Understanding soil contamination measurements

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In the one of the breaking news stories for today, September 5th, 2011, soil or surface contamination is reported for some mulch and for the roof of a condo.

To help give some perspective on the numbers, I found the following from this site.

Terrestrial Contamination Levels of Concern

3.7 Bq/m2: Begin monitoring of ambient exposure radiation levels (microsieverts per hour), terrestrial contamination levels above background (Cs-137, Bq/m2), and rainwater (I-131, Bq/l) via the EPA, CDC, DOE, FDA, IAEA, state, and local websites.

  • 37 Bq/m2: Expand monitoring to include measurements of local contamination of food, water, and milk by indicator nuclides I-131 and Cs-137 as measured in Bq/kg or Bq/l. Begin protective actions: avoid exposure to rainfall events, remove shoes and clothing before entering domestic environments, and shower after exposure to rain.

  • 370 Bq/m2: Expand protective actions: stay indoors whenever possible, close windows, seal openings, cover gardens with tarps, shelter livestock, avoid ingestion of leafy vegetables and fruits harvested in fallout areas. Expand monitoring of food, water, and milk; discard or avoid ingesting foods and water contaminated by the indicator nuclides I-131 and Cs-137 above 370 Bq/kg or Bq/l (10,000 picocuries, the protection action level used by the US FDA to dispose of imported foods contaminated by Chernobyl-derived fallout). Continue monitoring of ambient radiation levels.

  • 3,700 Bq/m2: Expand protective actions to restrict movement of children, outside workers, nonessential travel, and recreational activities such as hiking and sunbathing. Closely monitor food, milk, and water intake, sources, and radiation levels. Continue use of information technology to keep informed of ongoing emissions. Immediate sheltering is the best option to avoid exposure to a passing plume.

  • 37,000 Bq/m2: Prepare to evacuate to a safer zone, e.g. the southern hemisphere or another planet.
    Without the systematic compilation of the distribution pattern of the indicator radioisotopes I-131 (1/2T = 8 days) and Cs-137 (1/2T = 30 years), no reasonable evaluation of the health physics impact of the Fukushima Daiichi disaster or any other nuclear accident or point source can be tabulated.

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