Hydraulic parameter estimation of saturated sand using silica encapsulated, DNA tagged microparticles: - Laboratory experiments and numerical modeling

Abstract

Determining hydraulic parameters of aquifers, their associated uncertainties and spatio-temporal variation is important to characterize groundwater flow and mass transport. Of these hydraulic parameters, hydraulic conductivity, effective porosity, and dispersivity are the most crucial ones. Several ex-situ methods such as grain size analysis, and permeameter tests of drilled core samples, and in-situ methods including pumping tests, slug tests, and flowmeter tests, and tracer studies have traditionally been applied for estimating hydraulic conductivity. Effective porosity has been typically estimated by ex-situ and in-situ methods such as mercury intrusion porosimetry, Helium gas pycnometry, magnetic resonance imaging and tracer tests. Compared to the standard drilled core analysis and geophysical methods, groundwater tracer tests have been used for broader applications including in-situ direct hydraulic parameter estimation, transport velocity determination, spatio-temporal variation of hydraulic parameters, and establishing aquifer connectivities. Inorganic salts and fluorescent dyes are the most commonly used groundwater tracers due to their no or low reactivity with sediments, cost efficiency and non-toxicity. In addition to salt and dye tracers, particulate tracers including microspheres, bacteria and bacteriophages have been widely used for characterizing groundwater flow paths, and pathogen migration. Transport behaviour of these microparticle tracers, depending on physico-chemical properties such as size and surface charge, and process variables including ionic strength and particle concentration, can differ from the conservative tracers in terms of transport velocity, mass distribution, and recovery. This dissertation focuses on the applicability of silica encapsulated DNA tagged microparticles (SiDNA) in determining hydraulic parameters (hydraulic conductivity, effective porosity, longitudinal, and transverse dispersivities) of homogeneous and heterogeneous saturated medium grain and coarse grain sand. SiDNA particles are ~200 nm spherical silica particles encapsulating double stranded DNA (dsDNA) molecules. The uniqueness of the base pair sequences of the dsDNA, synthesized through combinations of nucleotides, overcomes the general limiation of lack of distinctiveness within a group of solutes (eg. salt) or particulate tracers (e.g. microparticles, bacteria). In laboratory column (1D) and sand tank (3D) experiments, SiDNA with a superparamagnetic core (SiDNAmag) was subjected to retention through first order kinetic attachment, resulting in 1-3 log less mass recovery as comapared to conservative tracers.