The Occurrence and Origin of Sand Bodies in Till, with Special Reference to the Franklin County, Ohio, Landfill Site

Many landfill siting reports, of which those of the Franklin County, OH, landfill are typical, imply continuity of minor sand bodies in till between widely-spaced test holes where sand deposits fall within similar depth ranges. This review of studies of the local origin of most sand and gravel "lenses" or "seams," and their transport in active glaciers, however, indicate that most such deposits probably have limited lateral continuity. Their role in the groundwater circulatory system is commonly exaggerated in landfill reports. OHIO J SCI 98 (2): 23-27, 1998 INTRODUCTION This report was prepared originally as an internal report to Metcalf & Eddy, Inc., as an outgrowth of reviews of reports on the Franklin County Landfill site made for the Solid Waste Authority of Central Ohio. The landfill site is in southern Franklin County, about 10 miles south of Columbus, in a fairly representative part of the generally flat till plain that extends over most of west central Ohio and into eastern Indiana. In the original investigation of the site (Zande 1981) the glacial stratigraphy was defined on the basis of sand interbeds in the till matrix occurring within arbitrarily designated zones or ranges in elevation. From top down, the A zone included sand beds between elevations 861 and 842 feet (MSL), or about 7 to 14 feet below ground surface. Zones Bl and B2, separated in some borings by up to 12 feet of till, included sand beds between 857 and 812 feet (MSL) in elevation, or 8 to 41 feet below ground surface. Zones Cl and C2 included sand beds between elevations 823 and 788 feet (MSL) or 28 to 90 feet below ground surface. All of the sand beds in zones A, B, and C were shown to be discontinuous in test drilling, and none of the beds were considered regional aquifers. The identified regional aquifer system is the so-called D-R zone, which includes basal sand and gravel deposits generally occurring beneath the C zone and in close association with, or directly overlying, the limestone bedrock. The Franklin County Landfill site was approved and the landfill has been operating since about 1985. Some of the shallower sands were removed during construction of the cells and others were not considered important as potential fluid migration routes. To provide for future expansion of the landfill, adjoining property was acquired and an investigation made of the glacial stratigraphy, chiefly to define the extent and depths of the sand interbeds, using the same arbitrary zoning as that at the original site. Thus, the A, Bl, B2, Cl, and C2 designations, with suitable adjustments for differences in elevation, were assigned to those sand and gravel "lenses," "stringers," and other stratified 'Manuscript received 17 November 1997 and in revised form 2 June 1998 (#97-18). bodies, that occur in the new areas in the upper several feet of the till matrix. This arbitrary classification, or grouping into specific ranges of elevations and depths of sand interbeds, has led investigators to attempt correlation of deposits over large distances simply because they may occur in widely-spaced test holes at roughly the same elevation. When shown in cross-sections it is implied that if intervening test wells were drilled, they would also show similar sand sections at appropriate depths. An impression is given that many, perhaps most, of these shallow sand beds are continuous over large areas and, therefore, they can act as permeable conduits that might conceivably transmit contaminants from a landfill to a distant well. The purpose of this report is to show that most sand bodies in the upper part of the glacial till are of limited extent. Conclusions are based on reports of studies of outcrops and test borings and studies by glaciologists on the genesis of glacial deposits, including their observations in active glaciers. These studies indicate the discontinuous nature and limited extent of most sand interbeds in the surficial till. Such deposits are of course, in contrast to the more extensive, and thicker, outwash sand and gravel deposits, typically formed at the base, and in front, of a wasting glacier. MATERIALS AND METHODS In preparing this report, more than a score of texts and technical papers on glacial geology, acquired from the Polar Studies and Geology libraries at The Ohio State University and from private collections of glacial literature, were studied. These references, cited or quoted herein, will show that most shallow sand interbeds are unlikely to be of large areal extent, and should not be shown as implied continuous strata between test holes, where such test holes are more than a few feet, or a few tens of feet apart.