In the old days, the newsroom at most local dailies had a police scanner squawking like a nervous parrot in the background, to get the jump in case something big happened. To get environmental news today, you need other tools.
NUCLEAR: Some reporters are in the habit of checking in daily at the Nuclear Regulatory Commission's web page for "Event Notification Reports" the NRC's equivalent of a police scanner. Most safety incidents that nuclear electric utilities and others regulated by NRC are required to report are posted daily here. 
Most of the incidents reported will be routine and not newsworthy. But regular checking will also disclose important safety issues at particular nuclear facilities. There may be time lags of several days before incidents are posted on the NRC site.
WILDFIRE: As fire season starts up, reporters in fire-prone areas may want to check in daily at the National Interagency Fire Center's incident reporting web hub.  The Incident Management Situation Report  comes out every morning in season around 5:30 am MDT.
At the NIFC's fire info hub, you will also find the searchable InciWeb database, press releases, year-to-date statistics, daily statistical summaries, and more.
OIL AND CHEMICAL: It used to be that you could get current information on oil and chemical spills rather quickly at the National Response Center's database (confusingly, yet another NRC). No more. The Coast Guard has begun scrubbing its raw incident reports to protect the privacy of companies who spill into public waterways oil and chemicals that may endanger the public. That takes time, the Coast Guard says. When the Coast Guard gets around to it, the edited incident reports are posted online. 
The US Chemical Safety and Hazard Investigation Board maintains a useful ticker of current news stories  related to chemical incidents.
EARTHQUAKES and TSUNAMIS: The US Geological Survey and other agencies worldwide maintain a network for detection of seismic incidents. Most of these are minor and remote. But as recent events in China show, they can also be big news. You can have instant notification of seismic events sent to you by e-mail or feed. Start here  and here. 
HURRICANES and SEVERE WEATHER: The National Hurricane Center at NOAA's National Weather Service tracks the formation of tropical storms that could turn in to hurricanes, in close to real time, on its website.  The National Weather Service gives a national overview of all kinds of severe weather watches and warnings on its website. 
AIR POLLUTION: The interagency (including Canada) AirNow site  gives forecasts for both smog and particulate pollution.
ALL HAZARDS RADIO: NOAA Weather Radio is part of a larger "all hazards" radio network that can be useful for news organizations. The warnings include not just tornadoes and floods, but theoretically things like terrorism or chemical releases. For a hundred dollars you can get a radio that will listen passively and bleep an alert when any agency issues an emergency advisory for your specific area. See NOAA's Weather Alert page. 
NATIONAL PARKS: If you cover National Park System units, you may want to look regularly at the National Park Service Morning Report.  It contains every manner of NPS-related news - from the policy-related to injured climbers, bear attacks, and car chases.