Wash. Admin. Code § 173-360A-0625 - Weekly manual tank gauging
Owners and operators using weekly manual tank gauging must comply with the requirements of this section.
(1)
Standards.
(a) Weekly manual tank gauging must be
performed in a manner that is able to detect any leaks greater than the
applicable test standards in Table 0625-1 with a probability of detection of at
least 0.95 and a probability of false alarm of no more than 0.05.
(b) Weekly manual tank gauging must be
performed using a gauge stick or an automatic tank gauge system that is able to
measure the following:
(i) Tank liquid levels
over the full range of the tank's height to the nearest one-eighth of an inch;
and
(ii) Water levels in the bottom
of the tank to the nearest one-eighth of an inch.
(2)
Performance.
Weekly manual tank gauging must be performed in accordance with the
requirements of this subsection. Automatic tank gauge systems must be operated
in accordance with the manufacturer's instructions.
(a) Each week, the following inventory volume
measurements and calculations must be performed:
(i) Select a period that is at least as long
as the applicable minimum test duration specified in Table 0625-1. During this
period, no liquid may be added or removed from the tank;
(ii) Take two consecutive tank liquid level
measurements to the nearest one-eighth of an inch at the beginning and at the
end of the selected period;
(iii)
Calculate the average of the two beginning measurements and the average of the
two ending measurements and convert the averages from inches to
gallons;
(iv) Calculate the change
in volume by subtracting the average ending measurement from the average
beginning measurement; and
(v)
Compare the change in volume to the applicable weekly standard in Table
0625-1.
(b) Each month,
calculate the monthly change in volume by adding together the four weekly
changes in volume and compare to the applicable monthly standard in Table
0625-1.
(c) At least once each
month, the level of any water in the tank must be measured to the nearest
one-eighth of an inch.
(3)
Suspected release. A release
is suspected based on weekly manual tank gauging if:
(a) Any weekly change in volume is greater
than the applicable weekly standard in Table 0625-1;
(b) Any monthly change in volume is greater
than the applicable monthly standard in Table 0625-1; or
(c) The presence of water in the tank is
unexplained.
Table 0625-1: Weekly Manual Tank Gauging Criteria
| Nominal Tank Capacity | Minimum Test Duration | Weekly Standard (one test) | Monthly Standard (four test average) |
| 550 gallons or less | 36 hours | 10 gallons | 5 gallons |
| 551 - 1,000 gallons (when tank diameter is 64 inches) | 44 hours | 9 gallons | 4 gallons |
| 551 - 1,000 gallons (when tank diameter is 48 inches) | 58 hours | 12 gallons | 6 gallons |
| 551 - 1,000 gallons (when tank diameter other than 64 or 48 inches) | 36 hours | 13 gallons | 7 gallons |
| 1,001 - 2,000 gallons | 36 hours | 26 gallons | 13 gallons |
Notes
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No prior version found.