Paso Robles aquifers could drop another 70 feet over 30 years

Posted: 8:34 am, December 23, 2014 by Reporter Heather Young

Supervisors to get presentation and discuss water basin issue in January

Even with the county of San Luis Obispo’s emergency ordinance in place that prohibits the development or planting of new irrigated crops in the Paso Robles Groundwater Basin, a hydrological analysis of the basin that shows aquifer levels could drop another 70 feet in the next 30 years if pumping continues as is. The study area consists of the Paso Robles Groundwater Basin, which includes 790 square miles in the upper Salina River watershed in the North County and southern Monterey County.

“In my opinion, the report spells out the most dramatic effect by indicating the 70-foot decline over the next 30 years,” said San Luis Obispo County Supervisor Frank Mecham, whose district includes most of the water basin. “Is this possible? I believe that it could be the case unless we take action to address it. I don’t believe we are in an extremely disastrous situation currently, but I do not believe we should wait until we are to react. I firmly believe that there should be local control — by that I mean that those that overlie the basin should be the ones to manage it.”

The primary groundwater discharge components for the basin from 1981-2011 are:

Agricultural pumping (average 68 percent)
Municipal pumping (11 percent)
Private Domestic pumping (3 percent)
Small commercial pumping (2 percent)
Evapotranspiration by riparian vegetation (3 percent)
Groundwater discharge to rivers (12 percent)
Subsurface outflow (1 percent)

According to the report’s executive summary, agricultural pumping makes up more than two-thirds of the water use and it is not metered, so it was subject to detailed analysis by the consultants, Geoscience and Todd Groundwater. The report gave the following recommendations for addressing the anticipated drop in water:

Reevaluate recharge mechanisms of water from the watershed entering the groundwater basin
Incorporate Streamflow Routing Package to simulate streamflow and groundwater discharges to rivers
Reevaluate deep percolation of direct precipitation and agricultural return flows in the groundwater basin

“I believe that the latest legislative bills that will go in effect are absolute game changers when it comes to managing groundwater,” Mecham said. “I think addressing the issue of water and its future is long overdue. Who, how and at what cost the Paso Robles Groundwater Basin is managed remains to be answered. However, I do believe there are the means to do so be it locally, via a water district, or county managed or state managed. Fundamentally, the cost of water in California, no matter where you are, is going up and the rules that will be applicable to that management program will apply across the board.”

A presentation and discussion on this issue is scheduled for the County Board of Supervisor’s meeting on Tuesday, Jan. 13, 2015.