Diked areas keep fluids released by leaks, spills, overflows, etc., from wreaking major environmental damage. Yet, secondary containment measures sometimes don’t get sufficient scrutiny. Consider what I found when called in as part of a team to repair and verify compliance for a solvent containment area at a paint manufacturer in southwestern Ohio in 1991 after the U.S. Occupational Safety and Health Administration had put that plant under its microscope. A few years earlier, a storage tank on the site blew up in a lightning storm for lack of a lightning rod; this led to a release into a nearby river. The plant also didn’t provide an automatic shutoff for tanker trucks and a local alarm. Moreover, the site’s procedure for emptying stormwater from the diked areas was simply to open a valve and drain the water into the river. Before you dismiss these lapses as ones that only occurred way back when, let me assure you that I’ve seen much worse, even recently.
Providing proper secondary containment is important. Getting it wrong can be expensive. Indeed, secondary containment is a last resort for preventing a potential turn-out-the-lights legal problem. If you release a flammable or toxic fluid into the environment, you’ve already committed a violation. Keeping it out of a creek avoids major liability for restitution.
First, know where to find the law: Title 40 of the Code of Federal Regulations (CFR) — Part 264.175 is for portable storage; Part 264.193 is for fixed storage of >1,320 gallons in aboveground storage tanks and 42,000 gallons in underground tanks.
Next, let’s consider stormwater. In U.S. Environmental Protection Agency documents, this is covered under the Stormwater Pollution Prevention Plan. For large permanent tanks, secondary containment must hold 100% of the volume of the largest tank in the containment area as well as the stormwater runoff for a 25-year flood with a 24-hour rainfall intensity. (Perhaps with global warming, stormwater containment requirements may increase.) A diked area surrounding portable tanks must contain 10% of the sum of the tank volumes or 100% of the volume of the largest tank, whichever is greatest. Assume the same stormwater requirement for portable tanks as for large, fixed ones. It’s safe to empty a diked area only if the pollutant stored is at less than the legal concentration for discharge. In New York, for instance, that’s 1% by mass of the liquid in the diked area. A list of toxic chemicals appears in 40 CFR 401.15 of the Clean Water Act. Typically, regulations exclude ethanol, biodiesel and other biodegradable chemicals, if unblended with fuels — but check with your specific reporting authority.
There are ways to avoid problems with secondary containment: 1) build on a hill, avoid a flood zone; 2) put tanks under cover to reduce stormwater accumulation; 3) properly anchor tanks so they can’t float away; 4) consider secondary power requirements to remove stormwater during a prolonged power failure; 5) use a double-walled tank in place of secondary containment; and 5) perform routine inspections of the concrete in the diked areas and the tanks — the American Petroleum Institute (API) generally recommends a 10-yr cycle that should include thickness testing and internal inspection.
Don’t count on concrete alone; get the proper concrete coating and expansion joints for pads. Cracks developing in the concrete can cause significant problems. Remember, it’s as important to keep groundwater out of the diked areas as chemicals in. Determine what happens to chemicals after exposure to water and air. If they produce an acid, you require an acid-proof coating. As a rough estimate, in 2019 dollars, a new concrete coating could cost $9–12/ft2 and demolition and repair of concrete could run $190/ft2.
Adequate control also is essential. API-RP-2350, “Overfill Protection for Storage Tanks in Petroleum Facilities” provides some guidance on instruments and controls. The National Fire Protection Association’s NFPA-30, “Flammable and Combustible Liquids Code,” also offers pointers. Both differentiate between attended and unattended (i.e., no one is present when liquids are transferred) facilities. According to API-2350, only unattended facilities must have automatic shutoff level control (API recommends a high-high alarm/trip at 15 minutes after a steady-rate transfer reaches the normal, safe level in a tank.) However, regulators often insist upon automatic control for attended facilities, and also may set requirements for level instruments and controls.
DIRK WILLARD is a Chemical Processing contributing editor. He recently won recognition for his Field Notes column from the ASBPE. Chemical Processing is proud to have him on board. You can e-mail him at email@example.com