Davis’ deep aquifer is safe

By From page A14 | February 24, 2013

In his letter of Feb. 10, David Musser claims that the No on Measure I camp has not been able to produce a single expert.

Well, on Feb. 13, Tom Sakash interviewed Walt Sadler, a distinguished expert in wastewater and water. Sadler noted that Davis meets all drinking water requirements and can meet the new 2017 wastewater effluent standards with minor operational changes. No river water or new deep-well water is required. Using intermediate-aquifer water, rich in nitrates and selenium, for city irrigation would further improve water and wastewater. Conservation and/or an unused deep-aquifer well could provide make-up.

In an earlier career, as a geophysicist, I logged wells drilled for water, gas and oil, in the Sahara Desert, etc. Electro-logs from Sacramento Valley wells and geological studies indicate that the lower (horizontal) porous layers and lenses of the Tehama formation underneath the Davis area constitute a huge fresh-water aquifer. This extends from above 1,000 down to 2,500 feet. Pumping tests show good horizontal permeability (connections).

Clay and shale layers isolate the deeper Tehama formations from the more fragmented upper sections and from saline marine formations below. These layers make it very difficult for the intermediate-aquifer water to travel down into the deep aquifer. Our water is not deteriorating, as recent op-ed columns claim. In fact, it has been improving and will continue to do so as intermediate-well water is replaced by that from these deeper aquifers. (On average, 80 percent of our summer water will come from wells, not from the river.)

The Tehama formation is exposed in the coastal range to the west and northwest from ground level up to 1,000 feet, and as far as the foothills northwest of Anderson. It is postulated that the Tehama aquifers are fed by rain onto, and runoff into, the exposed formations. The city and UC Davis use about 6.5 million gallons per day, or about 7,000 acre-feet per year from the deep aquifer. This is equivalent to 12 inches of rain falling onto, or running off into a mere 10.5 square miles of exposure.

A water manager at UC Davis verified that they have been drawing water from the deep aquifer for 50-plus years, and have not measured significant changes in the low nitrate and selenium levels present. California Department of Water Resources data show small ups and downs for wet and dry years, but no net decline in Sacramento Valley water storage over about 50 years.

Paul Brady


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