Confidential Client
Tacoma, WA, USA
Site photo


Our team is conducting a Remedial Investigation (RI) at the Superlon Plastics site, a former lead-arsenate manufacturing facility that is located on Tideflats in Tacoma, WA. The Tideflats were filled and developed in the early 1900s. Fill materials in the general area include dredge materials, native soils, and various types of waste and debris. The Superlon site shows evidence of historical filling activities; however, the nature and origin of all of the fill material is unknown.

We have developed work plans, conducted investigations, implemented interim actions, developed and implemented a Cleanup Action Plan strategy, and achieved cost recovery.

Our Solution

All work at the Superlon site is being conducted with future land use in mind. A conceptual land use plan was developed to support the development of a strategic plan focused on plausible risks, rather than unrealistic, unrestricted land use. This approach has been very effective in establishing remediation levels.

The RI was completed in phases to reduce cost and increase efficiency. Phase I involved sampling the site on a 75-foot grid system to a depth of 15 feet (i.e., the Model Toxics Control Act (MTCA) point of compliance for soil). Data was evaluated to determine the nature and extent of hazardous substances in soil, sediments, groundwater, and surface water, and to identify any data gaps that needed to be addressed to develop a risk assessment and feasibility study. Phases II and III involved collecting data to address the identified data gaps and installing a groundwater monitoring well network to determine groundwater conditions.


A survey was conducted in the Tide Flats to determine how often individuals such as utility workers could come into contact with soil at the site in the future. This information was used in combination with site characterization data to develop site-specific remediation levels which were approved by Ecology.

A feasibility study (FS) was also performed for the property. Remedial alternatives were identified and evaluated as part of the FS to select a cleanup action. Soil and perched water treatment pilot studies, which were designed and conducted to achieve remediation levels, were also documented in the FS. Ecology approved the FS and soil and perched water remedial actions are underway.