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The Mountain Home, Arkansas Water Treatment Plant had the ability to treat 8 million gallons per day and was nearing 80 percent of its rated capacity. The existing filters at the plant utilized “old” technology dating back to 1969, and the basins contained a dual media of anthracite and sand. With newer technology available, Garver recommended that a higher filtering rate could possibly be achieved by modifying the system with a mixed media and air/water backwashing. Ultimately, if the filter system could treat more water, it would eliminate the need to build additional and expensive basins during a future plant expansion.
The existing filters were rated at 2 gallons per minute per square foot of area (gpm/ft²). Garver recommended that testing be instituted to analyze a filtering rate at 4 gpm/ft². However, to reach this goal, the Arkansas Department of Health needed to approve the increase request.
Garver implemented a study to test and confirm the filtering capacity with mixed media and air/water backwashing. The project began in 2001 when pilot testing units were constructed at the treatment plant. The three-month test period indicated that the mixed media at the increased flow rate filtered as well and typically better than the existing dual media.
After reviewing the pilot plant results, the Arkansas Department of Health requested that a full-scale test be applied to one of the eight filters at the plant. Because the existing media was almost 10 years old and needed replacing, the City decided to place the mixed media in all the filters. In addition to changing out the filter media, an upgrade involved replacing the existing filter bottoms, substituting the surface wash system with air scour capabilities, replacing the backwash troughs to allow for media expansion during the backwash cycle, and modifying the pipes and valves to handle the increased capacity.
A full-scale study collected data for more than a year, and after reviewing the filter rate data, the Arkansas Department of Health approved the Mountain Home water treatment plant filtering rate to 4 gpm/ft². |
