Incubation with moist top soils enhances solubilization of radium and other components from oil-field scale and sludge: Environmental concerns from Mississippi

Abstract

Large quantities of brines are coproduced with hydrocarbons from oil and gas wells. Dissolved solutes from these brines precipitate, forming scale in and on production equipment and sludge in storage tanks. The most abundant component of these scales and sludges is barite. Radium is one of the solutes that may be incorporated into these precipitates, rendering them radioactive. One method for the disposal of scale and sludge is land spreading, in which the material is mixed into the top few centimeters of the soil and then covered with a layer of clean soil, such that the radioactivity is below governmental action levels. An assumption associated with this disposal method is that the inorganic components are highly insoluble, relatively immobile in the environment, and low in biological availability. To test this assumption, (1) radioactive scale and sludge samples were evaluated for leachability; then (2) leachability was evaluated after mixing scale and sludge samples with top soils and incubating them under moist conditions similar to what may be expected using land spreading; (3) soil-scale mixtures were also incubated wet or dry, followed by differential density separation of the scale and soil. Incubating the samples under moist conditions with top soils increased the Ra that was extractable from them by several fold. This finding is remarkable in that soil retains most of the soluble Ra added to it and soils mixed with scale or sludge retain even greater proportions of the soluble Ra added to them. The implication is that although the retained, solubilized Ra is difficult to extract from the soil, it will be much more biologically available and mobile in the environment than in its original, highly insoluble form. This conclusion is of particular concern in warm and humid climates such as those typical of Mississippi and the southeastern United States.