The City of Tualatin enlisted GSI’s expertise to determine if they could use aquifer storage and recovery (ASR) as a drinking water supply source. During initial pilot testing, the well experienced plugging or bio-fouling, limiting ASR feasibility. The decreased well performance was identified quickly by the GSI team during the early phases of ASR testing. From there GSI worked to identify the source, develop a solution, and a well rehabilitation program.


The City of Tualatin provides water to more than 25,000 residents, as well as commercial and industrial customers. Historically, the City has purchased wholesale water from the City of Portland, which is delivered through conduits from Portland’s Bull Run reservoirs. Faced with increasing wholesale water costs, particularly during peak demand periods, the City decided to test ASR as a solution to manage water costs by injecting up to 100 million gallons of water into the aquifer every year. During initial pilot testing of the injection system, well performance indicated that the ASR well was experiencing plugging or bio-fouling, limiting ASR feasibility.

GSI’s Solution

  • GSI identified the decreased well performance during the early phases of ASR testing
  • Conducted water quality analyses.
  • Preliminary results indicated that a low residual chlorine concentration combined with a high total and dissolved organic carbon load in the Portland Bull Run water was contributing to the bio-fouling and nitrification in the distribution system.
  • Teamed with Murray Smith & Associates, Inc. and Confluence Engineering Group LLC to evaluate the operation of the City’s distribution system to eliminate the low chlorine residual and nitrification.
  • Developed a comprehensive well rehabilitation program, which used both mechanical redevelopment and chemical treatment, to restore the performance of the ASR well.
  • Installed a booster chlorination system to control biological growth during injection.

The City resumed full-scale operational testing of the ASR well in 2011, exceeding the 100 MG target storage volume for 2011 and experienced cost savings during peak demand periods.