Evidently the black-helicopter crowd didn’t get too exercised over the Bell chopper that flew hundreds of transects just 300 feet above much of King and Pierce counties last month. Maybe that’s because the helicopter wasn’t black. Or maybe because the Washington Department of Health’s Office of Radiation Protection, which dispatched it, took pains to inform the public just what it was up to — to a point.

This aerial survey, which measured ambient gamma-ray levels at 600-foot intervals, was intended to establish a “radiological baseline” for Pugetopolis. “This baseline,” the Department of Health announced, “would be used to compare against measurements taken after a radiation emergency occurs. It helps state and local officials quickly determine where potential health effects may exist and to warn people in the affected area.” DOH didn’t mention just what sort of “radiation emergency” it was preparing for. But since the U.S. Department of Homeland Security fronted the entire $521,000 cost of the survey, and since Seattle’s downtown butts up against a major shipping port where high-end radiation screening has already been installed, it’s a safe bet that a dirty bomb or other terror attack was high on the list of concerns.

The Health Department insisted that another nightmare that has lately topped terrorism on the local fear-meter had nothing to do with the survey: “This project isn't related to the disaster in Japan. It began in September 2009, well before the earthquake in Fukushima. The helicopter flyover is part of a multi-phase project to improve our state readiness to respond to radiation emergencies.” And indeed, this is just the latest in a series of such flyovers that Homeland Security has sponsored over American cities, including New York and Washington, D.C.

But the March meltdown at Fukushima actually did prompt authorities to go ahead with the Seattle survey, which otherwise might not have happened. “For a while there was talk of putting off this survey,” says DOH spokesperson Donn Moyer. “It didn’t appear practical. But because Japan demonstrated the need for baseline information, showed that having this was important, they decided to go ahead on schedule.”

The aerial survey is just one lingering local consequence of the Fukushima disaster. Traces of radioactive cesium-137 released in the earthquake’s aftermath are still working their way through soils, waters, and bodies; with a half-life of about 30 years, they’ll be hot for a while. (By contrast, iodine-131, the radioisotope that sparked the most public anxiety — and a run on iodine tablets — has a half-life of only eight days, so its emissions were soon depleted.) Those traces are minute, however, and according to state and federal authorities constitute much less exposure than our ordinary, everyday radiation diet.

Such assurances don’t soothe those already disposed to mistrust America’s military-industrial-bureaucratic nuclear complex, among them Gerald Pollett, the executive director of the longtime Hanford watchdog group Heart of America Northwest. While saluting the EPA and state DOH for promptly posting local radiation readings on their websites, he faults them for several holes and inconsistencies in monitoring, and for minimizing and mischaracterizing the data’s significance.

Take for starters the EPA’s declaration, on its website, that it “took steps to increase the frequency of monitoring of precipitation, drinking water, and other potential exposure routes.” But whether these steps represented real increases is somewhat debatable. The EPA conducted one extra round of milk and drinking water sampling in March and then resumed its standard quarterly sampling in April. And, says Davis Zhen, a radiation expert in the EPA’s Seattle office, it deployed portable air monitors to parts of Alaska and Hawaii where it hadn’t previously sampled. Otherwise, as far as air and rainwater went, “the sampling schedule for these media was not affected,” the agency disclosed in response to a Freedom of Information request from an anti-nuke activist in Colorado.

Last month, Heart of America went public with another especially shocking-sounding complaint: In late March, about two weeks after the initial Fukushima disaster, rainwater in Portland had 27 times as much Iodine-131 as the federal drinking water standard. Rainwater falling on Olympia exceeded the federal standard by 41 times, Seattle’s had nearly 54 times the federal standard. And Boise topped the charts, with 130 times the standard on March 27. That’s not to say that Boise received more fallout than Seattle and other points west; the rain falling here was probably even more radioactive. But because the feds didn’t take measurements in Seattle, Olympia, or Portland that day — monitoring was done on varying weekly schedules at various points — there’s no way of knowing.

The EPA gathered and posted the rainwater data. But it didn’t highlight them, or compare them to the drinking-water standard. Officials say that’s because rainwater and drinking water are apples and oranges: People around here don’t consume rainwater directly, and brief spikes in radiation are quickly diffused as rain gets dispersed in the ground or diluted in reservoirs. “Tell that to someone who is collecting rainwater,” counters Heart of America Northwest's Pollett. “People do use rainwater — in gardens certainly. It should have been up to them to make the decision.” Indeed, March is just the time when many gardeners fill their rain barrels to grow zucchini and tomatoes in summer. A simple official announcement could have alerted them that they might want to dump that water and refill their barrels in April, after radiation levels returned to normal. (No jokes, please, about the special rosy glow on your tomatoes this year.)

Pollett also contends that the EPA and other agencies promulgate an “extremely misleading,” artificially high model for normal exposure to radiation, and that this high baseline induces a false complacency when events like Japan’s disaster raise actual exposures. That federal standard is 620 millirems (mrem) per year; the state still uses an earlier standard, 360 millirems. The former is the equivalent of around 400 dental x-rays, 60 chest x-rays, eight mammograms, or one CT scan, according to U.S. Nuclear Regulatory Commission data. Various everyday exposures contribute small loads: food, granite, cosmic radiation (26 mrem a year at sea level, double that at one mile high), air travel (2.5 mrem per transatlantic flight, more if you fly over the Arctic or when sunspots flare). Cigarette smoking contributes a whopping 280 mrem a year, according to the state Health Department, which catalogs many different exposures and often differs from the NRC’s numbers.

The largest exposure for most people is radon gas, emitted by natural radium in the soil. But radon levels are low in the Puget Sound region. And who gets 400, or even 60, x-rays a year? Pollett suggests that the official baselines are skewed by including cancer patients and others who receive high-radiation treatments. (For example, thyroid oblation can entail a whopping 18 million mrem.) A more realistic baseline, he plausibly argues, would be just 200 millirems.

None of these criticisms (nor others Pollett tenders) amounts to a brazen cover-up, or cause for panic. Taken together, however, they make you at least want to look twice at any radiation numbers and reassurances officials put out. These days you may need to be your own radiologist as well as doctor. When Fukushima Daiichi melted down, I was sorry to learn my neighbor had sold the Geiger counter he used to have (and which enabled me to uncover the radioactive dishware in my kitchen).