RESUMEN
Farm-scale desalination units are gaining popularity for agricultural irrigation in arid countries, such as Kuwait to meet freshwater demands. However, less attention has been given to the management of environmentally hazardous brine reject water they produce. In this study we investigated the fate of brine water produced by the inland desalination units on the underlying aquifers using numerical modelling and field investigations. The methodology involved developing groundwater flow and solute transport models using Flex VMF-SEAWAT to simulate the movement of reject brine. The field investigations included collecting 150 water samples and conducting pumping tests on newly drilled wells. This numerical simulation considered advection, dispersion, and adsorption processes with variable groundwater density following rigorous validation and calibration of the developed numerical models. The results show that the RO reject brine will significantly increase groundwater salinity, exceeding 10,000 mg/L when accounting for advection, dispersion, and adsorption processes. The sustainable yield of the aquifer, with a salinity of <10,000 mg/L, averages 500 Mm3 but is expected to be depleted within 16 years with the current extraction rate. The resulting hydraulic properties are favourable with K about 100 m/d, T > 1000 m2/day, and Sy just >0.1. The adopted values for dispersivity and adsorption coefficients for chloride and sulphate salts in the aquifer were 10 m and 1 × 10-7 [mg/L]-1 respectively. Chemical and numerical analyses indicate a mixing ratio between the reject brine and groundwater in the study area of approximately 10 %. Uncontrolled groundwater extraction, combined with the surface disposal of RO reject brine, has led to a significant decline in groundwater levels and an increase in the salinity. The adsorption ratio of simulated brine plume was 13 %. The authors recommend to dispose the RO reject water in a safe location or transfer it to the nearest wastewater treatment plant for proper treatment and reuse.
RESUMEN
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/SO4, Ca + Mg/SO4+HCO3), isotopes (34S, 87Sr/86Sr), relationships between 2H and 18O, and Ne/He and 3He/4He 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.