Hydraulic and earth engineering – Soil remediation – In situ contaminant removal or stabilization
Reexamination Certificate
2000-05-08
2001-09-04
Suchfield, George (Department: 3672)
Hydraulic and earth engineering
Soil remediation
In situ contaminant removal or stabilization
C210S747300, C210S760000, C405S128500
Reexamination Certificate
active
06283674
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method and apparatus for removing contaminants from groundwater, and, more particularly to an in-situ air stripping, oxidation, and adsorption method for removing volatile organic compounds (VOCs) from groundwater.
Contamination of the phreatic zone, also known as zone of saturation, or, groundwater, with potentially hazardous materials is a common problem facing industry, the government and the general public. The most common type of VOC pollutants are petroleum based products and chlorinated solvents. Frequently, as a result of spills, leakage from storage facilities or surface discharges, contaminants percolate into groundwater, thereby posing a threat to drinking water supplies.
While groundwater is not as susceptible to pollution as surface water, once polluted, its restoration is difficult and long term. Typically, contaminated groundwater is removed from the phreatic zone, treated and discharged or returned to the phreatic zone. These “pump-and-treat”, or above ground, methods, are relatively expensive. There have been some recent developments in insitu water treatment which employ air lift pumping as a means of producing gas bubbles to remove VOCs. The theory of these known methods is that gas is pumped into the wells which causes water and subsequently formed gas bubbles to rise upward. VOCs are transferred from the contaminated water to the gas bubbles which can then be collected for treatment. However, frequently these devices do not result in rapid mass transfer and vapor saturation which results in a slower and less efficient process. Vapor saturation occurs when the rising bubbles become saturated with VOC vapor. Therefore, there is a need for the development of an insitu air stripping, oxidation, and adsorption remediation method for removing contaminants in a relatively inexpensive and more efficient manner.
The present invention involves new concepts for in-well removal of contaminants from the saturation zone. It avoids expensive “above ground ” remediation methods, and provides a more efficient method of mass removal of dissolved contaminants. The present invention combines packing/stripping materials (balls) with air stripping techniques in the well. In addition oxidation and adsorption techniques can also be incorporated to compliment the air stripping effect to achieve higher mass removal efficiencies. The injected gas may be air or any specific or combination of gases such as nitrogen gas. The injected gas can be at any desired temperature.
SUMMARY OF THE INVENTION
Objects of the invention, as will be apparent herein, are accomplished by injecting a gas into the lower extent of a well to force groundwater up the well through air lifting, causing VOCs to be transferred to rising gas bubbles inside the well. The available surface area for contaminant mass transfer within the flow of the mixture of groundwater and gas bubbles is increased by placing packing balls (preferably JAEGER TRIPACK packing material) into the well. This step significantly increases the overall mass transfer efficiency of this device. The gas bubbles, containing VOC vapors are then separated from the groundwater at the upper extent of the well. As this process is repeated and the groundwater continues to circulate, the VOC concentrations in the water are reduced. In addition ozone can be mixed with the injected gas to enhance the mass removal by direct oxidation of the contaminants present.
It is preferable that the air be supplied to the lower extent of the well by operating an air pump which is in fluid communication with a tube positioned in the well in a conduit, where the tube has an opening at its lower extent. Ozone can be added to this line of injection.
It is also preferable that the separated gas bubbles and captured air be stored upon being released from the conduit. It is also preferable that the contaminants be removed from the captured air prior to discharge to the atmosphere.
The system for removing VOCs from contaminated groundwater is comprised of a means for supplying gas and ozone to the lower extent of a well which induces a flow of groundwater and gas bubbles up the well. The system contains a conduit within the well, which extends below the water table The conduit has a lower fluid-permeable section which is located below the water table and an upper fluid-permeable section which is adjacent the water table. The present invention is further comprised of an internal pipe or eductor tube contained in the conduit which extends from the top extent of the conduit to the saturation zone. Packing materials are located between the eductor tube and the means for supplying gas to the lower extent of the well to increase the available surface area for mass transfer. The present invention also contains a means, which is located near the top of the conduit, for separating the gas bubbles from the groundwater.
It is preferable that the system of the present invention contain a gas supplying means which includes a tube contained within the conduit and eductor tube, which extends from above the ground surface to below the water table, a pump which supplies air to the tube and an ozone generator to provide the right amount of ozone.
It is also preferable that the system of the present invention contain a bentonite seal located between said conduit and well wall to separate the treated clean water from the contaminated water.
It is preferable that the system of the present invention contain a means for capturing the gas bubbles which have been separated from the groundwater.
Objects and advantages of the present invention will be readily apparent upon a reading of the following description.
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ARCADIS Geraghty & Miller
Standley & Gilchrest LLP
Suchfield George
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