(a)     Design: Standards. Detention basins shall be designated in accordance with the Soil Cover Complex Method and the procedures developed by the U.S. Department of Agriculture, Soil Conservation Service, as outlined in its “Technical Release No. 55, Urban Hydrology for Small Watersheds,” with specific attention given to antecedent moisture conditions, flood routing and peak discharge and “Hydrology National Engineering Handbook Section 4.”

(b)     Design: Quantity of Water. Basins shall be designed to detain the quantity of water resulting from a 100-year, twenty-four hour storm (7.2 inches of rainfall) under full development conditions. Stormwater management calculations shall insure that the predeveloped discharge from the site for the following storms is not exceeded after development:

	2-year,	24 hour:	3.3 inches of rainfall
	10-year,	24 hour:	5.0 inches of rainfall
	25-year,	24 hour:	5.7 inches of rainfall
	50-year,	24 hour:	6.4 inches of rainfall
	100-year,	24 hour:	7.2 inches of rainfall

(c)     Calculation of Stormwater Runoff Value 5. The following criteria shall apply in the calculation of stormwater runoff values. The time of concentration method shall be utilized in the development of the runoff hydrographs and peak discharge. Storage discharge curves shall be provided for all basins.

(1)    Meadow condition shall be used as the basis for establishing the predeveloped runoff values for all area other than woodland, including areas which are presently covered by impervious surfaces, except as stated below.

(2)    In the case of an expansion of an existing development, a waiver may be requested from the Board of Commissioners, to exclude only existing impervious areas from the requirements of paragraph (c)(1) hereof, provided that the existing development does not presently contribute to an existing drainage problem downstream.

(3)   Average antecedent moisture conditions; and

(4)   A Type II distribution storm.

(d)     Outlet Control Structures.

(1)    All outlet control structures shall be constructed of galvanized steel, aluminum or concrete, properly anchored to prevent flotation, and equipped with childproof, nonclogging trash racks over all design openings twelve inches or greater in diameter, except those openings designed to carry perennial stream flows.

(2)    Temporary sedimentation controls shall be provided during construction to prevent the flow of sediment through the basin outlet pipe. Such measures may include temporary riser pipes, rock-filled gabions, plywood stand-boxes, silt fences and the like.

(e)     Emergency Spillways. Whenever possible, the emergency spillway for basins shall be constructed on undisturbed ground. Emergency spillways shall be constructed of reinforced concrete, vegetated earth, concrete rubble and the like. All emergency spillways shall be constructed so that the basin berm is protected against erosion. The minimum capacity of all emergency spillways shall be such that the combined capacity of the emergency spillway and the principal pipe spillway are equal to the peak flow rate from the 100-year design storm after development. Emergency spillways shall extend along the upstream and downstream berm embankment slopes. The emergency spillway shall not discharge stormwater over earthen fill and/or easily erodible material without adequate protection against erosion.

1994 Replacement

(f)     Freeboard. The minimum freeboard shall be two feet. (Freeboard is the difference between the design flow elevations in the emergency spillway and the top of the settled basin embankment.)

(g)     Antiseep Collars. Antiseep collars shall be installed around the principal pipe barrel within the normal saturation zone of the basin berms. The antiseep collars and their connections to the pipe barrel shall be watertight. The antiseep collars shall extend to a minimum of two feet beyond the outside of the principal pipe barrel. The maximum spacing between collars shall be fourteen times the minimum projection of the collar measured perpendicular to the pipe.

(h)      Basin Outlets. Energy dissipating devices (rip-rap, stilling basin, concrete aprons and the like) shall be placed at all basin outlets. Rock level spreader berms shall be required where basins do not discharge into an existing drainage swale, ditch or channel. Concrete endwalls shall be placed at all basin outlets. All basin outlet pipes twelve inches in diameter or greater shall be equipped with childproof devices.

(i)      Slope of Detention Basin Embankment. The maximum slope of earthen basin embankments shall be three to one. The top or toe of any slope shall be located a minimum of fifteen feet from adjacent property lines, with the exception of the downstream property line, where the toe of the embankment shall be placed a sufficient distance to allow for energy dissipating devices, but in no case less than thirty feet, unless approved by the Township. Whenever possible, the side slopes and basin slope shall blend with the natural topography.

(j)      Width of Berm. The minimum top width of detention basin berms shall be ten feet.

(k)      Depth of Basin. The maximum depth of the basin shall be ten feet.

(l)       Construction Specifications. The plans shall indicate the construction specifications and compaction requirements for all detention/retention basins.

(m)      Slope of Basin Bottom. In order to insure proper drainage of detention basins, a minimum grade of two percent shall be maintained for all sheet flow. A minimum grade of one percent shall be maintained for all channel flow.

(n)      Cut-Off Trench. A cut-off trench shall be excavated along the centerline of dam on earth fill embankments. The minimum depth shall be three feet. The minimum bottom width shall be ten feet or wide enough to permit operation of compaction equipment. The side slopes shall be no steeper than 1:1. The trench shall be kept free from standing water during the backfilling operations.

(o)      Grading and Landscaping of Basin.

(1)   Cuts and fills. No excavation or fill shall be made with a cut or fill slope steeper than three horizontal to one vertical, except where the excavation or fill is sufficiently stable to prevent sliding or erosion and will not result in property damage or personal injury. A written statement shall be required from a civil engineer licensed by the Commonwealth of Pennsylvania having experience in sails engineering, certifying that he has inspected the site and that any proposed deviation from the slope specified above should not endanger any property or result in personal injury. Retaining walls will be required if’ a stable slope cannot be maintained. Any retaining wall design must be designed by an experienced structural engineer licensed by the Commonwealth of Pennsylvania and approved by the Township. The toe of any cut or fill slope must be located a minimum of fifteen feet from adjacent property lines, with the exception stated in subsection (i) hereof.

(2)   Landscaping.

A.       A minimum of six inches of top soil shall be placed on all areas affected by the basin construction (bottom of basin, side slopes, top of berm, and the like).

B.       All earthen basins shall be stabilized with temporary and permanent grasses or other approved round covers within fifteen days after initial construction.

C.       Fencing and a suitable vegetation screening shall be provided around all detention/retention basins, unless the Board of Commissioners determines that such screening is not necessary.

D.       A landscape plan at a minimum scale of 1” 30’ of the basin plans shall be submitted with each application. Such plan must be scaled by a landscape architect registered in the Commonwealth.

E.      At the completion of construction an as-built” plan, signed and sealed by a registered engineer or surveyor, shall be submitted for the Township records.

(3)    Installations. Basins shall be installed prior to any earthmoving or land disturbances which they will serve.

(Ord. 644. Passed 8-17-88.)

 

1043.32   SUBSURFACE DISPOSAL OF STORMWATER.

(a)      Subsurface disposal of stormwater shall be allowed only where natural, well-drained soils exist and only after on-site soil percolation tests, certified by a registered professional engineer experienced in soils engineering, a geologist or a qualified soils scientist, or the like, are performed.

(1)     Soils testing to determine percolation rates shall be performed at several locations where the subsurface facility is proposed and also at the proposed inner elevation of the subsurface facility.

(2)     All percolation tests shall be conducted in accordance with the rules, regulations and procedures of the Pennsylvania Sewage Facilities Act (Act 637) as required by the Pennsylvania Department of Environmental Resources.

(b)     Various methods of subsurface disposal may be employed. The effectiveness and applicability of each should be evaluated at each location. Acceptable methods include, but are not limited to, infiltration basins and/or berms, seepage beds and/or trenches, and the like.

(c)     The design and construction of all subsurface facilities shall provide proper procedures to prevent silt from clogging the aggregate backfill.

(d)     The following procedures and materials shall be required for all subsurface facilities:

(1)     Excavation for the infiltration facility shall be performed with equipment which 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, free of fines, shall be allowed.

(4)     The top and sides of all seepage beds, trenches or like facilities shall be covered with drainage filtration fabric.

(5)     Perforated distribution pipes connected to centralized catch basins and/or manholes, with provisions for the collection of debris, shall be provided in all facilities. The perforated pipes shall distribute stormwater throughout the entire seepage bed/trench or like facility.

(6)     A positive outlet pipe placed at or near the bottom of the seepage bed and/or trench, or like facility, shall be provided.

(e)     The landowner or developer shall be responsible for the proper installation, operation and maintenance of all subsurface stormwater management facilities. If, in the opinion of the Township, the underground system is not functioning properly, the landowner or developer shall be required to make the necessary improvements/corrections to the system or provide an alternative stormwater management facility which is functional.

(Ord. 644. Passed 8-17-1988.)

 

1043.33   MAINTENANCE OF FACILITIES.

(a)     All stormwater management facilities, including retentiona and detention basins designed and constructed for the purposes specified under this chapter, shall be maintened in proper working order in accordance with those design plans filed with the Township and shall be the responsibility of the property owner(s) upon whose property the facilities are located. In the case of a homeowners association or other entity approved by the Township, the homeowners association or other entity shall be considered the responsible owner of all soormwater management facilities located in the area of development.

(b)     In order to ensure proper maintenance and function of stormwater management facilities, the Township or its designee shall perform inspections, carried out on a random basis.

(c)     If, at any time, the Township, or its designee, discovers any violation or condition not conforming with those designs or plans filed with the Township in regard to the operation of a stormwater management facility, the Township or its designee shall notify the responsible owners of the violation, informing them of the nature of such violation and the manner in which it can be corrected.

(d)     Under no condition shall any person be allowed to modify, alter or change a previously approved stormwater management facility unless an approved alternative facility is approved by the Township.

(e)     Under no conditions shall any person be allowed to modify, alter or change a previously approved stormwater management facility unless approved by the Township.

(f)     In the event the landowner, developer, occupant or homeowner's association, as the case may be, shall refuse or neglect to comply with the provisions of this chapter, as interpreted by the Township, the Township may direct the work to correct any violation or noncompliance with the provisions of this chapter.

(g)     Maintenance of all drainage facilities and watercourses within any subdivision and/or land development is the responsibility of the landowner or developer until they are accepted by the Township.

(h)     It is the responsibility of any landowner or developer doing any act on or across a communal stream, watercourse or swale, or upon the flood plain or right of way thereof, to maintain, as nearly as possible in its present state, the stream, watercourse, swale, flood plain or right of way for the duration of the construction activity and to return it to its original or equal condition after such activity is completed.

(i)     Maintenance of drainage facilities or watercourses originating on private property is the responsibility of the owner to their point of open discharge at the property line or at a communal watercourse within the property.

(Ord. 644. Passed 8-17-1988.) 

 

 

1043.99   PENALTY.

(EDITOR'S NOTE: See Section 202.99 for general Code penalty if no specific penalty is provided.)

1991 Replacement