Hydraulic and earth engineering – Soil remediation – In situ contaminant removal or stabilization
Reexamination Certificate
2000-05-08
2001-07-03
Will, Thomas B. (Department: 3673)
Hydraulic and earth engineering
Soil remediation
In situ contaminant removal or stabilization
C405S052000, C405S128100, C166S267000, C210S747300
Reexamination Certificate
active
06254310
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 sparging method and apparatus for removing volatile organic compounds (VOCs) from groundwater.
Contamination of the phreatic zone, also known as the 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. 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 then returned to the phreatic zone. These “pump-and-treat”, or above-ground, methods are extremely expensive. On the other hand, known in situ water treatment devices may employ air lift pumping as a means of producing gas bubbles to remove VOCs. The theory 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, known in situ water treatment devices may not result in rapid vapor saturation which results in a slow and inefficient process. Vapor saturation occurs when the rising bubbles become saturated with VOC vapor. Therefore, there is a need for the development of an improved in situ gas sparging remediation method for removing contaminants in an 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 gas sparging than recently developed in situ remediation methods. The present invention is an in-well air stripping and adsorption technique designed to provide inexpensive, efficient gas sparging. The injected gas may be air or any specific or combination of gases such as carbon monoxide. In addition, the injected gas may be at any temperature.
SUMMARY OF THE INVENTION
Preferred embodiments of the present invention provide an inexpensive and more efficient method and system for removing VOCs from contaminated groundwater. One preferred embodiment of the present invention injects a gas into the lower extent of a well to force groundwater up the well causing VOCs to be transferred to rising gas bubbles inside the well. The efficiency of the air stripping may be increased by placing packers, filters, and/or packing balls into the well. 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 concentration of VOCs in the water is gradually reduced.
It is preferred that the gas is supplied to the lower extent of the well by an air pump which is in fluid communication with a tube positioned within a conduit, where the tube has an opening at its lower extent.
It is preferred that the separated gas bubbles and the captured air be stored upon being released from the conduit. It is also preferred to remove the contaminants from the gas bubbles and captured air prior to returning the gas to the gas supply or discharging the gas to the atmosphere.
The system for removing VOCs from contaminated groundwater may be comprised of a means for supplying gas to the lower extent of a well which induces a flow of groundwater and gas bubbles up the well. The system may contain a conduit within the well which extends below the water table. The conduit may have a lower fluid-permeable section which is located below the water table and an upper fluid-permeable section which is adjacent to the water table. The present invention may be further comprised of an internal pipe or eductor tube contained in the conduit which extends from about the top extent of the conduit to the saturation zone. Packers, filters, and/or packing balls may be located between the eductor tube and the means for supplying gas to the lower extent of the well. The present invention may also include means located at about the top of the conduit for separating the gas bubbles from the groundwater.
The system for removing VOCs from contaminated groundwater preferably includes packing, filters, and/or packing balls on the interior of the eductor tube to increase the surface area for stripping. The stripping efficiency of VOCs depends on the air-to-water ratio.
It is preferred that the system of the present invention includes a gas supplying means which has a tube contained within the eductor tube which extends from above the ground surface to below the water table. The gas supplying means also preferably includes a pump to supply gas to the tube.
In addition, it is preferred that the system of the present invention includes a bentonite seal located between the conduit and well wall to separate the treated water from the untreated water.
It is further preferred that the system of the present invention include means for capturing the gas bubbles which have been separated from the groundwater.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following descriptions of the drawings and preferred embodiments.
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ARCADIS Geraghty & Miller, Inc.
Pechhold Alexandra K.
Standley & Gilcrest LLP
Will Thomas B.
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