A. 
Applicants proposing regulated activities in the municipality which are not exempt under § 225-6 shall submit a stormwater management site plan (SWM site plan) to the municipality for review and approval in accordance with Articles III and IV. SWM site plans approved by the municipality shall be on site throughout the duration of the regulated activity.
B. 
The stormwater management and runoff control criteria and standards in this chapter shall apply to the total proposed regulated activity, even if it is to take place in stages. The measurement of impervious surfaces shall include all of the impervious surfaces in the total proposed regulated activity even if the development is to take place in stages.
C. 
No regulated activity within the municipality shall commence until:
(1) 
The municipality issues approval of a SWM site plan, which demonstrates compliance with the requirements of this chapter; and
(2) 
The applicant has received a letter of adequacy or approval for the erosion and sediment control plan review by the municipality and the conservation district (if required), and has received all other local, state and federal permit approvals required for the project involving the regulated activity.
D. 
Neither submission of an SWM site plan under the provisions herein nor compliance with the provisions of this chapter shall relieve any person from responsibility for damage to any person or property otherwise imposed by law.
E. 
The applicant shall design the site to minimize disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall apply the procedures set forth in § 225-18 for the overall site design and for selection, location and design of features and BMPs to be used to comply with the requirements of this chapter.
F. 
To the maximum extent practicable, post-construction stormwater shall be discharged within the drainage area of the same stream or water body receiving the runoff prior to construction of the proposed regulated activity.
G. 
For regulated activities with one acre or more of proposed earth disturbance, existing drainage peak rate discharges up to and including the one-hundred-year storm onto or through adjacent property(ies) or downgradient property(ies), including diffuse drainage discharge, shall not be altered in any manner without written permission from and, where applicable as determined by the municipality, an easement and agreement with the affected landowner(s) for conveyance of discharges onto or through their property(ies). Such discharge shall be subject to any applicable discharge criteria specified in this chapter.
(1) 
For regulated activities with one acre or less proposed earth disturbance the applicant shall provide written notification to the affected landowner(s) describing the proposed regulated activity and proposed discharge(s), unless otherwise required by the municipality.
H. 
Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 225-19, 225-20, 225-21 and 225-22). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.
I. 
If site conditions preclude capture of runoff from limited portions of the disturbed area for achieving water quality volume control standards, stream channel protection standards, and the two-year storm event peak runoff rate reduction standards for new development required by this chapter, the applicant shall propose alternate methods to mitigate the bypass of the BMPs, subject to the approval of the Municipal Engineer. In no case shall resulting peak rate be greater than the predevelopment peak rate for the equivalent design storm.
J. 
For all regulated activities, erosion and sediment control BMPs shall be designed, implemented, operated and maintained during the regulated activities (i.e., during construction) as required to meet the purposes and requirements of this chapter, to meet the erosion and sediment control requirements of the municipality, if applicable, and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law.
K. 
For all regulated activities, permanent BMPs and conveyances shall be designed, implemented, operated and maintained to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law, and the Storm Water Management Act.
L. 
The design of all BMPs and conveyances shall incorporate sound engineering principles and practices in a manner that does not aggravate existing stormwater problems as identified by the municipality. The municipality reserves the right to disapprove any design that would result in construction in an area affected by existing stormwater problem(s) or continuation of an existing stormwater problem(s).
M. 
Existing wetlands, either on the site or on an adjacent property, shall not be used to meet the minimum design requirements for stormwater management or stormwater runoff quality treatment. Stormwater discharges to existing wetlands shall not degrade the quality or hydrologic integrity of the wetland.
N. 
Hot spots runoff controls. Specific structural or pollution prevention practices may be required, as determined to be necessary by the Municipal Engineer, to pretreat runoff from hot spots prior to infiltration.
O. 
Contaminated and brownfield sites. Where BMPs may contribute to the migration of contaminants in groundwater, the water quality and runoff volume, stream channel protection, and peak rate control standards shall be met; however, at the Municipal Engineer's discretion, the minimum infiltration requirement may be reduced or eliminated commensurate with the contaminated area, and the required water quality and runoff control measures may be increased to mitigate the reduced infiltration requirement for the contaminated area.
P. 
Additional water quality requirements. The municipality may require additional stormwater control measures for stormwater discharges to special management areas, including, but not limited to:
(1) 
Any water bodies listed as "impaired" by PADEP.
(2) 
Any water body or watershed with an approved total maximum daily load (TMDL).
(3) 
Any areas of known existing flooding problems.
(4) 
Any critical areas with sensitive resources (e.g., state-designated special protection waters, cold water fisheries, carbonate geology or other groundwater recharge areas that may be highly vulnerable to contamination, drainage areas to water supply reservoirs, etc.).
Q. 
Applicants shall utilize the Pennsylvania Stormwater Best Management Practices Manual (PA BMP Manual), as amended, or other sources acceptable to the Municipal Engineer, for testing and design standards for BMPs, and where there is a conflict with the provisions of this chapter, the most restrictive applies.
R. 
For areas underlain by karst or carbonate geology that may be susceptible to the formation of sinkholes and other karst features, the location, type and design of infiltration BMPs shall be based on a site evaluation conducted by a qualified licensed professional and based on the PA BMP Manual or other design guidance acceptable to the Municipal Engineer.
S. 
All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with any applicable floodplain management provisions enacted by the Borough of Elverson and shall be designed to maintain the flood-carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.
T. 
Disturbance of existing ground cover during construction of the proposed regulated activity is prohibited within 50 feet of top-of-bank of all perennial and intermittent waterways, water bodies (lakes, ponds, etc.) and wetlands, except for activities otherwise approved by state or local agencies (e.g., stream restoration projects, road crossings, subsurface utility projects, etc.). At the Municipal Engineer's discretion and with Conservation District and PADEP approval where necessary, the nondisturbance buffer may be reduced because of setback or other site constraints, but never be less than 10 feet.
The following permit or other regulatory requirements may apply to certain regulated activities and shall be met prior to (or as a condition of) final approval by the municipality of the SWM site plan and prior to commencement of any regulated activities, as applicable:
A. 
All regulated activities subject to permit or regulatory requirements by PADEP under regulations at Title 25 Pa. Code Chapter 102, or erosion and sediment control requirements of the municipality.
B. 
Work within natural drainageways subject to permit by PADEP under Title 25 Pa. Code Chapter 105.
C. 
Any BMP or conveyance that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by PADEP under Title 25 Pa. Code Chapter 105.
D. 
Any BMP or conveyance that would be located on or discharge to a state highway right-of-way or require access to or from a state highway and be subject to approval by PennDOT.
E. 
Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by PADEP under Title 25 Pa. Code Chapter 105.
A. 
No regulated activity within the municipality shall commence until:
(1) 
The municipality receives documentation that the applicant has received:
(a) 
A "letter of adequacy" from the Conservation District or other approval from PADEP in compliance with Title 25 Chapter 102 of the Pennsylvania Code of an erosion and sediment control plan for construction activities, if applicable;
(b) 
A PADEP NPDES construction activities permit as required under Title 25 Pa. Code Chapter 92a, if applicable;
[Amended at time of adoption of Code (see Ch. 1, General Provisions, Art. I)]
(c) 
Evidence of any other permit(s) or approvals required for the regulated activities.
(2) 
An erosion and sediment control plan has been approved by the municipality, if required.
B. 
A copy of the erosion and sediment control plan and any required permit(s), as required by PADEP regulations, shall be available on the site at all times.
C. 
Additional erosion and sediment control measures shall be applied where infiltration BMPs are proposed, at a minimum including those required in § 225-20M.
The applicant shall design the site to minimize the disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall demonstrate in its SWM site plan (as required in § 225-27C) that the design sequence, objectives and techniques described below were applied to the maximum extent practicable in the site design of the regulated activity while complying with all other requirements of this chapter. The site design shall:
A. 
First, identify and delineate all existing natural resources and natural and man-made hydrologic features listed in § 225-27B(8) that are located within the site or receive discharge from or may be impacted by the proposed regulated activity.
B. 
Second, provide a prioritized listing of these resources and features to identify:
(1) 
Those to be incorporated into the site design in a manner that provides protection from any disturbance or impact from the proposed regulated activity;
(2) 
Those to be protected from further disturbance or impact but for which the proposed regulated activity will provide improvement to existing conditions;
(3) 
Those that can be incorporated into and utilized as components of the overall site design in a manner that protects or improves their existing conditions while utilizing their hydrologic function within the limits of their available capacity (e.g., for infiltration, evapotranspiration, or reducing pollutant loads, runoff volume or peak discharge rates, etc.) to reduce the need for or size of constructed BMPs; and
(4) 
Those that may be considered for alteration, disturbance or removal.
C. 
Third, develop the site design to achieve the following:
(1) 
Recognize and incorporate the priorities identified in § 225-18B as the basis for the proposed site layout, grading, construction, and permanent ground cover design;
(2) 
Minimize earth disturbance (both surface and subsurface);
(3) 
Maximize protection of or improvement to natural resources and special management areas;
(4) 
Minimize the disturbance of natural site hydrology, in particular natural drainage features and patterns, discharge points and flow characteristics, natural infiltration patterns and characteristics, and natural channel and floodplain conveyance capacity;
(5) 
Incorporate natural hydrologic features and functions identified in § 225-18B into the site design to protect and utilize those features and their hydrologic functions to reduce the need for or size of constructed BMPs;
(6) 
Maximize infiltration and the use of natural site infiltration features, patterns and conditions, and evapotranspiration features;
(7) 
Apply selective grading design methods to provide final grading patterns or preserve existing topography in order to evenly distribute runoff and minimize concentrated flows;
(8) 
Minimize the cumulative area to be covered by impervious surfaces; and:
(a) 
Minimize the size of individual impervious surfaces.
(b) 
Separate large impervious surfaces into smaller components.
(c) 
Disconnect runoff from one impervious surface to another.
(d) 
Utilize porous materials in place of impervious wherever practicable.
(9) 
Minimize the volume and peak discharge rates of stormwater generated;
(10) 
Avoid or minimize stormwater runoff pollutant loads and receiving stream channel erosion;
(11) 
Locate infiltration and other BMPs:
(a) 
At or as near to the source of generation as possible; and
(b) 
At depths that are as shallow as possible.
(12) 
For flow volumes requiring conveyance from the source of generation to a BMP for management, give preference to open-channel conveyance techniques that provide infiltration and water quality benefits, and landscaped-based management in common open space areas, where practicable; and
(13) 
Consider additional guidance for incorporating natural hydrology into the site and BMP designs, methods and techniques that support the objectives of § 225-18B and C. Appendix A[1] presents additional discussion of natural hydrology site design and sources of information for conservation design, low-impact design, and sustainable design.
[1]
Editor's Note: Appendix A is an attachment to this chapter.
D. 
The procedures set forth above shall be utilized to the maximum extent practicable for the overall site design and selection, location and design of features and BMPs to be used to comply with the requirements of §§ 225-19, 225-20, 225-21 and 225-22.
To control post-construction stormwater impacts from regulated activities and meet state water quality requirements, BMPs shall be provided in the site design that replicate predevelopment stormwater infiltration and runoff conditions, such that post-construction stormwater discharges do not degrade the physical, chemical or biological characteristics of the receiving waters. The applicant shall comply with the following water quality and runoff volume requirements for all regulated activities, including all new development and redevelopment activities:
A. 
The post-construction total runoff volume shall not exceed the predevelopment total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation (design storm). The water quality and runoff volume to be managed shall consist of any runoff volume generated by the proposed regulated activity over and above the predevelopment total runoff volume and shall be captured and permanently retained or infiltrated on the site. Permanent retention options may include, but are not limited to, reuse, evaporation, transpiration and infiltration.
B. 
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 225-23D of this chapter.
C. 
The design of the facility outlet shall provide for protection from clogging and unwanted sedimentation.
D. 
BMPs that moderate the temperature of stormwater shall be used to protect the temperature of receiving waters.
E. 
Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 225-20. The infiltration volume required under § 225-20 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.
F. 
Runoff from the disturbed area shall be treated for water quality prior to entering existing waterways or water bodies. If a stormwater management practice does not provide water quality treatment, then water quality BMPs shall be utilized to provide pretreatment prior to the runoff entering the stormwater management practice.
G. 
The municipality may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 225-15P.
H. 
When the regulated activity contains or is divided by multiple drainage areas, the water quality and runoff volume shall be separately addressed for each drainage area.
I. 
Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.
J. 
Areas located outside of the site (i.e., areas outside of the regulated activity) may be excluded from the calculation of the water quality and runoff volume requirements.
K. 
Water quality and volume control practices shall be selected and designed to meet the criteria of § 225-18C that apply to water quality and volume control.
Providing for infiltration consistent with the natural hydrologic regime is required to compensate for the reduction in the recharge that occurs when the ground surface is disturbed or impervious surface is created or expanded. The applicant shall achieve the following infiltration requirements:
A. 
Wherever possible, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 225-19.
B. 
For regulated activities involving new development, the volume of a minimum of one inch of runoff from all proposed impervious surfaces shall be infiltrated.
C. 
For regulated activities involving redevelopment, whichever is less of the following volume options shall be infiltrated:
(1) 
The volume of a minimum of one inch of runoff from all proposed impervious surfaces; or
(2) 
The total water quality and runoff volume required in § 225-19 of this chapter.
D. 
If the requirements of § 225-20B or C cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Municipal Engineer why this infiltration volume cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated; however, in all cases at least the first 0.5 inch of runoff volume shall be infiltrated.
E. 
Only if a minimum of at least 0.5-inch infiltration requirement cannot be physically accomplished on the site shall a waiver from § 225-20 be considered by the municipality.
F. 
If site conditions preclude capture of runoff from portions of the impervious surfaces, the infiltration volume for the remaining area shall be increased an equivalent amount to offset the loss.
G. 
When a project contains or is divided by multiple watersheds, the infiltration volume shall be separately addressed for each watershed.
H. 
Existing impervious surfaces located in areas outside of the site (i.e., outside of the regulated activity) may be excluded from the calculation of the required infiltration volume.
I. 
A detailed soils evaluation of the site shall be conducted by a qualified professional and at a minimum shall address soil permeability, depth to bedrock, and subgrade stability. The general process for designing the infiltration BMP shall be conducted by a qualified licensed professional and shall be consistent with the PA BMP Manual (as amended) (or other guidance acceptable to the Municipal Engineer) and in general shall:
(1) 
Analyze hydrologic soil groups as well as natural and man-made features within the site to determine general areas of suitability for infiltration practices. In areas where development on fill material is under consideration, conduct geotechnical investigations of subgrade stability; infiltration may not be ruled out without conducting these tests.
(2) 
Provide field tests such as double-ring infiltrometer or other hydraulic conductivity tests (at the elevation of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Standard septic/sewage percolation tests are not acceptable for design purposes.
(3) 
Design the infiltration facility for the required retention (infiltration) volume based on field-determined infiltration capacity (and apply safety factor as per applicable design guidelines) at the elevation of the proposed infiltration surface.
(4) 
On-lot infiltration features are encouraged; however, it shall be demonstrated to the Municipal Engineer that the soils are conducive to infiltration on the identified lots.
J. 
Infiltration BMPs shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:
(1) 
A minimum depth of 24 inches between the bottom of the BMP and the top of the limiting zone. Additional depth may be required in areas underlain by karst or carbonate geology (see Subsection N).
(2) 
An infiltration rate sufficient to accept the additional stormwater volume and drain completely as determined by field tests conducted by the applicant.
(3) 
The infiltration facility shall completely drain the retention (infiltration) volume within three days (72 hours) from the end of the design storm.
K. 
All infiltration practices shall:
(1) 
Be selected and designed to meet the criteria of § 225-18C that are applicable to infiltration;
(2) 
Be set back at least 25 feet from all buildings and features with subgrade elements (e.g., basements, foundation walls, etc.), unless otherwise approved by the Municipal Engineer;
(3) 
For any infiltration practice that collects runoff from shared or multiple features and that is located within 50 feet of a building or feature with subgrade elements (e.g., basements, foundation walls, etc.), the bottom elevation shall be set below the elevation of the subgrade element.
L. 
Infiltration facilities shall, to the maximum extent practicable, be located to avoid introducing contaminants to groundwater:
(1) 
When a hot spot is located in the area draining to a proposed infiltration facility, an evaluation of the potential of groundwater contamination from the proposed infiltration facility shall be performed, including a hydrogeologic investigation (if necessary) by a qualified licensed professional to determine what, if any, pretreatment or additional design considerations are needed to protect groundwater quality.
(2) 
When located within a wellhead protection area of a public water supply well, infiltration practices shall be in conformance with the applicable approved source water protection assessment or source water protection plan.
(3) 
The applicant shall provide appropriate safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.
M. 
During site construction, all infiltration practice components shall be protected from compaction due to heavy equipment operation or storage of fill or construction material. Infiltration areas shall also be protected from sedimentation. Areas that are accidentally compacted or graded shall be remediated to restore soil composition and porosity. Adequate documentation to this effect shall be submitted to the Municipal Engineer for review. All areas designated for infiltration shall not receive runoff until the contributory drainage area has achieved final stabilization.
N. 
Consideration of infiltration BMPs for areas underlain by karst or carbonate geology is encouraged, but only where the design, supporting calculations, results of soils or other site investigations or other documentation are provided to the municipality demonstrating that the potential or likelihood of subsidence or sinkholes is minimal. Evaluation of site conditions and infiltration design shall rely on guidance in the PA BMP Manual (as amended) or other guidance acceptable to the Municipal Engineer.
O. 
Groundwater quality of the carbonate aquifer shall be protected from infiltration of pollutants. At a minimum, stormwater runoff from hot spots (i.e., sources of significant pollutant runoff) shall first be discharged through a water quality BMP(s) to remove pollutants prior to infiltration. Where soil characteristics are insufficient to provide removal of pollutants from sources other than hot spots, stormwater runoff shall first be discharged through a water quality BMP(s) to remove pollutants prior to infiltration.
P. 
Where sediment transport in the stormwater runoff is anticipated to reach the infiltration system, appropriate permanent measures to prevent or collect sediment shall be installed prior to discharge to the infiltration system.
Q. 
Where roof drains are designed to discharge to infiltration practices, they shall have appropriate measures to prevent clogging by unwanted debris (for example, silt, leaves and vegetation). Such measures shall include but are not limited to leaf traps, gutter guards and cleanouts.
R. 
All infiltration practices shall have appropriate positive overflow controls.
S. 
No sand, salt or other particulate matter may be applied to a porous surface material for winter ice conditions.
T. 
The following procedures and materials shall be required during the construction of all subsurface facilities:
(1) 
Excavation for the infiltration facility shall be performed with equipment that will not compact the bottom of the seepage bed/trench or like facility.
(2) 
The bottom of the bed and/or trench shall be scarified prior to the placement of aggregate.
(3) 
Only clean aggregate with documented porosity, free of fines, shall be allowed.
(4) 
The tops, bottoms and sides of all seepage beds, trenches or like facilities shall be covered with drainage fabric. Fabric shall be nonwoven fabric acceptable to the Municipal Engineer.
(5) 
Stormwater shall be distributed throughout the entire seepage bed/trench or like facility and provisions for the collection of debris shall be provided in all facilities.
For regulated activities involving new development with one or more acres of earth disturbance, the applicant shall comply with the following stream channel protection requirements to minimize stream channel erosion and associated water quality impacts to the receiving waters:
A. 
The peak flow rate of the post-construction two-year, twenty-four-hour design storm shall be reduced to the predevelopment peak flow rate of the one-year, twenty-four-hour duration precipitation, using the SCS Type II distribution.
B. 
To the maximum extent practicable, and unless otherwise approved by the Municipal Engineer, the post-construction one-year, twenty-four-hour storm flow shall be detained for a minimum of 24 hours and a maximum not to exceed 72 hours from a point in time when the maximum volume of water from the one-year, twenty-four-hour storm is stored in a proposed BMP (i.e., when the maximum water surface elevation is achieved in the facility). Release of water can begin at the start of the storm (i.e., the invert of the orifice is at the invert of the proposed BMP).
C. 
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 225-23D of this chapter.
D. 
The minimum orifice size in the outlet structure to the BMP shall be three inches in diameter unless otherwise approved by the Municipal Engineer, and a trash rack shall be installed to prevent clogging. For sites with small drainage areas contributing to the BMP that do not provide enough runoff volume to allow a twenty-four-hour attenuation with the three-inch orifice, the calculations shall be submitted showing this condition.
E. 
When the calculated orifice size is below three inches, gravel filters (or other methods) are recommended to discharge low-flow rates subject to the Municipal Engineer's satisfaction. When filters are utilized, maintenance provisions shall be provided to ensure filters meet the design function.
F. 
All proposed stormwater facilities shall make use of measures to extend the flow path and increase the travel time of flows in the facility.
G. 
When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate control shall be separately addressed for each drainage area.
The applicant shall comply with the following peak flow rate control requirements for all regulated activities including those that involve new development and redevelopment that are not located in the Conestoga River watershed.
A. 
Post-construction peak flow rates from any regulated activity shall not exceed the predevelopment peak flow rates as shown for each of the design storms specified in Table 308.1.
Table 308.1
Peak Rate Control Standards
(Peak Flow Rate of the Post-Construction Design Storm shall be Reduced to the Peak Flow Rate of the Corresponding Predevelopment Design Storm Shown in the Table)
Predevelopment Design Storm
Post-Construction Design Storm Frequency
(24-hour duration)
New Development Regulated Activities
Redevelopment Regulated Activities
2-year
1-year
2-year
5-year
5-year
5-year
10-year
10-year
10-year
25-year
25-year
25-year
50-year
50-year
50-year
One-hundred-year
One-hundred-year
One-hundred-year
B. 
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground-cover assumptions presented in § 225-23D of this chapter.
C. 
For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total proposed impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table 308.1, using the redevelopment ground cover assumptions presented in § 225-23D.
D. 
Only the area of the proposed regulated activity shall be subject to the peak flow rate control standards of this chapter. Undisturbed areas for which the discharge point has not changed are not subject to the peak flow rate control standards.
E. 
Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to peak flow rate control requirements. Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.
F. 
When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate controls shall be separately addressed for each drainage area.
G. 
The effect of structural and nonstructural stormwater management practices implemented as part of the overall site design may be taken into consideration when calculating total storage volume and peak flow rates.
H. 
Regulated activities located within the Conestoga River watershed shall achieve the applicable peak flow release rate control requirements presented in the approved Pennsylvania Act 167 plan for that watershed and as presented in the Conestoga River Watershed Release Rate Map in Appendix E of this chapter.[1] Peak flow rates for the two-year, five-year, ten-year, twenty-five-year, fifty-year and one-hundred-year post-development design storms shall be detained to the applicable release rate percentage of the two-year, five-year, ten-year, twenty-five-year, fifty-year and one-hundred-year predevelopment design storms, respectively.
[1]
Editor's Note: Appendix E is an attachment to this chapter.
A. 
Stormwater runoff from all regulated activity sites with a drainage area of greater than five acres shall be calculated using a generally accepted calculation technique(s) that is based on the NRCS Soil-Cover-Complex Method. Table 309.1 summarizes acceptable computation methods. The method selected for use shall be based on the individual limitations and suitability of each method for a particular site. The use of the Rational Method to estimate peak discharges for drainage areas greater than five acres shall be permitted only upon approval by the Municipal Engineer.
Table 309.1
Acceptable Computation Methodologies for SWM Site Plan
Method
Developed By
Applicability
TR-20 (or commercial computer package based on TR-20)
USDA NRCS
Applicable where use of full hydrology computer model is desirable or necessary.
TR-55 (or commercial computer package based on TR-55)
USDA NRCS
Applicable for land development plans where limitations described in TR-55 are met
HEC-1/HEC-HMS
U.S. Army Corps of Engineers
Applicable where use of a full hydrologic computer model is desirable or necessary
Rational Method (or commercial computer package based on Rational Method)
Emil Kuichling (1889)
For sites up to 5 acres, or as approved by the municipality
Other methods
Varies
Other computation methodologies approved by the municipality
B. 
All calculations using the Soil-Cover-Complex Method shall use the appropriate design rainfall depths for the various return period storms consistent with this chapter. Rainfall depths used shall be obtained from NOAA Atlas 14 values consistent with a partial duration series. When stormwater calculations are performed for routing procedures or infiltration, water quality and runoff volume functions, the duration of rainfall shall be 24 hours.
C. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration (duration) and storm events with rainfall intensities obtained from NOAA Atlas 14 partial duration series estimates, or the latest version of the PennDOT Drainage Manual (PDM Publication 584). Times-of-concentration shall be calculated based on the methodology recommended in the respective model used. Times-of-concentration for channel and pipe flow shall be computed using Manning's equation.
D. 
The applicant shall utilize the following ground cover assumptions for all predevelopment water quality and runoff volume, infiltration volume and peak flow rate calculations:
(1) 
For regulated activities involving new development, the following ground cover assumptions shall be used:
(a) 
For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."
(b) 
For all other areas (including all impervious surfaces), predevelopment calculations shall be based upon the predominant ground cover condition that has existing over the 50 years preceding the submission of the SWM site plan. The calculations shall also assume that each specific ground cover type is in "good condition."
(2) 
For regulated activities involving redevelopment, the following ground cover assumptions shall be used:
(a) 
For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."
(b) 
For all other areas (including all impervious surfaces), predevelopment calculations shall be based upon the predominant ground cover condition that has existing over the 50 years preceding the submission of the SWM site plan. The calculations shall also assume that each specific ground cover type is in "good condition."
(3) 
The applicant shall determine which stormwater standards apply to the proposed regulated activity as follows:
(a) 
Stormwater standards for new development shall apply to all proposed regulated activities that involve only new development activities as defined in this chapter.
(b) 
Stormwater standards for redevelopment shall apply to all proposed regulated activities that involve only redevelopment activities as defined in this chapter.
(c) 
At the discretion of the Municipal Engineer, regulated activities that involve a combination of both new development and redevelopment activities, as defined in this chapter, may either:
[1] 
Apply the stormwater standards (redevelopment or new development) that are associated with the activity that involves the greatest amount of land area; or
[2] 
Apply the redevelopment and new development stormwater standards to the corresponding redevelopment and new development portions of the proposed regulated activity.
E. 
Runoff curve numbers (CN) for both predevelopment and proposed (post-construction) conditions to be used in the Soil-Cover-Complex Method shall be obtained from Table B-1 in Appendix B of this chapter.[1]
[1]
Editor's Note: Appendix B is an attachment to this chapter.
F. 
Runoff coefficients (C) for both predevelopment and proposed (post-construction) conditions for use in the Rational Method shall be obtained from Table B-2 in Appendix B of this chapter.[2]
[2]
Editor's Note: Appendix B is an attachment to this chapter.
G. 
Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.
H. 
Hydraulic computations to determine the capacity of pipes, culverts and storm sewers shall be consistent with methods and computations contained in the Federal Highway Administration Hydraulic Design Series Number 5 (Publication No. FHWA-NHI-01-020 HDS No. 5, as amended). Hydraulic computations to determine the capacity of open channels shall be consistent with methods and computations contained in the Federal Highway Administration Hydraulic Engineering Circular Number 15 (Publication No. FHWA-NHI-05-114 HEC 15, as amended). Values for Manning's roughness coefficient (n) shall be consistent with Table B-3 in Appendix B of the chapter.[3]
[3]
Editor's Note: Appendix B is an attachment to this chapter.
I. 
Runoff calculations shall include the following assumptions:
(1) 
Average antecedent moisture conditions (for the Soil-Cover-Complex Method only for example, TR-55, TR-20).
(2) 
A type II distribution storm (for the Soil-Cover-Complex Method only, for example, TR-55, TR-20).
A. 
Any BMP intended to hold standing water for four days or longer shall be designed to incorporate biologic controls consistent with the West Nile Guidance found in Appendix C,[1] PADEP document 363-0300-001 "Design Criteria - Wetlands Replacement/Monitoring" (as amended), (or contact the Pennsylvania State Cooperative Wetland Center or the Penn State Cooperative Extension Office for design information.)
[1]
Editor's Note: Appendix C is an attachment to this chapter.
B. 
Any stormwater basin required or regulated by this chapter designed to store runoff and requiring a berm or earthen embankment shall be designed to provide an emergency spillway to safely convey flow up to and including the one-hundred-year proposed conditions. The height of embankment shall provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the facility functions for the one-hundred-year proposed conditions inflow. Should any BMP require a dam safety permit under 25 Pa. Code Chapter 105 regulations, the facility shall be designed in accordance with and meet the regulations of 25 Pa. Code Chapter 105 concerning dam safety. Chapter 105 may require the safe conveyance of storms larger than one-hundred-year event.
C. 
Any drainage conveyance facility and/or channel not governed by 25 Pa. Code Chapter 105 regulations shall be designed to convey, without damage to the drainage facility or roadway, runoff from the twenty-five-year storm event. Larger storm events (fifty-year and one-hundred-year storms) shall also be safely conveyed in the direction of natural flow without creating additional damage to any drainage facilities, nearby structures, or roadways.
D. 
Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from the facility.
E. 
Roadway crossings or structures located within designated floodplain areas shall be able to convey runoff from a one-hundred-year design storm consistent with Federal Emergency Management Agency National Flood Insurance Program floodplain management requirements.
F. 
Any facility located within a PennDOT right-of-way shall comply with PennDOT minimum design standards and permit submission and approval requirements.
G. 
Adequate erosion protection and energy dissipation shall be provided along all open channels and at all points of discharge. Design methods shall be consistent with the Federal Highway Administration Hydraulic Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as amended) and the PADEP Erosion and Sediment Pollution Control Program Manual (Publication No. 363-2134-008, as amended), or other design guidance acceptable to the Municipal Engineer.
A. 
Need for basins, storm sewers, culverts, bridges and other stormwater facilities. Basins, storm sewers, culverts, bridges and other structural installations shall be provided to safely accommodate stormwater, where natural nonstructural practices are not feasible and where stormwater flows otherwise would have adverse impact on the environment and the general welfare of the Borough of Elverson and its citizens in order to:
(1) 
Maintain natural hydrologic regimes of streams and watercourses. Such flows may be redirected as required, subject to the approval of PADEP.
(2) 
Promote drainage of all low points along the line of streets. Overflow swales shall be designed to convey the full one-hundred-year storm flows away from all street low points. These swales shall be located to prevent flooding of the downslope lots.
(3) 
Intercept stormwater runoff along streets at intervals reasonably related to the extent and grade of the area drained, and to prevent substantial flow of water across intersections or flooding of intersections during the design storm stipulated elsewhere in this chapter.
(4) 
Ensure adequate and unimpeded flow of stormwater under driveways in, near or across natural watercourses or drainage swales. Suitable pipes or other waterway openings shall be provided as necessary.
B. 
Design of basins, storm sewers, culverts, bridges and other stormwater facilities.
(1) 
Stormwater basins shall be installed prior to any earthmoving or land disturbances that they will serve, unless otherwise approved by the Borough Engineer. The phasing of their construction shall be noted on the erosion and sediment control plan. Permanent vegetation shall be established prior to denuding any other land, unless the basin functions as an erosion and sediment control measure.
(2) 
Stormwater facilities shall be designed to provide for stormwater infiltration wherever feasible. For any facilities proposed to be underlain by karst or carbonate geology, a detailed geologic evaluation of the project site shall be performed to determine the suitability for infiltration, including both the potential for groundwater contamination and potential for sinkhole formation. The evaluation shall be performed by a qualified geologist and/or soil professional and, at a minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. Soils used for the construction of basins shall have low-erodibility factors (K factors). The Borough may require an impermeable liner to be installed up to the one-hundred-year design water surface elevation for any proposed stormwater facilities that may be susceptible to causing sinkhole formation and/or groundwater contamination.
(3) 
Energy dissipaters and/or level spreaders shall be installed at points where pipes or drainageways discharge from stormwater facilities. Multiple outlet structures and multiple outlet piping from the facility may be required by the Borough to reduce the impact of point discharges.
(4) 
The following slope restrictions shall apply to stormwater basins:
(a) 
Exterior slopes of compacted soil shall not exceed one foot vertical for three feet horizontal and may be further reduced if the soil has unstable characteristics.
(b) 
Interior slopes of the basin shall not exceed one foot vertical in three feet horizontal, except with approval of the Borough; and:
[1] 
Where maximum water depth will not exceed three feet; or
[2] 
When a two-inch rainfall in one hour will not exceed the capacity of the basin in one hour; or
[3] 
Where concrete, stone or brick walls are used with side slopes proposed to be steeper than one foot vertical in three feet horizontal, in which case the basin shall be fenced by a permanent fence 42 inches in height; and a ramp of durable, nonslip materials for maintenance vehicles shall be provided for access into the basin.
(c) 
The minimum bottom slope shall be 3% for grass and 0.75% for concrete paving. One percent may be used for grass if an underdrain system is provided. A concrete low-flow channel may be required for basins where the distance from the inlet pipe to the outlet structure exceeds 100 feet, depending upon site conditions. The minimum channel width shall be four feet. The channel shall be constructed of four-inch-thick concrete (3,300 psi twenty-eight-day strength) over four inches of PennDOT No. 2A stone.
(5) 
Stormwater basins shall also be designed to meet the following requirements:
(a) 
The maximum berm height shall be 15 feet, unless otherwise approved by the Borough and the PADEP.
(b) 
The minimum top-of-berm width shall be eight feet.
(c) 
Outlet pipes shall have a minimum diameter of 12 inches, except for pipe lengths exceeding 100 feet, in which case, the minimum diameter shall be 15 inches.
(d) 
Properly spaced antiseep collars (six inches' minimum thickness) shall be installed on all basin outlet pipes. Design calculations shall be provided.
(e) 
All berms shall be constructed with a compacted relatively impervious (Unified Soil Classification CL-ML or CL) key trench and core. The key trench shall extend at least two feet into undisturbed subsoil (below topsoil layer). The minimum bottom width of the trench shall be four feet and the minimum top width of the core shall be eight feet. The side slopes of the compacted core and trench shall not exceed one horizontal to one vertical, and the top elevation of the core shall be set at or above the twenty-five-year design water elevation.
(f) 
The top of berm shall be constructed at least six inches above the design elevations to allow for settlement of the embankment.
(6) 
Stormwater basin outlet structures and emergency spillways:
(a) 
Outlet structures within basins which will control peak discharge flows and distribute the flows by pipes to discharge areas shall be constructed primarily of concrete or masonry material and shall have childproof, nonclogging trash racks over all design openings, except those openings designed to carry perennial stream flows. Trash rack material should be epoxy-coated galvanized or stainless steel. Other materials are subject to the approval of the Borough.
(b) 
Six inches of freeboard shall be provided between the crest of the primary outlet structure and the invert of the emergency spillway.
(c) 
Emergency spillways shall be constructed in undisturbed earth wherever possible. When constructed in fill, sod, precast concrete paving blocks, concrete or permanent erosion-control matting shall be used. Design calculations shall be submitted, indicating that the specified material can withstand velocities based on the one-hundred-year design storm event. When using sod, it shall be applied along the inside slope above the twenty-five-year water surface elevation, along the face and sides of the spillway and down the outside slope to existing grade. Emergency spillways shall be designed to safely convey the one-hundred-year basin inflow hydrograph through the basin assuming the principal outlet is completely blocked and the basin water surface elevation is equal to the spillway invert elevation.
(7) 
Stormwater basin inlet and outlet structures shall be located at maximum distances possible from one another. The Borough may require a rock filter berm or rock-filled gabions between inlet and outlet areas when the distance is deemed insufficient for sediment trappings.
(8) 
Permanent grasses or stabilization measures shall be established on the sides of all earthen basins by hydroseeding within five days of initial construction (or conversion from sediment basin or sediment trap). The Borough may require jute or erosion-control matting to be installed inside the basin or on the basin embankment.
(9) 
Stormwater runoff shall discharge to a suitable natural drainage course or storm sewer system. Where not possible or not permitted, level spreading devices or other suitable facilities shall be designed with sufficient capacity to convey the one-hundred-year storm event without creating any safety, flooding, or property hazard. Securing of necessary stormwater management easements for this purpose shall be the sole responsibility of the applicant.
(10) 
The Borough may require soil samples from the site to be analyzed to determine if these soils are suitable for berm embankment construction. If the soils are found to be unsuitable, the applicant shall import suitable soils for constructing any proposed berm embankments.
(11) 
Grass swales not specifically designed as BMP devices shall have a minimum bottom slope of 2%.
(12) 
Storm sewer design:
(a) 
Design for conveyance systems shall be based upon a twenty-five-year storm event (minimum).
(b) 
Storm sewer lines within street rights-of-way shall be placed immediately in front of the curb when parallel to the right-of-way. Locating storm sewers under curbs in curves or at street intersections shall be avoided.
(c) 
Storm sewers shall have a minimum diameter of 15 inches and only smooth-lined high-density polyethylene pipe or reinforced cement concrete pipe shall be used, unless otherwise approved by the Borough Engineer. The minimum grade of the pipe shall be 0.50%.
(d) 
In karst or carbonate areas, watertight pipe connections are required and appropriate specifications shall be included on the plans.
(e) 
Headwalls, endwalls or end sections shall be required on all open pipes.
(f) 
All storm sewer components (pipes, inlets, manholes, etc.) shall be constructed per current PennDOT standards and criteria as outlined in Publication 408 (Specifications), Publication 13M (Design Manual Part 2, Highway Design) and Publication 72M (Roadway Construction Standards), latest versions.
(g) 
All storm sewer inlets in paved areas shall be fitted with bicycle-safe grates.
(h) 
When there is a change in pipe size through an inlet, the top inside elevation of the outlet pipe shall be at or below the top inside elevations of all incoming pipes.
(i) 
Storm sewer design shall be based upon PennDOT design methods. Inlet efficiency and bypass flow shall be determined for all inlets, and the gutter flow spread shall not exceed 1/2 the travel lane width. Where parking is permitted, the maximum gutter flow spread shall not exceed eight feet. Gutter spread calculations shall be based upon a ten-year storm event (minimum). The Borough may require that a hydraulic grade-line analysis be performed on storm sewer systems.
(j) 
Culverts shall be evaluated for inlet and outlet control restrictions.
(k) 
Subsurface drainage systems shall have manholes, inlets or junction boxes spaced at intervals not exceeding 300 feet and located wherever there is a change in alignment or grade.
(l) 
For drainage lines of 48 inches diameter or greater, manholes may be spaced at intervals greater than 300 feet with approval of the Borough Engineer.
(m) 
PennDOT Type "C" concrete inlet top units are to be provided with a five-inch-by-twenty-four-inch cast iron "Dump No Waste - Drains To Waterways" (with 1/2-inch raised lettering) plate with trout logo as manufactured by E. Jordan Iron Works, or approved equal. PennDOT Type "M" concrete inlet top units are to be provided with a three-inch-by-twenty-four-inch cast iron "Dump No Waste - Drains To Waterways" (with 1/2-inch raised lettering) plate with trout logo as manufactured by E. Jordan Iron Works or approved equal. Bottom of covers are to be clearly marked with grade of iron (ASTM A48, Class 35B), product number and date of manufacture.
(n) 
The words "Dump No Waste - Drains To Waterways" in 1 1/4-inch raised letters with bass logo shall be cast or stamped into the storm sewer manhole covers as manufactured by E. Jordan Iron Works, or approved equal. Bottoms of covers are to be clearly marked with grade of iron (ASTM A48, Class 35B), product number and date of manufacture.
(o) 
Erosion shall be minimized at storm sewer discharge points through the use of proper ground cover or riprap.
(13) 
Design of bridges and culverts:
(a) 
Bridge and/or culvert construction shall be in accordance with the PennDOT specifications and shall meet the requirements of the PADEP. The appropriate permits and approvals must be acquired by the applicant.
(b) 
Culverts shall be provided with wing walls and constructed for the full width of the right-of-way. If the character of the road is expected to change for future planning, the cartway of the bridge shall be made to anticipate this condition. On each side of the bridge cartway, the bridge railing must be set back from the edge of the final cartway, and this area may be used to place sidewalks, present or future.
C. 
Graded slopes shall not be steeper than three horizontal units to one vertical unit, unless otherwise approved by the Borough Engineer.
D. 
A minimum of four inches of topsoil shall be provided on all disturbed areas prior to final seeding and mulching.