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Envirocon was awarded a contract for demolition and excavation activities at the former North Plants chemical warfare agent production area at Rocky Mountain Arsenal near Denver, Colorado. The Rocky Mountain Arsenal (RMA) is World War II era nerve and chemical warfare agent production facility that was owned and operated by the United States Army between in 1951 and 1987.
In 1989, the U.S. Army and the sole remaining chemical company entered into a Federal Facility Agreement (FFA) with the U.S. Environmental Protection Agency, the U.S. Department of the Interior, U.S. Fish and Wildlife Service, and the Agency for Toxic Substance and Disease Registry. As a condition of the agreement, the parties have agreed to implement a 10-year remedial action plan that is CERCLA compliant. The eventual goal of the remediation plan is to convert the entire RMA property into a national wildlife refuge.
The North Plants Area consisted of 54 production buildings and support structures interlaced with numerous roads, utilities, and open areas situated on 50 acres within the boundaries of RMA. The complex was used by the U.S. Army to manufacture, transfer, containerize, and store Sarin gas, a chemical warfare nerve agent. The facility was also used to neutralize and dispose of other chemical munitions.
Demolition
The scope of work for this contract included the demolition, sizing, transportation, and disposal of 54 structures within the North Plants Area at RMA. The buildings included large multi-story (up to 120 feet tall) heavily reinforced concrete structures, concrete block, concrete block and reinforced concrete structures, as well as steel framed, transite sided structures. The complex included extensive reinforced concrete pads, sumps, vaults, and sewers, all requiring demolition and removal. Substantial transite piping and ACM wrapped pipe were also encountered. Twenty-eight of the structures were declared under the Chemical Weapons Convention (CWC) treaty and required additional "hold point" considerations prior to and during demolition activities.
Envirocon's work tasks on this project included all aspects of demolition from initial inspection through final disposal. The process for each building began with a comprehensive inspection and hazardous materials survey. Each building was inspected for its structural integrity and surveyed for asbestos and other hazardous materials. This inspection was also used to identify potential workplace safety concerns and finalize appropriate demolition methodology in accordance with OSHA Subpart T. Subsequent to the inspection, an Engineering Survey Report was prepared which prescribes the actions necessary to prepare the building for demolition (removal of unsafe conditions, abatement of asbestos, removal of hazardous waste, capping or blinding of drains, utilities, etc.). Upon approval by the Program Management Contractor (PMC), abatement of all hazardous materials and elimination of all release points to the environment proceeded. A final inspection by the PMC Contractor subsequent to the hazardous materials abatement was required before demolition could proceed.
Standard demolition of the structures was performed using hydraulic excavators equipped with shears, grapples, and concrete pulverizers as well as a crane with a steel wrecking ball depending upon their height and the configuration of structural members. Building 1501, a heavily reinforced concrete structure, 120 feet tall, was demolished using a crane and ball. Many of the underground concrete structures were also broken up using the wrecking ball. During the demolition work, dust abatement was performed using water sprayed from water trucks and a water cannon. Waste materials generated during the project were sized appropriately and loaded onto haul trucks for disposal in at the on-site landfill. Recyclable materials were cut to the appropriate size and shipped to an accepted off-site recycling facility.
Soils Remediation
The second aspect of this project involved the precise excavation and transportation of approximately 200,000 cubic yards of contaminated soils from 8-9 SAR sites including the Basin F Exterior (BFE). Prior to the commencement of any excavation activity, stormwater and erosion control measures were established, monitoring wells and survey monuments were protected, and limits of excavation established. The SAR sites were excavated in Level C PPE upgrading to Level B as necessary based upon air monitoring results and historical data.
Additional excavation activities included the removal of approximately 7,200 linear feet of chemical sewer and excavation of associated soils. Chemical Sewers were excavated Level B PPE while conducting real-time monitoring for chemical warfare agents. These chemical sewer trenches were a minimum of 10 feet in depth and either 11.5' or 21' wide at the bottom per specifications. Because of insufficient records kept during the time that RMA was operating, Envirocon was required to perform exploratory excavations to locate the alignment and depth of chemical sewers. From this it became possible to establish the excavation limits required for the removal of the sewer pipe and associated contaminated soils. Excavation of SAR Sites was conducted utilizing a combination of excavators, rubber-tired loaders, and dozers, while chemical sewers were excavated entirely by excavator. All survey control of chemical sewers was accomplished in Level B PPE from a telescoping boom manlift with the basket suspended over the excavation.
All soils removed from the North Plants production areas and chemical sewers were hauled to the on-site Hazardous Waste Landfill (HWL) at production rates that attained contract milestones and ensured compliance with mandatory daily soil-to-debris ratios.
An important aspect of this project involved the management of the ratio between soil and debris being shipped to the landfill. Envirocon was required to manage the soil/debris ratio at between 2:1 and 3:1 to ensure adequate soils were available to cover the debris being generated. This aspect of the project was managed on a daily basis and the ratio was maintained successfully throughout the project. Additional tasks associated with this project included the establishment and maintenance of haul roads to support truck traffic, underground storage tank and piping removal, fencing removal, asbestos abatement, foundation removal, and support area maintenance.
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