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Prof. Thomas Harter

University of California, Davis, USA



"Groundwater nitrate in California: assessment and evaluation of sources and impacts“ & "Groundwater regulation and management in California`s agricultural regions"

© Prof. Thomas HarterProf. Thomas Harter
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Abstract: Groundwater nitrate in California: assessment and evaluation of sources and impacts

Anthropogenic groundwater nitrate contamination in the Central Valley aquifer system, California, is widespread, with over 40% of domestic wells in some counties exceeding drinking water standards. Sources of groundwater nitrate include leaky municipal wastewater systems, municipal wastewater recharge, onsite wastewater treatment (septic) systems, atmospheric nitrogen deposition, animal farming, application of organic waste materials (sludge, biosolids, animal manure) to agricultural lands, and synthetic fertilizer. At the site or field scale, nitrogen inputs to the landscape are balanced by plant nitrogen uptake and harvest, atmospheric nitrogen losses, surface runoff of nitrogen, soil nitrogen storage changes, and leaching to groundwater. Irrigated agriculture is a dominant player in the Central Valley nitrogen cycle: The largest nitrogen fluxes are synthetic fertilizer and animal manure applications to cropland, crop nitrogen uptake, and groundwater nitrogen losses. We construct a historic field/parcel scale groundwater nitrogen loading model distinguishing urban and residential areas, individual animal farming areas, leaky wastewater lagoons, and approximately 50 different categories of agricultural crops. The mass balance-based approach is compared to estimates of nitrate loading obtained from groundwater quality data in shallow domestic wells and deeper public supply and irrigation wells. We use both statistical approaches (Bayesian mixing models, Bayesian source apportionment, and machine-learning algorithms) and numerical modeling approaches (vadose zone modeling, regional groundwater modeling of nonpoint source pollution) to validate estimates of nitrate loading to groundwater, and as a means to predict future outcomes under stakeholder-defined management scenarios http://groundwaternitrate.ucdavis.edu.

Abstract: Groundwater regulation and management in California`s agricultural regions

California’s Porter-Cologne Water Quality Act of 1969 preceeded the U.S. Clean Water Act by three years. Unlike the federal framework, the California Act explicitly includes groundwater as a waterbody that requires waste discharges to be regulated under a permit program. Until 2002, nonpoint sources of surface water and groundwater discharges were largely exempt from the permit program. Instead, state regulatory agencies focused on developing and implementing programs to permit point source dischargers to surface waters (under the guidelines of the federal Clean Water Act), and cleaning up groundwater contamination from point sources (under federal and state “Superfund” legislation). In parallel, scientific efforts focused on wastewater treatment, water quality in streams and lakes, and on understanding pollutant fate and transport in the subsurface. Only in the late 1990s, federal efforts to control nonpoint source pollution to surface waters reached the agricultural community. In 2002, California exemptions sunset and new regulatory programs are being developed to now also regulate groundwater discharges, especially of nitrate and salts. California has already developed stringent dairy regulations to protect groundwater (2007), is currently developing an Irrigated Lands Regulatory Program to protect groundwater in alluvial basins under 3.5 million ha of irrigated lands (since 2012), and is writing new regulatory frameworks for nutrient and salt management in its groundwater and watershed basins (2017). The process, in some regions, is developing under a mostly authoritarian, top-down policy development by regional authorities, pressured by environmental groups, and embroiled in lawsuits; and under a largely collaborative, stakeholder-driven policy development in other regions. In either case, we argue that the development of the new framework is hampered by both, the history of the policy framework within which regulatory agencies are currently operating, and the history of groundwater science. Both, water quality policy frameworks and groundwater science have developed around the concepts related to point source pollution with sources less than a few hectare in size and contaminant sites of few tens of hectare. Policy and science concepts developed for point sources are insufficient and inadequate, and often counterproductive, when extended to regulating and monitoring nonpoint sources. We argue that U.S. regulatory agencies must divorce themselves from existing policy structures and science must reengage across disciplines to develop effective land use management programs, and groundwater quality monitoring schemes that will be successful in reversing decades of groundwater degradation.


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