|FREQUENTLY ASKED QUESTIONS|
- 1. Mt. Baker Silo - Frequently Asked Questions
- 1. What is the process for building a new water tank?More
You have decided that your system needs additional water storage. You ask, "Where do I start?" Your first step is to hire a civil engineer who has experience in water system management. He will evaluate your system and work with you to determine the best plan based on your needs. Part of the plan would be to determine the amount of water storage required. Once a plan and design is in place, it must be forwarded to the State Dept. of Health (DOH). Keep in mind, DOH will not even consider your plan without a civil engineer's stamp on it. DOH will then review the design and either approve it or make recommendations for changes based on minimum state requirements and 'known best practices.' Throughout the process, they will offer advise based on their expertise to help you achieve your goals and verify that your plan complies with all applicable regulations. Once the DOH has signed off, you can move on to your local county building department for a building permit. Among other things, the county will require a soils analysis from a licensed geotechnical engineer specific to the spot where the reservoir will sit. Once this analysis is complete, Mt. Baker Silo can provide the site specific structural design for the reservoir (including foundation). This engineering must then be forwarded to the county for their approval before the building permit can be issued.
At this point, construction can begin. First the site must be cleared and prepped for our foundation. Any underground service pipes must be brought in under the tank and stubbed up for the foundation to be poured around. This work may be done by Mt. Baker Silo or another earth work/piping contractor that you may select. Gravel may be brought in for sub-grade reinforcement and leveling. That gravel will have to be tested per county requirements for compaction. Once the sub-grade work is complete, it is time for our concrete crew to move in. They will form up and pour the base, walls and concrete roof, all poured in place. The walls are poured in 5' lifts where we make the pour, jack up the forms 5', set the reinforcing bar and pour again. Most often, this is done in 24 hour cycles. Once all concrete is poured, the 28 day clock starts. This is the industry standard time frame allowing for the concrete to gain sufficient strength before filling the reservoir with water.
- 2. Can I make my existing concrete tank taller?More
Unfortunately, the answer to this question is always "No." Base designs are specific to each individually sized reservoir. The concrete foundation will be inadequate to carry the additional loading of a taller reservoir. You may say that I have a reservoir that was specifically designed and built with plans of adding on height at a future date. It was built with a heavier base and has rebar sticking out of the roof to tie into a future wall pour. Unfortunately, the structural codes that tanks are designed to, change every 3 years. There is really no chance that the base and lower wall designs meet the strength and reinforcement requirements of the current codes for the larger storage volume you are hoping for. Your best bet is another reservoir next to your current one to supplement the existing storage to meet your current and future storage requirements.
- 3. What should I consider when deciding between concrete and steel for my new reservoir?More
Lets be honest up front. Concrete reservoirs may not always be the most aesthetically pleasing. Expect some weeping when the tank is first filled. As the concrete does its initial healing, expect vertical lines of efflorecence to form and some continued minor weeping from time to time. However, most people don't put water reservoirs in their front yards. Once you get beyond aesthetics, concrete gets a lot more appealing. If low initial design and construction costs coupled with lower maintenance costs down the road appeal to you, then you will want to take a good look at concrete.
Mt. Baker Silo's specialty is in concrete reservoirs between 10,000 and 500,000 gallons reservoirs. Other common reservoir options are steel tanks which include bolted steel (epoxy coated or glass fused), welded steel or corrugated steel with PVC liner.
Welded steel reservoirs, utilizing epoxy coatings and paint, have been around for a long time. However, these coatings do break down over time. It is recommended that to make one of these tanks reach its life expectancy, the coating needs to be reapplied about every 15 years or so. This can cost between 35 and 50 percent of the original tank price. These options can get expensive when you combine them with the higher cost of initial construction. Consider that after 3 recoatings, you have paid more for maintenance than was originally paid for the reservoir. Also consider when the time comes to recoat the reservoir, there is no way to get to the steel on the underside of the steel floor that sits on the concrete foundation. This is where we usually first see steel reservoirs fail. Other things to consider are the costs of extended down time for recoating, increased costs of accessory repairs and difficulties in attaching accessory upgrades. Also, when comparing construction costs, make sure that the concrete foundation and engineering is included. Often, this can be an additional cost not supplied by the tank contractor.
Glass fusion in water tanks is a more recent and very good technology. These reservoirs consist of panels bolted together much like a bolted steel tank and are commonly covered with an aluminum geodesic dome. The wall panels are factory coated with a glass lining before shipping. The metal inside the glass lining is very well protected. Gone undisturbed, the glass will not deteriorate and the tank will last a very long time. The drawback to these reservoirs is that when hit, the glass will break just like a window pane. Gun shots, hits by vehicles or equipment, falling trees, rocks, etc. can all damage the glass. Once there is a crack in the glass, there is a pathway to metal decay. As we understand, glass repair kits are available, but results have been mixed.
Corrugated steel tanks are the grain silo types that have been modified to hold water by using thicker metal and adding a PVC liner to make them water tight. These are considered more of a short term or portable solution. If this is a consideration for you, Mt Baker Silo does carry a line of this style reservoirs.
- 4. Can I backfill or bury my concrete tank?More
The short answer is "Absolutely". However, there are some things to consider. Under normal engineering, our tanks can be backfilled up to about 8' with no more than a 4' differential from the high point to the low point. If you have plans for anything outside those boundaries, please let us know up front so that we can consider your needs during the initial engineering stage. Also, if your reservoir is for potable water, the State Department of Health will not allow you to backfill above the full water mark on the walls. Backfilling above this mark and onto the roof does not allow for necessary exterior water dispersal. It can become a condition for outside water intrusion and potential contamination.
Your tank isn't for potable water? Bury away. Just let us know of any need for additional loading on the roof like driving vehicles, buildings, golf courses, etc. so that we can make sure that engineering is properly done up front.
- 5. How does Mt. Baker Silo figure the price per gallon?More
Mt. Baker Silo's reservoir prices are based on construction costs, not on a standard price per gallon. Concrete and mobilization prices can vary from area to area. Soil conditions, site access and accessory designs will also affect the final price. Structural variations due to poor soils or elevated snow loads will often affect the final price. Government projects which require certain wage and benefit rates must also be factored in.
Mt. Baker Silo has steel concrete forms for 4 different standard reservoir diameters: 14', 20', 26' and 30' We pour the walls of these reservoirs in 5' high lifts. Normally, you will get a better price per gallon from the larger diameter tanks as you increase the reservoir height. Also, as the tank gets taller, the cost of the roof and foundation are spread out over more gallons stored and the price per gallon goes down. However, reservoirs that get over 50 feet tall will start requiring foundations that grow exponentially to compensate for overturning. At this point, the price per gallon can start to rise again. Often two smaller reservoirs side by side is the more economical option and worth considering. But, if you need the extra elevation, we will accommodate your needs.
Feel free to contact us for estimates. We would be happy to talk with you to determine what configuration will most economically meet your needs.
- 6. Why does Mt. Baker Silo offer corrugated steel tanks?More
Over the years, these tanks have grown in popularity. They do offer some advantages. They can be erected very quickly and efficiently. They can be moved if necessary. Many people seem to like the looks of them. With more of a grain silo look, they may better fit into a farm setting. They have the stigma of being cheaper than concrete although we have not found that to necessarily be true. They do come in smaller sizes than we offer in concrete. With the demand that we were seeing for these tanks, we decided to take advantage of the chance to expand when that opportunity arose.
- 7. When designing a tank, what accessories should I consider?More
Venting, an inspection hatch in the roof, piping for getting water into and out of the tank and an overflow are items that are required on all reservoirs. Other items like ladders, railings and safe climb equipment may be required in order to comply with OSHA regulations. A mechanical water level indicator is often required for fire flow tanks and recommended as a convenient way to get a general idea of the water level for any tank. Probes for electrical sensor access, a side access hatch in the wall, sample ports for drawing water for testing and advanced inlet mixing systems are all available. Separate piping through the floor for inbound and outbound water, as well as an additional drain pipe for cleaning are highly recommended. See our accessories page.
- 8. My new tank has damp spots on the outside. Why?More
A known fact of concrete: All concrete will crack. Anyone who tells you anything different is not telling you the truth. As wet concrete cures, it shrinks. Unless the concrete is suspended in mid air, anything it is in contact with as it cures, creates a force counteracting the concretes need to shrink. Common examples are the ground, forms and reinforcing bars. The result is that something has to give and usually it is the soft concrete that is still trying to obtain strength. Much can be done to minimize cracking. The best plan is to slow concrete shrinkage and reduce it to a minimum. This allows concrete to increase tinsel strength before being pulled apart (cracking). Minimizing the amount of shrinkage will reduce the amount and size of the cracks that do happen. These goals can be obtained through special mix designs, water reduction and temperature controls in fresh concrete and proper curing of concrete as it hardens. Different reinforcing patterns in rebar placement and forming procedures can also help. However, to a small extent, some cracking is still going to happen.
The most obvious moisture you will see when a tank is first filled is from the horizontal construction joints or cold joints as we call them. During construction, these joints are lined with a bentonite strip. Bentonite is a type of clay material that expands when it comes in contact with water. As water moves through the joint, the bentonite expands. This creates hydraulic pressure within the joint and eventually seals it off. Most of the moisture you see from these joints will dry up within 10 to 14 days after initial filling with a few spots possibly remaining for up to 90 days.
Vertical cracks are also referred to as shrinkage cracks. These cracks are so small that water moves through at a very slow pace. Water movement is not visible, but damp spots may be there none the less. The good news is that concrete has it's own natural way of drying up these cracks. We call it efflorescence. For a better understanding, see the question on efflorescence. This process will eventually dry up these cracks. Expect most spots to dry within the first 6 to 9 months. Many will dry faster, although in some extreme cases it can take a year or more. If you see visible water movement from the crack, you will want to have it further evaluated. We may recommend monitoring the crack allowing time for the efflorescence take care of it, or we may consider options such as patching or injecting to help it seal up faster.
Keep in mind that hardened concrete will expand and contract with temperature. You may have driven under an overpass and noticed a space on each end of the concrete spans. This is to allow for expansion and contraction of the bridge span through normal cycles of temperature change like day vs. night, summer vs. winter. Although the water on the inside of the reservoir will suppress temperature changes and reduce this movement, it does happen on all types of reservoirs. This movement in concrete reservoirs may aggravate a crack from time to time. You may notice one day there is a damp spot where there was none before. But then, after a few days, efflorescence seals it and it dries back up. Later, another spot may appear somewhere else. All this is normal with concrete tanks and has no ill affect on the tank.
- 9. What is efflorescence?More
In short, when cement dust comes in contact with water in a cement mixer, a chemical reaction results. This reaction creates a bond between the cement molecules to the rock and sand producing hardened concrete. A byproduct of this reaction is a type of salt. This salt is carried to the exterior surface of the concrete wall by moisture moving through cracks or cold joints. As the moisture emerges from the concrete, much of it evaporates depositing the salt at the opening of the crack. The salt reacts with carbon dioxide in the air creating calcium carbonate. This is an insoluble material that gets very hard. Over time, it seals up the crack and where there once was moisture, there is now a dry white spot or small white ridge along the crack. There is a lot of good information to be found on the internet if you are interested in further learning about efflorescence.
- 10. What are the vertical white streaks on the side of my concrete tank?More
These harmless white streaks are going to happen on any concrete water containment structures. The white salt looking material is calcium carbonate caused by the process of efflorescence. Usually, when the concrete is left in it's natural gray color, these deposits are hardly visible until you get up close . They may be more noticeable if the concrete is painted a darker color or in the later years of the tank as the concrete darkens with age.
- 11. What warranties are included with our concrete tanks?More
Mt. Baker Silo offers a standard one year warranty on our reservoirs. That allows plenty of time for the project to be completed and make sure that the reservoir is performing as it should. It also gives the efflorescence time to work and dry up any damp spots. If there are any areas of concern during the warranty period, we will evaluate and work to resolve them if necessary. Some people will ask, "Your tank should last 75 to 100 years, why not a longer warranty?" We have found that unlike tanks with corners, once a round tank has sealed up and is working as it should, the chance of any problems are pretty minimal. If during that first year, any concerns do arise that can not be immediately addressed, we are willing to look at extending the warranty period to reach the point where everyone is comfortable that the tank is performing as it should and will continue to do so through out its expected lifetime.
- 12. Can I paint my concrete tanks? What about colored concrete?More
Mt. Baker Silo recommends leaving the reservoir the natural color of the hardened cement. However, that may not always be practical. A common question we get involves putting pigments in the concrete as we pour the walls. There are a couple of concerns with that. First, the pigmented concrete will come in contact with the drinking water on the inside of the tank. There have been concerns about that pigment leaching into and contaminating the drinking water. As far as we know, there has been no definitive study done to conclude one way or the other. The other issues is that it is very difficult to match colors 100% between 5' wall pours. More than likely, you would end up with a touch difference in shades between pours.
Painting our tanks is a possibility. However, because of the porous nature of concrete, moisture is always moving through it; all be it a very slow, unnoticeable rate. The paint seals off the outside of the concrete and the moisture backs up against the paint. Eventually, the water starts to push the paint off. Therefore, a paint job usually won't last as long as you might expect. However, if painting is still desired, we have found the price to have a professional painter come out and do it and when necessary, redo it is not usually very expensive. Many people have determined that it is worth the extra money spent. We do recommend that you stay with lighter colors when painting. Guaranteed, some vertical lines of white efflorescence will appear. The darker your paint color, the more these lines will be noticeable. It is also recommended that you sandblast the surface before painting the first time.
- 13. What maintenance is required on a concrete tank?More
All water storage tanks need to be cleaned on a regular basis. The frequency of those cleanings depends mostly on your water source. For example, some systems with a lot of manganese may need cleaned twice a year or more. Other systems can go 5 years or more and the tank looks as clean as the day it was first put into service. The majority of systems should consider a yearly cleaning and interior inspection. Cleaning our concrete tanks consist of taking the reservoir out of service, emptying it and going inside with a pressure washer. If the reservoir was built with a separate drain, all material is washed through the drain and disposed of properly. If a drain pipe is not an option, other methods like pumping, vacuuming or shoveling are utilized. Finish up with a disinfection procedure and the tanks is ready to fill, test and put back in service. The actual cleaning process usually takes less than a day and the whole process of draining, cleaning, filling and testing can normally be done in less than 72 hours. It is also recommended that the top of the roof be cleaned at the same time. This allows the roof to properly shed rain water as it was designed to and reduces risk of contaminants finding a way into the reservoir.
Other regular maintenance includes inspection of the accessories such as the air vent, roof inspection hatch, ladders, piping, railing, water level indicator, safety equipment, sample ports, etc. Make sure all items are securely fastened, locked, necessary screens in place and working as designed. Any signs that screens are not working properly or rain water may not be shedding properly will need to be addressed. It is recommended that these exterior inspections be done twice a year. Normally, they shouldn't take very long.
- 14. I have a bad water test on my existing tank. Why?More
If you have a bad test, there are three main areas of concerns. One is contamination from the water source. The second possibility is infiltration of contamination through an entry point in the reservoir, usually on the roof. Start with a general inspection. Is the roof clean? Are all screens, gaskets and caulking in place? Are there any possible entry points for bugs or rain water? If areas of concern are found, we can help. Repairing or upgrading accessories, sealing holes or cracks, making other modifications so rain water sheds better are all things we have experience and expertise in.
A third concern that has become more common in recent years is how water circulates in the reservoir. Common construction methods 20 years ago were to have one pipe come in the bottom of the reservoir used as an inlet and an outlet for the water. Level sensors would allow just a few feet of water to be used before a pump would kick on and refill the tank. The water at the top would go up and down, but stayed on the top never mixing with the water circulating at the bottom. Over the years, this water would warm and become contaminated even without a necessary contamination source. This situation continues until the water source is interrupted and the tank draws down farther than normal and some of the contaminated water is drawn into the system. All of the sudden there is a problem. To alleviate potential for this problem, most reservoirs that we build now are designed with water circulation in mind. This is usually as simple as placing the outlet to spill out near the roof. You can also allow for more service volume in the reservoir. This means allowing the water level to draw down further before the pump kicks on to refill it. If you have a reservoir and believe this may be a concern, give us a call. We do several retrofits every year to address this issue.
- 15. When do leaks in concrete tanks need repaired and how is this done?More
A common question is: "I have a spot on my tank that is leaking, does it need repaired?" One of the first things that we will normally ask for you to do is send us pictures. Digital cameras and email make this very easy. We can usually get a good sense of what is happening from pictures. What we are normally looking for is how much water is coming through, where it is coming from and what is the concrete condition around it. If it is just a damp spot that doesn't go to far, we normally recommend leaving it alone. If you can see water moving and pooling at the base, we normally recommend that it be fixed. If it is somewhere in the middle with a wet spot that moves to or near the base but you really don't see visible water movement, than that would be decided on a case by case basis analyzing all factors. The age of the reservoir is always a consideration. As tanks get older, the chance of getting any help from the efflorescence process diminishes.
Small damp spots in concrete are usually not much of a concern as they will normally come and go. Moving water is more of a concern as freeze/thaw cycles and long term water erosion can cause beak down in the integrity of the concrete.
We have two different options for approaching leak repair. The first is an exterior injection while the reservoir is still full and even in service. It is a NSF approved foam material that reacts with the water in the crack to expand and seal the crack. We have had very good success with this process in stopping cracks with visible water movement.
A second repair method that we use is to patch problem areas from the inside. We use a NSF approved, two part aquatapoxy material to put a patch on the inside of the reservoir. This method involves draining the tank and is usually combined with a thorough cleaning. It is more extensive, but may be recommended over exterior injection in some circumstances.
We have found patching and sealing concrete to be very difficult at times. Most of our experience comes from fixing corners on square or octagon tanks that were built by others. Even with all our experience, there is no guarantee of drying up every spot 100%. We do have some incredible success stories, though.