FIELD VERIFICATION OF REFERENCE FLOW AND WATER LEVEL METERS UNDER THE EPA'S ETV PROGRAM

A field verification of reference flow and water level meters was done as part of the Environmental Technology Verification (ETV) program of the U.S. Environmental Protection Agency (USEPA), under the “Wet-Weather Flow Technologies” pilot program managed by NSF International during the summer of 2001. One of the technologies verified under this pilot program is the “Flow Monitoring Equipment”, which requires the verification of reference meters under the terms of the Generic Protocol entitled “Verification of Flowmeters for Stormwater and CSO Applications in Mid-size Pipes”. A full description of the ETV program and a copy of the Generic Protocol can be consulted on the following web site: http://www.epa.gov/etv.This paper presents the testing site and the results of the field verification of the reference meters used to verify the vendors' flowmeters as part of the ETV program. The testing site is a section of the Quebec Urban Community's (QUC) interceptor network. The accuracy of three meters was verified: one four-path transit-time flowmeter and two level meters, a bubbler and an ultrasonic level meter. A total of nine active tests were performed: three tests B (dry-weather flow with and without backflow), C (wet-weather flow without backflow) and D (wet-weather flow with backflow and surcharge conditions). The verification of the accuracy was based on a comparison with a reference method. The concentrations of blank, concentrated and diluted samples obtained from the lithium dilution analyses were used to estimate flow rates. Manual level measurements were used to verify water levels.The Field Testing Organization recognized that the four-path transit-time flowmeter and both the bubbler and ultrasonic level meters did not meet the accuracy requirements specified in the Generic Protocol in order to be validated as the reference meters. Nevertheless, in light of the results obtained using the revised flow accuracy margins and considering the unexpectedly low accuracy of the tracer dilution analysis results, as well as the good fit with the flow rates estimated with the “flow under the gate” equation, the four-path transit-time flowmeter was validated as the reference flowmeter to verify the vendors' flowmeters. Furthermore, in light of the fact that the performance results are affected by the presence of waves during the two highest flow rates of Test C and knowing that the bubbler level meter is less impacted by waves than are the manual measurements and ultrasonic readings, the bubbler level meter was validated as the primary reference level meter and the ultrasonic as the secondary (or redundant) level meter to verify the vendors' flowmeters.