SOIL, SEDIMENT AND SLUDGE: IN-SITU CHEMICAL/PHYSICAL TREATMENT
Fracturing
Typical Pneumatic Fracturing Process
Process:
Cracks are developed by fracturing beneath the surface in low permeability and over-consolidated sediments
Opens new passageways that increase the effectiveness/enhance extraction efficiencies of many in situ processes (for the otherwise difficult soil conditions).
Fracturing:
Technologies commonly used in soil fracturing include pneumatic fracturing (PF) & blast-enhanced fracturing.
1) Pneumatic Fracturing (PF)
2) Blast-enhanced Fracturing
Uses:
Limitations:
Note: Studies have found:
Cracks are developed by fracturing beneath the surface in low permeability and over-consolidated sediments
Opens new passageways that increase the effectiveness/enhance extraction efficiencies of many in situ processes (for the otherwise difficult soil conditions).
Fracturing:
- Extends/enlarges existing fissures
- Introduces new fractures/cracks (primarily horizontal).
- When complete, vapour extraction can be more easily applied.
Technologies commonly used in soil fracturing include pneumatic fracturing (PF) & blast-enhanced fracturing.
1) Pneumatic Fracturing (PF)
- Here fracture wells are drilled in the contaminated vadose zone and left open (uncased) for most of their depth.
- A packer system is used to isolate small (0.6m) intervals so that short bursts (~20 seconds) of compressed air can be injected into the interval to fracture the surrounding soil.
- This is repeated for each interval within the contaminated depth.
2) Blast-enhanced Fracturing
- Used when have fractured bedrock formations.
- Explosives are detonated in boreholes to cause many fractures - increasing the hydraulic conductivity of the soil - hence flow and ease of capture of the contaminant.
Uses:
- No particular target group - applicable to all.
- Most commonly used to fracture silts, clays, shale, and bedrock (sands - less so).
Limitations:
- The technology should not be used in areas of high seismic activity.
- Get close fractures in non-clayey soils (e.g. sands).
- May open new pathways for undesirable spread of contaminants.
- Prior investigations required: underground utilities (cables/wires/drains), depth/areal extent of contamination, the concentration of the contaminants, soil type & soil properties.
Note: Studies have found:
- Normal operation makes 15 to 25 fractures (~5m long,~25m deep) per day
- With hot gas injection: PF increased the effective radius of influence by 3 times & the rate of mass removal by 25 times.
- For pumping of fuel oil: PF increased average removal rate by 15 times.
- In the unsaturated zone: PF increased air permeability by 5-30 times
- Typical cost: approx $8 to $12 per ton for the PF technology implemented over 1 year.