USING A CAMSIZER TO OPTIMIZE GRAIN SIZE-BASED HYDRAULIC CONDUCTIVITY ESTIMATION FOR ICE-MARGINAL SEDIMENTS

Characterization of subsurface groundwater flow and contaminant transport in ice-marginal environments can be exceedingly difficult when using conventional methods. A common approach to representing ice-marginal heterogeneity requires accurate measurement of subsurface grain sizes to identify distinct lithofacies, which can then be translated into hydrofacies using hydraulic conductivity values. Our work focuses on developing a hybrid grain size measurement process that uses a Camsizer in lieu of sieve analysis for any sand-sized sediment and applying this process to 35 Quaternary sediment samples deposited in an ice marginal environment to inform lithofacies characterization and support hydraulic conductivity estimation at a contaminated site. A Camsizer is able to measure the grain size distribution of a sample by slowly pouring grains past a set of two CCD cameras. By using test sediments similar to our site samples, we first determined that a minimum sample size of ~100g of sediment produced a representative grain size distribution by repeatedly splitting and measuring a large sample. We then developed a method for separating the sand fraction (63µm- 2mm in size) from the silt, clay and gravel fractions via wet and dry sieving. This was necessary because the Camsizer has a size limit of 30µm to 30mm and because losses of clay and silt sized particles occur when introducing the sample to the Camsizer. Our preliminary grain size curves representing solely the sand-fraction indicate several areas of distinct sorting that may be associated with distinct lithofacies. We are in the process of analyzing the fine-grained sediments using sedigraph and hydrometer techniques. The two data sets will then be combined into full grain size distribution curves for each sample and standard empirical equations will be used to estimate hydraulic conductivity and infer hydrofacies. Future research efforts will focus on incorporating the grain shape and sphericity data from the Camsizer into both the lithofacies characterization and hydraulic conductivity estimation.