[Ord. 2014-04, 4/28/2014, § 23-301]
1. 
Preparation of a stormwater management plan is required for all regulated activities, unless preparation and submission of such a plan is specifically exempted according to this chapter or the activity meets the criteria in § 23-402.
2. 
No regulated activities shall commence until the municipality issued unconditional written approval of the stormwater management plan. The approved plan shall be on-site during the duration of the regulated activity.
3. 
The Township may, after consultation with DEP, approve measures for meeting the state water quality 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. The Township shall maintain a record of consultations with DEP pursuant to this subsection. Where an NPDES permit for stormwater discharges associated with construction activities is required, issuance of an NPDES permit shall constitute satisfaction of consultation with DEP.
4. 
For all regulated activities, erosion and sediment control and stormwater management BMPs 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 and the Clean Streams Law. Various BMPs and their design standards are listed in the BMP Manual and E&S Manual.
5. 
Applicants have the option to propose a regional stormwater management plan or participate in a regional stormwater management plan developed by others. A regional stormwater management plan may include off-site volume and rate control, as appropriate and supported by a detailed design approved by the Township in accordance with Subsection 3. A regional stormwater management plan must meet all of the volume and rate control standards required by this chapter for the area defined by the regional stormwater management plan, but not necessarily for each individual development site. Appropriate agreements must be established to ensure the requirements of this chapter and the requirements of the regional stormwater management plan are met.
6. 
All stormwater management plans shall be designed and signed and certified by a qualified person.
7. 
Where applicable, stormwater management facilities shall comply with the requirements of Chapter 105.
8. 
Stormwater management facilities which involve a state highway or impacts drainage facilities associated with a state highway shall also be subject to the approval of the PennDOT.
9. 
Stormwater management facilities located within or affecting the floodplain of any watercourse shall also be subject to the requirements of the Zoning Ordinance of Penn Township [Chapter 27], as amended, or any future zoning ordinance, regulating construction and development within areas of the Township subject to flooding and any other applicable requirements of the Pennsylvania Floodplain Management Act.
10. 
Stormwater runoff from a project site shall flow directly into a natural watercourse or into an existing storm sewer system, or onto adjacent properties in a manner similar to the runoff characteristics of the pre-development flow. The Township may require written notification of downstream property owners. Where a concentrated flow cannot be directly discharged into a natural watercourse or an existing storm sewer system, the applicant shall be required to establish an easement through such adjacent properties until said flow enters a natural watercourse or existing storm sewer system.
11. 
Stormwater runoff shall not be transferred from one watershed to another unless the watersheds are sub-watersheds of a common watershed which join together within the perimeter of the development site, and the effect of the transfer does not alter the peak discharge onto adjacent lands, or drainage easements from the affected landowners are provided.
12. 
All stormwater runoff flowing over the project site shall be considered in the design of the stormwater management facilities.
13. 
Stormwater management control facilities (i.e., detention, retention basins, and BMPs) for all areas of the Township shall be provided to provide rate control so that the peak discharge of the calculated post-development runoff to an adjacent property does not exceed 50% of the predevelopment peak discharge for all regulated design storms (two-, ten-, twenty-five-, fifty- and one-hundred-year storm events), with the exception of small projects when exempt from rate control.
14. 
Runoff calculations for the pre-development and post-development comparison shall consider five different storm frequencies; the two-, ten-, twenty-five-, fifty- and one-hundred-year storm events.
15. 
Stormwater management facilities shall be supplemented by BMPs to minimize the impacts to water quality of receiving waters. Non-structural BMPs shall be utilized for all regulated activities unless proven to be impractical. Credit will not be provided for the use of soil amendment and restoration, except within stormwater basin bottoms. Credit will also not be provided for rain barrels.
16. 
Innovative methods for the detention and control of stormwater runoff may be used when approved by the Township. Various combinations of methods should be tailored to suit the particular requirements of the type of development and the topographic features of the project site. The following is a partial listing of BMPs which can be utilized in stormwater management systems where appropriate:
A. 
Decreased impervious surface area.
B. 
Routed and dispersed flows over grass areas.
C. 
Grass channels and vegetated strips.
D. 
Bio-retention areas and rain gardens.
E. 
Concrete lattice block or permeable surfaces with underlying systems.
F. 
Rooftop detention.
G. 
Cisterns and underground reservoirs (with water budget analysis and supplemental detention capacity acceptable to the Township).
H. 
Parking lot detention.
I. 
Retention basins.
J. 
Detention basins.
K. 
Other methods as may be found in the BMP Manual, when accepted by the Township.
17. 
Existing on-site natural and man-made facilities shall be used to the maximum extent practicable. If existing stormwater management facilities within a project site do not meet the design requirements of this chapter, and if such facilities are affected by new development being proposed within the site, then the existing stormwater management facilities must be redesigned and improved to meet the requirements of this chapter.
18. 
Where proposed development and improvements to existing stormwater management facilities will cause adverse impacts on adjacent downstream properties, the applicant shall mitigate such impacts.
19. 
All regulated activities in the Township which do not fall under the criteria in §§ 23-401 or 23-402 shall prepare and submit a stormwater management plan consistent with this chapter.
20. 
Runoff from impervious areas shall be drained to pervious areas within the development site, unless the site has 85% or more impervious cover and is a redevelopment, in which case the portion of the development site that discharges to pervious areas shall be maximized.
21. 
When final plan applications are submitted in sections or phases, and if temporary facilities are required for construction of a section, such facilities shall be included in the submitted plans for that section in accordance with Chapter 102.
22. 
The applicant or his agent shall demonstrate that any facilities intended to be installed and located on an individual or group of individual lots can be adequately maintained by the homeowner(s) and/or lot owner(s). When possible, stormwater management facilities shall be designed with consideration that facilities be effectively accommodated within the property of one private entity to simplify ownership and maintenance.
23. 
Minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the computed water surface during the one-hundred-year storm event. If basement or underground facilities are proposed, detailed calculations addressing the effects of stormwater ponding on the structure and waterproofing design information shall be submitted for approval.
24. 
In areas of carbonate geology, a detailed geologic evaluation prepared by a registered professional geologist (PG) must be submitted as part of the stormwater management plan and shall certify the following:
A. 
No stormwater facilities shall be placed in, over or immediately adjacent to the following features:
(1) 
Sinkholes.
(2) 
Closed depressions.
(3) 
Lineaments in carbonate areas.
(4) 
Fracture traces.
(5) 
Caverns.
(6) 
Intermittent streams.
(7) 
Ephemeral streams.
(8) 
Bedrock pinnacles (surface or subsurface).
It shall be the applicant's responsibility to verify if the development site is underlain by carbonate geology. Whenever a stormwater facility will be located in an area underlain by carbonate geology, a detailed geological evaluation of the proposed location shall be conducted by a registered professional geologist to determine susceptibility to sinkhole formation and/or other adverse impacts and a plan for remediation of any identified karst features. The applicant shall include following note on the stormwater management plans which shall be signed and sealed by the applicant's professional geologist: "I, __________, certify that the proposed stormwater management facility(s) (utilize applicable one) are/are not underlain by carbonate geology."
B. 
Stormwater management basins shall not be located closer than 100 feet from the rim of sinkholes or closed depressions, nor within 100 feet from disappearing streams; nor shall these basins be located closer than 50 feet from lineaments or fracture traces; nor shall these basins be located closer than 25 feet from surface or identified subsurface pinnacles.
C. 
Stormwater resulting from land development activities shall not be discharged into sinkholes.
25. 
A planting plan is required for all vegetated stormwater BMPs, subject to the following:
A. 
Native or naturalized/non-invasive vegetation suitable to the soil and hydrologic conditions of the development site shall be used unless otherwise specified in the BMP Manual.
B. 
Invasive vegetation may not be included in any planting schedule.
C. 
The limit of existing, native vegetation to remain shall be delineated on the plan along with proposed construction protection measures.
D. 
Prior to construction, a tree protection zone and protection measures shall be delineated at the dripline of the tree canopy. All trees scheduled to remain during construction shall be marked; however, where groups of trees exist, only the tress on the outside edge need to be marked. A forty-eight-inch high snow fence or forty-eight-inch high construction fence mounted on steel posts located eight feet on center shall be placed along the tree protection boundary. No construction, storage of material, temporary parking, pollution of soil, or regrading shall occur within the tree protection zone.
E. 
All planting shall be performed in conformance with good nursery and landscape practice. Plant materials shall conform to the standards recommended by the American Association of Nurseryman, Inc., in the American Standard of Nursery Stock.
(1) 
Planting designs are encouraged to share planting space for optimal root growth whenever possible.
(2) 
No staking or wiring of trees shall be allowed without a maintenance note for the stake and/or wire removal within one year of planting.
[Ord. 2014-04, 4/28/2014, § 23-302]
1. 
Runoff calculations shall include a hydrologic and hydraulic analysis indicating volume and velocities of flow and the grades, sizes, and capacities of water carrying structures, sediment basins, and retention and detention structures, and sufficient design information to construct such facilities. Runoff calculations shall also indicate both pre-developed and post-developed rates for peak discharge of stormwater runoff from the project site.
2. 
Post development conditions shall be modeled to include reasonably supplemental allocations for possible future impervious areas such as additions, patios, sheds, etc. For projects involving high density residential development or compact nonresidential development the Township may require post development modeling to reflect maximum impervious lot coverage permitted by Chapter 27 [Zoning].
3. 
The methods of calculation used to determine peak discharge and runoff values for sizing stormwater management facilities shall be:
A. 
For all projects with a total watershed area of 25 acres or more, the USDA Soil Conservation Service Soil-Cover-Complex Method as set forth in the latest edition of "Urban Hydrology for Small Watersheds, Technical Release No. 55," published by SCS (SCS - TR #55) or SCS TR-20, shall be used. An Antecedent Moisture Condition 1 and a Type II Distribution shall be used. CN values shall be as shown in Appendix 23-4; rainfall values shall be based on the twenty-four-hour storm events as determined through the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 data or PennDOT Publication 584 "PennDOT Drainage Manual," 2008 Edition, or latest.
B. 
For all projects with a total watershed area of less than 25 acres the Rational Method may be used. The Rational Method is based on the formula of Q=CIA where Q is the peak discharge of the watershed in cubic feet per second, C is the coefficient of runoff as shown in Appendix 23-5, "I" is the intensity of rainfall in inches per hour as determined through the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 data or PennDOT Publication 584 "PennDOT Drainage Manual," 2008 Edition, or latest, and "A" is the area of the watershed in acres.
C. 
Any other method approved by the Township Engineer.
4. 
For the purpose of calculating pre-development peak discharges and modeling, when the existing site contains impervious area, 20% of the existing impervious area to be disturbed shall be considered meadow in good condition.
5. 
For the purpose of calculating pre-development peak discharges and modeling, all existing non-forested pervious areas must be considered meadow in good condition.
6. 
Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious.
7. 
The criteria and assumptions to be used in the determination of stormwater runoff and design of management facilities are as follows:
A. 
Runoff coefficients shall be based on the information contained in Appendices 23-4 or 23-5 if the actual land use is listed in that Appendix. If the actual land use is not listed in Appendices 23-4 or 23-5, runoff coefficients shall be chosen from other published documentation deemed acceptable by the Township, and a copy of said documentation shall be submitted with the stormwater management report. Post-development runoff coefficients for off-site discharges used to design conveyance facilities shall be based on actual land use assuming winter or poor land conditions.
B. 
Times of concentration shall be based on the following design parameters:
(1) 
Sheet Flow. The maximum length for each reach of sheet or overland flow before shallow concentrated or open channel flow develops is 150 feet. Sheet flow may be determined by using Manning's kinematic solution as outlined in Chapter 3 of TR-55, "Urban Hydrology for Small Watersheds."
(2) 
Shallow Concentrated Flow. Guidance for the calculation of travel time for shallow concentrated flow can be found in Figure 3-1 in TR-55, "Urban Hydrology for Small Watersheds."
(3) 
Open Channel Flows. At points where sheet and shallow concentrated flows concentrate in field depressions, swales, gutters, curbs, or pipe collection systems, the travel times and downstream end of the development site between these design points shall be based upon Manning's Equation and/or acceptable engineering design standards as determined by the Township Engineer.
8. 
Hydrographs may be obtained from NRCS methods such as TR-55, TR20, or from use of the "modified" or "unit hydrograph" rational methods. If "modified" or "unit hydrograph" rational methods are used, the ascending leg of the hydrograph shall have a length equal to three times the time of concentration (3xTc) and the descending leg shall have a length equal to seven times the time of concentration (7xTc) to approximate an SCS Type II hydrograph. The Township may require longer time of concentration values or other alternative analysis for rational method hydrographs to realistically evaluate potential runoff volumes from impervious areas and resulting impact to the required stormwater facility storage capacity.
9. 
Runoff calculations shall include a hydrologic and hydraulic analysis indicating volume and velocities of flow and the grades, sizes, and capacities of water carrying structures, sediment basins, retention and detention structures and sufficient design information to construct such facilities. Runoff calculations shall also indicate both pre-development and post-development rates for peak discharge of stormwater runoff from all discharge points.
10. 
Peak rate control is not required for off-site runoff. Off-site runoff may be by-passed around the site provided all other discharge requirements are met. If off-site runoff is routed through rate control facilities, runoff coefficients for off-site discharges used to design those rate control facilities shall be based on actual land use assuming winter or poor land conditions.
[Ord. 2014-04, 4/28/2014, § 23-303]
1. 
All storm sewer pipes, culverts, bridges and stormwater conveyance facilities (excluding BMPs, detention, retention and wetland basin outfall structures), gutters and swales conveying water originating only from within the boundaries of the development site shall be designed for a twenty-five-year storm event (twenty-four-hour SCS Type II storm or an IDF Curve Rational Method storm). All storm sewer pipes, culverts and bridges (excluding detention, retention, and wetland basin outfall structures) conveying water originating from off-site shall be designed for a fifty-year storm event. If in the opinion of the Township Engineer there is potential for damage to property or the loss of life due to the failure of the system to carry flows above the minimum design flows as outlined above, the design storm event shall be increased. Conveyance facilities and associated drainage easements shall be provided to safely contain and convey the one-hundred-year frequency flood to appropriate peak rate control BMPs and throughout the development site. Easements shall begin at the furthest upstream property line of the proposed development site in a watershed.
A. 
Distribution System Requirements.
(1) 
Pretreatment Requirements. The facility shall be designed to provide a method to eliminate solids, sediment, and other debris from entering the subsurface facility.
(2) 
Loading/Balancing. 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.
(3) 
Observation/Access Ports.
(a) 
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.
(b) 
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 municipality shall be provided for access to and monitoring of the facility.
(c) 
The number of access points shall be sufficient to flush, vacuum extract or otherwise clean out the system.
B. 
Materials.
(1) 
Pipe Material. Distribution system piping may be PVC, SLHDPE, or RCP.
(2) 
Stone for Infiltration Beds. The stone used for infiltration beds shall be clean washed, uniformly graded coarse aggregate (AASHTO No. 3 or equivalent approved by the municipality). The void ratio for design shall be assumed to be 0.4. Clean AASHTO No. 57 shall be permitted to be used on the top surface of beds to facilitate improved stability of cover material.
(3) 
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. 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.
(4) 
Lining Material. 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.
C. 
Cover.
(1) 
When located under pavement, the top of the subsurface facility shall be a minimum of three inches below the bottom of pavement subbase.
(2) 
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.
D. 
Subsurface facilities shall be designed to safely convey and/or bypass flows from storms exceeding the design storm. Overflow points shall be strategically positioned to maximize dissipation of flow prior to discharge onto downstream properties.
2. 
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.
A. 
Design Criteria. Conveyance facilities shall comply with the design criteria in the following table:
Conveyance Facility Design Criteria
Location
Within Public Street Right-of-Way or Property Intended for Dedication
Outside Public Street Right-of-Way
Loading
All
Vehicular Loading
Non-Vehicular Loading
(1)
Pipe design
(a)
Material
SLHDPE, RCP
PVC, SLHDPE, RCP
PVC, SLHDPE, RCP
(b)
Slope (minimum)
0.5%
0.5%
0.5%
(c)
Cover
1 foot to stone subgrade
1 foot to stone subgrade
1 foot to surface
(d)
Diameter (minimum)
15 inches
15 inches
8 inches
(e)
Street crossing angle
75° to 90°
N/A
N/A
(f)
Access/ maintenance port frequency (maximum)
400 feet
400 feet
600 feet
(2)
Inlet design
(a)
Material
Concrete
Concrete
Concrete, HDPE (when permitted by Township)
(b)
Grate depression
2 inches
2 inches
1 inch minimum
(3)
Manhole design
(a)
Material
Concrete
Concrete
Concrete
(4)
Swale design
(a)
Freeboard (minimum)
6 inches
N/A
6 inches
(b)
Velocity (maximum)
Stability check
N/A
Stability check
(c)
Slope (minimum)
1%
N/A
1%
(d)
Side slopes (residential area)
4:1 max
N/A
4:1 max
(e)
Side slopes (nonresidential area)
4:1 max
N/A
3:1 max
(f)
Bottom width to flow depth ratio
12:1
N/A
12:1
(5)
Outlet design
(a)
End treatment
Headwall/ endwall
N/A
Headwall/ endwall or flared end section
(b)
Energy dissipater
Required
N/A
Required
N/A = Not applicable or no criteria specified
HDPE = High density polyethylene
SLHDPE = Smooth lined high density polyethylene pipe
PVC = Polyvinyl chloride
RCP = Reinforced concrete pipe
B. 
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 and PennDOT Form 408, latest editions. Conveyance pipes, culverts, manholes, inlets and endwalls which are otherwise subject to vehicular loading shall be designed for the HS-25 loading condition.
C. 
Conveyance Pipes.
(1) 
Backfill Material Requirements. 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.
(2) 
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 unless specifically authorized by the Township.
(3) 
Access/Maintenance Ports. An access/maintenance port is required may either be an inlet or manhole.
(4) 
Watertight joints shall be provided where pipe sections are joined, except for perforated pipe installed as pavement base drain.
(5) 
The street crossing angle shall be measured between the pipe centerline and the street centerline.
(6) 
Elliptical pipe of an equivalent cross-sectional area may be substituted in lieu of circular pipe where cover or utility conflict conditions exist. Dual or multiple parallel pipe installations are not permitted.
(7) 
The roughness coefficient (Manning "n" values) used for conveyance pipe capacity calculations should be determined in accordance with PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's specifications.
D. 
Inlets.
(1) 
All pipes must enter inlets completely through one of the sides. No corner entry of pipes is permitted.
(2) 
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.
(3) 
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.
(4) 
Curbed Streets.
(a) 
Inlets in streets shall be located along the curb line at or beyond the curb radius points.
(b) 
Top units shall be PennDOT Type "C." The hood shall be aligned with the adjacent curb height.
(5) 
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 stormwater management plan or inlet details therein.
(6) 
Inlets, junction boxes, or manholes greater than five feet in depth shall be equipped with ladder rungs and shall be detailed on the stormwater management plan.
(7) 
Inlet capacity shall be based on design data provided by the manufacturers and accepted by the Township. Where ponding occurs, inlet capacity shall be based on accepted engineering design practices.
E. 
Swales.
(1) 
Inlets within swales shall have PennDOT Type "M" top units or equivalent approved by the Township Engineer.
(2) 
Swale capacities shall be computed using the Manning equation using the following design parameters:
(a) 
Vegetated Swales.
1) 
Flow capacity for all swales shall be based on a Manning's "n" value of 0.05. Maximum velocities shall be based on a Manning's "n" value of 0.03. Allowable velocities shall be as outlined in the E&S Manual.
2) 
All vegetated swales shall have a minimum slope of 1% unless otherwise approved by the Township Engineer.
(b) 
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 Township Engineer.
(3) 
All swales shall be designed to maximize infiltration and concentrate low flows to minimize siltation and meandering, unless geotechnical conditions do not permit infiltration.
F. 
Culverts. 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. Culverts shall be evaluated for both inlet and outlet control.
G. 
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.
H. 
Energy Dissipaters.
(1) 
Energy dissipaters shall be designed in accordance with the requirements in the E&S Manual.
(2) 
Flow velocities from any storm sewer may not result in a deflection of the receiving channel.
I. 
End Treatments.
(1) 
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.
(2) 
Headwalls and endwalls shall be constructed of concrete.
(3) 
Flared end sections may be used in special cases at the discretion of the Township, and shall be of the same material as the connecting pipe and be designed for the size of the connecting pipe.
3. 
The proposed design discharge at the perimeter of the development site shall not be beyond the capacity of the existing storm sewer system into which it flows.
4. 
All existing and natural watercourses (including associated floodplains), channels, drainage systems and areas of surface water concentration shall be maintained in their existing condition unless an improvement alteration is approved by the Township. If existing conditions currently function in an erosive state, improvements shall be required as part of the overall site improvements.
5. 
Where proposed development is to be performed in phases, each phase of the project shall be designed to accommodate the full development of the project. If temporary facilities are required to properly implement the development of a phase, the design and construction of such facilities shall be included within the appropriate phase. In the event temporary facilities cannot adequately handle the stormwater runoff, proposed stormwater management facilities of future phases of development shall be incorporated within the current phase of development as necessary to adequately handle the runoff from the current phase of development.
[Ord. 2014-04, 4/28/2014, § 23-304]
1. 
Above-Ground Storage Facilities. Above-ground 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. Above ground storage facilities are located above the finished ground elevation. Above ground storage facilities do not include stormwater management facilities designed for conveyance or cisterns.
A. 
Design Criteria. Above ground storage facilities shall comply with the design criteria in the following table:
Above-Ground Storage Facility Design Criteria
Facility Depth
Less Than 2 Feet
2 feet to 8 feet
Greater Than 8 feet
(1)
Embankment Geometry
(a)
Top width (minimum)
2 feet
5 feet
8 feet
(b)
Interior side slope (maximum)
2:1
3:1
5:1
(c)
Exterior side slope (maximum)
2:1
3:1
3:1
(2)
Embankment construction
(a)
Key trench
Not required
Required
Required
(b)
Pipe collar
Not required
Required
Required
(c)
Compaction density
Not required
Required
Required
(3)
Internal Construction
(a)
Dewatering feature
N/A
Required
Required
(b)
Pretreatment elements
Not required*
Required
Required
(4)
Outlet Structure
(a)
Pipe size (minimum)
6 inches
12 inches
15 inches
(b)
Pipe material
SLHDPE, PVC, RCP
SLHDPE, RCP
RCP
(c)
Anticlogging devices
Required
Required
Required
(d)
Antivortex design
Not required
Required
Required
(e)
Watertight joints in piping
Yes
Yes
Yes
(5)
Spillway Requirements
(a)
Spillway freeboard (minimum)
Not required
3 inches
6 inches
(b)
Width (minimum)
Not required
10 feet
20 feet
(c)
Width (maximum)
Not required
50 feet
50 feet
(d)
Spillway channel design
Not required
Required
Required
(e)
Routing of one-hundred-year storm
Permitted
Permitted
Permitted
*
Pretreatment required for infiltration BMPs unless shown to be unnecessary.
N/A = Not applicable
SLHDPE = Smooth lined high density polyethylene pipe; PVC = Polyvinyl chloride;
RCP = Reinforced concrete pipe
B. 
Facility Depth.
(1) 
For the purposes of the design criteria, the facility depth is defined to be the depth between the bottom invert of the lowest orifice and the invert of the spillway. If there is no spillway, the top of the berm shall be used. For basins with no orifices or outlet structure, the bottom elevation of the basin shall be used.
(2) 
Facilities with a facility depth greater than eight feet shall not be permitted in residential areas.
(3) 
Facilities with a facility depth greater than 15 feet require a dam permit from DEP.
C. 
Embankment Construction.
(1) 
Impervious Core/Key Trench. 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 to the satisfaction of the Township.
(a) 
Materials. 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.
(b) 
Dimensions.
1) 
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.
2) 
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.
3) 
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.
(c) 
Compaction.
1) 
Compaction requirements shall be the same as those for the embankment to assure maximum density and minimum permeability.
2) 
The core shall be constructed concurrently with the outer shell of the embankment.
3) 
The trench shall be dewatered during backfilling and compaction operations.
(2) 
Pipe Collars. All pipe collars, when required, shall be designed in accordance with Chapter 7 of the E&S Manual. The material shall consist of concrete or otherwise non-degradable material around the outfall barrel and shall be watertight.
(3) 
Embankment Fill Material. The completed structure and the foundation of all embankments shall be stable under all probable conditions of operation. The embankment fill material shall be taken from an appropriate on- or off-site borrow area which shall be free of roots, stumps, wood, rubbish, stones greater than six inches, frozen or other objectionable materials.
(4) 
Embankment Compaction. 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 (two-thirds 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. For berms six feet or greater, compaction testing may be required.
D. 
Internal Construction.
(1) 
Bottom Slope. The minimum bottom slope of facilities not designed for infiltration shall be one-percent. A flatter slope may be used if an equivalent dewatering mechanism is provided.
(2) 
Dewatering Features. When required, dewatering shall be provided through the use of underdrain, surface device, or alternate approved by the Township 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 time frame.
(3) 
Pretreatment Elements. When required, pretreatment elements shall consist of forebays, or alternate approved by the Township Engineer, to keep silt to a smaller portion of the facility for ease of maintenance.
(4) 
Infiltration Basins. 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 § 301.25. and the BMP Manual which is designed to promote infiltration.
E. 
Outlet Configuration.
(1) 
For facilities with a depth of two feet or greater, a type D-W endwall or riser box outlet structure shall be provided.
(2) 
For facilities with a depth less than two feet, no outlet structure is required. A protective concrete collar may be required.
(3) 
All discharge control devices with appurtenances shall be made of reinforced concrete and stainless steel. Bolts/fasteners shall be stainless steel.
(4) 
All outlet structures and emergency spillways shall include a satisfactory means of dissipating the energy of flow at its outlet to assure conveyance of flow without endangering the safety and integrity of the basin and the downstream drainage area.
F. 
Spillway.
(1) 
Material. The spillway shall be designed to provide a non-erosive, stable condition when the project is completed. Special consideration shall be given to protection of emergency spillways located in filled areas.
(2) 
Non-emergency Use. Use of the spillway to convey flows greater than the fifty-year design storm is permitted.
(3) 
Emergency Use. The spillway shall be designed to convey the one-hundred-year post-development peak inflow.
(4) 
When required, freeboard shall be measured from the top of the water surface elevation for emergency use.
G. 
Breach Analysis. The municipality 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 municipality.
2. 
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.
A. 
Design Criteria. Subsurface storage facilities shall comply with the design criteria in the following table:
Subsurface Storage Facility Design Criteria
Facility Type
Infiltration and Storage
Storage Without Infiltration
(1)
Facility Geometry
(a)
Depth from surface (maximum)
2 feet less than limiting zone
N/A
(b)
Loading ratio (maximum)
Per BMP Manual*
N/A
(2)
Distribution System Requirements
(a)
Pipe size (minimum)
4 inches
4 inches
(b)
Pretreatment
Required
Required
(c)
Loading/balancing
Required
Not required
(d)
Observation/access ports
Required
Required
*
Unless otherwise determined by professional geologic evaluation.
3. 
Stormwater management 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:
A. 
Stormwater management 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.
B. 
Additional requirements and analysis may be required by the Township to prove that the proposed facility has been designed to limit the potential risk to the life, safety or welfare of the general public.
[Ord. 2014-04, 4/28/2014, § 23-305]
1. 
All earthmoving activities shall be conducted in such a way as to minimize accelerated erosion and resulting sediment pollution. Measures to control erosion and sediment pollution shall, at a minimum, meet the standards of the Conservation District, Chapter 102, and concerns identified by the Township.
2. 
The erosion and sediment pollution control plan must be available at all times at the project site. When required, a permit allowing earthmoving activity shall be obtained by the applicant before any construction on the development site shall begin.
3. 
Approval of an erosion and sediment pollution control plan by the Township shall not be construed as an indication that the plan complies with the standards of any agency of the Commonwealth.
4. 
The erosion and sediment pollution control plan shall be submitted to the Conservation District for its review and approval with copies of materials submitted also provided to the Township and Township Engineer. A copy of the approval shall be provided to the Township prior to unconditional final plan approval.
[Ord. 2014-04, 4/28/2014, § 23-306]
No development or earthmoving activities shall involve uses, activities or improvements which would entail encroachment into, the regrading of, or the placement of fill in wetlands in violation of state or federal regulations.
[Ord. 2014-04, 4/28/2014, § 23-307]
1. 
The applicant shall reserve easements where stormwater management facilities, floodplains or wetlands are existing or proposed, whether located within or beyond the boundaries of the project site. If stormwater management facilities, floodplains or wetlands are to be installed or created beyond the boundary of the property, the applicant shall provide the Township with all necessary easements, in a form acceptable to the Township Solicitor, clearly demonstrating that the applicant has the right to install and maintain stormwater management facilities on such property and/or create floodplains or wetlands upon such property.
2. 
Easements shall have a minimum width of 20 feet or 30 feet when in close proximity to structures and shall be adequately designed to provide area for (A) the collection and discharge of water, (B) the maintenance, repair and reconstruction of all stormwater management facilities, (C) the passage of machinery for such work, and (D) the preservation of floodplains, riparian buffers and wetlands. The easements shall clearly identify who has the right of access and the responsibility of maintenance.
3. 
Stormwater management facilities shall be centered within the easement.
4. 
To the fullest extent possible, easements shall be centered on or be adjacent to lot lines. Where the Township has concerns about shared ownership and/or maintenance responsibilities, facilities and easements may not be allowed to be centered on property lines.
5. 
Nothing shall be placed, planted, set, or put within the area of an easement that would adversely affect the function of the facility within the easement or conflict with the easement agreement.
[Ord. 2014-04, 4/28/2014, § 23-308]
1. 
Volume control BMPs are intended to maintain existing hydrologic conditions for small storm events by promoting groundwater recharge and/or evapotranspiration as described in this section. Runoff volume controls shall be implemented using the Design Storm Method described in Subsection 1A below, or through continuous modeling approaches or other means as described in the BMP Manual. Small projects may use the method described in Subsection 1B to design volume control BMPs.
A. 
The Design Storm Method is applicable to any size of regulated activity and requires detailed modeling based on site conditions.
(1) 
There shall be no increase in the post development total runoff volume for all storms equal to or less than the two-year twenty-four-hour storm event.
(2) 
The maximum loading ratio for volume control facilities in Karst areas shall be 3:1 impervious drainage area to infiltration area and 5:1 total drainage area to infiltration area. The maximum loading ratio for volume control facilities in non-Karst areas shall be 5:1 impervious drainage area to infiltration area and 8:1 total drainage area to infiltration area. A higher ratio may be approved by the municipality if adequate justification is provided. Hydraulic depth may be used as an alternative to an area based loading ratio if the design hydraulic depth is shown to be less than the depth that could result from the maximum area loading ratio.
(3) 
In carbonate geology, a detailed geologic evaluation of the development site shall be performed to determine the design parameters of recharge facilities. The evaluation shall be performed by a registered professional geologist in accordance with other applicable sections of this chapter, and shall address loading rates, soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability, etc.
B. 
Volume Control for Small Projects. At least the first three inches of runoff from new impervious surfaces or an equivalent volume shall be permanently removed from the runoff flow (i.e., it shall not be released into the surface waters of the Commonwealth). Removal options include reuse, evaporation, transpiration and infiltration.
C. 
Storage facilities, including normally dry, open top facilities, shall completely drain the volume control storage over a period of time not less than 24 hours and not more than 72 hours from the end of the design storm. Any designed infiltration at such facilities is exempt from the minimum twenty-four-hour standard, i.e. may infiltrate in a shorter period of time, provided that none of this water will be discharged into waters of this Commonwealth.
D. 
Subregional (Combined Development Site) Storage. Runoff can be managed regionally by one or more applicants, either on-site or off-site when deemed acceptable by the Township. The design and release rate shall be consistent with this chapter.
E. 
Infiltration Design Standards.
(1) 
If more than one hydrologic soil group (HSG) is present at a development site, a composite recharge volume shall be computed based upon the proportion of total development site area within each HSG.
(2) 
Infiltration BMPs intended to receive runoff from developed areas shall be selected based on suitability of soils and development site conditions and shall be constructed on soils that have the following characteristics:
(a) 
A minimum depth of 48 inches between the bottom of the facility and the seasonal high water table and/or bedrock (limiting zones) may be required by the Township when concerns regarding the quality of runoff exist or in close proximity of water supply sources.
(b) 
An infiltration and/or percolation rate sufficient to accept the additional stormwater load and drain completely as determined by field tests conducted by the applicant's professional designer at the location and elevation of the proposed facility.
(3) 
Infiltration BMPs require a minimum depth of suitable soil of 24 inches between the bottom of the facility and the limiting zone.
(4) 
The recharge volume provided at the development site shall be directed to the most permeable HSG available.
[Ord. 2014-04, 4/28/2014, § 23-309]
1. 
In order to protect and improve water quality, a riparian corridor easement shall be created and recorded as part of any subdivision or land development that encompasses a riparian corridor.
2. 
The minimum riparian corridor easement shall extend to the widths identified in the Zoning Ordinance [Chapter 27], as amended, and encompass the entire one-hundred-year floodplain and adjacent wetland area as applicable, excepted when exceeded by the requirements of Chapter 102.
3. 
Minimum Management Requirements for Riparian Corridors.
A. 
Existing native vegetation shall be protected and maintained within the riparian corridor easement.
B. 
Whenever practicable, invasive vegetation shall be actively removed and the riparian corridor easement shall be planted with native trees, shrubs and other vegetation to create a diverse native plant community appropriate to the intended ecological context of the site.
4. 
The riparian corridor easement shall be enforceable by the Township and shall be recorded in the Lancaster 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 the continued private ownership and shall count toward the minimum lot area as required by the Zoning Ordinance [Chapter 27], unless otherwise specified.
5. 
Any permitted use within the riparian corridor easement shall be conducted in a manner that will maintain the extent of the existing ten-year floodplain, improve or maintain the stream stability, and preserve and protect the ecological function of the floodplain.
6. 
The following conditions shall apply when public and/or private recreation trails are permitted within riparian corridors:
A. 
Trails shall be for non-motorized use only.
B. 
Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.
7. 
Septic drainfields and sewage disposal systems shall not be permitted within the riparian corridor easement and shall comply with the most restrictive of the setback requirements established under 25 Pa.Code, Chapter 73, and in the Zoning Ordinance [Chapter 27].