SLO receives $6.6 million for wells to treat water pollution 

The city of San Luis Obispo expects a $6.6 million monetary injection from the state to cure its groundwater from a stubborn toxic chemical prevalent since the 1980s.

"Thankfully, the work done on the groundwater sustainability plan has provided a thorough understanding of the basin, and previous rounds of this project which focused on identifying the extent of the PCE contamination and studied the feasibility of the cleanup project," said Nick Teague, the city water resources program manager. "These have positioned us so that there should not be any roadblocks."

SLO first detected PCE—a colorless liquid byproduct of now-defunct dry cleaning and industrial activities—above its maximum contaminant level in the late 1980s. The contamination prevented the city from using the groundwater as a drinking water supply, Teague said. Instead, SLO's drinking water comes from Whale Rock Reservoir, Santa Margarita Lake, and Nacimiento Lake.

As the groundwater cleanup project lead, SLO conducted a character study of the San Luis Obispo Valley Groundwater Basin in 2022. It found a small plume of tetrachloroethylene or perchloroethylene (PCE) across a stretch of the basin overlayed by a portion of the city. The section of the basin beneath SLO is different from the section in Edna Valley because of a geological divide that limits the flow of groundwater between the two regions. Further, the SLO-side basin enjoys an annual surplus of 700 acre-feet of groundwater while the Edna Valley subarea is in overdraft by roughly 1,100 acre-feet per year, according to the city.

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• Map Courtesy Of Public Utilities
• LURKING BELOW A 2022 character study of the San Luis Obispo Valley Groundwater Basin found and measured a small plume of PCE across a segment of the basin overlayed by a section of the city, though dry cleaning and industrial practices that produced the toxin were no longer active.

The city wants to diversify its local water resources in the face of limited groundwater for consumption, and SLO's recent $6.6 million grant from the California State Water Resources Control Board will do just that.

Provided through the Proposition 1 Groundwater Grant Program, the fund will help build two new groundwater supply wells fitted with water treatment systems to remove water pollutants.

"Treatment of the groundwater is done by pumping the groundwater through granular activated carbon vessels," Teague said. "These vessels are similar to large Brita filters—the PCE will bind to the activated carbon within the vessels as the water flows through them."

The city expects the wells to be fully functional in 2026. Then, over the next decade, SLO will pump out and treat groundwater and work with state and local regulators to ensure the processed water meets safe standards before adding it to the drinking water system. Once active, the treatment process will contribute 10 to 12 percent of SLO's drinking water supply, Teague said in a press release, costing less than pumping and treating water from the reservoirs.

"Determining the location of the wells was one of the largest hurdles, and we have finalized the locations over the past year of work on this project," Teague told New Times.

The wells will be constructed on the east side of Highway 101, south of the SLO Water Resource Reclamation Facility. Currently, SLO runs three non-potable production wells used for irrigation. Teague said that a well is available in standby position too that makes it available to use in emergency situations.

"But we don't have any wells that are functional that we can kick on and provide drinking water with," he said.

The groundwater treatment project is set to appear before the SLO City Council soon, Teague added, as his department prepares to seek approval for awarding contracts related to construction activities like well drilling and well equipping. Δ