MIGRATEv10 vs POLLUTEv10: Hydraulic Trap (Finite Mass Source) Comparison

Knowledge Center

MIGRATEv10 vs POLLUTEv10: Hydraulic Trap (Finite Mass Source) Comparison

Comparison of hydraulic trap results from MIGRATEv10 and POLLUTEv10 showing reduced base concentrations due to upward flow

Written by

GAEA Technologies

in

,
Share the knowledge

Overview

This example compares results from MIGRATEv10 and POLLUTEv10 for a hydraulic trap scenario with a finite mass source.

A hydraulic trap occurs when upward (negative) advective velocity counteracts downward contaminant migration. In this case:

  • Vertical velocity = –0.001 m/a
  • Finite contaminant mass at the top boundary
  • Advective outflow at the base

This creates a system where contaminants are partially retained, significantly altering breakthrough behavior compared to standard downward flow cases.

Model Setup

Both models use consistent inputs:

  • Layer thickness: 4 m
  • Dispersion coefficient: 0.01 m²/a
  • Porosity: 0.4
  • Sorption: None (Kd = 0)
  • Vertical velocity: –0.001 m/a (upward flow)
  • Finite mass source:
    • Initial concentration: 1000 mg/L
    • Leachate collection: 0.3 m/a
    • Reference head: 7.5 m
  • Bottom boundary:
    • Advective outflow (aquifer)

Results Comparison

Concentration Profiles at 200 Years

POLLUTEv10 (1D)

Depth (m)Concentration (mg/L)
00.919
123.96
225.72
314.63
42.21

MIGRATEv10 (Centerline, x = 0 m)

Depth (m)Concentration (mg/L)
00.911
123.93
225.62
314.28
41.28

Key Observations

1. Excellent Agreement Through Most of the Profile

At depths 0–3 m:

  • Results are nearly identical between models
  • Differences are negligible (<2–3%)

👉 Confirms both models solve the advection–dispersion equation with reversed flow consistently

2. Difference at the Base (Depth = 4 m)

  • POLLUTEv10: ~2.21 mg/L
  • MIGRATEv10 (x = 0): ~1.28 mg/L

👉 MIGRATE predicts ~40–45% lower concentration

3. Why the Difference?

This is again due to dimensionality effects:

POLLUTEv10 (1D)

  • All contaminant mass moves vertically
  • No lateral spreading
  • Produces higher base concentrations

MIGRATEv10 (2D)

  • Includes lateral spreading
  • Some contaminant mass is diverted sideways
  • Results in reduced downward flux

4. Hydraulic Trap Behavior

This case highlights unique physics:

  • Upward flow opposes contaminant migration
  • Contaminants accumulate within the layer
  • Peak concentrations occur within the soil, not at the base

At ~2 m depth:

  • Concentrations exceed 25 mg/L
  • Indicates a zone of accumulation (trap region)

5. Lateral Variability (MIGRATEv10)

At 200 years:

DistanceBase Concentration (mg/L)
x = –100 m~0.008
x = 0 m~1.28
x = +100 m~2.46

This shows:

  • Strong lateral gradients
  • Edge effects can increase or decrease concentrations
  • Behavior depends on plume geometry and flow field

6. Mass Transport Insights

MIGRATEv10 provides mass balance information:

  • At 200 years:
    • Mass into soil ≈ 6.42 × 10³
    • Mass into base ≈ 5.62 × 10²

👉 Only a small fraction of mass reaches the base, confirming the trapping effect

Key Differences Summary

FeatureMIGRATEv10POLLUTEv10
Dimensionality2D (lateral + vertical)1D (vertical only)
Agreement (0–3 m)ExcellentBenchmark
Base concentrationLower (~1.3 mg/L)Higher (~2.2 mg/L)
Lateral spreadingIncludedNot included
Mass trackingYesNo
Trap representationRealistic plumeConservative

Interpretation

  • Both models correctly simulate hydraulic trapping behavior
  • POLLUTEv10 provides a conservative estimate of base concentration
  • MIGRATEv10 provides a more realistic distribution, accounting for lateral spreading and reduced vertical flux

This case demonstrates that:

In low or upward flow systems, lateral spreading becomes even more important, significantly reducing breakthrough.

Conclusion

The hydraulic trap scenario reinforces a consistent theme:

  • Physics is consistent between models
  • Differences arise from dimensionality

Key takeaway:

  • Use POLLUTEv10 for conservative screening
  • Use MIGRATEv10 when evaluating:
    • Trap efficiency
    • Plume distribution
    • Mass flux to underlying aquifers

Learn more about our Contaminant Transport Modeling Solutions

POLLUTE and MIGRATE Contaminant Modeling and Landfill Design


Comparison between POLLUTE and MIGRATE

1 / ?