Conceptualization Of The Lake Aquifer System

Author : Gabriela Patricia Flores Aviles
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (113 download)

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Download or read book A Groundwater Basin Multidisciplinary Approach to Conceptualize Subsurface Flow and Trace Nitrate Contamination Sources. Lake Titicaca, Bolivia written by Gabriela Patricia Flores Aviles and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Water quality degradation, climate variability and population growth are among the factors that constrains water availability in the semi-arid Katari and Lago Menor region (6,350 Km^2), leading to an increasingly exploitation of groundwater resources. This thesis aims to conceptualize subsurface flow and trace nitrate contamination sources in the groundwater system within the Katari and Lago Menor Region.A multidisciplinary approach for field investigation was used in this study, including a regional groundwater source inventory and groundwater level measurements, geophysical investigation techniques (e.g. TDEM-Time Domain ElectroMagnetic soundings), piezometer construction and installation, and a regional sampling campaign and analysis for major ion chemistry and dual isotopes of 15N-NO3 and 18O-NO3.The results allowed identifying the limits of two different geological settings (Piedmont subsystem and Lacustrine plain), the geometry of the Quaternary porous geologic media and the bottom boundaries of the aquifer.The groundwater flow regime corresponds to a classical gravity-driven regional flow system. Six subdomains possessing different hydraulic properties were identified. A large portion of the aquifer presents an unconfined behaviour, particularly on the Piedmont, whereas it remains confined in the plain areas. The thickness of the unconfined portion varies from 50 to 150 meters. Values of hydraulic conductivity for the unconfined portion range from 1.1E-04 to 5.9E-08 m/sec, specific yield ranges from 0.16 to 0.20 and recharge values range from 118 to 382 mm/year. While for the confined part the transmissivity values range around 6.0E-06 m^2/sec with a storavity value of 1.2E-02 to 6.0E-03.In the high Piedmont areas where the hydraulic heads are high, the low mineralization and the chemical and isotopic compositions showed that the groundwater source is of good quality. In contrast, in the lower sector of the Piedmont, the shallower water tables of the alluvial-fluvioglacial-lacustrine sequence, make this area more vulnerable to contamination. Chemical facies and the isotopic composition of the dissolved NO3 revealed that the main origin of this anion is related to nitrogen fertilizers towards the NW of the Piedmont and human/animal waste towards the SE. Moreover, natural nitrate attenuation processes occur mainly in the lower sector of the Piedmont, when groundwater mixes with the reservoir of lacustrine origin. Groundwater flowing in the plain areas, present primarily Na(K)-Cl facies relating the presence of evaporites. In this area groundwater is prone to contamination, especially when the clay layer is absent and in places where a connection to the Piedmont is evidenced (subterranean channels). The contribution of groundwater to the current Lake Titicaca (Cohana Bay) appears to be retarded due to the presence of the clay layer.This basin-scale conceptual groundwater flow model provides a good understanding of the aquifer functioning, and a guide to future data collection, in order to improve the robustness of future groundwater flow numerical modeling. All the science-based information generated from this research was arranged into a GIS spatial database to support decision makers in the management and protection of groundwater resources. This science-based information also contributes to the environmental remediation of Lake Titicaca, a national priority for the Plurinational State of Bolivia.