Located 20 miles southeast of Seattle, the 920-acre Cedar Hills Regional Landfill is one of the largest solid waste processing facilities in the Pacific Northwest. The landfill receives upwards of 800,000 tons of solid waste annually and has several cells, including Area 7 and Area 8. In July of 2019, the Area 7 cell was closed with an interim cover and Area 8 began accepting waste; it is currently the only active cell. In May of 2021, GBI began work on a permanent cover for the Area 7 cell as part of the Area 7 Stage 5 Closure and Area 7/8 Tie-In Project.
This project included the placement of more than 30 acres of linear low-density polyethylene liner (LLDPE) and geosynthetic clay liner to prevent water from infiltrating subsurface waste. GBI also drilled eight dual-phase landfill gas/leachate extraction wells that ranged from 80 to 200 feet in depth. After the wells were drilled to depth with a large drilling rig, a crawler crane was used to place leachate extraction pipes into the drilled wells. Well pumps were then installed to extract the leachate. By the end of the project, more than seven miles of high-density polyethylene pipe (HDPE) and advanced drainage system piping had been installed, along with stormwater vaults, header pipe tie-ins, and landfill gas tie-ins. GBI also completed rock crushing and screening operations that produced more than 60,000 cubic yards of screened embankment and more than 35,000 tons of crushed rock.
LLDPE and HDPE were essential components of this project. After a severe winter storm hit Texas in early 2021, obtaining these materials in a timely manner became exceedingly difficult, especially given the amount of liner that was needed for the job. However, by working closely with suppliers, GBI was able to obtain the proper materials and meet the strict deadlines set forth by the client. Additionally, GBI managed multiple change orders for this project. GBI worked closely with the client to ensure the change orders were feasible and completed each of them while staying within budget.