Township of East Cocalico, PA Design Criteria

Except where specifically prohibited under the "Discharges Not Authorized by this General Permit" section, this general permit authorizes the discharge of stormwater to surface waters from regulated small MS4s. In addition, the following nonstormwater discharges are authorized by this general permit as long as such discharges do not cause or contribute to pollution as defined in Pennsylvania's Clean Streams Law:[1]

Waterline flushing*

Air-conditioning condensation

Landscape irrigation

Irrigation waters

Diverted stream flows

Flows from riparian habitats and wetlands

Rising groundwaters

Uncontaminated groundwater

Lawn watering

Water from crawl space pumps

Springs

Routine external building wash down (which does not use detergents or other compounds)

Individual residential car washing**

Discharges from firefighting activities, including training

Discharges from potable sources

Water from geothermal systems

Uncontaminated discharges from foundation drains or footings

Noncontaminated hydrostatic test water discharges*

*	If such discharges do not contain detectable concentrations of total residual chlorine (TRC).
**	Where cleaning agents are not utilized.

Editor's Note: See 35 P.S. § 691.1 et seq.

In the event that the Township or DEP determines that any of the discharges identified in Subsection J significantly contribute to pollution of waters of the commonwealth, the Township or DEP will notify the responsible person to cease the discharge.

Upon notice provided by the Township, the discharger will have a reasonable time to cease the discharge consistent with the degree of pollution caused by the discharge.

The following connections to the Township storm sewers or stormwater drainage systems are prohibited:

Any drain or conveyance, whether on the surface or subsurface, which allows any nonstormwater discharge including sewage, process wastewater, and wash water to enter the separate storm sewer system, or waters of the commonwealth, and any connections to the storm drain system from indoor drains and sinks.

Any drain or conveyance from a commercial or industrial land use to the separate storm sewer system which has not been documented in plans, maps, or equivalent records, and approved by the Township.

This prohibition expressly includes, without limitation, connections made in the past, regardless of whether the connection, drain or conveyance was previously allowed, permitted, or approved by a government agency, or otherwise permissible under law or practices applicable or prevailing at the time of connection.

Roof drains shall not be connected to streets, sanitary or storm sewers or roadside ditches, except as provided in Subsection K(5).

When it is more advantageous to connect directly to streets or storm sewers, connections of roof drains to streets or roadside ditches may be permitted on a case-by-case basis by the Township. It shall be the burden of the person seeking to make the connection to demonstrate to the Township that such connection is more advantageous and such connection shall not violate any state or federal statute, rule or regulation.

(6)

Roof drains and sump pumps shall discharge to infiltration areas or vegetative BMPs to the maximum extent possible.

(7)

Sump pumps shall not be discharged directly to separate storm sewer systems or waters of the commonwealth.

Waste disposal prohibitions. No person shall throw, deposit, leave, maintain, keep or permit to be thrown, deposited, left, or maintained in or upon any public or private property, driveway, parking area, street, alley, sidewalk, or other component of the Township's separate storm sewer system any refuse, rubbish, garbage, litter, or other discarded or abandoned objects, articles, and accumulations, so that the same may cause or contribute to pollution. Wastes deposited in streets in proper waste receptacles for the purpose of collection are exempted from this prohibition.

§ 185-23 Volume control.

The green infrastructure and low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible. Volume control BMPs are intended to maintain existing hydrologic conditions for small storm events by promoting groundwater recharge and/or evapotranspiration as described in this chapter. Runoff volume controls shall be implemented using the Design Storm Method described in Subsection A below, or through continuous modeling approaches or other means as described in the BMP Manual. Small projects may use the method described in Subsection B to design volume control BMPs.

The Design Storm Method (CG-1 in the BMP Manual) is applicable to any size of regulated activity. This method requires detailed modeling based on site conditions.

The BMP selected may not increase the post-development total runoff volume for all storms equal to or less than the two-year twenty-four-hour storm event.

For modeling purposes:

Existing (predevelopment) nonforested pervious areas must be considered meadow in good condition.

When the existing project site contains impervious area, 20% of existing impervious area to be disturbed shall be considered meadow in good condition in the model for existing conditions.

The maximum loading ratio for volume control facilities in karst areas shall be 3:1 impervious drainage area to infiltration area and 5:1 total drainage area to infiltration area. The maximum loading ratio for volume control facilities in non-karst areas shall be 5:1 impervious drainage area to infiltration area and 8:1 total drainage area to infiltration area. A higher ratio may be approved by the Township if professional justification deemed satisfactory to the Township is provided. Hydraulic depth may be used as an alternative to an area-based loading ratio if the design hydraulic depth is shown to be less than the depth that could result from the maximum area loading ratio.

The Simplified Method (CG-2 in the BMP Manual) provided below is independent of site conditions and should be used if the Design Storm Method is not followed. This method is not applicable to regulated activities greater than one acre or for projects that require design of stormwater storage facilities. For new impervious surfaces:

Stormwater facilities shall capture at least the first two inches of runoff from all new impervious surfaces.

At least the first one inch of runoff from new impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of this commonwealth. Removal options include reuse, evaporation, transpiration, and infiltration.

Wherever possible, infiltration facilities should be designed to accommodate infiltration of the entire permanently removed runoff; however, in all cases at least the first 0.5 inch of the permanently removed runoff should be infiltrated.

This method is exempt from the requirements of § 185-24, Rate control.

Volume control for small projects. At least the first three inches of runoff from new impervious surfaces or an equivalent volume shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of this commonwealth. Removal options include reuse, evaporation, transpiration and infiltration.

A detailed geologic evaluation of the development site shall be performed in areas of karst geology to determine the design parameters of recharge facilities. A report shall be prepared in accordance with § 185-14A(10) of this chapter.

Storage facilities, including normally dry, open-top facilities, shall completely drain the volume control storage over a period of time not less than 24 hours and not more than 72 hours from the end of the design storm. Any designed infiltration at such facilities is exempt from the minimum twenty-four-hour standard, i.e., may infiltrate in a shorter period of time, provided that none of this water will be discharged into waters of this commonwealth.

Any portion of the volume control storage that meets the following criteria may also be used as rate control storage.

Volume control storage that depends on infiltration is designed according to the infiltration standards in this chapter.

The volume control storage which will be used for rate control is that storage which is available within 24 hours from the end of the design storm based on the stabilized infiltration rate and/or the evapotranspiration rate.

Volume control storage facilities designed to infiltrate shall avoid the least permeable hydrologic soil group(s) at the development site.

The developer may use stormwater credits for nonstructural BMPs in accordance with the BMP Manual. The allowable reduction will be determined by the Township Engineer.

§ 185-24 Rate control.

Rate control for large storms, up to the 100-year event, is essential to protect against immediate downstream erosion and flooding. The design storm volumes to be used in the analysis of peak rates of discharge should be obtained from the latest version of the Precipitation-Frequency Atlas of the United States, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland.

The post-development hydrograph must match the predevelopment hydrograph. Applicants shall provide infiltration facilities or utilize other techniques which will allow the post-development 100-year hydrograph to match the predevelopment 100-year hydrograph, along all parts of the hydrograph, for the development site. To match the predevelopment hydrograph, the post-development peak rate must be less than or equal to the predevelopment peak rate, and the post-development runoff volume must be less than or equal to the predevelopment volume for the same storm event. A shift in hydrograph peak time of up to five minutes may be allowable. "Volume control" volumes as given in § 185-23 above may be used as part of this option.

In all other cases, the post-development peak discharge onto adjacent property shall be 50% of the predevelopment peak rate of runoff. Runoff calculations for the predevelopment and post-development comparison shall be provided for the two-, ten-, twenty-five-, fifty-, and 100-year storm events. The 50% peak rate reduction is consistent with the approved Cocalico Creek Act 167 Plan and Conestoga River Act 167 Plan and associated release rate maps. A twenty-four-hour SCS Type II storm or an IDF Curve Modified Rational Method storm evaluation shall be performed as outlined within this chapter.

Peak rate control is not required for off-site runoff. Off-site runoff may be bypassed around the site, provided all other discharge requirements are met. If off-site runoff is routed through rate control facilities, runoff coefficients for off-site discharges used to design those rate control facilities shall be based on actual land use assuming summer conditions in the predevelopment and winter or poor land conditions in the post-development.

Normally dry, open-top storage facilities shall completely drain the rate control storage over a period of time less than or equal to 24 hours from the peak 100-year water surface design elevation.

A variety of BMPs may be employed and tailored to suit the development site. The following is a partial listing of BMPs which can be utilized in stormwater management systems for rate control where appropriate:

Decreased impervious surface coverage.

Routed flow over grass.

Grassed channels and vegetated strips.

Bioretention areas (rain gardens).

Concrete lattice block or permeable surfaces.

(6)

Seepage pits, seepage trenches or other infiltration structures.

(7)

Rooftop detention.

(8)

Parking lot detention.

(9)

Cisterns and underground reservoirs.

Amended soils.

Retention basins.

Detention basins.

Other methods as may be found in the BMP Manual.

Small projects are not required to provide for rate control.

§ 185-25 Methods of calculations.

The methods to calculate runoff shall be as follows:

The USDA SCS Soil-Cover-Complex Method.

The USDA SCS Soil-Cover-Complex Method, as set forth in the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55, as published by SCS, shall be used where the drainage area is greater than 20 acres; or the time of concentration is greater than one hour; or the calculated runoff to a point of interest requires the combination of multiple hydrographs from multiple subwatersheds of the study area.

If the SCS Method is used, Antecedent Moisture Condition 1 is to be used in areas of karst geology when required by the Township Engineer, and Antecedent Moisture Condition 2 is to be used in all other areas. A Type II distribution shall be used in all areas.

Rational Method.

The Rational Method of Q = CIA, where "Q" is the peak discharge of the watershed in cubic feet per second, "C" is the coefficient of runoff, "I" is the intensity of rainfall in inches per hour, "A" is the area of the watershed in acres.

The modified Rational Method shall be used where the drainage area is less than 20 acres; and the calculated runoff to a point of interest does not require the combination of multiple hydrographs from multiple subwatersheds of the study area.

If "modified" or "unit hydrograph" rational methods are used to develop hydrographs, the ascending leg of the hydrograph shall have a length equal to three times the time of concentration (3xTc) and the descending leg shall have a length equal to seven times the time of concentration (7xTc) to approximate an SCS Type II hydrograph.

Runoff calculations shall include a hydrologic and hydraulic analysis indicating volume and velocities of flow and the grades, sizes and capacities of water-carrying structures, sediment basins, retention and detention structures, and sufficient design information to construct such facilities. The capacities of the pipes, gutters, inlets, culverts, outlet structures, and swales shall consider all possible hydraulic conditions. Runoff calculations shall also indicate both predevelopment and post-development rates for peak discharge of stormwater runoff from all discharge points.

For the purpose of calculating predevelopment on-site peak discharges, all on-site runoff coefficients shall be based on actual land use assuming summer or good land cover conditions. Post-development runoff coefficients for off-site discharges used to design conveyance facilities shall be based on actual land use assuming winter or poor land conditions. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious.

Criteria and assumptions to be used in the determination of stormwater runoff and design of management facilities are as follows:

Runoff coefficients should be based on the following table. If the land use is not listed, runoff coefficients shall be chosen from other published documentation, and a copy of said documentation shall be submitted with the stormwater management report. Higher coefficients may be required by the Township Engineer due to local soil conditions.

	Runoff Coefficients "C" for Rational Formula
Soil Group	A			B			C			D
Slope	0-2%	2-6%	6%+	0-2%	2-6%	6%+	0-2%	2-6%	6%+	0-2%	2-6%	6%
Land use
Cultivated land
Winter conditions	0.14	0.23	0.34	0.21	0.32	0.41	0.27	0.37	0.48	0.34	0.45	0.56
Summer conditions	0.10	0.16	0.22	0.14	0.20	0.28	0.19	0.26	0.33	0.23	0.29	0.38
Fallowed fields
Poor conditions	0.12	0.19	0.28	0.17	0.25	0.34	0.23	0.33	0.40	0.27	0.35	0.45
Good conditions	0.08	0.13	0.16	0.11	0.15	0.21	0.14	0.19	0.26	0.18	0.23	0.31
Forest/woodland	0.08	0.11	0.14	0.10	0.14	0.18	0.12	0.16	0.20	0.15	0.20	0.25
Grass areas
Good conditions	0.10	0.16	0.20	0.14	0.19	0.26	0.18	0.22	0.30	0.21	0.25	0.35
Average conditions	0.12	0.18	0.22	0.16	0.21	0.28	0.20	0.25	0.34	0.24	0.29	0.41
Poor conditions	0.14	0.21	0.30	0.18	0.28	0.37	0.25	0.35	0.44	0.30	0.40	0.50
Impervious areas	0.90	0.91	0.92	0.91	0.92	0.93	0.92	0.93	0.94	0.93	0.94	0.95
Weighted residential
Lot size 1/8 acre	0.29	0.33	0.36	0.31	0.35	0.40	0.34	0.38	0.44	0.36	0.41	0.48
Lot size 1/4 acre	0.26	0.30	0.34	0.29	0.33	0.38	0.32	0.36	0.42	0.34	0.38	0.46
Lot size 1/3 acre	0.24	0.28	0.31	0.26	0.32	0.35	0.29	0.35	0.40	0.32	0.36	0.45
Lot size 1/2 acre	0.21	0.25	0.28	0.24	0.27	0.32	0.27	0.31	0.37	0.30	0.34	0.43
Lot size 1 acre	0.18	0.23	0.26	0.21	0.24	0.30	0.24	0.29	0.36	0.28	0.32	0.41

	Runoff Curve Numbers "CN" for SCS Method
Soil Group	A			B			C			D
Slope	0-2%	2-6%	6%+	0-2%	2-6%	6%+	0-2%	2-6%	6%+	0-2%	2-6%	6%+
Land use
Cultivated land
Winter conditions	48	60	65	62	73	73	68	78	79	77	88	81
Summer conditions	35	51	61	48	55	70	57	65	77	64	69	80
Fallowed fields
Poor conditions	45	54	76	56	63	85	64	74	90	69	77	93
Good conditions	30	44	74	43	48	83	48	54	88	56	60	90
Forest/woodland	30	40	30	42	46	55	45	50	70	50	56	77
Grass areas
Good conditions	35	51	39	48	54	61	56	59	74	62	63	80
Average conditions	45	53	49	52	55	69	60	63	79	65	69	84
Poor conditions	48	55	68	56	67	79	66	74	86	73	81	89
Impervious areas	96	97	98	96	97	98	96	97	98	96	97	98
Weighted residential
Lot size 1/8 acre	71	75	77	74	76	85	78	80	90	81	83	92
Lot size 1/4 acre	62	67	61	66	69	75	67	69	83	75	78	87
Lot size 1/3 acre	59	65	57	64	66	72	65	66	81	74	77	86
Lot size 1/2 acre	57	63	54	62	64	70	63	65	80	72	76	85
Lot size 1 acre	55	62	51	61	63	68	61	64	79	71	75	84

Conveyance Facility Design Criteria
Location			Within Public Street Right-of-Way or Dedicated Land	Outside Public Street Right-of-Way or Within Nondedicated Areas
Loading			All	Vehicular Loading	Nonvehicular Loading
(a)	Pipe design
	[1]	Material	SLHDPE, RCP	PVC, SLHDPE, RCP	PVC, SLHDPE, RCP
	[2]	Slope (minimum)	0.5%	0.5%	0.5%
	[3]	Cover	1 foot to stone subgrade	1 foot to stone subgrade	1 foot to surface
	[4]	Diameter (minimum)	15 inches	15 inches	8 inches
	[5]	Street crossing angle	75° to 90°	N/A	N/A
	[6]	Access/maintenance port frequency (maximum)	400 feet	400 feet	600 feet
(b)	Inlet design
	[1]	Material	Concrete	Concrete	N/A
	[2]	Grate depression	2 inches	2 inches	1 inch minimum
(c)	Manhole design
	[1]	Material	Concrete	Concrete	Concrete
(d)	Swale design
	[1]	Freeboard (minimum)	6 inches	N/A	6 inches
	[2]	Velocity (maximum)	Stability check	N/A	Stability check
	[3]	Slope (minimum)	1%	N/A	1%
	[4]	Side slopes (residential area)	4:1 max	N/A	4:1 max
	[5]	Side slopes (nonresidential area)	4:1 max	N/A	3:1 max
	[6]	Bottom width to flow depth ratio	12:1	N/A	12:1
(e)	Outlet design
	[1]	End treatment	Headwall/endwall	N/A	Headwall/endwall or flared end section
	[2]	Energy dissipater	Required	N/A	Required
Abbreviations: N/A = not applicable or no criteria specified; SLHDPE = smooth lined high density polyethylene pipe; PVC = polyvinyl chloride; RCP = reinforced concrete pipe

Times of concentration shall be based on the following design parameters:

Sheet flow. The maximum length for each reach of sheet, or overland flow before shallow concentrated or open channel flow develops, is 150 feet. Sheet flow shall be determined using Worksheet 3 from the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55, as published by SCS.

Shallow concentrated flow. Travel time for shallow concentrated flow shall be determined using Figure 3-1 from the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55, as published by SCS.

Open channel flows. At points where sheet and shallow concentrated flows concentrate in field depressions, swales, gutters, curbs, or pipe collection systems, the travel times and downstream end of the site between these design points shall be based upon Manning's Equation and/or acceptable engineering design standards, as determined by the Township Engineer. Supporting documentation and calculations must be submitted for review and approval.

§ 185-26 Hydrographs.

A predevelopment hydrograph is required at the site discharge point for the required twenty-four-hour design storm.

A post-development hydrograph is required at the site discharge point incorporating any "nondetention" techniques, such as pervious areas, swales, infiltration trenches, etc.

§ 185-27 Stormwater conveyance facility design standards.

Conveyance facilities consist of all stormwater facilities which carry flow, which may be located either above or below the finished grade. Conveyance facilities do not include stormwater management facilities which store, infiltrate/evaporate/transpire, or clean stormwater runoff.

Design criteria. Conveyance facilities shall comply with the design criteria in the following table:

Conveyance pipes, culverts, manholes, inlets and endwalls and other appurtenances shall conform to the requirements of PennDOT Standards for Roadway Construction, Publication No. 72M, in effect at the time the design is submitted, as modified by the adopted Township construction standards. Conveyance pipes, culverts, manholes, inlets and endwalls which are otherwise subject to vehicular loading shall be designed for the HS-25 loading condition.

Conveyance pipes.

Backfill requirements. Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select nonaggregate material should be indigenous to the surrounding soil material for nonvehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in Chapter 194, Subdivision and Land Development, or other governing Township road/street ordinances.

Inlets or manholes shall be placed at all points of changes in the horizontal or vertical directions of conveyance pipes. Curved pipe sections are prohibited unless specifically authorized by the Township Engineer.

Access/maintenance port. An access/maintenance port is required and may either be an inlet or manhole.

(d)

Watertight joints shall be provided where pipe sections are joined, except for perforated pipe installed as pavement base drain.

(e)

The street-crossing angle shall be measured between the pipe center line and the street center line.

(f)

Elliptical pipe of an equivalent cross-sectional area may be substituted in lieu of circular pipe where cover or utility conflict conditions exist. No double pipe can be used for conveyance.

(g)

The roughness coefficient (Manning "n" values) used for conveyance pipe capacity calculations should be determined in accordance with PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's specifications.

Inlets.

All pipes must enter inlets completely through one of the sides. No corner entry of pipes is permitted.

Within the public street right-of-way, the gutter spread based on the twenty-five-year storm shall be no greater than 1/2 of the travel lane and have a maximum depth of three inches at the curbline. A parking lane shall not be considered as part of the travel lane. In the absence of pavement markings separating a travel lane from the parking lane, the parking lane shall be assumed to be seven feet wide if parking is permitted on the street.

Flow depth within intersections. Within intersections of streets, the maximum depth of flow shall be 1 1/2 inches based on the twenty-five-year storm.

(d)

Curbed streets.

Inlets in streets shall be located along the curbline at low points and as required to comply with maximum allowable gutter flow depths. The Township may require redundant inlets upslope and in proximity to roadway low points as deemed necessary to provide secondary relief under potential obstructed conditions.

Top units shall be PennDOT Type "C." The hood shall be aligned with the adjacent curb height and normally placed outside of radii.

(e)

All inlets placed in paved areas shall have heavy-duty bicycle-safe grating consistent with PennDOT Publication 72M, latest edition. A note to this effect shall be added to the SWM site plan or inlet details therein.

(f)

Inlets, junction boxes, or manholes greater than five feet in depth shall be equipped with ladder rungs and shall be detailed on the SWM site plan.

Swales.

A swale shall be considered as any man-made ditch designed to convey stormwater directly to another stormwater management facility or surface waters.

Inlets within swales shall have PennDOT Type "M" top units or equivalent approved by the Township Engineer.

Swale capacities and velocities shall be computed using the Manning Equation using the following design parameters:

Vegetated swales.

[a]

The first condition shall consider swale stability based upon a low degree of retardance ("n" = 0.03);

[b]

The second condition shall consider swale capacity based upon a higher degree of retardance ("n" = 0.05); and

[c]

All vegetated swales shall have a minimum slope of 1% unless otherwise approved by the Township Engineer.

The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices, as approved by the Township Engineer.

(d)

All swales shall be designed to maximize infiltration and concentrate low flows to minimize siltation and meandering, unless geotechnical conditions do not permit infiltration.

(6)

Culverts.

In addition to the material requirements in this section, culverts designed to convey waters of the commonwealth shall be constructed with either SLHDPE pipe, RCP, reinforced precast concrete or reinforced cast-in-place concrete with headwalls/endwalls and cutoff walls extending three feet below channel flow line. The culvert shall include fish channels, as required by the PADEP or other governing agencies.

Protective parapets shall be provided when required by the Township based on roadway configuration and embankment slopes.

All culvert structures shall require submission of certified construction drawings to assure compliance and PennDOT standards and HS-25 loading.

(7)

Level spreaders.

Shall discharge at existing grade onto undisturbed vegetation.

Discharge at a depth not exceeding 3.0 inches for a fifty-year, twenty-four-hour design storm.

(8)

Energy dissipaters. Energy dissipaters shall be designed in accordance with the requirements in the E&S Manual.

(9)

End treatments.

Where the connecting pipe has a diameter 15 inches or greater, headwalls and endwalls shall be provided with a protective barrier device to prevent entry of the storm sewer pipe by unauthorized persons. Such protection devices shall be designed to be removable for cleaning.

Headwalls and endwalls shall be constructed of concrete.

Flared end sections, when authorized, shall be of the same material as the connecting pipe and be designed for the size of the connecting pipe.

§ 185-28 Aboveground stormwater management storage facility design standards.

Aboveground storage facilities. Aboveground storage facilities consist of all stormwater facilities which store, infiltrate evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is exposed to the natural environment. Aboveground storage facilities are located above the finished ground elevation. Aboveground storage facilities do not include stormwater management facilities designed for conveyance or cisterns.

Design criteria. Aboveground storage facilities shall comply with the design criteria in the following table:

Aboveground Storage Facility Design Criteria
			Facility Depth
			Less than 2 feet	2 feet to 8 feet	Greater than 8 feet
(a)	Embankment geometry
	[1]	Top width (minimum)	2 feet	5 feet	8 feet
	[2]	Interior side slope (maximum)	3:1	3:1	5:1
	[3]	Exterior side slope (maximum)	3:1	3:1	3:1
(b)	Embankment construction
	[1]	Key trench	Not required	Required	Required
	[2]	Pipe collar	Not required	Required	Required
	[3]	Compaction density	Not required	Required	Required
(c)	Internal construction
	[1]	Dewatering feature	N/A	Required	Required
	[2]	Pretreatment elements	Not required*	Required	Required
(d)	Outlet structure
	[1]	Pipe size (minimum)	6 inches	12 inches	15 inches
	[2]	Pipe material	SLHDPE, PVC, RCP	SLHDPE, RCP	RCP
	[3]	Anti-clogging device/trash rack	Required	Required	Required
	[4]	Anti-vortex design	Not required	Required	Required
	[5]	Watertight joints in piping	Yes	Yes	Yes
(e)	Spillway requirements
	[1]	Spillway freeboard (minimum)	Not required	3 inches	6 inches
	[2]	Width (minimum)	Not required	10 feet	20 feet
	[3]	Width (maximum)	Not required	50 feet	50 feet
	[4]	Spillway channel design	Not required	Required	Required
	[5]	Routing of 100-year storm	Permitted	Permitted	Permitted
Note: In certain situations 2:1 side slopes may be authorized by the Township on embankment berms of less than two feet when appropriately landscaped and mulched.
Abbreviations: *Pretreatment required for infiltration BMPs unless shown to be unnecessary; N/A = not applicable; SLHDPE = smooth lined high density polyethylene pipe; PVC = polyvinyl chloride; RCP = reinforced concrete pipe.

Facility depth.

For the purposes of the design criteria, the facility depth is defined to be the depth between the bottom invert of the lowest orifice and the invert of the spillway. If there is no spillway, the top of the berm shall be used. For basins with no orifices or outlet structure, the bottom elevation of the basin shall be used.

Facilities with a facility depth greater than six feet shall not be permitted in residential areas.

Facilities with a facility depth greater than 15 feet require a dam permit from DEP.

Embankment construction.

Impervious core/key trench. An impervious core/key trench, when required, shall consist of a cutoff trench (below existing grade) and a core trench (above existing grade). A key trench may not be required wherever it can be shown that another design feature, such as the use of an impermeable liner, accomplishes the same purpose.

Materials. Materials used for the core shall conform to the Unified Soil Classification GC, SC, CH, or CL and must have at least 30% passing the No. 200 sieve.

Dimensions.

The dimensions of the core/key trench shall provide a minimum trench depth of two feet below existing grade, minimum width of four feet and side slope of IH:IV or flatter.

The core should extend up both abutments to the ten-year water surface elevation or six inches below the emergency spillway elevation, whichever is lower.

[3]

The core shall extend four feet below any pipe penetrations through the impervious core. The core shall be installed along or parallel to the center line of the embankment.

Compaction.

Compaction requirements shall be the same as those for the embankment to assure maximum density and minimum permeability.

The core shall be constructed concurrently with the outer shell of the embankment.

[3]

The trench shall be dewatered during backfilling and compaction operations.

Pipe collars. All pipe collars, when required, shall be designed in accordance with Chapter 7 of the E&S Manual. The material shall consist of concrete or otherwise nondegradable material around the outfall barrel and shall be watertight.

Embankment fill material. The embankment fill material shall be taken from an appropriate borrow area or imported fill which shall be free of roots, stumps, wood, rubbish, stones greater than six inches, frozen or other objectionable materials.

Embankment compaction. When required, embankments shall be compacted by sheepsfoot or pad roller. The loose lift thickness shall be nine inches or less, depending on roller size, and the maximum particle size is six inches or less (2/3 of the lift thickness). Five passes of the compaction equipment over the entire surface of each lift are required. Embankment compaction to visible nonmovement is also required. The embankment shall be structurally sound under all probable conditions of operation.

Internal construction.

Bottom slope. The minimum bottom slope of facilities not designed for infiltration shall be 1%. A flatter slope may be used if an equivalent dewatering mechanism is provided.

Dewatering features. When required, dewatering shall be provided through the use of underdrain, surface device, or alternate approved by the Township Engineer. If the facility is to be used for infiltration, the dewatering device should be capable of being disconnected and only be made operational if the basin is not dewatering within the required time frame.

Pretreatment elements. When required, pretreatment elements shall consist of forebays, or alternate approved by the Township Engineer, to keep silt to a smaller portion of the facility for ease of maintenance.

Infiltration basins. Within basins designed for infiltration, existing native vegetation shall be preserved, if possible. For existing unvegetated areas or for infiltration basins that require excavation, a planting plan shall be prepared in accordance with § 185-14C(9) of this chapter and the BMP Manual which is designed to promote infiltration.

Outlet configuration.

For facilities with a depth of two feet or greater, a Type D-W endwall or riser box outlet structure shall be provided.

For facilities with a depth less than two feet, no outlet structure is required.

All discharge control devices with appurtenances shall be made of reinforced concrete and stainless steel. Bolts/fasteners shall be stainless steel.

Spillway.

Material. The spillway shall be designed to provide a nonerosive, stable condition when the project is completed.

Nonemergency use. Use of the spillway to convey flows greater than the fifty-year design storm is permitted.

Emergency use. The spillway shall be designed to convey the 100-year peak inflow in a manner which will not damage the integrity of the facility or the downstream drainage areas.

When required, freeboard shall be measured from the top of the water surface elevation for emergency use.

Breach analysis. The Township may require a breach analysis based on site-specific conditions and concern of threat for downstream property. When required, the breach analysis shall be conducted in accordance with the NRCS methodology, the United States Army Corps of Engineers methodology (HEC-1) or other methodologies as approved by the Township.

Fencing. Fencing, or other acceptable devices that adequately restrict access, shall be provided for basins with slopes greater than five horizontal to one vertical when the water surface area is greater than one acre, and/or more than five feet deep during a 100-year storm event. However, the Township, based upon the type and proximity of adjacent land use, may require the access restrictions to avoid a hazardous condition.

Wet ponds. Basins which are not designed to release all stormwater shall be specifically identified wet pond basins and designed in accordance with the BMP Manual to create biodiversity, ensure long-term viability and provide appropriate shoreline protection and buffering.

§ 185-29 Subsurface stormwater management storage facility design standards.

Subsurface storage facilities. Subsurface storage facilities consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is not exposed to the natural environment. Subsurface facilities are located below the finished ground elevation. Subsurface facilities do not include stormwater management facilities designed for conveyance.

Design criteria. Subsurface storage facilities shall comply with the design criteria in the following table:

Subsurface Storage Facility Design Criteria
			Facility Type
			Infiltration and Storage	Storage Without Infiltration
(a)	Facility geometry
	[1]	Depth from surface (maximum)	2 feet less than limiting zone	N/A
	[2]	Loading ratio (maximum)	Per BMP Manual*	N/A
(b)	Distribution system requirements
	[1]	Pipe size (minimum)	4 inches	4 inches
	[2]	Pretreatment	Required	Required
	[3]	Loading/balancing	Required	Not required
	[4]	Observation/access ports	Required	Required
Abbreviations: *Unless otherwise determined by professional geologic evaluation.

Distribution system requirements.

Pretreatment requirements. The facility shall be designed to provide a method to eliminate solids, sediment, and other debris from entering the subsurface facility.

Loading/balancing. The facility shall be designed to provide a means of evenly balancing the flow across the surface of the facility to be used for infiltration.

Observation/access ports.

For facilities with the bottom less than five feet below the average grade of the ground surface, a cleanout shall be an acceptable observation port.

For facilities with the bottom five feet or more below the average grade of the ground surface, a manhole or other means acceptable to the Township shall be provided for access to and monitoring of the facility.

The number of access points shall be sufficient to flush or otherwise clean out the system.

Materials.

Pipe material. Distribution system piping may be PVC, SLHDPE, or RCP.

Stone for infiltration beds. The stone used for infiltration beds shall be clean washed, uniformly graded coarse aggregate (AASHTO No. 3 or equivalent approved by the Township). The void ratio for design shall be assumed to be 0.4.

Backfill material. Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select nonaggregate material should be indigenous to the surrounding soil material for nonvehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in Chapter 194, Subdivision and Land Development, or any other Township ordinance or regulation. Furthermore, if the design concept includes the migration of runoff through the backfill to reach the infiltration facility, the material shall be well drained, free of excess clay or clay-like materials and generally uniform in gradation.

Lining material. Nonwoven geotextiles shall be placed on the sides and top of subsurface infiltration facilities. No geotextiles shall be placed on the bottom of subsurface infiltration facilities.

Cover.

When located under pavement, the top of the subsurface facility shall be a minimum of three inches below the bottom of pavement subbase.

Where located under vegetative cover, the top of the subsurface facility shall be a minimum of 12 inches below the surface elevation or as required to establish vegetation.

Subsurface facilities shall be isolated from property lines by a minimum of five feet and separated from dwellings with basements, sewer disposal facilities, wells, etc., as outlined in the BMP Manual.

Subsurface facilities shall be designed to safely convey and/or bypass flows from storms exceeding the design storm. Overflow locations shall be identified isolated from downstream property lines to the maximum extent possible and positioned to minimize potential for adverse downstream conditions.

§ 185-30 Phasing plans.

When applications are submitted in phases, and if temporary facilities are required for construction of a phase, such facilities shall be included in the submitted plans and secured with an improvement guarantee. All phases of development must comply with the provisions of this chapter. In the event temporary measures cannot adequately handle the stormwater runoff, the additional facilities shall be included as part of the construction of the proposed phase. An expected project time schedule shall be outlined on the plans.

§ 185-31 Stormwater management performance standards.

Runoff from impervious areas shall be drained to pervious areas within the development site, unless the site has 85% or more impervious cover and is a redevelopment, in which case the portion of the site that discharges to pervious areas shall be maximized.

Impervious areas:

The measurement of impervious areas shall include all of the impervious areas in the total proposed development even if development is to take place in stages.

For development taking place in stages, the entire development plan must be used in determining conformance with this chapter.

For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 185-23 and the peak rate controls of § 185-24 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.

Stormwater flows onto adjacent property shall be conveyed in a manner consistent with predevelopment runoff characteristics and shall not be altered without written notification of the adjacent property owner(s) by the developer. Based on the size and nature of the stormwater facilities proposed, the Township may require written notification of the adjacent property owner(s) by the developer. Altered stormwater flows shall be subject to the requirements of this chapter, including the establishment of a drainage easement. Copies of all such notifications and/or easements shall be included in SWM site plan submissions.

Existing on-site natural and man-made stormwater management facilities shall be used and enhanced to the maximum extent practicable. All existing and natural watercourses, channels, drainage systems, and areas of surface water concentrate shall be maintained in their existing condition, unless the Township approves an alteration or improvements are necessary to resolve eroded conditions.

Minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the 100-year water surface elevation. If basement or underground facilities are proposed, detailed calculations addressing the effects of stormwater ponding on the structure and waterproofing and/or floodproofing design information consistent with the floodplain standards in Chapter 220, Zoning, shall be submitted for approval.

All stormwater conveyance facilities (excluding detention, retention, and wetland basin outfall structures) shall be designed to convey a twenty-five-year storm event. (Note: A twenty-four-hour SCS Type II storm or an IDF Curve Rational Method storm.) All stormwater conveyance facilities (excluding detention, retention, and wetland basin outfall structures) conveying water originating from off site shall be designed to convey a fifty-year storm event. (Note: A twenty-four-hour SCS Type II storm or an IDF Curve Rational Method storm.) Safe conveyance of the 100-year runoff event (Note: A twenty-four-hour SCS Type II storm or an IDF Curve Rational Method storm) to appropriate peak rate control BMPs must be demonstrated in the design.

Erosion protection shall be provided along all open channels, and at all points of discharge including spillways. Flow velocities from any storm sewer may not result in erosion of the receiving channel.

Infiltration BMPs shall be spread out, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this chapter. Infiltration BMPs shall include pretreatment BMPs unless shown to be unnecessary.

Infiltration BMPs intended to receive runoff from developed areas shall be selected based on suitability of soils and development site conditions and shall be constructed on soils that have the following characteristics:

A minimum depth of 24 inches between the bottom of the facility and the limiting zone, unless it is demonstrated to the satisfaction of the Township that the selected BMP has design criteria which allow for a smaller separation.

A stabilized infiltration rate sufficient to accept the additional stormwater load and drain completely as determined by field tests conducted by the applicant's professional designer.

The stabilized infiltration rate is to be determined in the same location and within the same soil horizon as the bottom of the infiltration facility.

The stabilized infiltration rate is to be determined as specified in the BMP Manual with appropriate safety factors.

Infiltration systems and BMPs may not receive runoff until the entire contributory drainage area to the infiltration system has received final stabilization. Delay final construction of infiltration systems and BMPs until all other land-disturbing activities are complete to minimize the potential for clogging necessitating maintenance or remedial action.

§ 185-32 Soil erosion and sedimentation control.

The following principles shall be applied to the design plan and construction schedule to minimize soil erosion and sedimentation:

Stripping of vegetation, grading or other soil disturbance shall be done in a manner which will minimize soil erosion.

Natural wooded cover and vegetation shall be retained and protected, whenever feasible.

The extent of the disturbed area and the duration of its exposure shall be kept to a minimum, within practical limits.

Either temporary seeding, mulching or other suitable stabilization measures shall be used to protect exposed critical areas during construction.

Drainage provisions shall accommodate the stormwater runoff, both during and after construction.

Soil erosion and sedimentation facilities shall be installed before any earth-disturbing activities.

All earth disturbance activities shall be conducted in such a way as to minimize accelerated erosion and resulting sedimentation. Measures to control erosion and sedimentation shall, at a minimum, meet the standards of the LCCD, Chapter 102 (Erosion Control) of Title 25, Rules and Regulations of the PADEP, and the E&S Manual.

The erosion and sedimentation control plan must be available at all times at the project site. When required, a permit allowing earth disturbance activity shall be obtained by the developer before any construction on the project site shall begin.

Approval of an erosion and sedimentation control plan by the Township shall not be construed as an indication that the plan complies with the standards of any agency of the commonwealth.

The erosion and sedimentation control plan shall be submitted to the LCCD for its review and approval. Copies of all information submitted to the LCCD, including worksheets and calculations, shall be provided to the Township. Building permits will not be issued and construction shall not start until an NPDES permit, where required, is received.

§ 185-33 Easements.

Easements shall be provided where stormwater or surface water drainage facilities are proposed, whether located within or beyond the boundaries of the property. Although normal lot grading does not require easements, swales which receive runoff from more than one other lot or from more than 1/2 acre must be provided with an easement.

Easements shall have a minimum width of 10 feet from each side of the watercourse, water body, or drainage structure and shall be adequately designed to provide area for:

Collection and discharge of water;

Access, maintenance, repair and reconstruction of the drainage facilities with increased width required for deep facilities or facilities in close proximity to dwellings, structures or similar features that result in restrictive working conditions; and

Passage of machinery for such work.

Easements shall include a description of an ownership and maintenance program, in a recordable form, that clearly sets forth responsibility for all temporary and permanent stormwater management facilities.

Easements that are not described along a property line shall be located by a center line bearing and distance from a known point.

§ 185-34 Maintenance of stormwater management facilities.

Maintenance during development. Maintenance of stormwater management facilities during development of a project site shall be the responsibility of the developer and the landowner. Maintenance shall include, but not be limited to:

Removal of silt and debris from basins, traps or other structures and all programs stated in the approved erosion and sediment control plan. When required, cleanout shall restore the original design volume to the basin or other structure. The elevation corresponding to the maximum allowable sediment level shall be determined and stated in the design data as a distance below the top of the riser. The elevation shall be clearly marked on the riser to enable proper maintenance.

Periodic maintenance of temporary control facilities, such as replacement of silt fence, filter socks, stone filters, silt sacks or similar measures.

Establishment or restoration of vegetation by seeding, mulching or sodding of scoured areas or areas where vegetation has not been successfully established.

Installation of necessary controls to correct unforeseen problems caused by storm events within design frequencies.

Removal of all temporary stormwater management control facilities upon installation of permanent stormwater management facilities at the completion of the development.

Maintenance of facilities not dedicated or accepted by the Township.

The Township shall not become responsible for maintenance of stormwater management facilities, unless such facilities are within a street right-of-way dedicated to, and accepted by, the Township, or unless the Township specifically grants an exception to this standard. Maintenance of stormwater facilities shall be the responsibility of the developer and may be assigned to a private entity (e.g., property owner, homeowners' association, and condominium association), when deemed acceptable to the Township.

When possible, stormwater management facilities shall be owned and maintained by one entity. Stormwater management facilities shall be designed with consideration for facilities that can be effectively accommodated within the property of one responsible private entity and reasonably maintained by the private entity.

When maintenance of stormwater management facilities is assigned to the developer and/or private entity, a legally binding operation and maintenance agreement between the responsible parties and the Township shall be recorded. Such agreement shall provide the Township with the rights established in Section 705 of the Pennsylvania Municipalities Planning Code,[1] relating to the maintenance of common open space when a private entity fails to adequately maintain the facility. A deed restriction shall be recorded stating responsibilities of the property owner or private entity for the maintenance, as may be necessary to maintain the stormwater management facility in accordance with the terms of this chapter, the operation and maintenance agreement and the O&M plan. The O&M plan shall clearly establish the operation and maintenance necessary to ensure the proper functioning of all temporary and permanent stormwater management facilities and erosion and sedimentation control facilities and address the following:

Description of maintenance requirements, including, but not limited to, the following:

Regular inspection of the stormwater management facilities. To assure proper implementation of BMPs, maintenance and care stormwater management facility BMPs should be inspected by a qualified person, which may include the landowner, or the owner's designee (including the Township for dedicated and owned facilities), according to the following minimum frequencies:

[a]

Annually for the first five years.

[b]

Once every three years thereafter.

[c]

Immediately after the cessation of a ten-year or greater storm.

[d]

Inspections should be conducted during or immediately following precipitation events. A written inspection report shall be created to document each inspection. The inspection report shall contain the date and time of the inspection, the individual(s) who completed the inspection, the location of the BMP, facility or structure inspected, observations on performance, and recommendations for improving performance, if applicable. Inspection reports shall be submitted to the municipality within 30 days following completion of the inspection.

All pipes, swales and detention facilities shall be kept free of any debris or other obstruction and in original design condition.

[3]

Removal of silt from all permanent structures which trap silt or sediment in order to keep the material from building up in grass waterways, pipes, detention or retention basins, infiltration structures, or BMPs, and thus reducing their capacity to convey or store water.

[4]

Reestablishment of vegetation of scoured areas or areas where vegetation has not been successfully established. Selection of seed mixtures shall be subject to approval by the Township.

Editor's Note: See P.S. § 10705.

Deed restrictions shall also include notice that, in the event that the private entity fails to comply with the terms of this chapter, the Township shall have the authority to carry out those duties imposed upon the private entity.

The Township may, after giving notice to the private entity of improper maintenance, and providing a reasonable time for compliance, enter upon said property and take such actions as may be required to bring the area into compliance with this chapter.

The Township shall further have the right to file a municipal lien against such property for the cost of maintenance work carried out under this section, plus a penalty of 10% of the costs of such work. The Township may, in addition to the filing of a municipal lien, pursue any other remedies provided by law against any private entity that should fail to comply with the terms of this chapter.

Maintenance of existing facilities. No person shall modify, remove, fill, landscape, or alter stormwater management BMPs, facilities, areas, or structures unless a stormwater management plan has been approved or written approval is provided by the Township which authorizes such modification, removal, filling, landscaping, or alteration. No person shall place any structure, fill, landscaping, or vegetation into a permanent stormwater management facility or within a drainage easement or improperly maintain the stormwater facilities that limit, diminish or alter the functioning of the facility or easement in any manner or condition that constitutes a nuisance.

The Township may, after giving notice to the private entity of the improper condition and required corrective measures, and providing a reasonable time for compliance, not to exceed 30 days, enter upon said property or contract for performance of the work and take such actions as may be required to bring the area into compliance with this chapter.