Commissioning a New Double-Wall Site With the Sequence Backwards
A contractor is installing two 12,000-gallon double-wall fiberglass tanks with secondary-contained flexible piping and dispenser sumps. The planned sequence is:
- Excavate and set the tanks on a 12-inch bed of pea gravel with no anchors.
- Backfill with excavated native soil, including some rock, in 12-inch lifts.
- Install STPs, piping, and dispensers.
- Hydrostatically test the tank interstitial space and the sumps.
- Add 2,000 gallons of product to each tank and start up the ATG.
- Test the line leak detectors when the annual test comes due.
- Backfill the piping trench.
The water table seasonally rises to 18 inches above the tank bottom. The inspector notes that hold-down straps are missing, the ATG probes were installed without striker plates, and the contractor plans a 'temporary' plug in each spill bucket drain.
1. Identify each step that is out of sequence or noncompliant and state the correct requirement.
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Step 1 - bedding. Pea gravel is questionable for a fiberglass tank; it migrates and can point-load the shell. The manufacturer's written bedding requirement governs - typically compacted sand or a specified gravel bed, or a concrete pad.
Step 2 - backfill and anchorage. Native soil with rock is not acceptable backfill for FRP tanks or flexible piping; backfill must be per the manufacturer and free of sharp material, usually clean sand or approved fines. Anchorage is also missing: with groundwater 18 inches above the tank bottom, buoyancy is a real design load and hold-down straps or a concrete anchor are required.
Step 4 - test timing. Testing after backfill and with the trench open is backwards. Tank and piping must be tightness tested before being covered and before any product is introduced.
Step 5 - product before testing. The 2,000 gallons goes in only after the tank has passed its tightness test; adding product first converts a test failure into a cleanup.
Step 6 - LLD testing. The line leak detector must be tested at installation and annually thereafter, not 'when due.'
Step 7 - trench backfill. No backfill until the line passes tightness testing and the interstitial sensor positions are documented.
Also: ATG probes require striker plates, and a 'temporary' spill bucket plug defeats the drain and will be forgotten.
2. List the tests and inspections that must be completed before the first delivery and state who should witness or record each.
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Before first delivery, with trenches open or sumps accessible:
• Tank primary tightness test (0.1 gph or the state's installation standard) and interstitial-space test. • Piping primary line tightness test at 0.1 gph, plus a secondary containment/interstitial function test and sump-to-sump tightness. • Hydrostatic tests of all tank sumps and dispenser sumps. • Spill bucket tightness and drain-function test at every fill point. • Overfill prevention inspection: device set and functioning, alert at 90%, stop at 95%. • Line leak detector test at 3 gph within one hour, documented. • ATG installation certification: probe height, striker plate, water float, 0.1 gph test, alarm and shutdown set points. • Cathodic protection test if any steel component is present. • Anchorage verification before backfill is complete.
Who records what: the installing contractor performs and signs each test; the owner's representative or a third-party inspector witnesses. Many states require agency notification before installation and a state or third-party inspection before product is introduced. The commissioning package should include as-builts showing sensor locations, slope, and probe depths.
3. What records must the owner keep, and for how long?
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Installation records: manufacturer's instructions, as-built drawings, bedding and backfill documentation, anchorage design, and tightness test results.
Registration: notification of installation with the state.
Release detection records: ATG certification and monthly results, SIR reports, line leak detector tests, sensor tests, and alarm logs.
Inspection and testing records: the 3-year overfill, spill bucket, and sump tests, and the 30-day walkthroughs.
Repair and maintenance records: any lining, repair, or component replacement.
Operator training records for Class A, B, and C operators.
Release and closure records: spill reports, release investigations, and closure documentation.
Retention: at least 3 years under 40 CFR 280.35 and 280.45, but installation, closure, and site assessment records must be kept for the life of the tank or longer under many state rules. Build the retention schedule to the strictest applicable rule, and remember that when a site changes hands, the records go with it - an owner who cannot produce a commissioning package has effectively lost the proof that the system was ever tested.