Facility Site ID: 16655424 Cleanup Site ID: 3229

  • Site Status

  • Cleanup Started

Site Description & History

The SemMaterials site is in the historic Hillyard neighborhood and lies over the Hillyard Trough portion of the Spokane-Valley Rathdrum-Prairie Aquifer. The aquifer serves more than 600,000 residents in Washington and Idaho.

BNSF Railway Company, Koch Materials LLC, Marathon Oil Company, and SemMaterials, L.P., are responsible for addressing contamination at the site and paying to clean it up.

ERGON Asphalt & Emulsions, LLC, now operates the asphalt plant formerly operated by SemMaterials. The facility receives and stores petroleum products used in the manufacture of asphalt and sealants. The site has reportedly been used for petroleum-related operations since 1955.

Husky Oil Company of Delaware (now merged with Marathon Oil Company) operated the facility from the 1970s until 1982. Koch Materials operated the facility from 1983 to 2005. SemMaterials and its successors have operated the facility since 2005. BNSF Railway Company owns the property.
In December 1992, three petroleum storage tanks were removed from the northeast corner of the site. During the tank removal, petroleum-contaminated soil was found. Koch Materials notified Ecology. Soil borings were drilled to determine the depth of contamination. Contamination was found as deep as 125 feet.


Petroleumnaphthalene, and polycyclic aromatic hydrocarbons (PAHs) have been found in soil.


In 1993, Ecology conducted a site hazard assessment and ranked the site a three on the Hazardous Sites List. The Hazardous Sites List is a record of contaminated sites throughout the state that are ranked on a scale of one to five. One represents the greatest potential threat to human health and the environment; five represents the least potential threat. The site ranked a three because of the level of contamination in soil and the potential for aquifer contamination.

In 2008, Ecology entered into an Agreed Order with the responsible parties, requiring them to complete a remedial investigation and feasibility study. The purpose of the remedial Investigation was to gather information to determine the extent of petroleum-related contamination in soil and groundwater at the site. The purpose of the feasibility study was to evaluate cleanup alternatives and propose a preferred cleanup alternative.

In the Remedial Investigation and Feasibility Study (appendices) completed in 2013, the responsible parties presented four possible cleanup actions and recommended Alternative 2:
  • Alternative 1 – Take no further action beyond cleanup actions already completed at the site.
  • Alternative 2 (preferred by responsible parties) – Maintain the existing protective asphalt cover over the Northeast Tank Farm area, construct an additional cap where a soil boring was taken to prevent contact with contaminated soil, monitor groundwater, and place an environmental covenant on the property to limit how it's used. Contamination would then be allowed to decrease naturally over time.
  • Alternative 3 – Remove and properly dispose of the uppermost 15 feet of contaminated soil, demolish some existing facilities, replace the Northeast Tank Farm asphalt cap, monitor groundwater, and place a restrictive covenant on the property to limit how it's used. Contamination would then be allowed to decrease naturally over time.
  • Alternative 4 – Demolish all facilities, remove and properly dispose of contaminated soil and materials at an off-site facility, and backfill excavated areas with clean soil.

Ecology received no comments on the Remedial Investigation and Feasibility Study. We will publish our preferred alternative in a draft cleanup action plan. When it's ready, it will be available for public comment for 30 days.

Legal 3
Document Title Document Date Document Type
Sem Materials LP Draft AO 3/30/2008 Agreed Order
Agreed Order for RI/FS - Signature page for B. Hansen 3/1/2008 Agreed Order
Sem Materials LP AO Joint Remedial Action BNSF Railway Company 3/1/2008 Agreed Order
Public Information 4
Document Title Document Date Document Type
Responsiveness Summary SemMaterials RI FS Reports 2013 4/24/2013 Responsiveness Summary
Responsiveness Summary Work Plan PPP SemMaterials 2008 3/18/2013 Responsiveness Summary
Fact Sheet SemMaterials RIFS Report 2013 3/11/2013 Fact Sheet\Public Notices
Sem Materials LP Fact Sheet AO Investigation 2/29/2008 Fact Sheet\Public Notices
Technical Reports 3
Document Title Document Date Document Type
SemMaterials L.P. Monitoring Well Decommissioning Report 12/11/2019 Groundwater Monitoring Report
RI FS Report Appendices A-L 2013 1/31/2013 Remedial Investigation / Feasibility Study
RI FS Report SemMaterials 2013 1/31/2013 Remedial Investigation / Feasibility Study
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

  • Eastern Regional Office
    N 4601 Monroe St
    Spokane, 99205-1265
    Please schedule an appointment to view print documents at this location.
  • Spokane Public Library Hillyard Branch
    4005 N. Cook St.
    Spokane, 99207
    This location may only have print documents available during open comment periods.

Contaminants 1

Contaminant Type
Surface Water
Non-Halogenated Organics - Petroleum Products-Unspecified C S
Confirmed Above Cleanup Levels
Below Cleanup Levels
This contaminant list was based on our best information at the time it was entered. It may not reflect current conditions at the site.