Characterization of Soils A,\?) Saprolites from the Piedmont Region for M7aste Disposal Purposes
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CHARACTERIZATION OF SOILS A,\?) SAPROLITES FROM THE PIEDMONT REGION FOR M7ASTE DISPOSAL PURPOSES Aziz Amoozegar, Philip J. Schoeneberger , and Michael J. Vepraskas Soil Science Department Agricultural Research Service College of Agriculture and Life Sciences North Carolina State University Raleigh, North Carolina 27695-7619 The activities on which this report is based were financed in part by the United States Department of the Interior, U. S. Geological Survey, through the Water Resources Research Institute of the University of North Carolina. Contents of this publication do not necessarily reflect the views and policies of the United States Department of the Interior, nor does mention of trade names or commercial products constitute their endorsement by the United States Government. Also, the use of trade names does not imply endorsement by the North Carolina Agricultural Research Service of the products named nor criticism of similar ones not mentioned. Agreement No. 14-08-0001-G1580 UWProject Number 70091 USGS Project No. 02(FY88) ACKNOWLEDGMENT Special recognition should be given to Ms. Barbara Pitman, former Agricultural Research Technician, Soil Science Department, who devoted long hours conducting the laboratory solute flow experiments and assisted with other field and laboratory investigations in this project. Thanks to Mr. Stewart J. Starr, College of Agriculture and Life Sciences, for providing land on Unit 1 Research Farm and for his patience with our research program. Appreciation is extended to Mr. Kevin Martin, president of Soil and Environmental Consultants, for his assistance in locating research sites, and to Mr. J. B. Hunt (Oak City Realty) and Mr. S. Dorsett (Dorsett and Associates) for allowing our research team to collect soil samples and conduct research on properties located in Franklin and Orange Counties, respectively. We acknowledge the assistance of Mr. Barrett Richards for construction of observation pits and soil sample collection, Ms. Angela Barnes, for laboratory analyses of samples, Mr. Atwell Cook for assisting with field experiments and sample collection, Mr. Mark Carpenter and Ms. Beth Haines for preparing thin sections, and Ms. Betty Ayers for assisting with the mineralogical analyses of samples. Undergraduate students Mitch Dawes and Mark Kleiss also assisted with the projects and their efforts are appreciated. Our appreciation is also extended to Drs. S. B. Weed, S. W. Buol, D. K. Cassel and M. T. Hoover for their cooperation in the project. Finally, we would like to take the opportunity to thank the secretarial staff of the Soil Science Department, the Water Resources Research Institute staff, and all those individuals not named here who directly or indirectly assisted us with this project. ABSTRACT There is great interest in using saprolite for on-site wastewater disposal purposes in the Piedmont and Mountain regions of North Carolina. However, information regarding hydraulic properties and attenuation capacity of various saprolites for pollutants found in domestic wastewater is limited. Field and laboratory studies were initiated to assess characteristics of a number of soil-saprolite sequences in the Piedmont region. A laboratory soil column experiment was conducted to evaluate movement of five inorganic constituents of domestic wastewater through three different soils and their associated saprolites that were collected from Franklin, Orange and Wake Counties. Directional saturated hydraulic conductivities (K,) and other physical and mineralogical properties of Bt (soil), B/C (transitional) and C (saprolite) horizons were measured at three different landscape positions (a ridge top, shoulder and ridge nose) over a Cecil soil mapping unit in Wake County (referred to as site #I). In addition, the macropore network of the three horizons at each landscape position was assessed in the field. Samples collected from four different color zones around Mn oxide coated fractures (a type of macropore) at the shoulder position were also analyzed, and profiles for vertical K, were obtained for the three landscape positions. At a second site in Wake County (referred to as site #2), contributions of different types of water-conducting pores to water flow under saturated and unsaturated conditions were evaluated through thin section analysis. In the laboratory miscible displacement experiment all five ions appeared in the outflow of undisturbed soil cores faster than they appeared in the outflow of the repacked soil material. The overall rate of movement of each ion through intact soil material, however, was slow. No appreciable differences were observed between attenuation and movement of various solutes through disturbed and undisturbed saprolites. For the primary site in Wake County (site #I), saturated hydraulic conductivity at each of the three landscape positions was largest on top of the Bt horizon, reached a minimum value in the B/C horizon, and increased with depth in the upper 2-m part of the C horizon. No statistically significant differences were observed among the directional K, values at any horizonllandscape position. Analyses of various color zones around fractures indicated sharp differences in the chemical compositions of the material. The results show different degrees of oxidation/reduction around the fractures, which is indicative of water flow between the fractures and the saprolite matrix. At site #2 in Wake County, macropores (root channels 0.1 to 0.5 mm in diameter) comprised approximately 2% of the saprolite body, but accounted for 95% of the water flow through saprolite under saturated condition. At a soil water potential of -10 cm, 50% of the flow was through the saprolite matrix. TABLE OF CONTENTS ACKNOWLEDGMENT ................................... ABSTRACT ........................................... LIST OF FIGURES ...................................... LISTOF TABLES ....................................... SUMMARY AND CONCLUSIONS .......................... xvii RECOMMENDATIONS .................................. xxi INTRODUCTION ....................................... Defmition of Saprolite .................................. Role of Saprolite in Groundwater Protection ................. Properties of Saprolite .................................. Objectives ........................................... MATERIALS AND METHODS ............................. Wake County Sites .................................... Franklin County Site ................................... Orange County Site .................................... Solute Flow Study ..................................... Laboratory Study .................................... Simple Solute Flow Model ............................. Field Study ........................................ RESULTS AND DISCUSSION ............................. Solute Movement Through Soil and Saprolite .................. Laboratory Study .................................... Simple Error Function Model ........................... Potassium Bromide Field Study ......................... vii Macroporosity of Soil Profile and Color Zones within Saprolite ..... Macroporosity ...................................... Color Zones Within Saprolite ........................... Multi-Element Scans and Analyses ........................ X-Ray Diffraction .................................... SEM and EDAX Spectra Analyses ....................... Mossbaur Spectra .................................... Vertical K.. Particle Size Distribution. and Bulk Density .......... Directional Saturated Hydraulic Conductivity .................. In Situ Saturated Hydraulic Conductivity ..................... Soil Water Retention ................................... Thin-Section Analyses of Macroporosity and Hydraulic Conductivity . REFERENCES ......................................... GLOSSARY ........................................... PUBLICATIONS ........................................ APPENDIX ............................................ ... Vlll LIST OF FIGURES Figure Page 1. Map of North Carolina showing the relative locations of the study sites in Franklin County (F), Orange County (O),and Wake County 0. ........................................ 2. Key soils and their associated soil series from felsic (Appling, Cecil, Helena, Hiwassee, Madison, Pacolet , Vance, and Wedowee) and mafic (Coronaca, Davidson, Enon, Iredell, Mecklenburg , Sedgefield, and Wilkes) crystalline rocks in the Piedmont region (after Daniels et al., 1984). ............................. 3. Topographic map of the study area at the Wake County site #1 showing the locations of the observation pits at (1) ridge top, (2) shoulder, and (3) ridge nose landscape positions. Contour line elevations are in ft. ................................ 4. Orientations of the undisturbed cores collected from the Wake County site #1 for directional saturated hydraulic conductivity. ... 5. Schematic diagram of the cross sectional area of the soil column assembly for determination of saturated hydraulic conductivity. ... 6. The upper part of a block carved in situ from saprolite at a depth of 1.9 to 2.7 m with two distinct Mn oxide coated fractures. ..... 7. Areal view of the Wake County site #2 with relative locations of sampling pits. ....................................... 8. Shear plane (horizontal in core) produced a displacement of approximately 2 mm in the mineral bands of saprolite. The pores shown are coated with Fe/Mn oxides and are < 0.2-mm wide. Bar length represents 3 mm. ............................ 9. Key soils and their