We thank Vienken and Dietrich for their comment on our recent paper (Vienken and Dietrich 2014). As these researchers point out, there are a number of limitations on the accuracy of the various empirical methods developed for the estimation of hydraulic conductivity from grain-size distribution including the general lack of experimental database size to the physical aspects of the aquifer hydrogeology. Even relatively uniform deposits, such as beach sand, contain heterogeneities related to bedding with horizontal hydraulic conductivity commonly being three to five times greater than vertical hydraulic conductivity. In most cases, the empirical methods using grain-size distribution to estimate hydraulic conductivity produce lower values than found using slug, aquifer performance (pumping), and tracer tests, which is to be
Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1 m/day for the beach subgroups, 3.4 to 7.1 m/day for dune subgroups, and 2.2 to 11 m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23 m/day.
The transport and retention of a soybean oil-in-water emulsion was evaluated in laboratory columns packed with a medium to fine clayey sand amended with varying amounts of kaolinite. Results from these experiments demonstrated that appropriately prepared soybean oil-in-water emulsions can be distributed in clayey sand at least 80 cm away from injection point. Kaolinite addition to the clayey sand resulted in an increase in the maximum oil retention. However, the empty bed collision efficiencies in columns packed with clayey sand amended with kaolinite were lower than in columns packed with only clayey sand, suggesting that kaolinite is a less efficient collector of oil droplets than natural clayey sand. A standard colloidal transport model provided an adequate description of effluent breakthrough and the final oil distribution in the laboratory columns. This transport model was implemented as a user defined module within RT3D. Model parameters determined in replicate columns and at varying velocities were reasonably reproducible.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.