Author(s): Damian Sanchez Garcia; Alberto Barrera Garcia; Eva Mena Gil; Isabel Maria Hurtado Melgar; Pablo Cascales De Paz

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Keywords: Groundwater; Nitrate; Fe nanoparticles; SE Spain

Abstract: Nitrogen fertilizers are applied in agriculture to increase crop production but its extensive use has resulted in nitrate contamination, leading to the degradation of groundwater quality and contamination of drinking water supplies. This is specially the case in areas with intensive agriculture, that additionally suffer from cyclical and severe water scarcity; the degradation of water bodies by nitrates in these contexts worsens water stress and limits economic growth. Although the European Union (EU) has been developing environmental policies to protect water resources for 30 years now, nitrate is still the major responsible for the bad chemical status of European groundwater bodies. Therefore, this preventive approach needs to be coupled with new corrective approaches which should treat groundwater currently affected by high nitrate concentration. In this regard, the EU-funded LIFE NIRVANA project is validating under real conditions a novel methodology aiming at decreasing the concentration of dissolved nitrate in groundwater by the injection of nano-zero valent iron (nZVI). These nanoparticles (diameter around 50 nm) are characterized by large reactive areas (20-25 m²/g) and high reducing capacity, and are stabilised with an organic substrate which could stimulate microbiological activity in the aquifer. The objective of this contribution is to show the first results of the project concerning the site characterization and the first nanoparticles injection. The project’s pilot site is composed of two injection wells, seven monitoring piezometers and one pumping well, and has been built in a multi-layered porous aquifer located in Murcia (Southern Spain). The site characterization was carried out by means of a lithological well-log based on the drilled materials (mainly gravel, sand, and clay) during the wells and piezometers drilling, and four tracer tests with salt (NaCl) conducted in the two main permeable layers of the aquifer. The salt-flow pathway inside the aquifer was registered with CTD-Divers located in 4 monitoring piezometers. The injection of nanoparticles was done after the finalisation of the salt tests. 38 litres of 240 g/L Fe⁰ nanoparticles were injected in the deep permeable level using a small pump. The effect of nanoparticles in groundwater was controlled by means of water sampling for laboratory analysis and a pH-ORP submersible probe. Results of the tracer tests show flow velocities ranging from 108 m/d to 18 m/d depending on the monitoring point considered. Both flow velocities were clearly influenced by the water injected (around 500 L per test) and pumping in the area. Dilution rates ranged from 1:6 to 1:525 depending on the aquifer level and control point. Nanoparticle’s injection produced almost no effect on pH but clear ORP decreases. The assessment of the effects on nitrate will be done when receiving the results from laboratory, and will be included in the final communication.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221786

Year: 2022