Nels Ruud

California Environmental Protection Agency

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Z. J. Kabala

Duke University

JŠ

Jiřı́ Šimůnek

University of California, Riverside

Helen E. Dahlke

University of California, Davis

Thomas Harter

University of California, Davis

Cristina Prieto García

University of California, Davis

Giuseppe Brunetti

University of Calabria

Tiantian Zhou

University of California, Davis

Elad Levintal

Ben-Gurion University of the Negev

Marion W. Jenkins

University of California, Davis

David Schaad

Duke University

Cooperative Institutions

University of California, Davis

Federal Center for Technological Education of Minas Gerais

National Society of Professional Engineers

University of California System

University of California, Riverside

Duke University

University of California, Berkeley

New Orleans Public Library

Lawrence Livermore National Laboratory

Chinese Academy of Sciences

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Simulation of pesticide transport in 70-m-thick soil profiles in response to large water applications

Journal of Hazardous Materials (2025)

Tiantian Zhou Giuseppe Brunetti Nels Ruud Jiřı́ Šimůnek Wenyi Cui

Global groundwater depletion is a pressing issue, particularly in regions dependent on groundwater for agriculture. Agricultural Managed Aquifer Recharge (Ag-MAR), where farm fields are used as spreading grounds for flood water, is a promising strategy to replenish groundwater, but it raises concerns about pesticide leaching into aquifers, posing risks to both drinking water quality and ecosystems. This study employs a physically based unsaturated flow model, a Bayesian probabilistic approach and novel towed transient electromagnetic (tTEM) data to determine the fate and transport, especially the maximum transport depths (MTDs) of four pesticide residues (Imidacloprid, Thiamethoxam, Chlorantraniliprole, and Methoxyfenozide) in three 70-m-thick unsaturated zones (P1, P2, P3) of California's Central Valley alluvial aquifer. The results show that Ag-MAR significantly increased MTDs across all profiles for all pesticides and with higher variability in pesticide transport depths compared to the natural rainfall scenario. Profile P2, with the highest sand content exhibited the deepest MTDs under Ag-MAR, indicating a strong influence of soil texture on pesticide transport. While natural capillary barriers at the depth of 2.5-20 m impede water flow under natural rainfall conditions, the high-pressure infiltration during Ag-MAR overcomes these barriers, leading to deeper water and pesticide movement. Among various evaluated pesticides, Methoxyfenozide exhibited the smallest absolute MTDs but the largest relative increases in MTDs (RMTDs) under Ag-MAR due to its persistence and low mobility, posing a higher risk of deep transport during intensive recharge events. In contrast, Thiamethoxam showed the largest MTDs under both scenarios but smaller RMTDs due to its high mobility, suggesting a more consistent transport behavior regardless of recharge practices. The findings highlight the importance of understanding both site-specific and pesticide-specific behaviors to mitigate groundwater contamination risks during large water applications.

10.1016/j.jhazmat.2025.137517

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Citations (0)

Estimation of groundwater pumping as closure to the water balance of a semi-arid, irrigated agricultural basin

Journal of Hydrology (2004)

Nels Ruud Thomas Harter Alec Naugle

Water balance

Groundwater model

Water storage

Groundwater discharge

10.1016/j.jhydrol.2004.04.014

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Citations (85)

Numerical Evaluation of Flowmeter Test Interpretation Methodologies

Water Resources Research (1996)

Nels Ruud Z. J. Kabala

We evaluate systematic errors inherent in two flowmeter test interpretation methodologies. A physically consistent two‐dimensional groundwater flow model is used to numerically simulate the single flowmeter test and the double flowmeter test in 25 different two‐layer confined aquifers of a priori known horizontal hydraulic conductivities, K i ; specific storativities, S si , and hydraulic diffusivities, v i = K i / s si , in each layer ( i =1, 2). Values selected for the layer hydraulic parameters span those encountered in natural sandy formations with the ratios of the corresponding parameters in the two layers falling in the following ranges: 1 ≤ K 1 / K 2 ≤ 100, 0.0001 ≤ S s 1 / S s 2 ≤ 100, and 1 ≤ V 1 / v 2 ≤ 10,000. We find that the size of the hydraulic diffusivity contrast rather than the hydraulic conductivity ratio is the dominating factor for the parameter estimation accuracy in the two flowmeter methodologies. For the single flowmeter test methodology the ratio of the estimate over the corresponding true value falls within the range , whereas for the double flowmeter test it falls within . The double flowmeter test also provides estimates of layer specific storativity, S si . These are accurate only for the special case of equal layer hydraulic diffusivities. The test yields order‐of‐magnitude estimates of S si for layer hydraulic diffusivities differing from each other by up to an order of magnitude. For larger differences the estimation errors are much larger. Hydraulic parameters of a given layer are better estimated when the flowmeter is placed either exactly at the interlayer boundaries or, ideally, at two different points within each layer away from the boundaries. The results from simulated flowmeter tests in a five‐layer system are consistent with those for the two‐layer aquifers. This implies that the presented results most likely apply to flowmeter tests in arbitrary multilayer aquifers. Existence of significant errors in aquifer parameters estimated from synthetic flowmeter data demonstrate that the Theis [1935] model, which is assumed to be valid in each layer by the two considered interpretation methodologies, does not fully capture the flow dynamics in layered aquifers. This is illustrated by numerically calculated examples of simultaneously nonuniform and transient well face flux distributions in a layered aquifer. A model more sophisticated than that of Theis [1935] needs to be found.

Hydraulic head

10.1029/96wr00004

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Citations (43)

Response of a partially penetrating well in a heterogeneous aquifer: integrated well-face flux vs. uniform well-face flux boundary conditions

Journal of Hydrology (1997)

Nels Ruud Z. J. Kabala

Drawdown (hydrology)

10.1016/s0022-1694(96)03217-9

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Citations (49)

Introduction to Environmental Soil Physics

Vadose Zone Journal (2006)

Nels Ruud

10.2136/vzj2006.0013br

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Citations (25)

The dipole-flow test with a tracer: a new single-borehole tracer test for aquifer characterization

Journal of Contaminant Hydrology (2000)

D. J. Sutton Z. J. Kabala David Schaad Nels Ruud

TRACER

10.1016/s0169-7722(00)00083-8

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Citations (61)

Numerical evaluation of the flowmeter test in a layered aquifer with a skin zone

Journal of Hydrology (1997)

Nels Ruud Z. J. Kabala

10.1016/s0022-1694(97)00091-7

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Citations (27)

The impact of agricultural managed aquifer recharge on the fate and transport of pesticides in the unsaturated zone

Water Research (2024)

Tiantian Zhou Nels Ruud Jiřı́ Šimůnek Giuseppe Brunetti Elad Levintal

10.1016/j.watres.2024.122442

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Citations (1)

Economically Driven Simulation of Regional Water Systems: Friant-Kern, California

Journal of Water Resources Planning and Management (2006)

Guilherme Fernandes Marques Jay R. Lund Mark R. Leu Marion W. Jenkins Richard E. Howitt

This paper develops and applies an economically driven simulation model for California's Friant-Kern system, a region characterized by diverse water sources employed predominantly for commercial irrigated agriculture, with significant local water trading activity. The economic-engineering simulation approach highlights the importance of representing user economic decisions for water systems in a context of complex physical and infrastructure systems dominated by economic water uses. The model simulates how water users conserve, select supplies and make water exchange and market decisions in response to water costs and availability, and provides estimates of economic and operational impacts of alternative policies for the Friant-Kern system. Results show that high surface water prices cause farmers to pump more groundwater, disturbing an existing conjunctive use system and aggravating regional groundwater overdraft.

Overdraft

Conjunctive use

Water use

Water trading

10.1061/(asce)0733-9496(2006)132:6(468)

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Citations (40)

Evaluation of flowmeter-head loss effects in the flowmeter test

Journal of Hydrology (1999)

Nels Ruud Z. J. Kabala Fred J. Molz

Hydraulic head

Pressure head

10.1016/s0022-1694(99)00119-5

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Citations (33)