|M.Sc Student||Eid Khalil|
|Subject||Quantification, Calibration and Verification of QUEST|
Method as a Tool for the Assessment of
Exfiltration from Gravity Sewers
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Eran Friedler|
|Full Thesis text - in Hebrew|
Exfiltration of raw sewage from sewers poses negative environmental effects and human health risks. Exfiltration from sewers in Israel roughly approximates to 20-50 MCM/y nationally. Identification of the locations in the sewer network where the highest proportion of exfiltration occurs and its quantification is the first step towards solving the detrimental effects of sewage leakage.
The innovative QUEST/QUEST-C (Quantification of Exfiltration from Sewers with Artificial Tracers) methods were chosen to quantify exfiltration in the research. In these methods in order to calculate tracer mass balance, instead of flow measurement, two different tracers are used, indicator and references tracer which are injected in two different points, and their concentrations are measured in the same point downstream. In QUES method a pulse injection of the tracers is performed, while in QUEST-C continuous injection of both tracers is practiced. Hence, the methods are supposed to be less sensitive to errors in flow measurements. Nevertheless, the methods were developed theoretically and directly implemented in real sewer lines without examination under controlled conditions. These were the goals of this research: to quantify, calibrate and verify the QUEST methods as a tool for assessment of exfiltration from gravity sewers.
QUEST methods were tested under controlled conditions in a sewer rig (~ 300 m long), simulating a real sewer line. Under steady flow conditions the two methods, as expected, were able to quantify exfiltration with good degree of reliability (absolute average error 2%± .). Under unsteady flow conditions QUEST-C method was found to be much more accurate than QUEST method.
The length of the experiment had much more profound effect on the accuracy of exfiltration rate predictions than flow measurement downstream. Leakage outside the investigation reach was not found to affect the calculations. Inflow from lateral sewers (steady flow) did not affect the prediction ability provided that the background concentrations of the traces were the same as in the investigated reach. Leakage characteristics (i.e. single-point leakage or dispersed leakage) did not affect methods predictions and gave the same results.
The results of the experiments show that QUEST-C method is a feasible practical methods for determination of exfiltration from sewers with good degree of reliability under unsteady flow conditions with absolute average error of 20%± . QUEST-C should be implements for several hours at a time. QUEST, on the other hand, did not present good reliability and is not recommended to be implemented under unsteady flow conditions.