Llay Landfill Site Remediation Works

The closed Llay Landfill Site is located approximately 4.5km to the north west of Wrexham town centre at NGR 332990, 354510.

Planning permission was granted in 1988 for the reclamation of a derelict sand/gravel quarry by the controlled tipping of domestic, commercial and non-toxic refuse. Tipping commenced in August 1988 and was completed by August 1992. The landfill waste occupied an area of approximately 6.92ha out of a total site area of approximately 7.9ha.

Following the closure of the landfill site the area was restored to form part of the Alyn Waters Country Park. Part of the restoration of the site involved the “capping” of the area with a layer of clay.

Tankers have been visiting the site to remove landfill leachate. Over time the quantities of leachate requiring removal should have fallen to a point where tankers were no longer required. However the removal rates have remained constant and the leachate within the landfill site has not reduced as predicted.

Several investigations and monitoring have therefore been carried out at the site since 2004 and a number of issues have been identified. These principally relate to the integrity of the existing capping which has resulted in the ongoing generation of leachate within the waste mass and its subsequent migration off-site, possibly via overtopping of the landfill cell walls along the eastern boundary of the site.

A remediation project is therefore being procured that will reduce the generation of leachate within the waste mass and thereafter reduce the likelihood of its possible migration off-site.

The works involve improvements to the existing capping system where it is indicated to be either absent or less than 500mm thick. The linking of the existing clay cap to the side wall liners within the landfill area shall be undertaken around the full perimeter of the site.

There are a number of ways in which the perimeter repair could be undertaken. These include an extension of the clay cap to provide a link to the side wall liner or a geomembrane LLDPE liner with anchor trenches within the existing cap and linked to the existing side wall liner. If the side wall liner cannot be located it will be necessary to extend the liner to be outside the existing waste footprint to prevent surface water from entering the waste.

Ancillary works include the reinstatement of investigatory trial pits, installing additional gas venting, additional leachate wells, installation of a perimeter surface water drain and outfall to the nearby river Alyn, and landscaping and restoration works.

Detailed design is currently on-going.

Companies wishing to tender should note that Wrexham County Borough Council has appointed Mott MacDonald to act as their Employer’s Agent on this project.

A location plan and anticipated timescales are provided in the attached documentation.

SHOULD YOU BE INTERESTED IN THIS CONTRACT OPPORTUNITY YOU MUST IN THE FIRST INSTANCE EXPRESS YOUR INTEREST BY CONTACTING:

Richard Griffiths

Mott MacDonald

5 Woodland Road West

Colwyn Bay

LL29 7DH

Tel: 01492 534601

E-mail: richard.griffiths@mottmac.com

Suppliers wishing to be considered for inclusion on the tender list must demonstrate via a pre-qualification process that they have the necessary expertise and experience to undertake the works.

All pre-qualification information, including the pre-qualification questionnaire, is included as attachments to this notice.

Completed submission must be returned by the closing date of 12 Noon on Friday 11th May 2012.

Details of the assessment process are included in the attached documentation.

As part of this restricted procedure procurement exercise, following full evaluation of all Pre-Qualification Questionnaires received Wrexham County Borough Council will select a minimum of 5 and up to a maximum of 7 Companies to invite to tender.