Washington State Dept. of Ecology 3/27/2025

SSLAP – Lowell Snohomish River Road Agricultural Land ______________________________________________________________________________ ______________________________________________________________________________ 2 Metals and Organic Compounds There are trace amounts of metals and organic compounds found in most biosolids products. Some of the metals contained in biosolids are micronutrients essential for plant growth and include iron, copper, manganese, and zinc. Other nonessential elements, such as nickel, cadmium, and lead, are relatively immobile in the soil and remain in the surface soil after application. Trace organics remain in the soil where they are generally degraded by soil microorganisms. Trace organics are not readily taken up by plant roots and do not pose a significant risk to the food chain. The City of Everett’s most recent analyses are presented in Appendix C. Microorganisms Wastewater solids contain bacteria, viruses, protozoa, and helminths, all of which may be pathogenic. The treatment process reduces the concentration of these pathogens by maintaining conditions hostile to these types of organisms. The organisms that thrive under the treatment conditions out compete the potentially pathogenic organisms and digest or eat the wastewater solids. The digestion and stabilization process reduces the concentration of pathogens. Class B biosolids contain some pathogens, but levels have been reduced to protect human and environmental health when land applied. Class A biosolids are virtually free from pathogens. Pathogens remaining in Class B biosolids are exposed to sunlight, fresh air, and soil microbes. These conditions continue to reduce the risk that biosolids pose to human and environmental health. The City of Everett’s most recent analyses are presented in Appendix C. Vector Attraction Reduction Biosolids, as the remains of stabilized putrescible material, may attract vectors such as flying or crawling insects, birds, rodents, and other small vertebrates. These vectors can spread pathogens beyond the land application site boundaries and impact the surrounding environment. To reduce the biosolids’ attractiveness to vectors, Everett stabilizes its biosolids using an anaerobic process within the treatment ponds. Everett utilizes Option 1a under 40 CFR 503.33(b)(2) regulations, ensuring that less than 17% additional volatile solids are lost during bench-scale anaerobic batch digestion for 40 days at 30° to 37° Celsius. The City of Everett’s most recent analyses are presented in Appendix C. Solids Content Everett mechanically dewaters biosolids with centrifuges after aeration cell dredging, and solids concentrations typically range between 28% and 40%.