||CDM Federal Programs Corp., Fairfax, VA. ;Vista Research, Inc., Mountain View, CA.;Environmental Protection Agency, Cincinnati, OH. Risk Reduction Engineering Lab.
It is generally acknowledged that a small fraction of the total underground storage tank population is used to store chemicals. The detailed characteristics of these tanks, however, are not well understood. Additional information is required if competent decisions are to be made regarding leak detection, tank upgrading, and tank management practices. In order to obtain more detailed information regarding these tanks, two surveys were conducted over the course of several years. The first survey examined the chemical tank populations in two states, California and New York, along with data from the Chemical Manufacturers Association. The second survey focused on the chemical tank databases for 14 states covering a wide geographical area. Data from these two surveys were then analyzed to determine the primary features of the chemical tank population. The results of these analyses indicate that up to 2 percent of the total tank population contains non-petroleum chemicals, with roughly half of these tanks, either by number or tank volume, containing hazardous substances. Solvents were found to comprise the single largest fraction of hazardous chemicals. Of these, acetone, toluene, methanol and methyl ethyl ketone were found to be the most commonly stored chemical substances, comprising roughly 60 percent of hazardous materials stored in tanks, and 34 percent of all chemical tanks, which contain both hazardous and non-hazardous substances, in the sampled states. Tank age was found to average 18 years, with over 85 percent of the tanks being fabricated from steel. Roughly 60 percent of the tanks in the state databases had capacities between 1,000 and 10,000 gal (3,790 and 37,900 L), with the average tank size from all states being 7,205 gal (27,307 L). These characteristics suggest that a strong potential exists for corrosion-induced tank leakage, but that conventional tank integrity testing could be applied to detect leakage from a large fraction of the chemical tank
population, with no modifications to the leak detection performance requirements.