Drilling techniques for pollution pathway identification in exposed karst subterranean river systems in Guizhou

Abstract:

The exposed karst region in Guizhou features a complex network of underground river systems characterized by extensive karst development and intricate hydrogeological conditions. These systems are highly susceptible to severe contamination from surface pollutant sources due to percolation of leachates. The pollution pathways within these underground river systems are challenging to precisely identify owing to their concealed nature， narrow spatial extent， and anisotropy. To expose and identify contaminated channels， drilling operations face several difficulties， including alternating soft and hard layers， non-uniform weak zones， significant karstic formations causing borehole deviation， large cavities leading to casing misalignment or breakage， and slow tracer migration due to low natural hydraulic gradients in the underground river systems. Consequently， the identification and exposure of pollution pathways are both difficult and inefficient. To address these challenges， several technical measures were employed， including anti-deviation and vertical maintenance techniques， large karst casing passage and sealing， and in-hole activation to promote tracer migration. These measures ensured the verticality of exploration boreholes， facilitating accurate logging， tracer testing， and water sampling. This approach enabled the precise exposure and rapid identification of pollution pathways. The methodologies and technical measures adopted in this study offer significant reference and practical insights for the precise exposure and efficient identification of pollution pathways in similar geological formations.

Key words:Underground river systems; Pollution pathways; Precise identification; Anti-deviation and vertical maintenance; Large karst cavity passage; In-hole activation; exposed karst region