NASHVILLE PROJECT SHOWS LONG-TERM EFFECTIVENESS OF SEWER REHABILITATION FOR INFILTRATION REDUCTION

摘要

When planning a sewer rehabilitation project, municipal sewer agencies and design engineers sometimes ask: "What is the life span for these products, and how long will they remain effective for reducing groundwater infiltration as originally designed?"To address this issue, a major sewer rehabilitation project conducted by Nashville MWS (Metro Water Services) was studied for a period of 12 years following completion in January 1996. CIPP (cured-in-place pipe) was used to reline over 42,000 linear feet of 8" to 30" pipe. This represented about 15.5% of the project system. Contiguous manholes and services were rehabilitated. Flow monitoring was conducted prior to the project and the results compared to monitoring immediately following the rehabilitation work, then repeated in 1998, 2002, and ending in 2006-2007. The initial results showed that 620 mill. gal. of infiltration (~35%) were removed annually. The most recent monitoring showed a reduction of 488 mill. gal. (~28%). The results could suggest that the level of effectiveness has deteriorated slightly in the past ten years. However, it may also reflect the effect of continued deterioration of parts of the system that were not rehabilitated. The 5-year, 24-hour infiltration and the peak-hour infiltration rate showed year 2007 reductions of 43.4% and 43.6% respectively. This was sufficient to maintain the goal of containment for the 5-year (4.5 inch) storm. The monitoring results were objectively analyzed using all valid rainfall events during each study (typically >25 events for a year). The analytical procedures followed the Nashville "Standardized Approach" (Kurz, et al. 2003) which uses a set of rigorous rules and statistical tests for quality control and assurance.