Under the National Primary Drinking Water Regulations (NPDWRs), methods are incorporated by reference into the regulation and therefore must be followed as written, with no modifications. There are no currently approved methods that describe the use of a Durham tube being used in ECMUG medium, which would then allow for the detection of both Fecal Coliforms and E.coli (i.e. Standard Methods has not previously described this in either EC or ECMUG method descriptions).
Most importantly, under the Revised Total Coliform Rule (RTCR), Fecal Coliforms are no longer regulated. Use of such a modification of ECMUG could create a scenario whereby a laboratory receives 2 different results (FC+, E.coli negative) and without a descriptive approved method for this modification, the state would have no way to enforce that results from both determinative endpoints must then be reported.