Vulnerability assessment of coastal groundwater wells in Terengganu using TRUST Index

Coastal aquifers in Terengganu, Malaysia, face increasing challenges in groundwater quality and availability, necessitating a comprehensive assessment of their vulnerability. This study investigated groundwater vulnerability and susceptibility in the coastal region of Terengganu, Malaysia, where coastal aquifers face threats to groundwater quality and availability. A comprehensive groundwater vulnerability assessment was conducted using the TRUST Index. This index-based approach considers the lithology, river proximity, well usage, distance to the seashore, and well type. Field investigations were undertaken to obtain real-time measurements of well behavior. This included conducting constant-rate pumping tests on four private wells to gauge hydraulic conductivity. Consequently, flow rates were meticulously monitored throughout these tests, and water level measurements and physicochemical assessments were conducted over a 120-minute duration. Following this, the data was analyzed utilizing AQTESOLV software to determine the hydraulic conductivity, transmissivity, and storativity of the aquifer. The data from MW4, MW16, and MW20 collectively indicate favorable hydraulic characteristics, suggesting water movement within the aquifer, ranging from 4.02 m3/day to 11.39 m3/day. In contrast, MW7 displays an unexpectedly high discharge rate of 19.77 m3/day, suggesting a highly permeable and efficient water-transmitting unconfined aquifer with limited water storage capacity. The vulnerability assessment classified the wells as Low, Moderate, and High vulnerability. Wells MW1, MW6, MW7, and MW20 were categorized as low vulnerability, indicating relatively secure groundwater quality and availability. Wells MW2, MW3, MW8, MW9, MW12, MW13, and MW14 were classified as moderately vulnerable, suggesting a moderate level of potential risk. Meanwhile, wells MW4, MW5, MW10, MW11, MW15, MW16, MW17, MW18, and MW19 were labeled as highly vulnerable, signifying a higher susceptibility to threats. The correlation matrix revealed insightful connections between hydrological and water quality parameters. The distance from the seashore is inversely correlated with salinity and specific conductance, signifying a reduced seawater water impact farther inland. Note that wells near rivers exhibit higher salinity, likely due to potential saltwater intrusion, emphasizing the importance of understanding these relationships in coastal aquifer systems. This study comprehensively assesses coastal groundwater vulnerability, behavior, and water quality. Its unique contributions lie in the meticulous hydraulic characterization and identification of unconventional well behavior. These findings emphasize the importance of considering temporal variations, local influences, and tailored management strategies for sustainable coastal groundwater resource utilization.