Soil washing is the method championed by Terra Resources, Ltd. for the treatment of hydrocarbon and insoluble chemical contaminated soils. Soil washing is effective in the treatment of inorganic contaminates and organic contaminates. This method involves the treatment of contaminated soils by chemical means, such as a surfactant, in conjunction with mechanical agitation. The concept involves literally washing the contaminates from the soil using specially designed equipment. Terra Wash™ involves the use of soil washing units (SWUs) as the soil washing component.
Gravimetric Soil Washing
Gravimetric concentration of heavy metals contaminated soils utilizing soil reduction units (SRU) derived from Arctic Miner™ mining systems designed by Cyril and Lawrence Wood are the primary method and means for the treatment of heavy metals contaminated soils in the Terra Wash™ soil remediation concept. Contaminated soils are introduced into a gravity classification system and, at the very least, reduced in volume through concentration of the heaviest fractions containing the heavy metals. This reduces the resulting concentrate into manageable volumes. Reductions in volume of up to 500:1 are feasible. This would reduce the volume of soil that would normally have to be taken to a land fill for long term storage to 1/500th of the original volume, or one cubic yard for every 500CYDs treated. Used in conjunction with the soil washing units (SWUs), SRUs would provide an immediate heavy metals capability not found in competing systems. The use of Arctic Miner™ gravimetric SRUs have been used in Small Arms Firing Range and Shotgun range closeouts and safety remediation.
Costs for Treatment
Costs for treatment of contaminated soil using soil washing can be as low as $10/CYD. Operational costs vary with the dilution ratio of the surfactant or solvent used, the chemical loss, and the maintenance requirements of a given system.
Production capacities of up to 100CYD/HR are feasible utilizing the proposed Terra Wash™ method and apparatus. A prototype system with a capacity of 7.5TPH (5CYD/HR) was completed and tested in 1991.
The Terra Wash™ TW75 SWU prototype has operated in winter conditions down to -16°F (-26.7°C). Both Arctic Miner™ and Terra Wash™ equipment have worked well into winter in Alaska. The prototype TW75 worked a job on the Kenai Pennisula in -16°F (-26.7°C) temperatures. The TW10HM SAFR system worked in -5°F (-20.6°C) winter conditions in Iowa in 2008. Insulated tanks and integral tank heaters, and a properly trained crew have shown little or no operational limitations with respect to weather. Mining in Alaska has given TRL's principals the knowledge and ability to work in conditions varying from 110° F (43.33°C) to subzero Farhenheit temperatures. "Can't" never did anything.
Disadvantages of Soil Washing
The only real disadvantage of soil washing is the disposal of the fluids remaining onboard the machines at the end of each job. Another being the use of water, which may result in having water hauled to the work site. Disposal of volumes of from 1,000GAL to 4,000GAL of spent wash and rinse fluids maybe required, depending upon the size of the SWU. Disposal costs have run as high as $1/GAL of fluids treated. Alternatives to disposal are deepwell injection on oil field service projects; running the fluids through charged plates; centrifugal force and filtration.