Environmental impact by spill of geothermal fluids at the geothermal fieldof Los Azufres, Michoacan, Mexico

Monitoring of surface water and shallow aquifers inside and outside of the Los Azufres geothermal field during the period November 1994 to May 1996 le d to the detection of some contamination of surface water and shallow aquif ers due to exploitation of the deep brines. Leaking of evaporation ponds an d pipelines, occasionally overflowing of reinjection wells and pond rims as well as outflowing of brines during rehabilitation or drilling operations, are potential contamination sources within the cycle of geothermal product ion. Temporarily and/or permanently increased trace elements concentrations , especially Fe, Mn, F, B, and As in surface waters within the geothermal f ield as well as up to 10 km outside, were observed. Maximum values of 125 a nd 8 mg L-1 were observed for B and As, respectively. The discharge of hype rsaline geothermal brines also causes salinization of surrounding soils. It occasionally happens that cattle drink from the brines. The use of the riv er for irrigation and drinking water supply in the surrounding regions may cause accumulation of toxic elements in the human food chain or may endange r the public health. The establishment of a closed geothermal production cy cle can be achieved by simple remediation techniques, such as sealing of th e pond walls, removal of overflow channels, direct reinjection without any reposal time in evaporation ponds, as well as an improved security and cont rol system.