THE USE OF SLUG TESTS TO DESCRIBE VERTICAL VARIATIONS IN HYDRAULIC CONDUCTIVITY

Multilevel slug tests provide one means of obtaining estimates of hydr aulic conductivity on a scale of relevance for contaminant transport i nvestigations. A numerical model is employed here to assess the potent ial of multilevel slug tests to provide information about vertical var iations in hydraulic conductivity under conditions commonly faced in f ield settings. The results of the numerical simulations raise several important issues concerning the effectiveness of this technique. If th e length of the test interval is of the order of the average layer thi ckness, considerable error may be introduced into the conductivity est imates owing to the effects of adjoining layers. The influence of adjo ining layers is dependent on the aspect ratio (length of test interval /well radius) of the test interval and the flow properties of the indi vidual layers. If a low-permeability skin is present at the well, the measured vertical variations will be much less than the actual variati ons, owing to the influence of the skin conductivity on the parameter estimates. A high-permeability skin can also produce apparent vertical variations that are much less than the actual, owing to water flowing vertically along the conductive skin. In cases where the test interva l spans a number of layers, a slug test will yield an approximate thic kness-weighted average of the hydraulic conductivities of the intersec ted layers. In most cases, packer circumvention should not be a major concern when packers of 0.75 m or longer are employed. Results of this study are substantiated by recently reported field tests that demonst rate the importance of well emplacement and development activities for obtaining meaningful estimates from a program of multilevel slug test s.