The total drawdown (St) under pumping conditions can be expressed by the sum derived from the following equation: The well-aquifer system has a natural resistance to flow, and drawdown results from this resistance. To understand the reasons behind the unpredictability, we need to examine the governing equations and their physical basis in the well-aquifer system. These negatives can be offset with reliable preventative maintenance programs. Third, in order to have a reliable production rate of consistent water quality, it may require additional wells at a considerable expense. Second, sudden losses in specific capacity or large increases in drawdown make it impossible to obtain the needed raw water supply. Regional variability in hydrogeology makes the one-size-fits-all approach to scheduling maintenance unreliable. First, it makes it difficult to determine when a well requires maintenance in order to avoid rehabilitation. Losses in specific capacity over time can be nonlinear, and this behavior has negative consequences. A decrease in specific capacity is an indication of well fouling however, by the time large losses in specific capacity are observed, well plugging has progressed to the point where rehabilitation, rather than maintenance, is required to restore lost capacity. Specific capacity is a measure of well performance (Q/s) indicating the amount of water that is available per unit drawdown. Wells are often pumped at variable discharge rates, which vary with drawdown, and drawdown increases with the duration of pumping. Optimization of design results in a well that minimizes drawdown and construction costs while meeting the required discharge rates and intervals. If you try to discharge more water than can be supplied by the aquifer, or that will pass the aquifer-well connection, water levels in the well decrease until the pump is exposed and the well runs dry.ĭrawdown is reduced by the construction of more efficient wells. The pumping water level is called drawdown (s), and the greater the drawdown, the higher the power costs. This is often referred to as specific capacity, the vertical distance between the static, non-pumping water level.

There are several quantitative measures of well performance, the most common being discharge (Q), the volume of water produced per unit time. Neil Mansuy is vice president of technical services for Subsurface Technologies, Inc.

Astm treatment well drawdown