The Tubarão Aquifer System - TAS is a permo-carboniferous sedimentary aquifer, deposited in a glacial continental and shallow marine environment (DAEE/IG/IPT/ CPRM, 2005). The productivity is relatively low, presenting transmissivity between 1E-6 to 3E-4 m2/s (Iritani et al, 2009) and hydraulic conductivity between 1E-8 to 1E-5 m/s (DAEE, 1981; 1982).
Municipalities in the outcropped TAS are experiencing economic and population growth, driven by development policy implemented in the late 1980s. They are inserted in the water resources management units denominated UGRHIs 5 and 10 where the water availability has been strongly reduced during the last decades.
In 7 years, the availability per capita reduced over 7%, reaching, in 2017, 981 m3/hab.year in the UGRHI 5 and 1686 m3/hab.year in the UGRHI 10. According to published information, the regular extracted volume of groundwater, authorized by management agency, is less than 30% of the surface water (CBH-SMT, 2016, 2018; CBH-PCJ, 2016, 2018).
Studying the TAS in 12 municipalities, it was observed that groundwater plays an important role in the economic development of the region.
The TAS thickens to west and the well depth in the study area range from 50 to 455 meters. Due to its heterogeneity which imposes a semi-confinement condition, the well productivity is low, with average specific capacity and flow rate of 0.13 m3/h/m and 7.2 m3/h, respectively. In the southern portion of the study area the productivity is higher, where flow rates can be above 30 m3/h per well, allowing its use for public water supply in some municipalities as Tietê, Capivari, Rafard, Porto Feliz and Elias Fausto. The estimated rate in 2015 of 132 public water supply wells was around 0.61 m3/s.
However, the largest number of wells belongs to private users (929 wells) whose pumped volume was estimated at 1.05 m3/s. The industrial sector, with 564 registered wells, is the main user of groundwater. According to SEADE (2019), this sector accounts for 30% of jobs in these municipalities, playing an example of the groundwater importance for the economic development in São Paulo State.
According to TrataBrasil (2019) the total number of wells may be much higher due to the irregular wells not registered by the management agency (about 60% in the São Paulo Metropolitan Region). Besides that, in Capivari and Tietê, where intensive pumping occurs, locally water level drawdown is observed (Iritani et al., 2009; Ferreira et al., 2005).
In addition, radiocarbon isotope analyzes of TAS provided a range of pmc between 0.39 and 79.96, indicating high residence times, greater than 15,000 years BP, demonstrating the use of old groundwater.
These facts demonstrate that the improvement of knowledge of the TAS, especially about recharge processes, is necessary to subsidize a sustainable use of the aquifer.