Delineating the zone of topsoil disturbance around buried utilities on agricultural land

Installation of pipeline utilities (oil, natural gas, water) in central Canada prior to the 1970s often resulted in extensive mixing of topsoil with subsoil materials within the easements due to largely unregulated construction practices. The main objectives of this study were (1) to develop a simple field protocol for the rapid delineation of the zone of topsoil disturbance (or topsoil–subsoil mixing) around buried utilities on agricultural land in southern Ontario, and (2) to characterize the zone of topsoil disturbance in the vicinity of an existing pre-1970s pipeline in terms of agronomically important soil properties. The study was carried out at six farm sites chosen along a pipeline easement (30+ years old) in southern Ontario. Soil organic carbon content, CaCO₃ content and pH were found to be useful in delineating the zone of topsoil disturbance around the buried utility. Standardized laboratory techniques for determination of these three soil attributes were used to analyse surface soil samples (Ap horizons) taken at 1·5 m intervals along 45·7 m long transects oriented perpendicular to the easement. In addition, rapid field tests for these same three variables were adopted/developed and tested, and two portable instruments were evaluated for their usefulness for in situ soil property measurements. In particular, a Minolta^™ CR-310 Chroma Meter was successfully used to relate moist soil colour to the organic carbon content of the surface soil. The chromaticity coordinate a* (CIE L*a*b* colour space notation) was shown to provide good estimates of organic carbon content for soils of medium to fine texture in this region of Ontario. The zone of topsoil disturbance was most often characterized by an appreciable increase in per cent CaCO₃ equivalent and pH, and a decrease in organic carbon content (dilution), over the pipeline trench when compared to off-easement areas. The zone of topsoil disturbance was usually a minimum of 15 m wide (i.e. the approximate width of the original trench and workspace areas during construction), and frequently much wider due most likely to wet soil conditions at the time of construction, agricultural tillage translocation of topsoil over time, and other factors. It is recommended that rapid on-site determinations of the zone of topsoil disturbance should be based primarily on field estimates of CaCO₃ content (10 per cent HCl) and organic carbon content (a* chromaticity coordinate using a portable colorimeter). Copyright © 1999 John Wiley & Sons, Ltd.