Township of Union, PA Article III Stormwater Management Standards

§ 225-11 General requirements.

A. No regulated activities shall commence until the municipality approves a plan which demonstrates compliance with the requirements of this chapter.

B. Plans approved by the municipality shall be on site throughout the duration of the regulated activity.

C. The municipality may, after consultation with DEP, approve methods 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.[1]

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

D. For all regulated activities, implementations of water quality controls are required.

E. For all regulated activities equal to or greater than 1,000 square feet in area, implementation of peak rate controls and preparation of a SWM site plan are required.

F. Impervious areas.

(1) 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.

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

(3) For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter.

G. Discharges onto adjacent property shall not be created, increased, decreased or relocated, or otherwise altered, without permission of the adjacent property owner(s). Such discharges shall be subject to the requirements of this chapter.

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

(1) Protect health, safety and property;

(2) Meet state water quality requirements as defined in Article III;

(3) Meet the water quality goals of this chapter by implementing measures to:

(a) Minimize disturbance to floodplains, wetlands, natural slopes over 15%, and existing native vegetation.

(b) Preserve and maintain trees and woodlands. Maintain or extend riparian buffers and protect existing forested buffer. Provide trees and woodlands adjacent to impervious areas whenever feasible.

(c) Establish and maintain nonerosive flow conditions in natural flow pathways.

(d) Minimize soil disturbance and soil compaction. Cover disturbed areas with topsoil having a minimum depth of four inches. Use tracked equipment for grading when feasible.

(e) Disconnect impervious surfaces by directing runoff to pervious areas.

(4) Incorporate the techniques described in Appendix A of this chapter (Low-Impact Development Practices) whenever practical.[2]

[2] Editor's Note: Appendix A is attached to this chapter.

I. The design of all facilities over Karst shall include an evaluation of measures to minimize adverse effects.

J. The design storm volumes to be used in the analysis of peak rates of discharges should be obtained from the Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2, United States Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland, 20910. NOAA's Atlas 14 can be accessed at Internet address: http://hdsc.nws.noaa.gov/hdsc/pfds/.

§ 225-12 Water quality.

A. Low-impact development practices (Appendix A) are encouraged for all regulated activities.[1]

[1] Editor's Note: Appendix A is attached to this chapter.

B. Water quality control shall be implemented using the methodologies in Subsection B(1) and (2) below:

(1) The Simplified Method is independent of site conditions.

(a) Retention and detention facilities shall be sized to capture the first two inches of runoff from all impervious surfaces.

(b) The first one inch of runoff shall be permanently removed and shall not be released into the surface waters of this commonwealth. This is the permanently removed volume (PRV). Removal options include reuse, evaporation, transpiration and infiltration.

(c) For projects that meet the exemption criteria in Table 1A of this section, the subsequent one inch of runoff shall be detained. This is the extended detention volume (EDV).

(d) For projects that do not meet the exemption criteria in Table 1A of this section, the one-year twenty-four-hour runoff volume shall be detained.

(e) Infiltration of the first 1/2 inch of the PRV is encouraged. This portion of the PRV is the groundwater recharge volume (GRV).

(f) The permanently removed volume (PRV) requirement for land areas with existing cover consisting of meadow, brush, wood-grass combination, or woods proposed for conversion to any other nonequivalent type of pervious cover shall be 1/4 inch of runoff.

(g) Retention and detention facilities should be designed to drain both the PRV and EDV completely within 48 to 96 hours from the start of the storm.

(h) Retention facilities should be designed to accommodate infiltration of the PRV. Infiltration areas should be spread out and located in the sections of the site that are most suitable for infiltration.

	Table 1A Exemption Criteria
	Stormwater Credit	Description
	Natural Area Conservation	Conservation of natural areas such as forest, wetlands or other sensitive areas in a protected easement, thereby retaining their predevelopment hydrologic and water quality characteristics. Using this credit, a designer may subtract conservation areas from total site area when computing the required water quality volume.
	Disconnection of Rooftop Runoff	Credit is given when rooftop runoff is disconnected and then directed over a pervious area where it may either infiltrate into the soil or filter over it. Credit is typically obtained by grading the site to promote overland flow or by providing bioretention on single-family residential lots. If a rooftop area is adequately disconnected, the impervious area may be deducted from the total impervious cover.
	Disconnection of Nonrooftop Runoff	Credit is given for practices that disconnect surface impervious cover by directing it to pervious areas where it is either infiltrated or filtered through the soil. As with rooftop runoff, the impervious area may be deducted from the total impervious cover, thereby reducing the required water quality volume.
	Stream Buffer Credit	Credit is given when a stream buffer effectively treats stormwater runoff. Effective treatment constitutes capturing runoff from pervious and impervious areas adjacent to the buffer and treating the runoff through overland flow across a grass or forested area. Areas treated in this manner may be deducted from total site area.
	Grass Channel (Open Section Roads)	Credit may be given when open grass channels are used to reduce the volume of runoff and pollutants during smaller storms. If designed according to appropriate criteria, these channels may meet water quality criteria for certain types of residential development.
	Environmentally Sensitive Rural Development	Credit is given when a group of environmental site design techniques are applied to low-density or rural residential development. This credit eliminates the need for structural practices to address water quality volume. See Appendix A.[2]

[2] Editor's Note: Appendix A, Low-Impact Development Practices, is attached to this chapter.

(2) The Design Storm Method requires detailed modeling based on site conditions.

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

(b) Do not increase peak rate of runoff for one-, two-, ten-, twenty-five-, one-hundred-year storms (at minimum), predevelopment to post-development; as necessary, provide additional peak rate control as required by Act 167 planning.

(c) Existing (predevelopment) nonforested pervious areas must be considered meadow or its equivalent.

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

(3) In all cases, retention and detention facilities should be designed to completely drain water quality volumes (in the case of the Simplified Method this includes both the PRV and EDV) over a period of time not less than 48 hours and not more than 96 hours from the start of the design storm.

§ 225-13 Rate controls.

A. Areas not covered by a release rate map from an approved Act 167 stormwater management plan. Post-development discharge rates shall not exceed the predevelopment discharge rates for the two-, five-, ten-, twenty-five-, fifty- and one-hundred-year storms. 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 predevelopment analysis for two-, five-, ten-, twenty-five-, fifty- and one-hundred-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.

B. Areas covered by a release rate map from an approved Act 167 stormwater management plan. For the two-, five-, ten-, twenty-five-, fifty- and one-hundred-year storms, the post-development discharge rates will follow the release rate maps in this chapter. For any areas not shown on the release rate maps, the post-development discharge rates shall not exceed the predevelopment discharge rates.