66    SEMIVOLATILES SCREENING AT CERCLA SITES
Roy O. Ball, Principal
Mary Jo Anzia, Project Engineer
Environmental Resources Management
North Central, Inc.
Deerfield, Illinois 60015
INTRODUCTION
The Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA)
and the Superfund Amendments and Reauthorization Act of 1986 (SARA) require the investigation
and subsequent cleanup of hazardous waste sites listed on the National Priorities List (Superfund
sites). The history of Superfund site activities is frequently uncertain. In addition, disposal and/or
discharge records for Superfund sites are often inaccurate and incomplete. Thus, the nature and
extent of contamination is unknown and is usually highly variable over short distances. As a result,
thorough investigations of the soil and ground water at Superfund sites are generally required as part
of the site Remedial Investigation (Rl).
The collection and analysis of investigative soil samples utilizing the Contract Laboratory Program
(CLP) protocol, which is required by the United States Environmental Protection Agency (USEPA)
for Superfund sites, is tedious and expensive. The soil investigation can be accelerated by conducting a
soil screening program to delineate areas of suspected contamination, as well as areas of little or no
contamination. By implementing a screening program, the number of soil samples required for CLP
analyses can be significantly reduced. Generally accepted soil screening methods exist for volatile
organic compounds (HNu headspace technique), metals (plasma AA), PCBs (Clor-N-SoilrM), asbestos containing materials and petroleum hydrocarbons (Total Petroleum Hydrocarbons). However, a
literature review did not identify any generally accepted soil screening tools for semivolatile organic
compounds. This paper presents a discussion of the theory and use of fluorescence as an indicator of
soil contamination due to the presence of fluoresceable semivolatile organic compounds.
THEORY OF FLUORESCENCE
Fluorescence is the process in which radiation is emitted by molecules or atoms that have been
excited by absorption of radiation.1 Energy levels of an atom can be represented by a series of
horizontal lines. The difference in energy between energy levels is represented by the vertical distance
between two lines. If level N represents the ground state, or the state in which the atom is normally
found, by absorption of light of frequency >>r.N, the atom is raised to level F and, if no other energy
levels exist between N and F, can return to N only by reemission of light of the same frequency (i-vn)-
This type of fluorescent emission in which the wavelengths of the emission and absorption lines
coincide is called resonance radiation.2 Several levels (C,D, etc.) can exist between N and F. Under
these conditions, other transitions can occur, which result in the emission of frequencies smaller than
i>FN. The empirical law stating that the wavelength of light emitted by a fluorescent material is longer
(lower energy) than that of the radiation used (to excite the fluorescence was formulated by Stokes3.
Atoms and molecules that fluoresce have well-defined excitation and emission spectra. If an
organic compound is fluorescent, its emission band corresponds to the same electric transition as its
absorption band of the greatest wavelength (i.e., its first absorption band).4 There is an approximate
mirror-image relationship between the shape of the absorption spectrum and the shape of the fluorescence spectrum.5 In general, the fluorescence yield is independent of the wavelength of the exciting
light.6 The quantum efficiency of a molecule is the ratio of the total emitted light to the total absorbed
light. Therefore, the quantum efficiency is also independent of the wavelength of the exciting light. If
the exciting light used is of a wavelength that is different from that of the absorption peak, a smaller
portion of the light will be absorbed and proportionally less light will be emitted-illustrating the
constancy of the quantum efficiency. However, the shape and location of the emission spectrum will
not change.7
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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