Natal Brazil

Information about the city of Natal, in Brazil.

Sunday, March 19, 2006

Phreatic sheet in Natal is contaminated

Tribuna do Norte published an article about the contamination of the phreatic sheet in Natal. Phreatic sheet (in Portuguese, "lençol freático") is the name given to the water which naturally accumulates in the subsoil; the rain water penetrates the soil and flows downwards until reaching a rocky layer, where it accumulates.

According to geologists from the Federal University and from CAERN, the water and sewage company, most of the water which comes from wells (that is, from the phreatic) contaminated with nitrates; nitrates are associated to the presence of fecal coliforms. CAERN is having more and more difficulties to find areas to dig wells where waters is healthy.

Only 33% of residences in Natal are served by sewage system; of this sewage collected, only 14% is treated. Raw sewage is thrown into the phreatic.
Natal is a privileged city, because the dunes help filter the water; twenty years ago, the sewage was already thrown in the phreatic, but there was time for a natural depuration. Between 1980 and 2001, though, the population grew from approx. 416,000 to 712,000 (these are official; from 2001 to date, there are no official data, but it is easy to see that the growth happened at even higher rates), and the water has no time to recycle any more; besides the growth of population, there has been also the impermeabilization of the soil, for construction of new residences (the rain water, which used to filter down the soil, now flows to rivers and the sea).
The Secretary of Planning says that the government will make investments to improve the infrastructure for collecting and treating sewage; he says that within three years all the city will be served by sewage systems, but the works have not started yet.

How dangerous is this?
CAERN says that all water provided by the company is within international healthy levels. This is because not all water comes from wells. In the Northern Zone of Natal, 80% of the water comes from natural reservoirs (mostly, the Lagoon of Extremoz); in the Southern Zone (the touristic area), 80% comes from wells, and 20% from reservoirs (Lagoon of Jiqui). CAERN says that a combination of pre-treatment and dilution guarantees the quality of the water.
The main problem is in residences and businesses which have dug their own wells. Even though drilling a well requires permission, CAERN estimates that there are more than 2000 wells in Natal which are not registered or accompanied by the authorities (CAERN operates less than 200 wells).

The original article, in Portuguese, is here:


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