Using Fiber Optics to Detect Moisture Intrusion into a Landfill Cap Consisting of a Vegetative Soil Barrier

Abstract

The intrusion of moisture into landfills can pose a health hazard because of the possibility that the moisture will carry harmful substances into the groundwater. Early detection of moisture anywhere within these landfills is essential if corrective action is to be taken well before an occurrence of this kind. This paper presents the results of a field-scale simulation test of the use of fiber optics to detect the presence of moisture within landfill covers, using a detection method based on the thermal response of soils as a function of their moisture content. By sending electrical current through an embedded stainless-steel tube, soils of varying moisture content were heated and time-dependent temperature measurements were obtained with a fiber-optic distributed temperature sensor system. The optical fiber itself lay within the tube, but its temperature was a function of how rapidly heat was conducted into the surrounding medium. The results of this experiment, which are in agreement with those obtained using more traditional "point" sampling and laboratory analysis, are presented along with the strengths and limitations of the thermal-response method of detecting moisture.

Heated Distributed Temperature Sensing for Field Scale Soil Moisture Monitoring

“…Spatially distributed, temporally continuous estimates of θ were obtained by empirically relating D θ S measurements of Δ T 8 to colocated, dielectric measurements of θ at Stations 1 to 3 (Figure 3a). The slope of the Δ T 8 ‐ θ relationship (D θ S response curve) decreased with increasing θ , further suggesting decreased sensitivity at higher soil moisture contents, which is consistent with findings from previous studies (Weiss 2003; Sayde et al 2010). While fitting a biexponential function to the Δ T 8 ‐ θ relationship using least squares regression (Δ T 8 =1109 exp [−30.56 θ ] + 4.891 exp [−0.4412 θ ]); a subset of data (13 of 316 points) were omitted because of the effects of spatially variable wetting front dynamics.…”

Calibration of soil moisture sensing with subsurface heated fiber optics using numerical simulation

“…[] described a nearly linear relationship T cum ‐θ, our results are closer to Sayde et al . [] or Weiss [], in which the rate of change of T cum or ΔT 120s in the case of Weiss [] decreased at higher water contents (Table ).…”

“…Heat pulses of long duration must be handled carefully since water displacement due to excessive heating may occur, causing the soil to dry out in the proximity of the cable [ Weiss , ]. Also, as discussed by Sayde et al .…”

Evaluación del método activo para determinar contenidos de humedad en suelos

“…Recientemente, los métodos distribuidos de temperatura utilizando cables de fibra óptica (FO-DTS, por sus siglas en inglés), han sido empleados para determinar posibles fugas de agua en presas de materiales sueltos así como flujos de agua y contenidos de humedad volumétricos (θ) en el subsuelo (Weiss, 2003;Aufleger et al, 2005;Perzmaier et al, 2006;Steele-Dunne et al, 2010;Sayde et al, 2010Sayde et al, , 2014Ciocca et al, 2012;Striegl y Loheide, 2012;Gil-Rodríguez et al, 2013;Cao et al, 2015;Benítez-Buelga et al, 2016;Dong et al, 2016). Estos métodos utilizan la reflexión de luz al interior de un cable de fibra óptica para determinar la temperatura a lo largo del cable.…”