Chemical monitoring and evaluation of the water quality of the Douro Riverat the Crestuma-Lever dam

Water taken from the Crestuma-Lever dam on the Douro River was evaluated co nsidering the Portuguese Decree-law no. 236/98 of 1st August, 1998. This pa per presents the metrological characteristics, validation of analytical met hodologies and the data obtained from seasonal samplings. The test paramete rs selected are: temperature, pH, chloride, conductivity, carbon dioxide, a lkalinity, hardness, oxidability, dissolved oxygen, BOD5, total suspended s olids, sulfide, phosphate, silica, ammonium, nitrite, nitrate, sulfate, sod ium, potassium, calcium, magnesium, iron, manganese, copper and zinc. From data analysis we can conclude that the water presented the following charac teristics: a pH situated in the neutral zone; a median mineralization; a me dium hardness; well oxygenated water; and a carbonate hardness exclusively due to bicarbonates. The temperature, pH, dissolved oxygen, ammonia, chlori des, sulfates, copper, zinc and BOD5 were compared with the legal limits pr esented in annexes XXI and I of Decree-law 236/98. The results relating to total hardness, nitrites, calcium, magnesium, sodium, potassium, aluminium, sulfides and oxidability were compared with the legal values in annex VI a s there are no limits relating to these parameters in annexes XXI and I.