BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

This infiltration trench is too steep and is acting as a conveyance rather than infiltrationsystem. A subsurface drain could be added and connected to a subsurface infiltrationsystem at the bottom.INSTALLATION CONSIDERATIONS• Install infiltration trenches after other pollutant sources have been stabilizedto avoid clogging the trench during subsequent construction activities.• Avoid excessive compaction of the bottom of the trench duringconstruction. Use lightweight equipment to excavate the trench to protectthe Ksat of the underlying soil. Place excavated material downslope from thetrench in a stable location to avoid washing material back into the trenchshould a runoff event occur.• Excavate the system to the required size with enough extra width and lengthfor placement of a border.• The bottom of the trench shall be flat to provide uniform infiltration acrossthe surface area of the trench.• Consider wrapping the system with non-woven geotextile fabric to reducesediment accumulation throughout the infiltration trench. This shouldextend the effective life of the infiltration trench and reduce the need torebuild a clogged system.• Preferred Method: Excavate the trench and place geotextile fabric in thetrench with enough remaining fabric to overlap the top of the gravel.Place gravel in the trench to within 3 inches of the final grade. Overlapthe top of the gravel with the fabric. Add a final layer of gravel over thefabric to the final grade.CHAPTER 4: BMP ToolkitTRPA BMP Handbook4.1.1.3-Infiltration Trench 2012Page 4