President Barack Obama is notoriously ungenerous about granting pardons, but on Wednesday he handed down 13, bringing his five-year total to 52.

One of the lucky pardon recipients didn't go to prison, but rather spent six months confined to his home for dumping slaughterhouse waste into South Dakota's Big Sioux River.

Ronald Greenwood served as manager of the wastewater treatment plant at meat processor John Morrell & Co.'s Sioux Falls, S.D., facility in the early 1990s and oversaw the pollution.

Greenwood and his assistant manager, Barry Milbauer, pleaded guilty in January 1995 to conspiracy to violate the Clean Water Act.

The duo doctored water quality tests in 1991 and 1992, when the company ramped up its slaughterhouse operations.

A 1997 U.S. Court of Appeals decision denying an appeal from another Morrell employee summarized the pollution scheme:

"In the first technique, which the parties frequently refer to as 'flow manipulation' or the 'flow game,' Morrell would discharge extremely low levels of water (and thus low levels of ammonia nitrogen) early in the week, when Greenwood and Milbauer would perform the required tests. After the tests had been performed, Morrell would discharge an exceedingly high level of water (and high levels of ammonia nitrogen) later in the week. The tests would therefore not accurately reflect the overall levels of ammonia nitrogen in the discharged water.

In addition to manipulating the flow, Greenwood and Milbauer also engaged in what the parties call 'selective sampling,' that is, they performed more than the number of tests required by the EPA but reported only the tests showing acceptable levels of ammonia nitrogen. When manipulating the flow and selective sampling failed to yield the required number of tests showing acceptable levels of ammonia nitrogen, the two simply falsified the test results and the monthly EPA reports, which [plant manager Timothy] Sinskey then signed and sent to the EPA."

In 1996 Greenwood and Milbauer were sentenced to six months of home confinement, 100 hours of community service and a $1,000 fine. Greenwood was ordered to pay $5,000 and Milbauer $3,000 to the Big Sioux River Environmental Trust.

Despite admittedly breaking the law, Greenwood was apparently uncomfortable with what he was doing.

The appeals court upheld meat plant manager Wayne Kumm's conviction, noting that Greenwood "began complaining about the violations and campaigning for physical improvements... to decrease future violations," but that Kumm "silenced him." At one company meeting Kumm told Greenwood, "[n]ow is not the time or the place to discuss those matters," the court recounted. The wastewater plant manager would "rant and rave... several times a week about the permit violations" to Kumm, according to the appeals court.

A Department of Justice press release from February 1996 says the pollution was disclosed voluntarily by Chiquita Brands, the parent company of Morrell until late 1995.

Milbauer, Greenwood's deputy, resigned his position because of the pollution, the Justice Department said. He was not pardoned by Obama.

It's unclear how Greenwood's pardon application won rare approval by the president. A search of opensecrets.org revealed no significant political contributions.

Greenwood did not immediately respond to a request for comment. A woman who answered his home phone Thursday afternoon said he did not have a lawyer who could field questions.

A spokesperson for South Dakota's Department of Environment and Natural Resources was unable to immediately say if the Big Sioux River continues to face any issues from the 1990s slaughterhouse pollution.

Spokespeople for the Sierra Club and Greenpeace, two major U.S. environmentalist groups, did not offer immediate comment on the pardon.