A high-resolution nitrate vulnerability assessment of sandy aquifers (DRASTIC-N)

Groundwater protection against agricultural diffuse nitrate pollution is of paramount importance for safeguarding groundwater-dependent aquatic ecosystems and protecting human health by securing clean groundwater for drinking water production. Nitrate vulnerability assessment of aquifers is the core of a scientifically sound strategy for management and protection of groundwater by authorities. A multitude of methods exists for assessing intrinsic aquifer vulnerability. The objective of this paper is to develop a nitrate-specific groundwater vulnerability assessment method based on the globally recognized DRASTIC method, which was developed by the US Environmental Protection Agency in the 1980s. We propose a new method "DRASTIC-N″ for assessing aquifer nitrate vulnerability, which for the first time expands the seven original geological and hydrogeological parameters with a geochemical parameter for redox condition. The development of DRASTIC-N is based on the longstanding Danish practice of performing detailed groundwater mapping based on dense sampling of geophysical, geological, and geochemical data. DRASTIC-N is compared to the widely used and documented Danish nitrate vulnerability assessment method SCANVA in a study area where the primary aquifer used for drinking water production is composed of heterogeneous sandy glacial deposits. Both SCANVA and DRASTIC-N result in vulnerability maps, which show similar patterns of nitrate vulnerability with a fair overall agreement of 71%. DRASTIC-N provides a framework for systematic and transparent application, which can facilitate stakeholder involvement and help authorities in groundwater protection and decision-making with regards to nitrate pollution. DRASTIC-N is suitable for nitrate vulnerability assessments of glacially deposited sandy aquifers, an abundant and important water resource worldwide, potentially threatened by nitrate pollution from anthropogenic activities.