California Air Resources Board

CARB staff are studying the occurrence of overpressure in underground storage tanks (UST) at retail gas stations. Most gas stations are equipped with an In-Station-Diagnostic (ISD) system which monitors UST pressure and set alarms when the recorded pressures exceed a specified criteria. The ISD pressure monitoring is intended to limit emissions from fugitive leaks and vent line emissions that would compromise the control efficiency of the Phase II vapor recovery system.
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