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4 <br /> Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br /> TABLE OF CONTENTS <br /> SECTION PAGE <br /> ' 1.0 INTRODUCTION . 1-1 <br /> 1.1 PURPOSE OF THIS DOCUMENT . . . . . . . . . . . . . . . . . . . . . . . 1-1 <br /> ' 1.2 SITE BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 <br /> 1.2.1 Regional Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 <br /> 1.2.2 Site Description and Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 <br /> ' 1.2.3 Regional Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 <br /> 1.2.4 Site Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 <br /> 1.2.5 Local and Regional Hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 <br /> ' 1.2.5.1 Local Ground Water Gradient and Seasonal Fluctuatio-is . . . . . . . . . . . 1-4 <br /> 1.2.5.2 Local Ground Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5 <br /> ' 1.2.6 Summary of Site Investigations 1-5 <br /> 1.2.6.1 Soil Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6 <br /> 1.2.6.2 Ground Water Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7 <br /> ' 1.2.7 Summary of Remediation Activities . . 1-10 <br /> 1.2.7.1 Soil Remediation Activities • . . . . . . . . . . . . • . . . . . 1-10 <br /> 1.2.7.2 Ground Water Remediation Activities . . . . . . . . . . . . . . . . . . . . . . 1-11 <br /> 1.3 EVALUATION OF REMEDIAL ALTERNATIVES FOR <br /> SOIL AND GROUND WATER . . . . . . . . . . . . . . . . . . . . . . . . . 1-11 <br /> 1.3.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11 <br /> ' 1.3.2 Considerations of Final Remediation Plan . . . . . . . . . . . . . . . . . . 1-13 <br /> 1.3.3 Proposed Final Remediation Plan . . . . . . . . . . . . . . . . . . . . . . . . 1-14 <br /> 1.3.3.1 Fluid-Level Monitoring and Ground Water Sampling . . . . . . . . . . . . 144 <br /> 1.3.3.2 Human Health Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . 1-15 <br /> 1.4 REPORT OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17 <br /> 1.5 ORGANIZATION OF THE RISK ASSESSMENT REPORT . . . . . . . . 1-17 <br /> ' 2.0 ENVIRONMENTAL FATE AND TRANSPORT OF <br /> PETROLEUM HYDROCARBONS . . . . . . . . . . . . . . . . . . . . . . . 2-1 <br /> ' 2.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1 <br /> 2.2 PETROLEUM HYDROCARBON PERSISTENCE . . . . . . . . . . . . . . . 2-1 <br /> 2.3 DISSOLVED-PHASE HYDROCARBON MIGRATION . . . . . . . . . . . 2-2 <br /> ' 2.4 SUMMARY OF SITE-SPECIFIC OBSERVATIONS . . . . . . . . . . . . . 2-2 <br />' 3.0 HAZARD IDENTIFICATION . . . . . . . . . 3-1 <br /> . . . . . . <br /> 3.1 GASOLINE AND DIESEL RANGE FUELS . 3-1 <br /> 3.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1 <br /> 30-0136-11 <br /> 1 I <br />