What requirements may be added to a MS4/VPDES permits as a result of TMDLs?
The regulatory basis linking NPDES permits and TMDLs is 40 CFR ยง122.44(d)(vii) of the Code of Federal Regulations. In November 2002, EPA published a guidance memorandum on the linkage between MS4 permits and TMDLs. For TMDLs, EPA requires that loading from stormwater covered by an MS4 permit must be expressed as a wasteload allocation (WLA). For MS4 permits, EPA expects that most TMDL WLAs will be expressed as BMPs and that numeric limits will be used only in rare circumstances. At this time, DEQ expects to apply the BMP option to address TMDLs in waters covered by MS4 permits. Revisions of the MS4/VPDES permits that apply to water bodies with TMDLs would then require implementation of BMPs to specifically address the TMDL pollutants of concern.
