are exempt from the rate control and SWM site plan preparation requirements of this Part 3, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102, Erosion and Sediment Control.

(4) Use of land for gardening for home consumption.

(5) Agriculture when operated in accordance with an approved conservation plan.

B. Exemptions from any provisions of this Part 3 shall not relieve the applicant from the requirements in § 405-23E through L.

C. The City of Scranton 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).

§ 405-25 Volume controls.

The low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities to the maximum extent practicable. Where the design professional determines volume controls are not practical or will place an undue hardship on the development, he/she may request a waiver from complying with this section. The waiver request shall contain sufficient information for the City of Scranton to consider the request. If the City of Scranton determines the volume controls are not practicable or will place an undue hardship on the development, it shall grant the waiver. 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 to or less than one acre that do not require hydrologic routing to design the stormwater facilities, this Part 3 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 post-development total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration rainfall.

(2) For modeling purposes:

(a) Existing (predevelopment) nonforested pervious areas must be considered meadow or its equivalent.

(b) Twenty percent of existing impervious area, when present, shall be considered meadow in the model for existing conditions for redevelopment.

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 1.0 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 0.5 inch of the permanently removed runoff should be infiltrated.

(4) This method is exempt from the requirements of § 405-26, Rate controls.

§ 405-26 Rate controls.

A. Areas not covered by a release rate map from an approved Act 167 stormwater management plan. Post-development discharge rates shall not exceed the predevelopment discharge rates for the 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 post-development analysis are less than or equal to the peak rates of discharge indicated by the predevelopment analysis for 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 two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year storms, the post-development peak discharge rates will follow the applicable approved release rate maps. For any areas not shown on the release rate maps, the post-development discharge rates shall not exceed the predevelopment discharge rates.

§ 405-27 Technical design standards.

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 Part 3. Stormwater runoff shall be managed so that no downstream increases in flood damages or impairment of streets and other public facilities occurs. The City of Scranton may require that downstream impacts be evaluated at critical locations, such as dams, tributaries, existing developments, undersized culverts, and flood-prone areas. The City of Scranton 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 City of Scranton. At such downstream critical locations, stormwater management may be exercised by:

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

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

B. Groundwater recharge. The City of Scranton may impose stormwater quality measures in accordance with this Part 3 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.

C. 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).

D. Hydrologic methods. All plans and designs for stormwater management facilities shall be reviewed by the City of Scranton. 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 City of Scranton 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. Acceptable runoff coefficient values for use in the Rational Method equation are identified in Appendix C, of this Part 3.[1] When applying the Rational Method coefficients in Table A-3, open space coefficients shall be used for undeveloped, densely vegetated (nonforest) areas instead of meadow coefficients. Refer to PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended, for permissible curve numbers. 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.

[1] Editor's Note: Appendix C is attached to this chapter.

(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), United States 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 City of Scranton for approval, and the basins shall be used only in those areas where soils, geologic, and water table conditions permit.

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.

(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 City of Scranton, 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 City of Scranton, 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 City of Scranton.

(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 City of Scranton, 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.

(4) Criteria.

(a) Where vegetated drainage swales are used in lieu of or in addition to storm sewers, they shall be designed to carry the twenty-five-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.

(b) 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.

(c) 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.

(d) 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.

(e) 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.

(f) 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.

(g) Design standard. Because of the critical nature of vegetated drainage channels, the design of all vegetated channels shall, as a minimum, conform to the design procedures outlined in the PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended.

(5) 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 one foot (12 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.

(c) Storm inlet types and inlet assemblies shall conform to the Pennsylvania Department of Transportation Standards for Roadway Construction as approved by the City of Scranton.

[1] 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.

[2] Where the City of Scranton deems it necessary because of special land requirements, special inlets may be approved.

[3] 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.

[4] 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.

[5] The design of storm inlets shall be in accordance with PennDOT Drainage Manual, Publication Number 13, DM-2, Chapter 10, as amended.

[6] All inlets shall be marked with a four-inch stainless steel storm drain marker that indicates "NO DUMPING-DRAINS TO RIVER" or similar message approved by the City of Scranton.

(d) 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 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 City of Scranton.

(e) When evidence available to the City of Scranton 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.

(f) When the outlet of stormwater to the Scranton Sewer Authority combined sewer system is the only feasible stormwater control method, in addition to meeting the requirements of this Part 3, compliance with the Sewer Authority of the City of Scranton's "Policy on the Connection of Stormwater Discharges into the Combined Sewer System" shall be required and evidenced by providing the City of Scranton with a copy of the permit to discharge into Scranton Sewer Authority system.

G. 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 City of Scranton.

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.

(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 City of Scranton, 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 City of Scranton. 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 downstream analysis by the City of Scranton shall be obtained as deemed necessary.

(7) Detention basins may be waived by the City of Scranton 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, including: ballfields, 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 City of Scranton 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 City of Scranton 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 City of Scranton.

I. All calculations shall be submitted to the City of Scranton on computation sheets acceptable to the reviewer for approval. If the City of Scranton determines through review and independent computation that the size(s) of storm pipes or detention basins is insufficient, the City of Scranton may require the applicant to increase the size(s) of said storm pipes or detention basins. 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.

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 drainage plan shall be submitted, reviewed and approved as part of the zoning permit process for the proposed structure.

K. The City of Scranton 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. 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. 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 City of Scranton, 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 City of Scranton. Upon approval, such landscaping may be placed in maintenance easements, provided that 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 City of Scranton.

L. 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 City of Scranton 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 City of Scranton.

M. 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 Chapter 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 City of Scranton. Comments shall be received and E&SPC plan approval obtained from the Conservation District prior to stormwater plan approval.

N. All regulated activities that do not fall under the exemption criteria referenced herein shall submit a drainage plan to the City of Scranton 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 Part 3.

(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 Part 3. 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 the PA DEP through the joint permit application process or, where deemed appropriate by the PA DEP, through the general permit process.

(5) Any stormwater management facilities regulated by this Part 3 that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by the PA DEP through the joint permit application process or, where deemed appropriate by the 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 the PA DEP.

(6) Any stormwater management facilities regulated by this Part 3 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. When infiltration is utilized, appropriate testing is required.

(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 City of Scranton. Under no circumstances shall roof drains discharge directly to sanitary sewer systems.