1

ATTACHMENT 1 

Introduction 

This attachment is a discussion of ENVIRON’s limited update of the scientific 

assessment (“SA”) published in 20051

, including estimates of inputs to surface water 

from two potential emissions sources not previously addressed: medical incinerators and 

landfills. A sensitivity analysis is presented showing how varying levels of compliance 

with ADA’s 2004 Best Management Practices (“BMPs”) and use of amalgam separators 

affects the amount of mercury discharged to surface water. Absolute costs and costeffectiveness associated with the various levels of BMP compliance and separator use are 

also estimated and discussed. 

Mercury fate 

The primary purposes of this update are to 1) refine the analysis by including more recent 

data and study results; and 2) to account for potential mercury emissions from two 

sources that were previously not discussed, but that may receive mercury amalgam waste 

—medical incinerators and landfills. In our earlier assessment, we did not specifically 

state the ultimate disposal location of amalgam collected in chair-side traps (“traps”) and 

vacuum pump filters (“filters”). However, amalgam captured in these two devices 

comprises the large majority of amalgam removed from dental wastewater, and thus the 

fate of this mercury should be assessed. In 2004 ADA published BMPs that emphasized 

recycling of amalgam collected from all sources in dental offices, such as scrap amalgam 

and particulate amalgam caught in traps and filters2

. We assess here the fate of mercury 

that is handled in two ways that are not in accordance with BMPs (i.e., disposal of waste 

amalgam in regular trash, which is ultimately disposed in landfills, and disposal in 

biohazard bags, which are incinerated). 

 

1

 Vandeven, J.A. and McGinnis S.L. 2005. An assessment of mercury in the form of amalgam in dental 

wastewater in the United States. Water, Air, and Soil Pollut. 164: 349–366 (“2005 Vandeven/McGinnis 

Article”). 

2

 ADA. Best Management Practices For Amalgam Waste. 2004. Chicago, IL 
2

This assessment relies heavily on results from our previous assessment and on the results 

from recent assessments by EPA and others. We have incorporated new data where 

applicable to further refine our assessment. Our general approach is the same as that 

taken in our previous SA—we used statistics from the literature where possible, and 

made estimates to the extent necessary. Inherent in this process was the necessity to 

make several assumptions, which are discussed below. 

Amount of mercury discharged from dental offices 

We assumed that a total of 31.25 tons of mercury are discharged annually from dental 

offices. This is the amount of mercury which ERG estimated to be discharged, based 

primarily on results from our previous SA and also on updated statistics regarding the 

number of dentists3

. We assumed this discharge amount for ease of comparison with 

ERG’s study, though current data suggest that the actual amount is slightly lower—

probably closer to our previous estimate of 29.7 tons or perhaps even lower. The 

additional amount of 1.55 tons is due almost entirely to the greater number of dentists 

actively practicing4

. 

It is important to note, however, that though we believe the number of active dentists did 

indeed increase as ERG stated, the number of removals per dentist has likely decreased 

from our earlier estimate of 710 and 440 removals per general dentist and specialist per 

year, respectively. A lower removal rate is likely because amalgam placements have 

been decreasing for several years, including estimated decreases of 29% from 1990 to 

19995

, 30% from 1990 to 19966, and 20.5% from 1999 to 20057. Based on an amalgam 

 

3

 Memorandum from Derek Singer, ERG, to Jan Matuszko, EPA, Subject: Dental Amalgam Separators: 

Summary of Removal Efficiencies, Current Use and Cost Effectiveness (DCN 04851) (September 26, 

2007). 

4

 ADA. 2007. Survey and Economic Research on Dentistry, Frequently Asked Questions: How many 

dentists are there in the U.S.? http://www.ada.org/ada/prod/survey/faq.asp#howmany. 5

 Berthold, M. 2002. Restoratives: Trend data shows shift in use of materials. Am. Dental Assoc. News

33(11) 10-11. 

6

 Sznopek, J. and Goonan, T. 2000. The materials flow of mercury in the economies of the United States 

and the World. United States Geological Survey Circular 1197. Denver, Colorado. 7

 ADA, Economic Impact of Regulating Amalgam, Public Health Reports. September–October 2007 /Volume 

122. at 657, 659-660. http://www.ada.org/prof/resources/topics/amalgam_economic_impact.pdf 
3

lifetime of approximately 8-9 years8

, the number of amalgam restorations in place and 

available for removal is likely lower, due to the lower number of placements in 1999 as 

compared with 1990. Further, recent data from a municipal study show that removal 

rates are substantially lower, approximately 169 removals per dentist per year9

. 

Nevertheless, we have used ERG’s estimate of 31.25 total tons of mercury discharged 

from dental offices so as to facilitate comparisons between ERG’s estimates and our own. 

Capture efficiency of chair-side traps and filters

We assumed that chair-side traps and filters capture 78% of mercury in amalgam 

discharged in dental office wastewater, in accordance with our previous SA. ERG 

assumed the same chair-side trap and filter capture efficiencies as we did in the SA (i.e., 

68% efficiency for chair-side traps alone and 81% efficiency for chair-side traps and 

filters), though they calculated the amount of mercury not captured from the two sources 

separately. Though their calculation method varied slightly from our previous method, 

the results were not significantly different from ours for that portion of the flow with 

chair-side traps alone or chair-side traps and filters. 

Capture efficiency of amalgam separators

For purposes of this calculation, we assumed that amalgam separators capture 99.2% of 

particles exhibiting a size distribution of that presented in ISO11143, which is the median 

efficiency of separators as presented by ERG10. However, there is an important but 

subtle difference between the results presented by ERG and results from our current 

analysis. ERG has overestimated the incremental capture efficiency of amalgam 

separators downstream of chair-side traps and filters. 

 

8 Ibid.

9

 Barron, T. 2005. Mercury source analysis for 2004. Internal Review Draft. Prepared for San Francisco 

PUC. July. http://sfwater.org/Files/Reports/Hg_Tech_Memo_1d.pdf. The report showed 184 removals per 

dentist among those that actively remove amalgams and 169 removals per dentist if all dentists are 

considered. 

10 Memorandum from Derek Singer, ERG, to Jan Matuszko, EPA, Subject: Dental Amalgam Separators: 

Summary of Removal Efficiencies, Current Use and Cost Effectiveness (DCN 04851) (September 26, 

2007). 
4

As stated earlier, the effective capture efficiency of chair-side traps and filters is 78%, 

which is weighted by the efficiencies of each and their respective usage rates. These 

devices capture the largest amalgam particles in dental wastewater, resulting in a 

downstream particle size distribution that no longer matches that of ISO11143, but is 

weighted more toward smaller particles. Given that separators operate using one or more 

of centrifugation, sedimentation, and filtration to remove amalgam particles, the smallest 

are the most difficult to capture. Once the chair-side traps and filters remove the largest 

particles, the remaining distribution consists of smaller, more difficult to capture, 

particles. Therefore, the efficiency of separators downstream of traps and filters will be 

slightly lower than the efficiency in capturing particles from the ISO11143 distribution. 

In this case, the total efficiency of a trap+filter+separator train is 99.2%—the same 

efficiency as a separator alone. The incremental efficiency, EI, is calculated using the 

following equation: 99.2% = 78% + 22% × EI. Using this equation, we calculated the 

incremental efficiency to be approximately 96.4%11. ERG overestimated efficiency by 

assuming that 99.2% of amalgam particles not captured by traps and filters are captured 

by separators. 

Another way to look at the numbers is to calculate the efficiency of separators regardless 

of whether traps or filters are upstream. ERG stated that of 31.25 tons of mercury 

discharged from dental facilities, 26.21 are currently captured and that installation of 

separators would result in capture of an additional 4.93 tons, for a total of 31.14 tons per 

year. However, if the overall efficiency of any system that includes separators is 99.2%, 

the maximum amount that can be removed is 31.25 tons × 99.2% = 31.0 tons, not 31.14, 

as ERG has stated. Though the difference is small, it is significant, especially when 

considering the cost per ton removed. 

 

11 Note that in our previous SA, we estimated the incremental efficiency of separators downstream of chairside traps and filters to be 95%, based on results from studies by MCES and MDA (Metropolitan Council 

Environmental Services and Minnesota Dental Association. 2001. Evaluation of Amalgam Removal 

Equipment and Dental Clinic Loadings to the Sanitary Sewer. Minneapolis-St. Paul, Minnesota) and ADA 

(Fan, P.L., Batchu, H., Gasparac, W., Sandrik, J., and Meyer, D. 2002. Laboratory evaluation of amalgam 

separators. J. ADA. Vol 113, 577–584). Thus the current study assumes a slightly higher incremental 

efficiency than we previously used. 
5

Assuming that 100% of dental offices install separators with a median efficiency of 

99.2%, 0.25 tons of the initial 31.25 will not be captured and will be discharged to 

surface waters. Therefore, the amount of mercury discharged in POTW effluent even if 

all dental offices had separators would not drop significantly from the 0.3 tons of dental 

mercury that Vandeven and McGinnis estimated is currently being discharged from 

POTWs. The lack of a decrease in POTW effluent mercury concentrations after 

separator installations has been documented in the literature. Despite this lack of 

evidence demonstrating a decrease in effluent concentration after separator installation, 

NACWA (formerly AMSA) reported that one study from POTWs in the City of Wichita, 

Kansas preliminarily showed 29% reduction in effluent mercury concentrations when 

separators were installed12. Though several other studies contradict this conclusion, we 

have included in our sensitivity analysis a scenario in which effluent mercury 

concentrations decrease by 30%. 

Capture efficiency of POTWs

As stated in the previous SA, approximately 95% of mercury entering a POTW will be 

removed and not discharged with effluent. The high efficiency of POTWs in removing 

mercury from wastewater is supported by results from a number of studies showing that 

mercury capture efficiencies for POTWs ranging from 95% to 99%. A 2002 AMSA 

study included a review of 15 POTWs ranging in capacity from 4 million gallons per day 

(MGD) to 375 MGD13. AMSA found the average mercury capture efficiency to be 95%. 

Balogh and Liang (1995)14 and Balogh and Johnson (1998)15 found capture efficiencies 

for three POTWs to be 96%, 98%, and 99%. 

The high effectiveness of POTWs in capturing amalgam makes scientific sense as well. 

Amalgam particles are much denser than water and thus settled out and are removed with 

 

12 The anecdotal decrease in effluent concentrations was relayed by personal communication from C. 

Hornback to ENVIRON. 

13 Association of Metropolitan Sewerage Agencies (AMSA). 2002. Mercury Source Control and Pollution 

Prevention Program. Washington, D.C. 

14 Balogh, S. and L. Liang. 1995. Mercury pathways in municipal wastewater treatment plants. Water, 

Air, Soil Pollut. 80:1181–1190. 15 Balogh, S. and Johnson, L. 1998. Mercury mass balances at two small wastewater treatment plants. 

Metropolitan Council Environmental Services (MCES), Minneapolis-St. Paul, Minnesota. 
6

other particulates entering POTWs. The density of amalgam particles is approximately 

11 g/cm3, depending upon the particular composition. For example, amalgam can be 

composed of tin, copper, silver and mercury, with densities of approximately 7.3 g/cm3

, 

9 g/cm3

, 10 g/cm3, and 13.5 g/cm3, respectively . The composition of one amalgam type 

is 30% silver, 50% mercury, 5% copper and 15% tin, resulting in an amalgam with a 

density of approximately 11 g/cm3

. Amalgams with other compositions would have 

similar densities. 

Based on the above analyses, it is reasonable to conservatively estimate that POTWs 

remove 95% of influent mercury. As the processes used to remove particles in a POTW 

are similar to those in separators, the smallest particles that escape capture in separator 

will likely not be captured in a POTW. For this reason we have assumed that for 

wastewater treated with separators, the mercury not captured will also not be captured in 

POTWs. In other words, for the portion of flow from facilities with separators, POTWs 

will not capture any additional mercury, and for the portion of flow from facilities 

without separators, the capture efficiency is 95%. 

Implementation of BMPs

As stated earlier, a primary focus of this update is to assess the fate of mercury captured 

in chair-side traps and vacuum pump filters—in particular that portion which is not 

recycled. In 2004 ADA published BMPs for amalgam waste in an effort to reduce the 

amount of mercury entering the environment. These BMPs provide guidance regarding 

proper use and storage of mercury and proper disposal of amalgam waste. The BMPs 

state that amalgam waste should always be recycled and should not be placed in 

biohazard containers, infectious waste containers (red bags) or regular garbage. In the 

current analysis, mercury collected in chair-side traps and filters that was handled 

according to BMPs was assumed to be recycled and not enter the environment, including 

surface waters. Mercury not handled according to BMPs was assumed to either be sent to 

medical incinerators or to landfills. The amount of mercury emitted from either one was 

estimated based on emission rates from the literature. 
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Emissions from medical incinerators

ADA’s 2004 BMPs specifically state that amalgam waste should not be disposed in 

biohazard containers, infectious waste containers (red bags). This is primarily because 

this type of waste is typically incinerated, thus converting mercury from a bound 

(amalgamated) form into a volatile, mobile form. We assumed that 96% of mercury from 

amalgam waste sent to a medical incinerator was captured by pollution control 

equipment, based current regulations regarding emissions from medical waste 

incinerators16. Mercury captured in medical incinerator pollution control equipment was 

assumed to be handled according to applicable regulations and not released to the 

environment. We assumed that all dental offices with amalgam separators would recycle 

mercury captured in separators. 

As in our previous assessment, we assumed that 33% of mercury emitted from medical 

incinerators would enter United States surface waters, based on a 1997 USEPA 

estimate17. The resulting amounts of mercury entering surface waters are shown in 

Table 1 and are discussed further below. 

Emissions from landfills and land-applied biosolids

We estimated the amount of mercury that would be disposed in solid waste landfills 

assuming various levels of compliance with 2004 BMPs, which advise dentists not to 

dispose any amalgam waste in regular garbage. Total annual mercury emissions in the 

U.S. have been estimated at <0.1 tons per year in 1994–1995 and 0.2 tons per year in 

199618. The total mercury directed to landfills or collected as hazardous waste was 

estimated to be 295 metric tons (330 U.S. tons) in 199619. Therefore, we conservatively 

estimated the emission rate to be 0.2 tons emitted/330 tons disposed = 0.0606%. In other 

words, 0.0606% of mercury from dental offices that is disposed in landfills is emitted to 

 

16 Proposed regulations requiring that hospital/medical/infectious waste incinerators (HWIMI) capture 96% 

of mercury emissions were published in Federal Register, Volume 72, No. 24, February 6, 2007. 

17 United State Environmental Protection Agency. 1997. Mercury study report to Congress. EPA-452/R-97-

003. 

18 United Nations Environment Programme (UNEP). 2002. Global Mercury Assessment. Geneva, 

Switzerland. At page 98. December. This document cites to 

http://www.chem.unep.ch/mercury/Report/Final%20Assessment%20report.htm 

19 Ibid. page 99. 
8

the air. As with other emissions to air, we assume that 33% of total mercury emissions 

from landfills reach U.S. surface water. 

Based on EPA statements, we further assumed that mercury in land-applied biosolids 

would be bound as amalgam and would not be available for leaching to surface water or 

volatilization to the atmosphere in significant amounts20,21. 

Emissions from incinerated biosolids

We assumed that capture of mercury in from sewage sludge incinerator (SSI) emissions 

to be the same as presented in the previous SA, i.e., 79% capture efficiency, based on 

AP-42 emission factors22. As in the 2005 SA, we assumed that 33% of mercury emitted 

from SSIs to the atmosphere is deposited in U.S. surface waters23. 

Estimated costs 

A fundamental issue related to a regulation regarding mandatory installation of amalgam 

separators is the cost with implementing such a regulation. This section discusses our 

methods for estimating costs of implementation of BMPs and use of separators. 

To estimate costs incurred by dentists in implementing BMPs, ENVIRON obtained 

estimates for recycling waste that includes amalgam (e.g., scrap amalgam, traps and 

filters with amalgam, etc). ENVIRON spoke with several mercury recyclers, separator 

manufacturers and distributors to ask if they recycle amalgam waste or have estimates of 

the cost associated with recycling. Various methods for recycling amalgam waste exist. 

Some recyclers sell a recycling service in which the recycler will send the dentist an 

 

20 ADA Prior Comments, EPA-OW-2006-0771 at 54-55; 204-208; 213-215. 

21 EPA’s Road Map, Addressing Mercury Releases at 28 (July 2006), available at 

<http://epa.gov/mercury/pdfs/I_HgReleases.pdf>. The mercury in amalgam is bound into the mixture and 

the mercury in the amalgam in biosolids is less likely to be released into the air. The study cited by EPA in 

the administrative record is limited and measured mercury from all sources, not just mercury from 

amalgam and, therefore, was not a measure of the likelihood of mercury in amalgam being released from 

soil. 

22 United States Environmental Protection Agency. 1995. Compilation of air pollutant emission factors, 

AP-42, Fifth edition, Volume I: Stationary Point and Area Sources. Washington, D.C. 

23 United State Environmental Protection Agency. 1997. Mercury study report to Congress. EPA-452/R-97-

003. 
9

empty bucket to contain amalgam waste and a return shipping label. The dentist then fills 

the bucket with amalgam waste and ships it back to the recycler. ENVIRON asked if the 

recyclers were able to estimate a representative amount of time dentists take to fill a 

certain size (e.g., one gallon) recycling bucket. They reported that the times vary widely 

from as short as one month to as long as a year. Costs per bucket generally ranged from 

just under $100 per bucket to over $300, depending upon the service and on the size of 

the bucket. Based on our conversations with these manufacturers and distributors, we 

estimated that a conservative (low) cost to be approximately $150 per year. 

We assumed that the annual cost of owning and operating an amalgam separator to be 

$770.85, based on recent work by ERG. This cost is in general agreement with results 

from our conversations with amalgam separator manufacturers and distributors. Using 

the annual cost of $770.85 for ownership and operation of an amalgam separator and 

$150 per year for implementation of BMPs, we calculated the cost of implementing 

various scenarios, ranging from 65% compliance with BMPs and dental offices with 

separators installed to 100% compliance with BMPs and all dental offices with separators 

installed. 

In addition to estimating absolute costs associated with complying with BMPs and using 

separators, we estimated the cost per ton of mercury prevented from entering surface 

waters for the two scenarios of effectively 0% reduction in effluent mercury and 30% 

reduction in effluent mercury. The results of this analysis are summarized in Table 1 and 

discussed further below. 

Results 

Estimated amounts of mercury entering surface water

Table 1 summarizes the amounts of mercury that would reach surface waters in the U.S. 

under the various scenarios. Several observations are worth highlighting. First, it is 

important to note the very small quantities of mercury that are being considered in this 

analysis. Even in the worst case scenario in the table (65% implementation of BMPs and 

0% of facilities with separators), the amount of mercury released to surface waters is 
10

relatively small (0.532 tons, compared with a total of 31.25 tons discharged from dental 

offices). 

Second, the results from the present analysis are in agreement with those of our earlier 

SA. For example, in the case of 100% separator installation, 0.25 tons of mercury reach 

surface waters, which is similar in magnitude to the 0.3 tons estimated in the earlier SA. 

Also, for the case with 100% compliance with BMPs (i.e., no mercury captured in traps 

and filters reaches surface water), the result converges to 0.419 tons, similar to the value 

of 0.4 tons estimated previously. 

Third, the amount of mercury that is prevented from entering surface waters after 

installation of separators is very small. In the extreme case where 35% of those without 

separators are out of compliance with BMPs and send their amalgam waste to medical 

incinerator, 0.282 tons of mercury are prevented from entering surface waters if 100% of 

dentist offices have separators. 

Estimated costs of implementation of BMPs and use of separators

Our estimates of the costs associated with implementing BMPs and installing and 

maintaining amalgam separators are summarized in Table 1. At the low end, assuming 

no separators are installed and 65% of dental offices are complying with BMPs, the total 

cost is approximately $9.8M. At the other extreme, where 100% of dental offices are 

complying with BMPs and also have separators installed, the total cost is approximately 

$92.9M. Using ERG’s estimate of $770.85 per dental office and 100,843 dental offices, 

the total cost would be approximately $77.7M. Adding the cost of implementing BMPs 

at all dental offices would result in $92.9M, which matches our result. 

However, our current estimate of the cost of separator use per ton of mercury captured 

varies significantly from ERG’s. ERG calculated the cost of capturing amalgam to be 

approximately $11M per ton, based on total cost of $54.4M to remove approximately 

4.93 tons of mercury. We estimate that the cost would range from $319M to $461M per 

ton. ERG’s analysis falls short in at least two ways. 
11

First, ERG overestimated the effectiveness of separators by assuming that the efficiency 

of separators in capturing particles passing through chair-side traps and/or filters is the 

same as the efficiency in capturing particles from the entire size range of particles in the 

ISO11143 distribution. This is an incorrect assumption. ERG stated that only 0.1 tons 

would be discharged to surface waters. However, even if 99.2% efficiency can be 

achieved, the smallest amount of mercury that can be discharged to surface water is 0.25 

tons, even if all dental offices installed and used separators. Thus, the greatest amount 

removed would be 4.79 tons, not 4.93 tons. This works out to approximately $11.4M per 

ton. 

Second, and more importantly, ERG did not consider the effectiveness of POTWs in 

reducing mercury discharge to surface waters, but rather assumed that installing 

separators would decrease the amount of mercury released to surface waters by full 4.93 

tons. In reality, only 0.419 tons would ultimately reach surface water with no separators 

installed, and only approximately 0.169 tons from biosolids incineration emissions and 

POTW effluent would actually be prevented from entering surface waters by installing 

separators. According to our current calculations, an additional 0.118 tons would be 

captured if the remaining 70% of dental offices currently without separators installed 

them. Based on total costs of approximately $54.4M for 70% of dentists to install 

separators24, the estimated cost would be $461M per ton captured. 

Comparison with previous results

In our previous SA, we estimated the annual cost for all 95,066 dental offices to install 

and operate separators to range from $76M to $114M and the cost per ton to range from 

$380M to $1.14B. At the low end, we used as a basis the scenario in which 30% of 

0.3 tons (i.e., 0.1 tons) in effluent would be prevented from entering surface water. The 

net reduction, including 0.1 tons from incinerated biosolids, was 0.2 tons. Therefore, the 

low cost per ton was calculated to be $76M/0.2 ton = $380M/ton. 

 

24 Memorandum from Derek Singer, ERG, to Jan Matuszko, EPA, Subject: Dental Amalgam Separators: 

Summary of Removal Efficiencies, Current Use and Cost Effectiveness (DCN 04851) (September 26, 

2007). 
12

At the high cost end, we estimated that only 0.1 tons of mercury would be prevented by 

installing separators. Using the higher annual cost value of $1200, 95,066 dental offices 

and 0.1 tons, the resulting cost per ton prevented from entering surface water is $1.14B. 

The differences between our previous study results and the present results are due 

primarily to two factors. First, the higher end cost used previously is higher than the 

baseline cost used here ($1200 as opposed to $770.85). Second, the higher incremental 

capture efficiency used here (96.4% currently as opposed to 95% previously) results in 

greater mercury capture, which results in lower cost per ton for a given absolute cost. 

Conclusions

We performed a limited update of our previous assessment by 1) using more recent data 

and 2) estimating emissions from medical incinerators and landfills that may receive 

amalgam waste. Results were summarized as a sensitivity analysis for various scenarios 

in Table 1. In addition, we estimated the absolute cost of implementing 2004 BMPs and 

installing and using amalgam separators. Finally, we calculated the cost per ton of 

preventing mercury from entering surface waters by installing and using amalgam 

separators. Those costs ranged from $319M to $461M per ton. 
Percent compliance with pre-2007 BMPs (1) 65% 65% 80% 80% 90% 

Destination of non-recycled mercury Medical incinerator Landfill Medical incinerator Landfill Medical inciner

Baseline estimate of mercury reaching surface waters (2)

0% of dental facilities using separators 0.531 0.420 0.483 0.420 0.451 

30% of dental facilities using separators 0.447 0.369 0.413 0.369 0.391 50% of dental facilities using separators 0.391 0.335 0.367 0.335 0.350 75% of dental facilities using separators 0.320 0.293 0.308 0.292 0.300 90% of dental facilities using separators 0.278 0.267 0.273 0.267 0.270 

100% of dental facilities using separators 0.250 0.250 0.250 0.250 0.250 

"30% effluent mercury reduction" scenario (3)

0% of dental facilities using separators 0.531 0.420 0.483 0.420 0.451 

30% of dental facilities using separators 0.424 0.347 0.391 0.346 0.368 50% of dental facilities using separators 0.353 0.298 0.329 0.297 0.313 75% of dental facilities using separators 0.264 0.236 0.252 0.236 0.244 90% of dental facilities using separators 0.211 0.200 0.206 0.199 0.203 

100% of dental facilities using separators 0.175 0.175 0.175 0.175 0.175 

Baseline costs of implementation (4)

0% of dental facilities using separators $9,832,193 $9,832,193 $12,101,160 $12,101,160 $13,613,805 

30% of dental facilities using separators $34,740,918 $34,740,918 $36,329,195 $36,329,195 $37,388,046 50% of dental facilities using separators $51,346,735 $51,346,735 $52,481,218 $52,481,218 $53,237,541 75% of dental facilities using separators $72,104,006 $72,104,006 $72,671,247 $72,671,247 $73,049,409 90% of dental facilities using separators $84,558,368 $84,558,368 $84,785,265 $84,785,265 $84,936,529 

100% of dental facilities using separators $92,861,277 $92,861,277 $92,861,277 $92,861,277 $92,861,277 

Cost effectiveness baseline scenario (total cost per tons removed by separators) (5)

0% of dental facilities using separators NA NA NA NA NA 

30% of dental facilities using separators $295,087,979 $487,076,408 $346,449,196 $475,806,776 $394,397,282 50% of dental facilities using separators $295,087,979 $487,076,408 $346,449,196 $475,806,776 $394,397,282 75% of dental facilities using separators $295,087,979 $487,076,408 $346,449,196 $475,806,776 $394,397,282 90% of dental facilities using separators $295,087,979 $487,076,408 $346,449,196 $475,806,776 $394,397,282 

100% of dental facilities using separators $295,087,979 $487,076,408 $346,449,196 $475,806,776 $394,397,282 

Cost effectiveness - "30% effluent mercury reduction" scenario (total cost per tons removed by separators) (6)

0% of dental facilities using separators NA NA NA NA NA 

30% of dental facilities using separators $232,985,219 $338,253,352 $262,116,168 $329,992,739 $287,198,126 50% of dental facilities using separators $232,985,219 $338,253,352 $262,116,168 $329,992,739 $287,198,126 75% of dental facilities using separators $232,985,219 $338,253,352 $262,116,168 $329,992,739 $287,198,126 90% of dental facilities using separators $232,985,219 $338,253,352 $262,116,168 $329,992,739 $287,198,126 

100% of dental facilities using separators $232,985,219 $338,253,352 $262,116,168 $329,992,739 $287,198,126 

Notes: 6. Cost effectiveness for the "30% effluent mercury reduction" scenario was calculated the same way it was in the baseline scenario, except that the cost w

from entering surface water assuming an additional 30% reduction in effluent concentrations.4. This baseline cost estimate assumes $770.85/year for separators and $150/year for BMPs for 100,843 dental offices (ERG, 2007) that use amalgam. $operating an amalgam separator, as calculated by ERG, 2007. The cost includes $1,200 capital cost, spread over 10 years at 7% interest plus $600 annu5. Cost effectiveness was calculated by taking the cost of the dental community owning and operating separators and dividing it by the estimated amount example, the baseline cost for the scenario with 30% separators and 65% BMP compliance is (30%)(100,843)($770.85+$150)+(100%-30%)(100,843)(65%

Table 1

Annual amount of mercury entering surface water and costs

associated with varying levels of compliance with 2004 ADA BMPs and use of amalga

(tons; assuming 31.25 tons discharged in dental wastewater)

1. We assumed that 100% of dental offices with separators installed were in compliance with BMPs. The "Percent compliance with BMPs" refers to the peBMPs, yet do not have a separator installed. For example, where 100% of dental offices have separators installed, 100% are also in compliance with BM2. The baseline assessment scenario is the same as that in our previous SA. This assumes that POTWs capture 0% of that portion of mercury entering s3. This scenario is the same as the baseline, except that it includes an assumption that mercury entering separators but is not captured is actually reduced accordance with a scenario presented in our earlier SA.