FRACTURES IN GLACIAL TILL: HOW QUICKLY CAN THEY FORM AND HOW LONG CAN THEY PERSIST?

Fracture formation in fill derived from fine-grained Ohio glacial soils and tills was observed to occur rapidly, in less than five years, at the WillowCreek Landfill site in Portage County, Ohio. Conclusions drawn from these observations indicate how quickly fractures can form in fine-grained material and raise significant questions about the possibility that fractures are an underlying root cause of slope failure in built environments. Potential applications include landfill construction and leachate generation (HELP model), earthen dams, highway construction, and general cut-and-fill construction sites. The issue of how long fractures remain viable conduits for water movement and contaminant transport was explored in a separate field study of buried, Pre-Illinoian-age lacustrine deposits found in at least two separate bedrock valleys in Clermont County, Ohio. These unique deposits exhibit brilliant blue-green colors of “green rust” that alter rapidly when exposed to oxygen. In these settings, the materials are leached of calcium carbonate but the iron has not undergone the redoximorphic depletion typically observed in gleyed hydric soils. Thus water movement has occurred exclusively through fractures and along varved bedding planes for approximately 700,000 years, indicating that in these settings, matrix flow is not occurring. The overlying Pre-Illinoian-age Backbone Creek glacial till also exhibits gleyed coloration but these materials were not leached of calcium carbonate. These materials also oxidize when exposed to air, indicating that again, the iron was not removed from the till. A possible correlation to similar permeability properties in northwest Ohio Late-Wisconsinan-age lacustrine materials and fine-grained tills is drawn. The “green rust” provides evidence for minimal to no matrix flow in fine-grained materials and supports the recommendation that water movement along fractures, varved bedding planes, through sand stringers, and along paleosol unconformities be assumed unless matrix contributions have been documented and can be confirmed in these settings.