Devices and methods for directing migration of non-aqueous phase liquids from sediment
View Patent ↗Devices and methods for directing a non-aqueous phase liquid (NAPL) that migrate entrained in a fluid (e.g., a gas) from sediments in bodies of water by using trapping caps having an upwardly sloped surface toward an accumulation zone that contains a water table, in which migration of the gas carries the NAPL toward the accumulation zone.
1. A method for directing a non-aqueous phase liquid (NAPL) from a NAPL-contaminated sediment beneath a surface of a body of water towards a NAPL accumulation zone comprising the step of:
interposing in a path of a plurality of NAPL-entraining gas bubbles migrating between the sediment and the surface a device through which neither the gas nor the NAPL can percolate, the device defining, at or near one end, a vent in fluid communication with the accumulation zone and the device sloping upward towards the surface to an extent sufficient to direct the gas bubbles from under the device to the vent and into the accumulation zone.
2. The method of claim 1 , wherein the upward slope towards the accumulation zone is at least 1/60.
3. The method of claim 1 , wherein the accumulation zone contains a water table.
4. The method of claim 1 , wherein the device comprises a first layer of a material through which neither the gas nor the NAPL can percolate.
5. The method of claim 4 , wherein the material is selected from a group consisting of a high-density polyethylene, a geotextile, a sand, and a clay.
6. The method of claim 4 , wherein the device comprises a grading layer interposed between the first layer and the NAPL-contaminated sediment.
7. The method of claim 6 , wherein the grading layer comprises a material selected from a group consisting of sand and sand with amendments.
8. The method of claim 4 , wherein the device comprises a transmission layer interposed between the first layer and the NAPL-contaminated sediment.
9. The method of claim 8 , wherein the transmission layer and the first layer have a permeability contrast that is at least 100:1.
10. The method of claim 4 , further comprising an armoring layer between the first layer and the surface.
11. The method of claim 10 , wherein the armoring layer comprises a material selected from a group consisting of an articulated block mat, gravel, boulder-sized granular material and concrete.
12. A method for reducing toxicity of a NAPL from a NAPL-contaminated sediment beneath a surface of a body of water comprising the steps of:
interposing in a path of a plurality of NAPL-entraining gas bubbles migrating between the sediment and the surface a device through which neither the gas nor the NAPL can percolate, the device defining, at or near one end, a vent in fluid communication with a NAPL accumulation zone and the device sloping upward towards the surface to an extent sufficient to direct the gas bubbles from under the device to the vent and into the accumulation zone such that the gas vents and residual NAPL remains at the accumulation zone, and the device including a control layer having an inferior surface along which the gas bubbles are directed and a transmission layer below the control layer through which the gas bubbles permeate.
13. The method of claim 12 , wherein the upward slope towards the accumulation zone is at least 1/60.
14. The method of claim 12 , wherein the transmission layer and the control layer have a permeability contrast that is at least 100:1.
15. The method of claim 14 , wherein the transmission layer is poorly-graded gravel and the control layer is well-graded sand.
16. The method of claim 12 , further comprising the step of directing water within the device towards a toe drain disposed at an end of the device opposite the vent.
17. A device for directing movement in a body of water of a plurality of NAPL-entraining gas bubbles released from a NAPL-contaminated sediment disposed in the body of water to an accumulation zone, comprising:
a control layer disposed in the body of water above the NAPL-contaminated sediment, the control layer having an upward slope to direct the NAPL-entraining gas bubbles, and near one end the control layer defining a vent in fluid communication with the accumulation zone to direct the NAPL-entraining bubbles towards the accumulation zone; and
a transmission layer disposed in the body of water and interposed between the control layer and the NAPL-contaminated sediment, the transmission layer being more permeable than the control layer.
18. The device of claim 17 , wherein the control layer has a slope of at least 1/10.
19. The device of claim 17 , wherein the transmission layer and the control layer have a permeability contrast of at least 100:1.
20. The device of claim 17 , wherein the transmission layer defines a toe drain disposed at an end of the control layer opposite the vent.