A processing facility operates a wastewater treatment plant (WWTP) that includes an anaerobic lagoon, sequencing batch reactor (SBR) and wetlands. During the winter of 2015 an electrical failure culminated in the over drawdown of the HDPE lined SBR lagoon causing mechanical damage to the liner. Production at the facility was forced to halt, placing pressure on the business’s ability to fulfil customer orders and requiring a remediation of the SBR lagoon during the winter months.
This paper outlines the works undertaken to dewater, strip and clear the 6 metre deep benched lagoon of 12,000 m3 volume of sludge laden material ready for relining. Even though a tight construction programme was presented, the opportunity and challenge was taken to futureproof the lagoon for increased inflows, reline, refill, reseed and provide an operational SBR within a 10 week period.
Construction had to deal with the subgrade beneath the existing damaged liner which needed to be removed by excavator without damaging the clay base and embankment material that was soft due to wet winter conditions. Of concern were the winter groundwater conditions, embankment stability with the presence of the 5 m deep anaerobic lagoon directly adjacent to the now empty SBR lagoon and local river on the opposite side of the SBR, which flooded due to heavy rain during the construction period.
The paper describes how cooperative management, onsite design and supervision, and client consultation overcame compaction complications of working with clay in winter, laying HDPE liner in trying conditions of wind, rain and winter temperature variations and the installation of a concrete anchor trench to provide the client with an improved and operational SBR ready to receive process flows in time for the restart of processing.