November 23, 2014

Desalination plan expensive and ineffective

Desalination facility at Tampa Bay FL.

Desalination facility at Tampa Bay FL.

Correction (Jan. 6, 2014): an earlier version of this article stated that running the plant just during drought years would triple the cost per acre foot of the desalinated water. In fact, it would triple the capital cost of the desalinated water, and it would more than double the full cost including both capital and operational expenses.

 

A desalination plant being planned by Bay Area water agencies, allegedly for drought-year relief, would actually increase the need for water in drought years, and would also contribute to global climate disruption.

The Bay Area’s four largest water agencies–the East Bay Municipal Utility District (EBMUD), Contra Costa Water District (CCWD), San Francisco Public Utilities Commission (SFPUC,) and Santa Clara Valley Water District (SCVWD)–have been planning together since 2003 for the Bay Area Regional Desalination Project (BARDP), a large reverse-osmosis desalination plant at Mallard Slough, on Suisun Bay near Antioch. They were joined in 2010 by the Zone 7 Water Agency (Zone 7), which serves the Livermore area. Current project planning calls for a 20 million gallons per day (mgd) desalination plant, but allows for up to a 50 mgd plant, as large as the troubled Carlsbad desalination project in San Diego, the largest in the U.S.

Purportedly the project is designed primarily to provide additional water in drought years, as the Bay Area is not projected to face significant water supply problems in normal or wet years through 2040, but plans call for the plant to run every year. In a normal rainfall year, a 20 mgd plant would deliver 9 mgd to SFPUC and 5 mgd to Zone 7 for immediate consumption. The 9 mgd received by SFPUC would be used to guarantee a 9 mgd delivery to SCVWD, which is now an optional water sale. Theoretically, the remaining 6 mgd would be stored in CCWD’s Los Vaqueros Reservoir for use in dry years. (The water going into storage would be allocated among SCVWD [2.4 mgd], EBMUD [2.2 mgd], and CCWD [1.4 mgd].)

Los Vaqueros, however, has limited storage capacity. In normal and wet years, Los Vaqueros can be filled to capacity without any additional water from desalination. And so it seems that desalination would not increase the usable water in the reservoir.

In a drought year, the 20 mgd plant would continue its 9 mgd delivery to SFPUC (destined for SCVWD) and its 5 mgd delivery to Zone 7. EBMUD deliveries would increase to 3.5 mgd on average over three drought years, with SCVWD average deliveries falling to 1.6 mgd and CCWD average deliveries falling to .9 mgd. The only agency getting increased direct deliveries from the plant in a drought would be EBMUD, and the increase of 1.3 mgd represents less than 1% of EBMUD’s 2010 water demand. Without additional storage capacity, the other agencies could see a reduction in their supplies in drought years.

What about running the plant only in drought years (estimated as one in three)? This would more than double the cost per acre foot of the desalinated water. All current cost estimates for the BARDP, however, are based on continuous operation of the plant.

With sea levels rising, ocean waters are moving inland, and Bay/Delta salinity is rising. The U.S. Geological Survey reports that salinity levels in the Delta could double by 2050–exceeding the engineering specifications for the plant during much of the year, and increasing the dollar and energy costs of desalination the rest of the time. Since salinity rises in any case in drought years, the plant could be non-functional when needed most. The BARDP planning hasn’t taken these salinity increases into account.

Another problem is emission of greenhouse gases. In a normal rainfall year, the plant would produce just over 8,000 tonnes of CO2, the equivalent of consuming about 900,000 gallons of gasoline. In a drought year, increased salinity would increase CO2 emissions by 25%, to just over 10,000 tonnes.

In California the energy cost of recycled water averages 325 – 1,000 kilowatt-hours per acre-foot (kwh/af). Energy use at BARDP is estimated at 3,000 – 3,500 kwh/af, up to 10 times higher. In drought years, with higher salinity, BARDP’s energy costs would rise by another 20%. In a feedback loop, more drought would increase salinity, raising CO2 emissions from the plant, making a greater contribution to global warming, and thus bringing more frequent and intense droughts.

The best and cheapest protection against drought is to reduce the amount of water that must be delivered. Water supplies designed for drought shortfalls should never be used to increase the normal-water-year baseline water deliveries, as the current BARDP plan would do. By guaranteeing water in normal years to areas facing development pressure, BARDP would increase the amount of water that must be delivered in drought years, so that the pressure on other water sources will be increased, rather than relieved.

Each water-supply source must be evaluated for energy and dollar costs, and for its effects on global warming. The current BARDP plan supplies water that comes at very high energy and dollar costs, and needs to be reconsidered or abandoned in favor of less energy-intensive water recycling, or the cheapest and least energy-consumptive alternative of all–water conservation.

Charlotte Allen, co-chair, Sierra Club Bay Chapter Water Committee

Comments

  1. Your solution assumes there’s water to deliver in drought years.

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