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Foothill WTP Filter Upgrade Project,
City of Redding, Redding CA

View from inside filter plenum during installation of new filter underdrain system

The City of Redding operates the 28-mgd Foothill WTP treating surface water from the Sacramento River using conventional filtration and chlorine disinfection. The plant began experiencing blow-through of filter media in 2007 and was in need of immediate replacement of filter blocks and media. Additionally, the existing air scour system had been ineffective at providing adequate cleaning of the media during backwash. The existing air scour system was a passive air/water underdrain system which routed air through the filter plenum and through the filter blocks during a backwash.

A new dedicated air scour system was installed (Aries Managed Air System), which introduces air for air scour at the filter media/gravel bed interface to maximize the use of the energy in the air for scouring the media. The existing underdrain blocks were replaced with Roberts Infinity Underdrain system. The filter media was replaced with a new profile of sand and anthracite. Improved anticipated performance of the underdrain system allowed for deepening of the filter bed to provide better filtration with the same headloss profile. The finished filter media profile consists of 12-inches of filter sand and 20-inches of anthracite.

The project was fast-tracked through the design process in three months so that construction could commence in the winter of 2007-2008, as soon as demand from the facility began to drop (in October). Work on the facility could only occur during low-demand periods (October through March), so construction sequencing, timing and coordination with plant activities were critical. Water Works Engineers also provided inspection services during construction to ensure that the installation was accomplished in good order.