Innovative Desalination Delivers New Water Supplies to California

For years, the state of California has struggled with drought conditions. Traditional water supply sources are inadequate to keep up with growing populations. Southern California relies on water that is pumped hundreds of miles from the Colorado River and northern California. It is a limited supply—costly and energy-intensive to deliver—that is at risk of being cut off entirely by a major earthquake.

With abundant salt water at hand along the coast, seawater desali­na­tion plants are increas­ingly being evaluated and developed throughout the state. However, seawater desali­na­tion has its challenges—stringent permitting require­ments, and public concern over envi­ron­men­tal impacts and costs, have delayed many proposed facilities. CDM Smith has worked with a number of California communities to find water supply innovation options that provide new sources of potable water.

Permitting Success
The city of Sand City selected CDM Smith to design-build a 0.6-million-gallon-per-day (mgd) desali­na­tion plant. With the first full-scale desali­na­tion plant in California to receive permitting approval under new regulations—and the only municipal seawater desali­na­tion project that operates contin­u­ously—Sand City has set a new standard.

A unique solution allowed CDM Smith and Sand City to obtain the required permits from 20 different agencies, and complete the project for almost half the price of the original design proposal. The plant uses reverse osmosis (RO) and ultraviolet light to treat a highly brackish seawater blend drawn from four vertical beach wells. The city selected this intake approach to avoid adverse envi­ron­men­tal effects and provide a reduced level of salinity than pure seawater, making treatment more energy efficient and less costly.

Other cost savings resulted from several energy-efficient sources, including recovery devices that reduced the size of feed pumps by more than 70 percent; simplified chemical systems to minimize pretreat­ment; elimination of a lime feed system by using an operator-friendly limestone contactor; and the use of 90-percent efficient positive displace­ment pumps that can treat a wide range of salinities without variable frequency drives.

According to Greg Wetterau, CDM Smith discipline leader, “California’s permitting process for a new desali­na­tion plant is complicated, but these strategies can make them realistic and sustainable options. Sand City is the first in a new wave of plants to be built in California. It has performed better than anticipated and is considered by many in the envi­ron­men­tal community to be the right way to do seawater desali­na­tion.”

A Public Approach
In Santa Cruz, CDM Smith executed the design-build-operation of a pilot plant to evaluate treatment options and energy-saving measures for a seawater desali­na­tion facility fed by an open ocean intake. The pilot included four different pretreat­ment processes in parallel, upstream of four different RO systems, to determine the best pretreat­ment approach to minimize RO fouling.

After a year of pilot operation, CDM Smith is designing a full-scale, 2.5-mgd facility. According to Heidi Luckenbach, Santa Cruz desali­na­tion program coordinator, “The pilot project clearly demon­strated that the tech­nolo­gies can success­fully meet and exceed state and federal water quality standards to produce a reliable supple­men­tal supply for our community.”

An outreach program grounded in successful pilot results has been vital to engaging and informing the community on the critical need for a new water supply. The program included daily tours of the pilot plant to educate visitors on desali­na­tion, energy issues and the local water shortage. Residents and special interest groups also attended infor­ma­tional meetings to learn about the project and ask questions of agency staff and consultants.

Breaking Ground
In Dana Point, the first slant well desali­na­tion project is being developed by the Municipal Water District of Orange County (MWDOC) and other local agencies. Unlike Sand City’s vertical beach wells, the South Orange coastal ocean desali­na­tion project uses a slant well—pulling water through a sand and gravel aquifer under the ocean floor. These wells have the potential to draw much higher volumes of water than vertical wells, with minimal impacts to onshore aquifers and no risk of entrainment or impingement of marine life.

CDM Smith is coor­di­nat­ing the 18-month operation of a pilot facility, treating a portion of the water from the 2,200-gallon-per-minute demon­stra­tion slant well and leading the evaluation of pretreat­ment approaches to address the water’s unex­pect­edly high iron and manganese concen­tra­tions. Testing results have been positive, offering MWDOC an approach that is envi­ron­men­tally sensitive, reliable and less costly than a traditional seawater treatment approach.

Case by Case
Coastal communities in California and throughout the world are seeking alternative water supply options as they face drought, population increases and growing envi­ron­men­tal challenges. “To make seawater desali­na­tion a viable solution, we have to overcome concerns that it is unreliable and unaf­ford­able. We want to help communities develop new, sustainable supplies,” says Wetterau. “By gathering enough information and being creative in our solutions, we can help our clients develop the right, specific treatment approach for each situation.”