The Lerma River Upper Basin is located between Almoloya del Rio shallow lakes and Atlacomulco Municipality in the State of Mexico; is a natural resource essential to human activities in its surroundings and serves as a source of electricity and drinking water for Mexico City. However, this river is threatened by over-exploitation of its aquifers, disappearance of many of its wellsprings and uncontrolled discharges of wastewater from all sorts. Thus, the aim of this work was to evaluate the water quality in the Upper Lerma River Basin using WQI proposed by the NSF and compare these results with those obtained by the National Water Commission of Mexico (CNA). WQI was calculated using seven parameters: dissolved oxygen, pH, DOB5, temperature change, total phosphates, nitrates, and total solids obtained in four different sampling campaigns carried out in 2005, 2006 and 2012. The results showed that water quality in the Upper Lerma River is bad, mainly associated with high levels of BOD5, nitrates and phosphates found. The results obtained with WQI yielded the same diagnosis that the studies carried out by the CNA, in which water quality was unacceptable. It is worth noting that there is a significant water quality deterioration in the Upper Lerma River Basin with the course of the years, because in 2012 were observed the lower index values regarding 2005 and 2006, so it is imperative to implement measures to restore and preserve the water quality of this important river.
This study evaluated the impact of an abandoned Ag mine on the quality of surface and groundwater. The mining site of Huautla is in south Morelos State, central Mexico. Ag-Pb-Zn and Au-Cu sulfide ores were mined in the district. The ores were characterized by the presence of Ag, galena (PbS), sphalerite (ZnS), and stromeyerite (CuAgS). Ag was the metal of greater interest. Other metals included Cu, Pb, Zn, and Au. Mining activities stopped in the early 1990s when the market price of Ag decreased; the abandoned mines then were flooded by rising groundwater levels. Because of the urgent demand for water by the inhabitants in the area, this water has been used as drinking water and as waterholes for livestock. Water sampling points included abandoned mines (América, Pajáro, Santiago, Tlachichilpa, and San Francisco), dams, and dug wells. The greatest concentrations of As and other toxic chemical elements (Fe, Mn, Pb, Cd, F) were detected in groundwater samples from flooded mines. The presence of these elements was related to the rockwater interaction process. The oxidation of sulfides appears to be the cause of increased metal concentrations in groundwater samples from flooded mine. Other possible water-rock interaction processes that can control the presence of arsenic in groundwater were the adsorption of arsenic in iron oxyhydroxides, the adsorption in carbonates, and/or coprecipitation with calcite. In the case of the San Francisco and América mines, the oxidation conditions, low correlation of As with SO 4 2and Fe 2? , and concentrations of silica indicate that the presence of As in the groundwater could be due also to competition for adsorption sites.
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