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CARRINGTON REDEVELOPMENT

Tender Value: £600K
Client: Himor Carrington Limited
Engineer: Arup (Manchester)

64

Cable Boreholes

These were advanced through extremely challenging ground conditions; tough strata (glacial and soft rock) which was, in places, grossly contaminated.

10

Duration

The contract period lasted around 10 weeks and involved the majority of our resources in order to complete the scope within the timescale indicated.

33

Rotary Drillholes

To establish the extent of the contamination and its interplay with the groundwater regime. This included the installation of CMT and standard instrumentation.

12

Post-Site Monitoring

After the completion of the main phase of the investigation a long-term environmental monitoring and sampling period was undertaken - this involved both the groundwater and gas regimes.

CONTRACT DETAILSOUTLINE INFORMATION
Significant RisksWorking in an area of known and gross contamination.
Operating in an area that is occupied by various existing industrial concerns and activities.
Underground services and process critical installations.
Project IssuesPre-commencement radiological, unexploded ordnance and ecological surveys.
Multilevel groundwater monitoring installations.
Four areas of operation (Site A to D) within a extensive site setting.
RED site investigation conditions.
Geophysical down-hole logging.
Challenging ground conditions and environmental concerns.
Scope64 No. cable percussion boreholes
33 No. rotary drillholes
76 No. mechanically excavated trial pits
75 No. windowless sample holes
Associated ServicesNumerous rounds of gas and groundwater monitoring (over approximately a 12 month time-period) which included PID assessment of vapours, together with sampling events relating to in-ground and near-by surface waters.
In-situ testing using standard penetration (SPT(s/c)), hand shear (Pilcon vane), PID as well as geophysical downhole surveys and various instrumentation (19, 50mm and CMT well screen) requirements.
Undisturbed (U100(T)) and disturbed sampling.
Geotechnical (including effective stress) and specialist chemical laboratory testing services.
UXO survey and on-site supervision.
Ecological survey and on-site supervision.

CARRINGTON DEVELOPMENT INVESTIGATION
The investigation encompassed a former petrochemical site within Carrington, Trafford, and Greater Manchester as well as other offshoot areas of interest immediately adjoining the main site. Accordingly for manageability and future development planning the investigation was subdivided into four key area each having different environmental characteristics. An large scale and technically challenging investigation commissioned in order to assess the existing contamination of both the soil and groundwater at the former petrochemical site in Carrington, Trafford, Manchester.

The information gained from the investigation will be used to aid in the design of further works to monitor and remediate the site in lieu of redevelopment at a later stage.

CONTRACT HIGHLIGHTS
At the time, principal ecological constraints included breeding birds, Great  Crested Newts and badgers. In addition, steps were put in place with respect to tree root protection. Due to the potential presence of Great Crested Newts, toolbox talks were given to all site staff detailing the measures to be undertaken should evidence of any Great Crested Newts be found in proximity to the exploratory hole locations. A qualified Ecologist was present on site for the duration of the site works and fingertip searches undertaken as required in relation to the environment.  

The site was identified as a low to medium potential risk area for the presence of unexploded ordnance. A non-intrusive geophysical survey was undertaken by the specialist contractors BACTEC in order to identify any possible shallow unexploded ordnance. In addition to the walkover survey in order to mitigate the UXO risks, BACTEC were employed full time during the ground investigation. All site personnel were given Explosive Ordnance Safety and Awareness briefings and site instructions were issued to all site staff. Downhole geophysics was also carried out in all boreholes down to a maximum bomb penetration depth (estimated to be approximately 12 BGL). 
In addition to the above, part of the site is currently occupied by Basell Polyolefins Ltd. (Basell) who have detailed records of the services located on their site, both live and redundant. All exploratory hole locations within the Basell compounds were agreed before the commencement of site works in order to avoid any potential issues regarding the services and utilities on site. A separate induction and ‘Permit-to-Work’ form was required to enter the Basell compounds. These permits were issued on a weekly basis, signed daily by Basell staff and returned at the end of each day. All drilling crew and site visitors were required to undertake the induction prior to being allowed on site. 
To reduce the risk of cross contamination all equipment (including drill bits, casing and excavator buckets) was washed down using a pressure washer after the completion of each exploratory hole. A set-aside washdown area was used for such activities which incorporated a lined and bunded trench and collection IBC units. 

Specialist Continuous Multichannel Tubing (CMT) were installed into selected boreholes to allow discrete depth monitoring and sampling of groundwater across a range of depths. The CMT wells were installed using centralisers to maintain verticality at approximately 3m intervals. Each response zone was carefully backfilled with gravel and bentonite as appropriate.

All site personnel were equipped with appropriate overalls and personal gas alarms at all times during the site works. When contamination was encountered coveralls, masks and visors were provided as an extra protective measure. In addition, a decontamination unit was present on site at all times for site personnel which included delineated ‘dirty’ areas following HSE Guidance Booklet 66. 
In the case of an emergency escape hoods and fire extinguishers were also present with each crew, however these protective measures were not required to be used during the site works.

OUTCOMES
During the site works site operatives noted a number of locations where there was potential evidence of contamination, principally as a consequence of olfactory and visual identification.  Drilling conditions were problematic due to the depth and strata type and where difficulties occurred the continuation of the process required high levels of resourcing and technical input. From a company perspective these difficulties were managed by allocating the right personnel to the process, as well as having significant experience on-site to deal with each challenge. 

Management of the long-term monitoring and sampling requirements which needed to be adequately resourced and scheduled throughout a 12 month period. The supervision of a multi-disciplinary ground investigation was key, as well as the associated requirement to handle the overarching ecological, contamination and site constraint issues. One of the major difficulties was the sheer volume of information that was generated by the investigation and its subsequent control and distribution to various stakeholders.

Maintaining good levels of moral within the site work force in an environment that was significantly challenging was extremely important throughout the main investigation and subsequent long-term monitoring programme.

Management and supervision of the multi-disciplinary ground investigation requirements, as well as the associated requirement to handle the overarching ecological, contamination and site constraint issues.

One of the major difficulties was the sheer volume of information that was generated by the investigation and its subsequent control and distribution to various stakeholders.