Precast Concrete
Concrete tanks have been used for Septic systems since the 1860s and precast concrete tanks since the 1960s. Though our knowledge and understanding of soils and septic systems has come a long way since then, the actual tank structure has not really changed much, basically it’s still a large heavy sealed concrete box.
One of the biggest Pros of a concrete tank is its weight. Being in the lower mainland, we see a lot of rain and high seasonal water tables. When installing a system in an area where the water table is above the bottom of the tank, having a heavy tank that can sit firmly on grade is a necessity. Placing a tank at an exact grade is crucial for allowing the system to function properly and avoid the homeowner’s nightmare of a sewage backup into the house.
Adversely however, the biggest downfall of the concrete tank is also its weight. Most concrete tanks for residential purposes weight between 8000-24000lbs which is a little heavy for a small excavator to handle. Typically, the tanks are delivered onsite by the manufacturer using a crane truck and placed in the excavated area designated for them. Seems easy enough, off the truck and into the hole. The difficulty with that process is that truck usually cannot lift the tanks further than 10-20 feet away. Installing systems in areas that have limited access can be difficult if there isn’t a road or suitable surface close enough to get the crane truck to place the tanks. There are scenarios though where you can order a few truckloads of gravel and build your own road, but as you can imagine, not too many people are eager to get a gravel road put down through the middle of their backyard just to place a septic tank in the ground.
For all of our concrete tanks we use Manco Septic as our preferred supplier
Synthetic Septic Tanks
Synthetic and composite materials are already a huge part of modern technology and continue to replace older more antiquated materials every day. Septic is no exception, modern synthetic tanks are durable, long lasting, and most importantly they are light. Getting a plastic tank into their intended place is usually far less of an event. Unlike their concrete counterparts they weigh between 400-700lbs and can easily be moved into place and adjusted with small machinery or even a good push. This comes in handy when access prevents us from getting a crane truck near the designated or desired location of the septic tank.
The benefit of being able to move the tanks freely and place them wherever we want comes at a price though. Coming back to the high water tables in the lower mainland brings up the issue of empty tanks floating up. Synthetic tanks are highly buoyant and when empty and in a saturated area, have been known to break through the compacted material it’s buried under and float. This is not an issue in areas of high permeability or a low seasonal water table but many areas in the lower mainland sit in low permeability clay and silt, floodplains or areas where the seasonal high water table encroaches into the area that the septic tank is buried.
Many factors can play into what tank is right for your system and location. Both options have unique qualities. If you have further questions regarding your septic system, what septic system is best for you, or just want to know more about our experiences with concrete and synthetic tanks, be sure to contact us.