Township of Collier, PA Part 3 STORMWATER MANAGEMENT STANDARDS

§ 23-301 General Requirements.

[Ord. No. 703, 11/14/2018]

1. For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 23-302:

A. Preparation and implementation of an approved SWM site plan is required.

B. No regulated activities shall commence until the municipality issues written approval of an SWM site plan which demonstrates compliance with the requirements of this chapter.

2. SWM site plans approved by the municipality, in accordance with § 23-406, shall be on site throughout the duration of the regulated activity.

3. These standards apply to the landowner and any person engaged in regulated activities.

4. 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 chapter and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law.[1] Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual (E&S Manual), No. 363-2134-008, as amended and updated. (NOTE: See § 23-1001, Subsection 4, of this chapter.) Comment on the adequacy of the erosion and sedimentation controls may be provided by the municipality per the requirements of the Allegheny County Conservation District.

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

5. 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 chapter.

C. For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 23-303 and the peak rate controls of § 23-304 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.

6. Stormwater flows onto adjacent or downstream property shall not be created, increased, decreased, relocated, impeded, or otherwise altered without written notification of the affected property owner(s). Notification shall include a description of the proposed development and the stormwater flows that are being created, increased, decreased, relocated, impeded, or otherwise altered. Adjacent property shall at a minimum include any property having a shared boundary with the subject property of the SWM site plan; however, if in the judgement of the designated plan reviewer additional properties are being affected, additional notifications may be required. Proof of notification (signed postal receipt, for example) shall be included as part of the SWM plan submission to the municipality. Such stormwater flows shall be subject to the requirements of this chapter.

7. All regulated activities shall include such measures as necessary to:

A. Protect health, safety, and property.

B. Meet the water quality goals of this chapter by implementing measures to:

(1) Minimize disturbance to floodplains, wetlands, and wooded areas.

(2) Maintain 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 by directing runoff to pervious areas, wherever possible.

C. Incorporate methods described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual). (NOTE: See § 23-1001, Subsection 3, of this chapter.) If methods other than green infrastructure and LID methods are proposed to achieve the volume and rate controls required under this chapter, the SWM site plan must include a detailed justification, acceptable to the designated plan reviewer, demonstrating that the use of LID and green infrastructure is not practicable.

8. Infiltration BMPs should be dispersed throughout the project site at strategic locations, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this chapter.

9. Normally dry, open-top storage facilities should completely drain both the volume control and rate control capacities over a period of time not less than 24 and not more than 72 hours from the end of the design storm. Infiltration tests performed at the facility locations and proposed basin bottom depths, in accordance with the BMP Manual, must support time-to-empty calculations if infiltration is a factor.

10. The design storm precipitation depths to be used in the analysis of peak rates of discharge shall be as obtained in PennDOT's Drainage Manual, Publication 584, Appendix 7A; or obtained from the latest version of the Precipitation-Frequency Atlas of the United States, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 (NOTE: See § 23-1001, Subsection 5, of this chapter.) can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.

11. For all regulated activities, SWM BMPs 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,[2] and the Storm Water Management Act.[3]

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

[3] Editor's Note: See 32 P.S. § 680.1 et seq.

12. Various BMPs and their design standards are listed in the BMP Manual. (NOTE: See § 23-1001, Subsection 3, of this chapter.)

13. The municipality may, after consultation with DEP, approve measures for meeting the state water quality requirements other than those in this chapter, provided that they meet the minimum requirements of, and do not conflict with, state law, including, but not limited to, the Clean Streams Law.[4]

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

§ 23-302 Exemptions.

[Ord. No. 703, 11/14/2018]

1. Regulated activities that result in cumulative earth disturbances less than one-fourth acre and propose an increase in impervious area of less than 5,000 square feet are exempt from the requirements in § 23-401 of this chapter, except as provided in Subsection 2 below.

2. Earth disturbances between one-twentieth acre (2,178 square feet) and one-fourth acre (10,890 square feet) of earth disturbance must submit an SWM site plan to the municipality, which shall consist of the following items and related supportive material needed to determine compliance with §§ 23-303 through 23-305. The applicant can use the protocols in the Small Project Stormwater Management Site Plan Guidance (Appendix C).[1]

A. General description of proposed stormwater management techniques, including construction specifications of the materials to be used for stormwater management facilities.

B. An erosion and sediment control plan, including all reviews and letters of adequacy from the Conservation District, where appropriate.

C. Limits of earth disturbance, including the type and amount of impervious area that is proposed; proposed structures, roads, paved areas, and buildings; and a statement, signed by the applicant, acknowledging that any revision to the approved drainage plan must be approved by the municipality, and that a revised erosion and sediment control plan must be submitted to the municipality or Conservation District for approval.

D. All stormwater management facilities must be located on a plan and described in detail; and all calculations, assumptions, and criteria used in the design of the stormwater management facilities must be shown.

[1] Editor's Note: Appendix C is included as an attachment to this chapter.

3. Agricultural activity is exempt from the SWM site plan preparation requirements of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.

4. Forest management and timber operations are exempt from the SWM site plan preparation requirements of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.

5. Roadway resurfacing and maintenance projects, which do not increase impervious area, and underground infrastructure projects are exempt from the provisions of this chapter, provided the activities meet the requirements of all other municipal, state and federal requirements. Exemptions from any provisions of this chapter shall not relieve the applicant from the requirements in § 23-301, Subsections 4 through 10.

6. The municipality may deny or revoke any exemption pursuant to this section at any time for any project that the municipality believes may pose a threat to public health and safety or the environment.

7. Voluntary green stormwater infrastructure (GSI) retrofit projects that are solely intended to better manage runoff from existing development and are not part of new development or redevelopment are exempt from the stormwater management provisions of this chapter. This does not exempt such projects from any other municipal, state, or federal regulation.

§ 23-303 Volume Controls.

[Ord. No. 703, 11/14/2018]

1. The green infrastructure and low-impact development practices provided in the BMP Manual (NOTE: See § 23-1001, Subsection 3, of this chapter.) shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the Design Storm Method in Subsection 1A or the Simplified Method in Subsection 1B below. Water volume controls shall be implemented using the Design Storm Method in Subsection 1A or the Simplified Method in Subsection 1B below, or alternative design criteria as allowed by Pa. Code Title 25, Chapter 102.

A. The Design Storm Method (CG-1 in the BMP Manual) (NOTE: See § 23-1001, Subsection 3, of this chapter.) is applicable as a method to any size of regulated activity. This method requires detailed modeling based on site conditions. The following shall be incorporated into the CG-1 method:

(1) Do not increase the post-development total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation.

(2) At least the first one inch of runoff from the net increase in impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of this commonwealth. Removal options include reuse, evaporation, transpiration, and infiltration. If the developer provides justification that the listed removal options are not feasible, and the designated plan reviewer agrees, runoff shall be detained in a facility designed for a forty-eight- to seventy-two-hour dewatering time in an area with a dedicated stormwater system (not contributory to a combined sewer system) and shall be detained in a facility designed for a seventy-two-hour dewatering time in an area contributory to a combined sewer system before discharge to local stormwater systems or the environment. Justification, as prepared and sealed by a qualified professional, for assertion that permanent removal is not feasible must be provided, at a minimum, in the form of field measured infiltration rate testing and geotechnical evaluation of the existing site soils with regard to the impact of proposed infiltration. Applications omitting this justification, including infiltration rate testing, will be considered incomplete. BMPs proposing use of extended detention in lieu of permanent reduction through the listed methods shall include a valve to adjust or regulate dewatering time to achieve the performance standards noted herein. The valve system shall include an inspection/monitoring port for review of dewatering.

(3) For modeling purposes:

(a) Existing (pre-development) nonforested pervious areas must be considered meadow in good condition.

(b) Twenty percent of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions.

B. The Simplified Method (CG-2 in the BMP Manual) (NOTE: See § 23-1001, Subsection 3, of this chapter.) provided below is independent of site conditions and should be used if the Design Storm Method is not followed. This method is not applicable to regulated activities greater than one acre or for projects that require design of stormwater storage facilities. For new impervious surfaces:

(1) Stormwater facilities shall capture at least the first two inches of runoff from the net increase in impervious surfaces.

(2) At least the first one inch of runoff from the net increase in impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of this commonwealth. Removal options include reuse, evaporation, transpiration, and infiltration. If the developer provides justification that the listed removal options are not feasible, and the designated plan reviewer agrees, runoff shall be detained in a facility designed for a twenty-four-hour dewatering time in an area with a dedicated stormwater system (not contributory to a combined sewer system) and shall be detained in a facility designed for a seventy-two-hour dewatering time in an area contributory to a combined sewer system before discharge to local stormwater systems or the environment.

(3) 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.

(4) This method is exempt from the requirements of § 23-304, Rate Controls, if the project qualifies for exemption by the provisions of § 23-302, Subsection 1.

§ 23-304 Rate Controls.

[Ord. No. 703, 11/14/2018]

1. For areas not covered by a release rate map from an approved Act 167 stormwater management plan: Post-development discharge rates shall not exceed the pre-development discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storm events. This is the equivalent to a 100% release rate area when compared to those rates shown in the maps contained in Appendix A (Release Rate Management Districts).[1] This pre-development to post-development control is not to be misconstrued as the same as the "Conditional Direct Discharge" areas on the release rate maps. For comparison of peak flow rates, flows shall be rounded to a tenth of a cubic foot per second (cfs). If it is shown that the peak rates of discharge indicated by the post-development analysis are less than or equal to the peak rates of discharge indicated by the pre-development analysis for one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storms, then the requirements of this section have been met. Otherwise, the applicant shall provide additional controls as necessary to satisfy the peak rate of discharge requirement. Peak flows should be computed using the methods included in the chapter titled "Stormwater Calculations and Methodology" of the PA DEP Stormwater Management BMP Manual; except, however, where documented downstream flooding problems exist, the municipality may impose a 50% reduced release rate criteria.

[1] Editor's Note: Appendix A is on file in the Township offices.

2. For areas covered by a release rate map from an approved Act 167 stormwater management plan: For the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storm events, the post-development peak discharge rates will follow the applicable approved release rate maps. These maps are contained in Appendix A (Release Rate Management Districts) of this chapter.[2] For comparison of peak flow rates, flows shall be rounded to a tenth of a cubic foot per second (cfs). For any areas not shown on the release rate maps, the post-development discharge rates shall not exceed the pre-development discharge rates for the specified design events. Peak flows should be computed using the methods included in Chapter 8 of the PA DEP Stormwater Management BMP Manual.

[2] Editor's Note: Appendix A is on file in the Township offices.

§ 23-305 Riparian Buffers.

[Ord. No. 703, 11/14/2018]

1. In order to protect and improve water quality, a riparian buffer easement shall be created and recorded as part of any subdivision or land development that encompasses a riparian buffer. The intent of this chapter in establishing a riparian buffer is to protect and improve stream water quality. The riparian buffer is intended to slow overland flow to the stream through the presence of native grasses, trees and shrubs, allowing infiltration/groundwater recharge; causing deposition of sediment, nutrients, pesticides, and other pollutants in the buffer rather than in the stream; and reducing erosion by providing stream bank stabilization. The trees provide shade for streams, keeping waters cooler and reducing evaporation.

2. Except as required by Pa. Code Title 25, Chapter 102, the riparian buffer easement shall be required for all streams (as defined in Part 2) with a contributing watershed area of greater than 10 acres. The riparian buffer easement shall be measured to be a minimum of 35 feet from the top of the streambank (on each side).

3. Minimum Management Requirements for Riparian Buffers.

A. No use or construction within the riparian buffer shall be permitted that is inconsistent with the intent of the riparian buffer as described in Subsection 1 of this section.

B. Existing native vegetation shall be protected and maintained within the riparian buffer easement.

C. Whenever practicable, invasive vegetation shall be actively removed, and the riparian buffer easement shall be planted with native trees, shrubs and other vegetation to create a diverse native plant community appropriate to the intended ecological context of the site.

4. The riparian buffer easement shall be enforceable by the municipality and shall be recorded in the appropriate County Recorder of Deeds Office, so that it shall run with the land and shall limit the use of the property located therein. The easement shall allow for the continued private ownership and shall count toward the minimum lot area required by zoning, unless otherwise specified in the municipal Zoning Ordinance.

5. Any permitted use within the riparian buffer easement shall be conducted in a manner that will maintain the extent of the existing 100-year floodplain, improve or maintain the stream stability, and preserve and protect the ecological function of the floodplain.

6. Stormwater drainage pipes shall be permitted within the riparian buffer easement, but they shall cross the easement in the shortest practical distance. Other structural stormwater management facilities are not permitted within the riparian buffer easement.

7. The following conditions shall apply when public and/or private recreation trails are permitted by the municipality within riparian buffers:

A. It is preferred that trails be designed to be permeable and for nonmotorized use only; however, impermeable trails are permitted, provided they have adequate drainage.

B. Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.

8. Septic drainfields and sewage disposal systems shall not be permitted within the riparian buffer easement and shall comply with setback requirements established under 25 Pa. Code Chapter 73.

9. Underground utilities shall be permitted within the riparian buffer easement; however, work shall be performed to minimize disturbance area and removal of trees. Restoration within the riparian buffer easement shall be with native species of trees, grasses, and other plantings. One tree shall be planted for each tree removed, and the restoration shall be designed by a registered professional with the requisite experience. Aboveground utilities shall only be permitted to cross the easement perpendicular to the easement or in the shortest practical distance. Existing utilities may remain and be maintained as required.