Estimating Air Conductivity and Porosity from Vadose-Zone Pumping Tests

Field tests using air extraction and injection in both horizontal and vertical wells are evaluated to estimate air conductivity and porosity in the vadose zone. Six extraction tests and four injection tests were conducted. Sixty data sets were developed by measuring gas pressures as a function of time at six gas probes during each of the tests. Two analytical procedures are used to evaluate each data set. The first procedure, which is a modified Theis analysis, neglects the effects of leakage through the top boundary of the flow field. The second procedure, which is a modified Hantush analysis, includes the effects of leakage by assuming that it is generated within the flow layer. Image-well theory can be used to evaluate data from horizontal wells. Variations in parameter estimates are caused by spatial variability, measurement error, data analysis methodology, well configuration, and the direction of air flow. At this particular field site, variations due to measurement errors were of the same order as those due to spatial heterogeneity.