[HISTORY: Adopted by the City Council of the City of Harrisburg 5-14-2013 by Ord. No. 6-2013. Amendments noted where applicable.]
Stormwater Management Act: see 32 P.S. § 680.1 et seq.
Editor's Note: This ordinance also repealed former Part 9 (Chs. 9-901 through 9-915), Spring Creek and Paxton Creek Watershed Stormwater Management Plan, adopted 11-12-2006 by Ord. No. 17-2006, as amended.
For all regulated activities, unless specifically exempted in § 9-903.2:
Preparation and implementation of an approved SWM site plan is required.
No regulated activities shall commence until the City of Harrisburg issues written approval of a SWM site plan, which demonstrates compliance with the requirements of this Part 9.
The SWM site plan approved by the City of Harrisburg shall be on site throughout the duration of the regulated activities.
For all regulated earth disturbance activities, erosion and sediment control 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 9 and to meet all requirements under Title 25 of the Pennsylvania Code (including but not limited to Chapter 102, Erosion and Sediment Control) and the Clean Streams Law. Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual (E&S Manual), No. 363-2134-008 (April 15, 2000), as amended and updated.
For all regulated activities, stormwater BMPs shall be designed, installed, implemented, operated, and maintained to meet the purposes and requirements of this Part 9 and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law, conform to the state water quality requirements, and meet all requirements under the Stormwater Management Act and any more stringent requirements as determined by the City of Harrisburg.
Editor's Note: See 35 P.S. § 691.1 et seq.
The City of Harrisburg may, after consultation with PADEP and/or DCCD, approve measures for meeting the State Water Quality Requirements other than those in this Part 9, provided that they meet the minimum requirements of, and do not conflict with, state law, including, but not limited to, the Clean Streams Law.
All regulated activities shall include, to the maximum extent practicable, measures to:
Protect health, safety, and property.
Meet the water quality goals of this Part 9 by implementing measures to:
Minimize disturbance to floodplains, wetlands, natural slopes, existing native vegetation and woodlands.
Create, maintain, or extend riparian buffers and protect existing forested buffers.
Provide trees and woodlands adjacent to impervious areas whenever feasible.
Minimize the creation of impervious surfaces and the degradation of waters of the commonwealth and promote groundwater recharge.
Protect natural systems and processes (drainageways, vegetation, soils, and sensitive areas) and maintain, as much as possible, the natural hydrologic regime.
Incorporate natural site elements (wetlands, stream corridors, mature forests) as design elements.
Avoid erosive flow conditions in natural flow pathways.
Minimize soil disturbance and soil compaction.
Minimize thermal impacts to waters of the commonwealth.
Disconnect impervious surfaces by directing runoff to pervious areas wherever possible, and decentralize and manage stormwater at its source.
Applicants are encouraged to incorporate the techniques for low-impact development practices described in the "Pennsylvania Stormwater Best Management Practices Manual (BMP Manual)" to reduce the costs of complying with the requirements of this Part 9 and the state water quality requirements.
The measurement of impervious areas shall include all of the impervious areas in the total proposed development, even if development is to take place in stages.
For development taking place in stages, the entire development plan must be used in determining conformance with this Part 9.
For projects that add impervious area to a developed parcel, the new impervious area is subject to the requirements of this Part 9; and any existing impervious area that is within the new proposed limit of disturbance is also subject to the requirements of this Part 9.
Limits of existing impervious surfaces shall be determined based upon the predominant land use of the subject tract(s) for the period of time 10 years prior to the proposed development plan, using the limits in place during the development of the Paxton Creek or Spring Creek Act 167 Plans, as depicted on the 2003 photogrammetric mapping (not the composite existing Land Use Maps), or the limits in place based upon 2012 photogrammetric mapping prepared for The Harrisburg Authority, whichever is greatest, but not greater than the maximum impervious coverage prescribed by the current (2012) Zoning Ordinance.
If diffused flow is proposed to be concentrated and discharged onto adjacent property, the applicant must:
Document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding, or other harm will result from the concentrated discharge.
Provide an executed easement for newly concentrated flow across adjacent properties.
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this Part 9.
Where watercourses traverse a development site, drainage easements (with a minimum width of 20 feet) shall be provided conforming to the line of such watercourses. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Also, maintenance, including mowing of vegetation within the easement, may be required, except as approved by the appropriate governing authority.
When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by PADEP under regulations at 25 Pa. Code Chapter 105 through the joint permit application process or, where deemed appropriate by PADEP, through the general permit process.
Any stormwater management facilities or any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures, etc.) that are regulated by this Part 9, that will be located in or adjacent to waters of the commonwealth (including wetlands), shall be subject to approval by PADEP under regulations at 25 Pa. Code Chapter 105 through the joint permit application process or, where deemed appropriate by PADEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the applicant or his agent to show that the land in question cannot be classified as wetlands; otherwise, approval to work in the area must be obtained from PADEP.
Should any stormwater management facility require a dam safety permit under PADEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety which may be required to pass storms larger than a one-hundred-year event.
Any stormwater management facilities regulated by this Part 9 that will be located on or discharged onto state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
When stormwater management facilities are proposed within 1,000 feet of a downstream municipality, the stormwater analysis shall be submitted to the downstream municipality's engineer for review and comment.
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., are encouraged, where soil conditions and geology permit, to reduce the size or eliminate the need for detention facilities.
Infiltration BMPs should be dispersed throughout the site, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this Part 9.
The design of facilities over karst shall include an evaluation and implementation of measures to minimize adverse effects.
Roof drains shall not be connected to streets, sanitary or storm sewers, or roadside ditches in order to promote overland flow and infiltration/percolation of stormwater where it is advantageous to do so. When it is more advantageous to connect directly to streets or storm sewers, then the City of Harrisburg shall permit it on a case-by-case basis.
The applicant must demonstrate that the following BMPs are being utilized to the maximum extent practicable to receive consideration for the exemptions:
Design around and limit disturbance of floodplains, wetlands, natural slopes over 15%, existing native vegetation, and other sensitive and special value features.
Maintain riparian and forested buffers.
Limit grading and maintain nonerosive flow conditions in natural flow paths.
Maintain existing tree canopies near impervious areas.
Minimize soil disturbance and reclaim disturbed areas with topsoil and vegetation.
Direct runoff to pervious areas.
The applicant must demonstrate that the proposed development/additional impervious area will not adversely impact the following:
The purpose of this section is to ensure consistency of stormwater management planning between local ordinances and NPDES permitting (when required) and to ensure that the applicant has a single and clear set of stormwater management standards to which the applicant is subject. The City of Harrisburg may accept alternative stormwater management controls, provided that:
The applicant, in consultation with the City of Harrisburg, PADEP and/or DCCD, states that meeting the requirements of the volume controls or rate controls of this Part 9 is not possible or creates an undue hardship.
The alternative stormwater management controls, proposed by the applicant, are documented to be acceptable to the City of Harrisburg, PADEP and/or DCCD for NPDES requirements pertaining to post construction stormwater management requirements.
Forest management and timber operations are exempt from rate and volume control requirements and SWM site plan preparation requirements of this Part 9, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102. It should be noted that temporary roadways are not exempt.
Agricultural activities are exempt from the requirements of this Part 9, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.
Linear roadway improvement projects that create additional impervious area are not exempt from the requirements of this Part 9. However, alternative stormwater management strategies may be applied at the joint approval of the City of Harrisburg and the Dauphin County Conservation District (if an NPDES permit is required) when site limitations (such as limited right-of-way) and constraints (as shown and provided by the applicant), preclude the ability of the applicant to meet the enforcement of the stormwater management standards in this Part 9. All strategies must be consistent with PADEP's regulations, including NPDES requirements.
The City of Harrisburg may, after an applicant has demonstrated compliance with § 9-903.2A, B and C, grant a modification of the requirements of one or more provisions of this Part 9 if:
The literal enforcement will exact undue hardship because of peculiar conditions pertaining to the land in question, provided that such modification will not be contrary to the public interest and that the purpose and intent of this Part 9 is observed; and
The applicant submits a request for a modification, in writing, stating in full the grounds and facts of unreasonableness or hardship on which the request is based, the provision or provisions of this Part 9 involved, and the minimum modification necessary.
Stormwater runoff volume controls shall be implemented using the Design Storm Method or the Simplified Method. For regulated activities equal to or less than one acre, this Part 9 establishes no preference for either method; therefore, the applicant may select either method on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology, and other factors.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to any sized regulated activity. This method requires detailed modeling based on site conditions.
Do not increase the post-development total runoff volume when compared to the predevelopment total runoff volume for the two-year twenty-four-hour storm event.
For hydrologic modeling purposes:
Existing nonforested pervious areas must be considered meadow (good condition) for predevelopment hydrologic calculations.
Twenty percent of existing impervious area, when present on the proposed project site and contained within the new proposed limit of disturbance, shall be considered meadow (good condition) for predevelopment hydrologic calculations for redevelopment.
The Simplified Method (CG-2 in the BMP Manual) is independent of site conditions and should be used if the Design Storm Method is not followed. This method is not applicable to regulated activities greater than one acre. For new impervious surfaces:
Stormwater facilities shall capture at least the first two inches of runoff from all new impervious surfaces.
At least the first one inch of runoff from new impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into surface waters of the commonwealth. Removal options include reuse, evaporation, transpiration, and infiltration.
Wherever possible, infiltration facilities should be designed to accommodate infiltration of the entire permanently removed runoff; however, in all cases at least the first 0.5 inch of the permanently removed runoff should be infiltrated.
All applicable worksheets from Chapter 8 of the BMP Manual must be used when establishing volume controls.
Actual field infiltration tests at the location of the proposed elevation of the stormwater BMPs are required when 1,000 square feet or greater of new impervious surface is added. Infiltration tests shall be conducted in accordance with BMP Manual. The infiltration tests for new impervious surfaces of 5,000 square feet or greater shall be certified by a registered geologist or professional geotechnical engineer in the commonwealth, certified soil scientist or geomorphologist. The City of Harrisburg shall be notified 24 hours prior to infiltration tests being conducted so as to provide an opportunity for the City to witness the tests. Infiltration rates of all approved BMPs shall be field verified during construction, immediately prior to installing of the device.
A waiver from the infiltration requirement, regardless of the area of new impervious surface, must be requested, in writing, and include a report prepared and sealed by a registered geologist or professional geotechnical engineer in the commonwealth, or by a soil scientist or geomorphologist sealed by a registered professional. The report should include an analysis of field work performed on site supporting the location of testing, basis for establishing the limiting zone, and soils analyses with infiltration rates of likely locations of prospective BMPs. All other provisions of the approving agency shall be satisfied prior to issuance of a waiver.
If it is determined by the approving agency that infiltration of all or part of the increased runoff volume is not feasible, the increased volume shall be routed through a BMP that is deemed acceptable by the approving agency to provide volume reduction, flow attenuation, and water quality enhancement, which include underdrained filters, underdrained bioretention, swales with check dams, ponds/wet basins, and constructed wetlands. (See Table E-1, Appendix E, for a complete list.) Underdrained systems shall retain the increased volume for not less than 24 nor more than 72 hours.
For lands contained within the City of Harrisburg that have not had release rates established under an approved Act 167 stormwater management plan, post-development discharge rates shall not exceed the predevelopment discharge rates for the one-year, two-year, ten-year, twenty-five-fifty-year and one-hundred-year storms.
For lands contained within the City of Harrisburg that have had release rates established under an approved Act 167 stormwater management plan [Paxton Creek and Spring Creek (West)]:
Post-development discharge rates shall not exceed the predevelopment discharge rates for the one-year, fifty-year, and one-hundred-year storms.
For the two-, ten-, and twenty-five-year storms, the post-development peak discharge rates shall be in accordance with the approved Act 167 plan release rate map, or, for areas situated outside the limits of the Paxton Creek or Spring Creek watersheds, the post-development discharge rates shall not exceed the predevelopment discharge rates.
For lands contained within a Paxton Creek Watershed Provisional No-Detention District:
These watershed areas may discharge post-development peak runoff without detention facilities. However, the applicant must prove that the local runoff conveyance facility which transports runoff from the site to the Main Channel has adequate capacity to safely transport unattenuated increased peak flows for a twenty-five-year storm in accordance with § 9-903.5. Also, in the case of the site draining to a combined sewer, peak sewage flows shall be included in the hydraulic analysis. If there is inadequate capacity, the applicant shall either use 100% release rate control or provide increased capacity of downstream drainage facilities to convey increase peak flows consistent with § 9-903.5. When determining if adequate capacity exists in the local watershed drainage network, the applicant must assume that the entire local watershed is developed per current zoning and that all new development will use the least restrictive runoff controls specified by this Part 9.
Increases in peak flow to a combined sewer shall be considered in evaluating the site's Act 537 sewage facility planning.
Off-site areas that drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rate; however, on-site drainage facilities shall be designed to safely convey off-site flows through the development site.
For a proposed development site which is located within two or more release rate districts, the maximum runoff discharged at any point shall be equal to the release rate for the district in which the discharge point is located. In the event that a portion of the site is located in a provisional no-detention area, no runoff from portions of the site located in areas subject to release rate controls may be drained to or through the provisional no-detention area.
Any downstream capacity hydraulic analysis conducted in accordance with this Part 9 shall use the following criteria for determining adequacy for accepting increased peak flow rates:
Natural or man-made channels or swales must be able to convey the increased runoff associated with a twenty-five-year return period event within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the PADEP Erosion and Sediment Pollution Control Program Manual.
Natural or man-made channels or swales must be able to convey the increased twenty-five-year return period runoff without creating any hazard to persons or property.
Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with PADEP, Chapter 105 regulations (if applicable), and, at a minimum, pass the increased twenty-five-year return period runoff, except for facilities located within a designated floodplain which must, at a minimum, conform to FEMA and local floodplain ordinance requirements.
Combined sewer systems must pass or convey flows from the tributary area for a twenty-five-year return period plus the peak sewage flows from the tributary service area, (4.0 x average daily flow). The resulting energy grade line (EGL) in the main shall remain one foot below the basement floor elevations of properties serviced by the sewer, and the EGL shall not exceed the elevation of the CSO structure overflow weirs or otherwise cause sewage to enter the waters of the commonwealth. Increases in peak flow from a proposed development shall be considered as part of the proposed development's Act 537 sewage facility planning.