Township of Lower Makefield, PA Stormwater Management, Erosion and Sediment Control and Grading

General.

[Amended 12-15-1999 by Ord. No. 321; 12-20-2006 by Ord. No. 363]

The Township requires that all development comply with the low-impact development practices as outlined in the requirements of the Pennsylvania Stormwater Best Management Practices Manual, Draft April 2006 ("Manual"), as such Manual may be amended from time to time. The Manual provides guidance on the development of site controls through the use of Best Management Practices (BMPs). The most appropriate BMPs for stormwater management vary from site to site; however, the basic concepts are the same and they can be condensed into the following 10 principles:

(a)

Prevent stormwater impacts, especially pollutants.

(b)

Mitigate pollutants that cannot be prevented.

(c)

Manage stormwater as a resource.

(d)

Sustain the hydrologic balance (quantity and quality).

(e)

Integrate stormwater into the initial site design process.

(f)

Preserve and utilize natural systems (soil, vegetation, etc.).

(g)

Manage stormwater as close to the source as possible.

(h)

Disconnect/decentralize/distribute.

(i)

Slow down stormwater by increasing the time of concentration, rather than piping and accelerating it.

(j)

Inspect and maintain.

(2)

The control guidelines presented in the Manual are comprehensive and reflect the Pennsylvania Comprehensive Stormwater Policy to restore natural hydrology, including velocity, current, cross section, runoff volume, infiltration volume, and aquifer recharge volume. The guidelines will help sustain stream base flow and prevent increased frequency of damaging bank full flows in local waterways. The guidelines also will help prevent increases in peak runoff rates for larger events (two- through one-hundred-year) on both a site-by-site and watershed basis. When applicable, Act 167 watershed plans (Chapter 173, Stormwater Management — Delaware River South Watershed, and Chapter 174, Stormwater Management — Neshaminy Creek Watershed) may require additional rate controls to reduce cumulative flooding impacts downstream.

(3)

Where site conditions offer the opportunity to reduce the increase in runoff volume, groundwater recharge shall be utilized based on the following scientific observations:

(a)

The two-year event encompasses 95% or more of the annual runoff volume across the state;

(b)

Volume reduction BMPs based on this standard will provide a storage capacity to help reduce the increase in peak flow rates for larger runoff events;

(c)

In a natural stream system in Mid-Atlantic states, the bank full stream flow occurs within a period of approximately 1.5 years. If the runoff volume from storms less than the two-year event are not increased, the fluvial impacts on streams will be lessened.

(d)

Volume reduction BMPs based on this standard will provide a storage capacity to help reduce the increase in peak flow rates for larger runoff events.

(4)

Use of natural resources.

(a)

The Township requires all applicants to design using low-impact development techniques for stormwater design. Conventional land development too often results in extensive site clearing, where existing vegetation is destroyed, and the existing soil is disturbed, manipulated, and compacted. All of this significantly affects stormwater quantity and quality. These conventional land development practices too often fail to recognize that the natural vegetative cover, the soil mantle, and even the topologic form of the land are integral parts of the water resources system that needs to be conserved and kept in balance, even as land development continues to occur.

(b)

Identifying a site's natural resources and evaluating their values and functional importance is the first step in minimizing the impact of stormwater generated from land development. Where they already exist on a proposed development site, these natural resources should be conserved and utilized as a part of the stormwater management solution. Stormwater is a resource that must be conserved. In fact, many vegetation and soil-based structural BMPs are in fact natural structures that perform the functions of more structural systems (e.g., porous pavement with recharge beds). In addition, it is strongly recommended that the developer utilize the guidelines provided in the Manual, Chapter 4, Integrating Site and Stormwater Management, in planning the site design. In particular, the developer shall perform sufficient subsurface investigations (in accordance with the following guidelines) to accurately determine the existing conditions.

Preliminary subsurface investigation for determination of recharge characteristics of site.

[Amended 12-15-1999 by Ord. No. 321; 12-20-2006 by Ord. No. 363]

(1)

Statement and purpose. All major subdivisions and site plans will conduct a subsurface investigation prior to completing a layout of a development plan. The objective of the preliminary investigation is to obtain data that would allow for the development of a conceptual model of surface runoff and subsurface recharge on a development site. With regard to groundwater recharge it is important that the applicant, during the site design phase of the project, understand how groundwater recharges at a site. An understanding of these elements will provide the engineer with a guide for infiltration BMPs at the site (i.e., shallow or deep infiltration surfaces) and an understanding of the requirement to maintain the hydrogeologic characteristics of a site. All investigations shall be conducted in accordance with the most recent revision of the Manual and with the criteria listed below. All investigations shall be witnessed by a representative of the Township.

(2)

Method of investigation.

(a)

A subsurface investigation comprised of supervised test pits shall be undertaken to characterize the underlying hydrogeologic characteristics of a development site. The frequency of test pits shall be as follows:

	Site Size (acres)	Number of Test Pits
	Initial 5	1 per acre, minimum of 2
	More than 5 to 20	5 plus 1 per 2 acres beyond the initial 5 acres
	More than 20	13 plus 1 per 5 acres beyond the initial 20 acres

(b)

All test pits shall be progressed to a minimum depth of 10 feet or to bedrock refusal, whichever is less. The test pits shall be prepared in accordance with USDA National Cooperative Soil Survey (NCSS) standards, and identify all soil horizons and substratums, as well as limiting horizons, evidence of seasonal high groundwater (mottling) and observed groundwater seepage. This field investigation shall be conducted by an ARCPACS or PAPSS certified soil scientist.

(c)

Utilizing the data obtained through the preliminary subsurface investigation, a Pennsylvania licensed geologist or, ARCPACS or PAPSS certified soil scientist shall create a conceptual model of the surface and subsurface drainage patterns of the site for use by the design engineer in developing drainage system layout and infiltration BMPs. The conceptual model shall include estimates of predevelopment recharge of groundwater and a determination of the primary routes for subsurface drainage, either through recharge of on-site or off-site streams or wetlands, or through deeper recharge of regional aquifers. The conceptual model shall also discuss the impacts of the proposed development on adjacent wetlands and streams, and provide schematics or conceptual cross sections of the proposed method of maintaining the existing drainage and recharge patterns. The design engineer, in developing a concept and ultimately designing the site must match both the predevelopment recharge rates and patterns.

(3)

BMP specific subsurface investigation.

(a)

Statement and purpose. The purpose of the final subsurface investigation is to determine the recharge characteristics and ability of soils and the underlying aquifer to infiltrate the required volume of groundwater. All structural infiltration BMP designs shall be supported by an individual soil log and infiltration test to determine the infiltration rate at each BMP. The soils logs at each BMP will be conducted in the identical manner as in the preliminary subsurface investigation, identifying the soil profile, limiting horizons, seasonal high groundwater and observed seepage. For all developments using detention basins as the primary means of infiltration, a groundwater mounding analysis must be performed in addition to the tests below to determine whether or not the underlying aquifer will be able to manage the infiltration loading proposed without raising the groundwater to within two feet of the infiltration surface or affecting nearby structures. The mounding analysis shall be progressed utilizing at least three groundwater monitoring wells per detention basin, and one seventy-two-hour aquifer pumping stress test. The field testing procedure for a mounding analysis shall be submitted to the Township Engineer for review and approval prior to performing the work.

(b)

Frequency of infiltration testing. At the level of infiltration, testing shall conform to the following frequency:

[1]

Detention/retention BMPs (infiltration basins, dry wells/seepage pits, open bottom bioretention, sand filters, rain gardens, infiltration beds): one test per 5,000 square feet or fraction thereof of infiltrative surface; minimum of one test for up to 400 square feet, and two tests for infiltrative surfaces of 400 square feet and greater.

[2]

Linear infiltration BMPs (swales, trenches and strips): one test per 100 feet or fraction thereof; minimum two tests.

(c)

Testing procedures.

[1]

All infiltration testing methods shall be conducted in accordance with the most recent revision of the Manual, as amended from time to time. Currently, double-ring infiltrometer and percolation tests are the two principle methods for measuring soil infiltration. For infiltration basins, double-ring infiltrometer tests alone shall be utilized.

[2]

There may be instances where the rock content is sufficient enough to limit the use of either the double-ring infiltrometer or percolation tests. In this instance, the following infiltration test may be conducted after approval of the Township:

[a]

Procedure for pilot infiltration test (P.I.T.).

[i]

The following equipment is required for a P.I.T.:

[A]

Excavating equipment capable of producing a test basin as prescribed in Subsection B(3)(c)[2][a][ii] below; and

[B]

A water supply; and

[C]

A means for accurately measuring the water level within the basin as required in Subsection B(3)(c)[2][a][iii] below. It is recommended that a calibrated PVC pipe or rod be used to measure the drop.

[ii]

A pit meeting the following requirements shall be excavated within or immediately adjacent to the proposed infiltration BMP.

[A]

The bottom of the test basin shall be at the depth of the proposed level of BMP infiltration.

[B]

The bottom area of the basin shall be a minimum of 50 square feet.

[C]

A soil profile pit excavated for the purpose of logging the subsurface may be utilized for this test, provided that the requirements of Subsection B(3)(c)[2][a][ii] above are satisfied.

[D]

The bottom of the basin should be made as level as possible so that high areas of rock do not project above the water level when the basin is flooded as prescribed in Subsection B(3)(c)[2][a][iii] below. Within the depth of the pit where water will be filled, the side slopes should be as close to vertical and consistent in dimension as possible.

[E]

If groundwater is observed within the test basin, the basin flooding test shall not be used.

[iii]

The following test procedure shall be used for the P.I.T.:

[A]

Step One: Fill the excavated pit with the approximate depth of water expected to be stored within the specific infiltration BMP (water depths shall be a minimum of 12 inches and no greater than 48 inches) and record the time. Allow the basin to drain for a period of 24 hours. When designing the P.I.T. for a BMP, the designer should be aware that infiltration BMPs must completely drain within a period of 72 hours or less.

[B]

Step Two: If the basin drains completely within 24 hours after the first flooding, immediately refill the basin to the water depths as described in Subsection B(3)(c)[2][a][iii][A] above and start recording the rate of drop. If the basin has not emptied within 24 hours and the water level has dropped less than six inches, then the soil stratum being tested cannot be used for infiltration. If the water level has dropped six inches or greater, then fill the pit back to the water depth as described in Subsection B(3)(c)[2][a][iii][A] above and start recording the rate of drop every five minutes to four hours depending on the rate of drop until the pit is empty. If the rate of drop slows to less than 0.25 inches per hour over two consecutive hours, then the tested soil stratum shall not be used for infiltration.

[C]

Step Three: Calculate the rate of infiltration by averaging the time weighted rate of drop from initial filling until the pit has emptied. This rate of infiltration will be used in calculating the drainage time required for the BMP. To account for bio-fouling and clogging with fines, the design rate shall be 50% of the field determined infiltration rate. This rate shall be used in designing the infiltration BMP.

[iv]

Due to the potential safety hazards which are posed by the excavation of a P.I.T., adequate safety measures shall be taken including those required by OSHA to permit safe access to the excavation areas during the test procedure as well as the use of warning signs or a fence to limit access to the basin by the public during periods when the basin is left unattended, or both.

[v]

The basin flooding test shall not be conducted in rock strata which have been blasted with explosives.

Design criteria, general.

[Amended 12-15-1999 by Ord. No. 321; 12-20-2006 by Ord. No. 363]

(1)

The stormwater management system shall be designed to meet the requirements of the Manual. In the event that the site is also subject to the requirements of either Chapter 173, Stormwater Management — Delaware River South Watershed, or Chapter 174, Stormwater Management — Neshaminy Creek Watershed, then the more restrictive of the requirements shall apply as determined by the Township Engineer.

(2)

The Township requires use of nonstructural BMPs to the maximum extent possible because of their ability to prevent stormwater generation and not just mitigate stormwater-related impacts. If nonstructural BMPs cannot be used, the reasons why must be demonstrated to the Township's satisfaction. Prevention can be achieved as the result of making the land development happen in ways other than through use of standard or conventional development practices. Prevention and nonstructural BMPs go hand in hand and can be contrasted with structural BMPs that provide mitigation of those stormwater impacts, which cannot be prevented and/or avoided.

(a)

The following major areas of preventive nonstructural BMPs have been identified in the Manual:

[1]

Protect sensitive and special value features.

[2]

Cluster and concentrate.

[3]

Minimize disturbance and minimize maintenance.

[4]

Reduce impervious cover.

[5]

Disconnect/distribute/decentralize.

[6]

Source control.

(b)

More specific nonstructural BMPs have been identified for each of these generalized areas to better define and improve implementation of each of these areas. One of the most challenging technical issues considered in the Manual involves the selection of BMPs that have a high degree of non-point source (NPS) reduction or removal efficiency. In the ideal, a BMP should be selected that has a proven NPS pollutant removal efficiency for all pollutants of importance, especially those that are critical in a specific watershed. Exhibit 7, attached to this chapter,[1] sets forth a list of all of the BMPs and provides information on where each can be used and their pollutant removal performance or effectiveness.

[1]

Editor's Note: Exhibit 7 is included at the end of this chapter.

(3)

The Manual (Chapter 8) also provides a methodological approach to take credit for applying these non-structural BMPs, provided that the specifications defined for each BMP in Chapter 5 of the Manual are properly followed.

(4)

The developer shall construct and or install such drainage structures on site and off site as necessary to provide a fully functioning stormwater collection and control system meeting the requirements of the Manual. The developer's design shall utilize to the maximum extent possible nonstructural BMPs. In the event that the site is also subject to the requirements of either Chapter 173, Stormwater Management — Delaware River South Watershed, or Chapter 174, Stormwater Management — Neshaminy Creek Watershed, then the more restrictive of the requirements shall apply as determined by the Township Engineer.

Design criteria, detention and retention basins.

(1)

A stormwater collection system with capacity for the one-hundred-year storm shall be provided to carry run-off to a detention basin. When the capacity of the storm drain pipe is exceeded an overflow system shall have sufficient capacity to carry the run-off difference between the one-hundred-year-storm peak flow rate and the capacity of the storm drain pipe system. The one-hundred-year-storm peak shall be calculated by the Soil Cover Complex Method.

(2)

Unless permitted as a special exception by the Zoning Hearing Board, detention basins shall not be located within floodplain nor within areas of floodplain soils, with the exception that areas of alluvial soils may be utilized if proof is accepted by the Board of Supervisors that the area is not subject to flooding.

(3)

Detention basins shall be designed to facilitate regular maintenance, mowing and periodic de-silting and reseeding.

(4)

Whenever possible, the side slopes and basin shape shall conform to the natural topography. When such design is impracticable, the construction of the basin shall utilize slopes as flat as possible to blend the structure into the terrain.

(5)

The maximum water depth, measured from the invert of the lowest outlet orifice to the peak one-hundred-year water surface elevation, shall not exceed five feet zero inches.

[Amended 12-15-1999 by Ord. No. 321]

(6)

The maximum slope of the earthen detention basin embankments shall be four horizontal to one vertical.

(7)

The top or toe of any slope shall be located a minimum of five feet from any property line.

(8)

The minimum top width of the detention basin berm shall be 10 feet.

(9)

(Reserved)[2]

[2]

Editor's Note: Former Subsection D(9), which contained provisions on minimum grade, as amended 12-15-1999 by Ord. No. 321, was repealed 12-20-2006 by Ord. No. 363.

(10)

(Reserved)[3]

[3]

Editor's Note: Former Subsection D(10), which contained provisions on collecting swales, was repealed 12-20-2006 by Ord. No. 363.

(11)

If permanent ponds are used, the developer shall demonstrate that such ponds are designed to protect the public health and safety. The following minimum design criteria shall be maintained:

[Amended 12-15-1999 by Ord. No. 321]

(a)

An aquatic safety bench shall be provided around the perimeter of the permanent water surface. The depth of the bench shall be a maximum of one foot for a width of at least 10 feet.

(b)

An area at least 15 feet wide with slopes of three to one shall be provided from the edge of the safety bench toward the deep water portion of the pond.

(c)

Slopes in the remainder of the pond, below the permanent pool elevation, shall be a maximum of two to one.

(d)

Slopes above the permanent water surface shall be in accordance with the design criteria set forth for detention and retention basins within this ordinance.

(e)

Wet ponds shall have a deep water zone of at least eight feet deep measured from the bottom of the wet pond to the top of the aquatic safety bench in order to prevent stagnation.

(f)

Wet ponds shall be equipped with a manually operated drain that can be secured against unauthorized operation to allow the pond to be drained by gravity flow.

(g)

Wet ponds shall be provided with a water source so that the permanent water surface can be maintained, as necessary, between periods of rainfall.

(h)

Wet ponds shall be lined with a four-inch thickness of clay material in order to prevent excessive infiltration and to protect against saturation of, and seepage through, the berm.

(12)

Emergency spillways.

(a)

Emergency overflow facilities shall be provided for detention facilities to handle run-off in excess of design flows.

(b)

Whenever possible, the emergency spillway for detention basins shall be constructed on undisturbed ground.

(c)

Emergency spillways shall be constructed of reinforced concrete or other material approved by the Township Engineer.

(d)

All emergency spillways shall be constructed so that the detention basin berm is protected against erosion.

(e)

The minimum capacity of all emergency spillways shall be the peak flow rate from the one-hundred-year design storm after development.

(f)

The construction material of the emergency spillway shall extend along the upstream and downstream berm embankment slopes.

(g)

The upstream edge of the emergency spillway shall be a minimum of three feet below the spillway crest elevation.

(h)

The downstream slope of the spillway shall, as a minimum, extend to the toe of the berm embankment.

(i)

The emergency spillway shall not discharge over earthen fill and/or easily eroded material.

(j)

Dams.

[1]

All detention basins shall have a minimum top of embankment as follows:

Class of Dam	Drainage Area	Top of Embankment
a	Less than 320 acres	1 foot above maximum water surface elevation for emergency spillway storm
	Greater than 320 acres	2 feet above maximum water surface elevation for emergency spillway storm
b	Less than 150 acres	1 foot above maximum water surface elevation for emergency spillway storm
	Greater than 150 acres	2 feet above maximum water surface elevation for emergency spillway storm
c	Less than 150 acres	2 feet above maximum water surface elevation
	Greater than 150 acres	Special treatment. Criteria established for each individual case

[2]

The classification of dams shall be in accordance with the Soil Conservation Service's criteria as found in Technical Release 60, as amended.

(13)

Anti-seep collars.

(a)

Anti-seep collars shall be installed around the pipe barrel within the normal saturation zone of the detention basin berms.

(b)

The anti-seep collars and their connections to the pipe barrel shall be watertight.

(c)

The anti-seep collars shall extend a minimum of two feet beyond the outside of the principal pipe barrel.

(d)

The maximum spacing between collars shall be 14 times the minimum project of the collar measured perpendicular to the pipe.

(e)

A minimum of two anti-seep collars shall be installed on each outlet pipe.

(14)

Outlet pipes.

(a)

All outlet pipes through the basin berm shall be reinforced concrete pipe with watertight joints.

(b)

Energy-dissipating devices (rip-rap, end sills, etc.) shall be placed at all basin outlets.

(c)

Outlet pipes shall discharge to a defined watercourse having a capacity to carry proposed discharge flows.

(d)

Outlet pipes shall be sized to pass the one-hundred-year storm event.

[Added 12-15-1999 by Ord. No. 321]

(15)

(Reserved)[4]

[4]

Editor's Note: Former Subsection D(15), Perforated risers, was repealed 12-20-2006 by Ord. No. 363.

(16)

All detention/retention basin embankments shall be placed in a maximum of eight-inch lifts compacted to a minimum of 95% of modified proctor density, as established by ASTM D-1557. Prior to proceeding to the next lift, the compaction shall be checked by the Township Engineer or a certified soils engineer. Compaction tests will be run on the leading and trailing edge of the berm along with the top of berm.

[Added 12-15-1999 by Ord. No. 321]

(17)

The length of the pond between the inflow and outflow points shall be maximized to prevent short circuiting of the runoff flowing through the pond.

[Added 12-15-1999 by Ord. No. 321]

(18)

A cutoff trench (keyway) of impervious material shall be provided under all embankments that require fill material. The cutoff trench shall be a minimum of eight feet wide, two feet deep and have side slopes of one-to-one.

[Added 12-15-1999 by Ord. No. 321]

(Reserved)[5]

[5]

Editor's Note: Former Subsection E, Design criteria, drainage channels and swales, was repealed 12-20-2006 by Ord. No. 363.

Design criteria, stormwater collection and pipe system.

(1)

Storm sewers, culverts and related installations shall be provided to:

(a)

Permit the unimpeded flow of natural watercourses in such a manner as to protect the natural character of said watercourses and to provide regulated discharge.

(b)

Ensure adequate drainage of all low points along the line of streets.

(c)

Intercept stormwater run-off along streets at intervals reasonably related to the extent and grade of the area drainage and to prevent substantial flow of water across intersections.

(2)

The design discharge from drainage areas contributing to the system may be determined by use of the Rational Equation (Q=CIA) when the total drainage area does not exceed 100 acres.

(a)

The following run-off factors shall be utilized for the rational equation:

Description of Area		Run-Off Coefficient (C)
Residential
	2-acre single-family detached lots	0.40
	1-acre single-family detached lots	0.46
	1/2-acre single-family detached lots	0.50
	1/4-acre single-family detached lots	0.56
	Two-family and multifamily	0.70
Commercial		0.75
Industrial		0.80
Parks and cemeteries		0.38
Unimproved		0.35
Where the Table is not applicable the following factors may be used:
Roofs and all impervious surfaces		0.90
All other surfaces except forest		0.40
Forest		0.30

(b)

The coefficients in the above tabulations are applicable for storms of ten-year frequency and less. The coefficients are based on the assumption that the design storm does not occur when the ground is frozen. Less frequent, higher intensity storms will require the use of higher coefficients.

(c)

For less frequent storms, the coefficients can be used if they are multiplied by the following factors for the return frequency required:

	Storm Frequency (years)	Factors
	10 and less	1.0
	25	1.1
	50	1.2

(d)

The rainfall intensity I curves presented in Figure 1[6] shall be used in determining stormwater run-off.

[6]

Editor's Note: Figure 1 is located at the end of this chapter.

(e)

Storm frequency.

[1]

A ten-year storm for the design of all stormwater systems.

[2]

In all cases where storm drainage is picked up by means of a headwall or inlet structure, a hydraulic inlet or outlet conditions control, the pipe shall be designed as a culvert for a twenty-five-year storm.

(f)

Storm duration.

[1]

A five-minute storm duration shall be used if this duration does not result in a maximum expected discharge that exceeds the capacity of a thirty-inch pipe.

[2]

If a five-minute storm duration results in a pipe size exceeding 30 inches, the time of concentration approach shall be used in determining storm duration.

[3]

If a five-minute storm duration results in a pipe size exceeding 30 inches, within any run of pipe, the time of concentration approach may be used for sizing of pipes from that point on by adjusting the time of concentration.

(3)

Pipes.

(a)

Pipe shall be sized by use of Manning's Equation with the pipes flowing full. The design shall be based on gravity (nonpressure) flow.

(b)

The roughness coefficient (n) shall be in compliance.

(c)

The minimum diameter of all storm drainage pipe shall be 18 inches or an equivalent thereto. Where headroom is restricted, equivalent pipe arches may be used in lieu of circular pipe.

(d)

Increment size changes to storm drainage pipes shall be six inches in diameter.

(e)

Abrupt changes in direction or slope of storm drainage pipe shall be avoided. Where such abrupt changes are required, an inlet or manhole shall be placed at the point of change.

(f)

The minimum grade of piping shall provide a minimum velocity of 2.5 feet per second and shall have a minimum slope of 0.5%.

(g)

Storm sewers shall be placed within a street right-of-way, parallel to the cartway, and shall be designed as a combination storm sewer and underdrain. When located outside of a right-of-way, they shall be placed within an easement having a width of not less than 30 feet, if required by the Township.

(h)

The top of storm drainage pipes beneath cartways shall be at least six inches below sub-grade elevation. Cast iron pipe may be placed within three inches of sub-grade elevation. Outside of cartways, all pipes shall have a minimum cover of two feet.

(4)

Manholes.

(a)

Manholes shall neither be more than 300 feet apart on sizes up to 24 inches nor more than 450 feet apart on greater sizes.

(b)

Inlets may be substituted for manholes, on approval of the Township Engineer, at the same spacing as required for manholes.

(c)

Manhole covers and frames shall conform to Pennsylvania Department of Transportation specifications.

(5)

Inlets.

(a)

At street intersections, inlets shall be placed in the tangent portion rather than the curved portion of the curbing.

(b)

When there is a change in pipe size in an inlet, the elevation for the top of the pipes shall be the same or the small pipe shall be higher. A minimum drop of two inches shall be provided in the inlet between the lowest inlet pipe invert elevation and the outlet pipe invert elevation.

(c)

If the capacity of the shoulder, swale, curb section or depressed median section exceeds the assumed inlet capacities, the inlet capacities shall govern the spacing of inlets.

(d)

If the capacity of the shoulder, swale, curb section or depressed median section is less than the inlet capacities, then the shoulder, swale, curb section or depressed section capacity shall govern the spacing of inlets.

(e)

Type C inlets.

[1]

Type C inlets shall be installed unmountable curbs.

[2]

In order to achieve greater efficiency, Type C inlets shall be spaced so as to permit 5% of the gutter flow to bypass the inlet.

[3]

The capacity of a Type C inlet at a low point of a street's vertical curve may be designed to accept four cubic feet per second (cfs) from each direction or a maximum of eight cfs.

[4]

Inlet capacities shall be based on Figure 2, Inlet Capacity and Gutter Flow Curves.[7]

[7]

Editor's Note: Figure 2 is located at the end of this chapter.

(f)

Type M and Type S inlets.

[1]

Type S inlets shall be installed in shoulder swale areas with back slopes of six horizontal to one vertical and steeper.

[2]

Type M inlets shall be installed in swale areas where the back slope is flatter than six horizontal to one vertical.

[3]

Inlet capacities shall be based on Table 2, Type M and S Inlet Capacities (in Swale):

Table 2 Type M or S Inlet Capacities (in Swale)
Back Slope
Grade	2:1	4:1	6:1	12:1	Dike
1.0	3.2	3.6	3.9	4.1	9.1
2.0	3.5	3.5	3.5	3.7	8.3
3.0	2.5	2.8	3.5	3.5	7.4
4.0	1.6	2.0	3.4	3.2	6.4
5.0	1.6	2.0	3.5	3.0	6.3
6.0	1.6	2.0	3.3	2.8	6.1
7.0	1.5	2.0	3.0	2.6	6.0
8.0	1.5	2.0	2.8	2.4	5.8

[4]

Where a drainage dike is used, the side slope of the dike shall be eight horizontal to one vertical or flatter.

[5]

The capacity of an inlet at a low point in a swale (sump condition) shall be 16 cfs maximum.

(g)

Inlets shall conform to Pennsylvania Department of Transportation specifications, with the exception that the use of red brick for inlet construction is not permitted.

(h)

Shoulders in cut areas (without swales).

[1]

Water flowing in the shoulder shall not encroach more than 2/3 the shoulder width during a ten-year frequency storm of five-minute duration.

[2]

The maximum velocity, as determined by Manning's Equation, shall not exceed the allowable velocities in Table 2 for the specific type of shoulder material.[8]

[8]

Editor's Note: See Subsection F(5)(f)[3] above.

[3]

Inlets shall be provided to control the shoulder encroachment and water velocity.

(i)

Swales adjacent to shoulders.

[1]

Swales in cut areas shall be designed to prevent the passage of water onto the cartway during a ten-year frequency storm of five-minute duration.

[2]

The maximum velocity, as determined by Manning's Equation, shall not exceed the allowable velocities in Table 1[9] for the specific type of shoulder material.

[9]

Editor's Note: See Subsection D(15).

(j)

Curbed sections.

[1]

The maximum encroachment of water on the cartway shall not exceed two inches in depth at the curb during a ten-year frequency storm of five-minute duration.

[2]

Inlets shall be provided to control the encroachment of water on the cartway.

Design criteria for within Historic District, which includes all or a portion of the following zoning districts:

[Added 12-6-2004 by Ord. No. 346]

	H-C	Historic Commercial
	C-1	Commercial Neighborhood Shopping
	R-2	Residential Medium Density
	R-4	Residential Multiple Family High Density

(1)

All stormwater collection and management systems shall be designed to be underground, such as porous pavement with infiltration bed, underground tank or pipe storage, cisterns, all of which shall be subject to approval by the Township Engineer.

General provisions and compliance.

(1)

No changes shall be made in the contour of the land and no grading excavation, removal nor destruction of the topsoil, trees or other vegetative cover of the land shall be commenced until such time that a plan for minimizing erosion and sedimentation has been:

(a)

Processed and reviewed by the Township Engineer and the Bucks County Conservation district; and

(b)

Approved by the Board of Supervisors.

(2)

The Board of Supervisors, in its consideration of all preliminary subdivision and land development plans, shall condition its approval upon the execution of erosion and sediment control measures as contained in the standards and specification of the Bucks County Conservation District, the local designee for the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation.

(3)

Final approval of plans and specifications for the control of erosion and sedimentation shall be concurrent with the approval of the final subdivision or land development plans and become a part thereof.

(4)

Final plans for minimizing erosion and sedimentation as approved will be incorporated into the agreement and bond requirements as required by the Township.

(5)

No subdivision or land development plan shall be approved unless:

(a)

There has been an erosion and sedimentation plan approved by the Township Engineer and the Bucks County Conservation District that provides for minimizing erosion and sedimentation and an improvement bond or other acceptable security is deposited with the Township in the form of an escrow guaranty which will ensure installation and completion of the required improvements; or

(b)

There has been a determination by the Board of Supervisors that a plan for minimizing erosion and sedimentation is not necessary. The Board of Supervisors may waive the above requirement for minor subdivisions.

(6)

At the time a building permit is applied for, a review shall be conducted by the Township Engineer to ensure conformance with the plan as approved. During the construction, further consultative technical assistance will be furnished, if necessary, by the Township Engineer and the Bucks County Conservation District. The Township Engineer shall inspect the development site and enforce compliance with the approved plans.

(7)

Permission for clearing and grading prior to recording of plans may be requested under temporary easements or other conditions satisfactory to the Township Manager.

(8)

In the event that the developer proceeds to clear and grade prior to recording plans without satisfying conditions specified under Subsection A(6), the Township shall revoke its approval of the development plan.

General erosion control standards.

(1)

Measures used to control erosion and reduce sedimentation shall, as a minimum, meet the standards and specifications of the Bucks County Conservation District, the local design for the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation.

(2)

In cases where the Bucks County Conservation District does not have standards and specifications for erosion and sedimentation control, other known and commonly accepted standards and specifications may be used as approved by the Township Engineer.

(3)

The following standards to minimize erosion and sedimentation shall be followed:

(a)

Stripping of vegetation, regrading or other development shall be undertaken in a manner that will minimize erosion.

(b)

Development plans shall preserve salient natural features, keep fill operations to a minimum and ensure conformity with topography so as to create the least erosion potential and adequately handle the volume and velocity of surface water run-off.

(c)

Whenever feasible, natural vegetation shall be retained, protected and supplemented.

(d)

The disturbed area and the duration of exposure shall be kept to a practical minimum. Disturbed soil shall be stabilized within 20 days.

(e)

Temporary vegetation and/or mulching shall be used to protect exposed critical areas during development.

(f)

The permanent (final) vegetation and mechanical erosion control and drainage facilities shall be installed as soon as practical.

(g)

Provisions shall be made to effectively accommodate the increased run-off caused by changed soil and surface conditions during and after development. Where necessary, the rate of surface water run-off shall be mechanically retarded.

(h)

Sediment in the water run-off shall be trapped until the disturbed area is stabilized by the use of debris basins, sediment basins, silt traps or similar measures.

(i)

Swales shall be sodded, utilize jute matting or other similar measures to ensure proper growth of ground cover.

(j)

Tire cleaning areas shall be provided and properly maintained at each point of egress from the development site.

General grading standards.

(1)

All lots, tracts or parcels shall be graded to provide proper drainage away from buildings and dispose of it without ponding.

(2)

All land within a development shall be graded to drain and dispose of surface water without ponding, except where ponding in detention basins is part of the storm water management plan for the site.

(3)

Concentration of surface water run-off shall be permitted only in swales, watercourses or detention basins.

(4)

Edges of slopes shall be a minimum of five feet from property lines or right-of-way lines in order to permit the normal rounding of the edge without encroaching on the abutting property.

(5)

During grading operations, necessary measures for dust control shall be exercised.

(6)

Driveway slopes shall be less than 8%. Where driveway slopes in excess of 8% are unavoidable, an adjoining walk with steps should be provided (for pedestrian use during conditions of ice or snow).

(7)

In general, lot slope shall not be flatter than 2%.

(8)

Swales for surface runoff shall have a minimum slope of 2%.

(9)

Garage floor elevations shall be shown on the proposed grading plan. First floor elevations shall be based on architectural details of the proposed building.

(10)

A fifteen-foot protection slope around the building shall be provided with at least a six-inch fall.

(11)

Perimeter grades at the corners of the building shall be shown on the grading plan.

(12)

Proposed spot elevations for swale high points and at lot corners shall be shown on the grading plan.

(13)

Where inlets are proposed at low points in streets or lot grading, adequate relief shall be provided to prevent excessive ponding in the event of inlet clogging.

(14)

The grading plan shall not allow concentrated runoff on adjoining properties.

(15)

Drainage swales necessary to control surface drainage between lots shall be centered about the common property lines.

(16)

On-lot drainage swales shall be designed to provide positive conveyance of surface water from the individual lot. Each individual lot shall convey stormwater from the individual lot. Each individual lot shall convey stormwater from the lot to a storm sewer system, street or major drainageway without crossing or combining with stormwater from more than the adjacent lot.

(17)

Drainageways for major surface runoff (swales) shall be confined to open areas or along property lines. Drainageways on or adjoining private property may require drainage easements for maintenance purposes.

Excavations and fills.

(1)

No excavation or fill shall be made with a face or surface slope steeper than four horizontal to one vertical unless a retaining wall, constructed in accordance with approved standards, is provided to support the face or surface slope of said excavation or fill.

(2)

Adequate provisions shall be made to prevent surface water from damaging the cut face of excavations and the sloping surfaces of fills.

(3)

Cut and fill shall not endanger adjoining property.

(4)

Fill shall be placed and compacted so as to minimize sliding or erosion of the soil.

(5)

Fills shall not encroach in floodplain areas or wetlands.

(6)

Fills placed adjacent to floodways shall have suitable protection against erosion during flooding.

Responsibility.

(1)

Each person, corporation or other entity which makes any surface changes shall be required to:

(a)

Collect on-site surface run-off and control it to a point of discharge into the natural watercourse of the drainage area having adequate capacity.

(b)

Adequately handle existing off-site run-off through the development.

(c)

Provide and install all temporary and permanent drainage and erosion control improvements, as required by the approved sedimentation and erosion control plan.

(2)

Whenever sedimentation is caused by stripping of vegetation, regrading or other development, it shall be the responsibility of the person causing such sedimentation to remove it from all affected surfaces, drainage systems and watercourses on-site and off-site and to repair any damage at the developer's expense as quickly as possible following a storm event.

(3)

Maintenance of all drainage facilities and watercourses, both existing and proposed, within any proposed subdivision or land development shall be the responsibility of the developer 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; 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 then 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/of drainage facilities.

(4)

It is the responsibility of any person, corporation or other entity doing any work on or across a watercourse, swale, floodplain or right-of-way to return such areas to their original or equal condition after such activity is completed.

(5)

No person, corporation or other entity shall block, impede the flow of, alter, construct any structure, deposit any material or thing or perform any work which will affect normal or flood flow in any watercourse without having obtained prior approval from the Township and/or Pennsylvania Department of Environmental Protection, whichever is applicable.

Topsoil protection. All development plans shall include the preservation of topsoil on the site of the development. Topsoil from areas to be disturbed shall be stripped and piled on site and ultimately spread out on the site as appropriate. The site area stripped of topsoil shall be kept to a minimum, and no topsoil shall be removed from the site.

[Added 12-20-2006 by Ord. No. 363]