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Meeting Challenges
in The Pas

The town of The Pas, Manitoba (pop. 8,500) uses an eight-acre aerated aerobic sewage lagoon to treat municipal waste. After aeration, the waste is allowed to settle in the second part of the single cell system before being chlorinated and discharged into nearby Grace Lake. During the late 1980s and early 1990s the 20 year-old aeration guns began to fail due to fatigue, line failure, plugging with rags, etc. The BOD of the effluent rose to over 30mg/L causing the lake a great deal of distress. The consulting firm of UMA Environmental was contacted to carry out a study and select a means of remediation that would rectify the situation and keep the lagoon in operation for the duration of the project.

The study revealed that only three quarters of the burp tubes were working normally and that sludge in the cell was spread evenly throughout to a depth of 4 - 6 feet and contained an abnormal amount of mercury.

UMA Environmental prepared specifications that included, removing the existing system, replacing it with the polcon arrangement while adding 20%, more aeration tubes and desludging the entire cell. The specifications called for the work to be completed in two stages without taking the treatment procedure completely out of service for any extended time.

Of the five companies that were invited to submit proposals for the project, only three returned presentations and pricing. The proposal by Dominion Divers not only met all criteria but came in at one half the cost of the two that could not meet the requirements.

Our Approach

Using a combination of the SUBCAT, PORTA FLOAT barges, contaminated diving capabilities and excellent human resources the project was completed as follows.

  1. Desludging of the settling area of the cell using the SUBCAT was started immediately while preparations were made for installation of new helioxers by other members of the team.
  2. Upon completion of the above, the lines of the old air distribution system were marked and as the SUBCAT removed nearby material the lines were extricated from the cell along with the attached burp tubes.
  3. Whenever a pipe broke during this process contaminated diving operations were employed to reattach it to the line used to pull it from the cell.
  4. As lines were removed they were replaced using a PORTA FLOAT barge and a ramp system to install them at the correct location. Once in place the line, was charged and put into service while the next old line of tubes was removed. This process was completed repeatedly until the aeration system in the lagoon was completely reinstalled.
  5. The header feeding the system was found to be badly corroded and had to be replaced completely. This required steel pipe, eight inches in diameter, and schedule 80 complete with laterals and valves.

Dominion Divers staff had the welding certification, the ability and resources to complete the task without taking the treatment system out of service for more than four hours at a time. Studies done after the contract completion showed that the BOD count was down from over 30 to under 7 mg/liter at the discharge to the lake. This indicated that the design by UMA Environmental, the material used and the workmanship by Dominion Divers led to successful resolution of the project.

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