An environmental (friendly) engineering solution to mitigate potential impacts of deep aquifer mining

Extracting water from a deep aquifer can have negative impacts on the phreatic aquifer and on surface systems, in the present, and even more in the future with climate change conditions. When exploitation of such deep aquifers are unavoidable, if impacts happen, how could they be mitigated ?This issue is illustrated by the well field project "Landes du Médoc", Gironde county, France. Water mining from the Oligocene aquifer (excellent water quality and good hydrodynamic parameters) is planned as a substitute to part of the current domestic water resource (the Eocene aquifer, slighlty overexploited) for Bordeaux conurbation. Concerns have emerged that even if the simulated impact on the Plio-Quaternary aquifer, far above the Oligocene formation, is small (less than 40 cm of lowering of the water table), the biodiversity could suffer from it. Moreover uncertainties on the future climate could make these impacts worse.Thus an environmental engineering solution, requiring no additional infrastructure, is developed, inspired by artificial aquifer recharge techniques (MAR). A small amount of the extracted water in the deep aquifer Oligocene could be re-injected in the surface system, through existing streams or shallow wells. A heuristic numerical model is ran to evaluate the feasibility and efficiency of this solution. This system could offer a cost-effective mitigation solution to vital deep water mining.This study has been carried out with financial support from the French National Research Agency (ANR) in the frame of the Investments for the future Programme, within the Cluster of Excellence COTE (ANR-10-LABX-45).