Sunday, December 21, 2014

Groundwater update: high toxicity, stable aquifers, links to earthquakes

From page A1 | May 16, 2014 |

The last month has been rife with news and worries about groundwater, with statewide reports about water toxicity, aquifer depletion and, most recently, a correlation between small earthquakes and a dry earth.

Here’s where Yolo County stands.

Groundwater levels

The California Department of Water Resources released a report last month showing that groundwater levels have decreased in nearly all parts of the state since 2010.

But Yolo’s groundwater levels have stayed relatively stable in the past three years, setting us up in a feasible position to depend on it this year.

Even the wells where groundwater receded 10 or more feet (marked in red on the Sacramento basin map on Page 19 of the report) should not be cause for immediate concern, said Max Stevenson of the Yolo County Flood Control and Water Conservation District. Stevenson works on the countywide system that monitors groundwater levels, and he worries primarily when levels drop 50 or 100 feet.

“We’re going to lean on (groundwater) heavily,” Stevenson said. “Anyone that is farming will be pumping and water levels will drop a lot … but historically, we’re not close to the ’77 (drought) levels.”

The county’s groundwater completely recharged after 1977, when California experienced its worst drought in at least the last century. Stevenson predicts the same will happen here — we will rely on aquifers this year to make up for the lack of surface water, but when the rain comes, they will return to their pre-drought levels.

The report admits “there are significant monitoring data gaps in the Sacramento … hydraulic region.” The Yolo County Water Resources Association is developing its own comprehensive monitoring project, which will help provide more comprehensive data to the residents and the state.

In Davis, the city’s 20 drinking water wells have sunk to about 10 feet below average, said water manager Dianna Jensen.

“If this drought continues for another year or two, then, yes, this is going to be problem,” she said.

However, if the wells can hold on for another two years, the Woodland-Davis water project could help alleviate pressure on the wells by drawing on surface water from the Sacramento River.

Water toxicity risk

A separate report published last month showed many areas of Davis to be in the 95th to 99th percentile of water toxicity risk in the state. CalEnviroScreen 2.0 combined various pollution concerns, like air and water quality, with population vulnerabilities, including poverty levels and unemployment, to help measure relative impact of environmental risks on local communities. (See the interactive map and search for Davis. The map is broken up into census tracts.)

While Davis water is still safe to drink, and wells are taken offline before they reach state toxin limits, city wells likely rank among the worst because of high levels of hexavalent chromium, a naturally occurring contaminant now found in 12 out of 20 wells. Another well is close to exceeding its nitrate standards, and manganese remains a worry in a couple more.

If the surface water project continues on schedule, the city will take those wells offline by September 2016, Jensen said.

Earthquakes tied to pumping

Scientists theorize that excessive groundwater pumping may be responsible for a jump in the number of minor earthquakes in the Central Valley, the Los Angeles Times reported Wednesday. Water is heavy, so in the ground, it effectively helps compress the earth. As groundwater is pumped out, the pressure decreases and the crust rises — which could trigger earthquakes.

Groundwater depletion in the Central Valley is much more severe than in Yolo County, and the authors of the study cautioned it needs to be replicated in California and elsewhere before any certain conclusions can be drawn.

— Reach Elizabeth Case at or 530-747-8052. Follow her on Twitter at @elizabeth_case



Elizabeth Case

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