The pumping tests conducted in the Kharga oasis display a number of features that complicate their interpretation. Initially, there is a large head loss in all wells due to turbulent flow in the gravel pack (filter) and well screen and in the aquifer adjacent to the well where the flow is also turbulent. The initial drawdown (change in head) is also influenced by well-bore storage, so that the drawdown is lower than theoretically expected, but this effect is limited in time. After the initial phase, the drawdown in the well appears to increase as if the aquifer is confined, which is revealed in a diagnostic semi-log plot of the time-drawdown relationship as initially non-linear but gradually becoming linear over time. However, thereafter the drawdown slows down and reaches a pseudo steady state, which occurs for almost all the wells around a pumping time of 200–1000 min. The reason for this apparent stabilization of the drawdown in the wells is not clear, because the pumping tests only last about half a day, which is too short to reveal the long-term hydraulic behavior of the Nubian sandstone aquifer system. Ideally, the pumping tests should be conducted for several days to see if a true stable state has been achieved, which seems unlikely because there is no natural aquifer recharge, or that other phenomena are occurring that demonstrate the true nature of the aquifer, such as double porosity behavior, delayed yield or leaky aquifer conditions. The most likely explanation is double porosity behavior, which is very common for fractured sandstone aquifers. Field exploration and conceptual models [

20,

21] show that when a pumping test is performed in such media, the flow to the well initially consist of water released from the fractures, while gradually water is also released from the matrix so that the drawdown slows down and reaches a pseudo steady-state, after which the drawdown increases again as more and more groundwater is released from the matrix. Another possible explanation is a leaky aquifer system, whereby groundwater is gradually released from overlying, or more likely underlying, less permeable aquifers, which stabilizes the drawdown [

20,

21]. In this regard, we point out that none of the wells was reported to have reached the lower limit of the Nubian sandstone. Finally, it also possible that during a pumping test ground water levels fall below the top of the aquifer, causing unconfined conditions and dewatering of the aquifer [

20,

21,

22].

Because of these complications, we only analyze the drawdown in the initial phase before the transition to the pseudo steady-state using the Theis [

23] equation as proposed in the literature [

20,

21,

22] including a well loss term

where

${s}_{w}$ (L) is the drawdown in the well,

${s}_{0}$ (L) is the well loss due to turbulence,

$Q$ (L

^{3} T

^{−1}) is the pumping rate,

$T$ (L

^{2} T

^{−1}) is the local aquifer transmissivity around the well,

$W$ is the Theis well function [

23],

$S\text{}$(-) is the local storage coefficient around the well during the initial phase of the pumping test,

${r}_{w}$ (L) is the effective radius of the well,

$t$ (T) is the time since pumping started and

${r}_{c}$ (L) is the radius of the well casing. The time condition in Equation (1) is needed to exclude well-bore storage effects [

20], resulting in pumping times of 4–42 min for a well casing radius of 0.34 m (

Figure 2) and a possible range of transmissivity values of 100–1000 m

^{2}/d. Because the well loss is unknown, it is not possible to estimate the aquifer properties by traditional curve matching of the Theis equation and the observed drawdown in the well versus time. However, the effective radius of the well and the aquifer storage coefficient can be expected to be very small, so that the argument in the Theis function is small and the function can be simplified using the Jacob approach for sufficiently large times [

20,

21,

22]

Because the well loss is constant as it only depends on the pumping rate and the physical properties of the well, the slope of the drawdown plotted against the logarithm of time is constant and the transmissivity of the aquifer can be estimated as

Therefore, the transmissivity can be estimated provided that a linear segment is present in the observed

$s$ versus l

$\mathrm{og}t$ graph before the transition to the pseudo-steady state. Note that it is not possible to estimate the storage coefficient of the aquifer, because the well loss and the effective radius of the well are unknown.