Middlesex Secondary School

Redundant Heating Oil Tank Decommissioning and Removal

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 Feature in CL:AIRE Report

Claire Report

Ash Remediation Management’s gasworks stabilisation project is used as an example case study in CL:AIRE’S recent publication ‘Soil and Groundwater Remediation Technologies for Former Gasworks and Gasholder Sites’

The report can be downloaded here

A North Yorkshire Recycling Plant

Environmental Monitoring and Verification North Yorkshire

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.



Reigate Heath Garage

Groundwater Treatment Reigate Heath Garage

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:

  • Empty, clean and decommission the three underground storage tanks.
  • Excavate and recycle any grossly contaminated soils contained within the tank void.
  • Carry out chemical oxidation treatment of the contaminated groundwater plume.
  • Monitor groundwater quality for six months.

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.

Widnes Galligu Stabilisation 2

Galligu Stabilisation Treatment

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.

Widnes Galligu Stabilisation 1

Physical Stabilisation Treatment 2

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.

Audley Gasworks

Bioremediation Treatment Audley Gasworks

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.

Gould Street Gasworks

Chemical Stabilisation Treatment Gould Street Gasworks

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.


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.






Tank Deccommissioning Ealing

The site located in Ealing was previously utilised as a truck MOT and servicing unit and the redevelopment objective was to construct a fire fighting training facility. Site investigation identified contamination as a potential risk to human health, development infrastructure and controlled waters therefore remediation work formed part of the planning conditions.

Ash Remediation Management were involved with the site from an early stage which allowed us to advise our client on numerous issues which ultimately expedited the site development programme. The scope of our involvement entailed remediation and earthworks and a summary of our package is detailed below:

  • Clean, degas and remove the two underground fuel tanks, associated pipe work and interceptors
  • Delineate the soils surrounding the historical on site fuel storage apparatus and determine the extent of any potentially contaminated soils
  • Excavate material that exceeds the re-use acceptability criteria and send for off-site remediation/regeneration
  • Excavate and break out the existing hard standings/concrete slab and any underlying hard materials. Process the product of the breakout to 6F2 classification
  • Validate through chemical testing the excavations previously containing the fuel storage apparatus
  • Carry out six rounds of groundwater monitoring

Ash Remediation Management completed their work programme ahead of schedule and all paperwork and regulatory documents were submitted under the cover of a project report. This allowed release of the remediation based planning conditions and successful continuation of the development.



Tank Decommissioning Addlestone

Client – Independent Developer

Principal Contractor – Ash Remediation Management

Consulting Engineer – Geo Environmetal Group

Location – Addlestone

Contract Value – £50K

The former petrol filing station and motor repair garage is located in Addlestone, Surrey and a London Based property company purchased the site to enable its redevelopment into a small retail centre. However, owing to the sites previous use and its close proximity to a sensitive watercourse, remedial attention formed part of the planning conditions.

Ash Remediation Management were involved at the inception of the project and their initial responsibility was to take the lead role in the site investigation work.   On completing the exploratory work as well as attaining regulator approval of their remediation strategy, Ash Remediation Management were awarded the contract to carry out the remedial phase of the project.

The scope of the remediation work is summarised as follows:

  1. Removal of the underground storage tank (UST) and associated grossly contaminated soils
  2. Formation of a cut off/interception trench and disposal of any grossly impacted soils
  3. Abstraction of free product and contaminated groundwater from the UST and trench excavations
  4. Further, periodic disposal of any free product and groundwater that accumulated in the UST or trench excavations

All materials removed from site were disposed of at appropriately licenced waste treatment facilities. The capabilities of these sites allowed treatment and regeneration of the material, an important factor in Ash Remediation Managements commitment to sustainability. Moreover, this ‘green’ route of disposal minimised our clients costs as tax expensive landfilling was avoided.

To supplement and verify the above, Ash Remediation Management designed a monitoring scheme. The regulator approved document involved the installation and sampling of a series of groundwater monitoring wells as well as the sampling of an adjacent watercourse.

On conclusion of the monitoring program Ash Remediation Management produced a report of the remedial work. This was submitted and agreed by the regulator allowing the release of the associated planning conditions.