Geological formations or rock types under the earth's surface have distinct physical properties that affect the flow of groundwater and determine whether that zone would yield sufficient water from a well to be of use for household supplies, or larger yields that would be needed for industrial purposes, farm or municipal water supplies. These properties include:

• Effective porosity - the percentage of interconnected space in rock and soil that can contain water;
• Hydraulic conductivity (K)- indicates how easily water moves through the aquifer;
• Transmissivity (T) - is the ability of the aquifer to transmit water T = K * aquifer thickness;
• Storativity - the ability of a confined aquifer to take up or release water in response to a change in head resulting from recharge or extraction.

When we know these parameters, and have mapped the extent of formation, we'll know whether it will form an aquifer - capable of yielding useful water supplies - or an aquitard, which is a geological unit that impedes groundwater flow to the point where it will not release useful water supplies. A confined aquifer is sandwiched between two aquitard or confining layers.

Currently pumping tests on water wells are the most common way to determine an aquifers hydraulic parameters.

In the future, with increased demand, many wells may be drawing from the same aquifer. Pump tests will not be as reliable at estimating the aquifer yield due to interference from the other wells. Predictive computer modeling may become necessary to better understand the cumulative effects of production on aquifer yield.

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A pumping test, or aquifer hydraulic response test, is now mandatory on all newly constructed wells or wells deepened to access a lower aquifer. When water is pumped from a well, the water level in the well will drop. When pumping stops, the water level in the well will eventually return to its original position.

During a pumping test, water is pumped from a well at a specific rate, and measurements are taken to determine how fast and how far the water level in the well drops (time-drawdown data). Measurements are also taken to determine how fast the water level in the well returns to normal (time-recovery data) once pumping has stopped. This data is used to determine what will happen to the aquifer if water is pumped from it at a constant rate (progressive response to steady-rate pumping), and how much water can move through the aquifer and into the well.

Based on these values and the height of the water column from the top of the aquifer to the non-pumping water level (artesian pressure), a pumping rate referred to as ‘Safe Yield’ can be calculated. The safe yield is the pumping rate over a given time that will eventually remove enough water from the aquifer for the pumped water level to drop to the top of the aquifer at the well.

In Alberta a 'Safe Yield - Q₂₀' is used to rate a well’s performance. This is the rate of pumping that can be done continuously for 20 years that will draw down the pumped water level to the top of the aquifer. This value is deemed adequate for water supply in domestic wells.

For licensed applications, where larger volumes of water may be used, in addition to the production well or wells, the proponent will also drill one or more observation wells. These wells are used to obtain other data needed to calculate the storativity of the aquifer. These observation wells help give a more accurate assessment of the aquifer in terms of its capacity, geometry and flow direction. They also allow for more complex mathematical assessments with computer modeling to give a better picture of the potential for drawdown and recovery of the aquifer.

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In some areas of Alberta, drillers frequently access two or more aquifers through one well. This is done to provide a higher well yield and to ensure a more reliable water supply. This is ONLY done for domestic wells where there is little water available. However, analysis of pumping test data can only evaluate one aquifer, not two or more simultaneously. The two-hour minimum pumping test gives an overall pumping rate, but values of Q₂₀ for each individual aquifer cannot be reliably determined if more than one aquifer is accessed by a single well. Each aquifer should have its own well and independent pumping test to learn the safe yield.

During many two-hour tests conducted on domestic wells during drilling operations, a bailer is used instead of a pump. A bailer does not provide the constant and measured flow rate of a pump. In this circumstance, only recovery data can be obtained to estimate transmissivity values. Production with compressed air during drilling or following well completion is another way of conducting a test that uses recovery data. Transmissivity values calculated only from recovery measurements are less reliable than those obtained from a formal pumping test where drawdown and recovery measurements are taken. Aquifer parameters derived from short-term recovery tests performed during, or immediately following, drilling operations aren't very useful, but they do provide preliminary estimates of the transmissivity and yield of the aquifer zone.