Methods for characterizing subsurface volatile contaminants using in-situ sensors
First Claim
1. A method of estimating the distance from an underground source of volatile contaminant to an in-situ sensor, comprising:
- a) measuring a time-varying concentration of vapor from an underground source of volatile contaminant using an in-situ sensor located underground;
b) generating a time-dependent response curve from the measured concentrations;
c) providing an effective vapor diffusion coefficient, D;
d) estimating the distance, L, between the in-situ sensor and the contaminant source;
e) predicting the time-varying concentration C′
using the effective vapor diffusion coefficient, D, calculated in step c), and using the estimated distance, L, estimated in step d), by using a one-dimensional analytical solution for diffusion of vapor from a fixed source in an isotropic and homogenous porous media;
f) generating a time-dependent response curve based from the predicted concentrations;
g) normalizing both the predicted and measured response curves;
h) comparing the normalized predicted and measured response curves; and
i) repeating steps d) through h) as many times as necessary, each time adjusting the estimated distance, L, until the shape of the normalized predicted response curve matches sufficiently well the shape of the normalized measured response curve;
j) whereby the estimated distance L is finally estimated upon a sufficient match between the normalized predicted response and measured response curves.
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Abstract
An inverse analysis method for characterizing diffusion of vapor from an underground source of volatile contaminant using data taken by an in-situ sensor. The method uses one-dimensional solutions to the diffusion equation in Cartesian, cylindrical, or spherical coordinates for isotropic and homogenous media. If the effective vapor diffusion coefficient is known, then the distance from the source to the in-situ sensor can be estimated by comparing the shape of the predicted time-dependent vapor concentration response curve to the measured response curve. Alternatively, if the source distance is known, then the effective vapor diffusion coefficient can be estimated using the same inverse analysis method. A triangulation technique can be used with multiple sensors to locate the source in two or three dimensions. The in-situ sensor can contain one or more chemiresistor elements housed in a waterproof enclosure with a gas permeable membrane.
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Citations
23 Claims
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1. A method of estimating the distance from an underground source of volatile contaminant to an in-situ sensor, comprising:
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a) measuring a time-varying concentration of vapor from an underground source of volatile contaminant using an in-situ sensor located underground; b) generating a time-dependent response curve from the measured concentrations; c) providing an effective vapor diffusion coefficient, D; d) estimating the distance, L, between the in-situ sensor and the contaminant source; e) predicting the time-varying concentration C′
using the effective vapor diffusion coefficient, D, calculated in step c), and using the estimated distance, L, estimated in step d), by using a one-dimensional analytical solution for diffusion of vapor from a fixed source in an isotropic and homogenous porous media;f) generating a time-dependent response curve based from the predicted concentrations; g) normalizing both the predicted and measured response curves; h) comparing the normalized predicted and measured response curves; and i) repeating steps d) through h) as many times as necessary, each time adjusting the estimated distance, L, until the shape of the normalized predicted response curve matches sufficiently well the shape of the normalized measured response curve; j) whereby the estimated distance L is finally estimated upon a sufficient match between the normalized predicted response and measured response curves. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of estimating an effective vapor diffusion coefficient, D, which characterizes the diffusion of a vapor from an underground source of volatile contaminant located at a known distance, L, from an in-sift sensor, comprising:
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a) measuring a time-varying concentration of vapor from an underground source of volatile contaminant using an in-situ sensor located underground at a known distance, L, from the source of volatile contaminant; b) generating a time-dependent response curve from the measured concentrations; c) estimating the effective vapor diffusion coefficient, D; d) predicting the time-varying concentration C′
using the estimated effective vapor diffusion coefficient, D, estimated in step c), and using the known distance, L, by using a one-dimensional analytical solution for diffusion of vapor from a fixed source in an isotropic and homogenous porous media;e) generating a time-dependent response curve from the predicted concentrations; f) normalizing both the predicted and measured response curves; g) comparing the normalized predicted and measured response curves; and h) repeating steps d) through h) as many times as necessary, each time adjusting the estimated effective vapor diffusion coefficient, D, until the shape of the normalized predicted response curve matches sufficiently well the shape of the normalized measured response curve; i) whereby the effective vapor diffusion coefficient, D, is estimated. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification