Waste water pumping station – Warrington

Location: Warrington
Sector: Utilities
Development detail: Construction of a waste water pumping station to a depth of 20 m below ground level, through a former landfill site and adjacent to a surface watercourse
Roles: Providing advice to the principal design and build contractor
  1. Background:
    Desk study research and phased ground investigation data was made available for review by the Client.  In summary, the site lies between a canal and surface water course and within the boundary of a former landfill site.  Loose asbestos fibres, as well as a range of other potential contaminants, had been identified within the former landfill materials.

    It is proposed to construct a waste water pumping station to replace the existing pumping station located to the south of the site.   The new pumping station is to be built almost entirely below ground level.  There is a requirement to excavate down to 15 m depth and, due to construction requirements, the resulting excavation was 50 m diameter wide at ground level.  In order to minimise the volume of material removed from site, a landscaped area was proposed to the north of the pumping station.

    Crossfield Consulting was appointed to provide environmental advice relating to the control and movement of the excavated materials.

  2. Our involvement:
    Crossfield Consulting prepared a Remediation Implementation Plan to the satisfaction of the local authority and the Environment Agency.  The final location of the excavated materials within the landscaped area was determined on the basis of a quantitative risk assessment associated with potential pollution migration to the adjacent water courses.

    Crossfield Consulting undertook full time supervision of the excavation of landfill materials.  This included the controlled sampling and testing of the materials and the excavation, movement and placement of layers into managed stockpiles.  Following receipt of the laboratory test data, materials were then classified and placed into a suitable area within the proposed landscaping.

    The scheme involved the excavation of 12,500 m3 of Made Ground and all of these materials were re-used within the project in accordance with the CL:AIRE Code of Practice.  The materials were excavated in 1 m thick sections to the base of the landfill materials.  A ring of sheet piles were then installed and the natural soils within the sheet pile ring were then sampled, tested, excavated and placed within the proposed area of landscaping.

  3. Ongoing work:
    The proposed pumping station is currently being constructed and is due to be completed in 2013.  Following the construction of the pumping station, the excavation will then be backfilled to ground level with suitable site-won materials.

    The remedial works are being supervised by qualified staff from Crossfield Consulting and a verification report will be prepared on completion.