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Offsite sanitary sewer design budget doubled
City of Cranbrook council last night approved doubling the budget of the Shadow Mountain Offsite Sanitary Sewer Design, from $200,000 to $400,000.
The increase in the budget is to be funded from the development securities, noted Curtis Penson of the city’s Engineering and Development Services department.
“The Request for Proposals (RFP) for the Shadow Mountain Offsite Sanitary Sewer Design closed on February 3. Staff have completed their review and scoring of the proposals and determined that Urban Systems would be the successful proponent. Urban System’s cost is estimated at $274,930 for the most minimal design,” Penson explained in a report to council.
“This does not include the North Area Neighbourhood Sanitary Servicing Plan. Furthermore, a significant issue with Focus / WSP’s original concept design was identified by multiple consultants in the RFP process.”
Chiefly, the elevation between proposed Lift Station (LS) 1 and LS 2 is 70 metres and LS 2 to the connection to the city system is 20 metres, for a total of 90m elevation, Penson reported, noting “it is ideal to limit the pumping head for conventional sewage pumps to 40 to 50m (e.g. non-clog pumps) to maximize efficiency and reliability. An elevation difference of 70m that LS 1 would have to pump against warrants a review of high head-pumps. Two pump styles that are designed for higher head applications that can be considered include submersible turbine and vertical turbine pumps. These style pumps are more efficient than conventional sewage pumps, but the trade-off is that screening upstream of the pumps would be required.
“Therefore, prior to the design a high-level review of alternative means of collection and conveyance to optimize capital and life cycle costs balanced with long term operation, maintenance and performance considerations must be completed.”
As a result, depending on the outcome of the review, the design costs may come close to $400,000 due to additional structural and mechanical design, Penson said.
“While the design costs may be higher it will provide a better system with optimized capital and life cycle costs.”
The report also notes there is approximately $611,864.75 plus some interest held as security for the offsite sewer system to Shadow Mountain.
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