Using the dry-tomb technique in the remediation of heavily contaminated land. D. Kaliampakos, D. Damigos and T. Karachaliou

Transcription

1 375 Using the dry-tomb technique in the remediation of heavily contaminated land D. Kaliampakos, D. Damigos and T. Karachaliou School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece The paper deals with the biggest remediation project of mining brownfields in Greece. The project is taking place at a former mining and metallurgical site in Lavrion. Contamination of the soil is characterized by two basic parameters: high concentration levels of heavy metals, exceeding commonly applied thresholds by several orders of magnitude and significant heterogeneity in vertical and horizontal distribution due to successive deposition of wastes over the years. The remediation project provides for the excavation, transportation and disposal of contaminated soils (approximately 113,000 m 3 ) at an on-site repository, especially designed for that use. The technique applied is the dry-tomb method, which aims at the secure deposition of the contaminated soil into a water-tight construction. In this paper, the general concept of the project, the applied approach and the technological solutions to various problems are described. Furthermore, financial data both in terms of cost breakdown and comparative analysis with alternative remediation techniques are given. Keywords: Soil contamination; Heavy metals; Risk management; Remediation cost; Containment; Dry tomb 1. Introduction Contaminated land, as a result of uncontrolled mining or other industrial activities, has been a major concern in modern world during the last decades. There is currently no official data on the exact number of contaminated sites. So far, few countries have made surveys or other activities to specify the extent of the brownfield problem in terms of estimating the total size of land that is covered. For example, in Germany 128,000 ha, in the United Kingdom 39,600 ha, in France 20,000 ha, in the Netherlands between 9,000 and 11,000 ha, and in Belgium / Walloon about 9,000 ha of brownfields were estimated or identified (Ferber & Grimski, 2002). In total, it is estimated that there are more than 1,500,000 possibly contaminated sites in Europe. The cost to remediate all those sites would exceed 100 billion Euros (Carrera & Robertiello, 1993; EEA, 1999). In general, there are two ways to manage contaminated soil with regard to the so-called pollutant linkage, either by removing- modifying the source of the pollution or by cutting off the pathway (Nathanail et al, 2002; CLARINET, 2002). Treatment based approaches apply in the first category since they destroy, remove or detoxify the contaminants contained in the polluted material. They can be Corresponding author. dkarachaliou@metal.ntua.gr

2 376 described as biological, chemical, solidification- stabilization or thermal processes including technologies such as bioremediation, chemical oxidation/reduction, soil flushing, soil washing, solvent extraction, thermal desorption, vitrification, etc. The second category consists of two basic approaches: excavation and containment (e.g. removal to landfill or deposition within an on-site engineered cell), or in situ physical containment by means of engineering systems (in-ground barriers, capping and cover systems, hydraulic containment, etc.) (US EPA, 1997; Bridle). In this paper the biggest, so far, remediation project that is being carried out in a former industrial complex in Greece is presented. Special characteristics with regard to the concept, the applied technology and the precautions taken are highlighted. Further, financial data and the selection of the specific remedial action on a cost-effectiveness basis are discussed. 2. The Lavrion Technological and Cultural Park case 2.1. Description of the environmental problem- risk assessment results The site under investigation is a historical landmark of the Greek industrial past. It is situated in Lavrion, Athens, within an area of 24.5 ha. Its industrial history finds its roots in the 7 th century BC as an ancient mining complex. In the 19 th century, the site accommodated a metallurgical company, the most important industry in Greece at the time. When all industrial activities ceased permanently in the early 1990 s, a severe environmental problem was left behind posing high risks to human health and the environment. In 1995, the National Technical University of Athens (NTUA), recognizing the historical importance of the site and its strong potential towards the regeneration of the entire area that was suffering from high unemployment, took the initiative to redevelop the site as a Technological and Cultural Park (LTCP). However, an evident prerequisite for the realization of this vision was the solution of the environmental problem. An environmental site assessment was conducted. The results of sampling analysis indicated that the situation was characterized by two basic parameters: the extremely high concentration of several toxic contaminants and their strong heterogeneity (Karachaliou & Kaliampakos, 2005). The site was divided into four zones, based on historical data related to the nature and origin of the contaminated soils. Risk was estimated for the entire site as a whole as well as for each zone. Table 1 lists the 95% upper confidence limit (UCL) mean concentration of the contaminants in top soil in comparison with the corresponding German soil protection limits. Figure 1 provides a map of a sub-area of the site showing the distribution of arsenic concentration at various depths. Table 1. 95% UCL mean concentration of the contaminants in topsoil (ppm)

3 377 Contaminant As Cd Pb Cr Cu Mn Ni Zn 95% UCL of the mean 8, , ,253 11, ,644 German trigger values for industrial and commercial sites , Depth: 0 m Depth: 1 m Depth: 2 m Figure 1. Distribution of As concentration in various depths In order to define the actual risk posed to indoor and outdoor workers at the LTCP both deterministic and probabilistic risk assessments were conducted for ingestion, dermal contact and inhalation pathways (Karachaliou et al., 2007). Some synoptic results are presented in Table 2. Table 2. Deterministic and probabilistic risk assessment results Target group Risk model Deterministic Probabilistic (probability of exceeding the acceptable risk limits*) Indoor Cancer risk 4.5E % workers Noncancer risk % Outdoor Cancer risk 2.8E % workers Noncancer risk % *Acceptable risk levels: cancer: E-06, non-cancer: 1 Risk assessment indicated that the acceptable risk limits were almost certainly exceeded. More specifically, with regard to the probabilistic model, the probability for cancer risk to exceed the acceptable levels was more than 99% while the probability for noncancer risk to exceed the limits was approximately 64% for indoor and 97% for outdoor workers. Deterministic results, based on the mean concentration of the contaminants, also exceeded the limits in most of the cases. The most susceptible population to risk was outdoor workers. Risk was posed to humans mainly through the ingestion pathway, followed by dermal contact and inhalation. Significant diversity in risk was also observed between the different

4 378 subareas. Further, sensitivity analysis showed that the most critical parameter affecting the estimated risk result was arsenic concentration. 3. The LTCP dry tomb repository 3.1. General concept Selection of the remediation technique The selection of a remedial action is generally based on specific criteria, such as elimination of the risk to human health and the ecosystem, technical feasibility and suitability, cost, effectiveness in the short and in the long term, etc. (USEPA, 1996, 1997; Bardos et al, 1999 & 2002; Janikowski et al, 2000; Postle et al; Vegter, 2001; CLARINET, 2002). Table 3 presents some of the soil remediation technologies and indicative costs provided by CLARINET (2002) and compiled by the authors. Table 3. Costs of remediation technologies for soil contamination General category Remediation technology Indicative unit price ( ) Excavation and Excavation and disposal to landfill 74/m 3 containment In situ physical Engineering capping 22-44/ m² containment by means of Encapsulation (shallow cut-off wall) 59-89/ m² engineering systems Encapsulation (deep cut-off wall) / m² Treatment Bioremediation 52-67/ tonne Vitrification 59/ tonne In-situ vitrification (5t/hr) / tonne Soil washing 45-52/ tonne In situ chemical oxidation / m 3 Soil washing ex situ / tonne Stabilisation/ Solidification ex situ / tonne Landfarming 48/ tonne Pump and treat / tonne Source: Compiled on the basis of CLARINET (2002) data In general, treatment technologies act on the source of the problem, but they are effective on specific contamination agents. Hence, the presence of multiple toxic substances in the soil may require a combination of treatment technologies in order to completely eliminate risk. Containment options, on the other hand, can be applied to the entire range of soil contaminants. Yet, there is a continuing debate on the effectiveness of containment technologies, in the long-term, as far as the sealing systems are concerned (Lee & Jones-Lee, 1997 and 2000). In the case presented, the restoration target was to practically eliminate human health risks and to minimize environmental threats, as much as possible, over the entire area of concern within a predetermined restoration budget of 3.5 million Euros. Bearing in mind the site-specific characteristics (i.e. area and volume of the contaminated land, presence of multiple contaminants, etc.), a combination of timeand cost-consuming treatment technologies would be required in order to fulfill the cleanup requirements. To put matters in perspective, the remediation cost using treatment technologies was estimated to be from 7 million to more than 70 million

5 379 Euros. Considering the available funds, the application of treatment technologies over the entire area would be completely prohibitive. The latter stands also for the encapsulation techniques, given that the contaminated land covered an area of about 60,000 m 2 ; the estimated restoration cost was at least 4 million Euros and could climb even higher to 10 million Euros. Capping of contaminated soils, although affordable, was only a short-term solution and, in addition, could not sufficiently prevent the spread of contamination due to the infiltration of rainwater or the contact with shallow groundwater. Hence, it was inconsistent with the established cleanup requirements. Finally, excavation of the contaminated soils and disposal to a hazardous waste landfill not only was impractical, given the lack of hazardous waste repositories in Greece, but would also be unaffordable. Even if an appropriate landfill existed in the surrounding area, the total cost would be as high as 8 million Euros. Taking into consideration the above remarks, the cleanup project provides for the excavation, transfer and disposal of the contaminated soil at an on-site repository, using the so-called dry tomb technique in order to secure the deposition of the contaminated soil into a water-tight construction, and the backfilling of the excavated areas with clean soil. Figure 2 shows the areas that were excavated and the location of the repository. Figure 2. Map of the site- location of the dry tomb The construction of the repository within the boundaries of the LTCP facilitated the location and permission procedures. However, due to the particular character of

6 380 the entire complex, there were very strict environmental and land-use standards that limited the landfill to an area of 18,500 m 2 and capacity of 113,000 m 3. The lining system, which is the critical point against environmental impacts, was designed according to European standards specified in the Council Directive 1999/31/EC for hazardous waste landfill. The main steps of the landfill construction in LTCP were, as follows: Preparation of the area in which the landfill would be placed. Construction of the lower (base) part of the landfill. Transportation and placing of the contaminated soils. Construction of the upper part of the landfill. Construction of stormwater system. Installation of monitoring system. The design of the landfill was based on sophisticated analyses with respect to stability hazards, leachate production, expected stormwater runoff and erosion phenomena, etc. Nevertheless, for conciseness reasons, this section focuses only on construction issues and characteristics Site preparation The preparation of the area in which the landfill would be constructed was the first working phase of the project. The construction began with the cleaning and excavating of the existing terrain at an average depth of 3 m (Fig. 3). The excavation material consisted of contaminated soil, namely metallurgical slags, and marble, which is the geological bedrock of the area. The total volume of the excavation was 54,850 m 3. The contaminated soils and the crashed marble stone were temporarily stored in two different heaps. After the construction of the base, the soils were placed in the landfill, while marble stones were used as filling material for the excavated zones outside the area of the landfill. The basement was foreseen to be with a slope in a way to make possible the drainage of the leachate. In addition, the slope should ensure the stability of the disposed material and the artificial sealing system. Towards this direction, the sides were constructed with a maximum inner slope of 1:3 and the base with a minimum gradient of 3%.

7 381 Figure 3. General outline of the basement construction 3.3. Construction of the lower part of the landfill The lower part of the landfill involved the construction of the containment and leachate drainage and collection systems. Artificial systems were selected instead of geological barriers and drainage layers, i.e. clay and gravel, given that they provided better performance and increased volume capacity. More specific, the artificial sealing system consisted of the following items (from the lower to the upper level): a 4.5 mm thick protective non-woven polypropylene geotextile (800 gr/m 2 ) an 8/10 mm (dry/wet) thick Geosynthetic Clay Liner (GCL) comprised of a bentonite layer placed between two geotextiles, achieving hydraulic conductivity of 1, m/s and a 2.5 mm thick double-sided textured high density polyethylene geomembrane. The above sealing system was superior compared to the requirements of the Council Directive 1999/31, according of which any artificial barrier for hazardous waste landfills should be at least equivalent to a geological barrier with K m/s and thickness 5 m. For K= m/s, the thickness of the layer is estimated at 0.5 mm, well below the 8 mm thick GCL selected. The leachate drainage system was placed on the basic lining system and it consisted of a 16 mm thick 100% HDPE geosynthetic drainage layer and a nonwoven polypropylene geotextile (250 gr/m 2 ) for the protection of the geosynthetic

8 382 drainage product from the disposed material. For the collection of the leachate, a 154 m long perforated leachate collection pipe (D = 500 mm) was installed. The leachate is directed to a collection area and is pumped out through a discharged pipe to a tank. Details are shown on the following drawings (Fig. 4 & 5). Figure 4. Details of the containment and leachate drainage layers at the base of the landfill Figure 5. Details of the leachate collection system at the base of the landfill

9 Transportation and placing of contaminated soils After the preparation of the lower part, about 2,500 m 3 of contaminated soils were excavated, transported and disposed of in the landfill each day. In total, 113,000 m 3 of different types of contaminated land were placed in the repository. The contaminated soils were compacted to 95% of modified Proctor density at the optimum moisture content to meet a maximum saturated hydraulic conductivity. The surface and subsurface profiles of the excavations were determined from the environmental site assessment. The voids created from the excavations were backfilled using marble crashed stone from the earthworks carried out at the site of the landfill and aggregates from the surrounding area. Samples were taken from the backfilling material, which were analyzed for physical and chemical properties prior to any approval of use. The characterization of the samples, as far as the concentration of heavy metals or other elements is concerned, was based on the German soil standards (Federal Soil Protection and Contaminated Sites Ordinance) for residential areas Construction of the upper part of the landfill The upper part of the landfill was constructed after the total transportation and placing of the contaminated soils. This phase consisted of the construction of the upper sealing layer, the installation of the drainage system and the placement of the topsoil. The different layers of the sealing and drainage systems included the following (from the lower to the upper level): a 4.5 mm thick protective non-woven polypropylene geotextile (800 gr/m 2 ) an 8/10 mm thick (dry/wet) Geosynthetic Clay Liner (GCL) comprised of a bentonite layer placed between two geotextiles, achieving hydraulic conductivity of 1, m/s and an 1.0 mm thick double-sided textured high density polyethylene geomembrane a 10 mm thick 100% HDPE geosynthetic drainage layer and a non-woven polypropylene geotextile (250 gr/m 2 ). According to the legislative requirements, a 1 m thick topsoil cover will be placed. The concentrations of heavy metals and other chemical elements in the topsoil should be as close as possible to the trigger values set by German standards for residential areas. In any case, the concentrations should not exceed the trigger values set by German standards for park and recreational areas. As far as the shape of the final surface is concerned, two plateaus were formed at +28 m (area: 8,000 m 2 ) and + 33 m (area: 1,400 m 2 ), respectively. The slope of the inner, as well as the outer walls is limited to 1:3 maximum, in order to minimize erosion phenomena and to avoid any stability risks. The general outline of the final surface is depicted in Figure 6.

10 384 Figure 6. General outline of the final surface of the landfill 3.6. Construction of the stormwater drainage system The stormwater drainage system consists of drainage ditches and a pump station. In designing the facilities, discharge rates were determined by calculating the existing conditions flow rate based upon a 50-year storm event. Stormwater concrete drainage ditches were built around the perimeter of landfill as well as on top of its final surface to collect stormwater and divert it away (Fig. 6). Although topography is such that allows discharging the stormwater directly to an adjacent stream, the drainage ditches collect stormwater runoff to a pump station. This design was adopted as a sustainable solution in order to reuse the stormwater for the enrichment and improvement of the quality of groundwater table Installation of monitoring systems Taking into account that the repository lies in the vicinity of a residential area and within an operating commercial site, an integrated environmental monitoring system was designed and was implemented prior to the beginning, during the construction and after the completion of restoration works. The main purpose of the prerestoration campaign was to gather background values in order to evaluate the

11 385 baseline air quality and water quality characteristics. During construction of the repository, the environmental monitoring system aimed to ensure that restoration works would not affect activities and people in the vicinity. Finally, after construction is completed, long-term monitoring records will provide necessary data to estimate the effectiveness of restoration works (i.e. the improvement of groundwater quality), as well as to detect any potential impacts from the facility. Given the project characteristics and the legislative requirements, the following parameters were recorded: Climate data (e.g. temperature, wind speed and direction, etc.). Climate parameters were collected through a meteorological station installed at the site. Air quality data (e.g. dust emissions from earthmoving works and from truck movements for transportation of contaminated soils to the landfill, etc.). Data collection was carried out by two PM-10 high volume samplers (Hi- Vol) and a PM-10 TEOM real-time continuous monitor. All the devices were installed adjacent to the landfill on the ground level. Surface water and groundwater quality data (e.g. ph, heavy metals, suspended matter, etc.). For the collection of groundwater samples, six monitoring wells were constructed. Prior to selecting the location and depths for groundwater monitoring wells, the appropriate factors (e.g. topography, geologic formations, hydrologic and hydrogeologic characteristics, aquifer characteristics, etc.) were taken into account. Two of the wells were constructed along the up-groundwater-gradient and four of them along the down-groundwater-gradient perimeter of the landfill. Surface water samples will be periodically collected from stations installed uphill and downhill from the landfill. Leachate data (e.g. volume, chemical composition, leakage, etc.). Leachate volume will be measured through a vertical concrete shaft constructed at the lower level of the landfill base, while the quality of leachate will be monitored through samples taken from a collection pipe. In order to identify potential leaks, a particular below-liner system was constructed at the lower level of the landfill, comprised of an excavation with dimensions of 40 m by 3 m by 1 m in depth (Fig. 6). The bottom of the excavation was sealed by means of an impermeable mineral layer of 30 cm and a 2.5 mm thick geomembrane placed between two geotextiles. At the deepest point of this excavation a HDPE collection pipe was installed. The excavation void was filled up to the level of the lower sealing system by gravel of 32/64 mm (Fig. 7). Settlement / subsidence phenomena. Given that the contaminated soils have consolidated, the chance of differential settlement or subsidence is very small. Nevertheless, in order to record any subsidence phenomena, a coordinated network comprised of 18

12 386 observation points will be installed. The results of the annual monitoring survey will be a topographical map that can be compared with the baseline to determine if subsidence has occurred and at what extent Cost Figure 7. Details of the leak detection system below the lower sealing liner The total cost of the project was estimated at 3.5 million Euros covering the excavation, transfer and disposal of contaminated soils, the sealing and leachate collection systems, the environmental monitoring, sampling and analysis, the equipment, etc. The total cost of the project corresponds to approximately 31 euro per m 3 or 16 Euros per ton of disposed contaminated soil. Figure 8 illustrates the cost breakdown. Apparently, the lining systems and the top cover was the most expensive component, costing almost 50% of the total budget, followed by the excavation, transfer and disposal of contaminated soils (approximately 28%) and the environmental monitoring, sampling and analysis (about 14%). The leachate collection system and the corresponding equipment (e.g. pumps, monitoring devices, etc.) were far less costly.

13 387 Liners/ barrier systems- top cover 47% Leachate collection systems 2% Environmental Equipment and monitoring system supply 3% 2% Excavation, transfer and disposal of contaminated soil 28% Infrastracture 4% Environmental monitoring, sampling and analysis 14% Figure 8. Cost breakdown of the dry tomb 4. Conclusions In order to balance fiscal constraints with cleanup targets, a particular application of the dry tomb technique was selected; the contaminated soil was excavated and it was buried at a repository constructed within the boundaries of the LTCP. In other words, the method was practiced ex-situ but on-site. This approach met all the restoration requirements and it reduced transportation cost to a minimum. The latter contributed to a highly cost-effective solution. In addition, it prevented off-site pollution due to spreading of contaminants during transportation and it shortened the completion time of the project. Finally, there is another parameter that should be noted with regard to the sustainability of the method selected. As it has already happened twice in the past in the area of concern, there is a strong possibility that the contaminated soil of the site will be exploited again in the future. What is now considered to be a hazardous waste, tomorrow, given the depletion of mineral resources, could be considered as a worth exploiting, profitable ore. For example, the average concentration of lead in the contaminated soil is about 5%, while a lead-rich ore has a typical concentration range of 3-8% lead. From this point of view, the most sustainable solution, waste recycling could be attained. Notes on contributors Dr. Dimitris Kaliampakos is a mining engineer- metallurgist and an Associate Professor at the School of Mining and Environmental Engineering of the National Technical University of Athens. He is specialized in environmental impacts of mining, soil rehabilitation, brownfields, etc. He has published over 100 scientific papers. Dr. Dimitris Damigos is a Lecturer in the School of Mining & Metallurgical Engineering of the National Technical University of Athens (NTUA), Greece. He graduated from the School of Mining & Metallurgical Engineering in 1995 and he obtained his PhD in Environmental Economics in 2001.

14 388 His research interests include environmental valuation studies, mining economics, cost-benefit analyses, and environmental management. He has published over 35 scientific papers. Mrs. Theodora Karachaliou is a mining engineer- metallurgist and currently a PhD student at the School of Mining & Metallurgical Engineering (National Technical University of Athens), Greece. Her research is mainly focused on brownfields, risk assessment and risk management in contaminated lands. References Bardos, P., Martin, I. and Kearney, D., Framework for evaluating remediation technologies, IBC s 10 th Conference, Contaminated Land, London, July Bardos, P., Nathanail, J., Pope, B., General principles for remedial approach selection, Land Contamination & Reclamation, Volume 10, Number 3, 2002, pp (24). Bridle, T., Possible Technologies in Hazardous/Industrial Waste Treatment Precincts, Technical Paper A, Available at: %20Precincts%20for%20printer1.pdf Carrera, P., and Robertiello, A., Soil clean up in Europe - feasibility and costs. In: Eijsackers, H. J. P. and Hamers, T. (Eds). Integrated soil and sediment research: a basis for proper protection. Kluwer Academic Publishers, Dordrecht, The Netherlands, 1993, pp CLARINET, Remediation of Contaminated Land. Technology Implementation in Europe. A report from the Contaminated Land Rehabilitation Network for Environmental Technologies, European Council, Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste, Official Journal L 182, 16/07/1999, p European Environment Agency, Environment in the European Union at the turn of the century. Soil degradation, Ch. 3.6, (1999), pp Federal Ministry of the Environment, Federal Soil Protection and Contaminated Sites Ordinance note. (Bundes-Bodenschutz und Altlastenverordnung BbodSchV), Federal Law Gazette I p. 502, Ferber, U. and Grimski, D., Brownfields and redevelopment of urban areas, Austrian Federal Environment Agency on behalf of CLARINET, (2002), pp Janikowski, R., Kucharskiand, R. and Sas-Nowosielska, A., Multi-criteria and multi-perspective analysis of contaminated land management methods, Environmental Monitoring and Assessment 60: , Karachaliou, T. and Kaliampakos, D., Redeveloping derelict urban space, the case study of Lavrio, Greece. CABERNET The International Conference on Managing Urban Land, Belfast, Northern Ireland, UK, Karachaliou, T., Damigos, D., and Kaliampakos, D., Risk assessment in heavily contaminated lands. CEST th International Conference on

15 389 Environmental Science and Technology, September 5th - 7th, 2007, Kos island, Greece, Lee, G. F. and Jones-Lee, A., Evaluation of the Adequacy of Hazardous Chemical Site Remediation by Landfilling, Remediation of Hazardous Waste Contaminated Soils, Marcel Dekker, Inc., NY pp , Lee, G. F. and Jones-Lee, A., Hazardous chemical site remediation through capping. Problems with long term protection, Remediation, 7(4)51-57, Nathanail, J., Bardos, P. and Nathanail, P., Contaminated Land Management: Ready Reference, EPP Publications and Land Quality Press, Postle, M., Fenn, T., Grosso, A. and Steeds, J., Cost-benefit analysis for remediation of land contamination, R&D Technical Report P316. U.S.EPA, Office of Emergency and Remedial Response, Technology Alternatives for the Remediation of Soils Contaminated with As, Cd, Cr, Hg, and Pb, Engineering Bulletin, U.S.EPA, Rules of thumb for superfund remedy selection, EPA 540-R OSWER PB , August U.S.EPA, The role of cost in the superfund remedy selection process, Office of emergency and remedial response, EPA 540-F , OSWER FS, NTIS: PB , Vegter, J., Sustainable contaminated land management: a risk-based land management approach, Land contamination & reclamation, Volume. 9, Number 1, (4470 words)