Combined use of aquifer contamination risk maps and contamination indexes in the design of water quality monitoring networks in Mexico

Three scenarios are analyzed where risk maps were developed as the initial stage in the design of groundwater quality monitoring networks. In the León Valley, the main potential source of contamination is a diffused source which corresponds to the urban area, where high vulnerability values and indexes of contamination have been recorded. In the river valley, the Turbio river and a chromium processing plant stand out as potential sources of contamination. These sources are considered to be of the linear and point source type, respectively. The highest vulnerability values exist in the recharge areas, as well as in some areas inside the valley. The highest contamination indexes are observed at the intersection of the potential source of contamination with areas of high vulnerability. The third scenario is located in the region south of León, in the Penjamo-Abasolo graben, which is crossed by the Turbio, Lerma and Guanajuato rivers. The rivers are considered linear sources, and occasionally diffused sources when the rivers are in flood or irrigated with wastewaters. The highest vulnerability values are found in the main recharge areas. In this region the critical points are located at the intersection of highly vulnerable areas with the Turbio, Lerma and Guanajuato rivers. In each of these three scenarios the combination of three assessment parameters — areas of high vulnerability, presence of a potential source of contamination, and high contamination indexes is presented as a first step in the design of groundwater quality monitoring networks.