[Ord. 2011-12, 6/20/2011]
1. 
The standards contained in this Part shall apply as minimum design standards; however, federal, state and other Doylestown Borough regulations may impose additional standards subject to their jurisdiction. Approvals issued and actions taken under this Part do not relieve the applicant of the responsibility to secure required permits or approvals for activities regulated by any other code, law, regulation or ordinance.
2. 
Retention of Existing Watercourses and Natural Drainage Features.
A. 
Whenever a watercourse, stream or intermittent stream is located within a development site, it shall remain open in its natural state and location and shall not be piped, unless required or approved by the Borough.
B. 
No stormwater runoff or natural drainage shall be so diverted as to overload existing drainage systems (including existing stormwater management facilities) or create flooding.
C. 
The Borough Council may require a developer to provide a permanent easement along any watercourse located within or along the boundary of any property being subdivided or developed. The purpose of any such easement shall be for the maintenance of the channel of any watercourse and their structures and any alterations which may adversely affect the watercourse. The required width of any such easement shall be the greater width as determined by the Borough Engineer, U.S. Army Corps of Engineers, Pennsylvania Department of Environmental Protection or other public agency having jurisdiction, but, in no case, shall such easement be less than 50 feet in width. The developer will retain the easement until such time as one of the following is accomplished:
(1) 
The easement is offered for dedication by the developer and accepted by Doylestown Borough.
(2) 
If an easement acceptable to the Borough is established, the maintenance shall then be the responsibility of the individual lot owners over whose property the easement passes. For land developments, the maintenance shall then be the responsibility of the owner of the affected property. The maintenance responsibility shall be clearly established and recorded with the deed of easement.
(3) 
A homeowners' association or other legal entity, approved by Doylestown Borough, assumes responsibility for the maintenance of the development, including the retention and maintenance of the watercourse easement.
3. 
Developers shall construct and/or install stormwater management facilities, and BMPs on site and off site, as necessary to:
A. 
Prevent erosion damage and to satisfactorily carry off, detain or retain and control the rate of release of stormwater.
B. 
Manage the anticipated peak discharge from property being subdivided or developed and existing runoff being contributed from all land at a higher elevation in the same watershed.
C. 
Convey stormwater along or through the property to a natural outfall. If a developer concentrates dispersed stormwater flow or redirects stormwater flow to exit at another location on the property, the developer is responsible for constructing an adequate channel on the adjacent property and on all downstream properties until a natural outfall is reached. A natural outfall shall have sufficient capacity to receive stormwater without deterioration of the facility and without adversely affecting property in the watershed. This natural outfall may be a river, creek or other drainage facility so designated by Doylestown Borough for the proposed system.
D. 
Protect and maintain existing levels of water quality in all streams.
4. 
Where applicable, stormwater management facilities or programs shall comply with the requirements of Chapter 102 (Erosion Control), Chapter 105 (Dam Safety and Waterway Management) and Chapter 106 (Floodplain Management) of Title 25, Rules and Regulations of the DEP.
5. 
Stormwater management facilities which involve a state highway shall be subject to the approval of PennDOT.
6. 
Stormwater management facilities located within or affecting the floodplain of any watercourse shall also be subject to the requirements of any Doylestown Borough ordinance that regulates construction and development within areas which are subject to flooding.
7. 
Access to facilities shall be provided for maintenance and operation. This access shall be a cleared access that is, when possible, approximately 20 feet wide. Proximity of facilities to public rights-of-way shall be encouraged in order to minimize the length of accessways. Multiple accesses shall be encouraged for major facilities.
8. 
Additional studies and higher levels of control than the minimum provided in the requirements and criteria of this Part may be required by the Borough Council to ensure adequate protection to life and property.
9. 
In addition to runoff control, all stormwater management plans shall also incorporate BMPs in conjunction with the permitting, implementation and operation and maintenance of the selected stormwater runoff controls.
10. 
Applicants proposing regulated activities shall submit a stormwater management (SWM) site plan to the Doylestown Borough for review, unless exempt by provisions of this Part. The SWM criteria of this Part shall apply to the total proposed development even if development is to take place in stages. Preparation and implementation of an approved SWM site plan is required. No regulated activities shall commence until the Doylestown Borough issues written approval of a SWM site plan which demonstrates compliance with the requirements of this Part.
11. 
SWM site plans approved by Doylestown Borough shall be on site throughout the duration of the regulated activity.
12. 
Doylestown Borough may, after consultation with the Department of Environmental Protection (PADEP), approve measures for meeting the state water quality requirements other than those in this Part, provided that they meet the minimum requirements of, and do not conflict with, state law, including, but not limited to, the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
13. 
For all regulated earth disturbance activities, erosion and sediment (E&S) control best management practices (BMPs) shall be designed, implemented, operated, and maintained during the regulated earth disturbance activities (e.g., during construction) to meet the purposes and requirements of this Part and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law. Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual, No. 363-2134-008 (April 15, 2000), as amended and updated.
14. 
For all regulated activities, implementation of the volume controls is required as regulated by this Part.
15. 
Impervious areas:
A. 
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.
B. 
For development taking place in stages, the entire development plan must be used in determining conformance with this Part.
C. 
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this Part.
16. 
Stormwater flows onto adjacent property shall not be created, increased, decreased, relocated, or otherwise altered without written notification of the adjacent property owner(s). Such stormwater flows shall be subject to the requirements of this Part.
17. 
All regulated activities shall include such measures as are necessary to:
A. 
Protect health, safety, and property.
B. 
Meet the water quality goals of this Part by implementing measures to:
(1) 
Minimize disturbance to floodplains, wetlands, and wooded areas.
(2) 
Create, maintain, repair or extend riparian buffers.
(3) 
Avoid erosive flow conditions in natural flow pathways.
(4) 
Minimize thermal impacts to waters of this commonwealth.
(5) 
Disconnect impervious surfaces (i.e., disconnected impervious areas, DIAs) by directing runoff to pervious areas, wherever possible. See Appendix IX for detail on DIAs.[2]
[2]
Editor's Note: Appendix IX is on file in the Borough offices.
C. 
To the maximum extent practicable, incorporate the techniques for low-impact development practices (e.g., protecting existing trees, reducing area of impervious surface, cluster development, and protecting open space) described in the Pennsylvania Stormwater Best Management Practices Manual, Pennsylvania Department of Environmental Protection (PADEP) No. 363-0300-002 (2006), as amended and updated. See Appendix VIII for a summary description.[3]
[3]
Editor's Note: Appendix VIII is on file in the Borough offices.
18. 
Infiltration BMPs should be spread out, made as shallow as practicable, and located to maximize the use of natural on-site infiltration features while still meeting the other requirements of this Part.
19. 
The design of all facilities over karst shall include an evaluation of measures to minimize the risk of adverse effects.
20. 
Storage facilities should completely drain both the volume control and rate control capacities over a period of time not less than 24 hours and not more than 72 hours from the end of the design storm.
21. 
The design storm volumes to be used in the analysis of peak rates of discharge should be obtained from the Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2, Version 3.0, U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland, as amended. NOAA's Atlas 14 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
22. 
For all regulated activities, SWM BMPs shall be designed, implemented, operated, and maintained to meet the purposes and requirements of this Part and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law,[4] and the Storm Water Management Act.[5]
[4]
Editor's Note: See 35 P.S. § 691.1 et seq.
[5]
Editor's Note: See 32 P.S. § 680.1 et seq.
23. 
Various BMPs and their design standards are listed in the Pennsylvania Stormwater Best Management Practices Manual (PA BMP Manual).
[Ord. 2011-12, 6/20/2011]
1. 
Volume controls will mitigate increased runoff impacts, protect stream channel morphology, maintain groundwater recharge, and contribute to water quality improvements. Stormwater runoff volume control methods are based on the net change in runoff volume for the two-year storm event.
2. 
The green infrastructure and low impact development practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible. Volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below. For regulated activities equal to or less than one acre, this Part establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations of the procedures associated with each methodology, and other factors. All regulated activities greater than one acre must use the Design Storm Method.
[Amended by Ord. No. 2022-7, 9/19/2022]
A. 
Design Storm Method (any regulated activity): This method requires detailed modeling based on site conditions. For modeling assumptions refer to Section 8-124, Subsection 1.
(1) 
Post-development total runoff should not be increased from pre-development total runoff for all storms equal to or less than the two-year, twenty-four-hour duration precipitation.
(2) 
The following applies in order to estimate the increased volume of runoff for the two-year, twenty-four-hour duration precipitation event:
(a) 
To calculate the runoff volume (cubic feet) for existing site conditions (predevelopment) and for the proposed developed site conditions (post-development), it is recommended to use the Soil-Cover Complex Method as shown below. Table B-3 in Appendix VII[1] is available to guide a qualified design professional and/or an applicant to calculate the stormwater runoff volume. The calculated volume shall be either reused, evapotranspired, or infiltrated through structural or nonstructural means.
Soil-Cover Complex Method:
Step 1: Runoff (in) = Q = (P — 0.2S)2/(P + 0.8S)
Where
P
=
2-year rainfall (in.)
S
=
(1000/CN) — 10, the potential maximum retention (including initial abstraction, 1A)
Step 2: Runoff Volume (Cubic Feet) = Q x Area x 1/12
Where
Q
=
Runoff (in.)
Area
=
SWM Area (square feet)
[1]
Editor's Note: Appendix VII is on file in the Borough offices.
B. 
Simplified Method (regulated activities less than or equal to one acre):
(1) 
Stormwater facilities shall capture the runoff volume from at least the first two inches of runoff from all new impervious surfaces.
Volume (cubic feet) = (2" runoff/12 inches) x impervious surface (square feet)
(2) 
At least the first one inch of runoff volume from the new impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of the commonwealth. The calculated volume shall be either reused, evapotranspired or infiltrated through structural or nonstructural means.
Volume (cubic feet) = (1" runoff/12 inches) x impervious surface (square feet)
(3) 
Infiltration facilities should be designed to accommodate the first 0.5 inch of the permanently removed runoff.
(4) 
No more than one inch of runoff volume from impervious surfaces shall be released from the site. The release time must be over 24 to 72 hours.
C. 
Stormwater Control Measures. The applicant must demonstrate how the required volume is controlled through stormwater best management practices (BMPs) which shall provide the means necessary to capture, reuse, evaporate, transpire or infiltrate the total runoff volume.
(1) 
If natural resources exist on the site, per the Doylestown Borough Zoning Ordinance § 27-513, the applicant is required to submit a SWM site plan. The SWM site plan shall determine the total acreage of protected area where no disturbance is proposed. The acreage of the protected area should be subtracted from the total site area and not included in the stormwater management site area acreage used in determining the volume controls.
Stormwater Management Site Area =
[Total Site Area (for both pre- and post-development conditions) — Protected Area]
[Natural resource areas should be calculated based upon the Borough's Zoning Ordinance § 27-513. See Table B-2 in Appendix VI[2] for guidance to assess the total protected area. For additional reference, see Chapter 5, Section 5.4.1, of the PA BMP Manual.
[2]
Editor's Note: Appendix VI is on file in the Borough offices.
(2) 
Calculate the volume controls provided through nonstructural BMPs. Table B-5 in Appendix VI is recommended as guidance.
(3) 
Volume controls provided through nonstructural BMPs should be subtracted from the required volume to determine the necessary structural BMPs.
Required Volume Control (feet3)
Nonstructural Volume Control (feet3)
=
Structural Volume Requirement (feet3)
(4) 
Calculate the volume controls provided through structural BMPs. Table B-6 in Appendix VI is recommended as guidance. See PA BMP Manual Chapter 6 for description of the BMPs.
(5) 
Infiltration BMPs intended to receive runoff from developed areas shall be selected based on the suitability of soils and site conditions. (See Table B-6 in Appendix VI[3] for a list of infiltration BMPs.) Infiltration BMPs shall be constructed on soils that have the following characteristics:
(a) 
A minimum soil depth of 24 inches between the bottom of the infiltration BMPs and the top of bedrock or seasonally high water table.
(b) 
An infiltration rate sufficient to accept the additional stormwater load and dewater completely as determined by field tests. A minimum of 0.2 inch per hour should be utilized, and for acceptable rates a safety factor of 50% should be applied for design purposes (e.g., for soil which measured 0.4 inch per hour, the BMP design should use 0.2 inch per hour to ensure safe infiltration rates after construction).
(c) 
All open-air infiltration facilities shall be designed to completely infiltrate runoff volume within three days (72 hours) from the start of the design storm.
[3]
Editor's Note: Appendix VI is on file in the Borough offices.
(6) 
Soils. A soils evaluation of the project site shall be required to determine the suitability of infiltration facilities. All regulated activities are required to perform a detailed soils evaluation by a qualified design professional, which at minimum addresses soil permeability, depth to bedrock, and subgrade stability. The general process for designing the infiltration BMP shall be:
(a) 
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.
(b) 
Provide field tests, such as double ring infiltrometer or hydraulic conductivity tests (at the level of the proposed infiltration surface), to determine the appropriate hydraulic conductivity rate. Percolation tests are not recommended for design purposes.
(c) 
Design the infiltration structure based on field determined capacity at the level of the proposed infiltration surface and based on the safety factor of 50%.
(d) 
If on-lot infiltration structures are proposed, it must be demonstrated to the Borough that the soils are conducive to infiltrate on the lots identified.
(e) 
An impermeable liner will be required in detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the Borough.
[Ord. 2011-12, 6/20/2011]
Peak rate controls for large storms, up to the one-hundred-year event, is essential in order to protect against immediate downstream erosion and flooding. The following peak rate controls have been determined through hydrologic modeling of the Neshaminy Creek watershed:
A. 
Standards for managing runoff from each subarea in the Neshaminy Creek Watershed for the two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year design storms are shown in Table 8-123.1. Development sites located in each of the management districts must control proposed development conditions runoff rates to existing conditions runoff rates for the design storms in accordance with Table 8-123.1.
Table 8-123.1
Peak Rate Runoff Control Standards
by Stormwater Management Districts
in the Neshaminy Creek Watershed
(includes Little Neshaminy Creek)
District
Design Storm Post-Development (proposed conditions)
Design Storm Predevelopment (existing conditions)
A
2-year
1-year
5-year
5-year
10-year
10-year
25-year
25-year
50-year
50-year
100-year
100-year
B
2-year
1-year
5-year
2-year
10-year
5-year
25-year
10-year
50-year
25-year
100-year
50-year
C
2-year
2-year
5-year
5-year
10-year
10-year
25-year
25-year
50-year
50-year
100-year
100-year
B. 
General. Proposed conditions rates of runoff from any regulated activity shall not exceed the peak release rates of runoff from existing conditions for the design storms specified on the Stormwater Management District Watershed Map and in this section of this Part. Doylestown Borough is only in Stormwater Management Districts A and B listed above.
C. 
District Boundaries. The boundaries of the stormwater management districts are shown on official maps and are available for inspection at the county planning offices. A copy of the map for the Borough is included in Appendix III.[1] The exact location of the Stormwater Management District boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot topographic contours (or most accurate data required) provided as part of the SWM site plan.
[1]
Editor's Note: Appendix III is on file in the Borough offices.
D. 
Sites Located in More Than One District. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall meet the management district criteria for the district in which the discharge is located.
E. 
Off-site Areas. When calculating the allowable peak runoff rates, developers do not have to account for runoff draining into the subject development site from an off-site area. On-site drainage facilities shall be designed to safely convey off-site flows through the development site.
F. 
Site Areas. The stormwater management site area is the only area subject to the management district criteria. Nonimpacted areas or nonregulated activities bypassing the stormwater management facilities would not be subject to the management district criteria.
G. 
Alternate Criteria for Redevelopment Sites. For redevelopment sites, one of the following minimum design parameters shall be accomplished, whichever is most appropriate for the given site conditions as determined by Doylestown Borough.
(1) 
Meet the full requirements specified by Table 8-123.1 and Sections 8-123 A through 8-123 F; or
(2) 
Reduce the total impervious surface on the site by at least 20% based upon a comparison of existing impervious surface to proposed impervious surface.
[Ord. 2011-12, 6/20/2011]
1. 
The following criteria shall be used for runoff calculations:
A. 
For development sites not considered redevelopment, the ground cover used to determine the existing conditions runoff volume and flow rate shall be as follows:
(1) 
Wooded sites shall use a ground cover of "woods in good condition." A site is classified as wooded if a continuous canopy of trees exists over 1/4 acre.
(2) 
The undeveloped portion of the site, including agriculture, bare earth, and fallow ground, shall be considered as "meadow in good condition," unless the natural ground cover generates a lower curve number (CN) or Rational "c" value (i.e., woods) as listed in Tables B-4 or B-7 in Appendix VI of this Part.[1]
[1]
Editor's Note: Appendix VI is on file in the Borough offices.
B. 
For development and redevelopment sites, the ground cover used to determine the existing conditions runoff volume and flow rate for the developed portion of the site shall be based upon actual land cover conditions. If the developed site contains impervious surfaces, 20% of the impervious surface area shall be considered meadow in the model for existing conditions.
2. 
Stormwater runoff peak discharges from all development sites with a drainage area equal to or greater than 200 acres shall be calculated using a generally accepted calculation technique that is based on the NRCS Soil Cover Complex Method. Table 8-124.1 summarizes acceptable computation methods. The method selected by the qualified design professional shall be based on the individual limitations and suitability of each method for a particular site. The Borough may allow the use of the Rational Method (Q=CIA) to estimate peak discharges from drainage areas that contain less than 200 acres.
Q
=
Peak flow rate, cubic feet per second (CFS).
C
=
Runoff coefficient, dependent on land use/cover.
I
=
Design rainfall intensity, inches per hour.
A
=
Drainage area, acres.
3. 
All calculations consistent with this Part using the Soil-Cover Complex Method shall use the appropriate design rainfall depths for the various return period storms according to the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 rain data corresponding to the Doylestown rain gage. See Table B-1 in Appendix VI. This data may be directly retrieved from the NOAA Atlas 14 website. If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS is used for stormwater runoff calculations, then the duration of the rainfall shall be 24 hours.
Table 8-124.1
Acceptable Computation Methodologies For Stormwater Management Plans
Method
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 within limitations described in TR-55
HEC-1/HEC-HMS
U.S. Army Corps of Engineers
Applicable where use of full hydrologic computer model is desirable or necessary
PSRM
Penn State University
Applicable where use or a hydrologic computer model is desirable or necessary; simpler than TR-20 or HEC-1
Rational Method (or commercial computer package based on Rational Method)
Emil Kuichling (1889)
For sites less than 200 acres, or as approved by Doylestown Borough and/or the Doylestown Borough Engineer
Other methods
Varies
Other computation methodologies approved by the municipality and/or Municipal Engineer
4. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration for overland flow and return periods from NOAA Atlas 14, Volume 2, Version 2.1. Times-of-concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times-of-concentration for channel and pipe flow shall be computed using Manning's equation.
5. 
Runoff Curve Numbers (CN) for both existing and proposed conditions to be used in the soil cover complex method shall be based on Table B-4 in Appendix VI.[2]
[2]
Editor's Note: Appendix VI is on file in the Borough offices.
6. 
Runoff coefficients (C) for both existing and proposed conditions for use in the Rational Method shall be consistent with Table B-7 in Appendix VI.
7. 
Runoff from proposed sites graded to the subsoil will not have the same runoff conditions as the site under existing conditions because of soil compaction, even after topsoiling or seeding. The proposed condition "CN" or "C" shall increase by 5% to better reflect proposed soil conditions.
8. 
The Manning equation is preferred for one-dimensional, gradually varied, open channel flow. In other cases, appropriate, applicable methods should be applied; however, early coordination with the municipality is necessary.
9. 
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this Part using the generally accepted hydraulic analysis technique or method of the municipality.
10. 
The design of any stormwater management facility intended to meet the performance standards of this Part shall be verified by routing the design storm hydrograph through these facilities. For drainage areas greater than 200 acres in size, the design storm hydrograph shall be computed using a calculation method that produces a full hydrograph. The municipality may approve the use of any generally accepted full hydrograph approximation technique that shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
[Ord. 2011-12, 6/20/2011]
1. 
Design Storms. Any stormwater management controls, required by this Part and subject to the volume requirement (§ 8-122) and the stormwater runoff peak rate requirements (§ 8-123), shall meet the applicable requirements consistent with the calculation methodology specified in § 8-124. Provisions must also be made for safely passing the runoff greater than that occurring from the largest design storm.
2. 
Runoff Control Measures or Best Management Practices (BMPs).
A. 
Increased stormwater runoff, which may result from regulated activities, shall be controlled by permanent stormwater runoff control measures. Any selected BMP must meet the required volume and runoff peak rate requirements of this Part.
B. 
As a minimum, first flush detention basin BMPs must be used to meet the volume requirement, and dual purpose detention basin BMPs must be used to meet the water quality requirement and the stormwater runoff peak rate requirements where appropriate as specified in § 8-123.
C. 
Infiltration Best Management Practices (BMPs). Infiltration BMPs shall be designed in accordance with the design criteria and specifications in the PA BMP Manual and shall meet the following minimum requirements:
(1) 
Maximizing the groundwater recharge capacity of the area being leveled is encouraged. Design of the infiltration facilities shall consider groundwater recharge to compensate for the reduction in the recharge that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas. These measures are required to take advantage of utilizing any existing recharge areas.
(2) 
Minimum Requirements. Infiltration BMPs shall meet the following minimum requirements:
(a) 
Infiltration BMPs intended to receive runoff from developed areas 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.
2) 
An infiltration rate sufficient to accept the additional stormwater load and dewater completely as determined by field tests conducted by the applicant's design professional.
(3) 
Extreme caution should be exercised where infiltration is proposed in source water protection areas as defined by the Borough, county, DEP, or Water Authority.
(4) 
Infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities and nonstructural stormwater management alternatives.
(5) 
Extreme caution shall be exercised where salt or chloride (municipal salt storage) would be a pollutant since soils do little to filter this pollutant and it may contaminate the groundwater. The qualified design professional shall evaluate the possibility of groundwater contamination from the proposed infiltration facility and perform a hydrogeologic justification study, if necessary.
(6) 
The infiltration requirement in high quality or exceptional value waters shall be subject to the PADEP's Chapter 93, Antidegradation Regulations.
(7) 
An impermeable liner will be required in detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the municipality.
(8) 
The Borough shall require the applicant to provide safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.
(9) 
General note for all groundwater recharge/infiltration subsurface recharge system. The following note shall be placed on all plans which propose a groundwater recharge/infiltration system: "The infiltration facilities shown on these plans are a basic and perpetual part of the stormwater management system of the proposed site located in Doylestown Borough, Bucks County, Commonwealth of Pennsylvania and, as such, are to be protected and preserved in accordance with the approved final plans by the owners, their successors and assigns of these lands. Doylestown Borough and/or its agents reserve the right and privilege to enter upon these lands from time to time for the inspection of said facilities in order to determine that proper operation and maintenance and the structural and design integrity are being maintained by the owner."
D. 
Wet Pond and Artificial Wetland Best Management Practices (BMPs). Wet pond and artificial wetland BMPs shall be designed in accordance with the design criteria and specifications in the PA BMP Manual and shall meet the following minimum requirement:
(1) 
Wet pond and artificial wetland BMPs shall be constructed on hydric or wet soils and/or soils which have an infiltration rate and percolation rate of less than 0.2 inch/hour.
E. 
Regional or Subregional Control Alternatives. The initiative and funding for any regional or subregional runoff control alternatives are the responsibility of a prospective developer(s). The design of any regional control facility must incorporate reasonable development of the entire upstream watershed. The peak outflow of a regional facility would be determined on a case-by-case basis using the hydrologic model of the watershed consistent with protection of the downstream watershed areas. "Hydrologic model" refers to the calibrated Neshaminy Creek model as developed for the Stormwater Management Act 167 Plan. Nevertheless, the volume requirement of § 8-122 must be met by the regional facility design.
F. 
All stormwater control facility designs shall conform to the applicable standards and specifications of the following governmental and institutional agencies:
(1) 
American Society of Testing and Materials (ASTM).
(2) 
Asphalt Institute (AI).
(3) 
Bucks County Conservation District.
(4) 
Federal Highway Administration (FHWA).
(5) 
National Crushed Stone Association (NCSA).
(6) 
National Sand and Gravel Association (NSGA).
(7) 
Pennsylvania Department of Environmental Protection (DEP).
(8) 
Pennsylvania Department of Transportation (PennDOT).
(9) 
United States Department of Agriculture, Soil Conservation Service, Pennsylvania (USDA, SCS, PA).
G. 
If special geological hazards or soil conditions, such as carbonate-derived soils, are identified on the site, the developer's engineer shall consider the effect of proposed stormwater management measures on these conditions. In such cases, the Borough may require an in-depth report by a competent soils engineer.
3. 
Engineering Design Standards.
A. 
General.
(1) 
Storm drainage required. Overland or sheet flow is encouraged over concentrated flow. A storm sewer system and all appurtenances shall be required to be constructed by the developer or subdivider in any area from which the surface or subsurface drainage could impair public safety or cause physical damage to adjacent lands or public property. The system shall be designed to collect water at any point where three to five cubic feet per second is accumulated, at the bottom of all vertical grades, and immediately upgrade from all street intersections. The system shall discharge to the nearest practical natural drainage channel or storm sewer.
(2) 
Off-site improvements. Any increase in runoff may require necessary corrective measures, including deeds of easement, deemed appropriate by the Borough to alleviate any off-site drainage problem affected by the earth disturbance activity. The costs for such measures will be borne entirely by the developer or subdivider.
(3) 
Total watershed evaluation. The future use of undeveloped areas upstream, as shown on the approved Borough Comprehensive Plan, shall be taken into account in the design of all storm sewer systems. The capacity and maximum anticipated present flow of the body or system receiving the proposed system(s) discharge shall be calculated to verify its capability of receiving any additional flow caused by the development or subdivision. The runoff from any proposed development shall be subject to an evaluation, which includes the anticipated runoff from other existing or proposed developments within the same watershed. Stormwater management facilities designed to serve more than one property or development in the same watershed are encouraged. Consultation with the Borough is required prior to the design of such facilities.
B. 
Underdrains.
(1) 
All building foundations, grade slabs, and cellar floors located in soils that have a community development limitation degree of moderate to severe seasonal high-water table, as defined by an on-site soils test witnessed by the Borough Engineer, shall be provided with an underdrain system. This system shall provide for drainage of the enclosed volume above the slab and relief of subsurface water to a depth of not less than six inches below the slab or foundation bottom. The system shall consist of a perforated pipe field of the herringbone or gridiron configuration in coarse, gravel-filled trenches that are in direct contact with the slab or foundation sub base. The excavation shall provide a minimum of 0.005-foot/foot slope to the gravel-filled trenches.
(2) 
All proposed roadways shall be constructed with an underdrain system consisting of six-inch perforated pipe wrapped in a Class 1 geotextile material. The underdrain shall be bedded with a minimum of six inches of 2B stone. The bedding material shall extend to the bottom of the base course. The underdrain shall discharge to an inlet.
C. 
Storm drain pipes and inlets.
(1) 
All pipe and inlets shall meet material capacity and construction specifications as outlined in the latest revisions of the PennDOT Publication 408, as amended and the PennDOT Design Manual, as amended.
[Amended by Ord. No. 2022-7, 9/19/2022]
(2) 
Design flow rate. All stormwater collection pipes and inlets which flow to the detention basin's stormwater rate management facilities shall be designed to handle the peak flow rate for the twenty-five-year storm. All other stormwater system facilities shall be designed to handle the peak flow rate for the one-hundred-year storm. The design flow rate shall be determined by the rational formula, as follows:
Q = CiA
Where
Q
=
Peak runoff rate in cubic feet per second (cfs).
C
=
Runoff coefficient equal to the ratio of the peak runoff rate to the average rate of rainfall over a time period equal to the time of concentration.
i
=
Average rainfall intensity in inches per hour for a time equal to the time of concentration.
A
=
Drainage area in acres.
NOTE: Appropriate values for the runoff coefficient and rainfall intensity can be found in the Commonwealth of Pennsylvania Department of Transportation Design Manual, Part 2, as amended and updated.
(3) 
Inlet capacity. The capacity of all C-type, M-type or S-type inlets shall be determined from the Commonwealth of Pennsylvania Department of Transportation Design Manual, Part 2, as amended and updated.
(4) 
Straight pipe sections. Wherever possible, all storm drain pipes shall be designed to follow straight courses. No angular deflections of storm sewer pipe sections in excess of 5° shall be permitted. No vertical curves shall be permitted in the storm drain pipe system.
(5) 
Minimum grade and size.
(a) 
All storm drain pipes shall be designed to maintain a minimum grade of 1/2%. All storm pipes shall have a minimum inside diameter of 18 inches or a cross-sectional area of 254 square inches, except that pipes under a fill of 25 feet or greater shall not be less than 24 inches or have a cross-sectional area of less than 453 square inches.
(b) 
Reinforced concrete pipe shall be used in all public rights-of-way and when the pipe is subject to vehicular or excessive overburden loading conditions. High-density polyethylene pipe (HDPE) may be permitted only within field or lawn areas if approved by the Borough Engineer.
(6) 
Pipe capacity. The capacity of all pipe culverts shall, as a minimum, provide the required carrying capacity as determined by the following sources:
(a) 
United States Department of Transportation.
(b) 
Federal Highway Administration.
(c) 
Hydraulic Design Series No. 5.
(d) 
Hydraulic Design of Highway Culverts, latest edition.
(7) 
Pipe arches. Where headroom is restricted, equivalent pipe arches may be used in lieu of circular pipe.
(8) 
Allowable headwater depth. At all inlets or manholes, the maximum allowable headwater depth shall be one foot below the top of the inlet grate or the manhole cover.
(9) 
Horizontal pipe deflections. A manhole or inlet shall be provided at all horizontal deflections in the storm pipe system exceeding 5°.
(10) 
Minimum and maximum cover. A minimum of three feet of cover shall be maintained over all storm drain pipes. The top of storm drain pipes shall be at least 1/2 foot below subgrade elevation. The maximum cover over storm drain pipes shall be 10 feet unless special structural design calculations are submitted or approved.
(11) 
Match crowns. The crowns of all pipes tying into an inlet or manhole shall be set at equal elevations.
(12) 
Diversions of runoff. All storm drain pipes shall be designed to carry the runoff into a detention basin or similar facility utilized to control the rate of runoff.
(13) 
Structural backfill. All storm drainage structures shall be backfilled in twelve-inch layers with 2A stone to a dimension at the base of the structure 12 inches outside all faces of the structure tapering to a width of 24 inches outside all faces of the structure at the top of the structure.
D. 
Detention basins/stormwater rate management facilities.
(1) 
Design of detention basins. All detention basins shall be designed as per the procedures developed by the United States Department of Agriculture, NRCS, as outlined in its Technical Release No. 55, Urban Hydrology for Small Watersheds, Soil-Cover Complex Method.
(2) 
Basin design criteria. All detention basins and/or other stormwater management facilities in the Borough shall be designed in accordance with the stormwater runoff peak rate requirements and districts contained in § 8-123 herein and the runoff calculation methodology specified in § 8-124 herein. All flows in excess of the basin design standards shall flow over an emergency spillway.
(3) 
Maximum depth of detention basins. The maximum depth of water in a detention basin shall not exceed five feet.
(4) 
Emergency spillway. Whenever possible, the emergency spillway for detention basins shall be constructed on undisturbed ground. Emergency spillways shall be constructed of reinforced concrete, vegetated earth or other approved material. All emergency spillways shall be constructed so that the detention basin berm is protected against erosion. The minimum capacity of all emergency spillways shall be equal to the peak flow rate from the post-development one-hundred-year design storm. Emergency spillways shall extend along the upstream and downstream berm embankment slopes. The upstream edge of the emergency spillway shall be a minimum of three feet below the spillway crest elevation. The downstream slope of the spillway shall, as a minimum, extend to the top of the berm embankment. The emergency spillway shall not discharge over earthen fill and/or easily erodible material.
(5) 
Anti-seep collars. Anti-seep collars shall be poured-in-place concrete and installed around the principal pipe barrel within the normal saturation zone of the detention basin berms. The collar shall be poured against the pipe bell. The anti-seep collars and their connections to the pipe barrel shall be watertight. The anti-seep collars shall extend a minimum of two feet beyond the outside of the principal pipe barrel. The spacing between collars shall be 10 feet. The use of an O-ring pipe shall be required for all detention discharge pipes.
(6) 
Freeboard. Freeboard is the difference between the design flow elevation in the emergency spillway and the top of the settled detention basin embankment. The minimum freeboard shall be one foot, and the maximum freeboard shall be two feet.
(7) 
Slope of detention basin embankment. The maximum slope of earthen detention basin embankments shall be four to one. The top or toe of any slope shall be located a minimum of five feet from any property line. Whenever possible, the side slopes and basin shape shall be amenable to the natural topography. Straight side slopes and rectangular basins shall be avoided whenever possible.
(8) 
Width of berm. The minimum top width of detention basin berms shall be 10 feet.
(9) 
Slope of basin bottom. In order to ensure proper drainage of the detention basin, a minimum grade of 2% shall be maintained for all sheet flow.
(10) 
Energy dissipaters. Energy-dissipating devices (riprap, level spreaders, end sills, etc.) shall be placed at all basin outlets. Forebays or split flow controls are encouraged at the inlet to all basins. When a forebay or split flow control is not used, an energy-dissipating device shall be used and extend to the bottom of the basin.
(11) 
Key trench. All basin berms in fill areas are to have a key trench. The minimum depth shall be one foot and increased to a depth of three feet at the minimum point of fill. The minimum width of the key trench shall be eight feet.
E. 
Culverts and drainage channels.
(1) 
Design flow standard. All culverts and drainage channels tributary to detention basins/stormwater rate management facilities shall be designed to carry a flow rate equal to a twenty-five-year, twenty-four-hour storm. All other culverts and drainage channels shall be designed to carry a flow rate equal to a one-hundred-year, twenty-four-hour storm (Soil-Cover Complex Method by the NRCS, Technical Release No. 55).
(2) 
Erosion prevention. All drainage channels shall be designed to prevent the erosion of the bed and bank slopes. The flow velocity in all vegetated drainage channels shall not exceed the maximum permissible velocity to prevent erosion. Suitable bank stabilization shall be provided, where required, to prevent erosion of the drainage channels. Where storm sewers discharge into existing drainage channels at an angle greater than 30° from parallel to the downstream channel flow, the far-side bank shall be stabilized by the use of riprap or masonry and/or concrete walls. The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.
(3) 
Maximum side slope. Any vegetated drainage channel requiring mowing of the vegetation shall have a minimum grade of four horizontal to one vertical.
(4) 
Design standard. Because of the critical nature of vegetated drainage channels, the design of all vegetated channels shall, as a minimum, conform to the design procedures outlined in the Erosion and Sediment Control Program Manual. Several acceptable sources outline procedures for nonvegetated drainage channels, including the following:
(a) 
United States Department of Transportation.
(b) 
Federal Highway Administration.
(c) 
Hydraulic Design Series No. 5.
(d) 
Hydraulic Design of Highway Culverts, Second Edition.
[Ord. 2011-12, 6/20/2011]
1. 
No regulated earth disturbance activities within the Borough shall commence until approval of an erosion and sediment control plan for construction activities. The Bucks County Conservation District requires an Erosion and Sediment Control Plan for any earth disturbance activity of 1,000 square feet or more.
2. 
In addition, under 25 Pa. Code Chapter 102.5, a DEP NPDES permit for stormwater discharges associated with construction activities is required for any earth disturbance activity that involves equal to or greater than one acre of earth disturbance prior to commencing the earth disturbance activity. This includes earth disturbance on any portion, part, or during any stage of, a larger common plan of development or sale.
3. 
Detailed construction schedules shall be included in all erosion and sedimentation plans and stormwater management plans reviewed by the Bucks County Conservation District.
4. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the Borough. The issuance of an NPDES construction permit or permit coverage under the statewide general permit (PAG-2) satisfies the requirements of Subsection 1. A copy of the erosion and sediment control plan and any required permit, as required by DEP regulations, shall be available at the project site at all times.
[Added by Ord. No. 2022-7, 9/19/2022]
1. 
The landowner or the owner's designee (including Doylestown Borough for dedicated and owned facilities) shall inspect SWM BMPs, facilities and/or structures installed under an NPDES permit issued by the County Conservation District or the PADEP according to the following frequencies, at a minimum, to ensure the BMPs, facilities and/or structures continue to function as intended:
A. 
Annually for the first five years.
B. 
Once every three years thereafter.
C. 
During or immediately after the cessation of a ten-year or greater storm.
2. 
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 Doylestown Borough within 30 days following completion of the inspection.