Implementing FDEP Rule 62-555
 

As we discussed in a previous newsletter (TTM Newsletter, March 2003) the Florida Department of Environmental Protection (FDEP) has recently amended Florida Administrative Code (F.A.C.) Rule 62-555. Among other changes, this rule now includes the following statement: "Finished-drinking-water storage tanks, including conventional hydropneumatic tanks … shall be inspected for structural and coating integrity at least once every five years by personnel under the responsible charge of a professional engineer licensed in Florida." [62-555.350(2)]. This rule covers all types and materials of tanks including elevated, ground storage, concrete, steel, and hydropneumatic. So, now that the rule is in place, what do you as a tank owner need to do? The operation involved in inspecting and maintaining a tank is not a difficult procedure, if you plan ahead of time and implement the plan with trained professional personnel.

The first step, obviously, is to drain the tank. This may sound simple, but there are issues that should be addressed before you actually "pull the plug". When is the best time for you to drain your tank? Your off-peak times will have the least amount of impact on your system. If you have the capacity to bypass your tank and stay in operation, then you already have an advantage. Some systems, though, cannot operate without their tank for very long, if at all. If you absolutely cannot do without the tank, there are options, such as running high service pumps and controlling pressure externally with fire hydrants, or installing a temporary hydropneumatic tank while the main tank is out of service. Also, don't forget to include the time it takes to drain the tank. You may need a full day, or more, to "use" or pump the tank down.

Once the timing is decided, you should also look at the condition of your valves. Are they in good enough condition to isolate the tank? You may need to at least exercise the valve a few times with the system on-line to flush out the build-up in the valve and let it seat. If it still doesn't work, this is a good time to replace or rebuild the affected valve. While you're at it, don't forget to check your liquid level gauge for operation and accuracy. I have climbed or looked at many tanks that are supposedly "empty" and found a half-full tank!

Now that the tank is empty, you're ready for the tank inspector. As the FDEP rule states, the inspector needs to be under the responsible charge of a Florida licensed professional engineer. That requirement weeds out the fly-by-night tank inspectors that travel from site-to-site in their car, armed with a camera and a coating thickness gauge.

Safety should be a major concern. Entering a tank is a potentially hazardous event and should be treated with great care. OSHA Confined Space Entry rules must be utilized and followed at all times.

Tanks are specialty structures that need to be inspected by people with training and experience specifically in the tank industry. Typical structural standards do not usually apply to tanks. There are specific standards for each type of tank. Most are covered by the American Water Works Association (AWWA).

One specific specialty area of tank design is the hydropneumatic tank. These tanks are very common in the water industry, but they need to be inspected very carefully. Since these tanks are operated under pressure, they must be treated as ASME pressure vessels. The State of Florida does not require an ASME Code Stamp on hydropneumatic tanks at this time, but we feel that all hydropneumatic tanks should be analyzed using the ASME criteria. If a vessel is code stamped, the inspection process is slightly easier since the dimensions and design details are now a known factor. If the tank is not code stamped, additional analysis is required. This level of analysis requires taking detailed measurements and thickness readings on the tank to calculate the tank stresses and the maximum pressure for the vessel.

The coating system on any water storage tank is also very critical and should be inspected by knowledgeable inspectors. Once the tank is closed up you can't see what the interior coating is doing. You may open the tank five years from now and the coating is in bad shape or it may be in very good shape. What's the difference? A good coating system consists of proper surface preparation, properly specified coating, properly applied coating, and a pinhole detection test, known as a "holiday test". These factors coupled with in-progress inspections by a National Association of Corrosion Engineers (NACE) Certified inspector, will usually result in a long lasting coating. Needless to say, any coating problems should be corrected while the tank is out of service to avoid extensive down-time. Current technologies allow coatings to be applied, and the tank returned to service the same day.

Once the tank is inspected and all maintenance items are covered, it's time to return the tank to service. Before water can be put in the tank, the interior must be disinfected. Tank disinfection is covered in AWWA Standard C652. There are three methods given to achieve acceptable disinfection. The most common of these methods is performed with common HTH (pool chlorine), or liquid chlorine. Once the initial disinfection is complete, bacteriological tests must be performed on water samples taken from the tank. These tests are typically handled by the tank owner at their chosen laboratory. Most state and local health departments will require 2 tests taken 24 hours apart before the tank can be returned to service.

As you see from this scenario, a typical inspection, even with little or no maintenance, requires about three days of down time. One day to drain, wash, and inspect the tank, and two 24 hour periods for bacteriological tests.

As I stated at the beginning of this article, the procedure to inspect a tank may sound like an involved process, but it can run very smoothly if managed by knowledgeable personnel. We at Tank Engineering And Management Consultants, Inc., perform this type of work on a daily basis. When you decide to inspect your tanks, give us a call to keep everything running smooth.