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Characterization and Modeling of the Cape Cod Aquifer EE&S 816

Characterization and Modeling of the Cape Cod Aquifer EE&S 816. James K. Henderson May 5, 2005. What are Lead Scavengers?. The lead scavengers 1,2-dibromoethane (ethylene dibromide, or EDB) and 1,2-dichloroethane (DCA) were added to leaded gasoline to prevent lead buildup in engines

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Characterization and Modeling of the Cape Cod Aquifer EE&S 816

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  1. Characterization and Modeling of the Cape Cod AquiferEE&S 816 James K. Henderson May 5, 2005

  2. What are Lead Scavengers? • The lead scavengers 1,2-dibromoethane (ethylene dibromide, or EDB) and 1,2-dichloroethane (DCA) were added to leaded gasoline to prevent lead buildup in engines • EDB and DCA have low allowable Maximum Contaminant Levels (MCLs) and are suspected carcinogens • Almost 20 years after leaded gasoline was banned, available field evidence suggests that EDB and DCA persist at some sites where leaded gasoline was released

  3. MMR EDB Plumes • The Massachusetts Military Reservation is one of the few sites where EDB plumes have been delineated • How are EDB plumes able to persist in the subsurface at low levels years after their release?

  4. Objectives • Characterize Cape Cod geology and hydrogeology • Model EDB plume behavior

  5. Cape Cod Overview • Cape Cod is a hook-shaped peninsula that extends eastward from the Massachusetts mainland and curves north over a total length of approximately 110 • The population of Cape Cod is 229,545 • Over 4.6 million visitors come to Cape Cod every year • Dave Hisz is from there

  6. Map of Cape Cod Dave Dave’s House

  7. Topography

  8. Geology • Four broad classes of geologic materials are present on Cape Cod: • sand and gravel in glacial outwash plains • fine-grained silt and clay layers that underlie outwash plains • glacial till overlying bedrock • crystalline rock

  9. Stratigraphy

  10. Geomorphology

  11. Hydrostratigraphy • Six interbedded lenses of highly permeable glacial outwash sand and gravel are the principal hydrostratigraphic unit on the Cape • The Cape Cod aquifer is relatively homogeneous and mildly anisotropic

  12. Permeability Characteristics

  13. Hydraulic Conditions

  14. Hydraulic Head

  15. Water Balance

  16. Water Quality

  17. Contaminant Sources

  18. Conceptual Model Recharge Streams Cape Cod Bay Fine-grained Sand/Silt Groundwater Flow Paths Saline Groundwater Bedrock Glacial Till Freshwater/Saltwater Interface South North

  19. Fuel-Spill 28 Plume • Discovered in 1992; source unknown • Highest concentration of EDB is 0.031 ug/l • Top of plume 60 to 100 feet below ground surface • Groundwater upwells into bogs

  20. FS-28 Plume

  21. FS-28 Plume Conceptual Model Water Table Coonamessett Pond EDB Plume Coarse-grained sand/gravel Fine-grained silt/sand Bedrock Graphic design rendering support provided by M. Iannacone and J. Soberaski

  22. Release Simulation • Simulate release of aviation fuel as contaminated recharge • Run the model for 20 years • Expect to reproduce groundwater upwelling into bogs

  23. Model Development Overview Model of Cape Cod Calibration Refinement (TMR) Transport Simulation (MT3D)

  24. Overview Model • Based on three DEMs • 64 rows by 72 columns • Each cell is one square kilometer • Of 4608 total cells, 2860 were imported as constant head using StreamBC

  25. MMR Model Layers

  26. Overview Model contd.

  27. Overview Model, contd. • Overview model reproduced six groundwater mounds • Calibration using actual head targets unsuccessful • Calibration achieved by adding three head targets and one flux target • Calibrated K = 224 m/d • Calibrated R = 0.002 (compare to 0.001, CUHydrograph)

  28. MMR Model • TMR used to refine overview model • 100 by 100 grid used • Each cell is 220 by 240 meters • Focus is FS-28 release area • MT3D used to simulate EDB transport

  29. FS-28 Plume

  30. Stratigraphy

  31. Model Layers Ground Surface

  32. MMR Model Layers with Till

  33. Source Determination • Source of FS-28 unknown • Location of bogs chosen as discharge point of FS-28 • ModPath run in reverse (layer by layer) until flow ended at a single cell (R50, C32). • This cell selected at source of EDB plume

  34. ModPath Results (forward model) Coonamessett Pond

  35. ModPath Results, contd. Coonamessett Pond

  36. FS-28 Transport Simulation

  37. FS-28 Transport Simulation

  38. FS-28 Transport Simulation

  39. FS-28 Transport Simulation

  40. FS-28 Transport Simulation

  41. FS-28 Transport Simulation

  42. FS-28 Transport Simulation

  43. FS-28 Transport Simulation

  44. FS-28 Transport Simulation

  45. FS-28 Transport Simulation

  46. FS-28 Transport Simulation

  47. FS-28 Transport Simulation

  48. FS-28 Transport Simulation

  49. FS-28 Transport Simulation

  50. FS-28 Transport Simulation

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