This is a genuine plan-view (top-down) solve, not a flattened version of the 3D scene. Instead of assuming a velocity profile, it solves the steady 2D Darcy pressure field directly on a grid: gas generation is a distributed source everywhere in the waste body, so pressure p(x,y) obeys a Poisson equation
k·∇²p = -G
k — waste permeability (slider)
G — areal gas generation rate (slider)
BC: p = p_well on the well boundary (vacuum-driven)
p = 0 at the site margin (atmospheric)
This is solved every time a slider moves by iterating a finite-difference relaxation (Gauss–Seidel/SOR) on a grid over the whole site footprint until it converges. The Darcy velocity field is then the actual gradient of that solved field, v = −k∇p — read directly off the grid, not assumed. Gas parcels are advected by that field plus a small random walk for dispersion.
The radius of influence is not a formula plugged in — it is found by scanning the solved field outward from the well until the radial component of v changes sign: inside, the well's suction wins and gas is captured; outside, generation pressure wins and gas migrates past the site margin as a fugitive emission. That sign-change radius is exactly where the net flux through a circle of that radius is zero — a direct conservation check on the solved field.
- Vacuum sets the well's boundary pressure directly — a mechanical pump setting, independent of the waste itself.
- Permeability scales how strongly a given pressure gradient drives flow (Darcy's law) and also how far a pressure disturbance reaches before the generation source dominates again.
- Generation rate is the Poisson source term — raise it and the pressure bump from continued decomposition grows, shrinking the capture zone.
- Site radius is the outer (atmospheric) boundary of the solve — a real design trade-off for well spacing.