Clear Creek WWTP Rehabilitation and Expansion Project, Redding, California, United States of America

Chemical resistant coating applied to the ferric chloride foundation within the new chemical facility

Scheduled for completion in 2013, the major rehabilitation and expansion project currently underway at the Clear Creek WWTP will provide the city of Redding with a modern wastewater treatment facility that's able to meet expected demand up to 2025.

Treatment capacity at the plant will ultimately be increased to 151,500m³/day - more than doubling the current maximum peak flow - and energy efficiency will be improved.

The work involves repairing, rehabilitating or replacing existing equipment, enhancing biosolids treatment and disposal and augmenting and improving odour control measures at the plant. In addition, a number of new facilities will be constructed, including a new dissolved air flotation thickener (DAFT), ultra-violet building, outfall pipeline, blower building, administration block and laboratory.

The total cost of the entire project is anticipated to be around $71m.

Background to Clear Creek WWTP

"Solids are digested and then dewatered in large drying beds before being transported off-site for disposal."

The original plant was constructed in 1966 and underwent upgrading and expansion in 1977, to accommodate a dry weather flow of 33,000m³/day from May to October and a peak 62,000m³/day wet weather flow during November to April.

The existing plant design is largely conventional. Influent passes through bar screens before entering the primary clarifiers, subsequently undergoing secondary treatment in a series of aeration basins.

Filtration of the clarified effluent uses sand and crushed coal media, with chlorine being added for disinfection, followed by sulphur dioxide to neutralise the remaining chlorine prior to discharge to the Sacramento River.

Solids are digested and then dewatered in large drying beds before being transported off-site for disposal.

Having served the city since 1979 in its present form, the ageing works has now reached its design capability, leading the city to instigate the current project to rehabilitate the plant and extend its treatment capacity to meet the demands of the predicted future wastewater flows. Work began on the project towards the end of October 2006 and will be completed in seven phases, finally scheduled to finish by 2013.

Rehabilitation and modernisation project details

As part of phase one, a new 8in water pipeline was installed, coating was applied to the ferric chloride foundation within the chemical facility, electrical equipment was installed at the head-works and new piping was put in place from the chemical facility.

Also during this phase the two mechanically cleaned influent bar screens were replaced with new fine screen units, with an associated sluice and new processing equipment installed to wash, dewater and subsequently compact the screenings.

A new influent wastewater pump was also installed, along with a new biofilter system to control odour. The existing belt conveyor was demolished. A new chemical storage and feed facility was built, the existing chlorine and sulphur dioxide storage arrangements were renovated and a new toxic gas scrubber system was installed.

"The total cost of the entire project is anticipated to be around $71m."

Started in September 2007, phase two involved refurbishment of one of the facultative sludge lagoon ponds, the construction of a new access-way and the installation of a tie-in to the city's potable water supply.

Phase three began in December 2007 and was completed in 2010. The plant's existing dissolved air flotation thickener (DAFT) was refurbished and a new DAFT was built. The primary clarifiers were rehabilitated along with one of the pump stations, the head-works and aeration basin. The existing secondary clarifier was refurbished, the filters renovated and a new secondary clarifier constructed.

Phase four, which commenced in May 2008, involved expansion of the plant's diffuser and the construction of a new outfall and associated building work.

Phase five followed in July 2011, principally involving the conversion work to some of the existing ponds. One was converted to two wet weather storage ponds, another was turned into lined facultative sludge lagoons and two more were converted into drying beds. The works under this phase also include the extension of the filtration system and construction of a new digester. Phase five is scheduled for completion in April 2013.

The construction of a new ultra-violet building forms the entirety of phase six, while phase seven includes rehabilitating the facility's existing aeration basin and the construction of a new blower building.

Phase six started in March 2010 and was completed in December 2011. Construction works involved aeration basins, a blower building, chlorine contact basins, yard piping and digester crack repairs.

The final phase will involve building the new administration building and laboratory, together with rehabilitation of the non potable water system. Construction works for phase seven started in October 2012.

Contractors involved with Redding's wastewater treatment plant

The plant is owned by the city of Redding and operated by its wastewater utility. CH2M Hill is acting as the construction manager and engineer, with TICO Construction being the main contractor for the project. Project funding is being provided by city wastewater revenues and low-interest loans from the California Water Resources Control Board's State Revolving Fund.

The contract for phase six rehabilitation and expansion project was awarded to Auburn Constructors.

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