Transforming Water: Pure Water Soquel Embraces One Water Approach

overhead shot of a city
By Melanie Mow Schumacher, Dave Carlson & Ashu Shirolkar

Water management strategies tend to evolve gradually with slowly changing community needs. That’s rare in California, where continued population growth and prolonged drought exacerbated by climate change have sparked dramatic change, through initiatives such as the Pure Water San Diego program and Orange County’s Groundwater Replenishment System, now undergoing final expansion. Further north along the Pacific Coast, Pure Water Soquel is another example of timely, transformative action for a more resilient and reliable water supply.

Groundwater is the sole source of water for more than 40,400 residents served by the Soquel Creek Water District. Historic overdrafting prompted the California Department of Water Resources (DWR) to classify the Santa Cruz Mid-County Groundwater Basin as one of 21 “critically over-drafted basins” that must meet the state sustainability mandate by 2040. The basin’s overdraft condition has resulted in seawater contamination of the basin along the coastline, confirmed at multiple locations. To meet that mandate and ensure an adequate, clean, sustainable water supply for the future-where reliance on only rainfall for groundwater replenishment is not a viable option-the Soquel Creek Water District Board launched the Pure Water Soquel Groundwater Replenishment and Seawater Contamination Prevention (Pure Water Soquel) Project in 2015.

Once all new facilities are constructed and operational in late 2023/early 2024, the project will deliver myriad benefits for the community, wildlife and habitat.

One Water, Many Benefits

Embracing a One Water approach to water management is a crucial part of the Pure Water Soquel transformation. Pure Water Soquel features this holistic approach that enables the water district to address multiple needs.

The Soquel Creek Water District serves residents, businesses, and industries located in Soquel and six other communities on California’s central coast in Santa Cruz County. Located between San Francisco and Monterey and adjacent to the City of Santa Cruz, the District’s service area includes seven miles of shoreline and extends inland to the foothills of the Santa Cruz mountains.

Creating a new supply of recycled water is a substantial benefit for the entire service area. The District’s per-capita water use is already among the lowest in the United States, so implementing additional conservation measures wasn’t an option. Other options — including desalination and conjunctive use — were considered, but recycling was selected as the best path forward for this mid-county region.

New facilities will reclaim approximately 25 percent of the City of Santa Cruz Wastewater Treatment Facility’s (SCWWTF) secondary effluent, and then purify it to replenish the groundwater basin. This will optimize beneficial reuse of this precious resource on land rather than just being discharged into the Monterey Bay National Marine Sanctuary. The new supply of purified water will meet all state and federal water quality criteria and will help quench the area’s thirst for safe drinking water as it meets the State’s mandate for basin sustainability.

The purified water will create a barrier against seawater intrusion moving further inland, thus improving water quality and ensuring the groundwater basin remains a fresh drinking water supply, not only for the District but for the thousands of private well users in the region. Additional environmental benefits include reduced ocean discharge as well as maintaining baseflows in local rivers and creeks to support critical wildlife habitat.

Delivering the Good

The District obtained significant federal and state funding from numerous sources. Creativity, resourcefulness, and collaboration helped the District secure funding from the California Proposition 1 Groundwater Grant Program, U.S. Bureau of Reclamation’s Title XVI Grant Program, U.S. Environmental Protection Agency’s Water Infrastructure Finance and Innovation Act Low-Interest Loan Program, and the California State Water Board’s Seawater Intrusion Control Low-Interest Loan Program.

Under a progressive design-build agreement, Black & Veatch is working with the District to drive sustainable groundwater supply management through design and construction of treatment facilities and associated infrastructure. The company has completed Phase 1 of the agreement, which included design of the treatment facilities and preconstruction activities. In fall 2021 the green light was given for Phases 2 and 3 – construct, startup, commission, and warranty the new treatment facilities.

A unique element is that the Pure Water Soquel treatment facilities are split between two sites. New facilities under construction at the SCWWTF include a source-water pump station and electrical transformer, brine-return pipeline, electrical metering enclosure, and cloth-filter/ultraviolet light (UV) system for tertiary treatment. An Advanced Water Purification Center, now under construction at a different site, will feature ozone pretreatment, a three-step purification treatment train, and post-treatment processes.

Collectively, the new facilities will recycle up to 1,500 acre-feet of water per year from the SCWWTF by processing it through the Advanced Water Purification Center before pumping it into the groundwater basin. Delivered under separate contracts are eight-mile pipelines that will convey water from the SCWWTF to the water purification center and three Seawater Intrusion Prevention Wells that will inject purified water underground for aquifer recharge.

Pure, But Not Simple

The Advanced Water Purification Center is the heart of the Pure Water Soquel project. A series of three advanced treatment technologies will enable the District to produce water comparable in quality to that flowing from taps across the United States and cleaner than most bottled water:

Microfiltration. In this initial filtration process, water is pumped through tubes filled with tiny membranes. Each membrane is composed of hollow fibers perforated with microscopic holes. Solids, protozoa, bacteria, and some viruses are removed from the water as it is drawn through the microfiltration tubes.
Reverse osmosis. Water is forced through membranes under high pressure. Contaminants 100 times smaller than a virus, as well as chemicals, are stopped by this barrier, resulting in water of nearly distilled quality. Salts, viruses, most pharmaceuticals, personal care products, and pesticides are rejected and returned to the wastewater treatment plant for safe disposal.

UV-AOP. UV disinfection with advanced oxidation is the final step in the purification process. The concentrated light kills any organisms that may remain after reverse osmosis. UV combined with hydrogen peroxide effectively disinfects the water.

Groundbreaking Celebration Highlights Collaboration and Transformation

With a theme of “Water Transformed!” the District held a groundbreaking ceremony in December 2021 to commemorate the official start of construction on the advanced water purification center. Approximately 50 invited guests representing numerous organizations and agencies attended the event. The broad spectrum of participants spotlighted interagency and other collaborative relationships, which ultimately led to ceremonial shovels in the ground to memorialize the start of construction.

Speakers included dignitaries from agencies involved in funding and regulating the project along with prominent political leaders including California State Water Board Chair, E. Joaquin Esquivel, EPA Water Division Director for the Pacific Southwest Region Tomás Torres, State Senator John Laird, and State Assemblymember Mark Stone. Members of the Soquel Creek Water District Board of Directors, the Santa Cruz City Council, and the Sant Cruz County Board of Supervisors also offered remarks. Many participants posed for pictures in front of an oversized butterfly-wing backdrop to illustrate and socially share support for the Pure Water Soquel project.

The Future is Here

Water reuse — also known as water recycling — yields not only a resilient new source of supply but also potential environmental benefits through the reduction or elimination of effluent discharge to sensitive water bodies. Pure Water Soquel will produce up to 1,500 acre-feet per year of purified water and an additional 300 acre-feet per year of Title 22 unrestricted, non-potable recycled water. The new non-potable water will be used at the SCWWTF for in-plant water usage, irrigation of a nearby park, and at a fill station for use by construction trucks for dust control. This reduces the use of potable water that instead is available for the Santa Cruz community.

In a region that relies on groundwater and must optimize every drop, the recycling project will help preserve water quantity and quality and boost water resilience. One Water thinking provides an opportunity for communities to best manage water resources on a regional basis and to co-develop innovative and sustainable solutions that achieve multiple benefits related to economic, environmental, and societal returns.

At the groundbreaking ceremony, EPA’s Tomás Torres noted that Pure Water Soquel represents the future of the west. It also represents transformative action in the present to solve problems created in the past. And, as the State Water Board’s E. Joaquin Esquivel said at that ceremony, “Climate change is challenging us all to become more creative and inclusive as we accelerate efforts to preserve our water supply.”


Melanie Mow Schumacher, P.E., is Pure Water Soquel Program Director for Soquel Creek Water District. She has worked in municipal water sector for more than 25 years and has overseen the progression of the project including technical feasibility, environmental compliance, funding, design, permitting and construction. 

Dave Carlson, P.E., is a vice president with Black & Veatch Governments and Environment. He has 40 years of experience providing water and wastewater solutions throughout the United States using multiple delivery methods.  

Ashu Shirolkar, P.E., is senior project manager with Black & Veatch Governments and Environment. Shirolkar brings extensive experience in water, wastewater, and recycled water treatment and served as the design director for the Pure Water Soquel Treatment Facilities.

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