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 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 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 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

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

Objectives Characterize Cape Cod geology and hydrogeology Characterize Cape Cod geology and hydrogeology Model EDB plume behavior Model EDB plume behavior

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 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 The population of Cape Cod is 229,545 Over 4.6 million visitors come to Cape Cod every year Over 4.6 million visitors come to Cape Cod every year Dave Hisz is from there Dave Hisz is from there

Dave Dave’s House Map of Cape Cod

Topography

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

Stratigraphy

Geomorphology

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

Permeability Characteristics LithologyPorosityHorizontal K (m/day) Ratio of Vertical K:Horizontal K Silt or clay0.68 – :1 Very fine sand :30 Fine-grained sand :30 Medium-grained sand :5 Coarse-grained sand 0.34 – :5 Gravel0.34 – :5

Hydraulic Conditions

Hydraulic Head

Water Balance Published ValueComputed Value Flux (m/yr)% of Prec ip. Flux (m/yr)% of Precip. Precipitation Recharge BaseflowNA RunoffNA ET StormflowNA StorageNA0.0041

Water Quality ConstituentConcentration (mg/L) Dissolved Oxygen10.0 pH5.8 Total Dissolved Solids39.0 Alkalinity (as CaCO3)6.0 Bicarbonate (as HCO3)7.0 Chloride (Cl)8.1 Sulfate5.2 Calcium7.0 Magnesium1.7 Sodium5.5 Total Organic Carbon2.1 Ferrous Iron0.07 Manganese<10.0

Contaminant Sources

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

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

FS-28 Plume

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

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

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

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

MMR Model Layers

Overview Model contd.

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

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

FS-28 Plume

Stratigraphy

Model Layers Coarse Sand and Gravel, K = 30 Coarse Sand and Gravel, K = 75 Coarse Sand and Gravel, K = 100 Coarse Sand and Gravel, K = 150 Fine silt/sand, K = 1 m/d Bedrock, K = m/d Ground Surface

MMR Model Layers with Till

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

ModPath Results (forward model) Coonamessett Pond

ModPath Results, contd. Coonamessett Pond

FS-28 Transport Simulation

Conclusions MT3D predicts impact to downgradient surface water, but also disperses the plume MT3D predicts impact to downgradient surface water, but also disperses the plume This is likely a problem of upstream weighting This is likely a problem of upstream weighting This may be resolved with calibration of the MMR model, which was not conducted here This may be resolved with calibration of the MMR model, which was not conducted here The effectiveness of other means of modeling FS-28 in Groundwater Vistas will be evaluated The effectiveness of other means of modeling FS-28 in Groundwater Vistas will be evaluated