Tens of thousands of miles of oil and gas pipelines crisscross the US, and they spilled more than 2 million gallons of oil in 2009 alone, according to EPA. Stark evidence of such problems surfaced on July 26, 2010, when the Calgary, Alberta-based company Enbridge Energy Partners informed officials that a 30-inch oil pipeline it owns near Marshall, Michigan, had burst, spilling about 1 million gallons of oil into nearby watersheds, including the Kalamazoo River.
- EPA, Enbridge spill. 
EPA revealed another case of widespread problems with its Aug. 10, 2010, announcement of a pending settlement with the Houston-based company Plains All American Pipeline, spurred by a series of large and small crude oil spills that dumped about 273,000 gallons into the environment from 2004 to 2007. The settlement calls for a civil penalty of $3.25 million and requires the company to spend an additional $41 million to repair more than 10,400 miles of crude oil pipeline in KS, LA, OK, and TX, and to improve monitoring and management of its pipelines. The company owns another 6,000 miles of pipeline, but company officials did not respond to a query regarding what other states they operate in.
- "Plains Pipeline to Spend $41 Million to Prevent Oil Spills Across 10,000 Miles of Pipeline,"  EPA press release, Aug. 10, 2010; Web site. 
- Plains All American Pipeline, main page;  statement regarding settlement,  Aug. 10, 2010; Ray Lamoreaux, 800-564-3036 or 713-646-4222.
There likely are many more problematic oil and gas pipelines, some in your audience area. Finding the evidence before one bursts is challenging, but there are viable avenues to pursue.
For the Enbridge spill in Michigan, there was extensive evidence of looming problems. In February 2010, the Pipeline and Hazardous Materials Safety Administration (PHMSA, created in 2004 within the US Department of Transportation) met with Enbridge officials regarding problems with corrosion monitoring and other issues in this pipeline, according to a July 31, 2010, Associated Press article. The company had known since 2008 that there were at least 250 problem spots in the line, and more than 200 still needed fixing when the line ruptured. The company or its affiliates, which own at least 15,000 miles of liquids pipelines in the US and Canada, have been cited for violations 30 times since 2002.
- "Feds Warned Company in Mich. Spill About Pipeline,"  Associated Press, July 31, 2010, by Mike Householder and John Flesher.
The possibility that these kinds of disasters will occur has been anticipated to some degree. Just a few days before the Michigan spill, the US House Subcommittee on Railroads, Pipelines, and Hazardous Materials (under the umbrella of the House Transportation and Infrastructure Committee) held a prescient hearing.
- "Pipeline Safety, Public Awareness, and Education,"  July 21, 2010.
In the two months prior to that, the Subcommittee held three other related hearings:
- "The Safety of Hazardous Liquid Pipelines (Part 2): Integrity Management"  [the term used to address how pipeline operators manage pipeline safety], July 15, 2010.
- "The Safety of Hazardous Liquid Pipelines: Regulated vs. Unregulated Pipelines,"  June 29, 2010.
- "Implementation of the Pipeline Inspection, Protection, Enforcement and Safety Act of 2006 and Reauthorization of the Pipeline Safety Program,"  May 20, 2010.
The Subcommittee is actively pursuing additional information about the Enbridge spill, which may lead to insights about other looming pipeline disasters.
Since 9/11, much of the pipeline location information has been pulled from government Web sites. That has led many journalists to conclude that reporting on pipeline threats is essentially impossible. However, there are many threads to follow that, together, can lead you to specific problems in specific areas.
One starting point is the county-level mapping provided by PHMSA. The maps are labeled as general, and some pipelines may not be included, but the maps are valid up to 2007, according to the Pipeline Safety Trust's Riley Sweeney,  360-543-5686.
Decade-old information from 2000 or 2001 is available for a price from the company PennWell.  A detailed state map of oil and gas pipelines costs $395. A detailed national map runs $995 for natural gas, $795 for either crude oil, liquefied petroleum gas, or refined products, and $750 for petrochemical olefins.
- PennWell: Oil & Gas  and MAPSearch.  Sales manager, Bonnie Damstra,  713-963-6247, cell 281-546-1505.
Another way to begin to get a feel for where pipelines are located and whether they have had any past officially-acknowledged problems is to search the EPA ECHO (Enforcement & Compliance History Online) database. For instance, you can select a state, enter an SIC code such as 4612 for crude petroleum pipeline or 4922 for natural gas transmission (and you can look up other pertinent SIC codes on this site), and select "no restriction" under the section "Compliance Information." If you get any hits, they will note information such as company names, project ID numbers (which can provide more details when you look them up), and whether there have been any inspections, violations, or penalties in recent years, However, a search of this data for Michigan doesn't turn up any indication of the 250 problem areas in Enbridge's pipeline, even though its Lakehead pipeline in Marshall, MI, is specifically included in the results.
- ECHO. 
Another line of inquiry is to sift through the information in the Pipeline Risk Management Information System. There, various companies acknowledge certain pipelines or related facilities known to have problems, and outline their proposed plans of action to remedy the problems. You can find numerous leads to follow for additional investigation tucked into the text for each company. The information often appears to be quite dated, but it still may provide leads into the number of miles of pipeline a company owns, the states in which it operates, and other basic information.
Authorized government officials and pipeline operators can find pipeline information via the online Pipeline Integrity Management Mapping Application. However, this may be impossible for journalists to use unless you have the right source.
Regulation of oil and gas pipelines is an evolving labyrinth, though PHMSA is considered the lead agency. For more information on the many federal and state players who can be involved, see:
One division of federal labor is that PHMSA is responsible for inspection and enforcement related to pipeline operation and safety rules, and EPA deals with inspection and enforcement related to the Clean Air Act, Clean Water Act, and hazardous waste laws, says the National Wildlife Federation's Ryan Salmon,  202-797-6606.
As of June 2010, there were only 88 fulltime PHMSA inspectors for the country. There are additional inspectors at the state level who do the majority of inspections, with responsibility for who does what varying by state and pipeline.
PHMSA officials did not respond by press time to a phone call and three emails requesting more information about what data they have available regarding pipelines that are known to have problems, but which have not yet had official violations or enforcement actions taken to address those problems, and have not yet turned into a spill, explosion, or other disaster.
- Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety  (includes links to inspections, enforcement, data and statistics, and more); media, 202-366-4831, firstname.lastname@example.org  or email@example.com 
However, Salmon says some of this information is available by searching the following site by pipeline operator, turning up information from 2002 onward such as cases opened, cases resolved, and warning letters issued.
Since much of the regulatory responsibility for oversight of pipelines is at the state level, it may be best to also ask your state agency for this kind of data.
To get beyond any limited or recalcitrant information sources, it may be necessary to FOIA either PHMSA or other federal or state agencies involved. According to the Pipeline Safety Trust, agencies sometimes will cite national security interests and decline to provide any information, but in some cases the agencies will comply with a FOIA request.