GROUNDWATER AND LEACHATE: IN-SITU CHEMICAL/PHYSICAL TREATMENT
Passive/Reactive Treatment Walls
Typical Passive/Reactive Treatment Wall
Typical Passive/Reactive Treatment Wall
- A permeable reaction wall (barrier) is installed across the flow path of a contaminant plume to allow the passage of water while causing the degradation (if reactive) or removal (if passive) of contaminants. .
- The contaminated water passively moves through the wall, while the barrier prohibits the movement of contaminants by employing such agents as zero-valent metals, sorbents, microbes, and others.
- Generally intended for long-term operation to control migration of contaminants in ground water.
Modifications to the basic passive treatment walls:
Funnel and Gate
- In situ treatment of contaminated plume consisting of low hydraulic conductivity (e.g., 1E-6 cm/s) cutoff walls (the funnel) with a gate that contains in situ reaction zones.
- Ground water primarily flows through high conductivity gaps (the gates).
- One of the most common type of cutoff walls are slurry walls, however innovative methods such as deep soil mixing and jet grouting are also being considered.
- An iron treatment wall consists of iron granules or other iron bearing minerals.
- Used to treat chlorinated contaminants (e.g. TCE)
- As the iron is oxidized, a chlorine atom is removed from the compound by a reductive de-chlorination mechanism, using electrons supplied by the oxidation of iron .
- The iron granules are dissolved by the process, but the metal disappears so slowly that the remediation barriers can be expected to remain effective for many years, possibly even decades.
- Commonly used to treat VOCs, SVOCs, and inorganics.
- It can also be used but generally less effective for some fuel hydrocarbons.
Limitations/Disadvantages:
- Passive treatment walls may lose their reactive capacity - may limit the permeability of the passive treatment wall. Would requie replacement of the reactive medium.
- Passive treatment wall permeability may also decrease due to precipitation of metal salts.
- Treatment medium can be expensive.
- Need to pre-investigate the hydraulic gradient; contaminant characteristics (depth, areal extent, type, and concentration); depth to ground water, depth to impermeable barrier key-in; ground water hydrology; water quality, flow rate, and direction; soil conditions & permeability
Cost:
Unknown as highly variable - dependent on the quantity of material to be treated, the choice of wall materials, the size of the wall required.