Clear Creek WWTP Rehabilitation and Expansion Project, Redding, California, USA

Scheduled for completion in 2012, 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 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 are to be constructed, including a new dissolved air flotation thickener (DAFT), ultra-violet building, outfall pipeline, blower building, administration block and laboratory.

The estimated cost of the first phase, which will be completed in October 2007 is $3.5m; the total cost of the entire project is anticipated to be around $71m.

BACKGROUND

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 eight phases, finally scheduled to finish in April 2012.

THE PROJECT

Currently, as part of phase 1, a new 8in water pipeline is being installed, coating applied to the ferric chloride foundation within the chemical facility, electrical equipment installed at the head-works and new piping put in place from the chemical facility.

Also during this phase the two mechanically cleaned influent bar screens will be 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 will be installed, along with a new biofilter system to control odour, and the existing belt conveyor will be demolished. A new chemical storage and feed facility is to be built, the existing chlorine and sulphur dioxide storage arrangements renovated and a new toxic gas scrubber system installed.

Scheduled to start in June 2007, phase 2 involves the 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. This phase is expected to be completed by the end of 2007.

Phase 3 will begin in July 2007 and is scheduled to take two years. The plant’s existing dissolved air flotation thickener (DAFT) will be refurbished and a new DAFT built. The primary clarifiers are to be rehabilitated along with one of the pump stations, the head-works and aeration basin. The existing secondary clarifier will be refurbished, the filters renovated and a new secondary clarifier constructed.

Starting in June 2008 and continuing through to February 2009, phase 4 involves the expansion of the plant’s diffuser and the construction of a new outfall and associated building work. Phase 5, which follows on in June, principally involves the conversion work to some of the existing ponds; one is destined to become two wet weather storage ponds, another will be turned into lined facultative sludge lagoons and two more will be converted into drying beds.

The construction of a new ultra violet building forms the entirety of phase 6, which is scheduled to span June 2008 to January 2010, while phase 7 includes rehabilitating the facility’s existing aeration basin and the construction of a new blower building.

This element of the project is scheduled to get underway in July 2009 and be completed by July 2011. The final phase, which is planned to run from October 2010 until April 2012, involves building the new administration building and laboratory, together with rehabilitation of the non potable water system.

KEY PLAYERS

The plant is owned by the city of Redding and operated by its wastewater utility. CH2Hill 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.

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