Promising Results Shown For California American Water’s Seawater Desalination Slant Wells

Data gathered from boreholes drilled along California’s Central Coast shows an alternative way of collecting seawater for desalination may be feasible. California American Water has proposed subsurface intakes wells that are to be drilled close to the coastline at a diagonal angle and will collect sufficient ocean water to produce nearly 10 million gallons of potable water a day to supply to the Monterey Peninsula.

Subsurface intakes have become the preferred technology for desalination plants among state regulators and environmental groups because unlike an open pipeline to the ocean, they do not trap and harm marine life. While the technology has been used in Europe and tested in the United States, it is still considered a relatively novel approach. Near the Monterey Peninsula, where California American Water’s water supply project is proposed, the questions are what will slant wells produce in terms of quantity and quality of ocean water and what their impacts will be, if any, on the underlying inland groundwater aquifer.

The company and key stakeholders of the affected area of the Salinas Valley groundwater basin brought together a team of hydrogeological experts to research and help provide answers to these questions. The group studied the results of 13 boreholes that were drilled at several locations along the coast from Marina to Moss Landing area.

Boreholes are narrow shafts drilled into the ground that can be used to gather soil and water samples. In this case, data from the boreholes is being looked at to see if subsurface slant wells can physically be drilled, and to see what portion of the water underground is ocean water or groundwater. Agricultural interests in the Salinas Valley have supported the investigations in an effort to determine if the project will impact the groundwater supply on which they rely for irrigation.

While the tech memo released today does not conclusively answer that question, it shows promising results for the feasibility of slant wells, both in terms of geologic conditions and water quality. Data from the borehole study is being used to create groundwater models to further inform key environmental studies on the project. These studies are scheduled to be released in draft form later this summer. Simultaneously, California American Water is seeking approval for a test slant well at the sand plant site in Marina that will also provide further data for the project.

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