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 Infrastructure Sustainibility: Evaluating Saskatoon's 1912 Interceptor Mark Andrews, P.Eng., AndrewsInfrastructure, Ottawa, ON
ABSTRACT The City of Saskatoon’s main Interceptor Sewer comprises some 10 km of sewer ranging in size from 600 to 2100 mm diameter and was built and commissioned in stages. The first stage was completed in 1912 to service the original town-site, but curiously wasn’t commissioned when completed. The Interceptor wasn’t actually put into service until 1948, after the construction of a comminuter/lift station facility and an outfall. The final stage of work was completed in 1970 which included a 4.5 km extension to a new activated sludge sewage treatment plant. The entire Interceptor was evaluated in 2005 as part of the City’s on-going asset management program using the WRc approach and based upon findings from combined CCTV/Sonar inspections, manhole inspections, material testing, hydrogen sulphide monitoring and ventilation monitoring. The purpose of this paper is to present an overview of the design and construction of the 1912 portion of the Interceptor and to show how historical investigations lead to a better understanding of the sewer’s performance. Historical evidence was used to determine the materials and products integrated in the Interceptor and to determine construction techniques. The staging of the Interceptor construction presented a somewhat unique situation in terms of assessing its performance and thereby forecasting its long term maintenance needs. In order to evaluate the current condition of the original 1912 portion of the Interceptor it was necessary to understand something about how it was designed and constructed. But more importantly, in order to forecast future maintenance and rehabilitation requirements it was necessary to understand how, and at what rate, the existing sewer might be deteriorating; and hence the need to confirm the delay between construction and commissioning. Historical investigations enabled the engineering team to establish and confirm critical aspects of the age and life-expectancy of the sewer. This enabled the team to confidently forecast on-going maintenance needs. It also enabled the team to better evaluate performance and key characteristics of the sewer, such as joint condition, structural distress, deviations in longitudinal slope and corrosion impacts. Recommendations were made regarding maintenance issues and rehabilitation needs. Findings indicate that the 1912 Interceptor is in relatively good condition; with on-going maintenance the sewer is expected to provide useful service for many decades to come. INTRODUCTION The 1912 Interceptor comprises 48", 60", 66" and 72" (1200, 1500, 1650 and 1800 mm) diameter pipe as summarized in Table 1. The 1970 sections comprise 72” and 84” (1800 and 2100 mm) diameter pipe. The Spadina Lift Station is an on-line facility that lifts sewage approximately 15 m from the original outfall location adjacent to the river, to the upstream end of the new extension. The assessment of the sewer was carried out in two steps. First a detailed internal inspection program, utilizing specialized inspection equipment, was undertaken to document existing field conditions. Second, a detailed review and assessment of the inspection findings was carried out in order to assign condition grades. It was during this later stage that historical issues were taken into consideration. Concrete cores and H2S monitoring results were used to supplement inspection findings and refine condition assessment conclusions. Condition assessment rating and conclusions were based on the well-known WRC methodology.
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