The fracking process involves three separate stages that produces different types of pollutants: 1) the well drilling and completion stage, 2) the well stimulation stage, especially in hydraulic fracturing, and 3) the well production stage.
The well drilling and completion stage produces drilling fluids (drilling muds), cuttings, and wastewater.
The well stimulation stage usually produces fracturing fluid returns and wastewater while the final production stage produces waste water plus the final product, usually oil or gas.
The fracturing fluid consists of 98 to 99% water by volume plus 1 to 1.9 vol% of proppants and typically less than 1 vol% of additives. Proppants are small grains of sand or ceramics.
There are many types of chemical additive but the most common ones include biocides, buffers, breakers, corrosion inhibitors, crosslinkers, friction reducers, gelling agents, surfactants, and scale inhibitors.
In most cases, wastewater is either treated in wastewater decontamination plants or isolated in specific ponds. However, a paper from August 2017 claimed that the process of decontamination is very inefficient.