Water quality aspects from Spanish sites to support managed aquifer recharge (MAR) guidelines not based on maximum allowable concentration standards

Most countries that have technical guidelines or regulations for artificial recharge or managed aquifer recharge (MAR), that include water quality aspects are based on the establishment of standards or Maximum Allowable Concentrations (MACs) to regulate the quality of the water percolated or injected into an aquifer. The number of parameters in these guidelines vary considerably (from 6 in Spain to 156 in the USA) and often apply to all aquifers within administrative boundaries (e.g., national territory), regardless of the nature of the receiving medium, the depth of the water table, and other key factors. Eleven MAR systems in Spain have been studied (eight operational and three experimental, with limited number of data from three sites), characterising both, the recharge water quality and the water resulting from the interaction processes recharge water-soil-unsaturated zone-saturated zone of the aquifer. In all cases, an improved effect on groundwater quality is observed, even though some parameters in the recharge water don’t comply with the standards employed in some European countries, where this article focuses. The article suggests that regulating water quality for MAR through MACs at national level gives room for another alternative approach specific for each site. It might be recommendable to establish local standards at the regional or aquifer-wide level to better reflect the diversity of groundwater occurrence. As per the article, sectoral water authorities could receive more decision-making power on granting permits for MAR based on the quality of the hydrogeological and risk studies for each request. This would help reduce the application of the precautionary principle when in granting permission.