CONDUCTING AND INTERPRETING SLUG TESTS IN MONITORING WELLS WITH PARTIALLY SUBMERGED SCREENS

Conducting and interpreting slug tests in wells with screen sections a nd sand packs that span the water table are severely complicated by sa nd pack drainage and resaturation. Sand pack drainage greatly reduces the actual head difference between the well and the formation. Resatur ation of the drained sand pack must be properly accounted for, or the formation hydraulic conductivity will be underestimated. The magnitude of error is a function of the well geometry, sand pack properties, an d the model chosen to interpret the data. A method has been developed to correct for sand pack resaturation by calculating the specific yiel d of a drained sand pack using the early recharge data of a slug test. Slug tests were conducted in one well in which the water table varied over time, creating both partially and fully submerged screen and san d pack conditions for comparative testing. The mid-time, log-linear po rtion of slug test data was corrected using the calculated specific yi eld of the drained sand pack to yield essentially the same hydraulic c onductivity value as the fully submerged screen results. Not accountin g for sand pack resaturation would have yielded a hydraulic conductivi ty value that was lower than the submerged screen results by a factor of seven.