Brownfield development - Biotechnology cleans contaminated soil

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The Tooele Army Depot (TEAD) is in Tooele, Tooele County, Utah, 35 miles southwest of Salt Lake City. It consists of two separate areas, the North Area and the South Area. The North Area covers about 25,000 acres in Tooele Valley south and west of Tooele. Since 1943, TEAD has had a fourfold mission: store ammunition, demilitarize ammunition, rebuild military equipment and store military equipment. In fulfilling its mission, TEAD decommissions munitions by cutting the casings and removing and recycling the explosive material.

The casings are then rinsed with water to remove residual explosives. Between 1948 and 1965, rinse water was discharged into the “TNT Washout Area,” which covers less than one acre in the North Area. The Army detected trinitrotoluene (TNT) and cyclomethylenetriamine (RDX) in soil near the TNT Washout Area (designated as SWMU-10), threatening ground water. About 2,500 people depend on wells within three miles of the site as a source of drinking water.

The Challenge:

Project plans included treatment of approximately 10,000 yards of soil impacted with TNT and RDX at concentrations as high as 2,500 and 1,000 mg/kg, respectively. In addition, soils were required to be treated to levels below the remediation goals of 86 mg/kg TNT and 31 mg/kg RDX.

Initial treatability and feasibility analyses suggested that conventional composting would be the most cost-effective alternative for soil treatment, utilizing organic amendments at a rate of 70 weight percent (wt %) of the total compost mass, and treating in seven batches over the course of 12 months. However, a combination of factors resulted in an increase in projected costs. The combination of a considerable rise in fuel and shipping costs, a long-haul distance to the site from agricultural areas, and the need for relatively large quantities of compostable organic materials, combined to make the originally-preferred alternative economically unfavourable.

As a consequence of changes in project economics, the contractor recommended the use of DARAMEND as an alternate form of treatment to make it possible for the project to be completed within budget. MWH and the Army Corps accepted this alternative following the completion of pilot-scale soil treatment that met the site remediation goals.

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