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Category 4b Demonstration for Point Source Impaired Waters and the Permit in Lieu of a Total Maximum Daily Load Process for the State of Missouri

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Section 303(d) of the Clean Water Act (CWA) and the US Environmental Protection Agency's (USEPA's) 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 prepare a TMDL for each water body/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 CWA.

For the 2006 reporting cycle, Missouri Department of Natural Resources (MDNR) assigned 16 impaired waters to Category 4b, where a single point source was identified as the sole source of the impairment. Hence, the foundation of MDNR's Category 4b demonstration for these waters is the discharge limits identified in the associated NPDES permits. MDNR refers to these Category 4b waters as permit in lieu of TMDL waters, or PILs for short. Pollutants covered under these PILs include ammonia, biochemical oxygen demand, non-volatile suspended solids and volatile suspended solids (or total suspended solids or non-filterable residue). MDNR has developed a comprehensive and efficient process for identifying PILs and developing the appropriate Category 4b documentation. PILs are initially identified when: (1) all segments have negligible nonpoint source loading for the pollutant of concern so the facility is the sole source of the pollutant, (2) a defensible Wasteload Allocation (WLA) can be calculated to meet in-stream water quality standards (WQS), and (3) an enforceable permit has been finalized that includes a date certain schedule of compliance to achieve water quality based effluent limits (WQBELs). In order to ensure date certain compliance with the WQS, the final Missouri State Operating Permit includes: (1) WQBELs or other requirements necessary to meet WQS in the impaired segment, (2) a schedule of compliance to meet WQBELs or other requirements (typically three years from issuance), and (3) an in-stream monitoring requirement to demonstrate WQS are being met. MDNR's Category 4b documentation for PILs includes the Final Missouri State Operating Permit, Missouri DNR Fact Sheet or Statement of Basis, Missouri Water Quality Review Sheet, stream survey and water chemistry data, and copies of model output and/or spreadsheets that demonstrate WLA will result in meeting WQS. MDNR tracks the progress of permit requirement implementation to ensure critical milestones and dates are met. PILs are being completed both during and between listing cycles allowing for progress on meeting consent decree requirements.

This paper presents MDNR's process for assigning PILs to Category 4b according to USEPA's Category 4b guidance, lessons learned in developing the process, and potential challenges for maintaining these waters in Category 4b for future 303(d) reporting cycles. This paper also describes several successful examples of PILs in Missouri.

Keywords: Category 4b; TMDL; alternative; dissolved oxygen; impairment; point source; suspended solids

Document Type: Research Article


Publication date: January 1, 2009

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