After years of hand-wringing and foot-dragging, Sonoma County is finally getting a clearer picture of what lies beneath the surface of the Santa Rosa Plain — at least in terms of water.

What did we discover?

Well, first, despite all the kvetching that the county shouldn't study the region's groundwater capacity because it was a slippery slope toward undo regulation of groundwater use, we discovered there were no big surprises.

The study by the U.S. Geological Survey simply provides a detailed — 199 pages in all — snapshot of what the county's groundwater supply looks like today. Given that ignorance has rarely proven to be bliss when it comes to settling water issues in California, this can only prove to be beneficial to the county — particularly in the years to come.

The study found that the roughly 12,000 wells that are operated by the county Water Agency, private homeowners, ranches and the five cities in the study area — Santa Rosa, Windsor, Sebastopol, Cotati and Rohnert Park — are pumping about 55,000 acre-feet of water per year out of the ground. That's about equal to all the water the Sonoma County Water Agency takes from the Russian River.

In addition, the study confirmed that the Santa Rosa Plain, which stretches from the Mayacmas Mountains to the east to the hills of Sebastopol to the west and is home to about of Sonoma County's population, is not served by a large underground reservoir of water. Rather it's served by an intricate web of underground water sources that occupy pockets in sand and gravel and rock fractures throughout the area. When the water levels within subsurface aquifers are lowered through pumping, they are recharged with rain water. But it's a cycle that needs to be tracked and protected.

For that reason, this information will now become the basis of a groundwater management plan for the region.

The need for such a plan has been evident for some time — since the underground water table in the Rohnert Park-Cotati area shrank as much as 100 feet due to heavy pumping from municipal water wells. According to USGS geologists, that "pumping depression" has been been replenished thanks to water conservation efforts and a shift to reliance on more Russian River water.

But the need to protect against such similar cases of overpumping is clear.

This is the first part of a seven-year, $2 million study. The next part, due to be released later this year, will include a computerized, three-dimensional model that shows how the county water flows move through groundwater and surface streams.

Up to now, the county has had little to work with — beyond guessing — in evaluating the real impacts of population growth, climate change and development on underground water resources. Tools such as this study and the three-dimensional model will be indispensable in projecting those impacts.

This county doesn't need to cut off its use of groundwater. But it did need to shut off its willful ignorance about where its water comes from — and prepare better for the future. This study helps do just that.