Above-Ground Storage Tanks

Q. Steve, our electroplating business is expanding and in our intent to improve safety during material handling and reduce costs, we are considering switching from receiving our muriatic (hydrochloric) acid, sulfuric acid, caustic and alkaline cleaners in drums or totes to dedicated bulk tanks. Before doing so, we want to know what regulations would apply to aboveground storage tanks for these chemicals in order to account for any regulatory compliance costs? Are they to be as burdensome as the underground tank rules? N.B.

 

A. Above ground storage tanks (ASTs) are generally not as heavily regulated as underground storage tanks, mostly due to the obvious nature of any leak that would occur from an AST.

Any storage tank, including ASTs, which vents to the atmosphere, may be subject to air pollution permitting requirements. Fortunately, most states have exemptions for vents of tanks used to store liquids, based upon tank capacity and/or vapor pressure of the stored liquid. The caustic (assuming either sodium hydroxide or potassium hydroxide), sulfuric acid and alkaline cleaners you mention have very low vapor pressures and seem to be good candidates for such exemption. However, muriatic acid (assuming that you are using the commercial grade of 31–33%) does have a significant vapor pressure (0.2–0.6 psi, which is 300–2,200 times greater than the muriaticacid vapor pressure of your pickle tanks) at ambient temperatures as evidenced by its fuming when a muriatic acid drum is opened. You can estimate emissions using USEPA’s AP 42 emission factor for liquid storage tanks (the website is www.epa.gov/ttn/chief/ap42/ch07/index.html); while the tank emission programs had been designed for organic liquids, such as solvents and gasoline, they can provide a good approximation regarding muriatic acid fume emissions. Unless the tank’s vent is controlled by either a scrubber or a simple water trap, you might be surprised how much muriatic acid fumes are lost to the atmosphere. And if you vent your muriatic acid tank to the outside as we would recommend, you need to be concerned that the negative pressure caused by your exhaust system does not pull muriatic acid vapors out of tank and into plant air, possibly causing employee exposure issues as well as corrosion of metal structures and equipment. In my 26 plus years working in the metal finishing industry, I have not personally seen bulk storage tanks for commercial grade muriatic acid, and the above issues is probably the reason why. This is not to say it is not worth it in your case, but I would investigate it more thoroughly. As a second thought, if your muriatic acid usage is that large to justify investigating bulk storage, I urge you also to investigate acid recovery. There are well proven acid recovery technologies, such as acid retardation and diffusion dialysis; for suppliers, refer to Product Finishing Directory and Technology Guide, Acid Recovery Systems (www.pfonline.com/suppliers.html).

Several state environmental agencies have regulatory requirements for chemical ASTs to safeguard human health and the environment. The state programs address tank system registration, design, operating, and inspection requirements.

Facilities that discharge to a Publicly Owned Treatment Works (POTW) can also be subject to “Spill & Slug Plan” contingency requirements to prevent uncontrolled discharge into the sewer system that may pass through or interfere with its wastewater treatment operations. Hence, there may be some local requirements. Generally, if these tanks have secondary containment and/or are located in plant areas without floor drains connected to the sewer, this is sufficient.

While not directly related to your question, this is an opportunity to briefly discuss other types of tanks.

ASTs that contain oil of any type (petroleum, mineral, synthetic, used) are subject to USEPA Oil Pollution Prevention Spill Prevention, Control and Countermeasure (SPCC) requirements (40CFR112) if the combined capacity of all containers 55 gallons or more is greater than 1,320 gallons. SPCC requires procedural and contingency plans, as well as various technical requirements, such as corrosion protection, overflow protection, secondary containment, inspections, and spill response. Tanks used to store flammable or combustible liquids, such as motor fuels, are typically regulated by the local or state Fire Marshal. EPA provides the following guidance: “ASTs can increase the risk of fire and hazards resulting from damage caused by vehicles or vandals. AST owners should install AST systems that have adequate safeguards against fire, overfills, and damage. At a minimum, most ASTs need to meet state and local fire codes, which usually have some mix of construction, installation, operation and maintenance requirements that are intended to prevent fires and other hazards that can come from mismanaged or substandard ASTs. For more information, check with your local authority having jurisdiction, such as your local fire marshal.” Tanks used to store hazardous waste are subject to significant design, certification, inspection, and containment requirements. Federal hazardous waste tank systems requirement may be found at 40 CFR 264 and 265 Subpart J, or you can review my “Hazardous Waste Storage Tank” article of the January 2002 Product Finishing Pollution Control Clinic.

Even when there are no specific regulatory requirements, you still need to consider the liability and risks of an unplanned spill or release. Is the spill inside or outside? What is the spill path? Is there a nearby direct connection to sewer or storm drain to surface water? Is there a nearby pathway to groundwater, such as a storm water dry well? What is the toxicity and/or hazard of the released material? What would be involved in cleaning up such an uncontained spill? How could this material damage nearby structures and/or equipment?

In closing, the best way to prevent a spill or release from a tank system is to follow good engineering practice principles of as a foundation:

• Material Compatibility—all components of a tank system must be suitable for extended contact with the stored liquid over the range of foreseeable temperatures and concentrations.
• Spill Protection During Filling—tank truck and/or rail car unloading areas should be paved or lined with impervious material and constructed to provide sufficient containment volume or use portable “spill pans” under hose connections. Transfer operations should be attended at all times. Trucks should be secured with dock locks or wheel chocks.
• Overflow Protection—tank system design should incorporate tank level indicators, high level alarms that can automatically deactivate transfer pumps and/or close feed line valves, and/or direct overflows into secondary contain ment. Another option is to have a tank large enough so that when a tanker load is ordered, there is sufficient volume already in tank to accept entire load.
• Containment—tanks should be placed within containment areas that are imper- vious and corrosion resistant to the stored liquid. EPA guidance allows that a building itself may be used as containment as long as there are no drains that would allow any spill to leave the site. Use of building walls and floors for containment purposes must be suitable consider- ing material hazards, clean-up issues and potential damage to infrastructure.
• Labels—tanks and associated piping should be labeled as to contents and health, flammability, chemical stability, and special hazards of the stored material.
• Tank Stability—provide additional structural considerations in seismic or flood-prone areas.
• Security—especially for tanks located outside, provide security to prevent vandalism and/or theft.
• More and more chemical suppliers are providing tank systems that not only incorporate many of the above criteria, but also provide a low level alarm to indicate a reorder point. In fact, one of our client’s chemical suppliers offers automatic reordering through a wireless connection when the low level alarm set point is reached.

Hope this information helps you in your evaluation.

(Note: thank you to Mr. Ryne Stefanacci of my staff for assisting me with responses to this month’s column.)