OII LANDFILL – Engineering, Closure, CQA & Long‑Term Monitoring
The 190‑acre OII Landfill in Monterey Park, California, operated from 1948 to 1984 and is one of the most prominent Superfund landfills in the country. The site contains steep slopes (up to 250 feet high at 1.5:1 grades) adjacent to residential neighborhoods, commercial areas, and the 60 Freeway, creating significant design and construction complexities.
Verdantas has provided continuous engineering and CQA support from the original closure design completed in 2000 through ongoing slope improvements and post‑closure monitoring. As a key member of the Design‑Build team for the $100M final closure, Verdantas delivered:
Major Scope Elements
- Solid waste & geotechnical engineering for final closure and post‑closure design packages
- Preparation of all closure and post‑closure plans, technical design reports, and construction specifications
- Unsaturated flow modeling to support approval of an evapotranspirative (ET) cover system, including development of hydraulic properties for cover soils
- Implementation of a moisture monitoring system with Time Domain Reflectometry (TDR) probes
- CQA services for approximately 1 million cubic yards of final cover construction, including earthwork, geosynthetics, and onsite borrow evaluations covering more than 25 potential borrow sources
- Regulatory coordination with EPA, DTSC, U.S. Army Corps of Engineers, RWQCB, and Caltrans
- Post‑closure monitoring including slope repair recommendations, monitoring program execution, TDR data evaluation, and preparation of annual inspection and compliance reports
Long‑Term Performance Modeling
Verdantas performed advanced long‑term performance and sustainability modeling over a 60‑year horizon, evaluating:
- Cover settlement and deformed slope geometry
- Lateral displacement
- Performance of alternative final cover systems
- Slope stability using finite element SIGMA/W analysis
The project earned direct praise from regulators for exceptional QA/QC performance and high‑quality technical work.
CASMALIA RESOURCES SUPERFUND SITE – CDA Cap CQA & Construction Support
The Casmalia Resources Site is a 252‑acre hazardous waste treatment, storage, and disposal facility that required extensive closure work, beginning with the Central Drainage Area (CDA) Cap. Verdantas provided CQA services for construction of an RCRA‑compliant, multi‑layer engineered final cover designed to tie into several previously capped landfill units.
CDA Cap Engineering & CQA
The 25‑acre CDA Cap included:
- Grading of 275,000 cubic yards of engineered foundation fill
- 40,000 cubic yards of cut
- 85,000 cubic yards of vegetative cover material
Verdantas oversaw installation of all cover system components, including:
- GCL
- HDPE geomembrane
- Geocomposite drainage layer
- Geonet biotic barrier
- Protective soil cover
Additional CQA Services
- Contractor submittal reviews
- MQC data review for geosynthetics
- Conformance testing on soils and geosynthetics
- Field observation & testing of clearing, processing, engineered fill, subgrade prep, and vegetative soil placement
- Drainage and erosion control improvements including CMP storm drains, concrete structures, TRM‑lined swales, geoweb channels
- Daily written and photographic documentation
- Preparation of the Construction Certification Report submitted to EPA
Regulators and client representatives commended Verdantas for outstanding technical rigor, sophisticated modeling, and high‑quality reporting.
Solution
Expertise
Hydrology, Hydraulics, & Fluids
Natural Resources & Environmental Planning
Site & Roadway Civil Engineering
Geotechnical & Geological Engineering
Environmental Assessment & Remediation
Market
Location
OII Landfill – Monterey Park, California and Casmalia Resources Superfund Site – Northern Santa Barbara County, California
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