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Deep Water Desalination Proposed in Monterey Bay

A seawater desalination proposal in Monterey Bay aims to draw water from one of the world’s deepest submarine canyons, claiming this will result in less harm to ocean life.

Written by Matt Weiser Published on Read time Approx. 7 minutes
Montereycanyon
An image of the submarine Monterey Canyon, one of the deepest ocean canyons in the world. The canyon terminates at Elkhorn Slough on the right, where Deep Water Desal proposes to build a seawater desalination facility.U.S. Naval Postgraduate School

Backers of a new Monterey Bay desalination project think they have found a fix for the environmental problems posed by most seawater intakes: Instead of drawing seawater from the beach, they plan to draw from the one of the world’s deepest marine canyons.

The Deep Water Desal project is proposed at Moss Landing, exactly midway along the curving shore of Monterey Bay. As such, it may be ideally positioned to serve the chronic water shortages affecting the region. Cities from Santa Cruz to Monterey are plagued with long-time water problems, including overdrafted groundwater, diminishing surface water and a lack of storage reservoirs. The region also has no access to the State Water Project, a key source of imported water for many Californian communities.

Moss Landing also sits at the head of Monterey Canyon, the deepest submarine canyon on the west coast of North America. It plunges 1,600 feet deep (488 meters) just two miles (3.2km) from Moss Landing, and eventually reaches more than 10,000 feet deep – twice as deep as the Grand Canyon.

Deep Water Desal proposes to draw seawater from an intake constructed at the edge of this abyss, about 1,000 feet offshore at a depth of 130 feet.

The goal is to produce 25,000 acre-feet (30m cubic meters) of freshwater per year, enough to serve 50,000 average homes.

Kim Adamson, general manager of the project, said their studies show the density of marine life in this deeper, colder water is about one-fourth that found in shallower waters near shore, where desalination intakes are typically constructed. As a result, she said, the project will pose a much smaller threat to the marine environment.

“Down in the canyon, there’s a very significant difference,” Adamson said. “It’s also very clean. What we can do with that really clean water is, we can reduce the need for some of the energy-intensive pre-treatment required in a water treatment facility that has more turbidity and other contaminants in it.”

The layout of the proposed Deep Water Desal project in Moss Landing, Calif. The red outline on the right shows the plant location, and the green lines show the proposed intake and discharge pipelines. Elkhorn Slough, a protected natural area, runs along the top of the image, and the Dynegy powerplant is the developed area in the center. (Deep Water Desal)

The layout of the proposed Deep Water Desal project in Moss Landing, Calif. The red outline on the right shows the plant location, and the green lines show the proposed intake and discharge pipelines. Elkhorn Slough, a protected natural area, runs along the top of the image, and the Dynegy powerplant is the developed area in the center. (Deep Water Desal)

Most desalination plants require at least two stages of filtration before the water undergoes reverse osmosis for desalination, she said. The Deep Water Desal project will require only one stage, which will significantly reduce the plant’s energy requirements.

In another unusual move, the developers also propose to build the desalination plant in tandem with a large data storage facility. Besides water, Adamson said, the Monterey Bay region also has a need for data storage and faster internet speeds. The cold seawater would first meet the cooling needs of the data storage facility before being routed to the desalination plant.

This solves a problem at the desalination plant as well. Cold water is not ideal for desalination because it is more dense and, thus, requires more electricity to force through the micropores of the reverse-osmosis filters, Adamson said.

The data center would warm up the seawater before it reaches the desalination facility.

In total, Adamson said, the electricity required to operate the project will be reduced by an estimated 40 percent compared to a conventional desalination project. This will help contain the price of the freshwater it produces, and also reduce the project’s greenhouse gas emissions.

The developers are negotiating with the city of Salinas to create a municipal power authority. This would allow the desalination facility to acquire all its electricity from designated “green” sources, such as a wind farm. It could also be acquired at wholesale prices.

“We’re dedicated to having a carbon-neutral or carbon-negative project,” she said. “It’s about how can we meet all of these different needs and make a better project for everybody.”

The project nevertheless faces significant obstacles. One is that it proposes development inside Monterey Bay National Marine Sanctuary, which is managed by the National Oceanic and Atmospheric Administration. Any new desalination facility in the sanctuary must receive approval from NOAA, which prepared a set of guidelines in 2010 for desalination projects within the sanctuary.

Those guidelines assert that NOAA has approval power over any seafloor development within the sanctuary, which includes seawater intakes, and for the discharge of highly concentrated brine, a waste product of desalination.

Both NOAA and the State Water Resources Control Board prefer subsurface seawater intakes that draw water though the sand and soil floor of the ocean. Such intakes use the substrate to filter the water so the intake doesn’t kill plankton, fish larvae and other important marine species. But these are much more expensive to build than the open-water intakes that are more common around the world.

Adamson said a subsurface intake isn’t possible because there aren’t enough deep sand deposits in the area. So Deep Water Desal is proposing an open-water intake using a fish screen with 1mm openings.

Carol Reeb, a research scientist at Stanford University’s Hopkins Marine Lab, said she is “not that worried” about the marine life that could be killed by an open-ocean intake. That’s because the volume of water drawn in by a project of this size is not great.

She is more concerned that the desalination plant could be affected by frequent algae blooms – such as red tides – that occur in Monterey Bay. These blooms are fueled, in part, by nutrients that well up from the deep underwater canyon.

The algae often contain harmful neurotoxins that could enter the desalination plant, she said.

“In fall and spring, we can see huge fans of algal blooms in that area,” said Reeb, who has studied marine life in the canyon. “To me, the bigger issue is how are we going to prevent the [desalination] plant from clogging.”

Reeb also noted the project can’t be guaranteed that its intake water will always come from the canyon depths at all times. The upwelling that brings deep, cold water up from the canyon depths is a regular event only in summer. In winter, the upwelling often stops, and the intake would instead draw water that is closer to the surface, more stagnant and possibly warmer.

NOAA also prefers that brine be diluted by mixing with some other water supply before discharge, such as treated wastewater or power plant cooling water already being discharged in the bay.

Brine produced by desalination is a concern because it is two to three times saltier than the ocean. As a result, it does not disperse easily. It can settle on the ocean floor like “syrup,” smothering marine life, Reeb said.

Aerial photo of Elkhorn Slough, looking west toward Moss Landing and Monterey Bay. The Deep Water Desal facility is proposed on the property in the upper left where an old crude oil storage tank farm was once located. (Moss Landing Marine Laboratories/California State Universities)

Aerial photo of Elkhorn Slough, looking west toward Moss Landing and Monterey Bay. The Deep Water Desal facility is proposed on the property in the upper left where an old crude oil storage tank farm was once located. (Moss Landing Marine Laboratories/California State Universities)

Adamson said Deep Water Desal is negotiating with Dynegy, owners of the large natural gas-fired power plant in Moss Landing, to use its cooling water discharge to dilute the brine. But nothing has been finalized yet. For now, Adamson said, the discharge plan calls for a diffuser device to disperse the brine through a new pipeline extending about 2,000 feet (600 meters) offshore, on an underwater shelf area north of Monterey Canyon’s edge.

Another concern is that the desalination plant would be located next to Elkhorn Slough Ecological Reserve, a protected wildlife area in Moss Landing operated by the California Department of Fish and Wildlife. Deep Water Desal plans to purchase a 100-acre parcel adjacent to the reserve that is now owned by Dynegy.

Dave Feliz, manager of the reserve, said he is concerned that a large, industrial desalination facility will degrade the area’s natural scenery. He also worries about an accident at the plant that could discharge brine into the Elkhorn estuary.

“I’m not quite sure why it has to be right next to a very scenic, biologically rich area,” said Feliz. “It’s going a different direction from the conservation path we’re taking in the slough.”

Adamson said a draft environmental impact study is now being prepared for the desalination project, and she hopes it will be approved in mid-2017. Numerous other permits are required from state, federal and local agencies, but Adamson is optimistic construction could begin in 2018.

Adamson estimates the project will cost around $300 million to construct. That sounds like a bargain compared to the recently completed Carlsbad Desalination Plant in San Diego County. That project is about twice as large and cost $1 billion.

Several water agencies in the region have expressed interest in purchasing water from the plant, including the Monterey Peninsula Water Management Agency, which contributed $800,000 to help pay for environmental studies.

Adamson could not yet estimate how much water will cost from the desalination facility, except to say it will be less than $2,000 per acre-foot. That is the approximate cost of water from the Carlsbad desalination facility, considered the most expensive in California.

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