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3. VOC CONCENTRATION AND PHASE DISTRIBUTION <br /> As discussed in previously prepared workplans submitted to the regulatory agencies for <br /> each of the sites in Lodi, the primary objective of the soil source control program at each <br /> of the respective sites is to reduce the mass and concentrations of VOCs present in the <br /> vadose zone. VOCs have been identified by regulatory agency investigations as being <br /> present in the subsurface either on or immediately adjacent to each of the Lodi sites. <br /> Identification of specific VOCs has been made by both soil gas surveys and discrete soil <br /> sampling methods. Based on regulatory agency and responsible party investigations, it <br /> is probable that VOCs exist in the soil both in the form of liquid phase and vapor phase on <br /> potentially all of the sites. However, VOCs in the vapor phase may also be the result of <br /> continuing volatilization of dissolved VOCs contained in the groundwater. <br /> In a general report summarizing five years of investigation of specific VOCs in groundwater <br /> (RWQCB, 1992), five methods were presented by which VOCs could penetrate sewer <br /> lines, including: <br /> 1. Through breaks or cracks in the sewer pipes; <br /> 2. Through pipe joints and other connections; <br /> 3. By leaching in liquid form directly through sewer lines into the vadose zone; <br /> 4. By saturating the bottom of the sewer pipe with a high concentration of VOC <br /> containing liquid and the VOCs volatilizing from the outer edge of the pipe <br /> into the soils; and <br /> 5. By penetrating the sewer pipe as a gas. <br /> Some or all of these methods may be applicable to the presence of the apparent soil vapor <br /> concentrations detected at each of the three Lodi sites. <br /> 3 <br />