Cowichan Wastewater Plus Inc. is fully-certified to plan, install maintain, and repair septic systems. All septic system designs follow the guidelines of the Ministry of Health’s Standard Practice Manual (SPM).

Onsite system design is a crucial aspect of wastewater management in areas not served by centralized sewer systems. A well-designed septic system typically consists of a septic tank, pump tank and a dispersal field.

The septic tank acts as a primary treatment unit where solid waste settles to the bottom, sludge accumulates, and lighter materials like oil and grease float to form a scum layer. Microbial activity in the tank breaks down the solids, partially treating the wastewater. An effluent filter in the outlet of the septic tank screens lighter scum from carrying over into the pump chamber. The pump tank is where effluent is pumped on timed intervals to the dispersal area. The dispersal field consists of an area (generally 10’ wide by 40 to 60’ long) with small diameter pipe (1” to 1.25”) spaced 2’ apart on a bed of drain rock. Orifices drilled in the 12 o’clock position at equal spacing along the pipe are covered with orifice shields allowing the wastewater to spray through the orifices, hit the underside of the shield and trickle into the rock and then the surrounding soil. The soil acts as a natural filter, further purifying the effluent as aerobic bacteria break down organic matter, removing pathogens and nutrients before it reaches the groundwater.

Planning Process

The planning process must consider several factors, including

• Soil composition
• Hydraulic loading rates,
• Topography of the land,
• Area available on the lot
• Size of the household

Sometimes on smaller lots, a treatment plant is required to reduce the field size. Proper soil evaluation is essential, as soil type and permeability directly affect how wastewater is dispersed and absorbed by the ground. Permeameter tests are typically conducted to determine the soil’s absorption rate, which will guide the size and design of the drain field. The septic tank must be sized appropriately to accommodate the household’s wastewater production. Size is dependent on number of bedrooms and house square footage.

For instance, a three-bedroom house is typically 4540 L (1000 Imperial gallons). Attention must also be given to setback distances to water bodies and wells to avoid contamination of water sources. Proper design also includes planning for easy access for maintenance, ensuring that the system can be inspected and pumped regularly. A well-designed septic system is a sustainable way to manage household wastewater, protecting both human health and the environment when maintained properly.

All of our designs include drawings done in AutoCad and are stamped and submitted to Island Health as a Record of Sewerage System (ROSS) where they are assigned a filing number. Chris Bayley of Cowichan Wastewater Plus has the Pl (Planner) designation on his stamp.