Case Study Sept 2023: ‘Small but Mighty’ Soquel Creek Water Answers Threat to Groundwater Supply

  • by ACWA Staff
  • Sep 15, 2023
  • Newsletters

SqCWD employee Amanda Bunte conducts a water quality sampling test. The district relies on an array of methods to measure the impacts of seawater intrusion into its groundwater, which provides 100% of the district’s water supply.

Called “small but mighty” by its staff, the Soquel Creek Water District (SqCWD) in Santa Cruz County has attracted international attention while persevering in the face of daunting challenges. 

Not too long ago, the Central California Coast district faced the impending loss of most, if not all, of its most productive groundwater wells for drinking water through seawater intrusion. But in a classic example of measuring a problem to manage it, SqCWD today is slowing the pace of that intrusion through a mix of conservation, pioneering mapping technology and plans to accelerate progress through water recycling.

The situation looked dire in 2014, when SqCWD General Manager Ron Duncan learned that seawater could hit their main well field in three years with current levels of pumping. 

“We realized that if we didn’t do something, we’re done. We’re just done, and we’ve failed as stewards of our community’s water,” Duncan said. 

Cutting water use was an obvious strategy, and the district has since worked with its customers to reduce residential water use from 80 to 55 gallons per day. The basin SqCWD relies on is one of 21 critically overdrafted basins in California under implementation of the Sustainable Groundwater Management Act, or SGMA. 

Addressing the problem required getting a much more precise picture of exactly where seawater was seeping into the basin offshore, essential to understanding the immediate risk to coastal wells from seawater contamination. But how to get that picture remained unknown, until a call from halfway around the world.

When Duncan picked up the phone five years ago, the caller identified himself as being from the Danish embassy. Duncan thought it was a prank and hung up.  But when he called again, Duncan listened. Denmark, no stranger to understanding the mysteries of groundwater, had utilized airborne mapping technology to map and characterize its country’s groundwater systems. Its U.S. embassy had heard of SqCWD’s situation through its efforts to engage American water suppliers with its nation’s water-related technology sector. 


Duncan’s telephone conversation led to the Danish-based companies SkyTEM and Ramboll in 2017 deploying what was then cutting-edge mapping technology along the Monterey Bay. This included SqCWD’s territory and the surrounding coastal region, covered by the Santa Cruz Mid-County Groundwater Agency, which coordinated the research work.

With SkyTEM, a low-flying helicopter can criss-cross over land or water towing a hexagon-shaped electromagnetic device that beams radio waves at the surface and measures the response. Ramboll’s website compares it to taking an MRI of the ground’s subsurface. The technology, in SqCWD’s instance, could also peer 600-feet beneath the ocean surface and into the seabed to collect data, which produced 3D image modeling showing exactly where seawater was seeping into the groundwater supply. 

Today, the technology is well-recognized and being used across California and the U.S. However, this mapping technology got its early start on California’s Central Coast and gave SqCWD what it needed to move forward in addressing the threat of seawater intrusion.

“Now, we know our sense of urgency. It is defined,” Duncan said.

Pure Water Soquel

SqCWD analyzed water supply solutions and determined the most effective option would be using purified recycled water to bring its basin into sustainability. Today, construction of Pure Water Soquel is on track for completion in late 2024. When it goes online, the facility will capture and purify through advanced water technologies about 25% of secondary effluent from the region’s wastewater treatment plant. Typically discharged into Monterey Bay, that water, once purified, will be conveyed to three Seawater Intrusion Prevention Wells to replenish the groundwater basin and create a barrier against seawater intrusion.

Funding for Pure Water Soquel included $63.25 million through California Proposition 1 and a $29.9 million grant through the federal WaterSMART Title XVI program, in addition to other funding sources. However, a big part of the project’s successful start cost far less.

Laying the groundwork for Pure Water Soquel, SqCWD recognized the need for a comprehensive public education campaign to increase its community’s understanding of purified water as a safe, reliable and sustainable supply of drinking water. As part of that campaign, SqCWD developed a mobile education trailer outreach effort on a shoestring budget of less than $8,000. SqCWD staff have driven the trailer throughout the community, including visits to farmers markets, Earth Day events and school presentations.  

International Attention

The educational campaign and its butterfly logo earned awards from the WateReuse Association and California Association of Public Information Officials. However, the Pure Water Soquel project as a whole received international attention in 2022 when BBC StoryWorks selected it as one of 16 projects worldwide, and among two in the U.S., for its mini-documentary video series, “Beneath the Surface, The Journey of Water.” The documentary can be viewed by scanning the QR code on the opposite page. 

For SqCWD, the documentary framed the success of a years-long effort to overcome what remains a serious threat from seawater intrusion, but a threat where an effective solution is now on the horizon.

“This mini-documentary points to our valued partnerships, which are crucial to successfully implementing this groundwater replenishment project. That includes the City of Santa Cruz, as well as the Santa Cruz Mid-County Groundwater Agency and especially our community as a whole,” SqCWD Board President Carla Christensen said. “Our partnerships also extend to the state and federal levels, which have provided generous grants and low-interest loans to help build Pure Water Soquel. From the Board to staff and our community partners – we are all in this together to ensure that our water supply is sustainable for current and future generations.”

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