Borough of West Grove, PA Article III Stormwater Management Standards

§ 342-301 General requirements.

A. Applicants proposing regulated activities in the Borough which are not exempt under § 342-106 shall submit a Stormwater Management Site Plan (SWM site plan) to the Borough for review and approval in accordance with Articles III and IV. SWM site plans approved by the Borough shall be kept on site throughout the duration of the regulated activity.

B. The stormwater management and runoff control criteria and standards in this chapter as well as the measurement of the impervious surfaces shall apply to the total proposed regulated activity, even if it is to take place in stages.

C. No regulated activity within the Borough shall commence until:

(1) The Borough issues approval of a SWM site plan in the form of a SWM permit, which demonstrates compliance with the requirements of this chapter; and

(2) The applicant has received a letter of adequacy or approval for the erosion and sediment control plan review by the Borough and the Conservation District (if required), and has received all other local, state and federal permit approvals required for the project involving the regulated activity.

D. Neither submission of a SWM site plan under the provisions herein nor compliance with the provisions of this chapter shall relieve any person from responsibility for damage to any person or property otherwise imposed by law.

E. The applicant shall design the site to minimize disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall apply the procedures set forth in § 342-304 for the overall site design and for selection, location and design of features and BMPs to be used to comply with the requirements of this chapter.

F. To the maximum extent practicable, postconstruction stormwater shall be discharged within the drainage area of the same stream or water body receiving the runoff prior to construction of the proposed regulated activity.

G. For regulated activities with one acre or more of proposed earth disturbance, existing drainage peak rate discharges up to and including the 100-year storm and the volume of runoff up to and including the two-year storm onto or through adjacent property(ies) or downgradient property(ies), including diffuse drainage discharge, shall not be altered in any manner by regulated activities under this chapter without written permission from, and, where applicable as determined by the Borough an easement and agreement with, the affected landowner(s) for conveyance of discharges onto or through their property(ies). Altered stormwater discharges shall be subject to any applicable discharge criteria specified in this chapter.

(1) For regulated activities with one acre or less proposed earth disturbance the applicant shall provide written notification to the affected landowner(s) describing the proposed regulated activity and proposed discharge(s), unless otherwise required by the Borough.

H. Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 342-305, 342-306, 342-307, and 342-308). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.

I. If site conditions preclude capture of runoff from limited portions of the disturbed area for achieving water quality volume control standards, stream channel protection standards, and the two-year storm event peak runoff rate reduction standards for new development required by this chapter, the applicant shall propose alternate methods to mitigate the bypass of the BMPs, subject to the approval of the Municipal Engineer. In no case shall resulting peak rate be greater than the predevelopment peak rate for the equivalent design storm.

J. For all regulated activities, erosion and sediment control BMPs shall be designed, implemented, operated, and maintained during the regulated activities (i.e., during construction) as required to meet the purposes and requirements of this chapter, to meet the erosion and sediment control requirements of the Borough, if applicable, and to meet all requirements under Title 25 of the Pa. Code and the Clean Streams Law.[1]

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

K. For all regulated activities, permanent BMPs and conveyances 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,[2] and the Storm Water Management Act.[3]

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

[3] Edtior's Note: See 32 P.S. §§ 680.1 et seq.

L. The design of all BMPs and conveyances shall incorporate sound engineering principles and practices in a manner that does not aggravate existing stormwater problems as identified by the Borough. The Borough reserves the right to disapprove any design that would result in construction in an area affected by existing stormwater problem(s) or continuation of an existing stormwater problem(s).

M. Existing wetlands, either on the site or on an adjacent property, shall not be used to meet the minimum design requirements for stormwater management or stormwater runoff quality treatment. Stormwater discharges to existing wetlands shall not degrade the quality or hydrologic integrity of the wetland.

N. Hotspots runoff controls. Specific structural or pollution prevention practices may be required, as determined to be necessary by the Borough Engineer, to pretreat runoff from hotspots prior to infiltration. Following is a list of examples of hotspots:

(1) Vehicle salvage yards and recycling facilities;

(2) Vehicle fueling stations;

(3) Vehicle service and maintenance facilities;

(4) Vehicle and equipment cleaning facilities;

(5) Fleet storage areas (bus, truck, etc.);

(6) Industrial sites based on Standard Industrial Classification Codes;

(7) Marinas (service and maintenance areas);

(8) Outdoor liquid container storage;

(9) Outdoor loading/unloading facilities;

(10) Public works storage areas;

(11) Facilities that generate or store hazardous materials;

(12) Commercial container nursery;

(13) Contaminated sites/brownfields;

(14) Other land uses and activities as designated by the Borough.

O. Contaminated and brownfield sites. Where BMPs may contribute to the migration of contaminants in groundwater, the water quality and runoff volume, stream channel protection, and peak rate control standards shall be met; however, at the Borough Engineer's discretion, the minimum infiltration requirement may be reduced or eliminated commensurate with the contaminated area and the required water quality and runoff control measures may be increased to mitigate the reduced infiltration requirement for the contaminated area.

P. Additional water quality requirements. The Borough may require additional stormwater control measures for stormwater discharges to special management areas including, but not limited to:

(1) Water bodies listed as "impaired" by PADEP.

(2) Any water body or watershed with an approved total maximum daily load (TMDL).

(3) Areas of known existing flooding problems.

(4) Critical areas with sensitive resources (e.g., state-designated special protection waters, cold water fisheries, carbonate geology or other groundwater recharge areas that may be highly vulnerable to contamination, drainage areas to water supply reservoirs, etc.).

Q. Applicants shall utilize the Pennsylvania Stormwater Best Management Practices Manual (PA BMP Manual), as amended, or other sources acceptable to the Borough Engineer, for testing and design standards for BMPs, and where there is a conflict with the provisions of this chapter, the most restrictive applies.

R. For areas underlain by karst or carbonate geology that may be susceptible to the formation of sinkholes and other karst features, the location, type, and design of infiltration BMPs shall be based on a site evaluation conducted by a qualified licensed professional and based on the PA BMP Manual (as amended) or other design guidance acceptable to the Borough Engineer. The following certificate shall be included on all stormwater site plans and shall be signed and sealed by the Developer's Professional Geologist, "I, __________, certify that the proposed stormwater/BMP facility (circle one) is/is not underlain by carbonate geology."

S. All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with the West Grove Borough Zoning Ordinance[4] section(s) regarding floodplain management and shall be designed to maintain the flood carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.

[4] Editor's Note: See Ch. 400 of this Code.

T. Any disturbance of existing ground cover during construction of the proposed regulated activity is prohibited within 50 feet of top-of-bank of all perennial waterways and intermittent waterways, water bodies (lakes, ponds, etc.) and wetlands, except for activities otherwise approved by state or local agencies (e.g. stream restoration projects, road crossings, subsurface utility projects, etc.). At the Borough Engineer's discretion, and with Conservation District and PADEP approval where necessary, the non-disturbance buffer may be reduced because of setback or other site constraints, but never be less than 10 feet.

U. Riparian buffers shall be designed to meet the requirements of § 342-312.

§ 342-302 Permit requirements by other governmental entities.

The following permit or other regulatory requirements may apply to certain regulated activities and shall be met prior to (or as a condition of) final approval by the Borough of the SWM site plan and prior to commencement of any regulated activities, as applicable:

A. All regulated activities subject to permit or regulatory requirements by PADEP under regulations at Title 25 Pa. Code Chapter 102, or erosion and sediment control requirements of the Borough.

B. Work within natural drainage ways subject to permit by PADEP under Title 25 Pa. Code Chapter 105.

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

D. Any BMP or conveyance that would be located on or discharge to a state highway right-of-way or require access to or from a state highway and be subject to approval by PennDOT.

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

§ 342-303 Erosion and sediment control.

A. No regulated activity within the Borough shall commence until:

(1) The Borough receives documentation that the applicant has received:

(a) A "letter of adequacy" from the Conservation District or other approval from PADEP in compliance with Title 25 Chapter 102 of the Pennsylvania Code of an erosion and sediment control plan for construction activities for projects where the area of disturbance exceeds one acre, where pond dredging is involved, or when the disturbance is associated with activities described under Title 25 Chapter 105 of the Pennsylvania Code permits;

(b) A PADEP NPDES Permit for Stormwater Discharges Associated with Construction activities as required under Title 25 Pa. Code Chapter 92a, if applicable;

(c) Evidence of any other permit(s) or approvals required for the regulated activities; and

(2) An erosion and sediment control plan has been approved by the Borough, if required.

B. A copy of the erosion and sediment control plan and any required permit(s), as required by PADEP regulations, shall be available on the site at all times.

C. Additional erosion and sediment control measures shall be applied where infiltration BMPs are proposed, at a minimum including those required in § 342-306M.

§ 342-304 Site design process.

The applicant shall design the site to minimize the disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. For regulated activities with 10,000 or more square feet of proposed earth disturbance OR 2,000 or more square feet of regulated impervious surfaces, the applicant shall demonstrate in its SWM site plan (as required in § 342-402C) that the design sequence, objectives and techniques described below were applied to the maximum extent practicable in the site design of the regulated activity while complying with all other requirements of this chapter. The site design shall:

A. First, identify and delineate all existing natural resources and natural and man-made hydrologic features listed in § 342-402B(8) that are located within the site, or receive discharge from, or may be impacted by the proposed regulated activity.

B. Second, provide a prioritized listing of these resources and features to identify:

(1) Those to be incorporated into the site design in a manner that provides protection from any disturbance or impact from the proposed regulated activity;

(2) Those to be protected from further disturbance or impact but for which the proposed regulated activity will provide improvement to existing conditions;

(3) Those that can be incorporated into and utilized as components of the overall site design in a manner that protects or improves their existing conditions while utilizing their hydrologic function within the limits of their available capacity (e.g., for infiltration, evapotranspiration, or reducing pollutant loads, runoff volume or peak discharge rates, etc.) to reduce the need for or size of constructed BMPs; and

(4) Those that may be considered for alteration, disturbance or removal.

C. Third, develop the site design to achieve the following:

(1) Recognize and incorporate the priorities identified in § 342-304B as the basis for the proposed site layout, grading, construction, and permanent ground cover design;

(2) Minimize earth disturbance (both surface and subsurface);

(3) Maximize protection of or improvement to natural resources and special management areas;

(4) Minimize the disturbance of natural site hydrology, in particular natural drainage features and patterns, discharge points and flow characteristics, natural infiltration patterns and characteristics, and natural channel and floodplain conveyance capacity;

(5) Incorporate natural hydrologic features and functions identified in Subsection B into the site design to protect and utilize those features and their hydrologic functions to reduce the need for or size of constructed BMPs;

(6) Maximize infiltration and the use of natural site infiltration features, patterns and conditions, and evapotranspiration features;

(7) Apply selective grading design methods to provide final grading patterns or preserve existing topography in order to evenly distribute runoff and minimize concentrated flows;

(8) Minimize the cumulative area to be covered by impervious surfaces and:

(a) Minimize the size of individual impervious surfaces,

(b) Separate large impervious surfaces into smaller components,

(c) Disconnect runoff from one impervious surface to another, and

(d) Utilize porous materials in place of impervious wherever practicable;

(9) Minimize the volume and peak discharge rates of stormwater generated;

(10) Avoid or minimize stormwater runoff pollutant loads and receiving stream channel erosion;

(11) Locate infiltration and other BMPs:

(a) At or as near to the source of generation as possible; and

(b) At depths that are as shallow as possible;

(12) Prioritize the selection and design of BMPs as follows:

(a) Nonstructural and vegetation BMPs; then

(b) Structural (surface and subsurface) BMPs;

(13) For flow volumes requiring conveyance from the source of generation to a BMP for management, give preference to open channel conveyance techniques that provide infiltration and water quality benefits, and landscaped-based management in common open space areas, where practicable; and

(14) Consider additional guidance for incorporating natural hydrology into the site and BMP designs, methods and techniques that support the objectives of Subsections B and C. Appendix D[1] presents additional discussion of "conservation design" and "low-impact development."

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

D. The procedures set forth above shall be utilized to the maximum extent practicable for the overall site design and selection, location and design of features and BMPs to be used to comply with the requirements of §§ 342-305, 342-306, 342-307 and 342-308.

§ 342-305 Water quality and runoff volume requirements.

To control postconstruction stormwater impacts from regulated activities and meet state water quality requirements, BMPs shall be provided in the site design that replicate predevelopment stormwater infiltration and runoff conditions, such that postconstruction stormwater discharges do not degrade the physical, chemical, or biological characteristics of the receiving waters. The green infrastructure and low-impact development (LID) practices provided in the PA BMP Manual, as well as the guidance on green infrastructure, LID and conservation design (CD) provided in Appendix B, shall be utilized for all regulated activities wherever possible. The applicant shall comply with the following water quality and runoff volume requirements for all regulated activities, including all new development and redevelopment activities:

A. The postconstruction total runoff volume shall not exceed the predevelopment total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation (design storm). The water quality and runoff volume to be managed shall consist of any runoff volume generated by the proposed regulated activity over and above the predevelopment total runoff volume and shall be captured and permanently retained or infiltrated on the site. Permanent retention options may include, but are not limited to, reuse, evaporation, transpiration, and infiltration.

B. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 342-309.D of this chapter.

C. The design of the stormwater management facility outlet shall provide for protection from clogging and unwanted sedimentation.

D. BMPs that moderate the temperature of stormwater shall be used to protect the temperature of receiving waters.

E. Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 342-306. The infiltration volume required under § 342-306 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.

F. Runoff from the disturbed area shall be treated for water quality prior to entering existing waterways or water bodies. If a stormwater management practice does not provide water quality treatment, then water quality BMPs shall be utilized to provide pre-treatment prior to the runoff entering the stormwater management practice.

G. The Borough may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 342-301P.

H. When the regulated activity contains or is divided by multiple drainage areas, the water quality and runoff volume shall be separately addressed for each drainage area.

I. Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.

J. Areas located outside of the site (i.e., areas outside of the regulated activity) may be excluded from the calculation of the water quality and runoff volume requirements.

K. Water quality and volume control practices shall be selected and designed to meet the criteria of § 342-304C that apply to water quality and volume control.

L. Evapotranspiration may be quantified and credited towards meeting volume requirements according to the PADEP Post Construction Stormwater Management (PCSM) Spreadsheet and Instructions (December 2020) or the most recent guidance from PADEP.

§ 342-306 Infiltration requirements.

Providing for infiltration consistent with the natural hydrologic regime is required to compensate for the reduction in the recharge that occurs when the ground surface is disturbed, or impervious surface is created or expanded. The applicant shall achieve the following infiltration requirements:

A. For regulated activities involving both new development and redevelopment, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 342-305. Infiltration BMPs should be consistent with the design and infiltration period guidelines included in the PA BMP Manual or other PA DEP design guidance. If the runoff volume required by § 342-305 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) or other PA DEP guidance, such as the Managed Release Concept, may be used to manage this volume with approval from the Borough Engineer.

B. For regulated activities involving both new development and redevelopment, the volume of a minimum of one inch of runoff from all regulated impervious surfaces shall be infiltrated.

C. If the requirements of Subsections A or B cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Borough Engineer why this infiltration volume cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated.

D. Only if a minimum infiltration of the first 0.5 inch of runoff volume cannot be physically accomplished on the site, shall a waiver from § 342-306 be considered by the Borough unless the proposed activity involving earth disturbance of one acre or greater as described in § 342-111C.

E. If site conditions preclude capture of runoff from portions of the impervious surfaces, the infiltration volume for the remaining area shall be increased an equivalent amount to offset the loss.

F. When a project contains or is divided by multiple watersheds, the infiltration volume shall be separately addressed for each watershed.

G. Existing impervious surfaces located in areas outside of the site (i.e., outside of the regulated activity) may be excluded from the calculation of the required infiltration volume.

H. A detailed soil evaluation of the site shall be conducted by a qualified professional and at a minimum shall address soil permeability, depth to bedrock or other limiting zone, and subgrade stability. The general process for designing the infiltration BMP shall be conducted by a qualified licensed professional and shall be consistent with the PA BMP Manual (as amended) (or other guidance acceptable to the Borough Engineer) and in general shall:

(1) 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.

(2) Provide field tests such as double ring infiltrometer or other hydraulic conductivity tests (at the elevation of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Standard septic/sewage percolation tests are not acceptable for design purposes.

(3) Design the infiltration facility for the required retention (infiltration) volume based on field-determined infiltration capacity (and apply safety factor as per applicable design guidelines) at the elevation of the proposed infiltration surface.

(4) On-lot infiltration features are encouraged; however, it shall be demonstrated to the Borough Engineer that the soils are conducive to infiltration on the identified lots.

I. Infiltration BMPs shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:

(1) A minimum depth of 24 inches between the bottom of the BMP and the top of the Limiting Zone. Additional depth may be required in areas underlain by karst or carbonate geology (see Subsection M).

(2) An infiltration rate sufficient to accept the additional stormwater volume and drain completely as determined by field tests conducted by the applicant.

(3) The infiltration facility shall completely drain the retention (infiltration) volume within three days (72 hours) from the end of the design storm.

J. All infiltration practices shall:

(1) Be selected and designed to meet the criteria of Subsection C that are applicable to infiltration;

(2) Be set back at least 10 feet from all buildings and features with sub-grade elements (e.g., basements, foundation walls, etc.), unless otherwise approved by the Borough Engineer;

(3) For any infiltration practice that collects runoff from shared or multiple features and that is located within 50 feet of a building or feature with sub-grade elements (e.g., basements, foundation walls, etc.), the bottom elevation shall be set below the elevation of the sub-grade element unless a smaller setback is justified by a flow net calculation for the facility.

K. Infiltration facilities shall, to the maximum extent practicable, be located to avoid introducing contaminants to groundwater:

(1) When a hotspot is located in the area draining to a proposed infiltration facility, an evaluation of the potential of groundwater contamination from the proposed infiltration facility shall be performed, including a hydrogeologic investigation (if necessary) by a qualified licensed professional to determine what, if any, pre-treatment or additional design considerations are needed to protect groundwater quality.

(2) When located within a "well head protection area" of a public water supply well, infiltration practices shall be in conformance with the applicable approved source water protection assessment or source water protection plan.

(3) The applicant shall provide appropriate safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.

L. During site construction, all infiltration practice components shall be protected from compaction due to heavy equipment operation or storage of fill or construction material. 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 Borough Engineer for review. All areas designated for infiltration shall not receive runoff until the contributory drainage area has achieved final stabilization.

M. Consideration of infiltration BMPs for areas underlain by karst or carbonate geology is encouraged, but only where the design, supporting calculations, results of soils or other site investigations or other documentation are provided to the Borough demonstrating that the potential or likelihood of subsidence or sinkholes is minimal. Evaluation of site conditions and infiltration design shall rely on guidance in the PA BMP Manual (as amended) or other guidance acceptable to the Borough Engineer.

N. Groundwater quality of the carbonate aquifer shall be protected from infiltration of pollutants. At a minimum, stormwater runoff from hotspots (i.e., sources of significant pollutant runoff) shall first be discharged through a water quality BMP(s) to remove pollutants prior to infiltration. Where soil characteristics are insufficient to provide removal of pollutants from sources other than hotspots, stormwater runoff shall first be discharged through a water quality BMP(s) to remove pollutants prior to infiltration.

O. Where sediment transport in the stormwater runoff is anticipated to reach the infiltration system, appropriate permanent measures to prevent or collect sediment shall be installed prior to discharge to the infiltration system.

P. Where roof drains are designed to discharge to infiltration practices, they shall have appropriate measures to prevent clogging by unwanted debris (for example, silt, leaves and vegetation). Such measures shall include but are not limited to leaf traps, gutter guards and cleanouts.

Q. All infiltration practices shall have appropriate positive overflow controls.

R. No sand, salt or other particulate matter may be applied to a porous surface material for winter ice conditions. This shall be noted on the stormwater site plan.

S. The following procedures and materials shall be required during the construction of all subsurface facilities:

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

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

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

(4) The tops and sides of all seepage beds, trenches, or like facilities shall be covered with drainage fabric. Fabric shall be non-woven fabric acceptable to the Borough Engineer.

(5) Stormwater shall be distributed throughout the entire seepage bed/trench or like facility and provisions for the collection of debris shall be provided in all facilities (i.e., cleanout with sump).

§ 342-307 Stream channel protection requirements.

For regulated activities involving new development with one or more acres of earth disturbance, 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, twenty-four-hour design storm shall be reduced to the predevelopment peak flow rate of the one-year, twenty-four-hour duration precipitation, using the SCS Type II distribution.

B. To the maximum extent practicable, and unless otherwise approved by the Borough Engineer, the postconstruction one-year, twenty-four-hour storm flow shall be detained for a minimum of 24 hours and a maximum not to exceed 72 hours from a point in time when the maximum volume of water from the one-year, twenty-four-hour storm is stored in a proposed BMP (i.e., when the maximum water surface elevation is achieved in the facility). Release of water can begin at the start of the storm (i.e., the invert of the orifice is at the invert of the proposed BMP).

C. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 342-309D of this chapter.

D. The minimum orifice size in the outlet structure to the BMP shall be three inches in diameter unless otherwise approved by the Borough Engineer, and a trash rack shall be installed to prevent clogging. For sites with small drainage areas contributing to the BMP that do not provide enough runoff volume to allow a twenty-four-hour attenuation with the three-inch orifice, the calculations shall be submitted showing this condition.

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

F. All proposed stormwater management facilities shall make use of measures to extend the flow path and increase the travel time of flows in the facility.

G. When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate control shall be separately addressed for each drainage area.

§ 342-308 Stormwater peak rate control requirements.

The applicant shall comply with the following peak flow rate control requirements for all regulated activities including those that involve new development and redevelopment.

A. Postconstruction peak flow rates from any regulated activity shall not exceed the predevelopment peak flow rates as shown for each of the design storms specified in Table 308.1.

Table 308.1 Peak Rate Control Standards
Postconstruction Design Storm Frequency (24-Hour Duration)	Predevelopment Design Storm
	New Development Regulated Activities	Redevelopment Regulated Activities
2-year	1-year	2-year
5-year	5-year	5-year
10-year	10-year	10-year
25-year	25-year	25-year
50-year	50-year	50-year
100-year	100-year	100-year

B. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 342-309D of this chapter.

C. For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total regulated impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table 308.1, using the redevelopment Ground Cover Assumptions presented in § 342-309D. This design criterion for redevelopment is only permitted with approval of Borough Engineer. It shall result in no impact on downstream properties.

D. Only the area of the proposed regulated activity shall be subject to the peak flow rate control standards of this chapter. Undisturbed areas for which the discharge point has not changed are not subject to the peak flow rate control standards.

E. Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to peak flow rate control requirements. Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.

F. When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate controls shall be separately addressed for each drainage area.

G. The effect of structural and non-structural stormwater management practices implemented as part of the overall site design may be taken into consideration when calculating total storage volume and peak flow rates.

§ 342-309 Calculation methodology.

A. Stormwater runoff from all regulated activity sites with a drainage area of greater than five acres shall be calculated using a generally accepted calculation technique(s) that is based on the NRCS Soil Cover Complex Method. Table 309.1 summarizes acceptable computation methods. The method selected for use shall be based on the individual limitations and suitability of each method for a particular site. The use of the Rational Method to estimate peak discharges for drainage areas greater than five acres shall be permitted only upon approval by the Borough Engineer.

Table 309.1 Acceptable Computation Methodologies for SWM Site Plan
Method	Developed By	Applicability
TR-20 (or commercial computer package based on TR-20)	USDA NRCS	Applicable where use of full hydrology computer model is desirable or necessary
TR-55 (or commercial computer package based on TR-55)	USDA NRCS	Applicable for land development plans where limitations described in TR-55 are met
HEC-1/HEC-HMS	US Army Corps of Engineers	Applicable where use of a full hydrologic computer model is desirable or necessary
Rational method (or commercial computer package based on rational method)	Emil Kuichling (1889)	For sites up to five acres, or as approved by the Borough
Other methods	Varies	Other computation methodologies approved by the Borough

B. All calculations using the Soil Cover Complex Method shall use the appropriate design rainfall depths for the various return period storms consistent with this chapter. Rainfall depths used shall be obtained from the latest version of the Precipitation-Frequency Atlas of the United States, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland (NOAA Atlas 14) values consistent with a partial duration series. When stormwater calculations are performed for routing procedures or infiltration, water quality and runoff volume functions, the duration of rainfall shall be 24 hours.

C. All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration (duration) and storm events with rainfall intensities obtained from NOAA Atlas 14 partial duration series estimates, or the latest version of the PennDOT Drainage Manual (PDM Publication 584). Times-of-concentration shall be calculated based on the methodology recommended in the respective model used. Times of concentration for channel and pipe flow shall be computed using Manning's equation. (Refer to Appendix B-3.[1])

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

D. The applicant shall utilize the following ground cover assumptions for all predevelopment water quality and runoff volume, infiltration volume and peak flow rate calculations:

(1) For regulated activities involving new development, the following ground cover assumptions shall be used:

(a) For areas that are woods, predevelopment calculations shall assume ground cover of "woods in good condition."

(b) For all other areas (including all impervious surfaces), predevelopment calculations shall assume ground cover of "meadow."

(2) For regulated activities involving redevelopment, the following ground cover assumptions shall be used:

(a) For areas that are woods, predevelopment calculations shall assume ground cover of "woods in good condition."

(b) For areas that are not woods or not impervious surfaces, predevelopment calculations shall assume ground cover of "meadow."

(c) For areas that are impervious surfaces, predevelopment calculations shall assume at least 20% of the existing impervious surface area to be disturbed as "meadow" ground cover.

(3) The applicant shall determine which stormwater standards apply to the proposed regulated activity as follows:

(a) Stormwater standards for new development shall apply to all proposed regulated activities that involve only new development activities as defined in this chapter.

(b) Stormwater standards for redevelopment shall apply to all proposed regulated activities that involve only redevelopment activities as defined in this chapter.

(c) At the discretion of the Borough Engineer, regulated activities that involve a combination of both new development and redevelopment activities, as defined in this chapter, may either:

[1] Apply the stormwater standards (redevelopment or new development) that are associated with the activity that involves the greatest amount of land area; or

[2] Apply the redevelopment and new development stormwater standards to the corresponding redevelopment and new development portions of the proposed regulated activity.

E. Runoff curve numbers (CN) for both predevelopment and proposed (postconstruction) conditions to be used in the Soil Cover Complex Method shall be obtained from Table B-2 in Appendix B of this chapter.[2]

[2] Editor's Note: Said appendix is included as an attachment to this chapter.

F. Runoff coefficients (C) for both predevelopment and proposed (postconstruction) conditions for use in the Rational Method shall be obtained from Table B-1 in Appendix B of this chapter.[3]

[3] Editor's Note: Said appendix is included as an attachment to this chapter.

G. Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.

H. Hydraulic computations to determine the capacity of pipes, culverts, and storm sewers shall utilize the roughness coefficient (Manning "n" values) in accordance with the manufacturer's specifications or with PennDOT Publication 584, PennDOT Drainage Manual (Appendix B-7).

I. Runoff calculations shall include the following assumptions:

(1) Average antecedent moisture conditions (for the Soil Cover Complex Method only for example, TR-55, TR-20).

(2) A type II distribution storm (for the Soil Cover Complex Method only for example, TR-55, TR-20).

§ 342-310 Other requirements.

A. Any BMP intended to hold standing water for four days or longer shall be designed to incorporate biologic controls consistent with the West Nile Guidance found in Appendix E, PADEP document 363-0300-001 "Design Criteria — Wetlands Replacement/Monitoring" (as amended) (or contact the Pennsylvania State Cooperative Wetland Center or the Penn State Cooperative Extension Office for design information.)

B. Any stormwater basin required or regulated by this chapter designed to store runoff and requiring a berm or earthen embankment shall be designed to provide an emergency spillway to safely convey flow up to and including the 100-year proposed conditions. The height of embankment shall provide a minimum one foot of Freeboard above the maximum pool elevation computed when the facility functions for the 100-year proposed conditions inflow. Should any BMP require a dam safety permit under 25 Pa. Code Chapter 105 regulations, the facility shall be designed in accordance with and meet the regulations of 25 Pa. Code Chapter 105 concerning dam safety. Title 25 Pa. Code Chapter 105 may require the safe conveyance of storms larger than 100-year event.

C. Any drainage conveyance facility and/or channel not governed by 25 Pa. Code Chapter 105 regulations shall be designed to convey, without damage to the drainage facility or roadway, runoff from the twenty-five-year storm event. Larger storm events (fifty-year and 100-year storms) shall also be safely conveyed in the direction of natural flow without creating additional damage to any drainage facilities, nearby structures, or roadways.

D. Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from the facility.

E. Roadway crossings or structures located within designated floodplain areas shall be able to convey runoff from a 100-year design storm consistent with Federal Emergency Management Agency National Flood Insurance Program — Floodplain Management Requirements.

F. Any stormwater management facility located within a PennDOT right-of-way shall comply with PennDOT minimum design standards and permit submission and approval requirements.

G. Adequate erosion protection and energy dissipation shall be provided along all open channels and at all points of discharge. Design methods shall be consistent with the Federal Highway Administration Hydraulic Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as amended) and the PADEP Erosion and Sediment Pollution Control Program Manual (Publication No. 363-2134-008, as amended), or other design guidance acceptable to the Municipal Engineer.

§ 342-311 Other conveyance and system design standards.

A. General.

(1) For all aboveground storage facilities, the bottom of the excavated basin shall be a minimum of two feet or 24 inches above the seasonal high water table or bedrock. Soil sampling, test pits or auger testing must be completed in the proposed location of the facilities in support of the design.

(2) Aboveground storage facilities without restricted access shall have impoundment areas with side slopes no greater than five horizontal to one vertical. Basins with side slopes steeper than five horizontal to one vertical shall be protected by fencing that will discourage access.

(3) Aboveground storage facilities with a facility depth greater than eight feet shall not be permitted in residential areas.

(4) Aboveground storage facilities with a facility depth greater than 15 feet require a dam permit from DEP.

(5) All pipe collars, when required, shall be designed in accordance with Chapter 7 of the DEP E&S Manual. The material shall consist of concrete or otherwise non-degradable material approved by the Borough Engineer around the outfall barrel and shall be watertight.

(6) The embankment fill material shall be taken from an appropriate borrow area which shall be free of roots, stumps, wood, rubbish, stones greater than six inches, frozen or other objectionable materials.

(7) When required, embankments shall be compacted by sheepsfoot or pad roller. The loose lift thickness shall be nine inches or less, depending on roller size, and the maximum particle size is six inches or less (2/3 of the lift thickness). Five passes of the compaction equipment over the entire surface of each lift is required. Embankment compaction to visible non-movement is also required.

(8) The minimum bottom slope of facilities not designed for infiltration shall be 1%. A flatter slope may be used if an equivalent dewatering mechanism is provided.

(9) When required, dewatering shall be provided through the use of underdrain, surface device, or alternate approved by the Borough Engineer. If the facility is to be used for infiltration, the dewatering device should be capable of being disconnected and only be made operational if the basin is not dewatering within the required timeframe.

(10) When required, pretreatment elements shall consist of forebays, filter strips or alternate approved by the Borough Engineer, to keep silt to a smaller portion of the facility for ease of maintenance.

(11) Within basins designed for infiltration, existing native vegetation shall be preserved, if possible. For existing unvegetated areas or for infiltration basins that require excavation, a planting plan shall be prepared in accordance with § 301.N and the BMP Manual which is designed to promote infiltration.

(12) For facilities with a depth of two feet or greater, a type D-W endwall or riser box outlet structure shall be provided.

(13) For facilities with a depth less than two feet, no outlet structure is required.

(14) All discharge control devices with appurtenances shall be made of reinforced concrete and stainless steel. Bolts/fasteners shall be stainless steel.

(15) The spillway shall be designed to provide a non-erosive, stable condition when the project is completed.

(16) The spillway shall be designed to convey the 100-year peak inflow when required.

(17) Freeboard shall be measured from the top of the water surface elevation for emergency use.

(18) West Grove Borough may require a breach analysis based on site-specific conditions and concern of threat for downstream property. When required, the breach analysis shall be conducted in accordance with the NRCS methodology, the US Army Corps of Engineers methodology (HEC-1) or other methodologies as approved by the Borough.

(19) Embankment construction.

(a) An impervious core/key trench, when required, shall consist of a cutoff trench (below existing grade) and a core trench (above existing grade). A key trench may not be required wherever it can be shown that another design feature, such as the use of an impermeable liner, accomplishes the same purpose.

(b) Materials used for the core shall conform to the Unified Soil Classification GC, SC, CH, or CL and must have at least 30% passing the No. 200 sieve.

(c) The dimensions of the core shall provide a minimum trench depth of two feet below existing grade, minimum width of four feet and side slope of 1H:1V or flatter.

(d) The core should extend up both abutments to the ten-year water surface elevation or six inches below the emergency spillway elevation, whichever is lower.

(e) The core shall extend four feet below any pipe penetrations through the impervious core. The core shall be installed along or parallel to the centerline of the embankment.

(f) Compaction requirements shall be the same as those for the embankment to assure maximum density and minimum permeability.

(g) The core shall be constructed concurrently with the outer shell of the embankment.

(h) The trench shall be dewatered during backfilling and compaction operations.

B. Aboveground storage facilities. Aboveground storage facilities consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is exposed to the natural environment. Aboveground storage facilities are located above the finished ground elevation. Aboveground storage facilities do not include stormwater management facilities designed for conveyance or cisterns.

(1) Design criteria. Refer to Table 311.1.

(a) Aboveground storage facility with facility depth of less than two feet.

[1] The minimum top of embankment width shall be two feet.

[2] Maximum interior side slope 2:1.

[3] Maximum exterior side slope 2:1.

[4] Minimum outlet pipe diameter shall be six inches.

[5] Outlet pipe material: PVC, HDPE or RCP.

[6] Anti-clogging device is required.

[7] Watertight joints shall be provided in karst areas.

[8] The spillway freeboard shall be a minimum three inches.

[9] The spillway may be used to route the 100-year storm.

(b) Aboveground storage facility with depth of two to eight feet.

[1] Embankment minimum top width of five feet.

[2] Maximum interior side slope 5:1.

[3] Maximum exterior side slope 3:1.

[4] A key trench and anti-seep collar shall be provided.

[5] Compaction density of the embankment is required.

[6] A dewatering feature is required.

[7] Pretreatment filtering of runoff is required.

[8] Minimum outlet pipe diameter of 12 inches.

[9] Outlet pipe material: HDPE or RCP.

[10] An anti-clogging device is required.

[11] An antivortex design is required.

[12] Watertight joints shall be provided.

[13] The spillway freeboard shall be a minimum six inches.

[14] The minimum spillway width is 10 feet.

[15] The maximum spillway width is 50 feet.

[16] The downstream channel into which the spillway discharges shall be checked for adequate capacity and stability.

[17] The spillway shall not be considered to function as part of the primary outlet structure and shall be only for emergency situations.

(c) Aboveground storage facility with depth greater than eight feet.

[1] Embankment minimum top width of eight feet.

[2] Maximum interior side slope 5:1.

[3] Maximum exterior side slope 3:1.

[4] A key trench and anti-seep collar shall be provided.

[5] Compaction density of the embankment is required.

[6] A dewatering feature is required.

[7] Pretreatment filtering of runoff is required.

[8] Minimum outlet pipe diameter of 15 inches.

[9] Outlet pipe material: RCP.

[10] An anti-clogging device is required.

[11] An antivortex design is required.

[12] Watertight joints shall be provided.

[13] The spillway freeboard shall be a minimum 12 inches.

[14] The minimum spillway width is 20 feet.

[15] The maximum spillway width is 50 feet.

[16] The downstream channel into which the spillway discharges shall be checked for adequate capacity and stability.

[17] The spillway shall not be considered to function as part of the primary outlet structure and shall be only for emergency situations.

(d) General requirements for aboveground storage facilities:

[1] Where practical, the spillway shall be constructed in undisturbed ground.

[2] The effect on the downstream areas if the facility embankment fails shall be considered in the design of all facilities. Where possible the facility shall be designed to minimize the potential damage caused by such failure of the embankment.

[3] For all aboveground facilities that do not rely on infiltration to dewater the runoff, a flow path length to width ratio of 2:1 shall be provided to maximize the treatment time between the inflow point and the outlet structure.

Table 311.1 Aboveground Storage Facility Design Criteria
	Facility Depth
	Less Than 2 Feet	2 Feet to 8 Feet	Greater Than 8 Feet
Embankment Geometry
Top width (minimum)	2 feet	5 feet	8 feet
Interior side slope (maximum)	2:1	5:1	5:1
Exterior side slope (maximum)	2:1	3:1	3:1
Embankment construction
Key trench	Not required	Required	Required
Pipe collar	Not required	Required	Required
Compaction density	Not required	Required	Required
Internal Construction
Dewatering feature	N/A	Required	Required
Pretreatment elements	Not required	Required	Required
Outlet Structure
Pipe size (minimum)	6 inches	12 inches	15 inches
Pipe material	HDPE, PVC, RCP	HDPE, RCP	RCP
Anticlogging devices	Required	Required	Required
Antivortex design	Not required	Required	Required
Watertight joints in piping	No**	Yes	Yes
Spillway Requirements
Spillway freeboard (minimum)	3 inches	6 inches	12 inches
Width (minimum)	Not required	10 feet	20 feet
Width (maximum)	Not required	50 feet	50 feet
Spillway channel design	Not required	Required	Required
Routing of 100-year storm	Permitted	Not permitted	Not permitted

C. Subsurface storage facilities. Subsurface storage facilities consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is not exposed to the natural environment. Subsurface facilities are located below the finished ground elevation. Subsurface facilities do not include stormwater management facilities designed for conveyance.

(1) General.

(a) The stone used for infiltration beds shall be clean washed, uniformly graded coarse aggregate (AASHTO No. 3 or equivalent approved by the Borough of West Grove). The void ratio for design shall be assumed to be 0.4.

(b) Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select non-aggregate material should be indigenous to the surrounding soil material for non-vehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in governing municipal road/street or subdivision and land development ordinances. Furthermore, if the design concept includes the migration of runoff through the backfill to reach the infiltration facility, the material shall be well drained, free of excess clay or clay like materials and generally uniform in gradation.

(c) Non-woven geotextiles shall be placed on the sides and top of subsurface infiltration facilities. No geotextiles shall be placed on the bottom of subsurface infiltration facilities.

(d) When located under pavement, the top of the subsurface facility shall be a minimum of three inches below the bottom of pavement subbase. Where located under vegetative cover, the top of the subsurface facility shall be a minimum of 12 inches below the surface elevation or as required to establish vegetation.

(e) Subsurface facilities shall be designed to safely convey and/or bypass flows from storms exceeding the design storm.

(f) Infiltration systems shall be located a minimum of 10 feet away from the foundation wall of any building.

(g) Infiltration rates shall not be used in computing the storage volume of the infiltration system.

(2) Design criteria. Refer to Table 311.2.

(a) Infiltration and storage facility.

[1] Maximum depth from surface: two feet less than limiting zone.

[2] Loading ratio: Per December 2006 BMP Manual, as amended. The maximum impervious loading ratio of 5:1 relating impervious drainage area to infiltration area. The maximum total loading ratio of 8:1 relating to total drainage area to infiltration area. In areas of Karst Geology, the maximum impervious drainage area to infiltration area is 3:1.

[3] Minimum distribution pipe size shall be four inches. Distribution system piping may be PVC or HDPE.

[4] Pretreatment of runoff to the facility is required to provide a method to eliminate solids, sediment, and other debris from entering the subsurface facility.

[5] Observation/access ports shall be provided in the facility. For facilities with the bottom less than five feet below the average grade of the ground surface, a clean-out shall be an acceptable observation port. For facilities with the bottom five feet or more below the average grade of the ground surface, a manhole or other means acceptable to the Borough of West Grove shall be provided for access to and monitoring of the facility. The number of access points shall be sufficient to flush or otherwise clean out the system.

[6] The facility shall be designed to provide a means of evenly balancing the flow across the surface of the facility to be used for infiltration.

(b) Storage without infiltration facility.

[1] Minimum distribution pipe size shall be four inches. Distribution system piping may be PVC, HDPE, or RCP.

[2] Pretreatment of runoff to the facility is required to provide a method to eliminate solids, sediment, and other debris from entering the subsurface facility.

[3] Observation/access ports shall be provided in the facility. For facilities with the bottom less than five feet below the average grade of the ground surface, a clean-out shall be an acceptable observation port. For facilities with the bottom five feet or more below the average grade of the ground surface, a manhole or other means acceptable to the Borough of West Grove shall be provided for access to and monitoring of the facility. The number of access points shall be sufficient to flush or otherwise clean out the system.

Table 311.2 Subsurface Storage Facility Design Criteria
	Facility Type
	Infiltration and Storage	Storage Without Infiltration
Facility Geometry
Depth from surface (maximum)	2 feet less than limiting zone	N/A
Loading ratio (maximum)	Per BMP Manual*	N/A
Distribution System Requirements
Pipe size (minimum)	4 inches	4 inches
Pretreatment	Required	Required
Loading/balancing	Required	Not required
Observation/access ports	Required	Required

NOTES:
*	Unless otherwise determined by professional geologic evaluation.

D. Conveyance facilities. Conveyance facilities consist of all stormwater facilities which carry flow, which may be located either above or below the finished grade. Conveyance facilities do not include stormwater management facilities which store, infiltrate/evaporate/transpire, or clean stormwater runoff.

(1) General.

(a) Conveyance pipes, culverts, manholes, inlets and endwalls within the public street right-of-way or proposed for dedication shall conform to the requirements of PennDOT Standards for Roadway Construction, Publication No. 72M.

(b) Conveyance pipes, culverts, manholes, inlets and endwalls which are otherwise subject to vehicular loading shall be designed for the HS-25 loading condition.

(c) Backfill material. Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select non-aggregate material should be indigenous to the surrounding soil material for non-vehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in governing municipal road/street or subdivision and land development ordinances.

(d) Inlets or manholes shall be placed at all points of changes in the horizontal or vertical directions of conveyance pipes. Curved pipe sections are prohibited.

(e) Access/maintenance ports. An access/maintenance port is required may either be an inlet or manhole.

(f) Watertight joints shall be provided where pipe sections are joined, except for perforated pipe installed as pavement base drain. The watertight joints shall be of a type approved by the Borough or Borough Engineer. This requirement shall be noted and/or on the plans.

(g) The street crossing angle shall be measured between the pipe centerline and the street centerline.

(h) Elliptical pipe of an equivalent cross-sectional area may be substituted in lieu of circular pipe where cover or utility conflict conditions exist.

(i) All pipes must enter inlets completely through one of the sides. No corner entry of pipes is permitted.

(j) Within the public street right-of-way, the gutter spread based on the twenty-five-year storm shall be no greater than 1/2 of the travel lane and have a maximum depth of three inches at the curb line. A parking lane shall not be considered as part of the travel lane. In the absence of pavement markings separating a travel lane from the parking lane, the parking lane shall be assumed to be seven feet wide if parking is permitted on the street.

(k) Flow depth within intersections. Within intersections of streets, the maximum depth of flow shall be 1 1/2 inches based on the twenty-five-year storm.

(l) Inlets in streets shall be located along the curb line.

(m) Top units shall be PennDOT Type "C." The hood shall be aligned with the adjacent curb height.

(n) All inlets placed in paved areas shall have heavy duty bicycle-safe grating consistent with PennDOT Publication 72M, latest edition. A note to this effect shall be added to the SWM site plan or inlet details therein.

(o) Inlets, junction boxes, or manholes greater than five feet in depth shall be equipped with ladder rungs and shall be detailed on the SWM site plan.

(p) A swale shall be considered as any man-made ditch designed to convey stormwater directly to another stormwater management facility or surface waters.

(q) Inlets within swales shall have PennDOT Type "M" top units or equivalent approved by the Borough engineer.

(r) Swale capacities and velocities shall be computed using the Manning equation using the following design parameters:

[1] Vegetated swales.

[a] The first condition shall consider swale stability based upon a low degree of retardance ("n" = 0.03);

[b] The second condition shall consider swale capacity based upon a higher degree of retardance ("n" = 0.05); and

[c] All vegetated swales shall have a minimum slope of 1% unless otherwise approved by the Borough Engineer.

[d] The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices, as approved by the Borough Engineer.

(s) Where the connecting pipe has a diameter 18 inches or greater, headwalls and endwalls shall be provided with a protective barrier device to prevent entry of the storm sewer pipe by unauthorized persons. Such protection devices shall be designed to be removable for cleaning.

(t) Headwalls and endwalls shall be constructed of concrete.

(u) Flared end sections shall be of the same material as the connecting pipe and be designed for the size of the connecting pipe.

(v) Level spreaders:

[1] Shall discharge at existing grade onto undisturbed vegetation.

[2] Discharge at a depth not exceeding 3.0 inches for a fifty-year, twenty-four-hour design storm.

(w) Energy dissipaters shall be designed in accordance with the requirements in the DEP E&S Manual.

(x) SWM facilities which qualify as a dam per DEP regulations or facilities deemed a potential threat to the life; safety or welfare of the general public shall be subject to the following requirements.

[1] Facilities which qualify as a dam per DEP regulation shall obtain the required permit through DEP and design the facility in accordance with DEP standards.

[2] Additional requirements and analysis may be required by the Borough to prove that the proposed facility has been designed to limit the potential risk to the life, safety or welfare of the general public.

(y) In addition to the material requirements in this section, culverts designed to convey waters of the commonwealth may be constructed with either a corrugated metal arch or a precast concrete culvert.

(z) Trash racks shall be provided on all endwalls and storm sewer discharge points for pipe diameters of 18 inches or greater. The proposed trash rack shall be subject to review and approval by the Borough.

(2) Design criteria. Refer to Table 311.3.

(a) Within public street right-of-way.

[1] Conveyance system material shall consist of HDPE or RCP pipe.

[2] The minimum pipe slope shall be 0.5%.

[3] A minimum one foot of cover to the stone subgrade shall be provided over the conveyance pipes.

[4] The minimum pipe diameter shall be 15 inches.

[5] The minimum street crossing angle for the conveyance system shall be 75° to 90°.

[6] Maximum spacing between access or maintenance ports shall be 400 feet.

[7] Inlets and manholes shall be concrete.

[8] Inlets shall be depressed a minimum of two inches below the surface grade to provide positive flow.

[9] Swales shall be provided with a minimum freeboard of six inches.

[10] The maximum swale velocity shall be determined based on the stability of the channel.

[11] The minimum swale slope shall be 1%.

[12] Side slopes in residential areas shall be a maximum of 4:1. Side slopes in non-residential areas shall be a maximum of 4:1.

[13] The bottom width to flow depth ration shall be 12:1.

[14] Pipe entrances/discharges in public street rights-of-way shall be provided with a headwall/endwall treatment.

[15] The pipe discharge locations shall be provided with an energy dissipater designed to handle the anticipated flow conditions.

(b) Outside public street right-of-way: vehicular loading.

[1] Conveyance system material shall consist of PVC, HDPE or RCP pipe.

[2] The minimum pipe slope shall be 0.5%.

[3] A minimum one foot of cover to the stone subgrade shall be provided over the conveyance pipes.

[4] The minimum pipe diameter shall be 15 inches.

[5] Maximum spacing between access or maintenance ports shall be 400 feet.

[6] Inlets and manholes shall be concrete.

[7] Inlets shall be depressed a minimum of two inches below the surface grade to provide positive flow.

(c) Outside public street right-of-way: non-vehicular loading.

[1] Conveyance system material shall consist of PVC, HDPE or RCP pipe.

[2] The minimum pipe slope shall be 0.5%.

[3] A minimum one foot of cover to the surface shall be provided over the conveyance pipes.

[4] The minimum pipe diameter shall be eight inches.

[5] Maximum spacing between access or maintenance ports shall be 600 feet.

[6] Manholes shall be concrete.

[7] Inlets shall be depressed a minimum of one inches below the surface grade to provide positive flow.

[8] Swales shall be provided with a minimum freeboard of six inches.

[9] The maximum swale velocity shall be determined based on the stability of the channel.

[10] The minimum swale slope shall be 1%.

[11] Side slopes in residential areas shall be a maximum of 4:1. Side slopes in nonresidential areas shall be a maximum of 3:1.

[12] The bottom width to flow depth ration shall be 12:1.

[13] Pipe entrances/discharges in public street rights-of-way shall be provided with a headwall/endwall or flared end section treatment.

[14] The pipe discharge locations shall be provided with an energy dissipater designed to handle the anticipated flow conditions.

Table 311.3 Conveyance Facility Design Criteria
Location	Within Public Street Right-of-Way	Outside Public Street Right-of-Way
Loading	All	Vehicular Loading		Non-vehicular Loading
Pipe design
Material	HDPE, RCP	PVC, HDPE, RCP		PVC, HDPE, RCP
Slope (minimum)	0.5%	0.5%		0.5%
Cover	1 foot to stone subgrade	1 foot to stone subgrade		1 foot to surface
Diameter (minimum)	15 inches	15 inches		8 inches
Street crossing angle	75° to 90°	N/A		N/A
Access/maintenance port frequency (maximum)	400 feet	400 feet		400 feet
Inlet design
Material	Concrete		Concrete	N/A
Grate depression	2 inches		2 inches	1 inch minimum
Manhole design
Material	Concrete		Concrete	Concrete
Swale design
Freeboard (minimum)	6 inches		N/A	6 inches
Velocity (maximum)	Stability check		N/A	Stability check
Slope (minimum)	1%		N/A	1%
Side slopes (residential area)	4:1 max		N/A	4:1 max
Side slopes (nonresidential area)	4:1 max		N/A	3:1 max
Bottom width to flow depth ratio	12:1		N/A	12:1
Outlet design
End treatment	Headwall/endwall		N/A	Headwall/endwall or flared end section
Energy dissipater	Required		N/A	Required

E. Capture and reuse facilities.

(1) Design requirements:

(a) Calculation of water usage to ensure adequate capacity is available for storage of follow-up rainfall events. The property will draw from the cistern on a daily basis; the cistern shall be dewatered in 72 hours to maintain the capacity of the storage facility.

(b) Verification of conveyance pipe capacity in the roof leader design.

(c) The water storage container(s) shall be protected from direct sunlight to minimize algae growth.

(d) An alternative supply of water shall be available for the property use during dry periods.

(e) Water storage containers should be watertight with smooth interior surfaces.

(f) The cover (or lid) should have a tight fit to keep out surface water, children, animals, dust and light. The cover or lid opening should be a minimum 24 inches in order to access the facility for maintenance and repair.

(g) Cisterns shall be designed to store the runoff volume of a 100-year storm event for the area served by the water storage facility.

(h) Every water storage facility (cistern, rain barrel, etc.) shall be provided with an overflow or an emergency spillway. The overflow shall be designed to discharge away from buildings and other structures and towards existing natural or man-made channels, stormwater facilities or vegetated slopes.

[1] The plans proposing a water storage facility shall include the following:

[2] All calculations and assumptions used in the design.

[3] Sufficient detail showing the proposed method of dewatering (i.e., pump).

[4] Structural details.

(i) Maintenance responsibilities for water storage and reuse facilities shall include flushing the storage units to remove any accumulated sediment, the inside surfaces shall be brushed and thoroughly disinfected.

(j) The water shall not be allowed to freeze in the devices.

§ 342-312 Riparian buffers.

A. In order to protect the existing environmentally sensitive areas within the Borough, protect the natural resources and aid in the improvement of water quality riparian buffer easements shall be created as part of any subdivision or land development or SWM Plan (except exemptions and Small Project applications). For any site located immediately adjacent to or encompassing a watercourse (i.e., stream, creek or other natural body of water), a "riparian buffer easement" shall be measured to be the greater of the limit of the 100-year floodplain or a minimum of 35 feet in width from the top of the streambank (on each side) of the watercourse shall be provided and maintained. The riparian buffer easement shall not be designated along industrial ponds, sewerage treatment lagoons, man-made irrigation ditches, stormwater management basins and other artificial features with similar water quality or storage facility. The purpose of the riparian buffer easement shall be to protect and preserve the existing natural features and environmental resources subject to the following requirements:

(1) Preservation of existing buffer plantings: Within the riparian buffer easement the existing natural trees and vegetation shall be preserved.

(2) Required buffer plantings: To create a riparian Forested buffer, the required easement area shall be planted with additional native trees, shrubs and other plant material as determined necessary (depending on site conditions) in order to create a suitable "riparian buffer."

(3) The riparian buffer easement shall be incorporated into the deed for the property or lot(s) and shall limit the use of the property located therein. The easement shall allow for the continued private ownership and count toward the minimum lot area as required by the West Grove Borough Zoning Ordinance,[1] but restrict land uses to the current use or to other non-damaging activities such as:

(a) Regulated activities permitted by the Commonwealth of Pennsylvania (i.e., permitted stream or wetland crossing). Maximum area disturbance permitted for this use shall be 5% of the designated riparian buffer.

(b) Provision for unpaved, ungraded, or natural trails parallel to the watercourse not to exceed six feet in width. Such trail shall not come within 10 feet of any stream bank.

(c) Clearing of a foot-path to the watercourse or trail access not to exceed six feet in width, provided that a cleared line of sight to the watercourse through the buffer is not created.

(d) Selective removal of a safety hazard, diseased trees, or invasive plant species.

(e) A soil conservation project, including reforestation and streambank stabilization, or stormwater management practices approved by the Chester County Conservation District.

(f) Installation and maintenance of municipal government infrastructure, in accordance with all other applicable permits, regulations, and requirements as applicable (DEP, etc.).

(g) 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, and preserve and protect the ecological function of the floodplain.

(h) The following conditions shall apply when public and/or private recreation trails are permitted within riparian buffers:

[1] Trails shall be for non-motorized use only.

[2] Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.

(i) Septic drainfields and sewage disposal systems shall not be permitted within the riparian buffer easement and shall comply with setback requirements established under 25 Pa. Code Chapter 73.

[1] Editor's Note: See Ch. 400 of this Code.

(4) The outlet of any storm sewer piping system or stormwater management facility shall not be permitted within the riparian buffer easement. The riparian buffer easement will create a setback or separation distance from the receiving watercourse. In this way, a natural filter strip will be created so that the quality of stormwater runoff will be improved before reaching the watercourse.

(5) Any activities within the riparian buffer easement shall be completed in a manner that will preserve and protect the existing limits of the 100-year floodplain and floodway.

B. Resource protection standards.

(1) Buffer composition. A riparian buffer shall be a dense ground cover of grasses, shrubbery, and trees preserved with no buildings, structures, or impervious surface. This buffer shall not be cleared, regarded, filled, built upon or otherwise altered; with the exception to restore such area to its natural state or for those uses or activities listed below. Riparian buffers shall be established and maintained in accordance with the following guidelines:

(a) Established through natural succession. Vegetation may be established through natural succession. Selective planting may be incorporated on site devoid of vegetation to stimulate native species and discourage invasive plant species.

(b) Planted in accordance with the following:

[1] Planting plans may be prepared jointly by a PA-registered landscape architect in consultation with other professionals having a practical knowledge of riparian ecosystems (such as horticulturist, wetlands specialists, wildlife biologists, ecologists) such as the Chester County Conservation District, the Department of Environmental Protection, of the Department of Conservation and Natural Resources. All planting plans shall include a planting schedule that summarizes the quantity, size, type and root condition of all plantings. All riparian buffer enhancements shall be installed using practices accepted by the American Association of Nurserymen.

[2] The preparation and planting procedures may include, but shall not be limited to, invasive plan removal and control; stream bank stabilization; the provision of animal browse protection, such as plastic tubes for seedling trees; erosion control matting; the provision of any markers or signs identifying the riparian buffer; and mowing schedules for meadow grass establishment.