Difference between revisions of "Guidance for categorical TMDLs"
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| + | It is not necessary or required for an MS4 to derive an individual waste load allocation (WLA) for a Total Maximum Daily Load (TMDL) that developed categorical MS4 WLAs. However, if you do want to determine your MS4’s portion of the categorical WLA, the following approaches can be used: | ||
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| + | # Area approach. The WLA can be divided based on the relative area of each MS4. Only the areas within the study watershed should be considered. For example, if two MS4s have a WLA of 100 lbs/day, MS4 A covers 75% of the study area and MS4 B covers 25% of the study area, the target loads would be 75 lbs/day for MS4 A and 25 lbs/day for MS4 B. This is a desirable approach if the pollutant loading per unit area is considered similar across all MS4s. | ||
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| + | The TMDL report may contain information that is useful for this approach. For example, the Ramsey Washington Metro Watershed District Watershed TMDL report contains the following table. This information, along with the TMDL table can be used to derive an individual WLA. | ||
Revision as of 15:10, 18 October 2019
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It is not necessary or required for an MS4 to derive an individual waste load allocation (WLA) for a Total Maximum Daily Load (TMDL) that developed categorical MS4 WLAs. However, if you do want to determine your MS4’s portion of the categorical WLA, the following approaches can be used:
- Area approach. The WLA can be divided based on the relative area of each MS4. Only the areas within the study watershed should be considered. For example, if two MS4s have a WLA of 100 lbs/day, MS4 A covers 75% of the study area and MS4 B covers 25% of the study area, the target loads would be 75 lbs/day for MS4 A and 25 lbs/day for MS4 B. This is a desirable approach if the pollutant loading per unit area is considered similar across all MS4s.
The TMDL report may contain information that is useful for this approach. For example, the Ramsey Washington Metro Watershed District Watershed TMDL report contains the following table. This information, along with the TMDL table can be used to derive an individual WLA.