Environmentalists have launched a new mapping tool that allows people in the U.S. to see whether they live and work in areas at risk of harmful air pollution from nearby oil and gas activities.

According to the map, which was published online Wednesday by the advocacy groups Earthworks and the Clean Air Task Force, a lot of people do: about 12.4 million people live within a half-mile of active oil and gas wells and related facilities that could release harmful pollutants such as benzene and formaldehyde into the air. The map also details the 238 counties in 21 states that potentially face a high cancer risk because of that pollution.

“Oil and gas air pollution isn’t somebody else’s problem, it’s everybody’s problem,” said Alan Septoff, the communications director at Earthworks. Septoff hopes this map not only helps people determine whether they live in an area of concern but also motivates them to pressure state and federal environmental regulators to address the issue.

“We need a strong rule from the Environmental Protection Agency and states in order to protect people from this pollution,” said Septoff. The EPA has already proposed new rules to reduce emissions of methane, a greenhouse gas, from new and modified oil and gas activities. Starting in May and running through early August, the EPA is inviting public comment about whether it should consider similar rules for existing oil and gas facilities.

Although methane contributes to global warming, it has not yet been definitively tied to any long term or chronic health impacts. But other pollutants that spew into the air along with methane do pose a respiratory and cancer risk to humans, said Lesley Fleischman, an analyst at Clean Air Task Force; so reducing methane emissions can also reduce other dangerous chemicals.

Colorado was the first state to pass rules controlling methane emissions from the fossil fuel industry, in 2014. California is now drafting similar rules. If these states can do it, there’s no reason the federal government can’t follow suit, said Fleischman.

‘… You Have Cause to Worry’

The new map shows how two analyses identified different health risks tied to oil and gas air emissions. For one analysis, the environmental group Earthworks, along with members of FracTracker Alliance, plotted the nation’s active oil and gas wells, using data submitted to the federal government by states. They combed through various data sources to find the locations of compressor stations, which move gas through pipelines, and facilities for processing natural gas.

Then they drew a half-mile radius around all these sites and labeled it the “threat zone.” According to Septoff, several scientific studies have previously suggested homes, offices, schools and other infrastructure within a half-mile of these sites could be exposed to the related air pollution.

“Choosing a half-mile radius was a reasonable, conservative choice,” said Catherine Thomasson, executive director of Physicians for Social Responsibility. Thomasson, who was not involved in the project, said the threat could even extend beyond a half mile.

“What it suggests is you should be concerned for your health from these pollutants because of the proximity,” said Septoff. “But it doesn’t mean that you have suffered negative health impacts or even that you will. It means you have cause to worry.”

To find out if you live in a threat zone, type your address into the map and it will zoom to your location. Make sure the “Threatened Population” layer is checked. Areas colored gray are considered safe; yellow areas are considered at risk.

Another analysis, conducted by the Clean Air Task Force, used an EPA analysis called the National Air Toxics Assessment, combined with EPA’s 2017 emissions projection data, to identify counties with a potentially high cancer- and respiratory risk linked to pollution from oil and gas. To view the results of this analysis on the map, click the “Air Toxics” layer. Texas’s Gaines and Yoakum counties, shown in dark red, have the highest cancer risk tied to air pollution from the oil and gas industry. The research suggests people there have a 1-in-100,000 risk of getting cancer. Hundreds of other at-risk counties are also colored different shades of pink on the national map.

“If anything, these results are probably conservative,” said Seth Shonkoff, executive director of PSE Health Energy. (He was not involved in the study.) According to Shonkoff, the EPA data likely underestimates the emissions from smaller oil and gas facilities, among other data issues.