The Overfill That Went Out the Vent
A 10,000-gallon gasoline tank installed in 1994 has coaxial Stage I vapor recovery, a 5-gallon spill bucket whose drain is plugged with hardened product, and a ball-float vent valve on the 2-inch vent line as its only overfill prevention. The ATG probe rests directly on the tank bottom because no striker plate was installed, and the vent line's pressure-vacuum cap has been replaced with a plain rain cap.
During a delivery, product began discharging from the vent line at about 9,600 gallons. The driver stopped the delivery. Roughly 15 gallons ran onto the pad and into a catch basin. No alarm ever sounded. The last spill bucket inspection record is dated six years ago. The owner asks whether the tank can go back into service and what he has to fix.
1. Explain why the overfill prevention failed to stop the delivery and identify each appurtenance deficiency with its basis.
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Why the delivery was not stopped. The tank holds 10,000 gallons; product reached the vent at about 9,600 gallons, or 96%. Overfill prevention is required to alert at 90% and stop or restrict flow at 95%. A ball-float vent valve is an allowed method, but it works by restricting the vent and creating backpressure that shuts off the transport - it does not alarm. With no 90% alert device on the site, the driver had no warning, and no alarm sounded because no overfill alarm was configured.
Deficiencies:
• Ball-float valve last inspected six years ago. The 3-year overfill inspection is overdue; a stuck or product-fouled float explains the failure to restrict at 95%. • Spill bucket drain plugged, last tested six years ago. The 3-year spill bucket tightness test is overdue, and a bucket that cannot drain cannot return product to the tank after a delivery. • No striker plate under the ATG probe. A probe resting on the tank bottom cannot be trusted for 90%/95% set points and is vulnerable to damage. • Plain rain cap in place of the pressure-vacuum cap. The tank cannot breathe correctly, which both compromises the ball float's backpressure mechanism and risks overpressure or vacuum damage. • No annual release detection equipment test recorded for the ATG.
Any one of these is a violation. Together they explain the spill.
2. What are the immediate actions after the spill, including notification and recordkeeping?
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Immediate actions:
- Stop the delivery and shut down the affected dispensers. Eliminate ignition sources - no engines, no tools in the area.
- Contain the product with absorbent and dikes, and cover the catch basin if product has not yet entered. Never flush it.
- Notify the fire department if the public or a storm drain is at risk, the state spill/emergency line, and the National Response Center if a federal reportable quantity is reached (gasoline's CERCLA reportable quantity is 100 gallons). Notify the implementing agency within 24 hours of a suspected release under 40 CFR 280.50, plus the owner and insurer.
- Recover the product and contaminated absorbent for proper disposal - not into the dumpster.
- Document the delivery ticket, the tank reading at the spill, photographs, the catch basin condition, and every person notified.
The catch basin is the critical fact: once product reaches it, the release may have left the site and the water-quality agency needs to know. Keep the documentation with the site records for at least three years.
3. What is the required ongoing inspection frequency for the overfill prevention, spill bucket, and release detection equipment, and what does each inspection involve?
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Overfill prevention equipment - at installation and at least every 3 years. Verify the device is set to alert at 90% and stop or restrict flow at 95%, that it moves freely, that the vent line is clear, and that the installation matches the manufacturer's instructions.
Spill prevention equipment - tested for tightness at least every 3 years. Fill the bucket with liquid, confirm it holds, confirm the drain valve opens and drains back to the tank, and clear debris.
Containment sumps - tested at least every 3 years, with more frequent visual inspection.
Release detection equipment - tested at least annually: ATG 0.1 gph certification, line leak detector 3 gph test, sensor function checks, and alarm verification.
Walkthrough inspections - every 30 days: spill buckets, sumps, dispensers, and the monitoring panel.
The real failure here was ownership of the calendar. A lapsed 3-year inspection is not a paperwork issue - this spill is its direct consequence. Build a single compliance calendar covering every item above, keep records on site, and retain them at least 3 years or longer where state rules require.