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The volume of methane gas produced at standard conditions (32°F and 1 atm) (0°C and 101.3 kPa) is calculated by using formula VCH4 = 5.62 ft3/lb * [(BODin, lb/d) - (BODout, lb/d) - 1.42Px]. Natural gas is a product coming from the earth. As discussed previously, the major component of natural gas is the chemical compound methane, CH4. Methane is the product formed when organic matter like trees and foliage decays without sufficient oxygen available to completely transform the carbon in these materials to carbon dioxide. Theory is natural gas deep in the ground is a product of decaying material from past millions of years of the earth's history. Chemical elements available as the matter decayed gives the methane such contaminants as hydrogen sulfide, carbon dioxide, nitrogen, and many more compounds and elements. Natural gas comes from shallow depths as little as a few thousand feet into the earth and as deep as 20 to 25 thousand feet. Natural gas wells are drilled on dry land and on water covered land. Current drilling in the Gulf of Mexico deep waters is in water depths up to around 3,000 feet.