ImPAC Lyon: evaluation of the environmental impact due to the thermal modifications on aquifers associated with shallow geothermal energy

Abstract : The objective of the project ImPAC Lyon was to evaluate the thermal, physico-chemical and microbiological impacts potentially associated to a ground water heat pump. It is based on two experimental parts : one in laboratory and the other on land (8th district of Lyon). The main results indicate that : - On land, no physical and microbiological disturbances were able to be revealing in the conditions of the study (range of temperature : 16-24 °C). Only thermal disturbances were observed. - The bad sizing of the doublet (which seems significant of the practices in urban with few space) could leads thermal disturbances and a progressive heating of the aquifer in an interannual scale. In these conditions, it seems all the more necessary to pursue the works begun in Lyon by treating the other ranges of temperatures. - The experimental approach of laboratory displayed in this study (range of temperature: 15-25 °C) indicates a sure influence of the temperature on the native bacterial microflora, but not enough to compromise the ecosystem balance. However, the other conditions of environment have to be studied (T > 25 °C and T< 15 °C, different redox conditions). - Behavior of pathogenic bacteria and organic pollutants in front of thermal modifications were not able to be observed to Lyon (no pollutions observed). They will also have to be studied in new projects.