Lake Waco is a primary water source for the citizens of Waco, Texas, a growing college town. The watershed surrounding the lake has the highest concentration of dairy farms anywhere in the state, which means high nutrient loadings and algae growth. When the algae bloom, they release the organic compound geosmin, which gives the water an unpleasant taste and odor.
Prior to 2005, potable water from the lake flowed into two separate water treatment plants (WTPs): One had a 42-million-gal-per-day (mgd) capacity, and the other held 24 mgd. City officials found the existing facilities were not able to correct the geosmin problem, making the water virtually undrinkable at points throughout the year.
While water quality was an issue, the city also wanted to expand its capacity for water treatment. City officials decided a dissolved-air flotation (DAF) plant was the answer to both questions. The first step was getting regulatory approval for the idea. This led to a series of five pilot studies, which gained the desired endorsement and also increased the load rating from the standard 6 gal per minute (gpm) per square foot to 12 gpm per square foot; the increase resulted in approximately $10 million in construction cost savings.
In 2005, work began on Texas’s first DAF plant. The building was sited directly adjacent to Lake Waco for quicker algae removal. To prevent stray odor from escaping, the design team covered the DAF cells, supplied by Leopold. Trapped air then was blown directly into the lake to reduce the algae infestation and improve fishing.
The design team wanted to make the new plant as inconspicuous as possible, which led them to build 75% of the buildings underground, including the ozone facilities and balancing basins. The DAF plant was completed in June 2011.
The original WTPs were kept intact, with new biological filters installed to help remove organic carbon after ozonation. Residents have noticed a marked difference in water quality, as evidenced by blind taste tests conducted by a local newspaper.
“This project has been a great win for everybody,” said Brain Fuerst of CH2M Hill. “The water quality improvement has been incredible. Water quality has gone from a source of woe to a source of pride for the city of Waco.”