Source: https://ecode360.com/9517969
Timestamp: 2019-10-18 06:31:44
Document Index: 254561800

Matched Legal Cases: ['§ 124', '§ 124', '§ 124', '§ 124', '§ 124', '§ 124', '§ 124', '§ 124', '§ 124', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', '§ 124', 'art 1', 'art 1', '§ 124', '§ 124', '§ 124', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1']

Township of Tobyhanna, PA Stormwater Management
Ch 124 Pt 1 Art III Stormwater Management
§ 124-8 General requirements.
§ 124-9 Nonstructural project design (sequencing to minimize stormwater impacts).
§ 124-10 Water quality and streambank erosion requirements.
§ 124-11 Groundwater recharge (infiltration; recharge; bioretention).
§ 124-12 Stormwater management districts.
§ 124-13 Calculation methodology.
§ 124-14 Other requirements.
§ 124-15 Erosion and sediment control requirements.
§ 124-16 Consumptive use tracking report.
Article III Stormwater Management
All stormwater management system designs, plans and/or construction shall comply with the following:
Be compatible with this Part 1.
Comply with all the requirements of the Township of Tobyhanna ordinances and/or the Pennsylvania Department of Environmental Protection and the United States Army Corps of Engineers. Should any stormwater management facilities qualify as a dam under DEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety.
Be conducted in such a way as to minimize accelerated erosion and resulting sediment pollution. Measures to control erosion and resulting sediment pollution shall, at a minimum, meet the standards of Chapter 102, Erosion and Sediment Control, of Title 25, Rules and Regulations of the Pennsylvania Department of Environmental Protection and Erosion and Sediment Pollution Control, as amended.
Be conducted in such a way as to conserve, minimize and mitigate impact upon regulated wetlands. Such areas shall not be altered in any way without obtaining design approval, required certifications and permits from the Township of Tobyhanna, the Philadelphia District United States Army Corps of Engineers and the Pennsylvania Department of Environmental Protection. Wetlands include swamps, marshes, bogs and similar areas. As significant natural resources, wetlands serve important functions relating to fish and wildlife food-chain production, habitat, nesting, spawning, rearing and resting sites for protected aquatic and land species; protection of other areas from erosion and sediment pollution, storage areas for storm- and floodwaters; natural recharge areas where ground- and surface water are interconnected; and natural water filtration and purification functions.
Be designed so that the construction of basins within the one-hundred-year floodplain should be avoided, where possible, but where unavoidable, the situation shall be examined for its functionality and supporting documentation submitted to the governing body for review and shall be consistent with Chapter 106, Floodplain Management, of Title 25, Rules and Regulations of the DEP, as amended. All zoning, subdivision and floodplain management regulations at the state and municipal level must be complied with, and the more restrictive regulation(s) supersede(s) all other regulations.
Include financial guarantees for all drainage plan controls as specified herein.
Be designed by a person trained and experienced in stormwater management and erosion and sediment pollution control. (The design, structure interim and installation of the control measures are the responsibility of the developer.)
Be consistent with the stormwater management criteria (Appendix B[1]) and DEP's Erosion and Sediment Pollution Control Program Manual.
Additional studies and a higher lever of control than the minimum provided in the design criteria may be required by the Township of Tobyhanna to assure adequate drainage to protect life and property.
It is the responsibility of the developer not to adversely affect water quality of receiving waters. Best management practices are required by the Township of Tobyhanna to maintain water quality in the watershed.
Control facilities which receive stormwater from areas which are potential sources of oil and grease contamination shall include a baffle, skimmer, grease trap or other mechanism suitable for preventing oil and grease from leaving the facility in concentrations that would cause or contribute to violations of applicable water quality standards in the receiving waters.
Applicants proposing regulated activities in the Brodhead and McMichaels Creek Watershed which do not fall under the exemption criteria shown in this Part 1 shall submit a drainage plan required by this Part 1 consistent with the Brodhead and McMichaels Creek Watershed stormwater management plan to the municipality for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
The applicant is required to perform an alternatives analysis to find practicable alternatives to the surface discharge of stormwater, the creation of impervious surfaces, and the degradation of waters of the commonwealth.
The drainage plan must be designed through an alternatives analysis consistent with the sequencing provisions of this Part 1 to reasonably ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with this Part 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 1.
The existing points of concentrated drainage that discharge onto adjacent property shall not be altered in any manner which could cause property damage. Proposed discharges shall be subject to any applicable discharge criteria specified in this Part 1. The existing points of concentrated drainage that discharge onto adjacent property shall not be altered without written permission from the affected property owner(s). Drainage easements shall be established and recorded.
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 1. If diffused drainage discharge 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 impacts will result from the concentrated discharge. Any area(s) of existing diffused drainage that are proposed to be converted to concentrated discharge(s) onto adjacent property shall be supported by written permission from the affected property owner(s).
Where a development site is traversed by existing watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall conform to the stream buffer requirements contained in this Part 1.
All drainage plans shall include a consumptive use tracking report as required in this Part 1.
Any stormwater management facility regulated by this Part 1 that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by PaDEP through the joint permit application process or, where deemed appropriate by PaDEP, 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 PaDEP.
Any stormwater management facility regulated by this Part 1 that would be located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
Infiltration of runoff through seepage beds, infiltration trenches, or similar facilities, where soil conditions permit, and minimization of impervious surfaces to the extent permitted by the municipality's Zoning Ordinance,[2] are encouraged to reduce the size or eliminate the need for detention facilities or other structural BMPs.
Roof drains shall not be connected to street, sanitary or storm sewers or roadside ditches in order to promote overland flow and infiltration/percolation of stormwater where advantageous to do so. Considering potential pollutant loading, roof drain runoff in most cases will not require pretreatment.
All stormwater runoff, other than rooftop runoff discussed above, shall be treated for water quality prior to discharge to surface water or groundwater.
The design of all regulated activities shall include the following steps in sequence to demonstrate that stormwater runoff and water quality impacts have been minimized:
The applicant is required to find practicable alternatives to the surface discharge of stormwater, the creation of impervious surfaces and the degradation of waters of the commonwealth.
An alternative is practicable if it is available and capable of being done after taking into consideration cost, existing technology and logistics in light of overall project purposes.
Prepare an Existing Resource and Site Analysis Map (ERSAM), showing environmentally sensitive areas, including, but not limited to, steep slopes, ponds, lakes, streams, wetlands, hydric soils, floodplains, buffer areas, hydrologic soil groups A and B (areas conducive to infiltration), any existing recharge areas, compliance with the map preparation criteria denoted in § 124-19B and any other plan preparation criteria set forth in the municipality's Subdivision and Land Development Ordinance[1] as may be required by the municipality.
Establish buffers according to this Part 1.
Prepare a draft project layout avoiding earth disturbance in sensitive areas identified in this Part 1 and minimizing total site earth disturbance as much as is practicable. The ratio of the disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included on the ERSAM.
Identify site-specific predevelopment drainage areas, discharge points, recharge areas to be preserved and hydrologic soil groups A and B to be utilized for recharge.
Minimize use of large impervious surfaces.
Satisfy water quality and streambank erosion protection objective (§ 124-10).
Satisfy groundwater recharge (infiltration) objective (§ 124-11) and provide for stormwater treatment prior to infiltration.
Determine what management district the site falls into (Appendix D),[2] and conduct a predevelopment runoff analysis.
Prepare final project design to maintain predevelopment drainage areas and discharge points to minimize earth disturbance and impervious surfaces and to control runoff as required by the Ordinance.
Conduct a post-development runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (§ 124-12).
In addition to the performance standards and design criteria requirements of this Part 1, the applicant shall comply with the following water quality requirements:
For water quality and streambank erosion, the objective is to design a water quality BMP to detain the proposed conditions two-year, twenty-four-hour design storm to the existing conditions one-year flow using the SCS Type II distribution. Additionally, provisions shall be made so that the proposed conditions one-year storm takes a minimum of 24 hours to drain from the facility from a point where the maximum volume of water from the one-year storm is captured. At the same time, the objective is not to attenuate the larger storms in "no detention" areas (District C) only. This can be accomplished by configuration of the outlet structure not to control the larger storms or by a bypass or channel to divert only the two-year flood into the basin or divert flows in excess of the two-year storm away from the basin.
Where practicable, wet basins may be utilized for water quality control and shall meet the requirements found in the Pennsylvania Stormwater BMP Manual, as revised.
Release of water can begin at the start of the storm. The design of the facility shall consider and minimize the chances of clogging and sedimentation. All orifices less than 18 inches in diameter or as deemed necessary by the Municipal Engineer shall be protected from clogging by the use of baffles, trash racks, etc. Orifices smaller than three inches in diameter are not permitted unless the design professional can provide proof that the smaller orifices are protected from clogging by the use of baffles, trash racks, etc.
For areas within defined special protection subwatersheds which include exceptional-value (EV) and high-quality (HQ) waters, the temperature and quality of water and streams shall be maintained through the use of temperature-sensitive BMPs and stormwater conveyance systems.
The applicant may consider the guidelines for constructed wetlands as found in the Pennsylvania BMP manual.
Pretreatment in accordance with this Part 1 shall be provided prior to infiltration.
Streambank restoration projects shall include the following:
No restoration or stabilization projects may be undertaken without examining the fluvial geomorphology of stable reaches above and below the unstable reach.
Restoration project design must then consider maintenance of stability in the adjacent stable reaches of the stream channel.
An erosion and sediment control plan approved by the Conservation District must be provided by the applicant.
All applicable state and federal permits must be obtained.
Biology shall be incorporated into the design of all wet basins in accordance with the West Nile Virus Guidance found in Appendix E.[1]
To accomplish the above, the applicant shall submit original and innovative designs to the municipality's engineer for review and approval. Such designs may achieve the water quality objectives through a combination of BMPs (best management practices).
Where resource buffers overlap, the more restrictive requirements shall apply.
Preexisting lots or parcels in inner or outer buffers. In the case of legally preexisting lots or parcels, which were approved by subdivision or land development of record at the Monroe County Recorder of Deeds, prior to the effective date of this Part 1, where the usable area of a lot or parcel lies within an inner or outer buffer area, as set forth in Subsection I(5)(b), (6)(a) and (7)(a) below, rendering the lot or parcel unable to be developed in accordance with the allowable use per municipal zoning, the development within the inner or outer buffer areas may be permitted subject to the approval of the Board of Supervisors.
Utility uses in inner or outer buffers. Utility uses, including only stormwater, water, sewer, telephone, telecommunication and electric uses, and not including any buildings or other impervious surfaces relating to said uses, may be permitted within the inner or outer buffer areas set forth in Subsection I(5)(b), (6)(a) and (7)(a) below subject to the approval of the Board of Supervisors.
Improvements to existing structures in buffer areas. The provisions of this Part 1 do not require any changes or improvements to be made to lawfully preexisting structures within the buffer areas. However, when any improvement to a preexisting structure is proposed within the buffer areas, this Part 1 and all other applicable ordinances or laws shall govern.
Wetland identification. For purposes of this section of the chapter, wetlands that are subject to buffers under this section of the chapter shall be identified in accordance with the 1987 U.S. Army Corps of Engineers Manual for Identifying and Delineating Wetlands, by way of a jurisdictional determination, and properly flagged and surveyed on site to ensure they are protected.
Wetlands in an artificial watercourse. Wetlands contained within the banks of an artificial watercourse shall not be considered for buffer delineation purposes.
Wetlands in a natural watercourse. Wetlands contained within the banks of a natural watercourse shall be considered for buffer delineation purposes.
Wetlands. A five-foot inner buffer and a five-foot outer buffer, measured perpendicular to and horizontally from the edge of the delineated wetland, for a total distance of 10 feet, shall be maintained in its natural state or planted with sufficient native species of shrubs and trees subject to the municipality's engineer review and approval for all wetlands.
Inner buffer.
The inner buffer shall be measured perpendicular to and horizontally from the edge of the delineated wetland for a distance of five feet. The following uses are the only uses permitted within the inner buffer:
Stormwater conveyance required by the Township;
Buffer maintenance and restoration;
The correction of hazardous conditions;
Stream crossings permitted by DEP; and
Passive unpaved stable trails.
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided within Subsection I(2) and (3) above. The area of the inner buffer altered by activities permitted in accordance with this section shall be minimized to the greatest extent practicable.
Outer buffer.
The outer buffer shall be measured perpendicular to and horizontally from the outer edge of the inner buffer for a distance of five feet. The following uses are the only uses permitted within the outer buffer:
Stream crossings permitted by DEP;
Roads constructed to existing grade;
Unpaved trails; and
Limited forestry activities that do not clear-cut the buffer (e.g., selective regeneration harvest) in accordance with a forestry management plan.
No other earth disturbance, grading, filling, buildings, structures, new construction or development shall be permitted, except as provided within Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
Lake and pond buffer delineation. A twenty-five-foot inner buffer measured perpendicular to and horizontally from the edge of any lake or pond, and a twenty-five-foot outer buffer measured perpendicular to and horizontally from the outer edge of the inner buffer, for a total distance of 50 feet, shall be maintained in its natural state or planted with sufficient native species of shrubs and trees subject to the municipality's engineer review and approval around any lake or pond.
The inner buffer shall be measured perpendicular to and horizontally from the top-of-bank of the lake or pond for a distance of 25 feet. The following uses are the only uses permitted within the inner buffer:
Boat docks; and
The outer buffer shall be measured perpendicular to and horizontally from the outer edge of the inner buffer for a distance of 25 feet. The following uses are the only uses permitted within the outer buffer:
In areas of the outer buffer which are not wetlands or slopes of more than 15%, stormwater management facilities which improve water quality of stormwater discharge shall be permitted unless prohibited by other Township or state requirements.
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided within Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
Streams and watercourses.
Stream and watercourse buffer delineation. A twenty-five-foot inner buffer and twenty-five-foot outer buffer, measured perpendicular to and horizontally from the top-of-bank on both sides of any stream or watercourse, for a total distance of 50 feet, shall be maintained in its natural state or planted with sufficient native species of shrubs and trees subject to the municipality's engineer review and approval on both sides of any stream or watercourse. See Figure 124-10.1.
The inner buffer shall be measured perpendicular to and horizontally from the top-of-bank of the stream for a distance of 25 feet. The following uses are the only uses permitted within the inner buffer:
Fish hatcheries;
Boat launch sites constructed so as not to alter the floodplain cross section; and
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided in Subsection I(2) and (3) above. The area of the inner buffer altered by activities permitted in accordance with this section shall be minimized to the greatest extent practicable.
Parking lots constructed to existing grade;
Temporary fairs and carnivals;
Accessory uses for residential purposes;
Private sportsmen's club activities;
Boat launch sites;
Unpaved trails;
Limited forestry activities that do not clear-cut the buffer (e.g., selective regeneration harvest) in accord with a forestry management plan; and
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided in Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
Buffer averaging for lakes, ponds and streams.
If an applicant can establish, and the municipality and the municipality's engineer agree, that a situation exists wherein the conditions and physical characteristics of the applicant's lot and the location of the watercourse on or near the applicant's lot creates a unique physical characteristic wherein it would be unreasonable to require the buffer distances as stated in Subsection I(6)(a) and (7)(a), then an applicant can propose the use of buffer averaging in lieu of the specifically required buffer distances set forth in Subsection I(6)(a) and (7)(a), so long as the proposed buffer averaging does not negatively impact the stormwater quantity and quality, the total buffer area remains the same as if the buffer distances in Subsection I(6)(a) and I(7)(a) were adhered to, and the municipality agrees to the proposed buffer averaging.
Buffer averaging consists of reducing certain buffer distances at one location and increasing other buffer distances at other locations on the applicant's lot, based on the unique physical characteristics of the applicant's lot. The total required buffer area (i.e., square footage), as required by Subsection I(6)(a) and (7)(a), would stay the same, but the buffer distance at one location may be greater or smaller than the buffer distance at another location in order to meet the unique physical characteristics and conditions of the applicant's lot. Any such buffer averaging shall be subject to the approval of the municipality.
Buffer averaging shall only be permitted along and/or around lakes, ponds and streams and shall not be permitted along and/or around wetlands.
At no time shall the total buffer along or around a pond, lake or stream, at any given location, be less than 30 feet, measured perpendicular to and horizontally from the top-of-bank of the pond, lake or stream, when using buffer averaging.
Figure 124-10.1
Maximizing the groundwater recharge capacity of the area being developed is required. Design of the infiltration/recharge stormwater management facilities shall give consideration to providing groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with this Part 1 and take advantage of utilizing any existing recharge areas.
Maximum infiltration requirements:
Regulated activities will be required to recharge (infiltrate), where practicable, a portion of the runoff created by the development as part of an overall stormwater management plan designed for the site. The volume of runoff to be recharged shall be determined from this section, depending upon demonstrated site conditions.
A minimum depth of 24 inches, and where practicable 36 inches, between the bottom of the BMP and the limiting zone.
The recharge facility shall be capable of completely infiltrating the recharge volume within four days.
The size of the recharge facility shall be based upon the following volume criteria:
The NRCS runoff shall be utilized to calculate infiltration requirements. (P) in inches. For zero runoff:
P = I (Infiltration) (in.) = (200/CN)-2
(Eq. 124-11.1)
C N = SCS (NRCS) curve number of existing conditions contributing to the recharge facility.
This equation is displayed graphically in and the infiltration requirement can be determined from Figure 124-11.1.
Figure 124-11.1.
Infiltration Requirement Based Upon NRCS Curve Number.
The recharge volume required would therefore be computed as:
Rev = I* impervious area
(Eq. 124-11.2)
I = Infiltration requirements (in.).
Rev (in cubic feet) = [I (inches)] x [Impervious Area (square feet)]/[12 inches/1 foot]
Annual recharge: water budget approach.
It has been determined that infiltrating 0.6 inch of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goal of this section cannot be achieved, then 0.6 inch of rainfall shall be infiltrated from all impervious areas, up to an existing site condition curve number of 77. Above a curve number of 77, Equation 124-11.1 or the curve in Figure 124-11.1 should be used to determine the infiltration requirement.
The recharge volume (Rev) required would therefore be computed as:
Rev = 0.6 or I, whichever is less,* impervious area.
Soils. A detailed soils evaluation of the project site shall be required where practicable to determine the suitability of recharge 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:
Analyze hydrologic soil groups as well as natural and man-made features within the watershed to determine general areas of suitability for infiltration practices.
Provide site-specific infiltration test results (at the level of the proposed infiltration surface) in accordance with ASTM Guide No. D 5126 to determine the appropriate hydraulic conductivity rate.
Design the infiltration structure for the required storm volume based on field-determined capacity at the level of the proposed infiltration surface.
If on-lot infiltration structures are proposed by the applicant's design professional, it must be demonstrated to the municipality that the soils are conducive to infiltration on the lots identified.
A "stormwater hotspot" is defined as a land use activity that generates higher concentrations of hydrocarbons, trace metals or toxicants than are found in typical stormwater runoff, based on monitoring studies. Table 124-11.1 provides samples of designated hotspots. If a site is designated as a hotspot, it has important implications for how stormwater is managed. First and foremost, untreated stormwater runoff from hotspots cannot be allowed to infiltrate into groundwater where it may contaminate water supplies. Therefore, the Rev requirement is not applied to development sites that fit into the hotspot category (the entire WQv must still be treated). Second, a greater level of stormwater treatment may be needed at hotspot sites to prevent pollutant washoff after construction. EPA's NPDES stormwater program requires some industrial sites to prepare and implement a stormwater pollution prevention plan.
Table 124-11.1
Classification of Stormwater Hotspots
The following land uses and activities are samples of stormwater hotspots:
Facilities that generate or store hazardous materials as defined in this Part 1
Extreme caution shall be exercised where salt or chloride would be a pollutant since soils do little to filter this pollutant and it may contaminate the groundwater. The qualified design professional shall evaluate the possibility of groundwater contamination from the proposed infiltration/recharge facility and perform a hydrogeologic justification study if necessary. The infiltration requirement in high-quality/exceptional-value waters shall be subject to the Department's Chapter 93 antidegradation regulations. The municipality may require the installation of an impermeable liner in detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the municipality.
The municipality shall require the applicant to provide safeguards against groundwater contamination for uses which may cause groundwater contamination, should there be a mishap or spill.
Extreme caution shall be exercised where infiltration is proposed in source water protection areas or that may affect a wellhead or surface water intake.
Recharge/infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.
The Brodhead and McMichaels Creek Watershed has been divided into stormwater management districts as shown on the Watershed Map in Appendix D.[1] Standards for managing runoff from each subarea in the Brodhead and McMichaels Creek Watershed for design storms are shown in Table 124-12.1. Development sites located in each of the A, B, or C Districts must control proposed conditions runoff rates to existing conditions runoff rates for the design storms in accord with Table 124-12.1. In addition to the requirements specified in Table 124-12.1 below, the water quality and streambank erosion, groundwater recharge and erosion control requirements set forth herein shall be implemented.
Table 124-12.1
(Reduce To)
Provisional Direct Discharge District. Development sites which can discharge directly to the main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e., storm sewer or tributary) which meets the "downstream hydraulic capacity analysis" in this Part 1 and is shown by the design professional not to cause a downstream problem may allow an increase in flow as long as no downstream harm is demonstrated. However, sites in District C shall comply with the criteria for water quality and streambank erosion and groundwater recharge. If the proposed conditions runoff is intended to be conveyed by an existing stormwater drainage system to the main channel, assurance must be provided that such system has adequate capacity to convey the increased peak flows or will be provided with improvements to furnish the required capacity. When adequate capacity of the downstream system does not exist and will not be provided through improvements, the proposed conditions peak rate of runoff must be controlled to the existing conditions peak rate as required in District A provisions (i.e., ten-year proposed conditions flows to ten-year existing conditions flows) for the specified design storms.
General. Proposed conditions rates of runoff from any regulated activity shall not exceed the peak release rates of runoff prior to development for the design storms specified on the Stormwater Management District Watershed Map (Appendix D)[2] and within this Part 1.
District boundaries. The boundaries of the Stormwater Management Districts are shown on an official map that is available for inspection at the office of the municipality. A copy of the official map at a reduced scale is included in this chapter, Appendix D.[3] The exact location of the Stormwater Management District boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot topographic contours (or most accurate data required) provided as part of the drainage plan.
Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the existing conditions peak discharge for that subarea as indicated in this Part 1. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea. An exception to the above may be granted by the municipality if discharges from multiple subareas recombine in proximity to the site. In this case, peak discharge in any direction may be a one-hundred-percent release rate, provided that the overall site discharge meets the weighted average release rate.
Site areas. Where the site area to be impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area utilizing stormwater management measures shall be subject to the management district criteria. Unimpacted areas bypassing the stormwater management facilities would not be subject to the management district criteria.
"No harm" option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less-restrictive runoff control (including no detention) if the applicant can prove that no harm would be caused by discharging at a higher runoff rate than that specified by the stormwater management plan and this Part 1. The "no harm" option is used when an applicant can prove that the proposed hydrographs can match existing hydrographs or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of no harm must be shown based upon the following downstream impact evaluation, which shall include a downstream hydraulic capacity analysis consistent with this Part 1 to determine if adequate hydraulic capacity exists. The applicant shall submit to the municipality this evaluation of the impacts due to increased downstream stormwater flows in the watershed. The applicant must also establish, in a manner acceptable to the municipality, that there is an undue hardship.
The downstream impact evaluation shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications due to the proposed development upon a dam, highway, structure, natural point of restricted streamflow or any stream channel section, established with the concurrence of the municipality.
The peak flow values to be used for downstream areas for the design return period storms (two-, five-, ten-, twenty-five-, fifty- and one-hundred-year) shall be the values from the calibrated model for the Brodhead and McMichaels Creek Watershed. These flow values can be obtained from the original Act 167 watershed stormwater management plans.
Applicant-proposed conditions for runoff controls which would generate increased peak flow rates at storm drainage problem areas, by definition, are precluded from successful attempts to prove "no harm," except in conjunction with proposed capacity improvements for the problem areas consistent with this Part 1.
A financial distress shall not constitute grounds for the municipality to approve the use of the no-harm option.
Downstream capacity improvements may be provided as necessary to achieve the no-harm option.
Any no-harm justifications shall be submitted by the applicant as part of the drainage plan submission per this Part 1.
Downstream hydraulic capacity analysis. Any downstream hydraulic capacity analysis conducted in accordance with this Part 1 shall use the following criteria for determining adequacy for accepting increased peak flow rates:
Existing natural or man-made channels or swales must be able to convey the increased runoff associated with a two-year return period event within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the DEP Erosion and Sediment Pollution Control Program Manual.
Existing natural or man-made channels or swales must be able to convey increased twenty-five-year return period runoff without creating any hazard to persons or property.
Hardship option. The stormwater management plan and its standards and criteria are designed to maintain existing conditions peak flows and volumes throughout the Brodhead/McMichaels Watershed as the watershed becomes developed. There may be certain instances, however, where the standards and criteria established are too restrictive for a particular applicant. The existing drainage network in some areas may be capable of safely transporting slight increases in flows without causing a problem or increasing flows elsewhere. If an applicant cannot meet the stormwater standards due to lot conditions or if conformance would become an undue hardship to an applicant, the hardship option may be applied. A financial distress shall not constitute grounds for the municipality to approve the use of the hardship option. The applicant would have to plead his/her case to the Board of Supervisors, with the final determination made by the municipality. Any applicant's pleading the "hardship option" will assume all liabilities that may arise due to exercising this option.
Regional detention alternatives. For certain areas within the study area, it may be more cost effective to provide one control facility for more than one development site than to provide an individual control facility for each development site. The initiative and funding for any regional runoff control alternatives are the responsibility of prospective developers. The design of any regional control basins must incorporate future development of the entire upstream watershed. The peak outflow of a regional basin would be determined on a case-by-case basis using the hydrologic model of the watershed consistent with protection of the downstream watershed areas. Hydrologic model refers to the calibrated version of the Penn State Runoff Model as developed for the stormwater management plan.
Stormwater runoff from all development sites with a drainage area of greater than 200 acres shall be calculated using a generally accepted calculation technique that is based on the NRCS soil cover complex method. Table 124-13.1 summarizes acceptable computation methods, and the method selected by the design professional shall be based on the individual limitations and suitability of each method for a particular site. The municipality may allow the use of the Rational Method to estimate peak discharges from drainage areas that contain less than 200 acres.
Table 124-13.1
For sites less than 200 acres or as approved by the municipality and/or Municipal Engineer
Other computation methodologies approved by the municipality and/or Municipal Engineer
All calculations consistent with this Part 1 using the Soil Cover Complex Method shall use the appropriate design rainfall depths for the various return period storms according to the region in which they are located as presented in Table B-1 in Appendix B of this Part 1.[1] If a hydrologic computer model such as PSRM or HEC-1 is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours. The SCS "S" curve shown in Figure B-1, Appendix B, of this Part 1 shall be used for the rainfall distribution. For total developed site impacts of less than one acre which do not require an NPDES permit, the Modified Rational Method may be utilized. Hydrographs with storm durations of at least 10 times the time of concentration shall be utilized.
For the purposes of existing conditions flow rate determination, undeveloped land shall be considered as "meadow" in good condition, unless the natural ground cover generates a lower curve number or Rational "C" value, as listed in Table B-2 or Table B-3 in Appendix B of this Part 1.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the design storm curves from Pennsylvania Department of Transportation Design Rainfall Curves (1986) (Figures B-2 to B-4). Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's equation.
Runoff curve numbers (CN) for both existing and proposed conditions to be used in the Soil Cover Complex Method shall be obtained from Table B-2 in Appendix B of this Part 1.
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from Table B-3 in Appendix B of this Part 1.
The designer shall consider that the runoff from proposed sites graded to the subsoil will not have the same runoff conditions as the site under existing conditions, even after topsoiling or seeding. The designer may increase his proposed condition "CN" or "c" to better reflect proposed soil conditions.
Where uniform flow is anticipated, the Manning equation shall be used for hydraulic computations and to determine the capacity of open channels, pipes, and storm sewers. Values for Manning's roughness coefficient (n) shall be consistent with Table B-4 in Appendix B of this Part 1.
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this Part 1 using any generally accepted hydraulic analysis technique or method.
The design of any stormwater detention facility intended to meet the performance standards of this Part 1 shall be verified by routing the design storm hydrograph through these facilities using the Storage-Indication Method. For drainage areas greater than 20 acres in size, the design storm hydrograph shall be computed using a calculation method that produces a full hydrograph. The municipality may require full hydrographs for sites less than 20 acres. The municipality may approve the use of any generally accepted full hydrograph approximation technique that shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
The municipality 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 variations may be made upon review and recommendations of the Municipal Engineer. Calibration shall require detailed gauge and rainfall data for the particular site in question. Calibration should not be misrepresented to mean a best guess as to what might happen based on experience, as is oftentimes the case.
Any stormwater facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
All wet basin designs shall incorporate biologic controls consistent with the West Nile Guidance found in Appendix E.[1]
Any stormwater management facility designed to store runoff and requiring a berm or earthen embankment required or regulated by this Part 1 shall be designed to provide an emergency spillway to handle flow up to and including the one-hundred-year proposed conditions. Emergency spillways shall be constructed on undisturbed ground and shall not be constructed on embankment fill. The height of embankment must provide a minimum one foot of freeboard above the maximum pool elevation computed when the facility functions for the one-hundred-year proposed conditions inflow. Should any stormwater management facility require a dam safety permit under PaDEP 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 one-hundred-year event.
Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures), and any work involving wetlands governed by PaDEP Chapter 105 regulations, as amended, shall be designed in accordance with Chapter 105 and will require a permit from PaDEP.
Any other drainage conveyance facility that does not fall under PaDEP Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum one foot of freeboard measured below the lowest point along the top of the roadway. Any facility that constitutes a dam as defined in PaDEP Chapter 105 regulations may require a permit under dam safety regulations.
Any drainage conveyance facility and/or channel not governed by PaDEP Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm. Conveyance facilities to or exiting from stormwater management facilities shall be designed to convey the design flow to or from that structure. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year design storm with a minimum one foot of freeboard measured below the lowest point along the top of the roadway.
Storm sewers must be able to convey proposed conditions runoff from a twenty-five-year design storm without surcharging inlets, where appropriate, unless otherwise required by this Part 1.
The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The municipality reserves the right to disapprove any design that would result in the construction of or continuation of a stormwater problem area.
Any drainage conveyance facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements. Any drainage conveyance facility located within a municipality's right-of-way must meet the municipality's minimum design standards and permit submission requirements.
Any earth disturbance must be conducted in conformance with Title 25 of the Pennsylvania Code, Chapter 102, Erosion and Sediment Control.
Additional erosion and sediment control design standards and criteria that must be or are recommended to be applied where infiltration BMPs are proposed shall include the following:
Submissions. All regulated activities shall submit a consumptive use tracking report (CUTR) if there exists a threshold for consumptive use by the designated County departments that is based upon sound scientific data and acceptable to the Township of Tobyhanna at the time of the applicant's submittal. The consumptive use shall be developed in accordance with Appendix F[1] as follows:
Residential subdivisions and/or land developments or redevelopment and/or planned residential developments. The CUTR shall be submitted to the municipality for review and comment prior to the applicant's submittal to the Monroe County Conservation District.
Commercial/industrial development or redevelopment. The CUTR shall be submitted to the municipality during the preliminary and/or final plan approval process, whichever first occurs, for review and comment prior to being forwarded to the Monroe County Conservation District.
A CUTR is not required for existing single lots in recorded subdivisions.
Editor's Note: Appendix F is included at the end of this chapter.