Regional Basalt Aquifer Groundwater Flow Model

(Beaverton, OR)  Landau Associates provided remedial investigation(RI) and environmental cleanup services for a former toy manufacturer in Beaverton, Oregon. Environmental impacts to soil, surface water, groundwater, and air at the 56-acre site were a result of historical film processing and metal degreasing activities adjacent to Fanno Creek, a tributary to the Tualatin River. Groundwater contaminants were identified in a thin shallow alluvial aquifer and a deeper regional aquifer system composed of a thick sequence of basalt from the Wanapum and Grande Ronde Formation of the Columbia River Basalt Group.

As part of the RI, Landau Associates developed a regional conceptual model and a numerical groundwater flow model of the basalt aquifer system to inform remediation design including the hydraulic impact of pumping the facility water supply well. The conceptual model identified important regional and local hydrogeologic components to be represented in the numerical model, including boundary conditions, geologic units, a number of faults, land uses, and water supply wells surrounding the site. The 8-layer numerical model was calibrated using field observations, including pumping test results. The model helped confirm local faults as no-flow groundwater boundaries and the relatively high vertical hydraulic conductivity of the basalt flow interiors. Ultimately, the numerical model was used for conceptual design and capture zone analyses for site groundwater extraction and treatment (GET) systems.

 Landau Associates’ engineers designed and implemented the GET systems as an interim remedial action measure (IRAM). The IRAM employed extraction wells, air stripping technology, and granular activated carbon treatment to contain and clean up the groundwater contaminant plume. Landau Associates also performed air quality dispersion modeling to demonstrate that off-gas treatment from the air stripper was not needed.

Landau Associates has operated, monitored and maintained the site groundwater treatment systems for 11 years. In that time, over four hundred million (400,000,000) gallons of groundwater have been treated. The extraction and treatment systems have also been effective in restoring surface water quality in nearby wetlands and Fanno Creek.