Properties of hydrocarbon- and salt-contaminated flare pit soils in northeastern British Columbia (Canada)

Abstract

Many contaminated sites in Canada are associated with flare pits generated during past petroleum extraction operations. Flare pits are located adjacent to well sites, compressor stations and batteries and are often subjected to the disposal of wastes from the flaring of gas, liquid hydrocarbons and brine water. This study was conducted to evaluate the physical, chemical, electrical and mineral properties of three flare pit soils as compared to adjacent control soils. Results showed that particle size distribution, pH, total N, cation exchange capacity, exchangeable Mg 2+, and sodium adsorption ratio were similar in soils from flare pits and control sites. Total C, exchangeable Ca 2+, K + and Na +, soluble Ca 2+, Mg 2+, K + and Na + and electrical conductivity were higher in flare pit soils compared to control soils. X-ray diffraction and scanning electron microscopic analyses showed the presence of gypsum [CaSO 4 · 2H 2O], dolomite [CaMg(CO 3) 2], pyrite [FeS 2], jarosite [KFe 3(OH) 6(SO 4) 2], magnesium sulphate, oxides of copper and iron + copper in salt efflorescence observed in flare pit soils. Soils from both flare pits and control sites contained mica, kaolonite and 2:1 expanding clays. The salt-rich materials altered the ionic equilibria in the flare pit soils; K Mg–Ca selectivity coefficients in control soils were higher compared to contaminated soils. The properties of soils (e.g., high electrical conductivity) affected by inputs associated with oil and gas operations might render flare pit soils less conducive to the establishment and growth of common agricultural crops and forest trees.