We report on the first large-scale production of low radioactivity argon from underground gas wells .
Low radioactivity argon is of general interest , in particular for the construction of large scale WIMP dark matter searches and detectors of reactor neutrinos for non-proliferation efforts .
Atmospheric argon has an activity of about 1 Bq/kg from the decays of ^ { \mathrm { 39 } } Ar ; the concentration of ^ { \mathrm { 39 } } Ar in the underground argon we are collecting is at least a factor of 100 lower than this value .

The argon is collected from a stream of gas from a CO _ { 2 } well in southwestern Colorado with a Vacuum Pressure Swing Adsorption ( VPSA ) plant .
The gas from the well contains argon at a concentration of 400-600 ppm , and the VPSA plant produces an output stream with an argon concentration at the level of 30,000–-50,000 ppm ( 3–-5 % ) in a single pass .
This gas is sent for further processing to Fermilab where it is purified by cryogenic distillation .
The argon production rate is presently 0.5 kg/day .