Reverse osmosis endorsed

Officials in a few cities in southern San Luis Obispo County are looking for new sources of water to ensure their supplies won't run dry in the years to come. And although there are many options, some say desalination plants are the wave of the future.

In August, the cities of Arroyo Grande and Grover Beach and the Oceano Community Services District hired the Wallace Group to weigh the options of participating in the Nacimiento Water Pipeline project and constructing a desalination plant.

The consultant's report, presented for the first time to the Arroyo Grande City Council last week, indicated desalination would be half the cost of extending the Nacimiento pipeline to the South County and maintaining it. The Grover Beach City Council is expected to discuss the matter Tuesday.

Based on a 30-year life cycle, the estimated capital cost for a desalination facility would be about $14 million, and it would cost $2,400 per acre-foot a year to produce water. The combined water demands of all three jurisdictions is estimated to be 2,300 acre-feet a year when they reach full buildout.

An acre-foot is equal to about 326,000 gallons, or enough to meet the average yearly water needs of two families of three.

According to the Wallace Group's study, the logical location for such a facility is next to the South San Luis Obispo County Sanitation District Wastewater Treatment Plant in Oceano. Brine from the desalination process could be disposed of using the existing treated wastewater outfall line.

The desalination process is a fairly simple one, consisting mainly of taking in ocean water, using one of several techniques to reduce the number of dissolved solids to a potable level and treating it so it matches the taste and quality of other drinkable water.

Desalination has become more appealing and cost-effective over the last several years as a result of advances in treatment technology, according to experts. Reliance on ocean water instead of other sources also gives municipalities the assurance of a solid water supply even in years without much rain, they say.

“The one ‘plus' to a desal project is that it's essentially drought-proof,” Steve Tanaka, a Wallace Group consultant, told the City Council.

Tanaka said the best system for this particular area would likely be a reverse osmosis method for removing the salt from the water. Reverse osmosis uses pressure and synthetically produced membranes to separate the solids from the feed water source with higher recovery rates and lower energy usage than other methods.

There are two common methods for collecting sea water. One is brackish water wells, which pump groundwater along the coastline. An advantage to brackish water is that it has a lower concentration of dissolved solids in the water, making it easier to treat, said Tanaka.

However, that process could result in sea water intrusion on the existing fresh groundwater basin and may not be suitable for the site, he said.

The alternative is sea water intake using beach wells, which pull the water in through some type of geologic material, such as sand, rock or gravel, separating most of the marine organisms from the water. Those shallow wells consist of nonmetallic screens and vertical turbine pumps.

For every unit of sea water taken in through beach wells, the desalination process is able to recover about 30 to 50 percent of that as usable water.

To achieve the final product, the desalinated water is chemically treated to disinfect it and reduce corrosiveness. Then it's blended with the existing water supply and ready for use.

The facility itself could fit on a 100-foot by 100-foot base, according to Tanaka, and there would be room for it at the Sanitation District site.

“It's amazing how small the operation really is, and it's not a particularly noisy operation,” remarked Councilman Ed Arnold.

However, there are quite a few obstacles to cross before desalination becomes a reality in the South County. Approval from such agencies as the California Coastal Commission, U.S. Army Corps of Engineers, Central Coast Regional Water Quality Control Board, California Department of Fish and Game and more.

Environmental concerns include impacts on marine habitats, energy use and water quality. But many other agencies along the California coast have already successfully built desalination facilities, and several others are going through the approval process.

More thorough research to determine the feasibility of a desalination facility is being recommended. Arroyo Grande officials will begin applying for a state grant to help pay for the study in conjunction with Oceano and Grover Beach.

If the project moves forward successfully, construction could begin in about six years.

Karin Hill can be reached at 489-4206, Ext. 5015, or khill@

santamariatimes.com.

January 15, 2006