VENTING TEST ANALYSIS USING JACOBS APPROXIMATION

Field venting tests were conducted in alluvial sands residing between the water table and a clay layer. Flow rate, barometric pressure, and well-pressure data were recorded using pressure transmitters and a per sonal computer. Data was logged as frequently as every second during p eriods of rapid change in pressure. Tests were conducted at various ex traction rates. The data from several tests were analyzed concurrently by normalizing the well pressures with respect to extraction rate. Th e normalized pressures vary logarithmically with time and fall on one Line allowing a single match of the Jacob approximation to all tests. Though the Jacob approximation was originally developed for hydraulic pump test analysis, it is now commonly used for venting test analysis. Only recently, however, has it been used to analyze several transient tests simultaneously. For the field venting tests conducted in the al luvial sands, the air permeability and effective porosity determined f rom the concurrent analysis are 8.2 X 10(-7) cm(2) and 20%, respective ly.