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3. 1 Soils <br /> The concentration of PCBs in the soil above which some <br /> action should be considered (i.e. , treatment or containment) <br /> will depend primarily on the exposure estimated in the <br /> baseline risk assessment based on current and potential <br /> future land use. This section has correspondingly been <br /> organized according to categories of alternatives <br /> differentiated by the expected direct contact that will <br /> occur. Other factors influencing the concentration to which <br /> soils should be excavated or contained include the impact <br /> the residual concentration will have on ground water and <br /> potential environmental impacts. Since these pathways are <br /> pertinent to all site categories, they are discussed in <br /> separate sections. The guideline concentrations provided in <br /> 1 this section do not imply that action must be taken at a <br /> Superfuiid site, rather they indicate the area over which <br /> some action should be considered once it has been determined <br /> that action is necessary to provide protection of human <br /> health and the environment. <br /> A summary of the guidelines discussed in this section is <br /> presented in Table 3-1. <br /> TABLE 3-1 <br /> Recommended Soil Action Levels -- Analytical Starting <br /> Points <br /> (Considers ingestion, inhalation, and dermal contact only) <br /> Land Use PCB Action Levels (ppm) <br /> ' Residential 1 ppm <br /> Industrial 10 - 25 ppm <br /> These action levels and the assumptions discussed in the <br /> following sections can be used to reduce the need for <br /> detailed site-specific risk assessments; however, future <br /> site uses should be well understood and final cleanup levels <br /> must still reflect all relevant exposure pathways and be <br /> defensible on a site-specific basis. <br /> The analysis of PCBs is complicated by the fact that <br /> there are 209 different PCB compounds (Alford-Stevens, <br /> 1986) . Common analytical methods are listed in Table 3-2. <br /> 1Aracholors are groups of PCBs with different overall <br /> percentages of chlorine. For example, Arochlor 1242 contains 423 <br /> ' chlorine made up of tri- and tetra- chlorinated biphenyls. PCB <br /> isomers are those compounds that have the same number of chlorine <br /> atoms. Individual PCBs isomers, of which there are 209, are <br /> called congeners. <br /> 27 <br />