July 25, 2002
Home Depot builds atop an old Oregon landfill
By DAVID A. PISCHER and FRANK M. PARISI
Special to the Journal
On May 22, Home Depot hosted the grand opening celebration for its new retail store in Oregon City, located southeast of Portland. While some may notice that the new store is located just up the road from the large covered wagons at the Oregon Trail Interpretive Center, most may not be aware that it is constructed on top of a closed solid waste landfill.
Build on a landfill?
Rossman’s Landfill is an unlined landfill located near the intersection of two major highways — Interstate 205 and Highway 213, the Cascade Highway. Home Depot liked the site because, as they say, “location, location, location!” So, Home Depot negotiated a long-term ground lease with the landfill owner for use of a 16.7-acre portion of the 100-acre site.
The former solid waste landfill operated from about 1969 to 1983 and was closed and covered with vegetated soil. The refuse is about 30 to 40 feet thick and is in contact with shallow groundwater below the site. There are controls in place to prevent use of groundwater that has been contaminated by the landfill and other local sources. Landfill monitoring and maintenance activities are being conducted by the landfill owner under a closure permit issued by the Oregon Department of Environmental Quality (DEQ).
So what does it take to get DEQ’s approval and keep a project like this on schedule? The Home Depot project team took a proactive approach to identify and address DEQ’s environmental concerns during design and construction.
DEQ Project Manager Tim Spencer noted some of the agency’s concerns, which included: fire or explosion hazards due to potential landfill gas (LFG) buildup in confined spaces; potential human exposure to LFG emissions; additional groundwater contamination from construction activities; settlement of the refuse; and potential disturbance to unknown wastes that may be in the landfill.
Home Depot enlisted Landau Associates and Parisi & Parisi to prepare the environmental engineering design report that summarized the key environmental design, construction and monitoring provisions that would address DEQ’s concerns.
Initial site preparation began in fall 2000. Up to 10 feet of imported fill was placed over the existing soil cover to achieve desired site grades, and a 5-foot surcharge fill was placed to compress onsite materials and reduce post-construction settlement. Additional environmental monitoring conducted for DEQ indicated that site grading and surcharging did not have a significant effect on groundwater and LFG conditions in the vicinity of the development.
The facility is supported on pile foundations driven through the refuse into the underlying sand and gravel. About 1,230 closed-end, 2-foot-diameter steel pipe piles were installed during May to July 2001 to support the store, the perimeter concrete slab and entrance driveway, and certain other structures.
The pile spacing was adjusted to avoid an existing 4-foot-diameter leachate collection pipe that crosses the landfill. A cathodic protection system was installed to control external corrosion of the steel piles and other buried metallic structures and piping at the site. Measures taken to accommodate potential differential settlement on utility lines included use of ductile iron piping where appropriate; installation of flex-joints at manholes and other selected locations; and pile support of the water line and storm sewer manholes within the structural slab areas.
A landfill gas control and monitoring system was installed to provide a safe environment for the customers and employees of the Home Depot store, and to address the potential risks associated with LFG accumulating beneath the development.
The system consists of a gas barrier to minimize LFG migration into the store and up through paved areas; a gas extraction system to remove LFG from beneath the store and paved areas; and a gas monitoring system to monitor LFG concentrations in the store and beneath the development. The concern for migration of LFG along buried utilities and into confined spaces was addressed by the installation of various seals and plugs, and the use of gas-proof electrical conduits and vaults.
The long-term benefits of this challenging brownfield development project outweigh the short-term issues of construction on a landfill. Overall environmental benefits achieved from Home Depot’s development include: increased monitoring and oversight of the landfill; enhanced stormwater management and landfill cap performance; and an additional revenue source to help fund future landfill operational activities.
The project also qualified for DEQ certification under the Brownfields Initiative portions of the Taxpayer Relief Act of 2000. And...the residents of Oregon City have a great new Home Depot store.
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