The Crazy Horse Landfill (CHLF) is located on a 160-acre parcel west of, and adjacent to, Crazy Horse Canyon Road about nine miles north of the city of Salinas in northern Monterey County, Calif. The landfill, owned and maintained by the Salinas Valley Solid Waste Authority (SVSWA), had been in service for 75 years, with final in-place waste volume estimated at 4.3 million cubic yards.
The primary landfill is a canyon fill of approximately 66 acres that required a closure system able to fulfill five criteria: withstand various environmental conditions including wind erosion and uplift, rainfall erosion, concentrated flow erosion, ultraviolet light degradation, and traffic; provide a static factor of safety (FS) of at least 1.5 and resist seismic deformation due to the San Andreas Fault zone located about five miles northeast of the site; provide excellent groundwater protection to halt continued impact to the local groundwater supply; minimize risk to motorists during construction; and the new system could not create additional nuisance conditions for nearby residents.
A final cover system consisting of five layers was chosen. From bottom to top:
- A minimum 1 ft thick (2 ft thick in traveled areas) soil foundation layer beneath a structured geomembrane.
- A structured geomembrane low-permeability layer.
- A woven polypropylene geotextile layer over the geomembrane.
- A geosynthetic erosion protection layer of engineered synthetic turf with tufted grass blades.
- A sand ballast layer placed in the artificial grass blades to provide anchoring against wind and water erosion.
With regard to engineer and agency skepticism, a testing program was already started to prove the system’s ability to withstand extreme environmental conditions: wind erosion and uplift, rainfall erosion, concentrated flow erosion, ultraviolet radiation degradation, and traffic.
Final cover design for the closure of the CHLF went through three iterations before the SVSWA settled on an artificial turf final cover system. The project marks the first large-scale implementation of this type of cover system in California. The completed project, from finish grading to geomembrane installation, including construction management and quality assurance cost, was approximately $10.5 million.
The annual post closure maintenance cost was estimated at $46,600 per year. The CHLF closure design eliminated the soil component, all vegetation maintenance costs, and reduced drainage maintenance costs by approximately 70%. The total savings over a nominal 30-year post closure cost for the reduced final cover maintenance is projected at $1.4 million. To date, the site owner has had to perform no significant final cover maintenance activities.
Additionally, the final cover system eliminated about 11,000 truck trips to import soil to the site. The project’s carbon footprint was reduced by 70% due to the combined project size reductions of soil import elimination and reduced heavy equipment needs.
Typical landfill closures require specialized equipment and labor due to their complicated combinations of earthworks and specialty geosynthetic materials. With a CHLF artificial turf system that is relatively easy to construct, the SVSWA could hire local labor to perform the work since Monterey County was experiencing high unemployment rates at the time.
The closed landfill, with its artificial green grass top layer mottled with gray sand infill, is barely discernible from the natural hillside behind it. Aesthetic and odor complaints from neighbors abutting the landfill have diminished, with many of the residents contacting the SVSWA to compliment the appearance of the site. Intrusive and noisy post closure care efforts, including slope reconstruction, revegetation, fertilization, and mowing, are now reduced to essentially zero.
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