Selective-placement burial of drilling fluids: effects on soil properties, buffalograss and fourwing saltbush after 4 years

A field study was established in 1986 to evaluate selective-placement burial as an alternative technique for on-site disposal of drilling fluids in arid and semiarid areas. Soluble salt and heavy metal migration in the soil, and establishment, yield and chemical composition of fourwing saltbush (Atriplex canescens (Pursh) Nutt.) and buffalograss (Buchloe dactyloides (Nutt.) Engelm.) were determined 44 months after simulated reserve pits were constructed to provide burial depths of 30, 90 (with and without a 30-cm thick, coarse limestone capillary barrier), and 150 cm, with sequential replacement of stockpiled subsoil and topsoil. Soluble salt concentrations increased most significantly in the 30-cm zone immediately above buried drilling fluids, regardless of treatment. Upward salt movement was greatest in the 90- and 150-cm treatments, with significant increases in Electrical Conductivity (EC) and Exchangeable Sodium Percentage (ESP) values observed as much as 60 and 30 cm above buried drilling fluid, respectively. Capillary barriers reduced the extent of upward salt migration, but had little effect in soil zones immediately overlying the drilling fluid. There was no evidence of upward migration of Ba, Cr, Cu, Ni, or Zn from buried drilling fluids into overlying soil, but concentrations of Cu and Zn were greater in saltbush stems grown on plots with buried drilling fluids on 1 site. Fourwing saltbush survival averaged 92 to 100% and was not affected by depth of drilling fluid burial. Significant reductions in saltbush canopy cover and yield on the 30-cm burial treatment were observed on 1 study site. Elevated Na concentrations in aboveground tissue of both species in the 30-cm burial treatment on 1 site did not adversely affect survival or plant growth. Differences between study sites in the extent of upward salt movement in the soil and in plant response were attributed to differences in soil clay type and content.