Total dissolved solids
Total dissolved solids (TDS) refers to the gritty substance that is a mixture of salt and other dissolved minerals that come from deep underground in the Marcellus shale. Drilling waste water has enough TDS to make it up to five times as salty as seawater.
Large quantites of TDS can produce a salty sediment. If it is used in industrial processes, this polluted water can corrode and clog any machinery that is being employed.
When waste water contaminated with TDS is left untreated and finds its way into the drinking water supply, it can affect the color, tastes and odor of the water. Should it come in contact with freshwater streams it can also be very harmful to fish and other creatures who make it their habitat.
Waste water containing TDS is typically treated in sewage treatment plants, although it can also be recycled by the drillers before its final disposal. The substance is not considered to be a major health risk.
TDS are not unique to natural gas drilling. They are also produced as a by-product of other extraction industries--the most notable in the Appalachian area is coal mining.
Increasingly, drillers are recycling all flowback water including produced water.
An increase in the concentration of TDS in a stream can be detected by higher electrical conductivity measurements of the water. For example, a spill of frac water, high in TDS, into a body of water could be determined in this way.