Sectorization of environmental risk and human consumption of manganese in groundwater extracted from the Sinaloa River Aquifer

The research reported in this paper had three objectives. The first was to draw a map of the piezometric contours of the Sinaloa River Basin to enable an interpretation of the hydrodynamic behavior of the basin. The second objective was to establish a relationship between the hydrodynamics of the basin and levels of concentration of manganese (Mn), an element which is vital for human survival but toxic at high levels. Given that some of the rural and urban inhabitants of the basin consume untreated groundwater, the third objective was to create a map of the region showing the locations of high manganese level risk in the water. To characterize the hydrodynamics, 40 wells were selected at random. Groundwater depth, ground elevation, hydraulic load and piezometric surface were measured. A water sample was taken from each selected well, and spectrometric laboratory techniques employed to measure manganese and iron levels; the latter as a check on the robustness of Mn measurements on untreated water. The piezometric analysis showed the presence of a regional water source and a local water source, which has protected the basin from saline intrusion for many years. However there are sources of high manganese concentrations in a range of 0.01 to 1.2 mg L^-1, which are moving with these two flows at average receptive velocities of 4.2×10^-3 mh^-1 and 1.6×10^-3 mh^-1. In an analysis of groundwater samples, 22 (55%) of the samples exceeded the EPA standard for commercial bottled drinking water and 12 (30%) exceeded the Mexican NOM- 127-SSA1-1994-2000 standard for water for human use and consumption. The risk level was very high in two samples (5%), high in 4 (10%), moderately high in 3 (7.5%), intermediate in 9 (22.5%), low in 2 (5%), and zero in 16 (40%). This information can be used for numeric models of Mn transport and flow useful for safeguarding human health and for provision of sustainable management strategies in one of the largest aquifers in northwest Mexico.