1. The problem is too many trees.

Pepco executives complained for years that electrical outages were hard to avoid, given that Washington’s tree cover is the “fourth most dense” in the nation. And it’s true that during storms, the region’s toppling trees wipe out a lot of power lines.

But forestry experts — including those cited in Pepco reports — told me in 2010 that the D.C. region’s tree canopy is about average. As my Washington Post colleague Mary Pat Flaherty and I reported, in the few cities that Pepco said had a denser canopy than the District, the local electric companies did a better job of keeping the power flowing. That suggests that a lack of pruning, not the number of trees, may be to blame.

In addition, Pepco’s reliability ratings began dropping in 2005, a period during which internal company reports show that spending on tree trimming and other vegetation management remained “relatively stagnant or decreased.”

Detailed outage statistics add another piece to the puzzle. Although Pepco executives have publicly stated in the past that most outages were “tree-related,” company records show that in 2009, equipment failures — not trees — were an even bigger source of blackouts, accounting for 44 percent. By comparison, the internal records blamed trees for just 24 percent of outages.

2. If it weren’t for extreme weather, power service would be fine.

No electrical system can be made immune to 75-mile-per-hour winds or a major ice storm. That’s what Pepco executives stress, and it may be true enough. But industry records show that Pepco has trouble keeping the lights on during tranquil days as well.

When stormy days are excluded, records show that in 2009, Pepco’s customers experienced 70 percent more power failures than customers of other big-city utilities that took part in one major survey. And when the lights blinked out for Pepco customers, they tended to stay out more than twice as long.

Pepco ranked at or near the bottom compared with other major power companies that took part in indexing surveys.

3. Pepco’s outages are reasonable, given the size of the storms.

Company executives say it’s difficult to make comparisons among utilities based on power failures caused by hurricanes, blizzards and other major storms. Storm intensity varies, and each community presents unique challenges based on terrain and the percentage of power lines underground. Even so, storm performance reports filed with the federal government raise questions about Pepco’s response.

Most memorable among those past events was the “Snowmageddon” storm in 2010 that dumped more than two feet of snow and shut down the region for days.

Almost 98,000 Pepco customers lost power at the storm’s height, in an outage that began on the evening of Feb. 5. The company did not fully restore service for about a week. Meanwhile, Dominion Virginia Power, which serves about three times as many customers in Virginia and parts of North Carolina, lost power to 105,000 customers in an outage that began seven hours after Pepco’s and was declared resolved after about 29 hours.

In other words, Dominion’s service stayed active longer and was fully restored more quickly — even though it affected about the same number of customers. Similar patterns can be found in other storm reports from recent years. Dominion customers have suffered widespread and lingering outages related to this summer’s storm, too, but the company appeared to be getting the lights back on more quickly than Pepco was.

Adding to the evidence is a study by the Maryland Office of People’s Counsel, which represents consumers. It found that, during the storms in February 2010, Pepco customers suffered the longest outages among customers of the six biggest power companies serving Maryland. Pepco outages averaged 13.6 hours. Other companies had average outages of about six to eight hours; BGE customers suffered interruptions averaging 8.1 hours.

4. Burying power lines is a clear solution.

A two-year-old study commissioned by District regulators found that burying all overhead lines in the city would cost $5.8 billion. The work would take years to complete and would be a major disruption. Costs in Montgomery County might add an additional $4 billion. The result would be a big increase in customers’ monthly bills, perhaps hundreds of dollars.

And burying lines in selected neighborhoods wouldn’t necessarily solve the problem. Overhead lines that deliver power to particular areas could still be taken down by an ice storm. When problems eventually did occur in a buried line, it could take twice as long for crews to find and then fix them.

Despite all that, officials say they are looking into whether it would be cost-effective to bury more feeders, the major distribution lines that reach into neighborhoods. In the District, almost 80 percent of high-voltage lines are underground. In Maryland, only 57 percent are.

5. Fining Pepco will improve service.

In the wake of a public outcry and a Washington Post investigation, District regulators tightened performance standards for Pepco last year, threatening to fine the company unless it improved reliability within two years and matched the performance of the nation’s most dependable power providers within a decade. Not to be left behind, Maryland regulators in December fined Pepco $1 million — the largest penalty in the public service commission’s 102-year history.

That should take care of the problem, right? Maybe not. At the time of the fine, Pepco’s parent, Pepco Holdings, took about a day and a half to earn $1 million, according to company filings. The previous year, Pepco Holdings paid out more than $240 million in dividends.

Pepco executives say fines are unproductive, because the company is already motivated to improve. Pepco has spent heavily on hardening its wires and trimming trees over the past two years, and executives say they have internal data showing that the work has enhanced reliability. Improving service, they say, is their top priority.

So far, though, no one is offering the company a pat on the back. As D.C. Mayor Vincent C. Gray (D) said last week: “People are fed up with power outages.”

Joe Stephens is an investigative reporter for The Washington Post.

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It was a rough week for hundreds of thousands of Washington area residents, who sweated through record-breaking heat without lights or air-conditioning. Worst hit by the mega-storm were customers of Pepco, which delivers electricity to 778,000 homes and businesses in the District and neighboring parts of Maryland. About half those customers lost their lights on June 29, and nearly a week later, thousands remained in the dark. There’s plenty to complain about, but some of the Pepco misery is mired in myth.