10.2190/3NYD-DVGB-FNGH-EWBL 3NYDDVGBFNGHEWBL 3 Estimate of Soil Permeability and Porosity Using An Analytical Solution Considering Gas Compressibility 29 40 20020509 20020509 20020509 20020509 3NYDDVGBFNGHEWBL.pdf http://baywood.metapress.com/link.asp?target=contribution&id=3NYDDVGBFNGHEWBL 1 Xun-Hong Chen University of Nebraska-Lincoln An analytical solution considering gas compressibility is developed for radial gas flow in the vadose zone. Simulation results indicate that a solution not considering the gas compressibility provides a close approximation only when the change in pressure is less than 0.2 atmosphere. Error increases with the increase of pressure variation, and the error can reach about 20 percent when the pressure variation is 0.5 atmosphere. This article also presents two methods for the estimate of the soil parameter values from pneumatic test data using the developed analytical solution. the first method is a computer automatic fitting procedure using time-pressure data from a single observation well, and the second method requires gas pressure data from two observation wells and steady-state gas flow. Numerical experimental examples show that the inversely estimated permeability and porosity values considering the gas compressibility are different from these estimated not considering the gas compressibility. P. C. Johnson, M. K. Kemblowski, and J. D. Colthart, Quantitative Analysis for the Cleanup of Hydrocarbon-Contaminated Soils by In-Situ Soil Venting, <i>Ground Water, 28</i>, pp. 413-429, 1990. C. V. Theis, the Relation between the Lowering of the Piezometric Surface and the Rate and Duration of Discharge of a Well Using Groundwater Storage, <i>Transactions of American Geophysical Union, 2</i>, pp. 519-524, 1935. A. L. Baehr and M. F. Hult, Evaluation of Unsaturated Zone Air Permeability through Pneumatic Tests, <i>Water Resources Research, 27</i>, pp. 2605-2617, 1991. A. L. Baehr and C. J. Joss, An Updated Model of Induced Airflow in the Unsaturated Zone, <i>Water Resources Research, 31</i>, pp. 417-421, 1995. C. Shan, R. W. Falta, and I. Javandel, Analytical Solutions for Steady-State Gas Flow to a Soil Vapor Extraction Well, <i>Water Resources Research, 28</i>, pp. 1105-1120, 1992. R. E. Kidder, Unsteady Flow of Gas through a Semi-Infinite Porous Medium, <i>Journal of Applied Mechanics, 24</i>, pp. 329-332, 1957. S. N. Davis and R. J. M. DeWiest, <i>Hydrogeology</i>, John Wiley & Sons, Inc., New York, 1966. T. A. Prickett, Type Curve Solution to Aquifer Tests under Water Table Conditions, <i>Ground Water, 3</i>, pp. 5-14, 1965. C. D. McElwee, Theis Parameter Evaluation from Pumping Tests by Sensitivity Analysis, <i>Ground Water, 18</i>, pp. 56-60, 1980. S. Chander, P. N. Kapoor and S. K. Goyal, Analysis of Pumping Test Data Using Marquart Algorithm, <i>Ground Water, 19</i>, pp. 275-278, 1981. H. D. Yeh, Theis' Solution by Nonlinear Least-Squares and Finite-Difference Newton's Method, <i>Ground Water, 25</i>, pp. 710-715, 1988. E. W. Swokowski, <i>Calculus with Analytical Geometry</i>, Prindle, Weber & Schmidt, Boston, 1983. B. Carnahan, H. A. Luther, and J. O. Wilkes, <i>Applied Numerical Methods</i>, John Wiley & Sons, Inc., New York, 1969. M. Abramowitz and I. A. Stegun, <i>Handbook of Mathematical Functions: With Formulas, Graphs, and Mathematical Tables</i>, Dover Publications, Inc., New York, 1972. R. A. Freeze and J. A. Cherry, <i>Groundwater</i>, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1979.