Note: Descriptions are shown in the official language in which they were submitted.
W O 95/07773 2 1 7 I 8 3 ~ PCT~NL94/00225
Method and device for detecting soil pollution or cleaning up polluted
soil in situ, respectively.
The present invention relates to a method for detecting soil
pollution or cleaning up polluted soil in situ, respectively.
The detection of soil pollution by taking samples of soil
material and analyzing these samples elsewhere is generally known. Taking
such a sample is very time-consuming, since, for this purpose, a tube is
driven into the ground vertically or at an angle and then pulled out of
the ground again together with the soil material to be analyzed. Such
taking of samples is considerably impeded by buildings, cables, sewer
systems and the like. If, subsequently, soil pollution is observed upon
chemical analysis, the polluted soil often has to be excavated and taken
to a purifying installation for purification. The purified soil material
can then be put back or new, clean soil material is put back. Cleaning up5 polluted soil in this way is very costly.
The aim of the present invention is to provide a method for
detecting soil pollution or cleaning up polluted soil in situ,
respectively, which, inter alia, does not have these drawbacks.
A further object of the invention is to provide a method to0 prevent environmental pollution at a chemical installation.
This object is achieved according to the invention, in that
- polluted (soil) air is extracted via one or more air drainage
lines, which are located in the soil above the groundwater
level, and/or
25 - polluted liquid is extracted via one or more further liquid
drainage lines, which are located in the soil below the ground-
water level,
from the polluted soil, and the air and/or liquid thus extracted is
analyzed or decontaminated, respectively.
By means of such drainage lines which are preferably
permanently provided in the soil, air and/or liquid can be extracted from
the soil and subsequently analyzed. Moreover, the air and/or liquid
extracted can also be decontaminated so that the polluted soil can be
cleaned up in situ without being excavated and purified elsewhere. If
samples are taken and analyzed with sufficiently great freguency via the
air and/or liquid drainage lines, pollution of the soil is detected in
good time so that it can be cleaned up quickly via the drainage lines
before said pollution has been able to spread far out into the soil.
-
W 095/U7773 ~83~ ~ ~ PCT~L94/00225 ~
The method according to the invention may be used at locations
where environmentally damaging substances (such as, fo,r example,
solvents, mineral oils, volatile hydrocarbons or mixtures thereof) can
penetrate into the soil, and contamination of the soil and/or the
groundwater and/or the soil air may occur. The method according to the
invention lends itself particularly to fuel sales outlets (filling
stations), transfer stations, storage depots and other locations where
there is an increased risk of soil pollution as a result of aboveground
and underground activities, such as, inter alia, at chemical production
sites, bus garages, car repair premises, etc.
At a large number of fuel sales outlets the ground is polluted
as a result of leakages from the installations or as a result of spills,
for example, during filling. A great number of measures are currently
taken against this. However, despite these measures, such as the cathodic
protection of the tanks, overfill safety devices, liquid-tight containers
around filling outlets, and liquid-tight surfacing around the so-called
pump islands, etc., it cannot be ruled out that further instances of
pollution will arise. On the one hand, this may occur as a result of
accidents and, on the other hand, also because the efficiency and the
service life of the materials used for the measures are not totally
known. With the method according to the invention it is possible, for
example in the case of such fuel sales outlets, to extract air and/or
liquid from the soil at regular intervals, to analyze this air and/or
liquid for pollution, and, if pollution is observed, to clean up the
polluted soil directly, if appropriate, by removing polluted air and/or
liquid from the soil and decontaminating it. The spread of soil pollution
can in this way be prevented at an early stage. To purify the air and/or
liquid extracted from the soil, use may be made, for example, of a device
as described in EP-B1-0,385,555.
The method according to the invention may also be used to
continuously extract air and/or liquid from the soil and to purify it
without pollution having first being observed. The detection and
cleaning-up can thus take place simultaneously or interdependently and
also independently of each other.
According to an advantageous embodiment, the air and/or liquid
drainage lines extend principally horizontally. In this manner, a large
area can be covered with one drainage line.
It is also advantageous according to the invention if a number
of air and/or liquid drainage lines are arranged in a principally
W O 95/07773 l 71 8 33 ~ . PCT~L9410~225
horizontal plane parallel to one another and with a mutual spacing of
preferably at least 2 to 3 m. In this manner a large a,rea of soil can be
covered efficiently with a number of drainage lines.
To extract air and/or liquid from the soil, a reduced pressure
is advantageously applied in the air and/or liquid drainage lines, for
example a reduced pressure of l to lO kPa and, preferably, from 3 to 6
kPa. At such a reduced pressure, the extraction of air and/or liquid from
the soil is such that the concentrations of any pollutants are not too
small (this is not, for example, conducive to analysis), whilst,
moreover, not too little air and/or liquid is extracted from the soil.
By sucking up air via the air drainage lines, air is also
sucked into the soil from the environment. This environmental air is
beneficial to any bioactivity in the soil. Such bioactivity may have a
favourable influence in combating soil pollution. According to an
advantageous embodiment, the bioactivity of the soil is further
stimulated by introducing biomass and/or nutrients for biomass into the
soil, which can be effected, for example, via the air and/or liquid
drainage lines. During this introduction of biomass and/or nutrients
therefor into the soil, in the latter case the extraction of air and/or
liquid from the soil will be halted temporarily, if required.
Moreover, according to the invention, it is advantageous if the
decontamination installation for decontaminating air and/or liquid
extracted from the soil is also used for treating waste fluids. In this
case, waste fluids includes fluids other than air and/or liquid extracted
from the soil, such as domestic waste water, vapours collected above
ground, fluids originating from production processes, etc.
In a chemical installation, for example a filling station for
fuel, volatile vapours originating at fuel pumps, filling outlets,
venting points, etc. are preferably collected and conveyed to the same
decontamination installation in order to be purified. Such a method
offers a complete concept to prevent environmental pollution. It may be
sufficient to have one decontamination device to purify both polluted air
and/or liquid extracted frtom the soil and to purify volatile vapours
~ c ~ ,~ c~ n~ . r~
collected elsewhere. The ~-1rifica~ion devices described in EP-Bl-385,555
~ 35 and EP-442,157 are very suitable for purifying both gases and liquids and
may be used particularly advantageously according to the invention.
In this context, it is advantageous according to the invention
if the waste water, such as domestic waste water is, furthermore,
collected and supplied to the decontamination device in order to be
W 095/07773 ~ 833 PCTn~L94/00225 ~
decontaminated. This waste water may be released directly into the
environment which, in the case of remote chemical installations which are
often not connected to the sewers, is very favourable in preventing
environmental pollution.
Since, at chemical installations, such as filling stations for
fuel, potentially polluting substances are often spilt, it is furthermore
advantageous according to the invention if the rinse water flowing away
from the chemical installation (such as, for example, that used for
clearing out and removing the spill) and/or rain water, which has taken
up volatile pollutants, is collected and is supplied to said purification
device.
The invention further relates to a method for the construction,
conversion or renovation of a chemical installation, such as a filling
station, in which
15 - a number of drainage lines preferably extending principally
horizontally are provided in the soil under the chemical
installation,
- said drainage lines are provided above and/or under the
groundwater level,
20 - the drainage lines are connected to suction means for the
application of a reduced pressure in the drainage lines, and
- the drainage lines are connected to a treatment device.
The treatment device can, in this case, be a.device for sampling, and/or
analyzing, and/or purifying fluid extracted from the soil.
Using this method, it is possible, on the one hand, to ensure
that existing and future filling stations do not cause further
environmental pollution and, on the other hand, that all soil pollution
present can be cleaned up, whilst a filling station located on this
polluted soil can be or remain in operation. When a filling station is to
be built, less time is lost by thoroughly cleaning up the soil prior to
constructing the filling station. In the case of an existing filling
station, one to be converted or to be renovated, this means that the
filling station will be out of operation for less time.
In this case, it is furthermore advantageous according to the
invention if a portion of the soil is firstly excavated and replaced with
a sandy soil material, and drainage lines are provided in said sandy soil
material. In this case, it is particularly advantageous if a number of
trenches are firstly dug in the soil and replaced by moderately fine to
coarse sand, and drainage lines are provided in said moderately fine to
W0 95/07773 1 718~ PCTA~L94/00225
coarse sand. This is particularly advantageous in the case of clay and/or
loamy soils, since the permeability of such soils is low, which renders
the extraction of air and/or liquid via drainage lines more difficult. A
soil with moderately fine to coarse sand is, however, very suitable for
extracting air and/or liquid from the soil by means of drainage lines.
To further prevent environmental pollution it is, in this case,
advantageous also to provide collector means for collecting vapours
originating from fuel pumps, filling outlets~ venting points, etc. and to
connect said collector means to the decontamination installation.
According to a further advantageous method, collection means
for waste water, such as domestic waste water, are also provided and
connected to the decontamination installation. Preferably, the collection
means are provided in such a manner that they also collect rinse water
and/or rain water.
The invention further relates to the application of an
underground drainage system having:
- air drainage lines located in the soil above the groundwater
level, and/or
- liquid drainage lines located in the soil under the groundwater
level,
for analyzing (soil) air and/or groundwater and optionally cleaning up
polluted (soil) air and/or polluted groundwater.
Finally, the invention also relates to a device for applying
the methods according to the invention.
In the text which now follows, the invention will be further
described on the basis of an illustrative embodiment illustrated in the
attached figure.
The figure shows a service station for filling up cars 6 with
fuel. A number of fuel pumps 5 are placed on liquid-tight surfacing 4.
Under the liquid-tight surfacing 4 and above the groundwater level 3, a
number of parallel air drainage lines 1 are provided in the unsaturated
zone of the soil. Moreover, a number of parallel liquid drainage lines 2
are provided in the soil under the groundwater level 3. The fuel pumps 5
are connected to supply tanks 7 via lines 9. It is advantageous according
to the invention if, along the lines 9, yet further drainage lines (not
shown) are provided. These may, depending on the depth at which the lines
9 lie, be air or liquid drainage lines. At the fuel tanks 7, further air
and fluid drainage lines 1 and 2 are also advantageously provided.
The drainage lines 1 and 2 are connected to a treatment device
W 0 95/07773 2 ~ 3 ~ PCTA~L9~/00225
8 via suction means which can create a reduced pressure in the drainage
lines. This treatment device may comprise sampling means and/or analyzing
means and/or detection means and/or purification means for purifying air
and/or liquid extracted from the soil. When extracting air from the soil,
a forced evaporation of volatile components present in the soil takes
place as a result of the reduced pressure provided in the air drainage
lines. The soil air with the evaporated components is collected in the
air drainage lines and conveyed to the treatment device 8. Here, the soil
air is treated, in the sense that pollutants are detected or analyzed, or
that soil air is sampled for, for example, laboratory analysis, and/or
that the soil air is purified.
For the detection and analyzing means, use may be made of a PID
meter (PID = Photo Ionization Detector), FID meter (FID = Flame
Ionization Detector), the Drager method, activated carbon tubes, air bags
with supplementary GC analysis (GC = Gas Chromatography), the FTIR method
(FTIR = Fourier Transformed Infra Red), etc. For the purification means
use may be made advantageously of a device such as described in
EP-B1-0,385,555. However, it will be obvious that other detection/
analyzing means and purification means are also perfectly usable.
The air and/or liquid drains are provided particularly at those
points where the risk of soil pollution is great. In the case of a fuel
sales outlet, these points are located particularly: under and around the
liquid-tight surfacing; around the storage tanks 7; around the fuel lines
9; and close to the filling points for the storage tanks 7.
In particular, the portion of soil above the groundwater level
(the unsaturated zone) is outstandingly suitable for handling any
pollution since, by extracting soil air from this portion of soil, micro-
organisms present in said portion of soil are stimulated. As a result of
the reduced pressure in the air drainage lines, there will also be a
transfer of oxygen from the ambient air to the portion of soil lying
above the groundwater level. This oxygen is an outstanding source of
oxygen for microorganisms living in this portion of soil. These
microorganisms may then biologically degrade any pollutants to form non-
harmful compounds or less harmful compounds.
Such biostimulation can be enhanced by adding biomass and
nutrients therefor to said portion of soil lying above the groundwater
level. This biomass and these nutrients may optionally be introduced into
the soil via the air drainage lines. The availability for biodegradation
of the pollutant may be enhanced by introducing surface-active
W O 95/07773 1 7~ 8 3~ `~ PCTn~L94/00225
substances, such as detergents. These substances may also enhance the
effectiveness of flushing or leaching of the soil as a result of enhanced
absorption. During this introduction via the drainage lines, the
extraction of fluids from the soil may be halted for a shorter or longer
period, if required.
The air drainage lines and the liquid-tight surfacing are
preferably provided near the fuel pumps in a service station, as
illustrated in the figure. In order to extract soil air from the soil, it
is advantageous if the air drainage lines lie at least approximately 1
metre above the groundwater level, since, in that case, little or no
groundwater is sucked up. The air drainage lines also have to lie
sufficiently deep in the soil so that they are not damaged during laying
of, interalia, the liquid-tight surfacing and other installations on the
ground. The air drainage lines along the underground lines 9 and/or at
the storage tanks 7 preferably lie in the vicinity of these lines 9 and
storage t~nks 7, respectively.
The liquid drainage lines are preferably laid principally
perpendicularly under the air drainage lines, but at a greater depth than
the air drainage lines. Preferably, these liquid drainage lines lie at
least 1 metre under the groundwater level, in a sandy environment.
Depending on, inter alia, the condition of the soil and the
groundwater level, it is possible to provide both air drainage lines and
liquid drainage lines, but it is also conceivable to provide only air
drainage lines or only liquid drainage lines. If, for example, the
groundwater is very high, it will, in practice, be very difficult if not
impossible to provide air drainage lines. In the case of a lower level of
the groundwater, such as from 4 metres under the surface, and in the case
of soils with solid rock, the drainage lines can also be provided
vertically, optionally combined with horizontal drainage lines, in which
case they are suitable for so-called deep-well and/or controlled
drainage. Furthermore, in the case of low groundwater, and thus in the
case of a large unsaturated zone, there can be provided a number of
layers or levels with horizontal air drainage lines. However, liquid
drainage lines at greater depth levels are also conceivable in principle.
The frequency of taking samples from the soil air and/or
groundwater must particularly be adjusted to the spread of the pollution
in the groundwater. A decisive factor in this case is, on the one hand,
the natural flow rate of the groundwater and, on the other hand, the
possibility of using the installed drainage system to draw polluted
W 095/07773 PCTn~L94/00225 ~
3 8
groundwater against the natural direction of flow of the groundwater.
Taking into account a specific time interval between the taking
of samples, analysis and the taking of organizational and logistic
measures, a sampling frequency of preferably twice per year is desirable.
The sampling fre~uency must be such that any pollution of the groundwater
can still be controlled with the aid of the drainage lines so that
drainage lines present in the ground are sufficient for cleaning-up and
no additional measures have to be taken. A soil pollution situation may
serve as an example, where a soil having a water permeability factor (k)
of 30 m/day, a groundwater flow rate (v) of 30 m/year, a pack thickness
(D) of 50 m and an extraction rate (Q) of 353 m3/day (=15m3/hour) and a
pollution spot which has spread in the groundwater to 25 m in the
downstream direction can be controlled with a sampling frequency of twice
per year. In soils in which the flow rate of the groundwater is very high
or very low, the sampling frequency can be adjusted.
Many variarts and extensions are possible with the methods and
device according to the invention. Thus, in the case of a petrol station,
it is conceivable to guide the (domestic) waste water, optionally after
preliminary decontamination, for example, by means of a septic tank, to
the treatment device 8 and to purify it there and to collect vapours
originating from the fuel pumps, filling points, venting points 10, etc.,
to guide them to the treatment device 8 and to purify them there.
When building new chemical installations, the extraction means
for groundwater and soil air may be provided at very limited cost. In
existing chemical installations, the installation costs will be higher,
since aboveground and underground infrastructure has to be removed and
replaced. Removal and replacement of aboveground and underground
infrastructure can be avoided, if desired, by providing the drainage
pipes in the ground under the existing installation in another manner
known per se in the prior art. The drainage pipes may, in this case, be
provided both horizontally and vertically.
A further advantage of the methods and devices according to the
invention is that the time between observation of soil pollution and the
commencement of the clean-up can be kept extremely short (for example, a
few days), and that, during the clean-up, the operation of the chemical
installation can be continued.
By coupling the drainage lines, collector means, collection
means and suction means to, preferably, one purification system, it is
possible to reduce the emission of pollutants considerably. In this
~ W 095/07773 71 8~3 ~ f ~ PCT~L94100225
connection, in the case of a petrol station, it is conceivable for there
to be additional suction of air originating from fuel pumps, filling
points and venting points. Waste water and rain water originating at the
petrol station can also be purified via the same purification system
which further combats environmental pollution. For it was found that rain
water flowing away may be slightly polluted, on the one hand as a result
of the washing-out of the air near to the chemical installation and, on
the other hand, through contact with, for example, oil and petrol
residues at the fuel pumps and at parking spaces.
The various air and water flows are brought to a purification
device (purification installation). This purification installation has to
be able to treat gases (air and soil air) and liquids (such as soil
water, waste water and rain water) simultaneously. For this purpose,
purification installations may be used such as those described in
European Patent EP-o,385,555 and EP-0,442,157. The content of said
European Patents must be regarded as a component of the present patent
application as regards the purification device.
