water Article Investigating Groundwater Condition and Seawater Intrusion Status in Coastal Aquifer Systems of Eastern India Subrata Halder 1, * , Lingaraj Dhal 2 and Madan K. Jha 1   Citation: Halder, S.; Dhal, L.; Jha, M.K. Investigating Groundwater Condition and Seawater Intrusion Status in Coastal Aquifer Systems of Eastern India. Water 2021, 13, 1952. https://doi.org/10.3390/w13141952 Academic Editors: Thomas M. Missimer and Maurizio Barbieri Received: 21 May 2021 Accepted: 9 July 2021 Published: 16 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 AgFE Department, IIT Kharagpur, Kharagpur 721302, India; madan@agfe.iitkgp.ac.in 2 WRD&M Department, IIT Roorkee, Roorkee 247667, India; ldhal@wr.iitr.ac.in * Correspondence: shalder_2007@yahoo.co.in; Tel.: +91-943-259-4699 Abstract: Providing sustainable water supply for domestic needs and irrigated agriculture is one of the most significant challenges for the current century. This challenge is more daunting in coastal regions. Groundwater plays a pivotal role in addressing this challenge and hence, it is under growing stress in several parts of the world. To address this challenge, a proper understanding of groundwater characteristics in an area is essential. In this study, spatio-temporal analyses of pre-monsoon and post-monsoon groundwater levels of two coastal aquifer systems (upper leaky confined and underlying confined) were carried out in Purba Medinipur District, West Bengal, India. Trend analysis of seasonal groundwater levels of the two aquifers systems was also performed using Mann-Kendall test, Linear Regression test, and Innovative Trend test. Finally, the status of seawater intrusion in the two aquifers was evaluated using available groundwater-quality data of Chloride (Cl ) and Total Dissolved Solids (TDS). Considerable spatial and temporal variability was found in the seasonal groundwater levels of the two aquifers. Further, decreasing trends were spotted in the pre-monsoon and post-monsoon groundwater-level time series of the leaky confined and confined aquifers, except pre-monsoon groundwater levels in Contai-I and Deshpran blocks, and the post- monsoon groundwater level in Ramnagar-I block for the leaky confined aquifer. The leaky confined aquifer in Contai-I, Contai-III, and Deshpran blocks and the confined aquifer in Nandigram-I and Nandigram-II blocks are vulnerable to seawater intrusion. There is an urgent need for the real-time monitoring of groundwater levels and groundwater quality in both the aquifer systems, which can ensure efficient management of coastal groundwater reserves. Keywords: groundwater fluctuation; spatio-temporal variability; trend analysis; seawater intrusion; coastal aquifers 1. Introduction Water is a vital substance on earth and forms the principal constituent of all living things. Therefore, it is called the lifeblood of the biosphere. The unabated population growth and implacable rise of water demand in different sectors have huge repercussions for a growing freshwater scarcity in several parts of the world, including India. Providing sustainable water for domestic use and irrigated agriculture is one of the big challenges for the 21st century. To address this challenge, efficient planning and management of water resources are of utmost importance. Groundwater is a renewable but finite resource. Generally, it is preferred for drinking water supply because of its good quality, pleasant taste, and from a safety point of view. Due to rapid population growth, water resources potential is decreasing day by day in general, and groundwater resources potential in particular. Furthermore, mismanagement of water resources and climate change create an imbalance between water supply and demand. For proper planning and management of groundwater, assessment of groundwater is very important. Nowadays, the management of coastal aquifer systems is becoming essential due to dramatic climate change. Unfor- tunately, groundwater management has been neglected in coastal areas, though coastal Water 2021, 13, 1952. https://doi.org/10.3390/w13141952 https://www.mdpi.com/journal/water