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Weldon Church Residence - December 2013 <br /> 104 West Beverly Place, Tracy <br /> Claim No: 8502 <br /> Downgradient Well <br /> BENZENE Results for MW8 <br /> 400- <br /> 350- <br /> 300 <br /> 00350300 -- <br /> J 250 <br /> C� <br /> 200 ata <br /> 5 \\a <br /> a\ <br /> 150- <br /> 100- <br /> 50 <br /> 00 50 \ <br /> j � aaa I <br /> 01 <br /> _ a <br /> -- ---- BENZENE Trend <br /> Evaluation of Current Risk <br /> • Estimate of Hydrocarbon Mass in Soil: 2,650 pounds of TPHg remain in site soils (AGE, 2011). <br /> • Soil/Groundwater tested for methyl tert-butyl ether (MTBE): Yes, no longer regularly monitored <br /> because little or no MTBE has been detected. <br /> • Oxygen Concentrations in Soil Vapor: None reported. <br /> • Plume Length: <100 feet. ',;�-_5r <br /> • Plume Stable or Decreasing: Yes. <br /> • Contaminated Zone(s) Used for Drinking Water: No. <br /> • Groundwater Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion 1 <br /> by Class 1. The plume that exceeds water quality objectives is less than 100 feet in length. <br /> There is no free product. The nearest water supply well or surface water body is greater than <br /> 250 feet from the defined plume boundary. <br /> • Indoor Vapor Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion <br /> 2a by Scenario 3a. The maximum benzene concentration in groundwater is less than 100 <br /> pg/L. The minimum depth to groundwater is greater than 5 feet, overlain by soil containing less <br /> than 100 mg/kg of TPH. In addition, a vapor survey investigation was conducted in August <br /> 2013, which concluded the calculated cancer risk was 4.8 x 10-7 and the hazard index was less <br /> than 1 (0.000001). <br /> • Direct Contact Risk from Residual Petroleum Hydrocarbons: This case meets Policy Criterion <br /> 3b. Although no document titled "Risk Assessment" was found in the files reviewed, a <br /> professional assessment of site-specific risk from potential exposure to residual soil <br /> contamination was performed by Fund staff. The assessment found that maximum <br /> concentrations of petroleum constituents remaining in soil will have no significant risk of <br /> adversely affecting human health. Excavation was conducted to a depth of 12 feet. Residual <br /> hydrocarbons are limited to a thin zone between 6 and 10 feet and accidental exposure to site <br /> soils is highly unlikely. Residual hydrocarbons present in along the excavation walls in 1995 are <br /> not confirmed in recent samplings conducted in 2003. <br /> Page 10 of 12 <br />