1001 N BROADWAY LEARNING RESOURCE CENTER 2026-01-15

Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) Maintenance Com- Recommended Frequency a Condition when Maintenance is Needed (Stand- Inspection Routine Main- ards) Action Needed (Procedures) tenance Erosion control at inlet A Concentrated flows are causing erosion Maintain a cover of rock or cobbles or other erosion protection measure e.( g., matting)to protect the ground where con- centrated water enters the facility(e.g., a pipe, curb cut or swale) Trash rack S Trash or other debris present on trash rack Remove/dispose A Bar screen damaged or missing Repair/replace Overflow A, S Capacity reduced by sediment or debris Remove sediment ordebris/dispose Clean orifice at . Plant roots, sediment or debris reducing capa- Clean pipe as least biannually city of underdrain Underdrain pipe needed (may need more fre • Jet clean or rotary cut debris/roots from underdrain(s) quent cleaning dur- • Prolonged surface ponding(see"Ponded • If underdrains are equipped with a flow restrictor e. — ing wet season) water ( g., orifice)to attenuate flows, the orifice must be cleaned regularly. Vegetation • Determine cause of poor vegetation growth and correct condition Facility bottom area Vegetation survival rate falls below 75%within first • Replant as necessary to obtain 75% survival rate or greater. Refer to original planting plan, or approved jurisdictional and upland slope veget- Fall and Spring two years of establishment(unless project O&M species list for appropriate plant replacements (See Appendix 3-Bioretention Plant List, in the LID Technical Guid- ation manual or record drawing stipulates more or less than ance Manual for Puget Sound, (Hinman and Wulkan 2012)). 75% survival rate). • Confirm that plant selection is appropriate for site growing conditions • Consultation with a landscape architect is recommended for removal, transplant, or substitution of plants • Remove any diseased plants or plant parts and dispose of in an approved location e. risk of spreading the disease to other plants ( 9 , commercial landfill)to avoid Vegetation(general) As needed Presence of diseased plants and plant material • Disinfect gardening tools after pruning to prevent the spread of disease • See the Pacific Northwest Plant Disease Management Handbook(Pscheidt and Ocamb 2016)for information on dis- ease recognition and for additional resources • Replant as necessary according to recommendations provided for"facility bottom area and upland slope vegetation". All pruning seasons • Prune trees and shrubs in a manner appropriate for each species. Pruning should be performed by landscape pro- (timing varies by Pruning as needed fessionals familiar with proper pruning techniques species) • All pruning of mature trees should be performed by or under the direct guidance of an ISA certified arborist A Large trees and shrubs interfere with operation of the • Prune trees and shrubs using most current ANSI A300 standards and ISA BMPs. Trees and shrubs facility or access for maintenance • Remove trees and shrubs, if necessary. • Remove standing dead vegetation • Replace dead vegetation within 30 days of reported dead and dying plants (as practical depending on weather/planting Fall and Spring Standing dead vegetation is present season) • If vegetation replacement is not feasible within 30 days, and absence of vegetation may result in erosion problems, temporary erosion control measures should be put in place immediately. • Determine cause of dead vegetation and address issue, if possible 2019 Stormwater Management Manual for Western Washington Volume V-Appendix -Page 1021