STORING RAINWATER FOR FUTURE USE

Each winter, when excess Carmel River water flows into the Pacific Ocean, the Aquifer Storage and Recovery or ASR Project captures millions of gallons which is stored in the Seaside Groundwater Basin for future use as drinking water. The ASR Project allowed this excess water to be diverted, treated, and delivered to injection wells off General Jim Moore Boulevard in Seaside.

The ASR Project

The Monterey Peninsula Water Management District began the ASR Project in 2001 with one test well. Its success led to the planning and construction of a permanent ASR Project. The project is currently comprised of four wells that can inject or extract water at different times of the year. Well No. 1’s first full year of operation under a State Water Board permit was in 2009, followed by a second well in 2010. The third and fourth wells became operational in 2016.

Until 2021, the State of California and federal fisheries regulators did not allow the wells to operate as intended (i.e., building up a reservoir of stored water) while Cal-Am exceeded its pumping limits on the Carmel River. Except for a very wet 2017, the regulators required water that went into storage in the winter to be withdrawn from storage the following summer to protect the Carmel River steelhead. It wasn’t until the Pure Water Monterey project came online in 2021 that regulators allowed ASR to start storing water year-to-year.

Based on long-term historical precipitation and streamflow data, ASR was designed to produce as much as 1,920 AF each year. Using the United States Geological Service methodology for the District’s yearly streamflow estimates, annual yields show that water can be banked as the project operates over many years. This conclusion supports using the average long-term estimated operational yield of 1,300 acre-feet per year for ASR when planning for supply.

A Balancing Act

Many system constraints have to be delicately balanced to truly optimize ASR performance. The project permits allow up to 29 acre-feet (AF) of injection per day, but many factors can reduce that. More water can be delivered for injection with the large diameter Monterey Pipeline, but far less if that pipeline is unavailable.

When an ASR well is being used to extract Pure Water Monterey water, it cannot be used for injection of ASR water. If Carmel River extraction wells are offline for repair or emergency, less water can be delivered or injected. Cal-Am and the District work in choreographed coordination to make all these elements work together, or ASR will miss opportunities to capture excess river water.

ASR Exceeds Storage Goals – Half a Million Gallons!

495 Million Gallons of Rainwater from the Carmel River were injected into the Seaside Groundwater Basin in 2024 by MPWMD in partnership with California America Water—the third best ASR injection season ever!

That’s enough water to serve 8,000 homes for a year. We now have 3,677 acre-feet stored in the ground for use in a future dry period. That’s almost 40% of the Monterey Peninsula’s annual use.

With the success of the Aquifer Storage and Recovery (ASR) project and the Pure Water Monterey Expansion on track for completion next year, the Peninsula will have all the water supply needed for housing, jobs, and drought for decades to come.