Natural gas production has increased in recent years in the northeastern Appalachian forests. The natural gas generally is extracted by a procedure known as hydraulic fracturing or fracking. A mixture of acids, water, gasses, and other additives is injected under high pressure into the bore hole to fracture the bedrock and thus releasing the natural gas. Once fracturing is completed, a portion of the injected fluid, called flowback, is recovered and stored in open pits or tanks. Because flowback often has high chloride concentrations, it is important that flowback chemistry is properly characterized so that disposal can be carried out safely. Forest Service scientists tested two technologies that measure chloride concentrations and determined that the concentrations increased with the depth in the tank. They also found that laboratory analyses were more accurate than field test kits.