United States Environmental Monitoring November 1990 Environmental Protection Systems Laboratory Agency P.O. Box 93478 ^ V^as NV 89193-3478 OFFICE OF RESEARCH AND DEVELOPMENT TECHNOLOGY SUPPORT PROJECT &EPA Field Screening Methods for Radioactive INTRODUCTION The complexity of hazardous waste sites presents a challenge to field scientists and decision makers in the remediation process. There is growing concern in the technical and secular com- munities about the likelihood of radioactive contaminants at sites previously thought to contain only organic or inorganic material. Hazard- ous waste site problems can be described broadly as: • Low level without radioac- tive contamination High level without radioac- tive contamination Low level with low level radioactive contamination Low level with high level radioactive contamination High level with low level radioactive contamination Radioactive contamination only High level with high level radioactive contamination Surveys are recommended for sites that are suspected of containing radioactive waste. This cautionary measure can identify problems early in the site characterization proce- dure and can isolate areas that require special care in the remediation program. Portable instruments are available that will determine the presence of radioactive hot spots in a quick, semi- quantitative manner. These instruments are not isotope specific, but do identify the source as an alpha, beta, or gamma ray emitter. INSTRUMENTATION EPA EMSL- TSP- 1190x Several portable instruments are commercially available that can detect alpha, beta, and gamma radiation. The alpha counter is a separate unit from the beta/gamma counter. Each is battery operated, smaller than a shoebox, and easily man- aged by one field scientist. The beta/gamma counter operates in two modes: with the shield closed, it detects gamma rays; with the shield open, it detects beta plus gamma rays. The amount of beta radiation can be deter- mined by the subtraction of gamma from beta plus gamma. The readings are displayed on an analog meter in millirems/hour or counts/ minute. Another device that is amenable to field survey use is the portable ion chamber. It is a hand-held instrument with charged gas in a cham- ber and is useful for the detection of gamma radiation. A "pancake" detector is often used for quick screening of clothing and flat surfaces. It is sensitive to beta and gamma radiation and gets its name from its flat round shape. ------- Portable radiation survey instruments are calibrated with laboratory sources placed at various distances from the detectors before the site survey. A sampling grid is established following data quality objective goals. Once the instruments are ready and ail health and safety precautions have been addressed by the field team, the survey can begin. A typical approach may consist of two field personnel, one with an alpha counter and the other with a beta/gamma (also known as Geiger) counter. Each sampler would have a log book in which to record the readings at the pre-ordained locations on the grid. Due to the character of gamma radiation, gamma signals will be detected and counted. It is important that the sampler hold the counter just above the ground surface consistently through the study. For screening pur- poses, it is essential that any radiation greater than back- ground level be investigated further to assure a thorough knowledge of the radioactive character of the site. Commercially available detectors are generally reliable, consistent and easy to use. The strong advan- tage of knowing the radioac- tive character of a hazardous waste site is obvious. It allows future characterization and remediation to be performed intelligently and safely. When combined with a carefully planned laboratory confirmation, field screening can be a quick and effective method for assessing the extent and location of radio- active contamination. Liquid scintillation methods, alpha/ beta counting, alpha spec- Advantages • Rapid, real-time results • Low cost (compared with full laboratory analysis) • Easy to use troscopy, and high resolution gamma spectroscopic methods can identify the isotopes and better quantify the radioactivity at the site. Limitations ¦ Inability to probe beneath surface • Doesn't reveal specific isotope identity • Difficulty detecting tritium A low-energy photon detector system (LEPS) is being investigated for use at mixed- waste sites. Using germa- nium diodes with a high sensitivity to gamma-and x- ray energies, this detector can be encased in a water- tight container and used above ground or lowered into a drilled borehole. This technology promises remote sensing of radiation by the employment of rugged, submersible detectors. REFERENCES Field Monitoring Standard Operating Procedures, U.S. EPA Field Monitoring Branch, #003 EMSL-ORS, 1990, 88 pp. Moe, H. J., and E. J. Vallario, Operational Health Physics (particularly Chs. 10-12), ANL publication #88-26, 1988, 930 pp. FOR FURTHER INFORMATION For further details on field screening meth- ods for radioactive contamination, contact: Mr. Terry Grady Nuclear Radiation Division U.S. Environmental Protection Agency Environmental Monitoring Systems Laboratory P.O. Box 93478 Las Vegas, Nevada 89193-3478 (702) 798-2136 FTS 545-2136 For general Technology Support information, contact: Mr. Ken Brown, Manager Technology Support Center U.S. Environmental Protection Agency Environmental Monitoring Systems Laboratory P.O. Box 93478 Las Vegas, NV 89193-3478 (702) 798-2270/734-3207 FTS 545-2270 FAX/FTS 545-2637 The Technology Support Center fact sheet series is developed and written by Clare L. Gerlach, Lockheed Engineering & Sciences Company, Las Vegas. ------- |