Eljen GSF A42 Modules vs Infiltrator Systems in Idaho: Why I Choose Eljen

When comparing onsite wastewater systems in Idaho, Eljen (GSF A42) and Infiltrator chamber systems each have their advantages. The biggest difference is how they approach treatment, dispersal, installation, and overall system complexity.

Eljen GSF A42

The Eljen GSF A42 uses a geotextile-wrapped module/bale installed over a 6" specified sand layer. The module, sand, and native soil work together to provide treatment and dispersal. The A42 Eljen module is only 4 feet long by 2 feet wide by 7 inches high.

Advantages in Idaho:

• Simple, passive treatment approach without requiring an aerobic treatment unit.
• Compact design that can reduce the amount of excavation and drainfield size.
• The lightweight Eljen bales are easier to transport and install than large quantities of Infiltrator domes.
• Uses a basic combination of the Eljen bales, sand, perforated pipe, and native soil.
• Idaho has a dedicated Eljen Design Program and Installation Manual, for Eljen configurations.
• Here at R.C. Worst, we are the exclusive Idaho distributor. We offer design work, training, and technical support, not just the materials.

Infiltrator Domes

Infiltrator's chamber systems are primarily meant for effluent dispersal rather than filtering effluent through the Eljen bales, before entering into the ground. Chambers provide a large open space for wastewater distribution and infiltration into the surrounding soil.

Infiltrator domes aren't giant, but are not as compact as the Eljen. The infiltrator domes do have size options compared to Eljen though. A 34 inch by 53 inch by 12 inch option and a 34 inch by 53 inch by 8 inch option.

Why an Idaho Installer Might Prefer Eljen

For a contractor, one of the biggest advantages of Eljen is install simplicity. The Idaho TGM requires only 6 inches of specified sand below the module, 6 inches at the sides and ends, and 12 inches of cover above the module. Any cover less than 18 inches eliminates the need for a vent. Eljen designs allow for systems in compact and restricted spaces as well. Idaho installers have expressed to me how much easier the installation is and how much labor they save using Eljen over Infiltrator domes.

That standardized configuration can make material estimation, transportation, and installation easier to manage.

The Bottom Line

Eljen GSF A42 sits between a basic drainfield and more complicated engineered systems. Eljen is versatile and can be used for a variety of applications. IE, gravity flow, pump to gravity, or pressurized.

Compared to Infiltrator domes, the argument is more about installation approach, site configuration, material handling, and familiarity rather than claiming dramatically different treatment performance.

For Idaho projects where a passive alternative system is appropriate, Eljen offers a compact, lightweight, treatment-focused system without adding pumps (Gravity System), blowers, or complex treatment equipment.

The ultimate choice should still be based on the soil type, groundwater, slope, available area, design requirements, and approval from Idaho DEQ, but from my experience, Eljen can do it all.