The City of Stanwood wastewater treatment facility generates biological sludge that is treated in two 1.25-acre sludge stabilization ponds using an aerobic and facultative digestion process. This process reduces the mass and stabilizes the sludge to produce biosolids that can be beneficially used or disposed of as solid waste.

The Washington State Department of Ecology (DOE) requested that the City develop a long-term plan for the removal and disposal of the biosolids and a plan outlining future biosolids management practices. The Biosolids Management Engineering Report written by TetraTech was completed in September 2015; final version pending approval from DOE.