SITE INFORMATION AND CORRESPONDENCE

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Sent Bye: BASELINE; 510 420 1707; Nov-9-99 16:31 ; Page 25129 V corresponding standards, criteria, or concentrations derived from toxicity reference values maximum contaminant limits in drinking water). • Chemicals were excluded as COPCs if they are common laboratory contaminants (e.g.' acetone, z-butanone) (EPS,, 1089). Laboratory contaminants were excluded in this manner because they are not known to be historically used at the site. • if chemicals that are not common laboratory contaminants were present in any sample at a concentration greater than five times the concentration of the sauce chemical detected in the associated method blank(s), they were retained in the assessment. if they were less than five times the concentration in the method blank, they were omitted from further consideration. • Metals were included as COPCs if the maximum concentration exceeded the U.S. EPA preliminary remediation goals (PBGs) for metals in soil (Smucker, 1998). The mean, maximum,and 95d'upper confidence limit concentrations formetais that exceeded these PRGs, were further screened against the mean, maximum, and 95"' upper confidence limit concentration of these metals from soil samples collected at a nearby site,but not collected in an area that is likely to have been influenced by the contaminant or former facility operations at the Weber Block property(Resna Industries, 1992). Where the maximum concentration of metals exceeded the applicable U.S. EPA PRO, but the mean, maximum, and 95" upper confidence limit for Weber property did not exceed these same parameters for a nearby site, these metals wcrc excluded as COPCs. Background samples were not specifically collected as part of the Phase II Sampling and Analysis Workplan that was reviewed and approved by U.S. EPA and DTSC. • Metals that were reported in groundwater that did not exceed the primary Maximum Contaminant Limit (MCL), or the Cal/EPA Public Health Goal (if no MCL), or U.S. EPA PRG for tap water(if no PHG) were excluded from further consideration as COPCs. Metals in groundwater samples that exceeded these criteria were included as COPCs in the assessment. • Chemicals known to be associated with historic site uses or degradation products of chemicals present at the site were included as COPCs. • Essential nutrients,such as iron,magnesium,calcium,potassium,and sodium,were eliminated from consideration as COPCs. The following chemicals were selected as chemicals of potential concern(See Tables 7A and 7B for a screening of COPCs for chemicals in soil and groundwater.) Organic compounds Chloromethane (soil only) 2-hexanone (soil only) Benzene (soil and groundwater) Toluene(soil and groundwater) Ethylbenzene(groundwater only) 97369%ik.pea.wpd-i 1/9i99 19