Water Saturation Measurements by Gas Tracers in Unsaturated Porous Media—Effect of Mass Transfer Limitations

Abstract

saturation in the vadose zone (Whitley et al., 1999; Dwarakanath et al., 1999;Nelson et al., 1999) and to Water saturation is a key parameter in studies of pollutant transport measure water saturation in lab-scale experimental sysin the vadose zone and an important factor controlling the rate of waste degradation in municipal solid waste landfills. The partitioning tems (Deeds et al., 1999a; Dwarakanath et al., 1999). interwell tracer test (PITT) has been suggested as a useful tool forRecently, this same technology has been used to meameasuring water saturation over large measurement volumes in both sure water in solid waste (Imhoff et al., 2003). systems. However, heterogeneous water distributions may result inDuring a field-scale PITT, injection and extraction mass transfer limitations, which can affect the accuracy of the measurewells are installed such that chemical tracers flow in the ments. In this study, we examined the influence of water saturation, zone of interest. This region typically contains mobile Henry's Law constant, injected tracer mass, tracer quantification limit, (e.g., air or water) and immobile (e.g., water and/or and local rates of mass transfer between air and water on PITT measure-NAPL) fluid phases. Partitioning tracers and a conserments. A single-region model was used to describe transport of gasvative tracer are injected simultaneously in the mobile phase tracers in a one-dimensional system and to investigate the effect phase into the injection well and later removed from of these factors on measurement error. To verify the conclusions drawn from this modeling exercise, laboratory-scale partitioning tracer tests the extraction well. Partitioning tracers partition into were conducted in four different sand packings. Finally, the results the immobile phases, retarding the transport of these from the mathematical modeling and laboratory experiments were tracers with respect to a conservative tracer. A compariused to suggest guidelines for minimizing measurement error in fieldson of partitioning and conservative tracer breakthrough scale PITTs for water saturation measurement.as the injected tracer mass decreased, and as the tracer Published

Field Application of Partitioning Gas Tracer Test for Measuring Water in a Bioreactor Landfill

“…Another potential limitation of the PGTT method is that it is expected to result in underestimates of water saturation and moisture content when water saturations are high. For this situation, mass transfer limitations may require larger injected tracer masses or lower tracer quantification limits to achieve unbiased results (22). Water saturations in the Yolo County bioreactor, even with liquid addition, were at most 30% and in previous tests in the Sandtown landfill were 32% (7).…”

“…Temperatures in the regions sampled by Test 1 and Test 2 in the aerobic bioreactor cell at Yolo County were 54 ( 7 and 48 ( 2 °C, respectively, where ( values represent the range of temperatures recorded by the two sensors in the region of each test. Higher temperatures result in larger Henry's law constants and a loss in measurement accuracy at small water saturations (22). More importantly, though, temperature variations result in spatially variable Henry's law constants.…”

Single-well experimental design for studying residual trapping of supercritical carbon dioxide

“…Partitioning tracer tests that are done between two wells are referred to as partitioning interwell tracer test (PITT). PITTs have been developed to detect crude oil (Cooke, 1971;Dean, 1971;Tang and Harker, 1991), measure water saturation (Imhoff et al, 2003;Li and Imhoff, 2005), and characterize and quantify nonaqueous phase liquid (e.g., NAPL) saturation Jin et al, 1995;Mariner et al, 1999;Nelson et al, 1999;Whitley et al, 1999;Young et al, 1999). In PITT, tracers are injected upstream and the recovered tracer breakthrough curves (BTCs) at the downstream extraction well are used to analyze tracer retardation, which is used to infer phase saturation.…”

Review of Techniques to Characterize the Distribution of Chromate Contamination in the Vadose Zone of the 100 Areas at the Hanford Site

“…• Soil moisture measurements in a landfill A number of recent studies have been performed for measurement of in situ soil moisture (Li and Imhoff 2005;Peng and Brusseau 2005;Han et al 2006Han et al , 2007.…”