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The Pennsylvania Code website reflects the Pennsylvania Code changes effective through 53 Pa.B. 6142 (September 30, 2023).

25 Pa. Code § 96.4. TMDLs and WQBELs

§ 96.4. TMDLs and WQBELs

 (a)  The Department will identify surface waters or portions thereof that require the development of TMDLs, prioritize these surface waters for TMDL development, and then develop TMDLs for these waters.

 (b)  The Department will develop WQBELs for point source discharges using applicable procedures described in this chapter when the Department determines that water quality protection requirements specified in §  96.3 (relating to water quality protection requirements) are or would be violated after the imposition of applicable technology based limitations required under sections 301(b), 306, 307 or other sections of the Federal Clean Water Act (33 U.S.C.A. § §  1311(b), 1316 and 1317) and The Clean Streams Law (35 P. S. § §  691.1—691.1001) to the point source.

 (c)  TMDLs and WQBELs shall be developed to meet the requirements of §  96.3.

 (d)  WLAs developed in accordance with this chapter shall serve as the basis for the determination of WQBELs for point source discharges regulated under Chapter 92 (relating to National Pollutant Discharge Elimination System permit-ting, monitoring and compliance). When LAs are developed in accordance with this chapter, they shall serve as the basis for the development of nonpoint source restoration plans.

 (e)  In developing TMDLs and WQBELs, the Department will:

   (1)  As appropriate consider, relevant design factors, including, but not limited to: water quality criteria duration, flow duration and frequency, natural seasonal variability in water temperature, the natural variability of pH and hardness, the physical characteristics of a watershed, reserve factors, factors of safety and pollutant contributions from other sources.

   (2)  Treat all pollutants as conservative unless it finds based on scientifically valid information that the substance is not conservative and adequate information is available to characterize the substance’s fate or transformation, or both.

 (f)  The allocation procedure is as follows:

   (1)  WLAs, LAs and effluent limitations assigned or allocated to individual pollutant sources shall be the more stringent of the following:

     (i)   The pollutant loading authorized to be discharged under applicable technology-based requirements.

     (ii)   Where applicable, the pollutant loading determined under § §  96.5 and 96.6 (relating to nutrient discharges; and heated wastewater discharges).

     (iii)   The pollutant loading that will achieve the water quality protection requirements specified in §  96.3.

   (2)  WLAs, LAs and effluent limitations shall be made more stringent if the cumulative loading determined after the application of paragraph (1) does not meet the requirements of §  96.3.

 (g)  Mathematical modeling at the design flow conditions listed in Table 1 shall be used as applicable to develop TMDLs and WQBELs for point source discharges.


Water Quality Criteria Steady State Design Flow
Fish and Aquatic Life, Except Ammonia-Nitrogen Q7-10
Ammonia-Nitrogen Q30-10
Threshold Human Health Q7-10
Nonthreshold Human Health (Carcinogens) Harmonic Mean Flow

 The LA portion of the TMDL will be allotted to nonpoint source pollutant loadings and natural quality.

 (h)  The Department will revise WLAs and LAs because of new or increased pollutant loadings. WLAs shall be revised at or before the expiration date of the current point source discharge permit term.

 (i)  The Department may require NPDES dischargers and other persons subject to regulation under The Clean Streams Law (35 P. S. § §  691.1—691.1001) to conduct appropriate monitoring of pollutant sources and waters and report the results and data, to obtain data needed to develop TMDLs and effluent limitations and to determine their effectiveness.

Cross References

   This section cited in 25 Pa. Code §  95.10 (relating to treatment requirements for new and expanding mass loadings of Total Dissolved Solids (TDS)).

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