Multi-well and multi-tracer tests to characterize the groundwater aquifers in southern Kuwait

摘要

In the water-starved arid climate of Kuwait, useable (both fresh and brackish) reserves of groundwater constitute a strategic resource. Therefore, effective management policies are essential for ensuring sustainable management of the groundwater resources in the state. Although the general pattern of groundwater flow is known, the detailed pattern of the flow paths of water within the Kuwait aquifer system and the variation of hydraulic and transport properties are not known. Applied tracers are powerful hydrogeological investigative tools because the tracer application (source term) is controlled and well characterized which permits quantification of subsurface properties often unmatched by standard physical methods. Aquifer pumping tests and multi-well and multi-tracer (rhodamine-WT, fluorescein, sodium bromide) tests were carried out, under both natural and forced gradient conditions, at Al-Shegaya and Umm-Gudair sites. The objectives of the tracer tests are to determine the groundwater flow directions, flow rates, inter-and intra-aquifer hydraulic communications, effective porosity, dispersivity, etc., in the established groundwater well fields of southern Kuwait at Al-Shegaya Umm-Gudair. The tests involved drilling, construction and development of groundwater wells, and injection of tracers in the injection wells and monitoring its concentrations in the injection and monitoring wells. Inverse numerical modeling (MOD-FLOW and MT3DMS codes) was used for data interpretation. The Kuwait Group and Dammam Formation have a high degree of hydraulic separation, and it is likely that there is little recharge of the Dammam Formation from downward leakage from the Kuwait Group (at least in the study area). Groundwater resources in the Dammam Formation may be largely restricted to the flow into Kuwait from Saudi Arabia. The lower Kuwait Group aquifer has dual-porosity conditions: likely a rapid flow through fracture and/or conduit system (n(eff) = 0.5 %) and a slow flow through the formation (calcareous) matrix (n(eff) = 20 %), with very low dispersivity (longitudinal and transverse/vertical dispersivities of 0.1 and 0.01 m, respectively). The injection wells indicate more than one linear line segment in the tracer dilution plot (concentration in natural logarithmic vs. time), which suggests varying transmissivity across the well screen depths. The filtration velocity, hydraulic conductivity and transmissivity of the aquifers have also been estimated. At both the sites, the groundwater flow in the underlying carbonate formation is very slow (0.028 m/d). The hydrogeological parameters obtained from the present tracer study will be used for more reliable conceptualization, development and calibration of a suitable statewide flow and solute transport model for the regional groundwater system of Kuwait.