Township of Union, PA Article IV Stormwater Management for Tributaries to the Schuylkill River Outside Berks County

§ 165-21 General requirements for stormwater management.

A. No approval of any subdivision or land development plans, or issuance of any building or occupancy permit, or the commencement of any earth disturbance at a project site within the unclassified area of Union Township (as mapped and shown in Appendix D[1]) shall proceed until the requirements of this chapter are met, including approval of a stormwater management plan under Article IV and a permit under PADEP regulations, where applicable.

[1] Editor's Note: Appendix D is included as an attachment to this chapter.

B. Techniques described in Appendix E (Low-Impact Development) of this chapter are encouraged because they reduce the costs of complying with the requirements of this chapter and the state water quality requirements.

C. All stormwater management site plans shall be designed and certified by individuals registered in the Commonwealth of Pennsylvania and qualified to perform such duties based on education and training in hydrology and hydraulics.

D. Runoff from impervious areas shall be drained to pervious areas of the development site.

E. Stormwater management facilities located within or affecting the floodplain or any watercourse shall also be subject to other ordinances of Union Township that regulate construction and development within areas of Union Township subject to flooding (e.g., Chapter 106, Floodplain Management), and any other applicable requirements of the Floodplain Management Act.[2]

[2] Editor's Note: See 32 P.S. § 679.101 et seq..

F. Stormwater runoff from a development site shall flow directly into a natural watercourse or into an existing storm sewer system or onto adjacent properties in a manner similar to the runoff characteristics of the predevelopment flow. Maximum use shall be made of the existing on-site natural and man-made stormwater management facilities.

G. Stormwater runoff shall not be transferred from one watershed to another unless they are subwatersheds of a common watershed which join together within the perimeter of the development site, or the effect of the transfer does not alter the peak discharge onto adjacent lands, or drainage easements from the affected landowners are provided.

H. All stormwater runoff flowing over the development site shall be considered in the design of the stormwater management facilities.

§ 165-22 Permit requirements by other government entities.

The following permit requirements apply to certain land development activities and must be met prior to municipal approval of subdivision approval or land development plans or issuance of building or occupancy permits, where applicable:

A. All earth-disturbance activities subject to permit requirements by PADEP under regulations at 25 Pa. Code, Chapter 102.

B. Work within natural drainageways subject to permit by PADEP under 25 Pa. Code, Chapter 105.

C. Any stormwater management facility that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by PADEP under 25 Pa. Code, Chapter 105.

D. Any stormwater management facility that would be located on a state highway right-of-way subject to approval by the Pennsylvania Department of Transportation (PennDOT).

E. Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by the DEP under 25 Pa. Code, Chapter 105.

§ 165-23 Erosion and sediment control during land development.

A. Earth-disturbance activities of 5,000 square feet or greater require design, implementation and maintenance of erosion and sediment control BMPs that control erosion and prevent sediment pollution during the earth-disturbance activities.

B. The BMPs shall be identified in a plan, and a permit, if applicable, as required by PADEP regulations at 25 Pa. Code, Chapter 102.

C. Evidence of any necessary permits for the earth-disturbance activities from the Berks County Conservation District and/or PADEP must be provided to Union Township.

D. A copy of the erosion and sediment control plan and any required permit under 25 Pa. Code, Chapter 102, shall be available at the project site at all times.

§ 165-24 Standards for permanent stormwater management.

A. The following land disturbances shall comply with provisions of this section:

(1) All minor and major subdivisions and land developments where land disturbance exceeds 5,000 square feet.

(2) An impervious cover addition to an existing developed property that exceeds 5% of lot area or 1,500 square feet, whichever is smaller.

(3) A semi-impervious cover addition (gravel, lattice blocks) to an existing developed property which exceeds 2,000 square feet.

B. Permanent stormwater management standards.

(1) Standard 1. After development and installation of impervious cover, there shall be no increase in the total volume of stormwater runoff being discharged from the site for up to the two-year-frequency rainfall, predevelopment to postdevelopment, calculated using a methodology as described in this chapter. This volume standard can be achieved through use of infiltration-oriented stormwater management practices, although other techniques for volume control, such as vegetated roofs, cisterns, etc., are also possible. First priority should be given to use of preventive approaches as set forth in Appendix E, Low-Impact Development Practices,[1] reducing the total volume calculation.

(a) Alternative standard. Applicants may request to use Alternative Standard 1A where a portion of the Standard 1 volume requirement is excused but at least 50% of the total volume is provided (i.e., volume control is achieved for a lesser storm such as the one-year storm). Applicants may also request Alternative Standard 1B where less than 50% of the entire Standard 1 volume requirement is set aside. The need for alternative standards of any type must be based on demonstration by the applicant that, due to the existing soil, bedrock, water table, or other natural conditions and limitations at the site, the Standard 1 volume requirement cannot be satisfied through use of reasonable best management practices, as defined in this chapter. Alternative standards are discouraged by the Township and will be authorized only after thorough scrutiny has been directed toward all possible stormwater management options at all possible locations at the site.

(b) Criteria for alternative standards. Alternative Standard 1A or 1B may be used in those situations where natural site conditions indicate that infiltration is not occurring substantially in the predevelopment condition, resulting in greater runoff volumes. Such natural site factors include presence of bedrock at or near the surface (defined as less than two feet in depth), and/or presence of seasonal high-water table (SHWT, typically defined as at less than two feet), and/or presence of "heavy" soils with extremely low permeability (generally less than 0.5 inch per hour; in some cases 0.25 inch per hour). Alternative Standard 1A or 1B is to be authorized in only those cases where the applicant has demonstrated that one or all of these conditions exist throughout the majority of the site such that no reasonable building program can be undertaken which includes feasible infiltration BMPs. As site size increases, all else being equal, obtaining the use of an alternative standard becomes more difficult because there is greater ability to accommodate both the building program and stormwater management systems. Finally, Alternative Standard 1A or 1B is not to be issued simply because a building program preferred by the applicant precludes otherwise feasible site areas from being utilized for stormwater management BMPs.

(c) Specifically, determining feasibility for infiltration BMPs is a function of:

[1] Extent of site area with SHWT (less than two feet). Alternative standards will only be authorized in those cases where the applicant has demonstrated that site areas free of SHWT constraints are not feasible for use as stormwater BMPs (e.g., located upgradient from site building areas).

[2] Extent of site area with less than two feet to bedrock. Alternative standards will only be authorized in those cases where the applicant has demonstrated that site areas free of shallow bedrock constraints are not feasible for use as stormwater BMPs (e.g., again, located upgradient from site building areas).

[3] Extent of site area with less than 0.5 inch per hour or 0.25 inch per hour permeability. The preferred permeability rate after recommended soil testing should be at least 0.5 inch per hour (can be reduced to 0.25 inch per hour in those cases with low density being proposed and large site areas available for infiltration). Soils classified as Hydrologic Soil Group (HSG) D may be assumed to be infeasible without recommended soil testing. Soils classified as HSG C or B (virtually all soils) must be verified with additional soil testing.

[4] Size of site.

[a] The larger the site, all else equal, the more flexibility for accommodating runoff volume/infiltration BMPs; as site size increases, Alternative Standard 1A or 1B requirements are more stringent. Size of the site relates also to the extent of proposed building/impervious area: the more intense (defined both in terms of building coverage and total impervious area) the program, the more challenging is accommodating the runoff volume.

[b] If the total of infiltration-constrained areas exceeds 75% (for sites less than five acres), 80% (for sites of five to 10 acres), or 85% (for sites greater than 10 acres) of the total site area and no feasible site area or highly restricted site area in excess of the above limits (defined as free of any of the above constraining features) exists downgradient from any logical site building areas, then alternative standards may be authorized by the Township. The applicant determines whether Alternative Standard 1A or 1B is requested based on the specific site and the proposed building program.

[1] Editor's Note: Appendix E is included as an attachment to this chapter.

(2) Standard 2.

(a) After installation of impervious cover and all improvements, and assuming full compliance with Standard 1, the peak rate of stormwater discharges from the site for all design storms up to and including a one-hundred-year-frequency storm, postdevelopment, shall not exceed the peak discharges from the site from the same storms before disturbance. Design storms include:

[1] Two-year, twenty-four-hour storm.

[2] Five-year, twenty-four-hour storm.

[3] Ten-year, twenty-four-hour storm.

[4] Twenty-five year, twenty-four-hour storm.

[5] Fifty year, twenty-four-hour storm.

[6] One-hundred year, twenty-four-hour storm.

(b) If Alternative Standard 1A has been authorized and at least 50% of the volume requirement specified under Standard 1 is being met, these Standard 2 provisions for peak rate also apply.

(3) Standard 3. In those cases where Alternative Standard 1B is requested, then additional peak rate standards are set forth so that the postdevelopment peak rate discharges from the site for the one-year and two-year storms do not exceed 75% of predevelopment peak rates, for the five-year and ten-year storms, do not exceed 80% of predevelopment peak rates, and for all storms larger than the ten-year storm, do not exceed 85% of predevelopment peak rates.

(4) Standard 4. Significant loadings of nonpoint-source pollutants shall not be discharged into either surface water or groundwater. If the total volume and peak rate standards above are met as in Standards 1 and 2 (including if Alternative Standard 1A for volume control is approved by the Township), then water quality impacts are assumed to be adequately controlled.

(a) If the requirements set forth in Standards 1 and 2 above are not achieved and Alternative Standard 1B is authorized, then an additional water quality requirement must be met in order to guarantee that significant water quality impacts will not result from the proposed development action. Water-quality-oriented best management practices (BMPs) designed to capture and treat stormwater generated for up to the one-inch rainfall event for all site areas being disturbed must be employed. These BMPs include but are not limited to:

[1] Constructed wetlands/wetland forebays.

[2] Detention/retention pond forebays.

[3] Retention ponds/extended detention ponds.

[4] Filters (sand-peat, underground sand, perimeter sand filter, organic sand, pocket sand filter, gravel).

[5] Grass channels.

[6] Dry swales.

[7] Filter strips.

[8] Other bioretention BMPs.

(b) In cases of Alternative Standard 1B, the applicant must demonstrate that, for stormwater generated up to the one-inch rainfall event for all site areas being disturbed, two BMPs from the above list are employed to treat stormwater runoff. This dual treatment is required because research findings relating to pollutant-removal effectiveness has demonstrated that infiltration BMPs are substantially more effective at pollutant removal (nonsoluble pollutants) than the primarily noninfiltration BMPs listed above. BMP selection, design, and implementation shall be based upon appropriate reference materials such as the Pennsylvania Handbook of Best Management Practices for Developing Areas, Design of Stormwater Filtering Systems, and other manuals.

(5) Special provisions for hotspot land uses.

(a) Water quality requirements in addition to those contained in Standard 4 above may be imposed by the Township Engineer for projects involving land uses considered to be high pollutant producers or hotspots.

(b) Hotspots include but are not limited to:

[1] Vehicle maintenance and repair facilities.

[2] Vehicle fueling stations.

[3] Fast-food establishments.

[4] Convenience stores.

[5] Storage areas for public works.

[6] Outdoor storage of liquids.

[7] Commercial nursery operations.

[8] Salvage yards and recycling facilities (regulated under the NPDES stormwater program).

[9] Fleet storage yards and vehicle cleaning facilities (regulated under the NPDES stormwater program).

[10] Facilities that store or generate regulated substances (regulated under the NPDES stormwater program).

[11] Marinas (regulated under the NPDES stormwater program).

[12] Certain industrial uses (listed under NPDES) (regulated under the NPDES stormwater program).

[13] Other uses or activities designated by appropriate authority.

NOTE: As used in this list, the term "regulated substances" shall mean any substances regulated under federal, state, or county environmental, pollution control, hazardous substance, and drinking water laws and regulations.

(c) Sample pretreatment requirements are listed below:

[1] Oil/water separators.

[2] Sediment traps/catch basin sumps.

[3] Trash/debris collectors in catch basins.

[4] Water quality inserts for inlets.

[5] Use of drip pans and/or dry sweep material under vehicles and/or equipment.

[6] Use of absorbent devices to reduce liquid releases.

[7] Spill prevention and response program.

[8] Diversion of stormwater away from potential contamination areas.

[9] Vegetated swales/filter strips.

[10] Constructed wetlands.

[11] Stormwater filters (sand, peat, compost, etc.).

[12] Stormwater collection and reuse (especially for irrigation).

[13] BMPs that are part of a stormwater pollution prevention plan (SWPPP) under an NPDES permit.

(6) Under certain conditions, the Township, upon recommendation by the Township Engineer, may impose the following additional restrictions on stormwater discharges:

(a) Peak discharge may be further restricted when it can be shown that a probable risk to downstream structures or unique natural areas exists or that existing severe flooding problems could be further aggravated.

(b) Measures shall be imposed to protect against groundwater or surface water pollution where the type of business activity may result in significant nonpoint-source pollution (so-called "hotspots") or the nature of the soils or bedrock underlying a stormwater management structure constitutes substantial risk of contamination, such as might be the case in limestone formations. Special provisions to be followed in these cases will be provided by the Township Engineer.

(c) Where groundwater yields are very low or where a groundwater supply already is heavily used, the Township may require that the entire volume of the two-year-frequency rainfall (3.2 inches in 24 hours) be retained and infiltrated. If substantial irrigation needs are anticipated, a portion of stored stormwater may be reused for irrigation purposes.

C. Incentives for environmentally sensitive conservation design. The applicant may, subject to approval of Union Township, use any of the following incentives, or credits, in the design of stormwater BMPs for the site. These credits can affect both quantity and quality of stormwater calculations, as set forth above.

(1) Credit 1: conservation of natural areas.

(a) Definition. Natural areas include woodland areas, buffers of wetlands and riparian zones, steep slopes, wellhead protection areas, carbonate/sinkhole zones, and others.

(b) Credit. Subtract these natural areas from the total site area when calculating the one-inch design volume requirement pursuant to Standard 4 above (assumes use of Standard 1B); if Standards 1 and 2 are otherwise being satisfied, these natural areas may be subtracted from Standards 1 and 2 calculations as well.

(c) Requirements. Natural areas must not be disturbed during construction; limits of disturbance must be delineated on construction drawings and flagged in the field; the natural area must be protected in perpetuity, either through viable conservation easement or through enforceable regulation of some type; it must be properly inspected and managed.

(2) Credit 2: disconnection of runoff.

(a) Definition. Disconnection of runoff relates to all rooftop areas or other impervious ground surface areas which are directed into pervious areas where it is either infiltrated into the soil or filtered through vegetation, accomplished typically by grading; these areas must either have adequate size and permeability for adequate infiltration and/or extended detention with filtering; vegetated rooftops with storage also may be used.

(b) Credit. Disconnected areas may be subtracted from other areas on the site requiring water quality treatment pursuant to Standard 4 above; at the discretion of the Township Engineer, disconnected areas may also be subtracted from peak rate calculations pertaining to Standard 2 (not Standard 3).

(c) Requirements. Runoff must not be generated from hotspot uses (see above) to receive this credit; the maximum contributing flow length shall be 100 feet; the flow length of disconnection shall not be less than 1.5 times the contributing flow length; the disconnection shall drain continuously through a vegetated channel, swale, forest buffer, or other filter strip to the property line or BMP; and the disconnection shall consist of at least 50% of Hydrologic Soil Groups A and/or B with average slope not exceeding 5% (undisturbed Group C with shrub or woodland vegetation may be counted as B with Township approval). Also, all disconnected flows must be broadly and evenly distributed into vegetated areas in a manner such as through level spreading devices or other techniques which will maintain sheet flow characteristics, avoiding channelization.

(3) Credit 3: environmentally sensitive design.

(a) Definition. When site design techniques from Credits 1 and 2 are grouped and applied to residential developments, this credit is granted automatically, or when all of the design specifications listed below in Subsection C(3)(c) are utilized.

(b) Credit. This eliminates the need for additional BMPs to satisfy Standard 4 (assuming use of Standard 1B); and it eliminates additional peak rate requirements of Standard 3 regardless of Standard 1 satisfaction.

(c) Requirements. Where total site impervious areas is less than 15%, where clustering is used, where roof and ground surface impervious areas are disconnected as per Credit 2, where grass swales are used rather than conventional curbing with gutter, where at least 30% of the site is protected in natural areas as per Credit 1, and where all runoff from the site is directed as sheet flow to filter strips or riparian buffers, the design is deemed to be environmentally sensitive.

D. Stormwater management calculation methods.

(1) In all plans and designs for stormwater management systems, stormwater hydrographs and peak discharge shall be determined through the use of the Soil Cover Complex Method as set forth in Urban Hydrology for Small Watersheds, Technical Release No. 55. Specific attention shall be given to antecedent moisture conditions, flood routing, and peak discharge specifications included therein and in Hydrology National Engineering Handbook, Section 4, both by the United States Department of Agriculture, Natural Resources Conservation Service (Soil Conservation Service).

(2) Note that TR-55 requires watersheds to be divided into subareas for accurate modeling. It is generally not acceptable to evaluate a watershed as a single subarea, unless it can be demonstrated that further division is not practical from a hydrologic standpoint.

(3) Runoff Curve Numbers (CN) for both existing and proposed conditions shall be obtained from Appendix B-1 of this chapter. If the actual land use is not listed in these appendixes, runoff coefficients shall be chosen from other published documentation, and a copy of said documentation shall be submitted with the stormwater management report.

(4) All calculations using the Soil Cover Complex Method shall use the appropriate design rainfall depths for the various return-period storms according to NOAA's National Weather Service Precipitation Frequency Data Server (PFDS) or NOAA Atlas 14. If a hydrologic computer model such as PSRM or HEC-1 / HEC-HMS is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours.

(5) The Township Engineer may permit the use of the Rational Method for calculation of runoff on a case-by-case basis, provided that any Rational Method modeling involving storage volumes must be fully documented.

(a) Rational Method runoff coefficients (C) for both existing and proposed conditions shall be obtained from Appendix B-2 of this chapter. If the actual land use is not listed in these appendixes, runoff coefficients shall be chosen from other published documentation, and a copy of said documentation shall be submitted with the stormwater management report.

(b) All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration for overland flow and return periods from NOAA's National Weather Service Precipitation Frequency Data Server (PFDS) or NOAA Atlas 14.

(6) For residential land development and subdivisions, anticipated impervious cover per lot shall be increased by a factor to account for future impervious surfaces attributable to building additions, sheds, patios, swimming pools, etc. These factors shall be as follows: for lot size up to and including 1/2 acre, multiply anticipated impervious cover by 1.2; for lot size greater than 1/2 acre, multiply anticipated impervious cover by 1.3. Impervious assumptions relative to stormwater management shall be identified on the record plan for subdivisions and land developments to be recorded and on the stormwater management plan for individually permitted proposals.

(7) Times of concentration shall be based on the following design parameters:

(a) Sheet flow. The maximum length for each reach of sheet or overland flow before shallow concentrated or open channel flow develops is 150 feet. Flow lengths greater than 100 feet shall be justifiable based on the actual conditions at each development site. Sheet flow shall be determined using Manning's kinematic solution described in Chapter 3 of TR-55, Urban Hydrology for Small Watersheds.

(b) Shallow concentrated flow. Travel time for shallow concentrated flow shall be determined using Figure 3-1 from TR-55, Urban Hydrology for Small Watersheds.

(c) Open channel flows. At points where sheet and shallow concentrated flows concentrate in field depressions, swales, gutters, curbs, or pipe collection systems, the travel times and downstream end of the development site between these design points shall be based upon Manning's Equation and/or acceptable engineering design standards as determined by the Municipal Engineer.

(8) In establishing the antecedent conditions for calculating runoff prior to land disturbance (i.e., predevelopment), the following assumptions shall apply:

(a) Average antecedent moisture conditions.

(b) An SCS Type II distribution storm (when using TR-55 methodology).

(c) Pennsylvania Region 4 storm intensity-duration-frequency curves (when using Rational Methodology).

(d) Woodland shall be used as the prior condition for those portions of the site having trees of greater than six inches' caliper DBH or where such trees existed within three years of application.

(e) If the initial condition of the site is undeveloped land, the land use shall be considered as "meadow," unless the natural land cover is proven to generate lower CNs or Cs, such as forested lands.

(f) In performing the TR-55 calculations, all those areas to be disturbed during construction shall be assumed to be reduced one hydrologic soil group category level during postdevelopment runoff calculations (e.g., HSG B is reduced to HSG C, and so forth).

(9) In calculating runoff after development, those areas covered by concrete lattice blocks on an appropriate base, porous pavement areas on an appropriate base, and roof areas which drain to properly designed and installed storage/groundwater infiltration beds shall be considered adequate to infiltrate any increased runoff from a two year storm.

(10) All calculations must be fully supported by complete documentation concerning assumptions and criteria used to compute hydrographs and discharge.

§ 165-25 Specific stormwater management design requirements.

A. Infiltration/recharge facilities.

(1) Infiltration devices shall be selected based on suitability of soils and site conditions. Measures may include porous pavement with underground infiltration beds, vegetated infiltration beds, swales and trenches, or other seepage structures as proposed in the Pennsylvania Handbook of Best Management Practices for Developing Areas (1998) and related references prepared by the USEPA, the Washington Metropolitan Council of Governments, the Soil Conservation Service, the Pennsylvania Department of Environmental Protection (PADEP), or other guidance documents.

(2) Soils. A detailed soils evaluation of the project site shall be required where practicable to determine the suitability of infiltration facilities. The evaluation shall be performed by a qualified design professional and, at a minimum, address soil permeability, depth to bedrock and subgrade stability. The general process for designing the infiltration BMP shall be:

(a) Analyze hydrologic soil groups as well as natural and man-made features within the site to determine general areas of suitability for infiltration practices. In areas where development on fill material is under consideration, conduct geotechnical investigations of subgrade stability; infiltration is not permitted to be ruled out without conducting these tests.

(b) Provide field tests such as double-ring infiltrometer or hydraulic conductivity tests (at the level of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Percolation tests are not recommended for design purposes.

(c) Design the infiltration structure for the required retention (Re_v) volume based on field determined capacity at the level of the proposed infiltration surface.

(d) If on-lot infiltration structures are proposed by the applicant's design professional, it must be demonstrated to Union Township that the soils are conducive to infiltrate on the lots identified.

(3) The lowest elevation of the infiltration area shall be at least two feet above the seasonal high-water table (SHWT) and bedrock, except in the case of limestone formations, in which case the distance shall be four feet.

(4) All roof drains shall discharge to infiltration systems, unless specifically approved by the Township Engineer, with appropriate measures such as leaf traps and cleanouts taken to prevent clogging by vegetation.

(5) All infiltration systems shall have appropriate positive overflow controls to prevent storage within one foot of the finished surface or grade.

(6) All infiltration systems shall have a setback of 15 feet from all residential structures. Care should be taken to prevent any seepage into subgrade structures. Recharge systems greater than three feet deep shall be located at least 50 feet from any basement wall, wastewater treatment or wastewater treatment system replacement area. Any recharge system designed to handle runoff from any commercial or industrial impervious parking or outside storage areas shall be a minimum of 100 feet from any water supply well and 50 feet from any wastewater treatment or wastewater treatment system replacement area.

(7) All infiltration systems shall be designed to infiltrate the stored volume (or otherwise empty) within 48 hours of the end of the storm.

(8) All surface inflows shall be designed to prevent the discharge of sediment into the infiltration system; accumulated sediment reduces stormwater storage capacity and ultimately clogs the infiltration mechanism. If sediment is reasonably expected to be generated, treatment to remove this sediment prior to entering the infiltration device must be provided. No sand or other particulate matter may be applied to a pervious surface for winter ice conditions.

(9) Construction phase precautions. During site construction, all recharge system components shall be protected from compaction due to heavy-equipment operation or storage of fill or construction material. Recharge areas shall also be protected from sedimentation. All areas designated for recharge shall not receive runoff until the contributory drainage area has achieved final stabilization.

(10) System overflow design. All recharge facility designs shall incorporate measures to provide for the flow of runoff which exceeds the capacity of the system without increasing erosion or creating damage to any other stormwater management system components.

(11) Construction requirements. The following procedures and materials shall be required for all subsurface facilities:

(a) Excavation for the infiltration facility shall be performed with equipment which will not compact the bottom of the infiltration bed/trench or like facility.

(b) The bottom of the bed and/or trench shall be scarified prior to the placement of filter fabric and aggregate.

(c) Only double-washed, clean aggregate, free of fines, shall be allowed. A stone slip is required to document washing, and the Township Engineer may reject any stone deemed unsuitable for infiltration/recharge facilities.

(d) The top, bottom, and sides of all infiltration beds, trenches, or like facilities shall be covered with drainage filtration fabric in order to prevent sediment and soil from migrating into the infiltration system.

(e) Perforated distribution pipes connected to centralized catch basins and/or manholes with provisions for the collection of debris shall be provided in all facilities. The perforated pipes shall distribute stormwater throughout the entire infiltration bed/trench or like facility.

(f) A positive outlet drainpipe placed at the top of the infiltration bed and/or trench or like facility shall be provided to safely convey larger storm events, as needed. Provision for positive outlet drains also may be made at lower elevations in the infiltration facility in those cases where permeability of the soil is near the lower acceptable limit and concern exists that water may remain in the infiltration facility for extended periods.

B. Basins and impoundments. Any BMP that is a dam, as defined in 25 Pa. Code, Chapter 105, shall be designed according to the requirements in those regulations. Any stormwater BMP that does not constitute a dam under 25 Pa. Code, Chapter 105, but is designed to store runoff and requires a berm or earthen embankment (i.e., detention basin), shall be designed to comply with the following:

(1) Basins with earthen embankments shall be designed with an emergency spillway that has capacity and stability to accommodate the one-hundred-year postdevelopment hydrograph in a manner that will not damage the integrity of the facility and will not create a downstream hazard. Emergency spillway design shall assume that all other basin outlets are nonfunctional. Where practical, the emergency spillway shall be constructed in undisturbed ground, and locations in fill should be avoided. Regardless of location, appropriate stabilization measures shall be provided.

(2) The height of the embankment shall be designed to provide a minimum 1.0 foot of freeboard above the maximum elevation, computed when the one-hundred-year peak postdevelopment flow passes through the emergency spillway. Embankment heights shall not exceed 15 feet, unless approved by Union Township.

(3) The minimum top width of earthen embankments shall be equal to 3/4 of the embankment height, but in no case shall the top width be less than eight feet.

(4) Interior and exterior embankment side slopes shall not be greater than three horizontal to one vertical.

(5) All pipes, conduits, etc., passing through basin embankments shall have properly spaced anti-seepage collars. Minimum collar projection beyond the pipe shall be two feet, and maximum collar spacing is 14 times the projection. The joint between collar and pipe shall be watertight.

(6) A key trench of relatively impervious material shall be provided within all basin embankments. The key trench shall be at least two feet deep or extend down to stable subgrade, whichever is deeper. The minimum bottom width for the key trench shall be four feet. Maximum side slopes for the key trench shall be one horizontal to one vertical. A compacted impervious core at least three feet wide at the top, having maximum side slopes of one horizontal to one vertical, shall extend for the full length of the embankment, and the top elevation shall be set at the ten-year design water surface elevation.

(7) All basins shall be structurally sound and shall be constructed of durable materials. The completed structure and the foundation of all basins shall be stable under all probable conditions of operation. Embankments shall be placed in maximum eight-inch lifts to a minimum of 95% of maximum dry density, as established by ASTM D-1557. Compaction test results shall be provided to Union Township upon request. Embankments shall be constructed six inches above design elevations to allow for settlement.

(8) All basins not including groundwater recharge and/or water quality storage shall include an outlet structure to permit draining the basin to a completely dry condition within 24 hours following the end of the design rainfall.

(9) All discharge control devices with appurtenances (except discharge pipes) shall be made of reinforced concrete and stainless or hot-dip galvanized steel. Bolts/fasteners and any orifice plates are to be stainless or galvanized steel. Outlet barrels/pipes shall have a minimum diameter of 15 inches and shall be made of reinforced concrete pipe with watertight joints, or approved equivalent. Where installation conditions merit, structural calculations that address the actual design requirements will be required.

(10) All basins employing small orifices (i.e., less than six inches in diameter or equivalent area) shall be provided with an apron of concrete or similar durable material which abuts the orifice invert and extends a minimum of 18 inches in all directions from the orifice, to prevent potential blockage by vegetative growth or debris and to allow for easy cleaning of the area approaching the orifice. Appropriate trash racks are required for all orifice openings.

(11) The minimum slope within a basin that does not include groundwater recharge and/or water quality storage shall be 2% positive grade to the low-flow channel.

(12) Design storms for the computation of retention basin volumes shall be based upon a twenty-four-hour storm with a one-hundred-year return period (SCS Type II storm).

(13) The effect on downstream areas if the basin embankment fails shall be considered in the design of all basins. The basin shall be designed to minimize the potential damage caused by such failure of the embankment.

(14) All structures (detention basins, cisterns, etc.), other than those used for groundwater recharge volume and water quality volume, must completely drain within 24 hours after the end of the design storm.

(15) Soils used for the construction of basins shall have low erodibility factors (K factors).

(16) The minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the one-hundred-year water surface. If basement or underground facilities are proposed, detailed calculations addressing the effects of stormwater ponding on the structure and waterproofing and/or floodproofing design information shall be submitted for approval.

C. Stormwater collection and conveyance systems. Gutters, inlets, pipes, conduits, swales, ditches and any other means for collecting and/or conveying stormwater shall be designed to comply with the following:

(1) All storm sewer pipes, culverts and bridges (excluding detention and retention basin outfall structures), gutters and swales conveying water originating only from within the boundaries of the development site shall be designed for a twenty-five-year storm event. All storm sewer pipes, culverts and bridges (excluding detention and retention basin outfall structures) conveying water originating from off site shall be designed for a fifty-year storm event. Facilities that convey runoff to stormwater management facilities (e.g., detention basins, etc.) shall be designed for the one-hundred-year storm event, unless adequate alternate means for conveying one-hundred-year flow to the facilities are provided. Drainage easements having widths no less than 20 feet shall be provided to contain and convey the one-hundred-year-frequency flood throughout the development site. Easements shall begin at the furthest upstream property line of the proposed development site in a watershed.

(2) Water obstructions shall convey runoff from the twenty-five-year design storm with a minimum of 2.0 feet of freeboard, measured below the lowest point along the top of the roadway, without damage to the drainage structure or the roadway, unless more restrictive local, state and/or federal regulations apply. A concentrated discharge of stormwater to an adjacent property shall be within an existing watercourse, or otherwise an easement and appropriate agreements shall be required.

(3) Storm sewer pipes, other than those used as roof drains, detention basin underdrains, and street subbase underdrains, shall have a minimum diameter of 15 inches and be either Class III reinforced concrete pipe (RCP) or smooth-lined corrugated high-density polyethylene pipe (HDPE). Corrugated metal pipe is not permitted. HDPE pipe joints shall be silt-tight at a minimum (e.g., ADS N-12 ST/IB, or equal), and RCP joints shall have prelubed O-ring gaskets. Watertight specification is required in areas of carbonate geology and elsewhere as may be specified by the municipality. Where installation conditions merit (e.g., deep fills), structural calculations that address the actual design requirements will be required.

(4) Storm sewer pipes and culverts shall be installed on sufficient slopes to provide a minimum velocity of three feet per second when flowing full.

(5) Storm sewers shall be placed within the cartway of curbed streets and parallel to the road shoulders of streets without curbs. At curbed street intersections, inlets shall be placed on the tangent and not on the curved portion of the curbing. Storm sewer crossings of streets shall be perpendicular to the street center line to the maximum extent practicable.

(6) Storm facilities not located within a public right-of-way shall be contained in and centered within an easement not less than 20 feet wide. Easements shall follow property boundaries where possible.

(7) Manning "n" values used for design of pipes and culverts shall be in accordance with generally accepted engineering practice. Adequate documentation shall be provided in support of the chosen values.

(8) All storm sewer pipe and culverts shall have a minimum cover of 18 inches. Embedment for all storm sewer pipe and culverts shall consist of AASHTO No. 8 (1B) aggregate from a minimum of six inches of bedding beneath the pipe to a minimum of 12 inches over the pipe. Aggregate requirements for street construction shall take precedence over the 1B specification, but in no case shall total aggregate cover over the pipe be less than 12 inches. Compaction shall be in conformance with manufacturer's specifications. Select backfill shall complete the trench to pavement subgrade or topsoil layer in grassed areas. Properly spaced trench plugs are required in areas of high groundwater.

(9) Curves, tees, elbows and wyes are not permitted in pipes other than those used as roof drains, detention basin underdrains, and street subbase underdrains. Manholes or inlets are required to facilitate such configurations.

(10) Manholes and inlets shall not be spaced more than 400 feet apart for pipes with diameters of 24 inches and less and not more than 500 feet apart for pipes of greater diameter. Ladder rungs shall be placed in manholes and inlets with depths exceeding five feet.

(11) When there is a change in the pipe size in a manhole or inlet, the elevations of the top of the pipes shall be the same, or the smaller pipe(s) higher. A minimum drop of 0.1 foot shall be provided from the inlet invert elevation(s) to the outlet invert elevation. Nonsumped inlets shall have flow channels.

(12) Inlets in grassed areas or BMPs are to be sealed at all joints and pipe penetrations.

(13) Manholes, inlets, headwalls, endwalls and end sections proposed for dedication or located along streets or subject to vehicular traffic shall conform to the requirements of PennDOT or to specifications as otherwise modified by Union Township. Manhole covers shall have the word "STORM" cast clearly on the lid.

(14) Inlets along curbed streets shall be spaced to limit depth along the curb to a maximum of three inches during a ten-year storm. Inlet capacities and bypass calculations shall be determined by PennDOT design techniques.

(15) Pipe underdrains and/or pavement base drains shall be provided in areas known or otherwise documented to have a seasonal high-water table and as directed by the Union Township Engineer.

(16) Appropriate headwalls, endwalls or end sections shall be used where stormwater runoff enters or leaves the storm sewer horizontally from a natural or man-made channel. Such facilities shall conform to the requirements of PennDOT or to specifications as otherwise modified by Union Township.

(17) Adequate erosion and sediment control protection shall be provided along all open channels and at all points of discharge.

(18) Stormwater roof drains, sump pumps, and pipes shall not directly discharge water into a street right-of-way or discharge into a sanitary sewer or storm sewer.

(19) All existing and natural watercourses, channels, drainage systems, wetlands and areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by Union Township and any other necessary approving body.

(20) Flow velocities from any storm sewer may not result in erosion of the receiving channel.

(21) Energy dissipaters shall be placed at the outlets of all storm sewer pipes, culverts, and bridges where flow velocities exceed maximum permitted channel velocities as specified in the PADEP Erosion and Sediment Pollution Control Manual, as amended.

(22) The following conditions shall be met for all swales:

(a) Capacities and velocities shall be computed using the Manning Equation. Stabilization (i.e., linings, etc.) shall be as specified in the PADEP Erosion and Sediment Pollution Control Manual, as amended.

(b) All vegetated swales shall have a minimum slope of 1%, unless approved by the municipality.

(c) "n" factors shall be based upon accepted engineering design practices as approved by the municipality.

(d) All swales shall be designed to concentrate low flows to minimize siltation and meandering.

(e) All roadside swales along Township streets, or streets to be dedicated to the Township, are to be lined with appropriate erosion-control blanket or turf reinforcement mats for permanent stabilization.

(f) V-shaped (triangular) swale sections are not permitted.

§ 165-26 Riparian buffer zone (RBZ).

Areas immediately adjacent to the Township's perennial streams and waterways, as mapped on U.S. Geological Survey 1:24,000-scale quadrangle maps ("blue lines"), shall be defined as the riparian buffer zone (RBZ). In the RBZ, special requirements as set forth in this section shall apply in order to maintain important natural functions. These RBZ requirements are based on both the heightened sensitivity of the RBZ zone and the potential to negatively impact the stream system when this RBZ zone is disturbed, as well as the potential of this RBZ zone to mitigate to the maximum extent the negative effects of development in areas adjacent to the stream system. The RBZ shall include three subzones, Zones 1 through 3, extending landward from the top of the stream bank where different requirements are imposed.

A. Zone 1, a fifteen-foot setback zone, measured from the top of the bank of the water body, where no disturbance of vegetation and soil except for restoration shall occur, in order to shade the stream with natural vegetation, to provide a source of numerous other organic inputs to the aquatic system, to anchor the stream bank and floodplain areas, and to consume and otherwise remove nitrogen, sediment, and other substances which can adversely affect stream systems.

B. Zone 2, a sixty-foot managed buffer zone, extending outward from Zone 1, where disturbance of natural vegetative cover shall be limited to selective logging and other activities which minimally disrupt existing tree cover and soil mantle, in order to maximize filtering and overall physical removal of particulate-form pollutants from runoff generated upgradient and to promote subsurface vegetative uptake of nitrogen and other nonparticulate elements from stormwater generated upgradient.

C. Zone 3, a zone of varying width extending outward from Zone 2. Zone 3 is defined as anywhere land disturbance is occurring adjacent to the RBZ, causing direct discharge of stormwater into the RBZ. Zone 3 must include level spreading devices as necessary to ensure that any directly discharged stormwater flows are properly distributed as sheet flow, and channelization and point-source discharges are avoided.

D. An RBZ adjacent to high-quality waters and exceptional-value waters, designated under the PADEP Chapter 93 Rules and Regulations, shall be subject to the provisions of the PADEP Special Protection Waters Implementation Handbook and its amendments. To the extent that Union Township and PADEP requirements are not consistent, the more-restrictive requirements shall apply.