40 CFR §98.477

1. (a)You must follow the record retention requirements specified by § 98.3(g). In addition to the records required by § 98.3(g), you must retain quarterly records of CO2 received, including mass flow rate or contents of containers (mass or volumetric) at standard conditions and operating conditions, operating temperature and pressure, and concentration of these streams. You must retain all required records for at least 3 years.
2. (b)You must complete your monitoring plans, as described in § 98.3(g)(5), by April 1 of the year you begin collecting data.