First Advisor

Shu-Guang Li

Term of Graduation

Winter 1997

Date of Publication


Document Type


Degree Name

Master of Science in Civil Engineering (MSCE)


Civil Engineering




Plumes (Fluid dynamics) -- Mathematical models, Sanitary landfills -- Oregon -- Multnomah County -- Leaching, Water -- Pollution -- Oregon -- Multnomah County, St. Johns Landfill (Multnomah County, Or.)



Physical Description

1 online resource (ix, 357 pages)


The St. Johns Landfill is a 225-acre site that lies near the confluence of the Columbia and Willamette Rivers, in the North Portland Industrial District of Portland, Oregon. A slough system surrounds the landfill on three sides with the fourth side adjacent to a shallow lake. The landfill first opened in 1930 when it was operated as an open dump. It operated as an open dump until 1969 when it was converted to a sanitary landfill, employing daily cover and compaction. The landfill was closed in 1991.

The landfill sits directly on top of a thick layer of silty overbank deposits. Directly below the overbank deposits lie a highly productive aquifer system. Concern has arisen about the landfill' s impact on the underlying aquifers as well as the surface waters directly adjacent to the site. Past studies have hypothesized that the thick layer of overbank deposits provides a barrier to contaminant transport into the lower aquifers. The purpose of this project is to quantify the fate and transport of contamination exiting the landfill.

To properly assess the flow and transport dynamics, a telescopic approach is used which nests a series of six groundwater models; each designed to provide uniquely specific information concerning the site. Contaminant mounding within the landfill due to rainfall provides the driving force for contaminant migration. The modeling system represents the quantitative inter-relationships between the landfill, the surface waters, and the underlying aquifer system.

The distribution of fluxes between the surface and groundwater is controlled by the anisotropy of the overbank deposits. Predictions show that the majority of the contaminants move laterally out of the landfill and into the surrounding slough system. The model also predicts that the underlying aquifer system has been impacted, but only in localized 'hot spots'. After the landfill is capped in 1991, contaminant migration is slowed due to the reduction of the contaminant mound. Future impact on the surrounding area at this point is due to regional flow dynamics controlled mainly by the regional recharge characteristics and the Columbia and Willamette Rivers.


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