This memorandum provides design guidance to King County Wastewater Treatment Division (KCWTD) and Seattle Public Utilities (SPU) for presettling upstream of bioretention facilities that prioritizes effectiveness and the consolidation of presettling practices installed and related maintenance activities. Guidance is based on analyses of existing bioretention and proprietary and non‑proprietary presettling BMP effectiveness; a science review of basin particle production and settling; and KCWTD and SPU’s policies, procedures, and standards for capital projects.