Landfill Construction & Capping

Commerce City, Co

  • Hazardous/non-hazardous waste landfill operations
  • Borrow fill excavation, placement, and grading
  • Waste grading and compaction
  • Borrow area development
  • Construction of RCRA-compliant cover systems 

Forgen conducted hazardous and non-hazardous waste landfill operations and closure activities at the Rocky Mountain Arsenal (RMA) in Commerce City, Colorado. The site was a former World War II chemical weapons production facility which was later used for commercial pesticide formulation. The site (including more than 250 buildings and remaining structures) was demolished and remediated, then converted into a national wildlife refuge managed by the U.S. Fish and Wildlife Service. The work was broken down in 36 individual projects managed by the Program Management Contractor.

The crew managed, operated and/or closed three on-post landfills that were constructed for the disposal of millions of cubic yards of hazardous and non-hazardous remediation wastes. These key project managers were also responsible for the construction of interim and final covers on both hazardous waste landfills and the construction of several hundred acres of engineered subgrade during the 10 years they spent at RMA. Select individual project details follow.


RMA Basin A Consolidation Area

Basin A was a 144 acre contaminated surface depression contained within a combination of slurry walls and capped fill that was designated as the disposal area for non-hazardous remediation waste and demolition debris from the RMA. In addition to landfill operations, the team excavated, hauled, placed, and compacted clean cover soil for both Basin A and the Hazardous Waste Landfill from a variety of on-site borrow sources. Clean grade fill was placed over the waste media in 1 ft lifts and then compacted. Over the course of the project the team placed over 1,300,000 bank cy of solid waste and debris, then covered it with more than 1,700,000 bank cy of clean cover soil. Forgen was also responsible for all support operations including equipment decontamination, QA/QC, health and safety, heavy equipment and facility maintenance, and environmental compliance.


RMA Hazardous Waste Landfill (HWL) and Basin A Operations

In addition to continuing Basin A Operations, Forgen assumed operational responsibility for the HWL. The HWL was a 20 acre dual-lined, Resource and Recovery Act (RCRA)-compliant landfill comprised of two adjoining disposal cells, and was operated as a Corrective Action Management Unit. The final capacity of the HWL was 1,870,000 cy. The project team completed operations with the construction of an interim cap. Additional site operations included waste placement; daily cover; control of odors and fugitive dust emissions; vehicle decontamination operations; stormwater management; facility maintenance; leachate management; cover system construction; liquid waste solidification; QA/QC; and health and safety compliance. The HWL received hazardous wastes from numerous projects at RMA including high hazard materials requiring Level B PPE. In total, the project team placed over 978,901 bank cy of “in-place” hazardous waste at the HWL and set a single shift receiving record, managing 671 trucks in a single 8-hour day. The team also participated in the OSHA Voluntary Protection Program (VPP) recertification audit. The HWL and Basin A projects were each given superior marks that contributed significantly to RMA being awarded VPP status for a second time.


Enhanced Hazardous Waste Landfill (ELF) RCRA Cover Construction

The scope of work for the HWL Cap Construction included a multilayered landfill cover system for a 26 acre HWL. Over 363,000 bank cy of highly odorous hazardous waste was placed in record time (up to 380 trucks per 8-hour day) in Level B PPE. The project team also placed 127,398 bank cy of clean soil to construct the waste containment berms under strict moisture and density requirements. An additional 50,000 bank cy of clean soil was placed on top of the final lift to provide an intermediate cover prior to construction of the ELF cap. Cover construction consisted of surface preparation work followed by installation of five component goesynthetic liner system. In total, over 4,000,000 sf of geosynthetic liner components were installed including geotextile, geocomposite, HDPE geomembrane, and geosynthetic clay liner.


Shell Disposal Trenches RCRA-Equivalent Cap Construction

This project was the first of many RCRA-equivalent cover projects planned for large areas of impacted subgrade at RMA. This 21 acre project was a critical pilot of the RCRA-equivalent cover construction planned for more than 450 acres. The work consisted of covering a waste disposal area known as the Shell Disposal Trenches, with a combination of a 10 in crushed concrete known as Biota-Barrier Material (BBM), chokestone, geotextile, and a four foot layer of dry cover soil. The project team also protected 14 monitoring wells and installed four lysimeters within the cover area. Client and regulatory oversight were continuous due to the pilot nature of the project and its potential impact on future cover projects. In total, 160,000 cy of cover soil, 92,000 tons of BBM, and 17,000 tons of chokestone were excavated and placed within a very narrow winter time frame.


Complex Army Trenches Subgrade Construction

This project required the construction of the subgrade necessary to install the final cap/cover over the Complex Army (Disposal) Trenches. More than 1,200,000 bank cy of cover soil were borrowed on-site then placed, graded, and compacted over these former disposal trenches. One requirement of the subgrade construction process was to construct a “contact buffer layer” that would allow heavy equipment to operate on top of burial areas without exposing or contacting buried waste material. Extensive grading was required to modify drainage areas, restore borrow areas, and perform final surface contouring.


Section 36 Balance of Areas Subgrade Construction

This project involved the construction of subgrade necessary to install the final cap/cover over the Shell Disposal Trenches, Basin A, and Section 36 Balance of Areas. Project work included performing cut and fill operations, extending monitoring wells, cutting drainages and stormwater features, removing buried pipes and debris, and final grading and finish work. Excavation was performed using ten scrapers, two motor graders, a CAT D-10 dozer, a CAT 825 compactor, and three water trucks. Despite extensive dust and grade control requirements, the project averaged over 9,500 bank cy per day. At completion, over 800,000 cy of soil was placed and graded. Over 6,000 points were surveyed in conjunction with pre- and post-excavation surveys.