Skip navigation

Preventing the Formation of Ice in Water Storage Tanks

One very simple method to prevent or minimize the formation of ice in water storage tanks is to allow the tank to drop the head as much as possible (to the lowest water level and/or pressure that the owner is comfortable with) before starting to pump again.  The reasoning behind this method is that more warm water will be added to the tank during each pumping, as well as getting a much higher percentage of the water being agitated.

Conversely, if the water level is kept within a couple feet of the high water level (HWL), the pumps are running more, and the water that is added remains near the bottom of the tank, and is the first to be removed.  This allows the water near the top to cool, and ice to form.

By allowing the head in the tank to drop lower, the average residence time of water in the tank is more uniform, the water is in motion for a greater amount of time, and the pumps are in use for a smaller percentage of time, with fewer starts.

In tanks where this is feasible, lowering the HWL in conjunction with the above method will result in a higher water turnover in the tank, more water movement, higher water temperatures, and a lower possibility of ice formation.

A second alternative is to use a water agitator, or “de-icer.”  These basically consist of a motor/blade assembly which acts as a propeller to churn the water, the agitator should be located several feet below the water service level, such that it remains under water.  The reasoning behind this method is that simply keeping the water in motion prevents ice from forming.

Preventing the formation of ice in tanks can be critical in the value of the tank.  Ice formations can damage the tank, tank coating, and possibly piping.  Damaged tank coatings can lead to corrosion of the tank, causing structural damage.  By preventing ice from forming, the owner can reduce maintenance and reconditioning costs as well as extending the life of the tank.

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.

Floatdown
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.

ROV
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, www.klmengineering.com and while you are there, please check out all of the services we provide.

Don't Be A Statistic

Click to zoom.

Leaves are falling at a breakneck pace, winds a blowing a little colder, harvest and hunting seasons are in full swing, and the frost is beginning to settle in.  Wait – frost?  Yes, our old friend winter is around the corner.  It is time to remind ourselves and our operations personnel about the cold weather operations we employ to keep the water flowing in our water storage tanks, and keeping them from freezing and causing problems.

There are a number of options available for preventing the buildup of ice in water tanks, ranging from preliminary and periodic checks to daily operating variables to the installation of items specifically geared towards preventing freezing.

Perhaps the first thing to do is to review previous years’ water usage during the cold weather months, and consider how any changes in the past year will affect the usage this year.  This may even involve some consultation with local industries or other heavy users to determine if they anticipate any changes to their usage.

Based on the usage above, develop a plan for fluctuating the water level in the tank to try to incur as much turnover in the water in the tank as possible, and as much movement.  Communicate this plan to all supervisors and operators to ensure they understand its purpose, and their responsibilities in executing it.  The plan may include any or all of the following: minimizing the overall water level in the tank, based on usage and fire protection requirements; fluctuating the water level more than during warm weather months; regular drainage of the tank into the system, then refilling with warmer water.

Before the cold weather really sets in, and periodically (weekly or bi-weekly at a minimum) after that, ensure the vent and overflow pipe are clear of debris, and their screens are not frosted over.  If the vent screen is frosting over, and you don’t have a pressure-vacuum/frost-proof vent, the roof can actually be sucked in during rapid draw-down of the water level.  Even with the pressure vacuum relief style vent, periodic checks will help to ensure that it is working properly, and enable a timely reset if it does not automatically reset itself.

Another check to perform, at least before the weather begins freezing consistently, is to check the insulation on the inlet pipe to ensure there are no gaps, and that it has not been saturated by leakage or condensation.  Leaks, if found, should obviously be fixed immediately.  Gaps in and saturation of the insulation rob it of most of its R-value, and may require partial or complete replacement as soon as possible.

Click to zoom.

For those systems containing other systems, such as heat tape, recirculating pipes and pumps, bubblers, aeration systems, mixers and other water agitators, additional checks are in order.  First, verify the connectivity of the electrical system and that it is operating in the proper range(s).  Second, verify that the system is actually working properly through visual checks.  Third, verify any input switches, such as those using temperature or pressure, are also functioning properly.  If caught early enough, it is possible to repair deficiencies in most of these before major freezing occurs.   Oh yeah, don’t forget to turn the system on!

Periodic visual verification of the operations of these systems are important, because if its circuit(s) are blown or they aren’t working properly, it may lead to damage to your tower, rather than protection of it.

KLM Engineering has extensive experience with the installation and operation of most of these systems, and can provide consultation on their potential use and situations where one or more may be appropriate.

Remember, while there are costs to pumping more water and running other appurtenances, there could be a greater cost if your tank freezes up.  The goal is eliminate preventable damage from occurring in your water storage tank due to the formation and movement of ice.

PS.  The Minnesota Rural Water Association has some training on “Winterizing Your Water System” coming up soon.  Here is a link to their website: www.mrwa.com and the brochure for the training: http://www.mrwa.com/WinterizingFlyer2011.pdf .

It’s important to ensure that your utilities provide your residents and community with clean drinking water, from your reservoirs, water storage, and water towers. It’s also important that your facilities are clean and in good working condition, to make sure the coatings and your overall interior structures are undamaged and the tank bottom is free of excessive sediment.  Municipalities in some states are required to inspect water storage facilities at least once every 5 years and usually you can have your facilities inspected, cleaned, and disinfected all in one day.

Different types of Evaluations:

Floatdown Inspection

The floatdown inspection is KLM’s most popular and comprehensive method.  It provides the inspector with more information than any other method.  KLM provides a NACE and AWS certified inspector, who is specifically trained and qualified to perform this type of inspection.

At the beginning of the inspection, the water needs to be at the high water level (HWL).  KLM inspectors then insert and inflate a sterilized rubber raft into the tank interior and slowly float down as the tank is drained.  The inspector, while in the raft, will examine the interior structure and evaluate the existing coating integrity.

ROV Seamor Inspection

KLM uses a two-man crew and a Remote Operated Vehicle (ROV) to perform this inspection (primarily used when performing warranty and 5-year anniversary inspections).  KLM inspects the reservoir by floating in a sterilized rubber raft at the HWL, and sending the ROV to inspect all areas below the surface.  This method allows the tank to stay in service during the inspection, with no draining necessary! Videotaping is performed with a hi-def underwater camera, which shows any coating deficiencies.

KLM Crawler Clean out

This method uses the KLM Crawler ROV and is for tanks that need to be cleaned, but cannot be taken out of service.  An operator controls the KLM Crawler on the ground outside the tank using closed circuit video on the ROV during the operation.  The KLM Crawler vacuums bottom sediment with a rotating suction head and deposits it outside the tank.  All cleaning is verified with underwater video cameras on the KLM Crawler.

Dry Tank Inspection

The dry tank inspection is the method recommended by AWWA M 42 D101-53 (R1986) Part A.  However, this inspection is limited to areas accessible from a ladder or areas that can be reached from the floor.  While perhaps less detailed than the above methods, it is still a popular choice for tanks that can be taken out of service and cleaned.

For more information about inspections, along with some videos and pictures of the techniques in action, check out the “Inspection Services” on the KLM website!

You can make your water towers work to earn extra income for you!  KLM Engineering would like to introduce you to the engineering and inspection services we can provide during antenna installations on your water storage reservoirs. Having an antenna installed on your water storage tank, whether it be cellular phone, wireless internet or X-M radio, can provide the tank owner with extra income.

 

KLM Engineering has extensive experience with antenna installations, performing work on over 100 installation projects.  We are also experienced in dealing with reconditioning water storage tanks with antennas, which present a wide range of issues to the contractor.  KLM works closely with the companies that own the antennas, as well as the contractors that install the antennas.  As a result, these companies understand what we are looking for in our reviews and inspections and work with us to provide a product that is acceptable to the owner.

 

Our antenna services intend to reduce the long-term financial and maintenance burdens on the reservoir and owner by ensuring the telecommunications company performs the installation in a manner that best serves the primary purpose of the reservoir, and also ensures that company bears appropriate financial responsibilities.

 

KLM’s antenna services include:

– Reviewing lease agreements; to ensure that it includes several clauses that serve to protect the city, including working around the antennas and other maintenance costs.

 

– Reviewing engineering and design; to make sure the structural integrity of the antennas complies with OSHA regulations. We also want to minimize any hindrances to future maintenance.

 

– Shop inspection of blasting and coating (if necessary) to ensure the blasting and coating of the antenna support brackets complies with the plans and specifications, so that the coating on the brackets does not fail prior to that on the rest of the tower.

 

– Field inspections to ensure that the welding, blasting and coating operations are in compliance with the specifications.  KLM also ensures that landscaping and site clean up are performed to the satisfaction of the owner.

 

While KLM will bill you for the inspections services, this can be back charged to the antenna owner.  This means you get all the benefits of the antenna service with no financial burden (Federal Communications Act of 1996).

 

If you are interested in discussing KLM’s services during any antenna installations, or tower reconditioning, you can contact Kelly Mulhern or Matt Erickson, the primary antenna personnel, at 651-773-5111.