The Use of Test Pits to Investigate Subsurface Fracturing and Glacial Stratigraphy in Tills and Other Unconsolidated Materials

Author Institution: Department of Food, Agricultural, and Biological Engineering, The Ohio State University ; Bennett and Williams Environmental Consultants Inc.Joints and fractures, common in Ohio glacial tills, often influence shallow ground water flow paths and rates. Environmental site investigations in glacial till and lacustrine sediments should include determination of the glacial stratigraphy and evaluation of the presence, extent, and density of subsurface fractures. The test pit is one approach to directly assess fracturing and stratigraphy. The design and construction of deep test pits is examined in this research report, which includes an extensive literature review and case studies from three test pit sites in Ohio. A generic design is recommended that may be used for 1-meter, 2-meter, 3-meter, or 4-meter deep test pits. Scaled drawings are included

Further Explorations into Ohio's Fractured Environment: Introduction to The Ohio Journal of Science's Second Special Issue on Fractures in Ohio's Glacial Tills

Author Institution: Bennett and Williams Environmental Consultants Inc., Columbus, OHAuthor Institution: Dept of Food, Agricultural, and Biological Engineering, The Ohio State University, Columbus, OHAuthor Institution: Ohio Dept of Natural Resources, Division of Water, Columbus, OHThis paper summarizes the history of the Ohio Fracture Flow Working Group (OFFWG), describes their activities since the publication of the first special issue of The Ohio Journal of Science in 2000, and references selected recent publications by Ohio researchers, other researchers in the United States, and research efforts internationally. It also serves as an introduction to and overview of this second special issue of The Ohio Journal of Science. DEDICATION. This special issue is dedicated to Jane L. Forsyth and Truman W. Bennett for their foundational contributions to glacial geology and hydrogeology, respectively, and their roles in understanding fractures in unconsolidated (glacial) materials

DRASTIC Hydrogeologic Settings Modified for Fractured Till: Part 1. Theory

Author Institution: Bennett & Williams Environmental Consultants Inc., Columbus, OHAuthor Institution: Dept. of Food, Agricultural and Biological Engineering, The Ohio State University, Columbus, OHAuthor Institution: Ohio Dept. of Natural Resources, Division of Water, Columbus, OHAuthor Institution: Bennett & Williams Environmental Consultants Inc., Columbus, OHThe ground water vulnerability assessment model, DRASTIC, has been modified to better evaluate the effect of fractured till. In the mid-1980s, the Ohio Department of Natural Resources (ODNR) Division of Water began statewide, county-by-county mapping of the potential for ground water pollution. Eventually it was recognized that the original DRASTIC methodology needed to be modified to incorporate the concept of double-block porosity and preferential flow through Ohio’s fractured glacial tills. Glacial till was eventually recognized as a unique vadose zone media, and different ratings were assigned to the various till lithologies. It was determined that thin, weathered, highly-fractured tills should be more highly rated by increasing the rating of “R” Net Recharge and “I” Impact of the vadose zone media, where appropriate. In rare instances, the ratings of very thin soils (“S” Soil media) were modified to reflect the nature of underlying parent materials. In contrast, extremely thick sequences of unweathered till were given lower ratings for “R” Net Recharge and “I” Impact of the vadose zone media. DRASTIC maps have been completed for 76% of the 88 counties in Ohio. With the advent of Geographic Information Systems (GIS) applications, compiling a county DRASTIC map has become faster, and publication costs have been significantly reduced. GIS provides the tools to review and quickly modify historical mapping efforts that predate the fracture modification. This paper reviews the history of DRASTIC mapping in Ohio, presents the theory of modifications for fractures, and includes some discussion of Ohio regulatory applications

DRASTIC Hydrogeologic Settings Modified for Fractured Till: Part 2. Field Observations

Author Institution: Bennett & Williams Environmental Consultants Inc., Columbus, OHAuthor Institution: Dept. of Food, Agricultural and Biological Engineering, The Ohio State University, Columbus, OHAuthor Institution: Ohio Dept. of Natural Resources, Division of Water, Columbus, OHAuthor Institution: USDA-Natural Resources Conservation Service, Columbus, OHAuthor Institution: Bennett & Williams Environmental Consultants Inc., Columbus, OHDeveloped as a companion paper to "DRASTIC Hydrogeologic Settings Modified for Fractured Till: Part 1. Theory," twenty-one field sites around glaciated Ohio were visited to determine if fractures were present in the soils and underlying parent materials at each location. Four sites were featured with indepth discussions. In all, 23 of the original 95 fractured soils identified in Tornes and others (2000) were confirmed in the field and four new soils were added to the list: Amanda, Avonburg, Blanchester, and Clermont. Settings were grouped by common glacial and soils characteristics where they were linked to predict similar conditions over a wider ranging area. Modifications to their site specific DRASTIC ratings can be extrapolated to the larger geologic regions. All 21 sites were evaluated for their DRASTIC settings and new Ground Water Pollution Potential numbers were assigned where necessary. Modification of the DRASTIC mapping method has made the Ohio Ground Water Pollution Potential mapping program more protective of Ohio's ground water supplies. DRASTIC mapping efforts can play an important role in not only statewide but also local ground water pollution protection efforts

Properties of the Fractured Glacial Till at the Madison County, Ohio, Field Workshop Pit Site

Author Institution: USDA/ARS, Soil Drainage Research Unit ; School of Natural Resources, The Ohio State University ; Department of Food, Agricultural and Biological Engineering, The Ohio State UniversityWater and contaminants obviously do move through the so-called impermeable glacial tills in Ohio. This study was conducted to illustrate the extensive presence of fractures in the till and to quantify the differences in hydraulic conductivity and physical and chemical properties between the fractureaffected zones and the till matrix. In situ measurements of the saturated hydraulic conductivity were made in small boreholes positioned either in the matrix or intersecting the fractures. Soil samples from both the fracture faces and the matrix were analyzed for particle size distribution, clay mineralogy, calcite, dolomite, and iron content. Hydraulic conductivity measured in boreholes intersecting fractures was 1.25 x 105 cm/sec (0.018 in/hr), one order of magnitude greater than in boreholes in the matrix. Particle size distribution was the same for the fracture faces and the matrix. The fracture faces showed no significant change in total clay content and a slight increase in expandable clay. Calcite content was 62% greater, dolomite content was 6% lower, and iron content was 73% lower on the fracture faces as compared to the matrix. The fractures affected approximately 7% of the soil volume