The Regulator’s View of Rural Subdivision Wastewater Treatment

This is adapted from a presentation by Alf Durnie, Administrator, Private Sewage Systems, Alberta Municipal Affairs, at the June 8 workshop on Wicked Problems in Natural Resources and Land-use.

Each speaker on the panel for the session on Rural Subdivision Wastewater Treatment as a Wicked Problem was asked to address:

• What we know
• What we don’t know
• What we need to make better decisions

Here is Alf Durnie’s summary:

What We Know

Options for Rural Wastewater Treatment:

• Sewage holding tanks – pump and haul
• Private sewage system discharge to soil (septic fields, mounds, etc.)
• Larger communal private sewage system soil based discharge and treatment.
• Municipal wastewater collection and treatment system.

Planning choices have implications on the effectiveness of the proposed sewage system:

• Density of planned development.
• Does the sewage system proposed require lower density than is desired by overall planning goals?
• Development density required by sewage system type affects other servicing costs.
• Receiving environment’s capacity and sensitivity.
• Level of wastewater treatment achieved.

Planning considerations for each sewage treatment option:

• Sewage holding tanks (pump and haul):
  • Where will the sewage go?.
  • Cost of hauling sewage and energy used.
  • Impact on municipal infrastructure:
    • Municipal sewage facility receiving capacity
    • Impact of increased traffic on roads
    • Hauling limitations during road ban
  • Impact may extend outside originating municipality
• Private sewage system discharge to soil (septic fields, mounds, etc.)
  • Suitability and receiving capacity of soil for private sewage systems:
    • at each site
    • on the subdivision scale
    • At the density proposed
  • Impact of added sewage effluent to near surface ground water table
  • Treatment capacity of soil
  • Capacity and sensitivity of receiving environment – nutrient loading on surface waters and groundwater under direct influence of surface waters (GWUDI).
  • Effective management and maintenance is difficult to ensure.
• Larger soil based communal onsite sewage systems - suitability considerations:
  • Suitability and receiving capacity of soil for private sewage systems
  • on the subdivision scale
  • at the wastewater volume generated
  • Impact of added sewage effluent to near surface ground water table
  • Treatment capacity of soil
  • Capacity and sensitivity of receiving environment – nutrient loading on surface waters and GWUDI.
  • Effective management and maintenance can be achieved with involvement of municipality.
  • Higher treatment levels can achieved and maintained.
• Municipal wastewater collection and treatment system:
  • Typically requires a suitable discharge location or receiving stream. Not always available.
  • Sensitivity and capacity of receiving environment.
  • Initial capital cost may be higher.
  • Effective and consistent treatment is achieved by management and operation.
• Planning decisions drive the selection criteria that leads to a specific sewage treatment system:
  • Selection of the suitable system must be made at time of proposing the development and subdividing land.
  • Municipality has the key role at that point in considering the long term suitability of the proposed method of wastewater management.
  • Onsite soil based wastewater treatment systems are not always suitable for a site or subdivision.
  • Safe, effective and sustainable systems are the goal.
• A model process for considering the suitability of private sewage in a proposed subdivision has been developed for use by municipalities. AAMDC runs training sessions.

Uncertainties Now (What We Don’t Know)

• The standards for private sewage system design look at one lot at a time. It does not anticipate varying development density and sensitivity of the receiving environment.
• Those considerations are needed but the criteria to apply is not well established..
• Additional info on the potential impact of on-site soil based treatment systems on the receiving environment will help in decision making.

Wider Considerations (What We Need for Better Decisions)

• What is the impact on development limitations or possibilities by choosing a particular method of sewage management?
• How will that impact other land-use considerations and choices and what is the resulting impact?
• The choices of sewage management need to be integrated with all the larger land use issues.
• Should the subdivision and development occur at all at that location or as proposed?