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4 � <br /> ` Report.• Groundwater-quality ndli Monitoring-March 29-31,2006, 7500 West Eleventh Street, Tracy, CA. Page i <br /> 9 h' <br /> f Table of Contents <br /> t PROFESSIONAL CERTIFICATION AND LIMITATIONS..................................111 <br /> 1.0 INTRODUCTION.................. ............................................................. 1 <br /> 1.1 Site Location.......................................................................................................................... 1 <br /> 1.2 Site Codes....................................................................................-----.................................... 1 <br /> 1.3 Background ........................................................................ 1 <br /> .................................................. 2 <br /> 1.3.1 Site Characterization Studies........................................................................................2 <br /> 1.3.2 Groundwater-quality Monitoring..................................................................................3 <br /> 1.3.3 Monitoring of LNAPL.................................................................................................. <br /> 1.3.4 Evaluation of Natural Attenuation................................................................................4 <br /> 1.3.5 Testing of Water in Potable Water-supply Wells..........................................................4 <br /> 1.4 Geology and Hydrogeology....................:......................................................I........I............5 <br /> 1.5 Distribution of Hydrocarbons in the Subsurface.................................................................. <br /> 1.5.1 Primary Plume.......................................................... <br /> .....................................................6 <br /> 1.5.2 Secondary Plume...................................................................................•----...................7 <br /> 1.5.3 Dispersed Petroleum Hydrocarbons in Shallow Soils...................................................8 <br /> 2.0 MARCH 2006 GROUNDWATER-QUALITY MONITORING ROUND..............................9 <br /> 2.1 Groundwater Elevations and Flow Direction.......................................................................9 <br /> 2.1.1 Groundwater Mound................................................................................................... <br /> 10 <br /> 2.2 <br /> 2.2 Purging of Groundwater-quality Monitoring Wells......................................................... 10 <br /> 2.2.1 Disposal of Purge Water...............................................................................•----..--..... 11 <br /> 2.3 Recovery of Groundwater Samples from Monitoring Wells.............................................. 11 <br /> 2.4 Analyses of Groundwater Samples ..... 11 <br /> 2.5 Groundwater Quality in the Near-Surface Unconfined Aquifer......................................... 12 <br /> 2.5.1 Analytes of Concern in Groundwater Along Principal Plume Axis ........................... 12 <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 ............................................ 13 <br /> 3.0 MONITORING OF FLOATING PRODUCT........................................................................ 14 <br /> 4.0 ON-GOING NATURAL ATTENUATION OF ANALYTES OF CONCERN..................... 15 <br /> 5.0 GROUNDWATER MONITORING PROGRAM OPTIMIZATION STUDY...................... 16 <br /> 5.1 MAROS Input Data........................ .... 16 <br /> 5.2 Plume Stability................................................................................................................... 17 <br /> 5.3 Optimal Sampling Frequency............................................................................................. 18 <br /> 5.4 Data Sufficiency Confirmation...........................................................................................20 <br /> 4 5.5 Optimal Monitoring Dates..................................................................................................21 <br /> 6.0 MONITORING OF POTABLE WATER SUPPLIES ...........................................................23 <br /> 6.1 Recovery and Analysis of Samples from Potable Water Supply Wells.............................23 <br /> 6.2 Results of Potable Water Sampling....................................................................................24 <br /> 6.3 Notification to Well Owners ..............................................................................................24 <br /> 7.0 CONCLUSIONS ....................................................................................................................25 <br /> 7.1 Groundwater Quality..............................................................•---........................................25 <br /> 7.2 Natural Attenuation............................................................................................................25 <br /> sic <br />