Explosives Groundwater Contamination Plume

Source & Aquifer

Groundwater (Darcy) velocity 0.50 m/day

Retardation factor R 2.0×

Longitudinal dispersivity α_L 8 m

Biodegradation half-life 120 d

Monitoring Well (120 m)

Signal at well

Peak seen

Status

below detection

Plume State

Plume front

0 m

Elapsed time

0 d

Active tracers

Attenuated

How it works

Explosive residues (TNT, RDX, HMX) leach out of legacy munitions burial pits, unexploded-ordnance fields and demilitarisation-plant discharge into the underlying aquifer. Their fate is governed by the 1-D advection–dispersion–reaction equation:

∂C/∂t + v_eff ∂C/∂x = D_L ∂²C/∂x² − λC
v_eff = v / R        (retarded seepage velocity)
D_L   = α_L · v_eff   (longitudinal dispersion coefficient)
λ     = ln(2) / t½    (biodegradation decay constant)

This simulator solves that equation with the random-walk particle-tracking method used by real contaminant-transport codes (MT3D, RWHet): each tracer particle takes a step every time tick,

x(t+Δt) = x(t) + v_eff·Δt + √(2·D_L·Δt)·Z,   Z ~ N(0,1)
P(removed this step) = 1 − exp(−λ·Δt)

and is removed with the biodegradation probability above. Particle density at any cross-section is statistically proportional to concentration, so the monitoring-well readout is the live particle count inside a transect 120 m downstream.

Retardation factor R — sorption of the explosive to soil organic carbon slows it relative to the water itself; RDX is weakly sorbed (R ≈ 1.5–2), TNT sorbs and reacts more (R ≈ 3–5).
Dispersivity α_L — controls how much the plume spreads and smears out along the flow path as it travels; transverse/vertical spreading is scaled to 10%/1% of it.
Half-life — natural attenuation from microbial biodegradation and abiotic reduction; shorter half-lives mean the plume self-destructs before reaching a receptor.
The well status badge turns from green → amber → red as the relative signal at the monitoring transect rises, mirroring how a real long-term monitoring network flags a plume approaching a compliance boundary.

Explosive tracer (TNT/RDX) Source (legacy munitions site) Monitoring well

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