SALINAS – A bold plan is being developed that would convey tens of thousands of acre-feet of brackish water — a mix of freshwater and seawater — from near the coast to where it would be treated and then injected in front of an encroaching underground plume of seawater licking at the heels of the Salinas and Castroville areas – intrusion that threatens the major economic driver of Monterey County.
The project is called the Brackish Groundwater Restoration Project. When or if implemented, it aims to dramatically help stem seawater intrusion that is threatening segments of the $11.7 billion agriculture industry in Monterey County. It would also help raise the aquifer levels in some seriously overdrafted groundwater basins to a sustainable level, as required by law.
“There is no issue more critical than water this year,” said Monterey County Supervisor Glenn Church, who represents the northern end of the county. “The decisions made in the coming months (on moving ahead with projects) will impact the entire county for the next 30 to 50 years. This is a matter that will impact everyone — residents, businesses and agriculture. We have to get it right. The consequences of not doing so are dire.”
The task of bringing those aquifers into sustainable levels is a major effort, water and elected officials say. Leading the project is the Salinas Valley Basin Groundwater Sustainability Agency, which was established after the California Legislature passed the Sustainable Groundwater Management Act in 2014.
The act oversees 94 groundwater basins in the state, which account for 98% of California’s groundwater pumping, including 21 basins designated as critically overdrafted. The Salinas Valley basin is considered one of the critically overdrafted basins.
All the basins and subbasins must stop overdrafting and bring those aquifers up to sustainable levels by certain deadlines. The deadline locally is 2040 to bring groundwater into sustainability. There are nine subbasins in the Salinas Valley. The Sustainability Agency manages six northerly basins.
There are multiple project scenarios being considered, but one needs to be chosen by the end of the year.
The one common denominator entails digging a number of wells roughly between Marina and Moss Landing that will extract brine-like water with high levels of chloride. That water will then be conveyed to a facility that will use reverse osmosis to filter out the salts. The filtered water will then be injected into underlying aquifers in front of the intrusion.
The concept works in two ways. The first would remove the brackish water – called an “extraction barrier” – so it won’t join the plume migrating east. Also, by injecting the water into the aquifer in front of the plume and raising the water level, pressure would be restored that would keep the seawater at bay.
Aquifers can be thought of as giant underground sponges. When water volume and pressure are decreased by over-pumping, a type of void allows intrusion. Increasing the volume would be a counterforce to the seawater.
Originally, there were a couple of different scenarios, one of which would inject the water but also pipe it to a number of end users. The preferred scenario, according to the Sustainability Agency, is called “Injection Only,” and would not supply end users, such as agriculture and municipal wells. The preferred scenario will be less expensive because it would save on costly conveyance infrastructure to get the water to the end users. Piret Harmon, the general manager of the Sustainability Agency, said none of the projects are off the table.
Estimated costs of the project vary, according to the various scenarios, but the preferred scenario would have a price tag of roughly $950 million. The project would provide 46,900 acre-feet a year of injection volume.
One acre-foot equals 325,800 gallons, so the preferred scenario would inject in the neighborhood of 15.2 billion gallons into the aquifers annually. To put these volumes in context, for the 2025 water year, the Monterey Peninsula used about 9,092 acre feet of water, or about 3 billion gallons.
The effort is critical to the county, particularly to agriculture. In the Salinas Valley, annual water use is over 470,000 acre-feet. Ninety percent of that water used in the valley is for growing food, according to the Sustainability Agency.
Overdraft and seawater intrusion in the Salinas Valley Groundwater Basin were first identified and documented in the 1930s to early 1940s, according to the state Department of Water Resources. The Castroville area is already facing serious seawater intrusion, and by 2040 the salty plume could push its way into the city limits of Salinas.
The year 2040 is important in another way. It is the deadline for Monterey County to bring its overdrafted groundwater back into sustainable levels, as required by the Groundwater Management Act.
If that deadline is not met, the state can come in and put the Salinas Valley “on probation,” including actions that would severely curtail pumping by as much as between 35% to 50%, according to the Sustainability Agency. And it’s not just agriculture at risk. Residential wells are typically shallower than agricultural or municipal wells and are also vulnerable to lowering groundwater levels.
If that were to happen, the blow to the regional economy would be catastrophic. Agriculture and all the periphery businesses that support it contribute $11.7 billion into the local economy, according to Assistant Monterey County Agricultural Commissioner Rich Ordonez. Agriculture also supports a little over 81,300 jobs. If the state were to cut pumping by 50% and growers could leave half their fields fallow, the ripple effect and job loss loss would dramatically change the nature of the local economy.
Project costs are only estimates and could vary by the time the project reaches fruition.One thing is certain: Whichever scenario is chosen, it will be one of the most cost-intensive theintensive infrastructure projects in the history of Monterey County, rivaling only theNacimiento Nacimiento and San Antonio dams and reservoirs.
“Everyone who benefits must pay,” said Church, who also sits on the board of directors of the Sustainability Agency. “Yet we are still at the point where the scope and vision of the project is not completely clear. So we don’t know who all those who will benefit are. In the next four to six weeks, a lot of this should become clearer.”
The agency is considering several projects: the current project (Brackish GroundwaterRestoration MontereyRestoration Project), the Castroville and Eastside Canals, alternatives using a Monterey County water right on the Salinas River known as Permit 11043 and a New Seawater Intrusion Project to directly deliver alternate irrigation supplies with surface water and recycled water sources.
Demand management programs, where water use is curtailed, are also being developed.
These projects are all described on the Sustainability Agency’s website: https://svbgsa.org/monitoring-wells/.
Local groundwater is the primary water supply for the Salinas Valley communities, farms and environment, but it is being used faster than being replenished,” the feasibility study states. “In parts of the valley, where groundwater levels continue to decline, seawater is moving farther inland. Consequently, more wells are at risk of failure.
In the face of these warning signs, management efforts have historically been fragmented, infrastructure is aging and opportunities to capture and store water are limited. Climate extremes, data uncertainty and the high cost of new projects add to the challenge,” the feasibility study states.
The brackish water would use reverse osmosis to remove the salinity before injecting the water ahead of the plume. Common in desalination systems, reverse osmosis works by forcing the brackish water through a semipermeable membrane. On one side of the membrane is the salty concentrate and on the other is injectable water. The system is expected to achieve 70% recovery of treated water with the remaining 30% discharged through through Monterey One Water’s outfall into the ocean, the Sustainability Agency said.
During significant storms, Monterey One Water needs the entire capacity of its outflow to channel stormwater. At that point, the brine-like water would be stored until the capacity increases again.
It’s expected that this month the local Sustainability Agency will release the second phase of the feasibility study that will contain both updated scenarios and provide more detail on the project vision. The additional project feasibility studies will be released at the same time. These studies will be considered this summer and a decision will need to be made about which project will move forward this fall in order to meet the 2040 deadline.