Addendum to Quality Assurance Project PlanStatus and Trends Monitoring of Marine Nearshore Mussels in the Puget Lowland Ecoregion for Stormwater Action Monitoring (SAM) 2021-2025

This addendum to the original Quality Assurance Project Plan (QAPP) Status and Trends Monitoring of Marine Nearshore Mussels in the Puget Lowland Ecoregion for Stormwater Action Monitoring (SAM) 2021-2025, updates several sections describing previous studies, criteria and standards for status assessment, project organization and schedule, list of candidate sites (2025/26 and 2027/28 surveys), field sampling procedures, laboratory processing of mussels, measurement quality objectives, and data management/verification. All sections from the original QAPP and those updated in this addendum apply to future surveys (after 2025) conducted under this ongoing SAM study. Future addendums will at minimum include updates to the project schedule and list of candidate sites for new surveys conducted. This long-term status and trends monitoring study will continue to provide a regional assessment of whether and how stormwater discharge and the stormwater management actions implemented in the region are affecting nearshore biota contaminants levels.