Final Closure CM/CQA Services

Verdantas provided long‑term Construction Management (CM) and Construction Quality Assurance (CQA) services for the final closure of two major Orange County landfill sites: the Olinda‑Alpha Landfill and the Santiago Canyon Landfill. Both projects involved large‑scale earthwork, extensive geosynthetic installations, landfill gas improvements, and complex stormwater and site infrastructure upgrades, ensuring each site met all regulatory requirements for permanent closure.

Olinda‑Alpha Landfill

Opened in 1960, the Olinda‑Alpha Landfill is a Class III facility covering 565 acres, with 453 acres permitted for disposal and an average intake of 7,000 tons per day. Verdantas served as the CQA provider for both Phase 1 and Phase 2 closures, which included construction of 5‑foot‑thick monolithic soil covers across 64 acres (Phase 1) and 88 acres (Phase 2).

Work included:

• Placement of approximately 520,000 cubic yards of cover soil for Phase 1 and 700,000 cubic yards for Phase 2
• Cover thickness verification and characterization
• Landfill gas (LFG) system improvements
• Installation of 125,000 square feet of geomembrane liner
• Construction of surface water drainage features and access road upgrades
• Review of alternative cover design, plans, specifications, and the CQA plan
• Construction of a test pad for soil oversize control and placement procedures
• CQA for refuse removal, reconsolidation, and installation of geomembrane infiltration barriers, geocomposites, and drainage collectors
• Oversight of concrete, asphaltic concrete, CLSM, and grouted riprap for drainage structures and walls
• Inspection and testing for utility improvements including water, graywater, sewer, electrical systems, storage tanks, and pumping stations
• Preparation of the final As‑Built CQA Report for regulatory agency approval

Santiago Canyon Landfill

The Santiago Canyon Landfill operated from 1968 to 1996 and is now designated as Natural Community Conservation Plan mitigation land and open space. Verdantas provided CM and CQA services for final closure involving construction of a 5‑foot‑thick monocover across 100 acres of side slopes and 30 acres of top deck—requiring placement of approximately 900,000 cubic yards of soil.

Additional services included:

• Earthwork and cover thickness control
• Surface water and access road improvements
• LFG system enhancements and installation of multi‑depth perimeter gas probes
• Digital Terrain Model (DTM) optimization for soil use
• CQA services for concrete, asphalt, soil cement, and grouted riprap used in drainage structures
• Foundation and structural inspections for a new on‑site office building
• Preparation of the As‑Built CQA Report

Verdantas’ high‑quality work and responsiveness earned direct commendation from OC Waste & Recycling for long‑term excellence on Santiago Canyon and multiple subsequent closure projects.