Methods for characterizing subsurface volatile contaminants using in-situ sensors

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:

• 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.