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e No.21-Maintenance Standards and Procedures for Bioretention Facilities. Note that the Inspection and routine maintenance frequencies listed below are recommended by Ecology.They do not supersede or replace the municipal stormwater permit requirements for Inspection frequency required of municipal stormwater permittees for"stormwater treatment and flow control BMPs/facilities." Maintenance Recommended Frequency. Condition when M•Intenanoe Is Needed Action Needed Component Impaction Routine (Standards) (Procedures) Maintenance Facility Footprint Earthen side slopes B,S Erosion(gullies/rids)greater than 2 Inches deep around •Eliminate cause of erosion and stabilize damaged area(regrade,rock,vegetation,erosion control matting) and berms Inlets,outlet,and alongside slopes •For deepchannels or cuts over 3 Inches in( pending depth),temporary erosion control measures should be put in place until permanent repairs can be made. •Properly designed,constructed and established facilities with appropriate flow velodties should not have erosion problems except perhaps In extreme events.If erosion problems persist,the following should be reassessed:(1)flow volumes from contributing areas and bioretention facility sizing;(2)flow velocities and gradients within the bodily;end(3)flow dissipation and erosion protection strategies at the facility Inlet A Erosion of sides causes slope to become a hazard Take actions to eliminate the hazard and stabilize slopes A,S Settlement greater than 3 Inches(relative to undisturbed Restore to design height sections of berm) A,S Downstream face of berm wet,seeps or leaks evident Plug any holes and compact berm(may require consultation with engineer,particularly far larger berms) A Any evidence of rodent holes or water piping In berm •Eradicate rodents(see Pest condor) •Fill holes and compact(may require consultation with engineer,particularly for larger berms) Concrete sidewalls A Cracks or failure of concrete sidewalls •Repair/seal cracks •Replace it repair is Insufficient Rockery sidewalls A Rockery side walls are insecure Stabilize rockery sidewalls(may require consultation with engineer,particularly for walls 4 feet or greater in height) Facility area All maintenance Trash and debris present Clean out trash and debris visits(at least biannually) Facility bottom area A,S Accumulated sediment to extent that infiltration rate Is •Remove excess sediment reduced(see Tended water')or surface storage capacity •Replace any vegetation damaged or destroyed by sediment accumulation and removal significantly impacted •Mulch newly planted vegetation •Identify and control the sediment source(If feasible) •If accumulated sediment is recurrent,consider adding preset/ement or instating berms to create a forebay at the inlet During/after fall leaf Accumulated leaves in facifdy Remove leaves B there is a risk to clogging outlet structure or water flow is impeded drop Low perneabflity A,S Sediment,vegetation,or debris accumulated at or blocking Clear the blockage check dams and (or having the potential to block)check dam,flow control weirs weir or orifice A,S Emden and/or undercutting present Repair and take preventative measures to prevent future erosion and/or undercutting A Grade board or top of weir damaged or not level Restore to level position •Frequency:A•Annually;B-Biannually(twice per year);M-Monthly;W.At least one visit should occur during the wet season(for debris/clog related maintenance,this inspection/maintenance visit should occur in the early fall,after deciduous trees have lost their leaves);S=Perform inspections after major storm events 124-hour storm event with a 10.year or greater recurrence interval). IPM-Integrated Pest Management ISA-International Society of Arboriculture Volume V—Runoff Treatment BMPs—December 2014 4-54