Borough of Hanover, PA Stormwater Management Standards

For the purposes of this chapter, the term "new impervious area" shall refer to any amount of impervious area that is in excess of the predevelopment impervious coverage.

The term "altered impervious area" shall refer to any predevelopment impervious areas that are demolished or significantly altered through the course of development and are replaced or rebuilt and remain impervious areas post-development. Soils under areas that are converted from existing impervious to pervious must be restored (tilled and amended) in accordance with this chapter [Subsection H(3) below].

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 phases.

For development taking place in phases, the entire development plan must be used in determining conformance with this chapter.

(5)

For projects that add impervious area to a parcel or alter any existing impervious area, the total impervious area on the parcel is subject to the requirements of this chapter.

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 chapter.

All regulated activities shall include such measures as necessary to:

Protect health, safety, and property.

Meet the water quality goals of this chapter, as stated in § 310-3, Purpose, by implementing measures to:

Avoid and/or minimize disturbance to floodplains, wetlands, wooded areas, and existing vegetation. Where existing wooded areas are disturbed or diminished, suitable replacement features shall be provided.

Maintain or expand 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.

Minimize soil disturbance and compaction. Topsoil, if removed, shall be replaced to a minimum depth equal to its depth prior to removal or eight inches, whichever is greater. Prior to placement of topsoil, subsoil shall be decompacted and amended per Pennsylvania Stormwater Best Management Practices Manual (BMP Manual) Section 6.7.3, as most recently amended. A soil test shall be conducted prior to the selection of project specific amendments to ensure proper soil chemistry and structure.

To the maximum extent practicable, incorporate the techniques for low-impact development practices described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual).

The design of all facilities in areas of carbonate geology or karst topography shall include an evaluation of measures to minimize adverse effects, including hydrogeologic studies if required by the Borough.

Infiltration BMPs shall 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. In addition, infiltration BMPs shall include pretreatment BMPs where appropriate.

All-natural streams, channels, swales, drainage systems, and/or areas of surface water concentration shall be maintained in their existing condition unless the Borough approves alteration. All encroachment activities shall comply with the requirements of the DEP 25 Pa. Code Chapter 105 (Water Obstructions and Encroachments), rules and regulations of DEP. Any approvals or permits issued do not relieve compliance as referenced in § 310-8, Compatibility with other requirements.

Normally dry, open-top storage facilities, designed as such, shall 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 unless approved by the Borough Engineer. However, any designed infiltration at such facilities is exempt from the minimum twenty-four-hour standard, that is, may infiltrate in a shorter period of time, so long as none of the stormwater flowing into the infiltration facility is discharged directly into the surface waters of the commonwealth. (Inordinately rapid infiltration rates may indicate the presence of large fractures or other conditions for which an additional soil buffer may be required.)

The design storm volumes and precipitation intensities to be used in the analysis of discharge or runoff shall be obtained from the latest version of the Precipitation-Frequency Atlas of the United States, U.S. Department of Commerce, 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/. In order to improve on the Borough's long-term resiliency of stormwater assets, where NOAA Atlas 14 data is being used for the design and analysis of stormwater collection and conveyance facilities that are either currently owned or will be offered for dedication to the Borough, post-developed estimates of precipitation (for purposes of design) shall be increased no less than 15% to account for projected increases in the depth and/or intensity of precipitation events due to changing precipitation patterns.

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, and the Storm Water Management Act.[2] For all nonexempted stormwater activities, oversight of BMP construction must be provided at predefined "critical" stages (to be noted on the plan).

[2]

Editor's Note: See 35 P.S. § 691.1 et seq. and 32 P.S. § 680.1 et seq., respectively.

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

All work shall be in accordance with the Borough's Standard Construction Details and PennDOT Publications 408 and 72M.

§ 310-14 Exemptions.

Any regulated activity that meets the following exemption criteria is exempt from the part(s) of this chapter as specified herein. However, the requirements of this chapter shall otherwise remain in effect. The criteria for exemption in this section apply to the total development proposed, including instances in which the development is proposed to take place in phases. The date of enactment of the previous stormwater management ordinance (September 23, 2015) shall be the starting point from which future development and the respective proposed impervious surface computations shall be cumulatively considered and regulated. Exemption shall not relieve an applicant from implementing such measures as necessary to meet the intent of this chapter or compliance with any NPDES permit requirements. The applicant must also demonstrate that the proposed development/additional impervious area will not adversely impact the adjacent properties and/or the existing drainageways and storm sewer systems.

Regulated activities that create full DIAs or are less than 500 square feet of new or altered impervious surface are exempt from the volume, peak rate control and the SWM site plan requirements; however, a stormwater permit application is required to be submitted in order to track cumulative impervious area for the parcel.

Regulated activities that create full DIAs or are equal to or more than 500 square feet but less than 1,000 square feet are exempt from the peak rate control requirement but are obligated to provide volume controls [permitted to use Chapter 8.7 of the PA Stormwater BMP Manual: Guidance for Stormwater Calculations for Volume Control Guideline 1 and Volume Control Guideline 2 (providing generalized control of runoff volumes associated with a two inches rainfall event)], and a SWM site plan and complete an O&M agreement.

Maintaining SWM BMPs and stormwater collection and conveyance (C&C) facilities in accordance with a land development plan approved by the Borough.

Implementing emergency repairs to protect public health, safety and welfare. (A verbal notification, with reasoning for emergency status, shall be provided to the Borough before the work is initiated. Pending Borough concurrence, a written description of the location, situation, threat, and work shall be submitted to the Borough within two calendar days of activities commencement. If the Borough finds that work does not constitute an emergency, the work shall cease immediately, and the requirements of this chapter shall be met as applicable.)

Projects involving only/principally the construction of sidewalks and curbing within public rights-of-way.

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

Domestic gardening and landscaping with trees, shrubs, and flowers are exempt from specific approval and permitting under this chapter so long as those activities are associated with one, and only one, dwelling unit and the activities comply with all other applicable ordinances and statutes.

Exemptions from certain provisions of this chapter shall not relieve the applicant from the requirements in § 310-13D through L of this chapter.

The Borough may deny or revoke any exemption pursuant to this section at any time for any project that the Borough determines poses a threat to public health, safety, property, or the environment.

For all regulated activities that are exempt from the SWM site plan preparation, the applicant shall submit a site plan in sufficient detail to show the existing conditions and proposed improvements as well as basic design calculations.

For projects that are beyond the maximum extent practicable to provide the required stormwater management volume within their parcel shall coordinate with the Borough to identify alternate off-site locations where a BMP or contribution towards a joint BMP project could result in the proper management of stormwater runoff. Alternate BMPs must reside in the same subwatershed as the project (subject) parcel. Any fees paid in lieu of actual construction site improvements shall be based upon a fee schedule as set, managed and approved by the Borough's stormwater authority.

§ 310-15 Volume controls.

The low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities to the maximum extent practicable. Water volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below. For regulated activity areas equal to 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 (CG-1 in the BMP Manual) 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 or 2.86 inches in 24 hours, whichever is greater.

For modeling purposes:

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

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

The Simplified Method (CG-2 in the BMP Manual) 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 or altered impervious surfaces:

Stormwater facilities shall capture at least the first two inches of runoff from all new or altered impervious surfaces.

At least the first one inch of runoff from new or altered 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 for the first one inch of runoff 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 stormwater runoff shall be infiltrated.

This method is exempt from the requirements of § 310-16, Rate controls.

Infiltration alternative. Where infiltration is not possible due to soil characteristics or is not desirable given other characteristics, water quality control may be proposed as an alternative to strict adherence to the volume control standards of § 310-15 of this chapter. Where water quality control is proposed, the following standards shall be achieved:

At a minimum, the following documentation shall be provided to justify the proposal to reduce the infiltration requirements:

Description of and justification for field infiltration/permeability testing with respect to the type of test and test locations.

An interpretive narrative describing existing soils of the site and their structure as these relate to the interaction between soils and water characteristics of the site. In addition to providing soil and soil profile descriptions, this narrative shall identify depth to seasonal water tables and depth to bedrock and provide a description of all subsurface elements (restrictive layers, geology, etc.) that influence the direction and rate of subsurface water movement.

(c)

A qualitative assessment of the site's contribution to annual aquifer recharge shall be made, along with the identification of any restrictions or limitations associated with the use of designed infiltration facilities.

(d)

The provided documentation must be signed and sealed by a qualified professional.

(e)

Infiltration testing shall be performed at the proposed bottom elevation of the facility.

Water quality BMPs shall be implemented on all permanent stormwater discharges from the proposed project site to achieve pollutant removal efficiencies in accordance with the following table. [Efficiency removal rating shall be based on a testing specification for particle size distribution as required per TARP, the Technology Acceptance and Reciprocity Partnership (http://www.dep.state.pa.us/dep/deputate/pollprev/techservices/tarp/), Tier 1 and 2 protocol testing. The minimum design flow shall be based on the peak flow produced from one inch of rain as calculated.]

Required Pollutant Removal Efficiencies for Infiltration Alternatives
Pollutant Load	Units	Required Removal Efficiency
Total suspended solids (TSS)	Pounds	85%
Total phosphorus (TP)	Pounds	85%
Total nitrate (NO₃)	Pounds	50%

Design guidance from the most current version of the BMP Manual, or equivalent resource as precoordinated with Hanover Borough, shall be consulted when choosing design criteria for water quality BMPs.

Where proposed practices are based on the use of disconnected impervious areas, the pathway upon which the discharge will occur shall be deep ripped and/or soil amendments included to improve the infiltrative capacity of the soil/turf section. Physical testing of the soils infiltrative capacity will be required to be conducted and submitted to the Borough, prior to the closeout of the project. Further, an operations and maintenance agreement will be required to ensure that testing occurs on no less than a three-year cycle to ensure proper infiltration.

§ 310-16 Rate controls.

For computation of predevelopment peak discharge rates, 20% of the existing impervious area of a project site, when present, shall be considered meadow.

Post-development discharge rates shall not exceed the predevelopment discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour 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 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.

§ 310-17 Department of Transportation and Turnpike Commission roadways and associated facilities.

For the purposes of the Act 167 stormwater management (plan) elements, contained within the York County Integrated Water Resources Plan and this chapter, design policy pertaining to stormwater management facilities for Pennsylvania Department of Transportation (PennDOT) and Pennsylvania Turnpike Commission (PTC) roadways and associated facilities is provided in Section 13.7 (Antidegradation and Post Construction Stormwater Management Policy) of PennDOT Publication No. 13M, Design Manual Part 2 (August 2009), as developed, updated, and amended in consultation with the Pennsylvania Department of Environmental Resources (DEP). As stated in DM-2.13.7.D (Act 167 and municipal ordinances), PennDOT and PTC roadways and associated facilities shall be consistent with Act 167 plans. DM-2.13.7.B (Policy on Antidegradation and Post Construction Stormwater Management) was developed as a cooperative effort between PennDOT and DEP. DM-2.13.7.C (Project Categories) discusses the anticipated impact on the quality, volume, and rate of stormwater runoff.

Where standards in the Act 167 elements of the IWRP and this chapter are impractical, PennDOT or the PTC may request assistance from DEP, in consultation with the county, to develop an alternative strategy for meeting state water quality requirements and the goals and objectives of the Act 167 elements within the IWRP.

For the purposes of the Act 167 elements in the IWRP and this chapter, road maintenance activities are regulated under 25 Pa. Code Chapter 102.

§ 310-18 Additional stormwater management design standards.

General SWM site plan requirements and standards.

SWM site plan requirements shall comply with the guidance, procedures and policies provided in the latest version of the BMP Manual and PennDOT Publication No. 13M, Part 2, Chapter 10.

The Borough reserves the ability to require additional stormwater controls for special management areas (impaired streams, areas with sensitive resources, hot spots, flood-prone areas, etc.)

Detention and retention basins.

Basin maximum water depth shall be less than eight feet for a one- through 100-year, twenty-four-hour post-development storm event.

Embankment top widths shall be at least eight feet.

The maximum permitted side slopes shall be 4.0 horizontal to 1.0 vertical. In order to obtain a waiver for slopes steeper than 4:1, the plan must include a planting schedule to stabilize the embankments. The proposed vegetation shall be of the low-maintenance variety.

Any open-top facility shall be subject to the following fencing requirements:

The facility must be completely surrounded by a chain-link fence of not less than four feet in height. Alternative fences and barriers may be permitted upon request to and approval by the Borough.

The fence shall not be installed on earth fill embankment tops, on fill embankment downstream face slopes, across emergency spillway weirs, or across emergency spillway downstream face channel sections (above the toe of embankment slopes).

(c)

All gate or door openings through such enclosure shall be equipped with a self-closing and self-latching device for keeping the gate or door securely closed at all times when not in actual use.

Stormwater collection and conveyance facilities and/or systems.

All stormwater pipes, other than those for existing channels, which discharge from residential lots to a street or from a street to residential lots, shall extend from the street right-of-way a minimum distance of 67% of the length of the longest adjacent lot dimension.

SWM collection and conveyance facilities not located within a public right-of-way shall be centered in an easement. Said easement shall be a minimum of 20 feet wide for subsurface facilities or shall be of sufficient size to encompass the entire facility and provide for 10 feet of easement on either side for open swales or trenches. The SWM site plans shall clearly state to whom the easement and all future maintenance and responsibility is to be granted and shall include a space for the grantee to sign in acknowledgment of the easement.

Miscellaneous SWM site plans and SWM BMP requirements and standards.

Roof drain(s) and sump pump(s) connections shall not discharge into sanitary sewers, streets, gutters, roadside channels, or into the legal street or road right-of-way, except with the express permission of the Borough.