ISU Environmental Monitoring Program

Department of Physics
School of Arts and Sciences
Idaho State University
Campus Box 8106
Pocatello, Idaho 83209
(208) 282-4308

• Introduction
• Analyses Performed
• Quality Assurancemeasures

1 Introduction

The Health Physics Program at Idaho State University (ISU) operates an Environmental Monitoring Program (EMP) that provides independent radiological monitoring of the Idaho National  Laboratory (INL) by a public institution and educational opportunities for students. Students learn environmental research techniques, analytical skills, and the regulatory aspects of monitoring. Challenges encountered in this program generate hypotheses for graduate research projects.

The EMP has contracted with the State of Idaho INL Oversight Program (OP) to analyze environmental samples and to conduct research and other activities in support of environmental surveillance. The EMP analyses are performed in the ISU Environmental Monitoring Laboratory (EML) located on the ISU campus in Pocatello or, in a few cases, a subcontractor laboratory. The EMP is directed by Thomas F. Gesell. Laboratory activities are coordinated by Roy Dunker. Tom Baccus is a staff member of the EML and serves as the Quality Assurance Officer. The EMP publishes its data in quarterly reports which are provided to the OP. The OP subsequently publishes interpretive reports which are available to interested agencies, organizations and members of the public.

2 Analyses Performed by the EML

Analyses and QA measures in the EML are performed in accordance with written procedures maintained by the EML. Sample collection is performed in accordance with procedures maintained by the OP. The EML procedures are described briefly in the following sections.

2.1 Gross Alpha and Beta Measurement

Two thin-window gas flow proportional counting systems are used to measure the total (gross) alpha and beta radioactivity of air particulate filters and water samples. Calibration for alpha counting is performed using ²⁴¹Am for particulate filters and ²³⁰Th for gross alpha in water determinations. Both standards are traceable to the National Institute of Standards and Technology (NIST). Calibration of the proportional counting systems for beta counting is performed using ¹³⁷Cs sources traceable to NIST.

2.2 Measurement of Gamma-emitting Radionuclides

Gamma detection is accomplished with one of two high resolution, shielded intrinsic germanium detectors that use a single control and analysis system. This multi-tasking system controls and acquires data from both detectors simultaneously and all data are analyzed using the same software system. The software provides background subtraction, efficiency correction, nuclide identification, interference correction, weighted mean activity (including negative values), uncertainty, and minimum detectible activity. The detectors are calibrated in the range from 88 to 1836 keV at 0.25 keV per channel. Media analyzed include charcoal cartridges, airborne particulate filters and water.

2.3 Measurement of Tritium by Liquid Scintillation Counting

Liquid scintillation counting is used to determine the quantity of tritium (³H) present in water. Calibration for tritium counting is accomplished using tritium solutions traceable to NIST. Samples are counted for ten 20-minute periods in a Wallac model 1415 liquid scintillation counter and the average count rate (counts per minute) determined. Count rate is converted to activity concentration through calibration with standards traceable to the National Institute of Standards and Technology (NIST).

2.4 Tritium Enrichment

Hydrologic studies often require knowledge of tritium concentrations below the MDC of approximately 160 pCi/L obtainable with direct liquid scintillation counting of water as described in section 1.3 above. In order to improve the MDC, tritium is concentrated in aqueous samples by electrolysis. Electrolysis can decrease the MDC to less than 25 pCi/L. The enriched distillate is counted using the liquid scintillation counting procedures described in section 2.3. The concentration of the enriched sample is determined using a calibration factor determined from an established calibration curve. At least one standard and one blank are enriched with each group of samples to provide a comparison with the calibration factor.

3 Quality Assurance Measures

3.1 Instrument Checks

Instrument performance checks are made on those days on which a system is to be used. Performance checks are also made after an event which might lead to potential changes in the system and following maintenance and calibration activities. The performance checks consist of both background and check source counts for the proportional and liquid scintillation counters and check source counts and full width at half maximum determinations for the gamma spectrometers. Results of the checks are plotted on control charts.

3.2 Blanks, Split and Recounted Samples

Water samples are split and analyzed and a fraction of the air filters are recounted. The purpose of this effort is to check the overall reproducibility of the analyses. NIST standards or commercial standards traceable to NIST are used to prepare the spiked water samples and the NIST or commercial certificate values for the concentrations of activity in these samples are normally assumed to be correct. Reagent blanks are used to determine if analyses will provide a "zero" result when no activity is expected to be present. Samples are prepared and analyzed as for the spiked sample program but no activity is added.

3.3 External Quality Control

The EML participates in the EPA Cross Check Program. Blind samples are provided by EPA and analyzed by ISU. The ISU analytical results are submitted to EPA before EPA announces the actual concentrations of activities in the samples.

3.4 Chain of Custody and Sample Tracking

Samples collected by staff of the INEEL Oversight Program and the EMP are transferred to the EML. Chain of custody procedures are carefully adhered to during this operation. The chain of custody form includes sample identification, dates and signatures of persons relinquishing and accepting the samples. When analyses are subcontracted to another laboratory, a new chain of custody sheet is completed and sent with the sample. Chain of custody sheets are retained for laboratory records. Samples are tracked in the laboratory using a logbook.