Navegando por Autor "Halihan, Todd"

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Recharge sources and hydrochemical evolution of an urban karst aquifer, Sete Lagoas, MG, Brazil.
(2017) Galvão, Paulo Henrique Ferreira; Hirata, Ricardo; Halihan, Todd; Terada, Rafael
The current water supply for the city of Sete Lagoas, Brazil, is almost entirely groundwater from the Sete Lagoas Karst Aquifer, with a small contribution from a fractured-basement rock aquifer. Characterizing the hydrogeologic processes is important for proper water resource management, avoiding contamination and other future issues. The main goal of this study is to identify active hydrogeological processes, such as possible surface– ground water interactions, sources of recharge, and the hydrochemical evolution of groundwater through the use of stable isotopes 18O and 2H and major ion data. The groundwater samples were collected from the karst aquifer (central urban area) and from the fractured aquifer (southern part of the city). Surface water samples were collected from the seven main lakes, and rainwater was sampled over a period of one year. The stable isotope results indicated the groundwater origin is directly from local precipitation, having a limited recharge period, and locally receiving surface water contributions. Groundwater quality in the central urban area may be influenced by surface water infiltration where the karst aquifer is in contact with overlying unconsolidated sediments. Some samples with nitrate concentration of 10 mg/L or higher indicates the natural composition of the groundwater has been altered by urban sewage contamination. The highest concentrations of major ions were found in the central region, where the most karstified area from the Sete Lagoas Formation is located. These data suggest a longer residence time for this water, indicating more mineralization, in accordance with the geological information.
Transmissivity of aquifer by capture zone method : an application in the Sete Lagoas Karst aquifer, MG, Brazil.
(2017) Galvão, Paulo Henrique Ferreira; Halihan, Todd; Hirata, Ricardo
Transmissivity is an important hydraulic parameter to determine the amount of water passed horizontally across a given saturated thickness of an aquifer. The techniques to quantify this parameter, such as grain size analyses or pumping tests, can have limitations of time/spatial scale, viability, or economically. One technique that can be used, but little adopted, is the capture zone analysis. In this paper, capture zone analytical equations were used to estimate transmissivity values in order to verify the effectiveness of this methodology as alternative in situations where other traditional methods present implementation difficulties. The results were compared with field data estimated by aquifer tests conducted in the same region. A sensitivity analysis was also performed to identify possible discrepancies between the analytical and field data results. The aquifer studied was the Sete Lagoas Karst Aquifer in the urban region of the municipality of Sete Lagoas, Brazil. The method proved to be a viable and economical tool, where the analytical values compared to the aquifer tests showed similarities, being confirmed by a sensitivity analysis. However, a reliable potentiometric surface map, which enables the identification of the parameters for analytical capture zone equations, is needed.