Back to HTML Index CHAPTER 5K: DESALINATION

Desalination, the process of converting saline water into potable water, has provided a limited source of water for some of California's coastal communities. This technology can be invaluable for coastal and island communities whose groundwater supplies have been reduced or eliminated by events such as droughts and salt water intrusion, and when no other sources are available. Thus, desalination receives increasing attention in drought years when water supplies become greatly threatened or diminished, while in above-average water years, permit requests for desalination facilities are frequently withdrawn. Due to the high cost and energy demand of the desalination process, it is rarely the first choice as a water supply alternative. Therefore, facility proposals are generally not made when conventional water sources are available. The current drought-response approach to desalination forces local governments and the State to conduct expedited review of these facilities during scarce water periods. Currently, neither the State nor most local governments have a long-term contingency plan regarding use of desalination plants for potable water production.

BACKGROUND

Desalination facilities use two basic technologies to extract potable water from seawater. Reverse osmosis works by forcing seawater through a semipermeable membrane, which restricts salt and other minerals, but allows potable water to pass through. The second method is distillation where intake water is heated to produce steam, which is then condensed to produce water with a low salt concentration. Depending on the technology used, the final water product is generally high quality, ranging from 1 to 500 parts per million total dissolved solids (the recommended California drinking standard for total dissolved solids is 500 parts per million maximum).

Because desalination plants are located in the coastal zone, they fall under the jurisdiction of the California Coastal Act, administered by the California Coastal Commission (Coastal Commission). If a facility were to be proposed in the San Francisco Bay Area, it would fall within the jurisdiction of the San Francisco Bay Conservation and Development Commission. Discharge of liquid brine waste from desalination operations is regulated under the 1987 amendments to the Clean Water Act, through the National Pollutant Discharge Elimination System (NPDES) administrated by the State's nine Regional Water Quality Control Boards. Other State agencies having some role over the planning, environmental review, or operation of desalination plants include: the California Department of Fish and Game, Air Quality Management Districts, the California Energy Commission, and the California Department of Water Resources.

ISSUE ANALYSIS

Desalination provides water for domestic purposes, industrial processing, power plant applications, and the recharging of groundwater supplies. Desalination can provide significant benefits to 

California's Ocean Resources:  An Agenda for the Future					     Chapter 5K:  Desalination
The Resources Agency of California						 		    July  1995  (Draft)

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communities along the coast that do not have access to traditional groundwater supplies. Unfortunately, certain characteristics about desalination make it an extremely costly technology. The high capital investment and substantial energy requirements for facility operations result in water costs that substantially exceed traditional water sources.

The efficiency of desalination is between 15-50%; in other words, 15-50 gallons of potable water are produced for every 100 gallons of seawater (California Coastal Commission, 1993). The remaining seawater consists of brine and solid waste. Operations are expensive because pipes and equipment require frequent backwashing to remove the rapid accumulation of salt solids, chemicals must be used in the pretreatment of the source water, de-fouling chemicals must be used to remove organisms in reverse osmosis systems, and the chemicals used and solid wastes generated from the process must be disposed of properly. The energy required to produce this potable seawater is approximately 2,500-12,000 kilowatt hours/acre-foot, depending on the quantity of salt in the intake water. The cost of producing potable seawater ranges between $1,300-$2,200 per acre-foot, depending again on its salt content and necessary pretreatment, while costs of other water sources are substantially less. For example, the Los Angeles Metropolitan Water District water costs range between $27-$195 per acre-foot.

Environmental effects associated with desalination processing include the construction and operation impacts to marine wildlife, water quality, air quality, and recreational uses. The most significant of these impacts is to water quality, including the discharge of significant levels of liquid wastes such as disinfectants (chlorine and biocides), de-fouling agents, and brine effluent. Solid wastes and/or toxic metals are also generated in lesser quantities. Disposal of liquid or solid wastes may involve direct discharge into the ocean, combining the waste with sewage treatment plant wastewater or with power plant cooling water before discharge into the ocean, drying wastes and disposing in land fills, or discharging into a sewer for treatment by a sewage treatment plant.

The 1993 Coastal Commission report titled, "Seawater Desalination in California," identifies 12 existing or approved desalination facilities on the mainland coast, offshore oil platforms, or offshore islands. The report also identifies 19 desalination facilities that are being considered or have been proposed along the coast.

An interesting case study to help demonstrate some of the environmental, economic, and permitting issues that arise from desalination facilities is the City of Santa Barbara desalination facility. The City of Santa Barbara had been experiencing severe water shortages resulting from the statewide drought and was in need of a dependable water source. Many technologies and ideas were investigated, including proposals to use tankers to bring fresh water from sources as far away as British Columbia. After an exhaustive review of alternatives, the City Planning Commission approved a coastal development permit in March 1991 for the onshore portion of a temporary desalination plant. In May 1991, the Coastal Commission approved a coastal development permit (with conditions) for installation of a liner sleeve in an abandoned ocean outfall line and the for construction and operation of ocean intake structures and auxiliary facilities to service a temporary five-year facility with a maximum production capacity of 10,000 acre feet per year. The six permit conditions specified the life of the permit (5 years) and required a water quality monitoring program, submittal of an NPDES permit, a plan to reduce construction impacts, special measures to assure navigation safety, and methods to assure the protection of archaeological resources in the area. 

California's Ocean Resources:  An Agenda for the Future					     Chapter 5K:  Desalination
The Resources Agency of California						 		    July  1995  (Draft)

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The Santa Barbara facility began operation in March 1992 using reverse osmosis. The facility operated for several months to allow the testing of components but was then placed on long-term standby status due to the increased availability of reservoir supplies replenished by rainfall during the winter of 1992-93, as well as through reduced demand from water customers. The plant has a capacity of 7,500 acre-feet per year, enough to provide 21% of the average pre-drought water needs of the City of Santa Barbara, Goleta, and Montecito. The cost of the water to the City was projected to be $1,918 per acre-foot, with the City's contract requiring capital costs to be paid within five years. If the plant operates beyond five years, the cost of the water would be reduced. The unknowns regarding future drought conditions and the subsequent use of desalination facilities, make it difficult to estimate future revenues from these operations.

FINDINGS AND RECOMMENDATIONS

Finding

Desalination can be an important technology for ensuring a reliable coastal water supply. Desalination is used in several locations along the California coast, although it is relatively expensive and can have adverse environmental impacts. The State should encourage research on how to minimize the costs and inherent environmental impacts associated with the use of this technology. 

















California's Ocean Resources:  An Agenda for the Future					     Chapter 5K:  Desalination
The Resources Agency of California						 		    July  1995  (Draft)

5K - 3