A. The design and construction requirements for stormwater management and stormwater conveyance systems, described in Article VI of this chapter, are hereby established as indicated in said article.
B. Runoff control measures or BMPs.
(1) Any selected BMP must meet the required water quality and runoff peak rate requirements of this chapter.
(2) Developers shall consider the use of innovative BMP's (e.g., infiltration techniques, wet ponds, riparian buffers, bioretention areas, underground detention, seepage beds, artificial wetlands), if appropriate, to provide for water quality improvement and groundwater recharge. Guidelines for the selection and design of a wide variety of BMP's are available in the Pennsylvania Handbook of Best Management Practices for Developing Areas (Pennsylvania Association of Conservation Districts, 1998) and its successor document or documents when available Other design guides, approved by the Township, may also be used in preparing stormwater management plans. In selecting the appropriate BMP's or combinations thereof, the following must be considered:
(a) Contributing drainage area served by the BMP.
(b) Hydraulic conductivity of soils and bedrock.
(c) Depth to seasonal high water table and bedrock.
(d) Erodibility of soils.
(e) Land availability and topographic constraints.
(f) Existing natural resources which require conservation or enhancement.
(g) Other factors as may be identified by the Township Engineer, MCCD, DEP, EPA or other state and federal agencies.
(3) Exemptions.
(a) Any regulated activity specified in Article IV which meets the stormwater management plan exemption criteria is exempt from meeting the water quality requirements of § 206-35. This exemption shall apply to the total proposed development even if development is to take place in stages. Exemption shall not relieve the applicant from providing adequate stormwater management to meet the purpose of this chapter. Nevertheless, the following control techniques are encouraged where appropriate:
[1] Small on-site bioretention areas, providing detention storage, with grassed overflow.
[2] Oversized storm sewers with flow constrictions (reduced orifice) at discharge.
[3] Stream channel preservation and protection of vegetation; energy reduction spillways.
[4] Reduction of maintained landscaped areas.
[5] Preservation of existing vegetation, especially native plantings and woodland.
[6] Planting of wetland species along drainage swales and depressions.
[7] Fertilization practices minimized/eliminated.
[8] Site design criteria which prevent significant alteration of existing topography.
[9] Sites that have suitable soils are encouraged to incorporate on-site infiltration methods, such as grassed waterways, shrub filter strips, and french drains and trenches, into the design of the development.
(b) All sites with suitable conditions must comply with the groundwater recharge requirement. The groundwater recharge requirement may be satisfied using a variety of BMP's.
(4) Subregional (combined site) storage.
(a) Traditionally, the approach to stormwater management has been to control the runoff on an individual site basis. However, there is a growing commitment to finding cost-effective comprehensive control techniques which both preserve and protect the natural drainage system. In other words, two developers developing sites adjacent to each other could pool their capital resources to provide for a community stormwater management facility in the most hydrologically advantageous location or locations,
(b) The goal is the development and use of the most cost effective and environmentally sensitive stormwater runoff controls which significantly improve the capability and flexibility of land developers and communities to control runoff.
(c) An advantage to combining efforts is to increase the opportunity to utilize stormwater management facilities to meet other community needs and safety considerations. For example, certain stormwater management facilities could be designed so that recreational facilities, such as ball fields, open space, sand volleyball courts, etc., could be incorporated. Natural or artificial ponds and lakes could serve both recreational and stormwater management objectives.
(d) To take this concept a step further, there is also the possibility that the stormwater could be managed off site; that is, in a location off the property(s) in question. There could be a regional detention, retention, lake, pond or other physical facilities to serve multiple developments. Any such facility shall have a construction, ownership and maintenance program, in a recordable form.
(5) All stormwater management facility designs shall conform to the applicable standards and specifications of the following governmental and institutional agencies:
(a) American Society of Testing and Materials (ASTM).
(b) Asphalt Institute (Al).
(c) Montgomery County Conservation District. (MCCD).
(d) Federal Highway Administration (FHWA).
(e) National Crushed Stone Association (NCSA).
(f) National Sand and Gravel Association (NSGA).
(g) Pennsylvania Department of Environmental Protection (DEP).
(h) Pennsylvania Department of Transportation (PennDOT).
(i) United States Department of Agriculture, Natural Resources Conservation Service, Pennsylvania (USDA, NRCS, PA)
(j) Montgomery County Planning Commission. (MCPC).
(k) Environmental Protection Agency. (EPA).
(l) Federal Emergency Management Agency. (FEMA).
(m) U.S. Army Corps of Engineers (ACOE).
(6) If special geological hazards or soil conditions, such as carbonate derived soils, are identified on the site, the developer's engineer and geologist shall consider the affect of proposed stormwater management measures on these conditions. In such cases, the Township may require an in-depth report by a competent registered professional engineer and/or geologist.