An employee at a recycling centre in the South East of England identified some suspect material on the companies premises. Ash Remediation Management carried out a site investigation and confirmed the presence of asbestos cement board and oil contamination. The contamination hotspot was delineated and the material was disposed of at an off site facility.
In all piling projects stability of the plant is key and as such, a suitable piling mat is essential if the works are to be executed in a safe and controlled manner. It is particularly important that the working platform does not deteriorate or encounter heave because in piling work the specialist equipment used has a high centre of gravity and the consequences of a collapse can be fatal.
A traditional method of constructing a piling mat is to import and layer stone. This can be an expensive and unsustainable method with the transport alone adding numerous unnecessary lorry movements. In contrast to this method Ash Remediation Management offer on site stabilisation of material to piling mat standards. We have achieved specifications of in excess of 30% CBR (dependent on the ground type) and all on site testing is included.
The stabilisation process was facilitated through the use of a tractor pulled Spader. The Spader dosed the specifically designed binder and ensured maximum mixing and pulverisation of the soil material. This was completed to the required compacted depth with a minimum of three passes. The validation testing confirmed that the target of CBR of 30% had been exceeded allowing the piling work to commence. Ash Remediation Management also carried out the trimming works. This was achieved using GPS guided machinery and to a tolerance of +20 – 30mm.
As part of the construction of a state of the art sports facility, Ash Remediation Management carried out a programme of earthworks and physical stabilisation.
Ash Remediation Management achieved CBR values of in excess of 30% which more than exceeded the development requirements. Additionally, the project was completed in a timely and efficient manner allowing the client to achieve their project completion deadline.
As part of an extensive refurbishment project, a redundant heating oil tank required decommissioning and removal. The tank was located in an underground basement making its removal slightly more complicated and as the work had to be completed within the school holidays there was a very tight time constraint.
Ash Remediation Management ‘pulled out all the stops’ to provided a fast and efficient turnaround. The tank was cut up in-situ (post decommissioning) and all contractual and regulatory paperwork was completed and filed within 24 hours.
Ash Remediation Management designed a regultor approved monitoring and verification programme for a national recycling company. Environmental monitoring and verification was carried out before, during and after the trial of a new screening and recycling process. Quantitative data was collated and this was interpreted and reported in a factual, concise document.
The Flanchford Road site in Reigate, Surrey was purchased by Stanton Construction whose development proposal entailed the refurbishment of three existing cottages and the construction of three new residential properties.
The site was previously utilised as a petrol filling station and vehicle repair workshop and site investigation identified groundwater contamination at concentrations that posed a risk to the underlying aquifer and nearby SSSI. It was at this stage that Ash Remediation Management became involved with the project and their first task was to prepare and gain Local Authority approval of a remediation strategy.
The remediation strategy was promptly agreed and the scope of the remedial work is summarised below:
In addition to the remedial work Ash Remediation Management also carried out the controlled demolition of the vehicle repair garage. All demolition material was carefully segregated before been sent for recycling.
The project ran smoothly from start to finish and the on site stage of work was completed in a little under three weeks. Ash Remediation Management compiled a Verification Report summarising the work completed which enabled release of the related planning conditions.
Following successful completion of the initial galligu stabilisation project our client did not hesitate to get Ash Remediation Management back on board when a second area of galligu was identified.
Ash Remediation Management always complete treatability trials prior to site works commencing and despite previously carrying out galligu stabilisation on the same site these bench top trials were still conducted. Again the treatment was applied through the use of the Allu Power Mixer and Pressure Feeder and a total of 850m3 of galligu was stabilised.
In the late 19th Century the synthetic production of sodium carbonate was prevalent in the Widnes and St Helens region of North West England. The rapid growth of the chemical industry dictated the requirement for this product however there were some associated problems.
The process used in manufacturing sodium carbonate was massively inefficient with the quantity of raw materials outnumbering the saleable product by a ratio of 6:1. Moreover, large amounts of a waste material called galligu were produced. Geotechnically galligu is an interesting material and the properties it exhibits differ according to its oxidation state and water content. When dry galligu is similar in texture to silt however an increased water content or indeed physical handling quickly transforms the material into a thixotropic mass.
Huge quantities of galligu were produced and owing to the unregulated manner in which it was disposed it underlies much of the region. The presence of galligu can heavily constrain land development and construction and this was certainly the case for our client Britcon.
This shift between geotechnical states of galligu presented an issue for Britcon as part of their development required excavation of up to 4.5m bgl for installation of underground tanks and basement floor levels. Simple excavation of the galligu did not prove successful as the physical handling process changed the physical state from solid to liquid. Even if the excavation had have been successful the sides of the void would not have been stable enough to allow work to continue safely.
It was at this stage that Ash Remediation Management were appointed as the stabilisation contractor. Ash Remediation Management conducted laboratory based trials to optimise a treatment mix and through the use of the Allu Power Mixer and Pressure Feeder stabilisation of the galligu was carried out. A total of 1500m3 of galligu was stabilised and following approximately seven days curing the galligu was in solid state and subsequent excavation was possible. Moreover, the sides of the excavations were stabilised which allowed work to be completed safely within the void.
The former gasworks is located in Shropshire and it was purchased by a midlands based house builder. The site was polluted with typical gasworks contaminants (namely polycycic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), lead and cyanide) and in order to comply with planning regulations a detailed remediation programme was undertaken.
Ash Remediation Management provided a full remediation scheme including stabilisation/solidification, bioremediation and the removal of contaminated waters. This case study discusses the ex- stabilisation/solidification aspect of the project.
A site specific stabilisation / solidification slurry was produced on site and through the use of an excavator and associated processing bucket it was combined with the contaminated soils to form a homogenous mass. A total of 2200m3 of material was stabilised. The treatment phase was completed over a 4 week period and the subsequent curing phase lasted 3 weeks. Following treatment, curing and compliance testing, material was utilised as a sub base for the future roads and footpaths.
All phases of the project were achieved within budget and the stabilisation work was concluded 3 weeks inside the project deadline.
The Gould Street site is owned by National Grid Properties and formerly operated as a gasworks. Dating from 1848, the site is located in a residential redevelopment in central Manchester and covers an area of 2.67 hectares.
Historical records indicated that as part of the gasworks decommissioning, some of the former gas holder bases were backfilled with spent oxide materials. The backfill was impacted with typical gasworks contaminants including hydrocarbons, metals, cyanide and ammonium. These elevated contaminant levels triggered the formation of the remediation objective to reduce contaminant leachate to risk assessment derived acceptable concentrations.
The agreed remediation programme designed and executed by Ash Remediation Management entailed in-situ and ex-situ stabilisation/solidification of the spent oxide material.
In-situ Stabilisation
From the outset it was evident that significant odour issues were associated with the largest gasholder and the significance of this was amplified by the site’s close proximity to commercial and residential receptors. Ash Remediation Management’s solution to this was to apply the stabilisation process using an in-situ technique. This system negated the requirement to physically excavate the odorous material thereby minimising this potential nuisance.
The in-situ treatment operation utilised the soil mixing capabilities of a piling rig. The piling rig auger rotates and bores down whilst injecting the treatment slurry (derived from feasibility trials) via ports located within the modified drilling head. Once the desired drilling depth is achieved the auger is withdrawn with the direction of rotation remaining the same to further facilitate homogenisation of the column. This description summarises the installation of a single column and the principle of the in-situ treatment method is based on a series of overlapping columns.
An auditable level of quality control was achieved through the use of a flow meter which measured the volume of treatment slurry injected. All other drilling parameters were measured and recorded via the rig’s on board instrumentation which generated daily production data that was used in the quality control regime.
The in-situ treatment process was validated through a series of window sample holes spread across a theoretical grid system. Samples were taken from various depths and submitted for either chemical or geotechnical laboratory testing. An important additional benefit of the stabilisation process is a reduction in material permeability which physically resists contaminant leaching. In the case of the Gould Street site, permeability testing demonstrated values of less than 10-9m/s.
Ex-situ Stabilisation
Spent oxide from a further two gasholders also required treatment and, with odour not being problematic an ex-situ approach was deemed most suitable and cost effective. The process involved excavating and screening material prior to delivery to a bunded treatment area. In the treatment zone a tractor mounted spader dosed and mixed the stabilisation additives and spent oxide. The advantages of the spader unit include the ability to dose additives at specific rates ( kg/m2), to ensure full homogenisation of material and to achieve high treatment rates (up to 500m3/day).
The ex-situ treatment process was validated through conventional composite sampling. Samples were acquired at a predetermined frequency prior to laboratory submission. Treated spent oxide was reinstated within the original gasholder structures thus eliminating any requirement to import fill material.
The Gould Street project was completed on time, on budget and with a 100% safety record.
Awards
The forward thinking and sustainable approach adopted by Ash Remediation Management proved to be instrumental in the Gould Street site being awarded the Civil Engineering Contractors Association Innovation prize.
The in-situ work was also nominated for the 2011 Brownfield Briefing ‘Best In-situ Treatment’ award. The Gould Street site was awarded a creditable second place and was highly commended by the judges.