Article 945
STORMWATER MANAGEMENT STANDARDS
Sections:
945.02 Exemptions/modifications.
945.06 Sensitive areas and stormwater hotspots.
945.01 General requirements.
A. For all regulated activities, unless specifically exempted in MMC 945.02:
1. Preparation and implementation of an approved SWM site plan is required.
2. No regulated activities shall commence until the City of Meadville issues written approval of a SWM site plan, which demonstrates compliance with the requirements of this title.
3. The SWM site plan shall demonstrate that adequate capacity will be provided to meet the volume and rate control requirements, as described under MMC 945.04 and 945.05.
4. The SWM site plan approved by the City of Meadville shall be on-site throughout the duration of the regulated activities.
B. 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 title 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.
C. For all regulated activities, stormwater BMPs shall be designed, installed, implemented, operated, and maintained to meet the purposes and requirements of this title 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 Storm Water Management Act and any more stringent requirements as determined by the City of Meadville.
D. The City of Meadville may, after consultation with PADEP, approve measures for meeting the state water quality requirements other than those in this title; provided, that they meet the minimum requirements of, and do not conflict with, state law, including, but not limited to, the Clean Streams Law.
E. All regulated activities shall include, to the maximum extent practicable, measures to:
1. Protect health, safety, and property.
2. Meet the water quality goals of this title by implementing measures to:
a. Minimize disturbance to floodplains, wetlands, natural slopes, existing native vegetation and woodlands.
b. Create, maintain, or extend riparian buffers and protect existing forested buffers.
c. Provide trees and woodlands adjacent to impervious areas whenever feasible.
d. Minimize the creation of impervious surfaces and the degradation of waters of the commonwealth and promote groundwater recharge.
e. Protect natural systems and processes (drainageways, vegetation, soils, and sensitive areas) and maintain, as much as possible, the natural hydrologic regime.
f. Incorporate natural site elements (wetlands, stream corridors, mature forests) as design elements.
g. Avoid erosive flow conditions in natural flow pathways.
h. Minimize soil disturbance and soil compaction.
i. Minimize thermal impacts to waters of the commonwealth.
j. Disconnect impervious surfaces by directing runoff to pervious areas, wherever possible, and decentralize and manage stormwater at its source.
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 developments taking place in stages, the entire development plan must be used in determining conformance with this title.
3. For projects that add impervious area to a parcel, the city engineer, in his discretion, may require that the total impervious area on the parcel is subject to the requirements of this title.
G. 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.
1. The applicant must provide an easement for proposed concentrated flow across adjacent properties to a drainage way or public right-of-way.
2. Such stormwater flows shall be subject to the requirements of this title.
H. 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 title.
I. Where watercourses traverse a development site, drainage easements (to encompass the 100-year flood elevation 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.
J. 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 drainage ways 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.
K. 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 title, 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.
L. 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.
M. Any stormwater management facilities regulated by this title that will be located on or discharged onto state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PENNDOT).
N. 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.
O. 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 title.
P. 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 City of Meadville shall permit it on a case-by-case basis.
Q. Applicants are encouraged to use low impact development practices to comply with the requirements of this title and the state water quality requirements.
R. When stormwater management facilities are proposed within 1,000 feet of a downstream municipality, the SWM plan shall be submitted to the downstream municipality’s engineer for review and comment. (Ord. 3687, 2011; Ord. 3628 § 1, 2005)
945.02 Exemptions/modifications.
A. Under no circumstance shall the applicant be exempt from implementing such measures as necessary to:
1. Meet state water quality standards and requirements.
2. Protect health, safety, and property.
B. The applicant must utilize the following BMPs to the maximum extent practicable to receive consideration for the exemptions:
1. Design around and limit disturbance of floodplains, wetlands, natural slopes over 15 percent, existing native vegetation, and other sensitive and special value features.
2. Maintain riparian and forested buffers.
3. Limit grading and maintain nonerosive flow conditions in natural flow paths.
4. Maintain existing tree canopies near impervious areas.
5. Minimize soil disturbance and reclaim disturbed areas with topsoil and vegetation.
6. Direct runoff to pervious areas.
C. The applicant’s proposed development/additional impervious area may not adversely impact the following:
1. Capacities of existing drainageways and storm sewer systems.
2. Velocities and erosion.
3. Quality of runoff if direct discharge is proposed.
4. Existing known problem areas.
5. Safe conveyance of the additional runoff.
6. Downstream property owners.
D. An applicant proposing regulated activities, after demonstrating compliance with applicable sections of this title, may be exempted from the SWM site plan, rate control, or volume control requirements of this title according to the following table:
|
New Impervious Area1, 2 (square footage) |
Applicant Must Provide |
|---|---|
|
0 – 1,000 |
— |
|
>1,000 – 2,500 |
Documentation of new impervious surface3 |
|
>2,500 – 5,000 |
Volume controls and small project SWM application3 |
|
>5,000 |
Rate controls, volume controls and SWM site plan |
Notes:
1 New impervious area since the date of adoption of the ordinance codified in this title.
2 Gravel in existing condition shall be considered pervious and gravel in proposed condition shall be considered impervious. Existing maintained municipal roads are considered impervious.
3 The small project stormwater management application shall be used to establish eligibility for the exemptions listed in the above table for projects under 5,000 square feet or for single-family home construction. The small project SWM application satisfies the requirement for demonstrating compliance with subsections (A), (B), and (C) of this section and for documentation of new impervious surface; credits for disconnection of impervious surfaces and tree planting; and for computing the size of volume control BMPs, when required.
E. An applicant proposing regulated activities, after demonstrating compliance with subsections (A), (B), and (C) of this section may be exempted from various requirements of this title if documentation can be provided that a downstream manmade water body (i.e., reservoir, lake, or manmade wetlands) has been designed or modified to address the potential stormwater flooding impacts of the proposed development.
F. 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 City of Meadville may accept alternative stormwater management controls under this section; provided, that:
1. The City of Meadville, in consultation with the PADEP, determines that meeting the volume control requirements (see MMC 945.04) is not possible or places an undue hardship on the applicant.
2. The alternative controls are documented to be acceptable to PADEP for NPDES requirements pertaining to post construction stormwater management requirements.
3. The alternative controls are in compliance with all other sections of this title, including but not limited to MMC 945.01(D) and subsections (A) through (C) of this section.
G. Agricultural activity is exempt from the rate control and SWM site plan preparation requirements of this title provided the activities are performed according to the requirements of 25 PA Code Chapter 102.
H. Forest management and timber operations are exempt from the rate and volume control requirement and SWM site plan preparation requirement of this title 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. (Ord. 3687, 2011)
945.03 Waivers.
A. The provisions of this title are the minimum standards for the protection of the public welfare.
B. All waiver requests must meet the provisions of subsections (G) and (H) of this section. Waivers shall not be issued from implementing such measures as necessary to:
1. Meet state water quality standards and requirements.
2. Protect health, safety, and property.
The City of Meadville then will consider waiver requests in accordance with MMC 945.01(D), except that requests for waivers from the design requirements of MMC 949.01 and 949.02 will be considered by the City of Meadville at its sole discretion.
C. If an applicant demonstrates to the satisfaction of the governing body of the City of Meadville that any mandatory provision of this title is unreasonable or causes unique or undue unreasonableness or hardship as it applies to the proposed project, or that an alternate design may result in a superior result within the context of MMC 941.02 and 941.03, the governing body of the City of Meadville upon obtaining the comments and recommendations of the municipal engineer may grant a waiver or relief so that substantial justice may be done and the public interest is secured; provided, that such waiver will not have the effect of nullifying the intent and purpose of this title.
D. The applicant shall submit all requests for waivers in writing and shall include such requests as a part of the plan review and approval process. The applicant shall state in full the facts of unreasonableness or hardship on which the request is based, the provision or provisions of this title that are involved, and the minimum waiver or relief that is necessary. The applicant shall state how the requested waiver and how the applicant’s proposal shall result in an equal or better means of complying with the intent or purpose and general principles of this title.
E. The City of Meadville shall keep a written record of all actions on waiver requests.
F. The City of Meadville may charge a fee for each waiver request, which shall be used to offset the administrative costs of reviewing the waiver request. The applicant shall also agree to reimburse the City of Meadville for reasonable and necessary fees that may be incurred by the municipal engineer in any review of a waiver request.
G. In granting waivers, the City of Meadville may impose reasonable conditions that will, in its judgment, secure substantially the objectives of the standards or requirements that are to be modified.
H. The City of Meadville may grant applications for waivers when the following findings are made, as relevant:
1. That the waiver shall result in an equal or better means of complying with the intent of this title.
2. That the waiver is the minimum necessary to provide relief.
3. That the applicant is not requesting a waiver based on cost considerations.
4. That existing down gradient stormwater problems will not be exacerbated.
5. That runoff is not being diverted to a different drainage area.
6. That increased flooding or ponding on off-site properties or roadways will not occur.
7. That potential icing conditions will not occur.
8. That increase of peak flow (design storms up to 100-year) or volume (design storms up to two-year) from the site will not occur.
9. That erosion causing conditions due to increased peak flows or volume will not occur.
10. That adverse impact to water quality will not result.
11. That increased 100-year floodplain levels will not result.
12. That increased or unusual municipal maintenance expenses will not result from the waiver.
13. That the amount of stormwater generated has been minimized to the greatest extent allowed.
14. That infiltration of runoff throughout the proposed site has been provided where practicable and predevelopment groundwater recharge protected.
15. That peak flow attenuation of runoff has been provided.
16. That long-term operation and maintenance activities are established.
17. That the receiving streams and/or water bodies will not be adversely impacted in flood-carrying capacity, aquatic habitat, channel stability and erosion and sedimentation. (Ord. 3687, 2011)
945.04 Volume controls.
A. The low impact development practices provided in the BMP manual and in the city’s stormwater procedures manual shall be utilized for all regulated activities to the maximum extent practicable.
B. Stormwater runoff volume controls shall be implemented using the design storm method or the simplified method as defined below:
1. 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.
a. Do not increase the post-development total runoff volume when compared to the pre-development total runoff volume for the two-year/24-hour storm event.
b. For hydrologic modeling purposes:
i. Existing nonforested pervious areas must be considered meadow (good condition) for predevelopment hydrologic calculations.
ii. Twenty percent of existing impervious area, when present within the proposed project site, shall be considered meadow (good condition) for predevelopment hydrologic calculations for redevelopment.
2. 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 or for projects that require detailed design of stormwater storage facilities. For new impervious surfaces:
a. Stormwater facilities shall capture at least the first two inches of runoff from all new impervious surfaces.
b. 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.
c. 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.
d. Actual field infiltration tests at the location of the proposed elevation of the stormwater BMPs are required. Infiltration test shall be conducted in accordance with the BMP manual. Notification of the City of Meadville shall be provided to allow witnessing of the testing.
3. In cases where it is not possible or desirable to use infiltration-based best management practices to partially fulfill the requirements in subsection (B)(1) or (B)(2) of this section, the following procedure shall be used:
a. At a minimum, the following documentation shall be provided to justify the decision to not use infiltration BMPs:
i. Description of and justification for field infiltration/permeability testing with respect to the type of test and test locations.
ii. An interpretive narrative describing existing site soils and their structure as these relate to the interaction between soils and water occurring on the site. In addition to providing soil and soil profile descriptions, this narrative shall identify depth to seasonal high water tables and depth to bedrock, and provide a description of all subsurface elements (fragipans and other restrictive layers, geology, etc.) that influence the direction and rate of subsurface water movement.
iii. A qualitative assessment of the site’s contribution to annual aquifer recharge shall be made, along with identification of any restrictions or limitations associated with the use of engineered infiltration facilities.
iv. The provided documentation must be signed and sealed by a professional engineer or geologist.
b. The following water quality pollutant load reductions will be required for all disturbed areas within the proposed development:
|
Pollutant Load |
Units |
Required Reduction (%) |
|---|---|---|
|
Total Suspended Solids (TSS) |
Pounds |
85 |
|
Total Phosphorus (TP) |
Pounds |
85 |
|
Total Nitrate (NO3) |
Pounds |
50 |
c. The performance criteria for water quality best management practices shall be determined from the Pennsylvania Stormwater Best Management Practices Manual, most current version.
C. The applicable worksheets from the BMP manual must be used in calculations to establish volume control. Worksheets documenting volume control credits are also acceptable. (Ord. 3687, 2011)
945.05 Rate controls.
A. Lands contained within Crawford County that have not had release rates established under an approved Act 167, Stormwater Management Plan:
1. Post-development discharge rates shall not exceed the pre-development discharge rates for the one-year, two-year, 10-year, 25-year, 50-year, and 100-year storms.
B. Lands contained within Crawford County that have had release rates established under an approved Act 167, Stormwater Management Plan:
1. The post-development peak discharge rates shall be in accordance with the approved release rate map for the individual watershed.
a. Conneaut Outlet Watershed. For the two-year, 10-year, 25-year and 100-year storms, post-development peak discharge rates shall follow the approved release rate map. (Ord. 3687, 2011)
945.06 Sensitive areas and stormwater hotspots.
A. Sensitive Areas, Defined as Follows, and Stormwater Hotspots Which Require Special Consideration with Regard to Stormwater Management.
1. “Sensitive areas” are defined as those areas that, if developed, have the potential to endanger a water supply. These areas consist of the delineated one-year zone of contribution and direct upslope areas tributary to the water supply wells. Municipalities may update the sensitive area boundaries based on new research or studies as required.
2. “Stormwater hotspots” are land development projects that have a high potential to endanger local water quality, and could potentially threaten ground water reservoirs. The municipal engineer will determine what constitutes these classifications on a case-by-case basis. The PADEP wellhead protection contaminant source list shall be used as a guide in these determinations. Industrial manufacturing site and hazardous material storage areas must provide NPDES SIC codes. Industrial sites referenced in 40 CFR 125 are also examples of hotspots.
B. Performance Standards.
1. The location of the boundaries of sensitive areas is set by drainage areas tributary to any public water supply. The exact location of these boundaries, as they apply to a given development site, shall be determined using mapping at a scale which accurately defines the limits of the sensitive area. If the project site is within the sensitive area (in whole or in part), two-foot contour interval mapping shall be provided to define the limits of the sensitive area. If the project site is adjacent to but within 500 linear feet of a defined sensitive area, a five-foot contour interval map defining the limits of the sensitive area shall be included in the stormwater management plan to document the site’s location relative to the sensitive area.
2. Stormwater hotspot developments may be required to prepare and implement a stormwater pollution prevention plan and file notice of intent as required under the provision of the EPA Industrial Stormwater NPDES permit requirements.
3. Stormwater hotspot developments must use an acceptable pretreatment BMP prior to volume control and/or rate control BMPs. Acceptable pretreatment BMPs for these developments include those based on filtering, settling, or chemical reaction processes such as coagulation. (Ord. 3687, 2011)