Resolution 8245 - Laserfiche WebLink

City of Everett • 2024 Comprehensive Sewer Plan • October 2025 Executive Summary • ES-12 a consequence level that identifies the impact to the sewer service if the pair were to occur. The City identified a total of 65 prioritized threat-assets pairs, shown in . Results of the sewer system evaluation inform the Capital Improvement Plan. Water Pollution Control Facility The WPCF information contained in the 2024 Plan was taken from the 2021 Facilities Plan. The Facilities plan assessed the existing and projected future flows and loads through the year 2040 for the base condition (annual average), maximum month dry weather, and maximum month wet weather for flowrate, BOD, TSS, ammonia, and total Kjeldahl nitrogen (TKN), as summarized in Chapter 8. The WPCF is located on Smith Island in the northern portion of the City and was constructed in 1960 as an oxidation pond. The WPCF was upgraded over time to include a conventional secondary treatment process. The WPCF is designed to treat flows up to 27 million gallons per day (MGD) under low river levels (dry weather) maximum month conditions and 40 MGD under high river levels (wet weather) maximum month conditions, with corresponding influent loading under low river/high river conditions of 75,000/83,000 lbs/day biological oxygen demand (BOD) and 68,000/89,000 lbs/day total suspended solids (TSS). The WPCF splits influent flow into two interconnected “plants”, the South Plant and North Plant. The South Plant contains a conventional secondary treatment process with primary clarifiers, trickling filters, secondary clarifiers, aeration cells (AC), and chlorination system to treat base flows from the collection system. The North Plant contains the original oxidation pond, a polishing pond, and a disinfection system to treat peak flows associated with the combined sewer system. The water treated in the North Plant is discharged to the Snohomish River, and water treated in the South Plant is discharged to the Port Gardner Bay outfall. In addition, there are 13 permitted combined sewer outfalls which are located throughout the collection system as described in Chapter 6. The 2021 Facilities Plan evaluated and documented equipment condition, redundancy, operation, and resiliency. The Facilities Plan also evaluated the capacity of the plant and evaluated the risk at the plant due to natural hazards. The condition evaluation process assigned a score for plant components that considered equipment condition and criticality. The result shows that the following locations have equipment that requires critical needs: headworks, primary treatment, trickling filters, solids contact, secondary clarifiers, South Effluent Pump Station (SEPS), aerated cell two (AC2), oxidation/polishing, Final Effluent North (FEN), odor control system, increased current cathodic protection system, and roadway. The risk evaluation process considered the risk to the WPCF associated with seismic events and climate change. The evaluation found that the diversion structure, headworks, and dechlorination building are at higher risk during a seismic event and should be further evaluated. Climate change will result in increased rainfall intensity and sea level rise, and which could impact the WPCF. A biological process model and hydraulic model were developed to evaluate the capacity of each unit process through the year 2040 based on current operations and considered the potential actions required in response to the currently under appeal PSNGP. The results indicate that secondary clarifiers, north and south effluent pump stations, and lagoon/aeration cells will not have adequate capacity through 2040.