WA ST Dept of Ecology Biosolids 9/8/2022

City of Everett, Public Works Department, Water Pollution Control Facility BIOSOLIDS SAMPLING & ANALYSIS PLAN 1 1. Introduction The Everett Water Pollution Control Facility (WPCF) is comprised of a parallel treatment system consisting of a Trickling Filter/Solids Contact (TF/SC) process and an Aeration/Oxidation Pond lagoon system. These parallel systems are connected by Aeration Cells 1 and 2. Biosolids are the treated solids produced by wastewater treatment. Everett employs a biological treatment process that uses endogenous microbes to oxidize organic components of wastewater, including pathogens. Everett’s biosolids are composed of organic and mineral particulates that have settled out of the process and contain nutrients, microorganisms, and digested solids which can be utilized in land application as a soil amendment. The mission of the Everett Biosolids Management Program is to safely and beneficially reuse the biosolids produced at the WPCF. The WPCF Biosolids Management Program also ensures optimal operation of the lagoon system for both biosolids and water treatment. This document provides information on the WPCF’s plan for sampling and analysis of biosolids as required under the Biosolids General Permit. a. Lagoon Treatment Overview The WPCF is a combined TF/SC treatment facility and lagoon system used for both solids storage and biological wastewater treatment. The lagoon system consists of two mechanically aerated cells in series (AC1 and AC2) followed by an unaerated Oxidation Pond and a Polishing Pond. The TF/SC plant receives part of its flow from aerated lagoon effluent (ALE). See Figure 1. AC1 and AC2 are two 14.7-acre lagoons in series, each with a volume of approximately 33.5 million gallons. AC1 receives water from three sources: 1. Secondary clarifier effluent (SCE) in excess of the South Effluent Pump Station discharge, 2. Effluent from the primary clarifiers (PCs) in excess of the process flow through the TF/SC, and 3. Screened and partially de-gritted wastewater from the Headworks (HDWKs), during periods of unusually high flow, when plant influent exceeds the primary clarifier influent maximum. AC1 uses mechanical aeration to control odor and to move solids from AC1 to AC2; because it is unaerated, solids accumulate at a higher rate in AC2 than AC1. Primary Clarifier Sludge (PCS) and Waste Secondary Sludge (WSS) are introduced to AC1 or AC2 through ports 1-6. Ports 1-5 may be used to discharge both PCS and WSS; by design, Port 6 can discharge only WSS. By selecting the discharge ports, plant staff can introduce solids at different points in the aeration cells. Port selection, along with aerator locations, encourages solids to deposit and stabilize in AC2. Between dredging events, ports 5 and 6 are typically used. Two months prior to dredging, PCS and WSS discharges are eliminated at AC2 and shifted to ports in AC1, typically port 2. By discharging solids in AC1, newer and less treated solids are prevented from mixing with the solids that have been stabilizing in AC2. Solids are dredged from AC2 typically every three years.