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Coastal groundwater is extremely vulnerable to land-based human activities and seawater intrusion. In Brazil, a developing country, several coastal cities are undergoing recent urbanization with no planning, giving rise to problems such as groundwater overexploitation, sanitation, and chemical contamination. This study provides seasonal and spatial groundwater chemical and microbiological characterization of a recently urbanized coastal region, discussing contamination and salinization. The recent urbanization event affected both shallow and deep wells represented by the extensive presence of Escherichia coli on groundwater and nitrate, ammonium, arsenic, and lead (NO3-, NH4+,As and Pb) levels above groundwater safety guidelines. In contrast, iron and manganese (Fe and Mn) concentrations above the safety limit were associated with lithological enrichment, but might also restrict groundwater consumption. In addition to chemical and microbiological contamination, salinization of coastal aquifers did not pose a threat in this shoreline, but brackish groundwater was found in one well influenced by a coastal lagoon sandbar opening that allowed seawater to enter the aquifer.