Less than a month after California passed historic groundwater laws aimed at halting overpumping, Sonoma County supervisors this week adopted a groundwater management plan for the Santa Rosa Plain — a 261-mile watershed covering Santa Rosa, Windsor, Sebastopol, Cotati and Rohnert Park.

Two years in the making, the 314-page plan found that groundwater pumping is diminishing the aquifer in places, which could affect supplies for streams and wells in the future. The aquifer helps supply drinking water for roughly half the county’s population.

The plan calls for additional monitoring of groundwater supplies, encouraging conservation and increasing the use of recycled water.

It includes a study from the United States Geological Survey that analyzed surface and groundwater supplies and contained input from agricultural groups, well users, business leaders and environmental organizations. The USGS study found that between 1976 and 2010, agriculture accounted for 32 percent of groundwater use, while rural domestic pumping comprised 50 percent. The remaining 18 percent was used by cities for drinking water supply.

Supervisors on Tuesday applauded efforts they said put Sonoma County ahead of the curve in preparing for looming regulation of groundwater, which could include monitoring of wells and restrictions in areas that are overpumped.

You can reach Staff Writer Angela Hart at 526-8503 or angela.hart@pressdemocrat.com. On Twitter @ahartreports.