Michael R. Niemet

A new method for quantification of liquid saturation in 2D translucent porous media systems using light transmission

Abstract Five physically based models for predicting liquid saturation from light transmission in 2D laboratory systems containing translucent porous media were developed and tested (Models A–E). The models were based upon various simplifying assumptions concerning pore geometry, wettability, and drainage. Models A–D assumed uniform-sized pores, and liquid saturation was an explicit function of light transmission. Model E considered a distribution of pore sizes whose drainage characteristics were inferred from the Laplace equation. Mass balances were calculated using data from drainage and infiltration experiments, in four textures of silica sand with water as the fluid. Model E performed the best overall, with systematic errors of less than 2.3% saturation. Model E represents a robust easily applied new method for the determination of liquid saturation by light transmission. The other four models are presented, and compared, for reasons of historical interest and to investigate the impact of the various simplifying assumptions.

Considerations for modeling bacterial-induced changes in hydraulic properties of variably saturated porous media

Bacterial-induced changes in the hydraulic properties of porous media are important in a variety of disciplines. Most of the previous research on this topic has focused on liquid-saturated porous media systems that are representative of aquifer sediments. Unsaturated or variably saturated systems such as soils require additional considerations that have not been fully addressed in the literature. This paper reviews some of the earlier studies on bacterial-induced changes in the hydraulic properties of saturated porous media, and discusses characteristics of unsaturated or variably saturated porous media that may be important to consider when modeling such phenomena in these systems. New data are presented from experiments conducted in sand-packed columns with initially steady unsaturated flow conditions that show significant biomass-induced changes in pressure heads and water contents and permeability reduction during growth of a Pseudomonas fluorescens bacterium.

Relationships Between Gas-Liquid Interfacial Surface Area, Liquid Saturation, and Light Transmission in Variably Saturated Porous Media

[1] Liquid saturation and gas-liquid interfacial area are important parameters for evaluating the transport and fate of contaminants in unsaturated subsurface environments. Recent findings indicate that interfacial surface area controls the relative degree of transmitted light in laboratory systems containing translucent porous media. Equations are derived to estimate the specific gas-liquid interfacial area from the area under the primarydrainage branch of the Seff-h characteristic curve as parameterized using common water retention functions. The total area under the curve provides the maximum available specific gas-liquid interfacial area available at residual saturation, which can be incorporated into the relationship to determine the gas-liquid interfacial area at intermediate degrees of saturation via light transmission. Experimental results, and analysis of external data sets, support these findings. Closed-form relationships are presented as enhancements to a recent method for determination of liquid saturations above residual using light transmission. A physically based model is developed and tested for the quantification of liquid contents below residual saturation. INDEX TERMS: 1829 Hydrology: Groundwater hydrology; 1866 Hydrology: Soil moisture; 1875 Hydrology: Unsaturated zone; 1894 Hydrology: Instruments and techniques; KEYWORDS: light transmission, gas-liquid interfacial surface area, liquid saturation, residual saturation, unsaturated porous media, characteristic curve

Imbibition of saline solutions into dry and prewetted porous media

Infiltration of saline solutions and pure water into homogeneous packs of prewetted and air-dry silica sands was investigated using a light transmission system. Four sand grades and five solutions were considered. Narrow fingers with a sharp, almost saturated, wetting front were observed in the air-dry sands. The water content left behind the fingertip of saline solutions was higher than for pure water, resulting in a greater lateral expansion of the saline fingers over time. The rate of lateral expansion scaled with the square root of time, likely due to classic liquid sorption with the possible addition of water vapor diffusion. At early time, the salty fingers moved faster, but were ultimately overtaken by the pure water fingers. In prewetted sand, the wetting fronts were diffuse and never exceeded 26% saturation, less than third that seen in the initially air-dry media. The plumes in the prewetted sand were also much wider and their shape varied. In the prewetted sand the elevated surface tension of the saline solutions was the major cause for the observed differences in finger width and velocity, yet appeared to be insignificant in air-dry sand. Here, in addition to the density effect, absorption of the saline solution to the silica sand influenced the depth of wetting, finger velocity, and subsequent lateral expansion.