Comparison of hydraulic conductivities by grain-size analysis,pumping, and slug tests in Quaternary gravels, NE Slovenia

Abstract

Abstract Hydraulic conductivities (K) can be obtainedfrom pumping and slug tests as well as grain size analysis.Although empirical methods for such estimations are longstanding,there is still insufficient comparison of K valuesamong the various approaches. Six grain-size analysismethods were tested on coarse-grained alluvial sedimentsfrom 12 water wells in NE Slovenia. Values of K from grainsizemethods were compared to those of pumping testsand slug tests. Six grain-size methods (USBR, Slichter,Hazen, Beyer, Kozeny-Carman, and Terzaghi) were usedfor comparison with the Theis and Neuman pumping testmethod and the Bouwer-Rice method for slug tests. Theresults show that the USBR (US Bureau of Reclamation)method overestimates K values and there is no correlationwith other results, so its use is not advised. Conversely,whilst the Slichter method gives much lower estimatesof K, it is the only one to completely fulfill the grainsize requirements. Other methods (Hazen, Beyer, Kozeny-Carman, and Terzaghi) result in intermediate values andare similar to the Slichter method; however they should beused for smaller-sized sediments. Due to their high transmissivityand small radius of inffiuence, slug tests shouldbe avoided in the analysis of gravels, as they only test asmall portion of the aquifer compared to pumping tests.This is confirmed by the low correlation coefficients betweenhydraulic conductivities obtained from pumpingtests and slug tests.