Evaluating Fiberglass Underground Storage Tanks

Indications of Possible Tank Issues
Mr. Hoffman cited the following as indications of possible problems with USTs:
•  Filter clogging
    -Complaints of slow flow
    -Examine for presence of fiberglass residue/debris
•   Failed or erratic leak detection results
    -Automatic test gauging (ATG) system or statistical inventory reconciliation (SIR) test results
    -Perhaps intermittent
•   Water ingress into primary tank
•   Water or product into interstitial space
•   Product identified in wells

Types of Observed Fiberglass Tank Problems
These common defects were revealed by remote visual inspections via video of the interiors of tanks suspected to have problems:
•   Deflection and/or flattening of tank bottom
•   Degradation of gel coat and tank interior (blistering, delamination, crazing, exposed fibers)
•   Filter clogging due to fiberglass debris drawn into the submersible turbine pump (STP)
•   Crack formation – often along rib lines
•   Leaks of product into rib space
•   Product or water in normally dry interstice
•   Crack through wall allowing ingress of groundwater
•   Crack through wall allowing leak of product

Observation Summary
Based on the videos taken of the tanks’ interiors, the observations that stood out concerning the USTs with known or suspected problems were:
•   Mostly older fiberglass tanks (20+ years)
•   Widespread geographic representation
•   Higher number in warmer parts of country
•   Most tanks store ethanol blended products
Mr. Hoffman noted that his sample size was small in relationship to tank population.

Possible Causes of Fiberglass Tank Problems
Mr. Hoffman offered the following as possible reasons for the fiberglass tanks’ problems:
•   Product compatibility issues?
    -Tank materials may have been selected for different product
    -Formulations have changed over the years (MTBE, Ethanol)
    -Concentrations of additives may vary due to splash blending
•   Age of tanks? (Most over 25 years old)
•   Local weather? (Problems seem common in “warm” regions)
•   Physical stresses on tanks?
    -Poor installation
    -Backfill
    -Water table
    -Construction activity
    -Traffic conditions

Additional Resources:

Out of Sight, Out of Mind? How to Evaluate USTs
Guidance on Ethanol Compatibility with Fiberglass UST Systems
Class C UST Operator Training