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HomeMy WebLinkAboutMCM 5 supporting documentsPage D1 Appendix D Minimum Control Measure 5 Supporting Documentation Page D2 Establish Procedures for Operating and Maintaining Post-Construction BMPs (Part II.B.5.a.iv & b.vi) BMPs are only effective as long as they are properly maintained. Table G describes the appropriate operation and maintenance (O&M) procedures and frequency for permanent BMPs. City owned and operated BMP facilities shall be maintained according to this schedule and document through the City’s GIS-centric tracking software. Privately owned and operated BMPs which connect to the MS4 shall be required to keep BMP O&M records on file and present the records to the City upon request. For more information regarding post-construction BMP maintenance, visit the following EPA website: http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=factsheet_results&view= specific&bmp=91 MCM 5 Supporting Table G – Stormwater Post-Construction BMP Maintenance Management Practice Maintenance Activity Schedule Detention/Retention Practices Ponds/Wetlands Cleaning and removal of debris Occasionally after large storms, (>2 yr event, typically biannually) Harvesting vegetation When vegetation causes 50% reduction of original open water surface area (annually) Repairing embankment and side slopes Annual or as needed Repairing control structure Annual or as needed Removing accumulated sediment from the forebay Remove when 50% of original volume has been lost (typically 5 years) Removing accumulated sediment from main cells of pond Remove when 50% of original volume has been lost (typically 5 years Infiltration Facilities Infiltration Trench Cleaning and removal of debris Occasionally after large storms, (>2 yr event, typically biannually) Mowing and maintaining vegetated areas Annually or as needed Sediment cleanout Annual or as needed Repairing or replacing stone aggregate Annual or as needed Maintaining inlets and outlets Annual or as needed Removing accumulated sediment from forebays Remove when 50% of original volume has been lost (typically 4 years) Page D3 Management Practice Maintenance Activity Schedule Infiltration Basin Cleaning and removal of debris Occasionally after large storms, (>2 yr event, typically biannually) Mowing and maintaining vegetated areas Annually or as needed Sediment cleanout Annual or as needed Removing accumulated sediment from forebays Remove when 50% of original volume has been lost (typically 3 to 5 years) Filtration Facilities Sand Filters Remove trash and debris from control openings Annual or as needed Repair leaks from the sediment chamber As needed (annually) Remove top few inches of sand and cultivate the surface when filter is clogged As needed (annually) Clean out accumulated sediment from the filter bed When depth reaches ½-inch or filter takes longer than 24 hours to drain (typically 3 to 5 years) Clean sediment from sediment chamber When depth reaches 12 inches (typically 3 to 5 years) Dry swales, grassed channels, biofilters Mowing and removing debris/litter Annual or as needed Stabilize erosion Annual or as needed Manage nutrient and pesticide use Annual or as needed Dethatch swale bottom Annual or as needed Disc or aerate swale bottom Annual or as needed Scrape swale bottom and remove sediment to restore to original condition 5 years or as needed Seed or sod to restore ground cover 5 years or as needed Filter Strips Mowing and removing litter/debris Annual or as needed Manage nutrient and pesticide use Annual or as needed Aerate soil Annual or as needed Repair erosion or sparse cover Annual or as needed Bioretention Repair erosion Biannually or as needed Mulch void areas Biannually or as needed Remove and replace dead vegetation Biannually or as needed Water plant material As needed Remove mulch and apply a new layer Annually Page D4 Develop a Plan for Site Plan Review (Part II.B.5.a.v & b.ix) A drainage plan ordinance and standards manual will only be effective with adequate site plan review and inspection procedures. The Phase 2 Stormwater NPDES rule requires a plan review for water quality related issues. Plans will be reviewed for compliance with the Engineering Standards. The reviewer will review/verify the following, at a minimum:  Drainage area,  Post-development conditions match pre-development,  BMPs are appropriate and are designed, sized and located properly,  BMPs are adequate for future phases/development,  O&M manuals are complete and adequate, and  LID techniques are employed, as applicable. A sample Stormwater Post-Construction BMP Plan Review is presented below. All construction projects meeting the thresholds established in the ordinance (greater than 1 acre land disturbance or new or redevelopment projects that include greater than 5000 square feet of impervious area) will be reviewed for post-construction BMPs. Develop a Plan for Post-Construction BMP Inspections (Part II.B.5.a.vi & b.x) A drainage plan ordinance and standards manual will only be effective with adequate site plan review and inspection procedures. Post-construction BMPs may only be used once appropriate vegetation has been established and construction debris/sediment has been removed. Construction site BMPs will only be removed once the permanent post-construction BMPs are approved by the City. Final plat will be approved and the property will be annexed by the City, if applicable, only after post-construction BMPs are deemed functional and properly constructed by the City. The City will inspect each permitted site prior to final acceptance and before permanent BMPs may be utilized. In addition, the City will inspect City owned and operated facilities according to the Utility Maintenance Department’s O&M schedule. The City will also inspect a minimum of 10 privately owned BMPs annually, primarily determined by complaints received by the Department. Additional inspections may be conducted on an as required basis, including but not limited to: public complaints, violation follow-up, inspector concerns/drive-bys, etc. Post- construction BMPs will be tracked using the GIS-centric software utilized by the City for mapping and maintenance requirements. A sample Stormwater Post-Construction BMP Inspection Report is presented below. Any violations observed during the site inspection will be handled as indicated in the ordinance. Page D5 Stormwater Post-Construction BMP Plan Review Project/Development Name: File No: Review Date: Reviewed by: Plan Review Checklist Estimated drainage area? Does post-development runoff match pre-development conditions? Are post-construction BMPs required at the site? What BMPs are to be installed? Where? Are identified BMPs and locations appropriate for flows and conditions? Will BMPs be adequate for future development? Are existing drainage ways maintained and utilized? Are BMPs properly sized and designed per Engineering Standards? What LID techniques are in place for first 0.5 inches of rainfall? (Required after January 1, 2012) Are BMP O&M Manuals complete and appropriate? Is the BMP operator identified? Are procedures in place for maintaining BMPs after property transfers? Application: __ Approved __ Denied Reason/Comments: _________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ Page D6 Stormwater Post-Construction BMP Inspection Report Development Name: File No: Inspection Date: Time: Inspected by: BMPs Onsite Detention/Retention Ponds Filtration Infiltration Inspection Checklist Yes No NA Have the temporary construction BMPs been removed? Were permanent BMPs installed according to design? Are permanent BMPs ready to properly treat stormwater runoff? (i.e. Are sand filters free of construction debris? Is vegetation adequately established in swales, wetlands, ponds, etc.?) Are O&M records present and up to date? What LID technique is employed for first 0.5 inches of rainfall for sites constructed after January 1, 2012? Are embankments adequately maintained? Vegetated or armored; free of erosion, burrows, unauthorized vegetation; free of leaks. Is debris properly cleaned from BMP, inlet and outlet pipes, spillways, etc.? Are risers, spillways, and drainage pipes adequately maintained? Free of debris; free of sediment; free of rust, holes, cracks; valves operate properly. Is the pond adequately maintained, if present? Free of odors, debris, and unwanted vegetation; visible sheen present; desired vegetation present. Are sedimentation bays adequately maintained, if present? Free of odors, debris, and excess sediment. How deep is sediment? Should be cleaned once sediment reaches 50% of sediment design depth. Is the facility in good repair? Inlet and outlet pipes/structures; banks; concrete; fence; access Is vegetation properly maintained and appropriate? Does the basin dewater properly between storms? Is oil and grease present or previous evidence of oil and grease present? Comments: _______________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ Verbal/Written notification given to: Report by: Date: Page D7 Establish Procedures for Low Impact Development for First 0.5” of Rainfall from a 24-hour Storm (Part II.B.5.a.vii) Infiltration systems are discussed in the Engineering Standards. Appropriate low impact development techniques for this requirement and discussion about each are presented below.  Rain gardens – Typically used on small scale projects, such as single-lot residential or commercial properties to infiltrate runoff water and use it to water gardens of native plant species  Cisterns or rain barrels – Typically used on smaller sites by connecting the downspout to a barrel for storage. Cisterns have a valve located at the bottom of the barrel to allow gravity flow to water grass and plants during drier weather. This system could possibly be modified to contain large volumes of water from larger sites and then pump the water to the desired location.  Green roofs – Vegetated building roofs. These roofs typically store rainwater on the roof to water plants also located on the roofs. The roofs require additional structural design considerations to ensure the weight of the water/snow, vegetation, and soils are accounted for. These roofs typically increase building insulation.  Permeable and porous pavements – Allows runoff to infiltrate over the site instead of runoff from roads, parking lots and other typically impermeable surfaces. This technique often requires additional maintenance to ensure proper operation. This technique is also limited in cold weather climates.  Grass buffer strips and bioinfiltration swales - Biofiltration swales and grass buffer strips both act to filter stormwater. These “biofilters” must be vegetated with fine, close- growing, water-tolerant grasses. The vegetation must be established prior to biofilter use for stormwater management.  Infiltration swales and basins (currently included in Engineering Standards)  Bioinfiltration basins – Similar to swales and rain gardens, just utilized on a larger scale.  Evaporation pond – Store runoff until the weather can evaporate it. Requires large area and can cause undesired affects (mosquitos, drowning hazard, etc.) The City should evaluate which LID techniques they feel are appropriate to the City and implement and require these items prior to January 1, 2012 to ensure permit compliance. These items should be amended to the Engineering Standards.