A. 
Storm sewers, culverts, endwalls, inlets and related installations and improvements shall be provided in order to:
(1) 
Permit unimpeded flow of natural watercourses;
(2) 
Ensure adequate drainage of all streets including all low points;
(3) 
Intercept stormwater runoff along streets at intervals related to the extent and grade of the area drained;
(4) 
Provide positive drainage away from on-site sewage disposal facilities and buildings;
(5) 
Accommodate runoff so that there shall be no increase in rate of stormwater peak discharge leaving the subdivision or land development during or after construction based on the required release rates established in this chapter, except as allowed by the chapter;
(6) 
Ensure adequate drainage at intersections of driveways with streets;
(7) 
Provide that where existing storm sewers are reasonably accessible and of adequate capacity, subdivisions and land developments shall connect to the existing storm sewers;
(8) 
Provide that when no existing storm sewer is accessible and of adequate capacity, stormwater shall discharge to an existing watercourse with defined bed and barriers. Runoff shall not be increased or concentrated onto adjacent properties, nor the velocity of flow increased beyond that existing prior to subdivision or land development unless written approval is given by the adjacent property owners for the proposed discharge of surface runoff and the written agreements are approved by the Township;
(9) 
Provide that when storm drainage will be directed into an adjacent municipality, all provisions for accommodating such storm drainage shall be submitted to the governing body of that municipality for review.
B. 
Any proposed storm drainage plans which affect the drainage basin of any river or stream shall be approved by the Division of Dams & Waterway Management of the Pennsylvania Department of Environmental Protection if the affected drainage area is more than 100 acres.
A. 
Complete stormwater calculations shall be prepared in accordance with the design standards and appendixes of this chapter. All designs for drainage facilities shall be submitted to the Township for review and approval.
B. 
Where a subdivision or land development is traversed by or contains a pond, lake, watercourse, drainage way, channel, storm drainage system, or stream, a drainage easement shall be provided in accordance with § 138-7D of this chapter. The minimum easement width shall be 10 feet from each side of the watercourse, waterbody, stream, pond, lake or drainage facility, but the Township may require a greater easement when necessary. When required by the Township, bearings and distances shall be provided to define the boundaries of the easements.
C. 
Any changes in an existing drainage way shall be subject to the approval of the Pennsylvania Department of Environmental Protection; the Army Corps of Engineers; or the Federal Emergency Management Agency when each or all have jurisdiction. All permits and approvals shall be issued prior to construction of storm drainage related improvements.
D. 
The developer shall properly grade and seed slopes, and fence open ditches when a safety hazard can result. Areas within easements shall be kept as lawn or in natural conditions to allow maintenance and entrance.
E. 
All drainage facilities shall be designed to adequately handle surface runoff and carry it to suitable outlets and shall be designed in accordance with the minimum design standards established by this chapter.
F. 
Storm sewers, culverts, swales, channels, and related facilities shall be designed to accommodate and discharge all runoff from adjacent upstream drainage areas, assuming the upstream area is fully developed.
G. 
Flood protection. No stormwater runoff or natural drainage water shall be so diverted as to overload existing drainage systems, or create flooding or the need for additional drainage structures on other private properties or public lands, without proper and approved provisions being made for taking care of these conditions.
H. 
Scour and erosion prevention. In areas in which street curbs are not required by any ordinance of the Township, drainage may be accomplished by natural or artificial swales and culverts. Special structures such as check dams, drop-outlets, or other energy dissipating structures or riprap may be required to prevent scour or erosion in locations with large runoff quantities or steep slopes. In no case may a change be made in the existing topography which would result in a slope exceeding the normal angle of slippage or the material involved. No paved swales will be allowed without the approval of the Township.
I. 
Fixed pipe collection system. The Township may require a fixed pipe collection system with catch basins. Such fixed pipe collection system with catch basins shall be used in all areas with street curbs and gutters, when required. The Township may require foundation pipe underdrains.
J. 
Low point drainage. Developer shall grade and install all necessary drainage facilities to insure the drainage of all low points on subdivided lots or within the subdivision or developed land areas.
A. 
General requirements.
(1) 
Where retention (permanent pool) and detention (dry bottom) basins are required by the Township, adequate assurances of maintenance, indemnification, liability insurance, and security shall be provided and approved by the Township.
(2) 
Retention and detention facilities shall be designed and located so as to not present a hazard to the public health or safety. Their design shall be approved by the Township.
(3) 
Such facilities shall be designed so that no adverse effects will result from backwater flooding.
B. 
General design considerations.
(1) 
The required volume for stormwater detention or retention shall be calculated to reduce the increased rate of runoff caused by development of the property as established by this chapter. The volume of storage shall be provided for the tributary watershed within the subdivision or land development in a fully developed state and the tributary watershed outside the subdivision or land development assuming it is fully developed per the current zoning requirements.
(2) 
The number and location of detention facilities are subject to the approval of the Township.
(3) 
The detention facilities shall be designed to retard stormwater runoff rates after development to the peak runoff rate established for each district in § 138-8 and as depicted on the applicable release rate map per the Act 167 Watershed Plan.
(4) 
All land within the subdivision which are farm fields shall be considered as pasture with good ground cover.
C. 
Specific design considerations.
(1) 
Detention basins shall meet the following restrictions to minimize the negative visual impact, to prevent hazard to public health and safety and to avoid the need for fencing:
(a) 
Maximum depth of detained runoff shall be 24 inches for a ten-year storm event; and
(b) 
Maximum depth of detained runoff shall be 36 inches for a one-hundred-year storm event; and
(c) 
Interior slopes shall not be steeper than a ratio of 4:1 horizontal to vertical; and
(d) 
A water surface limit shall be no closer than 100 feet to any residential building and no closer than 25 feet to any other type of building.
(2) 
These depths may be exceeded by permission of the Board of Supervisors of the Township, on a case-by-case basis if lot runoff, topography and/or existing downstream systems make the required pond area unreasonable large. In such a case, a deeper depth may be allowed if the basin is designed to the following specifications:
(a) 
A maximum depth of detained runoff shall be 24 inches for a two-year storm event; and
(b) 
A maximum depth of detained runoff shall be 36 inches for a ten-year storm event; and
(c) 
A maximum depth of detained runoff shall be 48 inches for a one-hundred-year storm event; and
(d) 
Interior side slopes shall not be steeper than a ratio of 5:1, horizontal to vertical; and
(e) 
A water surface limit no closer than 100 feet to any residential building and no closer than 25 feet to any other type building.
(3) 
If the maximum water depths as stipulated in Subsection C(1) and (2) above are exceeded, a four-foot-high chain link fence is required around the detention ponds. The fence shall be landscaped from adjacent streets and properties. A fenced detention pond shall have a maximum berm outside side slope of 4:1.
[Amended 3-8-2016 by Ord. No. 2015-14]
(a) 
In the PRRC zone, Subsection C(1) and (2) may apply, but the Board of Supervisors may allow depths in excess of those identified in Subsection C(2). In the PRRC zone, all detention ponds shall incorporate a decorative four-foot-high post-and-rail fence with mesh backing. A fenced detention pond shall have a maximum berm outside slope of 3:1 and inside slope of 4:1.
(4) 
An access ramp of 10:1, 10 feet wide, shall be provided to allow maintenance equipment to reach the basin floor of detention basins.
(5) 
The minimum slope of the bottom of a detention basin shall be 2%. In the PRRC zone, ponds incorporating an infiltration function shall be exempt from this requirement.
[Amended 3-8-2016 by Ord. No. 2015-14]
(6) 
If percolation of runoff is considered as a method of runoff abatement, percolation tests shall be taken at the site of proposed detention facilities and the results submitted to the Township for review.
(7) 
All detention/retention facilities utilized in areas of limestone geology, whether ultimately privately or publicly owned, except facilities including an infiltration function, shall be lined with a synthetic impervious liner meeting the following requirements:
[Amended 3-8-2016 by Ord. No. 2015-14]
(a) 
The minimum liner allowed is 30 mil PVC. Actual individual liner specifications shall be provided by the manufacturer for each individual pond.
(b) 
The liner must be placed on a layer of fine-grained soil that has been rolled with a smooth drum roller in both directions to produce a smooth level base for the liner. The soil may not contain sharp angular rock or other debris which could puncture the liner, and must meet all manufacturer’s specifications for a liner bedding. All vegetation, roots, and grass must be removed and any cracks or voids shall be filled.
(c) 
If rock is encountered in the bedding area, this rock must be excavated to a depth of six inches below the liner and backfilled with a fine-grained soil. This area should then be covered with geotextile fabric, extending three feet beyond the limits of the rock outcrop before placing the pond liner.
(d) 
Installation of the liner may only take place when the ambient temperature is within the manufacturer’s recommended range. Installation and testing shall be in accordance with manufacturer’s specifications. The number of field seams shall be minimized by requiring factory fabrication of large panels. Any field seams performed must be in accordance with the manufacturer’s specifications.
(e) 
All structures (i.e., headwalls, pipes, outlet structures) which come in contact with the liner must have a waterproof seal installed to prevent leaks around the structure. These seals shall be installed per manufacturer’s recommendations.
(f) 
A minimum of 12 inches of earth cover shall be placed over the lining. Soil containing sharp jagged rocks, roots, debris, or any other material which may puncture the liner shall not be used as cover material.
(g) 
The liner must be installed to a minimum height of the one-hundred-year flood water elevation in the facility.
(8) 
Every stormwater storage area shall be provided with an emergency spillway in accordance with § 138-10C. The spillway shall either be placed in undisturbed earth or be of concrete construction and shall be designed to function without attention.
(9) 
Paved surfaces that are to serve as stormwater storage areas shall have minimum grades of 0.5% and shall be restricted to storage depths of 1/2 foot maximum.
(10) 
If a portion of an area within a stormwater storage area is to be paved for parking or recreation purposes, the paved surface shall be placed at the highest elevation within the storage area as possible.
(11) 
The following additional conditions shall be complied with for wet bottom stormwater storage areas:
(a) 
Water surface area shall not exceed 1/10 of the tributary drainage area.
(b) 
Shoreline protection shall be provided to prevent erosion from wave action.
(c) 
Minimum normal water depth shall be four feet. If fish are to be used to keep the pond clean, a minimum of 1/4 of the pond area shall be a minimum of 10 feet deep.
(d) 
Facilities shall be provided to allow the pond level to be lowered by gravity flow for cleaning purposes and shoreline maintenance.
(e) 
Aeration facilities as may be required to prevent pond stagnation shall be provided. Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Township.
(f) 
In the event that the water surface of the pond is to be raised for the purposes of storing water for irrigation or in anticipation of the evapotranspiration demands of dry weather, the volume remaining for storage of excess stormwater runoff shall still be sufficient to contain the design year storm runoff.
(12) 
Retention and/or detention basins which are designed with earth fill dams shall incorporate the following minimum standards:
(a) 
The height of berm shall not exceed 15 feet, unless approved by the Township.
(b) 
The minimum top width of berms up to 15 feet in height shall be equal to three-fourths of the dam height, but in no case shall the top width be less than eight feet.
(c) 
A key trench shall be provided under all berms. The key trench shall be at least two feet deep, or extend down to stable subgrade, whichever is deeper. Minimum bottom widths for the cutoff trench and key trench shall be four feet. Maximum side slopes for key trenches shall be one horizontal to one vertical. A compacted impervious core at least three feet wide at the top, having a maximum side slope of one horizontal to one vertical, shall extend for the full length of the embankment, and the top elevation shall be set at the ten-year design water surface elevation.
(d) 
All pipes and culverts through berms shall have properly spaced concrete cutoff collars or factory welded anti-seep collars.
A. 
All streets shall be designed to provide for the discharge of surface water from their rights-of-way.
B. 
Unless a more conservative design is required by another regulation, or is required because of conditions particular to an individual development, the design storm for fixed pipe systems shall be a ten-year frequency for residential subdivisions with a gross density less than six units per acre, and a twenty-five-year frequency for all other subdivisions, land developments or crossings of any road through culverts. In all instances listed above, total conveyance systems shall be provided to carry the one-hundred-year design storm to the detention basin or drainage facility.
C. 
The pavement cross slope on streets shall not be less than 1/4 inch per foot and not more than 1/2 inch per foot. The slope of the shoulder areas shall not be less than 3/4 inch per foot and not more than one inch per foot.
D. 
Surface cross drainage at intersections or other roadway sections will not be permitted.
E. 
Inlets shall be spaced to limit the gutter flow spread into the travel lanes to 1/2 the lane width during the design storm.
F. 
Inlet efficiency and bypass flows, per PennDOT design charts, shall be considered in the design of storm sewer systems.
A. 
The collection system shall be designed by the Rational Method of Design in accordance with American Society of Civil Engineers Manual No. 37 except where noted, using the formula Q = CiA, unless otherwise approved by the Township.
(1) 
Capacity. "Q" is the required capacity in cubic feet per second for the collection system at the point of design.
(2) 
Runoff coefficient. "C" is the runoff coefficient applicable to the entire drainage area. It shall be based on consideration of soil conditions, slope of the drainage area and the ultimate development of the entire drainage area according to comprehensive plans. For the various types of ultimate development, the runoff coefficient shall be taken from the appropriate table in Appendix C,[1] unless sufficient engineering data has been presented to the Township Engineer by the Developer which information in the judgment of the Township Engineer and the Board of Supervisors is sufficient to warrant the use of an alternate runoff coefficient.
(3) 
Rainfall intensity formula. "i" is the rainfall intensity in inches per hour and shall be determined from rainfall intensity charts for this area, based on time of concentrations, including Overland Flow Time, Mannings Formula for channelized flow time and pipe flow time. The design rainfall frequency shall be taken from the PennDOT Intensity-Duration-Frequency Field Manual, Region 4, as presented in Appendix C.
(4) 
Drainage area. "A" is the drainage area, in acres, tributary to the point of design, and shall include areas tributary from outside sources as well as from within the subdivision or developed land area itself.
B. 
The collection system shall be designed and installed in accordance with the design standards and requirements set forth in this chapter, the Township, the Township Engineer and as follows:
(1) 
Subsurface drainage systems shall have accessible manholes spaced at intervals not exceeding 300 feet and shall be located wherever branches are connected or sizes are changed and wherever there is a change in alignment or grade. Inlets or other means of interconnection may be used instead of manholes when approved by the Township, or as required for curbed streets.
(2) 
For drainage lines of 36 inches in diameter or greater, manholes may be spaced at intervals no greater than 400 feet with the approval of the Township.
(3) 
On curbed streets, inlets shall be placed at points of abrupt changes in the horizontal or vertical directions of storm sewers, at curb tangents on uphill side of street intersections, at a maximum distances as specified in accordance with the required pipe size, and to limit gutter flow as required. The Manning Equation shall be used to calculate the capacities of gutters. Pennsylvania Department of Transportation inlets should be used in accordance with the design procedures outlined in PennDOT Design Manual, Part 2. Manholes may be substituted for inlets at locations where inlets are not required to handle surface runoff.
(4) 
Inlets shall be designed and located to prevent hazards to vehicles, bicycles, and pedestrians.
(5) 
Storm sewer lines, within street rights-of-way, shall be located between the center line of the street and the curbline, and shall parallel the center line of the street as far as practical.
(6) 
Drainage structures that are to be located within state highway rights-of-way shall be approved by the Pennsylvania Department of Transportation, and a letter from that Department indicating such approval shall be submitted to the Township.
(7) 
Storm sewers shall have a minimum diameter of 15 inches.
(8) 
Storm drains shall be designed to produce a minimum velocity of 3.0 feet per second when flowing full and shall not be designed or installed at less than a 0.5% slope. The maximum permissible velocity shall be 15.0 feet per second.
(9) 
Reinforced concrete pipe shall be used for all storm sewer lines, including retention/detention facilities. Smooth-lined high-density polyethylene pipe with watertight joints may be used subject to review by the Township Engineer. All pipe materials shall meet PennDOT requirements. Storm sewers shall have a minimum diameter of 15 inches. The Manning Equation shall be employed in computing pipe capacities. Sewers shall be installed on sufficient slopes to provide a minimum velocity of three feet per second when flowing full.
[Amended 6-14-2011 by Ord. No. 2011-1]
(10) 
PennDOT approved endwalls or end sections shall be used in lieu of inlets where feasible to minimize clogging of grates with leaves, debris, etc.
(11) 
Headwalls shall be used where storm runoff enters the storm sewer horizontally from a natural or man-made channel. The capacity of such storm sewers shall be evaluated using both Mannings Equation and inlet/outlet control procedures. The lower flow derived from these two procedures shall be the design capacity of the storm sewer.
(12) 
Provisions shall be made to minimize erosion within watercourses and at points of discharge from storm drainage facilities through the use of proper ground cover. Any riprap swale area shall be constructed with mixed stone sizes in accordance with PennDOT criteria for riprap and shall be lined with PennDOT approved geotextile fabric.
(13) 
Roof drainage. Stormwater roof drains and pipes shall not discharge water directly over a sidewalk, driveway or paved area. Roof drains may be connected to a storm drain system.
[Amended 3-8-2016 by Ord. No. 2015-14]
(14) 
Open swales shall be designed on the basis of the Manning Formula as indicated for collection systems with the following considerations:
(a) 
Roughness coefficient. The roughness coefficient shall be 0.040 for earth swales and 0.015 for paved swales.
(b) 
Bank slopes. Slopes for swale banks shall not be steeper than one vertical for three horizontal.
(c) 
Flow velocity. Design velocity in grass or vegetated swales shall not exceed four feet per second.
(d) 
Right-of-way. A swale right-of-way of sufficient minimum width to include a ten-foot access strip in addition to the width of the swale from bank top, shall be shown as an easement for drainage purposes. The Township may, under unusual conditions, require a wider swale right-of-way.
(15) 
Discharge structures shall be designed to minimize the impact of development on downstream properties. Flow retarding and dissipating facilities are required to meet this goal. Such structures shall be no closer than 20 feet to downstream, off-site properties or drainage easement boundaries.
(16) 
Open pipe ends must be fitted with concrete end walls or wing walls.
(17) 
All pipe endwalls or wingwalls and all detention basin intake and discharge structures shall be protected from frost related movement and scour activity by the construction of a concrete footer with a minimum depth of 30 inches below ground level.
(18) 
Trash racks shall be placed on all stormwater entrance structures.
C. 
Materials and construction requirements shall be as specified by the Township, the Township Engineer and as follows:
(1) 
Pipe materials.
(a) 
All pipe materials shall be reinforced cement concrete pipe, Class III, and shall comply with PennDOT SP 408, Section 601.
(b) 
Joints for concrete pipe shall be of the "O" Ring Type III per current ASTM Specifications C425 or mortared type as approved.
(c) 
If the use of smooth-lined high density polyethylene pipe is approved by the Township, pipe shall be provided with watertight joints meeting all PennDOT requirements.
(2) 
Manholes and inlets shall be equivalent to PennDOT design standards.
(3) 
Manhole frames and covers must be heavy duty, have a minimum clear opening of 24 inches, and be equal to Neenah Foundry Co. Model P-1030 or Campbell Foundry Co. Pattern 1004 and shall have the words "storm sewer" cast thereon in letters two inches high.
(4) 
Appropriate safety grates shall be attached to all catch basins, stormwater inlets, pipe openings and other stormwater receiving structures, as needed, to ensure that maximum openings do not exceed 25 square inches. Along streets and pedestrian areas, safety grates shall be used as needed for bicycle safety.
D. 
Installation.
(1) 
All pipe laying shall carefully progress uphill with hubs upgrade and ends fully and closely jointed. Trench widths shall not exceed the outside diameter of the pipe plus 16 inches and depths shall be as required. Trench walls shall be vertical and bottoms shall be horizontal.
(2) 
Prior to laying the pipe in the trench, a bedding of Class B fine aggregate shall be placed on the trench bottom in accordance with PennDOT Publication 408. This material shall be a minimum of four inches in depth and thoroughly compacted with approved mechanical tampers. The bedding shall be graded by hand to provide a uniform and continuous bearing support for the pipe throughout its entire length.
E. 
Backfill. After proper installation of the pipe, backfilling may be performed. All backfill shall be thoroughly compacted through the use of approved mechanical tampers. All backfill material is subject to Township approval. Trenches within street right-of-ways shall be backfilled for the entire width and depth with PennDOT Type 2A coarse aggregate, in accordance with PennDOT Publication 408. Trenches outside street right-of-ways may be backfilled with ordinary backfill material consisting of clean dry earth or granular material with a maximum stone size of eight inches, in accordance with PennDOT Publication 408.