Evolution of hydrogeochemistry in groundwater production fields of Kuwait - Inferences from long-term data.

Kuwait Group aquifers and Dammam Formation are the two prominent aquifers, the wells tapping Dammam Formation and Dual completion wells are used for groundwater production. The current study investigates the spatiotemporal evolution of hydrochemical characteristics of the Shagaya water field utilizing long-term (1975-2019) hydrochemical data from 116 water wells. The Shagaya water well field has been differentiated into A to F sub-Fields. Mann-Kendall and Sen's Slope method along with spatial interpolation of change in TDS with time identified a significant decrease in TDS with time in the major portions of the Shagaya B, C, D, and E Fields. The study infers that 82% of wells extracting water from the Dammam Formation and 42% of Dual completion wells show a decrease in TDS concentration. The most plausible explanation for this phenomenon was the inflow of better-quality water from the up gradient parts of the Kuwait Group and the Dammam Formation aquifers due to the fall in the potentiometric head with high volume production in the well field. The results of ionic ratios (Na/Cl, Ca/Mg, Ca/SO, Ca + Mg/SO+HCO), isotopes (S, Sr/Sr), relationships between H and O, and Ne/He and He/He ratios identified that salinization was due to the result of rock-water interaction, ion exchange, mixing between groundwater of Kuwait Group and Dammam Formation and with groundwater from deeper parts of the aquifer. The long-term analysis of the data shows a notable variation of chemistry in a few locations and thus the study helps to manage, sustain groundwater resources, and protection of host aquifers.