A. All regulated activities for within the Township which do not fall under the exemption criteria contained within Section 105 of this Ordinance shall submit a stormwater management plan consistent with this Ordinance to the Township for review. These criteria shall apply to the total proposed development even if development is to take place in stages. Impervious surface shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks. All gravel and crushed stone areas shall be assumed to be impervious unless designed as a BMP (e.g. pervious paver blocks, reinforced turf, gravel filled grids, etc.). (Refer definition of Impervious Surface within Article II of this Ordinance).
B. Regulated activities shall be designed, implemented, operated, and maintained to meet the purposes of this Ordinance, through these two elements:
1. Erosion and sediment control prevention during land development (e.g. earth disturbance during construction), and
2. Water quality protection measures after completion of land development (e.g. postconstruction).
C. No approval of any subdivision or land development plan, or issuance of any building, Erosion and Sedimentation Control and Grading Permit, occupancy permit, or the commencement of any earth disturbance at a project site within the Township, shall proceed until the requirements of this Ordinance are met, including approval of a Stormwater Management Plan under Section 401 and a permit under PADEP regulations, where applicable.
D. Erosion and sediment control during land development shall be addressed as required by Section 310.
E. Water quality protection and infiltration shall be addressed as required by Sections 305 and 306.
F. All Best Management Practices (BMPs) shall conform to the design criteria of this Ordinance and Pennsylvania Stormwater Management Practices Manual, December 30, 2006.
G. Techniques described in Appendix E (Low Impact Development) of this Ordinance are encouraged because they reduce the costs of complying with the requirements of this Ordinance and the State Water Quality requirements.
H. Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities designed to encourage infiltration, groundwater recharge, and improved water quality.
I. Existing points of concentrated drainage that discharge onto adjacent property shall not be altered without written approval of the affected property owner(s) and shall be subject to any applicable discharge criteria specified in this Ordinance.
J. Areas of existing sheet flow discharge shall be maintained wherever possible. If sheet flow is proposed to be concentrated and discharged onto adjacent property, the developer must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding or other harm will result from the concentrated discharge; and submit written approval from the affected adjacent property owner(s).
K. For all subdivision and land development applications, the tributary area discharging drainage to any location along the site property boundary shall not increase by more than twenty-five (25) percent over the predevelopment condition without written approval from the adjacent affected property owner(s).
L. Where a development site is traversed by watercourses, drainage easements shall be provided conforming to the line of such watercourses. The width of the easement shall be adequate to provide for the unimpeded flow of stormwater runoff from the one hundred (100) year storm event. However, in no case shall the easement be less than thirty (30) feet in width. Terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Periodic maintenance of the easement shall be required by the landowner to ensure proper runoff conveyance. The developer will retain the easement until such time as one of the following is accomplished:
1. For subdivisions or land developments, the individual lot owner assumes responsibility for the maintenance of the portion of their property through which the easement passes. The record plan shall contain a description of such easement(s) and notation indicating the maintenance responsibilities.
2. A homeowner's association or other legal entity approved by the Township, assumes responsibility for the maintenance of the development, including the watercourse easement. The record plan shall contain a description of such easement(s) and notation indicating the maintenance responsibilities.
M. When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by Solebury Township and PADEP through the Joint Permit Application process, or, where deemed appropriate by PADEP, through the General Permit process.
N. Any stormwater management facilities regulated by this Ordinance that will be located in or adjacent to Waters of the Commonwealth or wetlands shall be subject to approval by PADEP and/or US Army Corps of Engineers through the Joint Permit Application process, or, where deemed appropriate by PADEP and/or US Army Corps of Engineers, the General Permit process. When there is a question whether wetlands may be involved, it is the responsibility of the Developer 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 and/or US Army Corps of Engineers.
O. Any stormwater management facilities regulated by this Ordinance that would be located on state highway rights-of-way, or discharge stormwater to facilities located within a state highway right-of-way, shall be subject to approval by the Pennsylvania Department of Transportation (PADOT).
P. Site disturbance and impervious surface shall be minimized. Infiltrating stormwater runoff through seepage beds, infiltration trenches, etc. shall be required, where soil conditions permit, to reduce the size or eliminate the need for retention/detention facilities.
Q. Roof drains and sump pumps shall discharge to an infiltration bed, natural watercourse, storm sewer system, or drainage swale (within a stormwater easement). Roof drains and sump pumps shall be connected to a storm sewer, drainage structure, or other approved stormwater conveyance facility that is designed as part of a stormwater management BMP. In no case shall roof drains or sump pumps be connected to a sanitary sewer or permitted to discharge across a sidewalk, walkway, or to a street through the curb.
R. Whenever a watercourse is located within a development site, it shall remain open in the natural state and location and shall not be piped, impeded, or altered (except for road crossings).
S. Special requirements for watersheds draining to high quality (HQ) and exceptional value (EV) waters: The temperature and quality of water and streams that have been determined to be exceptional value and high quality are to be maintained as defined in Chapter 93, Water Quality Standards, Title 25 Pennsylvania Department of Environmental Protection Rules and Regulations. Maintaining the multiple values of these Special Protection Waters occurs through maintaining the pre-development or natural water cycle; not decreasing infiltration and recharge; and not increasing runoff. In so doing, critical temperature considerations are provided (optimal temperature control is achieved through infiltration of precipitation to groundwater which maximizes temperature-moderated stream base flow). In those cases where Runoff Volume Control can not be achieved as per Section 303.a.1, temperature sensitive BMPs and stormwater conveyance systems are to be used and designed with storage pool areas (drawing outflow from the bottom of the pool) and supply outflow channels shall be shaded with trees. This will require modification of berms for permanent ponds and the relaxation of restrictions on planting vegetation within the facilities, provided that capacity for volumes and rate control is maintained. At a minimum, the southern half of pond shorelines shall be planted with shade or canopy trees within ten (10) feet of the pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is ten (10) to one (1). This will lessen the destabilization of berm soils due to root growth. A long-term maintenance schedule and management plan for the thermal control BMPs is to be established and recorded for all development sites.
T. All stormwater runoff shall be pretreated for water quality prior to discharge to surface or groundwater as required by Section 305 of this Ordinance
U. All Regulated Activities which result in earth disturbance shall comply with the requirements of the Solebury Township Erosion and Sedimentation Control and Grading Ordinance.
V. Completed stormwater management facilities, including detention/retention basins, shall be surveyed by a professional land surveyor or engineer licensed in the Commonwealth of Pennsylvania, to verify compliance with the character of stormwater management facilities as depicted on the approved final plan (or subsequently approved revision, thereof). As-constructed plans shall be submitted to Solebury Township for review and approval, upon completion of construction of all facilities and prior to offer of dedication of any public facilities and/or submission of financial security for the required maintenance period. Public facilities will not be accepted by Solebury Township until such time the as-constructed plans have been reviewed and approved by the Township Engineer.
W. The record plan and development agreement for the approved subdivision or land development shall define the ownership and maintenance responsibilities as well as access rights for all drainage related easements. Specifically, the record plan shall contain a provision permitting access to such easement(s), at any reasonable time, for inspection and/or emergency repair/maintenance, by Solebury Township or its designee, of all facilities deemed critical to public welfare. In the event the lot owner or homeowner's association fails to honor their maintenance responsibilities set forth herein, in any manner, Solebury Township shall have the right of entry upon and within the area of the easement to undertake any required corrective or maintenance effort. The total cost of such, including administrative, engineering, and legal costs for enforcement, may be imposed upon the responsible party as determined by Solebury Township. Failure to remedy all associated costs described above, may be subject of the imposition of a lien by the Township against the owner(s) in question, in the same manner as the Township might otherwise be empowered by law to assess or impose a lien against a property for municipal improvements.
A. Mapping of Stormwater Runoff Peak Rate Districts - In order to implement the provisions of this Ordinance, the Delaware River (South) Watershed Stormwater Management Plan and Neshaminy Creek Watershed Stormwater Management Plan, Solebury Township is hereby divided into Stormwater Runoff Peak Rate Districts consistent with the plans. The boundaries of the districts are indicated on the runoff peak rate district map that is available for inspection at the Township building. A large-scale boundary map is included as Appendix D for reference.
B. The exact location of the Stormwater Runoff Peak Rate District boundary as it applies to a given development site shall be determined by mapping the boundaries using the two (2) feet or five (5) feet topographic contours provided as part of the stormwater management plan developed for the site in accordance with the Subdivision and Land Development Ordinance. The District boundaries as originally drawn coincide with topographic divides or, in certain instances, are drawn from the intersection of the watercourse or a potential flow obstruction to the topographic divide consistent with topography. The locations determined on the stormwater management plan shall be reviewed and verified by the Township engineer.
C. For the purposes of implementing the provisions of the Delaware River (South) Watershed Stormwater Management Plan, the peak release rates of runoff, predevelopment, for the design storms as specified in the table below; this table of release rates is keyed to Stormwater Management District Watershed Map (refer Appendix D).
Development site located in each of the A, B, C, or D Districts must control postdevelopment runoff rates to predevelopment runoff rates for the design storms as follows:
* In District C, development sites which can discharge directly to the Delaware River South main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e. storm sewer or tributary) may do so without control of postdevelopment peak rate of runoff greater than the five (5) year storm. If the postdevelopment 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 flows greater than the two (2) year predevelopment peak flow or will be provided with improvements to furnish the required capacity. When adequate capacity of downstream system does not exist and will not be provided through improvements, the postdevelopment peak rate of runoff must be controlled to the predevelopment peak rate as required in District A provisions (e.g. ten (10) year postdevelopment flows to ten (10) predevelopment flows) for the specified design storms.
A. General Standards.
1. Runoff Volume Standard - Post-development stormwater runoff volume being discharged from any regulated activity shall not exceed pre-development stormwater runoff volume being discharged for up to the two (2) year frequency rainfall (for each watershed on-site). An Alternative Standard is allowed in this Ordinance where it can be demonstrated that due to existing natural site conditions (refer subsection b.), substantial infiltration and recharge are not occurring, pre-development, resulting in greater than anticipated runoff volume.
a. Alternate Standard for Runoff Volume
Applicants may request from Solebury Township that an Alternate Standard be applied, where a portion of the Runoff Volume Standard is not achieved but at least fifty (50) percent of the total required volume of infiltrated runoff is achieved. Use of this Alternate Standard is permitted by the Township only after thorough scrutiny has been directed toward all possible stormwater management options at all possible locations at the site, consistent with the process set forth in the following subsections.
b. Required Analysis for Allowing Use of Alternate Standard for Runoff Volume
The Alternate Standard shall be used only in those situations where it is demonstrated to the satisfaction of the Township that due to natural site conditions infiltration is not occurring in the pre-development condition, resulting in greater runoff volumes (than would normally be anticipated) due to bedrock near or at the surface (less than two (2) feet in depth); presence of Seasonal High Water Table (SHWT) (less than two (2) feet in depth); and soils with low permeability (e.g. 0.20 inches per hour). Alternate Standard shall be permitted by the Township only in those cases where the applicant has demonstrated that one or all of the above described conditions exist throughout the site, such that there is no reasonable means of infiltrating required stormwater volumes and that the property cannot be reasonably developed utilizing a stormwater management system which infiltrates the two (2) year frequency storm event volume (pre to postdevelopment). The applicant must demonstrate that there is no area of the site where the Runoff Volume Standard can feasibly be infiltrated. It is not grounds for approval of the Alternate Standard that infiltrating the Standard Runoff Volume will utilize areas that could otherwise be developed to obtain the most building area or lots.
c. Applicants requesting to utilize the Alternate Standard must provide a Feasibility Study (also refer Section 402) for infiltration utilizing BMPs as well as other runoff volume stormwater management systems and provide the following information:
(1) Site plan demonstrating the extent of site area with seasonal high water table (SHWT) (less than two (2) feet): The site will be evaluated both as to the extent of site with SHWT and the actual locations of SHWT areas. Use of the Alternate Standard shall be permitted by the Township only in those cases where it is demonstrated that site areas free of SHWT are not feasible for use as stormwater BMPs (i.e., they are located upgradient from reasonable site building areas).
(2) Site plan demonstrating extent of site area with less than two (2) feet to bedrock: The site will be evaluated both as to the extent of site with shallow depth to bedrock and actual locations of shallow bedrock areas. Use of the Alternate Standard shall be permitted by the Township only in those cases where it is demonstrated that site areas free of shallow bedrock constraints are not feasible for use as stormwater BMPs (i.e., they are located upgradient from reasonable site building areas).
(3) The site plan shall demonstrate the extent of site area with less than 0.20 inches/hour of permeability in accordance with the soil testing protocol set forth in Appendix B.
(4) In order to utilize the Alternate Standard, the applicant must demonstrate that the total of infiltration "challenged" areas (the total of areas described in c(1) through c(3) hereof) exceed the following percentages of the total site:
75 percent (sites less than 5 acres)
80 percent (sites 5 to 10 acres)
85 percent (sites greater than 10 acres)
In addition, the applicant must demonstrate that there is no feasible site area free of the above described infiltration constraining features which exist in a location such that the Runoff Volume Standard can be achieved.
d. If the applicant's professional engineer can demonstrate based upon site specific soil testing to the satisfaction of the Township that due to existing soil, bedrock, water table, or other conditions on the parcel, that such a standard is not achievable on the site (all or in part), the standard contained in Section 303.A.3 shall apply.
2. General Proposed conditions peak rates of runoff from any regulated activity shall meet the peak release rates of runoff prior to development for the design storms specified on the Stormwater Management District Watershed Map (Ordinance Appendix D) and Section 302, of the Ordinance.
3. If it is determined to the satisfaction of the Township that the volume standard set forth in Section 303.A.1 cannot be achieved, then the peak rate standards are modified so that post-development peak rate discharges from the site for all storms up to the ten (10) year storm must be equal to or less than seventy-five (75) percent of the design peak rates permitted within Section 302.
B. Sites Located in More Than One District - For a proposed development site located within two or more release category subareas, the peak discharge rate from any subarea shall be the pre-development peak discharge for that subarea multiplied by the applicable release rate. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea.
C. Off-Site Areas - Off-site areas that drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rates or volume reduction. However, on-site drainage facilities shall be designed to safely convey off-site flows through or around the development site to existing points of discharge from the property. The future use of undeveloped areas upstream shall be taken into account in the calculation of pipe sizes for storm sewer system designs. The capacity and maximum anticipated present flow of the body or system receiving the proposed system(s) discharge shall be calculated to verify its capability of receiving any additional flow caused by the development or subdivision. The runoff from any proposed development shall be subject to an evaluation that includes the anticipated runoff from other existing or proposed developments with the same watershed.
D. Where the area of a site being impacted by a proposed development activity differs significantly from the total site area, only the proposed disturbed area utilizing stormwater management measures shall be subject to the management district criteria. Unimpacted or undisturbed areas that do not flow into or are bypassing the stormwater management facilities shall not be subject to the Stormwater Management District criteria.
E. Stormwater Conveyance Corridor Protection (Riparian Corridor Preservation and Vegetation) Runoff from developed areas of the site, including but not limited to areas of impervious surface, shall be managed through a series of riparian corridor vegetation facilities whenever possible. This will be accomplished in a manner satisfactory to the Township, utilizing the "Pennsylvania Stormwater Best Management Practices Manual, December 30, 2006", as amended. Riparian Forested Buffer, and the priority goal of the riparian vegetation will be the reduction of thermal impacts on stormwater runoff associated with impervious areas, with a secondary goal being the protection of capacity of existing stormwater conveyance channels. These goals will be achieved through the use of design criteria within this Ordinance and the Pennsylvania Stormwater Best Management Practices Manual, and shall be in addition to any other Township ordinance provisions.
F. 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 reasonable 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 model as developed for the stormwater management plan.
**Webmasters Note: According to the original document subsection G. is missing.
H. "Downstream Hydraulic Capacity Analysis"` Any downstream capacity hydraulic analysis conducted in accordance with this Ordinance shall use the following criteria for determining adequacy for accepting increased peak flow rates:
1. Natural or man-made channels or swales must be able to convey the increased runoff associated with a two (2) 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
2. Natural or man-made channels or swales must be able to convey the increased twenty-five (25) year return period runoff without creating any hazard to persons, or property, or wildlife and aquatic habitat. Habitat impact should be minimized or avoided.
3. Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with DEP, Chapter 105 regulations (if applicable) and, at a minimum, pass the increased twenty-five (25) year return period runoff.
A.The design of all regulated activities shall include the following steps in sequence to minimize stormwater impacts.
1. 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, and must maintain as much as possible the natural hydrologic regime of the site.
2. An alternative is practicable if it is available and capable of being completed after considering cost, existing technology, and logistics in light of overall project purposes, and other Township requirements.
3. All practicable alternatives to the discharge of stormwater are presumed to have less adverse impact on quantity and quality of Waters of the Commonwealth unless otherwise demonstrated.
B. The applicant shall demonstrate that regulated activities are designed in the following sequence to minimize the increases in stormwater runoff and impacts to water quality:
1. Prepare an Existing Resource and Site Analysis Plan (ERSAP), as required by the Subdivision and Land Development Ordinance, showing environmentally sensitive areas including, but not limited to, steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools, floodplains, riparian corridors, hydrologic soil groups A, B, C, and D, "prime agricultural soils" (prime farmland and farmland of statewide importance as designated in the soil survey of Bucks County), woodlands, surface waters regulated by the State or Federal Government, any existing recharge areas, and any other requirements outlined in the Subdivision and Land Development Ordinance.
2. Prepare a draft project layout avoiding sensitive areas identified in Section 304.B.1 (and as further defined by Article 15 of the Zoning Ordinance) and minimizing total site earth disturbance as much as possible. The ratio of disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included in the ERSAP.
3. Identify site specific existing conditions, drainage areas, discharge points (points of interest), recharge areas, and hydrologic soil groups A and B.
4. Evaluate Nonstructural Stormwater Management Alternatives (Refer Appendix B, Table B-6).
a. Minimize earth disturbance.
b. Minimize impervious surfaces.
c. Break up large impervious surfaces.
5. Satisfy water quality objective (Section 305).
6. Satisfy groundwater recharge (infiltration) objective (Section 306) and provide for stormwater treatment prior to infiltration.
7. Satisfy stream bank erosion protection objective (Section 307).
8. Determine the Management District within which the site is located (refer Appendix D) and conduct a predevelopment runoff analysis.
9. Prepare final project design to maintain predevelopment drainage areas and discharge points, to minimize earth disturbance and impervious surfaces, to reduce runoff to the maximum extent possible, and to minimize the use of surface or point discharges.
10. Conduct a proposed conditions runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (Section 307).
11. Manage any remaining runoff through treatment prior to discharge, as part of detention, biorentention, direct discharge or other structural control.
A; The project plan shall specify permanent stormwater BMPs to be implemented, operated, and maintained to meet water quality requirements. Because water quality requirements vary depending on the "uses" of the waterbodies in the watershed, a framework methodology is provided here.
B. In order to protect and maintain water quality, additional stormwater runoff created by the development project must be captured, stored, and treated. In addition, post construction stormwater infiltration of runoff must replicate preconstruction infiltration of runoff to the maximum extent possible, in High Quality and Exceptional Value Watershed, special requirements may apply.
C. The volume of additional stormwater runoff to be captured, stored, and treated is called the Water Quality Volume ("WQv"),
1. The formula for determining WQv is:
WQv = [(P)(Rv)(A)]/12, where
i. P = Rainfall depth in inches, using the "00% storm" the volume of rainfall for 90% of the storm events which produce runoff in the watershed annually. For PennDOT Region 5, the current P value is 2.04 inches.
iii. Rv = Volume Runoff Coefficient [0.05 + 0,009(I)], where I is the impervious surface percentage (impervious area + total project area) X 100%
2. In Special Protection Watersheds, as described in 25 Pa Code Chapter 93, this volume is required to remain onsite through infiltration and other methods, to protect water quality. Guidance can be obtained from PADEP.
D. The following factors must be considered when evaluating the suitability of BMPs used to control water quality at a given development site:
1. Total contributing drainage area.
2. Permeability and infiltration rate of the site soils.
3. Slope and depth to bedrock.
4. Seasonal high water table.
5. Proximity to building foundations and wellheads.
6. Erodibility of soils.
7. Land availability and configuration of the topography.
8. Peak discharge and required volume control.
9. Streambank erosion.
10. Efficiency of the BMPs to mitigate potential water quality problems.
11. Volume of runoff that will be effectively treated.
12. Nature of the pollutant being removed.
13. Maintenance requirements.
14. Creation/protection of aquatic and wildlife habitat.
15. Recreational value.
16. Enhancement of aesthetic and property value.
To accomplish the above, the applicant shall submit original and innovative designs for review. Such designs may achieve the water quality objectives through a combination of BMPs (Best Management Practices).
E.The applicant may, subject to- approval of Solebury Township, use any of the following non-structural stormwater credits, generally described in the following table, in computing the required water quality volume.
For design and applicability of non-structural BMPs refer to Chapter 5 of the "Pennsylvania Stormwater Management Practices Manual", December 2006, as amended. For the nonstructural BMPs proposed, the applicant shall utilize and submit appropriate checklists included in Chapter 8, Section 8.8 of the "Pennsylvania Stormwater Best Management Practices Manual", December 2006, as amended (refer Appendix E) to demonstrate that the BMPs are applicable to the project and to determine the amount of volume or peak rate credit is applicable.
F. The volume and rate of any stormwater discharges allowed under this Ordinance must be managed to prevent the physical degradation of receiving waters, such as by streambank scour and erosion. If a detention facility is proposed which is part of the BMPs approved for the project, the facility(ies) must be designed to provide for a twenty-four (24) hour extended detention of the one (1) year, twenty-four (24) hour storm event (i.e., the stormwater runoff will be released over a minimum twenty-four 24 hours for the one (1) year, twenty-four (24) hour storm event from the time of peak inflow to zero outflow).
