Borough of Carlisle, PA Stormwater Management Standards

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 chapter.

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 § 217-14 and the peak rate controls of § 217-15 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.

Stormwater flows onto adjacent property shall not be created, increased, decreased, relocated, or otherwise altered without written notification to the adjacent property owner(s). Such stormwater flows shall be subject to the requirements of this chapter.

For all regulated activities not exempted by § 217-13, implementation of the volume controls in § 217-14 is required.

All regulated activities shall include such measures as necessary to:

Protect health, safety, and property.

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

(a)

Minimize disturbance to floodplains, wetlands, and wooded areas.

(b)

Maintain or extend riparian buffers.

(c)

Avoid erosive flow conditions in natural flow pathways.

(d)

Minimize thermal impacts to waters of this commonwealth.

(e)

Disconnect impervious surfaces by directing runoff to pervious areas, wherever possible.

Incorporate methods described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual). 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 demonstrating that the use of LID and green infrastructure is not practicable.

For all new development projects, 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. Similarly, for new development projects taking place in stages, the entire proposed new development plan must be used in determining conformance with this chapter.

Stormwater flows/direct discharges onto adjacent property shall not be created, increased, decreased, relocated, or otherwise altered without written notification to the adjacent property owner(s). Such stormwater flows shall be subject to the requirements of this chapter.

The design of all facilities over karst topography shall include an evaluation of measures to minimize adverse effects in accordance with the procedures outlined in Section 7.4 (Special Management Areas – Karst Areas) of the most current version of the SWM Manual. [Pennsylvania Department of Environmental Protection (DEP). No. 363-0300-002 (2006), as amended and updated. Pennsylvania Stormwater Best Management Practices Manual. Harrisburg, PA.]

Infiltration BMPs should be spread out, 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.

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.

The design storm volumes to be used in the analysis of peak rates of discharge should be 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 can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.

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 Stormwater Management Act.[3]

[2]

Editor's Note: See 53 P.S. 691.1 et seq.

[3]

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

Various BMPs and their design standards are listed in the BMP Manual.

§ 217-13 Exemptions.

Regulated activities resulting in less than or equal to 1,000 square feet of new impervious surface are exempt from Article IV Stormwater Management (SWM) Site Plan Preparation Requirements, including §§ 217-14 and 217-15 of this chapter. Regulated activities greater than 1,000 square feet and less than or equal to 5,000 square feet of new impervious area may be exempt from the SWM site plan preparation requirements, including §§ 217-14 and 217-15 of this chapter when justification is provided that stormwater impact is minimal.*

Regulated activities that create new disconnected impervious areas greater than 1,000 square feet and less than or equal to 5,000 square feet that are proven to meet the seventy-five-foot minimum pervious flow path requirement outlined in Appendix B[1] are exempt from the SWM site plan preparation requirements, including §§ 217-14 and 217-15 of this chapter.*

[1]

Editor's Note: Appendix B is on file in the office of the Borough Secretary.

Regulated activities meeting the following parcel size and square footage requirements are exempt from the peak rate control requirements, but not the volume control or SWM site plan preparation requirements of this chapter. These criteria shall apply to the total proposed development even if development is to take place in phases. The effective date of this chapter shall be the starting point from which to consider tracts as "parent tracts" in which future subdivisions and respective impervious area computations shall be cumulatively considered.*

New Impervious Area Exemption Criteria for Peak Rate Control
Total Parcel Size (acres)	Total Parcel Size (square feet)	New Impervious Area Exemption (square feet)
Less than 0.25	Less than 10,890	1,500
0.25 to 0.5	10,890 to 21,780	2,500
Greater than 0.5	Greater than 21,780	5,000

Agricultural plowing and tilling are exempt from the SWM site plan requirements, including §§ 217-14 and 217-15 of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.

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

NOTE: The Borough has, at its discretion, the ability to deny exemption from any requirements of this chapter. Exemption from any requirements of this chapter does not convey exemption from any requirements of any other applicable local codes or ordinances (i.e., local building permit requirements).

§ 217-14 Volume controls.

[Amended 10-10-2019 by Ord. No. 2348, approved 10-10-2019]

The green infrastructure and low impact development practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below for all regulated activities not otherwise exempted by § 217-13. For regulated activity areas equal or less than one acre that do not require hydrologic routing to design the stormwater facilities, this chapter establishes no preference for either methodology; therefore, the applicant may select either methodology 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 [see Section 8.7 of the most current version of the SWM Manual (Pennsylvania Department of Environmental Protection (DEP). No. 363-0300-002 (2006), as amended and updated. Pennsylvania Stormwater Best Management Practices Manual. Harrisburg, PA.)] is applicable to any size of regulated activity. This method requires detailed modeling based on site conditions.

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.

For modeling purposes:

(a)

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

(b)

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

The Simplified Method [see Section 8.7 of the most current version of the SWM Manual (Pennsylvania Department of Environmental Protection (DEP). No. 363-0300-002 (2006), as amended and updated. Pennsylvania Stormwater Best Management Practices Manual. Harrisburg, PA.)] 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 detention or rate control facilities. For new impervious surfaces:

Stormwater facilities shall be sized to 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 the surface waters of this commonwealth. Removal options include reuse, evaporation, transpiration, and infiltration.

Infiltration facilities should be designed to accommodate infiltration of the entire permanently removed runoff; however, in all cases at least the first 1/2 inch of the permanently removed runoff should be infiltrated.

(4)

The second one inch of runoff from new impervious surfaces should be detained using structural and nonstructural BMPs (as outlined in the most current version of the SWM Manual) and released at a controlled rate.

(5)

Regulated activities eligible under this method are exempt from the requirements of § 217-15, Rate controls.

(6)

This method is exempt from the requirements of § 217-15, Rate controls.

§ 217-15 Rate controls.

See Section 8.3 of the most current version of the SWM Manual. [Pennsylvania Department of Environmental Protection (DEP). No. 363-0300-002 (2006), as amended and updated. Pennsylvania Stormwater Best Management Practices Manual. Harrisburg, PA.]

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 one-, 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 one-, 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.

Areas covered by a release rate map from an approved Act 167 stormwater management plan (see Appendix C[1]). For the one-, two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year storms, the post-development peak discharge rates will follow the applicable approved release rate maps (see Appendix C). For any areas not shown on the release rate maps, the post-development discharge rates shall not exceed the predevelopment discharge rates.

[1]

Editor's Note: Appendix C is on file in the office of the Borough Secretary.

§ 217-16 Additional SWM and drainage requirements.

Subbasin requirements. Special requirements shall apply to activity within a geographical area which supplies stormwater runoff to a point directly west of the intersection of the terminus of West South Street and Orange Street [A map of this area is on file in the Borough Engineer's Office and is incorporated into this paragraph.]:

Use of stormwater pond facility. Fully on-site stormwater management shall not be required in this area, but development in the area shall make use of a Borough-constructed jointly used stormwater pond facility for purposes of stormwater handling, control and management.

Additional responsibilities of applicant, developer or party seeking subdivision, earth disturbance or land development approval. Payment of a fee for the use of this stormwater pond facility shall be a requisite to any area development, earth disturbance, subdivision or land development within the scope of this chapter, which fee shall be determined by Borough Council from time to time and set forth in Chapter 120, Fees. It shall also be the responsibility of the applicant, developer or other party to construct and maintain any and all drainage structures necessary to direct flow off the site in question and into the jointly used drainage swales and facilities in such manner as not to erode or otherwise compromise the integrity of existing or future facilities; the method used to bring flow to the jointly used facilities shall be subject to approval of the Borough Engineer. This responsibility shall also include the acquisition of any easements or other interests necessary to the delivery of flow to the jointly used facilities.

Limitation on meaning of "jointly used facility or facilities." The jointly used facility or facilities shall include only those facilities owned by the Borough and maintained by it. The term shall not include any common ditches, swales or other facilities used by two or more landowners or any other private arrangement or agreement for the use and/or conveyance of stormwater.

(4)

Use of jointly used facility. Nothing herein is intended to preclude Borough Council from authorizing use of the jointly used facility by parties outside of the area upon such terms and conditions as it deems proper and in a manner not inconsistent with its purpose as described herein.

§ 217-16.1 Riparian buffers.

[Added 10-10-2019 by Ord. No. 2348, approved 10-10-2019]

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.

Except as required by Chapter 102, the riparian buffer easement shall be measured to be the greater of the limit of the 100-year floodplain or a minimum of 35 feet from the top of the streambank (on each side).

Minimum management requirements for riparian buffers.

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

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.

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 a required by zoning, unless otherwise specified in the municipal Zoning Ordinance.

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.

The following conditions shall apply when public and/or private recreation trails are permitted within riparian buffers:

Trails shall be for nonmotorized use only.