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Cr <br /> Report:Groundwater-quality Monitoring—October 27,2004:7500 West Eleventh Street, Tracy,CA. Page i <br /> ki Table of Contents <br /> PROFESSIONAL CERTIFICATION AND LIMITATIONS..................................iii <br /> 1.0 INTRODUCTION ............•• 1 ' <br /> 1.1 Site Location.........................................................................................................................2 j <br /> i1.2 Site Codes.............................................................................................................................2 <br /> 1.3 Background <br /> 1.4 Geology and Hydrogeology.................................................................................................4 <br /> �w 1.5 Distribution of Hydrocarbons in the Subsurface..................... 5 <br /> 1.5.1 Primary Plume................................................................................................................6 <br /> 1.5.2 Secondary Plume..........................................................................................................:7 <br /> � 1.5.3 Dispersed Petroleum Hydrocarbons in Shallow Soils.............. 7 <br /> _�. 2.0 OCTOBER 2004 GROUNDWATER-QUALITY MONITORING ROUND........................:.8 <br /> 2.1 Groundwater Elevations and Flow Direction.......................................................................8 <br /> 2.2 Purging of Groundwater-quality Monitoring Wells................ <br /> 2.2.1 Disposal of Purge Water <br /> 2.3 Recovery of Groundwater Samples from Monitoring Wells..............................................10 <br /> 2.4 Analyses of Groundwater Samples............................................ .................................... 10 j <br /> 2.5 Groundwater Quality in the Near-Surface Unconfined Aquifer......................................... 11 <br /> 2.5.1 Analytes of Concern in Groundwater Along Principal Plume Axis........................... 11 <br /> 2.5.2 Analytes of Concern in Groundwater around Fringes of Principal Plume.................. 12 <br /> 2.5.3 Analytes of Concern in Secondary Groundwater Plume ............................................12 <br /> F . 2.5.4 Groundwater Quality in the Deeper Confined Aquifers.............................................13 <br /> r <br /> 3.0 MONITORING OF FLOATING PRODUCT........................................................................ 14 , <br /> 4.0 MONITORING OF POTABLE WATER SUPPLIES <br /> 4.1 Recovery and Analysis of Samples from Potable Water Supply Wells............................. 15 <br /> 4.2 Results of Potable Water Sampling.................................................................................... 1b <br /> 4.3 Notification to Well Owners. 16 <br /> 5.0 DISPOSAL OF DRILL CUTTINGS...................................................................................... 17 <br /> 6.0 CONCLUSIONS ......... 18 <br /> 7.0 RECOMMENDATIONS........................................................................................................ 19 <br /> 7.1 Evaluation of Natural Attenuation of Plumes of Affected Groundwater........................... 19 <br /> 7.2 Closure of Groundwater-quality Monitoring Wells .. 19 <br /> 7.3 Monitoring of Potable Water Quality...................................... .......20 <br /> 8.0 REFERENCES ...............................21 <br /> sic <br />