STP1288

    Tools to Improve Models for Design and Assessment of Soil Vapor Extraction Systems

    Published: Jan 1996


      Format Pages Price  
    PDF (376K) 18 $25   ADD TO CART
    Complete Source PDF (8.0M) 18 $112   ADD TO CART


    Abstract

    Although soil vapor extraction (SVE) is well established as an effective method of removing volatile organic compounds from soil, the spatial extent of extraction influence is often poorly understood. Typically, the limit of a detectable vacuum response in vadose monitoring wells is used to define radius of influence without regard for the pneumatic conductivity, vacuum measurement limitations, or barometric pressure effects. Vapor flow conditions are often assumed to be confined, but even beneath surface pavement or clay layers, vertical leakance of air is usually a dominant influence.

    Transient-response pneumatic testing and analysis with a leaky aquifer solution can quantify vertical leakance of air as well as the horizontal pneumatic conductivity of the primary extraction zone. An additional benefit of automated transient-response testing is that the extent of SVE influence detected is usually substantially larger, because much smaller pressure changes can be detected and attributed to SVE than is possible with manual static measurements. Simple vapor flow models incorporating leakance based on the results of pneumatic testing can be developed as tools for design and evaluation of SVE systems.

    Soil gas tracer (SGT) investigations utilizing sulfur hexafluoride (SF6) can be used to determine vapor travel times for assessing variability of pneumatic conductivity at an SVE site. The SGT technique can also be used evaluate extent of SVE influence, to investigate relative influence of extraction wells, and evaluate flow within and between different horizons. In a case study, the tracer data indicated the presence of preferential flow through macropores and provided the opportunity to calibrate and verify models of subsurface vapor flow.

    Keywords:

    Soil Vapor Extraction, Pneumatic Testing, Soil Gas Tracers


    Author Information:

    Thrupp, GA
    Senior Hydrogeologist, Principal Hydrogeologist, and Principal Geological Engineer, Geomatrix Consultants, Inc., San Francisco, CA

    Gallinatti, JD
    Senior Hydrogeologist, Principal Hydrogeologist, and Principal Geological Engineer, Geomatrix Consultants, Inc., San Francisco, CA

    Johnson, KA
    Senior Hydrogeologist, Principal Hydrogeologist, and Principal Geological Engineer, Geomatrix Consultants, Inc., San Francisco, CA


    Paper ID: STP38391S

    Committee/Subcommittee: D18.21

    DOI: 10.1520/STP38391S


    CrossRef ASTM International is a member of CrossRef.