Samuel Belay Alamne

Alamne et al. Environmental Systems Research (2022) 11:8 https://doi.org/10.1186/s- Open Access RESEARCH Mapping groundwater nitrate contaminant risk using the modified DRASTIC model: a case study in Ethiopia Samuel B. Alamne1, Tewodros T. Assefa2*, Sisay A. Belay2 and Misbah A. Hussein2 Abstract Background: Nitrate contamination of groundwater often occurs in urban and industrial areas due to point and non-point sources of anthropological activities. Groundwater constitutes a a significant portion of the water supply system for Bahir Dar City in Ethiopia, though the level of groundwater pollution is not known. This study was conducted to assess the the extent of the aquifer and groundwater pollution (nitrate) based on contaminant vulnerability risk mapping using the GIS integrated modified DRASTIC model. A field survey was conducted to collect samples from boreholes for nitrate analysis and to modify the DRASTIC model. Results: Compared to the original intrinsic vulnerability assessment, land use as external factors changed from moderate-high to high vulnerability class from 18 to 88%. The FR-APH modified model showed a good correlation (0.53) compared to the other methods. Based on the FR-APH modified model, about 31% of the area was under moderate to high and high vulnerability range, 39% was under moderate vulnerability range while 30% was under low and moderate to low vulnerability range. Conclusions: The integrated vulnerability map showed high risk in the central part of the City due to the flat slope and shallow depth to groundwater. Besides, the sensitivity analysis indicated that the contribution of aquifer media and vadose zone to contaminant risk was found trivial. In general, groundwater at Bahir Darwas found vulnerable to nitrate contamination and needs proper management. Keywords: Drastic model, GIS spatial analysis, Groundwater vulnerability Introduction Groundwater is a potential alternative source of domestic water supply for the main cities, towns, and villages due to its less initial cost, better water quality, and availability throughout the year compared to surface water sources (Mengistu et al. 2019; Nwobodo et al. 2015). However, groundwater contamination by nitrate is increasing locally and globally in general (Hu et al. 2005). A water quality study in Sub-Saharan countries by Lapworth et al. (Lapworth et al. 2017) showed that domestic waste *Correspondence:-2 Faculty of Civil and Water Resource Engineering, Bahir Dar Institute of Technology, Bahir Dar, Ethiopia Full list of author information is available at the end of the article contamination occurred in shallow wells, especially in highly populated cities. Among the major groundwater quality problems in Ethiopia, are high microbial and nitrate concentrations in shallow unconfined aquifers around major cities (Mengistu et al. 2019). Regardless of challenges associated with contaminants, several research findings (Worqlul et al. 2017; Siebert et al. 2010; Gowing et al. 2020) indicated that groundwater will remain the main source of fresh water in the face of climate change and variability. People use groundwater for drinking and domestic purposes using various extraction systems from the aquifer and its contribution to surface water sources (Schwartz 2003). However, groundwater contamination has significantly degraded due to population pressure and unwise water use without © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.