Facility Site ID: 61559576 Cleanup Site ID: 9890

Current Status

The Washington Department of Ecology held a public comment period for the Riffe Lake/Kosmos Flats site between May 25 and June 23, 2020.  One comment was received.  The responsiveness summary can be found at the following link:

Riffe Lake/Kosmos Flats Responsiveness Summary

The Agreed Order became effective on August 19, 2020. Tacoma Power will prepare a remedial investigation, feasibility study, and a preliminary cleanup action plan.  These documents will be available for public comment in the future.

Site Background

A fact sheet has been prepared about this site and can be viewed HERE.

The town of Kosmos was flooded with water in 1968 to create Riffe Lake, a part of Tacoma Power’s Cowlitz River Project.  Residents were relocated and business including a lumber mill were abandoned and demolished.  Currently, the surrounding land and water are used for recreational activities such as boating, camping and a hang-gliding landing area.

 In 1992, Tacoma Power removed two underground storage tanks (USTs) related to the lumber mill. One of the tanks located near the former mill foundation contained petroleum product and halogenated hydrocarbons.  Petroleum product contaminated surrounding soil at levels exceeding state cleanup standards.  A total of 87 cubic yards of contaminated soil was removed and disposed of appropriately. 


In April 2019, the Department of Ecology (Ecology) was notified about seeps of Bunker C oil found on the eastern bank of Rainey Creek near Champion Haul Road and at the former lumber mill area. In December 2019 as an emergency cleanup action, Tacoma Power capped the seeps to keep oil from moving into Rainey Creek before the water level in Riffe Lake inundated the site. They collected soil and groundwater samples from test pits and soil borings and found other contamination that include diesel, gasoline, and heavy oil. Approximately 11,000 tons of impacted soil were removed and disposed of appropriately.

Possible sources for the seeps are from former lumber mill operations, including old underground storage tanks and piping, or petroleum-impacted soil. 

Contact with these hazardous substances can be harmful to human health and the environment.  Tacoma Power has closed the area to protect the public until cleanup is complete.
Legal 4
Document Title Document Date Document Type
Kosmos AO 16955 Schedule Extension 2/3/2022 Administrative Order on Consent Amendment
Agreed Order DE16955 Change of Designated Tacoma Power Project Coordinator 3/10/2021 Agreed Order Amendment
Agreed Order 8/19/2020 Agreed Order
Riffe Lake Site - Final Determination of PLP - Tacoma Public Utilities 2/13/2020 Final Potentially Liable Person Status Letter
Public Information 7
Document Title Document Date Document Type
Riffe Lake/Kosmos Flats Responsiveness Summary 8/1/2020 Responsiveness Summary
Riffe Lake Comment Period Comment _ Squaxin Tribe 6/24/2020 Responsiveness Summary
Riffe Lake Comment Period Contact List 6_24_20 6/24/2020 Responsiveness Summary
Public Participation Plan Riffe Lake/Kosmos Flats 5/15/2020 Public Participation Plan
Riffe Lake/Kosmos Flats Fact Sheet 5/12/2020 Fact Sheet\Public Notices
Riffe Lake Photo Log from TCP 5/2/2019 Multimedia
Riffe Lake Photo Log from Spills 5/1/2019 Multimedia
Technical Reports 5
Document Title Document Date Document Type
Kosmos Town Site - Project Manager Change Notice 10/25/2022 Site Specific Administrative Document - other (Administrative correspondence)
RI Work Plan Kosmos Mill Oil Cleanup 12/30/2021 Remedial Investigation Work Plan
Kosmos Town Site - Kosmos Data Summary Report 2/19/2021 Site Specific Technical Document - other
Kosmos Town Site - Kosmos Data Summary Report App G 12/20/2019 Site Specific Technical Document - other
RI Work Plan Kosmos Mill Oil Cleanup 12/6/2019 Remedial Investigation Work Plan
There may be more documents related to this site. To obtain documents not available electronically, you will need to make a public records request.

Places to see print documents

  • Southwest Regional Office
    300 Desmond Dr SE
    Lacey, 98503-1274
    Please schedule an appointment to view print documents at this location.

Contaminants 3

Contaminant Type
Soil
Groundwater
Surface Water
Air
Sediment
Bedrock
Halogenated Organics - Polychlorinated biPhenyls (PCB) B
Halogenated Organics - Other Halogenated Organics B
Non-Halogenated Organics - Petroleum-Other C S C C
S
Suspected
C
Confirmed Above Cleanup Levels
B
Below Cleanup Levels
RA
Remediated-Above
RB
Remediated-Below
R
Remediated
This contaminant list was based on our best information at the time it was entered. It may not reflect current conditions at the site.