Speciation and Geochemical Implications of Carcass Burial Leachate

Abstract

Abstract. In the event of a mass livestock mortality situation, disposal routes such as burial are commonly chosen. The impact of burial on the environment could be substantial, but the composition of the leachate arising from a burial site has not been well documented. This study was performed to determine the chemical composition of leachate arising from animal mortalities in a burial setting. Three species of livestock were used: bovine, swine, and poultry. Leachate collected from lined burial pits over two years of decomposition was analyzed for major and minor ions. Analysis indicated that livestock mortality leachate contains, on average, concentrations of 46,000 mg L-1 of alkalinity (as bicarbonate), 12,600 mg L-1 of ammonium-N, 2600 mg L-1 of chloride, 3600 mg L-1 of sulfate, 2300 mg L-1 of potassium, 1800 mg L-1 of sodium, and 1500 mg L-1 of phosphorus, along with lesser amounts of iron, calcium, and magnesium. Select samples had maximum concentrations of ammonium-N and bicarbonate up to 50% higher than these average values. In comparison to earthen swine manure storages and landfills, the ionic strength of the leachate was 2 to 4 times higher, and therefore its impact on water resources could be greater. Following the study of the chemical composition of livestock mortality leachate, the potential impacts of this leachate on the soil/water systems below a burial site were investigated. The ionic strength of the leachate presents its own set of challenges. Basic modeling of ion activity using the five most common activity coefficient equations (Debye-Hückel, extended Debye-Hückel, Truesdell-Jones, Davies, and Pitzer) were considered to assess the sensitivity of these methods for calculated ion activity as impacted by the ionic strength of the leachate. This was completed to further enhance the modeling and speciation efforts. Based on the results and the applicability of the Truesdell-Jones equation, PHREEQC was used to assess the chemical speciation of the leachate. The speciation of this leachate provides evidence of phosphate and sulfate compounds available for potential unattenuated transport. Understanding the geochemical implications of livestock mortality burial will give scientists and regulators more information for performing future risk analyses when considering mortality burial as a management option, either routinely or during a mass mortality event. Keywords: Ion activity coefficient, Ionic strength, Leachate chemical composition, Livestock burial leachate, Speciation.