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ARCADIS Mr. McKinley Lewis, Jr. April 20, 2011 Three shallow soil boring locations (B-8, B-29, and B-43)were identified as "hot spots" during the PEA investigation based on shallow sample results (0 to 0.5 foot below ground surface [bgs]). Lead was detected in soil samples B-29(1,600 milligrams per kilogram [mg/kg])and B-43 (1,300 mg/kg)at concentrations above California's Total Threshold Limit Concentration (TTLC)of 1,000 mg/kg. These samples were subsequently analyzed for the Soluble Threshold Limit Concentrations (STLC)for lead. The STLC criterion for lead is 5 micrograms per liter(mg/1). Lead was not detected above the TTLC in B-8 (680 mg/kg); however, the STLC lead result for B-8 indicated a concentration of 49 mg/I. Soluble lead was also detected at 67 mg/I in sample B-29. Soluble lead was not detected above the STLC in B-43 (2.4 mg/1). The dioxin 95 percent(%) Upper Confidence Limit (UCL)calculated for the Site based upon five soil samples was 5.75 picograms per gram (pg/g or parts per trillion [ppt]), slightly above the California Human Health Screen Level (CHHSL)of 4.6 ppt. The ash sample collected from within the silo(S-3) indicated a dioxin total toxic equivalency of 26.9. This result was not included in the calculation because the sample was obtained from a different media and the ash is contained within the silo. Dioxin 95 %UCL for the site soil was slightly above the CHHSL; however, it does not appear to be a significant concern except for the ash material within the silo. A screening number of 12 mg/kg was selected for evaluating arsenic in soil for this Site based on the background plot from the data and assumed past agricultural use of the Site. In the Interim Guidance for Sampling Agricultural Properties(Third Revision) by the DTSC California Environmental Protection Agency, dated August 7, 2008 (DTSC 2008b), the DTSC cites results of soil sampling at multiple former agricultural sites for proposed school locations. The document references a screening level of 12 mg/kg for school locations. Eleven shallow soil samples (B-7-0.5, B-8-0.5, B-9-0.5, B-11-0.5, B-18-0.5, B-21-0.5, B-22-0.5, B-26-0.5, B-29-0.5, B-31-0.5, and B-48-0.5)collected and analyzed at the Site indicated arsenic concentrations above background ranging from 16 to 59 mg/kg. Elevated arsenic concentrations appear to be relatively shallow based on deeper soil samples analyzed from soil borings B-7-2.0 (9.8 mg/kg) and B-11-2.0 (8.5 mg/kg)with concentrations below the background. Areas of elevated arsenic concerns are depicted on Figure 1. Based on the analytical sampling and results, arsenic detected at the Site above background concentrations is shallow and defined in discrete areas. Page: Final PEA Work Plan Addendum-Apr71-RV009808.doc 4/11