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Understanding septic systems

Better treatment.
A different field footprint.

Treatment quality, loading rates and the shape of the land work together to determine the dispersal area.

01 / Septic tank treatment

Type 1 Septic Systems

A Type 1 system consists of a single septic tank followed by a dispersal system. At Wrightway, we design our Type 1 systems using time-dose dispersal to ensure even and consistent soil loading.

Rather than letting effluent flow into the field whenever the house uses water, a timed pump sends small, measured doses throughout the day. This spreads the effluent across the entire dispersal area, gives the soil time to rest between doses, and helps your system perform reliably for years to come.

02 / Higher effluent quality

Type 2

Type 2 treatment can be achieved in several ways. We can use an aerobic treatment unit (ATU), such as a Fuji Clean or Bionest system, or provide passive Type 2 treatment by placing a layer of clean, coarse sand between the gravel dispersal area and the native soil. All Type 2 systems are designed with time-dose dispersal.

03 / A stricter treatment standard

Type 3

A stricter effluent standard, including a bacterial indicator limit. Type 3 work requires qualified professional involvement and supervision.

The Wrightway approach

Small doses.
Spread through the day.

Why we use time-dosed pressure distribution.

This little cartoon explains the thinking behind the time-dosed pressure distribution systems we install at Wrightway.

Instead of pumping whenever the tank reaches a set level, our controls deliver measured doses on a schedule. This spreads the load throughout the day and gives the soil time between doses to drain and breathe—supporting the natural bacteria that help treat your wastewater.

Timing and distribution work together.

Time dosing controls when effluent is delivered. Pressure distribution spreads each dose across the designed dispersal area. The dose volume, timing and layout are selected for the property and its design flow.

Thoughtful design, dependable controls and care in every installation.

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Wrightway cartoon comparing tank-level-triggered demand dosing with scheduled time dosing, and illustrating soil bacteria, controls and installation materials. — Tap or click the cartoon to view it at full size.

Type describes treatment quality.

BC’s classifications describe the effluent leaving the treatment process. They do not identify the distribution method. Type 2 and 3 have progressively tighter effluent limits than septic-tank treatment alone.

How hydraulic loading rate changes the area.

Hydraulic loading rate (HLR) is the daily volume applied per square metre of infiltrative surface, in L/day/m². The SPM assigns different maxima by effluent type. Selection also considers soil condition and permeability, using the lower applicable result and required adjustments.

The area calculation

Required infiltrative area = daily design flow ÷ selected HLR

One example: the same 1,800 L/day design flow.

For favourable sand or loamy sand, Table II-22 lists the following maxima. This illustration assumes permeability results and the other site checks support those rates.

Illustrative effective infiltrative area, not total site footprint
Treatment type	HLR L/day/m²	Calculation	Area
Type 1	30	1,800 ÷ 30	60 m²
Type 2	60	1,800 ÷ 60	30 m²
Type 3	90	1,800 ÷ 90	20 m²

Here, Type 2 needs 50% less infiltrative area than Type 1. These rates are an example, not standard rates for every property.

Less area does not
necessarily mean less length.

Linear loading rate (LLR) limits daily flow per metre along the land’s contour. Its selection depends on receiving soil, depth and slope. A higher HLR does not automatically shorten the required contour length.

Assume the selected LLR is 60 L/day per metre. The same 1,800 L/day flow requires 1,800 ÷ 60 = 30 metres of contour length in both examples below.

Type 1 · 60 m²30 m × 2 m

30 m along contour

Type 2 · 30 m²30 m × 1 m

The same 30 m length

Illustrative infiltrative rectangles. Final bed and trench layouts must meet the applicable standards.

The Type 2 area is narrower in this illustration, while its contour length stays the same.

The whole footprint still matters.

Setbacks, spacing, access, cover and side slopes affect total space. Sand mounds also need separate sand-media and native-soil basal-area checks; the example above is not a mound-footprint calculation.

Choosing the system.

We bring the site assessment, treatment requirements, pressure distribution and timed-dosing options together. Mike plans Type 1 and 2 systems within his ROWP scope; Type 3 work is coordinated with an appropriately qualified professional.

Sources: BC Sewerage System Regulation, sections 1 and 6; BC SPM v3 (2014), Volume II, sections 5.5–5.6, Tables II-22, II-23 and II-26–II-28 (pages II-34–II-41). Calculations and rectangles are illustrative.

Better treatment.A different field footprint.