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Category 4b - Current National Status and Trends

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Section 303(d) of the Clean Water Act and the US Environmental Protection Agency's (USEPA) supporting regulations in 40 CFR Part 130.7 require States to develop lists of waterbodies impaired by a pollutant and needing a Total Maximum Daily Load (TMDL) (i.e., the Section 303(d) list) and to develop a TMDL for each waterbody-pollutant combination. USEPA's regulations also recognize that other pollution control requirements may obviate the need for a TMDL. These alternatives to TMDLs are commonly referred to as Category 4b waters as described in USEPA's Integrated Reporting Guidance for Sections 303(d), 305(b), and 314 of the Clean Water Act.

This paper presents the results of a survey conducted in May 2009 to assess the extent to which States have successfully employed TMDL alternatives to address impaired waters and assigned these waters to Category 4b. The survey, which was based primarily on States' USEPA-approved 2008 Section 303(d) lists, showed that over 400 impaired waters (including more than 600 waterbody-pollutant combinations) are currently assigned to Category 4b in 26 States. Types of pollutants addressed and the general types of controls used to support the Category 4b assignments are also discussed. Results of the survey show that the number of impaired waters successfully assigned to Category 4b and the number of States assigning waters to Category 4b have increased from the 2006 to 2008 Section 303(d)/IR reporting cycle.

Keywords: Category 4b; TMDL; alternative; impairment

Document Type: Research Article


Publication date: 2009-01-01

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