Reedbed Project Example
Lagoon Emptying and Relining: A Complex Environmental Engineering Project
In the heart of Lancashire, 4R took on a challenging project for a prominent abattoir. The task was to assess, empty, and reline a storage lagoon that had reached the end of its design life. This lagoon played a crucial role in the site's wastewater management site as the primary settlement point in a series of reedbeds designed to clarify abattoir wash waters before discharge into a local watercourse.
4R, already familiar with the site's operations through the site's ongoing work obtaining EA deployments and sourcing land for washwater recycling, approached the project with a wealth of experience and insight.
Lagoon Clean out and Reline
Image: Lagoon prior to emptying
The Challenge
An initial site visit was undertaken so that our project team could take samples to determine the physical and nutrient contents of the lower levels of the lagoon. The surface layers are regularly pumped out, but the lagoon had not been wholly emptied for at least 20 years, and the depth and content of the settled sludge were unknown.
Initial Assessment and Planning
The 4R projects team began with a thorough site visit, collecting samples to determine the physical and nutrient contents of the lagoon's lower levels. Laborlagoon's analysis revealed that the sludge was suitable for recycling at permitted field sites, aligning with 4R's sustainable practices.
Drawing from their experience with similar cleanout projects, the team anticipated that the settled sludge would require extensive agitation to lift solids into suspension, enabling efficient pumping. However, before this operation could commence, the lagoon had to be taken offline, and a bypass pipe was installed to redirect daily production to a downstream reedbed.
Image: Liquid re-circulating
The Emptying Process
A specialised contractor agitated the slurry using a high-volume pump and jetter unit, while another pump removed the suspended solution for land spreading via an umbilical/tanker system. This approach initially proved effective in removing a significant portion of the liquid and settled solids.
However, the team soon encountered an unexpected challenge: a heavier fraction of gritty solids that resisted suspension. The lagoon's large surface area makes it impossible to maintain sufficient circulation to keep these particles in suspension.
Image: Settled gritty solids in the bottom
Adapting to Challenges
Faced with this unforeseen obstacle and unable to use traditional excavation methods due to concerns about bank stability and the size of the lagoon, the team pivoted to an innovative solution. They brought in a specialist tanker firm equipped with a liquid ring super sucker tanker. This powerful machine effectively extracted the stubborn solids, depositing them into an adjacent empty sealed pond.
Relining for the Future
The relining process began with the lagoon emptying and thoroughly cleaning its sides. The team left the existing liner in a strategic decision that balanced efficiency and additional protection. This approach provided an extra layer of security for the new liner and created a clean working environment for the lining team.
The relining process involved several steps:
· Digging an essential trench around the lagoon's perimeter to anchor the lagoon's liners.
· Laying and welding a geotextile protective membrane on top of the existing liner.
· Sequentially placing and securing a 2mm HDPE liner over the geotextile.
· Weather proved to be an additional challenge, with tropical-like rainfall sometimes hampering the welding process, which required dry conditions for the heat welding to work.
Image: Liner being laid
Finishing Touches
The team installed a depth marker gauge and a wildlife escape ladder to complete the project and enhance its functionality, demonstrating their commitment to operational efficiency and environmental responsibility.
Image: HDPE liner completed and depth gauge installed.
Conclusion
This project showcases 4R's ability to tackle environmental engineering challenges with innovation, adaptability, and perseverance. By successfully emptying and relining the lagoon, 4R has ensured the continued efficient operation of the site’s wastewater management system, contributing to environmental compliance and sustainable water use in the region.
Image: Completion and commissioning - April 2024.