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RadNet

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RadNet System


Why is RadNet needed?

RadNet is one of many radiation monitoring systems in the U.S. For example, there are highly sensitive detectors set up to monitor compliance with the Comprehensive Nuclear Test Ban Treaty and many states and all nuclear power plants have monitoring systems.

However, RadNet is the only nationwide system that continuously monitors ambient environmental radiation levels and those resulting from major nuclear accidents, such as the Fukushima nuclear reactor incident in Japan. RadNet data are used to inform the public, providing assurance if contamination levels are very low or helping to make science-based decisions about taking protective actions if contamination levels are high enough to warrant them.

RadNet System Questions

Why does EPA test air, precipitation, drinking water, and milk for radionuclides?

Contamination from nuclear incidents typically travels through air in the form of particulates, although some contamination may be gaseous or waterborne. By monitoring for airborne particulates, EPA's health physicists can estimate inhalation doses to humans. Testing precipitation helps determine the amount of contamination that has been stripped from the air by rain or snow and deposited on the ground. EPA monitors drinking water and milk to help public officials determine if food and water supplies are safe for consumption.

RadNet System Questions

Does RadNet cover the whole U.S.? How does EPA decide where to set up air monitors?

RadNet air monitoring and sampling stations are widely distributed across the entire U.S. The system is designed to follow trends in environmental radioactivity levels and to measure widespread impacts from incidents that occur in the U.S. or abroad. RadNet air monitoring locations were selected to provide optimum population and geographical coverage throughout the United States. These stations are widely dispersed, covering each geographical region and most major population centers. EPA has an additional 40 monitors, which are portable and can be deployed as needed anywhere in the U.S.

RadNet System Questions


RadNet Data


Where can I see RadNet monitoring data and sampling analysis/laboratory results?

RadNet monitoring and laboratory results are available online:

  • Envirofacts is an EPA database that includes current and historical RadNet air filter data sent from each monitor, as well as drinking water, milk, and precipitation sampling analyses.
  • EPA's Central Data Exchange (CDX) reports hourly environmental radiation data from stationary and deployable monitors.
  • Environmental Radiation Data (ERD) is a quarterly report issued by EPA's National Analytical Radiation Environmental Laboratory (NAREL). It contains data from RadNet and its predecessor system, ERAMS.

RadNet Data Questions

How does EPA use RadNet Data?

National Average H-3 Concentrations in Precipitation

Example: Tritium
Trend in Precipitation
(1978-2001)
(Click to Enlarge)

The Envirofacts RadNet data are a rich source of radiation data. For example, the graph above shows the long-term trends of tritium in precipitation (rain, snow, sleet) that were compiled from monthly concentrations measured  between 1978-2001.
The graph shows that between 1978 and 1980, the tritium concentration was about 350 (pCi/l), but spiked to about 680 pCi/l during the last above ground nuclear test in 1980, then declined to levels below what instruments can detect.

Beta particles and gamma rays may come from natural sources that are part of our environment, or they may come from man-made sources, such as nuclear fuel. Tracking beta and gamma radiation helps us determine the type and amount of the radioactive material in the air. By looking at the data over time, scientists recognize what is "normal" or "background" radiation in a particular location. Any reading above normal will trigger an alert to EPA scientists to review the data. If a high reading is determined to have been caused by instrument error or local radiofrequency interference, scientists remove the data point from the database.

During a radiological incident, RadNet data can be used to help decision-makers decide whether protective actions need to be taken to safeguard the public. You can read more about RadNet data and its uses in the publication, Historical Uses of RadNet Data (PDF) (36 pp, 564K, About PDF)

RadNet Data Questions

Why are there fluctuations in the data?

Spikes in data can occur in a variety of situations, including fluctuations in naturally occurring radiation like a release of radon from soil or water, concentration of natural radiation by rain, or changes in atmospheric (barometric) pressure.

Occasionally, you may see brief gaps in the data. Scientists remove data points from the database that are caused by instrument error or radiofrequency interference. Larger gaps generally mean the RadNet monitor was temporarily taken offline for maintenance or repair.

Even when an individual monitor is offline, the RadNet system as a whole continues to provide a national view of airborne radiation in the environment.

RadNet Data Questions

Where can I find beta monitoring data?

Reviewed and approved near real-time beta air monitoring data are available in the RadNet Database in EPA's Central Data Exchange (CDX). Note that there may be large gaps in these data due to local radiofrequency interference. For this reason, near real-time beta monitoring graphs are not displayed on the RadNet site.

Gross beta activity levels from laboratory analysis of air filters are available in Envirofacts. Envirofacts houses sampling data for air filters and cartridges, precipitation, milk and drinking water.

RadNet Data Questions

Why do I see higher levels of radiation at some monitor locations?

The normal background radiation levels in one location may be different from the radiation levels in another. There are often large differences in normal background radiation across the nation. Background radiation levels depend on factors including altitude and the amount of naturally occurring radioactive elements in the soil.

RadNet Data Questions

Why are radiation levels higher during, or after precipitation events?

It is very common for natural background radiation levels to rise during precipitation events such as rain, sleet or snow. Radon and radon decay products, which occur naturally and normally dissipate in the air, are held closer to the ground by cloud cover, significant snow coverage, pressure changes, and may also be captured in the precipitation itself and brought to the ground. This causes the gamma radiation levels to rise in some measurements.

RadNet Data Questions

How does EPA use gamma energy ranges?

EPA uses RadNet monitors to track fluctuations in gamma radiation emitted from airborne radioactive particles at each air monitoring site. Tracking these changes over time gives a picture of the background (normal) levels and allows EPA scientists to detect any unusual changes. This data comes to the laboratory as  a "gamma count rate," which shows how many gamma rays the monitor detects each hour.

Each hour’s worth of data is split into energy ranges (see Picture 1). When multiple hours of data are looked at together we can track "normal" or "background" radiation levels by energy range at each air monitoring location (see Picture 2). Adding the energy ranges  together provides an even simpler way of tracking trends at each monitoring location (see Picture 3). Gamma Gross Count Rate by energy range graphs (Picture 2) and cumulative Gamma Gross Count Rate graphs (Picture 3) are both available on the RadNet site for individual monitoring locations.  

When the RadNet computer system detects an elevated reading from an air monitor in any of the gamma energy ranges, those data are reviewed by EPA scientists who are specially trained in understanding the data. They can look at various peaks across energy ranges to help identify a specific radionuclide. When peaks occur, air filters from the monitor are usually analyzed to help further identify the type and amount of radionuclides present.

Picture 1- one hour of data
(Click to Enlarge)
Picture 2 - Multiple hours of data by
energy range
(Click to Enlarge)
Picture 3 – single line created with
energy ranges are added together
(Click to Enlarge)

RadNet Data Questions


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Air Monitoring


Why does EPA monitor the air for radiation?

EPA monitors the air for radiation to understand levels of natural background radiation. Following trends allows scientists to detect elevated levels so that scientists and officials can determine whether protective actions are required to safeguard the public. The RadNet system has been used to detect and track radioactive material associated with foreign atmospheric nuclear incidents such as the Chernobyl disaster in Ukraine and the accident at the Fukushima nuclear reactor incident in Japan .

Air Monitoring Questions

How does EPA monitor the air for radiation?

EPA operates more than 130 radiation air monitors across the United States as part of its RadNet nationwide monitoring system. RadNet runs 24 hours a day, 7 days a week, and transmits near real-time measurements of beta and gamma radiation to EPA's National Analytical Radiation Environmental Laboratory (NAREL). The near real-time air monitoring data is continually reviewed by computer, and if the results show a significant increase in radiation levels, EPA laboratory staff is immediately alerted to investigate. The monitors have equipment to collect air samples for laboratory analysis and weather stations to record atmospheric conditions. The RadNet system also has 40 portable monitors that can be deployed to any location in the U.S.

Air Monitoring Questions

How do stationary monitors work?

RadNet Stationary Monitor
(Click to Enlarge)

RadNet stationary air monitors pull in air at an approximate flow rate of 60 cubic meters per hour. (Adults typically breathe at a rate of about 20 cubic meters per day.) The monitors collect any particles in the sample on a filter. Radiation detectors continuously measure the beta and gamma radioactivity from particles on the filter. Every hour, the stationary monitor sends an electronic report to EPA's National Analytical Radiation Environmental Laboratory (NAREL).

Most naturally occurring and man-made radionuclides emit either beta particles or gamma rays, and many emit both. The RadNet monitor sends a report to EPA that contains the total number of beta particles and gamma rays  recorded by the detectors during the previous hour, called the count rate. The RadNet system alerts EPA staff if levels are significantly higher than normal for any monitor. EPA scientists then investigate the nature of the increased radiation level.

Air Monitoring Questions

What is a deployable monitor and how is it different from RadNet stationary monitors?

A deployable monitor is portable and can be set up in any location as needed. After the Fukushima nuclear reactor incident in Japan, EPA set up deployable monitors in Hawaii, Alaska and U.S. Pacific territories to expand the reach of RadNet monitoring. RadNet deployable monitors send both weather data and average gamma exposure rates to EPA's National Analytical Radiation Environmental Laboratory (NAREL). The deployable monitors do not measure beta radiation and use slightly different air sampling equipment.

Air Monitoring Questions

Why isn't there a monitoring station in my hometown?

RadNet monitoring stations were selected to provide optimum population and geographical coverage throughout the United States. These stations are widely dispersed throughout the nation, covering each geographical region, most individual states, and most major population centers.

Air Monitoring Questions

How does the EPA measure radiation if there isn't an operating monitor in my area?

EPA placed more than 130 monitors across the country to provide overlapping coverage. If a monitor in one area is being repaired, EPA's network will still be able to detect any fluctuation in background levels areas across the nation.

Air Monitoring Questions

When is air data available to the public?

The near real-time air monitoring data are continually reviewed by computer and are usually posted to EPA's Central Data Exchange (CDX) website within three hours of arriving at the laboratory.

If the results show an abnormality in radiation levels, EPA laboratory staff is alerted immediately and reviews the data to ensure that they meet quality control criteria before posting.

EPA scientists analyze RadNet air filters and cartridges. Data are posted in EPA's Envirofacts database.

Air Monitoring Questions

Why aren't the results for my location up to date?

EPA's RadNet monitors are highly sophisticated technical devices which occasionally require maintenance and repair. RadNet monitors are returned to normal operation when maintenance and/or repairs are complete.

Air Monitoring Questions

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Air Filter, Precipitation, Drinking Water and Milk Sampling

Air Filters

Precipitation

Drinking Water

Milk


Air Filters and Cartridges, Precipitation, Drinking Water, and Milk

Air Filters and Air Cartridges

Why does EPA test air filters for radionuclides?

RadNet's laboratory analyses provide confirmation of the near real-time air monitoring results. Air filters are used on RadNet stationary and deployable monitors. Air cartridges may be used on deployable monitors when radioactive gases may be present, such as following a nuclear reactor accident. By monitoring air and testing air filters on a regular basis, EPA is able to establish normal background levels of radioactivity and detect additional activity from man-made radioactive sources.

Air Filter, Precipitation, Drinking Water, Milk Questions

How does EPA analyze air filters?

RadNet operators ship air filters or cartridges to EPA’s  National Analytical Radiation Environmental Laboratory (NAREL) for analysis. All air filters go through an initial screening for beta radiation. Extremely low readings, which fall below a conservative threshold, are posted to the Envirofacts webpage. Any filter that exceeds the threshold goes through additional analysis to determine the exact type and amount of radioactive material present on the sample.

Air Filter, Precipitation, Drinking Water, Milk Questions

Where can I find the analytical results from air filter and cartridges?

You can obtain EPA's analytical results from RadNet air filters and cartridges on the Envirofacts site.

Air Filter, Precipitation, Drinking Water, Milk Questions

Precipitation

Why does EPA test precipitation for radionuclides?

By monitoring precipitation on a regular basis, EPA is able to establish normal background levels of radioactivity and detect additional activity from man-made radioactive sources. Analyzing precipitation samples along with air filters helps estimate the amount and type of radioactive material that will be deposited on the ground.

It is very common for natural background radiation levels to rise during precipitation events such as rain, sleet or snow. Radon and radon decay products, which occur naturally and normally dissipate in the air, are held closer to the ground by cloud cover, significant snow coverage, pressure changes, and may also be captured in the precipitation itself and brought to the ground. This causes the gamma radiation levels to rise in some measurements.

Air Filter, Precipitation, Drinking Water, Milk Questions

How does EPA sample precipitation?

More than 30 stations across the U.S. collect precipitation samples such as rain, snow or sleet. Under routine circumstances, EPA scientists test the samples on a monthly basis. EPA performs gamma analysis on each sample. Routine analysis of precipitation for gamma emissions takes about a week from the time the lab receives the sample. The results are checked to assure that they meet quality assurance criteria and are posted periodically to the Envirofacts database.

Air Filter, Precipitation, Drinking Water, Milk Questions

Are there EPA standards for radionuclides in rainwater?

There are no standards for radionuclides in precipitation. The data we collect helps establish trends and serves as a reference during radiological incidents.

Air Filter, Precipitation, Drinking Water, Milk Questions

Where can I find the analytical results from precipitation samples?

You can obtain the analytical results of RadNet precipitation samples on the Envirofacts site.

Air Filter, Precipitation, Drinking Water, Milk Questions

Drinking Water

How does EPA sample drinking water for radionuclides?

EPA's  obtains quarterly drinking water samples from more than 50 RadNet drinking water sampling sites across the country. EPA performs gamma analysis on each sample. Routine analyses of drinking water for gamma emissions takes about a week from the time the lab receives the sample. The results are checked before release to assure that they meet quality assurance criteria.

Air Filter, Precipitation, Drinking Water, Milk Questions

What if there is no RadNet water sampling in my town?

The RadNet radiation monitoring system provides a national network for tracking radiation levels across the country; it was not designed to monitor local water quality. Local water authorities test for compliance with EPA's drinking water standards.

Air Filter, Precipitation, Drinking Water, Milk Questions

What federal standards exist that address radiation in drinking water?

Under the Safe Drinking Water Act (SDWA), EPA has set maximum contaminant levels (MCLs) to establish limits for certain substances in drinking water, including microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, and radionuclides. The MCLs for radionuclides were calculated based on long-term, chronic exposures over the course of a lifetime 70 years.  RadNet drinking water data should not be substituted for SDWA data because the analytical methodologies are not the same.

Air Filter, Precipitation, Drinking Water, Milk Questions

Where can I find the analytical results from drinking water samples?

You can obtain EPA's analytical results from RadNet drinking water samples on the Envirofacts database.

Air Filter, Precipitation, Drinking Water, Milk Questions

Milk

How does EPA sample milk?

Milk samples are collected and sent to EPA's National Analytical Radiation Environmental Laboratory (NAREL) by RadNet partners in more than 30 locations throughout the United States. These partners have an agreement with EPA to send milk samples on a quarterly basis. The milk that is sampled is sent to the lab before it is sent to stores, but generally after it has been pasteurized. The milk does not necessarily come from a specific farm.

EPA analyzes the milk samples for gamma emitters and selected sites are tested for strontium-90. A complete gamma analysis requires at least seven days, but preliminary results may be available within four hours. Results are posted periodically on the Envirofacts site.

EPA samples milk as an environmental indicator. FDA and states check radioactivity in milk to ensure food safety.

Air Filter, Precipitation, Drinking Water, Milk Questions

What federal standards exist that address radiation in milk?

The Food and Drug Administration (FDA) sets standards for radioactivity in milk. FDA uses derived intervention levels (DILs) to recommend safety precautions to protect public health. These levels also help the agency determine whether domestic food in interstate commerce or food offered for import into the United States presents a safety concern.

Air Filter, Precipitation, Drinking Water, Milk Questions

Where can I find the analytical results from milk samples?

You can view EPA's analytical results from milk samples on the Envirofacts site

Air Filter, Precipitation, Drinking Water, Milk Questions

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Food and Imports

Where can I find information about the radiation screening of imported products?

The U.S. Customs and Border Protection (CBP) is the federal agency tasked with screening imported products for harmful substances. You can find information about CBP screening of cargo for radiation at the Agency's Cargo Examinations page.
You can reach CBP staff by phone at 877-227-5511.

Food and Imports Questions

How do I know that the food that I am eating is safe? Who monitors radioactivity in U.S. and imported foods?

The U.S. Food and Drug Administration (FDA) is the federal agency tasked with monitoring food for radioactivity. You can find information about testing food for radiation by visiting FDA's Public Health Focus-Radiation Safety webpage. For information about U.S. food recalls and alerts, please visit, U.S. Food Safety: Recalls and Alerts.

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