As maintenance is critical to the proper functioning of a sewerage system, the owner of the system is responsible under the SSR to ensure that the appropriate maintenance and monitoring is carried out for all components of the system. This requires the designation of an AP as a system maintainer on the permit documents. This learning task will cover the standard expectations for maintenance of a septic system.

Maintenance Plan

The maintenance plan should specify the initial schedule of system maintenance. Table II-62 of the SPM shows minimum intervals for maintenance visits and testing for the first 12 to 14 months of operation depending on system or treatment type. Thereafter, the AP and owner would agree on an appropriate maintenance schedule over the next 5–10 years.

The maintenance plan furnished to the customer by the AP should include:

• An operation manual for the system
• A schedule for maintenance and monitoring including prescribed maintenance tasks
• A statement of the allowable average flow for any 30-day period
• Contact information and emergency contact information for the AP who filed the system, the installer, a maintenance provider and the electrician
• Information and advice for the system owner, and
• Sign off by owner that they have received and understood the requirements of the plan

Pump Outs

Pumping of sewage and effluent involves a pumper truck. They are trucks that vary in size from single-axle units meant for servicing small tanks such as found in a portable toilet, to large tandem-axle units meant to service septic and holding tanks. A vacuum pump at the top of the onboard tank creates a partial vacuum within it, which is transferred to a hose connected to the lower portion of the onboard tank. The hose is inserted into the septic tank, and the liquefied contents are drawn into the onboard tank through it. The contents of the truck’s onboard tank are emptied at a municipal sewage treatment facility.

Regular monitoring of the scum and sludge levels is the best way to determine a pump out frequency for a specific installation. Assess the sludge and scum accumulations and pump out when any of the following are noted:

• Total solids accumulations are more than ⅓ of the internal height of the tank
• The scum layer reaches the top of outlet T in a one compartment tank
• The scum layer reaches the top of inlet T in a two-compartment tank
• Any obvious carry-over of solids to the second compartment
• Premature effluent filter clogging
• An increase in TSS or FOG (fats, oils and grease) noted in downstream components

There is no longer a suggested minimum pump-out interval for all tanks, due to the requirement to have the maintenance of systems overseen by a designated AP. Because some digestion of sludge and reduction of sludge volume occurs after approximately 3 years, it is not appropriate to pump out tanks when scum/sludge accumulations do not warrant it. As noted earlier in D1, pump-out intervals of at least 5 years or longer are preferred.

The table shown below, Table III-35, is from the SPM and is an estimate only. In this table, entries that are shaded, which are also indicated by asterisks after their value, show septic tank sizes that are not recommended. (Table III-35 is based on year-round occupancy, and accumulation rates taken from T. R. Bounds “Design and Performance of Septic Tanks,” Site Characterization and Design of On-Site Septic Systems, p. 217, 1997.)

Vegetation and Dispersal Systems

In many cases the natural ecosystem of a site is important for maintaining the soil characteristics that made the site usable for a dispersal system. Tree and shrub cover in the dispersal and receiving area can improve system performance by:

• Reducing effective rainfall (the amount of rain that actually soaks into the soil)
• Maintaining soil structure and organic matter content in the long term
• Reducing temperature extremes, and particularly reducing risk of freezing

However, depending on the system type, tree roots may harm the dispersal system. In general, the recommended procedure is to leave trees and stumps in place. For trees with highly invasive roots (i.e., willow, aspen, bamboo, and maple), it may be best to remove the tree and stump or to kill the stump if it is left in place. Reestablishment of natural vegetation cover should be encouraged after system installation, in as far as is practical. Choose trees and shrubs to suit the area and which are known to not have invasive roots. For BC zero discharge lagoons it is important to prevent tree growth on or near lagoon berms.

Biomat: Good, Bad, or Both?

The SPM lists the following definition for “biomat”:

Soil clogging layer at and below the infiltrative surface to soil or to sand or other media. The layer of biological growth, organic compounds (including polysaccharides and polyuronides produced by bacteria in the mat) and inorganic residue that develops at the wastewater soil interface and extends up to about 25 mm into the soil matrix. The term is used loosely to include all soil “clogging” affects, including pore size reduction, alteration of soil structure and gas production by the micro-organisms. Also referred to as Biocrust, Clogging Mat, and Clogging Zone.

From the above definition, it suggests that biomat buildup clogs the soil and will cause the dispersal system to fail over time. This is partially true, if there is not a calculated and stringent adherence to the planning and execution of procedures as laid out in the SSR and SPM. The following excerpt is taken from the blog post Understanding The Biomat in Septic Systems and may help in explaining the importance of biomat and its function in a properly designed, installed, and maintained septic system:

A black, jelly-like permeable layer forms in the soil just below or around the drain field trenches where the septic effluent is discharged. This layer is what is referred to as biomat, clogging mat, biocrust, or clogging zone, and it plays an important role in the processing of pathogens and biological solids. Without biomat, the septic system would be releasing partially treated effluent into the soil thereby resulting in pollution of groundwater and any nearby wells, ponds, and streams. As the wastewater from the septic tank is fed into the soil absorption system for further treatment, bacteria grow under the distribution lines where they meet the soil or gravel. This biological mat forms on the sides and bottom parts of a leach field trench, helping to reduce the infiltration rate of water into the soil and thereby giving bacteria more time to treat the water before it is released, which translates to a “good thing.”

Biomat is made up of live and dead anaerobic bacteria and their by-products which attach themselves to the soil particles. These microorganisms usually rely on the organic matter in the effluent for sustenance and therefore biomat is often referred to as the actual site for treatment of effluent. In a new system, biomat will start forming at the trench bottom where the effluent discharges from and then it will slowly grow along the trench walls. Because biomat is not as permeable as soil, effluent will trickle along the trench looking for a place with little or no biomat and this helps to slow down the infiltration of wastewater. Biomat slows down the flow rate of wastewater thereby giving it time to filter out viruses and other pathogens.

How to Prolong the Biomat Lifetime (Extend the Life of the Dispersal System)

The “bad thing,” as far as biomat formation goes, is that the hydraulic application rate might exceed the infiltration rate due to too much biomat growth, and that is when ponding starts, indicating the system is failing. In such a case, wastewater could back up into the house or gush out on the soil surface. Biomat plays a vital role in the purification of wastewater, and it should therefore not be prevented from forming. However, there are some steps that can be taken to ensure it doesn’t overgrow to the point of causing backups. The simple steps to avoid the overgrowth of biomat include the following:

• Proper maintenance. Taking good care of a septic system will help to avoid many issues including ponding in the leach field area due to the overgrowth of biomat. The AP Maintainer designated for the system will ensure that routine maintenance in the official Maintenance Plan is performed.
• Avoid hydraulic overload. Hydraulic overloading is one of the main causes of the overgrowing of biomat. Through the force of gravity, effluent is distributed somewhat evenly across the drain field area from where it slowly sips through the trenches and back into the groundwater. As has already been established, biomat slows down this process which is a good thing. In an ideal scenario, this process continues day in day out. However, when too much water is sent into the disposal field at one time, the field will become waterlogged. When the field gets too wet, the rate of breaking down organic matter reduces greatly and the waste products that are produced by the bacteria get more time to settle. This ultimately leads to unprecedented growth of biomat. To avoid this, it is a good idea to avoid sending too much water to the septic tank all at once. If there are lots of people living in a household, space out showers instead of taking all of them in a row. Also, spread out laundry across the week instead of doing a huge load of laundry in a single day.
• Septic tank filter system. Septic tanks filters help trap suspended solids from going into the drain field. Because the bacteria rely on organic waste for sustenance, giving them too much food around the clock will increase their numbers exponentially and will, in turn, increase their waste which will increase the rate at which the biomat grows. Proper maintenance of filters avoids this.
• Don’t flush harmful products. When harmful products are flushed, they can deplete the number of bacteria in the septic tank as well as in the dispersal system. This will mean that organic waste will not be properly digested in the tank and much of it will end up in the field. When too much of the suspended solids flow into the field, they contribute to the excessive growth of biomat. To avoid this, do not flush anything apart from human waste and tissue paper. Installing washing machine filters can also help to prevent fibres from clogging the effluent filter in the tank. Additionally, avoid any substance that might harm bacteria. These include:
  • bleach and disinfectants
  • antibacterial soaps
  • antifreeze
  • chlorinated backwash from hot tubs, swimming pools, R/O units, water treatment filters, etc.

Additionally, the SPM advises that floor drains should not be connected to the sewerage system.

Conclusion

Biomat plays a vital role in the treatment of wastewater. Without biomat, conventional septic systems would be sending partially treated water into the environment, so its formation shouldn’t be stopped. That said, biomat that grows too fast can cause problems usually exacerbated by poor septic tank care and maintenance. A properly functioning septic system, designed to the soil conditions that is well-maintained, shouldn’t pose any biomat problems for at least 25 years.

Additives

There is much debate over the introduction of additives or treatments commonly called “starters,” and the SPM does not address them at all. Their exclusion from commentary in the SPM suggests that they are frowned upon and should not be used. However, there is much written on the internet that suggests the use of biological (not chemical) additives can assist in the formation and propagation of “good” bacteria in the tank and field and may be beneficial for the long-term health of the system. Much of that information is offered by the manufacturers of these products, and so the points presented should be considered carefully. In conclusion, it must be said that the “jury is still out” on the use of additives to help maintain the system.