Specific Capacity is an assessment of the productivity of the well, and is defined as the well yield per unit drawdown* (i.e. Igpm/ft of drawdown). This translates into the amount of water level drop in a well at a designated pumping rate, over a specific time interval.
A general specific capacity measurement can be calculated using the maximum and minimum (i.e. non-pumping and pumping) water levels collected over a designated time interval. For future comparison purposes, these water levels should be collected over similar time intervals, with the same pumping rate.
A more accurate measurement of specific capacity can be made by conducting a pump test to determine any changes in the well's capacity. These tests can also be conducted about twice a year (e.g. spring and fall), to indicate if there are seasonal fluctuations in the specific capacity of the well. Pump tests to measure the specific capacity and overall well performance should also be conducted prior to any anticipated groundwater development or exploration activity in your area. This includes new commercial developments, irrigation well development, and drilling activity by the petroleum industry.
Follow these steps to calculate the Specific Capacity of your water well:
*Note: Drawdown is the difference between the initial non-pumping water level and the pumping water level at a specified time interval.