Remediation is always more expensive and less effective when treating across a diffuse area (which happens when moving the toxic sediment downstream) than in a single contained area.
As a civilization we're gradually getting better over time at remediation of large-scale "waste" like this, but still primitive considering our state of the art capabilities; we still don't recognize at a systemic, industrial design level that waste is materiel that we don't understand an economic use for yet, or understand how to transform into materiel we want at a thermodynamically desirable cost.
As a civilization we're gradually getting better over time at remediation of large-scale "waste" like this, but still primitive considering our state of the art capabilities; we still don't recognize at a systemic, industrial design level that waste is materiel that we don't understand an economic use for yet, or understand how to transform into materiel we want at a thermodynamically desirable cost.