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Table - .21 o Maintenance Standards ® Bioretention Facilities (continued) Recommended Frequency a Maintenance Com- Condition when Maintenance is Needed (Stand- Action Needed (Procedures) ponent Inspection Routine Main- ards) tenance Determine cause and resolve in the following order: 1. Confirm leaf or debris buildup in the bottom of the facility is not impeding infiltration. If necessary, remove leaf lit- ter/debris. Excessive ponding water:Wateroverflows during 2. Ensure that underdrain(if present)is not clogged. If necessary, clear underdrain. storms smaller than the design event or ponded water inputs 3• Check for other water in groundwater, illicit connections Ponded water B, S P ( �9�.9 )• remains in the basin 48 hours or longer after the end of a storm. 4. Verify that the facility is sized appropriately for the contributing area. Confirm that the contributing area has not increased. If steps#14 do not solve the problem,the bioretention soil is likely clogged by sediment accumulation at the surface or has become overly compacted. Dig a small hole to observe soil profile and identify compaction depth or clogging front to help determine the soil depth to be removed or otherwise rehabilitated(e.g.,tilled). Consultation with an engineer is recommended. Minimize all loading in the facility footprint(foot traffic and other loads)to the degree feasible in orderto prevent com- paction of bioretention soils. ® Never drive equipment or apply heavy loads in facility footprint. Bioretention soil mix protection is needed when per- - Because the risk of compaction is higher during saturated soil conditions, any type of loading in the cell(including foot As needed forming maintenance requiring entrance into the facil- ity footprint traffic)should be minimized during wet conditions. • Consider measures to distribute loading if heavy foot traffic is required or equipment must be placed in facility.As an example, boards may be placed across soil to distribute loads and minimize compaction. ® if compaction occurs, soil must be loosened or otherwise rehabilitated to original design state. l nl a ts/Ou tl ets/Pipes A Water is not being directed properly to the facility and Reconfigure/repair blocks to direct water to facility and away from structure away from the inlet structure M during the wet season and Weekly during fall - before severe leaf drop Accumulated leaves at curb cuts Clear leaves(particularly important for key inlets and low points along long, linear facilities) (0/A storm is fore- casted A Pipe is damaged Repair/replace W Pipe is clogged Remove roots or debris A, S Sediment, debris,trash, or mulch reducing capacity o Clear the blockage Pipe inlet/outlet of inlet/outlet . Identify the source of the blockage and take actions to prevent future blockages Weekly during fall Accumulated leaves at inlets/outlets Gear leaves(particularly important for key inlets and low points along long, linear facilities) leaf drop Clear vegetation(transplant vegetation when possible)within 1 foot of inlets and outlets, maintain access pathways A Maintain access for inspections ® Consultation with a landscape architect is recommended for removal,transplant, or substitution of plants 2019 Stormwater Management Manual for Western Washington Volume V-Append&A-Page 1020