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Envirocon successfully completed a project at the DOE facility in Oak Ridge, Tennessee. The Melton Valley Completion (MVC) Site Project consisted of the construction of four collection trenches and a soil-bentonite cutoff wall. The collection trenches had depths of up to 22 feet and consisted of gravel and sumps for collection and treatment of radioactive contaminated groundwater. The collection trenches were constructed at four locations that previously served as disposal sites of solid low-level waste, non-RCRA low-level radioactive waste, and low-level liquid waste. The soil-bentonite cutoff wall was installed at one of the sites in order to prevent clean water from infiltrating the collection trench.
Envirocon excavated the collection trenches with a PC400 hydraulic excavator. Excavated soils were cast alongside the trench alignment or loaded directly into 30-ton articulated trucks for disposal at the stockpile area. Three of the collection trenches were excavated without the use of shoring. One of the trenches was excavated using the bio-polymer slurry trenching technique, which allowed excavation of the trench with nearly vertical sides without the need for shoring. Envirocon mixed the bio-polymer slurry in a custom-designed, high-speed colloidal mixer with the capacity to produce up to 500 gallons of hydrated bio-polymer slurry per minute. Following construction of the collection trenches, Envirocon mobilized a drill rig to install the sump wells.
Envirocon excavated the cutoff wall through a working pad using the PC400 excavator. Bentonite slurry was produced at the batch plant using a jet shear mixer with the capacity to produce up to 500 gallons of hydrated bentonite slurry per minute. The slurried bentonite was transferred from the mixer into an adjacent slurry pond where the slurry was circulated and hydrated prior to introduction into the trench. The bentonite slurry level in the trench was maintained between 6 and 18 inches of the working pad elevation.
Excavated soils were placed alongside the working pad for use in soil-bentonite backfill preparation. Material and objects greater than 3 inches in diameter were segregated and stockpiled at an approved on-site location. Envirocon mixed the soil-bentonite backfill at the mixing area using a bulldozer and/or hydraulic excavator until a thoroughly consistent mixture was achieved.
The soil-bentonite backfill was initially placed using a ramp excavated in the soil on one end of the trench. The ramp, or lead-in trench, facilitated the smooth easing of the backfill into place without the potential for segregation of the backfill or the accidental entrapment of slurry. Placement continued from one end of the trench to the other by inserting new backfill on the leading face of previously placed backfill. The backfill displaced the slurry, creating a continuous barrier of soil-bentonite backfill without voids or entrapped slurry. Backfill in the trench formed a relatively flat slope of approximately 5:1 to 8:1. The toe of the backfill slope was kept at a minimum distance of 30 feet from the toe of excavation to maximize the stability of the trench.
Envirocon stabilized the excess slurry by blending it with excess soils. Based on the cutoff wall area of 21,375 square feet, 800 cubic yards of excess excavated material was generated. Excess slurry, soils, and waste were transported to an approved on-site area.
Many challenges were overcome during the project, including underground utilities, site access, weather conditions, and coordination with several ongoing projects. Despite these challenges, the project was completed without incident and ahead of schedule, earning an early completion incentive.
Based upon the successful execution of this project at the Oak Ridge facility, Envirocon received the Bechtel Jacobs Company (BJC) 2004 Large Business of the Year Award. BJC has established a program to recognize subcontractors who best demonstrate their commitment to excellence in a safe performance of their project and their commitment to responsible corporate citizenship. Envirocon was given this award at a special ceremony celebrating this outstanding achievement.
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