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HomeMy WebLinkAboutNC0026051_Other_20230401Wce DURHAM COUNTY UTILITIES DIVISION MERCURY MINIMIZATION PLAN April 1, 2023 SECTION I - PURPOSE The purpose of this Mercury Minimization Plan ("MMP") is to describe best management practices through which Durham County Utilities Division will seek to reduce the amount of mercury discharged into its system and, ultimately, to the environment. The MMP compiles mercury reduction -related efforts to -date and potential future action items. It is designed to be a working document to help guide Durham County Utilities Division in its efforts to control mercury loadings discharged into its Publicly Owned Treatment Works (POTW) by users of the sewer system. Such a reduction in loadings to the sewer system should translate to a reduction in the amount of mercury which is discharged from the treatment plant. SECTION II - FACILITY DESCRIPTION Durham County operates a publicly owned treatment works (POTW), including a collection system and wastewater treatment plant (WWTP), that serves Research Triangle Park and surrounding areas in Durham, North Carolina. The Collection system consists of approximately one hundred and five (105) miles of gravity sewer, eleven (11) miles of pressurized force mains, and thirteen (13) pump/lift stations. The Triangle Wastewater Treatment Plant (TWWTP) is designed and permitted to treat twelve million gallons per day (12MGD). The process consists of: 1. Fine screens — fine materials such as grit, sand, eggshells, etc. is removed and the organic materials are washed off and used in the biological treatment process 2. Five Stage Biological Nutrient Removal (BNR) System — all biological treatment occurs, such as removing ammonia through nitrification and denitrification process to remove phosphorous 3. Chemical Polishing — removes any phosphorous remaining by adding methanol to increase the biological oxygen demand (BOD) to support the denitrification process 4. Clarifiers — biomass is separated from the treated wastewater and returned for further treatment 5. Tertiary Filters — removes the remaining unsettled biomass 6. Ultraviolet Disinfection — removes disease causing bacteria without creating harmful by- products 7. Reaeration — dissolved oxygen (DO) is added to the treated wastewater to meet permit limits 8. Dewatering Facility — centrifuges remove water from the biosolids, biosolids are hauled off -site to a composting facility 9. Reclaimed Water System — treated wastewater that can be reused for industrial cooling, industrial process cleaning, landscape irrigation Most treatment plants are not designed to remove mercury and it is exceedingly expensive to do so to very low levels. Incidental mercury removal occurs through typical treatment with trace levels of mercury (and other metals) ending up in solids removed from the raw wastewater. Mercury is not used in the treatment processes at the WWTP. Mercury may be introduced into the sewer system through a variety of sources, such as from industrial users, laboratories, and other businesses. Residual deposits of mercury are also possible in the sewer system from historic practices. Finally, trace amounts from household products and atmospheric deposition (both wet and dry) contribute to sewer system mercury loadings. While there is typically some mercury contributed to public sewer systems statewide, it is usually in minute quantities and comprises a tiny portion of the already insignificant statewide loading for all point sources - just two percent of the annual mercury loadings to all State waters. Durham County's NPDES Permit NCO026051 contained a mercury limit for many years of 12.0 ng/L but was removed in the permit that became effective October 1, 2022. Removal from the permit was based on Mercury TMDL evaluation showing no individual results exceeded the TBEL of 47.0 ng/L and no annual average exceeded the WQBEL of 12.0 ng/L. Mercury will be tested as part of the Long Term Monitoring Plan (LTMP) and the Priority Pollutant Scan. Any wastewater containing mercury in concentrations greater than 142 ng/L as measured by EPA Test Method 1631 and sampled by EPA Method 1669 will remain a prohibited discharge standard in Section 26-96 of the Durham County Sewer Use Ordinance. SECTION III - PROGRAM PLAN A. EVALUATION OF POTENTIAL NON -DOMESTIC SOURCES CONTRIBUTING MERCURY TO THE POTW Within 24 months from the NPDES required 180-day period for development of an MMP, Durham County Utilities Division will evaluate available information to assess the potential for non - domestic users of the sewer system to contribute mercury to the system. The information to be reviewed may include: (1) POTW influent and effluent mercury data and trends; (2) industrial user permits and associated mercury monitoring data; (3) Toxics Release Inventory (TRI); (4) state hazardous site registry and the National Priority List relating to mercury contamination; and (5) historical records of industrial sites which have contributed mercury loadings to the sewer system. Durham County will also survey and evaluate the following common sources of mercury in its service area: (1) dentist offices; (2) hospitals; (3) laboratories; (4) auto recyclers; and (5) other potential sources of mercury based on existing information. Durham County will request that industrial users review mercury concentrations in high -volume process chemicals and demonstrate that the mercury concentrations are below industry average. Durham County will request that alternative sources for chemicals be explored if the mercury levels are determined to be significantly higher than would normally be expected. The evaluation of potential non -domestic sources of mercury to the sewer system will be updated every five years, as warranted by prior sampling results and any additional new potentially significant sources to the system. B. ADDITIONAL CONTROL MEASURES This MMP identifies reasonable and cost-effective control measures to minimize mercury being discharged into the POTW. Below is a listing of initial BMPs for this POTW. Pollution Prevention Substances used at the WWTP will be evaluated to determine if they contain mercury or mercury - based compounds. Any such chemicals will be evaluated for substitution with non -mercury - containing substances. Housekeeping, Spill Control and Collection, and Education Durham County Utilities Division will develop procedures to minimize the possibility of any spill or release at the WWTP involving mercury containing substances. Durham County will add mercury identification and proper disposal to ongoing and future operator training procedures. Durham County Utilities Division recycles fluorescent bulbs and continues to switch out bulbs to LEDs when and where feasible. Public Outreach Durham County Utilities Division will make available educational information regarding sources of household mercury and appropriate use/disposal practices. This information may be posted on the Durham County Utilities Division's website. Durham County Utilities Division will also facilitate public awareness regarding community collection points for mercury -containing products from residents/customers for proper disposal. Periodic reminders of such collection programs will be provided as part of Durham County Utilities Division's ongoing public outreach. Laboratory Practice Durham County Utilities Division operates a laboratory for purposes of complying with state and federal monitoring and sampling requirements. The laboratory is a potential source of small quantities of mercury -containing compounds. Laboratory employees will be trained in the proper handling and disposal of these materials. The laboratory has also replaced mercury thermometers with non -mercury thermometers, whenever practical. All mercury containing compounds used in the laboratory are collected and hauled off -site as hazardous waste for treatment. In the event that a mercury spill occurs in the laboratory, mercury spill recovery kits are available for use. C. TRACKING AND MONITORING In order to assess the implementation of the control measures, Durham County Utilities Division proposes to undertake the following evaluations beginning after the first full year that this MMP is implemented: 1. Survey annually at least ten percent (10%) of any non -domestic users identified as possible significant sources of mercury to the POTW; 2. Track the implementation of the programs outlined above; 3. Monitor influent mercury at least annually. Require significant non -domestic sources of mercury to monitor periodically, as warranted; and 4. Measure effluent mercury as required by the NPDES permit. These efforts will allow Durham County Utilities Division to establish a baseline of influent and effluent mercury levels to assist in identifying any trends in mercury contributions from domestic and non -domestic users of the sewer system. This baseline will be tracked annually. SECTION IV - IMPLEMENTATION OF CONTROL MEASURES Triangle WWTP operates a pretreatment program that regulates industrial and commercial users through permit issuance that contains monitoring and reporting requirements. Industrial Waste Surveys are also a tool used to gage what industrial and commercial users do at their facilities and what processes and chemicals are used on -site. Any wastewater containing mercury in concentrations greater than 142 ng/L as measured by EPA Test Method 1631 and sampled by EPA Method 1669 will remain a prohibited discharge standard in Section 26-96 of the Durham County Sewer Use Ordinance. Durham County will implement the control measures summarized in Section III over the permit term and will update this MMP as warranted. SECTION V - REPORTING A summary of the MMP activities will be submitted as part of the NPDES permit renewal process.