MEMORANDUM

TO: Public Docket for the Dental Amalgam Effluent Guidelines

EPA Docket Number EPA-HQ-OW-2014-0693

FROM: Jill Lucy, ERG

Kimberly Bartell, ERG

DATE: September 22, 2014

SUBJECT: Impacts of Amalgam Separators and Recommended Practices on Mercury 

Discharges

EPA is proposing technology-based pretreatment standards under the Clean Water Act

(CWA) for discharges of pollutants into publicly owned treatment works (POTWs) from existing 

and new dental offices that discharge dental amalgam. The proposed rule would require dental 

offices to control the discharge of mercury and other metals in dental amalgam into POTWs

based on the best available technology or best available demonstrated control technology

(amalgam separators) and the use of best management practices (BMPs). This memorandum 

provides supplemental information on the impacts of amalgam separators and recommended 

practices on mercury discharges in addition to the information presented in the Technical and 

Economic Development Document for the Proposed Effluent Limitations Guidelines and 

Standards for the Dental Category (EPA 821-R-14-006). 

Table 1 summarizes the effectiveness of amalgam separators and BMP programs on 

mercury discharged to POTWs, based on several case studies. Although most of these studies 

show mercury reductions in POTW influent following the introduction of BMPs and/or amalgam 

separators in dental offices, some studies show an increase in mercury concentrations. Thus, it is 

apparent that other factors can influence mercury levels and the measure of a program’s 

effectiveness in reducing mercury discharges. The following are examples of additional criteria 

that affected the mercury reduction by BMP programs, as described in the National Association 

of Clean Water Agencies (NACWA) case studies (NACWA, 2007a): 

Many programs are voluntary, and low participation rates affect the program 

effectiveness in reducing mercury discharges.

Dental offices are not the only source of mercury to POTWs. The next largest sources are 

domestic sources (human waste, household products, and laundry graywater) and 

hospitals (Larry Walker Associates, 2002).

The time required to flush accumulated amalgam particles from the collection system is 

not known.

The time needed for mercury reductions at POTWs to be measurable after 

implementation of BMPs or installation of amalgam separators is not known.
Memorandum

September 22, 2014

Page 2

Table 1. Impact of BMPs and Amalgam Separators on Mercury Discharges to POTWs

BMP Program Description

Percent of Dental Offices Using 

Amalgam Separators Percentage of Mercury 

Before Program After Program Loading Reduction Source

California Dental 

Association

Voluntary installation of amalgam 

separators.

No information No information 78% of amalgam to POTW Condrin, 2004

Corvallis, OR Voluntary installation of amalgam 

separators.

No information No information 79% of POTW influent Lamperti, 2007

Springfield, MO BMP outreach program. No information No information 34% of POTW influent A a MU Extension, 

2007

Springfield, MO BMP outreach program. No information No information 96% of POTW influent B b MU Extension, 

2007

Madison, WI Voluntary installation of amalgam 

separators.

No information 22% (as of 2005) No trend in POTW influent Walsh, 2007 

EBMUD Required installation of amalgam 

separators.

No information 96% No trend in POTW influent Walsh, 2007

Wichita, KS Voluntary installation of amalgam 

separators.

60% 99% No trend in POTW influent Walsh, 2007

Milwaukee, WI Required installation of amalgam 

separators.

No information No information Decrease in POTW influent Walsh, 2007

Duluth, MN St. Louis River Beneficiary Group 

provided a grant to purchase amalgam 

separators for all offices.

No information 100% Decrease in POTW sludge Walsh, 2007

Palo Alto, CA Required installation of amalgam 

separators.

No information 96% No trend in POTW influent Walsh, 2007

Narragansett Bay, 

RI

Voluntary installation of amalgam

separators.

No information No information No trend in POTW influent Walsh, 2007

King County, WA Voluntary installation of amalgam 

separators and mandatory 

implementation of BMPs.

No information 95% 50% of POTW biosolids 

(concentration-basis)

King County,

2008
Memorandum

September 22, 2014

Page 3

Table 1. Impact of BMPs and Amalgam Separators on Mercury Discharges to POTWs

BMP Program Description

Percent of Dental Offices Using 

Amalgam Separators Percentage of Mercury 

Before Program After Program Loading Reduction Source

POTW “A” Required offices to either install 

amalgam separators or demonstrate 

compliance with a mercury limit of 

0.005 ppm.

0% 100% No trend in POTW influent NACWA, 2007b

POTW “B” Mandatory BMP program began in 

2002. Installation of amalgam separators 

was not required.

5% 9% (out of 219 

offices)

56.4% of POTW influent NACWA, 2007b

POTW “C” BMP program began in 2002. Some 

BMPs were mandatory. Installation of 

amalgam separators was voluntary.

6% 6% (out of 18 offices) 43% of POTW influent NACWA, 2007b

POTWs “D” and 

“E”

Program required implementation of 

BMPs by 2004 and installation of 

amalgam separators by 2008.

0.6% 38% (total number of 

offices unknown)

60.5% of influent to POTW 

“D”;

22.0% of influent to POTW “E”

NACWA, 2007b

POTW “F” Voluntary amalgam separator program 

began in 1997.

0% 20% (total number of 

offices unknown)

38.0% of POTW influent NACWA, 2007b

POTW “G” Voluntary installation of amalgam 

separators.

44% 100% (100 offices 

total)

90% increase to POTW influent NACWA, 2007b

POTW “H” Voluntary amalgam separator program 

began in 2002.

60% 98% (out of ~200 

offices)

No trend in POTW influent NACWA, 2007b

POTW “I” Mandatory amalgam separator program 

began in 2001.

94% 98% (total number of 

offices unknown)

27.5% of POTW influent NACWA, 2007b

POTWs “J” and 

“K”

Mandatory program required dentists to 

meet a limit of 0.2 mg/L by July 2003.

94% 98% (total number of 

offices unknown)

8.9% increase to POTW “J”;

44.1% reduction to POTW “K”

NACWA, 2007b

POTW “L” POTW recommends installation of 

amalgam separators to dentists.

No information 11% (total number of 

offices unknown)

50.6% of POTW influent NACWA, 2007b

a — Northwest Treatment Plant.

b — Southwest Treatment Plant.
Memorandum

September 22, 2014

Page 4

References

Condrin, A.K. 2004. The Use of CDA Best Management Practices and Amalgam Separators to 

Improve the Management of Dental Wastewater. Journal of the California Dental 

Association 32(7):583-592. DCN DA00024.

King County. 2008. Mercury Levels in King County Biosolids. 

http://dnr.metrokc.gov/wlr/indwaste/amalgdiff.pdf. DCN DA00212.

Lamperti, L. 2007. City of Corvallis’ Comments on EPA’s Preliminary 2008 Effluent Guidelines 

Program Plan. December 21. DCN DA00235. 

Larry Walker Associates. 2002. Mercury Source Control and Pollution Prevention Program 

Evaluation, Final Report. Prepared for AMSA (Association for Metropolitan Sewerage 

Agencies). March (Updated July). DCN DA00006.

MU Extension (University of Missouri Extension Environmental Assistance Center). 2007. 

Maximizing Voluntary Reductions in Dental Amalgam Mercury: Reduction in Mercury 

Discharges. EPA#E0000127. P1-98765101-0. November. DCN DA00223. 

NACWA (National Association of Clean Water Agencies). 2007a. NACWA Comments on ELG 

Preliminary Plan. December. DCN DA00236. 

NACWA. 2007b. An Examination of Mercury Levels at Clean Water Agencies 2003-2006.

December 18. DCN DA00108.

Walsh, William. 2007. The American Dental Association’s (ADA) Comments on EPA’s Study 

of a Pretreatment Requirement for Dental Amalgam. Pepper Hamilton, LLP. December 

21. DCN DA00238.