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2013 Semiannual Groundwater Monitoring and Evaluation Report Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation Former Marley Cooling Tower Site,Stockton,California August 2013 TABLE OF CONTENTS 1.0 INTRODUCTION.............................................................................................................1-1 2.0 BACKGROUND...............................................................................................................2-1 3.0 GROUNDWATER MONITORING AND SAMPLING...............................................3-1 3.1 MONITORING AND SAMPLING PLAN..................................................................3-1 3.1.1 Analytical Methods and Field Parameters..............................................................3-1 3.1.2 Background and Compliance Wells........................................................................3-2 3.1.3 Northern Injection Area Wells................................................................................3-3 3.1.4 Southern Injection Area Wells................................................................................3-3 3.2 GROUNDWATER ELEVATION, ESTIMATED GRADIENT, AND LINEAR VELOCITY ..................................................................................................................3-4 3.2.1 Shallow Zone..........................................................................................................3-4 3.2.2 100-Foot Sand Zone................................................................................................3-5 3.2.3 Intermediate Zone...................................................................................................3-5 4.0 LABORATORY AND FIELD SAMPLE RESULTS AND DISCUSSION.................4-1 4.1 DATA VALIDATION AND QUALITY ASSISTANCE/QUALITY CONTROL.....4-1 4.2 ANALYTICAL RESULTS ..........................................................................................4-1 4.2.1 Hexavalent and Total Chromium............................................................................4-2 4.2.2 Iron..........................................................................................................................4-6 4.2.3 Manganese..............................................................................................................4-7 4.2.4 Arsenic....................................................................................................................4-8 4.2.5 Sulfate.....................................................................................................................4-8 4.2.6 General Chemistry..................................................................................................4-9 4.3 FIELD PARAMETERS..............................................................................................4-10 5.0 PERFORMANCE EVALUATION.................................................................................5-1 5.1 EXTENT OF TREATMENT ZONE IN GROUNDWATER......................................5-1 5.1.1 Phase I and Phase 11 of the Pilot Study...................................................................5-1 5.1.2 Full-Scale In Situ Groundwater Remediation.........................................................5-1 5.2 GROUNDWATER GEOCHEMISTRY.......................................................................5-2 5.3 ANALYSIS OF IN SITU REMEDIATION EFFECTIVENESS..................................5-3 5.4 DECISION LOGIC FOR PERFORMANCE MONITORING DATA EVALUATION.............................................................................................................5-4 5.5 GROUNDWATER EXTRACTION AND TREATMENT..........................................5-4 6.0 SUMMARY AND CONCLUSIONS...............................................................................6-1 7.0 RECOMMENDATIONS..................................................................................................7-1 (a M WHA