Cech: Castroville desal water is not smoke and mirrors

Melodie Chrislock’s article is correct in pointing out that 700 plus acre-feet of desalinated water from Cal Am’s proposed desal will go to the Castroville Community Services District and that the Peninsula will have to pay an extreme price for this water.  She is also correct in saying this is the motivation for North County ag members on the Monterey One Water Board to oppose the expansion of the Pure Water Monterey Project.

Cal Am’s test slant well draws water from two aquifers. The upper intake is drawing fresh water from the Dune Sand Aquifer (DSA) and the lower intake drawing brackish water from the 180-foot aquifer. The water drawn is around 46 percent from the DSA and 54 percent from the 180-foot aquifer based on slant well intake volume. 

The test slant well that Cal Am bases its calculations on uses an electrical conductivity sensor that determines the total dissolved solids. The majority of which is sodium chloride (table salt). This sensor is located near the top of the 180 foot intake; but it is beneath the DSA intake. With the sensor in this location it primarily measures the electrical conductivity of the 180 foot aquifer brackish water, not measuring intake water mixed with the fresh DSA water.  The sensor should have been placed at the top of the test slant well to accurately measure the percentages of mixed fresh and brackish water.  

According to state law Cal Am cannot export any groundwater from the Salinas Valley Groundwater Basin and must return the fresh water component to the basin. Ron Weitzman’s estimate that only 1 percent is groundwater must have overlooked that 46 percent of the water being drawn might be DSA fresh water.  The quality of the DSA water has been confirmed by Stanford University using high tech measurement techniques.

Cal Am says they will return 7 percent fresh water, but when DSA fresh water is included in the intake water fresh water content might be as high as 45 percent during Monterey rainy season. So Weitzman’s idea that zero water must be returned to the Salinas Valley Groundwater Basin is most likely based on Cal Am questionable measurement data.

Because of this, just how much water will have to be returned to Castroville, and how much it will cost the Peninsula cannot be determined. But if it is 700 acre-feet as Cal

Am claims, it will cost Cal Am peninsula customers a minimum of $4 million per year and it could be much higher, while Castroville will pay only $110 per acre-foot for that water.

Chuck Cech


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