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The complexities of building atop a long-vacant landfill soon became apparent for the team creating a Buddhist retreat in Northeast Portland.

The Dharma Rain Zen Center will include a 6,200-square-foot meditation hall and eventually 31 apartment-like units on 14 acres of the 26-acre H.G. LaVelle Landfill site. Redevelopment of that brownfield is being overseen by the Department of Environmental Quality and posed a host of challenges.

Before work could begin, the project team had to figure out how it would build upon a mountain of unstable soil that included roughly 2 million cubic yards of solid waste. Typically, pilings would be driven deep into the ground for support, said Gant Enderle, principal of B&G Builders 鈥� the project’s general contractor. That approach was used to build a Home Depot store on a former landfill site in Oregon City, he said.

鈥淚t took a bit of work to try and figure out what the best approach was,鈥� he said. 鈥淲e could have sunk piles down into terra firma, but it would have cost a lot of money.鈥�

The project team, including Tigard-based GeoDesign Inc., looked at several options and eventually settled on one that required pouring 10 feet of dirt interspersed with a specially designed, mesh 鈥済eo-mat鈥� fabric. The test took three months and the dirt only settled about three inches during that time, Enderle said.

Developers also have taken special steps to meet DEQ requirements that the threat of methane release be eliminated, said Mike Coenen, an associate engineer for GeoDesign.

The hazards of methane gas appear only when it is allowed to accumulate, according to Coenen. That made design of building ventilation systems critical.

鈥淲hat we’ve done is to incorporate features into the design of the building that do not allow it to accumulate,鈥� he said.

GeoDesign raised the foundation of the meditation building, essentially putting it on tiny stilts to ensure sufficient air space will be available for ventilation between the floor and the ground, Coenen said. The building will have sub slab vents allowing natural ventilation and preventing methane buildup.

For the development’s smaller buildings, GeoDesign used a passive venting system so that methane can disperse, he said.

CWK2 designed a pressurized sanitary sewer pump system, rather than a gravity sanitary sewer, to keep utilities closer to the surface, Enderle said.

鈥淲ith a pressurized system, you don’t have to slope it; it is easier to access and fix,鈥� he said. 鈥淭he trade-off is you have to replace it every 25 years.鈥�

Special considerations also were made to ensure water from the site will not enter the landfill. In a typical development, water would be treated on site before going into the city’s sewer system. At the Dharma Rain site, the water must be kept at surface level so that it can be treated off-site, Coenen said.

鈥淲e have to line our stormwater swales and treat the water above ground,鈥� he said. 鈥淭hen it goes down off-site.鈥�

Dharma Rain’s development team, in its due diligence phase, worked closely with the city’s Bureau of Environmental Services to get a pair of grants 鈥� one for $50,000 to pay for an environmental site assessment and one for $200,000 to pay for cleanup, said Jenn Bildersee, coordinator of the Portland Brownfield Program.

The grants, which came from the Environmental Protection Agency through BES, helped clear the way for Dharma Rain to purchase the property in 2012, Bildersee said.

鈥淭he grant is for innocent purchasers who did not cause the damage and gives them liability protection,鈥� she said. 鈥淭his helps so that people don’t have to be afraid to purchase a contaminated site as long as they take appropriate steps to clean up the site.鈥�

Dharma Rain also got support from the Madison South neighborhood. Volunteers contributed thousands of hours to clean up the site, said Kakumyo Lowe-Charde, the nonprofit’s development director.

鈥淭his has been a site that has been an eyesore for the community and a haven for drug use and prostitution,鈥� he said. 鈥淣eighbors were eager to take an active role.鈥�

Financing for the project came in part from the sale of Dharma Rain’s three buildings in the Hawthorne neighborhood. The organization has moved its operations into temporary facilities until construction is completed.

Additional financing will come from the sale of membership interest in the development, which includes the right to rent one of the apartment-like units that will be constructed next summer. Twenty-five memberships have been sold, Lowe-Charde said.

Dharma Rain Zen Center, first phase

Address: 8500 N.E. Siskiyou St.

Owner: Dharma Rain Zen Center

Project cost: $5 million

Construction start date: August 2014

Anticipated completion date: February 2015

General contractor: B&G Builders

Architect: Howells Architecture + Design

Engineers: CWK2 (civil), Horn Consulting Engineers (structural), GeoDesign Inc. (geotechnical)