Sewer Replacement Research Articles

Relationship between infiltration, sewer rehabilitation, and groundwater flooding in coastal urban areas.

The aging of sewer networks is a serious issue in urban areas because of the reduced functionality of the system that can have negative impact on the urban environment. Aging pipes are not water-tight anymore and they can leak untreated sewage or allow infiltration of groundwater. In the latter case, more frequent combined sewer overflows (CSOs) may occur. Generally, prompt intervention to repair damaged conduits is envisaged. However, in low-lying coastal regions, sewer systems may provide an unplanned drainage that controls the groundwater table from flooding the urban ground. Here, a study is presented to investigate the influence of the repair of damaged sewer on the water table of an urban shallow aquifer. Sewer and groundwater models were built to describe the effect of sewer replacement. Based on a real dataset, simulations were run for a city located along an estuary. Results show that the presence of infiltration into the sewer system increases the frequency of CSOs, which trigger the discharge of untreated sewage after a minor precipitation or even in dry weather conditions. As the sewer is repaired, CSO spills diminish occurring only upon significant precipitation. However, the water table rises and eventually, during the high tide, the groundwater floods the low-lying part of the city. Overall, this work highlights the susceptibility of shallow aquifers in coastal urban areas and suggests that they should be regarded in flooding predictions.

Valuing information for sewer replacement decisions.

Decision-making for sewer asset management is partially based on intuition and often lacks explicit argumentation, hampering decision transparency and reproducibility. This is not to be preferred in light of public accountability and cost-effectiveness. It is unknown to what extent each decision criterion is appreciated by decision-makers. Further insight into this relative importance improves understanding of decision-making of sewer system managers. As such, a digital questionnaire (response ratio 43%), containing pairwise comparisons between 10 relevant information sources, was sent to all 407 municipalities in the Netherlands to analyse the relative importance and assess whether a shared frame of reasoning is present. Thurstone's law of comparative judgment was used for analysis, combined with several consistency tests. Results show that camera inspections were valued highest, while pipe age was considered least important. The respondents were pretty consistent per individual and also showed consistency as a group. This indicated a common framework of reasoning among the group. The feedback of the group showed, however, the respondents found it difficult to make general comparisons without having a context. This indicates decision-making in practice is more likely to be steered by other mechanisms than purely combining information sources.

Decision-making for sewer asset management: Theory and practice

Operational decision-making for sewer asset management has hardly been empirically analysed, hampering the current challenge for cost-effectiveness in the urban drainage sector. This paper analyses how decisions for sewer replacement are actually made and to what extent complexity of the decision-making environment is addressed. Decision argumentation of 150 sewer replacement projects in the Netherlands was obtained by interviews. The decision process was analysed by the rational and streams model. The decision argumentation is a relatively wide variety of information sources, of which the majority is case-specific. Yet, decision-making does not rely purely on data analysis; it also includes negotiations between involved infrastructure managers. Then, replacement planning of a sewer asset manager depends on other public works. Consequently, individual cost-effectiveness as an evaluation criterion should be expanded to include group utility.

How Much to Spend on Sewer Inspection, Renewal and Replacement? A Risk-Based Assessment for DC Water

How Much to Spend on Sewer Inspection, Renewal and Replacement? A Risk-Based Assessment for DC Water

Quality and use of sewer invert measurements

Sewer replacement and rehabilitation is the most capital-intensive issue in urban drainage. Currently visual sewer inspection is the primary investigation technique. This information source, however, has a large uncertainty and does not provide the necessary information; therefore, for areas with soft soil conditions (e.g. river delta areas) the potential of a new information source, namely settlement data, is assessed. To analyse settlement, the vertical position of a sewer invert is determined by measuring the position of the manhole cover and the distance between cover and sewer invert. Measurement of the sewer invert is a common practice in the city of Amsterdam, the Netherlands. The use of the measurement data to assess settlement, however, is new. When multiple measurements of the same sewer invert are available over a period of time, the settlement process can be described and future positions can be estimated. Based on these estimations, the occurrence and location of stagnant water zones in the system were predicted for a case study area. The formation of these locations reduces the storage capacity and increases the accumulation of sediments. The settlement model can be used to develop and assess suitable rehabilitation strategies.

Evaluation of Life-Cycle Costs and Cost/Benefit Analysis in Comparing Sewer Replacement versus Sewer Rehabilitation

Evaluation of Life-Cycle Costs and Cost/Benefit Analysis in Comparing Sewer Replacement versus Sewer Rehabilitation

Improving Capacity through Sewer Replacement – Potomac Interceptor Project

Improving Capacity through Sewer Replacement – Potomac Interceptor Project

Leveraging GIS & Hydraulic Modeling for Prioritizing Water and Sewer Renewal and Replacement

Leveraging GIS & Hydraulic Modeling for Prioritizing Water and Sewer Renewal and Replacement

Developing an Effective, Reasonable, and Defensible Sewer Rehabilitation and Replacement Plan – “Getting the Biggest Bang for your Buck”

Developing an Effective, Reasonable, and Defensible Sewer Rehabilitation and Replacement Plan – “Getting the Biggest Bang for your Buck”

Controlled treatment with nitrate in sewers to prevent concrete corrosion

It has generally been accepted that concrete corrosion is caused by bacterial oxidation of hydrogen sulphide in sewage systems. Costs related to sewer replacement and remediation are quite high, but there is limited knowledge and documentation on the relationship between hydrogen sulphide levels and corrosion rates. This is necessary information in order to select the appropriate means of hydrogen sulphide control and to conduct cost-benefit evaluations. This pilot scale study shows that the concrete corrosion rate can be modeled by a Monod type function with Ks=2 ppm H2S in gas and a maximum concrete corrosion rate at 25°C of 16 mm/year. Complete hydrogen sulphide control with 0 ppm H2S in water and gas is required to prevent concrete corrosion. This can be achieved by controlled treatment with nitrate using the Nutriox® Concept where the nitrate dose is based on flow, temperature, sewer design, and sewage concentration. The local conditions will be important for the cost-benefit evaluations, but in general terms, one can say that the longer the hydraulic retention time is, the more cost effective will a controlled treatment with nitrate be for corrosion control.

CITY OF PHOENIX LOWER BUCKEYE SEWER EMERGENCY REPAIR, REHABILITATION, AND REPLACEMENT

CITY OF PHOENIX LOWER BUCKEYE SEWER EMERGENCY REPAIR, REHABILITATION, AND REPLACEMENT

Microtunnelling chosen for sewer replacement : P. Darling, Tunnels & Tunnelling, Special Issue (Spring), 1994, pp 7–10

A description is given of the upgrading of part of Kuwait City's sewer system to replace corroded pipes and increase gradients. Three Euro Iseki Unclemoles (T300, T400 and T600) are being used for the work which varies from 5 to 11m in depth under existing roads parallel to existing sewer lines. The decision to use microtunnelling is discussed. Ground conditions are sand, a hard cemented sandstone with a high silica content and a high watertable. The use of a steel shutter-tower method for shaft sinking is outlined. Pre-excavation treatment has included extensive dewatering. The humid conditions have caused a number of problems with equipment. Details are given of measures taken to avoid corrosion. These include the use of vitrified clay pipes.

An occurrence of palygorskite in a fault gouge, Karori, Wellington, New Zealand

Abstract Palygorskite has been identified from a fault gouge in the south Karori outfall sewer replacement tunnel, Wellington. It is believed to be the first report of such an occurrence in New Zealand in a fault gouge, and possibly the first in the world. The origin of such unusual clay mineral is uncertain at this stage, but further study is continuing.