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Frequently Asked Questions
Q. Why is mercury a wastewater issue?
A. Under Section 303(d) of the Clean Water Act, states are required to develop a list of water bodies with water quality impairments. The water bodies on the list do not meet water quality standards. San Francisco Bay is listed with 12 toxic pollutants including mercury. Because of mercury impairment, fish consumption advisories have been issued for San Francisco Bay.
The California Regional Water Quality Control Board, San Francisco Bay Region (Regional Board) issues the National Pollutant Discharge Elimination System permit (NPDES Permit) for wastewater treatment plants. The NPDES Permit requires compliance with wastewater discharge limitations for pollutants, including mercury.
The San Francisco Bay Mercury TMDL (Total Maximum Daily Load), which was recently approved by the EPA and Regional Board, requires the Plant to develop and implement an aggressive source control and pollution prevention program to comply with new mercury limits and to maximize the Plant’s control over mercury sources impairing the San Francisco Bay. Studies have shown that approximately 61% of the mercury entering the San José/Santa Clara Water Pollution Control Plant (Plant) is from dental practices.
In addition, U.S. EPA's Section 503 Sludge Regulations and state and local biosolids regulations require the Plant to meet concentration limits for heavy metals, including mercury. These regulations ensure that biosolids can be safely reused for land application and landfill cover.
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A. Wastewater treatment plants are designed to treat wastewater containing conventional pollutants such as human and food waste. Heavy metals, including mercury, are not completely removed by the treatment process. As a result, some mercury remains in the treated wastewater discharged to the South San Francisco Bay or in the biosolids, which are used for landfill cover.
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Q. What is the timeline for the program?
A. The first permit application packets are planned to be mailed to dentists in July 2009. The target is to have all dental practices compliant by December 2010.
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Q. Will dental practices be charged permit fees like large industries?
A. Currently there is no permit fee proposed.
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Q. Will separators installed before the program requirements take effect be acceptable for compliance?
A. Yes. Provided that the unit is an approved ISO 11143 certified Amalgam Separator.
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Q. How much will this new requirement cost?
A. There is no cost for the Dental Practice Discharge Permit.
The cost of amalgam separators varies, but the most popular model in other programs currently costs $600-$700 installed. Some amalgam separators can cost more than $2,000. Only one separator will be required per vacuum system, so that cost may be shared among dental practices with a shared vacuum line. If significant plumbing modifications are required to complete the installation of a separator, then the installation cost may be higher.
The estimated cost of additional disposal of amalgam and other wastes is about $200 per year.
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Q. Will you sample the discharge or require the dental office to sample?
A. Sampling will not be required. Installation and maintenance of an amalgam separator and adherence to the proposed Best Management Practices is intended to determine compliance with the permit. If an inspector finds that an individual dental practice is improperly maintaining the amalgam separator, sampling may be performed to document the condition.
We may initiate a program to sample sewer lines outside dental offices to determine overall effectiveness of the dental program to reduce mercury in the sanitary sewer system. And will continue to sample the Plant’s influent, effluent, and biosolids for mercury.
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Q. How will you assess compliance if no sampling is performed?
A. Under the proposed program, submittal of self-certifications that an amalgam separator has been installed and is being properly maintained will determine initial compliance. Scheduled inspections will take place at each dental practice no less than once during the five-year permit. Inspectors will review waste records, compliance with BMPs, amalgam separator maintenance, waste storage and disposal practices, etc., in order to determine compliance with the dental permit conditions.
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Q. What is the penalty for non-compliance?
A. A fine may be assessed if non-compliance is not corrected after a process of verbal warnings and written warnings has been concluded.
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Q. Why is disposing of amalgam in the red bag or garbage a problem?
A. Red bag waste may require incineration. Incinerated mercury volatilizes and becomes an air pollutant. Through air deposition, it also may eventually end up in surface water. If the amalgam is disposed of with other garbage, the mercury may end up in the landfill leachate, which may eventually contaminate groundwater or surface water.
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Q. Can chair-side traps and vacuum filters capture all scrap amalgam and particulates?
A. Not all of the scrap amalgam and particulates are captured by the chair-side traps and vacuum filters. Grinding, drilling, and polishing of amalgam fillings may result in the production of fine particulate matter that passes through the chair-side traps and vacuum filters. The residual particulates remain in the wastewater discharged to the sanitary sewer. Additionally, mercury may enter the wastewater from instrument washing, and chair-side trap and vacuum filter cleaning. Amalgam separators are designed to capture this form of amalgam from wastewater prior to discharging to the sanitary sewer.
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Q. What are the regulators doing about the clean-up of abandoned mines? The majority of the mercury is coming from this source.
A. The Regional Board and local agencies for wastewater treatment plants collaborated in the development of Total Maximum Daily Loads (TMDL) for pollutants, including mercury, that are impairing the San Francisco Bay. The TMDL is a quantitative assessment of water quality problems, contributing sources, load reductions or control actions needed to restore and protect water-bodies. The TMDL process included waste load assessments for non-point sources including abandoned mines.
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References
- Massachusetts Water ResourcesAuthority (MWRA) - Dental Control Program Overview, December 19, 2000.
- Arenholt-Bindslev, D. 1992. Dental Amalgam - Environmental Aspects. Adv. Dent. Res., 6: 125-130.
- Bay Area Pollution Prevention Group - Dental Mercury Study 2001.
- Brune, D., H. Beltesbrekke and G. Strand (1980) Dust in Dental Laboratories, Part II: Measurement of Particle Size Distributions, J. Prosth. Dent., 44(1): 82-87.
- Nimmo, Werley, Martin and Tansy. 1990. Particulate Inhalation during the Removal of Amalgam Restorations. J. Prosth. Dent., 63: 228-233.
- Arenholt-Bindslev, D. and A.H. Larsen. 1996 Mercury Levels and Discharge in Wastewater From Dental Clinics. Water, Air, and Soil Pollution, 86: 93-99.
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