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Work Plan for Refined Plume Definition and Management of Floating Product-7500 W 11th St., Tracy, CA. Page ii 10N" 8.0 INVESTIGATION OF EXTENT OF FLOATING PRODUCT...................................................30 8.1 Floating Product Monitoring Well Array.................................................................................30 8.2 Well Drilling and Soil Sampling..............................................................................................31 8.3 Disposal of Drill Cuttings.........................................................................................................32 8.4 Well Design......................................................................................................... ...33 .................. 8.5 Well Development................................................................•--.................................................33 8.6 Survey of Well-head Locations and Elevations........................................................................33 8.7 Field Modification ..............•.•33 ................................................................................................... 8.8 Groundwater Elevations and Measurement of Thickness of Floating Product........................34 8.9 Schedule ...................................................................................................................................34 *• 8.10 Cost Estimate...........................................................................................................................34 9.0 PROGRAM FOR MANAGEMENT OF FLOATING PRODUCT..............................................35 9.1 Floating Product Managed During Tank Removal...................................................................35 9.2 Interim Measures to Manage Floating Product in Area of Monitoring Well MW-7.............:..35 9.2.1 Procedure for Measurement of the Thickness of Floating Product..................................35 9.2.2 Pump Apparatus and Pumping Technique.......................................................................36 z. 9.2.3 Post-pumping Procedures.................................................................................................37 9.2.4 Floating Product Removed to Date..................................................................................37 9.2.5 Cost of Interim Measures.................................................................................................39 9.3 Hydrogeologic and Engineering Design Issues Related to LNAPL Remediation ...................39 9.3.1 Zone of Influence and Groundwater Drawdown Gradient...............................................39 9.3.1.1 Dual Floating Product Extraction/Groundwater Draw-down Systems....................40 9.3.2 Representative Elementary Volume.................................................................................41 9.3.3 Well Diameter, Excavation Dimensions and Construction Method Considerations........43 9.3.3.1 Influence of Well or Excavation Size on Effectiveness of Extraction Systems.......43 9.3.3.2 Effect of Construction Method on Well and Excavation Hydraulic Efficiency.......44 9.3.4 Scale of System Required for Successful Removal of All Recoverable LNAPL ............45 9.3.5 U.S. Environmental Protection Agency Recommendation..............................................46 9.4 Floating Product Remediation Technologies Considered........................................................47 9.4.1 Technology A—Cut-off Trench and High-volume Pumping of LNAPL .......................48 9.4.1.1 Trench Location and Dimensions............................................................................49 9.4.1.2 Trenching Technique ...............................................................................................50 ,,. 9.4.1.3 Soil Sampling in Cut-off Trench..............................................................................51 9.4.1.3.1 Analysis of Soil from Trench Bottom and Wails...............................................51 9.4.1.4 High-volume Extraction of Floating Product...........................................................52 9.4.1.4.1 Bulk Extraction of Contaminated Groundwater.................................................53 9.4.1.5 Placement of Permeable Crushed Rock into Cut-off Trench...................................53 9.4.1.6 Disposal of Soil Excavated from Cut-off Trench.....................................................54 9.4.1.7 Restoration of Site........................................................................... ...........55 9.4.1.8 Schedule ......56 9.4.1.9 Estimated Cost.........................................................................................................57 9.4.1.10 Advantages and Disadvantages...............................................................................58 9.4.2 Technology B—Pumping of LNAPL from Extraction Wells into Vacuum Trucks........60 9.4.2.1 Extraction Well Installation---•.................................................................................60 9.4.2.2 Measurement of Depth to Groundwater and Thickness of Floating Product...........60 9.4.2.3 Vacuum Extraction of LNAPL ................................................................................61 9.4.2.4 Additional Extraction Points....................................................................................63 9.4.2.5 Schedule.....................................................................•.............................................63 �. 9.4.2.6 Estimated Cost.........................................................................................................64 9.4.2.7 Advantages and Disadvantages................................................................................65 sic