PUMPING TEST METHODOLOGY FOR IGNEOUS AND METAMORPHIC ROCK AQUIFER/WELL SYSTEMS: AN UPDATE
Water supply system design requires knowledge of the maximum sustainable yield and maximum drawdown for an aquifer/well system. Because of limited time and limited funds, many groundwater users need to evaluate these parameters within a short pumping period, without installation of observation wells and monitoring systems. Because of this, we propose a form of severely modified step-drawdown pumping tests or constant-head drawdown tests as the most cost-effective methods to determine the aquifer/well parameters.
The modified step-drawdown stabilizes the pumping water level at a predetermined level early in the test, and holds that pumping level for 72 hours. A constant-head test is performed by initiating and sustaining a pumping rate well above the anticipated capacity of the well until such time as a designed pumping water level is achieved. Once this pumping water level is achieved, changes in the pumping rates are used, as necessary, to maintain the predetermined pumping water level. In either method, after the flow rate has stabilized and been maintained for the term of the pumping test, the pump is turned off and the recovery is monitored. The recovery curve can then be used to estimate the maximum sustainable yield of the aquifer/well system being tested.