New Search
Methodologies To Determine RDII <br />Removal <br />There are a variety of methods that have been used in the wastewater industry for quantifying <br />RDII. Eight ways were documented in the 1999 Water Environment Research Foundation <br />report entitled Using Flow Prediction Technologies to Control Sanitary Sewer Overflows <br />(Project Number: 97-CTS-8). The report is available from the WERF website, ~,vww.werf.or6. <br />The report also contains cases studies upon which these methods were applied in three <br />separate climates in the United States, including Portland, OR. Recommendations are made <br />in the report with regard to the usefulness and applicability of the eight methods to quantify <br />RDII given available information. <br />The eight methods documented in the WERF report that have been used for quantifying RDII <br />are: <br />1) Constant unit rate methods <br />2) Percentage of rainfall volume (R-value) methods <br />3) Percentage of stream flow methods <br />4) Synthetic unit hydrograph methods <br />5) Probabilistic methods <br />6) Predictive equations based on rainfall/flow regression <br />7) Predictive equations based on synthetic stream flow and basin character <br />8) RDII as a component of hydraulic software <br />Each of these methods could be used in evaluating RDII reduction, applying the methods <br />before and after sewer rehabilitation. However, particular data needs for each method may <br />limit the method that can be applied in any given situation. <br />;' : Another useful resource for estimating RDII reduction is the Water Environment Research <br />' , ~ Foundation publication, Reducing Peak Rainfall-Derived Infiltration/Inflow Rates-Case <br />Studies and Protocol (Product Number 9WWF8, 2003). This report is also on the WERF <br />~~`~ website, www.werf.or~. <br />The 2003 report analyzed 12 RDII reduction projects, both successful and non-successful <br />ones. The authors used RDII models to simulate the UI during the calibration period and then <br />used along-term rainfall record to produce a simulated long-term flow record. The long-term <br />flow record is then used to compare peak RDII reduction prior to, and following, a <br />rehabilitation project. The reduction in peak RDII (of a desired return interval) is estimated <br />based on a probability analysis of the long-term simulation records. The report also suggests a <br />standard reporting protocol for documenting RDII response both prior to, and following, <br />rehabilitation projects. The suggested protocol includes information about rainfall and flow <br />monitoring data to be documented such that the information is most useful to both the agency <br />and to the wastewater industry as a whole. <br />The analysis on which the Eugene report is based uses the Return Value or R-Value Method. <br />This method seeks to correlate volume and/or peak RDII volume and/or peak intensity of <br />rainfall. The method requires that dry-weather base wastewater flows are extracted from the <br />