Definition
of Discipline Activities: Storage-Tank InspectionsDefinition
of Discipline Activities: Storage-Tank Inspections
There
are over 700,000 aboveground storage tanks (ASTs) and more than 4.5 million
underground storage tanks (USTs) in the U.S. 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 occur, leaks occur, and litigation often follows
to determine blame and responsibility for clean-up.
The cost to clean-up such ground-water contamination can run into hundreds
of thousands of dollars. Some of the larger volume leaks can cost millions
of dollar to remediate. With the stakes high, litigation
can often lead to resolution and exoneration, if the investigations turn out
to be in the company's favor. Of course, this does not always happen, so 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 the 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 mandatory
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). That involvement requires experience in the following activities:
1) Conducting root-cause analysis of failed ASTs,
2) Performing hazardous waste AST integrity assessments,
3) Performing inspections of ASTs according to API 653,
4) Consulting on legal cases involving AST and UST failures,
5) Specifying coating, linings, and galvanic systems for AST and UST corrosion protection, and
6) 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: a) tank integrity, b) inspection issues, and c) 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 that 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, they store corrosive crude feed stocks, which tend to accellerate
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 (i.e., API 653: Tank Inspection, Alteration, Repair, and Reconstruction), has become the lead industry standard governing tank inspection. It's 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 environmental where galvanic currents, combined with the appropriate subsurface conditions, cause metal tanks and piping to corode 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, Tolulene,
Ethybenzene, Xylines, and MTBE (or other so-called oxidizers). All are slightly
soluble (MTBE is highly soluble) in water 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 (usually by natural
or induced bioremediation) with time, and because
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
for the leak.
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.
For further information on the discipline, the Institute
of Environmental Technology sponsors an Internet Resources Portal, click (here).
The ELA Principal responsible for the tank-inspection and evaluation activities is:
Note: The environmental field is multi-disciplinary by nature and, for maximum effectiveness, ELA incorporates input from complimentary disciplines when appropriate in most projects undertaken.
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Last Update: November 23, 1997
