A. 
General.
(1) 
All land areas shall be graded to secure proper drainage away from buildings. Drainage provisions shall be of such design as to carry surface waters to the nearest practical adequate street, storm drain or natural watercourse. Developers must carry surface water to the practical storm drain or natural watercourse. The developer shall construct and/or install such drainage structures and/or pipes as required to prevent erosion, damage and siltation and to satisfactorily carry off surface waters. The rate of stormwater runoff from any proposed earth disturbance activity after full development shall not exceed the peak rate of discharge prior to development.
(2) 
Stormwater discharge shall be carried by conduit to prevent excessive surface flow on or across streets, sidewalks, drives, parking areas and any other paved surface or traveled way where infiltration practices, such as pervious paving, would not be feasible. Culverts or bridges shall be required at all stream crossings of any street or roadway, using design criteria for a one-hundred-year peak flow rate appropriate to the contributing watershed. Natural swales or open drains of any type may be used only where there is no danger to structures or abutting property.
(3) 
Identified natural watercourses (streams or creeks) which have continuous flow shall remain open and shall not be piped or covered unless:
(a) 
Required by the Board of Supervisors, as approved by the Township Engineer; and
(b) 
Approved by the DEP.
(4) 
The stormwater management plan for each earth disturbance activity shall take into account and provide for upstream areas within the entire watershed in computing discharge quantities, sizing of pipes, inlets and other structures. The runoff from any proposed development shall be subject to evaluation which includes the anticipated runoff from other existing or proposed developments within the same watershed. Stormwater management facilities designed to serve more than one property or development in the same watershed are encouraged, in which case consultation with the Township Engineer is required prior to design.
(5) 
The Township Engineer may require stormwater retention devices, basins, subsurface recharge facilities or other delayed-release devices or designs to contain the excess storm discharge, prevent downstream flow increases and encourage groundwater recharge.
B. 
Storm sewer.
(1) 
Storm sewers (pipes or other structures) shall be reinforced concrete or HDPE pipe, have a minimum grade of 1/2% and a minimum inside diameter of 18 inches or a cross-sectional area of 254 square inches. Roof drains or yard drains shall not connect to any sanitary sewer and shall not discharge water directly over any sidewalk. Storm drainage facilities should be located within the paved areas of roadways whenever practical. Where storm sewers discharge into existing drainage channels at an angle greater than 30° with the downstream channel flow, the far side bank shall be stabilized by the use of riprap, masonry, concrete walls and/or vegetative materials. The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.
(2) 
Storm sewer systems shall be constructed in accordance with Township specifications, which are approved by resolution of the Board of Supervisors. If a particular design or device is not specifically approved within the Township specifications, the Township Engineer must review the particular design or device for conformance with the objectives of this section.
C. 
Erosion and sedimentation control. Prior to the commencement of any regulated earth disturbance activity, the following criteria shall be met:
(1) 
No changes shall be made in the contour of the land and no grading, excavating, removal or destruction of the topsoil, trees or other vegetative cover of the land shall be commenced until such time as a plan for minimizing soil erosion and sedimentation has been submitted and approved.
(2) 
Measures used to control erosion and reduce sedimentation shall meet or exceed the standards and specifications of the Conservation District. The Township Engineer shall review the plan to ensure compliance with the appropriate specifications, copies of which are available from the Conservation District.
(3) 
Plans shall preserve salient natural features, keep cut/fill operations to a minimum and ensure conformity with natural topography so as to create the least erosion potential and adequately handle the volume and velocity of surface water runoff. Whenever feasible, natural vegetation shall be retained, protected and supplemented. The disturbed area and the duration of exposure shall be kept to a practical minimum. Disturbed soils shall be stabilized as quickly as practicable. Temporary vegetation and/or mulching shall be used to protect critical areas during development.
(4) 
The permanent (final) vegetation and mechanical erosion control and drainage shall be installed as soon as practical. Provisions shall be made to effectively accommodate the increased runoff caused by changed soil and surface conditions during and after development. Where necessary, the rate of surface water runoff will be mechanically retarded. Sediment in all runoff water shall be trapped by the use of debris basins, filters, sediment basins, silt traps or similar measures until the disturbed area is fully stabilized. Such devices shall be periodically cleaned of all silt and debris to ensure proper operation.
(5) 
During grading operations, necessary measures for dust control must be exercised. Grading equipment will not be allowed to cross flowing streams. Provision shall be made for the installation of temporary culverts or bridges, including the procurement of appropriate regulatory permits.
(6) 
Permanent retention basins shall be provided when required by the Board of Supervisors. The location of such basins shall be approved by the Board of Supervisors upon advice from the Township Engineer, subject to the approval of the DEP. Any requirement for a permanent retention basin by the Board of Supervisors shall not represent any liability on behalf of the Township.
(7) 
No person, corporation or other entity shall block, impede the flow of, alter, construct any structure or deposit any material or thing or commit any act which will affect normal or flood flow in any communal stream or watercourse without having obtained prior approval from the Township and/or the Department of Environmental Protection, whichever is applicable. It is the responsibility of any person, corporation or other entity doing any act on or across a communal stream, watercourse or swale or upon the floodplain or right-of-way during the period of the activity to return it to its original or equal condition after such activity is completed.
(8) 
Whenever sedimentation is caused by stripping vegetation, regrading or other development, it shall be the responsibility of the person, corporation or other entity causing such sedimentation to remove it from all adjoining surfaces, drainage systems and watercourses and to repair any damage at his expense as quickly as possible.
(9) 
Maintenance of all stormwater management facilities and watercourses, both existing and proposed, within the proposed site shall be the responsibility of the developer during construction and any required maintenance guaranty period until such time as one of the following is accomplished:
(a) 
A right-of-way for these facilities is offered for dedication by the developer and is accepted by the township, at which time it shall then be the responsibility of the Township.
(b) 
An easement acceptable to the Township is established. In the case of a subdivision, the maintenance shall then be the responsibility of the individual lot owners over whose property the easement passes. For land developments, the maintenance shall thereafter be the responsibility of the owner.
(c) 
A homeowners' association, approved by the Township, assumes responsibility for the maintenance of the development, including the maintenance of the watercourses and/or drainage facilities, provided that the Township Engineer approves the assumption of maintenance of such facilities in writing.
(10) 
The installation and design of the required erosion and sediment control measures, listed below, shall be in accordance with standards and specification found in the Erosion and Sediment Pollution Control Program Manual available through the Conservation District, Montgomery County Planning Commission or Township (see also Township specifications) or the Pennsylvania Handbook of Best Management Practices for Developing Areas.
(11) 
Criteria contained in this chapter shall not remove or alter the requirement for the developer to submit plans and specifications to the Department of Environmental Protection under the Clean Streams Act of 1972 where Department of Environmental Protection's permits are required.
(12) 
Three days prior to the commencement of any operation in the construction or installation of any drainage facilities or erosion and sedimentation control facility, the owner shall notify the Township Engineer, who shall inspect the work, materials, construction and installation for compliance with Township requirements. The Township Engineer shall be authorized to have such tests of materials made as are provided in the Skippack Township Specification and Design Standards in order to have proper control of materials. Such fees for tests of materials as provided above shall be in accordance with the fee schedule as established by resolution of the Board of Supervisors.
(13) 
Sediment basins, retention basins and detention basins shall neither be located within nor discharge into a tree protection zone.
A. 
General.
(1) 
Storm drainage required. A storm sewer system and all appurtenances shall be required to be constructed by the owner or subdivider in any area from which the surface or subsurface drainage could impair public safety or cause physical damage to adjacent lands or public property. The system shall be designed to collect water at any point where three to five cubic feet per second is accumulated, at the bottom of all vertical grades and immediately upgrade from all street intersections. The system shall discharge to the nearest practical natural drainage channel or storm system.
(2) 
Off-site improvements. Any increase in runoff, if permitted, may require necessary corrective measures, including deeds of easement, deemed appropriate by the Board of Supervisors to alleviate any off-site drainage problem affected by the earth disturbance activity. The costs for such measures will be borne entirely by the developer or subdivider.
(3) 
Total watershed evaluation. The future use of undeveloped areas upstream, as shown on the approved Township Comprehensive Plan, shall be taken into account in the design of all storm sewer systems. The capacity and maximum anticipated present flow of the body or system receiving the proposed system(s) discharge shall be calculated to verify its capability of receiving any additional flow caused by the development. The runoff from any proposed development shall be subject to an evaluation which includes the anticipated runoff from other existing or proposed developments within the same watershed. Stormwater management facilities designed to serve more than one property or development in the same watershed are encouraged. Consultation with the Township is required prior to the design of such facilities.
(4) 
Contribution to Comprehensive Drainage Plan. In addition to any other requirement of this chapter, the developer may be required to participate in off-site storm drainage improvements in the drainage basin within which the proposed development is located. The specific off-site drainage improvements required shall be those specified by the Township Board of Supervisors as part of the Skippack Township Comprehensive Stormwater Drainage Plan.
B. 
Underdrains.
(1) 
All building foundations, grade slabs and cellar floors located in soils that have a community development limitation degree of moderate to severe seasonal high-water table, as defined by an on-site soils test witnessed by the Township Engineer, shall be provided with an underdrain system. This system shall provide for drainage of the enclosed volume above the slab and relief of subsurface water to a depth of not less than six inches below the slab or foundation bottom. The system shall consist of a perforated pipe field of the herringbone or gridiron configuration in coarse, gravel-filled trenches that are in direct contact with the slab or foundation subbase. The excavation shall provide a minimum of 0.005-foot/foot slope to the gravel-filled trenches.
(2) 
If required by the Township Engineer, proposed roadways shall be constructed with an underdrain system consisting of six-inch perforated pipe wrapped in a Class 1 geotextile material. The underdrain shall be bedded with a minimum of six inches of 2B stone. The bedding material shall extend to the bottom of the base course.
C. 
Storm drain pipes and inlets.
(1) 
All pipes and inlets shall meet material, capacity and construction specifications as outlined in the latest revisions of the Penn DOT Form 408 and the Penn DOT Design Manual or as outlined in the township specification as approved by resolution of the Board of Supervisors.
(2) 
Design flow rate. The storm drain system shall be designed to carry a fifty-year peak flow rate. The design fifty-year peak flow rate into each inlet shall be indicated on the stormwater drainage plan. The fifty-year flow rate shall be determined by the rational formula as follows:
Q
=
CIA
Where
Q
=
Peak runoff rate in cubic feet per second (cfs)
C
=
Runoff coefficient equal to the ratio of the peak runoff rate to the average rate of rainfall over a time period equal to the time of concentration.
I
=
Average rainfall intensity in inches per hour for a time equal to the time of concentration.
A
=
Drainage area in acres.
NOTE:
Appropriate values for the runoff coefficient and rainfall intensity can be found in the Commonwealth of Pennsylvania Department of Transportation Design Manual, Part 2, Highway Design, Chapter 12.
(3) 
Overflow system. An overflow system shall be provided to carry flow to the detention basin when the capacity of the storm drain pipe system is exceeded. The overflow system shall be of sufficient capacity to carry the difference between the hundred-year and the fifty-year peak flow rates.
(4) 
Inlet capacity. All inlets must be designed to accommodate the fifty-year peak flow rate. The capacity of all C-type, M-type or S-type inlets shall be determined from the Commonwealth of Pennsylvania Department of Transportation Design Manual, Part 2, Highway Design.
(5) 
Straight pipe sections. Wherever possible, all storm drain pipes shall be designed to follow straight courses. No angular deflections of storm sewer pipe sections in excess of 5° shall be permitted. No vertical curves shall be permitted in the storm drain pipe system.
(6) 
Minimum grade and size. All storm drain pipes shall be reinforced concrete pipe designed to maintain a minimum grade of 1/2%. All storm pipes shall have a minimum inside diameter of 18 inches or an elliptical equivalent, except that pipes under a fill of 25 feet or greater shall not be less than 24 inches or an elliptical equivalent.
(7) 
Pipe capacity. The capacity of all pipe culverts shall, as a minimum, provide the required carrying capacity as determined by the following sources:
(a) 
United States Department of Commerce.
(b) 
Bureau of Public Roads.
(c) 
Hydraulic Engineering Circular No. 5.
(d) 
Hydraulic Charts for the Selection of Highway Culverts.
(e) 
United States Department of Commerce.
(f) 
Bureau of Public Roads.
(g) 
Hydraulic Engineering Circular No. 10.
(h) 
Capacity Charts for the Hydraulic Design of Highway Culverts.
(8) 
Pipe arches. Where headroom is restricted, alternative culvert sections may be used in lieu of circular pipe, subject to the approval of the Township Engineer.
(9) 
Allowable headwater depth. At all inlets or manholes, the maximum allowable headwater depth shall be one foot below the top of the inlet grate or the manhole cover.
(10) 
Horizontal pipe deflections. A manhole or inlet shall be provided at all horizontal deflections in the storm pipe system exceeding 5°.
(11) 
Minimum and maximum cover. A minimum of three feet of cover shall be maintained over all storm drain pipes. The top of storm drain pipes shall be at least one foot below subgrade elevation. The maximum cover over storm drain pipes shall be 10 feet unless special conditions warrant otherwise, in which case structural design calculations shall be submitted.
(12) 
The elevation difference or invert of pipes entering and exiting any drainage structure shall be a minimum of 0.2 feet.
(13) 
Match crowns. The crowns of pipes of variable size tying into an inlet or manhole shall be set at equal elevations.
(14) 
Diversions of runoff. All storm drain pipes shall be designed to carry the runoff into a detention basin or similar facility utilized to control the rate of runoff.
D. 
Runoff control.
(1) 
The rate of stormwater runoff from any proposed subdivision or land development after full development shall not exceed the peak discharge prior to development. Where, in the judgment of the Township Engineer, the quantity of stormwater runoff will cause detrimental impact, a further reduction in quantity will be a consideration in the method of stormwater regulations. This standard shall be maintained for all storms, that is, both high frequency and low frequency.
(2) 
Runoff control devices. The increased runoff which may result from any earth disturbance activity shall be controlled by permanent runoff control measures that will provide the required runoff control specified above. All runoff control devices will be evaluated for the effectiveness to maintain the above-mentioned standard for all storms with a return period of up to 100 years.
E. 
Detention basins.
(1) 
The use of regional detention basins to combine and eliminate numerous smaller basins is encouraged. Consultation with the Township is required prior to design of a regional detention basin.
(2) 
Design of detention basins. All detention basins shall be designed as per the procedures developed by the United States Department of Agriculture, Soil Conservation Service, as outlined in its Technical Release No. 55, Urban Hydrology for Small Watersheds. The Township Engineer may approve an alternative model.
(3) 
Basin design criteria. The following design criteria shall be used in the design of all detention basins and/or other stormwater management facilities in the township. The basins shall be designed to detain the quantity of water resulting from a one-hundred-year, twenty-four-hour storm (see Soil Conservation Service Technical Release No. 55) under full development conditions releases at a maximum outflow rate no greater than the peak discharge prior to development. This criteria shall be met for all frequency storms and must be analyzed of the one-year, two-year, five-year, ten-year, twenty-five-year, fifty-year and one-hundred-year storms. All flows in excess of the above-mentioned standard shall flow over an emergency spillway.
(4) 
Outflow rate control. A concrete structure shall be provided at the outlet of all detention basins. The structure shall extend to an elevation two feet below the crest elevation of the emergency spillway and shall be designed so that the rate of outflow is controlled through the basin berm when the depth of water within the basin exceeds the height of the riser.
(5) 
Maximum depth of detention basins. The maximum depth of water in a detention basin shall not exceed four feet.
(6) 
Emergency spillway. Whenever possible, the emergency spillway for detention basins shall be constructed on undisturbed ground. Emergency spillways shall be constructed of reinforced earth, concrete pour blocks or other approved material. All emergency spillways shall be constructed so that the detention basin berm is protected against erosion. The minimum capacity of all emergency spillways shall be equal to the peak flow rate from the one-hundred-year design storm. The dimensions of the emergency spillways can be determined from the DEP's Erosion and Sediment Pollution Control Program Manual. Emergency spillways shall extend along the upstream and downstream berm embankment slopes. The upstream edge of the emergency spillway shall be a minimum of three feet below the spillway crest elevation. The downstream slope of the spillway shall, as a minimum, extend to the toe of the berm embankment. The emergency spillway shall not discharge over earthen fill and/or easily erodible material.
(7) 
Antiseep collars. Antiseep collars shall be installed around the principal pipe barrel within the normal saturation zone of the detention basin berms. The antiseep collars and their connections to the pipe barrel shall be watertight. The antiseep collars shall extend a minimum of two feet beyond the outside of the principal pipe barrel. The maximum spacing between collars shall be 14 times the minimum projection of the collar measured perpendicular to the pipe. The use of an O-ring pipe is required for all detention discharge pipes.
(8) 
Freeboard. Freeboard is the difference between the one-hundred-year design flow elevation in the emergency spillway and the top of the settled detention basin embankment. The minimum freeboard shall be one foot.
(9) 
Slope of detention basin embankment. The maximum slope of earthen detention basin embankments shall be 3 to 1. The top or toe of any slope shall be located a minimum of five feet from any property line. Whenever possible, the side slopes and basin shape shall be amenable to the natural topography. Straight side slopes and rectangular basins shall be avoided whenever possible.
(10) 
Width of berm. The minimum top width of detention basin berms shall be 10 feet.
(11) 
Slope of basin bottom. In order to ensure proper drainage of the detention basin, and unless designed as a naturalized basin providing BMPs, a minimum grade of 2% shall be maintained for all sheet flow. A minimum grade of 1/2% shall be maintained for all channel flow.
(12) 
Low flow channel. Low flow channels shall be constructed on the basin floor extending from all inflow structures to the outflow structure. The low flow channel shall be constructed of a minimum of four inches of concrete. The center of the low flow channel shall be lower than the outside edges by six inches, thus creating a swale to carry the flow to the outflow structure, causing little or no erosion of the basin floor. A footer on both sides of the channel shall be placed to a minimum depth of six inches where subsurface conditions warrant as approved by Township Engineer.
(13) 
Energy dissipaters. Energy dissipating devices (riprap, end sills, etc.) shall be placed at all basin outlets. Forebays or split flow controls are encouraged at the inlet to all basins.
(14) 
The distance from the highest free water surface of any detention basin or drainage facility to a dwelling unit shall be a minimum of 100 feet.
(15) 
Landscaping and grading of detention basins. All landscaping and grading standards particularly applicable to detention basins, as required by § 172-23, shall be met.
F. 
Wet ponds and other facilities designed to retain water year round.
(1) 
Wet ponds and other facilities shall meet all design standards outlined in § 172-22E for detention basins.
(2) 
The minimum permanent pool level shall be maintained to allow sufficient depth throughout the year to reduce the growth of unwanted vegetation and mosquitoes.
(3) 
The pond shall be of sufficient size to allow the appropriate aquatic community needed to maintain a healthy pond ecology.
(4) 
An outlet structure shall be designed to allow complete drainage of the pond for maintenance purposes.
(5) 
The design of a detention facility with a permanent pool shall include a determination of the proposed site's ability to support a viable permanent pool. The design should account for such factors as the required rate and quality of dry weather inflow, the quality of stormwater inflow, seasonal and longer-term variations in groundwater table and effects of expected pollutant loadings. The Pennsylvania Fish Commission and the Conservation District should be consulted during the design of these facilities.
G. 
Stormwater wetland basins.
(1) 
Stormwater wetland basins shall meet all design standards outlined in § 172-22E for detention basins.
(2) 
Wetland areas within stormwater wetland basins shall be designed in accordance with the Handbook of Constructed Wetlands, Volumes 1 and 5, United States Department of Agriculture, 1995, as may be revised.
H. 
Naturalized detention basins.
(1) 
Naturalized detention basins shall meet all design standards outlined in § 172-22E for detention basins.
(2) 
The detention basin shall be very free-form and curvilinear in shape so that from most edges of the basin, the whole basin will not be within view. When the natural topography lends itself to a straight-sided detention basin, the basin shall contain an island or peninsula planted with trees which is large enough and appropriately placed to reduce the perceived size of the detention basin. Such basins shall have a perimeter length that is greater than or equal to the length derived by the following formula, where ""x" equals the area of the basin in square feet:
As an alternative, naturalized detention basins may be created by constructing berms or using gabions to dam up stormwater in a natural depression or valley, provided that the topography and natural vegetation in the remainder of the basin is left in its natural condition.
(3) 
Naturalized planting materials, such as wildflowers and nonaggressive meadow grasses, which tolerate wet, intermittently wet and usually dry areas of the basin, shall be planted throughout the basin. Trees and shrubs may be planted in the basin where they will not interfere with the function of the basin.
I. 
Culverts and drainage channels.
(1) 
Design flow standard. All culverts and drainage channels shall be designed to carry a flow rate equal to a fifty-year, twenty-four-hour storm, except for culverts in streets which shall be designed to carry a flow rate equal to a one-hundred-year, twenty-four-hour storm (Soil Conservation Service, Technical Release No. 55).
(2) 
Erosion prevention. All drainage channels shall be designed to prevent the erosion of the bed and bank areas. The flow velocity in all vegetated drainage channels shall not exceed the maximum permissible velocity to prevent erosion. Suitable bank stabilization shall be provided where required to prevent erosion of the drainage channels. Where storm sewers discharge into existing drainage channels at an angle greater than 30° from parallel to the downstream channel flow, the far-side bank shall be stabilized by the use of riprap, masonry, concrete walls and/or vegetation. The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.
(3) 
Maximum side slope. Any vegetated drainage channel requiring mowing of the vegetation shall have a maximum grade of three horizontal to one vertical on those areas to be mowed.
(4) 
Design standard. Because of the critical nature of vegetated drainage channels, the design of all vegetated channels shall, as a minimum, conform to the design procedures outlined in the Erosion and Sediment Pollution Control Program Manual. Several acceptable sources outline procedures for nonvegetated drainage channels, including the following:
(a) 
Bureau of Public Roads.
(b) 
Hydraulic Engineering Circular No. 5.
(c) 
Hydraulic Charts for the Selection of Highway Culverts.
(d) 
Federal Highway Administration.
(e) 
Hydraulic Engineering Circular No. 13.
(f) 
Hydraulic Design of Improved Inlets for Culverts.
J. 
Groundwater recharge.
(1) 
General. The difference between the two-year post-development volume and the one-year pre-development volume of runoff must be infiltrated for all subwatersheds at the site.
(2) 
Subsurface recharge systems.
(a) 
Soil investigation. In designing a subsurface stormwater system, a key element is an analysis of the soil. The Township Engineer shall require, witness and receive a certification from an experienced soils scientist in accordance with commonly accepted professional standards. Said certification shall include:
[1] 
The results of all test borings, test pits or auger holes in order to determine the type of soil;
[2] 
The high-water level; and
[3] 
The depth to bedrock.
(b) 
Permeability. A minimum infiltration rate of 0.27 inches per hour shall be required for all subsurface systems.
(c) 
Infiltration capacity.
[1] 
For any earth disturbance activity of less than one acre, infiltration rates shall be determined from field investigation, permeability testing, percolation testing or empirically from the following table:
Hydraulic Soil Properties Classified by Soil Textures*
Texture Class
Minimum Infiltration Rate (f)
(inches per hour)
Hydrologic Soil Groupings
Sand
8.27
A
Loamy sand
2.41
A
Sandy loam
1.02
B
Loam
.52
B
Silt loam
.27
C
Sandy clay loam
.17
C
Clay loam
.09
D
Silty clay loam
.06
D
Sandy clay
.05
D
Silty clay
.04
D
Clay
.02
D
NOTE:
*
Source: Rawls, W.J. Brakensiek, D.L., and Saxton, K.E. Estimation of Soil Properties. Transactions of the American Society of Agricultural Engineers. Volume 25, No. J, pages 1316-1320, 1982.
[2] 
For any earth disturbance activity over one acre, infiltration capacity shall be determined by an infiltration test.
(d) 
Infiltration rate. Percolation tests shall be accepted as a means of determining the infiltration rate of a soil. The tests must be completed at the location and depth of the proposed infiltration area. The percolation rate may be converted to infiltration rate in inches per hour as follows:
Infiltration rate (inches per hour) = 60 ÷ (percolation rate, minutes per inch)
(e) 
Limiting factors.
[1] 
A minimum two-foot soil buffer between the bottom of the trench and seasonally high-water table or bedrock shall be provided.
[2] 
The subsurface recharge system must not be located within 10 feet of the building foundation.
(f) 
Sediment and debris. Various measures shall be taken to guarantee that the subsurface recharge system does not become filled with sediment during and after construction and that the system is kept free of debris (leaves, twigs, etc.) to prevent clogging. These measures include, but are not limited to, temporary siltation berms and other erosion controls and gutter screens for direct piping from roofs to the system.
(g) 
An inspection/testing port shall be installed by the developer to ensure that the postconstruction permeability rate is preserved to the pre-development permeability testing rate.
(h) 
Storage requirements.
[1] 
Except in cases where infiltration is utilized and designed as a separate system from the primary detention facility, the amount of storage shall be designed to adequately store the quantity of water resulting from the difference, measured in cubic feet, of a one-hundred-year, twenty-four-hour post-development storm and a one-hundred-year, twenty-four-hour pre-development storm.
[2] 
The void rate of the aggregate shall be a maximum of 40%.
(i) 
Aggregate/filter material. Aggregate fill shall be clean stone between two inches and four inches in diameter. Larger stone shall be placed near the bottom of the system and smaller stone near the top. An appropriate geotextile fabric shall line the bottom and sides, with sufficient excess material left at the top to fold over the aggregate fill when placed, prior to the placement of the topsoil layer.
(j) 
Prefabricated systems. When prefabricated systems are proposed, the applicant shall adhere to all recommended manufacturer's specifications, in addition to the requirements of this section.
(k) 
Emergency overflow. Each subsurface recharge system shall be designed with an emergency overflow/surcharge system to protect the system in the event of a storm of higher intensity.
(l) 
General note for all subsurface recharge systems. The following note shall be placed on all plans which propose a subsurface recharge system: "The subsurface recharge facilities shown on these plans are a basic and perpetual part of the stormwater management system of the proposed site located in Skippack Township, Montgomery County, Commonwealth of Pennsylvania, and as such are to be protected and preserved in accordance with the approved final plans by the owners, their successors and assigns of these lands. Skippack Township and/or its agents reserve the right and privilege to enter upon these lands from time to time for the inspection of said facilities in order to determine that the structural and design integrity is being maintained by the owner."
A. 
Cuts. No excavation shall be made with a cut face steeper than three horizontal to one vertical, except under the condition that the material in which the excavation is made is sufficiently stable to sustain a slope of steeper than three horizontal to one vertical. A written statement to that effect is required from a civil engineer licensed by the Commonwealth of Pennsylvania having experience in soils engineering and must be submitted to the Township Engineer and approved by him. The statement shall affirm that the site has been inspected and that the deviation from the slope should not result in injury to persons or damage to property. Retaining walls will be required if a stable slope cannot be maintained. Any retaining wall design must be approved by the Township Engineer. The toe of the slope or headwall of any cut must be located a minimum of five feet from property lines.
B. 
Fills. No fill shall be made which creates any exposed surface steeper in slope than three horizontal to one vertical, except where the fill is located so that settlement, sliding or erosion will not result in property damage or be a hazard to adjoining property, streets or buildings. A written statement is required from a civil engineer licensed by the Commonwealth of Pennsylvania having experience in soils 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 property damage, and such statement must be submitted to and approved by the Township Engineer. A concrete or stone masonry wall designed and constructed in accordance with these specifications and standards may be required to support the face of the fill where the above specified slopes are exceeded. The top of any fill or toe of the slope of any fill shall be located five feet from any property line.
C. 
Retaining walls. All retaining walls shall be designed as per the procedures outlined in the American Association of State Highway Officials, Standard Specifications for Highway Bridges, 1973.
D. 
Landscaping.
(1) 
Grassed areas or grass/ground cover combinations. All such areas specified on proposed or approved plans shall be prepared, installed and maintained in accordance with the Pennsylvania Department of Transportation Form 408 specifications, as amended.
(2) 
Drainage channels and retention areas. All storm drainage channels and retention areas, whether existing or proposed, shall be graded and planted to effectively naturalize area(s) so as to become an integral and harmonious part of the landscape by contour and type of plant materials used.
(3) 
All detention basin side slopes and bottoms shall be seeded with an appropriate nonmowable seed mixture specifically suited to the levels of periodic inundation for which the facility is designed.
(4) 
A suitable, naturalized, native plant screening shall be provided around all detention basins. Fences may be required at the discretion of the Board of Supervisors. Native Plants acceptable for use are listed as part of the Recommended Native Plants for Landscaping in Pennsylvania, as issued by the Pennsylvania Department of Conservation and Natural Resources. The use of native grasses and wetland tolerant plants is highly encouraged.
(5) 
Trees and shrubs shall be placed in informal irregular groupings so as to provide a suitable visual barrier at the time of planting. Trees may be placed in the basin bottom, subject to the approval of the Township Engineer and Township Planner. Whatever materials are used, they shall be placed sufficiently far back from the cut or fill slope so as to allow ease in mowing.
(6) 
Minimum standards.
(a) 
The following are minimum sizes for plant material:
[1] 
Deciduous trees: two-and-one-half-inch caliper at six inches above grade.
[2] 
Shrubs: 18 to 24 inches in height.
[3] 
Evergreen trees: six to eight feet in height.
(b) 
Trees and shrubs shall be spaced in accordance with the characteristic spread for each specific species at maturity, but in no case shall said trees and shrubs be planted closer than five feet on center.
(7) 
The screening requirement shall be waived only with the expressed consent of the Board of Supervisors.
E. 
Topsoil. A minimum of six inches of topsoil material shall be placed on all areas affected by the basin construction (bottom of basin, side slopes, top of berm, etc.). The material must meet the requirements of the Pennsylvania Department of Transportation Form 408 specifications, as amended.
F. 
Subsurface recharge system. In order to preserve the integrity of the system, at no time shall any trees be planted in or around a subsurface recharge system. As a general rule, the dripline of a mature tree should not be located within five feet of a subsurface recharge system.
G. 
Grading design criteria.
(1) 
Fill placement and compaction. All fill shall be placed mechanically and shall be free of any debris or organic material, roots and stumps. Fill shall be placed in consecutive, maximum eight-inch layers and compressed or compacted mechanically with equipment weighing not less than 10 tons or with similar sheepsfoot roller or compactors having equivalent compression capability. The township may require, at the owner's expense, a test certifying the adequate compaction of fill materials as required above or in accordance with the requirements of the Township Engineer if an on-site inspection was not performed at the time of placement of the fill.
(2) 
Large-scale removal of topsoil. Permanent removal of topsoil shall be prohibited. The only exception to this prohibition shall be under the circumstance where design of a large-scale development permits the removal of excess topsoil in locations of large parking areas or large buildings where the topsoil removed may be more appropriately used elsewhere on the site or on a nearby site. A special permit for such topsoil removal is required, as issued by the Board of Township Commissioners.
H. 
Tree protection standards.
(1) 
General requirements shall be as follows:
(a) 
Grade changes and excavations on any location within the site shall not:
[1] 
Encroach upon a tree protection zone; or
[2] 
Result in an alteration to soil or drainage conditions which would adversely affect existing vegetation to be retained following site disturbance, unless adequate provisions are made to protect such vegetation and its root systems.
(b) 
No toxic materials shall be stored within 100 feet of a tree protection zone, including petroleum-based and/or -derived products.
(c) 
The area within a tree protection zone shall not be built upon or covered by impervious materials, either temporarily or permanently.
(d) 
The storage of equipment, materials, debris or fill and the parking of vehicles shall be prohibited within a tree protection zone.
(2) 
Tree protection zone construction requirements shall be as follows:
(a) 
Prior to construction, any tree protection zone shall be identified on the site in conformance with the approved subdivision or land development plan and in the following manner:
[1] 
All trees scheduled to remain shall be clearly marked. Only trees on the outer edge of tree groups or forests are required to be marked.
[2] 
A four-foot-high wooden snowfence mounted on steel posts located eight feet on center, or similar fencing materials or barrier approved by the Township Arborist, shall be placed along the boundary of the tree protection zone. Immediately following the installation of said fencing, the Township Arborist shall inspect and approve the same prior to the commencement of any development activity on the site. The fencing shall be properly maintained until all development activity has ceased, and damaged fencing shall be repaired or replaced before any development may recommence.
[3] 
In addition to such fencing, trees outside the tree protection zone may be temporarily retained to the limits of grading and utilized as an additional buffer area during construction. Such trees shall be removed prior to the completion of development.
(b) 
The operation of heavy equipment shall not occur within a tree protection zone.
(c) 
Trees being removed shall not be felled, pushed or pulled into a tree protection zone or into any other trees which are required to be retained.
(d) 
Any tree stumps located within (ten) 10 feet of a tree protection zone shall be removed by means of a stump grinder to minimize their effect on surrounding root systems.
(e) 
Tree roots which must be severed shall be:
[1] 
Cut by a backhoe or similar equipment, aligned radially to the tree, in such a manner so as to reduce the lateral movement of roots during excavation.
[2] 
Trimmed cleanly so that their edges are smooth and are cut back to a lateral root, if exposed.
[3] 
Covered temporarily with peat moss, moist burlap or other moist biodegradable material within four hours of any severance in order to avoid their drying out.
(f) 
Damaged areas shall be treated promptly and as may be required by the Township Arborist.
[1] 
Damaged bark shall be cut back to a point where the bark is intact and tight to the tree.
[2] 
Exposed roots shall be cleaned up and covered with topsoil.
[3] 
Tree limbs shall be cut back in proportion to root area loss.
[4] 
Liquid or dry fertilizer shall be applied to trees with disturbed root zones to compensate for any loss of roots.
[5] 
All pruning shall be undertaken in accordance with the standards of the National Arborist Association, as noted in the National Arborist Association Book of Standards, as amended.
[6] 
Trees shall not be used for roping, cables, signs, fencing or lighting. Nails and spikes shall not be driven into trees.
(g) 
Fertilization.
[1] 
All trees which have been disturbed or have tree roots which have been damaged as a result of development shall be fertilized.
[2] 
Such trees shall be fertilized during the months of September through October or April through May.
[3] 
Fertilizer having approximately three parts nitrogen to one parts phosphorus and potassium (3 to 1 to 1 ratio) shall be broadcast over the soil surface in an area twice the size of the tree protection zone at a rate equivalent to one pound nitrogen per 1,000 square feet. A minimum of 1,000 square feet per tree shall receive fertilization.
(h) 
Retaining walls.
[1] 
Any regrading which causes a change in the original grade at the tree protection zone line shall require the installation of a retaining wall outside of the tree protection zone, designed to comply with township standards.
[2] 
The top of such retaining wall shall be four inches above the finished grade line.
[3] 
The retaining wall shall be constructed of large stones, brick, building tile, concrete blocks or treated woodbeams.
[4] 
A means for drainage through the wall shall be provided, as approved by the Township Engineer.
[5] 
A layer of clean stone, sized 3/4 to one inch, shall be placed one foot out from the retaining wall to aid in drainage.
(i) 
Trenching and tunneling.
[1] 
Utility lines shall be located outside tree protection zones.
[2] 
Tunneling shall be used for the installation of any utility line approved by the Board of Supervisors for location within a tree protection zone. Trenching may only be used where, in the opinion of the Township Arborist, the survival of a tree or trees would not be affected.
[3] 
Upon the completion of the installation of any utility line, the trench shall be filled immediately and tamped lightly to avoid air spaces.
A. 
In conjunction with the review of the BMP operations and maintenance plan, the adequacy of existing or proposed off-site stormwater drainage systems accommodating runoff from the development site shall be determined. A contribution shall be paid towards that portion of the cost for any off-site capital improvements and/or maintenance costs of the existing stormwater drainage systems which may be necessitated by the proposed earth disturbance activity or which may confer benefit upon the proposed development site.
B. 
Off-site stormwater drainage contributions shall be as set forth in the fee schedule of Skippack Township.
C. 
The off-site stormwater drainage contribution shall be in addition to the obligation of the developer to construct and install at its sole expense the on-site and off-site drainage improvements required as a condition to subdivision or land development approval.
D. 
When, in the discretion of the Board of Supervisors, circumstances surrounding the development of a site warrant special consideration, these contributions may be reduced or waived.
A. 
The BMP operations and maintenance plan for the project site shall establish responsibilities for the continuing operation and maintenance of all permanent stormwater BMPs, as follows:
(1) 
If a plan includes structures or lots which are to be separately owned and in which streets, sewers and other public improvements are to be dedicated to the Township, stormwater BMPs may also be dedicated to, and maintained by, the Township;
(2) 
If a Plan includes operation and maintenance by a single ownership or if sewers and other public improvements are to be privately owned and maintained, then the ownership and maintenance of stormwater BMPs shall be the responsibility of the owner or private management entity.
B. 
The Township shall make the final determination on the continuing operations and maintenance responsibilities. The Township reserves the right to accept or reject the operations and maintenance responsibility for any or all of the stormwater BMPs.
A. 
The property owner shall sign an operations and maintenance agreement with the Township covering all stormwater facilities and BMPs that are to be privately owned. The agreement shall be substantially the same as the agreement in Appendix B of this chapter.[1]
[1]
Editor's Note: Appendix B is at the end of this chapter.
B. 
Other items may be included in the agreement where determined necessary to guarantee the satisfactory operation and maintenance of all permanent stormwater facilities and BMPs. The agreement shall be subject to the review and approval of the Township.
A. 
Where stormwater or surface water will be gathered within a proposed earth disturbance activity site and discharged or drained in volume over lands within or beyond the boundaries of the subdivision or land development, the applicant or owner shall reserve or obtain easements over all lands affected thereby, provided that no easement or right-of-way for drainage purposes exists on such affected land. Such easements shall be adequate for such discharge of drainage and for the carrying off of such water and for the maintenance, repair and reconstruction of the same, including the right of passage over and upon the same by vehicles, machinery and other equipment for such purposes, and which shall be of sufficient width for such passage and work and that would provide ingress to and egress from a public right-of-way. The width of the easement shall be determined by the Township Engineer. The owner shall convey, free of charge or cost, such easements to the Township upon demand.
B. 
Stormwater management easements shall be provided by the property owner if necessary for access for inspections and maintenance or preservation of stormwater runoff conveyance, infiltration and detention areas and other BMPs by persons other than the property owner. The purpose of the easement shall be specified in any agreement under § 172-26.
C. 
All easements shall be fully described with metes and bounds on the Plan.