Assessment of groundwater quality in a Brazilian semiarid basin using an integration of GIS, water quality index and multivariate statistical techniques

Globally speaking, groundwater is the predominant source of water for populations living in arid and semiarid regions. The tools used to assess the quality of this resource contribute to the water security of the populations that depend on it. This study evaluated the quality of groundwater sampled from 22 monitored wells in the Araripe Sedimentary Basin (ASB), located in the Brazilian semiarid region. We used probability curves to identify the critical variables and a regional Water Quality Index (WQIR) to assess groundwater quality. The National Sanitation Foundation index (WQINSF) was adapted using multivariate statistical analyses. The Principal Component Analysis (PCA) was employed to determine the principal water quality parameters and their weights. GIS technology was used to build geospatial behavior maps for the hydrogeochemical variables. The results for the variables phosphorus, Nitrate-N, thermotolerant coliforms, pH, and turbidity exceeded the regulatory limits, mainly in areas affected by anthropogenic sources with an insufficient sewage network. Nitrate-N and turbidity had a marked seasonal behavior. The WQIR showed that the aquifer's waters can be classified mainly as Regular (18.2%) or Good (82.8%). The spatial behavior maps of the hydrogeochemical variables and the WQIR allow us to prioritize those areas requiring mitigation and monitoring actions. The water quality curves and the WQIR are important tools for the management and handling of aquifers. This study contributes to the assessment of water quality by policy makers and stakeholders, enabling the planning and management of groundwater resources.