Mercury is a naturally-occurring element that can be toxic to people and wildlife. It is released to the environment through the burning of fossil fuels, or the improper disposal of mercury-containing products. PCBs are a class of synthetic, chlorinated organic chemicals which were produced for their excellent insulating capabilities and chemical stability, but banned by US EPA in 1979 due to their toxic properties. These persistent pollutants can travel long distances in the atmosphere and do not readily degrade. Atmospherically deposited mercury and PCBs have accumulated in water and fish, and are responsible for impairing thousands of inland lakes and streams.
Waters impaired by mercury and PCBs have been placed on Michigan’s Clean Water Act Section 303(d) list of water bodies. Total Maximum Daily Loads (TMDLs) must be developed for water bodies on the 303(d) list to determine the amount of these pollutants that the water bodies can receive and still meet Clean Water Act Standards.
LimnoTech worked closely with US EPA staff, and MDEQ modelers, fisheries and database experts within the water resources, air quality and remediation divisions to develop technically sound mercury and PCB TMDLs that protect human health and wildlife. We developed a state-wide project database and conducted a geospatial and modeling analysis to evaluate pollutant air, water and fish concentrations and quantify loads. Atmospheric pollutant load reductions described in the TMDL were based on a regional analysis that considered geographic variability in deposition and accumulation in fish tissue.
We also led public meetings and webinars for both the mercury and PCB TMDLs, assisted MDEQ in responding to public comments, and finalized the TMDLs for submittal to US EPA Region 5. Ultimately, the TMDLs developed describe the atmospheric mercury and PCB load reductions necessary to achieve Clean Water Act targets and address all required TMDL elements. The TMDLs were approved by US EPA Region 5 in September of 2018.