2016 British Columbia Design & Installation Manual 8 www.eljen.com
2.0 Design Guidelines
2.1 Basic System Design
2.1.1 DISPOSAL FIELD SIZE: The total basal area required is site specific and determined by the
Daily Design Flow (DDF) and soils analysis as specified in the SPM or by a professional.
The GSF system is a Type 2 - Combined Treatment and Dispersal System thus requiring about ½ the
field size of a standard Type 1 stone and pipe system or chamber system.
The number of GSF modules required (See 2.1.10) typically fits the required basal area and can be
configured to properly cover any shape required and is the same for trench, bed or mound systems.
In beds and mounds, a minimum of 30 cm separation is required between parallel rows of a GSF to
utilize sidewall infiltration area.
Maximum edge-to-edge and end-to-end separation for Modules in all applications is 91 cm.
2.1.2 Vertical Separation: As required by the BC Sewerage System SPM- V3 or as specified by a
professional.
Note in Version 3 of the SPM, an additional 15 cm of Vertical Separation has been added, in some soil
categories, for Type 2 systems that reduce or remove the Type 1 bio-mat. In the case of the Eljen GSF, the
bio-mat is retained allowing for the required Vertical Separation to remain the same as Type 1 designs.
2.1.3 SPECIFIED SAND SPECIFICATION FOR ALL SYSTEMS: The first 15 cm of Specified Sand
immediately under, between rows and around the perimeter of the GSF system must be ASTM C33
WASHED CONCRETE SAND WITH LESS THAN 10% PASSING A #100 SIEVE AND LESS THAN 5%
PASSING A #200 SIEVE. Please place a prominent note to this effect on each design drawing. See page 6
of this manual for more information on the Specified Sand specification.
2.1.4 FILL FOR RAISED SYSTEMS: Fill material below the Specified Sand in Section 2.1.3 for raised bed
systems must be ASTM C-33 or fill per the latest BC Regulations. Fill must be consolidated in lifts to
prevent differential settling. Refer to SPM Version 3 for detailed fill specification.
2.1.5 PLACING GSF MODULES: Each row of modules are laid level and end to end on the above
Specified Sand bed with a minimum spacing of 30 cm between parallel rows. No mechanical connection is
required between units. Alternatively, in all applications modules may be spaced up to 91 cm end-to-end
and edge-to-edge to increase effective basal area. See Figures 9 and 10 for an example.
2.1.6 DISTRIBUTION PIPE: Place the approved perforated pipe on top of GSF modules with holes at 4 and
8 o’clock. Complete system piping with solid pipe and fittings. Refer to Sections 2.2 and 2.3 for level and
serial piping information respectively. Secure pipe to GSF modules with provided wire clamps, one clamp
per Eljen module. In all applications, any pipe distribution holes not discharging onto the GSF module must
be sealed. See Figure 9 for suggested method of sealing holes. See Figure 15 for a pressure distribution
illustration.
2.1.7 DISTRIBUTION BOX: Set gravity system D-box outlet invert a minimum of 1 cm per meter (1/8” per
foot) above invert of distribution pipe over modules (5 cm minimum for pumped D-Box systems). The fill
below the D-Box and piping must be compacted to avoid settling. Flow Equalizers (speed levelers) are
recommended for gravity systems.
2.1.8 COVER FABRIC: Geotextile fabric, provided with the system, is placed over the top and sides of the
module rows to prevent long-term siltation. Cover fabric substitution is not allowed. Fabric should drape
vertically over the pipe and must neither block holes nor be stretched from the top of the pipe to the outside
edge of the modules. “Tenting” will cause undue stress on fabric and pipe. Note: If modules are spaced
end-to-end in trench applications, fabric must be cut and allowed to drape over and protect the ends of each
spaced module. A continuous run of geotextile fabric is not allowed for these applications.
