Why is this happening? The amalgam rule 40 CFR Part 441 placed dental facilities into an industrial category. Though you do not have to do annual reports like an industry must, you must comply with the city discharge limit if established. If you contribute enough mercury to the POTW (Wastewater Treatment Plant) to cause the plant to violate their permit limit to discharge mercury into a natural waterway, they must find and rectify the problem. The city’s discharge limit to customers is based upon a factor called loading. Each city is different based upon their MGD or Millions of Gallons per Day flow.
Because of this factor, cities may need to regulate or set a maximum discharge limit for mercury to assure that they (the city) don’t violate their permitted limit. If they violate their limit, they can be assessed fines daily until the problem is resolved. The need to control the mercury influent into the plant supersedes everything and the only solution is to control the discharges from known mercury sources.
All industries and medical facilities have been required to meet discharge limits when they are known mercury sources. In all cases the limits for those facilities are low based upon their “loading” or contribution to the POTW Influent and Effluent. The suggested limit for Industries in Ohio, for example, is 125 ng/L. This limit will vary based upon city and flow, but it is being met by those facilities on average. The dental industry is now the highest discharger of mercury into the aquatic environment averaging over 14,300ng/L. Though there have been arguments that it is small, it is a controllable source.
There have been known cases of dental discharges contributing to the POTW at a concentration high enough to directly affect the discharge plant limit. In these cases, the dental facility was causing the POTW to violate their permitted discharge limit to the natural waterway causing potential fines to the POTW. These issues were resolved by getting the dental facility discharge under control. The current Amalgam Separator Technology is outdated and ineffective.
The reason there can be a difference between the Separator Manufacturer’s compliance is due to an apple and oranges comparison. The USEPA regulation is based upon solids collection and percentage capture. Under the regulation the separator must meet a 95% capture rate. That leaves 5% to discharge into the sewer. The State and Local regulation is based upon total mercury at levels less than 0.0001%. That leaves a discrepancy that is very large. The separator can meet the USEPA regulation but not the local regulation. The other issue is that Amalgam dissolves in water very slowly by up to 0.1%. This issue was never understood by both the USEPA and the ADA. This misunderstanding is a huge problem. The dissolving of the amalgam produces high concentrations of mercury that can’t be removed efficiently by the wastewater treatment plant. This then causes the plant to violate their permitted mercury limit. The need to comply with the local limit SUPERCEDES the USEPA regulation.