WA ST Dept of Ecology Biosolids 9/8/2022

City of Everett, Public Works Department, Water Pollution Control Facility BIOSOLIDS SAMPLING & ANALYSIS PLAN 4 In 2021, a small area of AC2 was found to have a lower pond bottom than what was designed. To track any potential changes to the pond bottom, Ecology has requested a pond bottom survey be completed after dredging projects. Pond bottom surveys are conducted by City Staff using a Garmin device to mark GPS coordinates and take depth data using a rigid, incremented pole. The manual depth measurements and Garmin coordinates are compiled by City Staff and forwarded to the CAD division to produce bottom surveys similar to the hydrographic surveys. Any remarkable depths are called out by City Staff and can be marked on the bottom survey for further review, or liner sampling to verify the liner is intact. c. Biosolids Pond Sampling Overview The concentrations of nutrients, pathogens, and pollutants in biosolids vary over time and by location in the WPCF Ponds. The testing in this document was designed to follow Ecology regulations and to help plan for contract dredging removals and disposal. Chemical analysis of 40 CFR part 503 regulated metals, vector attraction reduction (VAR), and pathogen reduction provide the basis for establishing Class B biosolids. Nutrient concentrations determine agronomic rates when biosolids are land applied. All chemical analysis of biosolids follow the methods outlined in WAC 173-308-140. Everett produces approximately 2,000 dry tons of biosolids annually, which sets sampling per WAC 173- 308-150 at six times per year. However, because legacy solids within the Oxidation Pond have been surveyed, sampled, and characterized, Ecology has agreed that the Oxidation Pond will be sampled on an annual basis. As the characterization of solids within AC2 have been shown to be consistent in meeting Class B and Table 3 standards, AC2 has been approved to be sampled three times a year. Historically, the Recirculation Channel has been sampled with the Oxidation Pond. Considering the Recirculation Channel is closer in quality to AC2 solids than the Oxidation Pond legacy solids and are expected to be land applied in the same manner as solids from AC2, solids from the Recirculation Channel will also be sampled tri-annually. A summarized timeline of all pond and biosolids sampling is shown below in Table 2.