Japanese Nuclear Emergency: EPA’s Radiation Air Monitoring, EPA, March 27, 2011:

[Emphasis Added]

Elevated levels of radioactive material in rainwater have been expected as a result of the nuclear incident after the events in Japan since radiation is known to travel in the atmosphere. There have been reports received that the states of Pennsylvania and Massachusetts have seen elevated levels of radiation in recent precipitation events. EPA is reviewing this data – however, in both cases these are levels above the normal background levels historically reported in these areas.

While short-term elevations such as these do not raise public health concerns – and the levels seen in rainwater are expected to be relatively short in duration – the U.S. EPA has taken steps to increase the level of nationwide monitoring of precipitation, drinking water, and other potential exposure routes to continue to verify that.

See also:

• EPA: Radioactive isotope levels are increasing in US — “These types of findings are to be expected in the coming days”
• Radioactive particles from Fukushima found in Massachusetts rain — “25 times less risky than it would need to be in order to cause any health concerns” (VIDEOS)