LAND-BASED DISPOSAL OF FLOWBACK WATER RESULTING FROM HYDRAULIC FRACTURING OF GAS WELLS IN THE MARCELLUS SHALE
Open Access
- Author:
- Cogan, Cody Clair
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 18, 2013
- Committee Members:
- Herschel Adams Elliott, Thesis Advisor/Co-Advisor
- Keywords:
- Marcellus Shale
Flowback Water
Land-based Disposal
Hydraulic Fracturing - Abstract:
- Natural gas is extracted through hydraulic fracturing, the pumping of water under high pressure into the shale, fracturing the strata, thereby allowing gas to escape. Gas returns to the surface under high pressure carrying with it brackish or brine water known as flowback. Flowback is generally contaminated with fracturing fluids and substances naturally occurring in the shale strata. Flowback ranges from 1,000-150,000 ppm total dissolved solids (TDS) including sulfates, chlorides, bromides, and toxic proprietary fracturing chemicals (Shramko et al., 2009). Flowback contains several components that are linked to harmful environmental and health effects. Due to these potentially toxic substances contained within flowback waters, discharge directly into the aquatic systems is not permitted. Flowback water requires extensive treatment at specialized treatment facilities to meet Pennsylvania discharge regulations. Due to the high quantities of flowback produced in Pennsylvania, 4 million gpd (15 million Lpd), a more efficient and cost effective disposal method is needed. Land-based disposal of flowback waters could potentially meet this need. Feasibility of land-based disposal of flowback in Pennsylvania was evaluated specifically focusing on the effects on soil saturated hydraulic conductivity (Ksat) and leaching of selected flowback components (Ba, Cd, Pb, Se, Sr, and Cl) through 66 cm soil cores collected from an area mapped as the Morrison soil series. The soil Ksat was estimated in-situ at the soil collection location with double-ringed infiltrometers and in the laboratory column leaching experiments. Leachate samples (100 mL) were collected from soil columns until one pore volume (~1,000 mL) had leached. Leachate concentrations of Ba, Cd, Pb, Se, Sr, and Cl were evaluated by the PSU Agricultural Analytical Services Laboratory and compared to federal drinking water standards and EPA lifetime advisory levels. The flowback water collected from an active well pad in SW Pennsylvania was characterized by very high salinity (EC = 87.7 dS/m), sodicity (SAR=68.8 (meq/L)0.5), and extremely high TDS (219,000 ppm). Chloride (141,000 mg/L) was a major contributor to the high TDS level. Elevated Ba and Sr concentrations were comparable to values reported in the literature for other flowback waters. The Ksat values measured using flowback were not significantly different (α=0.05) from those determined for a 0.05 M CaCl2 solution in both the field infiltrometer and laboratory column leaching experiments. Results therefore indicate that flowback water will not likely impact the hydraulic capacity of the soil if applied directly to the land surface as a disposal method. Application of flowback water to soil columns resulted in leachate concentrations of Ba, Cd, and Pb that significantly exceeded Federal Drinking Water Standards. Leachate Sr levels were far in excess of the EPA Drinking Water Lifetime Advisory Level of 4 mg/L. The Ba and Sr leachate concentrations increased progressively as more flowback was applied to the soil columns so that the leachate concentrations were equal to the initial flowback concentrations of Ba and Sr. Based on the estimated total soil cation exchange capacity, it is likely that the extremely high content of cations in the flowback quickly saturated all available exchange sites in the column soils. Equilibrium calculations based on tabulated thermodynamic stability constants suggest that high Cl- in the flowback enhanced leaching of Cd and Pb by forming non-adsorbing complexes with these metals. Some leachate Cd and Pb concentrations were higher than levels in the flowback water applied to the soil columns, implying that the high Cl- in the flowback water was mobilizing Cd and Pb from the soil itself. Results indicate that direct application of flowback water will not initially have a negative impact on the hydraulic capacity of the Morrison soil used in this study. However, the presence of Ba, Cd and Pb at levels above drinking water standards in soil column leachates suggest land application of flowback water potentially represents a groundwater pollution risk. Further investigation is needed under a variety of soil, flowback water, and vegetation conditions for a more comprehensive evaluation of the feasibility of land-based disposal of flowback waters generated in hydrofracturing operations.