X-ray Fluorescence (XRF)
Subsurface contaminant plumes are usually characterized using a drilling rig to install monitoring wells. Soil and groundwater samples are collected and sent to a laboratory for analysis. This traditional approach is slow and costly. In its most common use, an X-ray Fluorescence (XRF) sensor is employed with a cone penetrometer for real-time, in-situ field screening of heavy metals in soils. The XRF sensor system uses an x-ray source located in the probe to bombard the soil sample with x-rays. The bombardment excites various atoms and induces them to emit fluorescence that is correlated to specific metals.
The Department of Energy (DOE) has also demonstrated a handheld battery-operated XRF to detect lead in paint. It performs in-situ real-time analyses to identify and quantify lead, chromium, cadmium, and other metals in lead-based paint. The analyzer can test for antimony, barium, cadmium, indium, iodine, palladium, silver, tin, arsenic, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel, rubidium, selenium, strontium, titanium, zinc, and zirconium.
At the Idaho National Laboratory (INL), XRF was also used to detect the possible presence of polychlorinated biphenyls (PCBs) in various media (soil, paint, personal protective equipment, liquid, and oils) by measuring the total chlorine concentration.
Paint and soil samples are placed in a stainless steel cup and ground into a powder and mixed thoroughly. With a binding agent the powder is placed in a press to form a pellet. The sample analysis can be completed the same day the samples are collected. The XRF measures the concentration of total chlorine in a sample. The user can determine that PCBs are not present if chlorine is not found in the sample, since chlorine is an elemental component of PCB.
Limitations and Concerns
XRF is a field screening method that does not eliminate the need for traditional laboratory analyses. As the technology is now applied, random samples are taken to the laboratory to recalibrate the XRF sensor and confirm that the results are accurate.
XRF may have difficulty detecting small concentrations. For example, while field XRF cannot generally provide the low detection limits attained by laboratory methods, it can often provide detection limits well below regulatory levels. For example, field XRF can easily provide detection limits for lead-in-soil of less than 100 ppm, well below typical regulatory levels of 300 to 1500 ppm.
The Site Characterization and Analysis Penetrometer System (SCAPS) XRF is limited to the depth of the cone penetrometer system used to push an instrumented probe into the ground. This is usually about 100 feet.
Handheld analyzers use two radioactive sources: Americium-241 and Cadmium-109. The unit can be carried, shipped, and transported without exterior labeling, conforming to 49 Code of Federal Regulations (CFR) 173.421. The analyzer should be controlled and accounted for at all times. Also, the Cadmium-109 source must be replaced every three years.
The XRF sensor can only detect the possibility of PCB contamination. It detects chlorine, but it cannot differentiate between the two chlorine species. Therefore, if chlorine is found further tests must be conducted to determine if the chlorinated compounds are PCBs.
Some states require that the user of an XRF device wear a dosimeter to measure his/her radiation exposure.
XRF technology analyzes metal and PCB contamination in soil and on building surfaces.
Technology Development Status
XRF technology is commercially available.
Other Resources and Demonstrations
See http://www.clu-in.org/programs/21m2/navytools/rsc/ for a description of rapid sediment screening tools, including XRF.
See http://www.osti.gov/bridge/servlets/purl/116667-H6tl01/webviewable/ for a demonstration INEEL of a Lead Paint Analyzer for a decommissioning project.