Bredbury Drainage Remediation
Overview
The works were on a closed landfill that currently houses a domestic waste reception centre for trade and domestic waste processing. The waste processing facility is operated for GMCA (Greater Manchester Combined Authority) by a private contractor.
GMCA operate a landfill leachate wastewater processing plant that receives run-off through a network of land drains located in the base of the capped landfill. The processing plant strips methane from the run-off and pumps the treated effluent into the site foul drainage system from where it is conveyed to the public sewer.
The purpose of the project was to replace a failing rising main that runs through the middle of the landfill.
The scope of the project was as follows:
- Replace approximately 90m of 150mm diameter perforated landfill leachate drainage pipe with 300mm nominal bore perforated pipe; at depths of 4 to 7m in landfill waste material
- Construct a new MH LMH6A 1500mm diameter 6m deep, including landing slab, ventilation pipe and cowl
- Replace existing MH LMH7 1500mm diameter 8m deep including landing slab, ventilation pipe and cowl
- Replace existing MH LMH8 1500mm diameter 7.5m deep including landing slab, ventilation pipe and cowl
- Repair an existing 150mm diameter clay drainage pipe in 2 separate locations at depths 4m to 5m deep
- Replace the cover slab of MH LMH9 and installation of ventilation pipe and cowl.
Key Challenges
A landfill site is a dangerous and unpleasant environment and our works went through the middle of the tip.
Adverse weather: The poor weather conditions with ice, snow and heavy rain, made it difficult to access the site, so we imported quarried material to form hardstandings.
A HV cable crossed the working area: We used temporary works to support the cable whilst the pipe was laid beneath.
Groundwater control was difficult but critical to avoid pollution. The landfill site had been restored but did not have an engineered capping system so required the management and treatment of leachate water percolating through the waste. This contaminated run-off is treated to reduce methane levels and is subsequently discharged to the public foul sewer.
Poor ground conditions: We segregated excavated material so that the better quality material could be used as trench backfill.
Added Value
With the bearing capacity of the waste material within which the drainage was constructed, our design anticipated settlement/movement and incorporated a more robust pipe material.
A reduced level dig was undertaken to make the drainage installation shallower. This approach was required because of the poor ground conditions in the waste tip.
There was originally a requirement to remove waste off-site, however, all surplus drain arisings were left on site and the ground re-profiled to incorporate this material.
Social Value
EWCE delivered over 20% of the contract value in social value commitments.
Our team included Stockport residents as Contract Manager and Site Manager and most of the materials were bought locally.
Our skips were sourced through Greater Manchester based Kenny Waste Management, a Social Enterprise who provide employability programmes for Greater Manchester residents.
Two of our staff members used their company volunteering day to help out on community projects. Scott Latta, Eric Wright Social Value Manager, volunteered 8 hours with Urban Out Reach helping to sort and distribute food parcels over the school holidays and Christmas hampers. Whilst Andy Leach, EWCE Health and Safety Advisor volunteered 8 hours at Little Heaton Primary School helping at a PTA event.
We attended several local schools and colleges delivering presentations, mock interviews and taking part in careers fairs.