By Daniel Cozad, Central Valley Salinity Coalition
Ken Miller, Formation Environmental
Richard Meyerhoff, GEI Consultants
Tom Grovhoug, Larry Walker Associates
The Central Valley (Valley) watershed is the epicenter of California’s economy—encompassing just over 35% of the land in the state. It provides water for millions of people, agriculture, industry, and other businesses from San Francisco to San Diego, as well as food for California, the nation, and the world. Over the last 150 years, increased agricultural, industrial, and municipal activities, coupled with population growth, have resulted in significant increases in salts in soils, groundwater, and surface waters in various areas within in the Central Valley.
Normal activities in all homes, farms, businesses, cities, and towns contribute to the salt problem by adding or concentrating salts. Irrigation, food processing, municipal wastewater treatment, and water management practices are just some of the water uses that influence the salt problem in the Central Valley. Salt conditions are also impacted in parts of the Valley as a result of importing and exporting water supplies.
High levels of salt can impair water quality, reduce crop production, affect drinking water supplies, and alter ecological functions and habitats. Salt accumulation has resulted in approximately 250,000 acres being taken out of production and 1.5 million acres out of approximately 7 million irrigated acres have been declared salinity impaired in the Valley. If not addressed, the future economic impacts of salts on the Valley could exceed $1.5 billion per year. (Central Valley RWQCB, 2018).
The challenge has resulted in research and technical analysis for many years. Salinity Distribution and Impact in the Sacramento Valley (Dickey, J., and G. Nuss. 2002) is a paper submitted for a U.S. Committee on Irrigation and Drainage Conference that combined weather, water, soil, and crop data in an overview of regional salt distribution and impacts in 12 irrigation and reclamation districts in the Sacramento Valley, from Yolo to Butte Counties. The paper found that “Field drainage and position within the complex of irrigation and drainage facilities combine to determine the severity of the problem at specific locations. At a regional level, salinity generally increases with the distance from the water sources (from north to south). At the local level, salinity depends on irrigation management and drainage. When water supplies suffice, salinity is adequately controlled in most of the region through dilution and removal with drainage.”
Dickey and Nuss (2002) identified a “focused effort to improve and update salinity mapping, and to monitor trends over time” as critical data needs that “would refine our understanding of the problem and focus efforts at resolution.” The paper recognized water management as fundamental to salinity management, that “salt management strategies must explicitly consider the dynamics of water supply quantity and quality.”
The findings of Dickey and Nuss (2002) and others provided the technical foundation for formation of the Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) program in 2006. After more than a decade of work by a diverse stakeholder group, the CV-SALTS effort culminated in the adoption of a Salt Control Program for California’s Central Valley Region in 2018. This Program recognized the critical need to implement a phased approach to long-term salt management in the Valley. As a result, the CV-SALTS Prioritization and Optimization (P&O) Study is now under way to advance the understanding of current and future salt conditions at the Central Valley scale. The P & O Study is an innovative framework of technical studies, modeling, and data management which will be used to develop and plan effective solutions for managing and controlling salt accumulation in the Valley. A watershed model (see figure below), which accounts for the processes and sources shown in this diagram, is the centerpiece of the suite of modeling tools that will be employed in the study.
Initial work under the P&O study has confirmed that salt concentrations in the groundwater are naturally high in some areas and increasing at different rates in different regions of the Central Valley. In addition, the P&O Study’s use of sophisticated modeling tools has confirmed earlier estimates of salt found in irrigation water, fertilizers, amendments, wastewater, and soils are leaving the root zone towards groundwater from different salt sources. As shown in the bar plot, in the San Joaquin Valley and Tulare Lake Basin, roughly 4 and 9 million tons of salt, respectively, are concentrated in the root zone and move downward to groundwater every year. In the Sacramento River hydrologic region, approximately 2 million tons of salt moves to groundwater, while about a third of that is exported from the watershed through drainage, as summarized in the Baseline Characterization Report prepared by the P&O Study team of scientists and engineers at Formation Environmental, GEI Consultants, and Larry Walker Associates. The spatial differences in salt loading to surface water and groundwater is a function of the water supply and quality for different uses (e.g., agricultural, municipal) in addition to the factors described by Dickey and Nuss (2002). This variability is depicted in the map below showing the average annual amount of salt moving to below the root zone in the Sacramento River Hydrologic Region. Work is ongoing to estimate the anticipated future groundwater salinity conditions throughout the Central Valley under different future scenarios by using a state-of-the-art groundwater model and considering the complete hydrologic cycle.
The overarching purpose of the P & O Study is to develop a plan to implement new or maintain existing salinity management projects and activities to address long-term salt accumulation in groundwater, protect surface waters, achieve long-term economic vitality for Central Valley agriculture, communities, and other entities, and avoid future significant adverse impacts to salt-sensitive crops and other sensitive uses. While this plan is being developed, an interim salinity permitting approach has been implemented by the Central Valley Water Board that provides certainty for existing Valley dischargers that must manage salt now while the P&O Study is ongoing.
Ultimately, the technical work being performed by the P & O Study and its associated policy and planning efforts crafted by the Water Boards and stakeholders will help guide local actions to support groundwater sustainability with regard to salt accumulation and establish alternative permitting strategies that result in the best, practicable salt management outcomes for the Valley.
