Field evidence of hydraulic connections between bedrock aquifers and overlying granular aquifers: examples from the Grenville Province of the Canadian Shield [Preuves de terrain des connexions hydrauliques entre des aquifères de socle et des aquifères sédimentaires détritiques sus-jacents: exemples de la province de Grenville dans le bouclier canadien] [Evidências de conexões hidráulicas entre o substrato geológico e o aquífero granular sobrejacente obtidas em trabalhos de campo: exemplos da Província de Grenville, no Escudo Canadiano] [Evidencias de campo de las conexiones hidráulicas entre los acuíferos del basamento y los acuíferos granulares suprayacentes: ejemplos de la Provincia de Grenville en el escudo canadiense]

Field evidence of hydraulic connections between a bedrock aquifer and an overlying granular aquifer in the Canadian Shield (Grenville Province) is presented. This issue is rarely considered and investigated despite its important hydraulic and chemical consequences and its widespread occurrence worldwide. The methodology employed is based on complementary field tests conducted at specific experimental sites instrumented both in the rock and in the overlying deposits. One of the bedrock sites revealed a natural hydraulic connection with the overlying granular aquifer caused by the weathered surface of the uppermost bedrock. Another site revealed an artificial hydraulic connection between the bedrock and the granular aquifer created by an improperly sealed casing. A regional study showed that hydraulic connections yield an erroneous interpretation of the true hydraulic properties of the tested aquifer. The detection of hydraulic connections is therefore essential to properly define well-capture areas and contamination conditions. It is recommended to practitioners that pumping tests be performed as well as hydrochemical comparisons of each existing aquifer unit. Falling-head permeability tests are also helpful in verifying the quality of the seal at the bedrock–casing contact. More effective procedural controls and better well-construction practices are necessary to reduce the risks of cross-contamination induced by defective seals. © 2014, Springer-Verlag Berlin Heidelberg.