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n r, • San Joaquin County, Local Oversight Program March 30, 2001 Page 3 Total petroleum hydrocarbons in the gasoline range (TPHG) were detected at low concentrations in three wells, MW-5 (82 µg/L), MW-6 (58 µg/L), and MW-8 (57 µg/L) A moderate concentration (470 µg/L) was found m MW-4 See Figure 3 These four wells are the closest to the tank excavation The TPHG concentration is highest when water leveds are shallowest (Attachments C and D) Benzene was found at concentrations exceeding the maximum contaminant level (drinking water standard) in ail five of the monitoring wells at concentrations ranging from 3 3 to 16 µg/L (Table 3 and Figure 3) The other aromatic hydrocarbon compounds, toluene, ethylbenzene, and total xylene isomers, were detected as indicated in Table 3 MTBE was found in seven of the monitoring wells as indicated m Table 3 and Figure 3, three of which(MW-4, MW-5, and MW-8) were above the maximum contaminant level (drmkmg water standard) of 19 µg/L The other U S EPA Method 8260B Fuel Oxygenates were detected above their respective detection limits(TBA<5 0 µg/L,MTBE <5 0 pg/L, DIPE <10 0 µL / , ETBE <5 0 µg/L, and • TAME <5 0 µg/L) in groundwater samples as mdicated in Table 3 Ethylenedibromide and 1,2- Dichloroethane were below their respective detection hmits The following schedule will be observed for groundwater monitornng during 2001 Second Quarter 2001 Sampled Mid 2 weeks of May Report by July l 1 Third Quarter 2001 Sampled Mid 2 weeks of August Report by October 10 Fourth Quarter 2001 Sampled Mid 2 weeks of November Report by January 9 Please do not hesitate to call the undersigned at 925-373-9211 and/or telefax at 925-373-9222 should you have any questions D Ge VD !0 Sincere GARY D LOWSJ► tares ( D 4W 1559 � M IV CER7151ED ► CRAW ENGNEERNG GEQiAGIST 41� �Q Gary D Lowe, R G , C E G , C HG OPCAt- er Cl�►1� Principal, Hydrogeologist H2OGEOL A GroundWater Consultancy H20GEOL A GROUNDWATER CONSULTANCY