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Chevron:#9-0557 June 2013 <br /> 139 Center Street South, Stockton <br /> Claim No: 5820 <br /> Near Downgradient Well Far Downgradient Well <br /> BENZENE Results for MW-7 BENZENE Results for MW-8 <br /> _ �. <br /> 5•Q 15 50 �__. __,.:�—, __�� 75 <br /> t <br /> 45i ,7 451 �. _ 17 <br /> aa' � ao i. 19 <br /> 35 .. i 1 t9 g5 _ 21 <br /> _ <br /> SIT _ I 1 21 30 -.� i--. 23 <br /> 36.�.. ' I 7 <br /> .. 25' I. 1 i i � 3 25 � I 25 c <br /> w 2C z <br /> 20 I 4 25 p 27 C3 <br /> 15 ---� -- j 15 29 <br /> 27 <br /> 10 -� i ' 15 I 33 <br /> 31 <br /> 29 <br /> O t -. -1,.� c,..•..z=_•.=.. a l– .� ,J.. _ _ 35 . <br /> .or BENZENE to Water -- Trend m.BENZENE Depth to Wafer ---Trend <br /> Evaluation of Current Risk <br /> • Estimate of Hydrocarbon Mass in Soil: 7,700 pounds of TPH-g (HFA 2013). <br /> • Soil/Groundwater tested for methyl tert-butyl ether(MTBE): Yes, see table above. <br /> • Oxygen Concentrations in Soil Vapor: None reported. <br /> • Plume Length: <250 feet long. <br /> • .Flume Stable or Decreasing: Yes. <br /> • Contaminated Zone(s) Used for Drinking Water: .No. <br /> • Groundwater Risk from Residual Petroleum Hydrocarbons: The case meets Policy <br /> Criterion 1 by Class 4. The contaminant plume that exceeds water quality objectives is less- <br /> than 1,000 feet in length. There is no free product. The nearest water supply well or <br /> surface water body is greater than 1,000 feet from the defined plume boundary. The <br /> dissolved concentrations of benzene and MTBE are each less than 1,000 pg/L.' <br /> • Indoor Vapor Risk from Residual Petroleum Hydrocarbons: The case meets Policy <br /> Criterion 2a by Scenario 3b. The maximum benzene concentration in groundwater is less <br /> than 1,000 pg/L. The minimum depth to groundwater is greater than 10 feet, overlain by <br /> soil containing less than 100 mg/kg of TPH. <br /> • Direct Contact Risk from Residual Petroleum Hydrocarbons: The case meets Policy <br /> Criterion 3b. A professional assessment of site-specific risk from exposure shows that <br /> maximum concentrations of petroleum constituents in soil will have no significant risk of <br /> adversely affecting human health. Residual contamination was removed by excavation. <br /> Page 10 of 11 <br />