Temporal conceptual model of contaminated complex sites applied for the management of a former supply well area in tropically weathered bedrock

Abstract

Temporal Conceptual Model can enhance the long-term management of contaminated Complex Sites. This type of contaminated land model is defined here as the sequential or combined representation over time of single time conceptual models (named here as Snapshot Conceptual Models) including contaminant evolution, most likely causes, eventual receptor changes and uncertainties. Understanding contamination behaviour in crystalline fractured rock within tropical humid regions involves several technical complexities and typically requires long term management. This was the case of a Former Supply Well area managed over 20 years for land reuse, located in the water stressed Metropolitan Region of Sao Paulo. A Temporal Conceptual Model approach was voluntary developed for the Former Supply Well area that, together with complementary characterization activities, was used to enhance the understanding, remediation and monitoring of its unconfined aquifer system. They indicated that the contamination concentrations in the Former Supply Well and multilevel wells changed intensively over time. It was identified that the contaminant distribution was controlled by the extensive rock weathering levels and variations in: pumping regimes, well reconfigurations, effects of several stages of remediation works, influence of other source areas and dynamics of a likely commingled plume. The further understanding of the hydrogeology specific conditions allowed the advancement of communication with stakeholders, management works and local land reuse plans.