SOURCE DELINEATION & ISHERWOOD PARK
The investigation site, an area of c. 60 hectares and is located within the eastern part of a former operational petrochemical plant located within Carrington Estate; centred approximately at National Grid Reference 374000, 392300. This ground investigation had two prime purposes, (a) to provide data for the design of enabling works covering the area designated as Isherwood Park, located in the east of the main investigation site, and (b) to improve understanding and delineate potential contamination sources thereby facilitating the design and accurate pricing of future remediation schemes. For the purposes of this investigation these prime objective areas were referred to as Isherwood Park and Source Delineation. In some areas of the site the ground investigation objectives overlap which needed to be taken into account during the course of the site operations and final report.
Allied Exploration & Geotechnics Limited (AEG) had been involved with the ongoing redevelopment at Carrington on a number of previous occasions the most significant being the large scale investigation undertaken, with appreciably different technical aims, back in 2015 - see here. Further to the original investigation this new scope of works considered the environmental characteristics of the ground and groundwater in greater detail. The outline value of the works was roughly similar to the previous involvement, although the distribution of intrusive elements was principally directed towards providing a more comprehensive and complete site wide coverage. This was scheduled in order to pin-down, with greater accuracy, sources of contamination potentially affecting the groundwater and soil strata.
The site works period was 6 weeks, with a proportion of time beforehand (i.e. during the lead-in) to carry out preparatory operations and liaise with tenants. This process was considered to be critical to ensure the efficient and effective management of the intrusive stage of the contract due to the volume of investigation points scheduled. The whole of the investigation was 18 weeks which included undertaking six fortnightly monitoring rounds which included all new installations and those selected from previous investigations (a total of 190 positions).
The Principal Contractors role was undertaken by AEG for the duration of the works and was encompassed by full Construction Phase Health, Safety and Environment documentation.
The site is owned by HIMOR Carrington Ltd (HIMOR) however at the time of the investigation certain parts were leased to a range of tenants. Contact details for the tenants were provided by HIMOR via the Investigation Supervisor, whereby the investigation team then held the responsibility for liaising with them over access and logistical issues. Initial an information pack was compiled to notify the tenants of the operational requirements and intrusive techniques that would be used, as well as outline timescales. All intrusive locations were scanned using GPR and radio detection techniques in order to mitigate the risk of intersecting buried underground services, which then linked into the governing in-house permit-to-dig procedure.
The petrochemical site was still operational and specific health and safety measures were put in place to ensure personnel welfare. This included specific PPE requirements (including personal gas monitoring devices) for safe operation within the confines of the site to the satisfaction of HIMOR and their tenants.
The majority of the operations occurred to the west of the disused railway line which bisects the site (known as the Burford Railway). Most of the investigation comprised hard-standing, with some light industrial and storage operations involving the placement of shipping containers or parking of heavy goods vehicles (HGVs). Some vegetated areas exist, in particular a wooded area which was designated a Site of Biological Importance situated within the Isherwood Park investigation area.
GEOLOGY, TOPOGRAPHY & HYDROLOGY
The topography of the Carrington site was relatively flat having an average elevation of c. 20mOD which decreases to the north and west to a level of c. 15mOD relative to the River Mersey/Manchester Ship Canal.
Generally hard-standing (0.10 to 0.70m thick) over variable made ground comprising an average thickness of c. 1m. The main glacial sequence essentially comprises cohesive deposits (firm to stiff slightly sandy CLAYS) with intermittent granular (sand and gravel) interbeds. Locally, depending on location within the site more extensive fluvio-glacial (mainly sand deposits) and glacio-lacustrine deposits (laminated clay) may be encountered. Bedrock related to the Sherwood Sandstone Group (Wilmslow). The uppermost rock was identified to be weathered and uncemented (>17.5m thick in places). Intact rock was described as generally weak, thinly bedded sandstone. Occasional well cemented beds are likely interbedded within the poorly cemented layers.
Groundwater can be expected within the made ground (perched) and/or in the granular fluvio-glacial deposits at reasonably shallow depths. There is also a deeper seated regional groundwater table within the Sherwood Sandstone.
All sitework was completed in accordance with the Investigation Supervisor's objectives and encompassed by our quality management systems.
The main difficulties experienced during the investigation operations were addressed by a strong management lead, thereby ensuring that the extensive scope of works was addressed at every level. Steps were taken to avoid cross-contamination (designated wash-down areas) between investigation points and a site compound was set-up as a focal point to manage all daily activities. Due to the amount of work AEG successfully managed a supplementary team of subcontract drilling personnel which were employed to compliment our own in-house resources. Subcontract drilling was procured using our approved subcontractor database in accordance with quality management procedures, specifically AEG-12. The Contract Coordinator and Site Supervisor were responsible for monitoring the operational and technical conduct of all site operatives and for taking appropriate action where required. During the site works phase the site team included up to seven, over short periods eight, operational rigs supervised by a seven engineering professionals; this excludes the allocation of the office based resources. The engineering team was mainly sourced from our in-house professional personnel with the Northwest Contracts and Business Development Manager actively engaged on a day-to-day basis on site during the whole of the main operational phases.
During the course of the works the tenants and HIMOR were proactively involved to assess site protocols; this included assistance with the location of underground services and convenient phasing to accommodate site-wide activities. The Isherwood Park area required some enabling access vegetation clearance under the supervision of an ecology professional.
A bespoke information system was put in place to facilitate continuous progress reports from site and to enhance the submission speed of technical information. Trackers were initialised to allow the Investigation Supervisor to assess the status of the investigation throughout the operations. Specific data that was tracked included the collection and testing of contamination samples, geotechnical testing, general hole-by-hole investigation progress and the status of the reported elements pertaining to the investigation points. From a company perspective this facility allowed a coordinated full cognisance of site progress by senior management and Directors at all stages of the investigation. Thereby resources could be specifically targeted to counter any problems. This was a second implementation of this bespoke system by the Company and the process assisted in achieving the relatively tight contractual site period with the diligence it deserved from the outset. After completion of the site phase of the investigation the focus transferred into our UKAS accredited laboratory which was then tasked with meeting the specified soil testing requirements. Geoenvironmental samples were administered during the site works by the company, however, determinant testing was carried out under a subcontract agreement with a local supplier. Post work monitoring was undertaken by in-house personnel in conjunction with the Clause 14 programme submitted during the preparatory stage to the contract. Resourcing was set at a level to achieve the monitoring timescales required by the Investigation Supervisor.
Throughout this reporting phase there was a concerted quality approach at all times in order to ensure accuracy and data integrity. The volume of data being received on a daily basis from site was significant with all elements needing to be checked at various stages prior and post data entry; which itself is underpinned by our robust quality management system. There was constant liaison with site personnel to address any inconsistencies that arose or indeed to clarify the data being presented. This upfront process was implemented to avoid any minor issues influencing the short turnaround times required by the Investigation Supervisor and to mitigate any loose-ends becoming a potentially larger problem going into the report preparation phase.
The same is also true in relation to the report preparation phase and the iterative system that AEG have in place to fully quality check submissions to client organisations. Factual report was subdivided into two sections, Source Delineation and Isherwood Park, whilst monitoring reports were also submitted at the completion of each monitoring round during the post site works phase. All data acquired during the course of the investigation finally being issued in a digital AGS compliant format.