Title
MINT FARM WATER SUPPLY IMPROVEMENTS - DISSOLVED OXYGEN ADDITION & INVESTIGATION OF SILICA REMOVAL TECHNOLOGIES
COUNCIL INITIATIVE ADDRESSED:
Provide sustainable water quality & environmental infrastructure
CITY ATTORNEY REVIEW: N/A
SUMMARY STATEMENT:
Earlier this year, four test sites along the Cowlitz River were explored to investigate horizontal collector wells as a potential source of water to replace the Mint Farm aquifer. The water quality from the four test sites was generally lower than the Mint Farm aquifer, prompting a decision by the City Council and Beacon Hill Water & Sewer District Commissioners to cease further study of alternate sources and focus instead on optimizing Mint Farm water quality. Several enhanced treatment technologies are available to improve water quality and address customer complaints. The most prolific objections tend to revolve around taste/odor issues and white deposits that are difficult to remove. Both of these issues are complex and distinct, there is no one remedy which will address both, and there are multiple technologies available to address each issue.
To improve taste and odor issues, dissolved oxygen (DO) addition is recommended. Based on an evaluation of life cycle costs and risk-benefit analysis, the preferred method for DO addition at the Mint Farm Regional Water Treatment Plant (MFRWTP) is aeration. Other DO technologies include bulk liquid oxygen, onsite generation, and hydrogen peroxide injection. Dissolved oxygen addition was previously evaluated at the pilot-scale level using liquid oxygen injected into sections of pipe removed from the water distribution system, and at the home-level using commercially available aeration equipment. The use of DO for corrosion control is common practice and the benefits of DO to reduce iron release from pipe scales and inhibit hydrogen sulfide reversion are well documented. Dissolved oxygen provides another weak but stable oxidant which, when slowly introdu...
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