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Long-term Risk Analysis of Irrigation and Groundwater Management Impacts on Water Quality of the Non-Shallow Aquifer Systems in the Western San Joaquin Valley

Principal Investigator:
Thomas Harter

Graham Fogg

Post-Graduate and Student Researchers:
Nels Ruud, Hua Zhang, Nazrul Islam, Bellie Sivakumar

The project funds a half-time postgraduate researcher through the California Salinity/Drainage Program (P6). Project implementation, which began in the spring of 1998, is aided by our participation in the Groundwater Management Technical Advisory Committee of the State/Federal Drainage Implementation Program.

In a regional-scale area located on the westside of the central San Joaquin Valley (Figure 1), naturally occuring salinity and selenium have severely contaminated shallow groundwater resources. According to a previous modeling study [Belitz and Phillips, 1995], this shallow groundwater migrates downward at an estimated rate of 0.5 - 1.0 ft per year. Assuming the maintenance of current irrigation and groundwater management practices, this contaminated groundwater is estimated to take between 200 and 600 years to reach production wells located in the underlying semi-confined and confined aquifers (Figure 2), where the groundwater is naturally less contaminated with salinity and selenium. Although useful as a first approximation, this previous study did not account for the spatial variability encountered in the hydrogeology of this region and, consequently, cannot be used to further estimate the risk of accelerated well contamination due to unfavorable local geologic conditions, leakage inside wells and boreholes, or locally strong vertical hydraulic gradients.

Our project was initiated to ammend the Belitz and Phillips (1995) study by accounting for the spatial variability of the hydrogeologic properties in the modeled area. To achieve this, a geostatistical analysis of well-drilling logs and area soil maps is being performed to characterize the spatial variability of hydraulic conductivity in the semi-confined and confined aquifers. A stochastic model capable of simulating salinity and selenium transport in this heterogeneous aquifer system for spatially and temporally variable stresses will then be developed. The eventual goal is to use this model to implement a risk analysis of groundwater degradation in the underlying semi-confined and confined aquifers for 25, 50, and 100 years under two different irrigation and groundwater management scenarios previously evaluated by Belitz and Phillips (1995).

The geostatistical methodology we are using to characterize the spatial variability of the hydrostratigraphic units is based on a transition-probability/Markov chain modeling approach developed by Carle (1996). We are presently using a software package developed by Carle and Fogg (1998) called TPMOD (Transition Probability MODel) to analyze and model the spatial variability of texture data supplied by the United States Geological Survey (USGS) [Laudon and Belitz, 1991]. We are also participating in meetings with members of the academic community, and state and federal water agencies in a coordinated effort to address the problem of saline contaminated groundwater, drainage water, and subsurface sediments in the western San Joaquin Valley. A major function of these meetings is to document and assess previous groundwater flow or contaminant transport models used to simulate and study the impact of saline groundwater or drainage water in this region. This screening process will provide valuable information concerning the limitations of these models and insight into more effective modeling strategies for our study.

Publications and References:

Harter, T., 2005, Finite-size scaling analysis of percolation in three-dimensional correlated binary Markov chain random fields, Physical Review E 72(2), 26120 (8 pages), DOI: 10.1103/PhysRevE.72.026120. (pdf file for personal use only)

Sivakumar, B., T. Harter, and H. Zhang, 2005. Solute transport in a heterogeneous aquifer: A search for nonlinar deterministic dynamics, Nonlinear Processes in Geophysics 12(2):211-218. (pdf file for personal use only)

Sivakumar, B., T. Harter, H. Zhang, 2005. A fractal investigation of solute travel time in a heterogeneous aquifer: Transition probability/Markov chain representation, Ecological Modelling 182:355-370. (pdf file for personal use only)

Harter, T., C. Knudby, 2004. Effective conductivity of periodic media with cuboid inclusions. Advances in Water Resources 27(10):1017-1032. (pdf file for personal use only)

Vrugt, J. A., G. H. Schoups, J. W. Hopmans, C. Young, W. W. Wallender, T. Harter, W. Bouten. 2004. Inverse modeling of large-scale spatially-distributed vadose zone properties using global optimization, Water Resour. Res.  Vol. 40, No. 6, W06503 10.1029/2003WR002706.

Belitz, K. and S. P. Phillips, Alternative to agricultural drains in California's San Joaquin Valley: Results of a regional-scale hydrogeologic approach, Water Resources Research, 31(8), 1845-1862, 1995

Carle, S. F., A transition probability-based approach to geostatistical characterization of Hydrostratigraphic architecture, Report 100033, Reprint of Ph.D. dissertation, Hydrology Program, Department of Land, Air, and Water Resources, University of California, Davis, 1996

Carle, S. F and G. E. Fogg, TPMOD: A Transition Probability/Markov Approach to Geostatistical Modeling and Simulation, University of California, Davis, 1998

Laudon, J. and K. Belitz, Texture and depositional history of late Pleistocene- Holocene alluvium in the central part of the western San Joaquin Valley, California, Bull. Assoc. Eng. Geol., 28(1), 73-88, 1991