1. Design. All stormwater management facilities shall be located on a plan, described in detail and located wholly on a lot or property under single ownership responsible for maintenance. [Ord. 2-2003]
A. Storm sewers and culverts shall be provided, to:
(1) Permit unimpeded flow of natural watercourses.
(2) Insure adequate drainage of all low points along the line of streets.
(3) Intercept stormwater run-off along streets at intervals related to the extent and grade of the area drained.
(4) Provide positive drainage away from onsite sewage disposal facilities.
B. Where existing storm sewers are reasonably accessible, proposed subdivision shall be required to connect therewith.
C. Where a subdivision or development is traversed by a watercourse, drainage way, channel or stream, there shall be provided a drainage easement conforming substantially with the high water line of such watercourse attributable to a flood of 100 year frequency, in order to preserve the unimpeded flow of natural drainage, and to provide for future possible widening, deepening, relocating, improving or protection of such drainage facilities. Any changes in the existing drainage way shall be subject to the approval of the Township Engineer and the Pennsylvania Department of Environmental Protection.
D. All storm drainage design shall be in accordance with standards set forth in the Township Erosion, Sedimentation and Grading Control Ordinance [Chapter 9], as amended, accepted Engineering design standards, and subject to approval of the Township Engineer.
E. Before approval of any preliminary and/or final subdivision or land development plan, all stormwater calculations upon which the design of the stormwater drainage facilities are based shall be submitted as required and set forth in this Section and approved prior to final acceptance.
F. All materials, construction methods and details employed in the construction of storm drainage facilities shall be in accordance with the latest edition of the Pennsylvania Department of Transportation's "Specifications "(Publication 408) and "Standards for Roadway Construction" (Publication 72) or the Township's specifications, whichever is more stringent.
G. Any stormwater management facility (i.e., detention basin) designed to store runoff and requiring a berm or earthen embankment required or regulated by this Chapter shall be designed to provide an emergency spillway to handle flow up to and including the 100 year post-development conditions. The height of the embankment must be set as to provide a minimum 1 foot of freeboard above the maximum pool elevation computed when the facility functions for the 100-year post-development inflow. Should any stormwater management facility require a dam safety permit under PADEP, 25 Pa.Code, Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety which may be required to pass storms larger than the 100-year event.
H. The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The Township shall reserve the right to disapprove any design that would, in the opinion of the Township Engineer, result in the creation or continuation of an adverse hydrologic or hydraulic condition within the watershed.
I. For the purposes of predevelopment flow rate determination and undeveloped flow rate determination, undeveloped land shall be considered as "meadow-good condition," unless the natural groundcover generates a lower curve number or rational "C" value.
J. The 1-year, 24-hour design storm should be detained using the SCS Type II distribution. Provisions shall be made so that the 1 year storm takes a minimum of 24 hours to drain from the facility from a point where the maximum volume of water from the 1 year storm is captured (i.e., the maximum water surface elevation is achieved in the facility). Release of water can begin at the start of the storm (i.e., the invert of the water quality orifice is at the invert of the facility). The design of the facility shall consider and minimize the chances of clogging and sedimentation potential.
K. Such designs may achieve the water quality objectives through a combination of BMPs (best management practices). In selecting the appropriate BMPs, or combinations thereof, the developer shall consider the following:
(1) Total contributing area.
(2) Permeability and infiltration rate of the site soils.
(3) Slope and depth to bedrock.
(4) Seasonal high water table.
(5) Proximity to building foundations and well heads.
(6) Erodibility of soils.
(7) Land availability and configuration of the topography.
L. All stormwater management facilities must be located on a plan and described in detail.
M. All calculations, assumptions, and criteria used in the design of the stormwater management facilities must be shown.
N. Individual building lots shall be designed to assure that stormwater will flow unimpeded from all proposed dwellings/structures with a minimum 2% slope to an approved stormwater facility or other approved drainage way, when the foundation is set at a minimum height in compliance with all drainage and clearance require- ments of the Township Building Code, as amended.
O. All stormwater management facilities and infrastructure shall be installed prior to the issuance of building construction permits unless otherwise authorized by the Township. Adequate vegetation growth shall be developed with a minimum of 4 inches of topsoil.
2. Runoff.
A. In the design of storm drainage facilities, special consideration shall be given to avoidance of problems which may arise from the concentration of stormwater runoff into adjacent developed or undeveloped properties and streets.
B. Storm drainage facilities should be designed where feasible not only to handle the anticipated peak discharge from the property being developed, but also the anticipated increase in runoff that will occur when all the property at a higher elevation in the same watershed is fully developed.
C. Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., is encouraged, where soil conditions permit, to reduce the size or eliminate the need for detention facilities. Seepage beds are required for building- (above 250 square feet) roof runoff unless it can be demonstrated that the lot will not provide proper percolation.
D. Runoff from the site shall not be concentrated or increase runoff discharged onto adjacent property without the written consent of the adjacent landowners in the form of a drainage easement.
E. Post-development rates of runoff from any regulated activity shall not exceed the peak rates of runoff prior to development for the 2-, 5-, 10-, 25-, 50-, and 100-year frequency storms.
F. The Township has the authority to require that computed existing runoff rates be reconciled with field observations and conditions. If the designer can substantiate through actual physical calibration that more appropriate runoff and time-of-concentration values should be utilized at a particular site, then appropriate correction may be made upon review and recommendations of the Township Engineer. Calibration shall require detailed gauge and rainfall data for the particular site in question.
G. The ability to retain and maximize the ground water recharge capacity of the area being developed is required. Design of the stormwater management facilities shall give consideration to providing ground water recharge to compensate for the reduction in the percolation that occurs when the ground surface is paved and roofed over. A balance shall be made of the pre and post construction infiltration. A detailed geologic evaluation of the project site shall be performed to determine the suitability of recharge facilities. The evaluation shall be performed by a qualified geologist and/or soil scientist, and at minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. Where pervious pavement is permitted for parking lots, recreational facilities, nondedicated streets, or other areas, pavement construction specifications shall be noted on the plan.
H. Whenever a basin will be located in an area underlain by limestone, a geological evaluation of the proposed location shall be conducted to determine susceptibility to sinkhole formations. The design of all facilities over limestone formations shall include measures to prevent ground water contamination and, where necessary, sinkhole formations. Soils used for the construction of basins shall have low erodibility factors ("K" factors) . The Township may require the installation of an impermeable liner in detention basins.
I. The effect of the project (in terms of runoff volumes and peak flows) on adjacent properties and on any existing stormwater collection system that may receive runoff from the project site shall be provided. All drainage areas on a site shall be dealt with individually as part of the overall plan.
3. Installation and Maintenance.
A. The Township Engineer or his designated Township representative shall inspect all phases of the installation of the permanent stormwater management facilities.
B. During any stage of the work, if the Township Engineer determines that the permanent stormwater management facilities are not being installed in accordance with this Chapter, the Township may revoke any existing permits until a revised drainage plan is submitted and approved, as specified in this Chapter.
C. The drainage plan for the development site shall contain an operation and maintenance plan prepared by the developer and approved by the Township Engineer. The operation and maintenance plan shall outline required routine maintenance actions and schedules necessary to insure proper operation of the facility(ies).
D. The Board of Supervisors, upon recommendation of the Township Engineer, shall make the final determination on the continuing maintenance responsibilities prior to final approval of the drainage plan. The Board of Supervisors reserves the right to accept the ownership and operation responsibility for any or all of the stormwater management controls located in the Township rights-of-way and/or easements.
E. Prior to final approval of the site's stormwater management plan, the property owner shall sign and record a maintenance agreement covering all stormwater control facilities, which are to be privately owned. The agreement shall stipulate that, at a minimum:
(1) The owner, successor and assigns shall maintain all facilities in accordance with the approved maintenance schedule and shall keep all facilities in a safe and attractive manner.
(2) The owner shall convey to the Township easements and/or rights-of-way to assure access for periodic inspections by the Township.
(3) If the owner, successor or assigns fails to maintain the stormwater control facilities following due notice by the Township to correct the problem(s), the Township may perform, but shall not have the duty to perform, the necessary maintenance work or corrective work and the owner shall reimburse the Township for all costs.
F. Basins shall be inspected and a report submitted by the Township Engineer or the Township designated representative upon request of the Township on the following basis:
(1) Where evidence of drainage problems exists related to possible basin malfunction.
(2) During or immediately after the cessation of a 100 year or greater storm event.
(Ord. 2-2000, 4/5/2000, §71; as amended by Ord. 2-2003, 12/17/2003, §I)
1. The developer shall employ the guidelines for minimizing erosion and sedimentation as set forth in this Chapter and DEP BMP regulations as amended. In developing a plan for the control of erosion and sedimentation, the developer shall meet, as a minimum, the standards and specifications outlined in the aforementioned Chapter and regulations.
2. In addition, the developer, as part of the conservation plan required under this Chapter, shall submit data, including proposed dates where relevant, to indicate that the subdivision or development will be carried out in compliance with the following principles:
A. The smallest practical area of land shall be exposed at any one time during development or construction.
B. When land is exposed during development or construction, the exposure shall be limited to the shortest practical period of time.
C. Temporary ditches, dikes, vegetation and/or mulching shall be used to protect critical areas exposed during development or construction.
D. Sediment basins (debris basins, desilting basins, or silt traps) shall be installed and maintained to remove sediment from run-off waters from undergoing development.
E. Provisions shall be made to effectively accommodate the increased runoff caused by changed soil and surface conditions during and after development or construction.
F. Permanent vegetation and erosion control structures shall be installed as soon as practical during construction activities.
G. Wherever feasible, natural vegetation shall be retained and protected and natural grade alterations kept to a minimum.
H. Topsoil removed as part of the clearing process shall remain on site to be used in all grass planting areas.
(Ord. 2-2000, 4/5/2000, §72)
1. In reviewing subdivision and development plans, the Township Planning Commission shall consider whether community facilities in the area, especially schools, are adequate to serve the needs of the additional dwellings proposed by the development, and shall make such report thereon as it deems necessary to the public interest.
2. Developers shall give earnest consideration to the desirability of providing or reserving areas for facilities normally required in residential neighborhoods such as schools and other public buildings, parks, playgrounds and playfields. Areas provided or reserved for such community facilities should be adequate to provide for building sites, landscaping and off-street parking as appropriate to the use proposed. Prior to the preparation of plans, developers of large tracts should review with the staff of the County Planning Commission the minimum standards for various community facilities applicable to the tract being developed.
3. In subdivisions which are intended to provide housing for more than 50 families, the Township Planning Commission shall consider the need for suitable open areas for recreation and shall make recommendations thereon. Standards to be used by the Planning Commission in requesting the reservation of space for recreation shall be as follows:
(Ord. 2-2000, 4/5/2000, §73)
