DON’T BE AS MAD AS A HATTER, PREPARE FOR ADDRESSING MERCURY IN YOUR PLANT – BACKGROUND AND CASE HISTORY by Ralph B. “Rusty” Schroedel, Jr., P.E., BCEE, Brown and Caldwell Keith Hitzke, North Shore Environmental Construction, Inc. Background Mercury has been used for decades in many pieces of process and electrical equipment at wastewater treatment facilities, as well as many other items. Two of the most common and largest users of elemental mercury were manometers and trickling filter distributors. In 1972, the United States Environmental Protection Agency banned the use of mercury except for special cases. However, wastewater facilities have continued to use existing equipment that contains mercury. State and federal regulatory agencies are considering requiring that water and wastewater treatment facilities complete an audit for mercury and to address identified sources of elemental mercury, especially at facilities where trickling filters have been in use for decades. It is important for wastewater facilities to address elemental mercury and mercury added products. There are case histories where significant quantities of historically retained and accidentally spilled elemental mercury required a major cleanup effort should the history of mercury use at treatment facilities not be investigated and addressed properly. The common design for trickling filter distributors for much of the 20th century included a mercury seal. The seal used a combination of a reservoir, fill pipe, and the density of the mercury, as compared to the low water head required to distribute the wastewater, to create a seal at the rotating center column. A 10-inch unit would use about 30 pounds of mercury and a 15-inch unit would use about 40 pounds of mercury. (1) A technical paper cites distributors containing nearly 750 pounds of mercury. (2) Often, mercury was lost from the center column due to high flows forcing the mercury out of the seal onto the trickling filter media and center column support. Overfilling of the mercury seal during maintenance also occurred. It was not unusual to see water leaking from a center column that had lost its seal. Also, historical wastewater received at the plant and maintenance activities may have added to the volume of mercury. In addition to trickling filter seals and historical flows, mercury manometers, still seen in many older plants across North America, are another source for mercury spills. A report by The Northeast Waste Management Officials’ Association (3) summarized the sources of elemental mercury and mercury added products. The report also provides a detailed description of mercury added items. Lastly, that report provides a table of mercury added products likely to be found at wastewater treatment facilities and a checklist for those products developed by the Northeast Ohio Regional Sewer District. All of this information supports the need to address the sources of elemental mercury and mercury added products at wastewater treatment facilities, especially those with trickling filters. A “Case History” As part of an upgrade at a wastewater plant, existing trickling filters were being renovated and modified. Removal of the center pivot assemblies may require addressing unknown quantities of elemental mercury. A far more substantial monitoring and cleanup effort may be required if careful study, analysis, monitoring, and construction is not performed. North Shore Environmental Construction, Inc. (NESC) has performed clean up at a wastewater plant. The quantity and extent of elemental mercury on site requires a carefully planned and executed remediation effort. Conclusions and Recommendations Any wastewater facility with old trickling filters should anticipate the need to address historical mercury issues as well as more recent mercury spills in, and possibly around, the area of the TFB’s. Any upgrade or rehabilitation of existing trickling TFB’s should expect to address likely mercury contamination. It also appears that mercury throughout wastewater treatment plants will need to be investigated and audited in the near future. This paper will be of interest to any operators of older, existing wastewater plants, especially those operating trickling filters, and engineers designing rehabilitation of plants with trickling filters. References: (1) (2) (3) USFilter (Envirex), Memorandum Dated October 10, 2005 “A Case Study of Mercury and Methylmercury Dynamics in a Hg-Contaminated Municipal Wastewater Treatment Plant”, C.C. Gilmour and N.S. Bloom, Water, Air, and Soil Pollution, 80: 799-803, 1995 “Mercury-Added Products Found at Drinking Water & Wastewater Treatment Facilities”, The Northeast Waste Management Officials’ Association, June 30, 2010 Trickling filter rock with visible, elemental mercury Visible mercury in area beneath rock media support