Successful Combination of Remediation Techniques at a Former Silver Factory

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1 REMEDIATION Winter 2006 Successful Combination of Remediation Techniques at a Former Silver Factory Anneke Roosma Bas Godschalk Reinout Lageman Maurice Henssen Marc Van Bemmel A residential area that was formerly part of a silver factor)/ site severely contaminated with chlorinated solvents was remediated using an in situ electro-bioreclamation technique. Electro-bioreclamation is a method for heating soil and groundwater combined with soil vapor and low-yield groundwater extraction and enhanced reductive dechlorination (ERD). During the first two years of remediation in the source area (the intensive phase), a total of 80 kg of volatile organic compounds (VOCs) was removed by heating combined with ERD. After another two years of ERD in the source and plume areas (the attenuation phase), the VOC concentrations were reduced to a level below 100 pg/l in groundwater. Given these satisfying results, electro-reclamation in combination with ERD tumed out to be a successful in situ remediation technique for removing VOCs Wiley Periodicals, Inc. INTRODUCTION The site of a former silver factory at Zeist in the Netherlands was severely contaminated with chlorinated solvents such as perchloroethylene (PCE). Due to natural degradation, trichloroethylene (TCE) and degradation by-products, cis-1,2-dichloroehtylene (c-dce), and vinyl chloride (VC) were also present at the site. The contaminated face area covered approximately 3,500 m2. For the purpose of redevelopment into a residential area, the site was remediated in 1991 and 1992 by excavating 4,500 m3 of contaminated soil to a depth of approximately 3 m below ground surface (bgs). In 1993, a pump-and-treat system was installed to remediate the groundwater. After an initial reduction in contaminant concentrations during the first few years, no further progress was observed. In 1998, an additional investigation showed that contamination was stil present in the soil. Clearly, the alternating layers of sand and day underlying the site were not particularly well suited for pump-and-treat. The authorities in the Province of Utrecht tried to solve the problem by requesting remediation contractors to propose a solution at a fixed price. Among several options, the authorities chose electro-bioreclamation, an innovative technology. MATERIALS AND METHODS Electro-bioreclamation ' ' * WILEY interscience«discover SOMETHING GREAT Electro-bioredamation is a combination of various in situ remediation techniques: soil and groundwater heating combined with soil vapor extraction and low-yield groundwa- ter extraction in the source areas and enhanced reductive dechlorination (ERD) in the 2006 Wiley Periodicals, Inc. 69 Published online in Wiley Interscience ( D01: /rem.20113

2 Successful Combination of Remediation Techniques groundwater source and plume areas (Lageman & Pool, 2005). The soil is heated using an alternating current (AC). As the soil creates resistance, the resulting Joule effect leads to an increase in soil temperature, which has beneficial physicochemical and biological effects (Lageman & Pool, 2001). A significant advantage of this combination of techniques is that energy is used cost-effectively. Physicochemical Effects One of the striking effects of the increase in the temperature of soil and groundwater is a reduction in the relative density of the groundwater and, consequently, an increase in the hydraulic permeability of the soil. One of the striking effects of the increase in the temperature of soil and groundwater is a reduction in the relative density of the groundwater and, consequently, an increase in the hydraulic permeability of the soil. This facilitates groundwater extraction from low-permeability layers. In comparable electro-bioreclamation projects, it had already been shown that hydraulic conductivity almost doubles for every 20 to 25 C increase in temperature. Another effect of heating is that PCE and TCE adsorbed to the soil particles are released more easily as a result of the increased solubility of the chemicals. Because of this desorption effect, the concentrations of PCE and TCE in the groundwater increase, which increases the efficiency of removing these compounds by groundwater extraction and biological degradation. The vapor pressure of the organic components also increases when the temperature is raised, while at the same time the solubility of the gases in the groundwater decreases. This is why heating the soil is combined with soil vapor extraction. Biological Effects Apart from the physicochemical effects of electric heating, higher temperatures also enhance biodegradation. As a rule of thumb, with every 10 C increase in temperature, the degradation rate doubles (Arrhenius plot; Schlegel, 1986). This positive effect, which has been shown in previous projects (Lageman & Pool, 2001; Van Bemmel, 2001), was confirmed by bench-scale degradation tests at various temperatures (experiments carried out by Bioclear at a site in Nieuwpoort). Such tests also provide information about existing biological degradation conditions at a particular site. For biological degradation, an electron donor (carbon source), nutrients (nitrogen and phosphorus), and an electron acceptor are needed. The electron donor provides a source of energy. An additional effect of increased temperatures is that organic compounds, such as the humic and fulvic acids that are present in day and peat (soils rich in organic matter), dissolve more readily in the groundwater and can also act as a carbon source. This effect can be very significant and may have a large impact on reductive dechlorination rates. If these organic compounds are not naturally present, the carbon source and nutrients can be injected into the soil and groundwater. As the electron donor is degraded, the electrons that are released are transported to the chlorinated solvents, which act as electron acceptors. During this process, the chloride atoms are replaced step by step by hydrogen atoms, reducing PCE via TCE, c-dce, and VC to the harmless end products ethylene and ethane. This process is only successful when the following conditions are met simultaneously: 70 Remediation D01: rem 2006 Wiley Periodicals, Inc.

3 REMEDIATIONIVinter 2006 conditions that promote anaerobic (methanogenic) degradation; an adequate carbon source and sufficient nutrients; and the presence of specific microorganisms that are capable of degrading VOCs into harmless end products. The results of completed as well as ongoing electro-bioreclamation projects at sites contaminated with VO Cs have shown that first-order degradation rate constants, which were initially used to estimate the total remediation time, increased by one to two orders of magnitude (Exhibit 1) due to higher temperatures and increased carbon source concentrations. Remediation Phases Electro-bioreclamation is particularly suitable for both source areas and plumes. The source area is remediated during the first (intensive) phase both by heating and by applying ERD. When, during this phase, the concentrations in the source areas have decreased sufficiently, it is more efficient to stop the heating and switch to an enhanced reductive dechlorination (attenuation) phase. During the following months, the temperature decreases slowly, and, by using an existing or injected carbon source and nutrients (biopolishing), residual contamination is further reduced. In plume areas, heating is not an option, because the plume size is usually so large that the cost of installing electrodes is prohibitive. In this zone, BRD can be applied as a standalone technique for remediating VOC contamination. Implementation Electro-bioreclamation Systenn Installing a remediation system in any existing residential area requires special measures. Communication with the residents is of the utmost importance. They have to be told exactly what is going to happen and how long the disturbance vvill last. At this site, the implementation lasted six weeks. During this period, the pavement and the plants and bushes in gardens were removed. Subsequently, a soil layer of approximately 80 cm was removed (Exhibit 2). In the excavated area, 95 electrodes were installed in hexagonal Exhibit 1. First-order degradation rate constants Naturally Occurring Conditionsi KpcE = KTCE Kc_DcE Kvc Enhanced Conditions2 KKE = Kin = KC-DCE Kvc data from literature (averages) (Doelman et al., 1997). 2 data from the Nieuwpoort project (Van Bemmel, 2001) Wiley Periodicals, Inc. Remediation D01: rem 71

4 Successful Combination of Remediation Techniques Exhibit 2. Installation of the electro-bioreclamation system arrays. In the middle of each hexagon, a dual-phase extraction well was installed. The floors of the houses were made gas-tight, and underneath the floors, an air extraction system with a gas detector was installed. The remediation equipment is normally placed in one or more containers. In this upscale residential area, however, this was not appreciated, and therefore a wooden shed that fit well with the surroundings was constructed. The remediation equipment consists of an electrical power supply unit, a groundwater and soil vapor treatment unit, and a vapor extraction unit (Divisio unit). This is a computerized system consisting of numerous electrical valves, which make it possible for individual extraction filters to be activated separately. In order to maintain heat economy in the subsurface, a low pumping rate is used. Pumping takes place via a dense network of extraction wells positioned between the electrodes. The wells are not pumped at the same time but in succession and only for a short period. In this way, only small volumes of groundwater with relatively high concentrations of contaminants are extracted. Choice of Temperature Levels Observing some physical parameters of VOCs and their azeotropes, such as boiling point, vapor pressure, and dissolution product, it would seem desirable to raise the temperature as high as possible in order to "hou" the VOCs out of the soil. There are several reasons why this approach is not applied. First, temperatures above 100 C in the unsaturated zone can only be reached with high (radio) fi-equency heating, a very costly technology that is constrained by many regulations. Much less energy is required to heat soils up to 100 C using lower frequencies (50 or 60 Hz). However, at such temperatures, biological activity is suppressed. Finally, most of the equipment and materials used 72 Remediation D01: rem 2006 Wiley Periodicals, Inc.

5 REMEDIATION Winter 2006 for under- and aboveground infrastructure, such as pumps, extraction filters, and electrode filters, are damaged by contact vvith aqueous solutions and gases containing free or dissolved VOCs at such relatively high temperatures. Therefore, special expensive equipment and materials need to be installed. For these reasons, maximum temperatures are limited to 70 to 80 C. Temperatures of 70 to 80 C, however, should only be applied in a treatment area that is outside buildings. Wherever occupied structures are involved, temperatures have to be kept to a maximum of 40 to 50 C, for the following reasons: Experience with electro-bioreclamation projects in residential areas and underneath manufacturing facilities has shown that ground temperatures above 50 C may affect the mechanical properties of day and argillaceous sand, resulting in soil compaction and, subsequently, in subsidence. Relatively high temperatures in the soil under the floors of houses will ultimately increase the temperature of the floor itself, making living conditions unacceptable for residents as well as possibly affecting underground cables, ducts, and household devices, such as computers, televisions, and stereo equipment. RESU LTS Intensive In Situ Remediation of the Source (First Phase) Once the in situ system was installed in the source area, the electrodes were activated and, within 60 days, the temperature in the soil, measured at 3 m bgs, reached approximately 40 C (Exhibit 3). LEGEND Area between 16 and 20 C Area between 20 and 25 'C Area between 26 and 30 C Area between 30 and 40 C Area > 40 G Exhibit 3. Heat development during heating by electro-reclamation 2006 Wiley PeriodicaIs, Inc. Remediation D01: rem 73

6 Successful Combination of Remediation Techniques Exhibit 4. VOC degradation by intensive remediation in the source area (MW 623) During the first year, the concentrations measured in Monitoring Well 623 (Exhibit 4) showed a trend that is typical for remediation based on electro-bioreclamation: an initial increase in groundwater concentrations, as a result of desorption of the contamination from the soil, followed by a reduction of these concentrations due to groundwater extraction and biological degradation. MonitoringWell 623, which was placed at the heart of the source area, contained the highest concentrations of PCE at the start of the remediation. The change in the concentrations of VOCs at the site is shown in Exhibit 5. The exhibits show the presence and steady reduction of PCE and TCE during the first two years. As soon as the highest concentrations disappeared, switching off the electrical current to stop the heating ended the first or intensive phase. Overall, a total of 80 kg of VOCs were removed during the heating phase. PCE and TCE were no longer present in the groundwater in most of the monitoring wells, and the concentrations in the soil complied with target values. However, c-dce and VC concentrations were still too high. These residual contaminants were removed during the next phase, enhanced natural attenuation, by stimulating the microorganisms through additional injection of nutrients and electron donors. Enhanced Natura! Attenuation (Second Phase) Degradation Conditions The natural redox conditions at the site are iron reducing to sulfate reducing. Under these circumstances, degradation of PCE to c-dce is possible (Van Agteren et al., 74 Remediation D01: rem C) 2006 Wiley Periodicals, Inc.

7 REMEDIATION Winter 2006 Phase 1: Heating & extraction Exhibit 5. The change of VOCs during the intensive remediation phase 1998). However, further degradation of c-dce to VC and ethylene and ethane does not normally take place. Only when redox conditions are changed into more favorable anaerobic (methanogenic) conditions will further degradation occur. To create anaerobic (methanogenic) conditions, sufficient amounts of a carbon source and nutrients have to create a strongly reducing (methanogenic) environment. When the right conditions have been attained and a carbon source and nutrients are available, reductive dechlorination will start. Carbon Source and Nutrients To check whether sufficient amounts of a carbon source and nutrients are injected, the total organic compound (TOC) level in the groundwater should be determined. In general, a TOC level of approximately 20 mg/l is suitable for reductive dechlorination. Higher TO C levels are also suitable, as long as acidification is prevented. The exact TO C concentration needed is calculated on the basis of the concentrations of nitrate, sulfate, and VOCs present at the site. The concentrations of the nutrients nitrogen and phosphorus are calculated on the basis of a C:N:P mass ratio of 250:10:5. At this site, the groundwater contains high levels of sulfate and, therefore, the concentration of TO C in the groundwater needed to be increased to at least 30 to 50 mg/l. This was achieved by injecting an aqueous mixture of the carbon source and nutrients into the ground using compressed air and an injection tube: the tube is brought down to the required depth, where compressed air is blown into the formation, resulting in the creation of an air bubble inside the groundwater. The nutrient solution is then injected through the same tube and atomized into the ground and groundwater via the air bubble. The tube is C) 2006 Wifey Periodicals, Inc. Remediation D01: rem 75

8 Successful Combination of Remediation Techniques Exhibit 6. Injected amounts of carbon source and nutrients Intensive Phase Attenuation Phase Attenuation Phase* Substance (3 Injections) (6 Injections) (3 Injections) Total Carbon Sources Acetate (kg) ,100 Lactate (kg) Ethanol (L) Molasses (L) Protamylasse (L) Nutrients Calgon-P (kg) Ammonium chloride-n (kg) * Since November 2004, only protamylasse was injected. Bacteria can easily consume this carbon source, and it also contains nutrients such as nitrogen and phosphorus. then pulled up 0.5 or 1 m, and the procedure is repeated. The relative low amount of compressed air used does not change the originally anaerobic conditions to aerobic conditions. Exhibit 6 shows the amounts of carbon source and nutrients that were injected. The importance of a carbon source for reductive dechlorination is clearly illustrated by Monitoring Well 623 (Exhibit 7). As a result of the carbon-source injections, sulfate is reduced, followed by the reduction of PCE and TCE and the formation of ethylene and ethane within a time frame of just nine months. PCE and TCE degraded from respectively 100 and 1,200 p.g/l at Day 670 to 0 and 0.2 pg/l at Day 953. Bacterie! Population The degradation of c-dce to VC and ethylene/ethane requires a specific bacterial population. So far, only one microorganism (Dehalococcoides ethenogenes) is knovvn to be capable of completely biodegrading highly chlorinated ethylenes (PCE, TCE, and c- DCE) into harmless ethylene and/or ethane. Many other microorganisms are capable of degrading PCE and TCE but are incapable of dechlorinating c-dce. Exhibit 7. TOC, sulfate, ethylene, and ethane concentrations measured in MW 623 PCE TCE TOC Sulfate Ethylene Ethane Date; day (PD/L) (PD/L) (mg/l) (mg/l) (pg/l) (pg/l) ; , n.d.* n.d.* ; < n.d.: not detected. * Almost no biological degradation of PCE and TCE; therefore, ethylene and ethane concentrations were probably very low. 76 Remediation D01: rem 2006 Wiley Periodicals, Inc.

9 REMEDIATION Winter 2006 Phase 2: Enhanced biodegradation Exhibit 8. The change of VOCs by ERD during the attenuation phase The results obtained by applying BRD are presented in Exhibits 8 and 9. At the end of the intensive phase on May 26, 2003, 750 days after the start of the remediation, PCB and TCE had been removed from the soil particles and biologically degraded to c-dce. During the following attenuation phase, which lasted two-and-ahalf years, enhanced bioremediation was responsible for the degradation of c-dce into VC and finally into ethylene and ethane. This confirms the presence of Dehalococcoides ethenogenes at the site. Overall, the results are satisfactory. VOCs were biodegraded far below the target value of 100 ug/l in groundwater. Based on the monitoring results, redox conditions are still favorable, and therefore it is expected that the residual concentrations will be further degraded into the harmless end products ethylene and ethane. CONCLUSIONS After unsuccessful pump-and-treat remediation at the site for many years, a new method for cleaning up the site cost-effectively was investigated. Full-scale electro-bioreclamation, a combination of electrical heating, groundwater and soil vapor extraction, and enhanced reductive dechlorination, was applied to demonstrate that this in situ technique was capable of removing VOCs from a clayey soil. In addition, it was important to use a technology that would be acceptable to the inhabitants of an upscale residential area in Zeist, the Netherlands. During the intensive phase, which involved two years of electrical heating combined with BRD in the source area, 80 kg of VOCs were removed. After another two-and-ahalf years of enhanced reductive dechlorination in the source and plume areas, the atten Wiley Periodicals, Inc. Remediation DO!: rem 77

10 Successful Combination of Remediation Techniques.-:: ") g 1500 t c (-) Days after the start of the attenuation phase 0 PCE - - -NE - -TCE A----C-DCE X VC Target vaiue Exhibit 9. VOC degradation by ERD in the source area (MW 623) uation phase, the VOC concentrations were reduced far below the target value of 100 ug/l ofvocs in groundwater. Redox conditions are still favorable, and, with continued biopolishing, it is expected that the remaining residual compounds will be degraded into ethylene and ethane within a year. A total volume of 7,200 m3 of soil and groundwater, which was contaminated with maximum concentrations of 100,000 pg/l of PCE in the groundwater and 190 mg/kg of dry matter in the soil, was remediated within four-and-a-half years. By terminating electrical heating at the right time and switching to ERD, electro-redamation in combination with ERD has been shown to be a cost-effective in situ remediation technique. It has also been demonstrated that, with appropriate measures, this technique can be applied in residential areas without any adverse effects to the residents. REFERENCES Doelman, R, et al. (1997). Afbraak van per- en trichlooretheen onder sequentiële redoxomstandigheden. Gouda: CUR/NOBIS. Lageman, R., 8( Pool, W. (2001, April). Thirteen years of electro-reclamation in the Netherlands. EREM 2001, Third Symposium and Status Report on Electrokinetic Remediation, Karlsruhe. Lageman, R., & Pool, W. (2005). Electro-reclamation, a versatile soil remediation solution. Engineering Geology, 77, Remediation DOI: rem 2006 Wiley Periodicals, Inc.

11 REMEDIATION Winter 2006 Schlegel, H. G. (1986). General microbiology (6th ed.). Cambridge, UK: Cambridge University Press. Van Agteren, M. H., Keuning, S., & Janssen, D. B. (1998). Handbook on biodegradation and biological treatment of hazardous organic compounds. Dordrecht: Kluwer Academic Publishers. Van Bemmel, J. B. M. (2001). Evaluatie deelsanering voormalige zilverfabriek Nieuwpoort: Deelgebieden 1,2, en 3. Gemeente Liesveld; wbb-code ZH/312/002. Anneke Roosma is an assistant project leader employed at Bioclear Kv. in Groningen, the Netherlands. Her working experience includes consultancy projects in the field of biological in situ soli remediation and biofilm formation. She received her M.Sc. degree in environmental technology from Wageningen University and Research Center (the Netherlands). Bas Godscha I k is a project manager of remediation projects in the Netherlands and responsible for the development of remediation projects in Japan and China. He received his M.Sc. degree in geochemistry from Utrecht University (the Netherlands) in Reinout Lageman is director and principal consultant of Lambda Consult and senior advisor of Holland Milieutechniek. He received his M.Sc. degree in structural geology, geophysics, and hydrogeology from Leiden University (the Netherlands) in Maurice Henssen, M. Eng. Chemical Engineering (University of Eindhoven, the Netherlands), is associate director of Bioclear. In the past 13 years, his work was mainly focused on being a project leader and project manager on in situ soil remediation projects and processes. He initiated and managed various projects in which new remediation concepts were developed. Marc van Bemmel, M.Sc. Environmental Technology (Wageningen University, the Netherlands), is a project leader at Bioclear. He has been leading the project at Zeist since His work experience includes a great number of projects on natural attenuation and enhanced reductive dechlorination in the Netherlands and in Denmark Wiley Periodicals, Inc. Remediation D01: rem 79

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