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Main Street InvestorsNillas de Amistad Page 2 of 3 601 East Main Street November 14, 2012 Stockton, California 95202 closure summary Report— No Further Action Required, dated 10 January 2011, submitted by your consulting firm, Advanced GeoEnvironmental, Inc. (AGE), included comparisons of soil concentrations from UST removal samples TK-1 and TK-2, and soil boring B2, to ESLs for residential land use, where groundwater is not a potential drinking water source and soil samples are collected at maximum depths of three meters below surface grade (bsg), and AGE reported: • Total petroleum hydrocarbons quantified as diesel (TPH-d), detected at 3,700 milligrams per kilogram (mg/kg) in soil sample TK-1, collected at approximately ," Jm4� feet bsg, exceeded the ESL 83 mg/kg; • TPH-d, detected at 5,800 mg/kg in soil sample TK-2, collected at approximately to, b feet bsg, exceeded the ESL of 83 mg/kg; a�d • TPH-d and total petroleum hydrocarbons quantified as motor oil (TPH mo), detected at 2,700 mg/kg and 510 mg/kg, respectively, in soil sample 132-15 collected at approximately 15 feet bsg, exceeded the ESLs of 83 mg/kg and 370 mg/kg, respectively; • TPH-d and TPH-mo, detected at 3,600 mg/kg and 640 mg/kg, respectively, in soil sample 62-25 collected at appro�mately 25 feet bsg, exceed the ESLs of 83 mg/kg and 370 mg/kg, respectively; i AGE concluded that the residual soil concentrations presented above would likely not pose a significant threat from vapor intrusion, nor to human health or the environment as: • The depth where most of the soil contamination concentration was detected was more than 10 feet bsg and less than 25 feet bsg and the soil type was described as fine- grained silt and clay, reducing the potential for contaminant migration; • Petroleum hydrocarbon contamination was not detected in any soil samples collected at approximately 10 feet and 30 feet bsg from soil boring 61, advanced approximately 8 feet west of the soil sample TK-2; • The former UST area is surfaced by concrete, creating a barrier for potential direct exposure and soil vapor intrusion; and • The former UST area will remain a sidewalk for the foreseeable future and it is unlikely any construction will take place at this sidewalk location. As stated above, there is an indication that the soil from the "hot pile" may have been returned to the former UST pit. The contaminant concentrations detected in soil from the "hot pile" far exceed any of the soil concentrations compared to the ESLs listed above. The EHD is concerned that high concentrations of contaminants of concern, namely TPH-d and benzene detected at 9,300 mg/kg and 0.106 mg/kg, respectively, in soil samples from the "hot pile" may create a potential for soil vapor intrusion into the nearby basement since the potentially contaminated soil is capped by a cement sidewalk. The EHD also notes that soil samples collected from soil boring 61 do not include samples collected at 15 and 20 feet bsg, the depth where high concentrations of TPH-d and moderate concentrations of TPH-mo were detected in soil samples collected from soil boring B2. The EHD would like to move this site to closure; however, the concerns presented above and summarized below must be addressed before closure of this site will be considered: