PLT21 - Hydrochemical Monitoring of Dam Seepage in the State of São Paulo, Brazil

Hydrochemical monitoring of surface water, monitoring wells, and drains plays a pivotal role in assessing the risk of seepages in dams, offering insights into potential chemical reactions within the microporous structure and geological framework. These reactions can involve the dissolution or precipitation of chemical species, influencing the risk of pressure increase. While hydrogeochemical long-term monitoring provides valuable information on the dam's performance and its interaction with the hydrogeochemical environment, such practices are not consistently implemented in South America, particularly in Brazil.

This study aims to evaluate and compare hydrogeochemical interactions between water from the reservoir and concrete and earthfill dams, elucidating their applicability to dam safety management. Comparative analyses of hydrochemical signatures in seepage water from both dam types reveal distinct differences, suggesting that seepage acquires materials from the dam structures, resulting in diverse chemical products and impacting the microstructures of water infiltration. Although a more detailed hydrogeochemical assessment is required to understand the reactions with the geological background and concrete structures, the procedure proves effective in both cases, highlighting varied chemical signatures between concrete and earthfill dams.

The analysis includes water samples from drains, flow meters, and reservoir depth profiles, encompassing an array of parameters such as Cl-, PO43-, SO42+, SO3-, S2-, Ca2+, Mg2+, Mn2+, K+, Na+, CO32-, HCO3-, pH, temperature, total dissolved solids (TDS), turbidity, dissolved oxygen (DO), electric conductivity (EC), and redox potential (Eh). Results indicate a significant increase in electric conductivity in concrete dam seepage (1567-2122% increase) and earthfill dam drains (25-50% increase) compared to respective reservoir waters. Piper diagrams reveal distinct hydrogeochemical evolutions in seepage, with the concrete dam transitioning from Cl-Na-K to HCO₃-Ca-Mg and the earthfill dam shifting from HCO₃-Na-K to HCO₃-Ca-Mg. Ionic imbalances are identified in most seepage samples, prompting a reevaluation of parameters crucial for hydrochemical monitoring.

Additionally, a market research initiative identified the capacity of certified commercial laboratories to meet proposed quantification limits for hydrochemical monitoring, culminating in the establishment of a standardized monitoring procedure applicable to dams operated by the São Paulo State Basic Sanitation Company.