§ 280.43 Methods of release detection for tanks.
Each method of release detection for tanks used to meet the requirements of § 280.41 must be conducted in accordance with the following:
(a) Inventory control. Product inventory control (or another test of equivalent performance) must be conducted monthly to detect a release of at least 1.0 percent of flow-through plus 130 gallons on a monthly basis in the following manner:
(1) Inventory volume measurements for regulated substance inputs, withdrawals, and the amount still remaining in the tank are recorded each operating day;
(2) The equipment used is capable of measuring the level of product over the full range of the tank's height to the nearest one-eighth of an inch;
(3) The regulated substance inputs are reconciled with delivery receipts by measurement of the tank inventory volume before and after delivery;
(4) Deliveries are made through a drop tube that extends to within one foot of the tank bottom;
(5) Product dispensing is metered and recorded within the local standards for meter calibration or an accuracy of 6 cubic inches for every 5 gallons of product withdrawn; and
(6) The measurement of any water level in the bottom of the tank is made to the nearest one-eighth of an inch at least once a month.
Note to paragraph (a).
Practices described in the American Petroleum Institute Recommended Practice RP 1621, “Bulk Liquid Stock Control at Retail Outlets” may be used, where applicable, as guidance in meeting the requirements of this paragraph (a).
(b) Manual tank gauging. Manual tank gauging must meet the following requirements:
(1) Tank liquid level measurements are taken at the beginning and ending of a period using the appropriate minimum duration of test value in the table below during which no liquid is added to or removed from the tank;
(2) Level measurements are based on an average of two consecutive stick readings at both the beginning and ending of the period;
(3) The equipment used is capable of measuring the level of product over the full range of the tank's height to the nearest one-eighth of an inch;
(4) A release is suspected and subject to the requirements of subpart E if the variation between beginning and ending measurements exceeds the weekly or monthly standards in the following table: