Editorial

If sustainable is good, then what's happening to groundwater in California's Central Valley is bad.

How bad? The U.S. Geological Survey last week released a groundwater report that shows between 1962 and 2003 an estimated 57.7 million acre feet of subsurface water vanished.

Total Central Valley water use from all sources is pegged at just over 25 million acre feet a year. Of that total, 18.8 million acre feet goes to irrigated agriculture. The rest is split between domestic use and evaporation loss through plants or off the surface of water bodies.

There's no simple answer to questions such as "how long will the groundwater supply last?" That's because, as two computer models accompanying the report show, we are talking about complex underground plumbing.

In California's Central Valley, there's one hydraulic unit associated with the Sacramento drainage. Another ebbs and flows with surface activities in the San Joaquin Basin. A third reacts to water demand and the scant rainfall of the Tulare Basin. They are connected, but the water doesn't move freely between units.

A 1991 estimate puts fresh groundwater within 1,000 feet of the surface for all three basins -- plus sub-units beneath the Sacramento-San Joaquin Delta and estuary and other smaller places -- at 800 million acre feet.

Authors of the USGS study quickly point out that while the aquifers are linked, depletion of groundwater is far from uniform.

Over the 42 years upon which the computer models are based, groundwater beneath the Sacramento Valley has more or less held its own, including recovery from heavy drawdown during back-to-back droughts in the 1970s and the big one from 1987 through 1992.

On the other hand, water beneath the San Joaquin Valley, with 2 million irrigated acres of crop land, decreased significantly. The largest loss is in the Tulare portion of the aquifer, where 3 million acres of irrigated crop land are farmed.

This is an estimate based on scattered test well records, melded together by USGS and California Department of Water Resources.

With some notable exceptions -- aquifer recharge is carried out in the Tulare Basin -- pumping from wells isn't regularly monitored in California. In fact, state water law makes it clear that groundwater regulation is a local function. Most local governments have stayed away from monitoring what's happening beneath the surface of the ground.

The real trouble is south of the Delta where, in terms of farmgate value, 88 percent of California's agriculture production is. Lessons from the two previous droughts resulted in massive agricultural water conservation measures, a shift to crops yielding higher returns to offset added costs for deep wells and high-volume pumping costs.

It's time for California to mandate groundwater conservation districts. They can and should be locally run, as are the existing groundwater management operations.

If unconstrained pumping continues, regardless of how water transfers through the Delta eventually work out, California agriculture will be a ghost of what it was late in the past century.

It's not sustainable.