Excavation, of contaminated soil

Excavation of contaminated soils is required and may cause the uncontrolled release of volatile organic compounds, if they are present. 

For ex situ thermal desorption in general, 15 to 30 per ton ( 20 to 35 per metric ton) is required for direct operating costs including utilities and repairs. Unit transportation and setup costs typically range from 3 to 5 per ton ( 3.30 to 5.50 per metric ton). Excavation of contaminated soils and replacement of treated soils costs about 5 to 10 per ton ( 6 to 11 per metric ton) (D18527, p. 4)... 

Once the contaminated material is pretreated, it is treated in the TDU. There are two broad categories of TDUs in situ (also referred to as thermally enhanced recovery) and the more common ex situ. In situ involves heating the soil in place to remove contaminants, while ex situ units require the excavation of contaminated soil for treatment in the TDU. 

The Brio refining site is approximately 58 acres in size and is the location of a former chemical production, recovery, refinery, and regeneration facility. The site includes closed impoundments into which hazardous substances were disposed in bulk, storage tanks, and approximately 1,750 drums of hazardous substances. Remediation activities included the excavation and incineration of contaminated soil, installation of protective liners around selected pits, and the installation of a groundwater extraction system adjacent to a gully. 

Soil surveys relating to construction work require samples from at least the depth of excavation water seepage may cause cross-contamination of land. Some guidelines for the classification of contaminated soils are summarized in Table 13.11 some materials are difficult to dispose of safely on land (Table 13.12). 

It is estimated that approximately 15,290 m3 (20,000 yd3) of contaminated soil would need to be excavated and treated. The incinerator would be operated continuously (24 h/d, 365 d/yr), although... 

Soil vacuum extraction is cost-effective if the volume of contaminated soil exceeds 382 m3 (500 yd3), and if the contaminated area is more than 6 m (20 ft) deep otherwise, soil excavation and... 

One source estimated the cost of bioremediating explosives-contaminated soil to be 50 to 400 (1995 dollars) per cubic yard of soil treated. This estimate does not always include all indirect costs associated with treatment such as excavation, permits, and treatment of residuals. A U.S. Army study estimated that to treat less than 10,000 tons of contaminated soil, the cost would be 651 per ton for mechanically agitated composting, and 386 per ton for windrow composting (D17224H, p. 29). 

The U.S. Department of Energy s (DOE s) Los Alamos National Laboratory (LANE) conducted a cost analysis of the circulating fluidized-bed combustor based on the full-scale remediation of a former oil field on the Kenai Peninsula in Alaska. The LANE determined that the remediation cost ranged from 150 to 300 per ton when treating 20,000 to 50,000 tons of soil. For the treatment of 10,000 to 15,000 tons of contaminated soil, the cost ranged from 350 to 400 per ton. These estimates exclude the cost of excavation (D21225Z, p. 63). 

The Pacific Northwest National Laboratories estimated that the total cost estimate for batch leaching of contaminated soils is 30 to 500 per ton of treated soil and for heap leaching of contaminated soils is 10 to 150 per ton of treated soil. These costs include excavation, capital, and operating and maintenance costs. This estimate is based on costs for leaching of precious metals from ores in the mining industry (D18769D, p. 5). 

Cost estimates for phytoremediation vary widely. One estimate for phytoextraction included 10,000 per acre for planting, with total remediation costs estimated at 60,000 to 100,000 per acre. Total costs included expenses associated with maintenance, monitoring, and verification testing. Another estimate placed phytoremediation costs at 80/yd of contaminated soil (D131431). Cleanup costs for an acre of metal-contaminated soil were estimated to range from 60,000 to 100,000. This estimate assumes remediation to a depth of 50 cm. In contrast, excavation and disposal storage without treatment for a comparable site would cost at least 400,000 (D16482T). 

With ex situ treatment of contaminated soils, a controlled environment for soil treatment can be maintained- With mixing, nutrient addition, aeration, and other environmental controls, mass transfer rates that typically limit in situ bioremediation can be greatly increased. Of course, the disadvantages of ex situ bioremediation are the costs of soil excavation and reactor operation. Thus, ex situ bioremediation is favored by localized, shallow soil contamination. 

Based on the information generated from these studies, a full scale treatment process was designed. The processing units will be located next to the final solidification cell so that the final treated material can be placed directly into the cell. In the treatment of contaminated soil, the soil will be excavated from the original site prior to processing and stockpiled near the CTI processing unit. 

When soil contamination extends to some depth it may be preferable to excavate the contaminated soil and put it into biopiles where oxygen, nutrient and moisture levels are more easily controlled. Composting by the addition of readily degradable bulking agents is also a useful option for relatively small volumes of excavated contaminated soil,... 

The Town of Greenwich realized that the costs of cleanup were going to be well beyond the capability of the community to pay. In 2004, the town applied for a US EPA brownfields cleanup grant. In its grant application, the town stated that it is committed to redeveloping the site as a public access and recreational park and that it planned to use the grant to excavate PCB-contaminated soil to depth of 4 ft over an area of approximately one-quarter acre. The town committed to backfilling the excavation with clean material, possibly from a local construction project. 

Ex situ remediation techniques require the excavation of polluted soil for subsequent treatment or disposal. Ex situ treatments can be broadly classified into extraction versus stabilization treatments that will render the polluted soil less harmful and suitable for deposition in a landfill or backfill. Soil washing is an example of an ex situ extraction technique in which the treated soil can either be returned to its original site (backfill) or be land filled, depending on the success of the cleanup stage. Asphalt incorporation, thermal treatment, and encapsulation are ex situ stabilization techniques in which the metal(loid)-contaminated soil is either incorporated (e.g., asphalt) or contained (encapsulation) by secondary materials that are subsequently land filled. Thermal treatments involve the incineration of the metal(loid)-polluted soil and the conversion of the pollutants into their metallic (zero-valent) states. In the following section we present an overview of the various technologies based on their mechanism of action. 

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