The lull in foreclosures nationwide has given real estate search engine RealtyTrac an opportunity to crunch its data in several other, somewhat unusual ways.

A recent example, prepared by RealtyTrac subsidiary Homefacts, ranked U.S. counties "based on the prevalence of man-made environmental hazards."

Which was interesting, of course, because Philadelphia's aggregate score placed it near the top of the hazard list of more than 3,100 counties.

Each county's score was based on five environmental hazards: bad air-quality days, the number of Superfund sites, the number of brownfield sites, polluters, and former drug labs per square mile.

A higher aggregate score represented a higher prevalence of these hazards.

Philadelphia's score was second only to that of the city of St. Louis. And No. 2 was way better than No. 1.

St. Louis has 5.35 Superfund sites per square mile on the national priority list, compared with 2.33 in Philadelphia, and 13.03 "other environmental hazards" (meaning brownfields) per square mile, versus Philadelphia's 3.95. More than 7 percent of St. Louis' days per year have bad air quality, compared with 1.39 percent here.

Because these were aggregates, the scores meant that St. Louis was not all bad and Philadelphia was not totally better. Yet St. Louis' aggregate score was 87.2, while Philadelphia's was 27.8, a very big difference.

Baltimore was third on the list, and Hudson County, N.J., was fourth (see the entire list at http://tinyurl.com/njkqulf), and they were not much worse than Philadelphia.

Several things are worth noting.

First, brownfields are not a total wash. Thanks to changes in Pennsylvania law, developers have been building on these sites - old factories, warehouses, and other sites - for a number of years.

Second, locales such as these have been inhabited for centuries, so it is natural, while not by any means acceptable, to have man-made environmental hazards scattered about.

What's more, RealtyTrac vice president Daren Blomquist said, "Somewhat surprisingly, short-term home price appreciation over the past year and five years is stronger in the 50 housing markets with the highest prevalence of man-made hazards."

Philadelphia's July 2014 median price is listed by RealtyTrac as $107,000. Though prices have dropped nearly a percentage point year over year, according to RealtyTrac calculations, they are have increased almost 18 percent in the last five years (boosted by high-end sales in Center City, I assume).

"Not all of these environmental hazards are created equal, ranging widely in scope and severity," Blomquist cautioned.

24/7WallStreet.com did its own report, and dropped Philadelphia to sixth on a list of 10, with St. Louis still first.

"While Philadelphia County has some of the worst levels of man-made pollution among all markets reviewed, the area has made considerable progress," it said.

It cited as an example the Metal Bank, a Superfund site at Cottman Avenue and Milnor Street on the Delaware River, that was "completely cleaned up in 2010." And, "the percentage of bad air days was far lower than the national average, at just 1.4 percent since 2008."

"However, local officials may still have their work cut out for them," 24/7WallStreet.com said, citing the larger number of brownfield sites in Philadelphia than in all but one other county reviewed by RealtyTrac.

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@alheavens