A PORTABLE SYSTEM FOR ON-SITE DETECTION OF SOIL CONTAMINANTS

Abstract: A portable battery operated apparatus is disclosed for detection of contamination of a solid substance, such as soil. The apparatus measures fluorescence and is adapted to be positioned on the surface of the solid substance during measurement. The apparatus excites fluorescent emission from contaminants within a specific area of the surface by transmission of a pulsed beam of electromagnetic energy towards the surface, an axis of the beam being substantially perpendicular to the surface, and detects the amount of fluorescent emission excited from the surface by the beam pulses. Further, the apparatus calculates a measurement value corresponding to the concentration of contaminant present within the specific area of the surface based on the amounts detected.

Description: A PORTABLE SYSTEM FOR ON-SITE DETECTION OF SOIL CONTAMINANTS FIELD OF THE INVENTION The present invention relates to detection of contaminants in solid substances, such as soil, by measurement of fluorescence and particularly to a method and a portable system for on-site detection of presence of contaminants containing hydrocarbons, such as oil, motor oil, gasoline, tar, diesel, domestic fuel, heavy petroleum products, and other substances containing aromatic compounds, in solid substances by measurement of fluorescence. BACKGROUND OF THE INVENTION Over the last decade contaminated land has become a major environmental issue as the general concern for possible toxicological effects of soil contamination has been steadily increasing. As a result, environmental authorities now issue regulations on permitted maximum threshold values for acceptable concentrations of contaminants based on toxicological considerations and, thus, the requirements of documentation on contaminated sites and the corresponding costs of site investigations are rapidly increasing. Most site investigations are based on chemical analysis of samples from the site performed in a central laboratory since these analysis provides the best known accuracy and precision, and the lowest detection limits and have the best quality documentation associated with them. However, chemical analysis of samples is time consuming and expensive. Typically, an analysis for hydrocarbons costs 125 ECU and several days elapses before analytical results are available. In many situations this is highly impractical. For example when excavating an area, each sub area has to be left for several days before the next step of the working process can be taken, such as start of foundation work, re-establishment of the area with clean soil, removal of an additional amount of contaminated soil, etc. The mobility of contamination in soil is very different for different soil types. Porosity is a major factor in determining the mobility of contamination. Sand, for example, has a high mobility of contamination while a layer of clay may be impossible to pass by contaminants. Typically, however, contamination in soil is distributed in a heterogeneous fashion due to a low mobility of contaminants in many types of soil, especially horizontally. In many cases, this makes it next to impossible to obtain reliable information about the areal extent of the contamination as a large number of samples are needed to properly map the contamination of a given site, e.g. in order not to overlook contamination hot spots. This inhomogeneity is the determining factor for the scale of sampling that is required. As an example of the number of samples needed to map hot spots within a given area, consider a residential area with single-family houses built on lots (700 m 2 excl. the house) on an old landfill site. The fill material is composed mainly of soil and is only one meter thick. Some of the fill material has been contaminated. However, no information as to where specific truckloads may have been placed is available. If it is assumed that the size of a hot spot corresponds to one truckload of fill material (approximately 8 m 3 ) and that the shape of a hot spot is an ellipse (approximately 4 by 2 and l m in depth) and that a square sampling grid is used, 110 sampling locations are needed for each lot to be able to detect a hot spot with more than 90 % probability. The cost of laboratory chemical analysis for one kind of contaminants in a sample is typically around 125 ECU. Thus, there is a need for inexpensive and fast methods of detecting presence of contaminants in a solid substance. From US 4.200.801 a portable apparatus is known for detection of contamination of a surface. The apparatus measures fluorescence and is adapted to measure contamination on surfaces in production areas, particularly in coal conversion work areas, caused by spills, leakage or contact transfer. The surfaces may be surfaces of machinery, plumbing, construction materials, personnel, and clothing. The fluorescence light is discriminated from background light by beam modulation with a l kHz signal and phase sensitive detection. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and a system for inexpensive and fast detection of presence of contaminants containing hydrocarbons in solid substances. It is another object of the invention to provide a portable system for on-site detection of presence of contaminants in solid substances. It is yet another object of the invention to provide a portable system for on-site detection of presence of contaminants in solid substances without use of an extraction liquid. It is still another object of the invention to provide a portable system for on-site detection of presence of contaminants in solid substances in which it is not required to use plastic bags or any other type of container for storage and/or transportation of samples of soil. It is still yet another object of the invention to provide a portable system for on-site detection of presence of contaminants in solid substances by measurement of fluorescence. It is a further object of the invention to provide a portable system that provides immediate information on presence of contaminants in solid substances useful in guiding further and future sampling of an area. It is a still further object of the invention to provide a portable system that provides immediate information on presence of contaminants in solid substances useful in selecting sample locations for samples to be analyzed chemically whereby the number of samples to be analyzed chemically are minimized and the overall accuracy of mapping of contamination on the site is optimized. It is a another object of the invention to provide a method for controlling the amount of soil removed from a contaminated area by immediate on-site detection of presence of contaminants whereby the amount of soil to be removed and to be cleaned can be minimized. It is a another object of the invention to provide a method of controlling cleaning of contaminated soil by immediate detection of presence of contaminants whereby cleaning of contaminated soil is optimized. According to a first aspect of the invention a method is provided for on-site detection of presence of contaminants in solid substances by measurement of fluorescence, comprising the steps of exciting fluorescent emission from contaminants within a specific area of a surface of a solid substance in which pre£' nee of contaminants are to be detected by transmission of a beam of at least one pulse of electromagnetic energy towards the surface, an axis of the beam being substantially perpendicular to the surface, detecting with a fluorescence detector each of the at least one amount of fluorescent emission excited from the surface by the at least one beam pulse, respectively, and calculating a measurement value corresponding to the amount of contaminants present within the specific area of the surface from the at least one amounts detected by the fluorescence detector. According to a second aspect of the invention a portable system is provided for on-site detection of presence of contaminants in solid substances by measurement of fluorescence, comprising a portable apparatus having a housing adapted to be positioned at a surface of a solid substance in which presence of contaminants are to be detected, excitation means positioned in the housing for exciting fluorescent emission from contaminants within a specific area of the surface of solid substance, a fluorescence detector for detection of the fluorescent emission excited by the excitation means, processing means for calculating a measurement value corresponding to the amount of contaminants present within the specific area of the surface of solid substance based on signal values generated by the fluorescence detector in response to fluorescent emission impinging on it and a calibration algorithm, and user interface means for presentation of the measurement value to an operator of the apparatus. An apparatus or system is said to be portable when it can be carried by one person and it can be operated on-site without being connected to a mains line. Preferably, a portable apparatus can operate under a variety of weather conditions. Presence of contaminants are, typically, measured by emitting ultraviolet radiation towards a specific area of the surface of a solid substance for interaction with hydrocarbons in the contaminants. Hydrocarbons emit fluorescence light upon interaction with the ultraviolet light which fluorescence light is detected by a fluorescence detector. The intensity of fluorescence light detected correlates with the amount of hydrocarbons in the specific area of the solid substance that is illuminated by the ultraviolet light and from which fluorescence light is received by the detector. The excitation means may, as mentioned above, be a radiator of electromagnetic radiation, e.g. in the ultraviolet range, such as a light bulb, a laser, such as a pulsed nitrogen laser, an excimer laser, etc, a flash lamp, such as a Xenon flash lamp, etc, etc. Preferably, a flash lamp is used due to the high intensity of ultraviolet radiation provided during a flash period. As the intensity may vary from one flash period to another, it is preferred to transmit a plurality of flash pulses, preferably from 2 to 10 pulses, more preferred from 3 to 8 pulses, even more preferred 5 pulses, during a measurement and calculate a fluorescence measurement value based on measurements performed during each pulse period. As intensity of radiation of the first pulse may vary significantly from intensity of radiation of the following pulses in a series of flash pulses, the measurement from the first pulse may be ignored in the calculation of a measurement value. Preferably, however, calculation of a fluorescence measurement value includes a measurement during the first pulse period. Alternatively, a first detector for detection of the intensity of the emitted ultraviolet radiation may be provided and a compensated fluorescence measurement value may be calculated from a signal value from the first detector to compensate for varying intensity of different pulses of the flash lamp. The apparatus may comprise a second detector for detection of radiation reflected by the surface of a solid substance in which presence of contaminants are to be detected. The reflected radiation contains information on the type of solid substance under measurement and, thus, the background signal from a sample containing no contaminants can be deduced from the signal generated by the second detector. A filter may be inserted between the surface and the second detector in order to enhance information on the type of material, such as soil, etc, constituting the solid substance. The excitation means may further comprise optical means for concentrating the radiated energy into a narrow beam of energy radiated towards the surface of a solid substance. The optical means may comprise a reflecting mirror of a collimating type or a converging type that generates a minimum spot size of the radiated beam at a specific distance from the excitation means. The fluorescence detector may be any detector with adequate sensitivity in the visible light range of the emitted fluorescence energy, such as a photodiode, a photomultiplier tube, etc. The processing means, typically, comprises a CPU and a memory, preferably a semiconductor memory, for storage of data and a program for calculation of concentration values of contamination based on the detector signal values. The fluorescence detector signal value is a known function of the intensity of the light impinging on an active area of the fluorescence detector. The detector, typically, generates an output current signal which is a known function of the intensity of the light impinging on an active area of the detector. This signal is typically allowed to charge a capacitor and the output voltage of the capacitor may be amplified in one or more amplifiers. A peak detector may then capture the peak output voltage from the amplifiers and the peak value may be transferred to an analog to digital converter converting the value into a digital detector signal value that is stored in the memory. This digital value may be displayed to an operator of the system or a concentration value calculated from the digital value using a calibration algorithm and calibration data may be displayed to the operator. The system may be calibrated against reference measurements in any known way, e.g. using multiple linear regression algorithms. Emission of fluorescence light by a specific substance is described by Beer's law, i.e. at low concentrations of the substance: F = K * c, (1) F is the intensity of emitted fluorescence light, K is a constant, and c is the concentration of fluorescent substance. At increased concentrations, the linearity is lost and F will be lower than calculated by (1) . At very high concentrations, quenching may occur causing F to decrease for increasing concentrations. Fluorescence caused by contamination by diesel is linear up to concentrations of 2500 mg/kg and to concentrations of 1000 mg/kg for tar. Typically, the solid substance in which presence of a contaminating fluorescent substance is to be detected is also fluorescent. Thus, even without contamination fluorescence light will be emitted upon excitation. If the intensity of this background fluorescence light is denoted F B , the intensity F of emitted fluorescence light can be calculated by F = K * C + F B (2) It is presently preferred to calibrate the apparatus according to equation (2), i.e. a linear regression algorithm is used. The system may be utilized without a calibration against reference measurements displaying and storing measurement values corresponding to F in equation (2). The apparatus may further comprise a GPS (Ground Positioning System) for recording of the position of the apparatus in global ground coordinates. The ground coordinates of a measurement position may then automatically be stored in the memory together with the corresponding measurement value for documentation of the position of the specific measurement in question. The user interface means may comprise display means, such as a liquid crystal display, a light emitting diodes display, a cathode ray tube display, a flat panel display, etc, for display of messages and measurement values to the operator. The user interface means may further comprise computer interface means for interfacing with an external computer, such as a serial interface, such as a RS 232 C interface, etc/ or an interface to a computer network, such as a local area network, etc. The computer interface means may be wireless, e.g. utilizing optical transmission of data, e.g. infrared serial transmission of data. Further, the computer interface means may be connected to a mobile telephone facilitating wireless communication between an external computer and the system or between an operator of the system and the system. Any commands or data may be communicated to the system through the computer interface means, for example new calibration data relating to a specific contaminant may be down-loaded from an external computer to the system, e.g. using wireless mobile telephone communication, or, measurement data may be transmitted from the system to an external computer that receives and combines data from a plurality of systems operated in a given area. It is an important advantage of a system and a method according to the invention that detection of contaminants are made on-site in a quick and inexpensive way. It is another advantage of a system and a method according to the invention that no chemical sample preparation is needed. It is yet another advantage of the invention that a portable system for on-site detection of presence of contaminants in solid substances is provided. It is still yet another advantage of the invention that the portable system provided for on-site detection of presence of contaminants in solid substances does not use an extraction liquid. It is another advantage of the invention that the portable system for on-site detection of presence of contaminants in solid substances does not require use of plastic bags or any other type of container for storage and/or transportation of samples of soil. It is a further advantage of the invention that the portable system provided provides immediate information on presence of contaminants in solid substances useful in guiding further and future sampling of an area. It is a still further advantage of the invention that the inexpensive, fast and portable method and system provided makes it possible to map presence of contaminants for the purpose of selecting sampling locations for samples to be accurately analyzed in a laboratory whereby the number of samples to be analyzed chemically are minimized and positions of locations of the samples for chemical analysis may be selected to optimize the overall accuracy of the mapping of the contamination of a given area. It is a another advantage of the invention that a method is provided for controlling the amount of soil removed from a contaminated area by immediate on-site detection of presence of contaminants whereby the amount of soil to be removed and to be cleaned can be minimized. It is a another advantage of the invention that a method is provided of controlling cleaning of contaminated soil by immediate detection of presence of contaminants whereby cleaning of contaminated soil is optimized. Having positioned the apparatus at the surface of the sample a single fluorescence measurement is performed in less than 10 seconds, preferably in less than 5 seconds, most preferred in less than 2 seconds. Soil samples are typically collected using a shovel, a hand auger, a hydraulic drill rig or a back hoe. With any of these methods, only a few minutes are needed to collect the sample. Although the accuracy of the method and system provided by the invention is lower than the accuracy of corresponding chemical analysis methods, the overall accuracy of mapping contamination of a given area is improved utilizing the method and system due to the large number of samples that can be measured quickly and inexpensively. Further, the present system and method may be utilized to continuously monitor presence of contaminants in solid substance, e.g. in a soil cleaning process. Further, the method and system according to the invention may be utilized for control of removal, e.g. by excavation, of contaminated soil, e.g. from a building site. Excavation fronts and floor may be analyzed using a system according to the present invention. If results show presence of contamination, excavation must be continued, additional samples collected, etc. If results show no contamination, excavation is terminated and laboratory analysis may be used for documentation purposes in order to fulfil requirements of environmental authorities. The system may further comprise a sample container adapted to receive a sample of solid substance in which presence of contaminants are to be detected. The sample container may have receiving means adapted to operationally engage with the housing of the apparatus. Further, the receiving means may be adapted to position the apparatus at the surface of the sample of solid substance. Further, moving means may be provided for moving the housing of the apparatus into a selected measurement position in which contaminants in a corresponding selected area of the sample of solid substance may be detected. For example, the moving means may be adapted to move the apparatus into a measurement position selected from a set of a plurality of predetermined positions. The moving means may be situated in the sample container or they may be situated in the housing of the apparatus. They may comprise a turn-table construction, e.g. with a number of fixed positions, such as 8, of the turn-table so that the housing of the apparatus may be rotated in relation to the surface of the solid substance to be measured, e.g. between 8 positions with a 45° angular distance between them. A measurement value of a sample may then be generated by doing one measurement for each fixed position of the housing of the apparatus in relation to the surface of the sample and averaging the measurement values into one measurement value for the sample. However, it is presently preferred to provide eight marks with a 45° angular distance between adjacent marks along the circumference of the sample container and one mark on the side of the housing of the apparatus and performing eight measurements by manually positioning the apparatus on the surface of the sample in the sample container with the mark on the housing successively adjacent to each mark on the sample container and making a measurement. As already mentioned, the excitation means may comprise a source of electromagnetic radiation for radiating a beam of electromagnetic energy towards the surface of the solid substance for interaction with the solid substance. Preferably, a centre axis of the excitation beam of electromagnetic radiation is substantially perpendicular to the surface of the solid substance when the apparatus is positioned at the surface so that the illuminated surface area receives maximum area energy density. The fluorescence detector is positioned so that a centre axis of a beam of fluorescence energy emitted from contaminants in the solid substance upon interaction with the excitation beam of electromagnetic energy radiated from the source and impinging on the detector forms an angle with the centre axis of the excitation beam. The detector is positioned at a non¬ zero angle in relation to the centre axis of the excitation beam to avoid disturbance of the detection of fluorescence energy by ultraviolet radiation reflected from the surface of the solid substance. The precise value of the angle is not critical to the operation of the apparatus. Presently, an angle in the range 20° - 80° is preferred, preferably 30° - 60°, most preferred 35° - 55°, presently most preferred approximately 37°. Preferably, an excitation filter is positioned between the source and the surface of the solid substance. As described further below, a filter with a centre wavelength of 254 nm and a FWHM (Full Width Half Maximum) bandwidth of 25 nm is presently preferred when measuring tar and phenanthrene. A detection filter may be positioned between the fluorescence detector and the surface of the solid substance. Different contamination compounds may require insertion of different combinations of excitation filters and detection filters having different centre wavelengths and different bandwidths. For example, one embodiment of the invention comprises a combination of a detection filter with a 450 nm centre wavelength and a FWHM bandwidth of 225 nm with an excitation filter with a centre wavelength of 254 nm and a FWHM bandwidth of 25 nm for detection of Phenanthrene and tar while a combination of a detection filter with 350 nm centre wavelength and a 65 nm FWHM bandwith with an excitation filter with a centre wavelength of 228 nm and a FWHM bandwidth of 25 nm is preferred for detection of naphthalene and diesel. However, it is more preferred to use a combination of a detection filter with a 462 nm centre wavelength and a FWHM bandwidth of 276 nm with an excitation filter with a centre wavelength of 254 nm and a FWHM bandwidth of 25 nm for detection of Phenanthrene and tar while a combination of a detection filter with 330 nm centre wavelength and a 90 nm FWHM bandwith with an excitation filter with a centre wavelength of 228 nm and a FWHM bandwidth of 25 nm is preferred for detection of naphthalene and diesel. The above-mentioned filter combinations provide a low detection limit of the corresponding contaminant in that the detected signal caused by fluorescence is substantially maximized while the background signal level is kept low. A system according to the invention may comprise memory means, such as removable memory means, for storage of data related to the apparatus and to measurements, such as a diskette, a smart card, etc. Data may then be transferred between the system and an external computer by moving the removable memory means between them. The removable memory means may also contain specific programs for calculation of concentrations of specific contamination compounds to be executed by the processing means of the system and may also contain calibration constants. Such programs and data may also be transmitted to or from the apparatus through the computer interface. During operation of the system, a reference designation may be assigned to each position of the apparatus in which a measurement is performed and the reference designation and the measurement value may be stored together in the memory means. In order to facilitate verification of correct operation of the system, it may comprise a set of verification samples, e.g. blocks of PMMA (Poly Methyl Met Acrylate) , each of which contains a known amount of fluorescent substance for veri f ication of the measurement accuracy of the apparatus. An exemplary embodiment of the invention will now be described with reference to the accompanying drawings. Throughout the figures, corresponding items are referenced by identical reference numbers. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a portable apparatus according to the invention, Fig. 2 is a schematic diagram of a portable apparatus according to the invention, Fig. 3 is a cross sectional side view of a preferred embodiment of the invention, Fig. 4 is a cross sectional side view perpendicular to the side view of Fig. 3 of a preferred embodiment of the invention, Fig. 5a is a blocked schematic of the CPU circuit of a and 5b preferred embodiment of the invention, Fig. 6 is a blocked schematic of a peak detector of a preferred embodiment of the invention, Fig. 7 is a blocked schematic of a power circuit of a preferred embodiment of the invention, Fig. 8 is a blocked schematic of a high power circuit of a preferred embodiment of the invention, Fig. 9 is a blocked schematic of a preamplifier of a preferred embodiment of the invention, Fig. 10 is a blocked schematic of the infrared interface of a preferred embodiment of the invention, Fig. 11 is a top view of sample container (upper part) and a cross sectional side view (lower part) of a preferred embodiment of the invention, Fig. 12 is a front plate of a preferred embodiment of the invention, Fig. 13 shows a first image displayed on the display of a preferred embodiment of the invention, Fig. 14 shows the main menu of a preferred embodiment of the invention, Fig. 15 shows the "Data" sub-menu of a preferred embodiment of the invention, Fig. 16 shows the "Inspection" data display of a preferred embodiment of the invention, Fig. 17 shows the "Calibration" sub-menu of a preferred embodiment of the invention, Fig. 18 shows the "Parameter" data display of a preferred embodiment of the invention, Fig. 19 shows the "Communication" sub-menu of a preferred embodiment of the invention, Fig. 20 shows a set of fluorescence spectra for various contamination compounds and a set of preferred transmission characteristics of filters, Fig. 21 shows another set of fluorescence spectra for various contamination compounds and another set of preferred transmission characteristics of filters, Fig. 22 shows a plot of fluorescence signal values as a function of concentration of diesel in soil, and Fig. 23 shows a plot of fluorescence signal values as a function of concentration of diesel in sand. DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 shows a portable apparatus according 10 to the invention in perspective. It is substantially cylinder formed with a diameter of approximately 150 mm and a height of approximately 300 mm. It weighs less than 5 kg. The apparatus 10 is battery operated. The apparatus 10 can be powered for 12 hours and make 1000 measurements before the battery has to be recharged. As will be realized from a review of the details of the structure of the apparatus 10 in Figs. 3 and 4, the apparatus 10 is represented in an idealized fashion in Fig. 2 for ease of illustration. With reference to Fig. 2, a battery 11 supplies electric energy to all of the electronic circuits of the apparatus. A high voltage supply 12, shown in Fig. 8, charges a capacitor C201, C202, C203 to an accurately controlled high voltage of approximately 1000 V. The high voltage has to be accurately controlled as the intensity of light generated by a Xenon flash lamp 14 varies with the value of the high voltage supplied to it. A trigger circuit 13 controlled by the CPU 40, shown in Figs. 5a and 5b, triggers a discharge of the charged capacitor through the Xenon flash lamp 14 whereby a pulse of ultraviolet radiation of a duration of approximately 1 μsec is generated. The CPU 40 controls the trigger circuit 13 to generate an approximately 10 Hz pulse train of five trigger pulses. The Xenon flash lamp 14 emits a high intensity excitation beam 16 of ultraviolet radiation during capacitor discharge. The flash lamp 14 is equipped with a built-in reflecting mirror 15 of the collimating type which increases the intensity of the emitted beam compared to beams emitted by lamps without a mirror. As shown in Fig. 2, the beam 16 comprises the collimated beam formed by the mirror 15 and a diverging beam generated by the lamp in the direction of the surface 20 of soil in which presence of contamination is to be detected. The beam 16 is transmitted through an excitation filter 18, e.g. of a centre wavelength of 254 nm and a FWHM (Full Width Half Maximum) bandwidth of 25 nm before hitting the surface 20 of the soil in which presence of contaminants are to be detected. The flash lamp 14 is positioned in the housing of the apparatus so that a centre axis of the beam 16 is substantially perpendicular to the surface 20. Hydrocarbons, if present in the soil, will emit fluorescence upon interaction with the ultraviolet light beam 16. The part of the fluorescence radiation 22 that is emitted at an angle of substantially 37° relative to the centre axis of the ultraviolet beam 16 is collected by a first lens 24 and the collected light 26 is transmitted through a detection filter 28, e.g. a 462 n centre wavelength and a 276 nm FWHM bandwidth for detection of Phenanthrene and tar, a 330 nm centre wavelength and a 90 nm FWHM bandwith for detection of naphthalene and diesel, and is then focused on a photo detector 30 by a second lens 32. The photo detector 30 generates a current that is proportional to the intensity of the light impinging on the active sensor area of the detector 30. The output current charges a capacitor C 106 and the output voltage of the capacitor is amplified in a preamplifier 34 and an amplifier 36, shown in Fig. 6, and the peak value of the amplified capacitor voltage is captured by the peak detector 37, shown in Fig. 6, and, finally, the output signal from the peak detector 37 is converted into a digital signal by an A/D converter 38. The digital signal is stored in a semiconductor memory on the CPU board 40 of the apparatus 10. The signal value from a single measurement may be displayed on the LCD display 42 or an average of eight measurements performed by rotating the housing of the apparatus 10 45° between each measurement may be calculated by the processing means on the CPU board 40 and displayed on the display 42. Fig. 3 and Fig. 4 are cross sectional side views of a preferred embodiment of the invention, showing details of the structure of the apparatus. Fig. 5 is a blocked schematic of the CPU circuit of a preferred embodiment of the invention. Fig. 6 is a blocked schematic of a peak detector of a preferred embodiment of the invention. Fig. 7 is a blocked schematic of a power circuit of a preferred embodiment of the invention. Fig. 8 is a blocked schematic of a high power circuit of a preferred embodiment of the invention. Fig. 9 is a blocked schematic of a preamplifier of a preferred embodiment of the invention. It is preferred to perform a measurement on a substantially flat surface. As it is desired to include fluorescence from volatile contaminants in the measurements, the apparatus is further positioned on a recently scraped surface for measurement. The apparatus may be utilized to make measurements at various positions at a site simply by positioning the apparatus on the ground at the desired measurement position and making a measurement. However, it may be preferred to enter, e.g. shovel, a sample into a sample container, such as the sample container 80 shown in Fig. 11 In Fig. 11, a circular sample container 80 is shown having a hollow 82 defined therein for reception of the sample. The depth of the hollow 82 is approximately 1 cm and the diameter of the hollow 82 is a little less than the diameter of the apparatus 10 so that the housing of the apparatus can be positioned on the rim 84 of the sample container 80, which rim surrounds the hollow 82. Two stops 86, 88 are positioned on the rim 84 and preferably, the housing of the apparatus is positioned abutting the two stops 86, 88. When the apparatus is turned around the centre axis, the housing is urged against the stops 86, 88 so that a centre axis of the apparatus 10 remains in a fixed position in relation to the sample container 80. Further, eight marks 90 are provided at the rim 84 with approximately 45° angular distance between adjacent marks along the rim 84. One additional mark is provided on the side of the housing of the apparatus. It is preferred to make eight measurements on each sample by manually positioning the apparatus on the rim 84 of the sample container, the housing abutting the stops 86, 88 and successively turning the mark on the housing into an adjacent position to each mark on the sample container and making a measurement. The eight measurement values are averaged to one measurement value for the sample in the sample container 80 and the standard deviation of the eight measurements is calculated. As shown in Fig. 2, the centre axis of the excitation beam 16 is rotated around the centre axis of the apparatus and thus, 8 different areas of the sample in the sample container 80 is illuminated by the excitation beam 16 when the apparatus is turned between measurements as described above. Thus, the accuracy and repeatability of a sample measurement are improved by making a plurality of measurements on each sample in a well defined repeatable way. Another sample container, such as a tub for bricklaying, may be used when a less compact sample, such as a sample of compost, is to be measured. Before measurement, a sample is entered into the tub and compressed and flattened in the tub. As shown in Fig. 12, the front plate comprises an alfa- nu eric display 42 having four lines 70, 72, 74, 76 of 20 characters each and 10 buttons 44, 46, 48, 50, 52, 54, 56, 58, 60, 62. The apparatus is turned on or off by activating button 44. Upon power on, a first image, shown in Fig. 13, is displayed in which the four lines are divided into three columns 64, 66, 68 whereby 12 display fields are defined at the intersection of the lines and columns. The name of the apparatus "Discover" is displayed in the upper left field. The next field (line 70, column 68) is used to display the state of the apparatus. Four states may be displayed: "Ready", the apparatus is ready for measurement; "Position Full", the maximum of 64 measurements at each position has been reached and thus, a new measurement can not be performed; "Memory Full", the maximum of 1000 measurements has been stored in the memory and thus, a new measurement can not be performed until data have been read out from the memory; "Battery Low", the battery has to be recharged and thus, a new measurement can not be performed. The time of day is displayed in the third field (line 70, column 68) . The second line 72 contains headings "Signal" (line 72, column 68) and "Std" (line 72, column 70) for data displayed in the lines 74, 76 below. The current average and standard deviation of measurements performed at the present position of the apparatus are displayed in line 72. The reference numeral of the position, e.g. "Pos 147", is displayed in the first field (column 64) and the current average value of measurements hitherto performed at the present position is displayed in the second field (column 66) and the current standard deviation of the measurements is displayed in the third field (column 68) . The measurement values of the most recent measurement at the present position of the apparatus is displayed in line 76. The reference numeral of the measurement, e.g. "No. 2", is displayed in the first field (column 64) and the average value of five individual measurements constituting each measurement is displayed in the second field (column 66 ) and the current standard deviation of the individual measurements is displayed in the third field (column 68) . A measurement is made upon activation of the button 46. The measurement number (line 76, column 64) is incremented each time the button 46 is activated. To make an accurate measurement at a specific position, eight measurements are preferably performed at the same position by rotation of the apparatus by substantially 45° between each measurement. The position number (line 74, column 64) is incremented upon activation of the button 48. The average value is stored together with the individual measurement values in the memory. A main menu, shown in Fig. 14, is displayed upon activation of button 50. From the main menu five sub-menus can be selected. The main menu comprises a header "Main Menu" displayed in line 70 and sub-menu headers displayed in lines 72, 74, 76. The three lines are scrolled so that more than three sub-menu headers can be displayed. A sub-menu is selected by moving a cursor 78 to the line displaying the corresponding sub-menu header and activating button 50. The button 54 scrolls the cursor 78 one line up and the button 58 scrolls the cursor 78 one line down in a well known manner. The apparatus leaves the main menu and displays the first image described above upon activation of button 52. From the sub-menu "Data", shown in Fig 15, two functions may be selected designated by the function headers "Inspection" and "Clear" . A function is selected in the same manner as described above for selection of sub-menus. When "Inspection" is selected the second image shown in Fig. 16 is displayed. The four lines of the display are divided into four columns, the first line 70 displaying column headers. The three lines 72, 74, 76 displayed below the first line 70 can be scrolled. The position reference numeral is displayed in the first column, the measurement reference numeral is displayed in the second column, the signal value is displayed is displayed in the third column, and the standard deviation of the five individual measurements constituting a measurement is displayed in the fourth column. The display may be scrolled through all the measurements stored in the memory using the buttons 54, 58 as described above. The apparatus leaves the "Inspection" function and displays the main menu upon activation of button 52. When "Clear" is selected, all measurements stored in the memory are deleted and the next measurement will be stored in position 1, measurement 1. From the sub-menu "Calibration", shown in Fig. 17, two functions may be selected designated by the function headers "Parameters" and "Standard". When "Parameters" is selected, the function header "Parameters" is displayed in line 70 as shown in Fig. 18, ' and the reciprocal value of the constant K in equation (2) is displayed in line 72 preceded by the word "Scale", and the value of the constant F B in equation (2) is displayed in line 74 preceded by the word "Background". Thus, a measurement value c of measured concentration of a fluorescent contaminating substance is calculated from c = K "1 * s - F B (3) s is the amplified fluorescence detector signal converted to a digital value. The displayed numerical values shown in Fig. 18 can be changed by moving the cursor 78 to the corresponding line and activating button 50. Then the 'cursor 78 is moved to the digit to be changed by activation of button 56 (one position to the right) and button 60 (one position to the left) and incrementing or decrementing the digit value by activation of buttons 54, 58, respectively. A new value is entered by activation of the button 50 or, the new value is ignored by activation of the button 52. From the sub-menu "Communication", shown in Fig. 19, two functions may be selected designated by the function headers "Data Transfer" and "Set-up". When "Data Transfer" is selected, a transfer of data from the memory through the computer interface is performed. Data are transferred as ASCII characters so that any computerized apparatus may receive and use the data. When "Set-up" is selected, the function header "Set-up" is displayed in line 70, and the baud rate is displayed in line 72 preceded by the words "Baud Rate", and the data format is displayed in line 74 preceded by the word "Format". The baud rates 1200, 2400, 4800, 9600, and 19200 may be selected. The baud rate value is changed using buttons 54 and 58 to step through the set of baud rates that can be selected. Two formats can be selected: "Column" in which data are separated by tabulators, and "Comma" in which data are separated by commas (spread sheet format) . The year, month, day, hour and minutes may be set when the sub-menu "Clock" has been selected. The sub-menu header "Clock" is displayed in line 70 and the values of the year, month, day, hour and minute are displayed in separate scrolled lines below. Values can be changed as described above. As different types of solid substances emit fluorescence light of different intensities (different F B 's in equation (2) and (3)), it is preferred to determine the background level F B at each site before detection of contamination. Clean samples, preferably at least 5 samples, and more preferred 5 samples, are selected from the site in such a way that local variations of the composition of the solid substance throughout the site are represented by the samples. The samples are then measured utilizing the system in the same way as by measurement of contaminated samples and F B is the calculated average of the measurement values of the selected samples. The standard deviation of the measurement values is also calculated and if it is larger than 10% it is preferred to collect further samples for measurement to determine the cause of the large variations in background signal. Different F B 's may be determined for a specific site, each F B representing a specific type of soil at the site. Preferably, the detection limit of the system is set to be equal to the calculated F B plus two times the calculated standard deviation. Samples with a measurement value larger than the detection limit are perceived contaminated. Fig. 20 shows a set of fluorescence spectra for various contamination compounds and a set of preferred transmission characteristics of filters. Fig. 21 shows another set of fluorescence spectra for various contamination compounds and another set of preferred transmission characteristics of filters. Fig. 22 shows a plot of fluorescence signal values as a function of concentration of diesel in soil. The 228 nm excitation filter and the 330 nm detection filter were used during these measurements. The detection limit is lower than 10 mg/kg (the background signal F B is 11 and the signal from a soil sample with 10 mg/kg diesel is 54) . The calibration curve is linear from 10 mg/kg to 2500 mg/kg. Fig. 23 shows a plot of fluorescence signal values as a function of concentration of diesel in sand. The 228 nm excitation filter and the 330 nm detection filter were used during these measurements. The detection limit is lower than 10 mg/kg (the background signal F B is 8.4 and the signal from a soil sample with 10 mg/kg diesel is 38) . The calibration curve is linear from 10 mg/kg to 1000 mg/kg. Thus, a system has been provided with a detection limit of a contaminant in soil that is lower than 30 mg/kg and lower than 20 mg/kg.

Claims: CLAIMS 1. A portable system for on-site detection of presence of contaminants in solid substances by measurement of fluorescence, comprising a portable apparatus having a housing adapted to be positioned at a surface of a solid substance in which presence of contaminants are to be detected, excitation means positioned in the housing for exciting fluorescent emission from contaminants within a specific area of the surface of solid substance, a fluorescence detector for detection of the fluorescent emission excited by the excitation means, processing means for calculating a measurement value corresponding to the amount of contaminants present within the specific area of the surface of solid substance based on signal values generated by the fluorescence detector in response to fluorescent emission impinging on it and a calibration algorithm, and user interface means for presentation of the measurement value to an operator of the apparatus. 2. A system according to claim 1, comprising a sample container adapted to receive a sample of solid substance in which presence of contaminants are to be detected and having receiving means adapted to operationally engage with the hous .ig of the apparatus and to position the apparatus at the surface of the sample of solid substance. 3. A system according to claim 2, wherein the sample container comprises moving means for moving the housing of the apparatus into a selected measurement position in which contaminants in a corresponding selected area of the sample of solid substance may be detected. 4. A system according to claim 3, wherein the moving means are adapted to move the apparatus into a measurement position selected from a set of a plurality of predetermined positions. 5. A system according to claim 4, wherein the processing means are adapted to calculate a measurement value for the sample of solid substance in the sample container based on measurements from more than one measurement positions of the apparatus. 6. A system according to any of the preceding claims, wherein the excitation means comprises a source of electromagnetic radiation for radiating a beam of electromagnetic energy towards the surface of the solid substance for interaction with the solid substance. 7. A system according to claim 6, wherein a centre axis of the beam of electromagnetic radiation is substantially perpendicular to the surface of the solid substance when the apparatus is positioned at the surface. 8. A system according to any of claims 6 or 7, wherein the fluorescence detector is positioned so that a centre axis of a beam of fluorescence energy emitted from contaminants in the solid substance upon interaction with the beam of electromagnetic energy radiated from the source and impinging on the detector forms an angle with the centre axis of the beam of electromagnetic radiation. 9. A system according to any of claim 6-8, wherein an excitation filter is positioned between the source and the surface of the solid substance. 10. A system according to claim 9, wherein the excitation filter transmits electromagnetic energy in the wavelength range having a centre wavelength of 254 nm and a FWHM bandwidth of 25 nm. 11. A system according to any of the preceding claims, wherein a detection filter is positioned between the fluorescence detector and the surface of the solid substance. 12. A system according to claim 11, wherein the detection filter transmits electromagnetic radiation in the wavelength range having a 330 nm centre wavelength and a FWHM bandwidth of 90 nm. 13. A system according to any of the preceding claims, comprising memory means for storage of data related to the apparatus and to measurements. 14. A system according to claim 13, wherein a reference designation is assigned to a position of the apparatus in which position a measurement is performed and the reference designation and the measurement value is stored in the memory means. 15. A system according to any of the preceding claims, comprising a set of calibration samples each of which contains a known amount of fluorescent substance for calibration of the apparatus. 16. A system according to any of the preceding claims, wherein the detection limit of the apparatus of a contaminant in soil is lower than 30 mg/kg. 17. A method for on-site detection of presence of contaminants in solid substances by measurement of fluorescence, comprising the steps of exciting fluorescent emission from contaminants within a specific area of a surface of a solid substance in which presence of contaminants are to be detected by transmission of a beam of at least one pulse of electromagnetic energy towards the surface, an axis of the beam being substantially perpendicular to the surface, detecting with a fluorescence detector each of the at least one amount of fluorescent emission excited from the surface by the at least one beam pulse, respectively, and calculating a measurement value corresponding to the amount of contaminants present within the specific area of the surface from the at least one amounts detected by the fluorescence detector. 18. A method for on-site detection of presence of contaminants in solid substances by measurement of fluorescence, comprising the steps of entering a sample of solid substance in which presence of contaminants are to be detected into a sample container, flaf'aning the surface of the sample into a substantially flat surface, positioning an apparatus according to any of claims 1-15 on the sample container, and operating the apparatus to determine a measurement value. 19. A method according to claim 18, further comprising the steps of rotating the apparatus an angle around a centre axis of the apparatus substantially without moving the position of the centre axis in relation to the sample container, operating the apparatus to make a measurement, and calculating a new measurement value from the measurement values of the measurements. 20. A method according to claim 19, wherein the angle is approximately 45°. 21. A method according to claim 20, wherein the steps of claim 18 are repeated seven times. 22. A method for controlling the amount of soil removed from a contaminated area, comprising the steps of taking a sample of soil to be removed if contaminated, measuring the amount of contaminating substance in the sample using a method according to any of claims 17-20, and stopping soil removal when a predetermined number of measurements lead to measurement values below a predetermined threshold measurement value whereby the amount of soil to be removed and to be cleaned is minimized. 23. A method of controlling cleaning of contaminated soil, comprising the steps of taking a sample of soil being cleaned, measuring the amount of contaminating substance in the sample using a method according to any of claims 18-21, and stopping soil cleaning when a predetermined number of measurements lead to measurement values below a predetermined threshold measurement value whereby cleaning of contaminated soil is optimized. 24. A method of determining the amount of contamination of an area by laboratory reference chemical analysis by selection of samples of the contaminated solid substance based on fluorescence measurements performed using a method according to any of claims 17-23, whereby the number of samples to be analyzed chemically are minimized.

Inventors: EISUM NIELS HENRIK, LYNGGAARD-JENSEN ANDERS, EISUM, NIELS, HENRIK, LYNGGAARD-JENSEN, ANDERS
Applicants: EISUM NIELS HENRIK, LYNGGAARD JENSEN ANDERS, SOIL SCAN A S, EISUM, NIELS, HENRIK, LYNGGAARD-JENSEN, ANDERS, SOIL-SCAN A/S
Application year: 1997
Main classification: G01N21
IPC codes: G01N21