Landfill Gas Emission Concern
Odour emissions gave cause for concern about PPC Permit breach
Investigation
OIS were contacted by a client that had concerns about landfill gas emissions that could potentially lead to a breach in the PPC Permit. The client was also concerned that renewable power production from landfill gas had fallen from 1000kwh to 750kwh. OIS were invited to carry out a detailed site inspection during which several issues were identified including perished concrete chambers, the pumps used for leachate collection were cumbersome and difficult to service and there were concerns about leachate compliance levels.
Based on our extensive experience, we were able to make remedial recommendations which were subsequently approved and we were able to provide a CQA Validation Report.
We noted:
- Landfill gas and leachate wells were of a concrete ring and biscuit construction that had perished over time.
- The Energy Contractor was unable to apply vacuum to the chambers to extract landfill gas due to oxygen ingress.
- Landfill gas was escaping from the chambers.
- The leachate pumps used were a pedestal type that were manually operated after daily dips were taken.
- The leachate compliance levels for this site are set at 1 metre, meaning the pump motors were potentially exposed to a gaseous atmosphere.
- The leachate pumps were difficult to remove for maintenance and repairs.
Recommendations
Our suggested remedial work included:
- Construct a new HDPE swan neck and well head, fitted with dip point lids, gas collector lines, gas sample taps and leachate collector lines. The swan neck system was designed and built with SGG and is the first of its type. Previously, the energy contractor could not apply a vacuum to the gas wells.
- The new well head type would be sealed using mechanical fixings, HDPE liner and bentonite.
- Change the leachate collection pump philosophy to a bore hole type pump controlled by Dry Running Protection Devices (DRP) - we recommended a rubber worm drive pump with the inlet mounted above the motor. The pumps dimensions were less than 1 metre with the intake for leachate set at the top of the pump giving a mechanical safety mechanism to ensure the pump motor is not exposed to atmosphere. In addition the DRP is set to 900mm above the base of the well, resulting in an automated pump without the need for SCADA, HMI’s and control panels that also ensures the leachate levels within the landfill cells are at a compliant level.
Solution
The recommendations were approved and Organic Innovative Solutions compiled a Draft CQA plan for approval by SEPA. The plan was agreed and OIS provided the CQA Engineering, Supervision and Project Management services for the project.
On completion of the project, OIS drafted and issued the CQA validation report.
The works were completed successfully which enabled the energy contractor to apply a vacuum to the landfill gas chambers. The site now operates its 1000kwh engine at 100% and has introduced a 250kwh engine that also runs at 100%. Based on flare rates and gas quality the second landfill gas engine is due to be upgraded with a 1000kwh engine. The total electrical generation exported from the site is expected to be 2000kwh. In addition, since the completion of the works, odour complaints out with the boundary of the site have ceased.
