Choosing the Right Material for Your Tank

You can avoid septic tank problems by ensuring your tank is made from the right material. The majority of septic tanks are constructed out of concrete, fiberglass, polyethylene or coated steel. Typically, septic tanks with a capacity smaller than 6,000 gallons are pre-manufactured. Larger septic tanks are constructed in place or assembled on-site from pre-manufactured sections.

Due to their higher weight, concrete tanks require specialized cranes in order to set the tanks in the system. Plastic tanks, however, are gaining in popularity due to the fact that they do not need cranes and, since they are lighter in weight, can be shipped greater distances. Tanks installed in locations where high ground water or saturated soils or other conditions that can cause tanks to float would be more suited to a concrete tank with its increased weight.  Please note that concrete tanks are also susceptible to floating and, in situations where floating is very likely, anchoring of tanks might be necessary.  It is also important to be aware of the tank manufacturer’s limit of depth – concrete tanks are typically reinforced to handle greater depths than other tank materials.

Hydrogen sulfide and sulfuric acid are both present in varying amounts in anaerobic septic tank effluent and sewer gas and can cause concrete and the rods that reinforce the concrete to corrode over time (note: this is not the case with aerobic septic tanks).  Because this is a known factor, many concrete tanks are overbuilt to compensate for normal amounts of both hydrogen sulfide and sulfuric acid. PVC and polyethylene tanks are not affected, but nylon tanks are affected by these gases.  Metal tanks are easily corroded in an anaerobic environment and are no longer widely used due to this reason.

Tank manufactures must follow strict requirements so that the anticipated loads will not crack or collapse the tank, and joints need to be watertight to suit varying soil saturations. Tanks must be sealed so that untreated waste water cannot enter the environment and contaminate groundwater used for drinking. This is also important to prevent water from entering from outside the tank, which could hydraulically overload the tank and upset the treatment process. A leaking tank can also allow the improper concentrations of sludge and scum layers by exfiltering the effluent.  Tank collapses have also been linked to a tank not being watertight. Tank manufactures are required to test the tank either hydrostatically or with a vacuum test that, hopefully, predicts the long term ability of the tank to stay watertight.

In conclusion, there are many factors to consider when selecting a septic tank material. Choosing the right material will help your system avoid problems.

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