The Prima Deshecha Landfill is a regional waste disposal facility operated by the County of Orange, California. Ancient landslide deposits characterize the landfill’s permitted area. During construction of the Zone 1 Phase A disposal area, a new landslide occurred underneath a soil stockpile. The landslide impacted the Prima Deshecha Cañada stream, a natural watercourse running between Zone 1 and the stockpile area. Tetra Tech prepared plans to remediate the landslide. The design provided an uninterrupted development of waste disposal cells and mitigated impacts to the stream and adjacent wildlife habitat.

Tetra Tech’s remediation design stabilized the landslide using a buttress fill and by realigning the Prima Deshecha Cañada stream channel. The overall landfill Zone 1 Master Plan, which Tetra Tech prepared, was revised to include the landslide remediation project and included designs for a revised Phase B disposal cell. The revised master plan with Tetra Tech’s innovative earth works design solution generates approximately 4.5 million tons of additional refuse capacity and approximately five years of additional site life. It delays major cut slope excavation to the north, development of Zone 4, and reduces expenditures in Zone 1. 

Tetra Tech designed an innovative biomitigation channel and wetlands area to offset impacts to biological resources. The channel incorporated gabion drop structures, gabion channel stabilizers, energy dissipaters consisting of woven wire mesh blankets filled with rock, and a modular concrete retaining wall system. Tetra Tech also oversaw preparation of plans to salvage existing plant species, recycle and relocate soil, establish mitigation areas, and improve irrigation.

To support the stream realignment, Tetra Tech assisted in obtaining a 404 Permit from the United States Army Corps of Engineers, 1601 Streambed Alteration Permit from the California Department of Fish and Game, 401 Water Quality Certification permit from the Regional Water Quality Control Board, and a Biological Opinion permit from the United States Fish & Wildlife Services. During the approval process, which took more than four years, Tetra Tech evaluated and designed Phases A1 and C1 ahead of the Phase B liner project, which is located within the landslide remediation area.  These liner sub-phases facilitated the facility’s continued operation while the Phase B landslide remediation project was approved.