SENSITIVITY ANALYSIS OF SLUG TESTS .2. OBSERVATION WELLS

An earlier paper (Part 1, this issue) dealt with the use of sensitivit y analysis for the design of a slug,test that would give reasonably ac curate estimates of the aquifer parameters by an informed choice of th e number and times of measurements. An investigation of the radial dep endence of the Cooper et al. analytical solution for a slug test in a confined aquifer shows that the use of one or more observation wells c an vastly improve the parameter estimates, particularly the estimate o f the storage parameter. Generally, the observation well must be fairl y close (about 10 m or less) to the slugged well to be effective. The storage coefficient must be small in order to see the effect of the sl ug at greater distances from the stressed well. Since the temporal and spatial dependence of the sensitivities for transmissivity and storag e are considerably different, the addition of one or more observation wells will substantially reduce the correlation between these two para meters, which will result in much better estimates than are usually ob tained in slug tests. These ideas are illustrated using typical data r epresentative of our research sites.