Chilled Mirror Hygrometer Research Articles

A graph-based approach for modeling the soil–water retention curve of granular soils across the entire suction range

This study investigates experimentally the water retention behavior of granular soils from saturation to oven-dry state. The soil–water retention curve (SWRC) tests were conducted on a well-graded sand with clay using tensiometer and chilled-mirror hygrometer techniques. The soil samples were statically compacted at various water contents to different initial densities. The results showed that individual linear segments in the log–log graph could characterize the desorption process of capillary and adsorption water. A novel water retention model in a simple mathematical form was developed by conceptualizing the total water content as the sum of the suction-dependent capillary and adsorption components. The model parameters possess an unambiguous physical meaning. They can be easily calibrated based on the graphical properties of the test data using simple linear regression, which is a significant advantage over conventional SWRC models. The model was validated using the water retention data of the tested soil in this study and the available data of granular soils in the literature. The reproduced curves agree well with the experimental results. This study also analyzed the influence of compaction water content, initial density, and clay content on the capillary and adsorption components of the water retention curve. Additionally, the proposed framework provides a quick approximation method for the adsorption capacity, which plays an essential role in assessing the effective stress and the simulation of liquid film flow in unsaturated granular soils.

Reliability of Chilled-Mirror Hygrometer (WP4C) for Soil Total Suction Measurement

Reliability of Chilled-Mirror Hygrometer (WP4C) for Soil Total Suction Measurement

A simplified approach to estimating the evolution of residual shear strength of unsaturated soils with suction

Several researchers have investigated the effect of suction and partial saturation on the angle of residual shear strength. Most of these investigations involve the adoption and application of a method of controlling suction on the ring shear apparatus and performing ring shear tests on the same soil for various values of suction. Methods adopted include both the axis translation technique for control of suction over the range 50-1500 kPa and the saturated salt solutions method for control of suction in the range of several MPa. The general picture from these investigations is that the residual shear strength failure envelope remains linear but corresponding to higher values of the angle of residual shearing resistance for constant suction; this value increasing with increasing suction. The paper presents an attempt to normalise values of measured angle of residual shearing resistance for various suction values with the angle of residual shear strength of the corresponding fully saturated soil. This normalisation verified the linear increase of the ratio tanφres(s)/tanφres(s=0)with suction. This linear increase allows for estimation of the evolution of tanφres(s)with suction if φres(s)for one specific suction can be measured. This observation led to the measurement of tanφres(s)of clayey soils in conventional ring shear apparatus without suction control, simply by removing water from the shear box while shearing continues and measuring shear strength until its stabilisation, taking place after the specimen in the shear box came to equilibrium with prevailing laboratory atmospheric conditions. Using the chilled mirror hygrometer to measure equilibrium suction after ring shear completion indicated that equilibrium suction due to laboratory atmospheric conditions is practically constant over the time needed for a single test on one soil. This observation along with the previous observation on the linear increase of the ratio tanφres(s)/tanφres(s=0)with suction, makes valid the estimation of evolution of residual shear strength of unsaturated soils with suction using only a conventional ring shear apparatus and a chilled mirror hygrometer. The paper concludes by outlining the approach, presenting measurements and a relation obtained between tanφres(s)/tanφres(s=0), suction and liquid limit.

Determining osmotic suction through electrical conductivity for unsaturated low-plasticity soils

Determining osmotic suction from the electrical conductivity (EC) of soil pore water was widely reported in the literature. However, while dealing with unsaturated soils, they do not have enough soil pore water to be extracted for a reliable measurement of EC. In this paper, the chilled-mirror dew-point hygrometer and contact filter paper method were used to determine the total and matric suctions for low-plasticity soils with different salinities (0.05‰, 2.1‰, and 6.76‰). A new piecewise function was proposed to calculate the osmotic suction, with the piecewise point corresponding to the first occurrence of precipitated salt in mixed salt solutions (synthetic seawater). EC, ion and salt concentrations used for osmotic suction calculation were transformed from the established relationships of mixed salt solution instead of experimental measurement. The calculated osmotic suction by the proposed equation and the equations in the literature was compared with the indirectly measured one (the difference between the measured total and matric suctions). Results showed that the calculated osmotic suction, especially the one calculated using the proposed function, was in fair agreement with the indirectly measured data (especially for specimens with higher salinity of 6.76‰), suggesting that the transformation of EC and concentrations from the established relationship is a good alternative to direct measurement for low-plasticity soil. In particular, the proposed method could be applied to unsaturated low-plasticity soils which do not have enough soil pore water for a proper EC measurement.

Defining relative humidity in terms of water activity: III. Relations to dew-point and frost-point temperatures

Relative humidity (RH) is a fundamental quantity used in many fields of engineering and science, and in particular in meteorology and climate research. Relative fugacity (RF) and, equivalently, relative activity of water vapour in humid air have recently been proposed as a physically well-founded, unambiguous common metrological reference quantity for several conventional but mutually inconsistent definitions of RH. The RF definition is valid is valid under real-gas conditions and above boiling and sublimation temperatures. While differences between RH and RF mostly remain within uncertainties of typical present-day RH measurements, such systematic discrepancies are expected to be of substantial climatological relevance. Consequently, interdisciplinary harmonisation of RH definitions is overdue within the SI framework. Dew-point and frost-point temperatures are preferred measurands in humidity metrology using, for example, chilled-mirror hygrometers. Here, relations are presented for estimating RF from those temperatures, based on equations of state of the 2011 IUGG 5IUGG: International Union of Geodesy and Geophysics, https://iugg.org/. standard TEOS-10, the ‘international thermodynamic equation of seawater—2010’. Recommendations are given for numerically computing RF using the open-source TEOS-10 SIA library 6 6SIA Library: Sea-Ice-Air Library of TEOS-10, http://teos-10.org.. The asymptotic limiting laws of RF for nearly saturated humid air exhibit the familiar form of Clausius–Clapeyron-like equations, despite departing from ideal-gas assumptions. Under various practical conditions, these simple equations may cover the full humidity range with only minor residuals compared to the full numerical TEOS-10 solution for RF.

Development and validation of a laser-absorption-based method for in-situ and high-precision water vapor dew point temperature measurement

Dew point temperature is an important gas state parameter. Accurately measuring dew point temperature is a challenge because it is not only related to gas concentration, but also gas temperature and pressure. We proposed a dew point temperature measurement method based on tunable diode laser absorption spectroscopy (TDLAS), in which water vapor temperature, pressure and concentration can be measured simultaneously with a single near-infrared laser source. Two H2O absorption lines near 1381 nm (7242.37 cm−1 and 7243.08 cm−1) were selected, and their coefficients of temperature-dependence of the self-broadened half-width were measured experimentally to improve the HITRAN databases. The wavelength shift of the laser was suppressed by a temperature compensation circuit. To confirm the capability of this method, a series of experiments were performed in a standard temperature and humidity chamber through the target absorption lines. In the whole dew point range of the experiment, the maximum deviation between the measurement results of our method and the high precision chilled mirror hygrometer is less than 0.9 ℃. According to the time-series measurements of atmospheric H2O, the measurement accuracy of 0.57% and the detection limit of −61.1 ℃ were verified under the condition that the optical path was only 10.5 cm. This result shows the potential of this method in low-cost, calibration-free, in-situ and high-precision dew point measurement.

Investigating the salinity effect on water retention property and microstructure changes along water retention curves for lime-treated soil

Lime treatment is a widely applied technique in improving the workability and geotechnical properties of soil. The water retention property and microstructure are highly related to the hydro-mechanical behaviour of unsaturated lime-treated soil. In this study, the water retention property and the evolution of pore size distribution (PSD) along the water retention curves (during drying) were studied for a lime-treated soil, with emphasis put on the curing time and salinity effects. Two soil powders with different soil salinities were prepared and stabilised by 2% lime. The chilled-mirror dew-point hygrometer and the contact filter paper method were used to measure the total and matric suctions, respectively. The PSD of lime-treated soil at various water contents was obtained using mercury intrusion porosimetry (MIP). Results showed that the matric suction increased significantly, while the total suction varied slightly during curing. At a given curing time, the specimens with higher salinity exhibited higher matric and total suctions. The difference between the soil water retention curves (SWRCs) determined by the filter paper method and from the PSD became more significant at longer curing time, as the production of cementitious compounds did not contribute to the SWRC from PSD, but contributed to the increase of matric suction measured by the filter paper method. The PSD of lime-treated soil changed from bi-modal characteristics (w > 14 %) to tri-modal pattern (w ≈ 8 %), and finally recovered to bi-modal characteristics (w ≈ 3 %), due to the shrinkage-related cracking of the clay fraction. The lime treatment inhibited the clay shrinkage, whereas the curing time and salinity effects on the drying-induced microstructure were insignificant.

Determination of the relative humidity at the parts-per-million (ppm) level in gases by a nanoporous alumina thin-film on a surface acoustic wave (SAW) resonator

Moisture measurement in parts per million (ppm) in electronic gases and in liquids for different industrial applications is challenging and a costly affair. There are numerous critical applications of ppm moisture measurement systems such as transformer oil, sulfur hexafluoride gas (SF6) in switchgear and protection, and the electronic industry for integrated circuit (IC) fabrication. Conventionally chilled mirror hygrometer and laser spectroscopy are used but some low-cost solutions using the thin-film capacitive sensors are also available in the market. This paper presents the fabrication of an inexpensive miniature moisture sensor using a commercial low-cost surface acoustic wave (SAW) resonator of 433.92 MHz frequency. To detect moisture, a hydrophilic metal oxide film is deposited on the interdigital electrodes (IDTs) of the SAW device. The film thickness is optimized to provide a sharp resonating peak under dry humidity conditions. Experiments were conducted to determine the frequency shift in the peak with the variation of moisture in nitrogen gas from 6 to 460 ppm using a vector network analyzer. The maximum sensitivity was 24 Hz/ppm with correlation coefficient of linearity equal to 0.99. An effort was also made to develop a prototype meter to measure moisture in ppm. Important features of the sensor are linear response, inexpensive fabrication, and appreciable sensitivity in the ppm range.

Unsaturated behaviour and cation self-diffusion of geosynthetic clay liners in Antarctica

The impact of time-dependent unsaturated behaviour of virgin and the impact of cation self-diffusion on the time-dependent unsaturated behaviour of exhumed geosynthetic clay liner (GCL) specimens were investigated using a chilled mirror hygrometer. Total suction values (after 7 weeks’ water homogenisation) are reported for ten virgin (six different bentonites) and one GCL exhumed after exposure to the thermo-hydro-mechanical (THM) conditions in Antarctica. The time-dependent unsaturated responses of four different virgin GCLs 1 day and 1 week after hydration are compared with the results at homogenisation and the implications discussed. For the suction (0.1–300 MPa) and water content range (5–140%) examined, the post-water homogenisation water retention behaviour of the GCLs is affected by bentonite characteristics. At a given gravimetric water content, the total suction of GCLs increased with increasing smectite content and total soluble salt content and decreased with increasing total bound cation content in the bentonite. Cation self-diffusion also increased the total suction in the GCL exhumed after exposure to Antarctic THM conditions. It is concluded that the impact of cation self-diffusion on the unsaturated behaviour of a GCL during its time in service before exposure to pollutants needs to be considered in designing hydraulic and gas barriers.

Miniature high-frequency chilled-mirror hygrometer for atmospheric measurements aboard fixed wing UAS

Miniature high-frequency chilled-mirror hygrometer for atmospheric measurements aboard fixed wing UAS

A ssessment of Various Methods to Measure the Soil Suction

The foundation of the lightweight structures is commonly in unsaturated state conditions because located above the ground-water table. The matric suction governs the hydro-mechanical behaviour of unsaturated soils. Soil suction estimation is challenging both in the field and lab. The indirect and direct techniques are utilized to measure the soil suction. Several types of equipment utilized to measure the soil suction have been developed with innovative technology. However, there are constraints on reliability, suction range estimation, application, etc. The primary objective of this study is to review, describe the working principle, report limits, and benefits of various techniques utilized to measure the soil suction and select the cost-effective. A comparative study on direct and indirect technique of soil suction estimation is conducted base on recent literature, with a focus on suction range, procedure, type of suction, processing time, and application (lab/field). The apparatus utilized to measure directly or indirectly the matric suction found in the literature displays the highest range in the order of 1500 kPa except for the filter paper. The thermocouple psychrometer and the transistor psychrometer can measure a maximal total suction of 8000 kPa. The chilled-mirror hygrometer can measure a maximal total suction of 30000 kPa in the laboratory. The filter paper technique and the chilled-mirror hygrometer are cost-effective techniques. However, the filter paper technique is likely the easiest and low-cost technique to measure the matric suction and total suction for the full range with extreme care in the test procedure both in the field and lab.

Suction and crack propagation in GCLs subjected to drying and wetting in CaCl2-solutions

The current study addresses the cracking and self-healing capacity of Geosynthetic clay liners (GCLs) subjected to drying and wetting in a divalent salt solution. Commercially available GCLs, initially saturated under a load of 3.92 kPa, were stepwise dried for different durations in an oven at 30 °C and rewetted afterwards in deionised water and divalent salt solutions (CaCl2) of different molarities (0.05 mol/l, 0.5 mol/l and 0.05 mol/l prehydrated). The evolution of cracks and their patterns were studied by analysing X-ray images. In parallel, the water retention behavior was tested on the raw bentonite using micro-cells and a chilled-mirror hygrometer. The morphology of the crack patterns in the GCLs was highly affected by the pore fluid, which was reasoned by reduced tensile strength caused by the salt induced aggregation. The ability to retain water at a given suction was found to be higher for the samples subjected to CaCl2-solutions in comparision to the sample saturated with deionised water. However, a calculation of the osmotic suction caused by the additional CaCl2 in the porewater shows that the matric suction of the samples subjeted to CaCl2 decreases. The crack intensitiy factor (CIF) followed a similar trend and three different drying regimes were identified.

The Chicago Water Isotope Spectrometer (ChiWIS-lab): A tunable diode laser spectrometer for chamber-based measurements of water vapor isotopic evolution during cirrus formation.

We describe a new tunable diode laser (TDL) absorption instrument, the Chicago Water Isotope Spectrometer, designed for measurements of vapor-phase water isotopologues in conditions characteristic of the upper troposphere [190-235 K temperature and 2-500 parts per million volume (ppmv) water vapor]. The instrument is primarily targeted for measuring the evolving ratio of HDO/H2O during experiments in the "Aerosol Interaction and Dynamics in the Atmosphere" (AIDA) cloud chamber. The spectrometer scans absorption lines of both H2O and HDO near the 2.64 µm wavelength in a single current sweep, increasing the accuracy of isotopic ratio measurements. At AIDA, the instrument is configured with a 256-m path length White cell for in situ measurements, and effective sensitivity can be augmented by enhancing the HDO content of chamber water vapor by an order of magnitude. The instrument has participated to date in the 2012-2013 IsoCloud campaigns studying isotopic partitioning during the formation of cirrus clouds and in the AquaVIT-II instrument intercomparison campaign. Realized precisions for 1-s measurements during these campaigns were 22 ppbv for H2O and 16 ppbv for HDO, equivalent to relative precisions of less than 0.5% for each species at 8 ppmv water vapor. The 1-s precision of the [HDO]/[H2O] ratio measurement ranged from 1.6‰ to 5.6‰ over the range of experimental conditions. H2O measurements showed agreement with calculated saturation vapor pressure to within 1% in conditions of sublimating ice and agreement with other AIDA instruments (the AIDA SP-APicT reference TDL instrument and an MBW 373LX chilled mirror hygrometer) to within 2.5% and 3.8%, respectively, over conditions suitable for all instruments (temperatures from 204 K to 234 K and H2O content equivalent to 15-700 ppmv at 200 hPa).

Calibration of hygrometers at non-static conditions

The current practice of calibrating humidity sensors at discrete measurement points under static conditions is time-consuming, i.e. expensive, due to the long stabilization times. In order to reduce the calibration time, we introduce a new calibration method based on humidity ramp measurements, i.e. measurements are performed at first while humidity is increased with constant speed and then decreasing with the same speed. A calibration system based on the mixing flow humidity generation principle was developed for generating linear humidity ramps inside a measurement chamber. Two different calibration approaches were investigated. In the first one, high accuracy was targeted with moderate ramp speeds (2 h to 12 h) and a large volume measurement chamber using a chilled mirror hygrometer as a reference. In the second approach, a shorter calibration time was achieved with fast ramp speeds (0.5 h to 2 h) and a small volume chamber using a fast capacitive humidity sensor as a reference. The developed calibration procedure was validated by comparing results of non-static and static calibrations to each other for five different capacitive humidity sensors from two manufacturers. The non-static calibration was found to provide equivalent results compared to the static calibration with a potential of reducing the overall calibration time by up to 50%. Preconditions of the non-static calibration related to the ramp speed and sensors response times are discussed, and an estimation of the calibration uncertainty is given. The main advantage of the developed non-static calibration method is that calibrations can be performed faster and more data on the sensor behaviour is obtained than with the conventional point-wise calibration without any significant increase in uncertainty.

Development of a near-infrared tunable diode laser absorption spectrometer for trace moisture measurements in helium gas

There is a demand for water vapor or moisture measurement in gas mixture at trace level from industries like combustion studies, semiconductor industry, environmental studies, cryogenic services, etc. There are few principles, direct or indirect, to measure moisture—each having individual limitations. Among all, the chilled mirror hygrometer is very accurate but response time is poor; therefore, it is suitable for calibration purposes not for online measurement. An instrument based on near-infrared absorption spectroscopy has been developed and discussed in this article. In this instrument, the laser is modulated with both sinusoidal and slower linear scan, split into two beams: an intense one is passed only through air and the other one through air and the absorption cell of 50 cm length. The balanced detection technique is adopted between the two beams called the reference and the measurement channels, respectively, and the difference signal between the two undergoes the 2-f lock-in detection. This method is good for elimination of moisture present in air and any common-mode noise present in both the channels and as well determines the splitting ratio keeping the absorption cell in vacuum. This method also eliminates the 1-f component present in the signal, which causes asymmetry in the two wings of the 2-f absorption spectra. For computation of absorption spectra, it is found that the Hitran database is sufficient to predict for air as the base gas but Exomol should be used in the cases where helium is the base gas. Simulation and experiment both were performed at different concentration and pressures and the results are found in good agreement for the central spectrum with little difference in wings’ peak. The sensitivity of this instrument achieved at 100 mb pressure in the absorption cell for helium as the base gas with refresh rate of 625 Hz is ∼17 ppmv and ∼4 ppmv for direct and 2-f measurement, respectively. The applicability of the instrument for air as the base gas is also shown in the paper.

Effect of Measurement of Dew Point Temperature in Moist Air on the Absorption Line at 1392.53 nm of Water Vapor

The HITRAN database (High-Resolution Transmission molecular absorption database) is an extremely helpful reference for selecting lines of molecular species. In the case of water vapor, a particular strong absorption line around λ ≈ 1392.5 nm is suitable for the detection of molecules, not only because of its high strength but also because it is well separated from the neighboring transitions, thus avoiding any overlap. First, we present the optical system that uses a distributed feedback (DFB) laser diode, emitting around λ ≈ 1392.5 nm with a power ≈ 3 mW and linewidth ≤ 10 MHz. For metrological needs, we are looking for a means to control the water vapor concentration in ambient air in near real time and especially when an optical chilled mirror hygrometer is used. The latter instrument is widely used due to its performance with regard to both accuracy and repeatability of measurements. Here, using the molecular absorption device the use of such an instrument is examined from the point of view of its impact on the measurement of relative humidity. This paper reports the measured frequency positions of the observed line at λ = 1392.5337 nm for different air pressures and compares them with the values given in the HITRAN database. In addition, we discuss the possibility of using water vapor detection by spectroscopy to observe the change of the shape and the position of the absorption line produced during measurements of the dew point temperature by the optical chilled mirror hygrometer.

Development of a low-temperature low-pressure humidity chamber for calibration of radiosonde humidity sensors

A low-temperature low-pressure humidity chamber has been developed at the Korea Research Institute of Standards and Science for the calibration of radiosonde humidity sensors. The humidity generator operates in a two-temperature and two-pressure mode in which a saturator and a test chamber are separately immersed in two baths. The saturation performance of the saturator is first evaluated at a low temperature (−75 °C) and at atmospheric pressure. In this condition, the uncertainty of the frost-point temperature by the saturator is 53 mK with the coverage factor k = 2. Then, a chilled mirror hygrometer is calibrated for the compensation of low-pressure effects such as a pressure drop along the tubing line inside the hygrometer. Significant differences between the frost-point temperature at the hygrometer inlet and that measured by the hygrometer are observed at a pressure lower than 20 kPa. An empirical formula for compensating the low-pressure effects on the hygrometer is obtained and, subsequently, is used for the validation of the frost-point temperature generated at a low temperature and low pressure in the test chamber. The corresponding uncertainty due to the calibration of the hygrometer including the compensation of low-pressure effects is 306 mK at k = 2. A representative humidity generation and its validation by the hygrometer is demonstrated at a temperature (−70 °C) and two pressures (4.6 kPa and 20 kPa) in the test chamber. Uncertainty budgets on relative humidity in the test chamber are presented from 10 %rh to 40 %rh with a 10 %rh interval at both pressures. Consequently, the combined uncertainty is less than 2%rh (k = 2) which includes uncertainty factors such as the saturation efficiency, the adsorption/desorption hysteresis, the validation by the hygrometer measurement at low pressures, and so on. The newly developed humidity chamber enables the calibration of radiosonde humidity sensors at low temperature and low pressure conditions that mimic upper air environments in a traceable manner to the International System of Units (SI).

Determination of Water Content of Nitrogen Containing Hydrogen Sulfide by Karl Fischer Coulometric Titration.

Measuring the water content in natural gas is important for safety; however, complex matrixes make the results inaccurate. Natural gas contains hydrogen sulfide (H2S), which react with iodine (I2), causing Karl Fischer coulometric titration (KFCT) to give higher results. The KFCT method for the determination of water content of nitrogen containing H2S was investigated. A chilled mirror hygrometer offered a reference water content to calibrate the KFCT. The interfering of H2S was reduced by subtracting I2 consumed by H2S according to the reaction mechanism of ISO 10101; however, the modified results remained higher. A possible reaction mechanism with a stoichiometry of H2S to I2 of 1:2.5 was proposed. The improved KFCT method had an error of water content no more than (3 + 2%·x) mg/kg (x, water content in mg/kg) and had the potential of online monitoring of natural gas.

Linkage between swelling pressure, total suction of saturated bentonites and suction of saturating aqueous solutions

In deep geological repositories, compacted bentonites have been proposed for use as barrier materials for isolating nuclear waste. The prevailing hydro-mechanical-chemical boundary conditions in the repositories can affect the swelling capacity of compacted bentonites. The present study examines the linkage between the swelling pressure of saturated bentonites, the total suction of saturated bentonites and the suction of hydrating fluids. An equation describing the linkage between these parameters was derived based on the thermodynamics of soil moisture. To validate the derived relationship, laboratory tests involving constant volume swelling pressure tests and total suction measurements after the swelling pressure tests were carried out on a selected Ca-Mg-rich bentonite. Seven bentonite samples with compaction dry density ranging from 1.20 to 1.83 Mg/m3 were hydrated with deionized water, whereas four samples with a dry density of 1.59 Mg/m3 were hydrated with 0.0001 to 2.0 M CaCl2 solutions. The total suctions of the saturated bentonite and the hydrating fluids were determined by using a chilled-mirror hygrometer. The total suction of the saturated bentonite was found to be affected by the compaction dry density and the suction of the hydrating fluids. The experimental results from the present study and from the literature demonstrated that the total suction of saturated bentonites minus the suction of the hydrating fluids used to saturate bentonites is approximately equal to the swelling pressure of saturated bentonites.

Sensitivity of Percolation Estimates to Modeling Methodology: A Case Study at an Unlined Tailings Facility with Limited Monitoring Data

Calculation of water budgets is critical to developing long-term management and remediation plans for legacy mine waste facilities. The effects of several modeling decisions commonly made by practitioners constructing numerical hydrologic models can significantly alter estimates of percolation and resultant management strategies. We investigated the effects of variations in several common modeling decisions for an unlined legacy tailings emplacement in Lincoln County, Nevada using predictions from HYDRUS 1D and 2D simulations. Modeling decisions investigated include choice of hydraulic property model, hydraulic properties, numerical mesh discretization, boundary condition representation, dimensionality, and geometry. Hydrologic parameterization was informed by measurement of field-saturated hydraulic conductivity, in-situ density, field moisture content, bulk (dry) density, and water retention curve by hanging column, pressure plate, and chilled mirror hygrometer. Numerical hydrologic models resulted in percolation estimates from 0 to 24 mm/year through the tailings. Choice of hydraulic properties and temporal resolution of boundary condition data contributed the most to variations in percolation estimates. For comparison, percolation was predicted with a simple water balance model (HELP), resulting in a percolation rate of 51 mm/year. Such a wide range of percolation rate predictions demonstrates the potential for significant variability in model output within a range of defensible modeling decisions, assumptions, and parameterization methods. To appropriately bound this uncertainty, several model assumptions and iterations should be considered.