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R <br /> levels in several communities. This variability arises from <br /> several sources including behavioral and cultural factors. <br /> The identification of lead exposures from other sources (due <br /> to air, water, diet, paint, etc. ) is an essential part of <br /> characterizing the appropriate blood lead distribution for a <br /> specific neighborhood or site. For the purpose of deriving a <br /> residential screening level, the background lead exposure inputs <br /> to the IEUBK model were determined using national averages, where <br /> suitable, or typical values. Thus, the estimated screening level <br /> of 400 ppm is associated with an expected "typical" response to <br /> these exposures, and should not be taken to indicate that a <br /> certain level of risk (e.g. , exactly 5% of children exceeding 10 <br /> µg/dl blood) will be observed in a specific community, e.g. , in a <br /> blood lead survey. <br /> Because a child's exposure to lead involves a complex array <br /> of variables, because there is population sampling variability, <br /> and because there is variability in environmental lead <br /> measurements and background levels of lead in food and drinking <br /> water, results from the model may differ from results of blood <br /> lead screening of children in a community. Extensive field <br /> validation is in progress. The model will be evaluated further <br /> once these efforts are completed. <br /> OBJECTIVE <br /> With this interim c.ire%tive, OSWER recommends using 400 ppm <br /> soil lead (based on application of the IEUBK model) as a <br /> screening level for lead in soil for residential scenarios at <br /> CERCLA sites and at RCRA Corrective Action sites. Residential <br /> areas with soil lead below 400 ppm generally require no further <br /> action. However, in some special situations, further study is <br /> warranted below the screening level. For example, agricultural <br /> areas, wetlands, areas with ecological risk, and areas of higher <br /> than expected human exposure are all situations that could <br /> require further study. For further guidance on ecological risks, <br /> Superfund risk managers are encouraged to consult their Regional <br /> Biological Technical Assistance Groups (BTAGs; see Appendix D) . <br /> Generally, the ground water pathway will not pose a <br /> significant risk since many lead compounds are generally not <br /> highly mobile. However, there are situations where, because of <br /> the form of lead, hydrogeology, or the presence of other <br /> contaminants at the site, lead may pose a threat to the ground <br /> water. In these situations, additional analysis is warranted, <br /> and the Superfund Regional Toxics Integration Coordinators <br /> (RTICs; see Appendix B) or RCRA hydrogeologists should be <br /> consulted. <br /> -9- <br />