BOREHOLE DATA IN GLACIATED TERRAIN: STRATIGRAPHIC UNCERTAINTY AT THE SITE SCALE

Glacial depositional and erosional processes typically result in a complex framework of materials with irregular geometries and bounding surfaces. Facies associated with various glacial sedimentological settings may have very short lateral correlation distances. Deposits are later affected by ice readvances, by soil formation processes in-between advances, and by fracturing of fine-grained materials. Because of the nature of this depositional setting, a hydrogeological conceptual model for a glaciated terrain may therefore have a high degree of uncertainty at most scales of study. Of importance in hydrogeological analyses is that the properties, such as hydraulic conductivity, of the subsurface vary dramatically, and flaws in conceptual models may lead to inaccurate or inappropriate numerical flow models.

Drilling data are typically an abundant source of subsurface information at groundwater contaminant or water resources study areas. These stratigraphic data provide an important means of initializing or refining a site conceptual model, yet hydrostratigraphic correlation may be complicated by the distances between boreholes.

We have conducted hydrogeological analyses of several Midwestern study areas that differ in their glacial geologic settings and in the type and density of available drilling data. Techniques include data visualization, geostatistical analyses, and flow modeling. While some sites may be adequately characterized using traditional cross sections, understanding of more complex sedimentary associations requires a combination of quantitative approaches.