Ensuring the efficiency of a residential septic system depends on many things!

Three elements are necessary to ensure the efficiency of the septic installation of an isolated dwelling. First of all, it must be adapted to the conditions of the site and the specific needs of the residence being serviced. Next, it must be made using quality materials and following the rules of the trade. Finally, the septic installation must have an adequate follow up plan. The attention given to each of these steps will make for a septic system that will continue to properly treat and evacuate wastewater for many years.

In Québec, it is regulation Q-2, r.8 on the treatment and evacuation of wastewater for isolated residences that dictates the basic rules to follow. The technical guide on collecting underground water and treatment of wastewater for isolated residences gives more details on the interpretation of this regulation. These two documents constitute the basis of the standard septic installation design for isolated residences and other small buildings whose total daily flow of domestic wastewater is 3240 liters or less.

Several types of installations are possible. The designer determines which installation to do according to prevalent conditions of the site to be serviced. The top priority is the soil infiltration. This is why a good evaluation of the nature of the soil and its evacuation capacity is necessary from the start to make the right choice. If the natural soil is unable to receive the flow of water to be treated and evacuated, it is possible to direct the water to a stream or ditch following certain criteria set out in the regulation.

The basic systems set out in the regulation consist of a septic tank and a leaching field that completes the treatment and permits the evacuation of the water. There are four types of leaching fields. They are, the classic leaching field, modified leaching field, the above ground sand filter and the classic sand filter. The choice of which type of leaching bed to use is done in hierarchical order. If the conditions permit, the first choice is the classic leaching bed. If not, we move on to the modified leaching bed and so on. Each type of leaching bed must meet certain conditions set out in the regulation.

The Ministère du Développement durable, de l’Environnement et des Parcs also recognizes a certain number of treatment systems. It is allowed to choose one of them instead of a traditional leaching bed. The principal systems recognized at the moment are biofiltration processes using peat moss (Bio-B from Berger Environnement and Eco from PT Aqua), biological processes using bacteria in synthetic media (Enviro-Septic from DBO Expert inc. and Bionest from Bionest Technologies inc.), and the horizontal flow artificial marsh from Roseaux Épurateurs. When these treatment systems are used and the water is evacuated by infiltration in the soil, the effluent is generally directed to a polishing field that completes the treatment and permits the evacuation of the water.

There are three types of discharge into the environment possible. The first choice is always infiltration into the soil, site conditions permitting. If infiltration is not possible, discharge into a waterway may be used if the dilution rate is above 1:300 and the local discharge criteria are respected. Otherwise, discharge into a ditch, lake, pond or marsh may ultimately be accepted. Disinfection is required and in some cases removal of phosphorus must be done. At all times, local discharge criteria must be respected.

Design of the septic installation

When preparing the plans and estimates of a septic installation, many elements must be considered. First is the nature and volume of the water to be treated. One must take into account the vocation of the residence or building in order to properly determine these two elements (nature and volume). The pollutant load of a restaurant is 2 to 3 times greater than that of a normal residence. These more elevated loads require the use of supplementary treatment elements in the treatment chain. The speed at which wastewater is generated also has an influence. A larger security factor must be applied if the daily volume is generated in a short period of time instead of over a 24 hour period. The designer must make an effort to accurately determine the water flow and the pollutant loads that will be generated in order to design the septic installation accordingly.

Evacuation of the water is of capital importance. Whichever leaching field or treatment system is used, if the evacuation is not done correctly, water will resurge into the system creating anaerobic conditions and the life of the system will be affected. We cannot stress strongly enough on the importance of having a good soil analysis done to determine its rate of permeability, presence of rock or a layer of less permeable soil as well as the high position of the groundwater table. The topography of the land should also be considered in order to determine in which direction the water will evacuate. Slope is a limiting factor for certain types of installation.

The shape of the bed or absorption trenches of the leaching field or polishing field also has its own importance. As a general rule, a long narrow surface is best, the long side being placed perpendicular to the flow of groundwater table.

Construction of the septic installation

When constructing the installation, particular attention should be paid to the materials used. The sand and the crushed rock may contain too large a quantity of fine particles which will, in effect, reduce the life of the system. Therefore it is important that the crushed rock be washed to get rid of these fine particles. The filtering sand should meet the granulometric criteria set out in the regulation. It must contain less than 3% of fine particles and be coarse and homogenous. Finally, the dirt used for fill must be air permeable. The pipes, septic tanks and treatment systems must conform to the specific standards of the Bureau des Normes du Québec.

When preparing the bed or absorption trenches, the receiving soil must be grated to allow an easier passage of water. Precautions must be taken not to compact the receiving soil which would close the natural pores of the soil affecting its permeability as well as its evacuation capacities.

The surface of the final covering should be seeded in grass and slightly sloped to allow streaming of rainwater away from the site.

Use of the septic installation

Once the installation is done, certain basic rules must be followed to maximize its efficiency.

The users must act according the capacities of the system installed. The quantity of wastewater generated must be reasonable and water bursts are to be avoided as much as possible. The septic installation risks being affected by a larger than expected wastewater flow. For this reason the plumbing for a swimming pool or whirlpool or drain pipes should never be connected to the system. Any leaky plumbing in the residence should be repaired quickly.

Also to be avoided is wastewater containing unexpected contaminants. Chemical products, medications, paint and others should never be emptied into the system. Garbage disposal units are also to be avoided. The backwash from a water softening system should not be directed into the treatment system because of the salt that is used.

A regular follow up is in order. The septic tank must be emptied regularly to conserve its efficiency. Additives sold to reduce sludge accumulation in the tank are not to be used because they have a tendancy to decrease the efficiency of the tank which means that more suspended matter ends up in the leaching field or treatment system. In the case of certain treatment systems, filtration materials and certain mechanical pieces need to be replaced with use. It is important to do the replacements as necessary.

Since the first of January 2005, the owner of any treatment system must be linked by contract at all times to the manufacturer of the system, their representative or a qualified third party. A copy of this agreement must be forwarded to the municipality.

The information you have just read is a starting point toward the making and use of an efficient septic installation. To learn more, we suggest you consult the regulation, the guides in effect, the representatives of the regional management of the Ministère du Développement durable, de l’Environnement et des Parcs, consultants specialised in the field and/or the promoters of the different treatment technologies.

1. Regulation respecting wastewater disposal systems for isolated dwellings, R.R.Q., c. Q-2, r.8, Last amendment: December 31, 2004, Official editor, 2-551-22144-7.

2. Captage des eaux souterraines et traitement des eaux usées des résidences isolées, Guide technique, Édition 2005, Ministère du Développement durable, de l'Environnement et des Parcs, 2-551-22713-5.