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ABSTRACT: Application of High-Resolution Soil-Gas Geochemical Data to Solving Organic Contamination Problems

James H. Viellenave, James C. Hickey

Soil-gas surveys are widely recognized as useful for reconnaissance for underground storage tank leaks and detecting volatile organic plumes, particularly where sources are few, depths are shallow, and soils are granular. Advanced, high-resolution soil-gas techniques have been developed to dramatically extend the application of soil gas to more difficult lithologic environments or where sources and plumes are more complex. In many situations where traditional soil-gas surveying is limited, high-resolution soil-gas reconnaissance screening would be quite valuable as a way of focusing drilling. This is accomplished by evaluating a broader range of organic chemicals and differentiating multiple sources, both on and off site. Among the applications most in need of high-resolu ion techniques are real estate conveyance, where unknowns and offsite impacts are key risks; landfills, where site information is lacking; multiple source areas, where sources may include several different mixtures of many common components (petrochemicals, fuels, lubricants, etc.); and sites with semivolatile contamination not traditionally detected by soil gas methods.

Demonstrated in this presentation are examples of the use of advanced, high-resolution soil-gas surveys, applying a variety of collection, analytical, and interpretive techniques to complex or difficult conditions described above. Case histories will be presented, complete with confirming soil and/or groundwater analyses, illustrating how soil-gas techniques can be used to reduce risk, focus expensive investigation methods, and direct remediation efforts. Included will be (1) property conveyance investigation, including identification of onsite and offsite sources; (2) a "blind" landfill evaluation, where no advance information on chemicals was available; (3) fingerprinting of hydrocarbon mixtures to discriminate among different contaminant plumes and source areas (using a fuel distri ution site and a fire training site as examples); and (4) identifying and mapping semivolatile compounds, including heavy hydrocarbons (C10+), explosives (nitroaromatics) and daughter products, and chlorinated chemicals.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990