Township of Londonderry, PA
Dauphin County
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Table of Contents
Table of Contents

§ 112 General Requirements.

[Ord. 2010-5, 12/6/2010, § 301]
1. 
For all regulated activities, unless specifically exempted in § 113:
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 a SWM site plan, which demonstrates compliance with the requirements of this Part.
C. 
The SWM site plan shall demonstrate that adequate capacity will be provided to meet the volume and rate control requirements, as described under §§ 114 and 115 of this Part.
D. 
The SWM site plan approved by the municipality shall be on-site throughout the duration of the regulated activities.
2. 
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 Part and to meet all requirements under Title 25 of the Pennsylvania Code (including, but not limited to Chapter 102, Erosion and Sediment Control) 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 (April 15, 2000), as amended and updated.
3. 
For all regulated activities, stormwater BMPs shall be designed, installed, implemented, operated, and maintained to meet the purposes and requirements of this Part and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law, conform to the state water quality requirements, meet all requirements under the Stormwater Management Act and any more stringent requirements as determined by the municipality.
4. 
The municipality may, after consultation with PADEP and/or DCCD, approve measures for meeting the state water quality requirements other than those in this Part, provided that they meet the minimum requirements of, and do not conflict with, state law including, but not limited to, the Clean Streams Law.
5. 
All regulated activities shall include, to the maximum extent practicable, measures 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. 
Applicants are encouraged to incorporate the techniques for low impact development practices described in the "Pennsylvania Stormwater Best Management Practices Manual (BMP Manual)" to reduce the costs of complying with the requirements of this Part and the state water quality requirements.
6. 
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 Part.
C. 
For projects that add impervious area to a developed parcel, the new impervious area is subject to the requirements of this Part; and any existing impervious area that is within the new proposed limit of disturbance is also subject to the requirements of this Part.
7. 
If diffused flow is proposed to be concentrated and discharged onto adjacent property, the applicant must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding, or other harm will result from the concentrated discharge.
A. 
Applicant must provide an executed easement for newly concentrated flow across adjacent properties.
8. 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this Part.
9. 
Where watercourses traverse a development site, drainage easements (with a minimum width of 20 feet) shall be provided conforming to the line of such watercourses. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Also, maintenance, including mowing of vegetation within the easement, may be required, except as approved by the appropriate governing authority.
10. 
When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by PADEP under regulations at 25 PA Code Chapter 105 through the joint permit application process or, where deemed appropriate by PADEP, through the general permit process.
11. 
Any stormwater management facilities or any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures, etc.) that are regulated by this Part, that will be located in or adjacent to waters of the Commonwealth (including wetlands), shall be subject to approval by PADEP under regulations at 25 PA Code Chapter 105 through the joint permit application process or, where deemed appropriate by PADEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the applicant or his agent to show that the land in question cannot be classified as wetlands; otherwise, approval to work in the area must be obtained from PADEP.
12. 
Should any stormwater management facility require a dam safety permit under PADEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety which may be required to pass storms larger than the one-hundred-year event.
13. 
Any stormwater management facilities regulated by this Part that will be located on or discharged onto State highway rights-of-ways shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
14. 
When stormwater management facilities are proposed within 1,000 feet of a downstream municipality, the stormwater analysis shall be submitted to the downstream municipality's engineer for review and comment.
15. 
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., are encouraged, where soil conditions and geology permit, to reduce the size or eliminate the need for detention facilities.
16. 
Infiltration BMPs should be dispersed throughout the site, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this Part.
17. 
The design of facilities over karst shall include an evaluation and implementation of measures to minimize adverse effects.
18. 
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. When it is more advantageous to connect directly to streets or storm sewers, then the municipality shall permit it on a case-by-case basis.

§ 113 Exemptions; Modifications.

[Ord. 2010-5, 12/6/2010, § 302]
1. 
Under no circumstance shall the applicant be exempt from implementing such measures as necessary to:
A. 
Meet state water quality standards and requirements.
B. 
Protect health, safety, and property.
C. 
Meet special requirements for high quality (HQ) and exceptional value (EV) watersheds.
2. 
The applicant must demonstrate that the following BMPs are being utilized to the maximum extent practicable to receive consideration for the exemptions:
A. 
Design around and limit disturbance of floodplains, wetlands, natural slopes over 15%, existing native vegetation, and other sensitive and special value features.
B. 
Maintain riparian and forested buffers.
C. 
Limit grading and maintain nonerosive flow conditions in natural flow paths.
D. 
Maintain existing tree canopies near impervious areas.
E. 
Minimize soil disturbance and reclaim disturbed areas with topsoil and vegetation.
F. 
Direct runoff to pervious areas.
3. 
The applicant must demonstrate that the proposed development/additional impervious area will not adversely impact the following:
A. 
Capacities of existing drainageways and storm sewer systems.
B. 
Velocities and erosion.
C. 
Quality of runoff if direct discharge is proposed.
D. 
Existing known problem areas.
E. 
Safe conveyance of the additional runoff.
F. 
Downstream property owners.
4. 
An applicant proposing regulated activities, after demonstrating compliance with Subsections 1, 2 and 3 above may be exempted from various requirements of this Part according to the following table:
New Impervious Area*
[Since the Date of Adoption of this Part]
(square footage)
Applicant Must Submit to the Municipality
0 to 1,000
1,000 to 5,000
Volume Controls and SWM site plan & Report
>5,000
Rate Controls, Volume Controls, SWM site plan & Report and Record Drawings
*
Gravel in the existing condition shall be considered pervious and proposed gravel shall be considered impervious.
5. 
The purpose of this Section is to ensure consistency of stormwater management planning between local ordinances and NPDES permitting (when required) and to ensure that the applicant has a single and clear set of stormwater management standards to which the applicant is subject. The municipality may accept alternative stormwater management controls, provided that:
A. 
The Applicant, in consultation with the municipality, PADEP and/or DCCD, states that meeting the requirements of the volume controls or rate controls of this Part is not possible or creates an undue hardship.
B. 
The alternative stormwater management controls, proposed by the applicant, are documented to be acceptable to the municipality, PADEP and/or DCCD for NPDES requirements pertaining to post-construction stormwater management requirements.
C. 
The alternative stormwater management controls are in compliance with all other sections of this Part, including but not limited to §§ 112.4, 113.1, 113.2 and 113.3.
6. 
Forest management and timber operations are exempt from rate and volume control requirements and SWM site plan preparation requirement of this Part, provided the activities are performed according to the requirements of 25 Pa Code Chapter 102. It should be noted that temporary roadways are not exempt.
7. 
Agricultural activities are exempt from the requirements of this Part, provided the activities are performed according to the requirements of 25 Pa Code Chapter 102.
8. 
Linear roadway improvement projects that create additional impervious area are not exempt from the requirements of this Part. However, alternative stormwater management strategies may be applied at the joint approval of the municipality and the Dauphin County Conservation District (if an NPDES permit is required) when site limitations (such as limited right-of-way) and constraints (as shown and provided by the applicant), preclude the ability of the applicant to meet the enforcement of the stormwater management standards in this Part. All strategies must be consistent with PADEP's regulations, including NPDES requirements.
9. 
The municipality may, after an Applicant has demonstrated compliance with §§ 113.1, 113.2 and 113.3, grant a modification of the requirements of one or more provisions of this Part if the literal enforcement will exact undue hardship because of peculiar conditions pertaining to the land in question, provided that such modification will not be contrary to the public interest and that the purpose and intent of the Ordinance is observed.
A. 
All requests for a modification shall be in writing and shall state in full the grounds and facts of unreasonableness or hardship on which the request is based, the provision or provisions of the Ordinance involved, and the minimum modification necessary.

§ 114 Volume Controls.

[Ord. 2010-5, 12/6/2010, § 303]
1. 
The low impact development practices provided in the BMP Manual and in Appendix B of this Part shall be utilized for all regulated activities to the maximum extent practicable.[1]
[1]
Editor's Note: Appendix B is included at the end of this Chapter.
2. 
Stormwater runoff volume controls shall be implemented using the Design Storm Method or the Simplified Method. For regulated activities equal to or less than one acre, this Part establishes no preference for either method; therefore, the applicant may select either method on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology, and other factors.
A. 
The Design Storm Method (CG-1 in the BMP Manual) is applicable to any sized regulated activity. This method requires detailed modeling based on site conditions.
(1) 
Do not increase the post-development total runoff volume when compared to the predevelopment total runoff volume for the two-year/twenty-four-hour storm event.
(2) 
For hydrologic modeling purposes:
(a) 
Existing nonforested pervious areas must be considered meadow (good condition) for predevelopment hydrologic calculations.
(b) 
Twenty percent of existing impervious area, when present on the proposed project site, and contained within the new proposed limit of disturbance, shall be considered meadow (good condition) for predevelopment hydrologic calculations for redevelopment.
B. 
The Simplified Method (CG-2 in the BMP Manual) 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. 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 surface waters of the 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 1/2 inch of the permanently removed runoff should be infiltrated.
3. 
All applicable worksheets from Chapter 8 of the BMP Manual must be used when establishing volume controls.
4. 
Actual field infiltration tests at the location of the proposed elevation of the stormwater BMPs are required when 5,000 square feet or greater of new impervious surface is added. Infiltration test shall be conducted in accordance with BMP Manual. The municipality shall be notified 24 hours prior to infiltration tests being conducted as to provide an opportunity for the municipality to witness the tests.

§ 115 Rate Controls.

[Ord. 2010-5, 12/6/2010, § 304]
1. 
Lands contained within Dauphin County that have not had release rates established under an approved Act 167 Stormwater Management Plan:
A. 
Post-development discharge rates shall not exceed the predevelopment discharge rates for the one-, two-, ten-, twenty-five-, fifty-, and one-hundred-year storms.
2. 
Lands contained within Dauphin County that have had release rates established under an approved Act 167 Stormwater Management Plan:
A. 
Post-development discharge rates shall not exceed the predevelopment discharge rates for the one-, fifty-, and one-hundred-year storms.
B. 
For the two-, ten-, and twenty-five-year storms, the post-development peak discharge rates shall be in accordance with the approved release rate map for the individual watershed.

§ 116 (Reserved)