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r... Bulk Transportation Page 8 Site Conceptual Model& Closure Report GPE Project No. 606.3 August 28, 2009 V 5.0 POTENTIAL HUMAN HEALTH IMPACT Insofar as no detectable soil contamination still exists, and the groundwater was never affected, there is no longer a possibility that human health will be affected. 5.1 Chemicals of Concern No individual chemicals, such as BTEX chemicals, were identified in association with this release, except trace concentrations of BTEX chemicals identified in the initial confirmation samples, which appear suspect. Diesel fuel, a "mid-range distillate", is a mixture of hundreds of individual chemical, and may vary considerably from refinery to refinery, and even batch to batch. %W No maximum allowable residual concentrations have been established by the regulatory agencies. In lieu of a regulatory allowable residual concentration below which residual contamination is allowed to remain, it is necessary to •• show that residual fuel contamination is unlikely to pose a human health hazard, and does not threaten the drinking water supply. In addition, the State of California has established a "screening level' concentration of 100 ppm_ In cases where diesel-impacted soil concentrations exceed this value, additional evaluation is recommended. 5.2 Exposure Pathways For a toxic material, to pose a health risk, it must first come into contact with humans and be taken into the body. This can only occur through ingestion, inhalation, or direct contact_ In evaluating the risk associated with a given release, it is important to understand the various possible exposure pathways (such as soil contact, inhalation of exuded vapor, ingestion of drinking water). 5.2.1 Soil Pathways Since diesel hydrocarbons are no longer present in the soil, ingestion or dermal contact with soil would not be expected to expose persons to contaminants. '-' 5.2.2 Surface Water Pathways Storm water coming into contact with contaminated soil may run off of the site and adversely affect adjacent lands or bodies of open water. In this case, there is no longer any surface contamination in the spoil soil, and storm water runoff is not expected to be a contaminant pathway. t. 5.2.3 Groundwater Pathways Meteoric water percolating through impacted vadose zone soil may leach contamination to the groundwater. Contaminated groundwater, in-turn, migrate off of the site to affect adjacent land and possibly be produced by �. 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone (209) 569-0293 Modesto, CA 95356 Fax(209) 569-0293