County’s latest seawater intrusion maps reveal an intractable problem that’s getting worse.

In the story of the lower Salinas Valley’s groundwater – which is the sole source of water for agriculture and residents – history repeats itself: groundwater levels continue to get lower, and seawater intrusion in that water continues its inexorable march inland.

On Feb. 21, hydrologists from the Monterey County Water Resources Agency presented the county’s 2022 seawater intrusion maps to the agency’s board, and they came bearing bad news.

The valley’s main aquifers – the 180-foot, 400-foot and deep aquifers, named for their depths – saw varying degrees of groundwater level decline. The worst was in the 400-foot aquifer, on account that many wells in the 180 have been taken offline due to seawater intrusion.

MCWRA staff assess groundwater levels every August for 143 wells stretching from Chualar to the coast. In the Espinosa Lake area between Castroville and Salinas – which is at risk of seawater intrusion into the 400-foot aquifer – groundwater levels declined by an alarming 20-25 feet between 2021 and 2022.

Seawater intrusion samples, meanwhile, are taken from 120 wells in June and then again in August, and in one year the amount of land overlying seawater intrusion in the 400-foot aquifer increased by 365 acres.

Much of the increase happened on borders of “islands” that are disconnected from the coastal pressure of seawater, and are thought to be from vertical migration of seawater from the 180-foot aquifer into the 400-foot.

MCWRA Associate Hydrologist Tamara Voss told the board there is likely no way to reverse the intrusion, and the best attainable outcome is to stop it from getting worse.