The modification to the MDL procedure in the February 19, 2015 proposed Part 136 Methods Update Rule (MUR) incorporates running a set of unfortified blanks (LRBs) alongside the seven fortified blanks. In general, the revised procedure is not expected to impact drinking water results. The blanks are indicators of system background and as long as the blanks are clean, the calculated MDL will be the same as an MDL calculated using the “old” procedure. High blanks would indicate the need for the laboratory to take corrective action prior to proceeding with using the method to analyze drinking water compliance samples. Until such time that regulations within Part 141 or analytical methods are revised, if there is a specific citation to performing the MDL determination following the procedure in Part 136, Appendix B, laboratories will need to follow the modified MDL procedure once the Part 136 MUR is finalized.