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Los Osos makes progress on water quality

State water officials say progress is being made to reverse the degradation of the Los Osos groundwater basin.

In a recently released report, the Central Coast Regional Water Quality Control Board said a combination of reduced demand, nitrate control and better management of underground aquifers is poised to begin improving water quality in the seaside community.

“We are very optimistic that it is going to be a long-term solution,” said David LaCaro, an environmental scientist with the regional board. “There is some momentum here.”

The groundwater basin faces two severe, interconnected problems: nitrate pollution in the upper aquifer and saltwater intrusion in the lower one.

“The nitrate problem has caused purveyors to curtail shallow well use in recent years,” LaCaro said. “This shallow aquifer abandonment has led to increased deeper pumping, which has greatly exacerbated seawater intrusion.”

A variety of steps are being taken to deal with the problem. One of the main ones is the planned construction of the $189 million sewer system, which is scheduled to begin later this year.

The sewer system will replace the hundreds of septic systems in the community that are the source of the nitrate pollution, LaCaro said. The system’s effluent will be used for irrigation and other uses that will reduce demand on the aquifers, and some of the effluent will be returned to the upper aquifer via percolation ponds.

Other steps being taken include:

Retrofits, installation of water meters and other conservation steps that will reduce pumping in the lower aquifer.

Increased upper aquifer pumping using nitrate removal via ion exchange and blending with cleaner water.

Minimizing pumping from the westerly portion of the aquifer to reduce intrusion.

Preparation of a management plan for the groundwater basin.

No one is willing to speculate on when improvements in water quality will be realized, however.

“With groundwater, we never know; it’s a tough call,” LaCaro said.

The Los Osos groundwater basin is jointly managed by the county and the three water purveyors serving the community: the Los Osos Community Services District, Golden State Water Co. and S&T Mutual Water Co. These four entities agreed to work together to manage the groundwater basin as a result of a San Luis Obispo Superior Court judgment reached in 2008.

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