Data being collected from California American Water’s ongoing geotechnical borehole investigation shows promising results for the subsurface slant wells it has proposed for the Monterey Peninsula Water Supply Project’s desalination plant. The company will post a work plan for the borehole and test well program on its project website, www.watersupplyproject.org. The plan is the result of numerous meetings and analysis by hydrogeologic experts assembled as part of the project’s settlement agreement.
Over the last four months, California American Water has drilled eight geotechnical boreholes in three areas along the Monterey coast in its study of preferred sites for a desalination plant subsurface intake. Borehole studies were conducted at Moss Landing, Potrero Road and further south down the coast at property owned by Cemex U.S, Inc.
Boreholes are used to collect deep soil samples to evaluate the geological and water quality aspects of subsurface soil layers. Two of the three sites – Potrero Road and Cemex properties – show highly favorable conditions for locating the subsurface slant wells. The Cemex boreholes indicated an almost continuous layer of sands and gravels to a depth of 240 feet. The Potrero Road boreholes revealed a thick layer of clay at a depth of approximately 140 feet, indicating a separation between the proposed ocean intake zone above from the lower aquifers also known as an aquitard.
“The results thus far are very promising,” said California American Water Director of Engineering Rich Svindland. “At the northern site near Potrero Road, we have a nice, deep layer of sand filled with salt water with a well-formed aquitard below, which, if drawn from, would likely avoid impacts to the Salinas Basin. At the Cemex site we have a very thick sand layer below the ocean floor which will work nicely for the subsurface slant well sea water supply. Unfortunately, the Moss Landing sites have not been as promising. There we found intermittent clay layers mixed with silt and fine sand, without enough continuous sand layers to use any type of subsurface intake system efficiently.”