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Evaluation ofNatural Attenuation: 7500 West Eleventh Street, Tracy, CA. Page i <br /> Table of Contents <br /> ..�1 <br /> PROFESSIONAL CERTIFICATION AND LIMITATIONS.............................................v <br /> 1.0 INTRODUCTION.................................................................................................................... 1 <br /> 1.1 Site Location........................................................................................................................ 1 <br /> 1.2 Site Codes <br /> 1.3 Background................................................................................................................... <br /> ....... 1 <br /> 1.3.1 Site Characterization Studies........................................................................................ 2 <br /> 1.3.2 Groundwater-quality Monitoring....................................................... <br /> 1.3.3 Monitoring of LNAPL.................. ............................. 3 <br /> .................................................. <br /> 1.3.4 Testing of Water in Potable Water-supply Wells.........................................................4 <br /> 1.3.5 Recommendations for Evaluation of Natural Attenuation.................. <br /> 1.4 Geology and Hydrogeology <br /> 1.5 Distribution of Hydrocarbons in the Subsurface.................................................................. 6 <br /> 1.5.1 Primary Plume.............................................................................................................. 6 <br /> 1.5.2 Secondary Plume....................... . 7 <br /> 1.5.3 Dispersed Petroleum Hydrocarbons in Shallow Soils.................................................. 8 <br /> G'3 <br /> 2.0 GROUNDWATER ELEVATIONS AND CONTOURS......................................................... 9 <br /> 2.1 Groundwater Mound.......................................................................................................... 11 <br /> 3.0 MONITORING OF FLOATING PRODUCT........................................................................ 12 <br /> 4.0 GROUNDWATER SAMPLING AND ANALYSIS............................................................. 13 <br /> - 4.1 Field Tests for Natural Attenuation Parameters..................... 13 <br /> 4.1.1 Ferrous Oxide .. 13 <br /> 4.1.2 Dissolved Oxygen and Redox Potential..................................................................... 14 <br /> 'f. 4.1.3 Temperature, Conductivity and pH ............................................................................ 14 <br /> 4.2 Sampling and Laboratory Analyses for Natural Attenuation Parameters.......................... 14 <br /> 4.3 Sampling and Laboratory Analyses for Components of Fuel Hydrocarbons..................... 16 <br /> 4.3.1 Purging of Groundwater-quality Monitoring Wells ...... 16 <br /> ............................................. <br /> 4.3.2 Well Recovery Time................................................................................................... 16 <br /> 4.3.3 Disposal of Purge Water...................................................................................... 17 <br /> f 4.3.4 Groundwater Sampling and Analyses for Components of Fuel Hydrocarbons.......... 17 <br /> 5.0 MONITORING OF POTABLE WATER SUPPLIES .. 19 <br /> 5.1 Recovery and Analysis of Samples from Potable Water Supply Wells............................. 19 <br /> 5.2 Results of Potable Water Sampling.................................................................................... 20 <br /> 5.3 Notification to Well Owners ... 20 <br /> 6.0 COMPONENTS OF FUEL HYDROCARBONS IN GROUNDWATER............................ 21 <br /> 6.1 Groundwater Quality in the Near-Surface Unconfined Aquifer............... <br /> 6.1.1 Analytes of Concern in Groundwater Along Principal Plume Axis........................... 21 <br /> 6.1.2 Analytes of Concern in Groundwater around Fringes of Principal Plume................. 21 <br /> 6.1.3 Analytes of Concern in Secondary Groundwater Plume............................................ 22 <br /> 6.1.4 Groundwater Quality in the Deeper Confined Aquifers............................................. 22 <br /> 6.2 Absence of Lead Scavengers in Groundwater................................................................... 22 <br /> 6.3 Absence of Alcohols in Groundwater................................................................................ 23 <br /> l 7.0 NATURAL ATTENUATION OF CONTAMINANTS IN GROUNDWATER................... 24 <br /> sic <br /> i <br /> __a <br />