Most water systems are required to monitor for radioactivity and certain radionuclides, and to meet Maximum Contaminant Levels (MCLs) for these contaminants, to comply with the Safe Drinking Water Act (SDWA). Currently, EPA requires drinking water to meet MCLs for beta/photon emitters (includes gamma radiation), alpha particles, combined radium 226/228, and uranium. However, this monitoring is required only at entry points into the system. In addition, after the initial sampling requirements, only one sample is required every 3 to 9 years, depending on the contaminant type and the initial concentrations.

While this is adequate to monitor for long-term protection from overall radioactivity and specific radionuclides in drinking water, it may not be adequate to identify short-term spikes in radioactivity, such as from spills, accidents, or intentional releases. In addition, compliance with the SDWA requires analyzing water samples in a laboratory, which results in a delay in receiving results. In contrast, security monitoring is more effective when results can be obtained quickly in the field. In addition, monitoring for security purposes does not necessarily require that the specific radionuclides causing the contamination be identified. Thus, for security purposes, it may be more appropriate to monitor for non radionuclide-specific radiation using either portable field meters, which can be used as necessary to evaluate grab samples, or on-line systems, which can provide continuous monitoring of a system. This document will focus on field meters and on-line systems that can be used in the field to provide quick, nonspecific measurements of radiation.

Ideally, measuring radioactivity in water assets in the field would involve minimal sampling and sample preparation. However, the physical properties of specific types of radiation combined with the physical properties of water make evaluating radioactivity in water assets in the field somewhat difficult. For example, alpha particles can only travel short distances and they cannot penetrate through most physical objects. Therefore, instruments designed to evaluate alpha emissions must be specially designed to capture emissions at a short distance from the source, and they must not block alpha emissions from entering the detector. Gamma radiation does not have the same types of physical properties, and thus it can be measured using different detectors.

Measuring different types of radiation is further complicated by the relationship between the radiation's intrinsic properties and the medium in which the radiation is being measured. For example, gas-flow proportional counters are typically used to evaluate gross alpha and beta radiation from smooth, solid surfaces, but due to the fact that water is not a smooth surface, and because alpha and beta emissions are relatively short range and can be attenuated within the water, these types of counters are not appropriate for measuring alpha and beta activity in water. An appropriate method for measuring alpha and beta radiation in water is by using a liquid scintillation counter. However, this requires mixing an aliquot of water with a liquid scintillation "cocktail." The liquid scintillation counter is a large, sensitive piece of equipment, so it is not appropriate for field use. Therefore, measurements for alpha and beta radiation from water assets are not typically made in the field.

Unlike the problems associated with measuring alpha and beta activity in water in the field, the properties of gamma radiation allow it to be measured relatively well in water samples in the field. The standard instrumentation used to measure gamma radiation from water samples in the field is a sodium iodide (NaI) scintillator.

This information is summarized in Table 1 below.

Although the devices outlined above are the most commonly used for evaluating total alpha, beta, and gamma radiation, other methods and other devices can be used. In addition, local conditions (i.e., temperature, humidity) or the properties of the specific radionuclides emitting the radiation may make other types of devices or other methods more optimal to achieve the goals of the survey than the devices noted above. Therefore, experts or individual vendors should be consulted to determine the appropriate measurement device for any specific application.

The section above described the different detection methods and equipment available to monitor radiation. An additional factor to consider when developing a program to monitor for radioactive contamination in water assets is whether to take regular grab samples or sample continuously. For example, portable sensors can be used to analyze grab samples at any point in the system, but have the disadvantage that they provide measurements only at one point in time. On the other hand, fixed-location sensors are usually used as part of a continuous, on-line monitoring system. These systems continuously monitor a water asset, and could be outfitted with some type of alarm system that would alert operators if radiation increased above a certain threshold. However, the sampling points are fixed and only certain points in the system can be monitored. In addition, the number of monitoring locations needed to capture the physical and radioactive complexity of a system can be prohibitive.

On-line instruments for monitoring alpha, beta, and gamma radiation in water assets have been developed, although there are a limited number of these currently available. Technical Associates offers the SSS-33-5FT, which is a continuous flow-through scintillation detection system for alpha, beta, and gamma radiation; and the MEDA-5T, which is designed for continuous gamma radiation monitoring. Both are outfitted with alarms that will be triggered if the radiation exceeds a certain threshold. Canberra has developed several on-line radiation monitoring systems, including the OLM-100 On-Line Liquid Monitoring System, which is an on-line monitor attached to a pipe that is designed to continuously measure the quantity of radioactive gamma isotopes in the liquid stream; and the ILM-100, which is a similar system that is installed within the pipe system. Canberra's 4Pi series offers on-line gamma or beta and gamma analysis using a specialized 3- or 4-Pi geometry monitor to enhance the effectiveness of the evaluation, while the LEMS-600 series offers continuous off-line evaluation of beta and gamma radiation. In addition, the Department of Energy (DOE) has tested a prototype on-line real-time alpha radiation detection instrument. Development of this technology was moved to the Los Alamos National Laboratory in 2001. Other applications of small-scale flow-through scintillation technology are being developed for field measurements of alpha, beta, and gamma radiation. In most cases, utilities interested in on-line monitors for radionuclides/radioactivity will need to work with a manufacturer to configure a custom monitor adapted from monitors intended for small-scale applications.

Because of the limited number and high costs of on-line analyzers, they may be of limited use for most facilities. Therefore, the regular analysis of grab samples for alpha, beta, and gamma activity may be more appropriate for many facilities.

In addition to choosing the most appropriate type of equipment for the evaluation to be performed, there are other important factors in choosing the specific type of detector. Among these other important features of individual radiation detectors are their specificity and their sensitivity. These attributes are discussed in more detail below.

Specificity is the ability of an instrument to quantify or evaluate the specific type of radiation or radionuclide for which it is designed without interference from other radiation or radionuclides. Such interference could lead to false conclusions about the nature and extent of potential radioactive contamination.

A general discussion of the sensitivities of the instruments summarized in Table 1 above is provided in Table 2 below. This information is summarized from the MARSSIM.

The Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM, EPA 402-R-97-016, August, 2000), which was developed as a multi-agency document by the Environmental Protection Agency (EPA), the DOE, the Department of Defense, and the Nuclear Regulatory Commission, defines the detection sensitivity of a given radiation measurement system as the radiation level or quantity of radioactive material that can be measured or detected with some estimated level of confidence. MARSSIM continues on to note that an instrument's sensitivity is a factor of both the instrumentation and the technique or procedure being used to measure the radiation. As described above, different types of radiation detection devices are designed for different purposes, and thus their sensitivities and detection limits will be very different and will reflect the purposes for which they were designed. However, a general discussion of the sensitivities of the instruments summarized in Table 1 above is provided in Table 3 below. This information is summarized from MARSSIM.

The sensitivity/detection limit of Canberra's OLM-100 On-line Liquid Monitoring System (which detects gamma radiation) depends on a preset Lower Limit of Detection (LLD) and normal background.

While certain radiation detectors are "maintenance free" in design, specialized expertise is usually needed for installation, setup, and routine calibration of radiation monitoring equipment, whether it is field survey detectors or on-line monitoring equipment.

MARSSIM also provides rough equipment costs for radiation detection equipment summarized in Tables 1-3 above.

Depending on the size of pipe for a specific application, the price of Canberra's ILM and OLM-100 On-line Liquid Monitoring Systems range from $35,000 to $75,000, with the OLM system in the lower part of the range because it can be clamped onto an existing pipe, and the ILM system closer to the higher end of the range because it must be fitted into the pipe. A major factor in determining the cost is the pipe size. The larger the pipe size, the higher the cost because of the added expense of ensuring that the detector is properly fitted into the pipe. However, the manufacturer notes that both systems can be fitted into ? inch to 16 inch pipes. Canberra's 4Pi series ranges from $60,000-$130,000, while the LEMS system is in the $100,000-$150,000 range. Technical Associate's MEDA-5T for continuous gamma radiation monitoring costs approximately $20,000, while the SSS-33-5FT continuous flow-through scintillation detection system for alpha, beta, and gamma radiation costs approximately $58,000.