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Groundwater Quality at the Independence Basin
in Central Mexico: Implications for Regional Development
Adrian Ortega Guerrero
Centro de Geociencias, Campus Juriquilla,
Universidad Nacional Autónoma
de México
Regional
and local studies were integrated for sustainable management of groundwater
resources in six municipalities of the State of Guanajuato in central
Mexico (San José Iturbide, Dr. Mora, San Luis de la Paz, San
Diego de la Unión, Dolores Hidalgo, San Felipe and San Miguel
Allende). Different hydrogeologic methods were used for understanding
of the process controlling groundwater flow conditions and water quality
at the watershed scale. A Geographic Information System (GIS) was used
to integrate all physical and chemical information of the basin. The
activities included geology, geophysics, hydrogeochemistry, environmental
isotopes, groundwater flow and chemical modeling and an inventory of
potential sources of contamination within the watershed.
Results
show that the size of the watershed comprises 6,840 square kilometers.
The thickness of the granular aquifer reflects a variation of 50 to
400 m in thickness overlying a volcanic fractured aquifer. Groundwater
quality showed important implications for human health and agricultural
practices, where arsenic and fluoride are present far above drinking
water limits, impacting more than 4,000 inhabitants in an area of 300
square kilometers of the watershed, and apparently increasing with time.
The presence
of major ions in groundwater and their impact on water quality are consistent
with reactions of volcanic rock mineral dissolution, which exist at
the recharge areas. Sodium concentration restricts about 18,000 hectares
of the total irrigated through aspersion and 12,000 hectares by gravity.
Radioactive isotopes show that recharge does not reach the water table,
indicating that groundwater is not renewed on an annual basis. High
arsenic, fluoride and sodium content are associated to residence time
in the order of thousands of years.
An educational
program in groundwater was designed for the above-mentioned municipalities
to understand the groundwater situation and implement adequate solutions
in the short and long terms, in coordination with the water authorities.
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