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Northwest communities have increasing pressures to improve performance in anticipation of both state and federal Sanitary Sewer Overflow (SSO) guidelines with decreasing financial resources—do more with less. As a result, solutions to collection system deficiencies are increasingly focused on increased use of existing facilities. This paper reviews master planning activities for three Pacific Northwest agencies that identified distinct solutions to meet their particular needs.

In Corvallis, Oregon, flows from combined sewers and rainfall dependent infiltration and inflow (RDII) are managed through a combination of storage in the collection system and an off-line storage facility, as well as wet and dry treatment. Options for operational strategies were modeled using XP-SWMM, with the Real Time Control module, to assess options for storing and treating flow based on various distributions of design storms and associated antecedent rainfall. The analysis defined operational options that met performance requirements without additional capital expenditures. The results are incorporated into strategies for regulatory compliance.

Oak Lodge Sanitary District's collection system analysis identified potential surface flooding for the anticipated regulatory rainfall design event. RDII reduction was not considered cost effective and District officials were interested in identifying less costly solutions than traditional pipe replacement projects to increase system capacity. The U.S. Environmental Protection Agency (EPA) SWMM 5 model was used to assess where available capacity exists even under future land use conditions. Additional analysis investigated subbasin flow transfers. Solutions have been developed to monitor and reduce RDII.

In the central Oregon City of Bend, historic system expansion and area geography combined to produce multiple pump stations serving many individual developments accompanied by increasing operations and maintenance costs. One of the highest growth rates in the nation has demanded an assessment of system expansion options. To avoid further increases to the existing series of pump stations, a solution is sought to phase service to growth areas, reduce the number of pumping systems and provide incremental investment in gravity interceptors that will allow the City to serve new areas with reduced upfront capital investment.

Each of these communities is meeting system capacity needs by leveraging existing available capacity. This preserves limited resources for other needed system investments such as monitoring, condition assessment, repair, rehabilitation, and RDII source controls.

Document Type: Research Article


Publication date: January 1, 2007

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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