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Exfiltrometer apparatus and method for measuring unsaturated hydrologic properties in soilRelated Patent Categories: Measuring And Testing, Borehole Or Drilling (e.g., Drill Loading Factor, Drilling Rate, Rate Of Fluid Flow)Exfiltrometer apparatus and method for measuring unsaturated hydrologic properties in soil description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060000267, Exfiltrometer apparatus and method for measuring unsaturated hydrologic properties in soil. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0002] This invention relates to apparatus and methods for measuring unsaturated hydrologic properties in porous media. BACKGROUND [0003] Hydrologic properties may be estimated in the laboratory on field cores or from special tests conducted in the field. By determining soil water content (.theta.) and water potential (.PSI.m), various properties of a sample including soil water flux (q), hydraulic gradient (I), hydraulic conductivity (K) and the soil water retention curve [soil water potential (.PSI.m) versus water content (.theta.)] may be estimated. This data is necessary for site characterization, including determination of recharge at waste disposal, agricultural and other sites, as well as for ground water protection and conservation. [0004] Laboratory testing requires removal of a sample from its native environment, causing disturbance to the sampling location. The sample must be transported to the laboratory for testing by a skilled technician. Labor and expense is involved with securing an undisturbed transport of the sample. The laboratory tests normally require several weeks to perform. The data obtained may be incomplete, particularly in the wet range, as the pristine condition of the sample is compromised. Thus, laboratory testing is not optimum as it is time consuming, expensive, and incomplete results may be obtained. [0005] Field testing also requires several weeks to months to perform. While the sample may be analyzed in its native environment, other factors, including weather, temperature and wildlife may affect the testing. Similar to laboratory testing, field testing is also expensive in time, money and human resources to perform. [0006] Estimation of unsaturated hydraulic properties under field conditions is frequently accomplished using the instantaneous profile method (IPM) (Davidson, et al., 1969). According to the IPM, when water movement takes place in a one-dimensional system, the soil moisture equation can be written as (Davidson, et al., 1969): d W .function. ( z , t ) d t = q .function. ( 0 , t ) - q .function. ( z , t ) [ 1 ] Where q(z,t) is the Darcian flux (LT.sup.-1) at depth z and time t, W is total water stored above z or W .function. ( z , t ) = .intg. 0 z .times. .theta. .function. ( z , t ) d t [ 2 ] When the soil column is undergoing drainage only q(0,t)=0, Equation [1] becomes: d W .function. ( z , t ) d t = - q .function. ( z , t ) [ 3 ] Darcian flux is given by: q .function. ( z , t ) = - K .times. .times. .differential. H .differential. Z [ 4 ] Where K is hydraulic conductivity (LT.sup.-1), H is total water potential (L) and q is approximated as: q .function. ( z , t ) .times. - .times. d W .function. ( z , t ) - W .function. ( z , t - .DELTA. .times. .times. t ) .DELTA. .times. .times. t [ 5 ] When the gradient term is approximated as a difference equation, it results in the IPM for obtaining hydraulic conductivity as a function of either water content or water potential: K q .function. ( z , t ) .times. .times. .DELTA. z .DELTA. .times. .times. H [ 6 ] [0007] Implementing the IPM in the field requires wetting the soil to field saturation, covering the experiment to prevent evaporation (i.e., set q(0,t)=0) and allowing the soil to drain freely. Since the IPM requires infiltration of 1 to 10 m.sup.3 of water, as well as instrument installations at multiple depths, the method is not being used at many hazardous waste sites. The entire IPM can take several weeks in the field (Davidson, et al., 1969; Sisson, et al., 1980). The apparatus and methods disclosed herein allow rapid determination of the soil hydraulic properties while using the IPM model. SUMMARY [0008] Exfiltrometer apparatus for estimating at least one unsaturated hydrologic property of a soil sample may comprise a container for holding soil. A sample container for holding the sample soil is positionable with respect to the container so that the sample soil contained in the sample container is in communication with soil contained in the container. A first tensiometer operatively associated with the sample container senses a surface water potential at about a surface of the sample soil contained in the sample container. A second tensiometer operatively associated with the sample container senses a first subsurface water potential below the surface of the sample soil. A water content sensor operatively associated with the sample container senses a water content in the sample soil. A water supply supplies water to the sample soil. A data logger operatively connected to the first and second tensiometers, and to the water content sensor receives and processes data provided by the first and second tensiometers and by the water content sensor. [0009] Exfiltrometer apparatus for estimating at least one unsaturated hydrologic property of in-situ soil in a soil environment comprises a sample container that is positionable within the soil environment so that a distal end of the sample container penetrates in-situ soil in the soil environment. A water supply operatively associated with the sample container introduces water to an in-situ soil sample isolated by the sample container. A first tensiometer operatively associated with the sample container senses a surface water potential at about a surface of the in-situ soil sample isolated by the sample container. A second tensiometer operatively associated with the sample container senses a first subsurface water potential below the surface of the isolated in-situ soil sample. A water content sensor operatively associated with the sample container senses a water content in the isolated in-situ soil sample. A data logger operatively connected to the first and second tensiometers and to the water content sensor receives and processes data provided by the first and second tensiometers and by the water content sensor. [0010] A method of estimating at least one unsaturated hydrologic property of sample soil comprises providing an amount of soil; positioning a sample container on the soil; filling the sample container with sample soil so that sample soil within the sample container communicates with the soil; adding water to the sample soil until the sample soil is substantially saturated; allowing the sample soil to dry by allowing the soil to absorb water from the sample soil contained in the sample container; and sensing at least a surface water potential, a subsurface water potential, and a water content of the sample soil as the sample soil dries. [0011] A method of estimating at least one unsaturated hydrologic property of in-situ soil in a soil environment: Positioning a sample container within the soil environment so that a substantially open distal end of the sample container penetrates in-situ soil in the soil environment, the sample container isolating an in-situ soil sample within an interior region defined by the sample container; adding water to the sample container until the in-situ soil sample isolated therein is substantially saturated; allowing the isolated in-situ soil sample to dry using in-soil within the soil environment and not isolated by the sample container to pull water from the isolated in-situ soil sample; and sensing at least a surface water potential, a subsurface water potential, and a water content of the isolated in-situ soil sample as the isolated in-situ soil sample dries. BRIEF DESCRIPTION OF THE DRAWING [0012] Illustrative and presently preferred embodiments of the invention are shown in the accompanying drawing in which: [0013] FIG. 1 is a side view schematic representation of one embodiment of an exfiltrometer apparatus for determining unsaturated hydrologic properties of sample soil; [0014] FIG. 2 is a side view in elevation of a second tensiometer configuration that may be utilized in the exfiltrometer apparatus; [0015] FIG. 3 is a partial side view in elevation of a second water content sensor configuration that may be utilized in the exfiltrometer apparatus; [0016] FIG. 4 is a partial side view in elevation of a third water content sensor configuration that may be utilized in the exfiltrometer apparatus; [0017] FIG. 5 is a side view schematic representation of another embodiment of exfiltrometer apparatus for determining unsaturated hydrologic properties of soil contained in a borehole; [0018] FIG. 6 is a graphical representation of unsaturated hydrologic data (i.e., water potential and water content as a function of time) obtained during a field test run; [0019] FIG. 7 is a graphical representation of unsaturated hydrologic data (i.e., water potential as a function of water content) obtained during a field test run; [0020] FIG. 8 is a graphical representation of unsaturated hydrologic data (i.e., hydraulic conductivity as a function of water content) obtained during a field test run; and [0021] FIG. 9 is a graphical representation of unsaturated hydrologic data (i.e., hydraulic conductivity as a function of water potential) obtained during a field test run. 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