GEO Brasil - UNEP

the state of water resources
the state of environment in Brazil
Cretaceous period During this long geological period (450
million years) the formation processes of deposits and paleo
climatic environments were most varied – at times marine,
somewhat deep, at times continental - of desert and humid
climate
In addition, during a good part of this period, there was
intense tectonics which commanded the process of South
Atlantic Ocean opening Thus, successive marine
transgression and regression periods which happened
excessively affected the quality of underground water found
in sedimentary basins During transgression phases,
deposits were formed in sea environment and the oldest
sediments were saturated with salt water
On the other hand, during the periods of sea regression,
aquifers were washed by waters of meteoric infiltration that
fallowed As a consequence, the underground water of our
main sedimentary basins, such as the Amazon, Maranhão-
Piauí, Potiguar and Coastal Basins, mainly those whose
deposits were flooded by the sea during transgression
Cretaceous periods, usually only presents appropriate
quality to human industrial consumption and irrigation, in
their borders or in depths which were washed by subsequent
infiltration waters
has affected the geological outline of Brazil are mapped in
almost four (4) millions km2 of Pre-Cambrian age crystalline
rocks However, their extensions in the covered sectors by
the most important sedimentary deposits are evidenced by
the correlation of geological profiles of the already
perforated deep wells and by data interpretation of
geophysical prospecting - gravimetric methods, refraction
seismic, electromagnetic and mainly electro- resistance
However, it is observed that tectonics which happened after
the Cretaceous period, originating the Andes for instance,
is very important from the hydro-geologic point of view It
is known now, that this Neo tectonics is responsible for
quantitative and qualitative characteristics of the
underground water which is drawn by some deep wells
already perforated in the sedimentary basins, as well as for
the occurrence of hot waters, sources with varied chemical
composition, for instance, One could also have, locally and
occasionally, rich underground water in sulphate, iron,
manganese, carbonate, fluorine or of varied composts
because of the tectonics intensity, of recharges and of the
pale environments of the geological domain concerned
28 Demands and Current Uses
On the other hand, in Brazil- the successive tectonic
reactivations supported the intrusion of diverse dikes and
the formation of sunk blocks –some “lifted up “graben”,
others “horst” These events compartmentalised sediment
packages which were deposited, whose maximum thickness
reaches close to 10 thousand meters
It is worth noting that only in the Sedimentary Basin of
Paraná, the base of the Underground Guarani Water Trans-
Border System of Triassic Age (fluvial -latchstring) and
Jurassic (air desert), there hasn’t been sea transgression
ever since During the Cretaceous and, above all, the Tertiary
Period, dominant climatic conditions in the area were
humid, causing abundant recharge rates, in such a way that
the waters of the Guarani Underground Water System are
fresh until the depth of 2000m, already reached by water
production wells
The most important structural lines of the tectonics which
The technological progress of well and pump construction
and the expansion of electric power supply have resulted in
fresh underground water in the world in general and in Brazil
in particular, accessible to technical and financial means
In Brazil, it is estimated that about 200,000 wells are
operational; however, without control of underground water
drawing and use at in federal, as well as state level- it is
difficult to characterise its use level According to data from
the last sanitation census, about 61 percent of the Brazilian
population is self-supplied by underground water, 43 percent
through tubular wells, 12 percent through water springs
and 6 percent through dug wells (IBGE, 1991) Data from
the 2000 census indicate that there was an increment of 191
percent in the offer of non treated water in the period from
1989 to 2000 This certainly means a wider perception than
the alternative of underground water use for supply, and it
is in general the cheapest , specially due to the fact that it
does not need to be treated for consumption Therefore, it
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