2018 Indiana Design and Installation Manual 5 www.eljen.com
GSF System Description
Primary Treatment Zone
Perforated pipe is centered above the GSF module to distribute septic effluent over and into corrugations
created by the cuspated core of the geotextile module.
Septic effluent is filtered through the Bio-Matt (geotextile) fabric. The module’s unique design provides
increased surface area for biological treatment that greatly exceeds the module’s footprint.
Open air channels within the module support aerobic bacterial growth on the modules geotextile fabric
interface, surpassing the surface area required for traditional absorption systems.
A cover fabric covers the top and sides of the GSF module and protects the Specified Sand and soil
from clogging, while maintaining effluent storage within the module.
Secondary Treatment Zone
▪ Effluent drips into the Specified Sand layer and supports unsaturated flow into the native soil. This Specified
Sand/soil interface maintains soil structure, thereby maximizing the available absorption interface in the native
soil. The Specified Sand supports nitrification of the effluent, which reduces oxygen demand in the soil, thus
minimizing soil clogging from anaerobic bacteria.
The Specified Sand layer also protects the soil from compaction and helps maintain cracks and crevices
in the soil. This preserves the soil’s natural infiltration capacity, which is especially important in finer
textured soils, where these large channels are critical for long-term performance.
Native soil provides final filtration and allows for groundwater recharge.
FIGURE 1: GSF SYSTEM OPERATION
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