Alvarado Water Treatment Plant, San Diego, CA, USA

The summer of 2008 brings the start of Phase IV of the Alvarado water treatment plant’s major upgrade and expansion project,which will see the construction of a new ozone generation facility. Delivered in six phases over a period of 20 years, the scheme is intended to provide a state-of-the-art water treatment facility, with an expected useful life of 75 years and able to meet the anticipated needs of San Diego’s growing population until 2030.

The new ozone facility – which includes providing the ozone contactor and associated equipment, together with a building to house it – and the overlapping Phase III rehabilitation of the original sedimentation and flocculation basins are both scheduled for completion in 2010.

BACKGROUND

The Alvarado plant is the oldest of the three facilities responsible for supplying San Diego City, having been first brought into service in 1951. San Diego County Water Authority began to modernise the plant back in 1993, completing two new 80,000m³ drinking water storage tanks in 1997. The following year, the work received the American Society of Civil Engineers’ National Award and the American Public Works Association Project of the Year.

However, despite this success, changes in federal and state drinking water regulations coupled with the compliance order issued by the California Department of Health Services in 1997 made further upgrades essential. In November 1998, Phase I of the project began.

WORK TO DATE

Completed in 2003, Phase I was a major construction programme aimed at enhancing the chemical treatment facilities and pumping arrangements, which involved providing a number of new elements including a raw water blending vault, head-works with an associated rapid mix structure and eight filters. The eight pre-existing filters also underwent a series of upgrades, including the addition of filter-to-waste piping. Molecular chlorination disinfection facilities were installed, together with the construction of day tanks, bulk tanks and dosing facilities for both liquid polymer and ferric chloride.

In addition, facilities were constructed for dry polymer and potassium permanganate storage and dosing, while two pre-existing aqua ammonia tanks were relocated as part of the new provisions made for the finished water chemical treatment. New tanks and dosing facilities for sodium hydroxide were also built.

Other components of Phase I were the construction of a 4,300m³ wash-water supply tank, together with the buildings for effluent control, switchgear and the emergency generator. The Lake Murray raw water pump station required a complete tear-down and re-build, while the one at College Ranch underwent a programme of rehabilitation. The existing operations building was also upgraded and improved.

The demolition of the ageing and seismically unsafe Earl Thomas reservoir in 2002 marked the start of Phase IA. Stability in a region prone to earth movement was a key consideration in the design of its replacement and the effects of vertical, horizontal and overturning movements were important factors in selecting the new pre-stressed concrete tank.

Neoprene pads separate the roof and floor from the core-wall, which permits each to move independently in the event of an earthquake. Special cables have been used to control lateral seismic forces while allowing free movement of the wall under normal conditions. The new Earl Thomas tank measures some 124m in diameter and 11.5m deep, making it the largest of its kind in the world.

In addition to the tank itself, nearly 300m of tunnel was also constructed to accommodate the 1.5m diameter pipe which links it with the existing two 80,000m³ reservoirs. Connections were made to the phase I filters, via the effluent control also constructed in phase I.

Other work in this phase included improvements to the treatment plant entrance and site security, together with a car park and other amenities for visitors to Lake Murray. Phase IA was completed at the end of 2005.

Phase II ran from April 2004 to March 2007, when the ribbon was cut on the new flocculation and sedimentation basins, built along the south-eastern shore of Lake Murray. In addition to these basins, the electrical and control systems of the plant’s eight original filters were also upgraded as part of this element of the project. Work on the SD-17 pump station overlapped Phase II, starting in July 2005 and being scheduled for completion in June 2009.

REMAINING PHASES

The current Phase IV work to provide major ozone treatment facilities, which includes installing ozone generators, contactors and associated equipment, is expected to be completed by mid-2010. The year-long Phase III – which will upgrade and modernise the plant’s existing flocculation and sedimentation basins – overlaps Phase IV, and is also scheduled for completion in 2010.

The final phase of the project is principally a finishing stage, including shoreline landscaping, post-construction provisions for storm-water, final site improvements and the construction of a back-up ozone generator and pump. Phase V is scheduled to begin in the summer of 2012 and be completed by the end of the following year.

Further work is expected at the plant after the completion of the main project in 2013, including the possible construction of sludge processing facilities and eight new filters, but no formal decision has been reached, nor timeframe suggested as yet.

KEY PLAYERS

The plant is owned by San Diego County Water Authority. Design work was done by Malcolm Pirnie and Richard Brady Associates, with construction management by CH2M Hill and Parsons acting as programme manager.

Nielsen Dillingham Builders was the main Phase I contractor with Helix Electric, J.R. Concrete, Pacific Coast Steel, Murphy Coatings and Watkins acting as major subcontractors. C.E. Wylie is the prime contractor for Phase IA and DYK is the tank subcontractor. Other subcontractors included The Tunnel Group, Hurricane Fencing, American Standard Concrete Pumping and A.O.

Reed. Ameron, Northwest Pipe, and American Pipe were the manufacturers and suppliers of the cement mortar lined and coated steel piping. Pratt Valve has supplied the valves and EIM the valve actuators. Victaulic has supplied pipe couplings, Tankentics provided chemical tanks and the pump supplier was Fairbanks Morse. The chlorination system and associated safety equipment was supplied by US Filter. Archer Western was the general contractor for Phase II.