Tetra Tech performed various installation services as part of the Sunshine Canyon Landfill Area 1 capping project in Sylmar, California, under challenging site conditions and in a very short time frame.

Tetra Tech completed a complex capping project on a 21-acre area with slopes of 2:1 or steeper. The work was completed in an area with limited access—often in congested areas during high-volume periods of daily landfill activity.

This installation enables the client to mitigate gas flow and protect the surface area from erosion, while providing a low-maintenance cover system.

Tetra Tech’s engineering services included installing 700 linear feet (LF) of 4-6-foot-high block walls to assist with slope stability, performing earthwork, decommissioning piping, removing or relocating down chutes, and importing and placing soil to required elevations to prepare for installation of geosynthetic lining. After completing subgrade preparation, Tetra Tech installed the liner system and 10,600 LF of gas collection piping in front of the liner system.

The liner system consisted of a 50-mil, textured linear low-density polyethylene geomembrane overlain with synthetic turf. The closure turf system required a 5/8-inch layer of sand broomed into the turf to act as ballast throughout the landfill. In some areas, such as haul roads where drainage was a concern, Tetra Tech sprayed the sand with 214,797 square feet (ft2) of Armorfill to facilitate binding. Tetra Tech also applied about 14,549 ft2 of cement-stabilized sand, or HydroBinder®, in the down chutes—the areas of highest flow. Tetra Tech also completed about 320 pipe penetrations for gas collection and relief valves.

Tetra Tech completed earthwork and geosynthetics installation in only four and a half months, despite the steep slopes, high heat, and prolonged periods of high winds. At peak periods, Tetra Tech staffed over 40 field employees.