Peter S. K. Knappett1, Richard T. Woodward2, Paulina Farias3, Jaime Hoogesteger4, Horacio Hernandez5, Saugata Datta6, Gretchen Miller7, Itza Mendoza8, Genny Carrillo8, Yanmei Li9, Isidro Loza9, Dylan Terrell10
1. Geology & Geophysics,
2. Agricultural Economics,
3. Environmental Health, Instituto Nacional de Salud Pública, México
4. Water Resources Management, Wageningen University, The Netherlands
5. Geomatic and Hydraulic Engineering, University of Guanajuato, México
6. Geological Sciences, University of Texas at San Antonio
7 Civil Engineering,
8 Public Health, Texas A&M University
9. Mines, Metallurgy & Geology Engineering, University of Guanajuato, México
10. Caminos del Agua, Mexico
In arid and semi-arid regions around the globe irrigation with groundwater has increased food security and economic well-being. These same aquifers are commonly relied upon for drinking water by the local population. In many of these highly exploited aquifers rising concentrations of anthropogenic and geogenic contaminants are making the water unsafe for human consumption. Rural populations are particularly vulnerable owing to lack of water quality testing. Aquifers in the Highlands of Central Mexico are heavily exploited with irrigation consuming up to 90% of extracted water. Water tables have fallen from near-surface to levels exceeding 150 m
and are no longer profitable for farms to pump without government electricity subsidies. This problem of over-exploited aquifers is often viewed as a politically intractable problem; more pumping means more jobs and food for the local population, and more profits for politically powerful groups. The water chemistry deterioration that accompanies over-exploiting an aquifer, however, inflicts an untold burden of disease and loss of human potential on the local population. Arsenic and fluoride are examples geogenic contaminants that inflict disease upon multiple human organs and diminish childhood intellectual development. Technological solutions exist
for removing these and other geogenic contaminants but public and private investments to safeguard drinking water quality has lagged behind investments to ensure access to water. State and Federal governments heavily subsidize the cost of drilling new municipal drinking water wells and electricity for irrigation pumping but few rural communities receive assistance detecting and mitigating their exposure to geogenic contaminants. A proper accounting of the costs of over-exploiting Central Mexican aquifers needs to be done to demonstrate the scale of investment that will be required to mitigate the human impacts. To link water table declines to groundwater
quality it is necessary to identify the subsurface processes that drive groundwater quality deteriorations. For example, deeper wells tap older, hotter, more mineralized groundwater which tends to have higher total dissolved solids (TDS), but when redoxand pH-sensitive elements like arsenic, iron and manganese are involved, other processes may drive the change in chemistry in less predictable ways. We expand upon on our work linking falling water tables to rising arsenic concentrations in the State of Guanajuato with a coupled hydrologic-public health-economic dynamic systems model. We present preliminary calculations of losses and gains in the basin’s four stocks (groundwater storage, quality, human health, State GDP) assuming different pumping and mitigation strategies.