Photo 4–1 A view of the Grand Drainage Canal (Gran Canal Desaugüe), which carries wastewater and stormwater runoff from the Mexico City Metropolitan Area. The canal exits the Basin of Mexico through the Tequisquiac tunnel and empties into the Moctezuma River, a tributary to the Panuco River, which flows into the Gulf of Mexico. Courtesy of Robert Farvolden.

Drainage Canal (dry weather flow) or the deep drainage line (wet flow). The values given for the several contaminants are the average concentration for 1992. The U.S. average and the concentrations of these same contaminants in a typical raw municipal wastewater in the United States, with respect to being either weak, medium, or strong, are also given for the purpose of comparison (U.S. Environmental Protection Agency and U.S. Agency for International Development, 1992).

The level of many of the contaminants in the wastewater and the combined flow during both the dry and rainy seasons is similar and sometimes greater than that of typical wastewater in the United States. The very high concentration of total solids, total dissolved solids, and phosphorous, and to a lesser extent nitrites and nitrates, could be the result of untreated industrial wastewater discharge.

Tables 4.4 and 4.5 list the treatment plants serving the Federal District and the State of Mexico service areas, together with their design and current opera-