GROUNDWATER AND LEACHATE: IN-SITU CHEMICAL/PHYSICAL TREATMENT
Dual Phase Extraction
Process:
A high vacuum system is applied to simultaneously remove various combinations of contaminated ground water, separate-phase petroleum product & hydrocarbon vapour from the ground.
- The vacuum extraction well removes liquid and gas from low permeability or heterogeneous formations & includes a screened section in the zone of contamination.
- It removes contaminants from both above and below the water table.
- The system lowers the WT around the well to make newly exposed contaminants (now in vadose zone) accessible to vapour extraction.
- Once above ground, the extracted liquids & vapour are usually separated, treated & disposed.
- DPE is combined with air sparging/bioventing (if the contamination includes long-chained hydrocarbons) or with pump-and-treat technologies (to recover ground water in higher-yielding aquifers) - reduces treatment time.
It is also referred to as multi-phase extraction, vacuum-enhanced extraction, very similar to bio-slurping.
Uses:
- Target contaminant groups: VOCs and fuels (e.g., LNAPLs).
- It is more effective than SVE for heterogeneous clays and fine sands.
- Not recommended for lower permeability formations - potential for residual undissolved product.
Limitations:
- Site geology and contaminant characteristics/distribution.
- May require complementary technologies (e.g. pump-and-treat) to recover ground water from high yielding aquifers.
- Both water & off-gas treatment is required.
Cost:
Highly variable - dependent on the soil type & depth to base of contamination.