King County LOOP CASE STUDY

In 2023, King County through HDR released a tender for a pilot composting facility as part of its Loop biosolids program. The objective was to perform a 5 year pilot project to explore the market demand for a Class A biosolids compost product, as part of Washington State Department of Ecologies objective of having 100% beneficial use of biosolids. The facility needed to have minimal environmental impact, be compliant with King Counties strict tendering requirements, and work on a small footprint.

Key requirements included:

• A pilot-scale composting system capable of producing high-quality, pathogen-free compost from biosolids.
• Odor control was essential, as the County aimed to prove that biosolids composting could be conducted without negatively impacting nearby communities.
• The facility needed to minimize runoff and oversaturation through effective moisture control and structural protection.
• Integration of mixing equipment, aeration systems, and real-time monitoring to support performance tracking and pathogen destruction.

The tender process was highly competitive, with very stringent technical, contractual, and documentation standards established by King County and HDR. Successfully navigating the intensive submittal and compliance process was a critical challenge for any selected vendor.

Green Mountain Technologies (GMT), in partnership with COP Construction, was selected through the competitive tender to provide a complete composting system and collaborate on facility implementation.

GMT delivered:

• A fully integrated 8-zone reversing Aerated Static Pile (ASP) system using pipe-on-grade aeration, specifically designed for biosolids.
• A high-performance feedstock mixer to ensure consistent blending of biosolids and bulking materials.
• Our COMPDACs™ control system with wired temperature probes for automated process control and data capture.
• A hoop house structure over the active composting area to protect the piles from excess moisture and support year-round operations.

In addition to meeting the technical and operational goals, GMT successfully adhered to the demanding project timeline and fulfilled all documentation, submittal, and compliance requirements outlined in the tender. Our ability to work within the rigorous framework established by HDR and King County was a key factor in the project’s success—allowing the facility to be commissioned on schedule and in full regulatory alignment.