The Development of Innovative Technologies For the Remediation of Contaminated Sites

Transcription

1 The Development of Innovative Technologies For the Remediation of Contaminated Sites Bill Wong 1, P.Eng., Kostantin Volchek 1, P.Eng., Ph.D. Monique Punt 1, P.Eng., Carl Brown 2, Ph.D. Abstract Experience from past projects involving difficult to treat soils has demonstrated that screening evaluations such as multiple technology bench scale testing are useful in providing an assessment of the particular strengths and weaknesses of available remediation tools. This would help increase the scientific and engineering knowledge of potentially viable technologies, while helping to identify any areas that may pose problems when processes are scaled-up to operations in the field. This paper illustrates the value in the use of a multiple-technology bench scale testing approach. As is often the case, proper testing infrastructure and overhead (such as Health and Safety, QA/QC, and project management) are significant portions of technology evaluation projects. By performing a multitude of technology tests in a single project, these infrastructure costs are spread over a range of activities, resulting in higher productivity levels. The use of screening methods such as the bench scale testing of technologies is recommended as a step in the development of solutions on difficult-to-treat soils. A number of innovative remediation technologies have been studied, including: membraneassisted soil leaching, chelation-based mixed contaminant extraction (heavy metals and organics), microwave treatment, two-phase partitioning bioreactor and electrokinetics. Introduction Environment Canada, through its Alternative Service Delivery (ASD) contractor SAIC Canada has embarked on a number of research and development (R&D) projects focused on contaminated site remediation. The emphasis of this work has been on the development of technologies to address substances that have been declared toxic under the Canadian Environmental Protection Act (CEPA 1999) or that have been placed on the CEPA priority substances lists (PSL1 and 2). Depending on the particular project, work is carried out at bench-, pilot- and field demonstration-scales. Research is conducted on technologies and the development of process trains that can assist in remediating difficult sites that are unsuitable for conventional cleanup. In this paper a number of innovative remediation technologies are introduced and discussed. SAIC Canada has performed several laboratory-, bench-, and field-scale evaluations whereby multiple treatment processes were combined in order to adequately remediate a 1 Science Applications International Corporation (SAIC Canada) 2 Environmental Technology Centre, Environment Canada

2 contaminated material. This paper will discuss the evaluation of a suite of bench scale processes used to remediate soil, sediments and water. Detailed scope, experimental plan and test results for each case study would be too much to include in this paper. Instead, an overview and qualitative summaries will be given to provide readers with a general knowledge on a wide range of remediation technologies. This paper illustrates, using several case studies, the value in the use of a multipletechnology bench scale testing approach. As is often the case, proper testing infrastructure and overhead (such as Health and Safety, QA/QC, and project management) are significant portions of technology evaluation projects. By performing a multitude of technology tests in a single project, these infrastructure costs are spread over a range of activities, resulting in higher productivity levels. The four case studies presented in this paper are as follows: 1. A PCB contaminated soil site; 2. A contaminated sediment site; 3. A landfill leachate treatment process; and, 4. A contaminated snow project. Brief discussions on two additional innovative remediation technologies are also included near the end of this paper. Technology Selection Many of the commonly available remediation processes have limitations with respect to the types of matrices for which they are amenable. Very often more than one technology is required to clean up a contaminated site, because of the variability in the contaminants and the soil or water types found. As well, many of the commonly used remediation processes, such as conventional bioremediation or soil vapour extraction, cannot treat soils containing recalcitrant contaminants (such as chlorinated compounds, PCBs, dioxins and furans) or those having high clay or moisture contents. Experience from past projects involving difficult to treat soils has demonstrated that screening evaluations such as multiple technology bench scale testing are useful in providing an assessment of the particular strengths and weaknesses of available remediation tools. This increases the scientific and engineering knowledge of potentially viable technologies, while helping to identify any areas, which may pose problems when processes are scaled-up to operations in the field. A decision on whether a multi-technology evaluation should be performed, as opposed to assessing only one technique, depends on a number of factors such as the nature and complexity of a contaminated matrix, cleanup targets, timeframe, etc. Typically, heterogeneous matrices with several different groups of contaminants warrant the evaluation of several treatment alternatives.

3 Case #1 PCB Contaminated Soil Over the past two years SAIC Canada has been involved in the evaluation of several techniques for the treatment of soil contaminated with polychlorinated biphenyls (PCBs) held in a temporary storage cell at a federal government site. The following technology evaluations were performed at the bench-scale using soil samples taken from the site: 1. Soil classification / volume reduction; 2. The isolation of native PCB degrading microbes; and 3. The use of these microbes in a Two-Phase Partitioning Bioreactor (TPPB) to destroy the PCBs. Soil Classification / Volume Reduction Very often only a fraction of contaminated soil (typically the fines fraction) contains most of the target contaminants that require removal while the rest of the soil (typically the large particles) will meet regulatory limits. By performing a classification procedure, it may be possible to dramatically reduce the volume of that requires treatment, thus reducing the overall cost of remediation. As a first step in this project, the soils were classified by particle size ranges using the sieves and the PCB content of the separated size ranges were analysed. The PCB contamination of greatest concern was found to be located in the fine fraction of the soil. As a result, a large portion of the soil would not require treatment because the contamination in the large particle size fractions was low. Based on the results of soil classification and an acceptable PCB limit of 50 ppm, it was found that only less than 30% of the soil would require treatment. Microbial Degradation The microbial degradation of PCB is known to occur via two main routes: highly chlorinated PCB congeners may be dechlorinated under anaerobic conditions (a reductive process) to form lower chlorinated congeners, which are more susceptible to aerobic degradation (an oxidative process). The aerobic bacterial biodegradation of PCBs is widely known and has been well studied, however, these organisms generally have a narrow congener specificity and are able to degrade only lightly chlorinated PCBs. In this project, the samples were tested for the isolated native microbe s ability to grow on biphenyl, the parent molecule of PCBs. The reason for growing the cultures on biphenyl is to induce the enzyme systems in the bacteria, which are used in the PCBdegradative pathways. It is easier to establish growth first on biphenyl before testing on Aroclor. Any culture not growing on biphenyl would not usually be expected to grow on PCBs. Preliminary results from Aroclor 1254 testing indicated that the native consortium was able to grow on Aroclor However, results from replicate experiments were unable to confirm this conclusion. Two-Phase Partitioning Bioreactor During this project a Two-Phase Partitioned Bioreactor (TPPB) was evaluated for the degradation of PCBs using native bacteria from the storage cell. The TPPB process,

4 developed at Queen s University in Kingston, Ontario, has been used successfully in degrading Polynuclear Aromatic Hydrocarbons (PAHs), benzene, toluene and xylenes (BTEX) and phenolic compounds. The TPPB is a novel bioreactor that uses two phases to deliver the contaminants to the bacteria in a controlled manner - a solvent-phase, which contains the contaminant; and an aqueous-phase, which contains contaminant-degrading microbes. The controlling mechanism is based solely on the diffusion of the contaminant into the aqueous phase. As such, the reactor can be run with very high levels of contaminant in the solvent, without affecting the bacterial growth. This work investigated the possibility of using native bacteria to degrade Aroclor 1254 in a single step using the TPPB process. Different parameters were tested to determine their influence on the degradation of PCBs including running the reactors anaerobically, aerobically, with biphenyl as the co-metabolite, and benzoic acid as the co-metabolite. As a result of the positive outcome of these tests, further tests are currently being conducted whereby the TPPB will be run sequentially using anaerobic microbes followed by aerobic microbes. Case #2 Contaminated Sediment Treatment The focus of this study was on the treatment of a contaminated sediment site in eastern Canada. Due to the unique mix of contaminants (PCBs, PAHs and heavy metals) and the nature of the soil and sediment matrix, this sediment was deemed to be very difficult to clean. This project looked at a suite of technologies and determined their performance impact. The chosen technologies included: Soils Washing Solvent Extraction Microwave Assisted Process Microwave Activated Cracking Supercritical Fluid Extraction Acid Leaching and Plasma Hearth Treatment Soil Washing Soil washing is a process which removes contaminants by either solubilising them in a washing solution or separating them along with finest size fractions of the soil. Soil washing is a generic term that includes both physical washing (conventional soil washing) and chemical leaching (soil leaching). It has been extensively used in site remediation practices in Europe where techniques involve both washing and leaching. In North America its application is mainly limited to washing but leaching is also becoming more common. Soil washing can be used not only as stand-alone process but also as a pre-treatment step followed by a physicochemical treatment of soil fines. In this case, soil washing is sometimes called wet classification. Soil washing was studied in this project with respect to its evaluation as pre-treatment technique (wet classification), as a remediation

5 technique enhanced with solvents and surfactants, and as a remediation technique enhanced with acid. Wet classification results on this sediment showed that particles greater than 1 mm size had contaminant concentrations less than the regulatory limited. However, being a very fine material to begin with, the portion of the sediment with particles greater than 1 mm made up less than 3% of total volume. As such, it would likely be impractical to use soil washing/wet classification as a pre-treatment step at full scale for these sediments. Enhanced Soil Washing It has been reported that the effectiveness of physical washing of petroleum-contaminated soils can be enhanced by using a hot water, surfactant, and a solvent of a combination thereof. A series of tests were carried out to estimate the effect of those factors on the removal of contaminants. Soil samples were analyzed for MOG only as metals removal was not expected. Tests results showed that the use of hot water, surfactants and solvents alone or in a combination was not effective in removing the petroleum hydrocarbons in the sediment tested. This is likely due to the presence of hydrocarbons primarily as heavy products. More vigorous conditions, such as higher temperatures and stronger solvents are likely required to enhance the removal. Acid Leaching Acid leaching is sometimes used in commercial cleanup operations to solubilize and remove heavy metals. Our bench-scale tests showed that only a small portion of metals could be solubilized whereas most of them remained incorporated into the sediment matrix. This finding suggested, however, that it might not be necessary to leach the metals since they are already strongly attached to the matrix. Being stable in the matrix metals would not migrate into the groundwater and thus would not pose a threat to the environment. Based on this information, a decision was made not to leach metals but leave them in the sediments. Solvent Extraction As part of this study, solvent extraction was evaluated to determine its viability as a method to remove the organic constituents in the sediment. Solvent extraction is a commercial technology that enables the effective removal of organic contaminants using solvents. Some of those solvents are non-toxic and can easily be regenerated from the extract and reused. Bench-scale test results using this sediment showed that the concentration of PCB, PAH and other organic contaminants was reduced significantly by solvent extraction and the treated sediments met cleanup guidelines. A higher treatment temperature resulted in a much better removal.

6 Microwave-Assisted Process The Microwave-Assisted Process (MAP TM, 3 ) technology uses microwaves to enhance the solvent extraction of target compounds from a wide range of materials. Past research has shown that microwave-enhanced extraction of contaminants from soil is an effective sample preparation method for the analysis of contaminated soils. The key to the technology is the use of solvents that are relatively transparent to microwaves compared to the matrix from which the target compound is being extracted. When the solvent/material mixture is exposed to microwaves, heating occurs only in localised microwave-absorbing areas within the material. The resulting pockets of high temperatures and pressure force the target compounds from the matrix into the solvent, which remains relatively cool. Microwave-enhanced solvent extraction has been shown to require far less energy than conventional solvent-extraction techniques because neither extensive mixing nor heating of the complete slurry is required. Test results showed, however, that for this particular matrix the effect of microwave on PAH removal was insignificant. It is possible that because of the high fines fraction in the soil the contaminants were so strongly bound that the amount of microwave energy used was not enough to enhance the extraction. It was concluded therefore that the solvent extraction alone would be sufficient for the removal of organic contaminants. Microwave Activated Cracking Microwave Activated Cracking is a destructive technology that uses microwave energy in conjunction with activators and catalysts to break down organic compounds in soil. A series of bench scale tests were performed to determine the effect of different variables on the efficiency of destruction. The analysis of MOG component in the untreated and treated samples showed no MOG soil samples after treatment. At the same time the formation of the petroleum hydrocarbons was observed under the microwave irradiation, especially with reactive compositions, which include hydroxides. These results would suggest that the process of the destruction of polymers had occurred under the conditions of the microwave irradiation. The best reactive additives for the destruction of the PAHs under those experimental conditions include sodium and potassium hydroxides and activated carbon. Simple microwave treatment of the plain soil provides 47% of PAH removal. The use of the activated additives in the reactive mixture resulted in up to 70% removal of PAHs. Some of the PAHs, such as acenaphthylene, acenaphthene, dibenzo-(a,h)-anthracene and indeno-(1,2,3-cd)-pyrene seemed to be removed completely from treated samples by microwave irradiation with reactive mixtures which included hydroxides. It was demonstrated by this study that microwave induced catalytic technology has potential for the treatment of this sediment by decomposition of PAHs and formation of TPH. 3 MAP is a registered trademark of Environment Canada as licensed by Her Majesty the Queen in Right of Canada as represented by the Minister of the Environment.

7 Plasma Hearth Treatment Plasma hearth treatment is a high-temperature process that destroys organic contaminates and vitrifies inorganic contaminants and the sediment matrix. Tests performed on the sediments revealed that the process produced non-toxic gaseous products such as carbon dioxide and water and glass-like solid residue. All products were found to be completely non-toxic. Hydrogen chloride, a product of PCB destruction, was completely absorbed and neutralized by a solution of sodium hydroxide and converted into non-hazardous sodium chloride. Selected Treatment Concept The above tested technologies demonstrated very different efficiencies. Some of them, such as solvent extraction and plasma treatment, were highly effective. The others were not as effective. Based on preliminary test results, a process train was selected to treat the sediments. It included solvent extraction followed by plasma destruction/vitrification. Recent bench-scale results confirmed a high efficiency of the selected treatment concept. Case #3 Municipal Landfill Leachate Treatment Working with the City of Ottawa, SAIC Canada developed and demonstrated a multiple technology process to treat the leachate generated at the City s Trail Road Waste Facility. The objective of the project was to evaluate a process for the destruction, removal and/or retention of target contaminants allowing for a safe disposal of the treated leachate in the municipal sewer system. The resulting process had to be a cost-effective pre-treatment method that would bring leachate characteristics to levels below the accepted sewer discharge limits. Parameters that exceeded or closely approached limits were: total kjeldahl nitrogen (TKN); total suspended solids (TSS); carbonaceous biochemical oxygen demand (CBOD); inorganic contaminants: hydrogen sulfide, boron, chloride, barium; volatile organic compounds: m/p-xylene and toluene. Based on a comprehensive analysis of published technical information and its own experience in dealing with contaminated groundwater and wastewater, SAIC Canada developed a treatment train incorporating the following main technologies: Solar oxidation for the destruction of volatile organic compounds; Enhanced membrane filtration for the removal of inorganic contaminants, TSS, CBOD, and a portion of TKN (non-ammonia fraction); and Steam stripping for the removal of TKN (mainly, the ammonia fraction of TKN). Solar Oxidation Photo-oxidation involves the use of ultraviolet (UV) light plus an oxidant to generate hydroxyl radicals. The hydroxyl radicals then attack the organic pollutants to initiate oxidation. There are two major oxidants that act as a source of hydroxyl radicals: hydrogen peroxide and ozone. For this study, hydrogen peroxide was used as the oxidant. Since hydrogen peroxide does not absorb significantly beyond 300 nm and absorbs only weakly in the range nm, it is not suitable on its own for the

8 treatment of polluted water using solar radiation whose wavelength is above 300 nm due to atmosphere absorption. An alternative for this is the injection of ferrioxalate that absorbs in the region of nm. This corresponds to approximately 18% of the incident solar radiation energy. As such, ferrioxalate was used as a catalyst for the generation of these hydroxyl radicals in the solar photo-oxidation process used in this study. Since these hydroxyl radicals are strong oxidants, they will react randomly with the organic pollutants within the aqueous solution. This begins a series of reactions that will lead to the mineralization of organic pollutants. Solar oxidation bench tests revealed that the process could effectively reduce the level of m- and p- xylene and toluene and bring it into compliance with sewer discharge limits. It was found that under optimum process conditions, the concentration of m- and p- xylene and toluene could be reduced down to acceptable levels within 30 minutes. The best results were observed at ph 4.0. Chemically-Enhanced Membrane Filtration Chemically-Enhanced Membrane Filtration (CEMF) involves adding a chemical reagent to water to alter some of the characteristics of target contaminants. Those components can then be effectively removed through a semi-permeable membrane because of a change in those characteristics. Without the chemical enhancement, the removal of those components would not be as effective. Bench-scale test results confirmed that chemically enhanced membrane filtration was very effective in removing the inorganic contaminants, along with TSS, CBOD, and a portion of TKN. The process, which was developed by SAIC Canada and targeted boron as a key contaminant, involved the use of selected nanofiltration membranes at elevated ph levels. For example, the rejection by boron by the membrane NF-70 was observed to be as high as 88% at ph 11, compared to 46% at a neutral ph. At higher ph s, the membranes were found to be non-sensitive to fouling and have a stable flux that made the process technically feasible. Steam Stripping Steam stripping is a technique designed to remove volatile organic compounds from contaminated wastewater. In the case of this study, the wastewater is the permeate from the membrane filtration unit and the target contaminant is ammonia. The process involves the use of a counter-current tower which draws steam through openings in the bottom, as the permeate is pumped through the top of a packed tower. Since the volatility of the organics is dependent upon heat, when the steam encounters the organic material, it transfers from the liquid phase into the vapour phase. The free ammonia is then stripped from the falling water droplets and transfers into the vapour stream that is condensed to form the tops. The result is that the tops form a concentrated organic solution and the bottoms form a clean stream devoid of the volatile organic compounds. The bottoms can then be returned to the landfill or can be disposed of through the sewer system. Stream stripping is now commonly used to remove ammonia from landfill leachates. In this study bench-scale tests were conducted to confirm the possibility of removing

9 ammonia from the leachate that was already treated with solar oxidation and enhanced membrane filtration. Test results showed an effective removal of ammonia. This was made possible due to the fact that the high ph of the leachate, resulting from enhanced membrane filtration, was favourable for a better ammonia stripping. Outcome of the Studies Results of the bench-scale study were used to design and build a pilot-scale system for field demonstration. The system contained a solar oxidation unit, a membrane filtration unit, a steam stripping unit, and other mechanical and electrical components. The system was operated at the Landfill in July September Pilot-scale demonstration generated results that confirmed the findings of the bench-scale study and the viability of the proposed treatment concept. Results of the pilot-scale demonstration showed that the process could work under varying conditions (light intensity, leachate composition, temperature, etc.) while achieving the objectives of treatment. Case #4 Contaminated Snow As a result of a fire, a remote northern site became contaminated by heavy metals, hydrocarbons, PCBs, dioxins, furans, and glycols. The contaminants were temporarily contained in the snow and it was mandatory to treat the snow before it melted and contamination moved into the soil and groundwater. Field survey and assessment revealed that a very large area was contaminated by the smoke plume of the fire. Because of the remoteness of the site, it was impractical to bring and run highly sophisticated physicochemical treatment equipment. Results of the initial analyses carried out by an outside laboratory suggest that the concentrations of contaminants greatly exceed environmental limits. At the same time, most of the heavy metal contamination is present in a solid (particulate) form. The melting of snow yielded turbid water indicating a high content of suspended solids. Gravity settling did occur, however, fine particles did not precipitate quickly suggesting that the gravity settling alone may not be effective in removing particulates if the treatment has to be done within a short period of time. Based on available information at the time, the contaminants appeared to be present in both suspended and dissolved forms. As far as suspended solids were concerned, a majority of them can be removed using settling followed by filtration. It was decided therefore to evaluate filtration as a means to reduce the level of contaminants. Dissolved contaminants can be removed via adsorption. Adsorption is a simple yet effective process. Activated carbon has been commonly used for the removal of organic substances whereas natural zeolites are reported to be effective in removing inorganic (heavy metal) contaminants. Consequently, adsorption on activated carbon and zeolites was chosen in the bench-scale testing for the removal of dissolved contaminants. It should be noted that adsorption should also help remove some suspended solids as the layer of adsorbent acts as a media filter.

10 The adsorption and filtration test results showed excellent removal of target contaminants. Based on bench-scale study, the following key steps of the treatment process train were successfully implemented: 1. Collection of the snow on a large tarped and bermed area; 2. Allow snow to melt with the spring thaw; 3. Contaminated water from melting snow was channelled to a settling pool; and 4. Water was then directed to flow through an adsorption/filtration bed of activated carbon. The results of a simple bench-scale study helped evaluate the effectiveness of each of the treatment techniques and the sizing of the treatment system. This enabled a quick decision to be made on the implementation of those technologies in the process train. Other Remediation Technologies Electrokinetics Electrokinetic remediation is an in-situ process during which an electrical field is created in a soil by applying a low-voltage direct current (DC) to electrodes placed in the soil. As a result of the application of this electric field, heavy metal contaminants may be mobilised, concentrated at the electrodes and finally extracted from the soil. Interest in electrokinetic remediation has been driven by the demand for technologies that are cost effective and eliminate the long-term liability that is incurred by landfilling contaminants. In addition since electrokinetics is performed in situ, the cost of excavation is eliminated and normal operations can continue during the cleaning process. The procedure is not labour consuming and can be fully automated. In addition, it s safe due to the low voltage used. This technology has been successfully implemented in Europe; however, it is still at the stage of bench and pilot scale studies in North America. The extraction rate and efficiency for heavy metals depends on a number of subsurface characteristics such as soil type and grain size, contaminant concentration, ionic mobility, etc. Electrokinetics is known to be effective in low permeability soils such as clay. It is also known that the mobility of metal ions can be greatly increased if certain reagents, such as chelating agents are added to the soil. This is important since one of the factors that limit the application of electrokinetic remediation is the relatively low mobility of metal ions when they are strongly bound to the soil matrix. A study is currently underway by SAIC Canada to use metal chelating agents to increase the mobility and removal of metal ions and MOG in clay soils thus enhancing the electrokinetic remediation. There is a variety of chelating agents that can be used for this purpose. The focus of this work, however, is on lignin derivative (LD), a by-product of the pulp and paper industry. LD is capable of binding a number of metals, is readily available, inexpensive and non-toxic. Membrane-Assisted Slurry Leaching Applications of membranes have been traditionally associated with processing of either fluids or gases. Treatment of contaminated soil involves processing of solid materials so

11 that any significant role for membranes seems to be unlikely. On the other hand, many of the soil treatment operations generate liquid streams whose treatment by membrane separation may be beneficial. Soil washing is a commercial technology for the removal of contaminants, mainly heavy metals and hydrocarbons, from soil. It includes the excavation of soil and its leaching in reactors followed by dewatering. Acid and/or chelating agents are often used to enhance the removal of heavy metals. Acid leaching is conducted in batch reactors (stirred tanks) filled with soil, water, and acid, usually under controlled conditions (ph and temperature). Leaching is generally a slow process that can take hours and sometimes days to achieve a desirable removal of metals. One of the main factors, which reduce the speed of leaching, is an accumulation of leached metal ions in the aqueous phase, or the leachate. As the leaching progresses, the concentration of metals in the solid phase decreases whereas their concentration in the liquid phase increases. Consequently, the difference between the actual metal concentration in the leachate and their concentration of the saturation diminishes. This difference in concentrations is the driving force for leaching. A lower driving force results in a slower process. In many cases soil leaching is done as a sequential batch process to remove the leachate along with excess metals. In order to accelerate the removal of metals, researchers at SAIC Canada combined leaching with microfiltration. In this hybrid process, soil slurry recirculates through a microfiltration membrane that rejects soil particles but allows for a free passage of the leachate. Fresh acid is added to the slurry to compensate for the losses of liquid and maintain the ph. The combined leaching/membrane separation system works therefore in a diafiltration mode. In this setup soil particles stay in the reactor as long as it is required and the concentration of the leached metals is never as high as it would have been in case of the conventional (batch) leaching. Series of bench-scale and pilot-scale tests were carried out to study the effect of process parameters, such as the liquid exchange rate, particle concentration and ph, on metal removal. It was found that the membrane-assisted leaching had higher metal leaching rates and the residual concentration of metals was lower compared to the conventional process. The leachate generated in the membrane-assisted leaching was then subjected to nanofiltration. This liquid contained heavy metals along with unused acid. The goal was to concentrate heavy metals for a subsequent precipitation and disposal and to recover the acid for possible reuse. It was found that both goals could be achieved. Under optimum process conditions the rejection of heavy metals exceeded 95% and the leachate volume could be reduced by as high as 90%. The recovered permeate contained the acid that was reused in leaching. Test results revealed that the effectiveness of the recovered acid as leaching agent was as good as that of the fresh acid. The permeate had to be fortified with fresh acid in many instances to

12 maintain the desirable ph for subsequent leaching cycles. This additional acid only accounted for a fraction of the acid that was recovered. Results of this study suggest that the use membrane processes in soil cleanup operations can be advantageous. It accelerates the removal contaminants, reduces the volume of waste to be treated and helps save reagents. The possibility of total water recirculation also eliminates the difficulties associated with the release of trace contaminants to the environment as a result of leaching operations. Overall, the incorporation of membrane separation in treatment schemes may lead to substantial cost savings. Conclusions and Recommendations A review of the case studies presented above indicate that the multi-technology approach used in bench-scale studies is valuable particularly if the matrix is difficult to treat and a workable solution needs to be developed. A number of new and innovative technologies have been evaluated and have potential in the remediation of some of these materials. Screening evaluations such as the multiple technology bench scale testing discussed in this report are useful in providing an initial assessment of the particular strengths and weaknesses of available remediation tools. This would help increase the scientific and engineering knowledge of potentially viable technologies, while helping to identify any areas, which may pose problems when processes are scaled-up to operations in the field. As such, some of the technologies may prove valuable in the development of solutions to some of our difficult to treat contaminated sites in Canada. In a number of recent studies conducted by SAIC Canada, this multiple-technology bench-scale testing approach was applied. Usually a team of scientists, technicians and engineers work through the various treatment technologies on the same contaminated material. Test procedures, observations and results are shared amongst the team members immediately. Experience gained in one technology (even if no positive results were obtained) has the potential to help the team in the development of a successful treatment train. Furthermore, efficiencies were realized in a number of project execution areas, including: health and safety, analytical work, project management and report preparation. By performing a multitude of technology tests in a single project, these infrastructure costs are spread over a range of activities, resulting in higher productivity levels. Continued use of screening methods such as the multiple-technology bench scale testing of technologies is recommended for use on difficult to treat soils.