GB2389360A

GB2389360A - Removing non aqueous liquids from the ground

Info

Publication number: GB2389360A
Application number: GB0212979A
Authority: GB
Inventors: Robert David Essler
Original assignee: Keller Ltd
Current assignee: Keller Ltd
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2003-12-10
Also published as: GB0212979D0

Abstract

A method of removing a denser than water non aqueous liquid from the ground 1 comprises the step of providing a drainage channel 9, 10, 11 extending from a retention zone 2 of the liquid to a collection zone 8 located below the level of the retention zone. The liquid together with groundwater are then collected in the collection zone. Preferably, a plurality of drainage channels extend from at least one collection zone. Valves may be provided to control the flow of liquid through the drainage channels, the valves typically being opened when all the drainage channels are in place. The method may further comprise the step of pumping the liquid from a level which is located above the level of the retention zone but below the groundwater level in the ground.

Description

i 2389360 REMOVING DENSE CONTAMINANT LIQUIDS FROM GROUND

The present invention relates to a method of removing denser than water non-aqueous phase liquids which are sometimes encountered as contaminants in ground. The present invention further relates to an arrangement for removing denser than water non-aqueous phase liquids from ground.

The denser than water non-aqueous phase liquids which are of particular concern are typically dense organic solvents such as carbon tetrachloride, trichloroethane and the dike. Until recently, carbon tetrachloride was widely used as an industrial solvent and has recently been replaced by trichlorethane. Both need to be removed from ground where they have been spilt. I-n particular, it is necessary to remove them from ground water. Removal of denser than water non-aqueous phase liquids presents a problem because they migrate downwards through ground water until they reach a barrier to their movement. This is most corntnonly a layer of clay in the ground.

In the past, such contaminants have been removed from ground water by sinking a pipe down to the level of the clay and using a pump operated at large volume throughput to flush out the denser than water non aqueous phase liquids in a flow of ground waier induced by the pump. However, the contaminant may be corrosive to pumps or dangerous when brought into contact with other substances or inhaled by operators.

Further, the interface of the clay with the ground water bearing strata may contain irregularities that can hold pools of denser than water non aqueous phase liquid. It is commonly necessary to deal with each pool in succession, which is time consuming.

The present inventors have sought a system for removing these types of contaminants from ground water which is simple and quick to use and safe for equipment and for users. The present inventors have realised that the denser than water non aqueous phase liquids can be collected gravitationally by excavating a collection zone below the level

of the interface between the water bearing strata and the clay, and extending a drainage charnel from the interface to the collection zone. Drainage of the contaminant and ground water will occur automatically without needing a pump. The contaminant will naturally collect below a level of water which will therefore protect the equipment and users from the contaminants.

Accordingly, the present invention provides a method of removing denser than water non aqueous phase liquids from ground, comprising the steps of providing a drainage channel extending from a retention zone of the denser than water non aqueous phase liquids to a collection zone located below the level of the retention zone, thereby collecting water from the ground and denser than water non aqueous phase liquid in the collection zone.

In a particularly preferred embodiment, a plurality of drainage channels are provided extending from the retention zone to at least one collection zone. Preferably, a plurality of drainage channels extend from the or each collection zone, the drainage channels being blocked to prevent a flow of liquid until all of the channels are in place. In this way, pools of denser than water non-aqueous phase liquid retained in irregularities in the surface of the clay can all be collected via a single collection zone. In order to protect operators or equipment used to insert the drainage channels, flow of the liquid is prevented until all drainage channels are in place.

In a further preferred embodiment, a pump is provided for pumping liquid from the collection zone from a level which is above the level of the retention zone but below the level of ground water in the ground.

That is, the intake to the pump will be located at a position above the level of the denser than water non aqueous phase liquid, so that no such liquid will be ingested into the pump. However, it will be located below the level of ground water in the ground.

Pumping starts, once the collection zone has filled up with liquid to the level of ground water in the ground. When the pumping starts, water is drawn out the collection zone, creating a flow of liquid from the ground along the drainage channels into the collection zone. This helps to flush out the contaminant in a particularly effective way. However,

because of its position, the pump is prevented from coming into contact with the contaminant. The collection zone may be constructed by any suitable means. For example, a bore may be sunk from ground level down to the selected level below the retention zone.

The collection zone may comprise a container for collecting denser than water non-

aqueous phase liquid. The collection zone may be specially shaped to collect the denser than water non-aqueous phase liquid at a given point within the removable container.

A removable container may be provided for collecting denser than water non-aqueous phase liquid. Once the container is substantially full, it can be sealed and withdrawn from the collection zone. A replacement container may be then placed in the collection zone. In this way, the contaminant can be sealed off and removed safely.

In a preferred embodiment, the collection zone is created first, drainage channels being subsequently provided extending from the collection zone. The drainage channels may be provided by inserting pipes into the ground. They may be driven into the ground by any suitable apparatus, in a manner well known in the art.

The pipes may be perforated at the end where they will intersect the retention zone, to allow liquid to pass into the pipe. The pipes are suitably formed of metal or plastic material, for example sintered steel. Each pipe is suitably provided with Al v c means for preventing flow of liquid down the pipe.

Means maybe provided at the end of the pipe which is inserted into the ground, for detecting the presence of water. For example, a conductivity measuring means may be provided. Accordingly, it can be determined when the end of pipe reaches the interface between the denser than water nonaqueous phase liquid and water. Once this interface is reached, insertion of the pipe is stopped.

Preferably, pipes are installed in a pattern covering the entire area which is to be treated.

Valve opening means may be provided. Control means may be provided for opening the valves in any selected pipes or all of the pipes. Suitably, the valve opening means

are remotely controllable so that the operator can open the valves without coming into contact with the contaminant.

The collection zone may be filled with water before the valve means are opened, in order to further protect operators from the contaminant.

The present invention further provides an arrangement for removing denser than water non aqueous phase liquid from ground, comprising at least one drainage channel extending from the retention zone of the denser than water non aqueous phase liquid to a collection zone located below the level of the retention zone, whereby a mixture of water from the ground and denser than water non aqueous phase liquid is collected in the collection zone.

The present invention will be described further below by way of example with reference to the accompanying drawings, in which: Figure I is a schematic illustration of the arrangement of a collection zone and drainage channels before commencing collection of the contaminants.

Figure 2 is a schematic illustration of the process of removing the contaminant using the arrangement shown in figure 1.

Figure 1 shows a schematically an area of ground which has been contaminated by a denser than water non-aqueous phase liquid which has collected at the position 2. It rests at the boundary between water permeable strata 3 and impermeable strata 4 typically clay. Also shown in figure 1 is the level 5 of ground water in the water permeable strata 3.

in order to remove the denser than water non aqueous phase liquid 2, a pit 6 is excavated from ground level to a level below the level of the interface 7 between the water permeable strata 3 and the impermeable strata 4. The bottom of the pit 6 defines a collection zone 8. Subsequently, drainage pipes 9, 10 and 11 are driven from the base of the pit G. passing through the impermeable strata 4, and extending through the interface 7 to the level of the denser than water non aqueous phase liquid 2. In practice,

the pipes are driven in sections which fit into the diameter of the pit. As each section is driven through the strata, another section is added at the rear of the previous section so that a continous pipe 9,10 or I 1 is created. The section which intersects the interface 7 is formed of perforated material, for example perforated plastic or sintered steel. The end of the pipe farther comprises valve means (not shown) operable by control signals sent along signal wires 12 from a control unit 13 located at ground level. As shown in figure 1, the valve means are closed and there is no flow of liquid through the pipe 9,10 or 1 1.

The sides of the pit are lined with impermeable material so that no liquid flows into the pit while the pipes are being inserted Once all the pipes 9,l 0 and 11 are in place, the pit 6 is flooded with water to the level of ground water 5 in the ground 1. Then, control signals are sent along the wires 12 from the control 13 to open the valve means. As a result, liquid flows down the pipes 9,10,1 1 and into the pit 6.

The liquid flowing into the pit 6 will comprise mainly ground water but it will also contain a small amount of denser than water non-aqueous phase liquid. The bottom of the pit is shaped as a collection zone 8 so that the denser than water non-aqueous phase liquid is collected in a receptacle which can be removed once it is full.

In order to maintain flow of liquid through the pit 6, a pump 14 is provided for pumping water from a first level 15 which is just above the level of the denser than water non aqueous phase liquid but below the ground water level 5. As a result, a flow of water is created which helps to flush the denser than water non-aqueous phase liquid 2 from the interface 7.

The pipes 9,10 anal 1 are designed so that they intersect the lowest parts of any depressions in the interface between water bearing strata 3 and impermeable strata 4 so that all of the non aqueous phase liquid is removed.

The present invention has been described above by way of example only and modifications can be made within the invention, which extends to equivalents of the features described. The invention also consist in any individual features described or implicit herein or shown or implicit in the drawings or any combinations of any such features or any generalization of any such features or combinations.

Claims

CLAIMS:

1. A method of removing a denser than water non aqueous phase liquid from ground, comprising the step of providing a drainage channel extending from a retention zone of the denser than water non aqueous phase liquid to a collection zone located below the level of the retention zone, whereby ground water and denser than water non aqueous phase liquid are collected in the collection zone.

2. A method according to Claim 1, wherein a plurality of drainage channels are

provided extending from at least one collection zone.

3. A method according to claim 1 or 2, wherein a plurality of drainage channels are provided some or all of which extend from a single collection zone, the drainage channels being provided with valve means for prevent flow of liquid Trough the drainage channel, the valve means being opened when all the drainage channels are in place.

4. A method according to any preceding claim, further comprising the step of pumping liquid from a level which is located above the level of the denser than water non aqueous phase liquid in the ground but below the ground water level in the ground.

5. A method of removing denser than water non aqueous phase liquid from ground, substantially as herein described with reference to the accompanying drawings.