Justin T. Kulongoski

Simulation of fluid, heat transport to estimate desert stream infiltration

In semiarid regions, the contribution of infiltration from intermittent streamflow to ground water recharge may be quantified by comparing simulations of fluid and heat transport beneath stream channels to observed ground temperatures. In addition to quantifying natural recharge, streamflow infiltration estimates provide a means to characterize the physical properties of stream channel sediments and to identify suitable locations for artificial recharge sites. Rates of winter streamflow infiltration along stream channels are estimated based on the cooling effect of infiltrated water on streambed sediments, combined with the simulation of two-dimensional fluid and heat transport using the computer program VS2DH. The cooling effect of ground water is determined by measuring ground temperatures at regular intervals beneath stream channels and nearby channel banks in order to calculate temperature-depth profiles. Additional data inputs included the physical, hydraulic, and thermal properties of unsaturated alluvium, and monthly ground temperatures measurements over an annual cycle. Observed temperatures and simulation results can provide estimates of the minimum threshold for deep infiltration, the variability of infiltration along stream channels, and also the frequency of infiltration events.

Applications of Groundwater Helium

Helium abundance and isotope variations have widespread application in groundwater-related studies. This stems from the inert nature of this noble gas and the fact that its two isotopes – helium-3 and helium-4 – have distinct origins and vary widely in different terrestrial reservoirs. These attributes allow He concentrations and 3He/4He isotope ratios to be used to recognize and quantify the influence of a number of potential contributors to the total He budget of a groundwater sample. These are atmospheric components, such as air-equilibrated and air-entrained He, as well as terrigenic components, including in situ (aquifer) He, deep crustal and/or mantle He and tritiogenic 3He. Each of these components can be exploited to reveal information on a number of topics, from groundwater chronology, through degassing of the Earth’s crust to the role of faults in the transfer of mantle-derived volatiles to the surface. In this review, we present a guide to how groundwater He is collected from aquifer systems and quantitatively measured in the laboratory. We then illustrate the approach of resolving the measured He characteristics into its component structures using assumptions of endmember compositions. This is followed by a discussion of the application of groundwater He to the types of topics mentioned above using case studies from aquifers in California and Australia. Finally, we present possible future research directions involving dissolved He in groundwater.

Status of groundwater quality in the San Fernando--San Gabriel study unit, 2005--California GAMA Priority Basin Project

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A novel high-frequency groundwater quality monitoring system

High-frequency, long-term monitoring of water quality has revolutionized the study of surface waters in recent years. However, application of these techniques to groundwater has been limited by the ability to remotely pump and analyze groundwater. This paper describes a novel autonomous groundwater quality monitoring system which samples multiple wells to evaluate temporal changes and identify trends in groundwater chemistry. The system, deployed near Fresno, California, USA, collects and transmits high-frequency data, including water temperature, specific conductance, pH, dissolved oxygen, and nitrate, from supply and monitoring wells, in real-time. The system consists of a water quality sonde and optical nitrate sensor, manifold, submersible three-phase pump, variable frequency drive, data collection platform, solar panels, and rechargeable battery bank. The manifold directs water from three wells to a single set of sensors, thereby reducing setup and operation costs associated with multi-sensor networks. Sampling multiple wells at high frequency for several years provided a means of monitoring the vertical distribution and transport of solutes in the aquifer. Initial results show short period variability of nitrate, specific conductivity, and dissolved oxygen in the shallow aquifer, while the deeper portion of the aquifer remains unchanged—observations that may be missed with traditional discrete sampling approaches. In this aquifer system, nitrate and specific conductance are increasing in the shallow aquifer, while invariant changes in deep groundwater chemistry likely reflect relatively slow groundwater flow. In contrast, systems with high groundwater velocity, such as karst aquifers, have been shown to exhibit higher-frequency groundwater chemistry changes. The stability of the deeper aquifer over the monitoring period was leveraged to develop estimates of measurement system uncertainty, which were typically lower than the manufacturer’s stated specifications, enabling the identification of subtle variability in water chemistry that may have otherwise been missed.

Status and understanding of groundwater quality in the San Francisco Bay groundwater basins, 2007—California GAMA Priority Basin Project

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Groundwater quality in the San Fernando--San Gabriel groundwater basins, California

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and increases public access to groundwater-quality information. The San Fernando and San Gabriel groundwater basins constitute one of the study units being evaluated.

Status and understanding of groundwater quality in the Monterey Bay and Salinas Valley Basins, 2005-California GAMA Priority Basin Project

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Groundwater quality in the Monterey Bay and Salinas Valley groundwater basins, California

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and increases public access to groundwater-quality information. The basins around Monterey Bay, and in the Salinas and Paso Robles Valleys, constitute one of the study units being evaluated.