Gravimetric concentration of heavy metals contaminated soils utilizing soil reduction units (SRU) derived from extant mining systems designed by Cyril and Lawrence Wood are the primary method and means employed for the treatment of heavy metals contaminated soils. The 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 proposed, the SRUs would provide an immediate heavy metals capability not found in competing systems. Costs for treatment of contaminated soils using Terra WashTM 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.
In Europe, soil washing is the predominate remedation method for removing heavy metals from soils.
Terra WashTM Soil Washing Units and Soil Reduction Units can be used to remove a wide variety of soil contamination including:
The emphasis on our equipment is mobility and efficiency. See Specifications and Tests.Hydrocarbons (petroleum and fuel residues)
Polychlorinated Biphenyls (PCBs)
Soil Washing Units (SWU) are specifically designed to wash soils. A prototype TW 75 SWU with a capacity of 7.5TPH (5CYD/HR) was completed and tested in 1991. A 45TPH (30CYD/HR) TW 300 SWU will soon be completed. Larger units with capacities of up 100 CY/HR are planned.
The Soil Reduction Units are converted or derived from our Arctic Miner(TM) gravimetric plants. When used as a component of Terra Wash(TM), the Arctic Miner(TM) carries a TW designation instead of a Mk designation.
Terra Wash(TM) and Arctic Miner(TM) are the property of Cyril L. Wood and Lawrence D. Wood. Terra Resources, Ltd.has been granted a license to manufacture and market soil remediation services using Terra Wash(TM).
The only disadvantage of soil washing is the disposal of the fluids remaining onboard the machines at the end of each job. These are volumes of from 1000GAL to 4000GAL, depending upon the size of the SWU. Disposal costs have run as high as $1/GAL of fluids treated.
Advantages of Terra WashTM Soil Washing:
Terra WashTM may be used to treat a wide variety of contaminates
Terra WashTM is effective in removing heavy metals
Terra WashTM is a MOBILE system
Terra WashTM is cost competitive with bio-methods
Terra WashTM has operated in winter temperatures as low as 16°F ( -8.9°C )
Terra WashTM has successfully processed contaminated bentonite drilling muds
Terra WashTM has a demonstrated fine soils processing capability
Terra WashTM features rough terrain capability, hydraulic leveling, and diesel generator
Bioremediation is the treatment of contaminated soils by biological means. The treatment of hydrocarbon contaminated soils is the area of greatest use. However, successful demonstration projects have included treatment of heavy metals and PCB contaminated soils. However, bioremediation is still considered to be a situation of "caveat emptor". Bioremediation "fell short of client expectations for an inexpensive, natural solution" to cleaning contaminates from soils. "People thought you could just take bacteria out of the soil, without doing anything to them...Biotreatment works best when specific microbes are targeted for specific contaminates and when the environment is optimized to keep microbes in good working order." ("Getting The Bugs Out," Chemical Engineering, July 1993, p93. Emphasis in italics added by LDW.)
Bioremediation involves the use of bacterium (anaerobic or aerobic) specifically suited to the contamination. The advantage to this method is that the microbes die off when the contaminate is consumed. The disadvantage is the time factor. Time and temperature are inversely related. The colder the ambient climate, the longer the clean-up time. Even in favorable conditions (70F), the time for clean-up can be measured in weeks and months. The time factor in colder climates can be measured in years. This means the property affected is lost to productive use during remediation.
A test conducted in 1991 on a fuel spill located at Atigun Pass on the Alaska Pipeline required three months for treatment. Costs were reported at $200/CYD for the treatment of approximately 200CYDS of diesel contaminated soils. The contaminated soils had to be continually heated and covered during the test period.
The most highly publicized use of bioremediation was for the treatment in 1989-90 of the affected beaches in Prince William Sound, Alaska during the EXXON VALDEZ oil spill disaster. The use of the bioremediation agents Correxxit and Inipol are still embroiled in controversy. According to "Soiled Shores," Scientific American, October 1991, the results of the use of these agents in Prince William Sound are uncertain. There was no apparent sub-surface penetration by these agents to the oil that had migrated to the beaches. Three years after the initial applications in 1989, and after subsequent applications in 1990 and again in 1991 to certain beaches, there still existed degraded crude oil between 4IN and 3FT below the surface of the beaches. An article titled "Old California Oil Spill Leaves Distant Legacy", Earth, May 1993, pp17-18, gave the experiences of U.S.G.S. scientists in investigating the aftermath of the oil spill in the summer of 1990. They found wide spread devastation to plant and animal populations because of the inadequate remediation processes involved in the cleanup effort. In 1993, Exxon settled out of court for $900,000,000 in damages to the State of Alaska. Another $100,000,000 settlement was reached recently with native populations in Prince William Sound. There has yet to be a settlement with fishermen or other communities in Prince William Sound claiming damages from the oil spill.
There is another consideration to the Prince William Sound example. That is the reality of the unknown long term health risk associated with the use of this type of treatment technology. There is at least one class action lawsuit on behalf of twenty-five former oil spill workers still before the Alaska State Superior Court concerning the alleged detrimental effect upon their health due to their exposure to Correxxit and Inipol. At least two workers were hospitalized from the effects of these agents during the initial application in 1989 to the beaches in Prince William Sound. There were also large scale bird kills (>125,000) reported after the first widespread applications.
Bioventing is an emerging technology associated with bioremediation that deserves comment. This method is being tested on hydrocarbon spills where it is not possible to disturb the contamination site. This method combines biotreatment with air injection, or soil vapor extraction. This method involves pumping small amounts of oxygen into the contaminated soil strata thereby stimulating microorganism growth, which then break down the hydrocarbons into carbon dioxide and water. Cost of the process ranges from $10-$50/TON of contaminated soil. The disadvantage is that this method takes five times as long as air sparging.
Air sparging is the injection of large volumes of air into a contaminated soil stratum to force the organic vapors to the surface where they are then treated by carbon filtering or other means. The cost of air sparging is estimated at $128/TON. Therefore, if air sparging takes 2YRS to complete a project, a comparable bioventing system will take 10YRS to do the same job. The actual time is dependent upon depth of the hydrocarbon contamination, pH factor of the soil, permeability of the soil, and the concentration level of the contaminate. High moisture content in the soils can degrade the process by preventing oxygen from reaching the bacteria, thereby inhibiting the promulgation of the bacteria necessary to breakdown the hydrocarbons.
Bioremediation research projects, both ex situ and in situ methods, comprise 42 projects receiving innovative technology research grants. There are presently 65 bioventing projects in the predesign stage awarded innovative research grants issued under the various SBIR (Small Business Innovative Technology Research) grant programs. ("Soil Clean-up: Best Of All Possible Worlds," Chemical Engineering, February 1994, pp33-37; "Dig-and-mix Bioventing Enhances Hydrocarbon Degredation At Service Station Site," Hazmat World, December 1993, p34)
Encapsulation involves the mixing of the contaminated soils with other products such as lime, concrete, or asphalt. The contaminated soil becomes part of the product mix and the contamination is thereby prevented from migrating to surrounding strata. Another type of encapsulation is vitrification which involves the glassification of the soil through heat generated by electrical current passed through electrodes set into the ground. Freezing the soil in place has also been proposed and tested in the northeastern U.S. on a limited scale.
The types of contamination treated varies with the desired end product mix. Encapsulations by lime and concrete have been used concurrently in the effective treatment of heavy metals and waste oil contaminated soil. Asphalt encapsulation has been used effectively on hydrocarbon contaminated soils. The major drawback to these methods is that there needs to be an immediate market for the end product, otherwise the end result is random patches of concrete and asphalt. Glassification has been tested on heavy metals with particular emphasis on radionuclide contamination. This method is expensive, dangerous, and highly questionable as to the effectiveness in creating other than radioactive glass. Freezing the soil has been proposed as a means of temporary containment of the perimeter of a contamination site, and not as a long term solution. Unless permafrost is already present, the likelihood of site remaining frozen is nil. Therefore, because of the limitations on encapsulation, this method will not be considered as serious competition.
Thermal remediation involves introducing hydrocarbon contaminated soils into a heated vessel and retaining those soils until they reach a uniform temperature. The operating temperatures are limited to less than 800F, due to the potential for releasing dioxins into the atmosphere. Most of these systems utilize a method whereby hydrocarbons are vaporized and ignited. Any remaining byproducts are removed from the system by convection and treated by filters, or re-ignition in a second stage. Thermal remediation systems are fueled by diesel oil or natural gas. The amount of fuel required varies with the size of the unit, but units operating in Alaska consume up to 200GPH of diesel and 1,465CUFT/HR of natural gas. These units, even in their most mobile form, are not easily moved, comprising several truck loads of equipment. The cost of these units is considerable. Units of up to 15TPH (10CYDS/HR) have prices in excess of $400,000. Units of up to 25TPH (16.67CYDs/HR) run in excess of $1million. Given rising fuel costs and increased taxes on fuels, the cost of operation of a thermal system will increase, not decrease.
In the March 1993 Alaska Business Monthly (p51), Clean Soils, Inc. reported that their 15TPH system was a $750,000 investment. The air monitoring equipment alone was a $65,000 investment. Maintenance costs are also high due to the combustion environment and sophisticated sensors and the associated computerized control system. 17% of operational time is lost due to system maintenance requirements (4HRS out of every 24HRS).
The drawbacks of this type of soil remediation are many. The lighter solids particles treated tend to separate from the overall fraction being processed and get carried out by the convection system designed to remove any remaining hydrocarbon vapors. These hot dust particles create a "vagrant" dust problem, as well as a potential explosion hazard. In association with this problem, heavily saturated soils have to be diluted with clean soils, as too great a concentration of fuels will cause detonation in the combustion chamber causing superheated air to escape into the bag houses designed to contain the vagrant dust problem. The Bag Houses are known to suffer ignition hazards. Most regulatory environments involve a permitting system requiring up to a year for acceptance for the installation and utilization of a thermal remediation system. This means a fixed site facility in most states.
This method is coming under increasing attack through criticism of the degradation of the ambient air quality where they are utilized. In many areas of the U.S., this method is banned outright, or severely restricted as to when it can be utilized as a result of inversions caused by weather conditions. There are studies underway in Congress which may lead to the banning of thermal remediation processes altogether, because of suspected contributions through their emissions to the worsening of the "green house" effect.
In May 1993, the EPA announced a moritorium on any further increase in incinerator capacity in the U.S. for the succeeding 18 months. This moritorium will remain in effect until the rules and regulations governing hazardous waste incinerators and industrial furnaces are reviewed. ( "Regulatory Actions Impact Treatment and Disposal", Hazmat World, May 1993, p56 )
Thermal remediation is not effective where heavy metals are present.
END OF DOCUMENT