Tmdl schedule and workplans status july 1999



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Additional Work Needed:

Enough data exist to support the listing of these two water bodies as impaired. However, questions still remain as to the spatial extent and magnitude of impairment. Additional investigative work to refine our understanding of the mercury problem may result in a delisting of unimpaired Bay segments. These tasks will be addressed in the source analysis section of this workplan.


Numeric Targets: The Desired Future Condition:

The desired goal is full attainment of water beneficial uses. Prior to establishing a numeric target such as a Total Maximum Daily Load (TMDL) for mercury, achievable and protective ambient objectives for biota, water, and sediments need to be developed. Scientific studies suggest that the majority of mercury in the watershed is bound to sediments. Therefore, attaining sediment objectives for bioavailable bay and stream sediments will be the first goal in this phased numeric target setting task. Sediment objectives will be based on an assessment of pre-mining ambient sediment concentrations. A quantitative mass balance model will be developed to evaluate the relationship between mercury loadings and the natural rate of burial/removal of mercury from the system. Loadings to the system will include new inputs (e.g. mine discharges) to the system and the reintroduction of mercury into the system from in-stream storage reservoirs. This model will be used to establish a preliminary sediment concentration and mass loading target.




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