While analyzing rising-head slug testing data collected from several monitoring wells completed in silty sand with a partially submerged screened interval; the actual displacement measured in the well exceeded the maximum theoretical displacement. Normally the bailer would have been submerged just to the potentiometric surface, however during performance of slug testing, the bailer was submerged one to four feet below the water surface and then, after equilibration, was extracted. Water above the bailer did not fall readily through the annular space, resulting in 50-120% more displacement than the theoretical maximum. Analysis of the geometry and physical properties of the well and components used in slug testing revealed that ~70% of the water above the bailer was dissipated into the well structure as the bailer was extracted, resulting in an observed displacement greater than the theoretical displacement of the bailer.

Due to migration of the dissipated water, the slope of the recovery curve, after initial borehole effects, is increased, yielding values for hydraulic conductivity as much as 3 times greater than the expected value. An equation was developed to correct the data, resulting in more accurate analysis, without the need for recollection of the field data.