Soil radioactivity, radiation levels, and a crude estimate

Contributions to soil radioactivity in the Refuge

A frequently overlooked National Institute of Standards and Technology "soil standard" places plutonium in its natural context.  At least 97% of soil radiation comes from natural radioisotopes.

Directly measured ambient radiation levels on trails inside the Refuge

The 'ambient dose equivalent [radiation] rate', a widely used measure, is 0.14 microSieverts per hour--low normal background for the Front Range.  It varies by less than 2% from place to place on the trails.  As more trails open, this document will be updated.  DMW reformatted existing USGS background radiation maps to focus on Colorado.

Not very technical poster summarizing the above two documents. Mighty colorful too!

Quick estimate of maximum radiation dose due to plutonium from visiting the Wildlife Refuge

This older document is not wrong, but is largely superseded by the May 2019 document above.


Plutonium-related radiation levels within the Refuge (part of the "Peripheral Operating Unit", not the "Central Operating Unit") were never considered high enough to require mitigation.  They are only moderately higher than around Candelas or Leyden Rock, where Pu and Am levels (and their health consequences) are covered in the documents in the Knowledge Base.  Contamination levels within the Refuge were designed to be low enough that a full-time employee would not exceed radiation exposure levels any different than the population at large.  As you can read here, "Rocky Flats isotopes" are responsible for less than 3% of total soil radioactivity-the rest is "all natural".  Your body doesn't care if a gamma ray came from (man-made) plutonium or (natural) thorium radioisotopes.  Alpha particles have a range in air of about 4 inches; they are stopped by a sheet of paper and are blocked by the layer of dead tissue on your skin. In Rocky Flats soil about 95% of alpha-particle emitters are natural.

The main concern about the Refuge is that the Fish&Wildlife has been inhibited from doing its job by external political pressure from groups intent on delaying, stopping, or reversing its opening.  They raise issues such as the (by now, quite unlikely) possibility of cancer clusters around the Refuge, the "dangers" of controlled burns by F&W, and the importance of animal burrows transporting plutonium from highly contaminated soil (if any exists that was not already carted away) to areas where humans could be exposed.  We suggest that you read the documents Cancer clustersHot particles no longer, and Burrowing critters and burning vegetation to decide for yourself about these possibilities.


Rocky Mountain National Park's famed Trail Ridge Road closed due to visitor risk

Peculiar thought.  But the risk of being killed by lightning increases above treeline since a 6 feet tall human being is a better lightning rod (pointier and more conductive) than a low-lying rock outcrop.  In assessing the wisdom of the policy above, a visitor might plausibly ask

  1. How probable is being killed by lightning?
  2. What can I do to mitigate risk?
  1. Very unlikely: certainly less than 1 in 100,000. What does this even mean? It might be that out of every 100,000 people walking on the Trail Ridge Road, 1 is hit by lightning.  Most people would unconsciously compare this with more plausible ways to be injured.
  2. I can watch the weather cautiously and minimize time exposed to the risk, or stay below timberline (and miss the scenery).

Any action entails risk, even if we are not fully aware of it. More generally, we might ask

  1. Are the risks to me or to my children significant on the scale of other risks I already choose to ignore?
  2. Should I choose not to visit (and miss possibly rewarding outcomes)?

Visiting the Rocky Flats National Wildlife Refuge is not so different (logically speaking). Although an adult's lifetime risk of dying of cancer is around 22% [and a child's may be more or less, depending on how prevention, diagnosis, and oncology progress], the added risk of cancer due to radiation within the Wildlife Refuge is in the range of 1 in 100,000 to 1 in 1,000,000. Thus one's lifetime risk of cancer has been changed from (to make a point) 22.00000% to 22.000001%. (This is before compensating with the relatively small fraction of his or her time a visitor would spend there.) This sort of quantitative thinking is crucial to understanding very very small risks.