Theme E: Remediation Concepts & Technologies Lecture Session (Les): E.16 Special Subjects-1 THE REMEDIATION OF THE ACID TAR LAGOONS AT RIEME, BELGIUM.

Pensaert Stany, De Puydt Sven, Janssens Tom 1 - DEC NV (DEME Environmental Contractors) Vanpée Natacha 2 – Total Belgium Vander Velpen Bart, De Cock Carl, Goorden Geert 3– Haskoning Belgium

1DEC NV (DEME Environmental Contractors) Haven 1025 – Scheldedijk 30 2070 Zwijndrecht Belgium tel. +32 3 250 54 11 fax +32 3 250 52 53 pensaert.stany@dredging.com www.decnv.be

2 TOTAL BELGIUM - HSEQ Handelsstraat 93 Rue du Commerce 1040 BRUSSEL - BRUXELLES Belgium tel: + 32 2 288 95 13 fax: + 32 2 288 37 87 natacha.vanpee@total.com www.total.be

3 Haskoning Belgium BVBA Hanswijkdries 80 2800 Mechelen tel: +32 15 40 56 25 fax: +32 15 40 56 57 b.vandervelpen@haskoning.be www.royalhaskoning.com

Key words: acid tar, stabilisation, solidification, design and build, controlled containment, complex water treatment. Abstract Acid tar is a residue of the chemical refining of oils by means of oleum – concentrated sulphuric acid. Oleum was added to the oils in order to extract impurities and heavy molecules, which were trapped in a tarry product. After decantation of the tar, the oil was filtered with active clays to remove the residual tar and acid. In the period this process was applied (early and middle 20th Century) it was common practice to dump both acid tar and the spent Fuller’s Earth filter cakes in lagoons near the production site. In Rieme, along the canal Ghent-Terneuzen, three large acid tar lagoons were present. The composition of the acid tars, which came from the production of white medicinal oils, varied in function of the period of production and the age of the tars. The largest lagoon, comprising an area of about 2 hectares, contained the oldest tars dating from before World War II. Here a mixture of solid and very viscous tars could be found. The other two smaller lagoons of both 0.5 hectares contained very liquid tars. In total, about 200.000 ton of lagoon material was present. As the lagoons were not lined and the site was intensively bombed during World War II, a serious pollution problem was caused to the subsoil and groundwater. It is obvious that, before any remedial action is taken in the vicinity of the lagoons, the source itself should be eliminated. Therefore the problem owner Total Belgium, together with the environmental consultant Haskoning Belgium, decided to remove the content of all lagoons, neutralize, stabilize and solidify the tars, and put the solidified material in a controlled containment cell on the former lagoon area above the groundwater level. Thanks to the innovative approach for excavation and treatment of the acid tars, DEC was appointed as contractor for the first phase – the source removal - of this remediation. The remediation concept consisted of the following items:

• Excavation of the lagoon materials taking into account the presence of WWII bombs and high potential emissions of SO2.

• Treatment of the tars and clay filter cakes in order to meet stringent geotechnical and chemical requirements.

• Construction of a lined containment cell for the controlled storage of the neutralized, stabilized and solidified tars.

• Treatment of the lagoon water and groundwater by means of a complex physicochemical technology.

The full scale remediation work has started in 2006 and is estimated to be completed by end 2009. Introduction Acid tar is a residue of the chemical refining of oils by means of oleum – concentrated sulphuric acid. Oleum was added to the oils in order to extract impurities and heavy molecules, which were trapped in a tarry product. After decantation of the tar, the oil was filtered over Fuller’s earth to remove the residual tar and acid. In the period that this process was applied (early and middle 20th Century) it was common practice to dump both acid tar and spent Fuller’s earth filter cakes in lagoons near the production site. In Rieme, along the canal Ghent-Terneuzen, three large acid tar lagoons could be found on the premises of Total Belgium. The composition of the acid tar, which came from the production of white medicinal oils, varies in function of the period of production and age of the tars. The largest lagoon, comprising an area of about 2 hectares, contained the oldest tars dating from before World War II. Here a mixture of solid and very viscous tars could be found. The other two smaller lagoons of each 0.5 hectares contain tars of low viscosity. In total, more than 200,000 tonnes of lagoon material was present.

As the lagoons were not lined and the site was intensively bombed during World War II, they caused a serious pollution problem to the subsoil and groundwater. The first phase of the remediation is obviously the elimination of the pollution source. After evaluating off-site treatment solutions, such as cement kiln co-incineration or landfilling, an on-site solution was elaborated. The problem owner Total Belgium, together with the environmental consultant Haskoning Belgium, decided to remove the content of all lagoons, stabilize and solidify the tars, and finally replace the stabilized material in a controlled containment cell on the lagoon area above the groundwater level. Once this source removed, the second phase of the remediation will take place, being the treatment of contaminated soils outside the lagoon area and the third phase consisting of groundwater treatment in the vicinity of the lagoons.

Thanks to the innovative approach with respect to execution of the remediation and approach to stabilization DEC NV (DEME Environment Contractors) was appointed as the contractor for the first phase of this remediation. Within the boundary conditions of the remediation concept that was set up by Total and Haskoning, and agreed with OVAM (Environmental Agency of Flanders), DEC NV worked out the design for the remediation scheme, which mainly consists of: • Methodology of dry excavation of the lagoon materials taking into account the presence of

unexploded ordnance and high emissions of SO2. • Design the mix formulation and design and build of the equipment for the stabilisation/solidification

the lagoon materials in order to meet stringent geotechnical and chemical requirements imposed by Total and OVAM.

• Design and build the BATNEEC water treatment concept for lagoon water and groundwater. • Design and build of the controlled containment area for storage of the stabilised lagoon materials. The actual work was divided into three steps: design & pilot tests (lot A), full-scale commissioning tests (lot B) and full-scale remediation (lot C).

The acid tar lagoons

Acid tars primarily consist of heavy sulphonated hydrocarbon compounds with high residual levels of sulphuric acid. However the nature of acid tars can vary from a low viscous oily substance to hard brittle glassy coal, it is believed that all are emulsions of hydrocarbons, sulphuric acid and water, as this is reflected by water contents of over 40 % w/w. Some examples are shown in Figure 1. As the sulphuric acid concentrations in the tars vary in the range of 1 tot 10 % w/w, the vapour pressure of sulphur dioxide in the material is high and a substantial potential exist in releasing the sulphur dioxide during any handling. The wide range of acid tar types and composition results in very different ways of treatment, as will be illustrated further on. As a result of the high acidity of the tars, a first common step for all types is chemical neutralization. This step is inevitable prior to further treatment. The amount of materials that was present in the lagoon is about 170,000 m³ in total, of which about 40,000 m³ of (semi-)liquid, 40,000 m³ of solid tars, 20,000 m³ of Fuller’s earth, 70,000 m³ of contaminated soil from the dikes and subsoil. In addition, some 10,000 m³ of filter cakes produced in the water treatment will be solidified prior to storage in the on-site containment cell. Figure 2 shows a view on the lagoons prior to remediation.

Figure 1: Left: liquid acid tars; right: hard acid tars.

Figure 2. View on the acid tar lagoons before the remediation started.

LOT A: Design phase and pilot tests during 2004 Although the conceptual framework of the remediation of the acid tar lagoons was defined by Total and Haskoning, a detailed design had to be carried out by DEC NV. This design covered various key aspects of the remediation work:

• Detailed characterization of the various lagoon materials, the lagoon surface water and the groundwater as a basis for the treatment options.

• Define the most cost-efficient treatment method for the various lagoon materials in order to achieve the strict geotechnical and chemical requirements.

• Performing a BATNEEC study for the treatment of the lagoon water and the groundwater by evaluating various water treatment techniques with respect to cost, operational aspects, and robustness for variations in water composition.

• Assess the impact with respect to safety and potential nuisance from the sulphur dioxide emissions during excavation, transport and treatment of the tars. Based on the acquired data, measures were designed for the mitigation of the emissions.

• Work out a tailor-made health and safety risk assessment and appropriate preventive measures.

The design was done in two phases: a laboratory based bench-scale study mainly focusing on the treatment of the lagoon materials and the water treatment in the first half of 2004, followed by large scale pilot trials in the second half of 2004. Meanwhile, the specialized subcontractor ADeDe carried out a historical research in order to assess the potential presence of unexploded ordnance (UXO) in the remediation area. Later on in the project, based on this research, safe excavation areas, free of UXO, were defined.

Areas that could not be declared free of UXO based on historical research, were qualified as potentially dangerous. In these areas, extensive UXO detections were performed by another specialized subcontractor G-tec, a geophysical expert. Anomalies resembling UXO were identified an removed by ADeDe prior to any excavation works in these areas. From the bench-scale study various important conclusions could be drawn:

• For each of the different lagoon materials (liquid, paste, solid acid tars, Fuller’s Earth and contaminated soils) a robust mix formulation was worked out, based on maximum four additives. It was possible to obtain a solid, non-leachable and durable matrix.

• The BATNEEC for the water treatment is the combination of acid neutralization and sulphate precipitation by means of lime, followed by activated carbon adsorption to reduce the complex COD present in the water. Other techniques such as chemical oxidation (UV+Fenton’s reagent, or ozone) and biodegradation proved not effective or too vulnerable to the highly contaminated water.

• In particular from the solid acid tars the sulphur dioxide emissions are extremely high (fluxes up to 500 g/(m².h) have been measured) and require special attention during excavation, handling and treatment. The conclusion was that the treatment plant had to be enclosed in an underpressurized building and the extracted air should be treated in a wet scrubber.

The pilot tests mainly covered two aspects of the project: first of all the treatment of the various lagoon materials with focus on choice of equipment and mitigation of emissions. Secondly a pilot-scale evaluation of the various potential water treatment techniques in order to estimate the real operational difficulties and have a more precise idea of operational costs. Figure 3 below shows the pilot mixing trials, while figure 4 shows the pilot trials needed for the design of the gas scrubber.

Figure 3: Pilot trials for acid tar treatment.

Figure 4: Pilot trials for the wet scrubbing of the extracted gases during treatment. LOT B: Full scale commissioning tests, evaluation and design adjustments: 2005 Based on the outcome of the design phase Total ordered the next step in the remediation work: the construction of the acid tar treatment plant. In order to commission the plant, DEC had to treat 1000 m³ of the various lagoon materials. Meanwhile the excavation, transport, and treatment methodologies and equipment were being evaluated on full-scale and adjusted where needed. LOT C: Full scale remediation: 2006-2009 After commissioning of the treatment plant and all working methods by Total and Haskoning, DEC started the remediation of the lagoons with the excavation of lagoon 2, followed by lagoon 1. The treated tars from these lagoons were put on a temporary storage area, that can be seen at the left hand side of figure 5. The treated tars will stay in the temporary storage area until all lagoons have been remediated, and will then be transferred to the final containment cell. After the excavation of both lagoons, the contaminated subsoil underneath these former lagoons was excavated and treated in the same plant. On the remediated area the first part of the containment cell was installed, in order to store the treated materials from lagoon 3. Figure 6 shows this situation: on the right hand side the containment cell is under construction. At left lagoon 3 which has been covered with a whitish lime slurry to stop the SO2-emissions.

Figure 5: The acid tar treatment plant in its underpressurized hall. Figure 7 shows the filling of this first part of the containment cell by treated tars from lagoon 3. At this time (spring 2008) the remediation of lagoon 3 is still ongoing and is expected to be finished by mid 2009.

Figure 6: View on acid tar lagoons after remediation of lagoons 1 and 2.

Figure 7: Filling of containment cell by treated material. The treated lagoon materials. Stabilisation/solidification of the acid tars and other lagoon materials (Fuller’s Earth and contaminated soil) was chosen as BATNEEC technology for this site. In order to guarantee long-term stability and durability, the treated material had to comply with a stringent set of geotechnical and chemical criteria. In particular the volume increase limit was a challenging criterion, as it limited the amount of additives in the mix formulation. The main geotechnical criteria are listed in table 1 below, together with the average values obtained during full-scale execution. The most relevant chemical leaching criteria are listed in table 2. Unit Average obtained value Objective

Volume increase by treatment

% 25 < 30

CBR % 14 – 50 > 11

Compressibility modulus MPa 15 - 80 > 11

Hydraulic permeability m/s 10-10 to 10-8 < 10-7

Strength loss by ageing (wet/dry – freeze/thaw)

% < 10 < 15

Table 1: Main geotechnical criteria.

Unit Initial value Average obtained

Objectives

pH 0 – 3 10 – 12,5 4 – 13

Water soluble part % on dry matter 5 – 20 1 – 4 < 10

DOC mg/l 3000 – 28000 35 - 150 90 % reduction

Table 2: Main chemical criteria. Conclusions. In the past, various acid tar stabilization projects failed due to a bad mix formulation design. Often lime was used as neutralizing and solidification additive, however with focus on short-term effect rather than on long-term durability. These bad experiences created major reluctance to the stabilization/solidification of acid tars. By consequence various problem-owners choose off-site (co)incineration as conservative but legacy-free solution. For the acid tar remediation project in Rieme-Belgium a tailor-made mix formulation was designed, resulting in durable and stable products. The durability was validated, based on a conservative set of geotechnical and chemical criteria, as well based on lab-scale as field scale trials. The design and know-how gathered in this project forms the solid basis for a valuable, reliable and cost-effective alternative treatment method for expensive off-site treatment techniques such as incineration.

References

CL:AIRE Subr:im bulletin sub 7 - Acid tar lagoons Pensaert S. The remediation of the acid tar lagoons, Rieme, Belgium. International conference on stabilization/solidification treatment and remediation. Advances in S/S for waste and contaminated land, 12-13 April 2005, Cambridge University, UK.