The Ohio State University 2000 - 06 Properties of the Fractured Glacial Till at the Madison County , Ohio , Field Workshop Pit

Water 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 10 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. OHIO J SCI 100 (3/4):107-112, 2000 INTRODUCTION The Ohio Academy of Science 1997 Summer Field Workshop on Joints and Fractures in Ohio Tills: Site Investigation Techniques & Field Hydraulic Measurements was held at The Ohio State University's Molly Caren Agricultural Center near London in Madison County, OH. The motivation for organizing and presenting this workshop was to illustrate the extensive presence of fractures in the so-called impermeable tills, and to demonstrate various investigation and measurement techniques for site assessments in areas with known or suspected fractured tills. Evidences of ground water contamination from sources such as leaking landfills, septic leach fields, and food processing wastewater lagoons indicate that these tills are not impermeable, and, in fact, that substantial amounts of water and contaminants can move through the tills. There is a need to increase awareness of the fractures and to understand more about their origin, their properties, and their contribution to ground water recharge and contaminant transport. Our initial goal was to demonstrate an in situ method for measuring hydraulic conductivity and to quantify the difference in hydraulic conductivity between the fractures and the till matrix. Ultimately we expanded our scope to include characterizing physical and chemical differences between the fracture-affected zones and the till matrix. MATERIALS AND METHODS Field Workshop Site The site is located in Deer Creek Township, Madison County, OH, at 39°56'51.33" N latitude, 83°25'39.17" W longitude. A large pit was excavated to allow participants at the field workshop to walk down into the pit to Manuscript received 27 August 1999 and in revised form 15 January 2000 (#99-26). observe the fractures at several levels and to appreciate their three dimensional orientation. The construction of this pit is described in detail in Christy and others (2000) with accompanying photographs. The site is representative of the Late Wisconsinan age till deposits in west central Ohio. Cores from vertical and angle boring drill rigs were taken adjacent to the pit to demonstrate the relative usefulness of cores to indicate the presence and intersecting nature of the fractures as seen in the pit. Discussions at the pit during the field workshop included a geologic history of the area, possible mechanisms causing formation of the fractures, soil profile description, and hydraulic conductivity measured in the fractures and the matrix. Geologic Description The study site is located on the proximal side of the London recessional moraine. This moraine is a portion of the body of dominantly loam and silt loam textured Wisconsinan glacial till which in central Ohio is located between the Powell moraine and the Reesville moraine (Pavey and others 1999). This till body can be traced westward into Indiana and Illinois (Mickelson and others 1983). Deposition of the London moraine is dated at 16,100 to 16,700 yr BP and has been designated as the Darby Till (Mickelson and others 1983). The till characteristically has 15 to 25% clay and 10 to 15% limestone rock fragments (carbonate). (Also see Brockman and Szabo 2000.) Soil Series Description The soils of the study site are dominantly an association of Miamian, Lewisburg, Celina, and Crosby soils (Gerken and Scherzinger 1981). These soils represent a toposequence of soils ranging in drainage from well to somewhat poorly drained. The Lewisburg and Celina are both moderately well drained soils with the Lewisburg L08 MADISON COUNTY, OHIO, TILL PROPERTIES VOL. 100 having thinner sola. All of these soils are considered to have developed from loam textured glacial till of Wisconsinan age. The major study pit was located in a unit of Lewisburg silt loam on a 0-2% slope. The Lewisburg soil is classified as fine, mixed, mesic Typic Hapludalf. A typical Lewisburg profile described in Madison County follows (Gerken and Scherzinger 1981). Ap 0 to 229 mm (0 to 9 in); brown (10YR 4/3) silt loam; moderate medium granular structure; friable; many roots; few pebbles; neural; abrupt smooth boundary. Bt 229 to 381 mm (9 to 15 in); dark yellowish brown (10YR 4/4) clay loam; weak coarse prismatic structure parting to moderate medium subangular blocky; firm; common roots; patchy dark yellowish brown (10YR 4/4) clay films on horizontal and vertical faces of peds; 5 percent pebbles; slightly acid; abrupt wavy boundary. BCt 381 to 533 mm (15 to 21 in); yellowish brown (10YR 5/4) clay loam; moderate coarse subangular blocky structure; firm; few roots; patchy dark yellowish brown (10YR 4/4) clay films on horizontal and vertical faces of peds; common light gray (10YR 7/1) weathered limestone fragments; 8 percent pebbles; slight effervescence; mildly alkaline; clear wavy boundary. Cl 533 to 838 mm (21 to 33 in); yellowish brown (10YR 5/4) loam; few fine distinct light brownish gray (10YR 6/2) mottles; massive; firm; 12 percent pebbles; strong effervescence; moderately alkaline; gradual wavy boundary. C2 838 to 1143 mm (33 to 45 in); yellowish brown (10YR 5/4) loam; common medium distinct light brownish gray (10YR 6/2) mottles; massive; firm; 12 percent pebbles; strong effervescence; moderately alkaline; gradual wavy boundary. C3 1143 to 1542 mm (45 to 60 in); yellowish brown (10YR 5/4) loam; massive; firm; 12 percent pebbles; strong effervescence; moderately alkaline. Sampling of the Pit The field workshop pit had benches constructed at approximately 1.1m (42 in), 1.9 m (73 in), and 2.7 m (108 in) below the ground surface. Saturated hydraulic conductivity measurements were made on the upper bench at 1.1 m (42 in) depth (Fig. 1) using the Compact Constant Head Permeameter (also known as the Amoozemeter) described by Amoozegar (1989). This technique involves maintaining a constant head of water in a 51 mm (2 in) diameter by 254 mm (10 in) deep cylindrical borehole and monitoring the water use over a period of time. Data were collected for two such holes, one intersecting a fracture and the other within the matrix (Fig. 2). Because the flow rates were very slow, readings were taken after 18 to 24 hours to increase the accuracy of the measurements. Bulk soil samples were taken from 0.9 to 1.1 m (36 to 42 in), 1.3 to 1.4 m (50 to 56 in), 1.7 to 1.8 m (66 to 72 in), and 2.1 to 2.2 m (82 to 88 in) for determining particle size analysis, carbonate content, and clay mineralogy of the 1997 Summer Field Workshop Site