As officials fret about how to protect the Seaside Basin, a bulwark of recycled water may provide the answer.

For all the talk about the Carmel and Salinas rivers, and the various groundwater subbasins in the Salinas Valley, the Seaside Basin receives remarkably little attention, despite being a cornerstone of the Monterey Peninsula’s water supply. It’s an underground reservoir that stores water injected from the Monterey Peninsula Water Management District’s aquifer storage and recovery project (ASR) and the recycled water project Pure Water Monterey.

And like most things related to water in Monterey County, it’s both wildly complicated and politicized. It’s also unique in that, due to a legal action brought by Cal Am in 2003, the pumping rights within the basin were adjudicated by the courts, which ultimately decided 3,000 acre-feet annually was a “natural safe yield” to keep the basin in balance – at the time, about 6,000 acre-feet annually were being pumped from the basin. The Seaside Watermaster oversees the basin.

The various pumpers from the basin – Cal Am being the biggest, and City of Seaside making up most of the rest – have finally gotten under that 3,000 acre-feet limit. But the board of the Seaside Watermaster remains concerned about potential seawater intrusion into the basin, and a 2024 report commissioned by the agency concluded “it is not if, but when, seawater intrusion… will occur.” That’s because currently, levels in the aquifer being pumped are 20 feet below sea level. In 1960, it was 50 feet above sea level.

To address what they view as an impending threat, the board voted in November to establish a goal of injecting 3,600 acre-feet into the basin for 10 years. George Riley, who served on the board at the time, brought up a lack of plans to fund a project.

At a Feb. 5 meeting, Watermaster board members wanted more detail and more explanation. One subject that kept coming up was leakage from the basin as being a major problem. One suggestion was that desalinated water could be injected into the basin to solve the problem.

But officials from the Monterey Peninsula Water Management District disagree with many of the conclusions reached by the Watermaster’s reports and framing of the problem.

One is the leakage. Jon Lear, MPWMD’s hydrogeologist, says the hydrogeological boundary of the basin is south of the political boundary created by the adjudication – specifically, some water in the political boundary flows north, as it should, and shouldn’t be considered “leakage.”

In addition, with the Pure Water Monterey expansion coming online late this year – water which Cal Am is contractually obligated to buy – there will be an additional 2,225 acre-feet of water pumped into the basin every year, and there should be about 3,000 acre-feet of supply in Cal Am’s service area that exceeds demand.

Whether Cal Am sells all of that recycled PWM water to customers or not, it would still be leaving its water rights in the basin – 1,474 acre-feet annually. Lear believes that amount, over time, will be enough to bring the basin back up.