David E. Hendrix, P.E.

In the U.S, there are over 700,000 aboveground storage tanks (ASTs) and more than 4.5 million underground storage tanks (USTs) with capacities ranging from 500 barrels to over 500,000 barrels. Many of these tanks leak. More importantly, many of these tanks leak without anyone knowing about it. Tank-floor failures are insidious because fluids can leak into the subsurface and into the ground water for years before the leak is detected. When failures happen, leaks occur and litigation often follows to determine blame and responsibility for clean-up.

The cost to clean up such ground-water contamination often runs into hundreds of thousands of dollars. Some of the larger volume leaks can cost millions of dollar to remediate. With the stakes this high, litigation often leads to resolution and exoneration if the investigations are in the company's favor. Of course this does not always happen. The risk to human health and the environment is high in some cases where exposure to humans is possible. Toxic torts are providing avenues for redressing such issues. A rigorous system of risk assessment helps to balance this process.

Just as senior environmental scientists are required to design and supervise site characterization, hydrogeological investigations and chemical data validation in environmental projects, so too are senior engineering consultants crucial for conducting investigations on tanks to determine the cause of such leaks and for the associated ground-water remediation. They must have been professionally involved with tanks for years in order to bring the appropriate experience and training (such as in metallurgical engineering) to bear on problems involving tank leaks (as well as preventative maintenance).

Professional involvement requires experience in:

  • Conducting root-cause analysis of failed ASTs
  • Performing hazardous waste AST integrity assessments
  • Performing inspections of ASTs according to API 653
  • Consulting on legal cases involving AST and UST failures
  • Specifying coating, linings, and galvanic systems for AST and UST corrosion protection
  • Developing AST and in some cases, UST inspection and repair specifications

Consulting personnel should be Certified API Aboveground Storage Tank Inspectors and Registered Professional Engineers. With such credentials, they would possess the qualifications required to conduct investigations on:

tank integrity | inspection issues | corrosion-related failures

In addition, tank consultants should have authored numerous papers and publications on the subject of tank inspection to confirm their involvement in such activities.

Many tank-floor corrosion and mechanical failures are caused by tanks that have settled over the years. This allows standing water to penetrate under the tank or exposes the tank's bottom to the water table which may be at shallow depths in the area, especially during some seasons of the year. This can cause corrosion and erode the foundation under the floor.
Large floating roof tanks are also particularly susceptible to floor leaks from both product-side and soil-side corrosion because they are more difficult to protect using cathodic-protection systems. Occasionally, these tanks store corrosive crude feed stocks which tend to accelerate corrosion processes.

Current federal and local legislation has raised the stakes for AST facility owners that contaminate the environment as a result of tank failures. Several spectacular AST failures within the last few years have spawned new industry standards and regulations which mandate tank integrity management and inspection programs.

New industry standards, API 653: Tank Inspection, Alteration, Repair, and Reconstruction, has become the lead industry standard governing tank inspection. The requirements are targeted at preventing tank-content releases as a result of brittle fracture and floor leaks.

UST and associated piping leaks are the primary concern with all state regulatory agencies in the U.S. today. Special UST funds have been set up in most states to pay for remediation of the contamination caused by leaking USTs and their associated piping. A vast majority of leaking USTs are owned by petroleum companies who market gasoline and diesel fuels.

USTs leak as a result of many years in an environment where galvanic currents combined with the appropriate subsurface conditions cause metal tanks and piping to corrode and eventually leak, contaminating the underlying soil and ground water below.

Aside from diesel fuel, there are five principal chemical constituents that often leak into the ground water:

~ Benzene
~ Toluene
~ Ethybenzene
~ Xylenes
~ MTBE (or other so-called oxidizers)

All are slightly soluble in water (and MTBE is highly soluble), but the products are lighter than water and float on the water table. Tracking down the source of some leaks and determining the direction of flow of the ground-water carrier can be a difficult task. Because gasoline degrades with time (usually by natural or induced bioremediation); and because of co-mingling of various potential sources of gasoline, identification of the actual source can be problematic and often results in litigation to recover costs or to obtain relief from alleged responsibility.

Even working in and around an environment where a subsurface leak has occurred has been shown too often to be dangerous. Appropriate precautions involving industrial health and safety have assumed major importance over the last 10 years. When there is an accident involving leaking materials, the prevailing safety plans come under heavy scrutiny. Too often in the environmental industry, project safety plans do not receive appropriate attention even by the State regulatory agencies. If found wanting, however, such plans may become the focus of litigation.

Note: The environmental field is multidisciplinary by nature, and ELA incorporates input from complimentary disciplines for maximum effectiveness whenever appropriate.