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Stormwater Management Design Criteria and Standards Model Stormwater Management Design Criteria and Standards The following design criteria and performance standards may be used for Special Permits or Site Plan Review in lieu of adopting a Stormwater Management / LID Bylaw inclusive of these requirements. Section 1.0 Stormwater Management Design Criteria and Standards Performance Standards No site plan shall be approved unless the plan adheres to the following performance standards: post-development peak discharge rates will not exceed pre-development discharge rates (based on a 24-hour, two year frequency storm event); no new stormwater conveyances will discharge untreated stormwater directly to or cause erosion and sedimentation in wetlands or any other surface water body; the annual groundwater recharge from the post-development site will be approximately the same as the annual recharge rate from the pre-development site, based on soil types; stormwater systems will remove 80 percent of the average annual post-development load of total suspended solids (TSS); pretreatment will occur prior to all infiltration systems; Low Impact Development (LID) stormwater systems will be employed to the greatest extent practicable; erosion and sedimentation controls must be implemented to prevent impacts during disturbance and construction activities; where it is not practical to meet these standards on previously developed sites, new stormwater management systems will improve existing conditions; and, For land uses with higher potential pollutant loads, source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable. When the proposed discharge may have an impact upon a sensitive receptor, including but not limited to lakes, ponds, streams, wetlands, vernal pools, storm sewers, and/or buildings, the permit granting authority may require an increase in these minimum requirements. Stormwater Management Measures Stormwater management measures shall be required to satisfy the performance standards and shall be according to the following order of preference: Infiltration, flow attenuation, and pollutant removal of runoff through the use of open vegetated swales, natural depressions, or underground systems. Stormwater detention structures for the temporary storage of runoff which are designed so as not to create a permanent pool of water. Stormwater retention structures for the permanent storage of runoff by means of a permanent pool of water. Infiltration Practices. Infiltration practices shall be utilized to reduce runoff volume increases where appropriate. A combination of successive practices may be used to achieve the applicable minimum control requirements. Justification shall be provided by the applicant for rejecting each practice based on site conditions. Best Management Practices. Best management practices shall be employed to minimize pollutants in stormwater runoff prior to discharge into a combined or separate storm drainage system, water body, or infiltration system. Emergency Overflow System. All stormwater management facilities shall be designed to provide an emergency overflow system, which shall incorporate measures to provide a non-erosive velocity of flow along its length and at any outfall. Designed Release Rate. The designed release rate of any stormwater structure shall be modified if any increase in flooding or stream channel erosion would result at a downstream dam, highway, structure, or natural point of restricted stream flow or result in increased combined sewer overflow or sewer backups. Specific Design Criteria Additional policy, criteria and information including specifications and design standards may be found in the Massachusetts Stormwater Handbook: Volume 2 Technical Guide for Compliance with Massachusetts Stormwater Management Standard (Massachusetts Department of Environmental Protection, February 2008). Low Impact Development Techniques All projects subject to these standards must consider the following environmentally sensitive site design and Low Impact Development (LID) techniques: Identify, map and preserve the site’s natural features and environmentally sensitive areas such as wetlands, native vegetation, mature trees, slopes, drainage ways, permeable soils, flood plains, woodlands, and prime agricultural soils to the maximum extent practicable; Minimize grading and clearing; Delineate potential building envelopes, avoiding environmental resource areas and appropriate buffers by clustering buildings and reducing building footprints; Develop methods to minimize impervious surfaces, and protect and preserve open space. Reduce impervious surfaces wherever possible through alternative street design, such as omission of curbs and use of narrower streets; shared driveways; and shared parking areas; Manage runoff using smaller, decentralized, low-tech stormwater management techniques to treat and recharge stormwater close to the source; Lengthen flow paths and maximize sheet flow; Use nonstructural, low-tech methods, including open drainage systems, disconnection of roof runoff, and street sweeping where possible; Use native plant vegetation in buffer strips and in rain gardens (small planted depressions that can trap and filter runoff); Use drought resistant vegetation; Integrate LID techniques into the site design to create a hydrologically functional site, including but not limited to the following: Grass swales along roads; Rain gardens; Buffer strips; Use of roof gardens where practicable; Use of amended soils that will store, filter, and infiltrate runoff; Bioretention areas; Use of rain barrels and other cisterns to provide additional stormwater storage; and Use of permeable pavement. Infiltration Systems Infiltration systems shall be equipped with clean stone and or filter fabric adjacent to the soil and have appropriate sediment removal mechanisms. Infiltration systems greater than three feet (3’) deep shall be located at least ten (10’) feet from basement walls. Infiltration systems shall not be used where there is a likelihood that they may lead to groundwater contamination. Due to the potential for groundwater contamination from dry wells, they shall not be an acceptable method for management runoff containing pollutants; Infiltration systems designed to handle runoff from commercial or industrial impervious parking areas shall be a minimum of four hundred feet (400’) from any water supply well. Infiltration systems shall not be used as sediment control basins during construction unless specific plans are included to restore or improve the basin surface. Infiltration basins shall be constructed with a three foot (3’) minimum separation between the bottom of the structure and the seasonal high groundwater elevation, as determined by a certified soil evaluator; and Provisions shall be made for safe overflow passage in the event of a storm which exceeds the capacity of an infiltration system. Retention and detention ponds shall be designed for flow volumes calculated in accordance with the criteria of the Massachusetts Stormwater Handbook: Volume 2 Technical Guide for Compliance with Massachusetts Stormwater Management Standard (Massachusetts Department of Environmental Protection, February 2008), as updated or amended. The applicant shall give consideration in any plan to incorporating the use of natural topography and land cover, such as natural swales and depressions as they exist prior to development, to the degree that they can accommodate the additional flow of water. The permitting authority shall give preference to the use of swales and other LID systems in place of the traditional use of curbs and gutters based on a case by case review of the stormwater management plan. The applicant shall consider public safety in the design of any stormwater facilities. The banks of detention, retention, and infiltration basins shall be sloped at a gentle grade into the water as a safeguard against personal injury, to encourage the growth of vegetation, and to allow the alternate flooding and exposure of areas along the shore. Basins shall have a 4:1 slope to a depth two feet (2’) below the control elevation. Side slopes must be stabilized and planted with vegetation to prevent erosion and provide pollutant removal. The banks of retention areas shall be designed with sinuous rather than straight shorelines so that the length of the shoreline is maximized, thus offering more space for the growth of vegetation. Where a Stormwater Management Plan involves direction of some or all runoff off of the site, it shall be the responsibility of the applicant to obtain from adjacent property owners any easements or other necessary property interests concerning flowage of water. Approval of a Stormwater Management Plan does not create or affect any such rights. All applicants for projects which involve the storage or use of hazardous chemicals shall incorporate handling and storage "best management practices" that prevent such chemicals from contaminating runoff discharged from a site into infiltration systems, receiving waterbodies, or storm drains, and shall include a list of such chemicals in the application and the Material Safety Data Sheets (MSDS) for each listed chemical. Runoff from parking lots shall be treated by oil/water separators or other controls to remove oil and sediment. Oil separators shall be located in non-infiltration catch basins or manholes. Outlets from the above described structures may be to infiltration systems. The basic design criteria, methodologies, and construction specifications shall be those generally found in the Massachusetts Stormwater Handbook: Volume 2 Technical Guide for Compliance with Massachusetts Stormwater Management Standard (Massachusetts Department of Environmental Protection, February 2008), as updated or amended). Design Requirements for Erosion and Sediment Control for Construction Related Activities  The design requirements of the Erosion and Sediment Control plan for construction related activities are: Minimize total area of disturbance; Sequence construction activities to minimize simultaneous areas of disturbance; Minimize peak rate of runoff; Minimize soil erosion and control sedimentation during construction. Prevention of erosion is preferred over sedimentation control; Divert uncontaminated water around disturbed areas; Maximize groundwater recharge; Install and maintain all erosion and sediment control measures in accordance with the manufacturer’s specifications and good engineering practices; Prevent off-site transport of sediment including off-site vehicle tracking of sediment; Protect and manage on- and off-site material storage areas (overburden and stockpiles of dirt, borrow areas, or other areas used solely by the permitted project are considered a part of the project); Comply with applicable federal, state, and local laws and regulations, including waste disposal, sanitary sewer, or septic system regulations, and air quality requirements, including dust control; Prevent adverse impact from the proposed activities to habitats mapped by the Massachusetts Natural Heritage and Endangered Species Program as habitats that contain species that are endangered, threatened, or of special concern; as estimated habitats of rare wildlife and certified vernal pools; and as priority habitats of rare species; Institute interim and permanent stabilization measures. The measures shall be instituted on a disturbed area as soon as practicable, but no more than 14 days after construction activity has temporarily or permanently ceased on that portion of the site; and, Properly manage on-site construction and waste materials. Maintenance and Performance Guarantee Operation, Maintenance and Inspection Agreement. Prior to issuance of any building permit for which stormwater management is required, the permitting authority shall require the applicant or owner to execute an inspection, operation, and maintenance agreement binding on all subsequent owners of land served by the private stormwater management facility. The agreement shall be designed to ensure that water quality standards are met in all seasons and throughout the life of the system. Such agreement shall provide for access to the facility at reasonable times for regular inspections by the city or its authorized representative, and for regular or special assessments of property owners to ensure that the facility is maintained in proper working condition to meet design standards and any provision established. The agreement shall be recorded by the applicant and/or owner in the land records of the _________ registry of deeds. The agreement shall also provide that, if after notice by the Town/City to correct a violation requiring maintenance work, satisfactory corrections are not made by the owner(s) within thirty (30) days, the Town/City may perform all necessary work to place the facility in proper working condition. The owner(s) shall be required to reimburse the Town/City for any and all costs incurred to correct a violation under this ordinance within thirty (30) days from the time in which said work is performed. Maintenance responsibility   The owner of the property on which work has been done pursuant to this division for private stormwater management facilities, or any other person or agent in control of such property, shall maintain in good condition and promptly repair and restore all grade surfaces, walls, drains, dams and structures, vegetation, erosion and sediment control measures, and other protective devices. Such repairs or restoration and maintenance shall be in accordance with approved plans. A maintenance schedule shall be developed for the life of any stormwater management facility and shall state the maintenance to be completed, the time period for completion, and who shall be legally responsible to perform the maintenance. This maintenance schedule shall be printed on the Stormwater Management Plan. Records of installation and maintenance shall be kept. Inspections No plan will be approved without adequate provision for inspection of the property before development activity commences. The applicant shall arrange with the [Building Inspector or other] scheduling of the following inspections: Initial inspection: Prior to approval of any plan. Erosion control inspection: To ensure erosion control practices are in accord with the plan. Construction inspection: Prior to backfilling of any underground drainage or stormwater conveyance structures. Final inspection: When all work including construction of stormwater management facilities has been completed. The [Building Inspector or other] shall inspect the work and either approve it or notify the applicant in writing in what respects there has been a failure to comply with the requirements of the approved plan. Any portion of the work that does not comply shall be promptly corrected by the applicant or the applicant will be subject to the bonding provisions or the penalty provisions set forth herein. The Town/City may conduct random inspections to ensure effective control of erosion and sedimentation during all phases of construction. Laboratory tests may be required at the owner’s expense to verify adequacy of soil, material and/or compaction.  Performance Bond  Project performance bonds, as described in [some other part of this bylaw or local code], shall include a security not less than the total estimated construction cost of the stormwater management facility. The bond so required in this subsection shall include provisions relative to forfeiture for failure to complete work specified in the approved Stormwater Management Plan, compliance with all of the provisions of this division and other applicable laws and regulations, and any time limitations. The bond shall not be fully released without a final inspection of the completed work by the [Building Inspector, City Engineer, or other] submission of "as-built" plans, and certification of completion by the [building Inspector, City Engineer, or other] of the stormwater management facilities being in compliance with the approved plan and the provisions of this division.  H.  Enforcement and penalties    1. Violations Any development activity that has commenced or is conducted contrary to this division may be restrained by injunction or otherwise abated in a manner provided by law.  2. Notice of violation When the [City Engineer or its designated agent] determines that an activity is not being carried out in accordance with the requirements of this division, it shall issue a written notice of violation to the owner of the property, subject to the notice of violation requirements in [some other part of this bylaw]. 3. Stop work orders Persons receiving a notice of violations will be required to halt all construction activities, subject to [some other part of this bylaw]. 4. Criminal and civil penalties  Any person who violates any provision of this division, valid regulation, or the terms or conditions in any permit or order prescribed or issued thereunder, shall be subject to a fine not to exceed $300.00 for each day such violation occurs or continues or subject to a civil penalty, which may be assessed in an action brought on behalf of the city in any court of competent jurisdiction.    5. Noncriminal disposition  As an alternative to criminal prosecution or civil action, the city may elect to utilize the noncriminal disposition procedure set forth in [Town/City Bylaw/Ordinance]. The [Department of Public Works] shall be the enforcing entity. The penalty for the first violation shall be up to $100.00. The penalty for the second violation shall be up to $200.00. The penalty for the third and subsequent violations shall be $300.00. Each day or part thereof that such violation occurs or continues shall constitute a separate offense.  COMMENT: Not all municipalities have adopted Noncriminal Disposition procedures. If your community has not done so, these procedures would need to be enacted separately as part of the General Bylaws/City Ordinance in order to utilize this alternative mode of enforcement.