San Juan-Chama Drinking Water Project, New Mexico, USA

As the final elements of the raw water system for the San Juan-Chama Drinking Water Project near completion, work on the scheme to supply up to 70% of the metropolitan area of Albuquerque remains on schedule for its planned conclusion in 2008.

The project stands as the main component of the city’s water resources management strategy to the year 2060 and involves diverting surface water from the Rio Grande for purification, to replace the city’s current dependency on an increasingly depleted deep aquifer.

The work entails the construction of a new water treatment plant with a capacity of 350,000m³/d on a 110-acre site near the Renaissance development, to the west of Interstate 25 and a 600ft long diversion dam at the Alameda Bridge, to the north-west of the city. The scheme also includes providing new raw-water and treated-water pumping stations and new pipelines.

The overall project cost is $280m, with plant building costs accounting for $160m of the budget.

BACKGROUND

In 1922, the Upper Colorado River Compact - an agreement between Arizona, California, Colorado, New Mexico, Utah and Wyoming - set out the basis for the equitable division of water in the Colorado River basin.

Constructed some 40 years later, the San Juan-Chama Diversion captures part of New Mexico's apportioned share and conveys it from southern Colorado, along 26 miles of tunnels, under the Continental Divide and into the Rio Grande Basin. The City of Albuquerque owns perpetual rights to 15 billion gallons of this, though historically it has been stored or leased and the municipality's consumption met from aquifer extraction.

Responding to the need to guarantee a sustainable supply into the future, the City of Albuquerque adopted a new water resources management strategy in 1997; developing and maximising the use of the San Juan-Chama water was one of the key objectives. Other aspects involved the implementation of a groundwater protection plan, the promotion of water conservation measures, the use of recycled water for irrigation and seeking new sources of supply.

In June 2003 the New Mexico State Legislature created the Albuquerque-Bernalillo Water Authority, a joint agency for all of Albuquerque and the County of Bernalillo. 13 months later, the State gave final approval to the Drinking Water Project, setting conditions to ensure that the environmental impact of the scheme would be minimised.

WATER TREATMENT PLANT

The design is conventional, using grit basins and settled water ponds, flocculation / clarification, ozone as the primary disinfectant, activated carbon deep bed filters for filtration / adsorption / assimilation and sodium hypochlorite for residual chlorination disinfection.

Water from the diversion site at Alameda Bridge will be pumped into two separate 190,000m³ pre-sedimentation ponds at the north of the site, which will hold the screened raw water for about 24 hours.

From here the water flows to the plant's main processing area, where coagulant will be added to remove turbidity in a mixed Actiflow –type flocculation / clarification system. After a settlement period, the water will then flow to the ozone contactors where organic material is oxidised and bacteria killed. Residual turbidity and any organic material remaining at this stage will then be removed by deep bed granular activated carbon and sand filters.

After the addition of chlorine and fluoride, the finished water will flow to storage tanks from which it will then enter the water utility’s distribution network. Settled solids and sediments from the treatment process will be held initially in drying beds before being trucked off-site for disposal or landscaping use.

ASSOCIATED WORKS

To divert the water to the new treatment plant, a new 600ft-long dam is being built across the full width of the Rio Grande River. An adjustable height bladder dam, it will be no more than 3ft high at its maximum extent, though in normal operation, there will be less than 3in difference between the water level upstream and downstream of the dam. The construction includes an intake screen to exclude fish from the pump station and a fish passage to provide a way through the dam.

There are also 15 separate transmission pipelines being constructed as part of the project, amounting to the installation of some 56 miles of large diameter pipeline in total.

CONSTRUCTION PROGRESS

Work began on the project in August 2004, shortly after final project approval was announced, starting with the pipeline construction, with work on the diversion dam getting underway in the following January.

The western section of the dam was finished by the April. Construction of the second section began in September and was completed by April 2006. The first of the raw water pipelines was completed in March 2007, with the second following in August. The raw water pump station is scheduled for completion in September 2007, followed by the final pipeline element later in the year and the Water Treatment Plant itself expected to be finished by the summer of 2008.

ENVIRONMENTAL PROTECTION

Many of the environmental safeguards within the project's permit - particularly relating to water conservation and planned reduction of average per capita water use - had already been embraced by the municipality in the 1997 management strategy. Other measures were imposed specifically to protect the Rio Grande, including ensuring that sufficient San Juan-Chama Project water is held in storage to offset effects of diversion and ceasing diversion when the river's flow is reduced.

The Rio Grande Silvery Minnow is listed as an endangered species and warrants special protection under US law, which led to the project meeting with some opposition. In response to these concerns, the water authority has taken steps to ensure that habitat loss will be minimised and funded studies which have enabled the design of fish passageways to be optimised, easing the minnows' journey upstream to spawn.

In addition, the authority has also taken a major role in developing a rearing and breeding facility at the Albuquerque Biological Park, with the goal of releasing 25,000 young fish a year back into the river.

KEY PLAYERS

The Albuquerque Bernalillo County Water Utility Authority instigated the project and a number of consultants have been involved in the various elements, including DMJM, Boyle, HDR, BHI and ASCG. The main contractor for the water treatment plant is CH2M Hill acting as water resources planning consultant, designer and construction manager, with McDade-Woodcock as electrical/I&C contractor. CDM has responsibility for the pipelines and other project elements, with ASI RCC building the diversion dam and RMCI Construction, AUI Construction and Shumate Constructors / TIC are constructing the various pipelines.