Performance Assessment of a Novel Proposed Analytical Method for Microbial Monitoring of Distribution Systems Under the Total Coliform Rule

A novel analytical method for automated detection of E. coli and total coliform bacteria (the TECTA EC/TC Method) was recently proposed for approval by US EPA as a compliance test under the Total Coliform Rule and related national primary drinking water regulations. The basis for approval was the EPA Alternate Test Procedure (ATP), where the candidate analytical method must be shown to be at least as effective as the EPA reference method for the detection of low levels of chlorine-stressed organisms. An ATP study was conducted at a US-based utility laboratory under an EPA-approved study plan, and intermethod comparison results were generated. Differences in positive detection rates were noted in the ATP study, resulting in apparently large false negative rates for the TECTA method compared to the EPA reference method. Challenges of intermethod comparison where there is a significant difference in sensitivity between the candidate and reference methods became evident and required further analysis. The new method was recently approved by US EPA as a compliance method under the Total Coliform Rule and related drinking water regulations in June, 2014 and, as such, is the first automated method to receive such approval.