Eau Claire Water Treatment Plant Phase II Improvements

Challenge

The City of Eau Claire’s water treatment plant has a rated capacity of 24 million gallons of water per day (MGD). Serving nearly 70,000 residents, the City has 16 operating wells that treat and pump approximately 3.5 billion gallons of water each year. In addition, the City performs more than 18,000 water quality tests per year.

Since its initial construction in 1952 and the filter addition in 1955, the City’s plant had received only minor improvements in its long service life. In recent years, the plant began experiencing deterioration of the filter underdrain system, filter media and back washing system. As a result, the City experienced water quality issues relating to breakthrough of iron and manganese at flow rates greater than 13 MGD.

Before the City could move forward, a critical question needed to be answered: “Should we build new or renovate?”

Solution

Setting the stage for water treatment plant improvements
The City partnered with SEH in 2014 to undertake a pilot test, identify the specific issues and determine the best-fit solution. The team performed pilot studies of filter media, including single silica media in combination with chemical oxidation and flocculation.

The pilot studies determined that a single filter media preceded by detention with plate settlers would allow the utility to remove manganese to well below secondary contaminant levels and more efficiently produce 24 MGD of high-quality water at the necessary rated capacity. The pilot studies also helped determine that rehabilitating the processes at the plant rather than building a new plant would be the most strategically sound and cost-efficient solution.

Ultimately, the SEH team identified and outlined a prioritized improvements list for plant’s needs over a period of several years. This project formed the basis for the City’s multi-year improvements program. This improvements program included Phase I construction and renovation (specifically, rehabilitation of the existing gravity filters and backwash systems, taking place between 2016-2017), as well as Phase II of the project explored below.

Phase II – Sedimentation basin improvements; design and construction
Following the pilot studies and careful evaluation, the City also partnered with SEH to plan, design and oversee construction for the needed Phase II renovations to its water treatment plant. Design took place between 2017-2018, with construction beginning in 2019. The renovations were completed in 2021.

Overall, the project has consisted of improvements to the pre-filter treatment processes to increase manganese solids removal in the sedimentation basins. The SEH team provided conceptual design with proposed costs and an engineering report, followed by the design and preparation of bidding documents.

Major project elements include a complete renovation of the two existing, 1 million gallon sedimentation basin tanks to include the following added water treatment processes:

• Chemical feed improvements to accommodate the new process treatment design
• Rapid mixers and rapid mixing addition at the headworks
• Installation of four-stage flocculation and Lamella plate settlers to help settle the manganese and iron more efficiently ahead of the filters
• Installation of an automatic sludge collection system below the plate settlers
• Installation of a settling basin overflow system to meet Wisconsin DNR code
• Lime feed modifications to the existing lime chemical room and new slurry pumps

Other major improvements to the plant include:

• Construction of new concrete walls and tank improvements in the existing sedimentation tanks to create the new flocculation process and to create structural supports for the plate settlers, flocculation mixers and rapid mixers Construction of the superstructure above the existing basins to house the new equipment and process
• Pre-cast walls with stained concrete exterior to match the existing limestone architectural treatments, and pre-cast roof planks for quick construction
• Sludge pump building improvements
• Construction of a new chemical feed room for polymer addition and a future lime storage tower
• Construction of a new electrical room and major electrical service upgrades requiring staged shutdowns of the plant operation

Collective results and budgeting efficiencies
The SEH team’s efforts incorporated water process engineering for more efficient processes to meet clean water standards; mechanical and electrical engineering to power and drive the new treatment system components and support the new buildings; and architectural design and structural engineering to renovate structures and tanks to support the system.

Uniquely, as touched on above, the team matched the limestone exterior of the tanks to the existing plant by integrating pre-cast concrete panels that are stamped on the outside with the limestone pattern to match the 1950s architecture of the limestone, hand-placed wall exterior.

In addition, the team supplied economic development assistance to secure key funding. The City’s budget required the project to be constructed in two phases. Planned by the SEH team, this approach, has enabled the project to move forward while keeping the City’s budget intact.

“Eau Claire” is the singular form of the original French name “Eaux Claires” – meaning “clear waters” in honor of the Eau Claire River. The City’s and SEH team’s collective efforts will preserve and renew clean, clear water for the City’s ~70,000 residents for generations to come.