North Colfax Petroleum Contamination Site

The site is about 1,000 feet south of the Palouse River and east of the South Fork of the Palouse River. The site is made up of three main properties that are current or previous gas stations whose owners are jointly responsible for cleanup:

• The Colfax Grange Supply Company, Inc. property at 105 E. Harrison Street and 102 E. Tyler Street
• The PetroSun/Time Oil Co. property at 804 N. Main
• The Cenex property bordered on the north by Tyler Street, to the west by North Main Street, to the south by the railroad tracks and to the east by an unopened City of Colfax right-of-way

In 1999, Time Oil upgraded their facility and found soil and groundwater with petroleum contamination. They installed seven groundwater monitoring wells in 2001 and more in 2002, which detected petroleum in groundwater beyond their property boundaries.

At Ecology's request, Colfax Grange installed groundwater monitoring wells at their nearby property in 2004.

Prior to sampling these wells but also in 2004, Cenex overfilled their underground unleaded fuel tank. An unknown amount of fuel seeped into soil surrounding the tank. Colfax Grange notified Ecology of the leak.

In 2007, Ecology entered into an Agreed Order with the Colfax Grange Supply Company, Inc., CHS, Inc., and Time Oil Co., requiring these companies to conduct a Remedial Investigation (Addendum) and Feasibility Study. The purposes of these reports is to determine the extent and locations of contamination and evaluate cleanup options.

In 2013, Ecology published a draft Cleanup Action Plan providing details about the cleanup action selected and how the cleanup will be conducted. Three cleanup alternatives were evaluated to address contamination at the site. Ecology selected Alternative 1, monitored natural attenuation, which is allowing contamination to dissipate through natural processes, for all three properties.

Ecology responded to public comments on the draft cleanup action plan and finalized the plan in June 2013. Cleanup is ongoing.