TABLE 1. Common Naturally Occurring Substances Found in Formations Containing Oil and Gas.

Type of contaminant	Examples
Inorganics (or common ions)	Brine (e.g., sodium chloride, bromide)
Gases	Natural gas (e.g., methane, ethane), carbon dioxide, hydrogen sulfide, nitrogen, and helium
Trace elements	Mercury, lead, and arsenic
Naturally occurring radioactive material (NORM)	Radium, thorium, and uranium
Organic material	Organic acids, polycyclic aromatic hydrocarbons, volatile, and semivolatile organic compounds