The purpose of this Advisory Opinion is to raise awareness of x-ray fluorescence (XRF) technology and its application in the Northeast.(1) This Advisory Opinion is intended to communicate Technology Review Committee (TRC) interest in the use of XRF technology to potential users of hazardous waste site characterization technology, such as consultants, as well as to project managers within the various state site cleanup programs. The Advisory Opinion is also intended to educate consultants and the state regulators who oversee projects about the factors that can affect the proper use of XRF technology.
All seven of the Northeast states participated in the development of this Advisory Opinion consensus statement. In addition, the technical information was reviewed by U.S. EPA Region I and a vendor of XRF technology. However, it should be noted that this Advisory Opinion is not intended to be an "approval" of this technology. The appropriateness of the use of XRF technology will need to be determined on a site-by-site basis. Potential users should contact officials in the state in which the project is located to determine if there are any state-specific requirements that could apply.
Regulatory and institutional barriers to the adoption of innovative hazardous waste site assessment technologies can result in increased expenditures to evaluate and remediate contaminated sites. Because innovative technologies have the potential to clean up and protect the environment and the public's health in a more cost-effective and efficient manner, finding ways to encourage their increased use is crucial.
Recognizing the need to overcome barriers to the acceptance of technology innovation, the six New England States, EPA Region I - New England, the Northeast Waste Management Officials' Association (NEWMOA) and the New England Governors' Conference signed a Memorandum of Agreement (MOA) in March 1998 to promote interstate regulatory cooperation for waste site assessment and cleanup technologies. Subsequently, NEWMOA has worked closely with EPA Region I and the Northeast Hazardous Substances Research Center (NHSRC) to increase the understanding of the factors that discourage the use of innovative technologies. NEWMOA held meetings and conference calls with NEWMOA's Waste Site Cleanup Workgroup and co-sponsored, with NHSRC, a Stakeholders Workshop held in May 1998 called "Increasing the Use of Innovative Technologies on Small Hazardous Waste and Petroleum Sites." The focus of this Workshop was on building consensus among the stakeholders regarding measures to reduce or eliminate obstacles to the use of innovative site assessment technologies.
At the May 1998 Stakeholder Workshop, participants identified the lack of an interstate forum in the Northeast to actively review technologies and communicate both public and private sector use of innovative technologies as a major impediment to the overall marketability of the newer field analytical, characterization and monitoring technologies. To address this need, NEWMOA has established the TRC, made up of one or more staff members from each of the Northeast states to coordinate state review, issue advisory opinions and disseminate information on the use of innovative technologies.
Overview of Technology:
XRF is a non-destructive analytical technique used to determine the metals composition of environmental samples, primarily soils. XRF can also be used to determine the metals concentration in water or air by filtering a known quantity and then using XRF to analyze the dried filter medium. The primary advantage of XRF analysis over laboratory analysis is that analytical results can be generated in real-time allowing decision-making in the field regarding the need for additional sampling or further remediation (provided that proper data validation procedures are followed). The time required for analysis depends upon the element(s) targeted; the concentration of a single element is typically determined in 30 seconds or less, and the analysis of several elements usually requires 2-5 minutes. Another advantage of XRF analysis over standard laboratory analysis is that the procedure does not involve altering the soil sample (other than mixing and possibly grinding) so no investigation derived wastes are generated as they are when extraction with solvent or acid is performed. Because the sample is not destroyed by the analysis, the same sample that was analyzed in the field can be sent to the laboratory for confirmatory analysis.
XRF analyzers emit X-rays that irradiate the sample and excite the electrons of the element(s) present. As these excited electrons return to their normal state they give off energy that is detected by the XRF equipment and the pattern is analyzed to determine the element. Generally, XRF technology can detect elements with an atomic number of 16 (sulfur) through 94 (plutonium). Different XRF analyzers use different elements to generate x-rays, with some using iron-55, cobalt-57, cadmium-109, or americium-241. The metals that can be detected by a particular XRF analyzer depend upon the element used to generate the x-rays:
Field XRF analyzers are generally relatively lightweight hand held instruments that gather data. After data collection, the analyzer is connected to a computer for data analysis and storage. XRF units utilize sophisticated software for internal calibration, to account for the natural decay of the radioactive x-ray source over time, and to analyze the data input from the probe. The software is all menu driven and can output the data in several formats so the user does not need to manipulate the data. Generally field XRF units utilize solid state detectors of lithium drifted silicon (Si(Li)), mercuric iodide or silicon pin-diode, with Si(Li) detectors the most precise. However, instruments that have a Si(Li) detector require liquid nitrogen to cool the detector, which can add time and expense to a project because of the need to: locate a source of the liquid nitrogen near the site; purchase the liquid nitrogen each day; and fill the internal dewar of the instrument and allowing the Si(Li) detector to cool down prior to analysis.
Some field XRF analyzers can be placed directly on the soil surface for in situ measurements. The analyzer measures the metal content of the sample over a surface area of approximately one square centimeter (1 cm2) area to a depth of approximately 2 millimeters (2 mm). Other field XRF analyzers require that soil samples are collected and placed in a sample cup that is then placed in a covered sample chamber for analysis. Most field XRFs can perform both in situ and ex situ analysis. In situ analysis provides qualitative data. Ex situ analysis can provide semi-quantitative or quantitative data depending upon the amount of soil preparation and the calibration standards used. Due to the inherent heterogeneity of soil, ex situ analysis is the preferred method because the soil can be homogenized to provide a sample that is more representative of the location from which it was collected. Average sample throughput for ex situ analysis generally varies from 50 to 100 samples per day, depending on the number of analytes, the particular analyzer used and the amount of soil preparation performed. In situ analysis allows a greater number of analyses at a given site because little or no sample preparation is performed.
Several different XRF analyzers have been evaluated in the EPA's Environmental Technology Verification (ETV) Program. The Technology Verification Statements for the evaluated XRF analyzers as well as more information about the ETV Program itself can be obtained at http://www.epa.gov/etv or by calling U.S. EPA Region I at (617) 575-CEIT. XRF technology has been used for site characterization or cleanup monitoring at over 35 Superfund sites, including several Department of Defense (DOD) and Department of Energy (DOE) facilities.(2) U.S. EPA Region I has used XRF technology at several sites in New England and published Standard Operating Procedure for Elemental Analysis Using the X-MET 920 Field X-Ray Fluorescence Analyzer in October 1996. The guidelines can be obtained at http://www.epa.gov/ region01/measure/xray/xrayfluor.html or by calling (617) 575-CEIT. In addition, several Northeast states have successfully used XRF technology during site characterization and/or remediation, including Massachusetts, New Hampshire, New York and Vermont.
The TRC has determined that, if used properly, XRF technology
can provide useful data that should improve site characterization and/or
cleanup verification. Potential users of XRF technology are strongly urged
to consult U.S. EPA Region I's Standard Operating Procedure for Elemental
Analysis Using the X-MET 920 Field X-Ray Fluorescence Analyzer (October
1996) and technology vendors prior to planning the field effort.
Although the EPA Region I document was developed for the specific make
of analyzer they owned at the time,(3) much
of the information in it is relevant to XRF in general. The project
planning methodology outlined in Figure 1 of the document is attached to
this Advisory Opinion. The intended use of the data and data quality
objectives (DQOs) must be determined prior to the field event and agreed
to by the appropriate regulatory authority. The TRC recommends the following
items to improve or insure product performance; however, users should recognize
that a particular XRF analyzer might have additional requirements:
The NEWMOA Technology Review Committee has issued this Advisory Opinion
on this 21st day of September 1999.
For More Information Please Contact:
|In New Hampshire:
|In New York:
|In Rhode Island:
|At EPA Region I:
1. In this document, the Northeast states are: Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island and Vermont.
2. U.S. EPA, Field Analytical and Site Characterization Technologies, Summary of Applications, EPA-542-R-97-011, November 1997.
3. Note: U.S. EPA Region I has subsequently purchased additional XRF analyzers from other manufacturers.
4. QA/QC requirements for qualitative data are less extensive and should be agreed upon with regulatory authorities prior to the field event. In some instances, less rigorous QA/QC might be accepted by regulatory authorities for semi-quantitative data.