WERF: Peak RDII Flow Reduction: Case Studies And Protocol

This paper describes the research conduced under WERF project 99-WWF-8. The purpose of that research project was to examine construction projects for the reduction of rainfall derived infiltration and inflow (RDII) and document their success. The research began with a literature search of all published records describing RDII removal projects. The search initially identified many potential projects. Subsequent evaluation of available information revealed that relatively few projects described in the literature maintained adequate data for a detailed, independent assessment or confirmation of results. Accordingly, a major recommendation of the WERF report was to establish a standard protocol for documenting RDII removal projects.Projects with sufficient information describing the conditions prior to the RDII-reduction project received a detailed analysis in the WERF project. In all, 12 case studies from six agencies presented in the WERF report document before and after RDII levels, quantify the RDII reduction achieved, and the cost-effectiveness of the removal. This paper presents the case studies and the results achieved. In addition, this paper presents results from four additional case studies examined after preparation of the final WERF report. The WERF research method is described in detail elsewhere (Lukas and Merrill, 2001; WERF, 2003).The projects examined include both those that “successfully” reduced peak RDII and those that did not. Our general conclusion is that utilities run the risk of not removing significant RDII unless the the projects address private sewer laterals. The only cases examined where significant RDII was removed addressed private sewers or inflow sources. This paper discusses the techniques used in the case studies, the results achieved, and measurements of cost-effectiveness. Table A-1 summaries the projects by type of construction and results achieved.