Monday, October 21st, 2019

Speaker: Steve Usher, Senior Hydrogeologist

Title: "Why a Geologic Framework Improves Engineering Performance: A British Columbia Case Study"

Time: 2:30 – 3:30 PM

Location: Rm. 103, Mitchell Hall (Event Commons), Queen’s University

Refreshments provided!

Bio

Steve Usher graduated from Civil Engineering at Queens in 1979 as a geotechnical engineer with a dangerous knowledge of geology and water resources.  He had the fortune to join Gartner Lee Limited, a leading hydrogeological consulting firm under the watchful eye of Grant Anderson, a geological engineer (Sc. 70) from dear old Miller Hall.  He obtained an M.Sc. from Waterloo (sorry) in 1986 in the field of groundwater science.  At Waterloo Steve’s mentors were John Cherry, Bob Farvolden, and Bob Gillham and his cohorts included Dr. Kueper of Ellis Hall fame.  Steve has practiced in multiple areas over the past 40 years including contaminant hydrogeology, groundwater resources, and was one of the first to practically apply groundwater methods to understanding the ecologic features of wetlands and coldwater creeks.  He joined SLR Consulting (Canada) Ltd. in 2009 after Gartner Lee was sold to a publicly traded engineering company, and ten or more of his colleagues followed suit in the ensuing months.  Steve has also served as president of the APGO in 2007-2008 and participated in its formation from 1998 to 2002.  After living in Whitby for 30 years, he currently maintains his national practice, but now from the warmer climes of the British Columbia gulf islands.

 

Abstract

Typically, clean up of old leaking gas stations are a “dig and dump” affair.  The level of science of assessment is limited to drilling and soil sampling and testing for hydrocarbons, including water samples.  In the majority of cases this is an effective and economic solution as the contamination is usually shallow.  In this case study a lacustrine clay aquitard appeared to be of substantial thickness, and one confirmatory borehole into the confined aquifer below yielded startling results, with LNAPL trapped under the aquitard.  150 downgradient private water wells existed starting about 100 m from the site.  Initial efforts focused on the dig and dump process, but engineers wisely chose not excavate too much of the aquitard, but an understanding of WHY it was in the confined aquifer was not attained.  A proper geologic model was constructed by experienced hydrogeologists, including review of the prehistoric glacial conditions which explained the source of aquifer penetration.  Successful remedial efforts then focused on a pump and treat with hydraulic containment, turning this high risk site into one of ongoing maintenance and progressive cleanup.

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