Underground Storage Tanks
Published:January 01, 1994
Much of the information in sections 6.1 and 6.2 is taken from Cheremisinoff et al. (1987). Of the estimated two to five million underground storage tanks (USTs) that exist in the United States, most are simple single-wall tanks made of steel. The major cause of leaks is corrosion of the steel, although improperly fitted or failed piping valves can also result in leaks. Corrosion results from the existence of an electrical current that permits an oxidation-reduction reaction to occur. Oxidation of iron to iron oxide (rust) occurs at the anode of the electrical cell, which can be an imperfection (e.g., scratch, etc.) in the wall of the tank or some other difference between that part of the tank and another part of the tank or piping that serves as the cathode (cf. Figure 6.1).
Alternatives to non-protected steel-walled tanks include (cf. Figure 6.2): 1) protecting a steel tank from corrosion using cathodic protection; 2) coating a steel tank with fiberglass; 3) lining a steel tank with a corrosion resistant liner; 4) using a double-walled tank with no monitoring system; i.e., a steel inner tank with a fiberglass-coated outer tank; 5) using a double-walled tank with a monitoring system; i.e., a steel inner tank and a fiberglass-coated outer tank, with a HC vapor or liquid sensing probe inserted between the two walls; and 6) using a fiberglass tank.
The lifetime of unprotected steel tanks (before they begin to leak) varies greatly. Factors that accelerate corrosion are high moisture content in
Figures & Tables
Introduction to Environmental Hydrogeology
These notes have been written to supply supporting material for a “short course” introduction to environmental hydrogeology. The assumption is that most people who take the short course (or purchase the notes without taking the short course) will be geologists, although the information could be useful to engineers or other scientists who desire an introduction to environmental consulting in general, or hydrogeology in particular. The notes, and course, are an introduction – a partial survey - of some aspects of environmental geology, with particular reference to subsurface hydrogeology and remediation of sites contaminated with petroleum hydrocarbons. No claim of completeness is made. Regulatory programs vary from state to state. The regulatory framework used in the state of New York is sometimes given as an example. The reader should be aware that rules and procedures may differ in other states.