After Diana Johns moved into an elegant new home 40 miles west of Washington, her sophisticated septic system -- which uses peat imported from Ireland to clean human waste -- morphed into a goopy green mess that sent sewage flowing onto her lawn.

For Falguni Patel, it was the mixture of suds, grime and urine flowing for months down her just-planted grass and the flies and mosquitoes the fetid discharge lured outside the French doors of her million-dollar house that caused alarm.

Expensive individual sewage treatment systems, which allow builders to squeeze more homes into once-rural areas across the United States, are failing in an array of new subdivisions across Loudoun County, according to a review of public records and interviews with residents.

Fueling the problem are vast financial incentives to build more homes more quickly in one of America's most lucrative housing markets and, builders say, confusion by owners who are used to simply flushing -- not systems that require maintenance. Sewer lines are expensive and have generally been kept out of western Loudoun to prevent urbanization.

The result has been numerous freshly built houses with failing systems, some of which have expelled tens of thousands of gallons of untreated or partially treated waste, polluting the environment and endangering human health.

"We're just afraid this is the tip of the iceberg," said Joe Lock, a Loudoun septic enforcement official. "What about the ones we don't know about?"

As booming population growth, migration to warmer climes and better jobs and the allure of rural scenery continue to spur development on the outskirts of America's metropolitan areas, a third of all new U.S. homes are being built with septic or other on-site systems, rather than the central sewer lines that have served urban areas for decades.

Boosters of conventional septic tanks and newer, more elaborate options cite the efficiency of dispensing flushed waste right outside a residence rather than miles away down expensive pipes. They also tout the environmental benefits of using advanced systems, which in some cases pump out water clean enough to drink.

"Even the president has one," said Linda Hanifin Bonner, executive director of the National Onsite Wastewater Recycling Association Inc., an Anne Arundel-based lobbying group, noting that the leader of the free world relies on one of her members' systems at his Crawford, Tex., ranch. The company's slogan: "Don't Pollute -- Install a HOOT!"

"Let's just say the future is very good for the on-site industry," Bonner said.

But that's not the story Barry Gibb tells standing behind his grand new home west of Leesburg in the Beacon Hill subdivision.

Gibb runs a general contracting business in Loudoun and is trained in electrical and plumbing work. He just upgraded his oversized lawn with a pool and spa for $140,000. But all he talks about over the trickling sounds of his new, chlorinated waterfall is the stench from the special, air-pumped sewage treatment system poking up from the grass nearby.

"You've got a million-dollar home. You've got a swimming pool in the backyard. You don't want to smell doo-doo," he said.

Gibb has been working as a builder in Loudoun for 20 years. So far, he said, neither his home builder nor the installer has solved the problem, leaving him holed up indoors rather than poolside.

"The way Loudoun County is building so fast, there's not enough good help. It's being slapped up," Gibb said. "Everybody's just cashing in and making a quick buck."

James S. Williams, executive vice president of the Northern Virginia Building Industry Association, said he has not heard concerns about widespread problems with systems but said that warranty programs should cover work, if necessary. "The purchaser is not too innocent going into these things, because he's done it with his eyes wide open," Williams said. "A lot of people who blame the problems on the builders haven't maintained the systems."

Across the street from Gibb's house at a recent block party, complete with pepperoni pizza, lemon bars and 13 kids tossing water balloons and splashing in a kiddie pool set up on the driveway, Vashti Curtis recalled her own problem.

She discovered it when Duke, the family's Labrador retriever, returned home, reeking and sick, after eating from a cracked pipe in their new-fangled septic system, which sits in the middle of her lawn.

"It's bubbling brown water. . . . I mean, it was real poop water," Curtis said. Duke "kept having diarrhea over and over and over again. I didn't know what it was. Thank God my kids didn't play out there."

Identifying the cause of such problems often requires a nose for sleuthing. A computer panel will short out. A distribution pipe will freeze. A filter will clog. A bulldozer will crush underground pipes. The possibilities can be seemingly endless, as can the finger-pointing.

"That's what's hard. It's like being Colombo all the time. 'Who destroyed what?' " said Joe Lock, who has spent years poking around the ooze of Loudoun's boom. "You have to take it all in and say, 'Is this what's really going on?' Sometimes it's what people don't say."

More than a half-dozen major participants are involved with a typical system. A soils specialist tests the ground. An engineer comes up with drawings matching a system to a specific landscape. Then there's the manufacturer, the home builder and the builder's installer. Officials must sign off. And residents decide what raw materials go down.

In traditional septic systems, household waste drains to an outside tank, where bacteria begin to feast and solids settle to the bottom. Liquid waste is piped out underground, where organisms in the soil keep working to clean it. Alternative systems rely on blowers, pumps, computer controls or various filters to better clean the effluent so it can be released into soils that couldn't safely absorb it otherwise. Sewer lines take waste to industrial treatment plants.

At least four recently built subdivisions in western Loudoun have had multiple residences with failed systems, according to health records and interviews: Beacon Hill and Shenstone Farm, both near Leesburg; Hamilton Station Estates outside the tiny town of Hamilton; and Chartwell Estates farther west.

The homes were constructed by leading national and regional home builders, including Pennsylvania-based Toll Brothers, K. Hovnanian Homes in New Jersey, NVR Inc. in Reston and M/I Homes, among others. They included numerous brands of septic and other on-site systems and a variety of installers. Representatives from Toll and NVR declined to comment, and no one from Hovnanian returned calls. An M/I vice president said only one of the company's septic systems had problems, and he blamed those partially on the homeowner.

Four days after moving into their new home in the Shenstone subdivision on Christmas Eve, Aaron Zeitlin, who works in the mortgage industry, and his pregnant wife, Hanh Chau, a veterinarian, were giving their 2-year-old son a late-night bath in the oversized tub in the master bedroom. Zeitlin heard water falling as he headed downstairs to shut off the lights.

"I could see water flowing out over the toilet -- material and all -- just really nasty stuff," Zeitlin said. He yelled for his wife, who was supposed to be on bed rest, to bring towels as it poured out on the hardwood floor in the hall and into the playroom. "She's standing there, in flip-flops, cleaning the stuff up. I hollered at her to get out. My 2-year-old is walking around in it with bare feet."

Workers with heavy equipment had rolled over their septic pipe to move earth behind the house before they moved in, stopping up the flow to the outside. The draining bathwater had pushed it over.

Falguni Patel and her husband, Rajesh, a real estate agent, said they were confronted with wastewater swishing past their window each morning as they peered out toward the sun for their Hindu prayers.

In other cases, it is the sensitivity and uncertainty of the new technology that gets homeowners rankled.

The high-pitched, high-decibel beep blaring inside Diana Johns's house started three months after she and her family moved in. It meant something was amiss with her yard's miniature sewage plant.

The alarm signaled that the family seemed to be using too much water for the peat-based sewage system to handle. She has four sons and was doing three loads of laundry a day. She also was running the dishwasher and the garbage disposal that her builder, M/I homes, had installed.

County officials came to investigate. They found evidence of high water usage but contradictory evidence of high waste concentrations. Searching for an explanation, they noted in county files that her kids often took antibiotics, making the officials wonder whether that might affect the system. A technician seemed to be joking when he quizzed her about possible criminal behavior, Johns said.

"At one point, they asked me if I had a meth lab in my house. I've never even smoked pot in my life," she said. They told her not to use her fabric softener or harsh cleaning products. "If they had said, 'You can't use these items,' I may not have bought this house. I can't live without my Downy and my fluffy towels."

Scott Donelson, an M/I homes vice president, said residents can't have unlimited expectations when they move to a setting served by on-site systems. He said the Johns case is the only instance he knows of in which a system in one of the company's homes in Loudoun had failed. It spent thousands of dollars to start over with new peat.

"They do work well," he said of the on-site systems. "I'm really confident in them if -- and the big qualifier on those is if -- the operator or homeowner doesn't try to exceed its limitations," Donelson said. "If you asked your Ferrari to go four-wheeling in the mountains, it probably wouldn't last too long."

Johns said she isn't sure whether she used too much water for the system but is certain she didn't do anything wrong. Still, she said, she uses paper plates for the kids to cut water usage and is choosier about whether to do laundry. "I do smell the clothes to make sure they are actually dirty. I never, ever would have considered that before."

Diana Johns and son Matt, 17, watch his brothers, Sean, 4, left, Nick, 8, and Mitchell, 6, bounce next to their home's peat-based septic system, on lawn at right, which overflowed recently, possibly because too much water was used.