Achieving Groundwater Source Control Using a Hydraulic Control and Containment System in a Tidally Influenced Hydrogeologic System

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Poster:

Achieving Groundwater Source Control Using a Hydraulic Control and Containment System in a Tidally Influenced Hydrogeologic System

Presenter:  John  Renda (Anchor QEA, LLC)
Authors:  John Renda, John Edwards, Ben Hung and Ben Johnson (Anchor QEA, LLC), Robert Wyatt (NW Natural)

Abstract:

The NW Natural Gasco Site is a former MGP site located along the banks of the Willamette River within the Portland Harbor Superfund site in Portland, Oregon. A hydraulic control and containment (HC&C) system has been installed along the shoreline to prevent migration of contaminated groundwater to the river. The HC&C system is comprised of 25 extraction wells installed along 2,000 feet of shoreline in the upper and lower alluvium; this maintains a hydraulic gradient from the river toward the shoreline, thereby preventing discharge of contaminated groundwater.  Groundwater elevations in the alluvium fluctuate constantly due to river tidal effects. Pressure transducers installed in the river and control wells located between the extraction wells are connected to programmable logic controllers that trigger increased or decreased pumping rates in real time to keep groundwater elevations below the river. The system is operated with a combination of fixed flow rates and set-point differentials between the groundwater and river elevations. The extracted groundwater is treated at an on-site treatment plant before being discharged to the Willamette River under a NPDES permit.  The HC&C system is equipped with a human machine interface (HMI) for programming, data acquisition, and alarm notifications. Alarm notifications are automatically sent out by phone and e mail to the system operator. The HMI can be operated remotely to respond to alarms, check the system status, and make adjustments in response to alarms. The offshore river seepage control area has been empirically verified using offshore transducers and an in-river distributed temperature survey. A MODFLOW model has been developed, calibrated, and validated for the groundwater flow system. Particle track model output shows the capture zone area consistent with the empirical data. Maintaining groundwater source control is required to prevent the migration of contaminants to the river as well as recontamination of the river sediments

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http://mgpsymposium.com/poster-presentations/

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