The values of transmissivity resulting from the pumping test of the Dammam confined aquifer were 43.99, 72.02, 22.21, 24.04, 24.26, 222.85, and 98.81 m2/day depending on the Moench’s (1984) method for wells 1 to 7, respectively. According to the Theis (recovery) method, the transmissivity values for wells 1 to 7 were 38.53, 44.81, 14.2, 10.92, 82.04, 207.8, and 92.99 m2/day, respectively.
The values of conductivity resulting from the pumping test method of wells 1 and 7, of the Dammam confined aquifer were 0.261, 0.37, 0.097, 0.139, 0.634, 1.027, and 0.482 m2/day, depending on Moench’s (1984). According to the Theis (recovery) method, the conductivity values of wells 1 to 7 were 0.229, 0.234, 0.062, 0.063, 0.418, 0.957, and 0.453 m2/day. Because of the presence of fractures and fissures, the transmissivity values in the northwest of the confined aquifer were higher than those in the south of the study area.
The variations in hydraulic conductivity values were perhaps due to the heterogeneous and anisotropic properties of the aquifer. There was a clear change in the hydrogeochemical characteristics of the Dammam Aquifer, as was represented by the increase in salinity resulting from the increase in TDS concentration.
According to the results of the permeability and the specific capacity of the studied wells, the Dammam Aquifer could be classified as a medium production with slight heterogeneity. This was due to the excessive withdrawal of groundwater against scientific controls.
When the data were compared, it was discovered that with the passage of time, the value of transmissivity dropped. The decrease in transmissivity was due to a large volume of groundwater being drawn from the Dammam Aquifer from a thousand drilled wells, the most significant of which were the flowing wells utilized to establish fish lakes. As a result, the aquifer piezometric pressure and groundwater levels decreased within the aquifer. Another factor was the lack of rainfall for groundwater recharge. In comparison with the previous studies, the difference in specific capacity values was another indicator of groundwater depletion in the Dammam Aquifer.
The lack of control over the number of drilled wells and the quantities of groundwater produced from the Dammam Aquifer, and the decline in the production values compared to previous years, has led to an increase in salinity and a change in the hydrogeochemical characteristics of the water. In addition to a decrease in the produced water to minimum levels, which can cause water full depletion. The decrease in the reserve and pressure of groundwater in the Dammam Aquifer and the increase in salinity might lead to mineral deposition in the pore space, resulting in a decrease in transmissivity. This could cause a change in the hydraulic conductivity and petrophysical aquifer characteristics.