The process of natural gas extraction through hydraulic fracturing produces large quantities of fluid containing naturally-occurring salt, radionuclides, and heavy metals which form residual solids during storage and treatment. The purpose of this research was to characterize the residual solids from hydraulic fracturing operations in the Marcellus Shale to predict the leaching behavior of select elements in disposal environments.

Samples collected for this research were: (1) drilling mud, (2) treated sludge from the chemical treatment of process waters, (3) solids from the gravity settling of produced water, and (4) sludge solidified prior to disposal in a municipal landfill. These samples were subjected to various digestion techniques to determine the composition and leaching potential for elements of concern. Strong acid digestions were performed to determine the total environmentally available composition, whereas weak acid digestions were used to predict the leaching potential of these solids under various environmental conditions. The extraction fluids for the leaching experiments included weak acetic acid, acid rain, reagent water, and synthetic landfill leachate. Solids were agitated in a standard tumbling apparatus to simulate worst-case conditions based on ASTM and EPA recommendations. Results from EPA's Toxicity Characteristic Leaching Procedure (TCLP) were used to determine if solids were considered hazardous based on the metal leaching potential.

The results from strong and weak acid digestions were compared to better understand the types and quantity of materials that have the potential to leach from the samples. This research may be used to develop best management practices for hydraulic fracturing residual solids.