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Impacts of Overflow Reduction Resulting from Sewer Renewal
Despite the growing number of sewer rehabilitation processes and products, few reports have been available in the literature about their effectiveness for I/I removal, SSO reduction, and water quality improvement. This paper presents results from flow monitoring studies, overflow reports, and water quality studies conducted over the past nine years in Nashville, Tennessee. I/I quantity, SSO duration and fecal coliform concentrations were selected as the parameters most likely to be affected by sewer renewal projects. To develop a data base of objective measurements of sewer rehabilitation effectiveness, twenty seven projects conducted in the Nashville, Tennessee, OAP (Overflow Abatement Program) were analyzed which included 83,781 m (274,871 ft) of sewer lining or replacement. This represents about half of the rehabilitation work conducted through this program since 1990. The goal of the program is to improve system characteristics, recapture capacity, and reduce I/I so the sewers can carry the peak flow from a design storm with a specified recurrence probability, without overflows. The most stringent design criteria used a 5-year, 24-hour storm. Linear regression analyses were used to predict the I/I expected from the selected design rainfall. Some of the projects showed sufficient I/I reduction to allow a five-year payback from treatment costs avoidance. A cumulative annual I/I reduction of 10.36 x 106 m3 (2,737 million gallons) has been documented for these projects. The trend of results indicate that an I/I removal rate of approximately 10,000 m3 /year/100m of lining (8.2 million gallons/year/1000 ft of lining) may be expected from rehabilitating deteriorated sewers in the Nashville area. I/I removal rates will likely vary in different locations due to groundwater levels, annual rainfall, previous construction techniques, soil types, etc. Accordingly, sewer rehabilitation programs should include procedures to measure I/I removal effectiveness as a program progresses. For I/I control programs that are just beginning and which lack performance data, the rehabilitation experience in Nashville illustrates a procedure to develop performance measures and procedures for long range program planning. Once defined for a given area, that removal rate can be coupled with rehabilitation construction costs and I/I quantities from flow monitoring. Knowing the relationship between I/I removal effectiveness and the quantity of sewer rehabilitation by lining required can assist planners and municipal officials in projecting the long-term program costs for sewer rehabilitation. State regulatory actions are increasingly focused on streams that have not achieved water quality levels appropriate for their designated uses. Lists of these streams have been published as required by Section 303d of the Clean Water Act. In many cases these streams have been listed because of SSOs or CSOs (separate sanitary sewer overflows or combined sewer overflows) that discharge during wet weather conditions. However, long-term water quality studies on tributary streams in Nashville have indicated that background or non-point pollution sources may be significant. In some cases, removal of wet weather discharges may not be sufficient to achieve compliance. TMDLs (total mass discharge limits) may be needed.
Impacts of Overflow Reduction Resulting from Sewer Renewal
Despite the growing number of sewer rehabilitation processes and products, few reports have been available in the literature about their effectiveness for I/I removal, SSO reduction, and water quality improvement. This paper presents results from flow monitoring studies, overflow reports, and water quality studies conducted over the past nine years in Nashville, Tennessee. I/I quantity, SSO duration and fecal coliform concentrations were selected as the parameters most likely to be affected by sewer renewal projects. To develop a data base of objective measurements of sewer rehabilitation effectiveness, twenty seven projects conducted in the Nashville, Tennessee, OAP (Overflow Abatement Program) were analyzed which included 83,781 m (274,871 ft) of sewer lining or replacement. This represents about half of the rehabilitation work conducted through this program since 1990. The goal of the program is to improve system characteristics, recapture capacity, and reduce I/I so the sewers can carry the peak flow from a design storm with a specified recurrence probability, without overflows. The most stringent design criteria used a 5-year, 24-hour storm. Linear regression analyses were used to predict the I/I expected from the selected design rainfall. Some of the projects showed sufficient I/I reduction to allow a five-year payback from treatment costs avoidance. A cumulative annual I/I reduction of 10.36 x 106 m3 (2,737 million gallons) has been documented for these projects. The trend of results indicate that an I/I removal rate of approximately 10,000 m3 /year/100m of lining (8.2 million gallons/year/1000 ft of lining) may be expected from rehabilitating deteriorated sewers in the Nashville area. I/I removal rates will likely vary in different locations due to groundwater levels, annual rainfall, previous construction techniques, soil types, etc. Accordingly, sewer rehabilitation programs should include procedures to measure I/I removal effectiveness as a program progresses. For I/I control programs that are just beginning and which lack performance data, the rehabilitation experience in Nashville illustrates a procedure to develop performance measures and procedures for long range program planning. Once defined for a given area, that removal rate can be coupled with rehabilitation construction costs and I/I quantities from flow monitoring. Knowing the relationship between I/I removal effectiveness and the quantity of sewer rehabilitation by lining required can assist planners and municipal officials in projecting the long-term program costs for sewer rehabilitation. State regulatory actions are increasingly focused on streams that have not achieved water quality levels appropriate for their designated uses. Lists of these streams have been published as required by Section 303d of the Clean Water Act. In many cases these streams have been listed because of SSOs or CSOs (separate sanitary sewer overflows or combined sewer overflows) that discharge during wet weather conditions. However, long-term water quality studies on tributary streams in Nashville have indicated that background or non-point pollution sources may be significant. In some cases, removal of wet weather discharges may not be sufficient to achieve compliance. TMDLs (total mass discharge limits) may be needed.
Impacts of Overflow Reduction Resulting from Sewer Renewal
Kurz, George E. (author) / Woodard, Scott (author)
National Conference on Environmental and Pipeline Engineering ; 2000 ; Kansas City, Missouri, United States
2000-07-17
Conference paper
Electronic Resource
English
Impacts of Overflow Reduction Resulting from Sewer Renewal
| British Library Conference Proceedings | 2000
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