310 CMR, § 80.31 - Requirements for Inventory Monitoring

(1) Daily Inventory Monitoring.

(a) The Owner or Operator of a tank that is not single-walled and does not have continuous monitoring in accordance with 310 CMR 80.19(3)(b)3. shall conduct inventory monitoring for abnormal regulated substance loss.

(b) The Owner or Operator of UST systems with tanks having a capacity of 111 to 1000 gallons may use manual tank gauging in accordance with 310 CMR 80.31(2) in order to satisfy the requirements of 310 CMR 80.31(1)(a).

(c) Inventory monitoring for abnormal regulated substance loss shall be performed as follows:

1. Take daily measurements and reconcile inventory data daily and monthly;

2. Measure the liquid in the tank using:

a. A gauge stick or tape with water sensitive paste which shall be capable of measuring liquid in the tank to the nearest 1/8 of an inch; or

b. An automatic tank gauging device of equivalent or better measuring accuracy.

3. At the close of each calendar month, determine, for that month and for each tank or combination of tanks, the number of days in which any amount of regulated substance was dispensed and the number of days in which a loss of regulated substance was recorded.

4. Record all daily measurements and monthly reconciliation information.

(d) An abnormal regulated substance loss from any tank or combination of tanks shall mean a loss not explainable by any spillage, temperature variations or other causes in excess of 1% of the volume plus 130 gallons of regulated substance dispensed over a period of a calendar month.

(e) In the event of abnormal regulated substance loss, the Owner or Operator shall take the following steps within the 72 hours following the discovery of the abnormal regulated substance loss:

1. Check the inventory input and output records for mathematical error; and

2. Check the inventory for an error in measurement.

(f) If the abnormal regulated substance loss cannot be reconciled in accordance with 310 CMR 80.31(1)(e)1. or. 2., the UST system shall be tested for tightness within 72 hours of the completion of 310 CMR 80.31(1)(e) in accordance with 310 CMR 80.32.

(g) If the tank fails a tightness test pursuant to 310 CMR 80.32, the Owner or Operator shall comply with 310 CMR 80.32(3).

(h) If the tank passes a tightness test pursuant to 310 CMR 80.32, the tank is considered tight, and the requirements for tightness testing in 310 CMR 80.32 are satisfied.

(2) Manual Tank Gauging for Small Tanks.

(a) Owners and Operators may use weekly manual tank gauging on tanks that have a capacity of 1000 gallons or less, in accordance with 310 CMR 80.31(2)(b) and (c), to satisfy the inventory monitoring requirements in 310 CMR 80.31(1)(a).

(b) Manual tank gauging shall be conducted every seven days as follows:

1. Tank liquid level measurements shall be taken and recorded, including date and time of measurements, at the beginning and ending of a period of at least 36 hours during which no liquid is added to or removed from the tank;

2. Level measurements shall be based on an average of two consecutive stick readings at the beginning and the ending of the period;

3. The equipment used shall be capable of measuring the level of regulated substance over the full range of the tank's height to the nearest 1/8 of an inch;

4. A release or leakage shall be suspected if the variation between beginning and ending measurements exceeds the weekly or monthly standard in 310 CMR 80.31(2)(b)4.: Table F:

Table F

Nominal Tank Capacity	Weekly Standard (One Test)	Monthly Standard (Average of Four Tests)
500 gallons or less	10 gallons	5 gallons
501 through 1,000 gallons	13 gallons	7 gallons

(c) In the event of a suspected release or leakage, the Owner and Operator shall comply with 310 CMR 80.31(1)(e) and (f).

(3) Abnormal Water Gain.

(a) Owners and Operators that are subject to the requirements of 310 CMR 80.31 shall also take daily measurements to determine if there is abnormal water gain in the tank.

(b) The measurement shall be taken using a method in 310 CMR 80.31(1)(c).

(c) All measurements shall be recorded.

(d) An abnormal gain of water inside the tank shall be a gain in the water level of more than one inch in a 24 hour period.

(e) The Owner or Operator shall have the water removed from the tank and managed in accordance with applicable local, state and federal laws and regulations.

(f) The Owner or Operator shall have the tank checked for water in accordance with 310 CMR 80.31(3)(b) through (d) within 24 hours of the removal of the water, during which time no regulated substance shall be added to the tank.

(g) In the event of any abnormal water gain, the Owner or Operator shall:

1. Within 72 hours of obtaining knowledge of the abnormal water gain, investigate the cause of the abnormal water gain and make repairs or replacements as necessary.

2. If the Owner or Operator cannot determine the cause of the abnormal water gain, the UST system shall be tested for tightness in accordance with 310 CMR 80.32.

a. If the tank fails a tightness test pursuant to 310 CMR 80.32, the Owner or Operator shall comply with 310 CMR 80.32(3) as applicable.

b. If the tank passes a tightness test pursuant to 310 CMR 80.32, the tank is considered tight, and the requirements for tightness testing in 310 CMR 80.32 are satisfied.

(4) Records. The Owner or Operator shall maintain all records of inventory monitoring including, but not limited to, sales receipts, weekly and monthly measurements, and records of monitoring for abnormal water gain found at 310 CMR 80.31(3), in accordance with 310 CMR 80.36.

(5) Waste Oil Tanks. Waste oil tanks that are subject to 310 CMR 80.31 and are connected to oil burning equipment shall be exempt from 310 CMR 80.31 during periods when oil burning equipment is in use.

Notes

310 CMR, § 80.31

Adopted by Mass Register Issue S1277, eff. 1/2/2015. Amended by Mass Register Issue 1453, eff. 10/1/2021.