Groundwater Quality in a Rural Fractured Aquifer: Evidence of Physicochemical–Microbiological Decoupling in Drinking Water Safety Assessment

Description

Groundwater is the main source of drinking water for many rural communities, and monitoring programs often treat physicochemical compliance as an indirect indicator of microbiological safety. This exploratory baseline study examined whether this assumption holds in a rural fractured crystalline aquifer in the Monte Bonito district, within the Santa Bárbara Stream watershed (southern Brazil). Ten wells (shallow dug wells and semi-artesian boreholes) were sampled during a single baseline campaign conducted between September and October 2021, and physicochemical and microbiological parameters were compared against Brazilian drinking-water standards (Portaria GM/MS nº 888/2021). Five of the ten wells exceeded at least one physicochemical threshold, most often iron, manganese, turbidity, or apparent color. In contrast, total coliforms were detected in all ten wells and Escherichia coli in nine, including a 35-m semi-artesian well that met all measured physicochemical criteria. Consequently, none of the ten wells met overall potability criteria once the microbiological domain was considered, even though half of the wells were physicochemically compliant. Physicochemical results therefore did not identify microbiological non-compliance in the sampled wells. The elevated iron and manganese concentrations were consistent with water–rock interactions within the Pinheiro Machado Suite, while the widespread occurrence of fecal indicator bacteria was consistent with surface-derived contamination associated with onsite sanitation, livestock activity, and inadequate well protection; specific sources and transport pathways could not be confirmed with the available data. These findings, based on a ten-well pilot dataset from a single sampling campaign, indicate that physicochemical compliance did not function as a reliable proxy for microbiological safety in this setting and support the parallel interpretation of physicochemical and microbiological indicators, combined with sanitary inspection and wellhead protection, in rural communities relying on fractured hard-rock aquifers.

Steps to reproduce

https://drive.google.com/drive/folders/1WwYVfhYUn9K4hCw8piVicWdWCYjlEGw5?usp=drive_link

Institutions

• Instituto Federal Sul-rio-grandense

  Rio Grande do Sul, Pelotas

Categories

Funders

• Coordenação de Aperfeicoamento de Pessoal de Nível Superior

  Ministry of Education

  Brasília

Licence