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Is it time to inspect your water storage tank or reservoir, or would another time of year work better for your system? Each owner has his own answer, and in many cases, there is a unique answer for each tank or reservoir.


Numerous factors will dictate when you can most easily take your tank out of service. Style, construction and location of the tank, required flow rates, peak demand, the ability to isolate the reservoir from the system, and the possibility of ice in the tank are all considerations which affect the final decision.


The type of water storage tank you have will certainly make a difference. Below grade and enclosed tanks, such as clearwells, underground (buried and partially buried) reservoirs, and GAC and filter tanks, are able to be evaluated in the winter months, as are many concrete reservoirs. Steel and elevated storage tanks are best inspected during the warmer weather between late spring and early fall. If your tank is susceptible to the formation of ice, inspection is not an option until the ice is completely out of the tank.


Perhaps the major concerns of owners are the peak and daily required flow rates. Seasonal water demand, particularly considering industrial uses, can place other limitations on the ability to take the tank out of service.


As each owner must decide on the best time to inspect their tank based on the characteristics of their water system, careful consideration must be given to these factors. Many of you know, there may not be an ideal time to take the tank out of service; you may need to choose the “least bad” time. We would urge you to consider this case in another way – as an opportunity to evaluate the extent to which your staff knows the water system and can handle issues involved with operating the system in non-standard conditions. Often the capabilities of the system are not used, and abilities can be degraded if not used, so seeing this as a challenge to shift the focus of the system’s operation, and isolating parts can be a rehearsal for times when problems may occur.


Of course, there are methods of inspection that can occur without taking your tank out of service, the easiest and best method in our opinion is the remote operated vehicle, or ROV inspection. You can find out more about this ROV inspection here.

As you are probably aware, there have been some changes to the Wisconsin Department of Natural Resources (WI DNR) administrative code that lists the requirements for the operation and maintenance of public water systems (Chapter NR 810). KLM Engineering would like to take this opportunity to summarize the current requirements.

The WI DNR requires that the interior and exterior of all water storage facilities of 10,000 gallons or larger shall be inspected and maintained a minimum of every 5 years by a professional tank inspection firm or by a registered professional engineer. Interior and exterior coatings on steel elevated water storage tanks or treatment structures shall be inspected by a person trained to evaluate the integrity of the paint system.

KLM Engineering can perform these periodic inspections, using inspectors who are NACE Certified Coatings Inspectors, trained climbers and riggers, trained in both destructive and non-destructive testing, are familiar with both AWWA D100 and M42 standards, and that have the knowledge and specialized training to perform a thorough evaluation and make unbiased recommendations.

The WI DNR allows for any of the following methods to be used for inspecting your reservoir or tank:

  1. Drain down inspection, which is a dry tank inspection where the tank is drained prior to inspecting the tank;
  2. Float down inspection, which is an inspection where a rubber raft is used to inspect all areas of the reservoir while it is being drained;
  3. Diver inspection, in which a tethered commercial diver enters the tank and performs the inspection; and
  4. Robotic inspection, where a remote operated vehicle (or ROV) with a fiber optic tether and video camera is used to visually inspect the reservoir.

KLM can provide any of the inspections allowed by the WI DNR, but recommend either the float down inspection or the robotic (ROV) inspection, each with its own benefits.

For tanks of unknown condition or that are known or suspected to require repairs, modifications, or repainting in the near future, the float down inspection should be performed. This gives the inspectors the ability to perform hands-on testing of all areas of the tank. Depending upon the type of tank, this can include both non-destructive testing, such as ultrasonic plate thickness, pit depth reading, and dry film thickness testing of the coating, as well as destructive testing, such as cross-hatch adhesion testing, all of which provide an excellent baseline for the true condition of the coating and structural condition of the reservoir. It provides the best opportunity to identify the coating (paint) failures and percentage of corrosion, which is often the main purpose of the inspection.

For tanks in which the condition is generally known or there is no reason to suspect that repairs or repainting will be required in the near term, such as those recently reconditioned or with a history of in depth inspections, or in cases where the owner does not wish to take the tank out of service, particularly in cases with minimal sediment and cleaning may not be required, the robotic or ROV inspection is an excellent option. This allows a visual inspection of the interior of the reservoir and provides a video record of the reservoir and inspection.

In all evaluations, KLM also performs a thorough exterior inspection, and provides a written evaluation report with color photographs to substantiate the conditions of the reservoir, as well as the WI DNR reservoir inspection form.

There are a few additional things for owners to remember:

  • The WI DNR regional drinking water staff shall be given 48 hours prior notice of the date and time of the inspection.
  • Upon completion of the inspection, a completed WI DNR report form shall be submitted to the regional drinking water staff person.
  • The water supplier/owner shall submit copies of any additional reports and videos prepared by the inspector.

To view and download the Chapter NR 810 Requirements for the Operation and Maintenance of Public Water Systems of the administrative code, click here: Chapter NR 810 Requirements.

To see all of the Wisconsin Administrative Codes that relate to private and public drinking water, click here: Wisconsin Administrative Codes.

For more information, to discuss these options, or to get a sample RFP, please contact us at our website, and while you are there, please check out all of the services we provide.