Monitoring Scheme for the Detection of Hydrogen Leakage from a Deep Underground Storage. Part 2: Physico-Chemical Impacts of Hydrogen Injection into a Shallow Chalky Aquifer  
[PERSON]  
1 Ineris, Parc Technologique Alata, 60550 Vermeul-en-Halatte, France; [EMAIL_ADDRESS] (SL.); [EMAIL_ADDRESS] (Z.P.); [EMAIL_ADDRESS] (E.L.)  
[PERSON]  
1 Ineris, Parc Technologique Alata, 60550 Vermeul-en-Halatte, France; [EMAIL_ADDRESS] (SL.); [EMAIL_ADDRESS] (Z.P.); [EMAIL_ADDRESS] (E.L.)  
[PERSON]  
1 Ineris, Parc Technologique Alata, 60550 Vermeul-en-Halatte, France; [EMAIL_ADDRESS] (SL.); [EMAIL_ADDRESS] (Z.P.); [EMAIL_ADDRESS] (E.L.)  
[PERSON]  
2 GeoBessources Laboratory, Universite de Lorraine-CNRS, 54500 Vanduevres-les-Nancy, France; [EMAIL_ADDRESS] 2 Ecole Polytechnique, Laboratoire CETRAHE, Universite d'Orleans, 8 Rue [PERSON] de Vinci, 45100 Orleans, France; [EMAIL_ADDRESS] 2 School Polytechnique, Laboratoire CETRAHE, Universite d'Orleans, 8 Rue [PERSON] de Vinci, 45100 Orleans, France; nevila.  
in salt caverns, entitled ROSTOCK-H. Among other things, this project focuses on the risks associated with possible hydrogen gas leaks from deep storage. In the event of such leakage, the hydrogen would migrate to the surface and encounter at least one aquifer where the gas would dissolve in the water until saturation [5]. However, considering the very low solubility of this gas (in the order of 1.8 mg\(\cdot\)L\({}^{-1}\) at saturation under surface conditions), there is a risk that the leak flow rate may exceed the dissolution potential for hydrogen in water. In this case, part of the gas would continue its migration to the surface in gaseous form until it encounters an impermeable formation or a void where it can accumulate (mine, underground networks, cellar, underground car park, tunnel, etc.): hydrogen may then cause asphyxiation or, due to its very weak lower flammability limit (around 4%), explosion or fire [2].  
To study the risks associated with this new storage technology, particularly in the event of a leak towards the surface, we carried out an experiment to simulate a hydrogen leakage from a possible deep geological storage. To do this, we injected hydrogen into the chalk aquifer, which is a major drinking water resource in the Paris region. Several monitoring devices were set up directly in the aquifer up to 60 m downstream from the injection point, in order to monitor the evolution of the dissolved hydrogen plume and the associated physico-chemical and hydrochemical phenomena. Under the proposed experimental conditions, and due to the brevity of the injection, we did not expect any biochemical reactions that require long time scales to occur. Moreover, additional studies [6; 7; 8; 9] pointed out that a sudden injection of hydrogen saturated water into an aquifer increases the dissolved hydrogen content of the water, and consequently reduces its oxidation-reduction potential, as well as the concentration of other dissolved gases (O\({}_{2}\), CO\({}_{2}\), N\({}_{2}\), etc.). The injection of hydrogen was preceded by the injection of tracers (helium and hydrogeological tracers) in order to facilitate the monitoring of its progress underground. This experiment was conducted at the Catenoy (Oise) experimental site in a surface aquifer representative of the carbonated hydrogeological context of the Paris Basin. It followed characterization work for this site, previously carried out during CO\({}_{2}\) leak simulations [10; 11], as well as the realization of a baseline and a preliminary injection of helium [6].