Viewing the subsurface in three dimensions: Initial results of modeling the Quaternary sedimentary infill of the Dundas Valley, Hamilton, Ontario

The Dundas Valley is a bedrock valley infilled with up to 180 m of Quaternary sediment that underlies the Hamilton- Wentworth region of southern Ontario. Although the infill of the Dundas Valley contains a valuable record of past environmental change and controls groundwater and contaminant migration pathways in the region, the nature, origin, and spatial distribution of sedimentary units comprising the infill are poorly understood. This paper presents the initial results from the compilation and three-dimensional modeling of subsurface geological data obtained from water well and borehole records, and engineering and construction reports from the Hamilton region. RockWorks v.2002 was used to model and create images describing the bedrock topography and valley infill stratigraphy. Analysis of cross sections and three-dimensional box models created by RockWorks v.2002 allows five texturally distinct stratigraphic units to be identified within the valley infill. These units include bedrock (unit 1), draped by a discontinuous veneer of coarse sand and gravel (unit 2) interpreted as fluvial in origin, extensive silty clays and fine-grained diamicts (unit 3) that record either glaciolacustrine or subglacial conditions, coarse sands and gravels (unit 4) formed under high-energy shoreface conditions associated with postglacial Lake Iroquois, and silts and silty sands (unit 5) formed in lagoonal environments. The three-dimensional images showing subsurface sediment distributions and geometries for the Dundas Valley can be used not only to better constrain the late Quaternary depositional history of the region, but also to identify and delineate major aquifers and aquitards, essential for groundwater protection and remediation planning.