Numerical Simulation of Radial Gas Flow: Effects of Soil Anisotropy, Well Placement, and Surface Seal

• Published in: Journal of hydrologic engineering 1998-01, Vol.3 (1), p.52-61
• Main Authors: Chen, Xunhong, Gosselin, David C
• Format: Article
• Language: English
• Subjects: TECHNICAL PAPERS
• ISSN: 1084-0699; 1943-5584
• DOI: 10.1061/(ASCE)1084-0699(1998)3:1(52)

A variety of methods have been used to control gas flow in the vadose zone in order to remove volatile organic compounds. The effects of well configuration and engineered surface seals on gas flow are recognized but have not been thoroughly analyzed for the design of a vapor extraction well. This paper presents a numerical model to simulate axisymmetric gas flow toward an extraction well in the unsaturated zone. Simulations were conducted to analyze the behavior of gas flow under a variety of system conditions. Results indicate that soil anisotropy, length of the well screen, depth of the gas extraction well, and surface sealing need to be considered in the analysis of a vapor well. Anisotropic soils can significantly affect the area of influence (AI) where the upper surface is open to the atmosphere but generally play a lesser role in a confined soil zone. Setting screens deeper can generate a larger AI, while a longer screen can reduce the pressure drop at the extraction well without causing a major impact on the AI. Simulations also show that surface seals for a shallow well and homogeneous soils are more effective in enhancing well efficiency when compared to a deep well and heterogeneous soils. Application of surface seals reduces air leakage from the ground surface and increases the horizontal gas flow.