Half of the wastewater facilities constructed in Mexico for wastewater treatment and projected to be constructed in the next ten years, are waste stabilisation pond systems. The existing facilities have several problems in their operation. A national programme was developed by federal and local authorities responsible for sanitation and treatment for the monitoring and evaluation of the existing pond systems. The aim of the programme was the monitoring and evaluation of pond performance and effluent quality of a number of waste stabilisation ponds systems in different regions in Mexico and to upgrade and expand them ii necessary. The programme was developed during 1998 and the specific sites selected were distributed within the country in the southern, central and northern part of Mexico. The evaluation of the specific ponds led to the production of a series of case studies on the various pond systems selected, that were discussed and jointly developed with local technicians in charge of the operation of the facilities. The case studies developed were: Gomez Portugal pond system located in the state of Aguascalientes, constituted by a baffled facultative pond; Guadalupe Victoria pond system located in the State of Durango and constituted by a primary facultative, a secondary facultative and a third facultative pond; La Reforma pond system in Sinaloa, with two facultative ponds in series; Gonzalez Ortega pond system in the State of Baja California Norte, with four anaerobic and four facultative ponds. and Chapilla pond system, located in the state of Chiapas. Plant effluents are intended for several purposes: irrigation and for discharge into receiving bodies. Effluent quality complies only with BOD limits, but not with microbiological limits established in national standards. For each pond, an upgrading plan is presented to comply with microbiological standards for discharge or for its use in irrigation.
