
Project 01
Sand lined bed replacement on a steep half-acre lakeside lot
- Location
- Sproat Lake area, rural Alberni Valley
- System type
- Type 1 sand lined bed, micro-time-dosed pressure distribution
- Timeline
- Filing report issued early January 2026; field commissioning in May 2026.
A dated, undersized system served a three-bedroom home with a new two-bedroom suite on a lot under half an acre, sloping roughly 20 per cent toward the lake the household also draws its drinking water from. There was no room for a conventionally sized dispersal bed. The replacement is a micro-time-dosed sand lined bed, sized by hydrogeological analysis instead of by rule of thumb.
What made this site difficult?
- Design flow of 2,300 L/day from two dwelling units — a three-bedroom house plus a newly added two-bedroom suite — on a 0.45-acre lot that leaves very little usable dispersal footprint once setbacks are honoured.
- About 20 per cent slope falling toward the lake, which is also the property's potable water source.
- Site constraints capped the bed at 14 m long. At that length the linear loading rate lands near 165 L/day/m, roughly double the 80 L/day/m the standard practice manual would ordinarily point to.
- The bed footprint the site allowed exceeds the 3 m maximum width the Standard Practice Manual provides for, so ventilation of the infiltrative surface had to be solved deliberately rather than assumed.
How was it solved?
- Test pits found 95 cm of friable, granular sandy loam with no mottling — seasonal high water table deeper than the deepest pit. Three permeameter tests returned a median field-saturated conductivity of 438 mm/day (range 355–473).
- Rather than accept the short bed on faith, the higher linear loading rate was justified with Darcy and Payne & Ralston water-table-mounding analysis: predicted maximum mounding 47 cm above the seasonal high water table, leaving 48–68 cm of excess vertical separation.
- Micro-timed dosing applies the daily flow in many small doses rather than a few large ones — 28 doses per day at design flow, about 82 L per dose over a 23-second pump run — distributing the load throughout the day to maximise pathogen attenuation through the sand.
- Because the bed exceeds the 3 m maximum width provided for in the Standard Practice Manual, an oversized ventilation pipe was incorporated to passively ventilate the full width of the infiltrative surface.
- The existing concrete lift station was retained and re-purposed rather than replaced, with effluent transported uphill to a new tank nest — less excavation on a slope that did not need disturbing.
- Six pressure laterals over 30 cm of specification sand, 108 orifices under shields, four observation ports and passive vent runs, then a field commissioning visit to prove the panel setpoints, squirt height and distribution.
What was the outcome?
The system was installed and commissioned, with a field commissioning visit to verify the panel, dosing setpoints and distribution before the certification package was completed for the owner.














