Using machine learning to predict 1,2,3-trichloropropane contamination from legacy non-point source pollution of groundwater in California's Central Valley

Elsevier | May 6th, 2023

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates t

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates that TCP is a probable human carcinogen. TCP leaches through the soil into groundwater where it persists and contaminates thousands of wells in Asia, Europe, and North America. In California, TCP contaminates drinking water wells, with the highest levels of TCP beneath agricultural land used to grow grapevines. This study performs a mass balance and evaluates the ability of three types of tree-based machine learning models to predict TCP concentration in California's Central Valley aquifer system: classification and regression trees (CART), Random Forest (RF), and Boosted Regression Trees (BRT). To construct the models, multiple spatial explanatory variables were used, including historical agricultural land use data, irrigation levels, precipitation, soil type, groundwater age, redox state, and the presence of the co-contaminant nitrate. To estimate the amount of TCP applied to farmland in California, state historical pesticide and land use documents were used in the mass balance. Between 110,000 and 4,300,000 kg of TCP are estimated to have accumulated in the subsurface. Machine learning models indicate that the most important explanatory variables to predict TCP contamination of groundwater are precipitation, redox state, and the presence of the co-contaminant nitrate. Additionally, a 1000-m buffer area offers a slightly higher predictive performance as compared to 500-m and 1500-m buffers. Furthermore, the RF model outperforms CART and BRT for predictive performance. Finally, modeling using decision trees can predict TCP contamination levels in areas where monitoring is lacking, help target future TCP monitoring efforts, and aid in identifying areas to avoid when drilling new drinking water wells.

Using Sentinel‐1 and GRACE satellite data to monitor the hydrological variations within the Tulare Basin, California

Nature Portfolio (Springer Nature) | March 9th, 2022

Subsidence induced by groundwater depletion is a grave problem in many regions around the world, leading to a permanent loss of groundwater storage within an aquifer and

Subsidence induced by groundwater depletion is a grave problem in many regions around the world, leading to a permanent loss of groundwater storage within an aquifer and even producing structural damage at the Earth’s surface. California’s Tulare Basin is no exception, experiencing about a meter of subsidence between 2015 and 2020. However, understanding the relationship between changes in groundwater volumes and ground deformation has proven difficult. We employ surface displacement measurements from Interferometric Synthetic Aperture Radar (InSAR) and gravimetric estimates of terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE) satellite pair to characterize the hydrological dynamics within the Tulare basin. The removal of the long-term aquifer compaction from the InSAR time series reveals coherent short-term variations that correlate with hydrological features. For example, in the winter of 2018–2019 uplift is observed at the confluence of several rivers and streams that drain into the southeastern edge of the basin. These observations, combined with estimates of mass changes obtained from the orbiting GRACE satellites, form the basis for imaging the monthly spatial variations in water volumes. This approach facilitates the quick and effective synthesis of InSAR and gravimetric datasets and will aid efforts to improve our understanding and management of groundwater resources around the world.

Water and the Future of the San Joaquin Valley

Public Policy Institute of California (PPIC) | February 14th, 2019

The San Joaquin Valley—California’s largest agricultural region and an important contributor to the nation’s food supply—is in a time of great change. The valle

The San Joaquin Valley—California’s largest agricultural region and an important contributor to the nation’s food supply—is in a time of great change. The valley is ground zero for many of California’s most difficult water management problems—including groundwater overdraft, drinking water contamination, and declines in habitat and native species. Local water supplies are limited, particularly in the southern half of the region. To irrigate their crops, many farmers use water imported from the Sacramento–San Joaquin Delta. But in many places farmers have also relied on groundwater overdraft—pumping groundwater in excess of the rate at which it is replenished. Worsening droughts, increasing regulations to protect endangered native fishes, and growing demand by Southern California for Delta imports have compounded surface water scarcity. The state’s Sustainable Groundwater Management Act (SGMA) requires local water users to bring groundwater use to sustainable levels by the early 2040s. This will have a broad impact on valley agriculture and the regional economy in coming years—likely including some permanent idling of farmland. This report explores three key challenges facing the San Joaquin Valley and reviews the most promising approaches to address them:  Balancing water supplies and demands. To close the groundwater deficit, groundwater sustainability agencies in the valley’s overdrafted basins will have to augment supplies, reduce demands, or use some combination of these two approaches. A range of options are under consideration but they are not equally effective or practical.  Addressing groundwater quality challenges. Poor groundwater quality impairs drinking water supplies in disadvantaged rural communities, reduces long-term agricultural prosperity, and degrades ecosystems. Providing safe drinking water is an urgent priority. Over the longer term, parties will also need to manage water quantity and quality together, to take advantage of synergies and avoid unintended consequences. The necessary coordination will be challenging because the various programs addressing valley water quality issues are carried out by numerous local and regional entities, whose lines of responsibility and geographic boundaries do not neatly align.  Fostering beneficial water and land use transitions. Effectively addressing water scarcity and the resulting land use changes in the San Joaquin Valley offers opportunities to put lands coming out of production to good use—and gain “more pop per drop” from limited water resources. Multiple-benefit approaches to water and land management can enhance groundwater recharge and improve air and water quality. They can also promote healthier soils, new recreational opportunities, additional flood protection, improved habitat, and new revenue streams for private landowners engaging in conservation-oriented management. Addressing these complex and intertwined issues requires significant changes in water and land management and a major ramp-up in cooperation and coordination among a wide circle of stakeholders. Pursuing solutions that deliver multiple benefits will boost the chances of success overall. The entire region—and California as a whole—will benefit if solutions to these challenges are cost-effective and support the valley’s economy while improving public health and the natural environment.

Water availability and land subsidence in the Central Valley, California, USA

Hydrogeology Journal (Springer) | November 17th, 2015

The Central Valley in California (USA) covers about 52,000 km2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on sur

The Central Valley in California (USA) covers about 52,000 km2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use. *Erratum: Water availability and land subsidence in the Central Valley, California, USA, Faunt, C.C., Sneed, M., Traum, J. et al. Hydrogeol J (2017) 25: 2215

Water availability and subsidence in California’s Central Valley

University of California, Davis (UC Davis) | September 5th, 2015

California’s Central Valley covers about 52,000 square kilometers (km2) and is one of the most productive agricultural regions in the world. More than 250 different c

California’s Central Valley covers about 52,000 square kilometers (km2) and is one of the most productive agricultural regions in the world. More than 250 different crops are grown in the broad alluvial filled structural trough, with an estimated value exceeding $20 billion per year (Faunt 2009) (Figure 1). Central Valley agriculture depends on state and federal water systems that divert surface water, predominantly originating from Sierra Nevada snowmelt, to agricultural fields. Because the valley is semi-arid and the availability of surface water varies substantially from year to year, season to season, and from north to south, agriculture, as it grew, developed a reliance on groundwater for irrigation.

Water Blueprint for the San Joaquin Valley Economic Impact Analysis: Phase One Results

Water Blueprint for San Joaquin Valley | February 15th, 2020

Water Quality Control Plan for the Sacramento and San Joaquin Basins

Central Valley Regional Water Quality Control Board (CVRWQCB) | November 8th, 2016

Water Quality Control Plans or “Basin Plans” provide the foundation for all Central Valley Water Board regulatory actions. Basin Plans identify beneficial uses of sur

Water Quality Control Plans or “Basin Plans” provide the foundation for all Central Valley Water Board regulatory actions. Basin Plans identify beneficial uses of surface and ground waters, water quality objectives to protect those uses, implementation actions to achieve objectives, and a monitoring and surveillance program to insure that implementation actions are effective. All actions by the Board must be compliant with the Basin Plans. The Central Valley Water Board has two Basin Plans: one for the Sacramento and San Joaquin River Basins and one for the Tulare Lake Basin. A public review process is conducted every three years (Triennial Review) to identify and prioritize actions needed to address water quality concerns and maintain effectiveness of the Basin Plans. Upon Board approval of the Triennial Review work plan, staff investigates water quality issues and proposes amendments to the Basin Plans for Board consideration. Amendments may range from developing site specific water quality objectives for a single constituent such as copper, to basin-wide control programs for a suite of potential pollutants such as pyrethroids, to policy recommendations and strategies for addressing emerging contaminants and/or climate change. This basin plan has many sections with many amendments, and so no attempt is made to house this document in the library.  Instead, please visit the Central Valley Regional Water Quality Control Board's basin planning page.

Water Quality Control Plan for the Tulare Lake Basin

Central Valley Regional Water Quality Control Board (CVRWQCB) | September 29th, 2016

The Central Valley Region includes about 40% of the land in California and stretches from the Oregon border to the Kern County/Los Angeles County line. It is bound by

The Central Valley Region includes about 40% of the land in California and stretches from the Oregon border to the Kern County/Los Angeles County line. It is bound by the Sierra Nevada Mountains on the east and the Coast Range on the west. The Region is divided into three basins: the Sacramento River Basin, the San Joaquin River Basin, and the Tulare Lake Basin. This basin plan covers only the Tulare Lake Basin. The Sacramento River Basin and the San Joaquin River Basin are covered in a separate basin plan. The Tulare Lake Basin comprises the drainage area of the San Joaquin Valley south of the San Joaquin River. Note: In 1976, the U. S. Geologic Survey, the Department of Water Resources, and the State Water Resources Control Board agreed upon the hydrologic boundaries for basins within California. The agreed boundaries did not match the planning boundaries in certain cases such as between the San Joaquin River Basin and the Tulare Lake Basin. The planning boundary between the San Joaquin River Basin and the Tulare Lake Basin follows the southern watershed boundaries of the Little Panoche Creek, Moreno Gulch, and Capita Canyon to boundary of the Westlands Water District. From here, the boundary follows the northern edge of the Westlands Water District until its intersection with the Firebaugh Canal Company’s Main Lift Canal. The basin boundary then follows the Main Lift Canal to the Mendota Pool and continues eastward along the channel of the San Joaquin River to the southern boundary of the Little Dry Creek watershed (Hydrologic Subareas No. 540.70 and 545.30) and then follows along the southern boundary of the San Joaquin River drainage basin. Surface water from the Tulare Lake Basin only drains north into the San Joaquin River in years of extreme rainfall. This essentially closed basin is situated in the topographic horseshoe formed by the Diablo and Temblor Ranges on the west, by the San Emigdio and Tehachapi Mountains on the south, and by the Sierra Nevada Mountains on the east and southeast. The Basin encompasses approximately 10.5 million acres, of which approximately 3.25 million acres are in federal ownership. Kings Canyon and Sequoia National Parks and substantial portions of Sierra, Sequoia, Inyo, and Los Padres National Forests are included in the Basin. Valley floor lands (i.e., those having a land slope of less than 200 feet per mile) make up slightly less than one-half of the total basin land area. The maximum length and width of the Basin are about 170 miles and 140 miles, respectively. This plan contains all amendments up to July of 2016.  To check for the latest version or for any new amendments, click here.

Water Quality Control Plan for the Tulare Lake Basin Third Edition

Central Valley Regional Water Quality Control Board (CVRWQCB) | May 31st, 2018

Water quality control plans, or basin plans, contain California's administrative policies and procedures for protecting state waters. Basin plans are required by the sta

Water quality control plans, or basin plans, contain California's administrative policies and procedures for protecting state waters. Basin plans are required by the state Porter-Cologne Water Quality Control Act (California Water Code Section 13240). In addition, Section 303 of the federal Clean Water Act requires states to adopt water quality standards that “consist of the designated uses of the navigable waters involved and the water quality criteria for such waters based upon such uses.” Each of California's nine regional water quality control boards must formulate and adopt a basin plan for all areas within its region. The basin plans must conform with statewide policy set forth by the legislature and by the State Water Resources Control Board. Basin plans consist of designated beneficial uses to be protected, water quality objectives to protect those uses, and a program of implementation needed for achieving the objectives {California Water Code, Section 13050(j)}. Beneficial uses, together with their corresponding water quality objectives, meet federal regulatory criteria for water quality standards. Hence, California's basin plans serve as regulatory references for meeting both State and federal requirements for water quality control {40 CFR Parts 130 and 131}.One significant difference between the state and federal programs is that California's basin plans establish standards for ground waters in addition to surface waters. Basin plans are adopted and amended by regional water boards under a structured process involving full public participation and state environmental review. Basin plans and amendments do not become effective until approved by the State Water Board. Regulatory provisions must be approved by the Office of Administrative Law. Adoption or revision of surface water standards are subject to the approval of the U. S. Environmental Protection Agency before they become accepted standards for the federal program. Basin plans complement water quality control plans adopted by the State Water Board. It is the intent of the state and regional water boards to maintain basin plans in an updated and readily available edition that reflects all current water quality control programs. The first edition of this Water Quality Control Plan for the Tulare Lake Basin (Basin Plan) was adopted by the California Regional Water Quality Control Board, Central Valley Region, on 25 July 1975, and became effective following approval by the State Water Board on 21 August 1975 and the U. S. Environmental Protection Agency (EPA) in June 1976. Although several revisions have been adopted and approved since 1975, this revision is the first complete rewrite of the text of the Basin Plan. Regional Water Board resolutions adopted prior to 17 August 1995, that revise or supplement the first edition of the plan which are not expressly incorporated by reference into the second edition of the plan are superceded. In this Basin Plan, "Regional Water Board" refers to the Central Valley Regional Water Quality Control Board and "State Water Board" refers to the State Water Resources Control Board. *Central Valley plans split between separate documents for Tulare basin and the Sacramento and San Joaquin basins. Click here for the plan for the Sacramento and San Joaquin basins.

Water shortage risks from perennial crop expansion in California's Central Valley

Environmental Research Letters (IOP) | October 15th, 2019

California's Central Valley is one of the world's most productive agricultural regions. Its high-value fruit, vegetable, and nut crops rely on surface water imports from

California's Central Valley is one of the world's most productive agricultural regions. Its high-value fruit, vegetable, and nut crops rely on surface water imports from a vast network of reservoirs and canals as well as groundwater, which has been substantially overdrafted to support irrigation. The region has undergone a shift to perennial (tree and vine) crops in recent decades, which has increased water demand amid a series of severe droughts and emerging regulations on groundwater pumping. This study quantifies the expansion of perennial crops in the Tulare Lake Basin, the southern region of the Central Valley with limited natural water availability. A gridded crop type dataset is compiled on a 1 mi2 spatial resolution from a historical database of pesticide permits over the period 1974–2016 and validated against aggregated county-level data. This spatial dataset is then analyzed by irrigation district, the primary spatial scale at which surface water supplies are determined, to identify trends in planting decisions and agricultural water demand over time. Perennial crop acreage has nearly tripled over this period, and currently accounts for roughly 60% of planted area and 80% of annual revenue. These trends show little relationship with water availability and have been driven primarily by market demand. From this data, we focus on the increasing minimum irrigation needs each year to sustain perennial crops. Results indicate that under a range of plausible future regulations on groundwater pumping ranging from 10% to 50%, water supplies may fail to consistently meet demands, increasing losses by up to 30% of annual revenues. More broadly, the datasets developed in this work will support the development of dynamic models of the integrated water-agriculture system under uncertain climate and regulatory changes to understand the combined impacts of water supply shortages and intensifying irrigation demand.