Holding Back the River - Zone A Catchment Build
One of our early goals in the project is to cut off leachate production which overwhelms the effluent lagoon at the bottom of the site thereby reducing the ongoing production of leachate to more manageable quantities. This in turn eases the treatment of the remnant leachate across the three large contaminated water lagoons within the site.. Leachate arrives at the lagoons through surface runoff, ground infiltration and along the hard standings via manholes leading to the lagoon.
The cover laid on top of the land drains has significantly reduced the volume of leachate we see in the effluent lagoons but increases the volume of clean run off within the site. Using impermeable clay, we constructed an embankment along the lowest part of the northern half of the job to hold back the clean surface runoff. By doing this we have further reduced the volume of leachate in the effluent lagoon. The clean surface run off is attenuated in the temporary pond and then discharged directly into the Collins Brook slowly to mitigate flood risk downstream.
We have also sealed the manholes off from clean surface runoff along the access track which cuts through the middle of the site These manholes and connecting pipework have historically collected leachate and delivered it to the leachate storage lagoons and by sealing them we have been able to further reduce the amount of leachate and increase the amount of clean runoff. With the manholes now only collecting leachate from below ground we are able to sample and test the leachate to identify ‘hot spots’ of contamination and to validate the effectiveness of our capping solution. As the cover increases the flow rate should decrease.