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This study deals with the development, calibration, and testing of an automated technology for using helium as a water tracer in continuous real-time monitoring. The instrument combines a gas extraction system and a helium mass spectrometer. The technology was tested in laboratory pipe, open-water, and porous- media experiments, and the results were used to test helium breakthrough curves against those for salinity expressed by electrical conductivity. The instrument promptly responds to concentration changes. In general, accurate results were obtained for first arrival times and peaks of solutes, as well as for the dispersive characteristics of the breakthrough curves. The accuracy of the elution curves needs some improvement due to limitations of the helium extraction system. In addition, the developed method is sensitive to the water flow rate and nitrogen pressure used in extracting helium from the solution. These issues can be addressed through calibration. Potential improvements are possible through the use of more precise helium concentration quantification equipment and through enhancement of the extraction method. The success of the methodology makes helium an attractive tracer for use near drinking water sources, in environmentally sensitive areas such as wetlands and fish farms, and near recreational or other areas where a esthetics are a concern. DOI: 10.1061/(ASCE)0733-9429(2008)134:5(672) CE Database subject headings: Water quality; Environmental issues; Tracers; Monitoring.

Introduction Agriculture activities are probably the most significant anthropogenic source of ground water contamination. As many as 29 states in the U.S. have identified ground water contamination from non-point sources [...]

Introduction Part 1 of this study (El-Kadi, 1992) dealt with verification of sharp-interface multidimensional models for NAPL infiltration. In addition to the sharp-interface approach, other classes of models exist (Abriola, [...]

A sharp-interface model for nonaqueous phase liquids (NAPL) flow through the unsaturated zone is presented. Results show that the sharp-interface model is useful in estimating the depth of the infiltrating front in soils that are characterized by important capillary effects. In order to protect the aquifer, an order-of-magnitude of the travel time in the unsaturated zone can be useful in emergencies caused by NAPL spills and leaks. Lastly, the sharp-interface models have to be field-validated in large-scale field problems.

Wells designated as groundwater under the direct influence (GUDI) of surface water have caused an ongoing boil‐water advisory afflicting the island of Tutuila, American Samoa for almost a decade. Regulatory testing at these wells found turbidity and indicator bacteria spikes correlated with heavy rainfall events. However, the mechanism of this contamination has, until now, remained unknown. Surface water may reach wells through improperly sealed well casings, or through the aquifer matrix itself. In this study, three independent surface water tracers, turbidity, indicator bacteria, and water isotopes were used to assess recharge timing and determine contamination mechanisms. Results from each method were reasonably consistent, revealing average GUDI well breakthrough times of 37 ± 21 h for turbidity, 18 to 63 h for bacteria, and 1 to 5 days for water isotopes. These times match well with estimated subsurface flow rates through highly permeable aquifer materials. In contrast, where one well casing was found to be compromised, turbidity breakthrough was observed at 3 to 4 h. These results support local management decisions and show repairing or replacing wells will likely result in continued GUDI contamination. Additionally, differences in observed rainfall response for each tracer provide insight into the recharge dynamics and subsurface flow characteristics of this and other highly conductive young‐basaltic aquifers. [ABSTRACT FROM AUTHOR]

Aly I. El-Kadi [a] Stan A. Williams [b] Abstract This paper introduces a computer program that uses matrix decomposition to generate two-dimensional fields of normally or log-normally distributed parameters (e.g., [...]

Hawaiian streams are flashy in nature because watersheds are small and steep and receive intense and unevenly distributed rainfall. As a result, stream chemistry is characterized by considerable spatiotemporal variability. To examine how rainfall and streamflow affect the solute content of the Manoa River in Hawaii, time-series geochemical data collected during 17 sampling campaigns in spring-fall of 2010 were evaluated in a coupled δ 13 C DIC /major ion inversion model. Spatially, the stream is characterized by a distinct shift from a low HCO 3 (43 mg/L), low pCO 2 (3760 ppmv) and heavy δ 13 C DIC (−6.5‰) fingerprint in the upper reaches to a high HCO 3 (91 mg/L), high pCO 2 (8961 ppmv) and light δ 13 C DIC (−11.7‰) signature in the lowlands. These trends are attributed to (1) progressive weathering of exposed aluminosilicates, and (2) downstream enrichment in CO 2 from organic matter decay in the soil zone. Solute (i.e., nitrate) yields from nitric acid weathering are generally low (<1% of TDS), even in the developed lowlands, where runoff of nitrate-enriched urban effluent has historically been documented. Data furthermore indicate a significant positive correlation between δ 13 C DIC and rainfall rates in the mid-stream section of the river which is consistent with an atmospheric CO 2 dilution effect during high rainfall events. This dilution effect needs to be accounted for to reliably describe the role of volcanic island river systems in global assessments of silicate weathering and CO 2 degassing. [ABSTRACT FROM AUTHOR]