Quantification of the Relative Importance of Factors Contributing to Intrusion in a Distribution System Using a Full Factorial Design

Abstract

Transient analysis of a pump trip event was conducted on a full-scale distribution system (~16,000 nodes) equipped with high speed pressure transient data loggers at the outlet of the water treatment plant (WTP) and at several distribution system (DS) sites. A calibrated transient model was used to perform intrusion volume computations considering two possible intrusion pathways: leakage orifices and submerged air vacuum valves (AVVs). For this pump trip event, a full 3-level 4-factor factorial design (3 4-0 ) with 82 runs was completed to understand the relative impact of the following factors on the total intrusion volume: (1) the external head of untreated water on leakage orifices, (2) the external head of untreated water on the outlet orifice of submerged AVVs, (3) the leakage rate (which translates into orifice size), and, (4) the diameter of AVVs’ outlet orifice. Although some of these factors may be highly uncertain, fieldwork (including installation of piezometers and visits of air valve vaults) is currently being conducted, and realistic values were assigned to these factors. The analysis showed that the factors and interactions associated with AVVs had a significant effect on the total intrusion volume. The importance of the external head on AVVs’ orifice on the total intrusion volume was highlighted in a plot of marginal means. When intrusion through both pathways occurs concurrently, the interactions between these intrusion flows influence the total intrusion volume. The latter can even decrease when the external head on leakage orifices increases creating surge dampening effects large enough to significantly reduce intrusion through submerged AVVs.