Estimating transverse dispersivity based on hydraulic conductivity

The modeling of depletion timeframe for a non-aqueous phase liquid (NAPL) layer is partially dependent on transverse vertical dispersivity. This paper provides guidance for estimating this parameter over the wide range of soil textures in which NAPL resides at contaminated sites. Transverse dispersivity is re-calculated for several previous NAPL dissolution studies based on a consistent methodology for estimating model input parameters. Through the compilation of a number of case studies from the literature including multiple NAPL dissolution experiments, the trend of transverse vertical dispersivity appears to be inversely proportional to the effective grain diameter when groundwater velocity (v) is below a critical threshold (upsilon(c)). A novel regression equation is derived for estimating transverse dispersivity based on hydraulic conductivity when v < v(c) and the NAPL length is on the order of meters. The critical velocity for NAPL pool dissolution appears to range from 3 to 5 m/d based on a limited number of studies with NAPL pool lengths of 1 m or more. The method derived by Klenk and Grathwohl (2002) is validated for estimating a correction factor for dispersivity when upsilon > upsilon(c). (C) 2018 Elsevier B.V. All rights reserved.