2181 MH Hillegom
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Fluorescence Detector Module (FFD)
All compounds exhibit adsorption (UV or visible), but only few fluoresce. The ones that do fluoresce mostly contain aromatic rings. Nearly all fuel compounds, such as BTEX, Naphthalene, Anthracene, Pyrene do fluoresce when excited by an ultraviolet (UV) light source; chlorinated solvents do not fluoresce in UV or visible range.
The Fuel Fluorescence Detector (FFD) a scientific instrument used to detect the fluorescence produced by aromatic hydrocarbons when excited by an ultraviolet (UV) light source. It is therefore an excellent instrument for detecting and delineating the extent of hydrocarbon fuel spills or leaking storage tanks. Typical contaminants detected by the FFD are jet fuel, diesel, unleaded gasoline, home heating and motor oil. Total petroleum hydrocarbon (TPH) values as low as 100 ppm can be detected in sandy soils.
The FFD contains an ultraviolet light source that excites aromatic hydrocarbons present. These hydrocarbons fluoresce, what is picked up by the FFD, amplified electronically, and fed to the GeoLogger and subsequently recorded on a computer.
Fuel Fluorescence Detector
The Fuel Fluorescence Detector features a dual photomultiplier system (PMT) that eliminates signal attenuation, allowing weakly fluorescent compounds to be detected at any depth below ground surface. Dual PMTs are tuned such, that differentiation between lighter fuels, which fluoresce more intensely at short wavelengths, and heavier fuels, which fluoresce more intensely at longer wavelengths can be made.
The Fuel Fluorescence Detector can either be equipped with a dummy tip or mounted on top of an electric CPT cone or piezocone. Due its high strength and small diameter (44 mm) the FFD is capable of penetrating soils up to greater depths with relative ease.
The FFD can, in the configuration with a (piezo-)cone, also collect CPT(U) data, such as cone tip resistance (qc), lateral sleeve friction (fs) and in-situ pore pressure (p) needed to produce soil profiles and pile designs simultaneously in one operation. As the FFD survey begins, the FFD module and, if mounted, the CPT(U) electric (piezo-)cone is pushed into the ground by means of a CPT penetrometer rig. This results in rapid site characterization and saves the time and cost of running two operations.
Recording FFD and CPT data in a single push contributes to highly accurate site information and project efficiency. A complete, real time continuous profile is created from ground surface to depth of penetration, identifying all important layers. Multiple FFD profiles across a site can be combined to develop a three-dimensional model of the plume.
The FFD and (piezo-)cone share the same CPT sounding cable for data transmission to the surface and fit directly on the GeoLogger data acquisition unit. The GeoExplorer data acquisition software fully supports the FFD and produces FFD test results graphed against depth in an Excel-format for further processing.
Possibilities and Advantages
The FFD provides a continuous, real-time output of fluorescence over the entire depth of the investigation. This information can be viewed graphically in real-time with the GeoLogger data acquisition system as the FFD probe is advanced. This provides a much more complete and easily interpreted view of the plume than traditional discrete sampling methods.
The Fuel Fluorescence Detector has some major advantages over other systems for hydrocarbon pollution modelling and site characterization, i.e.:
- In situ tests are done without pre-drilling or any other preparation
- Employees are not exposed to contaminants, adding to site safety
- It obtains both geotechnical and FFD field data simultaneously in one single push. It significantly reduces time required to delineate petroleum hydrocarbon contamination and provide detailed geotechnical information on the probed soil
- No (drilling or sampling) waste is generated, reducing considerably the cost of containerization and disposal of hazardous waste
- Soil sampling is still to be used to develop site specific calibrations, but far fewer physical samples are to be collected. This cuts down the costs associated with sample collection, preparation, handling and analysis.
- The continuity of the data reduces the time and effort required for data interpretation and presentation
- Immediate savings from reducing the number of field days required to complete the job
- Multiple FFD profiles across a site can be used to develop a three-dimensional model of the contamination plume
- Dual Photomultiplier Tubes (PMT) - Placing the PMTs downhole eliminates signal attenuation, allowing weakly fluorescent compounds to be detected at any depth below ground surface. Dual PMTs are tuned to different wavelengths providing the ability to differentiate between light and heavy contaminants
- Sapphire Window
- FFD uses standard CPT cable (special fibre optics not required)
- FFD can be pushed with standard 36 mm CPT sounding tubes