Low-Flow Purging Reduces Management of Contaminated Groundwater
Purging a monitoring well prior to sampling removes stagnant water in the well casing and ensures collection of groundwater samples representative of formation water. Traditionally, a number of well casing volumes are removed (from three to five) and water stabilization parameters are monitored during removal of the casing volumes. Temperature, pH and specific conductance are routinely monitored during purging to determine when a sufficient volume of water has been removed from the well. When these parameters exhibit stabilized readings with a specified range of values (i.e., plus or minus 10 percent over consecutive measurements), the water sample is considered representative of formation water. For deeper wells, purging a well in this manner can generate a large volume of contaminated groundwater, which requires proper handling and disposal. In addition, the amount of time purging multiple casing volumes can often be excessive for sites with many wells.