Township of Lower Makefield, PA Article III Stormwater Management Standards

§ 173-12 General requirements.

A. For all regulated activities, SWM Facilities shall be designed, implemented, operated, and maintained to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law,[1] and the Storm Water Management Act.[2] Various SWM BMPs and their design standards are listed in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual[3]), as amended, updated, and/or replaced (to be replaced by the Pennsylvania Post-Construction Stormwater Management Manual, PCSM Manual), which shall be followed unless otherwise noted within this or other ordinances or regulations of the Township.

[1] Editor's Note: See 35 P.S. § 691.1 et seq.

[2] Editor's Note: See 32 P.S. § 680.1 et seq.

[3] Editor's Note: See § 173-53E.

B. For all regulated activities, ESC Facilities shall be designed, implemented, operated, and maintained during the regulated earth disturbance activities (e.g., during construction) to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law. Various E&S BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual (E&S Manual[4]), as amended, updated, and/or replaced, which shall be followed unless otherwise noted within this or other ordinances or regulations of the Township. The erosion and sediment controls and grading guidance within Chapter 178, Subdivision and Land Development, shall apply for all regulated activities.

[4] Editor's Note: See § 173-53F.

C. For all regulated activities, implementation of the volume controls in § 173-18 of this chapter is required.

D. All regulated activities shall include such measures as necessary to:

(1) Protect health, safety, and property.

(2) Meet the water quality goals of this chapter by implementing measures to:

(a) Minimize disturbance to environmentally sensitive features including, but not limited to, floodplains, floodplain soils, ponds, wetlands, steep slopes, and woodland areas in accordance with Chapter 178, Subdivision and Land Development, and Chapter 200, Zoning.

(b) Create, maintain, repair or extend riparian buffers.

(c) Avoid erosive flow conditions in natural flow pathways.

(d) Minimize thermal impacts to waters of this Commonwealth.

(e) Disconnect impervious surfaces (i.e., disconnected impervious areas, DIAs) by directing runoff to pervious areas, wherever possible. See Appendix F for detail on DIAs.[5]

[5] Editor's Note: Appendix F, Disconnected Impervious Area (DIA), is included as an attachment to this chapter.

(f) Prevent pollution of stormwater runoff by ceasing activities that clearly contaminate runoff.

(3) Incorporate the techniques and practices for Low Impact Development (LID) practices as outlined in the BMP Manual. See Appendix E for a summary description.[6] The most appropriate BMPs for stormwater management vary from site to site; however, the following principles shall be implemented to the project site to the maximum extent practicable:

(a) Prevent stormwater impacts, especially pollutants.

(b) Mitigate pollutants that cannot be prevented.

(c) Manage stormwater as a resource.

(d) Sustain the hydrologic balance (quantity and quality).

(e) Integrate stormwater into the initial site design process.

(f) Preserve and utilize natural systems (soil, vegetation, etc.).

(g) Manage stormwater as close to the source as possible.

(h) Disconnect/decentralize/distribute.

(i) Slow down stormwater by increasing the time of concentration, rather than piping and accelerating it.

(j) Inspect and maintain.

[6] Editor's Note: Appendix E, Low-Impact Development (LID) Practices, is included as an attachment to this chapter.

(4) Utilize green infrastructure techniques as outlined in the BMP Manual to the maximum extent practicable.

(5) If methods other than LID and green infrastructure are proposed to achieve the stormwater controls required under this chapter, the SWM Site Plan and Report must include a detailed justification demonstrating that the use of LID and green infrastructure is not practicable.

E. For all regulated activities, unless preparation of a SWM Site Plan and Report is specifically exempted in § 173-13:

(1) Preparation, submission, and implementation of a SWM Site Plan and SWM Report is required.

(2) No regulated activities shall commence until the Township issues written approval of a SWM Site Plan and SWM Permit.

F. SWM Site Plans approved by the Township shall be on site throughout the time of construction of the regulated activity.

G. Impervious areas:

(1) The measurement of impervious areas shall include all of the impervious areas in the total proposed development even if development is to take place in stages.

(2) For development taking place in stages, the entire development plan must be used in determining conformance with this chapter.

(3) For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter. Volume and peak rate controls in Article III do not need to be retrofitted to existing impervious areas unless otherwise specified.

H. Stormwater flows onto adjacent and/or downstream property shall not be created, increased, relocated, significantly concentrated, and/or otherwise detrimentally altered without written approval from the affected property owner(s) and the placement of a SWM Conservation Easement on the affected property per § 173-24Z. Such stormwater flows shall be subject to the requirements of this chapter, including but not limited to downstream capacity and erosion analysis.

I. No stormwater or other related discharges shall discharge directly into a public right-of-way or onto paved surfaces intended for vehicular or pedestrian travel (including but not limited to parking lots, public or private roads, sidewalks, shared driveways, etc.) (collectively herein "Public Surfaces"). The term "directly" for the purpose of this chapter will be dependent upon site conditions, the concentration and volume of the discharge, and intermediary surfaces, but in no case shall a discharge point directed toward a Public Surface be closer than 10 feet to the Public Surface.

J. The design of all facilities over karst shall include an evaluation of measures to minimize the risk of adverse effects in accordance with § 173-26C.

K. All stormwater discharges with pipe sizes greater than or equal to 12" shall be provided with either reinforced concrete endwalls or plastic end section, and shall also include outlet protection consistent with the E&S Manual.

L. For all regulated activities proposing earth disturbances of greater than 5,000 SF, submission of an erosion and sediment control plan to the county conservation district/reviewing authority for either adequacy review or NPDES permit approval. Subsequent evidence of approval shall also be required.

M. Any regulated activities within an existing, known stormwater management problem area, or having the potential to negatively impact an existing, known stormwater management problem area, may be required by the Township to include additional, reasonable measures beyond those listed within this chapter in order to ensure that any effects of the regulated activity do not exacerbate or further contribute to the issues affecting said problem area. In no case shall the applicant be required to resolve the existing, known stormwater management problems beyond the obligations so listed.

N. The Township may, after consultation with Bucks County Conservation District and/or DEP, approve measure for meeting the state water quality and other stormwater runoff requirements other than those in this chapter, provided that they meet the minimum requirements of, and do not conflict with, state law, including but not limited to the Clean Streams Law.

§ 173-13 Exemptions.

A. Regulated activities that result in any one or more of 1) the alteration or development of 1,000 SF or less of land in a manner that may affect stormwater runoff; 2) earth disturbances of 5,000 SF or less; or 3) the cumulative increase of impervious area 1,000 SF or less since the first regulated instance under this chapter or the preceding versions of the Lower Makefield Township stormwater regulations, regardless of whether a permit was properly applied for and received, are exempt from the requirements in §§ 173-14 to 173-17, 173-19 to 173-23, and Article IV unless the activity is found to be a significant contributor of pollution to the waters of this Commonwealth.

B. Regulated activities that result in any one or more of 1) the alteration or development of 1,001 to 5,000 SF of land in a manner that may affect stormwater runoff; 2) earth disturbances of 5,001 to 43,559 SF; and/or 3) the cumulative, including incremental and phased, increase of 1,001 to 5,000 SF of impervious area shall require a Minor SWM Permit and are exempt from § 173-19, Peak rate control standards and methodologies. If the applicant of a Minor SWM Permit provides a completed Site Design Worksheet for the design of volume controls (see Appendix I),[1] their application is exempt from the requirement in §§ 173-14 to 173-23 and Article IV (except § 173-33, Project closeout, for Minor SWM Permits) of this chapter.

Impervious Surface Exemption Thresholds
Ordinance Article or Section	Type of Project	Proposed Impervious Surface
		0 to 1,000 SF	1,001 to 5,000 SF	5,000 + SF
Article IV (except § 173-33)	All Development	Exempt	*Not Exempt	Not Exempt
§§ 173-14 to 173-17 and 173-20 to 173-23	All Development	Exempt	*Not Exempt	Not Exempt
§ 173-18, Volume control	All Development	Not Exempt	Not Exempt	Not Exempt
§ 173-19, Peak rate control	All Development	Exempt	Exempt	Not Exempt
E&S Requirements	Must comply with 25 Pa. Code Chapter 102 and any other applicable state, county, and Township codes. PADEP requires an engineered postconstruction SWM plan for projects proposing earth disturbance greater than 1 acre

NOTES:
*	If the applicant of a Minor SWM Permit provides a completed Site Design Worksheet for the design of volume controls (see Appendix I), their application is exempt from the requirements in §§ 173-14 to 173-23 and Article IV (except § 173-33, Project closeout, for Minor SWM Permits).

[1] Editor's Note: Appendix I, Site Design Worksheet, is included as an attachment to this chapter.

C. Agricultural activity is exempt from the requirements in § 173-19 and Article IV of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.

D. Forest management and timber operations are exempt from the requirements in § 173-19 and Article IV of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.

E. Any aspect of SWM Facility or BMP maintenance to an existing stormwater management system made in accordance with the plans, specifications, and operations and maintenance agreement and plan (where applicable) approved by Lower Makefield Township is exempt.

F. The use of land for gardening for home consumption is exempt from the requirements of this chapter.

G. Exemptions from any provisions of this chapter shall not relieve the applicant from the requirements in §§ 173-12 and 173-18. If any of the requirements in § 173-12 or 173-18 are not met, the Township at its sole discretion may revoke any exemptions from any provisions of this chapter without the necessity of any proceedings for revocation, and the applicant may be required by the Township to cease all activities and/or comply with the provisions of this chapter.

H. Not eligible for exemption: additions, modifications, or alterations to sites, structures, projects, plans, or any other items that previously required stormwater management, whether in part or in whole (for example: adding a 500 SF patio onto a home built as part of a larger subdivision and land development plan that required stormwater management would not be an exempt regulated activity), unless the subject lot was allotted a set amount of increase to impervious area (for example: original subdivision and land development plan allocated each lot an additional 1,000 SF of additional impervious area).

I. An exemption shall not relieve the applicant from implementing such measures as are necessary to protect public health, safety, and property.

J. Where drainage problems are documented or known to exist downstream of or are expected from the proposed activity, the Township may deny exemptions.

K. Exemptions are limited to the specific referenced portions of this chapter.

L. The Township may deny exemptions in high quality (HQ) or exceptional value (EV) waters and source water protection areas (SWPA).

§ 173-14 Riparian buffers.

A. For all regulated activities requiring a Major SWM Permit, a Riparian Buffer Easement shall be created and recorded that encompasses an existing or potential Riparian Buffer.

B. Except as required by Chapter 102, the Riparian Buffer Easement shall be measured to be the greater of the limit of the 100-year floodplain or the watercourse buffer distance as specified in § 200-51, Natural resource protection requirements, of Chapter 200, Zoning, measured from the top of the bank for all watercourses, ponds, and wetlands.

C. When present, provision for permanent access to Riparian Buffer Easements shall also be granted to the Township via a note as listed in §§ 173-24DD(9).

D. Minimum Management Requirements for Riparian Buffers:

(1) Existing native vegetation shall be protected and maintained within the Riparian Buffer Easement. If no or limited existing native vegetation is present, additional native vegetation shall be specified and planted within the Riparian Buffer Easement to create a diverse native plant community appropriate to the intended ecological context of the site.

(2) Whenever practicable, invasive vegetation shall be actively removed, and the Riparian Buffer Easement shall be specified and planted with native trees, shrubs, and other native vegetation in the invasive vegetation's place to create a diverse native plant community appropriate to the intended ecological context of the site.

E. The Riparian Buffer Easement shall be enforceable by the Township and shall be recorded in the appropriate County Recorder of Deeds Office so that it shall run with the land and shall limit the use of the property located therein. The easement shall allow for continued private ownership and shall count toward the minimum lot area as required by zoning, unless otherwise specified in Chapter 200, Zoning.

F. Any permitted use within the Riparian Buffer Easement shall be conducted in a manner that will maintain the extent of the existing 100-year floodplain, improve or maintain the stream stability, leave native vegetation undisturbed as much as is practicable, and preserve and protect the ecological function of the floodplain and riparian buffer.

G. Specific Prohibitions within Riparian Buffer Easements:

(1) Septic drainfields and sewage disposal systems.

(2) Livestock grazing and access, except areas specifically necessary for livestock crossing of waterways.

H. Specific Requirements for Uses within Riparian Buffer Easements:

(1) All uses shall comply with the ordinances, provisions, and regulations of the Township and any other applicable entities.

(2) All uses shall limit vegetative clearing to the minimum extent necessary for the execution of the use; general clearing of the Riparian Buffer Easement is not permitted.

(3) Trails shall be for non-motorized use only.

(4) Docks, boat ramps, and other similar improvements shall be comprised of stable, non-erosive material(s).

(5) Fences shall not be located within a Riparian Buffer Easement. If a waiver of this chapter provision is granted, in no case shall a fence be installed within the Riparian Buffer Easement without proper approval from PADEP.

§ 173-15 SWM facilities standards.

SWM Facilities shall comply with the below standards as applicable to the proposed facility:

A. Nonstructural BMPs shall be utilized to the maximum extent possible in accordance with the methodology and specifications in the BMP Manual, but in no case shall quantitative nonstructural volume control BMPs be more than 25% of the required volume control. If nonstructural BMPs cannot be used, the reasons why must be demonstrated to the Township's satisfaction.

B. Surface, open-air BMPs shall be the preferred BMP for stormwater management controls. If methods other than surface, open-air BMPs are proposed to achieve the stormwater controls required under this chapter, a waiver of this chapter requirement shall be requested from the Township. Surface, open-air BMP plantings shall be comprised entirely of native plants as identified by Chapter 178, Subdivision and Land Development.

C. Pervious pavement systems are encouraged to be utilized in accordance with the standards in Chapter 200, Zoning.

D. Infiltration facilities shall be spread out, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this chapter.

E. All facilities shall drain over a period of time not more than 72 hours from the end of the facility's inflow hydrograph, except for bioinfiltration and bioretention facilities where they shall drain over a period of time not more than 96 hours.

F. Low-flow channels are prohibited.

G. Trash racks shall be provided for all orifices equivalent to 12 inches or smaller in diameter.

H. Anti-seep collars shall be provided on all outflow culverts in accordance with the methodology in the E&S Manual unless specified otherwise below:

(1) An increase in seepage length of 15% must be used in accordance with the requirements for permanent anti-seep collars.

(2) Anti-seep collars shall be installed around the pipe barrel within the normal saturation zone of the berm.

(3) Anti-seep collars and their connections to the outflow culverts shall be watertight.

(4) Anti-seep collars shall extend a minimum of two feet beyond the outside of the principal outflow culvert.

(5) The maximum spacing between collars shall be 14 times the minimum project of the collar measured perpendicular to the pipe.

(6) A minimum of two anti-seep collars shall be installed on each outflow culvert.

I. Embankments/berms shall:

(1) Not be planted with trees. Only vegetation that is five feet or lesser in mature height and tolerant to the conditions of embankment planting (for example: lack of water retainage in the soil) may be planted on berm tops. When this requirement is in conflict with other ordinances or regulations (for example: buffer screenings), relief may be granted from this requirement without the need for a waiver at the sole discretion of the Township Engineer.

(2) Whenever possible, conform to natural topography. When such design is impracticable, the construction of the basin shall utilize slopes as flat as possible to blend with the embankment/berm into the terrain.

(3) Designed to facilitate regular maintenance, mowing, and periodic de-silting and reseeding, where applicable.

(4) Have side slopes no steeper than 4:1.

(5) Have the top or toe of any slope located a minimum of five feet from any property line.

(6) Have a cross-sectional top width of at least 10 feet.

(7) Have low erodibility factors as per the E&S Manual and be identified on the SWM Site Plan.

(8) Have cutoff/key trenches of impervious material that require fill material. The cutoff trench shall be a minimum of eight feet wide, two feet deep, and have side slopes of 1 to 1.

(9) Be placed in a maximum of eight inch lifts compacted to a minimum of 95% of modified proctor density, as established by ASTM D-1557.

(10) Have outlet pipes:

(a) That shall be reinforced concrete pipe with watertight joints.

(b) With energy-dissipating device placed at the outlets.

(c) Sized to pass the 100-year storm event.

(d) Discharge to a defined watercourse with appropriate separation distance, when applicable, to carry proposed discharge flows.

(11) Have emergency spillways:

(a) Capable of providing non-erosive release of the entirety of the postdevelopment 100-year design storm with at least one foot of freeboard when the primary outlet structure is blocked.

(b) Whenever possible, be constructed on undisturbed ground.

(c) Be constructed of reinforced concrete or other material approved by the Township Engineer.

(d) Be constructed of material that extends along the upstream and downstream berm embankment slopes.

(e) With an upstream edge a minimum of three feet below the spillway crest elevation.

(f) With a downstream slope extend, as a minimum, to the toe of the berm embankment.

(g) That do not discharge over earthen fill and/or easily eroded material.

J. For subsurface SWM facilities:

(1) Subsurface facilities shall only be considered if surface facilities are not feasible.

(2) Pretreatment shall be provided for all inflows to the subsurface facility.

(3) The excavation shall be performed with equipment that will not compact the bottom of the subsurface facility.

(4) The bottom of the subsurface facility shall be scarified prior to the placement of aggregate, where applicable.

(5) Only clean aggregate with documented porosity, free of fines, shall be allowed.

(6) The tops, bottoms, and sides of all subsurface facilities shall be covered with nonwoven geotextile fabric acceptable to the Township Engineer.

(7) Runoff shall be distributed throughout the entirety of the subsurface facility.

(8) Provisions for the collection of sediment and debris shall be provided in all facilities, including but not limited to cleanouts and observation ports.

(9) Provide an overflow for extreme storm events that bypasses the proposed outlet structure, where applicable, to safely convey the 100-year design storm.

(10) A minimum of two feet of soil cover should be maintained above subsurface SWM facilities for healthy vegetative cover.

(11) Adequate Operation and Maintenance procedures shall be implemented to ensure the subsurface SWM facilities perform as they were intended including but not limited to 1) inspecting inlet controls, outlet controls, storage areas, and pre-treatment devices monthly for trash, sediment accumulation, and any other undesirable material; 2) as needed, or at least annually, clean out gutters and catch basins, replace filters, evaluate drawdown time after any storm greater than one inch; and 3) annually utilize cleanouts to vacuum or jet the sediment from the system, if present.

K. For permanent wet ponds:

(1) The developer shall demonstrate that such ponds are designed to protect the public health and safety.

(2) A safety bench shall be provided around the perimeter of the permanent water surface. The depth of the bench shall be a maximum of one foot for a width of at least 10 feet.

(3) An area at least 15 feet wide with slopes of 3 to 1 shall be provided from the edge of the safety bench toward the deep-water portion of the pond.

(4) Slopes in the remainder of the pond, below the permanent pool elevation, shall be a maximum of 2 to 1.

(5) Slopes above the permanent water surface shall be in accordance with the design criteria set forth for embankments/berms within this chapter.

(6) Wet ponds shall have a deep-water zone of at least eight feet deep measured from the bottom of the wet pond to the top of the aquatic safety bench in order to prevent stagnation.

(7) Wet ponds shall be equipped with a manually operated drain that can be secured against unauthorized operation to allow the pond to be drained by gravity flow.

(8) Wet ponds shall be provided with a water source so that the permanent water surface can be maintained, as necessary, between periods of rainfall.

(9) Wet ponds shall be lined with a four-inch thickness of clay material in order to prevent excessive infiltration and to protect against saturation of, and seepage through, the berm.

L. For dams:

(1) Have minimum top of embankment as follows:

(a) Class A dams.

[1] With a drainage area less than 320 acres, the top of embankment shall be one foot above the maximum water surface elevation for the emergency spillway storm.

[2] With a drainage area greater than 320 acres, the top of embankment shall be two feet above the maximum water surface elevation for the emergency spillway storm.

(b) Class B dams.

[1] With a drainage area less than 150 acres, the top of embankment shall be one foot above the maximum water surface elevation for the emergency spillway storm.

[2] With a drainage area greater than 150 acres, the top of embankment shall be two feet above the maximum water surface elevation for the emergency spillway storm.

(c) Class C dams.

[1] With a drainage area less than 150 acres, the top of embankment shall be two feet above the maximum water surface elevation for the emergency spillway storm.

[2] With a drainage area greater than 150 acres, the top of embankment criteria shall be established for each individual case.

(2) The classification of dams shall be in accordance with the Soil Conservation Service's criteria as found in Technical Release 60, as amended.

M. The primary outflow structure for all SWM Facilities shall be designed to pass all design storms (up to and including the 100-year event) without discharging through the emergency spillway.

N. Maximum water depth in any open SWM Facility shall be no greater than five feet when functioning through the primary outlet structure.

O. When deemed a public safety hazard at the sole discretion of the Township, any SWM facility may be required to be fenced with a minimum four-foot-high fence of material and design acceptable to the Township. The fence shall not have an opening or gap larger than two inches, and shall be provided with a self-closing and self-latching gate with a minimum opening of 10 feet.

P. The length between the inflow and outflow points of SWM Facilities shall be maximized to prevent short circuiting of the runoff flowing through the facility.

Q. Floodplains:

(1) Facilities and their points of discharge shall not be located within the 100-year floodplain and floodplain soils as determined by FEMA, HEC-RAS, or similar analysis. If no floodplain is defined, the floodplain is assumed to extend 50' from the top of stream bank in both directions.

(2) Facility bottom elevations must be greater than the 100-year floodplain elevations. If no floodplain is defined, the floodplain is assumed to extend 50' from the top of streambank in both directions.

(3) Novel approaches to stormwater management that require placement within the floodplain, including but not limited to floodplain restorations, may be exempted from the requirements in § 173-15Q(1) and (2) above at the sole discretion of the Township Engineer.

R. SWM Facilities shall not be placed within 10 feet of a property line, public right-of-way, or structure as measured from the nearest point of the facility that may provide water storage.

S. All infiltration facilities shall be set back at least 10 feet from all buildings and features with sub-grade elements (e.g., basements, foundation walls, etc.). If the infiltration facilities collect runoff from the buildings or features with sub-grade elements, the bottom elevation of the infiltration facility shall be set below the elevation of the sub-grade element, where practicable.

T. All infiltration practice components shall be protected from compaction due to heavy equipment operation or storage of fill or construction material during construction. Infiltration areas shall also be protected from sedimentation. Areas that are accidentally compacted or graded shall be remediated to restore soil composition and porosity. Adequate documentation to this effect shall be submitted to the Township Engineer for review.

U. The bottom elevation of all SWM Facilities shall be located a minimum of two feet above the seasonal high groundwater table or other soil limiting zone.

V. Where sediment transport in the stormwater runoff is anticipated to reach an infiltration system, appropriate permanent measures to prevent or collect sediment shall be installed prior to discharge to the infiltration system. Typical measures include sediment forebays within SWM Facilities and inlets with sumps for sediment collection. Compliance with this section is at the sole discretion of the Township Engineer.

W. Infiltration BMPs shall not receive runoff until the entire contributory drainage area to the infiltration BMP has received final stabilization.

X. Where roof drains are designed to discharge to infiltration practices, whether directly or indirectly, they shall have appropriate measures to prevent clogging by unwanted debris (i.e., silt, leaves, and vegetation). Such measures shall include, but are not limited to, leaf traps, gutter guards, and cleanouts.

Y. Stormwater management facilities excavated to rock must either be fitted with an impervious clay liner or over-excavated four feet and refilled with a suitable material mix. Suitable backfill material is subject to approval from the Township Engineer.

Z. All stormwater collection and management systems within the Historic District as defined in Chapter 200, Zoning, shall be designed to be underground, such as porous pavement with infiltration bed, underground tank or pipe storage, cisterns, all of which shall be subject to approval by the Township Engineer.

AA. All SWM facilities providing volume management functions must be protected from hydraulic overloading and excessive pollutant loading. The applicant must design SWM facilities providing volume management in a manner that protects these facilities from storm events that exceed their design capacities by diverting higher flows to peak rate management SWM facilities, unless the applicant can demonstrate that the SWM facility can receive higher flows without the need for increased maintenance, repair, or replacement.

BB. Underdrains may be proposed and installed beneath infiltration-based SWM facilities; however, where the design infiltration rate is at least 0.4 inch/hour, the underdrain must terminate at a structure that does not have a connected outflow pipe.

§ 173-16 Conveyance facilities standards and methodologies.

Conveyance Facilities shall:

A. Have the design discharge from drainage areas contributing to Conveyance Facilities be determined by use of the Rational Equation when the total drainage area does not exceed 100 acres.

B. Safely convey the 25-year design storm utilizing Manning's equation for one-dimensional, gradually varied, open channel flow, or pipes with gravity flow.

C. Be prohibited from connecting to or discharging into existing downstream conveyance or storage systems, whether man-made or natural, without verification of the adequacy of downstream hydraulic capacity. The downstream hydraulic capacity analysis shall either assume all peak flows are conveyed at the same time or complete a watershed analysis to the downstream system that includes time of concentration as a factor.

D. Be designed in accordance with Chapter 105 and will require a permit from DEP for any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures). Any facility of the like that does not require a permit from DEP must be able to convey, without damage to the drainage structure or roadway, runoff from the 100-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway. Roadway crossings located within designated floodplain areas must be able to convey runoff from a 100-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway.

E. In the case of storm sewer:

(1) Be designed as a culvert for a 100-year storm frequency where storm drainage is received by means of a headwall or inlet structure, a hydraulic inlet or outlet conditions control.

(2) Be sized for the design storm of the SWM Facility (i.e., stormwater basin designed for the 100-year storm shall have a tributary storm sewer system designed for the 100-year storm) for storm sewer systems that discharge directly into a SWM Facility. The conveyance calculations shall assume the downstream SWM Facility is 25% full. If site constraints do not allow for storm sewers to be sized for the SWM Facility design storm, an overflow system shall be provided to carry flow to the SWM Facility. The overflow system capacity shall be of sufficient capacity to carry the difference between the SWM Facility and storm sewer design storm.

(3) Utilize design storms with increased rainfall intensities and runoff coefficients by a factor of 1.2.

(4) Completely contain flows with a headwater depth one foot below the top of an inlet grate or manhole cover, and at no point cause surface discharge.

(5) Be constructed with watertight joints. If Conveyance Facilities are proposed that require watertight joints, provide a note as listed in § 173-24DD(6).

(6) Be designed and constructed without "knocking out" any inlet or structure corners. If inlets or structures are proposed, provide a note as listed in § 173-24DD(7).

(7) Have inlets, manholes, or similar structures at all horizontal and/or vertical directional changes. Tee joints, elbows, wyes, and similar structures are prohibited.

(8) Have a minimum diameter of 15 inches or an equivalent thereto. Where headroom is restricted, equivalent pipe arches may be used in lieu of circular pipe.

(9) Have incremental size changes of three inches in diameter or greater.

(10) Have the elevation of the crown (obvert) be the same, or the smaller pipe shall be higher, when there is a change in pipe size in a structure. The lowest inlet pipe invert elevation shall not be greater than the outlet pipe invert elevation.

(11) Have flow velocities greater than or equal to 2.5 feet per second. If the velocity is below 2.5 feet per second at the most upstream pipe in a storm sewer system, relief may be granted from this requirement without the need for a waiver at the sole discretion of the Township Engineer.

(12) Have slopes greater than or equal to 0.5%.

(13) Have a minimum top of pipe depth of at least 6" below roadway sub-grade elevations or per the manufacturer's specifications, whichever is greater, and at all locations have a minimum depth of at least two feet.

(14) Not have inlets, manholes, or similar structures spaced more than 300 feet apart on pipe sizes up to 24 inches nor more than 450 feet apart on greater pipe sizes.

(15) Have inlets designed and located in accordance with the following standards:

(a) At street intersections, inlets shall be placed in the tangent portion rather than the curved portion of the curbing.

(b) If the capacity of the shoulder, swale, curb section or depressed median section exceeds the assumed inlet capacities, the inlet capacities shall govern the spacing of inlets.

(c) If the capacity of the shoulder, swale, curb section or depressed median section is less than the inlet capacities, then the shoulder, swale, curb section or depressed section capacity shall govern the spacing of inlets.

(d) Type C inlets:

[1] Type C inlets shall be installed in curbed locations.

[2] In order to achieve greater efficiency, Type C inlets shall be spaced so as to permit 5% of the gutter flow to bypass the inlet.

[3] The capacity of a Type C inlet at a low point of a street's vertical curve may be designed to accept four cubic feet per second (cfs) from each direction or a maximum of eight cfs.

[4] Inlet capacities shall be based on PennDOT Publication 13M,[1] Chapter 10.

[1] Editor's Note: See § 173-53G.

(e) Type M and Type S inlets:

[1] Type S inlets shall be installed in shoulder swale areas with back slopes of six horizontal to 1 vertical and steeper.

[2] Type M inlets shall be installed in swale areas where the back slope is flatter than six horizontal to 1 vertical.

[3] Inlet capacities shall be based on PennDOT Publication 13M, Chapter 10.

[4] Where a drainage dike is used, the side slope of the dike shall be eight horizontal to 1 vertical or flatter.

[5] The capacity of an inlet at a low point in a swale (sump condition) shall be 16 cfs maximum.

(16) Be constructed to PennDOT specifications.

F. In the case of gutters:

(1) Not allow flow to encroach into adjacent roadway lanes more than one-half of the lane width.

(2) Not exceed two inches in depth.

(3) Not allow flow to cross intersections or street centerlines.

G. In the case of swales:

(1) Provide six inches of freeboard to the top of the swale.

(2) Have side slopes no steeper than 5:1 if the swale is to be mowed, and in no cases shall have side slopes steeper than 3:1.

(3) Be designed for erosion prevention and stability using velocity (slopes less than 10%) or shear (all slopes) criteria in both stabilized and unstabilized condition.

(4) Multiple velocities or shear stresses by the following factors when swale bends occur:

(a) 1.75: when the bend is 30 to 60 degrees.

(b) 2.00: when the bend is 60 to 90 degrees.

(c) 2.50: when the bend is 90 degrees or greater.

(5) Be designed for both temporary and permanent conditions.

(6) Have a minimum slope of 2%, unless specifically designed for stormwater infiltration, then have a minimum slope of 1%.

(7) Swales adjacent to roadway shoulders shall be designed to prevent the passage of water onto the cartway during a 25-year frequency storm of five-minute duration.

§ 173-17 General calculation methodologies.

A. Design storm values should be obtained from the following sources depending on methodology:

(1) TR-20/TR-55 precipitation frequency estimates: latest version of the Precipitation-Frequency Atlas of the United States,[1] National Oceanic and Atmospheric Administration (NOAA), National Weather Service, for the 24-hour storm. If the source is replaced in full, the latest version of the replacement sources shall be utilized.

[1] Editor's Note: See § 173-53H.

(2) Rational Method design intensity values: the latest version of PennDOT Publication 584,[2] Chapter 7A, for the 1-through 100-year Storm (U.S. Customary).

[2] Editor's Note: See § 173-53I.

B. Time of concentration (Tc) shall be calculated utilizing the TR-55 segmental method and the following standards:

(1) The maximum sheet flow length shall be 100 feet.

(a) For predevelopment conditions, the maximum sheet flow length shall be utilized unless the applicant can demonstrate, through site-specific analysis and documentation, that the actual on-site existing or proposed conditions do not support a maximum sheet flow length.

(2) Predevelopment Tc values may not be assumed; predevelopment Tc values must be calculated.

(3) The minimum Tc for any watershed or subwatershed shall be five minutes.

(4) Postdevelopment conditions may assume a five-minute Tc, but may never be greater than the predevelopment Tc for any watershed or subwatershed.

(5) The time of concentration for all inlets shall be the minimum Tc of five minutes.

(6) The time of concentration for channels and pipe flow shall be computed using Manning's equation.

C. Runoff coefficients and curve numbers are listed in Appendix B.[3]

[3] Editor's Note: Appendix B, Stormwater Management Design Criteria, is included as an attachment to this chapter.

D. Existing (predevelopment) non-forested pervious areas must be considered meadow in good condition, unless the natural ground cover generates a lower curve number or runoff coefficient.

E. Wooded areas shall be considered woods in good condition. An area is classified as wooded if a continuous canopy of trees exists over a 1/4 acre.

F. 20% of existing impervious area within the limit of disturbance, when present, shall be considered meadow in good condition in the model for existing conditions for Minor SWM Permits and Major SWM Permits with less than 5,001 SF of existing impervious area.

G. For regulated activities and redevelopment sites requiring a Major SWM Permit due to taking place on sites: 1) with greater than or equal to 5,001 SF of existing impervious area within the limit of disturbance; 2) that are not controlling the peak rate and volume of runoff from the existing impervious area in a manner consistent with this chapter; and 3) whose activities do not qualify for the exemptions listed in § 173-13, 100% of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions. This requirement replaces the requirement in § 173-17F above.

H. Meadow may not be used to model proposed (postdevelopment) non-forested pervious areas unless the area being modeled is specifically designed to be and is designated/delineated on the plan to remain as a bona fide meadow that may not be removed or altered by the property owner. Specified native plantings and O&M, including but not limited to routine weeding of invasive species, should be included on the plan and in any agreements if this option is chosen.

I. Runoff from proposed sites graded to the subsoil will not have the same runoff conditions as the site under existing conditions due to soil compaction, even after topsoiling or seeding. The proposed curve number or runoff coefficient shall increase by a minimum of 5% to better reflect proposed soil conditions.

J. Average antecedent moisture conditions and a Type-II distribution storm shall be utilized for runoff calculations.

K. Alternative methods of modeling volume and rate controls may be accepted on a case-by-case basis as approved by the Township Board of Supervisors.

§ 173-18 Volume control standards and methodologies.

Volume controls will mitigate increased runoff impacts, protect stream channel morphology, maintain groundwater recharge, and contribute to water quality improvements. Stormwater runoff volume control methods are based on the net change in runoff volume for the two-year, 24-hour storm event. Volume controls shall be implemented using the Design Storm Method in § 173-18B below.

A. Volume controls shall be required for all regulated activities. The green infrastructure and LID practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible.

B. Water volume controls shall be implemented using the Design Storm Method (CG-1 in the BMP Manual); this method required detailed modeling based on site conditions.

(1) Postdevelopment total runoff shall not be increased from predevelopment total runoff for all storms equal to or less than the NOAA partial duration 90% Upper Confidence Interval two-year, 24-hour rainfall depth with appropriate NRCS distribution.

(2) The following applies in order to estimate the increased volume of runoff for the two-year, 24-hour duration precipitation event:

(a) To calculate the runoff volume (cubic feet) for existing site conditions (predevelopment) and for the proposed development site conditions (postdevelopment), applicant shall use the NRCS Type-II Curve Number runoff method (SCS) as shown following this subsection. Table B-2 in Appendix B is available to guide a qualified professional and/or an applicant to calculate the stormwater runoff volume.[1]

NRCS Type-II Curve Number runoff method (SCS)
Step 1: Runoff(in) = Q = (P - 02S)2/(P + 0.8S) where
P	=	2-year 24-hour rainfall depth (in)
S	=	(1,000/CN) - 10, the potential maximum retention
Step 2: Runoff Volume (cubic feet) = Q x Area x 1/12
Q	=	Runoff (in)
Area	=	Drainage Area (sq ft)

[1] Editor's Note: Appendix B, Stormwater Management Design Criteria, is included as an attachment to this chapter.

(3) For all regulated activities, an additional 20% of water volume shall be captured and added to the required volume control.

(4) Runoff volumes shall be computed separately for each soil-cover complex of a drainage area and then combined. The use of a weighted CN value for volume calculations is not acceptable.

(5) The entirety of the calculated volume control shall be either reused, evapotranspired, or infiltrated through structural or nonstructural means.

C. The applicant must demonstrate how the required volume is controlled through SWM Facilities or Best Management Practices (BMPs) which shall provide the means necessary to capture and reuse, evaporate, transpire, or infiltrate the total runoff volume.

(1) If natural resources exist on the site, the applicant is required to submit a SWM Site Plan which shall determine the total acreage of protected area where no disturbance is proposed.

(a) The acreage of the protected area should be subtracted from the total site area and not included in the stormwater management site area acreage used in determining the volume controls.

SWM Site Area = Total Site Area (for both pre and postdevelopment conditions) - Protected Area

(b) Natural resource areas shall be calculated based upon the natural resource protection requirements within Chapter 200, Zoning. See Table B-1 in Appendix B for guidance to assess the total protected area.[2] For additional reterence, see Chapter 5, Section 5.4.2, of the PA BMP Manual.

[2] Editor's Note: Appendix B, Stormwater Management Design Criteria, is included as an attachment to this chapter.

(c) Natural resources shall be protected to their maximum extent possible but in no case shall be less than the requirements identified in Chapter 200, Zoning.

(2) Calculate the volume controls provided through nonstructural BMPs. Table B-4 in Appendix B is recommended as guidance.

(3) Volume controls provided through nonstructural BMPs should be subtracted from the required volume to determine the necessary structural BMPs.

Required Volume Control (ft³) - Nonstructural Volume Control (ft³) = Structural Volume Requirement (ft³)

(4) Calculate the volume controls provided through structural SWM Facilities and BMPs. Table B-5 in Appendix B is recommended as guidance. See PA BMP Manual, Chapter 6, for description of the BMPs.

(5) Infiltration SWM Facilities and BMPs intended to receive runoff from developed areas shall be selected based on the suitability of soils and site conditions (see Table B-5 in Appendix B for a list of Infiltration BMPs). Infiltration BMPs shall be constructed on soils that have the following characteristics:

(a) A minimum soil depth of 24 inches between the bottom of the infiltration BMPs and the top of bedrock, seasonally high groundwater table, or other soil limiting zones.

(b) An infiltration rate sufficient to accept the additional stormwater load and dewater completely as determined by double-ring infiltrometer tests as described in § 173-26A. The minimum infiltration to be utilized shall be a rate of 0.25 inch/hour and for acceptable rates a safety factor of 50% should be applied for design purposes (e.g., for soil which measured 0.5 inch/hour, the BMP design should use 0.25 inch/hour to ensure safe infiltration rates after construction).

(c) All infiltration facilities shall be designed to completely infiltrate runoff volume not less than one day (24 hours) and not more than three days (72 hours) from the end of the facility's inflow hydrograph.

(6) A soils evaluation of the project site shall be required to determine the suitability of infiltration facilities in accordance with § 173-26A. All regulated activities are required to perform a detailed soils evaluation by a qualified design professional which at minimum addresses soil permeability, depth to bedrock, depth to seasonally high water table, or other soil limiting zone, and sub-grade suitability in accordance with § 173-26A. 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 sub-grade stability; infiltration may not be ruled out without conducting these tests.

(b) Perform a subsurface investigation in accordance with the methodology and frequency identified in § 173-26A.

(c) Provide field tests (such as double ring infiltrometer tests) at the level of the proposed infiltration surface of SWM Facilities and BMPs to determine the appropriate infiltration rate. Percolation shall not be utilized for stormwater design purposes.

(d) Design the infiltration SWM Facility and BMP based on field determined capacity at the level of the proposed infiltration surface and based on the safety factor of 2 (50%). If the infiltration rates vary significantly across the subject site, a higher factor of safety may be required at the discretion of the Township Engineer.

(e) The applicant shall utilize on-lot infiltration structures to the maximum extent practicable. The applicant must demonstrate that the soils are conducive for infiltration on the lots identified.

(f) All runoff to an infiltration SWM Facility or BMP must either be pretreated or the volume control requirements must be increased to account for the loss of volume in the facility due to sediment accumulation. This loss should be based on the expected life of the facility. The pretreatment must remove 50% of the total suspended solids in the runoff from the facility's tributary area maximum design storm.

(g) Groundwater mounding may occur beneath stormwater management structures designed to infiltrate stormwater runoff. Concentrating recharge in a small area can cause groundwater mounding that affects the basements of nearby homes and other structures. A groundwater mounding analysis must be performed to determine whether or not the underlying aquifer will be able to manage the infiltration loading proposed without raising the groundwater to within two feet of the infiltration surface or affecting nearby structures. A simplified spreadsheet was developed by USGS to solve the Hantush Analytical Equation, which can be used to calculate groundwater mounding. The documentation and spreadsheet can be found in the USGS publication Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basin, also available at http://pubs.usgs.gov/sir/2010/5102/.

(h) If the regulated activity is not considered land development and requires a Minor SWM Permit, other information - such as soil survey data - supporting the use of infiltration SWM Facilities may be utilized in lieu of § 173-18C(6)(a) through (g).

D. For redevelopment sites, one of the following minimum design parameters shall be accomplished, whichever is most appropriate for the given site conditions as determined by the Township Board of Supervisors:

(1) All existing and proposed onsite impervious areas shall meet the full requirements specified by § 173-18A through C.

(2) Reduce the predevelopment onsite impervious area by at least 20% in postdevelopment conditions.

E. For sites which the applicant has adequately demonstrated are not conducive for infiltration (< 0.25 inch/hour infiltration rate), alternative volume control methods may be utilized including, but not limited to, PADEP Managed Release Concept[3] (MRC). Adequate demonstration and alternative methodology shall be approved by the Township Board of Supervisors.

[3] Editor's Note: See § 173-53J.

§ 173-19 Peak rate control standards and methodologies.

Peak rate controls for large storms, up to the 100-year event, is essential in order to protect against immediate downstream erosion and flooding. The following peak rate controls have been determined through hydrologic modeling of the Neshaminy Creek and Delaware River South Watersheds:

A. Rate controls shall be required only for regulated activities requiring a Major SWM Permit; regulated activities that require a Minor SWM Permit are not required to provide rate controls.

B. For regulated activities under 1 acre in size, Rational Method for peak rate determination and Modified Rational for routing design storms, or TR-55, may be used for the calculations of rate controls; this chapter shows no preference for either method. For regulated activities greater than or equal to 10 acres, utilize the TR-55 method.

C. Standards for managing runoff for the two-, five-, 10-, 25-, 50-, and 100-year 24-hour design storms are shown in the tables below. Development sites located in each of the management districts must control proposed development conditions runoff rates to existing conditions runoff rates for the design storms in accordance with § 173-19D.

Peak Rate Runoff Control Standards by Stormwater Management Districts in the Neshaminy Creek Watershed
District	Design Storm Postdevelopment (Proposed Conditions)	Design Storm Predevelopment (Existing Conditions)
A	2-year	1-year
	5-year	5-year
	10-year	10-year
	25-year	25-year
	50-year	50-year
	100-year	100-year
B	2-year	1-year
	5-year	2-year
	10-year	5-year
	25-year	10-year
	50-year	25-year
	100-year	50-year
C	2-year	1-year
	5-year	5-year
	10-year	10-year
	25-year	25-year
	50-year	50-year
	100-year	100-year

Peak Rate Runoff Control Standards by Stormwater Management Districts in the Delaware River South Watershed
District	Design Storm Postdevelopment (Proposed Conditions)	Design Storm Predevelopment (Existing Conditions)
A	2-year	1-year
	5-year	5-year
	10-year	10-year
	25-year	25-year
	50-year	50-year
	100-year	100-year
B	2-year	1-year
	5-year	2-year
	10-year	5-year
	25-year	10-year
	50-year	50-year
	100-year	100-year
C*	2-year	1-year
	5-year	2-year

NOTES:

*

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-year storm. Sites in District C will still have to comply with the volume control requirements, the water quality requirements, and stream bank erosion criteria. 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 flow greater than the two-year predevelopment peak flow or will be provided with improvements to furnish the required capacity. When adequate capacity in the 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 (i.e., 10-year postdevelopment flows to 10-year predevelopment flows) for the specified design storms.

D. Proposed conditions rates of runoff from any regulated activity shall not exceed 80% of the peak release rates of runoff from existing conditions for at any point in time during the design storms specified in the tables above and the Stormwater Management District Watershed Map (Appendix D).[1] The runoff rate control standards shall be applied at the site's boundary to each abutting lot, roadway, watercourse, or receiving storm sewer system.

[1] Editor's Note: Appendix D, Maps of Management Districts, is included as an attachment to this chapter.

E. If there is any increase in postdevelopment peak rate timing of runoff, a downstream analysis shall be performed to confirm downstream properties are not flooded, damaged, or adversely affected.

F. The boundaries of the stormwater management districts are shown on official maps and are available for inspection at the Township office and county planning offices. A copy of the maps at a reduced scale are included in Appendix D. 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 contours provided as part of the SWM Site Plan.

G. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall meet the management district criteria for the district in which the discharge is located.

H. When calculating the allowable peak runoff rates, off-site tributary drainage areas to the subject development site do not have to be accounted for. However, the applicant shall demonstrate that on-site SWM Facilities and BMPs are capable of safely conveying off-site tributary drainage areas through the development site without causing erosion or negative downstream impacts.

I. The stormwater management site area is the only area subject to the management district criteria. Nonimpacted areas or nonregulated activities bypassing the stormwater management facilities would not be subject to the management district criteria.

J. For redevelopment sites, one of the following minimum design parameters shall be accomplished, whichever is most appropriate for the given site conditions as determined by the Township Board of Supervisors:

(1) All existing and proposed onsite impervious areas shall meet the full requirements specified by § 173-19A through I.

(2) Reduce the predevelopment onsite impervious area by at least 20% in postdevelopment conditions.

§ 173-20 Water quality standards and methodologies.

SWM Facilities and BMPs shall be provided onsite to control post-construction stormwater impacts from regulated activities and meet state water quality requirements.

A. Water quality controls shall be required for all regulated activities requiring a Minor or Major SWM Permit.

B. SWM facilities must include pretreatment appropriate to the type of SWM facility and anticipated pollutant loading.

C. Applicants must manage the net change in pollutant loads for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN) up to and including the two-year, 24-hour storm event when compared to preconstruction pollutant loads (i.e., postdevelopment pollutant loads shall not be greater than predevelopment).

(1) The DEP PCSM Spreadsheet or similar worksheet shall be utilized to calculate the net change in pollutant loads.

D. If the applicant infiltrates, evapotranspires, or reuses the entirety of the volume control requirements in § 173-18, it is assumed the water quality standards of this section are met and § 173-20B is not required.

E. SWM Facilities and BMPs that moderate the temperature of stormwater shall be used to protect the temperature of receiving waters.

§ 173-21 Stream channel protection requirements.

For regulated activities requiring a Major SWM Permit, the applicant shall comply with the following stream channel protection requirements to minimize stream channel erosion and associated water quality impacts to the receiving waters:

A. The peak flow rate of the postconstruction two-year, 24-hour design storm shall be reduced to 80% of the predevelopment peak flow rate of the one-year, 24-hour duration precipitation.

B. The minimum orifice size in the outlet structure to the SWM Facility shall be three inches in diameter, and a trash rack shall be installed to prevent clogging. For sites with small drainage areas contributing to the SWM Facility that do not provide enough runoff volume to allow a 24-hour attenuation with the three-inch orifice, the calculations shall be submitted showing this condition.

C. When the calculated orifice size is below three inches, gravel filters (or other methods) are recommended to discharge low-flow rates. When filters are utilized, maintenance provisions shall be provided to ensure filters meet the design function.

§ 173-22 Hotspot uses.

A. All hotspot uses, as identified in Appendix G of this chapter.[1] shall include a Stormwater Pollution and Prevention Plan (SWPP) as part of the O&M Plan. The SWPP shall implement regular pavement sweeping, practice proper salt storage, maintain a spill prevention and response plan with on-site spill kit with oil booms, perform regular visual inspection of the site and SWM Facilities, and report to the Township every three years on the implementation and use of this plan.

(1) Infiltration of runoff from hotspot uses will only be allowed after the runoff has been pre-treated by one or more SWM BMPs designed to treat the quality of stormwater runoff based upon the pollutants expected at the hotspot use. The SWPP shall include routine maintenance and cleaning of the pre-treatment BMPs.

[1] Editor's Note: Appendix D, Maps of Management Districts, is included as an attachment to this chapter.

B. All hotspot uses shall utilize a "treatment train" that treats any and all required stormwater management volumes in a series of at least two water quality SWM BMPs.

§ 173-23 Erosion and sediment control and grading requirements.

A. General provision and compliance.

(1) No changes shall be made in the contour of the land and no grading excavation, removal nor destruction of the topsoil, trees or other vegetative cover of the land shall be commenced until such time that a plan for minimizing erosion and sedimentation has been:

(a) Processed and reviewed by the Township Engineer for all regulated activities;

(b) Processed and reviewed by the Bucks County Conservation District for all land development and regulative activities requiring an NPDES Permit; and

(c) Approved by the Board of Supervisors for all land development.

(2) The Board of Supervisors, in its consideration of all preliminary subdivision and land development plans, shall condition its approval upon the execution of erosion and sediment control measures as contained in the standards and specification of the Bucks County Conservation District, the local designee for the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation.

(3) Final approval of plans and specifications for the control of erosion and sedimentation shall be concurrent with the approval of the SWM permit or final subdivision or land development plans and become a part thereof.

(4) Final plans for minimizing erosion and sedimentation as approved will be incorporated into the agreement and bond requirements as required by the Township.

(5) No subdivision or land development plan shall be approved unless:

(a) There has been an erosion and sedimentation plan approved by the Township Engineer and the Bucks County Conservation District that provides for minimizing erosion and sedimentation and an improvement bond or other acceptable security is deposited with the Township in the form of an escrow guaranty which will ensure installation and completion of the required improvements; or

(b) There has been a determination by the Board of Supervisors that a plan for minimizing erosion and sedimentation is not necessary. The Board of Supervisors may waive the above requirement for minor subdivisions.

(6) At the time a building permit is applied for, a review shall be conducted by the Township Engineer to ensure conformance with the plan or permit as approved. During the construction, further consultative technical assistance will be furnished, if necessary, by the Township Engineer and the Bucks County Conservation District. The Township Engineer shall inspect the development site and enforce compliance with the approved plans or permit.

(7) Permission for clearing and grading prior to recording of land development plans may be requested under temporary easements or other conditions satisfactory to the Township and Township Engineer.

(8) In the event that the developer proceeds to clear and grade prior to plan or permit approval and recordation without satisfying conditions specified under § 173-23A(6), the Township shall revoke its approval of the plan or permit.

B. General erosion control standards.

(1) Measures used to control erosion and reduce sedimentation shall, as a minimum, meet the standards and specifications of the Bucks County Conservation District and PADEP.

(2) In cases where the Bucks County Conservation District does not have standards and specifications for erosion and sedimentation control, other known and commonly accepted standards and specifications may be used as approved by the Township Engineer.

(3) The following standards to minimize erosion and sedimentation shall be followed:

(a) Stripping of vegetation, regrading or other development shall be undertaken in a manner that will minimize erosion.

(b) Preserve salient natural features, keep fill operations to a minimum and ensure conformity with topography so as to create the least erosion potential and adequately handle the volume and velocity of surface water run-off.

(c) Whenever feasible, natural vegetation shall be retained, protected and supplemented.

(d) The disturbed area and the duration of exposure shall be kept to a practical minimum.

(e) Temporary vegetation and/or mulching shall be used to protect exposed areas during development.

(f) The permanent (final) vegetation and mechanical erosion control and drainage facilities shall be installed as soon as practical.

(g) Provisions shall be made to effectively accommodate the increased run-off caused by changed soil and surface conditions during and after development. Where necessary, the rate of surface water run-off shall be mechanically retarded.

(h) Sediment in the water run-off shall be trapped until the disturbed area is stabilized by the use of debris basins, sediment basins, silt traps or similar measures.

(i) Swales shall be sodded, utilize jute matting or other similar measures to ensure proper growth of ground cover.

(j) Tire cleaning areas shall be provided and properly maintained at each point of egress from the development site.

C. Temporary stabilization.

(1) Upon temporary cessation of an earth disturbance activity or any stage or phase of an activity where a cessation of earth disturbance activities will exceed four days, the site must be immediately seeded, mulched, or otherwise protected from accelerated erosion and sedimentation pending future earth disturbance activities.

(2) For an earth disturbance activity or any stage or phase of an activity to be considered temporarily stabilized, the disturbed areas must be covered with one of the following:

(a) A minimum uniform coverage of mulch and seed, with a density capable of resisting accelerated erosion and sedimentation; or

(b) An acceptable BMP which temporarily minimizes accelerated erosion and sedimentation.

D. Permanent stabilization.

(1) Upon final completion of an earth disturbance activity, or any stage or phase of an earth disturbance activity, the site must immediately have topsoil restored, replaced, or amended, seeded, mulched or otherwise permanently stabilized and protected from accelerated erosion and sedimentation. Acceptable soil restoration practices are identified by DEP.

(2) E&S BMPs must be implemented and maintained until the permanent stabilization is completed. Once permanent stabilization has been established and approved by the Township, the temporary E&S BMPs must be removed and, if an NPDES permit or E&S permit was obtained for the project, an NOT must be submitted to DEP or the District. Any areas disturbed in the act of removing temporary E&S BMPs must be permanently stabilized.

(3) For an earth disturbance activity, or any stage or phase of an earth disturbance activity, to be considered permanently stabilized, the disturbed areas must be covered with one of the following:

(a) A minimum uniform 70% perennial vegetative cover, with a density capable of resisting accelerated erosion and sedimentation; or

(b) An acceptable BMP which permanently minimizes accelerated erosion and sedimentation.

E. Protection of site infiltration properties during earth disturbance.

(1) Where a SWM Site Plan will be implemented to manage post-construction stormwater in whole or part through on-site infiltration, the permittee must protect areas proposed for infiltration stormwater facilities from sedimentation and compaction during earth disturbance activities to maintain the infiltration capacity of soils.

(2) Site access must be limited to designated access roads that are identified on an approved E&S Plan. As part of the permanent stabilization process, all post-construction pervious surfaces associated with access roads and other locations on-site that have been subjected to soil compaction must be restored using methods identified in DEP's guidance or other approved methods.

(3) Conversion of E&S BMPs to infiltration stormwater facilities may be completed when the drainage area to be treated by infiltration stormwater facilities is permanently stabilized.

(a) The applicant must remove accumulated sediment and soils from E&S BMPs to the design infiltration depth during conversion to infiltration stormwater facilities. Excavation to remove sediment must be performed to a depth where the underlying soils are dry.

(b) The applicant must perform construction confirmation testing for infiltration capacity in accordance with § 173-33C(2)(d).

F. Discharges to special protection and impaired waters.

(1) For stormwater discharges to surface waters with designated or existing uses of HQ or EV under 25 Pa. Code Chapter 93 and for stormwater discharges to surface waters impaired for sediment and/or nutrient-related causes, the applicant must design and implement non-discharge alternatives or ABACT BMPs for all earth disturbance activities.

G. Erosion Potential Analysis.

(1) For earth disturbance activities requiring an NPDES permit or E&S permit from DEP or the District that includes an overland discharge of stormwater, an erosion potential analysis is required to demonstrate that stormwater discharges from the project site during and following construction will not cause accelerated erosion up to the 10-year/24-hour storm event for the entire flow path to the surface water when stormwater flows are concentrated, such as outflows from BMPs and SCMs, and will be directed to areas on the project site and/or off-site that are not surface waters or conveyances that discharge directly to surface waters. A discharge point (DP) must be identified on E&S Plans and/or SWM Site Plans at the outflow of the BMP or SWM Facility to denote a location where an analysis has been performed. Non-surface waters include swales, ditches, channels, open areas, fields, forests, and riparian buffers.

(2) An erosion potential analysis is not required when a new channel will be designed and constructed to convey stormwater runoff in accordance with DEP's E&S Manual.

H. General grading standards.

(1) All lots, tracts or parcels shall be graded to provide proper drainage away from buildings and dispose of it without ponding.

(2) All land within a development shall be graded to drain and dispose of surface water without ponding, except where ponding in SWM Facilities is part of the SWM Plan for the site.

(3) Concentration of surface water run-off shall be permitted only in swales, watercourses, natural drainage channels, or SWM Facilities.

(4) Edges of slopes shall be a minimum of five feet from property lines or right-of-way lines in order to permit the normal rounding of the edge without encroaching on the abutting property.

(5) During grading operations, necessary measures for dust control shall be exercised.

(6) In general, proposed lot slope shall not be flatter than 2%.

(7) Finished floor elevations for all proposed buildings shall be shown on the grading plan.

(8) Where practical, the ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than 5% for a minimum distance of 10 feet measured perpendicular to the face of the wall, except as permitted by International Building Code Section 1804.4.

(9) Perimeter grades at the corners of buildings shall be shown on the grading plan.

(10) Proposed spot elevations for swale high points and at lot corners shall be shown on the grading plan.

(11) Where inlets are proposed at low points in streets or lot grading, adequate relief shall be provided to prevent excessive ponding in the event of inlet clogging.

(12) The grading plan shall not allow concentrated runoff on adjoining properties.

(13) Drainage swales necessary to control surface drainage between lots shall be centered about the common property lines.

(14) On-lot drainage swales shall be designed to provide positive conveyance of surface water from the individual lot. Each individual lot shall convey stormwater from the individual lot. Each individual lot shall convey stormwater from the lot to a storm sewer system, street or major drainageway without crossing or combining with stormwater from more than the adjacent lot.

(15) Drainageways for major surface runoff (swales) shall be confined to open areas or along property lines. Drainageways on or adjoining private property may require drainage easements for maintenance purposes.

I. Excavations and fills.

(1) No excavation or fill shall be made with a face or surface slope steeper than four horizontal to one vertical unless a retaining wall, constructed in accordance with approved standards, is provided to support the face or surface slope of said excavation or fill.

(2) Adequate provisions shall be made to prevent surface water from damaging the cut face of excavations and the sloping surface of fills.

(3) Cut and fill shall not endanger adjoining property.

(4) Fill shall be placed and compacted so as to minimize sliding or erosion of the soil.

(5) Fills shall not encroach in floodplain areas or wetlands.

(6) Fills placed adjacent to floodplains shall have suitable protection against erosion during flooding.

J. Responsibility.

(1) Each person, corporation or other entity which makes any surface changes shall be required to:

(a) Collect on-site surface run-off and control it to a point of discharge into the natural watercourse of the drainage area having adequate capacity.

(b) Adequately handle existing off-site run-off through the development.

(c) Provide and install all temporary and permanent drainage and erosion control improvements, as required by the approved sedimentation and erosion control plan.

(2) Whenever sedimentation is caused by stripping of vegetation, regrading, or other development, it shall be the responsibility of the person causing such sedimentation to remove it from all affected surfaces, drainage systems, and watercourses on-site and off-site and to repair any damage at the developer's expense as quickly as possible following a storm event.

(3) Maintenance of all drainage facilities and watercourses, both existing and proposed, within any proposed subdivision or land development shall be the responsibility of the developer until such time as one of the following is accomplished:

(a) A right-of-way for these facilities is offered for dedication by the developer and is accepted by the Township; it shall then be the responsibility of the Township.

(b) An easement acceptable to the Township is established. In the case of a subdivision, the maintenance shall then be the responsibility of the individual lot owners over whose property the easement passes. For land developments, the maintenance shall then be the responsibility of the owner.

(c) A homeowners' association, approved by the Township, assumes responsibility for the maintenance of the development, including the maintenance of the watercourses and/or drainage facilities.

(4) It is the responsibility of any person, corporation, or other entity doing any work on or across a watercourse, swale, floodplain or right-of-way to return such areas to their original or equal condition after such activity is completed.

(5) No person, corporation or other entity shall block, impede the flow of, alter, construct any structure, deposit any material or thing, or perform any work which will affect normal or flood flow in any watercourse without having obtained prior approval from the Township and/or Pennsylvania Department of Environmental Protection, whichever is applicable.

K. All plans and permits shall include the preservation of topsoil on the site of the development. Topsoil from areas to be disturbed shall be stripped and piled on site and ultimately spread out on the site as appropriate. The site area stripped of topsoil shall be kept to a minimum, and no topsoil shall be removed from the site unless otherwise approved in writing by the Township.