Pentachlorophenol (PCP) & Dioxins / Furans Remediation 

Native American Village Brownfield Site in Humbolt Bay, California


For generations, Tuluwat Village on Indian Island in California’s Humboldt Bay was considered the center of the world for the Wiyot Tribe, and was home to the Tribe’s annual World Renewal Ceremony. In 1862, settlers massacred the Wyot people and claimed the land on the island.

From 1870 to 1990, a dry dock and boat-repair facility operated there, polluting the soil and

Sustainability Award
EPA Region 9

Engineering Excellence Honor

American Council of Engineering
Companies, California

Wiyot Tribe.jpg


  • Remove the majority of pentachlorophenol (PCP) / dioxin-impacted soil, while minimizing the volume of soil disturbed

  • Find a technology to treat remaining contamination onsite without damage to contaminated shell mound

  • Prevent impacts to groundwater or surface water

  • Prevent human exposure to remaining soils impacted with metals, residual PCP, and dioxins

  • Restore the site for beneficial use


  • How to restore a highly contaminated site located in a remote and sensitive environment without impacting cultural artifacts for a Tribe with limited financial resources.

  • Minimal soil removal due to cultural significance and numerous artifacts of the site

  • No degradation of natural soil conditions, shell mound, potential artifacts, or ancestral remains could occur


  • Island in a tidally influenced bay

  • No direct road access or functional dock facilities

  • Access limited by boat at high tide or by foot from a bridge landing at low tide

  • No electricity or municipal water supply

  • Portion of contamination located in the intertidal zone


  • Conducted a bench scale treatability study to determine if PCP and Dioxin/Furan could be remediated by in situ chemical oxidation (ISCO), while meeting the requirements of the Tribe.

  • Cool-Ox® (calcium-peroxide blend) was selected for the bench scale treatability study due to its near neutral pH (~8) and proven ability to oxidize PCP in bay margin soils in the vicinity of the site.

  • Installed additional sheet pile to prevent potential runoff into the bay.

  • Implemented full-scale Cool-Ox® application for PCP and dioxins/furans.

limited soil removal

in situ treat

source area

cap residual



  • Dioxin/furan TEQ reduced by 84%

  • PCP reduced by 86.4%


  • Volume injected: 3,000 gallons of 14% Cool-Ox® solution 

  • 300 injection points

  • Treated 2,700 square-foot area from a depth of 0-5 feet below surface

  • Installed a permeable cap to prevent exposure to remaining metals in soil.


The comparison of soil analytical results from co-located pre- and post-injection soil samples indicated that Cool-Ox® was effective in reducing mass concentrations of COCs to below MCL target levels. To achieve mass reductions in concentrations of COCs, PCP mass had to be reduced by an average of 50%, and dioxins/furans by an average of 64%.

In August 2013, a protective cap was installed to limit exposure to residual contaminated sediments, which will allow continued restoration of the site for beneficial use by the Wiyot Tribe. In March 2014, the Wiyot Tribe held the first World Renewal Ceremony since February of 1860 at the restored Tuluwat Village.