Since 2013, GSI has been helping the City’s Columbia Slough Sediment Program (CSSP) meet its regulatory requirements with the Oregon Department of Environmental Quality (DEQ) Environmental Cleanup Program.


The Columbia Slough Watershed’s long history of multiple land uses—including industrial, agricultural, and major transportation uses—resulted in widespread contamination of sediments and fish tissue (e.g., PCBs, DDT, metals). More than 200 City stormwater outfalls drain approximately 13 percent of the Columbia Slough watershed.  There are several pathways for contaminants from upland sites and City rights-of-way to enter the stormwater systems and be transported to the Slough. The City’s CSSP focuses on identifying potential sources of contaminants, working collaboratively with DEQ to use appropriate state and/or city authorities to control pollutants at the source, conducting long-term sediment and fish tissue monitoring, and constructing stormwater treatment facilities in selected areas.

GSI’s Solution

Our work on this project includes:

  • Working with BES to develop project strategies and approaches to identify and evaluate potential contaminant sources discharging via stormwater to the Columbia Slough through City outfalls.
  • Analyzing historical stormwater system as-builts, permits, and geospatial data to assess the system configuration and connections and thus identify potential sources of potential contamination.
  • Preparing focused stormwater basin sampling and analyses plans for submittal to DEQ.
  • Preparing basin characterization and source tracing reports for submittal to DEQ.
  • Support BES in preparing the 2015 Fish Tissue Sampling Data Report and the 2017 Sediment Analysis Report to comply with long term monitoring requirements.
  • Conducting research to document potential current and historical contaminant sources.
  • With WildRose Consulting, preparing a project database that captures 20 years of current and historical analytical chemistry data for stormwater, stormwater solids, sediments, fish tissue, and surface water. Database queries automatically screen data against applicable DEQ risk-based levels values and present results in tabular form or can be visualized in map view using Google Earth™.