Excavated soil

Where there is available ground and the specific resistivity of soil in the upper layers is low, the anodes are laid horizontally [3]. A trench 0.3 to 0.5 m wide and 1.5 to 1.8 m deep is dug with, for example, an excavator or trench digger (see Fig. 9-2). A layer of coke 0.2-m thick is laid on the bottom of the trench. The impressed current anodes are placed on this and covered with a 0.2-m layer of coke. Finally the trench is filled with the excavated soil. No. IV coke with a particle size of 5 to 15 mm and specific gravity of 0.6 t m" is backfilled at a rate of 50 kg per meter of trench. The anodes are connected in parallel and every three to four anode cables are connected to the anode header cable by a mechanical cable crimp encapsulated in an epoxy splice kit to give an economical service life at high current output. 

Another classification of remediation technologies describes where the action is taking place. Ex situ methods are those applied to excavated soil and in situ processes are those applied to the soil in its original location. On-site techniques are those that take place on the contaminated site they can be either ex situ or in situ. Off-site processes treat the excavated soil in fixed industrial facilities, away from the contaminated site. 

Raghavan, A., Coles, E. and Dietz, D., Cleaning excavated soil using extraction agents a state-of-the art review, J. Hazard. Mater., 26, 81-87, 1991. 

The washed wastewater treatment techniques are basically the same as those used for pumped groundwater. Several integrated treatment technologies have been developed that can wash soil and treat washing water, such as that by BioTrol, Inc., in which the excavated soil is first screened, then washed, and finally the contaminated water is treated. As contaminants are difficult to wash from silt and clay, the clay and silt slurry contaminated with organics is treated in a bioslurry reactor. 

In the thermal desorption technique excavated soil is heated to around 200 to 1000°F (93 to 538°C). Volatile and some semivolatile contaminants are vaporized and carried off by air, combustion gas, or inert gas. Off-gas is typically processed to remove particulates. Volatiles in the off-gas may be burned in an afterburner, collected on activated carbon, or recovered in condensation equipment. Thermal desorption systems are physical separation processes that are not designed to provide high levels of organic destruction, although some systems will result in localized oxidation or pyrolysis. 

Remedying hazards posed by excavated soils resulting from response activities... 

All ex situ soil treatment methods involve a two-step approach soil excavation and aboveground treatment of the excavated soil. The differences in the various ex situ excavation/treatment methods for soil remediation lie only in the methods of soil treatment aboveground, such as soil washing plus extraction, and slurry biodegradation. 

The excavated soil is removed from the site and screened to remove large solid objects. The screened soil is washed and the washing water is treated.78 Clearly, the washing media used in in situ soil-flushing treatment can be used here. The most common washing medium is water. Surfactants are used to reduce the affinity of contaminants to the soil. 

Ex Situ Biological Treatment on Excavated Soil by Slurry Biodegradation... 

In situ SVE methods can be used for desorption of VOC from excavated soils. The excavated soil has the advantage that assist technologies may be applied to enhance vaporization, for example, through venting and heating. 

Trenches were constructed using conventional earthmoving equipment. During construction, air monitoring was continued to assure that explosive conditions were not present. However, odors persisted from the freshly excavated soils but disappeared within a few days. Operation of this trench system continues throughout frost-free seasons and has proved very successful. Initially, approximately 5 bar-... 

The top layer of the detonation ground was excavated to a depth of 0.5m. The exeavated soil was temporarily stored on the site. A Bentonit seal was installed and a protective and a drainage layer were built over the seal. The excavated soil was incorporated into the slopes of the reconstructed ground (Figure 6). The new top layer of the detonation ground was made Irom... 

Soil Type Phyto Remediation Bio Air Remediation Stripping Sparging Excavation Soil Washing Thermal Treatment Incineration ln- ltu Stablllzalion Encapsulation Thermal ... 

The BioTrol soil washing system is a patented, water-based volume reduction process used to treat excavated soil. It separates slightly contaminated, coarse, washed soil particles from heavily contaminated fine soil particles. The process operates on the premise that (1) contaminants tend to be concentrated in the fine size fraction of soil (sUt, clay, and soil organic matter) and (2) contaminants associated with the coarse soil fraction (sand and gravel) are primarily surficial. The BioTrol soil washing system can be used to treat soils contaminated with petroleum hydrocarbons, pesticides, polychlorinated biphenyls (PCBs), various industrial chemicals, and metals. 

The treatment costs for 2.5 million pounds of soil contaminated with metolachlor at a site in southwest Nebraska were estimated to be 65,000. The treatment involved using a Microen-fractionator to mix the excavated soil with zero-valent iron and water. The estimate included labor costs (D21578L, p. 2). 

The HRUBOUT process is a mobile in situ or ex situ thermal desorption process designed to remediate soils contaminated with volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs). For the ex situ process, excavated soil is treated in a soil pile or in a specially designed container. Heated compressed air is injected into the soil, evaporating soil moisture and removing volatile and semivolatUe contaminants. Heavier hydrocarbons are oxidized as the soil temperature is increased to higher levels over an extended period of time. The vapor is collected and transferred to a thermal oxidizer (incinerator) for destruction. 

The HRUBOUT process may also be applied as an in situ technology for excavated soils (see Hrubetz Environmental Services, Inc., HRUBOUT Process, In Situ, T0379). 

The technology was designed to be applied in situ for the treatment of contaminants in shallow soil. However, it can be applied as an ex situ treatment, for excavated soils, in specially constructed shallow treatment basins. 

The Maxymillian Technologies, Inc. (formerly Clean Berkshires, Inc.), mobile thermal desorption system (TDS) uses rotary kiln technology to remove contaminants from excavated soils and sediments. Thermal desorption is a physical separation process designed to volatilize water... 

The low-temperature thermal treatment (LT3) uses thermal desorption to volatilize organic compounds under noncombustion conditions. The contaminants are evaporated from excavated soil... 

Trausportiug excavated soil to the processiug uuit StockpUiug excavated soil temporarily... 

Bio-Raptor technology uses a combination of ex situ microbial and mechanical processes to treat soils and sludges that are contaminated with hydrocarbons. The Bio-Raptor unit shreds and screens the excavated soil to increase its surface area. Then, the unit sprays and inoculates the soil with a proprietary blend of microorganisms. The soil is heaped into biopiles while the microbes degrade the contaminants. Bio-Raptor systems are commercially available and have been used for full-scale site cleanups. 

The cost analysis provides a basis for calculating unit treatment costs associated with the in situ gas treatment. The proposed area, to be treated in the field demonstration, is 30 ft in diameter and has a depth of 40 ft, corresponding to approximately 28,274 ft. Based on the total treatment cost of 342,000, the unit treatment cost is 327/yd or 217 per ton of soil. This cost is comparable to costs for in-drum stabUization/solidification of excavated soils ( 200/yd ) but higher than in situ mixing ( 10 to 20/yd ) (D14727N, pp. 23-26). 

Figure 2. Landfarming of petroleum-contaminated soil. A 10-acre site for treatment of about 20 000 cubic yards of excavated soil.

Initially, the excavated soil had an average of 13g TPH per kg soil. After 34 weeks of treatment, TPH was reduced by about 90% to 1.27 g per kg. Gas chromatography showed a large reduction in the alkane fraction. No data were presented on the aromatic and PAH fractions. The residue remaining in the soil after treatment was immobile, as determined by repeatedly washing the soil with water and testing for hydrocarbons. 

U.S. EPA (1989). Cleaning Excavated Soil Using Extraction Agents A State-of-the-art Review. EPA/600/2-89/034. 

We need to make a decision related to the disposition of soil that has been excavated from the subsurface at a site with lead contamination history. Excavated soil suspected of containing lead has been stockpiled. We may use this soil as backfill (i.e. place it back into the ground), if the mean lead concentration in it is below the action level of 100 milligram per kilogram (mg/kg). To decide whether the soil is acceptable as backfill, we will sample the soil and analyze it for lead. The mean concentration of lead in soil will represent the statistical population parameter. 

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