HR: 11:35h
AN: H42A-05    [Abstracts]
TI: Management of the Arsenic Groundwater System Lagunera - MEXICO
AU: * Boochs, P W
EM: boochs@iww.uni-hannover.de
AF: Institute of Water Resources Management, Hydrology and Agricultural Hydraulic Engineering, Leibniz University Appelstrasse 9A, Hannover, 30167, Germany
AU: Billib, M
EM: billib@iww.uni-hannover.de
AF: Institute of Water Resources Management, Hydrology and Agricultural Hydraulic Engineering, Leibniz University Appelstrasse 9A, Hannover, 30167, Germany
AU: Aparicio, J
EM: japaricio@tlaloc.imta.mx
AF: Instituto Mexicano de Technologia del Agua -IMTA-, Coordinacion de Tecnología Hidrologica, Paseo Cuauhnahuac No. 8532 Progreso, Jiutepec, Morelos, 62550, Mexico
AU: Gutierrez, C
EM: cgutierr@tlaloc.imta.mx
AF: Instituto Mexicano de Technologia del Agua -IMTA-, Coordinacion de Tecnología Hidrologica, Paseo Cuauhnahuac No. 8532 Progreso, Jiutepec, Morelos, 62550, Mexico
AB: Arsenic in drinking water is considered one of the most important environmental causes of cancer mortality in the world. Groundwater resources of the Comarca Lagunera region (Northern Mexico), which represents the main source of drinking water for more than 2 million people in the area, show arsenic concentrations ranging from 5 to 750 micro g/l. Large areas have concentrations quite above the Mexican standard of 25 micro g/l for human use and consumption. The aquifer is overexploited and the groundwater levels at the central part of the aquifer are drawn down more than 100 m in less than 50 years. The drawdown provoked the dissolution and migration of the geogenic existing arsenic within the aquifer. The presence of arsenic has been related to several potential sources. It was found out, that the main source is geothermal activity, less mining and the use of arsenical pesticides. The process of the geneses of the arsenic pollution implicates, that the highest content is on the bottom of the aquifer. Data analysis showed, that arsenic concentration is correlated to the age of the groundwater. "Older" water has higher arsenic content than "younger" water and the oldest water can be found at the bottom of the aquifer. Before 1950 the groundwater level in the Comarca Lagunera was close to the surface and there were only dug and shallow wells with low groundwater abstraction. The water was pumped from the upper parts of the aquifer and because this was "young" water it had low arsenic content. Then after 1950 a lot of wells, mainly for irrigation, were built and in 2002 there were 2350 active wells with an abstraction of about 1088 Mio cbm/year. In consequence to this the groundwater level decreased extraordinary. More and more "older" water was pumped and the arsenic content increased. Furthermore at the beginning of 1960 the river Nazas was canalized and lined, so that the natural groundwater recharge by infiltration from the river was stopped. By this way, the mixing of "young" water with less arsenic and "old" water with high arsenic was excluded, which results in the long term to higher arsenic concentrations in the groundwater. In order to understand the actual situation and to prognosticate the further development of the arsenic concentration in the Comarca Lagunera region, it was necessary to reproduce the historical development with a simulation model which includes the different anthropogenic impacts. For this purpose the groundwater model MODFLOW was used and the investigation area of about 7000 sq km was divided by a regular square grid with a mesh size of 1 km. The calibration of the model started with steady state conditions, using an assumed, uninfluenced "original status" of 1900. Subsequently, the influence of the immensely rising groundwater discharge beginning 1950 and the canalization of the river Nazas were simulated and the results were compared with measurements at selected times. The prognostic calculations showed, that the increase of the arsenic concentration will go on in the future under the present conditions of overpumping. Therefore, it has to be reduced. To control the arsenic migration towards the urban wells for dringking water supply artificial recharge can be done. Another possibility is a treatment, especially subterranean, of arsenic or to use surface water for drinking water purposes.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1834 Human impacts
SC: Hydrology [H]
MN: 2007 Joint Assembly