Questions about eCode360? Municipal users Join us daily between 12pm and 1pm EDT to get answers and other tips!
Township of Lower Merion, PA
Montgomery County
By using eCode360 you agree to be legally bound by the Terms of Use. If you do not agree to the Terms of Use, please do not use eCode360.
Table of Contents
Table of Contents
[Amended 6-15-1988 by Ord. No. 3098; 5-17-1989 by Ord. No. 3155; 11-17-1999 by Ord. No. 3546]
A. 
General requirements.
(1) 
For all properties within the Township, the developer is required to control stormwater runoff both during and after construction in accordance with the provisions of this chapter.
(a) 
Non-watershed plan districts. The developer shall ensure that the peak discharge of runoff from all storms of up to and including five-year frequency shall be controlled to that peak discharge which occurred prior to development in a two-year frequency storm. The peak discharge rates of storms of ten-year, twenty-five-year and one-hundred-year frequencies shall be controlled to the peak discharges which occurred prior to development in the respective storm frequencies.
(b) 
Release rate districts.
[Amended 7-18-2007 by Ord. No. 3821]
[1] 
Lower Merion Act 167 drainage areas. The two-year postdevelopment peak rate of runoff shall be controlled to the one-year predevelopment peak rate of runoff. Storms up to the five-year frequency must be controlled to the lesser of the two-year predevelopment rate or the percentage of the predevelopment rate as listed in Appendix B for the particular subwatershed area. For the ten- and twenty-five-year storm, the postdevelopment rate shall be controlled to the percentage of the respective predevelopment rate as listed in Appendix B. The fifty- and one-hundred-year storms shall be controlled to the peak discharges which occurred prior to development in the respective storm frequencies.
[2] 
Darby-Cobbs Creek Act 167 drainage areas.
[a] 
The peak rate of runoff must be controlled according to the following table:
District
Proposed Condition Design Storm
Existing Condition Design Storm
A
2-year
1-year
5-year
2-year
10-year
10-year
25-year
25-year
50-year
50-year
100-year
100-year
B-1
2-year
1-year
5-year
2-year
10-year
5-year
25-year
10-year
50-year
25-year
100-year
100-year
B-2
2-year
1-year
5-year
2-year
25-year
5-year
50-year
10-year
100-year
100-year
[b] 
In addition to the general requirements for volume recharge applicable to all release rate districts, developments within the Darby-Cobbs drainage areas must document recharge and water quality controls in accordance with § 121-4B(2)(d).
(c) 
Provisional infiltration district. The developer shall control stormwater as described in § 121-4B(2)(b) of this chapter.
(2) 
In addition, seepage beds shall be provided to recharge 1/2 of the roof drainage from a two-year storm, with direct connection to the seepage beds from roof drains established wherever feasible.
(3) 
The design of all stormwater management facilities shall be in accordance with this chapter and submitted to the Township Engineer for review and, when required, to the Pennsylvania Department of Environmental Resources, the United States Department of Agriculture Soil Conservation Service or the United States Army Corps of Engineers.
(4) 
Where retention basins and/or other facilities are required, the responsibility for the continued maintenance and operation of the retention basins and/or other facilities shall be the obligation of the property owner or the condominium unit owners' association or the council or the homeowners' association, as applicable.
(5) 
Any deed given for the transfer of a lot where stormwater piping and/or a retention facility is provided on a recorded lot shall refer to such structures and facilities and provide that the maintenance and operation shall be the continued responsibility of the property owner or the condominium unit owners' association or the council or the homeowners' association, as applicable.
(6) 
The natural drainage system shall be preserved in an undisturbed state to the extent possible. Storm drainage systems shall be provided in order to permit unimpeded flow of natural watercourses except as modified by stormwater detention facilities or open channels consistent with this chapter.
(7) 
The existing points of concentrated stormwater discharge onto adjacent property shall not be altered without written approval of the affected property owner(s).
(8) 
Areas of existing diffused drainage onto adjacent property shall be managed such that, at a minimum, the peak diffused flow does not increase in the general direction of discharge, except as otherwise provided for in this chapter. Written permission from the adjacent property owner must be obtained first if diffused flow is to be concentrated and discharged onto adjacent property. The developer must also demonstrate that there are adequate downstream conveyance facilities to transport the concentrated discharge safely and prove that no harm will result from the concentrated discharge (including damage to downstream property, persons or increased scouring and bank erosion). Areas of existing diffused drainage discharge shall be subject to any applicable release rate criteria in the general direction of existing discharge, whether they are proposed to be concentrated or maintained as diffused drainage areas.
(9) 
In developments of more than one lot, stormwater control is to be achieved on an individual lot basis wherever feasible. Where control on an individual lot basis is determined to be infeasible, the stormwater basins shall be located on a separate, non-building lot or open space easement area. Maintenance of the basins shall be achieved in accordance with this chapter.
(10) 
Where a subdivision is traversed by watercourses other than those for which a one-hundred-year floodplain is defined by the municipality, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unimpeded flow of storm runoff based on calculations made in conformance with § 121-4D for the one-hundred-year return period runoff and to provide a freeboard allowance of one foot above the design water surface level and required maintenance. The terms of the easement shall prohibit excavation, the placing of fill or structures and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Also, periodic maintenance of the easement by the fee property owner(s) to ensure proper runoff conveyance shall be required. Watercourses for which the one-hundred-year floodplain is formally defined are subject to the applicable municipal floodplain regulations.
(11) 
When it can be shown that natural drainage swales on the site cannot adequately provide for drainage because of topographic conditions, open channels may be constructed conforming substantially to the line and grade of such natural drainage swales. Capacities of open channels shall be calculated using the Manning equation as described in § 121-4F(6).
(12) 
Volume controls for stormwater management, such as infiltration basins, shall be required unless waived by the Township Engineer.
(13) 
Any stormwater management facilities required or regulated by this chapter shall be designed to meet the performance standards presented in § 121-4B(2) of this chapter. Compensatory stormwater management facilities shall not be permitted outside of the drainage area developed.
(14) 
Any stormwater facilities shall be based upon the following downstream impact evaluation requirements. Hydraulic capacity analysis shall be conducted in accordance with the following criteria to determine if adequate hydraulic capacity exists:
(a) 
The developer shall submit to the Township an analysis of the impacts of the value and timing of stormwater flows from the proposal downstream in the watershed. The analysis shall include the hydrologic and hydraulic calculations necessary to determine the impact of the stormwater discharge on a downstream point to be one of the following:
[1] 
The first downstream tributary whose drainage area equals or exceeds the drainage area contributing to the detention basin.
[2] 
The first downstream tributary whose peak discharge exceeds the largest designed discharge rate of the detention basin.
[3] 
The confluence of the receiving stream with the Schuylkill River.
(b) 
If the designated release rate for the proposed stormwater system results in an increase in flooding or stream channel erosion at the downstream point, the discharge rate of the detention facility shall be reduced to a level that will prevent any increase in flooding or stream channel erosion at the downstream control point.
(15) 
Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls or stream enclosures), and any work involving wetlands as described in PA DEP Chapter 105 regulations (as amended or replaced from time to time by PA DEP), shall be designed in accordance with Chapter 105 and will require a permit from PA DEP. Any other drainage conveyance facilities that do not fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway. Any facility that constitutes a dam as defined in PA DEP Chapter 105 regulations may require a permit under dam safety regulations. Any facility located within a Pennsylvania Department of Transportation (PADOT) right-of-way must meet PADOT minimum design standards and permit submission requirements.
(16) 
Storm sewers must be able to convey post-development runoff from a twenty-five-year design storm without surcharging inlets.
(17) 
Storm sewer inlet spacing and road cross section design must ensure that post-development runoff resulting from a ten-year design storm floods not more than 1/2 of a driving land, or as required by the municipal engineer.
(18) 
Easements along open channels shall be provided. The minimum width of the required easement shall be equal to the width of the one-hundred-year water surface (for post-development conditions), including a minimum of 1.0 foot of freeboard.
(19) 
For development sites that would be located in two or more subareas, the applicable release rate for the portions of the site located in different subareas shall be based on natural subareas' drainage boundaries. The natural drainage boundaries between subareas shall not be modified, nor shall drainage from a development site be diverted or otherwise conveyed from one subarea to another subarea, except where runoff naturally crosses subarea drainage boundaries.
(20) 
No harm option. For any development site, the developer has the option of discharging post-development runoff at a higher rate than predevelopment runoff if the developer can provide that no harm would be caused to any person or property located upstream or downstream of the development site. The developer must assume that the entire subarea in which the site is located is developed. The type and amount of development that the developer must consider shall be either based on current zoning or established by the Township, whichever results in a greater amount of imperviousness. Proof of no harm must demonstrate conformance with the hydraulic capacity criteria specified in this chapter to demonstrate that no increase of erosion results and demonstrate no degradation of the quality of downstream waterways to the satisfaction of the Township Engineer. Areas that drain through documented drainage problem areas would be precluded from any no-harm-based peak runoff increases, except where hydraulic capacity improvements would be provided, consistent with this chapter.
(21) 
Regional or subregional stormwater management facilities. For certain areas within the watershed, it may be more cost effective to provide one stormwater management facility for an entire subarea, group of subareas or portion of a subarea incorporating more than one development site than to provide an individual stormwater management facility for each development site. The initiative and funding for any regional or subregional stormwater management alternatives are the responsibility of prospective developers. The design of any management alternatives are the responsibility of prospective developers. The design of any regional stormwater management facilities must assume development that the developer(s) must consider shall be either based on current zoning or established by the Township, whichever results in a greater amount of imperviousness. The peak outflow from a regional stormwater management facility would be determined on a case-by-case basis using TR 20 (the SCS Computerized Hydrological Model), as amended. When regional or subregional stormwater management facilities are utilized, the effect of phased growth on stormwater runoff flows must be considered. At no time from the initial phase through ultimate development shall the peak runoff flows exceed the predevelopment peak multiplied by the applicable release rate.
(22) 
Capacity improvements. If the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the existing drainage network, then adequate capacity improvements could be provided by the developer in lieu of stormwater management facilities on the development site. Any capacity improvements would be designed based on development of all areas tributary to the improvement and the capacity criteria specified in this chapter, or as required by the Township Engineer. The type and amount of development that the developer must consider shall be either based on current zoning or established by the Township, whichever results in a greater amount of imperviousness. It shall be assumed that all new development upstream of a proposed capacity improvement would implement applicable stormwater management techniques, consistent with this chapter.
(23) 
Adequate erosion protection which meets the regulations of Chapter 102 of the Clean Streams Law shall be provided along all open channels and at all points of discharge. If a perennial or intermittent stream passes through the site, the applicant shall create a stream buffer extending a minimum of 50 feet to either side of the top-of-bank of the channel. The buffer area shall be maintained with appropriate native vegetation (refer to Appendix H of the Pennsylvania Handbook of Best Management Practices for Developing Areas for plant list). If the applicable rear or side yard setback is less than 50 feet, the buffer width may be reduced to 25% of the setback to a minimum of 10 feet. If an existing buffer is legally prescribed (i.e., deed, covenant, easement, etc.) and it exceeds the requirements of this section, the existing buffer shall be maintained.
[Amended 7-18-2007 by Ord. No. 3821]
(24) 
Ponds and other similar water features that are not designed stormwater management facilities shall be designed in accordance with the United States Department of Agriculture, Soil Conservation Service (SCS), Ponds Planning, Design, Construction (as amended or replaced from time to time by SCS) and shall be treated as impervious surfaces for stormwater runoff computations.
(25) 
The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The Township shall reserve the right to disapprove any design that would result in the occurrence or perpetuation of adverse hydrologic or hydraulic conditions within the watershed.
B. 
Stormwater management districts.
[Amended 7-18-2007 by Ord. No. 3821]
(1) 
To implement the provisions of the Lower Merion Drainage Area and Darby-Cobbs Drainage Area Stormwater Management Plans, the Township is hereby divided into stormwater management districts. These districts are consistent with the Lower Merion Drainage Area Release Rate Map (Appendix A) and Darby-Cobbs Watershed Map (Appendix D) presented in the plans.[1] The boundaries of the stormwater management districts are shown on watershed maps which are available for inspection at the Township building.
[1]
Editor's Note: Said Appendixes A and D are on file in the Township's offices.
(2) 
Four types of stormwater management districts are applicable in the Township. Different BMPs may be used to achieve the required detention. The actual proposed method will be reviewed by the Township and the Township Engineer for compliance.
(a) 
Lower Merion Act 167 Drainage Area release rate district. A three-tiered control strategy is employed in the Lower Merion Drainage Area for all applicable activities as defined in § 121-2C of this chapter.
[1] 
Whenever feasible, 100% of the stormwater flows generated from the new development shall be infiltrated on site. Where not feasible, the release rate criteria as specified for the subwatershed shall be used to control post-development runoff. At a minimum, the increased volume of stormwater generated by the proposed development for the twenty-five-year storm shall be recharged.
[2] 
Where soils are determined to be unsuitable for infiltration of stormwater, control of all stormwater generated from proposed development shall be achieved according to the release rate criteria specified for the subwatershed(s) in question.
[3] 
Subwatersheds with direct discharge listed as the release rate criteria can release directly into the receiving system, provided that water quality and capacity issues are satisfied as required by this chapter.
[4] 
Appendix B contains the release rates for the various subwatershed areas depicted on a watershed map, which is available for inspection at the Township building. Rates shall be controlled as listed and in accordance with § 121-4A(1)(b) of this chapter.
(b) 
Lower Merion Act 167 Drainage Area provisional infiltration only district. Within this district, control of stormwater from the five-year storm shall be achieved through infiltration, wherever feasible. Beyond this infiltration requirement, no further control is necessary, provided that the capacity of the local runoff conveyance system is determined to be adequate to convey the flows from the site to the Schuylkill River without flooding or increased stream bank erosion. Adequate capacity shall be determined by:
[1] 
Calculating the peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition.
[2] 
Calculating the peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this chapter.
[3] 
The larger of the two peak flows calculated shall be used in determining if adequate capacity exists. If the adequate capacity exists to transport runoff from the site to the Schuylkill River safely, the developer may discharge postdevelopment peak runoff without detention facilities. If the calculations show that the local conveyance facilities lack adequate capacity to convey the flows without flooding or increased stream bank erosion, the developer shall either use a one-hundred-percent release rate control for the two- through one-hundred-year storm, or provide for additional capacity of downstream elements to convey the increased peak flows, consistent with § 121-4C. Before either option is approved, no harm to downstream properties shall be documented to the satisfaction of the Township Engineer. Any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 121-4C(3). By definition, a storm drainage problem area associated with the local runoff conveyance system indicates that adequate capacity does not exist in the conveyance system.
(c) 
Non-watershed plan district. All other watersheds not specifically identified on the subwatershed maps.
(d) 
Darby-Cobbs Act 167 Drainage Area Release Rate District:
[1] 
At a minimum, the increased volume of stormwater generated by the proposed development for the twenty-five-year storm shall be recharged.
[2] 
In addition, it shall also be demonstrated that the following recharge requirements have been met:
[a] 
The retention (infiltration) volume (Rev) must be demonstrated to be equivalent to capturing one inch of rainfall over all proposed impervious surfaces.
Rev = I * Proposed impervious area (square feet) ÷ 12 (inches) = cubic feet (cf)
An asterisk (*) in equations denotes multiplication.
Where: I=1.0 inch
[b] 
Where the Rev volume is not feasible due to site-specific limitations, then the retention (infiltration) volume Rev required shall be as much as physically accomplished with a minimum of 0.50 inch from all impervious surface, depending on demonstrated site conditions.
Rev = I * total impervious area (square feet) ÷ 12 (inches) = cubic feet (cf)
An asterisk (*) in equations denotes multiplication.
Where: I = The maximum equivalent infiltration amount (inches) that the site can physically accept or 0.50 inch, whichever if greater.
[3] 
Field tests such as double-ring infiltrometer or hydraulic conductivity tests shall be performed at the level of the soil infiltration in order to determine the hydraulic conductivity rate.
[4] 
A minimum depth of 24 inches between the bottom of the BMP and the top of the limiting zone shall be provided.
[5] 
The infiltration facility shall be capable of completely infiltrating the retention volume (Rev) within four days (96 hours).
[6] 
All developed areas must provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. The retention volume (Rev) may be a component of the water quality volume if both are managed in a single facility. If the retention volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than infiltration BMPs. The required water quality volume (WQv) is the storage capacity needed to capture and treat a portion of stormwater runoff from the developed areas of the site.
[7] 
The following calculation formula is to be used to determine the water quality storage volume (WQv) in acre-feet of storage in the Darby-Cobbs Release Rate District:
WQv = [(P)(Rv)(A)] ÷ 12
WQv = Water quality volume (acre-feet)
P = 1 inch
A = Area of the project contributing to the water quality BMP (acres)
Rv = 0.05 + 0.009(I), where I is the percent of the area that is impervious surface [(impervious area/A)*100]
[a] 
This volume requirement can be accomplished by the permanent volume of a wet basin or the detained volume from other BMPs. Where appropriate, wet basins shall be utilized for water quality control.
[b] 
Release of water can begin at the start of the storm (i.e., the invert of the water quality orifice is at the invert of the facility). The design of the facility shall provide for protection from clogging and unwanted sedimentation.
C. 
Stormwater management district implementation provisions.
(1) 
Any stormwater management controls required by this chapter and within the release rate district shall meet the applicable rate criteria.
[Amended 7-18-2007 by Ord. No. 3821]
(2) 
The exact location of the stormwater management district boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot topographic contours provided as part of the drainage plan. The district boundaries as originally drawn coincide with topographic divides, or, in certain instances, are drawn from the intersection of the watercourse and a physical feature, such as the confluence with another watercourse or a potential flow obstruction. The physical features act as the downstream limit of the watercourse and the downstream subarea boundary is drawn from that point upslope to each topographic divide along the path perpendicular to the contour lines.
(3) 
Any downstream capacity analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting increased peak flow rates:
(a) 
Natural or constructed channels or swales must be able to convey the increased runoff associated with a two-year return period storm within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the DEP Erosion and Sediment Pollution Control Program Manual (April 1990).
(b) 
Natural or constructed channels or swales must be able to convey the increased runoff peak rate from the twenty-five-year return period storm without creating any hazard to persons or property.
(c) 
Storm sewers or any other facilities which must pass or convey flows from the tributary area must have sufficient capacity to pass or convey the increased flows associated with the twenty-five-year return period storm runoff. Culverts, bridges and other facilities which constitute stream enclosures per DEP Chapter 105 regulations shall be designed to meet the requirements of DEP Chapter 105 and must be sized to pass the one-hundred-year storm.
(4) 
For a proposed development site located within only one release rate category area, the total runoff leaving the site shall meet the applicable release rate criteria. For development sites with multiple points of concentrated runoff discharge, individual drainage points may be designed for up to a one-hundred-percent release rate so long as the total runoff leaving the site is controlled to the applicable release rate.
(5) 
For a proposed development site located within two or more different rate category areas, the peak rate of runoff that may be discharged at any point is limited to the predevelopment peak rate of runoff at that point multiplied by the applicable release rate. The control rates shall apply regardless of any grading modifications which may change the drainage area which discharges at a given point. In no event shall a significant portion of the stormwater runoff generated from a subwatershed with a more restrictive release rate be diverted to a subwatershed with a less restrictive release rate.
(6) 
For proposed development sites located partially within a release rate category area and partially within a provisional infiltration only district, in no event shall a significant portion of the site area subject to the release rate control be drained to the discharge point(s) located in the detention area.
(7) 
For any proposed development site located outside of a provisional infiltration only district, the developer has the option of using a less restrictive runoff control (including no detention) if the developer can prove conclusively that no harm would be caused by discharging at a higher runoff rate than that specified by the plan. Proof of no harm must be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Schuylkill River. Proof of no harm must be shown using the capacity criteria specified in § 121-4C(3), if downstream capacity analysis is a part of the no harm justification. Attempts to show no harm based on downstream peak flow versus capacity analysis shall adhere to the following provisions:
(a) 
The peak flow values to be used for downstream areas for the design return period storm shall be the values from the calibrated Penn State Model for the Lower Merion Drainage Area.
(b) 
Any available capacity in the downstream conveyance system as documented by a developer may be used by the developer only in proportion to his development site acreage relative to the total upstream undeveloped acreage from the identified capacity. For example, if the site is 10% of the upstream undeveloped acreage, the developer may use up to 10% of the documented downstream capacity.
(c) 
Runoff controls proposed by the developer which would increase peak flow rates at a downstream problem area(s) shall be precluded from attempts to prove no harm, except in conjunction with proposed capacity improvements for the problem area(s) consistent with § 121-4C(9). Any no-harm justifications shall be submitted by the developer as part of the drainage plan submission per § 121-4H.
(d) 
Recharge volume requirements of this chapter must be met.
(8) 
Regional or subregional detention alternatives may be more cost effective for certain areas of the Lower Merion Drainage Area. The initiative and funding for any regional or subregional runoff control alternatives are the responsibility of the developer(s) involved. The design of any regional control basins must incorporate reasonable development of the entire upstream watershed. The peak outflow of a regional or subregional basin shall be determined on a case-by-case basis using the calibrated version of the Penn State Runoff Model as developed for the plan, consistent with protection of the downstream watershed areas.
(9) 
In some instances, including but not limited to the provisional infiltration only district, local drainage conditions may dictate more restrictive levels of runoff control than those based on protection of the entire watershed. In these instances, if the developer shows that it is more feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then these capacity improvements can be provided by the developer in lieu of runoff controls on the development site. The design of any capacity improvements would be based on development of all areas tributary to the proposed improvement and the capacity criteria specified in § 121-4C(3). In addition, all new development upstream of a proposed capacity improvement shall be assumed to implement the applicable runoff controls consistent with this chapter. Capacity improvements may also be provided as necessary to implement any regional or subregional detention alternatives. They may also be provided to implement a modified no-harm option which proposes specific capacity improvements in support of a less restrictive discharge control.
(10) 
Any proposed regulated activity for which a permanent stormwater quality control detention basin is required under the NPDES regulations shall use the more restrictive runoff control criteria between this chapter and the NPDES requirements.
(11) 
The required stormwater management criteria may be met through off-site stormwater management measures, provided that the proposed measures are in the same watershed and downgrade properties are adequately protected to the satisfaction of the Township Engineer.
[Added 7-18-2007 by Ord. No. 3821]
(12) 
Off-site areas. Off-site areas that drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the development site.
[Added 7-18-2007 by Ord. No. 3821]
(13) 
Site areas. Where the site area to be disturbed by a proposed development activity differs significantly from the total site area, only the proposed disturbed area utilizing stormwater management measures shall be subject to the management district criteria. Thus, undisturbed areas bypassing the stormwater management facilities would not be subject to the management district criteria.
[Added 7-18-2007 by Ord. No. 3821]
D. 
Calculation methodology.
(1) 
Stormwater runoff from all development sites shall be calculated using either the rational method or a soil-cover-complex methodology, according to the direction of the Township Engineer.
(2) 
The design of any detention basin intended to meet the requirements of this chapter shall be verified by routing the design storm hydrograph through the proposed basin. For basins designed using the rational technique, the detention volume shall, at minimum, equal the volume derived from the routing process as contained in SCS Technical Release Number 55 (TR55, 1986).
(3) 
All surface stormwater detention facilities shall provide a minimum one-foot freeboard above the maximum pool elevation associated with the two- through twenty-five-year storm. The two- through one-hundred-year storm runoff shall be controlled by the primary outlet structure. An emergency spillway for each basin shall be designed to pass the entire one-hundred-year return frequency storm peak flow rate with a minimum of 0.5 foot of freeboard. The spillway should function to control overflows in the event of a blockage of the basin outlet system. If this detention facility is considered to be a dam as per DEP Chapter 105, the design of the facility must be consistent with the Chapter 105 regulations and may be required to pass a storm greater than a one-hundred-year storm.
(4) 
All calculations using the soil-cover-complex method shall use the Soil Conservation Service Type II twenty-four-hour rainfall distribution. The twenty-four-hour rainfall depths for the various return periods to be used consistent with this chapter are:
[Amended 7-18-2007 by Ord. No. 3821]
Return Period
(years)
Twenty-four-Hour Rainfall Depth
(inches)
1
2.8
2
3.2
5
4.2
10
5.0
25
5.8
50
6.5
100
8.4
(5) 
All calculations using the rational method shall use rainfall intensities consistent with appropriate times of concentration and return periods and the intensity-duration-frequency curves as presented in Appendix C.[2]
[2]
Editor's Note: Appendix C is on file in the Township offices.
(6) 
Runoff curve number (CN's).
(a) 
Runoff curve numbers (CN's) to be used in the soil-cover-complex method shall be based on the following where more accurate information is unavailable:
[1] 
"Woodland" shall be used for any building lot having more than one viable tree having a caliper of six inches or greater per 1,500 square feet of lot area.
[2] 
"Meadow" shall be used for all other areas of vegetative cover.
[3] 
"Existing impervious cover" shall be used where it occurs.
(b) 
With concurrence from the Township Engineer, CN values can be used as presented in Appendix C.
(7) 
Runoff coefficients for use in the rational method shall be based on the table presented in Appendix C, with concurrence from the Township.
(8) 
The Manning equation shall be used to calculate the capacity of watercourses. Manning "n" values used in the calculations shall be consistent with the table presented in Appendix C. Pipe capacities shall be determined by methods acceptable to the Township Engineer.
(9) 
The PADEP Chapter 105 Rules and Regulations shall apply to the construction, modification, operation or maintenance of both existing and proposed dams, water obstructions and encroachments throughout the watershed, despite any possible differences with the criteria that are used in permitting of dams under the Dam Safety Program.
E. 
Stormwater management facility standards.
(1) 
Surface detention basins.
(a) 
Any stormwater management facility required or regulated by this chapter shall be designed to provide an emergency spillway to handle flow up to one-hundred-year post-development conditions. The height of the embankment must be set to provide a minimum 1.0 foot of freeboard from the flow depth elevation when stormwater is discharging via the emergency spillway to the top of the berm when the facility functions for one-hundred-year post-development inflow. Should any stormwater management facility require a dam safety permit under PA DEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety.
(b) 
Wherever possible, discharge from stormwater management basins shall convert a concentrated flow into a sheet flow at a noneroding velocity.
(c) 
Stormwater drainage system design shall safely route all runoff, especially that which cannot find its way into a storm sewer pipe.
(d) 
The riser pipe or pipe spillway shall have a red line painted at the maximum level to indicate when cleanout of sediment storage is required. If the riser is perforated, the hole diameter shall be a minimum of one-half-inch size.
(e) 
Wherever feasible, roof drainage shall be connected to the stormwater management system.
(f) 
For retention basins, a fence four feet in height with a self-closing gate surrounding the basin may be required as directed by the Lower Merion Director of Building and Planning.
[Amended 1-19-2002 by Ord. No. 3631]
(2) 
Infiltration seepage beds.
(a) 
Seepage beds shall be designed to recharge the increased volume of runoff generated by the twenty-five-year storm wherever the percolation rates will allow.
(b) 
Seepage beds shall be designed to empty the total design storm value in 24 hours or less.
(c) 
Design consideration shall not include infiltration rates in computing storage volume of a seepage bed. However, the infiltration rate shall be used to meet the requirements that the seepage bed and/or pit shall empty in 24 hours or less.
(d) 
The seepage bed shall have a minimum of 12 inches of cover and be located at least 10 feet from a basement wall. It shall be located downhill from a building in the direction of surface runoff where feasible.
(e) 
Compaction of the seepage bed subgrade shall not reduce the soil infiltration rate.
(f) 
All seepage beds shall contain sediment traps accessible for maintenance, as required by the Township Engineer.
(g) 
An overflow system shall be provided for a storm exceeding the volume of storage and safe discharge at a noneroding velocity, converting a concentrated flow into a sheet flow.
(h) 
A high-permeability filter fabric shall surround the stone seepage bed to prevent migration of soil fines into the bed.
(i) 
Soil permeability tests (percolation rates) shall be made to a depth below the bottom of the seepage bed as necessary in order to demonstrate that the basin will function properly. The test must be certified by a professional engineer or Sewage Enforcement Officer. Where seepage beds are to be placed in fill, geotechnical investigations of the subgrade stability must be performed as directed by the Township Engineer.
[Amended 7-18-2007 by Ord. No. 3821]
(j) 
Both horizontal and vertical seepage pits constructed of perforated pipes may be used. Perforations shall be not less than 5/16 inch in diameter and provide an opening area not less than 3.31 square inches per square foot of pipe surface unless documentation qualifying different dimensions is submitted by the design engineer and approved by the Township Engineer. Provision shall be made for maintenance of each seepage pit.
(k) 
Infiltration seepage beds may be combined with detention/retention surface basins.
(l) 
Seepage beds shall not receive runoff without the prior approval from the Township Engineer until the entire drainage area contributory to the infiltration BMP has achieved final stabilization.
[Added 7-18-2007 by Ord. No. 3821]
(m) 
Infiltration facilities are encouraged to be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.
[Added 7-18-2007 by Ord. No. 3821]
(n) 
Extreme caution shall be exercised where salt or chloride would be a pollutant since soils do little to filter this pollutant, and it may contaminate the groundwater. The qualified design professional shall evaluate the possibility of groundwater contamination from the proposed infiltration facility and perform a hydrogeologic justification study if necessary or as directed by the Township Engineer.
[Added 7-18-2007 by Ord. No. 3821]
(o) 
An impermeable liner will be required in seepage beds where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the Township Engineer.
[Added 7-18-2007 by Ord. No. 3821]
(p) 
The applicant shall provide safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.
[Added 7-18-2007 by Ord. No. 3821]
(q) 
Stormwater hotspots. Below is a list of examples of designated hotspots. If a site is designated as a hotspot, it has important implications for how stormwater in managed. First and foremost, untreated stormwater runoff from hotspots shall not be allowed to recharge into groundwater where it may contaminate water supplies. Therefore, recharge requirements shall not be applied to development sites that fit into the hotspot category. Water quality treatments will still be required. Second, a greater level of stormwater treatment shall be considered at hotspot sites to prevent pollutant wash off after construction. The Environmental Protections Agency's (EPA) NPDES stormwater program requires some industrial sites to prepare and implement a stormwater pollution prevention plan.
[Added 7-18-2007 by Ord. No. 3821]
[1] 
Examples of hotspots:
Vehicle salvage yards and recycling facilities
Vehicle fueling stations
Vehicle service and maintenance facilities
Vehicle and equipment cleaning facilities
Fleet storage area (bus, truck, etc.)
Industrial sites based on Standard Industrial Codes
Marinas (service and maintenance)
Outdoor liquid container storage
Outdoor loading/unloading facilities
Public works storage areas
Facilities that generate or store hazardous materials
Commercial container nursery
Other land uses and activities as designated by the Township Engineer
[2] 
The following land uses and activities are not normally considered hotspots:
Residential streets
Residential development
Institutional development
Office developments
Nonindustrial rooftops
Pervious areas, except golf courses and nurseries [which may need an integrated pest management (IPM) plan]
(3) 
Access and maintenance easements. An access and maintenance easement that is of sufficient width to provide access and egress from a public right-of-way shall be provided around all stormwater management facilities if required by the Township Engineer.
[Added 7-18-2007 by Ord. No. 3821]
(4) 
Maintenance and operation plan.
[Added 7-18-2007 by Ord. No. 3821]
(a) 
A description of how each undedicated permanent stormwater control and BMP will be operated and maintained shall be submitted by the design professional. In addition the plan shall include the following information:
[1] 
The frequency of any required inspection.
[2] 
The identity and contact information associated with the person(s) responsible for operation and maintenance.
[3] 
A statement signed by the owner of the property acknowledging that the stormwater controls and BMPs are fixtures that can be altered or removed only after approval by the Township.
(b) 
The plan shall be presented in recordable form to the Township as a covenant running with the land, shall be approved by the Township Solicitor, and shall be recorded in the Office for the Recording of Deeds of Montgomery County.
F. 
Storm sewer standards.
(1) 
Headwalls. Standard headwalls shall be installed on all pipes and, additionally, trash bars shall be installed on all pipes equal to or greater than 24 inches diameter.
(2) 
Pipeline design.
(a) 
Storm sewer pipelines shall be designed by either of the two methods described in Subsection F(2)(a) and (b) below. Both shall be based on the Manning equation and shall utilize the friction factors which have been established. Some of these values are as follows:
n
=
0.015 concrete pipe.
n
=
0.021 corrugated metal pipe.
n
=
0.010 PVC pipe.
n
=
0.020 helical metal pipe.
For other materials, an appropriate value must be approved by the Township Engineer.
The minimum allowable pipe size is 15 inches.
(b) 
Pipeline submerged.
[1] 
This method is based on the assumption that, when the storm sewer system is under maximum load, the hydraulic gradient will be at or above the crown of the pipe and that flow in the lines will be controlled by head differentials between structures or other locations where the system is open to the ground surface, such as inlets or outlets, manholes and stream inlets and outlets. The head of water above the crown of any pipe can range from zero feet to a point which will not cause surface flooding.
[2] 
The slope of the hydraulic gradient in any section of storm sewer between opening to the surface shall be calculated on the assumption that the pipe is flowing full at a constant velocity and at the required capacity.
[3] 
The elevation of the hydraulic gradient at any point in the pipe shall be no lower than the crown of the pipe and no higher than the surface of the ground.
[4] 
The elevation of the hydraulic gradient at any point where the system opens to the surface, such as an inlet or manhole, shall be three feet below the surface of the ground.
[5] 
At all structures such as manholes, inlets, etc., where the pipe size does not change and unless otherwise permitted by the Township Engineer, the elevation of the hydraulic gradient shall be dropped 0.2 foot to allow for losses therein. Where the inlet and outlet pipe sizes are not the same, the elevation of the hydraulic gradient shall be dropped an amount based on the following formula:
H = 0.2 inches + 0.8 (D2-D1)
Where
D1 = The diameter of inlet pipe.
D2 = The diameter of outlet pipe.
If D1 is larger than D2, head loss equals 0.2 foot.
[6] 
The minimum slope of any pipe shall be such that a minimum velocity of 2.5 feet per second shall be maintained when the pipe is flowing 1/4 full.
(c) 
Pipeline flowing full.
[1] 
This method is based on the assumption that the hydraulic gradient will match the inside top of the pipe when the system is under maximum hydraulic load.
[2] 
For this method, head losses through manholes, inlets, etc., shall be ignored.
[3] 
The minimum slope of any pipe shall be such that a minimum velocity of 2.5 feet per second shall be maintained when the pipe is flowing 1/4 full. When the pipe sizes change, the inside tops of the pipes shall be matched.
(3) 
Profiles. Continuous profiles for each reach of pipe shall be plotted along with the location of the hydraulic gradient and the hydraulic information pertinent to each reach within the system. This information shall include the pipe size and type, the n-factor, the slope of the hydraulic gradient, slope of the pipe, the design capacity and the velocity at the design capacity.
(4) 
Inlets. Unless adequate analysis is submitted with differing requirements:
(a) 
Single inlets shall be used on streets with grades of 4% or less. Double inlets shall be used on streets of more than 4%.
(b) 
Sufficient inlets shall be located and constructed so as to collect all of the stormwater flow in the drainage area tributary to the inlet.
(c) 
The gutter of all inlets shall be set not less than two inches nor more than four inches below the gutter grade. The surface of the paving adjacent to the inlets shall be constructed to blend into the lowered gutter grade at the inlet in such a manner that sudden dropoff or dip at the inlet will not be created.
(d) 
Where surface water is collected from two directions at one street corner, inlets shall be placed at, or near, the tangent points of both ends of the radius. The use of an inlet in the radius shall not be allowed unless no other location is feasible as determined by the Township Engineer.
(5) 
Manholes. Manholes shall be located at intervals of approximately 400 feet where pipe sizes of 24 inches or less are used and 600 feet apart for larger sizes. Inlets should be substituted for manholes where they will serve a useful purpose. Manhole and inlet castings may be obtained from the Lower Merion Department of Public Works where inventory permits.
(6) 
Open channel design. Open channel design should be based on the following hydraulic considerations:
(a) 
Mannings equation. "n" values as described in Appendix C[3] or as approved by the Township Engineer.
[3]
Editor's Note: Appendix C is on file in the Township offices.
(b) 
Allowable velocity.
Excavation Material
Velocity
(feet per second)
Fine sand and firm loam
2.50 to 3.5
Stiff clay and hardpan
3.75 to 6.0
Concrete-lined ditch
15
(c) 
Ample freeboard should be provided on all channels as discussed in this chapter.
(d) 
The channel should be designed to conform, wherever possible, to the adjacent ground conditions. This means that it should not be projecting excessively above the surrounding ground or placed excessively below the surrounding ground.
(e) 
Continuous profiles for each reach of open channel shall be plotted along with the adjacent average ground and the hydraulic information pertinent to each reach within the system. This information shall include the type of channel lining, in the n-factor, the width of the channel bottom, the side slopes, the water depth, the design capacity and the velocity at the design capacity.
(f) 
Open channels shall have a maximum side slope of three to one and shall have adequate slope protection as required by this chapter.
(7) 
Bridges and culverts. Single-opening culverts are desirable. The design of culverts shall be such as to minimize the probability of debris accumulation. Bridges and culverts shall be designed to meet current Pennsylvania Department of Transportation standards for expected loads. They shall be constructed for the full right-of-way.
(8) 
Permits may be required from the Department of Environmental Resources, Bureau of Dams and Waterway Management, for the construction of dams and any activity within a watercourse, floodway or wetland. No open watercourses shall be permitted within the right-of-way of any street.
(9) 
Location. Wherever practicable, storm drains shall be located behind the curb and within the right-of-way of the street. They shall be protected by a cover of at least 18 inches. The plan shall note that the continued maintenance of storm drains outside the street right-of-way shall be the continued responsibility of the property owner.
(10) 
Change in direction. Structures shall be used where abrupt changes are made in alignment.
(11) 
Stormwater roof drains. Stormwater roof drains and pipes immediately adjacent to a sidewalk shall not discharge water over a sidewalk but shall extend under the sidewalk to the gutter. Where accessible, the roof drain shall be connected with the storm drainage system of the Township.
(12) 
Underground utilities in the floodplain. All utilities shall be floodproofed to an elevation two feet above the one-hundred-year design storm.
(13) 
Runoff computations. Computation of the rate of flow at any given location shall be based on the rational formula:
Q = CIA
Where
Q = Volume in cubic feet per second.
C = Runoff factor.
I = Intensity of rainfall in inches per hour.
A = Watershed area in acres.
In setting the value of the runoff coefficient C, consideration will be given to the physical features of the drainage basin and the best available data on the future density of development of the drainage basin. In no case shall it be less than 0.40 in a developed area.
(14) 
Storm intensity. The intensity of the storm shall be based on the following:
(a) 
As a minimum, a ten-year storm shall be used at low points with a relief swale, or a twenty-five-year storm where carried in the pipe.
(b) 
As a minimum, all inlet and culvert designs shall be based on a twenty-five-year storm.
(c) 
As a minimum, a one-hundred-year storm will be used in connection with this chapter. The Rainfall-Intensity-Duration-Frequency Curve for Philadelphia presented in Technical Paper No. 25, prepared by the United States Department of Commerce Weather Bureau, a copy of which is available for public inspection at the office of the Township Engineer, shall be used.
(15) 
Special drainage problems.
(a) 
Unnatural drainage. Whenever construction stops or concentrates the natural flow of storm drainage in such a way as to affect adjoining properties, approval of the owners must be obtained in writing. Approval of plans by the Township does not authorize drainage affecting adjoining properties.
(b) 
Water originating from other than natural sources, such as swimming pools, air-conditioning units, sump pumps or other dry-weather flow, wherever practicable, shall be discharged into natural watercourses on the property or connected to the storm drainage system of the Township. These facilities may not be used for toxic drainage.
G. 
Landscaping of stormwater management facilities.
(1) 
Landscaping shall be required in and around all stormwater management facilities with a minimum surface area of 1,000 square feet for the purposes of:
(a) 
Assisting in the management of stormwater;
(b) 
Stabilizing the soil within such facilities to control erosion;
(c) 
Enhancing the visual appearance of such facilities; and
(d) 
Mitigating maintenance problems commonly associated with the creation of such facilities.
(2) 
A planting plan shall be submitted in accordance with the following:
(a) 
Wet meadows, including basin floors.
[1] 
Wet meadows and basin floors shall be planted with wildflowers and nonagressive grasses, the intent being to create a mixed meadow of such plantings, where appropriate. Selection of plantings should be based on whether the area in question is usually well drained or permanently wet and whether the area will be used for recreation purposes in accordance with Chapter A177 of the Appendix attached hereto. No woody plants shall be planted within the saturated zone (phreatic line) of a stormwater management basin.
[2] 
Seeding by drills, corrugated rollers, Cyclone or drop seeders or hand seeding of such areas is preferred; however, hydroseeding followed by hydromulching can be used on wet ground and steep slopes.
[3] 
Fertilizers, as a nutrient supplement, shall not be used unless it is documented that soil conditions warrant such use. Soil for planting of wildflowers shall contain not less than 3% nor more than 10% organic matter, as determined by an agricultural chemist, with certification of test before planting.
[4] 
Seeding should take place either between April 1 and May 1 or September 1 and October 15. Planting areas shall be soaked to maintain a consistent level of moisture for at least four to six weeks after planting.
[5] 
Once established, a single annual mowing when plants are dormant should be sufficient to maintain a wet meadow and/or basin floor.
(b) 
Wet edges which remain wet all or most of the year shall be planted with wildflowers, grasses and shrubs. Plants to be located on rims or banks which remain dry most of the year should be planted with species tolerant of dry soil conditions in accordance with Chapter A177 of the Appendix attached hereto.
(c) 
Wooded areas.
[1] 
Where stormwater management facilities adjoin wooded areas, trees and shrubs shall be selected and planted so as to blend with existing surroundings in accordance with Chapter A177 of the Appendix attached hereto.
[2] 
Plantings in such areas shall be of sufficient density to eliminate the need for mowing.
[3] 
It is recommended that clusters of trees and shrubs be planted around stormwater management facilities, where applicable, to provide for wildlife habitat, wind control and buffering and screening.
[4] 
Vegetation shall be planted during appropriate times of the year, predominantly between late March and mid-May from early October until evidence of ground freezing, depending upon the species selected. Most deciduous trees and shrubs can be planted in either spring or fall. Evergreens are best planted in late summer or early fall.
(d) 
Slopes.
[1] 
Where slopes are gentle, a mixture of meadow grasses and wildflowers (for wet meadows) shall be planted in accordance with Chapter A177 of the Appendix attached hereto.
[2] 
On steep slopes, dense spreading shrubs (shrubs tolerant of dry soils) shall be planted. A heavy mat mulch shall be used during the period of establishment.
[3] 
No woody plant materials or trees shall be located on a constructed or natural berm acting as the impoundment structure of a detention/retention basin. Trees shall be located on the downstream side of an impoundment berm a sufficient distance from the toe of the constructed slope to assure that the toe of the slope is outside the dripline of the mature species planted.
(e) 
Screening and buffering.
[1] 
Stormwater management facilities shall be appropriately screened in a manner which compliments the existing landscape and provides sufficient access for maintenance. In many cases, complete perimeter screening may not be necessary; however, it shall be the applicant's responsibility to demonstrate in the submitted planting plan why this is so.
[2] 
Plantings shall consist of clusters of evergreens interspersed with groupings of deciduous trees and shrubs in accordance with Chapter A177 of the Appendix attached hereto. Single species planting is prohibited.
[3] 
It is encouraged that plantings be used which provide food and shelter for wildlife.
H. 
Water quality.
(1) 
In addition to the performance standards and design criteria requirements of this chapter, the land developer shall implement the following water quality requirements unless otherwise exempted by the provisions of this chapter. The land developer shall:
(a) 
Where storm basins are used, the basins shall be designed so that the five-year, post-development peak rate of runoff is controlled to the two-year, predevelopment peak rate of runoff. The control of the five-year storm in this way will improve the water quality of the stormwater runoff. Further, the basin shall be designed to achieve the designated release rate for the subwatershed(s) in question for the twenty-five-year storm.
(b) 
As an alternative to the requirements of Subsection A, the water quality objectives may be achieved through a combination of BMP's. The combination of BMP's shall be designed according to the requirements listed under BMP selection criteria and in consultation with the Township Engineer. Appendix F[4] contains a description of BMP's for stormwater basins. Applicants are strongly urged to consider designing stormwater basins according to these BMP's to achieve improvements in stormwater quality and/or groundwater recharge.
[4]
Editor's Note: Appenix F is on file in the Township offices.
(c) 
In lieu of Subsections A and B above, the land developer may submit original and innovative designs to the Township Engineer for review and approval.
(2) 
BMP selection criteria.
(a) 
In selecting the appropriate BMP's or combinations thereof, the land developer shall consider the following:
[1] 
Total contributing area.
[2] 
Permeability and infiltration rate of the site soils.
[3] 
Slope and depth to bedrock.
[4] 
Seasonal high water table.
[5] 
Proximity to building foundations and well heads.
[6] 
Erodibility of soils.
[7] 
Land availability and configuration of the topography.
(b) 
The following additional factors should be considered when evaluating the suitability of the BMP's used to control water quality at a given development site:
[1] 
Peak discharge and required volume control.
[2] 
Stream bank erosion.
[3] 
Efficiency of the BMP's to mitigate potential water quality problems.
[4] 
The volume of runoff that will be effectively treated.
[5] 
The nature of the pollutant being removed.
[6] 
Maintenance requirements.
[7] 
Creation/protection of aquatic and wildlife habitat.
[8] 
Recreational value.
[9] 
Enhancement of aesthetics and property values.
I. 
Waiver procedure.
(1) 
The Township may hear requests for waivers where it is alleged that the provisions of this chapter inflict unnecessary physical constraint on the applicant. The waiver request shall be in writing, or on an application promulgated by the Township and accompanied by the requisite fee, based on a fee schedule adopted by the Township. A copy of the completed application form shall be provided to each of the following: Township, Township Engineer, Township Solicitor and Montgomery County Planning Commission. The application shall fully document the nature of the alleged hardship. The Township may grant a waiver provided that all of the following findings are made in a given case:
(a) 
There are unique physical circumstance or conditions, including irregularity of lot size or shape, or exceptional topographical or other physical conditions peculiar to the particular property and that the unnecessary hardship is due to such conditions and not the circumstances or conditions generally created by the provisions of the ordinance for the stormwater management district in which the property is located.
(b) 
That because of such physical circumstances or conditions, there is no possibility that the property can be developed in strict conformity with the provisions of this chapter, including the no-harm provision, and that the authorization of a waiver is therefore necessary to enable the reasonable use of the property.
(c) 
That such unnecessary hardship has not been created by the applicant.
(d) 
That the waiver, if authorized, will represent the minimum waiver that will afford relief and will represent the least modification possible of the regulation in issue.
(e) 
Financial hardship shall not constitute grounds for granting of a waiver.
(2) 
In granting any waiver, the Township may attach such reasonable conditions and safeguards, as it may deem necessary to implement the purposes of Act 167 and this chapter.
J. 
Liability disclaimer.
(1) 
Neither the granting of any approval nor the compliance with the provisions of this chapter or with any condition imposed by the Township, its officials, employees or designated representatives hereunder shall relieve any person from any responsibility for damages to persons or property resulting therefrom, or as otherwise imposed by law nor impose any liability upon the Township, its officials, employees or designated representatives to the maximum extent permitted by law.
(2) 
The granting of any permit which includes any stormwater management requirements shall not constitute a representation, guarantee or warranty of any kind by the Township, the officials, employees or designated representatives thereof of the practicability or safety of any stormwater structure or facility, use or other plan proposed and shall create no liability or cause of action upon the Township, its officials, employees or designated representatives for any damage that may result pursuant thereto to the maximum extent permitted by law.
[Amended 6-15-1988 by Ord. No. 3098]
A. 
General requirements.
(1) 
Minimum grading. The maximum bare area (without vegetative cover) shall not exceed 25% of the total area at any one time. This requirement shall apply only if the total area, before subdivision or land development, is greater than four acres.
(2) 
The maximum time of exposure for bare areas shall be 20 days before stabilization measures must be implemented.
(3) 
Fording of live streams or travel in their beds by mechanized equipment is not permitted; bridges or culverts shall be used when crossing streams is necessary.
(4) 
Roads and parking areas, in active construction areas, shall be completed (except for wearing course) before building construction is permitted. The binder course shall be repaired and regraded to grade before installing wearing course near the end of the project construction. Any regulated activity which would create 1,500 square feet or less of additoinal impervious cover is exempt from the stormwater management provisions of this ordinance. This criteria shall apply to the total proposed development, even if development is to be phased. Additonal impervious cover shall include any roof, parking area, driveway area and any new streets and sidewalks constructed as part of or for the proposed regulated activity. Any areas initially to be gravel, crushed stone, etc., shall be assumed to be impervious for the purposes of the waiver criteria.
[Amended 11-17-1999 by Ord. No. 3546]
(5) 
Temporary erosion control measures may be removed only after the construction area and contained silt is stabilized and the lawn area established.
(6) 
All newly graded slopes four to one (25%) or over shall be sodded or stabilized with erosion control netting.
(7) 
A routine end-of-day check shall be made during construction to make sure that all control measures are working properly. All persons engaged in land disturbance activities shall design, implement and maintain control measures which prevent accelerated erosion and sedimentation. There shall be no adverse discharge of the sediment or other solid materials from the site as the result of stormwater runoff. This should be accomplished by scheduling the construction in such a way as to utilize new plantings and properly installed erosion control fencing and hay bales to minimize erosion damage. This process shall be accomplished to the satisfaction of the Township Building and Planning Department and the Township Engineer and be shown on the plan in an outline form to attain environmental protection.
[Amended 1-19-2002 by Ord. No. 3629]
B. 
Permit requirements.
(1) 
No person shall commence or perform any grading, excavation, fill or clearing of trees without first having obtained a grading or runoff and erosion control permit from the Township Engineer. A separate permit shall be required for each site. One permit may cover both an excavation and any fill made on the same site. A runoff and erosion control permit will be required when stormwater management calculations and plans are required pursuant to § 121-6 hereof. A grading permit will not be required for the conditions set forth below. Where neither a runoff and erosion control permit nor a grading permit are required, all other provisions of this chapter shall nevertheless apply.
[Amended 12-17-1997 by Ord. No. 3470; 7-18-2007 by Ord. No. 3821; 7-18-2012 by Ord. No. 3980]
(a) 
An excavation that does not exceed three feet in vertical depth at its deepest point, measured from the natural ground surface, or that covers an area of more than 1,000 square feet. This exception shall not affect the applicability of this chapter to or the requirement for a permit for any fill made with the material from such excavation.
(b) 
A fill that does not exceed 10 cubic yards of material on any one site, or a fill that exceeds three feet in vertical depth at its deepest point, measured from the natural ground surface, or that covers an area of more than 1,000 square feet, provided that the surfaces of such fills do not have a slope at any point steeper than five horizontal to one vertical.
(c) 
An excavation below the finished grade for basements and footings of a building, swimming pool or underground structure authorized by a building permit where the area limitations set forth in this section have not been exceeded. This exception shall not affect the applicability of this chapter to or the requirement for a permit for any fill made with the material from such excavation. A permit shall not be required for the temporary stockpiling on the same site of the material from such excavation.
(2) 
Permits issued pursuant to this chapter do not relieve the owner of the site of responsibility for securing required permits for work to be done which is regulated by any other applicable code, rules, statutes, regulations or ordinances. This chapter shall not preclude the inclusion in such other permit of more stringent requirements concerning regulation of runoff and erosion.
(3) 
Application for permit. A written application from the owner of the site or his authorized representative, in the form prescribed by the Township Engineer, shall be required for each permit. No permit shall be transferable without the written consent of the Township Engineer. The permit application shall be accompanied by six copies of the runoff and erosion control plans and specifications, which shall meet as a minimum the standards and specifications required by the Montgomery County Soil and Water Conservation District and the Township Design and Construction Standards Manual, which shall be available to the public for inspection at the office of the Township Engineer, from whom copies of all or any part thereof may be obtained at the rate of $0.10 per page. The Erosion and Sediment Control Design Standards are hereby incorporated by reference in this chapter and shall be as much a part of this chapter as if it were fully set forth herein; provided, however, that said handbook may be amended from time to time by ordinance of the Township of Lower Merion.
[Amended 7-18-2007 by Ord. No. 3821]
(4) 
Any regulated activity which would create 1,500 square feet or less of additional impervious surface is exempt from the stormwater management provisions of this chapter. This criteria shall apply to the total proposed development even if it is to be phased.
[Added 11-17-1999 by Ord. No. 3546]
(a) 
This exemption shall not apply to any property where more than 75% of the principal building area is being demolished and a new principal building is being constructed. In such case the existing impervious surface on the property shall be considered as meadow for the purpose of calculating stormwater runoff required by this chapter.
[Added 1-19-2005 by Ord. No. 3734]
(b) 
The Township Engineer may authorize a reduction in the size of the stormwater management system if the installation of the stormwater management system will result in the removal of large trees or a large number of smaller trees, or where the Township Engineer determines that it is not feasible due to site constraints that would limit compliance.
[Added 1-19-2005 by Ord. No. 3734]
(c) 
Exemption criteria for permits.
[Added 7-18-2007 by Ord. No. 3821]
[1] 
Exemption responsibilities. An exemption shall not relieve the applicant from implementing such measures as are necessary to protect public health, safety, and property. Adequate erosion controls must always be provided.
[2] 
Emergency exemption. Emergency maintenance work is that required to be performed immediately for the protection of public health, safety, and welfare. A written description of the scope and extent of any emergency work performed shall be submitted to the Township Building Department within two days of the commencement of the activity. If the Township finds that the work is not an emergency, then the work shall cease immediately and the requirements of this article shall be addressed as applicable.
[3] 
Maintenance exemption. This exemption is provided for any routine maintenance to an existing stormwater management system made in accordance with plans and specifications approved by the Township Engineer. Any replacement of an existing seepage bed or stormwater basin must be coordinated with the Township so that necessary inspections can be performed.
[4] 
Even though a property owner or developer is exempt from permit requirements, he is not relieved from complying with other applicable regulations and codes.
[Amended 10-18-1978 by Ord. No. 1833; 6-15-1988 by Ord. No. 3098]
The applicant shall submit stormwater management by Ord. No. 3098 and erosion and sediment control plans which shall contain but are not limited to the following:
A. 
The date, name, address and telephone number of the preparer(s) of plans or each portion thereof; the owner of the site; and lot, block, tract or street address or similar description which identifies and locates the proposed work.
B. 
Certification from the preparer(s) of the plan, who shall be registered professional engineers or other registered professional(s) qualified by background and experience in runoff and erosion control design and computation, attesting to the completeness and correctness of existing conditions as shown, to the compliance of all proposed earthmoving and other work with all of the requirements of this chapter, except for specific waivers or modifications as listed, and that the proposed measures will meet, as a minimum, the standards and specifications contained in the Erosion and Sediment Control Handbook as incorporated in this chapter by § 121-5B(3).
C. 
A clear and definite delineation of the limits of work and the areas to remain undisturbed, along with a statement of the area, in square feet, of the total site and of the areas to remain undisturbed which currently have an effective runoff- and erosion-resistant ground cover or surface.
D. 
A narrative report describing the project and giving the purpose. The engineering assumptions and calculations for control measures and facilities shall include a hydrologic data sheet. The hydrologic data sheet shall include but not be limited to:
(1) 
Watershed area in acres and slope in percentages.
(2) 
Weighted soil cover complex numbers.
(3) 
Peak discharge rates in cubic feet per second and velocities in feet per second for emergency spillways and outlet structures.
(4) 
Total storage capacity in cubic feet.
(5) 
A plan showing the effective watershed.
(6) 
Inflow and outflow hydrographs for all detention/retention facilities.
E. 
A clear and definite delineation, with dimensions and locations, for all proposed fill.
F. 
Existing topography and proposed finished grade, including that for restoration of borrow pits and open-pit mines, and site work, with contours at two-foot intervals, drawn at a scale of one inch to 20 feet to 40 feet of the entire site, plus a minimum twenty-foot adjacent peripheral strip or as might otherwise clearly reflect existing conditions and proposed earthmoving and other work, provided that such other interval and scale has the Township Engineer's approval in advance of plan preparation.
G. 
Established or, in the case of new subdivisions, approved tentative street grades (elevations).
H. 
Size, location and construction details of all existing and proposed surface structures and storm drainage facilities; the location, species and size in diameter of trees two feet above the ground, alone and in groves, or street shade trees; and other site work.
I. 
Planting plan, in accordance with § 121-4D and the Natural Features Conservation Code, Appendix Chapter A177.
[Added 5-17-1989 by Ord. No. 3155[1]]
[1]
Editor's Note: This ordinance also provided for former Subsection I to be redesignated as Subsection J.
J. 
A timing schedule and sequence indicating the anticipated starting and completion dates of the development sequence. The schedule must include:
(1) 
Tree removal.
(2) 
Stripping, stockpiling and stabilizing of topsoil to a depth of six inches.
(3) 
Rough grading and construction.
(4) 
Final grading and vegetative establishment.
(5) 
Exposure time of each area prior to the completion of effective runoff and erosion control measures.
(6) 
Maintenance to time of occupancy permit.
(7) 
A description and clear and definite delineation of the interim and permanent runoff and erosion control facilities and measures to be provided.
(8) 
The estimated cost of the earthmoving and/or filling and the cost of the required runoff and erosion controls.
(9) 
A planting schedule.
[Added 5-17-1989 by Ord. No. 3155]
A. 
No excavation shall be made with a cut face steeper in slope than one horizontal to one vertical, except under one or more of the following conditions:
(1) 
The excavation is so located that a line having a slope of one horizontal to one vertical and passing through any portion of the cut face will be entirely inside the property lines of the property on which the excavation is made.
(2) 
The material in which the excavation is made is sufficiently stable to sustain a slope of steeper than one horizontal to one vertical, and a written statement of a civil engineer, licensed by the Commonwealth of Pennsylvania and experienced in erosion control, to that effect is submitted to the Township Engineer and approved by him. The statement shall state that the site has been inspected and that the deviation from the slope specified above will not result in injury of persons or damage to property.
(3) 
A retaining wall or other approved support is provided to support the face of the excavation.
B. 
The Township Engineer may require an excavation to be made with a cut face flatter in slope than one horizontal to one vertical if he finds that the material in which the excavation is to be made is unusually subject to erosion, or if other conditions exist which make such flatter cut slope necessary for stability and safety.
C. 
Excavations shall not extend below the angle of repose or natural slope of the soil under the nearest point of any footing or foundation of any building or structure unless such footing or foundation is first properly underpinned or protected against settlement.
D. 
Before commencing any excavation which can in any way affect an adjoining public or private property or structures thereon, the person making or causing the excavation to be made shall, in writing, notify the owners of adjoining buildings and the Township Engineer, not less than 30 days before such excavation is to be made, that the excavation is to be made. Adjoining properties and structures shall be protected as provided in the then-current Building Code of the Township of Lower Merion.[1]
[1]
Editor's Note: See Ch. 62, Building Construction.
A. 
No fill shall be made which creates any exposed surface steeper in slope than 1 1/2 horizontal to one vertical, except under one or more of the following conditions:
(1) 
The fill, in the opinion of the Township Engineer, is located so that settlement, sliding or erosion of the fill material will not result in property damage or be a hazard to adjoining property, streets, alleys or buildings.
(2) 
A written statement from a civil engineer, licensed by the Commonwealth of Pennsylvania and experienced in erosion control, certifying that he has inspected the site and that the proposed deviation from the slope specified above will not endanger any property or result in property damage, is submitted to and approved by the Township Engineer.
B. 
The Township Engineer may require that the fill be constructed with an exposed surface flatter than 1 1/2 horizontal to one vertical if he finds that under the particular conditions such flatter surface is necessary for stability and safety.
C. 
Whenever a fill is to be made of materials other than clean soil or earth, the permit shall be subject to the following additional limitations and requirements:
(1) 
The fill shall be completed within a reasonable length of time, said time limit to be determined by the Township Engineer and to be specified on the permit.
(2) 
Clean soil shall be placed over the top and exposed surfaces of the fill to a depth sufficient to effectively conceal all materials other than clean soil or earth within the fill. Where the nature of the fill requires, the Township Engineer may require clean soil or earth to be placed over the top and exposed surfaces of the fill to a depth sufficient to conceal all materials at the end of each day's operations.
(3) 
No permit shall be issued for the filling of materials other than clean soil or earth until a faithful performance bond is obtained pursuant to Article III of this chapter.
All fills shall be compacted to provide stability of material and to prevent undesirable settlement. The fill shall be spread in a series of layers, each not exceeding 12 inches in thickness, and shall be compacted by a sheepsfoot roller or other approved method after each layer is spread. The Township Engineer may require tests or other information if, in his opinion, the conditions or materials are such that additional information is necessary.
The top or bottom edge of slopes shall be at least three feet from property or right-of-way lines of streets in order to permit the normal rounding of the edge without encroaching on the abutting property. At property lines where walls or slopes are steeper than one to one and are six feet or more in height, they shall be protected by a substantial fence three feet or more in height. Before a permit is issued, a bond may be required to guarantee the protection of steep slopes.
A. 
Portions of tree masses or trees with caliper of four inches or greater shall not be cleared unless approved by Township Engineer. The Township Engineer will not approve clearing of tree masses that will result in substantially increased runoff.
B. 
During construction, care shall be exercised to prevent damage to trees which are to remain. The following procedures shall be followed:
(1) 
Where existing ground levels are changed, drainage tile will be placed at the old soil level and open into a well built around the base of the tree. Such well may be left open or can be filled with coarse stones or gravel. Tiles may be installed in a radiating pattern or laid in parallel lines.
(2) 
Trees within 25 feet of a building site or bordering entrances or exits to building sites shall be protected by wiring wooden slats around such trees.
(3) 
No boards or other materials shall be nailed to trees during construction.
(4) 
Heavy equipment operators shall be warned to avoid damaging existing tree trunks and roots. Feeder roots shall not be cut closer than 25 feet from tree trunks.
(5) 
Tree trunks and exposed roots damaged during construction shall be protected from further damage by being treated immediately with tree paint.
(6) 
Tree limbs damaged during construction shall be sawed flush to tree trunks and treated immediately with tree paint.
(7) 
Leaf trees shall be given a heavy application of fertilizer to aid in their recovery from possible damage by construction operations.
(8) 
Construction debris shall not be disposed of near or around the bases of such trees.
C. 
Trees with a minimum caliper of 1 1/2 inches shall be provided where deemed advisable by the Township Planning Commission and/or Board of Commissioners.
[Amended 7-18-2007 by Ord. No. 3821]
A. 
The following permit requirements from other agencies, as applicable, must be met prior to commencement of regulated earth disturbance activities in the Township:
(1) 
All regulated earth disturbance activities subject to permit requirements of DEP under regulations at 25 Pennsylvania Code, Chapter 102.
(2) 
Work within natural drainageways subject to permit by DEP under 25 Pennsylvania Code Chapter 105.
(3) 
Any stormwater management facility that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by DEP under 25 Pennsylvania Code Chapter 105.
(4) 
Any stormwater management facility that would be located on a state highway right-of-way or require access from a state highway shall be subject to approval by PennDOT.
(5) 
Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by DEP under Pennsylvania Code Chapter 105.
B. 
No regulated earth disturbance activities shall commence until the Township receives the required approval from the responsible agency.
C. 
No building permit will be issued on a site requiring an NPDES construction permit until evidence is provided to the Township that the permit for the regulated activity has been issued.
Major modifications of the approved application and plans shall be submitted to the Township Engineer and reprocessed in the same manner as the original application and plans. Field modifications of a minor nature may be authorized by the Township Engineer, provided that written authorization is given to the person performing work pursuant to this chapter, with a copy forwarded to the Montgomery County Soil and Water Conservation District.
[Amended 9-21-1977 by Ord. No. 1802]
The applicant shall pay a fee for each site as set forth in the Township Schedule of Fees, as adopted and amended from time to time by the Board of Commissioners.[1]
[1]
Editor's Note: For the current schedule of fees, see Ch. A167, Fees.
[Amended 12-17-1997 by Ord. No. 3470]
In granting any permit, the Township Engineer may attach such conditions thereto as he may deem reasonably necessary to prevent danger to public or private property or any sewer, storm drain or watercourse, or to prevent the operation from being conducted in a manner hazardous to life or property, or in a manner likely to create a nuisance. Such conditions may include, but are not limited to, the erection or installation of walls, drains, dams and structures, plantings and vegetation, runoff and erosion control measures or devices, furnishing necessary easements and a specified method of performing work. No runoff and erosion control permit shall be issued until a runoff and erosion control plan is approved by the Township Engineer and the developer certifies that all earthmoving, grading and filling shall be performed pursuant to the runoff and erosion control plan. The runoff and erosion control plan shall be a condition of the permit. No person shall violate any such conditions so imposed.
Every permit shall expire by limitation and become null and void if the work authorized by such permit has not been commenced within six months or is not completed within one year from the date of issue, provided that the Township Engineer may, if the permit holder presents satisfactory evidence that unusual difficulties have prevented work from being started or completed within the specified time limits, grant a reasonable extension of time, and provided further that the application for the extension of time is made before the date of expiration of the permit.
Any permit issued under this chapter may be revoked or suspended by the Township Engineer, after notice, for:
A. 
Violation of any condition of the permit.
B. 
Violation of any provision of this chapter or any other applicable law, ordinance, rule or regulation relating to the work.
C. 
Existence of any condition or the doing of any act constituting or creating a nuisance or hazard or endangering human life or the property of others.