[Ord. No. 2023-01, 5/1/2023]
1. 
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 28-302:
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 § 28-410, shall be on site throughout the duration of the regulated activity.
3. 
The Municipality may, after consultation with Dauphin County Conservation District and/or 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.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
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. 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.
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 § 28-303 and the peak rate controls of § 28-303 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 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.
7. 
No stormwater or other discharges shall discharge directly into a public right-of-way or onto paved surfaces intended for vehicular or pedestrian travel [including, but not limited to, parking lots, public or private roads, sidewalks, shared driveways, etc., collectively herein "public surfaces"]. The term "directly," for the purpose of this chapter, will be dependent upon site conditions, the concentration and volume of the discharge, and intermediary surfaces, but in no case shall a discharge point that is directed toward a public surface be closer than 25 feet to the public surface.
8. 
All regulated activities shall limit surface water runoff or stormwater discharges into areas of karst geology or where karst features are observed.
9. 
All stormwater discharges with pipe sizes greater than or equal to 12 inches shall be provided with either reinforced concrete endwalls or plastic end sections, and shall also include outlet protection consistent with the latest version of the PADEP Erosion and Sediment Control (E&S) Program Manual.
10. 
For regulated activities involving the subdivision and/or land development of six or more lots or structures, communal SWM and conveyance facilities with a single entity responsible for operation and maintenance of all facilities shall be utilized. Stormwater management may not be accomplished by utilizing SWM facilities individually designed for and placed within or on each lot or structure, and the operation and maintenance of facilities shall not be delegated to individual lot owners, tenants, or other multiples of entities within the project.
11. 
For regulated activities involving the subdivision and/or land development of six or more lots or structures, subterranean SWM facilities (such as, but not limited to, infiltration pits, beds, or trenches) are prohibited. Amended soils and similar items incidental to the construction of above-ground SWM facilities are not included in this prohibition.
12. 
All regulated activities shall include such measures as necessary to:
A. 
Protect health, safety, and property.
B. 
Meet the water quality goals of this Part by implementing measures to:
(1) 
Minimize disturbance to floodplains, wetlands, natural slopes, existing native vegetation and woodlands.
(2) 
Create, maintain, or extend riparian buffers and protect existing forested buffers.
(3) 
Provide trees and woodlands adjacent to impervious areas whenever feasible.
(4) 
Minimize the creation of impervious surfaces and the degradation of waters of the commonwealth and promote groundwater recharge.
(5) 
Protect natural systems and processes (drainageways, vegetation, soils, and sensitive areas) and maintain, as much as possible, the natural hydrologic regime.
(6) 
Incorporate natural site elements (wetlands, stream corridors, mature forests) as design elements.
(7) 
Avoid erosive flow conditions in natural flow pathways.
(8) 
Minimize soil disturbance and soil compaction.
(9) 
Minimize thermal impacts to waters of the commonwealth.
(10) 
Disconnect impervious surfaces by directing runoff to pervious areas wherever possible, and decentralize and manage stormwater at its source.
C. 
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.
13. 
The design of all facilities over karst shall include an evaluation of measures to minimize adverse effects.
14. 
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.
15. 
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.
16. 
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. Note: NOAA's Atlas 14 can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
17. 
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]
[2]
Editor's Note: See 35 P.S. § 691.1 et seq., and 32 P.S. § 680.1 et seq., respectively.
18. 
Various BMPs and their design standards are listed in the BMP Manual.
19. 
Any regulated activities within an existing, known stormwater management problem area, or having the potential to negatively impact an existing, known stormwater management problem area, may be required by the Municipality to include additional, reasonable measures beyond those listed within this chapter in order to ensure that any effects of the regulated activity do not exacerbate or further contribute to the issues affecting said problem area. In no case shall the applicant be required to resolve the existing, known stormwater management problems beyond the obligations so listed.
20. 
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. Except as expressly permitted by the Municipality, 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.
[Ord. No. 2023-01, 5/1/2023]
1. 
Regulated activities that result in any one or more of: (1) the alteration or development of less than 1,000 square feet of land in a manner that may affect stormwater runoff; (2) earth disturbances of less than 5,000 square feet; or (3) the cumulative increase of impervious area less than 1,000 square feet since the first regulated instance under this chapter or the preceding versions of the Londonderry Township stormwater regulations, regardless of whether a permit was properly applied for and received, are exempt from the requirements in Part 4 (except § 28-411, as-built plans, Completion Certificate, and Final Inspections) of this chapter.
2. 
If the applicant provides a completed site design worksheet and applicable stormwater facility calculations for the design of volume controls (see Appendix C),[1] the regulated activities that require a minor SWM permit, as defined Part 2 (Definitions) are exempt from the requirements in § 28-303, Subsection 11 (Rate Controls) and §§ 28-401 through 48-401 of this chapter.
[1]
Editor’s Note: Said appendix 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. 
Exemptions from any provisions of this chapter shall not relieve the applicant from the requirements in § 28-301. If any of the requirements in § 28-301 are not met, the Municipality at its sole discretion may revoke any exemptions from any provisions of this chapter without the necessity of any proceedings for revocation, and the applicant may be required by the Municipality to cease all activities and/or comply with the provisions of this chapter.
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 state water quality standards and requirements, public health and safety, or the environment.
7. 
Not eligible for exemption: additions, modifications, or alterations to sites, structures, projects, plans, or any other items that previously required stormwater management, whether in part or in whole (for example: adding a 1,000 square feet patio onto a home built as part of a larger subdivision and land development plan that required stormwater management would not be an exempt regulated activity).
[Ord. No. 2023-01, 5/1/2023]
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 § 28-303, Subsection 10B, or the Simplified Method in § 28-303, Subsection 10C, below. 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.
For modeling purposes of both volume and rate controls:
1. 
Design storm values should be obtained from the following sources depending on methodology, provided that if either source is replaced in its entirety, the latest version of the replacement source shall be utilized:
A. 
TR-20/TR-55 precipitation frequency estimates: the latest version of the Precipitation-Frequency Atlas of the United States, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, for the twenty-four-hour storm. If this method is used for volume and water quality, the two-year design storm value should be selected for the upper 90% confidence. For rate controls, the five through 100-year design storm should be selected from the mean value rainfall depth. For conveyance facilities, the twenty-five-year design storm value should be selected for the upper 90% confidence.
B. 
Rational Method design intensity values: the latest version of PennDOT Publication 584, Chapter 7A, Region 4, for the one- through 100-year storm (U.S. Customary).
2. 
Time of concentration (Tc) shall be calculated utilizing the TR-55 segmental method, with a maximum sheet flow length of 100 feet as follows:
A. 
The minimum Tc for any watershed or subwatershed shall be five minutes.
B. 
Postdevelopment conditions may assume a five-minute Tc, but may never be greater than the predevelopment Tc for any watershed or subwatershed.
C. 
Predevelopment Tc values may not be assumed; predevelopment Tc values must be calculated.
D. 
The time of concentration for all inlets shall be the minimum Tc of five-minutes.
3. 
Runoff coefficients and curve numbers are listed within Appendix B.[1]
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
4. 
Existing (predevelopment) nonforested pervious areas must be considered meadow in good condition.
5. 
Twenty percent of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions.
6. 
For regulated activities requiring a major SWM permit due to taking place on sites: 1. with greater than or equal to 5,000 square feet of existing impervious area; 2. that are not controlling the runoff from the existing impervious area in a manner consistent with this chapter; and 3. whose activities do not qualify for the exemptions listed in § 28-302, 50% of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions. This requirement replaces the requirement in § 28-303, Subsection 5, above.
7. 
Meadow may not be used to model proposed (postdevelopment) nonforested pervious areas unless the area being modeled is specifically designed to be and designated/delineated on the plan to remain as a bona fide meadow that may not be removed or altered by the property owner. Specified native plantings and O&M, including, but not limited to, routine weeding of invasive species, should be included on the plan and in any agreements if this option is chosen.
8. 
Alternative methods of modeling volume and rate controls may be accepted on a case-by-case basis at the sole discretion of the Municipal Engineer.
9. 
All redevelopment projects shall evaluate the feasibility of reducing site impervious area by at least 20%. Where project site conditions prevent the reduction of impervious area, then stormwater BMPs shall be evaluated to provide qualitative controls for at least 20% of the site's existing impervious area.
10. 
Volume Controls.
A. 
Volume controls shall be required for all regulated activities requiring a minor or major SWM permit.
B. 
Except as provided in Subsection 10C, water volume controls shall be implemented using the Design Storm Method (CG-1 in the BMP Manual):
(1) 
Do not increase the postdevelopment total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation.
(2) 
For modeling purposes, in addition to the modeling requirements of § 28-303, Subsections 1 to 9, above:
(a) 
Volume controls shall be calculated using the NRCS Type-II Curve Number runoff method (SCS), as provided in the National Engineering Handbook Part 630: Hydrology.
(b) 
Nonstructural and other credits not directly representative of a SWM facility's physical volume, including, but not limited to, tree planting, impervious area disconnection, and volume subtraction via infiltration rate, are prohibited from being used in the modeling of volume controls.
(c) 
For regulated activities requiring a major SWM permit utilizing the Rational Method, an additional 20% shall be added to the required volume. Alternative water quality methods that achieve equal or greater water quality results may be substituted in place of this additional volume requirement at the sole discretion of the Municipal Engineer.
C. 
The Simplified Method (CG-2 in the BMP Manual) provided below is independent of site conditions, and may only be used for regulated activities requiring only a minor SWM permit if the design storm method is not followed. For new impervious surfaces:
(1) 
Stormwater facilities shall capture at least the first two inches of runoff from all new impervious surfaces.
(2) 
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.
(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.
11. 
Rate Controls.
A. 
Rate controls shall be required only for regulated activities requiring a major SWM permit; regulated activities that require a minor SWM permit are not required to provide rate controls.
B. 
For areas within Dauphin County that are not covered by a release rate map from an approved Act 167 Stormwater Management Plan,[2] postdevelopment peak discharge rates shall not exceed the predevelopment peak discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storm events. Otherwise, the applicant shall provide additional controls as necessary to satisfy the peak rate of discharge requirement.
[2]
Editor's Note: See 32 P.S. § 680.5 et seq.
C. 
For areas within Dauphin County that are covered by a release rate map from an approved Act 167 Stormwater Management Plan, postdevelopment peak discharge rates shall not exceed the predevelopment peak discharge rates for the one-, fifty-, and 100-year, twenty-four-hour storm events as listed within the applicable, approved release-rate map. For the two-, ten-, and twenty-five-year, twenty-four-hour storm events, the postdevelopment peak discharge rates shall be in accordance with the approved release rate map for the individual watershed.
D. 
For modeling purposes of rate controls, in addition to the modeling requirements of § 28-303, Subsections 1 to 9, above:
(1) 
Infiltration, exfiltration, evapotranspiration, and/or any other environmentally dependent discharge rates are prohibited from being used in the modeling of rate controls.
(2) 
For regulated activities under 10 acres in size, Modified Rational Method or TR-55 may be used for the calculation of peak rates; this chapter shows no preference for either method. For regulated activities above 10 acres in size, TR-55 shall be used.
[Ord. No. 2023-01, 5/1/2023]
1. 
For all regulated activities requiring a major SWM permit, a riparian buffer easement shall be created and recorded that encompasses an existing or potential riparian buffer.
2. 
Except as required by 25 Pa. Code 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 50 feet from the top of the streambank (on each side).
3. 
When present, provisions for permanent access to riparian buffer easements shall also be granted to the Municipality via a note as listed in § 28-402, Subsection 24J.
4. 
Minimum Management Requirements for Riparian Buffers.
A. 
Existing native vegetation shall be protected and maintained within the riparian buffer easement.
B. 
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.
5. 
The riparian buffer easement shall be enforceable by the Municipality and shall be recorded in Dauphin 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.[1]
[1]
Editor's Note: See Ch. 27, Zoning.
6. 
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.
7. 
Specific Prohibitions within Riparian Buffer Easements.
A. 
Septic drain fields and sewage disposal systems, regulated under the Pennsylvania Sewage Facilities Act (35 P.S. §§ 750.1 - 750.20a);
B. 
Livestock grazing and access, except areas specifically necessary for livestock crossing of waterways.
8. 
Specific Requirements for Uses within Riparian Buffer Easements.
A. 
All uses shall comply with the ordinances, provisions, and regulations of the Municipality and any other applicable entities.
B. 
All uses shall limit vegetative clearing to the minimum extent necessary for the execution of the use; general clearing of the riparian buffer easement is not permitted.
C. 
Trails shall be for nonmotorized use only.
D. 
Docks, boat ramps, and other similar improvements shall be comprised of stable, nonerosive material(s).
E. 
Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.
[Ord. No. 2023-01, 5/1/2023]
SWM facilities shall comply with the below standards as applicable to the proposed facility:
1. 
Infiltration facilities 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.
2. 
Low-flow channels are prohibited.
3. 
Trash racks shall be provided for all orifices equivalent to 12 inches or smaller in diameter.
4. 
Antiseep collars shall be provided on all outflow culverts in accordance with the methodology in the E&S Manual. An increase in seepage length of 15% must be used in accordance with the requirements for permanent antiseep collars.
5. 
Embankment/berm tops in the SWM facility shall not be planted with trees, unless duly authorized. Only vegetation that is five feet or lesser in mature height and tolerant to the conditions of embankment planting (for example: lack of water retainage in the soil) may be planted on berm tops. When this requirement is in conflict with other ordinances or regulations (for example: buffer screenings), relief may be granted from this requirement at the sole discretion of the Board of Supervisors.
6. 
Embankment/berm side slopes shall be no steeper than 3:1.
7. 
Embankment/berm soils shall have low erodibility factors as per the E&S Manual and be identified on the SWM site plan.
8. 
Embankments/berms greater than or equal to three feet in height shall:
A. 
Have a cross-sectional top width of at least five feet.
B. 
Have emergency spillways capable of providing nonerosive release of the postdevelopment 100-year design storm with at least one foot of freeboard when the primary outflow structure is blocked.
C. 
Have cutoff/key trenches of impervious material.
D. 
The primary outflow structure must be designed to pass all design storms (up to and including the 100-year event) without discharging through the emergency spillway.
E. 
If a development of a property requires a major permit, all SWM facilities shall be designed to meet the requirements in § 28-305, Subsection 8, regardless of the SWM facility depth.
9. 
All facilities shall drain over a period of time not less than 24 hours and not more than 72 hours from the end of the SWM facility's inflow hydrograph.
10. 
Maximum water depth in any open SWM facility shall be no greater than six feet when functioning through the primary outlet structure.
11. 
When deemed a public safety hazard at the sole discretion of the Municipality, any SWM facility may be required to be fenced with a minimum four-foot-high fence of material and design acceptable to the Municipality. The fence shall not have an opening or gap larger than two inches, and shall be provided with a self-closing and self-latching gate with a minimum opening of 10 feet.
12. 
Floodplains.
A. 
SWM facilities and their points of discharge shall not be located within the 100-year floodplain as determined by FEMA, HEC-RAS, or similar analysis. If no floodplain is defined, the floodplain is assumed to extend 50 feet from the top of stream bank in both directions.
B. 
Facility bottom elevations must be greater than 100-year floodplain elevations. If no floodplain is defined, the floodplain is assumed to extend 50 feet from the top of stream bank in both directions.
C. 
Novel approaches to stormwater management that require placement within the floodplain, including, but not limited to, floodplain restorations, may be exempted from the requirements in § 28-305 Subsections 12A and B, above at the sole discretion of the Municipal Engineer.
13. 
SWM facilities shall not be placed within 15 feet of a property line, public right-of-way, or structure as measured from the nearest point of the facility that may provide water storage.
14. 
The bottom elevation of all SWM facilities shall be located a minimum of two feet above the seasonal high groundwater table or other soil limiting zone.
15. 
The type, location, and number of landscaping and planting specification shall be provided for all stormwater management facilities and be specific for each type of facility.
16. 
SWM facilities excavated to carbonate rock must either be fitted with an impervious clay liner or over-excavated four feet and refilled with a suitable material mix. Suitable backfill material is subject to approval from the Municipal Engineer.
[Ord. No. 2023-01, 5/1/2023]
Conveyance facilities shall:
1. 
Safely convey the twenty-five-year design storm utilizing Manning's equation.
2. 
Be prohibited from connecting to or discharging into existing downstream conveyance or storage systems, whether manmade or natural, without verification of the adequacy of downstream hydraulic capacity.
3. 
In the case of storm sewers:
A. 
Completely contain flows with no surface discharges.
B. 
Be constructed with watertight joints. If conveyance facilities are proposed that require watertight joints, provide a note as listed in § 28-402, Subsection 24G.
C. 
Be designed and constructed without "knocking out" any inlet or structure corners. If inlets or structures are proposed, provide a note as listed in Section 28-402, Subsection 24H.
D. 
Have inlets, manholes, or similar structures at all horizontal and/or vertical directional changes. Tee joints, elbows, wyes, and similar structures are prohibited.
E. 
Include inlets set 0.2 foot below the final paving elevation on both sides of the low point of a curbed street.
F. 
Not have inlets placed in front of or within three feet of a driveway.
G. 
Not have inlets spaced more than 600 feet apart.
H. 
Not have manholes spaced more than 600 feet apart without an inlet in between.
I. 
Have all upstream pipe crown elevations be greater than or equal to all downstream pipe crown elevations.
J. 
Have flow velocities greater than or equal to 2.5 feet per second.
K. 
Have slopes equal to or greater than or equal to 0.35%.
4. 
In the case of gutters:
A. 
Not allow flow to encroach into adjacent roadway lanes more than one-half of the lane width, exceed three inches in depth, or exceed 1.5 inches in depth across driveways.
B. 
Not allow flow to cross intersections or street center lines.
5. 
In the case of swales:
A. 
Provide six inches of freeboard to the top of the swale.
B. 
Have side slopes no steeper than 3:1.
C. 
Be designed for stability using velocity (slopes less than 10%) or shear (all slopes) criteria.
D. 
Multiply velocities or shear stresses by the following factors when swale bends occur:
(1) 
1.75 when the bend is 30° to 60°.
(2) 
2.00 when the bend is 60° to 90°.
(3) 
2.5 when the bend is 90° or greater.
E. 
Be designed for both temporary and permanent conditions.
6. 
Any conveyance facility that is part of a SWM facilities drainage area shall be sized appropriately to safely convey the 100-year design storm to the SWM facility. In the event that conveyance facilities can not be reasonably designed to convey the 100-year design storm, other methods should be incorporated to ensure the 100-year design storm is directed to the appropriate SWM facility.