Tanks for storing petroleum and hazardous substances routinely include state-of-the-art leak detection and corrosion protection systems. The vessels often feature secondary containment to bolster these protective measures and provide additional environmental benefits.

Such tanks showcase the strides made since 1984, when Congress set up the statutory framework for the regulation of underground storage tanks (UST). Also that year, the Steel Tank Institute (STI) introduced the first national construction standard for secondary containment tanks.

However, tank industry technology, as well as the regulatory environment, continues to evolve. This article describes several significant developments that impact the design and operation of storage tank facilities.

Changing mandates

Rules of the U.S. Environmental Protection Agency (EPA), published in 1986, require secondary containment for all tanks storing hazardous substances except petroleum USTs. They mandate the use of double-wall construction to keep any release from the inner tank within the outer shell and to protect the primary tank from corrosion. In addition, tanks must have a built-in continuous leak-detection system capable of spotting a release within 24 hours and must be checked for evidence of release at least every 30 days.

Some states went even further, requiring secondary containment for all USTs. California was among the first to mandate secondary containment for storage of petroleum liquids. Florida and most New England states demand secondary containment for all new USTs. Michigan, Nebraska and New Jersey prescribe secondary containment for any USTs in sensitive areas, such as near certain public water supplies and aquifers.

Other significant regulatory changes have occurred recently and more are in the works.

California now stipulates that all UST systems (tanks and piping) installed on or after July 1, 2003, be impervious to both liquid and vapor of the contained substance. Further, the interstitial space of underground tanks and product piping installed on or after July 1, 2004, must be maintained under constant vacuum or pressure, and any breach in the primary or secondary containment must be detected before the stored substance is released to the environment. Although the language addressing continuous monitoring for tank systems installed prior to July 1, 2004, is less specific, it calls for continuous monitoring "capable of detecting the entry of the hazardous substance stored in the primary containment into the secondary containment." The state also mandates testing of dispenser boxes and sumps, including piping, every three years to verify containment integrity. UST components monitored continuously using vacuum, pressure or interstitial liquid-level measurement methods do not require further testing.

Florida is considering new continuous monitoring requirements for secondary containment piping, including vacuum, pressure or brine systems (European Class I or II options, as outlined later). This is being driven by concern about the more than 175 polyethylene piping incidents in Florida documented by the state's Department of Environmental Protection (DEP); 12% of these resulted in discharges into the environment. Although the majority of the leaks were contained in the piping interstice, the DEP states that more stringent monitoring is warranted. Also under consideration is a stricter standard for an acceptable leak rate than that adopted by the EPA. Both of these measures are at least one year away from publication for comment.

However, more immediate storage-tank rule revisions are underway in Florida. The first changes, simply splitting the current rule into separate ones for aboveground storage tanks (ASTs) and USTs, currently are available for online review. The proposed split rules should be effective on July 1. Others, expected to be drafted this summer, will adopt industry standards developed since the state's last rule change in 1998. The regulations, as proposed, leave intact a 1991 requirement for the use of secondary containment on all existing USTs in the state by Dec. 31, 2009. The deadline for secondary containment of field-erected ASTs is Jan. 1, 2010. (Shop-fabricated ASTs should have had secondary containment by Jan. 1, 1990.)

Other drivers

Even without regulatory mandates, tank owners increasingly are opting for secondary containment because of its tangible benefits. The environmental advantage , additional insurance against product releases into soil or groundwater , is obvious. But secondary containment also provides operational and financial pluses. Operationally, it enables simple and cost-effective leak-detection monitoring. Also, secondary containment gives an added level of protection if a tank were improperly installed or maintained. Financially, it is a bargain compared to potential costs from fines, cleanup, report writing, lawsuits and business interruption should a release occur.

STI estimates that nearly 50% of all the steel USTs made in the United States today are secondary containment tanks, compared to about 15% when EPA regulations were first promulgated. This estimate reflects both informal industry surveys and our database of tanks constructed to STI standards. Similarly, double-wall units likely comprise about half the market of fiberglass USTs. Secondary containment predominates in other countries. Mexico, for example, requires all USTs to have secondary containment.

 

AST activity

During the past several years, shop-fabricated ASTs have gained increasing favor. Companies are attracted by the ability to visually monitor the tank, as well as the desire to avoid perceived risks and the myriad regulations surrounding USTs. AST installations still must comply with certain codes and regulations , and there have been revisions in these areas.

A key and long-standing EPA requirement is for the development and submittal of Spill Prevention Control and Countermeasure (SPCC) Plans for all bulk containers larger than 1,320 gal.; a professional engineer must certify the spill plan.