One in an occasional series.

The "pot house" sat on a quiet corner in a neighborhood of farmhouses, bilevels and ranchers in the hills just outside Pottstown.

For more than a year, Drug Enforcement Administration investigators believe, the low-slung, redbrick home, valued about $285,000, was an incubator for the indoor production of marijuana - a "grow house" filled with special lights and sophisticated equipment capable of turning out harvest after harvest of high-potency pot.

"We never really saw anybody over there," said a neighbor on Shenkel Road who asked not to be identified. "There wasn't a lot of activity. Then the DEA raided the place. Now people kid me. They say, 'You live near the pot house.' "

The raid in February 2006 and the arrest of a 32-year-old Vietnamese man who ran from the home when agents approached was part of an investigation into a new drug phenomenon taking hold in the Philadelphia area.

The case offers a microcosmic look at a national trend. In the last two years, in California, Texas, Florida, and the nation's Northeast and Northwest, law enforcement authorities have tracked a proliferation of grow houses, most of them tied to Vietnamese organized-crime members who have long operated them in Canada.

By setting up shop in the United States, these groups - often loosely knit organizations built around family ties and associations - can reduce shipping costs and, more important, cut down the risk of detection inherent in transporting tons of product across the border.

William Hocker, a spokesman for the DEA office in Philadelphia, said last week that while Mexico remains the source for most marijuana smuggled into the United States, the potency of grow-house pot - four to five times stronger than Mexican field-grown - and the involvement of Vietnamese organized crime in its production were growing causes for concern.

In obtaining a search warrant for the house on Shenkel Road, DEA Agent Philip Bernal told a U.S. magistrate judge that it was part of an investigation into Vietnamese marijuana and ecstasy traffickers who had begun to purchase homes in the United States as grow houses.

The DEA focused on the Pottstown house after mortgage and deed records for the property were found in the Philadelphia home of a top associate of the organized-crime group.

In a related development, federal and state authorities in November identified a half-dozen properties in the Scranton-Wilkes Barre area that may be part of the same operation.

DEA officials declined to discuss the investigation. A dozen people have been indicted in the Scranton case, in which 3,500 marijuana plants and more than $230,000 in cash were seized.

Authorities are still piecing the puzzle together, a source close to the investigation said. It is unclear, for example, what connection the Philadelphia group has to Canadian mob figures. It is also unclear who is calling the shots locally.

In the Pottstown case, the man arrested at the house identified his boss as "Peter Le," who, he said, was part of the "Vietnamese Mafia." Investigators believe Le is an alias.

What is certain is that grow houses are capable of generating substantial income.

The Pottstown rancher, for example, was set up to produce a 40-pound harvest every six to eight weeks. At the going wholesale rate of $2,400 a pound, that would result in more than $600,000 in high-quality pot a year.

From one house.

Dozens may be operating in the area.

"It's a very profitable business," said Assistant U.S. Attorney Ronald Cole, the prosecutor in the Pottstown case.

Within the last year:

California and federal investigators in the Sacramento area targeted 41 houses, part of a multimillion-dollar operation.

New Hampshire state police confiscated more than 10,000 plants being cultivated in 11 homes, most in quaint New England-style neighborhoods.

Federal and local police in Florida hit 50 homes in the Port St. Lucie area in coordinated raids that netted more than 4,000 pounds of pot.

All three investigations are believed to be tied to Vietnamese organized-crime factions.

Super-potent pot

The DEA hit the house in Pottstown on Feb. 7, 2006.

What it found was a high-tech operation that can shorten marijuana's six-month growing cycle to 12 weeks and turn out marijuana with a THC level of 12 to 15. Field-grown marijuana usually has a THC level of 3 or 4. (Delta-9-tetrahydrocannabinol, or THC, is the psychoactive ingredient in pot that causes the high.)

The DEA seized 729 plants in the house in various stages of development, staged for a harvest every six to eight weeks.

There were 300 plants growing in the closet of the first-floor master bedroom, each about three inches tall. In other rooms and the basement, agents found plants ranging from one to three feet in height.

They also found 55 large light reflectors, timing systems to turn the 1,000-watt lights on and off, a venting system with an air filter attached to the chimney, and copper piping set up to create a regular flow of water to the plant beds.

All the window shades were drawn. The meters on two electrical junction boxes on the rancher were "spinning at a high rate," according to a report filed by Bernal, the DEA agent who took part in the raid.

Six months after the raid, agents intercepted a courier for the drug organization and seized $345,000 in a duffel bag found in the trunk of his car, according to court documents.

The courier, who agreed to cooperate, said he had made similar pickups from leaders of the organization in Philadelphia every month for about a year, taking the cash to another partner.

That partner's take, authorities estimate, would have been more than $4 million a year. And he is believed to have had just a one-fourth interest in perhaps a dozen grow houses.

More arrests and seizures are expected.

Tending the crop

The man arrested at the Pottstown house was Dai Nguyen, a Vietnamese emigre who came to Philadelphia in 2005 by way of London.

His job was to tend to the plants, he said.

Nguyen is serving a 24-month prison sentence after pleading guilty in September to marijuana-manufacturing charges.

If he is telling the truth, he was at the bottom rung of a typical Vietnamese crime-syndicate grow-house operation.

It is a lonely and isolated existence.

"Usually some mope gets hired to take care of the plants," said Jeremiah A. Daley, executive director of the Philadelphia County High Intensity Drug Trafficking Area, a law enforcement narcotics clearinghouse.

Nguyen told authorities that he had been paid $300 a week, and that "friends" would drop him off at the Pottstown house and leave him alone for five days at a time. They would then return and drive him to a home "somewhere near Atlantic City" where he would stay two or three days before being taken back to the grow house.

DEA agents found food in the refrigerator and clothing in plastic bags in the living room where Nguyen apparently slept.

After the raid, the local fire marshal condemned the house as a fire hazard. It has since been rehabbed and sold, neighbors said.

Some investigators are skeptical of Nguyen's story, saying he may have been more than a pawn in a multimillion-dollar operation.

Nguyen said he came to Philadelphia in 2005 with his wife and three children to visit his sister in Collingdale.

While socializing with friends at a restaurant near Sixth and Washington Streets in South Philadelphia, he said, he met Peter Le, whom he knew from an earlier visit.

Nguyen and his wife had worked briefly in 1998 at a nail salon that Le owned. This time, he said, Le asked whether he would like to work for him "watering some plants." Nguyen declined, but after his family returned to England and after he lost money gambling with Le in Atlantic City, he agreed to take the job.

Andrew Gay, Nguyen's court-appointed lawyer, declined to comment on any aspects of the ongoing DEA investigation. But he insisted his client was a small cog in whatever operation existed.

"He was just the gardener," said Gay.

Contact staff writer George Anastasia at 856-779-3846 or ganastasia@phillynews.com.