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| The tank in place and partially buried. The black tube visible at the top of the tank is the manhole extension and the pipe beside the extension is the vent pipe. The vent pipe relieves any pressure or vacuum that occurs as the water in the tank rises or falls. I had looked for a premade vent cover designed to prevent dirt and and animals from entering the pipe, but could not find one I liked and ended up just epoxying a fine screen to the down-turned end of the pipe. In front of the tank is an improvised valve box made out of old tires that will be explained further down in this post. Finally, immediately next to the valve box is the manifold, which will also be explained further down in this post. |
I recently completed the installation of an underground water storage tank or cistern. This water distribution project has been somewhat different from many other projects in that I've had to think out in advance considerably more details before I could order materials and start work. In order to have the proper tank size I needed to consider the number of gallons the future bison herd would require per day and the number of continuous days there could be with not enough solar power to operate the water pump. I also needed to determine the proper tank elevation and placement to ensure that I had the had the correct water pressure and water flow rates in water lines leading from the storage tank to the water troughs.
Considerable research into my options for a buried tank revealed some interesting options. These options included items from the ready-made category, such as plastic and precast concrete tanks, as well as the do-it-yourself varieties, such as cast-in-place concrete and sections of grain storage silos. My eventual decision to purchase a plastic tank was based largely on regional availability, cost, ease of installation, and a minimum of long term maintenance requirements. Some additional research indicated to me that the average plastic tank cost was around $1 per gallon of capacity and there are a number of web-based companies selling tanks at this price range. I ultimately decided to purchased a 1175 gallon low-profile polyethylene underground tank manufactured by Norwesco.
In addition to the tank I also purchased one manhole extension, four bulkhead fittings (for the input, output, vent, and sensor wiring), HDPE pipe, and various PVC pipe fittings. Although the tank included two manholes, I really only needed one of them to rise up through the soil for access to the inside of the entire tank.
The following photographs outline some of the steps involved in installing the tank.
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| The manifold connected to the now buried output bulkhead of the tank. Each valve in the manifold allows me to control which of the five connected water lines are turned on or off. Currently attached to a barb on the end of each valve are 10 foot lengths of black HDPE pipe, which will later be connected to the underground waterlines. The large black pipe visible in the foreground of this photograph is a drain pipe that travels underground to a gravel bed underneath the manifold. This pipe, gravel bed, as well as a sand bed underneath the tank are intended to prevent the buildup of any rainwater around the buried tank. The need for this precaution became apparent after experiencing an inch of rain overnight during the initial installation of the tank. That 1 inch of rain, pooled to 6 inches of water in the tank hole, was enough to float all 360 pounds of the tank, which I found drifting around in the hole the next morning. While it is true that rainwater will likely behave differently once the tank is buried, I didn't feel it was worth the risk to not install the drainage system. |
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| The improvised tire valve box tipped on its side. A valve box is simply a box with a lid and no bottom that is placed over water valves and then buried so the ground surface is flush with the lid of the box. This allows people easy access to the underground valves by simply lifting the lid of the box and reaching in. Factory made valve boxes vary greatly in price depending on quality and size with most of them being very affordable. However, with the box depth and size that I needed for my manifold, the cost would have been over $400 dollars, so I decided to try to improvise with some old tires. To do this I cut portions of the side walls out of three old tires and then linked the tires together with bolts passed through the remaining portions of side wall. The result was a column of connected tires with an open bottom and top. For a lid I sewed together pieces of other old tires with wire. The end result was a durable valve box that cost me $0. The angle of the view in this photograph is from the bottom of the box looking towards the top. |
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| The cistern mostly buried with the tire valve box in place. |
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| The tank buried. The metal t-posts on the right side of the photo were sunk in the ground next to the buried pipes leading away from the manifold. Once the soil around the posts has settled, they will be replaced with buried metal markers that can be found with a metal detector. This will enable me to find the buried pipes later if I need to. |
