Modeling Natural Attenuation with GROUNDWATER SERVICES, INC. BIOSCREEN GROUNDWATER SERVICES, INC.

? ? Objectives BIOSCREEN Natural Attenuation Model  How Far Will Plume Migrate?  How Long Will Plume Be There? ? ?

Groundwater Transport Modeling Groundwater Transport Processes Groundwater Transport Modeling All groundwater transport models are based on the advective-dispersive-reactive equations. rate of change in HC conc. at any point net rate of advective transport to that point net rate of dispersive transport to that point net rate of degradation at that point = + - Transport at time t with dispersion & degradation Transport at time t advection only Transport at time t with dispersion

Fate and Transport Modeling Options GOAL: Predict steady-state NAF between source and receptor. Types of Models: • 1-D vs. 2-D vs. 3-D Advection • 1-D vs. 2-D vs. 3-D Dispersion • Deterministic vs. Statistical • Numerical vs. Analytical • Transient vs. Steady State • Constant Source vs. Changing Source

Products Air Force Natural Attenuation Initiative  Technical Protocol  Field Data  Modeling Tools

Transport: Groundwater in Source Zone Groundwater at Receptor Concentration at Downgradient Distance x Away from Source First-Order Decay Constant Groundwater Source Width and Depth Conc (x) = { 1/ 2 } [ ( ) ] [ ] [ ] x 4  x Sw Sd exp 1 - 1 + erf erf 2 x Vs/R 4 y x 4 z x Retardation Coefficient Error Function Transverse Dispersivity Vertical Dispersivity Longitudinal Dispersivity Hydraulic Conductivity Groundwater Seepage Velocity Hydraulic Gradient K i Vs = Effective Soil Porosity ne

Location: Downstream of Affected Soil Zone Source Term Configuration Location: Downstream of Affected Soil Zone Concentration Width Depth

BIOSCREEN Model: Other Features  Single Vertical Plane Source  Superimposed Sources (Connor et al., 1995) Source 1 Source 2 Source 3

Where to Get BIOSCREEN EPA Center for Subsurface Modeling Support (R. S. Kerr Lab)  Web: http://www.epa.gov/ada/bioscreen.html  Phone (405) 436 8718