Treating Contaminated soil with ImmoCem
ImmoCem is the brand name of an extraordinary product based on natural and synthetic zeolites and specifically designed for use in pollutant immobilization and remediation of polluted sites.
ImmoCem’s ability to act as an absorber, a flocculent, a catalyst, molecular sieve, neutralizer and an ion exchanger make it very versatile in application.
It can be used in support of existing pollution control technologies or it can form the basis for a fully new approach to pollutant immobilization and control.
ImmoCem can be used to turn contaminated soils and sludge into a harmless and strong construction materials for use in construction/piling mats, Road and car park base and foundations.
ImmoCem is unusual in that it is suitable for the effective immobilization of both organic and inorganic pollutions. It is also highly effective for immobilization of heavy metals.
ImmoCem offers unique and effective solutions for remediation of historically polluted sites making their continued and sustainable use possible.
ImmoCem closes the 'Technical Nutrients' cycle and helps to prevent the escape of toxics and carcinogens into the natural environment.
ImmoCem performance relies on the extended crystallization process by forming long needle and'cage' crystalline structure enabling pollutant entrapment and immobilization and preventing their leaching into the environment.
ImmoCem is application friendly and can be used for the treatment excavated materials with the use of a pugmill type mixer or in the ground treatment with a wirtgen or Stehr type rotavator.
ImmoCem can also be used in extremely difficult working conditions as it continues to give effectiveresults in both very cold (freezing) and very hot climates.
ImmoCem is always used in combination with Cement binders and has the ability to bond almost any type of material from nano particles to stone, including organic top soil producing a stabilised composite material which is water, salt and acid resistant.
In essence ImmoCem enables Cement and PFA to be used effectively for environmental applications.
ImmoCem use in solidification stabilization technologies
Stabilization/solidification (S/S) is a remediation/treatment technology that relies on the reaction between a binder and soil to stop/prevent or reduce the mobility of contaminants.
Stabilisation - involves the addition of reagents to a contaminated material (e.g. soil or sludge) to produce more chemically stable constituents; and to strengthen weak soils/materials.
Solidification - involves the addition of reagents to a contaminated material to impart physical/dimensional stability to contain or entrap contaminants in a solid product and reduce access by external agents (e.g. air, rainfall or groundwater).
ImmoCem aids both Stabilization and Solidification.
Conventional S/S is an established remediation technology for contaminated soils and treatment technology for hazardous wastes in many countries in the world. However, the uptake of S/S technologies has been relatively modest, and a number of barriers have been identified including:
o the previuosly low cost and widespread use of disposal to landfill;
o the lack of authoritative technical guidance on S/S;
o uncertainty over the durability and rate of contaminant release from S/S-treated material;
o experiences of past poor practice in the application of cement only stabilization processes used in waste disposal in the 1980s and 1990s (ENDS, 1992); and residual liability associated with immobilized contaminants remaining on-site, rather than their removal or destruction.
All of the above disadvantages and barriers can now be overcome by using ImmoCem in combination with the conventional binders.
ImmoCem S/S may be used on its own or in combination with other risk management approaches as part of a remedial strategy to address the pollutant linkages that need to be managed.
ImmoCem S/S Technology achieves immobilization by reaction of the soil matrix and contaminants with reagents to promote sorption, precipitation or incorporation into crystal lattices, and/or by physically encapsulating the contaminants. Pollutants encapsulated by ImmoCem S/S have been proven to stay safely encapsulated for a simulated 100 years.
The mixture of ImmoCem and cement binder used for ImmoCem S/S is referred to as the improved hydraulic cement binder (IHCB).
ImmoCem S/S has been used for effectively treating a wide range of both inorganic and organic contaminants, including:
o metals and metalloids;
o asbestos;
o radionuclide’s;
o inorganic corrosives;
o inorganic cyanides;
o solid organics (e.g. plastics, resins, tars);
o polychlorinated biphenyls (PCBs);
o poly aromatic hydrocarbons (PAHs);
o hydrocarbons, and
o dioxins.
In addition to contaminant type and properties, the efficacy of ImmoCem S/S can be influenced by the presence of inhibitory compounds, physical properties of the material treated, characteristics of the site and future land use.
As a result, treatability studies are considered an integral part of the selection and use of ImmoCemS/S technologies and usually require the selection of the binder and the demonstration of the efficacy of treatment using selected plant and equipment during a field trial before finalising the design for full- scale implementation.
A range of both ex-situ and in-situ methods of application have been developed to address potential practical constraints and site characteristics, including:
o excavation and mixing with reagent in plant designed for that purpose (e.g. mix-in- pugmill type plant);
o direct mixing of soil with reagent in layers, e.g. by rotovation, followed by compaction(e.g. mix-in-situ);
o in-drum processing; and
o using soil mixing equipment, e.g. modified hollow-stem auger, to inject and mix reagent.
o Pre mixed with cement to form an injectable slurry.
With conventional S/S the release of contaminants does often still occur and the durability of the remediation needs to be demonstrated. Key issues that need to be addressed include the structural integrity of the treated material, the buffering capacity of the system, and the rate and time scale of contaminant release.
With ImmoCem S/S the release of contaminants is minimized and the durability of the remediation is significantly improved.
The key issues that need to be addressed stay the same but uncertainty is significantly reduced since the structural integrity of the treated material has been shown to persist and the rate and time scale of contaminant release is significantly reduced/increased when compared to conventional S/S.
Testing of materials before, during and after stabilization/solidification with ImmoCem is essential.
The more you test the more you know.
Sampling And Testing Programmes
General
The sampling and testing programmes that may be carried out, particularly on treated material, during design, construction and post construction stages of ImmoCem S/S treatment.
It focuses particularly on the selection of an appropriate testing strategy to develop confidence in the long-term leaching performance of the ImmoCem S/S treated material.
Sampling and testing activities are an integral component of the activities described in the preceding sections, and separate strategies may need to be prepared for the following purposes:
1. Optimizing the Mix Design - sampling of the material to be treated will be required to confirm the specification of the optimum ratio of ImmoCem and cement for process control. Compliance testing is carried out on cured samples (usually stored for a pre-defined period) to verify that the treated material meets physical (e.g. strength, permeability) and chemical (e.g. contaminant leaching) remedial criteria.
2. Quality Control During Construction - for process and technology control and verification control. Compliance testing is carried out at all stages of the stabilisation to ensure the correct quantities are properly mixed and the mixed materials thoroughly compacted in specified layers, with the coorect amount of water to ensure optimum hydration.
3. Post-construction Performance Evaluation - further compliance or characterisation testing of cured material in its disposal or re-use scenario may be required at pre-defined time intervals to verify the long-term performance. Sampling in the event of an unexpected release of contaminants from the treated material, as identified from long-term monitoring may also be carried out.
Sampling Strategies
A sampling strategy should be developed for each stage of sampling carried out during the ImmoCem S/S remedial process, and may need to be developed for a number of activities including:
o sampling excavated soil before ex-situ treatment;
o sampling screened, blended and/or pre-treated soil before ex-situ treatment;
o sampling during in-situ treatment;
o sampling from a stockpile;
o sampling from an ex-situ moving stream process (e.g. a pugmill);
o sampling of a manufactured product (e.g. a sub-grade or capping layer) before reuse; or
o sampling of treated material that has to go to land fill.
The sampling strategy should identify the information presented in the following sections.
Sampling objectives
The objectives will be site-specific and will relate to the overall objectives of the remediation. Specific objectives may include establishing (adapted from BS ISO 10381-1:2002):
o the physical properties of the material and variability (e.g. pH, moisture content, particle size);
o the nature, concentrations and distribution of substances that may retard setting (e.g. humid acids, fine particulates, sulfides, borates);
o the nature, concentrations and distribution of contaminants; and
o the presence and distribution of biological species of interest (e.g. to assess the impact of binder addition to micro and macro size flora and fauna).
It is important that samples used for treatability studies are representative of the material designated for treatment and the objectives of the treatability study are clearly set out. It is not appropriate to conduct treatability studies on a sub-set of the material (e.g. a single stockpile or from a small part of the site to be treated) for the purpose of scaling up to implementation for the whole site.
Some of the above parameters may show significant variation with time caused by attenuation, migration, extrinsic effects (e.g. weathering, temperature, barometric pressure) or land use.
This should be taken into account in the event of any significant time delays between sampling exercises.
Sample locations
The selection of sampling locations will depend on:
o information already available;
o number and type of samples required;
o variability;
o site conditions (topography & access);
o depth of material; and
o remediation process (e.g. column patterns or moving-stream process).
Where in-situ auguring techniques are being used, sample locations after treatment should include both column centres and overlap areas to ensure that the remedial criteria are achieved.
An ex-situ moving stream process for pre excavated materials (e.g. pugmill mixing) will usually have a single designated sampling location for the treated material.
Direct mixing in-situ methods (e.g. spread, rotovate and compact) will tend to be verified by grid sampling material from each treated and compacted layer.
Sampling pattern
The sampling pattern will depend on the existing knowledge available and type and severity of remedial criteria.
Judgemental sampling is used when good information is available on the distribution of contaminants and when the objective of the exercise is to confirm that existing information is valid.
As the sample locations are based on prior knowledge and are not designed to collect representative samples, judgmental sampling should not be used when statistically based criteria (e.g. mean or percentile limits) are set.
Systematic sampling (e.g. sampling using a grid system) will be used when there is no prior knowledge of contaminant distribution and/or where samples representative of the site (or a part of the site, such as an area or a stratum) are required.
Statistical assumptions about the population (the volume of material that the samples are representative of) can be made from systematic samples and remedial criteria can be set with a pre-defined level of confidence.
Composite samples can be used with care to reduce variability in the data set.
However, composites will not be appropriate for certain contaminants (e.g. VOCs), where mixing may be physically difficult (e.g. clays) or where it would introduce uncertainty in the representation of land area or strata.
The number of samples will be dependent on:
o the objectives of the sampling exercise;
o the level of confidence required for verification of the encapsulation.
o the level of uncertainty associated with the parameters and their measurement; and
o the cost of data collection weighed against the benefit of reduced uncertainty.
Sample size
The sample size required will depend on the particle size of the material and also the number and type of tests to be used.
Sampling techniques
Sampling techniques will depend on the properties of the parameter, size and nature of the sample to be collected (e.g. disturbed or undisturbed), access for plant and equipment, and depth.
Sample preservation, labelling, storage, handling and transportation
There is little merit in collecting samples if, by the time they reach the laboratory, they are not "suitable for use".
This may be the case, for example, if the material contains volatile or readily oxidised components and preservation of a sample or sub-sample may be required for particular analyses.
Liaison with the laboratory should be carried out before a sampling exercise for advice on specific storage and handling requirements.
Regulations regarding the packaging, labelling and transport of hazardous materials should be complied with where applicable. Each sample should have a unique identification number.
Testing and analysis
The testing and analytical requirements will have a bearing on a number of sampling issues including sample quality (disturbed or undisturbed) and sample size.
The physical and chemical tests used for S/S materials will either be mandatory (e.g. to demonstrate compliance with waste acceptance criteria) or selected on a project by project basis (e.g. characterisation of a waste stream, or of a treated soil for a re-use scenario).
Chemical analytical methods will be selected, in consultation with the analytical laboratory, to meet specific data quality objectives, and may be used to identify:
o total concentrations of substances in a material, including major cations and anions, inorganic and organic contaminants;
o concentrations of substances in eluates from leach tests, porewater or groundwater; and
o other measurements, e.g. pH, electrical conductivity.
The designer should ensure that all appropriate analytes are specified, including substances that have the potential to affect the performance (e.g. set retardation for cement based systems) and those that may be mobilised as a consequence of S/S (e.g. aluminium).
A large range of standard analytical techniques are available and reference should be made to appropriate standards, such as BS, CEN or ISO, in consultation with a suitably accredited (e.g. UKAS, MCERTS) analytical laboratory to ensure that pre-defined data quality objectives can be met.
Testing Programme for Evaluating the Leaching Performance of ImmoCem S/S Waste Form
The durability, including physical and long-term leaching performance of the waste form is a key consideration that should be determined over realistic time scales.
To assess the performance of ImmoCem S/S material the following may be considered:
o post-construction (1-2 years);
o in the medium-term, e.g. 10-30 years; and
o in the long-term, realistically no more than hundreds of years.
The approach and time scale selected to address durability questions will depend on the design life, properties of the treated material, protection against extrinsic factors, and potential risk to receptors (e.g. groundwater).
Long-term assessment will require a modelling approach to predict performance and a period of monitoring to validate the model. Durability questions can be addressed by considering the failure mechanisms that may affect an S/S treated material, including:
o extrinsic effects (e.g. weathering, chemical attack, mechanical damage);
o intrinsic effects (e.g. solid-solid, solid-liquid reactions); and
o quality of construction (e.g. poor design, workmanship, QA/QC).
A testing framework is recommended to assess the long-term leaching behaviour of a ImmoCem S/S waste form, using both physical and leach tests, based on an approach outlined in ENV 12920 (CEN, 1997).
This approach relies on understanding the characteristics of the treated material and its behaviour in its environmental setting, whether contained in a landfill site, re-used on siteas a part of the construction or as a manufactured product to be exported off site.
The recommended framework involves steps to:
o define the problem and solution sought;
o define the disposal or re-use scenario;
o select appropriate test methods to understand the long term behaviour of the treated material;
o select compliance tests;
o predict long term performance; and
o validate the predictions.
The following sections describe the framework. Physical tests are included where they can contribute to an understanding of leaching performance of ImmoCem S/S treated material.
Definition of the problem and solution sought
From an environmental perspective, the problem for ImmoCem S/S treated materials will relate to the possibility of release of contaminants and the potential to impact identified receptors.
The solution may vary, depending on the perspective of the stakeholders including the regulator, problem holder and end-user.
One of the issues will be the time scale over which the release of contaminants is to be evaluated. This should be agreed at the outset as it may significantly influence the development of the disposal or re-use scenario.
Conclusion
Immocem has been proven to be effective in treating both Inorganic and organic pollutants in all sorts of situations all over the World.
Even in England we can boast to have our own major league polutant: Galligu; a by-product of a process that converted rock salt into sodium carbonate.
It is estimated that the production process produced 2 tonnes of galligu for every 1 tonne of soda ash and at its height in the 1870s Britain's soda output (about 200,000tonnes annually) exceeded that of the rest of the world combined.
The resulting millions of tonnes of waste galligu were either dumped into spoil heaps or spread on the ground surface to infill valleys or build embankments.
Looking and feeling like toothpaste, this is one material you would not want to put in your mouth.
With it’s high levels of arsenic and other heavy metals. In addition to the pollution risks posed, Galligu's uncontrolled disposal in areas surrounding the factories in and around Widnes has resulted in significant ground stability problems.
A trial version of ImmoCem was used successfully to solidify and encapsulate Galligu in 2002 and a report published by CL-AIRE follows:
Contaminated Widnes site remediation
The development of a highly contaminated site into recreationalfacilities has required a novel approach to the remediation process.The 2.5ha site is located within an area known as the Mersey Belt.
This area was at the forefront of the Victorian industrial revolutionand consequently developed a significant chemical manufacturing base and a contaminated landlegacy.
The site is located in Hutchinson Street, Widnes in the borough of Halton which was home to the LeBlanc chemical process, a process that converted common salt into soda ash using sulphuric acid,limestone and coal.
The waste by-products from this process were highly toxic and became knownlocally as 'Galligu'. This substance was found in the majority of locations on the site.
Indiscriminatewaste tipping over the decades had added to the problem and, as a result, the land was classified ashighly or very highly contaminated. Contaminants included arsenic, lead, zinc, cadmium, copper,sulphurous waste deposits (Galligu), nickel and chromium.
The pH of the contaminated fill materialvaried from 2.6 to 12.2. Typically, the low pH values were recorded in the upper 1.0 to 2.0m of fill.
Environmental concerns
One of the main environmental concerns about the contaminated fill was the level of heavy metal contamination.
Leachate testing demonstrated a high level of mobility for lead (1290g/L), zinc (1570g/L)and arsenic (580g/L).
These values were excessively high and posed a significant risk of future crosscontaminationvia surface water infiltration. Contamination of the River Mersey, located only 500 mfrom the site, was also considered.
To prevent the threat of cross-contamination a dig-and-dump solution was initially considered.
However, this scheme was later rejected as ground modelling revealed that approximately87,000 m3 of material required removing to landfill, based on data from previous siteinvestigations.
This was not a viable solution, both in terms of environmental and economic costs. Analternative, more sustainable solution was therefore required.
Remediation techniques
Several remediation techniques were investigated and considered during an open consultation period.Ultimately an in-situ stabilisation and solidification (S/S) technique was adopted.
However, due to thehigh levels of contamination, an ordinary cementitious binder (i.e. lime and/or cement) was notconsidered appropriate to result in adequate contaminant encapsulation.
Alternative technologiesenhancing the S/S process were therefore investigated. Field trials of five alternative S/S solutionswere extensively evaluated and monitored by Halton Borough Council, the Environment Agency andindependent environmental consultants.
The outcome of these trials was highly successful with allS/S systems performing well. Following extensive monitoring over nine months, together with theevaluation of associated costs, it was decided that a specialist cement additive known as Powercem,developed by PowerCem Technologies BV, Netherlands and supplied by Powerbetter Environmental Processes of Leeds, provided the end performance criteria required at the most competitive price. Inaddition, the Powercem treated system offered greater flexibility compared to the other systemsinvestigated.
This was significant as cracking of the treated cap was eliminated, thus preventingpotential pathways to the contaminated material beneath.
Field trials had confirmed that an soil stabilisation solution was appropriate for the redevelopment ofHutchinson Street. Full-scale remediation commenced in September 2003 with a total area of28,000 m2 being treated (see Figures 1 and 2).
The final design comprised the in-situ treatmentof the Galligu contaminated material with a cement/ Powercem matrix to a depth of 350 mm.
This created an impermeable, chemically stable cap. An imported, reclaimed granular material, geotextile,sand and topsoil was placed on top of the cap in order to develop the recreational facilities.
Elimination of cross-contamination
The purpose of the treated Galligu cap was to prevent surface water infiltration into the contaminatedmaterial beneath, thus eliminating cross-contamination.
The engineering/chemical criteria for the capwere as follows:
· to reduce the permeability of the Galligu contaminated soil to at least 10-8 m/s· to increase the strength of the Galligu soil to achieve at least a soaked Californian Bearing Ratio (CBR) strength of 15%· to reduce the leachate potential of the Galligu soil, and thus the risk to watercourses and the River Mersey. (Drinking water guidelines were used as a bench mark).
Tests undertaken seven days after remediation operations to validate the process demonstrated thefollowing:· soaked CBR strengths ranged from 50-85%· permeability of the treated Galligu soil varied from 0.13 x 10-9 / 0.86 x 10-9· leachate values for arsenic (<1g/L), cadmium (<1g/L), chromium (10g/L), lead (< 10g/L), zinc (19-250g/L), copper (20-200g/L), selenium (<8g/L) and nickel (<30g/L, with one at 110g/L)Were less than the maximum concentration values stipulated in the Water Supply (Water Quality)Regulations 2000 for England and Wales.
A programme of continued monitoring is demonstrating continued reductions in permeability andextractable leachate concentrations.
Concluding remarks
The soil stabilisation option for Hutchinson street achieved a sustainable solution.
The quantity ofhazardous waste material land filled was minimised significantly and thus, the quantity of importedinert material was also minimised.
Subsequently, lorry movements were reduced from an estimated12,500 (remove/replace) to just 32 (cement deliveries).In total, Halton Borough Council was able to save over £600,000 in development costs by adopting astabilisation and solidification remediation solution.
On-going programme
"A programme of continued monitoring is demonstrating continued reductions in permeability andextractable leachate concentrations.
"Acknowledgment
This article has been reproduced with permission from CL:AIRE view, Summer 2004, the quarterlynewsletter of CL:AIRE. Established as a public/private partnership in 1999, CL:AIRE facilitates thefield demonstration of remediation research and technology, including innovative methods for sitecharacterisation and monitoring, on contaminated sites throughout the UK
