# A N 

# E XAMINATION OF 

# M ERCURY 

# L EVELS AT 

# C LEAN 

# W ATER 

# A GENCIES 

# 2003-2006

N ATIONAL 

# A SSOCIATION OF 

# C LEAN 

# W ATER 

# A GENCIES 

# J ANUARY 

# 2008

### 2 

## A CKNOWLEDGMENTS



### The staff of all of the partic ipating agencies, who performed sampling, supplied data, answered questions, and provided editing.

The Hampton Roads Sanitation District Central Environmental Laboratory Patty Lee, Hampton Roads Sanitation District Danny Barker, Hampton Roads Sanitation District Anna Rule, Hampton Roads Sanitation District

Steve Anderson, Clean Water Services

Elizabeth Toot-Levy, Northeast Ohio Regional Sewer District Seth Hothem, Northeast Ohio Regional Sewer District Keith Linn, Northeast Ohio Regional Sewer District

Christopher Hornback, National Associ ation of Clean Water Agencies

The NACWA Mercury Workgroup Sampling Project Subgroup

The American Dental Associati on (for draft report review)

### 3 

## An Examination of Mercury Levels at Clean Water Ag encies: 2003-2006 A CKNOWLEDGMENTS 

### ..................................................................................................................... 2 L IST OF 

### F IGURES 

### ............................................................................................................................ 4 E XECUTIVE 

### S UMMARY 

### ................................................................................................................... 6 1. I NTRODUCTION 

### ........................................................................................................................... 9 2. M ETHODS



### ............................................................................................................................... ... 10 2.1 Sampling Methods ............................................................................................................ 11 2.2 Analytical Methods ........................................................................................................... 12 2.3 Statistical Methods ............................................................................................................ 13 3. I NDIVIDUAL 

### POTW R ESULTS AND 

### D ISCUSSION 

### ...................................................................... 14 3.1 POTW “A” ......................................................................................................................... 14 3.2 POTW “B” ......................................................................................................................... 19 3.3 POTW “C” ........................................................................................................................ 23 3.4 POTWs “D” and E” .......................................................................................................... 26 3.5 POTW “F” ......................................................................................................................... 31 3.6 POTW “G” ........................................................................................................................ 34 3.7 POTW “H” ........................................................................................................................ 38 3.8 POTW “I” .......................................................................................................................... 41 3.9 POTW S 

### “J” AND 

### “K” ........................................................................................................ 44 3.10 POTW “L” ....................................................................................................................... 50 4. C OMBINED 

### R ESULTS AND 

### D ISCUSSION 

### .................................................................................... 53 4.1 I NFLUENT 

### , E FFLUENT 

### , AND 

### B IOSOLIDS 

### ............................................................................. 53 4.2 R EMOVAL 

### E FFICIENCY 

### ...................................................................................................... 56 4.3 D ISSOLVED 

### M ERCURY 

### ........................................................................................................ 57 4.4 T OTAL 

### S USPENDED 

### S OLIDS 

### ................................................................................................ 59 4.5 D ENTISTS PER 

### F LOW 

### .......................................................................................................... 60 4.6 D ENTIST 

### W ITHOUT 

### S EPARATORS PER 

### F LOW 

### .................................................................... 63 4.7 P LANT 

### F LOW 

### ...................................................................................................................... 65 4.8 N ON 

### -I NDUSTRIAL 

### F LOW 

### .................................................................................................... 67 4.9 F RESHWATER VS



### . M ARINE 

### D ISCHARGERS 

### ........................................................................ 71 4.10 I RON 

### S ALTS 

### ....................................................................................................................... 73 4.11 H AULED



### - IN 

### W ASTES 

### ......................................................................................................... 75 4.12 P OPULATION 

### D ENSITY 

### ..................................................................................................... 77 4.13 C OMBINED OR 

### S EPARATE 

### C OLLECTION 

### S YSTEMS 

### .......................................................... 79 5. S UMMARY AND 

### C ONCLUSIONS 

### ................................................................................................. 81 6. I MPLICATIONS FOR 

### F URTHER 

### R ESEARCH 

### ............................................................................... 83 7. A PPENDICES 

### .............................................................................................................................. 8 6 7.1 A PPENDIX 

### A: DATA 

### ............................................................................................................. 86 7.2 A PPENDIX 

### B: S UMMARY OF 

### S TATISTICAL 

### A NALYSES FOR 

### C OMBINED 

### D ATA 

### ................ 114 7.3 A PPENDIX 

### C: S TATISTICAL ANALYSIS 

### ............................................................................. 117 7.4 A PPENDIX 

### D: S TUDY 

### P LAN 

### ............................................................................................... 360

### 4 

## L IST OF 

## F IGURES 

### Figure 3.1A: Effluent and Biosolids Merc ury Concentrations at POTW “A” ............................. 17 Figure 3.1B: Effluent Mercury and TSS Concentrations at POTW “A”...................................... 18 Figure 3.1C: Influent and Effluent Mercury Load at POTW “A” ................................................ 18 Figure 3.2A: Effluent and Biosolids Merc ury Concentrations at POTW “B”.............................. 21 Figure 3.2B: Effluent Mercury and TSS Concentrations at POTW “B” ...................................... 22 Figure 3.2C: Influent and Effluent Mercury Load at POTW “B” ................................................ 22 Figure 3.3A: Effluent and Biosolids Merc ury Concentrations at POTW “C”.............................. 25 Figure 3.3B: Effluent Mercury and TSS Concentrations at POTW “C” ...................................... 26 Figure 3.3C: Influent and Effluent Mercury Load at POTW “C” ................................................ 26 Figure 3.4A: Effluent and Biosolids Merc ury Concentrations at POTW “D” ............................. 28 Figure 3.4B: Effluent Mercury and TSS Concentrations at POTW “D”...................................... 29 Figure 3.4C: Influent and Effluent Mercury Load at POTW “D” ................................................ 29 Figure 3.4D: Effluent and Biosolids Merc ury Concentrations at POTW “E”.............................. 30 Figure 3.4E: Effluent Mercury and TSS Concentrations at POTW “E”....................................... 30 Figure 3.4F: Influent and Effluent Mercury Load at POTW “E”................................................. 31 Figure 3.5A: Effluent and Biosolids Merc ury Concentrations at POTW “F” .............................. 33 Figure 3.5B: Effluent Mercury and TSS Concentrations at POTW “F”....................................... 34 Figure 3.5C: Influent and Effluent Mercury Load at POTW “F”................................................. 34 Figure 3.6A: Effluent and Biosolids Merc ury Concentrations at POTW “G” ............................. 36 Figure 3.6B: Effluent Mercury and TSS Concentrations at POTW “G”...................................... 37 Figure 3.6C: Influent and Effluent Mercury Load at POTW “G” ................................................ 37 Figure 3.7A: Effluent and Biosolids Merc ury Concentrations at POTW “H” ............................. 40 Figure 3.7B: Effluent Mercury and TSS Concentrations at POTW “H”...................................... 40 Figure 3.7C: Influent and Effluent Mercury Load at POTW “H” ................................................ 41 Figure 3.8A: Effluent and Biosolids Merc ury Concentrations at POTW “I”............................... 43 Figure 3.8B: Effluent Mercury and TSS Concentrations at POTW “I” ....................................... 44 Figure 3.8C: Influent and Effluent Mercury Load at POTW “I”.................................................. 44 Figure 3.9A: Effluent and Biosolids Merc ury Concentrations at POTW “J”............................... 47 Figure 3.9B: Effluent Mercury and TSS Concentrations at POTW “J” ....................................... 48 Figure 3.9C: Influent and Effluent Mercury Load at POTW “J” ................................................. 48 Figure 3.9D: Effluent and Biosolids Merc ury Concentrations at POTW “K” ............................. 48 Figure 3.9E: Effluent Mercury and TSS Concentrations at POTW “K” ...................................... 49 Figure 3.9F: Influent and Effluent Mercury Load at POTW “K"................................................. 50 Figure 3.10A: Effluent and Biosolids Merc ury Concentrations at POTW “L”............................ 51 Figure 3.10B: Effluent Mercury and T SS Concentrations at POTW “L” .................................... 52 Figure 3.10C: Influent and Effluent Mercury Load at POTW “L”............................................... 53 Figure 4.1A: Influent Mercury Concentrations ........................................................................... 53 Figure 4.1B: Influent Mercury Concentra tions and Sample Collection Location....................... 54 Figure 4.1C: Effluent Mercury Concentrations ........................................................................... 55 Figure 4.1D: Biosolids Mercury Concentrations......................................................................... 56 Figure 4.2A: Mercury Removal Efficiency .................................................................................. 57 Figure 4.3A: Median Percent of Effluent Total Mercury that is Dissolved.................................. 58 Figure 4.3B: Presence of Recycle flows and the Median Percent of Effluent Total Mercury that is Dissolved...................................................................................................................... ............. 59 Figure 4.4A Effluent Mercury Concentrations versus Effluent TSS Concentrations................... 60

### 5 Figure 4.5A. Influent Mercury Concen tration and Dentists per Flow......................................... 61 Figure 4.5B. Effluent Mercury Con centration and Dentists per Flow........................................ 62 Figure 4.5C: Biosolids Mercury Concen tration and Dentists per Flow....................................... 63 Figure 4.6A: Influent Mercury Concentration an d Dentists without Separators per Flow.......... 64 Figure 4.6B. Effluent Mercury Concentration an d Dentists without Separators per Flow.......... 64 Figure 4.6C: Biosolids Mercury Concentration a nd Dentists without Separators per Flow ....... 65 Figure 4.7A: Influent Mercury Concen tration and Average Plant Flow ..................................... 66 Figure 4.7B: Biosolids Mercury Concen tration and Average Plant Flow................................... 66 Figure 4.7C: Effluent Mercury Concen tration and Average Plant Flow..................................... 67 Figure 4.8A: Influent Mercury Concen tration and Non-Industrial Flow .................................... 68 Figure 4.8B: EffluentMercury Concen tration and Non-Industrial Flow ..................................... 69 Figure 4.8C: Biosolids Mercury Concen tration and Non-Industrial Flow .................................. 69 Figure 4.8D: Influent Mercury Concentration and Non-Industrial Flow in Separate Sewer Systems ........................................................................................................................ ............. 70 Figure 4.8E: Effluent Mercury Concentration and Non-Industrial Flow in Separate Sewer Systems ........................................................................................................................ ............. 71 Figure 4.8F: Biosolids Mercury Concentration a nd Non-Industrial Flow in Separate Sewer Systems ........................................................................................................................ ............. 71 Figure 4.9A: Influent Mercury Concen tration and Receiving Water Type................................. 72 Figure 4.9B: Effluent Mercury Concen tration and Receiving Water Type................................. 72 Figure 4.9C: Biosolids Mercury Concen tration and Receiving Water Type............................... 73 Figure 4.10A: Effluent Mercury Con centration and Use of Iron Salts........................................ 74 Figure 4.10B: Biosolids Mercury Con centration and Use of Iron Salts...................................... 74 Figure 4.11A: Influent Mercury Concentrations and Hauled-in Waste....................................... 75 Figure 4.11B: Effluent Mercury Con centrations and Hauled-in Waste ...................................... 76 Figure 4.11C: Biosolids Mercury Con centrations and Hauled-in Waste .................................... 76 Figure 4.12A: Influent Mercury Concentration and Population Density .................................... 77 Figure 4.12B: Effluent Mercury Con centration and Population Density .................................... 78 Figure 4.12C: Biosolids Mercury Con centration and Population Density .................................. 78 Figure 4.13A: Influent Mercury Concen trations and Sewer System Type.................................. 79 Figure 4.13B: Effluent Mercury Concen trations and Sewer System Type .................................. 80 Figure 4.13C: Biosolids Mercury Concen trations and Sewer System Type ............................... 80

### 6 

## E XECUTIVE 

## S UMMARY



### The degree to which mercury concentrations at publicly-owned treatment works (POTWs) can be reduced by controlling potentially significant sources, such as dental clinics, is not well known. Therefore, the National Association of Clean Water Ag encies (NACWA) funded a study to examine the effect of practical and reasonabl e measures of controlling mercury discharged to the POTW collection system, such as dental am algam separator installation, on the ability of POTWs to reduce influent, effluent , and biosolids mercury levels.

This study provides insight into th e effect of amalgam separator installation and other factors on mercury concentrations at POTWs, but it does not, and was not intended to, address all the uncertainty surrounding such factors. Although th e data collected during the course of the sampling project provide useful information, this report’s evaluations of the collected data illustrate the limitations of the study and, in many cases, highlight the need for further research. A considerable limitation is the inability to identify and account for all the variation that necessarily exists among POTWs. POTWs are designed to accomplish the same basic goals, but they achieve these goals differe ntly, making some interfacility comparisons difficult. Among the potential sources of uncertainty are temporal va riations in influent mercury concentrations, differences in sampling techniques, inconsiste nt methods of counting dentists and dental facilities, and varying chemical us e by POTWs. It is these variables and others that lead to the implications for further research presented late r in the report. Such additional research may allow a better understandi ng of the factors affecting mercur y levels at POTWs, including the installation of amalga m separators.

The influent, effluent, and biosolids mercury c oncentrations from twelve POTWs in the United States and Canada, in various stag es of requiring dental facilities to install amalgam separators, were measured on a monthly basis from July 2003 through July 2006 to evaluate the impact of separator installation and other po tential factors. Information on other source control efforts and operational activities at the sampled POTWs was also collected in an effort to shed light on numerous issues related to controlling mercury releases by POTWs to the environment.

The influent mercury concentratio ns at the POTWs in the study were found to be highly variable within each facility as well as among facilities. Consistent with this variation, when considering facilities individually, some exhib ited decreases in their influent mercury concentrations over the course of the sampling project, while others ha d apparent increases. Thus, a great deal of uncertainty surrounds the influent sampling data, and it may not be prudent to draw conclusions based solely on the limited influent data. E ffluent mercury concentrations also exhibited variability between plants but less variability within plants. For the biosolids, there was some variability both within and among the plants. Ho wever, neither the effluent nor the biosolids mercury data were nearly as variab le as the influent mercury data.

The mercury removal efficiency from plant influent to plant effluent was generally greater than ninety percent. While the POTWs were similar in this aspect, in other ways they were not. For instance, the percentage of effl uent mercury that was dissolved was found to vary based on the POTW. Additionally, at eight of the POTWs, there appeared to be a direct relationship between

### 7 effluent mercury concentration and effluent tota l suspended solids concentration while, at the remaining five POTWs, this rela tionship did not appear to exist.

The study results strongly suggest that the density of dentists in a POTW’s collection system is positively correlated with mercury concentrations at the wastewater treatment plant. A higher number of dentists per flow was related to highe r influent and effluent mercury concentrations. There was no relationship, however, between number s of dentists per flow and biosolids mercury concentrations. This may be due to amalgam sepa rators being installed by dentists in many of the sampled POTWs’ service areas. Importan tly, though, it was found that, collectively, higher numbers of dentists without am algam separators per flow were related to higher biosolids mercury levels. This relationship was highly significant statistica lly and among the most significant relationships observed in the study.

Conversely, the effluent mercury concentration was found to be negatively correlated to the number of dentists without se parators per flow, indicating th at increasing amalgam separator installations does not necessarily lead to a decrease in effluent mercury concentrations. This result could be due, in part, to the limited numbe r of amalgam separator in stallations occurring at the POTWs with generally lower effluent merc ury concentrations at the study’s outset.

For individual plants, the installation of separators did not always lead to a decrease in biosolids mercury. It may be that amalgam separator installation alone is not enough to result in permanent mercury reductions. Some of the plan ts that did show decreases in mercury have programs in place to ensure that the separators ar e well-operated and maintained, and this may be a factor. It is also thought that mercury re ductions following separator installations can take several years or even longer to demonstrate sign ificant trends. Therefore, this study may not have been long enough to determine significant tre nds for some POTWs whos e dental facilities were in the process of installing amalgam separators during the course of the study. It is further possible that, on an individual-facili ty basis, apparent reductions or the lack thereof could be the result of other impacting factors such as previo usly elevated loadings related to sewer cleaning, construction activities, or historic depositions of mercury in the collection system.

Some of the treatment plants exhibited mercury reductions even without an increase in amalgam separator installation. These redu ctions may have resulted from changes in treatment processes or the implementation of best management practices at dental facilities. Therefore, on a facilityspecific basis, the effectiveness of amalgam sepa rators in reducing mercury should be examined in light of other activities that are occurring within the POTW a nd its service area to determine which factors are actually cont ributing to an observed reduction.

In addition to the presence of de ntists within a POTW’s collec tion area, several other factors were found to exhibit relationships with mercury levels at treatment plants. These included the discharge of effluent to marine waters and se wer cleaning projects occurr ing within the POTW’s collection system, which were each related to higher effluent mercury levels, and higher industrial flow and the use of iron salts, which were each related to lower effluent mercury levels.

### 8 Factors that were examined but not found to be re lated to mercury levels were higher plant flow, population density, whether the POTW accepts ha uled-in wastes, and whether the collection system is comprised of combined or separate sewers.

Overall, the results of this study indicate th at many factors, not just amalgam separator installation, influence mercury c oncentrations. While separators have been shown to reduce mercury loadings at dental offices, it should be recognized that the in stallation and use of separators may not result in demonstrable and immediate reductions at the receiving treatment facility due, at least in part, to the legacy issues from historic mercury c ontributions. Therefore, a facility cannot predict with certainty that amalgam separators will decrease mercury concentrations without also exploring the other po tential contributors to current mercury levels. Additionally, it should be noted that, even at those POTWs with dem onstrably successful amalgam separator programs, effluent merc ury concentrations were not low enough to consistently meet current and imminent effluent limits faced by some POTWs ( e.g ., 1.3 nanograms per liter in the Great Lakes).

According to the results, separator installation does not generally appear , at least within the timeframe of this study, to signi ficantly reduce effluent mercury concentrations. However, amalgam separator installation does generally appear to result in reductions in biosolids mercury concentrations. Therefore, despite the variabilit y and uncertainties descri bed in this report, the data strongly support a conclusion that the us e of separators can decrease the amount of particulate mercury entering POTWs, thereby d ecreasing the amount of me rcury that would be removed by plant processes and deposited in the biosolids.

### 9 

## 1. I NTRODUCTION



### The National Association of Clean Water Agencies (NACWA) represents the interests of more than three hundred of the natio n’s publicly owned treatment works (POTWs) and other similar organizations. NACWA is recognized as a nati onal leader in envir onmental policy and as a technical resource for many water quality issues. The organiza tion has been cr ucial in the development of environmental legislation and ha s worked with Federal regulatory agencies in implementing environmental programs since th e early 1970s. NACWA is currently involved with all aspects of water quali ty protection from point and non point source control to the protection of endangered species and is a key stakeholder in bot h the legislative and regulatory

arenas.

Mercury has been identified as one of NACWA’s priorities. Therefor e, the NACWA Mercury Workgroup began identifying information gaps re garding both the short-term and long-term abilities of POTWs to comply with anticipated mercury limits after implementing practical and reasonable measures to control sources of merc ury at the treatment facilities and within the collection systems. This led to the realiz ation that the relationship between mercury contributions to sewer systems and mercury c oncentrations in POTW effluents is not well understood. The degree to which in fluent, effluent and biosolids mercury concentrations can be reduced by controlling potentially significant so urces, such as dental clinics, is unknown. Therefore, NACWA has funded an attempt to better understand the impact of controlling mercury discharged from dental clinics on the ability of POTWs to meet stringent effluent limitations and biosolids requirements.

This study presents an opportunity to build a database depicting baseline mercury levels and trends that may occur as mercury control progr ams at POTWs progress. Due to their use of dental amalgam, both in the placement and re moval of dental fillings containing mercury amalgam, dental facilities are significant source s of mercury to wastewater treatment plants. Amalgam separators are treatment devices that can be installed in the plum bing of a dental clinic to remove some quantity of dental amalgam from the wastestream tributary to a POTW. Amalgam separators remove more amalgam from the wastestream than the typical chairside traps and vacuum filters found in a dental office.

This study was designed to examine the effect of practical and reasonable measures of controlling significant sources of mercury to the POTW collection system on the ability of POTWs to comply with anticipated effluent lim itations and address conc erns regarding mercury in plant influent and biosolids. In an attemp t to quantify the amount of dental amalgam removed from the wastestream by dental amalgam separators , the influent, effluent , and biosolids mercury concentrations, as well as other parameters, from POTWs in the United States and Canada already having implemented regulations requiring dental clinics to install amalgam removal equipment, were evaluated on a monthly basis from July of 2003 through July of 2006. POTWs that do not have these regulatory requirements were also evaluated.

### 10 Twelve POTWs were each sampled at least one time per month for the duration of the study. The sampled POTWs were in various stages of requiring dental facilitie s to install amalgam separators to capture particulate amalgam wast e. Table 1.1 shows the percentage of dental facilities/dentists with operating dental amalgam separators, i.e., amalgam separator units (ASU), for each POTW throughout the study. Samples from each POTW were analyzed for influent, effluent, and biosolids total mercury concentrat ions as well as influent and effluent total suspended solids concentrations. POTWs were also asked to monitor effluent turbidity and to collect a limited amount of effluent dissolved merc ury concentration data. As some facilities joined the project partway through the course of study, not every POTW was able to provide these additional data.

Table 1.1: Percentage of Dental Facilities/De ntists Operating Dental Amalgam Separators July 1, 2003 January 1, 2004 July 1, 2004 January 1, 2005 July 1, 2005 January 1, 2006 July 1, 2006 POTW "A" 0 0 0 98 100 100 100 POTW "B" 5678999 POTW "C" 6666666 POTW "D" 0.6 1.5 6.1 16 26 32 38 POTW "E" 0.6 1.5 6.1 16 26 32 38 POTW "F" 0 0 0 0 2 12 20 POTW "G" 44 86 95 98 100 100 100 POTW "H"* unknown 60 89 95 95 98 98 POTW "I" 93 93 93 93 93 93 93 POTW "J" 94 97 97 97 97 97 98 POTW "K" 94 97 97 97 97 97 98 POTW "L" unknown unknown unknown unknown unknown unknown 11 * The percentages for POTW "H" also include other approved control technologies.



### Recognizing that such data can also be impact ed by other source control efforts and operational activities at POTWs, NACWA co llected key information about the agencies and communities participating in the study. This information was u tilized in an effort to shed light on numerous issues related to controlling me rcury discharges to the environm ent. It is intended that the findings of this report can be us ed to assist agencies in making informed management decisions about controlling mercury discharges to POTWs and the environment.



## 2. M ETHODS



### One of the most critical aspects of this study was the collection of data. It was necessary for the data to be sensitive enough to determine with confidence whether effluent concentrations can be reduced to very low levels. The sampling and analytical methods historically used for the quantification of mercury were inadequate for the measurement of mercury concentrations at the low levels typically found in wastewater treatm ent plant effluents. Therefore, the USEPA developed a more sensitive analytical method, Method 1631, for analysis of mercury concentrations at low levels. When analyzing fo r mercury at such low concentrations, there is significant potential for contamination of the samples. USEPA also provides guidance in Method 1669, clean sampling techniques for collecti ng samples to be anal yzed with low-level methods. For the reliability of effluent data pr oduced by this study, it was necessary to use these clean sampling techniques and low-level analyt ical methods. In most cases, the laboratory typically utilized by the POTW wa s not capable of analyzing for mercury at this low level. Therefore, a NACWA member laboratory was enlisted to perform the low-level mercury

### 11 analysis for the study, when needed. The following parameters were analyzed for and reported from each POTW:

• Influent/Effluent Flow, million gallons per day (MGD);

• Influent Total Recoverable Mercury, nanograms per liter (ng/L);

• Influent Dissolved Mercury, ng/L;

• Effluent Total Recoverable Mercury, ng/L;

• Effluent Dissolved Mercury, ng/L;

• Biosolids Mercury, mg/kg (dry weight);

• Influent Total Suspended Solids (TSS), mg/L;

• Effluent Turbidity, NTU; and

• Effluent TSS, mg/L.

2.1 Sampling Methods

Sample points were chosen to be representative of the influent and/or e ffluent. Samples were collected by POTW personnel at eac h plant during conditions that were most representative of normal operating conditions. Each facility was to identify normal operating conditions based on a 95% confidence interval of the previous two years of effluent flow, total suspended solids, and turbidity. It was vital to the in tegrity of the study that samples co llected were representative of the process stream being sampled. Therefore, sampling was not to occur during the following conditions:

• Atypical plant flow;

• Unusual loss of solids in the effluent;

• Plant upset conditions;

• Receiving an unusual industrial discharge;

• Significant diversion of flow; or

• Atypical applications of chemical treatments.

Because of differences in operating procedures be tween treatment facilities, single grab, multiple grab, or composite samples could be collected throughout the study. Once the decision was made on sampling protocol, the fac ility’s continuing to use the same protocol for the duration of the study was preferred. Composite samples for total recoverable and dissolved mercury were collected from the influent at POTWs A, D, E, F, G, and H; the remaining facilities collected influent grab samples. Composite samples fo r total recoverable and dissolved mercury were collected from the effluent at POTWs A, G, H, and L; the remaining facilities collected effluent grab samples. Samples were collected utiliz ing U.S. EPA Method 1669 a nd other clean sampling protocols to minimize potential contamina tion introduced during sampling and, where the NACWA member laboratory providing analytical services was utilized, the samples were shipped on ice overnight. A study plan and scop e of work, which includes sampling protocols, was developed by this laboratory to be used by participating POTWs, as needed. This study plan is included as Appendix D.

To reduce the potential for contamination, samp ling protocols and equipment were specifically designed for each individual sample location. To reduce variability, the NACWA member

### 12 laboratory providing analyt ical services offered to provide necessary sampling equipment to the POTWs requiring outside laboratory services. In order to reduce contamination associated with grab sample collection, handling, and analysis, the “clean hands / dirty hands” technique was used. The individual designated as “dirty” hands provided support, and only the person designated “clean hands” could touch the sample bottles and anything that may have come into contact with the bottle.

2.2 Analytical Methods

Influent and effluent samples were analyzed for total recove rable mercury, dissolved mercury, and total suspended solids by either the NAC WA member laboratory providing analytical services or the laboratory typically used by the PO TW. All effluent mercury analysis, both total and dissolved, was done according to U.S. EP A Method 1631, Revision E. This method was necessary to detect the extremely low concentrations of mercury often present in treated effluent. Method 1631, Revision E is for the determination of mercury in filtere d and unfiltered water by oxidation, purge and trap, desorption, and cold-v apor atomic fluorescence spectrometry. For dissolved mercury analysis, the method specifies th at samples are to be filtered through a 0.45μm capsule filter. Mercury analysis on influent samples was performed using the least sensitive method that resulted in a quantifiable result. Ta ble 2.2A indicates the analytical methods and the detection limits most commonly used for the aqueous and solid samples.

Table 2.2A: Analytical Methods



### P ARAMETER 

### R EFERENCE 

### M ETHOD 

### M ETHOD 

### D ETECTION 

### L IMIT 

### Hg (total recoverable and dissolved) EPA Method 1631, Rev. E 0.3 ng/L

Hg (total recoverable and dissolved) EPA Method 245.7 0.7 ng/L

Total Recoverable Hg EPA Method 245.2 30 ng/L

Total Recoverable Hg EPA Method 245.5 or SW846 7441A 0.06 mg/L (TS values used for conversion to mg/Kg) TSS SM 2540D 1 mg/L

Throughout the analytical process, clean protocols were adhered to at all times for the effluent mercury samples. All sample preservation, prepar ation, and analyses were performed in special clean areas. Appropriate measures were taken to limit potential contamination of samples and labware. All of the data from each POTW in the study are located in Appendix A.

A total of 2,283 mercury analysis results were submitted for the study: 716 for influent total mercury; 120 for influent dissolved mercury; 458 for effluent total mercury; 151 for effluent dissolved mercury; and 838 for biosolids merc ury. In each case, the entities assuming responsibility for sample colle ction and analysis were relie d upon to comply with quality assurance/quality control (QA/QC) protocols specified in the study pl an that was prepared at the study's outset by the NACWA member laboratory that provided an alytical services (Appendix D) and/or specified in the re spective method documents for the particular analytical methods utilized and listed in Appendix A. Data report ed as not compliant with the applicable QA/QC

### 13 protocols were excluded with the sole exceptions of two (of the 458) effluent total mercury data points which were reported as lacking associ ated field blank data but which exhibited concentrations fully consistent w ith the relevant comparable data.

2.3 Statistical Methods

To determine the strength of associations betw een pairs of variables measured at individual POTWs during the study, the non-parametric, Mann- Kendall test for trend was selected. Many of the distributions from the NACWA Mercury Sampling Project were skewed to the right ( i.e ., at higher mercury concentrations, there were fe wer occurrences and outliers were very common. This indicates these variables were not de rived from normal distri butions. In addition, examination of plots of pairs of variables indica ted that the relationships between many of them were not linear. Therefore the assumptions of parametric statis tical tests (such as Pearson’s r) were often not met. This led to a choice between methods: the variables c ould be transformed to meet the assumption of the parametric tests or nonparametric tests, such as the Mann-Kendall test, could be used instead. The Ma nn-Kendall test, which uses Kendall’s τ (tau) as the test statistic, is a rank-based procedure that is resistant to the effect of outliers in the dataset. This test measures the strength of the monotonic relati onship between two vari ables; therefore the relationship could be curved or linear and still be detected by this test. The use of the MannKendall test is well-suited to data from skewed distributions, such as th e lognormal distributions often used to model water-quality variables. It was decided that use of nonparametric tests would be preferable to the extensive checking of assumptions and transformation of variables that would be required by use of the parametric techniques. A summary of the results of the Mann-Kendall tests for the combined data is lo cated in Appendix B; more detailed, computergenerated results for all statistical analyses ar e located in Appendix C. Appendix C is provided for readers who are familiar with the softwa re employed and are interested in further examination of the data.

For the present analyses, α was set at 0.05. That is, the nul l hypothesis of no correlation ( τ = 0) was rejected when the test resulted in a p-value that was ≤ 0.05. In such cases, the alternate hypothesis that the two va riables are correlated ( τ ≠ 0) was accepted. Using a value of 0.05 means that there is a 5% probabi lity that the null hypothesis will be rejected when it is actually true. There were a few instances in which relationships were not si gnificant at the 0.05 level, but were so at the 0.10 level. Even though there is a slightly gr eater probability that the null hypothesis will be falsely rejected at this level, these instances are included because it is thought that they still identify meaningful relationships.

Much of the data collected duri ng the study are presented as box-a nd-whisker plots. These plots show the range of the data as well as the 25 th 

### , 50 th 

### , and 75 th 

### percentiles. While the data for the individual POTWs are plotted in six-month incr ements, the Mann-Kendall tests were performed utilizing every sample result. For the collectiv e data, the Mann-Kendall tests were performed on the six-month median results to address sample variability, to correspond with the twice-yearly determinations of the number of dentists with separators in stalled, and to provide a more manageable quantity of data.

### 14 

## 3. I NDIVIDUAL 

## POTW R ESULTS AND 

## D ISCUSSION



### Results from the study were analyzed in terms of both individual POTWs and as overall results combining all of the data from each POTW. For the individual POTW results, mercury concentrations at the treatment plant were ex amined and then relate d to individual plant characteristics and activities. The Mann-Kendall test was used to determine the statistical significance of trends; those related to effluent mercur y, biosolids mercury, and TSS concentrations are presented. Influent and effl uent mercury loading results are also presented, although the statistical significance of trends related to these two parameters was not determined. For the combined results, potential factors influe ncing mercury concentrations were examined to determine any overall relationshi ps common to all or a portion of the treatment plants.

3.1 POTW “A”

P LANT 

### P ROCESSES 

### POTW “A” treats an average of 42.5 million gallons of wastewater per day (MGD). However, the capacity of the plant is such that 200 milli on gallons could receive preliminary and primary treatment and 65 million gallons c ould receive secondary treatment, if necessary. Treatment at POTW “A” consists of sc reenings removal, grit removal, pr imary treatment, aeration, secondary clarification, disinfection, and dechlorination. Hauled-in wastes are not accepted for treatment, at POTW “A”. Bar racks are employed for scre enings removal and grit is removed via aerated grit chambers. The grit slurry is then separated using a screw degritter and disposed of in a landfill along with the debris re moved by the bar racks. Approximately 1,000 wet tons of grit is removed annually. The primary and secondary tr eatments at POTW “A” include complete mix, fine-bubble diffused aeration a nd secondary clarification. The primary sludge and waste activated sludge are settled in grav ity thickeners and then blended w ith fats, oil, and grease. This mixture is then dewatered by filter presses. The dewatered sludge and fats, oil, and grease mixture was either incinerated in a multiple hearth incinerator or stabiliz ed with hydrated lime and disposed of in a landfill. The scrubber wate r effluent from the multiple hearth incinerator was discharged into the grit tank effluent. This biosolids incineration process ended on November 30, 2005. Thickened sludge blended with fats, oils, and grease is now collected and handled on site by a contractor for offsite disposal or composting. POTW “A” produces approximately 9000 dry tons of biosolids each year. Final effluent treatment includes disinfection with hypochlorite and dechlorina tion using sodium bisulfite. The following treatment chemicals are u tilized at POTW “A”:

• Sodium hypochlorite is used for disinfection of the final effluent, disinfection of the wet weather treatment tank influent, odor control in the gravity thickeners, odor control in the press room, a nd for the control of filament ous bacteria in the return activated sludge;

• Sodium bisulfite is used for dech lorination of the final effluent;

• Liquid cationic polymer is used to prom ote flocculation of the thickened sludge;

• Hydrated lime is added to dewate red sludge intended for the landfill;

• Caustic soda is used in unclogging grease lines.

### 15 S AMPLE 

### C OLLECTION 

### Composite influent samples were collected downstream of the bar racks, just prior to the grit removal chambers. Teflon suction tubing was used in a peristaltic pump along with clean methods. The effluent samples were flow-paced composite samples of dechlorinated final effluent. (Flow-paced composite samples are thos e in which the interval between samples is a specified volume of effluent that has passed a m easuring point in the flow stream.) Biosolids were sampled by conducting manual grab samples th at were composited to obtain a sample that represented a 24-hour period.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “A” is a marine discharger that treats por tions of ten communities. The service area for POTW “A” covers approximately 50 square m iles and has approximately 360,000 residents. Fifty percent of the collection system is combin ed sewer area and the remaining is separate sewer area. The combined sewer area contai ns sixty-seven combined sewer overflows. Approximately ninety-one percent of the influent flow at POTW “A” is from residential sources and approximately six percent is due to commerci al uses. The remaining three percent of the influent flow is from industrial us ers. While none have been iden tified as signifi cant sources of mercury, the types of industrial di scharges are listed in Table 3.1A.

Table 3.1A: Types of Significant Industrial Users (SIUs) in POTW “A” Service Area



### T YPE OF 

### SIU N UMBER 

### A PPROXIMATE 

### T OTAL 

### D AILY 

### F LOW 

### , GALLONS

PER DAY 

### (GPD) Electroplaters / Metal Finishers 61 1,069,305 Metal Molding & Casting 2 13,883 Metal Formers 1 2,000 Chemical Manufacturers 5 18,197 Printers 1 1,000 Specialty Paper Coaters 1 19,800 Electric Companies 1 93,000 Central Treatment Facilities 1 18,210

During the study period, POTW “A” was conducting an interceptor sewer cl eaning program that consisted of using a water jet to force grit contai ned in the larger sewer pipes of the collection system to manholes where it could be removed. This operation had the potential to suspend mercury that had accumulated in the sewers ove r many years and flush this mercury to the headworks of the POTW. This work was conduc ted at various points th roughout the collection system. The amount of suspended mercury that reached the headworks of the POTW was a function of the distance from the cleaning ope ration to the POTW and the specific flow conditions in that interceptor. The cleaning activities, which at ti mes also included releasing grit removed from the sewer lines directly into the headworks of the plant, may have occurred on days while sampling for this study was being conducted.

In July 2003, POTW “A” began construction of a large underground storage tunnel to eliminate or reduce combined sewer overflows. This c onstruction project genera ted a large amount of

### 16 mining/groundwater that was discharged to the h eadworks of the POTW. Flow rates from this project changed dramatically over the course of the project. Prior to May 2004, the flow rate was less than 0.5 MGD. Between May 2004 and December 2005, the flow rate increased to a steady maximum of just over 3.5 MGD. After December 2005, the flow rate from the tunnel project decreased to 2.25 MGD. The characteris tics of the wastewater from this project also changed. When mining was occurring, the wastew ater contained a significant amount of mineral grit. The mining ceased on December 1, 2005, and af ter this date the amount of TSS in the wastewater from the tunnel decreased.

M ERCURY 

### C ONTROL 

### P ROGRAM 

### In late 2003, POTW “A” began implementation of a best management practice program for dental facilities. The program inco rporates two options for the dental facilities. A dental facility may opt to install and maintain an ISO Certified Amalgam Separator and follow best management practices or the facility may constr uct a sampling location that collects all amalgam waste, routinely sample this wastestream and maintain full compliance with a mercury limit of 0.005 parts per million. There are 100 dental facilities/dentists locate d in the service area. At the beginning of the sampling project, none of th e facilities/dentists had installed amalgam separators. However by the culmination of the projec t, all of facilities/dentists had installed them accordingly. The amalgam separator status at this POTW is shown in Table 3.1B.

Table 3.1B: Amalgam Separa tor Status at POTW “A”



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### /D ENTISTS 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 0 January 1, 2004 0 July 1, 2004 0 January 1, 2005 98 July 1, 2005 100 January 1, 2006 100 July 1, 2006 100

R ESULTS 

### As Figures 3.1A and 3.1B indicate, effluent mercury concentrati ons decreased significantly (p <0.05) from July 2003 to July 2006. At the start of the study, the 6-month median effluent total mercury concentration was 10.7 ng/L and, by the cu lmination of the study, the 6-month median effluent total mercury concentration was 5.7 ng/L. This statistically significant decrease in effluent mercury concentration may be rela ted to amalgam separa tor installation. The concentration of mercury in the biosolids, as shown in Figure 3.1A, appears to have remained constant throughout the course of the study, possibly indicating that the effects of amalgam separator installation are being masked by the effects of the interceptor cleaning activities and the tunneling project. Figure 3.1B indicates that, while the e ffluent mercury concentrations were decreasing, the effluent TSS was increasing as a result of the tunne ling project and/or the interceptor cleaning activities. At the beginning of the study, th e 6-month median effluent TSS concentration was 9 mg/L and, by the culmination of the project, the 6-month median effluent TSS concentration was 14 mg/L. The increase in effluent TSS concentration was not found to be

### 17 statistically significant at the α = 0.05 level, but it was so at th e 0.10 level. The influent mercury loading was variable and the effl uent loading remained relativel y constant throughout the course of the study, as depicted in Figure 3.1C. The high variability in influent mercury loading is believed to be partly the result of drain line cleaning and drain trap replacements occurring at dental facilities as a required part of the installation of amalgam separators. It may further be due to the tunneling project and the ongoing interceptor sewer cleaning activities.

POTW “A” also collected additiona l influent and effluent samples during the course of the threeyear NACWA Mercury Sampling Pr oject. The results from these samples may demonstrate a decline in both the influent and effluent me rcury loading over the course of the study. The amount of data collected by PO TW “A” is substantial and w ould lend further support to the conclusion that the effluent mercury concentrat ions are decreasing at POTW “A.” However, these additional samples were not collected or analyzed using the same methods as in the NACWA Mercury Sampling Project and therefore are not presented here.

0 4 8 12 16 20

0% ASUs Installed0% ASUs Installed 98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 3 6 9 12Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.1A: Effluent and Biosolids Mercury Concentrations at POTW “A”

### 18 0 5 10 15 20

0% ASUs Installed0% ASUs Installed 98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 20 40 60Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.1B: Effluent Mercury and TSS Concentrations at POTW “A”

0 15 30 45 60 75 90

0% ASUs Installed0% ASUs Installed 98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 5 10 15Effluent Mercury Load, grams/day Effluent Hg Influent Hg

Figure 3.1C: Influent and Efflue nt Mercury Load at POTW “A”

### 19 3.2 POTW “B”

P LANT 

### P ROCESSES 

### The wastewater treatment at POTW “B” consists of preliminary, primary, and secondary treatment, including disinfection and phosphorus rem oval. The preliminary treatment consists of mechanical bar screens followed by grit remova l in non-aerated detritus tanks. The grit is landfilled in an approved landfill. The primary tr eatment is made up of settling tanks where the surface scum is skimmed and the biosolids are settled out and pumped from the bottom. Ferric chloride or “pickle liquor” is added during primary treatment to aid in the removal of phosphorus. (POTW “B” began usin g ferric chloride exclusively in July 2005). The skimmings are incinerated in an on-site grease reactor. The scrubber water from the grease reactor is reintroduced into the treatment process immediately before the primary settling tanks. No biosolids processing occurs at POTW “B”; all bi osolids are pumped via a force main to another facility for processing. Aeration basins and se ttling tanks make up the secondary treatment of the activated sludge process. POTW “B” produced 25,967 dry tons of biosolids in 2002. The final step in the treatment process at POTW “B” is chlorination by m eans of liquid sodium hypochlorite and dechlorination of the effluent w ith sodium bisulfite. The following treatment chemicals are utili zed at POTW “B”:

• Sodium hydroxide is us ed for pH control;

• Sodium hypochlorite is used in the disinfection of the final effluent;

• Sodium bisulfite is used for removal of chlorine residual;

• Ferric chloride (or “pickle liquor” from lo cal industry) is used in the reduction of phosphorus.

S AMPLE 

### C OLLECTION 

### Influent grab samples were obtained after the screening and degritting process. The sample location was prior to the recycle stream retur n, and the samples were collected using clean procedures. The effluent sample was a mont hly grab sample that was collected after dechlorination, also using clean procedures. The sludge samples were collect ed prior to transfer of the sludge to another fac ility for further processing.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “B” is owned and operate d by a regional utility that owns and operates two other POTWs. The average flow at POTW “B” is approximately 100 MGD; however, the plant has a design flow of 155 MGD and the capability to provide secondary treatment of up to 330 MGD during wet weather. POTW “B” serves a popu lation of over 334,000 people. This POTW does not accept hauled-in wastes for treatment. The se rvice area for POTW “B” is approximately 76 square miles. In the entire service area operate d by the regional utility, there are 75 square miles of combined sewer service area and 280 square miles of separate sewe r service area. Forty percent of the service area at POTW “B” is comb ined and sixty percent is separate. The major classifications of industrial users fo r the entire regional facility are pr ovided in Table 3.2A.

### 20 Table 3.2A: TYPES OF SIUs IN POTW “Regional Utility” SERVICE AREA



### T YPE OF 

### SIU N UMBER 

### A PPROXIMATE 

### T OTAL 

### D AILY 

### F LOW 

### , MGD Industry Subject to Categorical Pretreatment Standards 137 5.63 MGD Industrial Users Discharging>25,000 gpd of Process Wastewater 26 3.24 MGD >5% of the organic load 0 0 >5% of the hydraulic load 0 0 Others Designated by Control Authority 20 0.15 MGD

M ERCURY 

### C ONTROL 

### P ROGRAM 

### In 2002, a narrative local limit for mercury was deve loped and incorporated into the local sewer use code. This local limit requires industrial so urces of mercury to implement best management practices (BMPs) to minimize discharges of merc ury to the system. All significant industrial users were required to conduct mercury analysis to identify significant sources of mercury. Certain industrial users that we re identified as significant sources of mercury, which include dental facilities, must submit and implement BM P plans for mercury discharge minimization.

Implementation of the mercury BMP Program for de ntal facilities began in April of 2002. This program required all facilities th at provide dental care to design, submit, and implement BMP plans by December 31, 2002. Certain BMPs were mandated while others were recommended. The mandatory BMPs did not include installation of amalgam separators in dental clinics; however, some dental clinics have voluntarily installed amalgam separators. The regional utility’s service area ha s 546 known dental facilities; 219 of them are in the POTW “B” service area. The amalgam separator status at this POTW is shown in Table 3.2B.

Table 3.2B: Amalgam Separator Status at POTW "B"



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 5 January 1, 2004 6 July 1, 2004 7 January 1, 2005 8 July 1, 2005 9 January 1, 2006 9 July 1, 2006 9

R ESULTS 

### As indicated by Figures 3.2A and 3.2B, POTW “B ” exhibited a slight decrease in median effluent total mercury concentrations. At the star t of the study, the 6-month median effluent total mercury concentration was 3.21 ng/L but, by the cu lmination of the study, the 6-month median effluent total mercury concentration had decr eased to 2.64 ng/L. The decrease in effluent mercury concentration, though, was not found to be st atistically significant (p >0.10). However,

### 21 the biosolids mercury concentratio ns exhibited a statistically si gnificant increase (p <0.05) from July 2003 to July 2006. A study was conducted by th e regional entity du ring the late summer and fall of 2005 to determine the cause of these el evated biosolids mercury concentrations. It was concluded that the elevated biosolids concen trations were the result of cleaning operations that took place from June 2003 through November 2005 in two large interceptor sewers. The removal of grit and debris fr om the interceptors during cl eaning may have caused settled mercury and other heavy substances within the interceptors to be re-suspended and transported to POTW “B.” Throughout the course of the study, the effluent T SS concentrations and effluent mercury loading remained relatively constant (Figure 3.2B and 3.2C). As shown in Figure 3.2C, the influent mercury loadi ng was highly variable.

0 1 2 3 4

6% ASUs Installed 7% ASUs Installed 8% ASUs Installed 9% ASUs Installed 9% ASUs Installed 9% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Hg Concentration, ng/L

0 2 4 6Biosolids Hg Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.2A: Effluent and Biosolids Mercury Concentrations at POTW “B”

### 22 0 1 2 3 4 5

6% ASUs Installed7% ASUs Installed8% ASUs Installed9% ASUs Installed9% ASUs Installed9% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concetration, ng/L

0 5 10 15 20Effluent TSS Concentration, mg/L Effluent Hg

Effluent TSS

Figure 3.2B: Effluent Mercury and TSS Concentrations at POTW “B”

0 25 50 75 100

6% ASUs Installed 7% ASUs Installed 8% ASUs Installed 9% ASUs Installed 9% ASUs Installed 9% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 2 4 6 8 10 12 14 16Effluent Mercury Load, grams/day Effluent Hg Influent Hg

Figure 3.2C: Influent and Efflue nt Mercury Load at POTW “B”

### 23 3.3 POTW “C”

P LANT 

### P ROCESSES 

### POTW “C” uses a trickling filter/solids-contact biological process. The preliminary treatment consists of climber bar screens and aerated grit tanks. The grit is landfilled at an approved landfill. The primary treatment occurs in prim ary settling tanks. The skimmings generated are incinerated off-site. Secondary treatment consis ts of trickling filters, solids contact tanks, aeration, and final settling tanks. Biosolids ar e treated via gravity th ickening and centrifugal dewatering with cationic polymer addition prior to onsite incineration. Th e resulting dry ash is transported to an approved landfil l. The scrubber water from the in cinerator is reintroduced into the plant’s influent prior to the grit channels. This is followed by disinfection using sodium hypochlorite and dechlorination using sodium bisulf ite. Hauled-in wastes are not accepted for treatment. The following treatment ch emicals are utilized at POTW “C”:

• Sodium hypochlorite is used in the disinfection of the final effluent;

• Sodium bisulfite is used fo r residual chlorine removal;

• Ferric chloride is used for phosphorus removal;

• Sodium hydroxide is us ed for pH control;

• Cationic polymer is used in dewatering.

S AMPLE 

### C OLLECTION 

### Influent grab samples were initia lly obtained from an influent di version chamber before the flow actually reached the plant, and th erefore, prior to grit removal. In early 2004, the influent sampling location was relocated to a location within the plant; however the sampling location remained prior to grit removal. This sampling location was also pr ior to recycle stream return. The influent samples were collected using clean procedures. The effluent grab samples were collected after chlorination, but pr ior to dechlorination, adhering to clean procedures. The sludge samples were collected from the sludge handli ng facility after the addition of polymer.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “C” is owned and operated by a regional utility that al so owns and operates two other POTWs. POTW “C” has a design flow of 70 MGD and treats an average 26.3 MGD that includes wastewater from over 103,000 residents. The service area for POTW “C” is approximately 10 square miles. In the entire service area opera ted by the regional utility, there are 75 square miles of combined sewer service area and 280 square miles of separate sewer service area. Eighty-five per cent of the service area at POTW “C” is combined and fifteen percent is separate. The major classifications of industrial users in th e entire regional service area are identified in Table 3.3A.

### 24 Table 3.3A: Types of SIUs in PO TW “Regional Utility” Service area



### T YPE OF 

### SIU N UMBER 

### A PPROXIMATE 

### T OTAL 

### D AILY 

### F LOW 

### , MGD Industry Subject to Categorical Pretreatment Standards 137 5.63 MGD Industrial Users Discharging>25,000 gpd of Process Wastewater 26 3.24 MGD >5% of the organic load 0 0 >5% of the hydraulic load 0 0 Others Designated by Control Authority 20 0.15 MGD

M ERCURY 

### C ONTROL 

### P ROGRAM 

### In 2002, a narrative local limit was de veloped and incorporated into the local sewer use code. This local limit requires industria l sources of mercury to implement best management practices (BMPs) to minimize discharges of mercury to th e system. All significant industrial users were required to conduct mercury analysis to iden tify significant sources of mercury. Certain industrial users that were identified as signifi cant sources of mercur y, which include dental facilities, must submit and implement BMP plans for mercury di scharge minimization.

Implementation of the mercury BMP Program bega n in April of 2002. This program required all facilities that provide dental care to design, submit, and impl ement BMP plans by December 31, 2002. Certain BMPs were mandated while others were recommended. These mandatory BMPs did not include installation of amalgam separators in dental clinics; howev er some dental clinics have voluntarily installed amalgam separators. The regional utility’s service area has 546 known dental facilities; 18 of them are in the POTW “C ” service area. Table 3.3B indicates the percent of the dental facilitie s that have installe d amalgam separators.

Table 3.3B: Amalgam Separa tor Status at POTW “C”



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 6 January 1, 2004 6 July 1, 2004 6 January 1, 2005 6 July 1, 2005 6 January 1, 2006 6 July 1, 2006 6

R ESULTS 

### Throughout the course of the study, there was no statistically signi ficant trend (p >0.10) found in the effluent mercury concentrations at POTW “C” (as shown in Figure 3.3A). The same was found for the biosolids mercury and effluent T SS concentrations (Figures 3.3A and 3.3B).

### 25 0 1 2 3 4

6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 2 4 6 8Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.3A: Effluent and Biosolids Mercury Concentrations at POTW “C”

0 1 2 3 4

6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed6% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 4 8 12 16Effluent TSS Concentration, mg/L Effluent Hg

Effluent TSS

Figure 3.3B: Effluent Mercury and TSS Concentrations at POTW “C”

### 26 0 4 8 12

6% ASUs Installed 6% ASUs Installed 6% ASUs Installed 6 % ASUs Installed 6% ASUs Installed 6% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0.0 0.5 1.0 1.5Effluent Mercury Load, grams/day Effluent Hg Influent Hg

Figure 3.3C: Influent and Efflue nt Mercury Load at POTW “C”



### 3.4 POTWs “D” and E”

P LANT 

### P ROCESSES 

### POTWs “D” and “E” are operated by a regional agency. POTW “D” has a design flow of 300 MGD and an actual average flow of 90 MGD. POTW “E” has design and actual average flows of 390 and 83 MGD, respectively. These two POTWs are connected to each other in two ways. At several locations in the collection system, flows may be diverted to eith er plant. The plants are also directly connected by pipeline. This a llows transfer of sewage, biosolids, or both. Hauled-in waste that includes leachate from a landfill and airplane de-icing fluid are accepted for treatment at POTW “D,” how ever no hauled-in wastes are accepted at POTW “E.”

The two plants provide traditional secondary trea tment. Wastewater is subjected to coarse screening, grit removal, primary settling, aera tion, secondary settling, and hypochlorite and bisulfite addition prior to being discharged to a freshwater envi ronment. Iron salts are also added to aid in treatment at both fac ilities. For POTW “D,” this oc curs following grit removal, while for POTW “E,” it takes place after primary settling.

Biosolids processing at POTW “D” consists of anaerobic digestion, gravit y belt thickening, and occasional plate-and-frame dewatering. Processi ng of biosolids at POTW “E” involves gravity belt thickening followed by heat drying. In a ddition, a biosolids pipeline connects the two treatment plants. It may operate in either di rection to maximize production of the preferred

### 27 product. In most cases, biosolids flow from POTW “D” to “E.” The following chemicals are used at the two treatment plants:

• Sodium hypochlorite is used for chlorination;

• Sodium bisulfite is used for dechlorination; and

• Ferric chloride is used for phosphorus removal.

S AMPLE 

### C OLLECTION 

### Flow-proportionate composite infl uent samples were collected prior to the coarse screens and grit removal. The effluent samples were collect ed as grab samples taken after chlorination and dechlorination. Biosolid samples collected for analysis were weekly composites of the final product.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### The collection system for POTWs “D” and “E” encompasses 420 square miles and serves a population of 1.2 million people in twenty-eight communities. The sy stem for POTW “D” consists of only separated sewers, while that for POTW “E” is mostly combined sewers.

M ERCURY 

### C ONTROL 

### P ROGRAM 

### An amalgam program has been established by the agency that operates POTWs “D” and “E” as part of a mercury minimization program. A rule was adopted in 2004 that requires best management practices (BMPs) and amalgam sepa rators in dental facilities. BMPs were mandatory as of the date of a doption of the rule. A certificati on from all dental offices with amalgam was due in 2005. All facilities with amalgam must install amalgam separators by February 1, 2008. As shown in Table 3.4A, by th e conclusion of the study in July 2006, approximately 38% of dental facilities in the total service area of PO TWs “D” and “E” had done so. The number of dental facili ties that have installed amalga m separators in the individual service areas is not known.

Table 3.4A: Amalgam Separator Status at POTWs “D” and “E”



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 0.6 January 1, 2004 1.5 July 1, 2004 6 January 1, 2005 16 July 1, 2005 26 January 1, 2006 32 July 1, 2006 38

R ESULTS 

### At POTW “D,” there was an apparent decrease, not found to be statistical ly significant (p >0.10), in effluent mercury concentration over the course of the study. Th is is depicted in Figure 3.4A. However, the effluent mercury loading remain ed about the same throughout the study (Figure 3.4C). The biosolids mercury and effluent TSS concentrations also exhibited no changes during the study (Figures 3.4A and 3.4B).

### 28 Similar to POTW “D,” the effluent mercury concentrations for POTW “E” also showed an apparent, but not statistically signi ficant (p >0.10), decrease over the course of the study (Figure 3.4D). The 6-month median effluent concentr ation at the start of the study was 2.6 ng/L, compared to 1.8 ng/L at the end of the study. Th e biosolids mercury concentration and effluent loading showed no apparent trends at POTW “E ” (Figures 3.4D and 3.4F). Contrary to POTW “D,” though, the TSS appeared to increase throughout the study as s een in Figure 3.4E. It should be noted, however, that this appa rent trend was not found to be stat istically significant (p >0.10).

0 1 2 3 4

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 2 4 6 8Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.4A: Effluent and Biosolids Mercury Concentrations at POTW “D”

### 29 0 1 2 3 4

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 5 10 15 20 25Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.4B: Effluent Mercury and TSS Concentrations at POTW “D”

0 25 50 75 100

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 2 4 6Effluent Mercury Load, grams/day Effluent Hg Influent Hg

Figure 3.4C: Influent and Efflue nt Mercury Load at POTW “D”

### 30 0 1 2 3 4

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 0.5 1 1.5 2Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.4D: Effluent and Biosolids Mercury Concentrations at POTW “E”

0 1 2 3 4

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 5 10 15 20 25Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.4E: Effluent Mercury and TSS Concentrations at POTW “E”

### 31 0 25 50

1.5% ASUs Installed 6.1% ASUs Installed 16% ASUs Installed 26% ASUs Installed 32% ASUs Installed 38% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 1 2 3 4 5 6 7 8Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.4F: Influent and Efflue nt Mercury Load at POTW “E”



### 3.5 POTW “F”

P LANT 

### P ROCESSES 

### Treatment at POTW “F” consists of solids re moval, settling, aeration, clarification, sludge processing, and ultraviolet disinfect ion. Grit chambers are used to remove heavy solids. The grit is disposed of in a sanitary landfill. Primary and secondary treatment processes consist of primary settling, aeration, secondary nitrificat ion, biological phosphorus removal, and final clarification. The effluent from the secondary treatment process is disinfected in ultraviolet light chambers. The primary sludge is treated in grav ity sludge thickeners, an d waste activated sludge is treated in dissolved air flota tion thickeners. After thickenin g, the biosolids are digested in anaerobic digesters and thickened on a gravity belt thickener and then stored prior to hauling to local farm land for application as fertilizer. Th e following chemicals are used to aid in treatment processes at POTW “F”:

• Ferric chloride for bi osolids processing;

• Polymer for biosolids gr avity belt thickening;

• Sodium hypochlorite to disinfect effluent for internal reuse.

S AMPLE 

### C OLLECTION 

### Composite influent samples were collected prior to grit removal, using four automatic samplers that contribute to a single daily composite samp le, and analyzed for mercury one day per month. Effluent samples were collected as grab samples one day per month, adhering to clean sampling protocols. Grab samples of gravity belt thic kened sludge were collected approximately four

### 32 times per week. A monthly composite was prepar ed from these grab samples and analyzed for mercury.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “F” is a freshwater discharger that se rves a population of more than 320,000. The service area occupies 176 square miles. This POTW treats approximately 40 million gallons of wastewater each day. The collection system is se parate from the stormwater system. Over 130 pumping stations are required to pump wastewater to the POTW. Th e percentage of each type of flow entering the plant is shown in Table 3.5A.

Table 3.5A: Percentage of Flow at POTW “F”



### F LOW 

### (MGD) P ERCENTAGE OF 

### T OTAL 

### Residential 23.1 58.9 Commercial 11.3 28.7 Industrial 3.0 7.5 Infiltration 1.9 4.8

M ERCURY 

### C ONTROL 

### P ROGRAM 

### Since 1997, POTW “F” has been voluntarily worki ng to minimize mercury use in the community through outreach and education, focusing on dental facilities, hospitals, schools, and industry. Dental facilities within the se rvice area have been encouraged to voluntarily install amalgam separators. The amalgam separator status at this POTW is shown in Table 3.5B.

Table 3.5B: Amalgam Separator Status at POTW "F"



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 0 January 1, 2004 0

July 1, 2004 0 January 1, 2005 0

July 1, 2005 2 January 1, 2006 12

July 1, 2006 20

R ESULTS 

### POTW “F” joined the sampling proj ect after the project had alrea dy started, and therefore results are not available for the first si x-month period. The results from POTW “F” indicate relatively constant mercury concentrations in the effluent, but a statistica lly significant decrease (p <0.05) in biosolids mercury concentrations as depicted in Figure 3.5A. The effluent TSS concentrations remained about the same throughout the study and can be seen in Figure 3.5B. The influent and effluent loadings are shown in Figure 3.5C. Amalga m separators may be a factor in the decrease seen in the biosolids mercury c oncentrations; at the start of the study ther e were no separators installed within POTW “F’s” se rvice area, but by the conclusion of the study, 20% of dental facilities had installed amalgam separators.

### 33 0 1 2 3 4

0% ASUs Installed 0% ASUs Installed 0% ASUs Installed 2% ASUs Installed 12% ASUs Installed 20% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Hg Concentration, ng/L

0 2 4 6Biosolids Hg Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.5A: Effluent and Biosolids Mercury Concentrations at POTW “F”

0 1 2 3 4

0% ASUs Installed 0% ASUs Installed 0% ASUs Installed 2% ASUs Installed 12% ASUs Installed20% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 5 10 15 20Effluent TSS Concentration, mg/L Effluent Hg

Effluent TSS

Figure 3.5B: Effluent Mercury and TSS Concentrations at POTW “F”

### 34 0 10 20 30 40 50

0% ASUs Installed 0% ASUs Installed 0% ASUs Installed 2% ASUs Installed 12% ASUs Installed20% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 0.5 1 1.5 2Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.5C: Influent and Efflue nt Mercury Load at POTW “F”



### 3.6 POTW “G”

P LANT 

### P ROCESSES 

### POTW “G” has a design flow of 48.4 MGD, with an actual average flow of 38.2 MGD. Treatment consists of preliminary, secondary, an d tertiary processes. Hauled-in wastes are accepted at the plant. Preliminary treatment at POTW “G” includes bar screens followed by two detritor-type grit tanks. Due to the significan t industrial flow, primary treatment is not necessary. Secondary treatment includes bi ological treatment us ing high-purity oxygenactivated sludge aeration tanks and secondary clar ifiers. This is followed by flocculation tanks and dual media filters. Secondary sludge is th ickened using dissolved ai r flotation thickeners followed by thermophilic and mesophilic anaerobic di gesters. Digested sludge tanks hold the digested sludge until it is dewatered for land application by one of two centrifuges. The following treatment chemicals are utilized at POTW “G”:

• Polymer is used in sludge treatment;

• Ferric Chloride is used for nutrient removal;

• Anti-foam solution is used when needed.

S AMPLE 

### C OLLECTION 

### Influent samples were collected prior to scre ening and grit removal and composited every 15 minutes over 24 hours using an automatic sampler. Effluent grab samples were collected twice

### 35 per month at a sampling location following all plan t processes. Biosolids samples were collected after the digested sludge was dewatered by compositing three grab samples in a 24-hour period.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### The population served by POTW “G” is 110,000. The service area for POTW “G” is approximately 80 square miles and is served by a completely separate collection system. Approximately 7 percent of the in fluent flow can be attributed to infiltration and inflow and 52 percent of the influent at POTW “G” is attributed to industrial fl ow. The major classifications of industrial users in the POTW “G” serv ice area are provided in Table 3.6A.

Table 3.6A: Types of SIUs in POTW "G" Service Area



### T YPE OF 

### SIU N UMBER 

### A PPROXIMATE 

### T OTAL 

### D AILY 

### F LOW 

### , GPD Pulp & Paper 2 18,820,000 Metal Finishing 3 4100 Organic Chemical 1 3900 Other 11 1,010,000

M ERCURY 

### C ONTROL 

### P ROGRAM 

### POTW “G” has worked with loca l and state dental associatio ns and the American Dental Association (ADA) to develop best management practices for waste management for the 100 dentists in the service area, which included the voluntary installation of amalgam separators. A majority of the amalgam separator installations were funded either dir ectly by POTW “G” or by a grant received by POTW “G” a nd the local dental society prior to the start of the NACWA Mercury Sampling Project. Waste amalgam dispos al infrastructure is also offered through a small business/household hazardous waste program. Broad outreach programs to the general public, dentists, colleges, and high schools have been conducted. These have included fever thermometer and high school and college labor atory mercury exchanges. The amalgam separator status at this POTW is shown in Table 3.6B.

Table 3.6B: Amalgam Separa tor Status at POTW "G"



### D ATE 

### P ERCENT OF 

### D ENTISTS 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 44 January 1, 2004 86 July 1, 2004 94 January 1, 2005 98 July 1, 2005 100 January 1, 2006 100 July 1, 2006 100

R ESULTS 

### At the start of the study, POTW “G” had a relatively high per centage of dentists with amalgam separators installed and low mercur y concentrations in the effluent and biosolids. There were no statistically significant changes (p >0.10) in these mercury concen trations or in effluent TSS

### 36 concentrations over the course of the study, as depicted in Fi gures 3.6A and 3.6B, respectively. The influent and effluent loadings at POTW “G” are shown in Figure 3.6C.

0 2 4 6 8

86% ASUs Installed94% ASUs Installed98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Hg Concentration, ng/L

0 2 4 6 8Biosolids Hg Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.6A: Effluent and Biosolids Mercury Concentrations at POTW “G”

### 37 0 2 4 6 8

86% ASUs Installed 94% ASUs Installed 98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 10 20 30 40 50 60 70Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.6B: Effluent Mercury and TSS Concentrations at POTW “G”

0 5 10 15 20 25 30 35

86% ASUs Installed 94% ASUs Installed 98% ASUs Installed 100% ASUs Installed 100% ASUs Installed 100% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 1 2 3 4Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.6C: Influent and Efflue nt Mercury Load at POTW “G”

### 38 3.7 POTW “H”

P LANT 

### P ROCESSES 

### POTW “H” is one of f our POTWs operated by a large regional agency. The plant has a design flow of 54.4 MGD, but an actual average flow of approximately 35 MGD. Hauled-in wastes are accepted for treatment at the plant, with 90% of the hauled waste being domestic sewage. POTW “H” consists of two separa te influent streams that combin e at secondary treatment. The wastewater treatment at POTW “H” consists of preliminary, pr imary, secondary and advanced wastewater treatment, including disi nfection prior to discharge. Preliminary treatment consists of trash removal at bar screens, followed by cycl one grit removal at the headworks. From the grit chamber, wastewater passes into primary clar ifiers, where gravity settling separates the solid materials from the water. The primary sludge is screened and pumped to a dissolved air floatation thickener, where it is blended and then pumped into anaerobic digesters. Digested biosolids are then pumped to belt filter pres ses where polymer is added and excess water is pressed out. The dewatered bioso lids are then trucked to a storage facility where they are stored prior to being applied to agricu ltural land as a soil supplement. Secondary treatment is completed using trickling filters followed by clarifiers. Solids from the secondary clar ifiers are returned to the beginning of the treatment process. The secondary effluent is then pumped to activated sludge basins. Following final clar ification, the treated wastewater is disinfected using ultraviolet light disinfection. Treated effluent from POTW “H” is discharged to a river. The following treatment chemicals are u tilized at POTW “H”:

• Ferrous sulfate is used for odor control; and

• Polymer is used for sludge thickening.

S AMPLE 

### C OLLECTION 

### Influent samples were collected and flow-compos ited at the wet-well at the headworks of each influent stream, prior to grit removal. Effluent samples were collected and time-composited after the oxychargers prior to dischargin g to the river. Biosolids were collected after the belt filter press prior to being trucked to the biosolids storage facility.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### The population served by the POTW is 350,000, encompassing a service area of 165 square miles. The sanitary sewer system for the entire service area is completely separate from the storm drain system. Approximate ly 10% of the total flow to POTW “H” is from industrial dischargers. The major classifications of indus trial users in the POTW “H” service area are provided in Table 3.7A.

Table 3.7A: Types of SIUs in POTW "H" Service Area



### T YPE OF 

### SIU N UMBER 

### A PPROXIMATE 

### T OTAL 

### D AILY 

### F LOW 

### , GPD Electroplaters 6 225,000 Metal Finishers 32 5,629,300 Centralized Waste Treatment 2 25,000 Transportation Equipment and Cleaning 1 8,000 Petroleum Refining 1 102,000

### 39 M ERCURY 

### C ONTROL 

### P ROGRAM 

### In 2000, a mercury code of mana gement practices program was implemented by POTW “H.” This is a voluntary program designed to decr ease mercury levels entering the POTW through cooperation with mercury discharg ers. Among other actions, the program phased in guidelines for the 200 dentists in the service area to compl y, in Phase 1, by installing treatment systems to remove at least 50% of the mercury discharged fr om their facilities. In Phase 2, which began in 2002, dental offices installed ISO- certified amalgam separators for which removal efficiencies of at least 95% had been indicated. The dentists are also required to perform annual wastewater monitoring and periodically submit compliance documentation. Approximately 98% of the dentists in the service area have complied with the program by installing amalgam separators, particle traps or other technologies. Inspections and maintena nce of the dental offices were not mandated, resulting in POTW staff periodically conducting non-regulator y inspections. Annualsubmittal of self-monitoring reports was requested by the POTW. These reports included preand post-treatment mercury analyses and best management practices performed by the dental office. The amalgam separator status at this POTW is shown in Table 3.7B.

Table 3.7B: Amalgam Separa tor Status at POTW "H"



### D ATE 

### P ERCENT OF 

### D ENTISTS 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 unknown January 1, 2004 60 July 1, 2004 89 January 1, 2005 95 July 1, 2005 95 January 1, 2006 98 July 1, 2006 98

R ESULTS 

### There was no apparent trend in either the efflue nt mercury or TSS concentrations at POTW “H” during the course of the study, as depicted in both Figures 3.7A and 3.7B. There was, however, a statistically significant increase (p <0.05) in biosolids mercur y concentrations as shown in Figure 3.7A. The influent and effluent mercury loadings are shown in Figure 3.7C. In mid2005, the POTW lost key staff members who ha d been responsible for the mercury source control program. This resulted in limited staff and resources av ailable to oversee the dental office program. The absence of POTW staff re viewing the program performance resulted in several of the dental offices fa iling to maintain their amalgam separators, potentially increasing the mercury loadings. Also, between June 2005 and April 2006, POTW “H” underwent a construction upgrade that resulted in combining the two influent streams into one. This major construction project resulted in changing the entire primary treatment phase, and relocating influent transmission lines. This construction ac tivity may have resulted in resuspension of mercury particles that may have been residing in various stages of the treatment plant, thereby potentially contributing to the increase in biosolids me rcury concentrations.

### 40 0 2 4 6 8

60% ASUs Installed 89% ASUs Installed 95% ASUs Installed 95% ASUs Installed 98% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 2 4 6 8 10 12Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.7A: Effluent and Biosolids Mercury Concentrations at POTW “H”

0 2 4 6 8

60% ASUs Installed 89% ASUs Installed 95% ASUs Installed 95% ASUs Installed 98% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 10 20 30 40 50 60Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.7B: Effluent Mercury and TSS Concentrations at POTW “H”

### 41 0 5 10 15 20 25 30

60% ASUs Installed 89% ASUs Installed 95% ASUs Installed 95% ASUs Installed 98% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 5 10 15 20 25 30Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.7C: Influent and Efflue nt Mercury Load at POTW “H”



### 3.8 POTW “I”

P LANT 

### P ROCESSES 

### POTW “I” treats an average of 2.38 MGD but is designed for 4.79 MGD. No hauled-in waste is accepted at the treatment plant. POTW “I” is an activated sludge secondary treatment plant. The grit is removed at gravity grit removal stations located in th e trunk sewers and hauled to a sanitary landfill. At the headworks of the plan t, the sewage is screened through six-millimeter traveling screens. The liquid is then processe d in primary clarifiers, secondary aeration tanks, and finally, in secondary clarifiers. Solids ar e removed from both clar ifiers. The secondary sludge is thickened in a gravity belt thickener and added to the primary sludge. The combined sludge is then de-watered in a ro tary press, pasteurized and stab ilized with heat and lime in an RDP thermo-blender. Lime-stabilized, non-heat treated sludge is also produced for use in composting. The sludge produced during the thr ee-year study period was applied to farmland, used for top cover at the sanitary landfill, composted or buried. The landfilled material is usually de-watered sludge that has not been treated with lime or heat. The following treatment chemicals are utili zed at POTW “I”:

• Bioxide is used for odor control;

• Polymer (Hydrofloc 1620) is used for thickening; and

• Lime is used for pasteurization and stabilization.

### 42 S AMPLE 

### C OLLECTION 

### Influent samples were collected from the co mbined influent line after the trunk sewer grit removal stations, but before six-millimeter trave ling screens. Effluent samples were collected upstream of a Parshall Flume on the plant’s fi nal effluent, which is discharged to the environment through a marine outfall. The lim e-stabilized sludge samples were composites comprised of daily grabs from the slu dge bin collected over a 3-4 week period.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “I” serves a population of approximate ly 30,000 people and covers approximately 12 square miles. The entire servic e area is comprised of separate sanitary sewers. Approximately 4% of daily flow to POTW “I ” is from industrial users.

M ERCURY 

### C ONTROL 

### P ROGRAM 

### There are 15 dental clinics that handle mercury amalgam and discharge wastewater to the sewer located within the service area for POTW “I.” These account for approximately 50% of the total mercury load to the POTW, based on estimates made in a 1997 study. Eleven regulatory codes of practice have been developed and implemen ted within the servic e area since 1999, including codes for dental offices and la boratories. The dental code of practice (mandating separator installation) became effec tive throughout the service area in Ju ly 2001. All but one of the dental facilities in the collect ion area had amalgam separators inst alled throughout the study period. There have been no significant industrial mercury sources iden tified in the collection area.

R ESULTS 

### POTW “I” had amalgam separators installed for 93% of the dental facilities at the start of the study. The effluent mercury and TSS concentrati ons indicated no apparent trends throughout the study, as shown in both Figures 3.8A and 3.8B. The influent and effluent loadings for POTW “I” are depicted in Figure 3.8C. The biosolids mercury concentration ex hibited a statistically significant decrease (p <0.05) throughout the study. At the start of the study, the 6-month median biosolids mercury concentration was 1.0 mg/kg, but had decreased to 0.1 mg/kg by the end of the study. These results indicate that the use of amalgam separators may have more of an effect in reducing the amount of me rcury that ends up in the bioso lids as opposed to the effluent. The data also indicate that mercury reductions following separator installation may take several years, as the dental facilities had installed separators two year s before the start of the study.

### 43 0 2 4 6 8 10 12 14

93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 1 2 3 4 5Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.8A: Effluent and Biosolids Mercury Concentrations at POTW “I”

0 2 4 6 8 10 12 14

93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

-5 5 15 25 35 45 55 65 75Effluent TSS Concentration, mg/L Effluent Hg

Effluent TSS

Figure 3.8B: Effluent Mercury and TSS Concentrations at POTW “I”

### 44 0.0 0.1 0.2 0.3 0.4 0.5

93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed 93% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.8C: Influent and Efflue nt Mercury Load at POTW “I”



### 3.9 POTW S 

### “J” AND 

### “K”

P LANT 

### P ROCESSES 

### POTWs “J” and “K” are two of thr ee treatment plants operated by one agency that discharge to a saltwater estuary. They serve a population of approximately 1.4 million people. POTW “J” treats an average of 81.3 MGD but is designed fo r an average of 115 MGD. POTW “K” treats an average of 119.3 MGD, with a design flow of 133 MGD. Treatment at both POTWs includes preliminary, primary, secondary, an d disinfection processes. Pre liminary treatment consists of bar screens followed by aerated grit chambers. Th e debris and grit remove d during this process are trucked to a landfill. Af ter preliminary treatment, the wastewater settles in primary sedimentation tanks. The skimmings and sludge fr om this process are th en sent to the solids handling process, which includes blending and thickening in a dissolv ed air flotation tank followed by anaerobic digestion. Secondary treat ment involves the use of aeration tanks and secondary clarifiers. The seconda ry effluent is then disinfecte d using chlorine. Some of the secondary effluent also under goes advanced treatment (coagulat ion, filtration, disinfection) and is then reused on-site in plant processes.

S AMPLE 

### C OLLECTION 

### For both POTWs, influent samples were collected between the bar screens and grit removal at a point after chlorine had been added for odor cont rol. Samples were not collected if recycled streams from maintenance of process tanks had b een introduced into the system. Effluent grab

### 45 samples were collected downstream of chlori ne addition. Biosolids samples were 24-hour composites collected after dewatering.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### The treatment plants serve a to tal area of 64.7 square miles. The service area for POTW “J” consists of only separate sewers. In the POTW “K” service area, there are mostly combined sewers, with a total of 176 combin ed sewer overflows. For POTW “J,” 43% of incoming flow to the plant during the winter is residential, 17 % is commercial, and 3% is industrial. The remaining flow comes from stor mwater inflow and groundwater infiltration. At POTW “K,” 36% of incoming flow during the wi nter is residential, 19% is co mmercial, 1% is industrial, and 44% is from stormwater inflow and groundwater infiltration. POTW “K” participates in a “flow swap” program from May through October. During this time period the POTW receives approximately 2.0 MGD from an area over which it does not have pretreatment control.

M ERCURY 

### C ONTROL 

### P ROGRAM 

### In July 2001, POTWs “J” and “K” informed dental facilities that they needed to comply with local discharge limits for mercury. This limit was set at 0.2 mg/L. The dentists were given until July 2003 to be in compliance. A letter and a fact sheet were sent to ea ch dental practice with instructions on how to comply with the discharge limits. Inspectors then visited dental offices in the service area to explain the re gulations and assist dentists in getting their practices into compliance. The POTWs completed their informa tional visits in August 2003 and then started a program to inspect a portion of dental practices each year for compliance with the regulations. From 2004 through 2006, approximately 10 % of the o ffices were inspected each year. A dental facility in the service area can demonstrate that it is in compliance with sewer limits if it (a) follows best management practices (BMPs) for am algam wastes (detailed in a fact sheet), (b) properly handles used X-ray fixer, and (c) in stalls an approved amalgam separator—or has demonstrated that it meets the local limits through sampling and has obtained a permit to discharge. Currently, only one dental office ha s elected to receive a pe rmit and perform routine sampling rather than install an approved separator. The percentage of dental facilities that have installed amalgam separators in the total servi ce area is shown in Tabl e 3.9A. The number of dental facilities that have in stalled amalgam separators in th e individual servi ce areas is not known.

Table 3.9A: Amalgam Separator Status at POTWs "J" and “K”



### D ATE 

### P ERCENT OF 

### D ENTAL 

### F ACILITIES 

### O PERATING 

### D ENTAL 

### A MALGAM 

### S EPARATORS 

### July 1, 2003 94 January 1, 2004 97 July 1, 2004 97 January 1, 2005 97 July 1, 2005 97 January 1, 2006 97 July 1, 2006 98

### 46 These POTW’s have specifically exempted certain specialties from the requirement of installing amalgam separators or obtaining a permit. These specialties are: periodontics, orthodontics, oral pathology/oral medicine; oral and maxillofaci al surgery; radiology; prosthodontists and endodontists that do not place and remove amalgam as a courtesy for their clients. Dentists, such as some pediatric dentists, that place or remove amalgam on three days or fewer per year are also exempt from these requirements. If any of these exemptions applies to the dental office, it does not need to install separator or apply for a permit. However, it still needs to follow BMPs for waste amalgam and may be inspected for compliance.

In May 2005, POTW “J” stopped accepting septage waste from de ntal offices without prior screening and evaluation of me rcury concentration levels.

R ESULTS 

### For both treatment plants, there was a statistically significant decrease (p <0.05) in effluent and biosolids mercury concentrations throughout the study (Figures 3.9A and 3.9D). POTW “J” also had a statistically significant (p <0.05) effluent TSS decrease, wh ile POTW “K” did not (Figures 3.9B and 3.9E). Both plants showed an apparent decrease in effluent mercury loadings, as seen in Figures 3.9C and 3.9F. The effluent mercury concentrations showed a greater decrease than the biosolids mercury concentr ations. This may be due to the relatively high mercury concentrations present in the effl uent at the beginning of the st udy and the decreases in effluent TSS throughout the study period. Since a large pe rcentage of dental facilities had amalgam separators installed for the duration of the study (9 7% at beginning and 98% at end), it could be that reductions in mercury gained through th e installation of separators may not occur immediately. It is also possible that the apparent reductions in me rcury may also be the result of improvements to treatment processes suggested by the effluent TSS decreases or due to other activities occurring within the service area, su ch as implementation of BMPs recommended by the mercury control program.

### 47 0 2 4 6 8 10 12

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Hg Concentration, ng/L

0 2 4 6 8Biosolids Hg Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.9A: Effluent and Biosolids Mercury Concentrations at POTW “J”

0 2 4 6 8 10 12

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 10 20 30 40 50 60 70Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.9B: Effluent Mercury and TSS Concentrations at POTW “J”

### 48 0 25 50 75 100 125 150

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 2 4 6 8 10 12 14 16 18 20Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.9C: Influent and Efflue nt Mercury Load at POTW “J”

0 2 4 6 8 10 12

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentrations, ng/L

0 2 4 6 8Biosolids Mercury Concentrations, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.9D: Effluent and Biosolids Mercury Concentrations at POTW “K”

### 49 0 3 6 9 12

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 10 20 30 40Effluent TSS Concentration, mg/L Effluent Hg Effluent TSS

Figure 3.9E: Effluent Mercury and TSS Concentrations at POTW “K”

0 10 20 30 40 50 60 70 80

97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 97% ASUs Installed 98% ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 2 4 6 8 10 12 14 16 18 20Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.9F: Influent and Efflue nt Mercury Load at POTW “K"

### 50 3.10 POTW “L”

P LANT 

### P ROCESSES 

### POTW “L” is designed to treat 55 MGD, and ha s an actual average flow of 46 MGD. The treatment process at POTW “L” includes grit re moval, primary and secondary treatment, and UV disinfection. Hauled-in wastes are accepted for treatment at this POTW. Preliminary treatment includes bar screens and preaeration tanks to re move grit. Primary sludge is blended with Dissolved Air Flotation Unit-thickened waste ac tivated sludge and centrifuged. The cake is incinerated and the centrate and wet scrubber water are returned as influent to the secondary process. Following secondary treatment, the wastewater is disinfect ed using ultraviolet lightbulbs. A small portion of fi nal effluent flow is sent to the dual-media filter plant and chlorinated for recycled water use. The backwash water from dual-media filter plant returns as influent to the headworks. Hauled-in wastes, wh ich include residential septage, portable toilet waste, domestic septage from non-re sidential sites, and restaurant grease, are introduced into the plant at the headworks. The following chemicals are used in treatment processes at POTW “L”:

• Hydrogen peroxide – odor control;

• Sodium hypochlorite;

• Carbide lime; and

• Polymer.

S AMPLE 

### C OLLECTION 

### Influent grab samples were taken from the head works, prior to grit re moval. These included some recycled flows from both the treatment plan t and the filter plant. Effluent composite samples were taken at a point after UV disinfect ion. Biosolids samples were sludge cake, taken prior to incineration. Certain sidestreams carryi ng non-negligible concentr ations of mercury are returned as influent to the headworks. These sometimes include wet scrubber water and filter backwash water. On the days on which influent grab samples for this study were taken, none of these flows were being recycled. However, as a result of the customary recycling to the secondary process influent of incinerator wet scr ubber water, it is believed that effluent mercury concentrations on a day-to-day basis are affected.

C OLLECTION 

### S YSTEM 

### I NFORMATION 

### POTW “L” is an estuarine di scharger that serves a populat ion of 450,000. The service area encompasses approximately 143 square miles.

M ERCURY 

### C ONTROL 

### P ROGRAM 

### As part of the mercury control program at POTW “L”, about 23 industrial users are monitored up to four times per year for mercury: once or twice by the POTW and the rest through selfmonitoring. Dentists are encouraged to instal l amalgam separators, but there is no mandatory program requiring separators. In the future, PO TW “L” will be implementing a requirement for amalgam separators. Influent merc ury concentrations are anticipated to decline; the effect on the effluent concentrations will be evaluated. Household hazardous wastes and small quantity generator mercury waste is accepted at the H ousehold Hazardous Waste Collection Facility, where they are sequestered and hauled away for proper disposal. In addition, best management practices information has been distributed to all hospitals in the service area.

### 51 R ESULTS 

### At POTW “L”, the effluent mercury concentr ation ranged from 10.4 ng/L to 205 ng/L, effluent mercury loading ranged from 1.9 grams/day to 33.8 grams/day, and effluent TSS concentrations ranged from 3 mg/L to 29 mg/L, as shown in Figures 3.10A and 3.10B. No statisticallysignificant trends (p >0.10) are evident for a ny of these variables. The biosolids mercury concentration remained relatively constant throughout the sampli ng (Figure 3.10A). The influent and effluent loadings are depicted in Figure 3.10C. By the end of the study, an estimated 11% of the dental facilities/dentists in the service area of POTW “L ” had installed separators.

0 10 20 30 40 50 60 70

Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed 11 % ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentration, ng/L

0 3 6 9Biosolids Mercury Concentration, mg/kg (dry) Effluent Hg Biosolids Hg

Figure 3.10A: Effluent and Biosolids Mercury Concentrations at POTW “L”

### 52 0 10 20 30 40 50 60 70

Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed 11 % ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Effluent Mercury Concentrations, ng/L

0 5 10 15 20 25 30 35 40 45Effluent TSS Concentrations, mg/L Effluent Hg Effluent TSS

Figure 3.10B: Effluent Mercury and TSS Concentrations at POTW “L”

0 20 40 60 80

Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed Unknown ASUs Installed 11 % ASUs Installed

Jul 03 - Dec 03 Jan 04 - Jun 04 July 04 - Dec 04 Jan 05 - Jun 05 Jul 05 - Dec 05 Jan 06 - Jul 06Influent Mercury Load, grams/day

0 10 20 30 40Effluent Mercury Load, grams/day Influent Hg Effluent Hg

Figure 3.10C: Influent and Effluent Mercury Load at POTW “L”

### 53 

## 4. C OMBINED 

## R ESULTS AND 

## D ISCUSSION



### In addition to those for individual plants, trends were also examined by combining the results from all of the POTWs. A variety of potenti al factors that may be influencing mercury concentrations at POTWs were examined. Exclud ed from this analysis were those factors in which there were too many variable s to effectively establish a relatively conclusive relationship.

4.1 I NFLUENT 

### , E FFLUENT 

### , AND 

### B IOSOLIDS



### Figure 4.1A depicts, with a logar ithmic y-axis, the influent total mercury concentrations, for each facility, in six-month increments. There is clea rly a high degree of variability in the influent mercury concentrations within each facility as we ll as between the facilities. POTWs B, C, I, J, K and L collected influent samples as grab sample s while POTWs A, D, E, F, G, and H collected influent composite samples. Using composite sampling techniques to monitor influent mercury concentrations potentially reduces variability to some degree. The high va riability in influent concentrations is most likely due to the inconsistent nature of the influent and the fact that, because the samples have varying amounts of solid particles, a truly representative influent sample is virtually impossible to collect. Much of the mercury entering a POTW is thought to be in the particulate form and would be contained w ithin these solids. In light of this inherent variability, the ability to use in fluent mercury concentrations to determine impacts from potential mercury reduction techniques in th e collection system is limited.

10 100 1000Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "K" POTW "L"Influent Mercury, ng/L

Figure 4.1A: Influent Mercury Concentrations

### 54 POTWs “B” and “I” collected influent samples after grit removal while the remaining POTWs collected influent samples prior to grit remova l. Influent that contains a high amount of particulate matter is suspected to also contain a high amount of particulate mercury. However, as shown in Figure 4.1B, no difference is clearly evident in influent mercury concentrations between those facilities where in fluent samples were collected prior to grit removal and those facilities where influent samples were collected after grit removal processes.

10 100 1000Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "J" POTW "K" POTW "B" POTW "I"Influent Mercury, ng/L

Sample Collected Prior to Grit Removal Sample Collected After Grit Removal

Figure 4.1B: Influent Mercury Concentr ations and Sample Collection Location

### 55 0 5 10 15 20 25 30 35 40 45Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "K" POTW "L"Effluent Mercury Concentration, ng/L

Figure 4.1C: Effluent Mercury Concentrations



### Figure 4.1C depicts the effluent mercury concentra tions, in six-month increments, at each facility during the course of the sampling project. Simila r to the influent mercury concentrations, there is a high degree of variability in effluent merc ury concentrations between different POTWs. Effluent mercury concentrations ar e generally higher at POTWs A, I, J, K, and L than they are at POTWs B, C, D, E, F, G, and H. Speculations as to the potential causes of these differences are examined in later sections of this report. However, unlike the influent concentrations, the effluent mercury concentrations are more consistent at individual facilities . Some facilities, particularly POTW “E”, exhibited very little variability in efflue nt mercury concentrations. The decreased variability within individual PO TWs indicates that, generally speaking, each individual POTW is consistently performing to the same level.

### 56 0 2 4 6Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "K" POTW "L"Biosolids Mercury Concentration, mg/kg (dry)

Figure 4.1D: Biosolids Mercury Concentrations



### Similar to both the influent and the effluent mercury concentrations, the effluent biosolids concentrations exhibit considerable variability from POTW to POTW, as depicted in Figure 4.1D. It is also clear from this figure that some facilities have higher variability within their biosolids mercury concentrations than do other faci lities. Potential causes of this are examined further in later sections of this report. PO TW “E” demonstrates a very small degree of variability, while POTWs “B” and “L” each display a very high degr ee of variability. At POTW “B” the high variability is attributable to the in terceptor cleaning activities that were discussed in Section 3.2 of this report.

4.2 R EMOVAL 

### E FFICIENCY



### The mercury removal efficiency calculated fr om the median of each facility’s influent concentrations and the median of each facility’s effluent con centrations measured during the study was examined to determine if there were di fferences in the abilities of individual POTWs to remove mercury from the wet stream. As shown by Figure 4.2A, the treatment plants had median removal efficiencies ranging from 89% at POTW “L” to 99% at POTW “D.” It should be noted that POTW “D” is connected to POTW “E” via pipeline and it is likely that concentrations at POTW “D” are strongly affected by concentrations at POTW “E.” However, at POTW “F”, which has the second highest median removal efficiency and where results are not affected by those of another treatment facility, the median removal efficiency of 98.75% is only slightly lower that that of POTW “D”.

### 57 0 10 20 30 40 50 60 70 80 90 100

POTW "L" POTW "K" POTW "A" POTW "J" POTW "C" POTW "I" POTW "G" POTW "B" POTW "H" POTW "E" POTW "F" POTW "D"Removal Efficiency, %

Figure 4.2A: Median Merc ury Removal Efficiency



### 4.3 D ISSOLVED 

### M ERCURY



### A key factor often thought to affect the ability of a POTW to remove me rcury and the resulting effluent mercury concentration is the extent to which the mercury is in the dissolved or particulate form. Most of the pa rticulates are expected to settle in the collection system or be removed during treatment processes. The di ssolved form may pass through the treatment system, impacting effluent con centrations. A limited amount of sampling was performed in order to attempt to quantify the amount of dissolved mercury in the effluent. Dissolved mercury analysis was performed at all POTWs except POTW s “D,” “E,” and “F” during the first quarter of the study. POTWs “D,” “E,” and “F” volunteere d to submit their data for consideration in the study well after the study had begun and had not b een aware of the plan to collect dissolved mercury data.

Some POTWs provided additional dissolved mercury data as well. These data were used to observe the ratio of dissolved me rcury to total mercury in the effluent of the participating POTWs. Figure 4.3A shows the median percent of the effluent total mercury that is dissolved for each facility with available data. The percen t of effluent total mercury that was dissolved was found to vary based on the POTW. The highe st median dissolved mercury occurred at POTW “G” at 59%, while the lowest median was at POTW “A” at 22%.

It has been hypothesized that recycled incinerator scrubber wa ter flow within a POTW can increase the amount of dissolved mercury in the POTW effluent. Figure 4.3B indicates that, for the POTWs in the study, there does not appear to be a relationship between the presence of

### 58 recycle scrubber water flows and th e percentage of the effluent mercury concentration that is dissolved.

0 25 50 75 100

POTW "G" POTW "C" POTW "I" POTW "B" POTW "K" POTW "L" POTW "J" POTW "H" POTW "A"Percent of Effluent Total Mercury that is Dissolved

Figure 4.3A: Median Percent of Effluent Total Mercury that is Dissolved

### 59 0 25 50 75 100

POTW "A" POTW "B" POTW "C" POTW "L" POTW "G" POTW "H" POTW "I" POTW "J" POTW "K"Percent of Effluent Total Mercury that is Dissolved

Have recycle flows Do not have recycle flows

Figure 4.3B: Presence of Recycle flows and the Median Percent of Effluent Total Mercury that is Dissolved *Scrubber water flow at POTW “A” did not occur during the final seven months of the sampling project



### 4.4 T OTAL 

### S USPENDED 

### S OLIDS



### It has been hypothesized that th e quantity of TSS in POTW efflue nt can provide an indication of the amount of mercury that is found in the efflue nt. Figure 4.4A shows that, when the effluent mercury concentration is plotted versus effluent TSS concentra tion for all POTWs, there is a positive linear relationship. However, the R 2 

### value indicates the abilit y to predict the mercury concentration using TSS concentrations is very low. The relationship between effluent mercury concentration and TSS concentrations were also examined at the individual POTWs. Table 4.4A provides the equation of the linear trendlines and the associated R 2 

### values obtained from this analysis. For many of the POTWs, there wa s a strong positive linear relationship between effluent mercury concentrations and e ffluent TSS concentrations, and the R 2 

### values were higher. At POTWs “C”, “E”, “K”, and “L”, however, the predictive ability of the equation was low. The use of various chemicals, es pecially iron salts, may have an impact on the relationship between TSS and mercury concentrations. Beca use of this, POTWs that use iron salts were compared to those that do not. It was found that there was no clear rela tionship between the use of iron salts and the ability to predict efflue nt mercury concentrations from effluent TSS concentrations. Therefore, it is unknown why, at some POTWs, effluent TSS concentration appears to be an adequate predictor of effluent mercury concentration an d, at others, it is not.

### 60 y = 0.5221x + 2.8435 R 2 = 0.0605

0 5 10 15 20 25 30

0 5 10 15 20 25 30 Effluent TSS, mg/LEffluent TR Hg, ng/L

Figure 4.4A Effluent Mercury Concentrations versus Ef fluent TSS Concentrations

Table 4.4A. Trendline Equations and R 2 Values for Effluent Mercury Con centrations versus Effluent TSS Concentrations



### POTW Equation R 2 

### Value POTW “A” y = 0.2105x + 7.2324 0.3004 POTW “B” y = 0.2774x + 1.9742 0.3281 POTW “C” y = 0.1084x + 2.0188 0.0434 POTW “D” y = 0.1155x + 1.3448 0.2837 POTW “E” y = 0.089x + 1.5362 0.0711 POTW “F” y = 0.5491x - 0.4202 0.4194 POTW “G” y = 0.2649x + 1.5544 0.2964 POTW “H” y = 0.3133x + 2.6572 0.4879 POTW “I” y = 0.6743x + 1.937 0.3848 POTW “J” y = 0.2407x + 4.1588 0.2821 POTW “K” y = 0.2199x + 4.8325 0.0998 POTW “L” y = 1.0615x + 21.401 0.0181

4.5 D ENTISTS PER 

### F LOW



### In order to establish whether the density of dental facilities has an impact on mercury levels in treatment plants, the numbers of dentists per plan t flow were examined in comparison to influent, effluent, and biosolids mercury concentrations. POTWs “D”, “E ”,”J”, and “K” were excluded because the number of dentists for their indivi dual service areas was not known. Most POTWs track the number of dentist faci lities within the service area, however some count the number of

### 61 dentists, and it is not known, for every POTW, whether they counted the total number of dentists or excluded facilities that do not use amalgam. A further compli cation is that many dentists who do not place amalgam restorations nonetheless re move amalgam-containing restorations, and this is a significant contributor to dental mercury discharges. Although limitations of doing so are recognized, for the purposes of this analysis, the nu mber of facilities and the number of dentists are used interchangeably. As seen in Figur es 4.5A and 4.5B, a decrease in the number of dentists per million gallons per day (MGD) was rela ted to a general decrease in both influent and effluent mercury concentrations. Both of thes e relationships were found to be statistically significant (p <0.05) despite the limitations noted above. The median influent mercury concentration and the number of dentists pe r MGD resulted in a p-value of 0.00007, indicating that the median influent mercury concentration at a POTW is very hi ghly correlated to the number of dentists per MGD. The median effluent mercury concentration was also highly correlated to the number of dentists per MGD with a p-value of 0.002.

There was no relationship found between dentis ts per MGD and median biosolids mercury concentrations (Figures 4.5C). This was une xpected since a major portion of the mercury released by dentists is thought to be removed during treatm ent in the POTW and, therefore, would end up in the biosolids. One possible reas on for these results may be that the number of dentists with amalgam separato rs installed changed throughout th e study. Therefore, reductions in mercury gained in areas where more separato rs were being installe d may have offset the general trend of increasi ng mercury resulting from an increase in the number of dentists. This finding may also reflect th at biosolids mercury is more affected by separator installation than is effluent mercury.

0 100 200 300 400 500 600C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06A - Jul 06A - Jul 05B - Jul 05B - Jul 04A - Jan 06B - Jan 04A - Jul 04A - Jan 05A - Jan 04B - Jan 05B - Jan 06G - JanB - Jul 06G - JanG - Jul 06G - JanG - Jul 04G - Jul 05F - Jan 05F - Jul 04F - Jul 06F - Jul 05F - Jan 06H - Jul 05I - Jul 04I - Jul 06H - Jan 04H - Jul 04H - Jan 05H - Jan 06H - Jul 06I - Jan 04I - Jan 05I - Jul 05I - Jan 06L - Jul 06L - Jul 05L - Jul 04L - Jan 04L - Jan 05L - Jan 06

POTW and Time PeriodInfluent Mercury Concentration, ng/L

0 2 4 6 8 10 12 14 16 18Number of Dentists per MGD Influent Hg

Dentists per Flow

Figure 4.5A: Influent Mercury Con centration and Dentists per Flow

### 62 0 10 20 30 40 50 60 70C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06A - Jul 06A - Jul 05B - Jul 05B - Jul 04A - Jan 06B - Jan 04A - Jul 04A - Jan 05A - Jan 04B - Jan 05B - Jan 06G - JanB - Jul 06G - JanG - Jul 06G - JanG - Jul 04G - Jul 05F - Jan 05F - Jul 04F - Jul 06F - Jul 05F - Jan 06H - Jul 05I - Jul 04I - Jul 06H - Jan 04H - Jul 04H - Jan 05H - Jan 06H - Jul 06I - Jan 04I - Jan 05I - Jul 05I - Jan 06L - Jul 06L - Jul 05L - Jul 04L - Jan 04L - Jan 05L - Jan 06

POTW and Time PeriodEffluent Mercury Concentration, ng/L

0 2 4 6 8 10 12 14 16 18Number of Dentists per MGD Effluent Hg Dentists per Flow

Figure 4.5B: Effluent Mercury Concentration and Dentists per Flow

0 1 2 3 4 5C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06A - Jul 06A - Jul 05B - Jul 05B - Jul 04A - Jan 06B - Jan 04A - Jul 04A - Jan 05A - Jan 04B - Jan 05B - Jan 06G - JanB - Jul 06G - JanG - Jul 06G - JanG - Jul 04G - Jul 05F - Jan 05F - Jul 04F - Jul 06F - Jul 05F - Jan 06H - Jul 05I - Jul 04I - Jul 06H - Jan 04H - Jul 04H - Jan 05H - Jan 06H - Jul 06I - Jan 04I - Jan 05I - Jul 05I - Jan 06L - Jul 06L - Jul 05L - Jul 04L - Jan 04L - Jan 05L - Jan 06

POTW and Time PeriodBiosolids Mercury Concentration, mg/kg (dry)

0 3 6 9 12 15 18Number of Dentists per MGD Biosolids Hg Dentists per Flow

Figure 4.5C: Biosolids Mercury Concentration and Dentists per Flow

### 63 4.6 D ENTISTS 

### W ITHOUT 

### S EPARATORS PER 

### F LOW



### Once it was determined that a poten tial positive relationship between the numbers of dentists and mercury levels at POTWs exists, whether the use of amalgam separators by dentists also impacts mercury levels was examined. The number of den tists at each treatment pl ant that did not have separators installed was first determined. This number was then divided by total flow to the plant. In doing so, it was found that there is no statistically significant re lationship between this value and the median influent mercury concentration as shown in Figure 4.6A.

The median effluent mercury concentration is ne gatively correlated to the number of dentists without separators per flow (Fi gure 4.6B). This negative correla tion was highly significant with a p-value of 0.004. This clearly in dicates that increasing amalgam separator installations did not necessarily lead to a decrease in effluent mercury concentrations at the POTWs in the project. This result could be due, in part, to the limited number of amalgam separator installations that occurred at the POTWs with generally lower e ffluent mercury concentrations at the study’s outset.

For biosolids, there was a statis tically significant increase in th e median mercury concentration with an increase in the number of dentists per fl ow that do not have separators installed (Figure 4.6C). With a p-value of 0.0002, this correlation is highly statistically significant. In fact, of the relationships examined in the analysis of the data collected during th e sampling project, the strength of this relationship is second only to that of the relationship between influent total mercury concentrations and the number of dentists per MGD. Since the use of separators is expected to reduce particulate mercury entering wastewater treat ment plants, this relationship strongly supports the hypothesis that amalgam separators can re duce the quantity of mercury entering treatment plants.

### 64 0 100 200 300 400 500 600A - Jul 05A - Jan 06A - Jul 06G - Jul 05G - Jan 06G - Jul 06I - Jan 04I - Jul 04I - Jan 05I - Jul 05I - Jan 06I - Jul 06A - Jan 05G - Jan 05G - Jul 04G - Jan 04C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06B - Jul 05B - Jul 04B - Jan 04A - Jul 04B - Jan 05B - Jan 06A - Jan 04B - Jul 06F - Jul 06F - Jan 06F - Jan 05F - Jul 04F - Jul 05

POTW and Time PeriodInfluent Mercury Concentration, ng/L

0 1 2 3 4 5Number of Dentists Without Separators per MGD Influent Hg

Dentists without Separators per Flow

Figure 4.6A: Influent Mercury Concentration and Dentists without Separators per Flow

0 4 8 12 16 20A - Jul 05A - Jan 06A - Jul 06G - Jul 05G - Jan 06G - Jul 06I - Jan 04I - Jul 04I - Jan 05I - Jul 05I - Jan 06I - Jul 06A - Jan 05G - Jan 05G - Jul 04G - Jan 04C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06B - Jul 05B - Jul 04B - Jan 04A - Jul 04B - Jan 05B - Jan 06A - Jan 04B - Jul 06F - Jul 06F - Jan 06F - Jan 05F - Jul 04F - Jul 05

POTW and Time PeriodEffluent Mercury Concentration, ng/L

0 1 2 3 4 5Number of Dentists Without Separators per MGD Dentists without Separators per Flow Effluent Hg

Figure 4.6B: Effluent Mercury Concentration and Dentists without Separators per Flow

### 65 0 1 2 3 4A - Jul 05A - Jan 06A - Jul 06G - Jul 05G - Jan 06G - Jul 06I - Jan 04I - Jul 04I - Jan 05I - Jul 05I - Jan 06I - Jul 06A - Jan 05G - Jan 05G - Jul 04G - Jan 04C - Jul 04C - Jul 05C - Jan 04C - Jan 05C - Jan 06C - Jul 06B - Jul 05B - Jul 04B - Jan 04A - Jul 04B - Jan 05B - Jan 06A - Jan 04B - Jul 06F - Jul 06F - Jan 06F - Jul 04F - Jul 05

POTW and Time PeriodBiosolids Mercury Concentration, mg/kg (dry)

0 1 2 3 4 5Number of Dentists Without Separators per MGD Dentists without Separators per Flow Biosolids Hg

Figure 4.6C: Biosolids Mercury Concentration and Dentists without Separators per Flow



### 4.7 P LANT 

### F LOW



### An examination of plant flow as it is relate d to median mercury concentrations in POTW influent, effluent and biosolids re vealed no statistically significant (p >0.10) correl ations. These relationships are shown in Figures 4.7A through 4.7C.

### 66 0 200 400 600

POTW "K" POTW "D" POTW "B" POTW "E" POTW "J" POTW "A" POTW "L" POTW "F" POTW "G" POTW "H" POTW "C" POTW "I"Influent Mercury Concentration, ng/L

0 50 100 150Average Plant Flow, MGD Influent Hg

Plant Flow

Figure 4.7A: Influent Mercury Concentration and Average Plant Flow

0 1 2 3 4

POTW "K" POTW "D" POTW "B" POTW "E" POTW "J" POTW "A" POTW "L" POTW "F" POTW "G" POTW "H" POTW "C" POTW "I"Biosoilds Mercury Concentration, mg/kg (dry)

0 50 100 150 200Average Plant Flow, MGD Biosolids Hg

Plant Flow

Figure 4.7B: Biosolids Mercury Concentration and Average Plant Flow

### 67 0 10 20 30 40

POTW "K" POTW "D" POTW "B" POTW "E" POTW "J" POTW "A" POTW "L" POTW "F" POTW "G" POTW "H" POTW "C" POTW "I"Effluent Mercury Concentration, ng/L

0 20 40 60 80 100 120Average Plant Flow, MGD Effluent Hg

Plant Flow

Figure 4.7C: Effluent Mercury Concentration and Average Plant Flow



### 4.8 N ON 

### -I NDUSTRIAL 

### F LOW



### Another factor that was examined to determin e the effects on mercury concentrations was the percentage of industrial flow. POTWs “D” and “E” were excluded because the percent of the influent from industrial sources is not known. POTW “B” was excluded because the effects of the interceptor cleaning project c ould skew the results. The data collectively indicated that there is an increase in influent, e ffluent, and biosolids mercury conc entrations with an increase in relative non-industrial flow (F igures 4.8A through 4.8C). A lthough influent and biosolids mercury concentrations appear to be more strong ly related to non-industria l flow than effluent concentrations do, the correlations for median infl uent and median biosolid s are not statistically significant (p >0.05), while that for median effluent is, with a p-value of 0.036.

However, included within these results are those for both combined and separate sewer systems. If the stormwater included in the combined systems had a lower mercury concentration than other non-industrial flows did, the strength of these relationships may have been influenced. To eliminate this variable, only the results from POTWs with solely separa te sewer systems were examined (Figures 4.8D through 4.8F). The correlat ions between influent, effluent, and biosolids median mercury concentrations and percentage of non-industria l flow were all found to be statistically non-significant at the α = 0.05 level. However, these co rrelations for median influent and median effluent, but not median biosolids, mercury concentrations we re significant at the α = 0.10 level. Considering all of thes e results, it is possibl e that industrial flow generally contains less mercury than other wastewater s, thereby providing dilution when it is present. This is consistent with the findings of a 2000 NACWA (f ormerly Association of Metropolitan Sewerage

### 68 Agencies) report titled “Evaluati on of Domestic Sources of Merc ury” that demonstrated that domestic wastewater is a significant source of mercury at POTWs.

0 100 200 300 400 500 600

POTW "G" POTW "C" POTW "H" POTW "F" POTW "I" POTW "A" POTW "J" POTW "K" POTW "L"Influent Mercury Concentration, ng/L

0 20 40 60 80 100% of Flow due to Non-Industrial Sources Influent Hg

Non-Industrial Flow

Figure 4.8A: Influent Mercury Concentration and Non-Industrial Flow

### 69 0 10 20 30 40

POTW "G" POTW "C" POTW "H" POTW "F" POTW "I" POTW "A" POTW "J" POTW "K" POTW "L"Effluent Mercury Concentration, ng/L

0 25 50 75 100% of Flow due to Non-Industrial Sources Non-Industrial Flow Effluent Hg

Figure 4.8B: Effluent Mercury Concentration and Non-Industrial Flow

0 1 2 3 4 5

POTW "G" POTW "C" POTW "H" POTW "F" POTW "I" POTW "A" POTW "J" POTW "K" POTW "L"Biosolids Mercury Concentration, mg/kg (dry)

0 25 50 75 100% of Flow due to Non-Industrial Sources Non-Industrial Flow Biosolids Hg

Figure 4.8C: Biosolids Mercury Concentration and Non-Industrial Flow

### 70 0 100 200 300 400 500 600

POTW "G" POTW "H" POTW "F" POTW "I" POTW "J" POTW "L"Influent Mercury Concentration, ng/L

0 20 40 60 80 100% of Flow due to Non-Industrial Sources (Separate Sewer Systems) Influent Hg

Non-Industrial Flow

Figure 4.8D: Influent Mercury Concentration and Non-Industrial Flow in Separate Sewer Systems

0 10 20 30 40

POTW "G" POTW "H" POTW "F" POTW "I" POTW "J" POTW "L"Effluent Mercury Concentration, ng/L

0 25 50 75 100% of Flow due to Non-Industrial Sources (Separate Sewer Systems) Non-Industrial Flow Effluent Hg

Figure 4.8E: Effluent Mercury Concentration and Non-Industrial Flow in Separate Sewer Systems

### 71 0 1 2 3 4 5

POTW "G" POTW "H" POTW "F" POTW "I" POTW "J" POTW "L"Biosolids Mercury Concentration, mg/kg (dry)

0 25 50 75 100% of Flow due to Non-Industrial Sources (Separate Sewer Systems) Non-Industrial Flow Biosolids Hg

Figure 4.8F: Biosolids Mercury Concentration and Non-Industrial Flow in Separate Sewer Systems



### 4.9 F RESHWATER VS



### . M ARINE 

### /E STUARINE 

### D ISCHARGERS



### A comparison was made between the POTWs that have freshwater discharges and those with marine or estuarine discharges. There are no cl ear differences between these two categories of treatment plants for both influent and biosolids mercury concentrations (F igures 4.9A and 4.9C). It was found, however, that POTWs with discharges to freshwater generally have lower effluent mercury concentrations than did their saltwater counterparts (Figure 4.9B). The reason for this difference is unclear and should be further examine d. It is possible that POTWs that discharge to freshwater are providing diffe rent levels of treatment than POTWs that discharge to marine/estuarine waters for the removal of wastew ater constituents with which effluent mercury concentrations are incidentally lowered.

### 72 0 200 400 600 800 1000 1200 1400Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "A" POTW "I" POTW "J" POTW "K" POTW "L"Influent Mercury Concentration, ng/L Freshwater Discharges Marine/Estuarine Discharges

Figure 4.9A: Influent Mercury Concentration and Receiving Water Type

0 10 20 30 40 50 60Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "A" POTW "I" POTW "J" POTW "K" POTW "L"Effluent Hg Concentration, ng/L Freshwater Discharges Marine/Estuarine Discharges

Figure 4.9B: Effluent Mercury Concentration and Receiving Water Type

### 73 0 1 2 3 4 5Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "A" POTW "I" POTW "J" POTW "K" POTW "L"Biosolids Mercury Concentration, mg/kg (dry) Freshwater Discharges Marine/Estuarine Discharges

Figure 4.9C: Biosolids Mercury Concentration and Receiving Water Type



### 4.10 I RON 

### S ALTS



### The results from the sampling indicate that t hose POTWs that do not use iron salts (e.g., ferric chloride, ferrous sulfate) have generally higher effluent mercury concentrations (Figure 4.10A). Since iron salts are used as flocculants, especi ally for metals removal, this trend is not unexpected. The POTWs that use iron salts ar e the same as the POTWs with freshwater discharges. This may help to explain the differe nce in effluent mercury concentrations that was observed when freshwater discharg es were compared to saltwater /estuarine discharges. There was no relationship found between use of iron salts and biosolids mercury concentrations (Figure 4.10B). This finding suggests that effluent mercury levels may be affected by iron salt addition, while its impact on biosolids mercury levels is not significant. This would be consistent with the relative magnitude of effluent vers us biosolids mercury quantities.

### 74 0 10 20 30 40 50 60Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "A" POTW "I" POTW "J" POTW "K" POTW "L"Effluent Hg Concentration, ng/L Use Iron Salts Do Not Use Iron Salts

Figure 4.10A: Effluent Mercury Concentration and Use of Iron Salts

0 1 2 3 4 5Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"B" POTW "C" POTW "D" POTW "E" POTW "F" POTW "G" POTW "H" POTW "A" POTW "I" POTW "J" POTW "K" POTW "L"Biosolids Mercury Concentration, mg/kg (dry) Use Iron Salts Do Not Use Iron Salts

Figure 4.10B: Biosolids Mercury Co ncentration and Use of Iron Salts

### 75 4.11 H AULED



### - IN 

### W ASTES



### POTWs that accept hauled-in wastes were examined to determine if they have higher influent, effluent, and biosolids mercury concentrations. No differen ces were found in these three parameters between plants that do and do not accept hauled-in waste (Figures 4.11A through 4.11C).

0 100 200 300 400 500 600 700 800 900 1000

POTW "D" POTW "F" POTW "G" POTW "H" POTW "L" POTW "A" POTW "B" POTW "C" POTW "E" POTW "I" POTW "J" POTW "K"Influent Mercury Concentration, ng/L Accept Hauled-in Waste Do Not Accept Hauled-in Waste

Figure 4.11A: Influent Mercury Concentrations and Hauled-in Waste

### 76 0 5 10 15 20 25 30 35

POTW "D" POTW "F" POTW "G" POTW "H" POTW "L" POTW "A" POTW "B" POTW "C" POTW "E" POTW "I" POTW "J" POTW "K"Effluent Mercury Concentration, ng/L Accept Hauled-in Waste Do Not Accept Hauled-in Waste

Figure 4.11B: Effluent Mercury Concentrations and Hauled-in Waste

0 1 2 3 4 5

POTW "D" POTW "F" POTW "G" POTW "H" POTW "L" POTW "A" POTW "B" POTW "C" POTW "E" POTW "I" POTW "J" POTW "K"Biosolids Mercury Concentration, mg/kg (dry) Accept Hauled-in Waste Do Not Accept Hauled-in Waste

Figure 4.11C: Biosolids Mercury Co ncentrations and Hauled-in Waste

### 77 4.12 P OPULATION 

### D ENSITY



### Population density within each POTW’s service ar ea was also examined to determine if there was a correlation with mercury conc entrations. It was found that there is no clea r trend between an increasing number of persons per square mile and the influent, effluent , or biosolids mercury concentrations (Figures 4.12A through 4.12C). A mo re in-depth examination of influent trends, such as decreasing flow due to water conserva tion activities, could pr ovide more insight.

0 100 200 300 400 500 600

POTW "C" POTW "B" POTW "A" POTW "J" POTW "K" POTW "L" POTW "D" POTW "E" POTW "I" POTW "H" POTW "F" POTW "G"Influent Mercury Concentration, ng/L

0 1000 2000 3000 4000 5000 6000 7000 8000Persons per Square Mile Influent Hg Population Density

Figure 4.12A: Influent Mercury Concentration and Population Density

### 78 0 5 10 15 20 25 30 35 40 45 50

POTW "C" POTW "B" POTW "A" POTW "J" POTW "K" POTW "L" POTW "D" POTW "E" POTW "I" POTW "H" POTW "F" POTW "G"Effluent Mercury Concentration, ng/L

0 1000 2000 3000 4000 5000 6000 7000 8000Persons per Square Mile Population Density Effluent Hg

Figure 4.12B: Effluent Mercury Concentration and Population Density

0 0.5

1 1.5

2 2.5

3 3.5

4 4.5

5

POTW "C" POTW "B" POTW "A" POTW "J" POTW "K" POTW "L" POTW "D" POTW "E" POTW "I" POTW "H" POTW "F" POTW "G"Biosolids Mercury Concentration, mg/kg (dry)

0 1000 2000 3000 4000 5000 6000 7000 8000Persons per Square Mile Biosolids Hg Population Density

Figure 4.12C: Biosolids Mercury Co ncentration and Population Density

### 79 4.13 C OMBINED OR 

### S EPARATE 

### C OLLECTION 

### S YSTEMS



### Mercury concentrations at POTWs with combined collection systems were compared to those with separate collection systems. As show n in Figures 4.13A through 4.13C, there was not a clear difference between those areas with combined sewers versus thos e with separate sewers.

0 250 500 750 1000Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "K" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "L"Influent Mercury Concentration, ng/L Combined Sewer Systems Separate Sewer Systems

Figure 4.13A: Influent Mercury Concentrations and Sewer System Type

### 80 0 10 20 30 40 50 60 70Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "K" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "L"Effluent Mercury Concentration, ng/L Combined Sewer Systems S eparate Sewer Systems

Figure 4.13B: Effluent Mercury Con centrations and Sewer System Type

0 0.5

1 1.5

2 2.5

3 3.5

4 4.5

5Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06Jan-04Jul-04Jan-05Jul-05Jan-06Jul-06

POTW

"A" POTW "B" POTW "C" POTW "D" POTW "E" POTW "K" POTW "F" POTW "G" POTW "H" POTW "I" POTW "J" POTW "L"Biosolids Mercury Concentration, mg/kg (dry) Combined Sewer Systems S eparate Sewer Systems

Figure 4.13C: Biosolids Mercury Co ncentrations and Sewer System Type

### 81 

## 5. S UMMARY AND 

## C ONCLUSIONS



### An objective of this study was to examine the e ffect of practical and reasonable measures of controlling significant sour ces of mercury to the POTW collection system, such as installing dental amalgam separators, on the ability of POTWs to comply with anticipated effluent limitations. Mercury levels at various POTWs we re monitored for a three-year period. These levels were then compared to amalgam separato r use in the treatment plant’s service area and various other factors to determine which were most strongly related.

Collectively, the influent merc ury concentrations at the POTW s in the study were found to be highly variable, ranging from 14 ng/L to 3080 ng/L. When considering facilities individually, some exhibited decreases in their influent me rcury concentrations ove r the course of the sampling project, while others ha d apparent increases. Effluent mercury concentrations also exhibited variability between plan ts but less variability within plants. For six-month periods, median effluent mercury concentrations were as low as 1.4 ng/L and as high as 45.15 ng/L. For the biosolids, there was variab ility both within and among the plants. For six-month periods, median biosolids concentrations were as low as 0.1 mg/kg and as high as 2.5 mg/kg.

For the most part, the mercury removal efficiency from influent to effluent was relatively the same at each of the treatment plants and gene rally greater than 90%. While the POTWs were similar in this aspect, in other ways they were no t. For instance, the percent of effluent mercury that was dissolved was found to vary based on the POTW. The highest median effluent dissolved mercury percentage occurred at POTW “G” (59%), while the lowest was at POTW “A” (22%). Additionally, at eigh t of the POTWs, there appeared to be a direct relationship between effluent mercury concentration and effl uent TSS concentration while, at the remaining four POTWs, this relationshi p did not appear to exist. It is unclear as to why effluent TSS concentrations appear to be a good predictor of effluent mercury concentrations at some POTWs but not at others.

Since a primary an objective for this study was to determine whet her the installa tion of amalgam separators in dentists’ offices impacts mercury concentrations at treatment plants, it was first demonstrated that the mercury discharged by de ntists impacts the amounts of mercury observed at the plants. Collectively, the study results indica te that the presence of dentists in a POTW’s collection system influences mercur y concentrations at the plant. An increase in dentists per flow was significantly related to higher influent and effluent me rcury concentrations. There was no relationship, however, between numbers of den tists and biosolids mercury concentrations. This may be due to amalgam separators being installed by dentists in many of the POTWs’ service areas.

It was found that, collectively, an increase in the number of dentis ts without amalgam separators installed resulted in higher bi osolids mercury, indicating that amalgam separators could be reducing biosolids mercury concentrations. Howe ver, at individual plants, the installation of separators did not always lead to a decrease in biosolids mercury c oncentrations. It may be that the amalgam separator insta llation alone is not enough to result in permanent mercury reductions. Some of the plants that showed decr eases in mercury also have programs in place to ensure that the separators are well operated a nd maintained. It is al so possible that, on an

### 82 individual-facility basis, appare nt reductions or the lack thereo f could be the result of other impacting factors such as previous elevated loadings relate d to sewer cleaning, construction activities, or historic depositions of mercury in the collection system.

Effluent mercury concentrations were found to d ecrease at several POTWs as the percentage of dentists with amalgam separato rs increased. The POTWs that exhibited reductions all had relatively high effluent concentrations at the start of the study. It is possible that there were also reductions at the other POTWs, but these reducti ons were too small to be distinguished due to plant variability. Collectively, there was a negative correlation between the numbe r of dentists without separators per flow and effluent mercury concentration. This may partly be a result of the limited number of amalgam separator insta llations that occurred at the POTWs that had generally lower effluent mercury concen trations at the study’s outset.

In addition, based mostly on the results from POTW “I,” where 93% of the dental facilities had dental amalgam separators installed up to two ye ars prior to the start of the study, it may be hypothesized that mercury reductions following separa tor installations can take several years or even longer to demonstrate significa nt trends. If so, this is likel y due to the amount of time that is necessary to flush accumulated amalgam partic les from the collection system. The timeframe of this study may not have been long enough to determine significant trends for POTWs whose dental facilities were in the process of installing amalgam sepa rators during the course of the study.

It should also be noted that some of the treatme nt plants exhibited reductions even without an increase in amalgam separator installation. Th ese reductions may have come from changes in treatment processes or the implementation of BMPs . Therefore, on a facility-specific basis, the effectiveness of amalgam separato rs in reducing mercury should be examined in light of other activities that are occurring within the POTW an d its service area to dete rmine which factors are actually contributing to an observed reduction.

In addition to the presence of de ntists within a POTW’s collec tion area, several other factors were found to exhibit relationships with mercury levels at treatment plants. Those POTWs that use iron salts and those that disc harge to freshwater systems were generally found to have lower effluent mercury concentrations than those that did not. Iron sa lts such as ferric chloride are typically used at wastewater treatm ent facilities as flocculants to in crease settling; therefore, it is possible that iron salts lead to increased amounts of mercury se ttling out of the wastewater.

Based on individual results found at POTW “A” and PO TW “B”, sewer cleaning projects can have significant effects on bios olids mercury levels and poten tially on influent and effluent mercury levels. This is because sewer cleaning li kely resuspends particle s that have settled in the sewer collection system, enabling th em to migrate to the POTWs.

Effluent and biosolids mercury c oncentrations at a treatment plan t were also found to be related to industrial flow, although the st atistical significance of this re lationship was less than for other factors. An increase in the pe rcent of non-industrial flow to a pl ant mostly resulted in increasing mercury levels. This likely refl ects the fact that industrial fl ow generally has lower mercury

### 83 concentrations than other types of collection system flow and theref ore, when it is present, tends to dilute wastewater mercury from other sources.

Other factors that were examined but not found to be related to mercury levels were plant flow, population density, whether the POTW accepts ha uled-in wastes, and whether the collection system is comprised of combined or separate sewers.

Overall, the results of this study indicate th at many factors, not ju st amalgam separators, influence mercury concentrations. Therefore, a facility cannot predict with certainty that amalgam separators will decrease mercury conc entrations without also exploring the other potential contributors to current mercury levels. Without this, th e benefits resulting from dental amalgam separator installation canno t be reliably predicted. Each facility must look at its own individual conditions to determ ine the potential benefit of am algam separator installation. Additionally, it should be noted that, even in those POTWs with dem onstrably successful amalgam separator programs, effluent merc ury concentrations were not low enough to consistently meet current and imminent efflue nt limits faced by some POTWs (e.g., 1.3 ng/L in the Great Lakes).

While installing amalgam separators does not generally appear, at least within the timeframe of this study, to significantly reduce effluent me rcury concentrations, a resulting reduction in biosolids mercury concentrations does appear to be likely according to th e results. The data collected during the study do support a conclusion that the use of separa tors can decrease the amount of particulate mercury en tering POTWs, there by decreasing the amount of mercury that would be removed by plant processes and deposited in the biosolids.



## 6. I MPLICATIONS FOR 

## F URTHER 

## R ESEARCH



### Evaluations of the data resulti ng from this study have revealed several implications for further research. The apparent gaps, if filled, may lead to a better understanding of mercury at POTWs and the effects of installing amalgam separators . Additional work could be conducted by using the data that was collected dur ing the sampling project and suppl ementing it with additional data and information collection.

Only limited dissolved mercury analysis was c onducted during the sampling project. Further quantification of dissolved mercury levels would lead to a be tter understanding of the relative levels of particulate mercury verses dissolved me rcury. This would be he lpful since, at this point, it appears that amalgam separators mostly influence particulate mercury.

This sampling project indicates that the results of influent sampling for mercury concentrations at POTWs is highly variable with in each facility as well as be tween facilities. It has been suggested that influent loading, enabling an analysis of the over all quantity of mercury entering a POTW regardless of flow, would be a more usef ul indicator of the e ffectiveness of amalgam separator installation. However, the amount of data collected during the sampling project was too limited to address the influent variability and therefore beli eved to be not robust enough for

### 84 influent loading calculations to provide insight. More influent data could be collected that would enable in-depth examinations of influent loadin gs, including day-to-day and seasonal variability and the potential effects of wate r conservation activities.

In addition, biosolids loadings c ould not be determined with the information collected from the POTWs during the study. Further information collection that includes biosolids generation and/or disposal quantities would allow for the calculation of these loadings. While amalgam separators may not enable faciliti es to meet part-per-trillion-leve l effluent limits, they are likely reducing the overall loading to the POTW as re flected in biosolids mercury concentrations. Considering the interfacility differences in biosol ids characteristics, calculations of biosolids loadings would be a better measure than con centrations and could confirm this. It is hypothesized that the observed significance of the relationship between dental amalgam separator installation and biosolid s mercury levels could be impr oved even further if loadings were evaluated instead of concentrations. Such further evaluation may be possible with existing data and is therefore highly recomme nded as an addendum to this study.

This sampling project indicates a clear differenc e in effluent mercury concentrations between facilities that discharge to freshw aters and facilities that discharge to marine environments. The possible reason(s) for this, includi ng the use of iron salts, should be further explored. Looking at NPDES permit limits for parameters could prov ide some insight. However, often POTWs provide a higher level of treatment than what is required by NPDES permits; therefore, it is likely to be more useful to look at actual discharge concentrations.

Each POTW in the study provide d a list of chemicals used fo r treatment of wastewater. However, only limited information is currently ava ilable regarding the merc ury concentrations in the chemicals used at these part icular facilities. Previous unp ublished work by some POTWs in the study has indicated that the mercury concentr ations in such chemicals typically constitute negligible contributions to PO TW effluent and biosolids merc ury concentrations, but further research in this area is wa rranted. If, for example, chem ical addition associated with chlorination/dechlorination at a pa rticular treatment plant is found to potentially impact effluent mercury concentrations, a comparison between effl uent samples collected before dechlorination and those collected after dechlo rination could be necessary.

Each POTW in the study collect ed its own influent, effluent, and biosolids samples. Some facilities collected manual sample s, while other facilities used automatic samplers. Samples were also either grab samples or composite sa mples (both time- and flow-paced). The potential effect of these varying sampling techniques on the data is uncertain. A comparison of the different techniques may be warranted in the future , or further research may require all facilities to use the same sampling method.

It is also possible that temporal differences exist within the da ta. Further data collection and analysis could be conducted to establish whether s easonal, daily or hourly differences exist in the mercury concentrations in POTW influent, effluent, and biosolids.

### 85 No comparisons were made between the data coll ected from this study and other projects. By doing so, a more complete picture of mercury flux at POTWs could be seen. It may also clarify whether the variability that was seen in this pr oject is common to mercury sampling in general.

Finally, this sampling project clea rly warrants follow-up sampling a nd data analysis. It would be useful to examine mercury levels at each of the studied POTWs in the future to determine whether trends seen in the current study have continued or whether trends not previously apparent have developed. In a ddition, the results from future sampling could also be compared with how well amalgam separators are operated and maintained to establish the extent to which this may be a key factor for continuing mercury reductions.

### A



# A PPENDIX 

# A: D ATA

### Appendix A: POTW “A” A

87 Biosolids

Sam p le

Date Flow (MGD) TR H g (ng/L) TSS (mg/L) TR H g (ng/L) Dissolved Hg (ng/L) Turbidit y (NTU) TSS (mg/L) H g (mg/kg, dry) 7/15/2003 42 232 157 8.6 4.8 n/a 8 1.2 8/29/2003 39 126 137 9.5 2 8 3.1 9/24/2003 39 73.7 137 11.9 2.6 8 1.1 10/8/2003 35 63.2 102 9.4 9 1.1 11/18/2003 36.44 257 219 16.7 14 1.6 12/16/2003 56.73 137 106 15.6 15 1.1 1/13/2004 44.05 297 183 10.1 10 1.0 2/12/2004 39.81 247 161 12.6 14 1.0 3/10/2004 37.96 3080 641 19.3 44 2.3 4/21/2004 54.19 77.7 173 11.7 7 1.3 5/12/2004 46.91 117 260 9.3 10 0.9 6/16/2004 38.32 130 265 8.6 7 0.9 7/21/2004 37.16 146 214 13.6 16 0.7 8/10/2004 36.38 103 291 8.9 17 1.8 9/15/2004 40.57 103 211 10.9 16 0.6 10/13/2004 38.9 107 185 7.8 5 1.0 11/16/2004 43.97 220 135 15 24 1.1 12/15/2004 51.83 85.5 138 17.6 35 0.99 1/27/2005 46.78 82.3 140 7.4 18 0.808 2/22/2005 54.97 211 119 7.1 10 1.168 3/17/2005 49.69 61.1 182 14 0.765 4/19/2005 50.12 119 139 7.9 <1.0 14 0.8035 5/25/2005 73.09 146 128 15.2 2.9 15 1.1165 6/22/2005 43.35 231 6.8 2.2 13 1.0895 7/26/2005 38.88 229 257 7.8 12 0.828 8/30/2005 72.51 369 134 10.7 13 0.784 9/28/2005 37.88 125 263 17 0.9165 10/5/2005 37.29 663 221 11.0 25.0 0.984 11/9/2005 81.96 264 194 14 45 0.657 12/13/2005 47.5 71.9 127 8.4 21 1.116 1/10/2006 49.64 81.4 137 5.7 21 0.519 2/7/2006 63.77 203 94 7.5 12 0.935 3/28/2006 38.95 153 167 12.2 14 2.327 4/18/2006 38.52 189 153 1.4 9 2.067 5/23/2006 54.09 88.9 139 5.5 1.1 14 1.002 6/27/2006 78.79 68.6 71 4.9 1.2 11 Effluent Influent

Percent of Dental Facilities/Dentists Operating Dental Amalgam Separators

July 1, 2003 0 January 1, 2004 0 July 1, 2004 0 January 1, 2005 98 July 1, 2005 100 January 1, 2006 100 July 1, 2006 100

### Appendix A: POTW “A”

88 Influent Mercur y EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity n/a Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “B”

89 Sample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR Hg ( n g /L ) Dissolved H g ( n g /L ) Turbidity ( NTU ) TSS ( m g /L ) 07/09/03 181 46.4 166 3.50 1.06 12 08/07/03 88 26.3 126 1.56 0.92 1 09/04/03 87 415 130 1.83 0.89 2 10/02/03 96 218 69 3.86 1.05 2.95 2 11/06/03 82.4 193 136 3.75 1.16 9.02 3 12/03/03 99 286 83 2.91 0.515 2.5 3 01/08/04 104 24.3 87 3.34 0.927 5.88 4.1 02/05/04 104 15.9 59 2.48 1.05 3.4 7 03/04/04 133 50.2 110 1.84 1 2 2.5 04/06/04 114 64.2 140 4.73 1.06 3.01 4.3 05/06/04 106 47.8 174 3.18 1.07 2.07 4 06/03/04 95 69.8 100 2.33 0.916 1.99 2 07/07/04 106 79.6 110 2.42 0.978 2.24 1.7 08/05/04 104 238 165 2.55 1.02 2.24 2.6 09/13/04 72 82.7 159 7.11 1.23 7.03 8 10/07/04 66 75.4 135 3.47 1.07 11.1 4 11/10/04 77 106 112 2.06 0.805 1.4 3 12/08/04 84 54.8 119 2.11 0.82 1.28 1 01/05/05 206 49 60 3.23 0.95 1.99 3 02/02/05 95 33.8 83 2.56 0.933 2.01 7 03/03/05 104 80.3 185 5.79 0.93 3.52 8 04/06/05 120 116 80 1.68 0.98 1.55 1 05/03/05 113 91.5 116 3.50 1.06 4.86 3 06/13/05 98 365 123 1.40 0.777 0.95 1 07/07/05 77 59.5 99 1.64 0.971 1 2 08/03/05 89 184 110 2.24 0.97 1.26 1 09/13/05 78 236 172 2.47 0.9 0.91 1 10/05/05 75 448 150 2.88 1 1.37 2 11/02/05 75 51 108 3.75 1 2.1 4 12/08/05 83 90.5 121 2.90 1.09 1.87 4 01/12/06 86 21.8 58 2.51 84 1.28 2 02/09/06 100 37.35 55 2.49 0.96 2.8 4 03/06/06 69 225 503 3.34 1.78 2.56 3 4/6/2006 69 91.15 93 2.77 0.93 2.2 3 5/3/2006 64 45.15 91 2.08 1.08 2.14 5 6/7/2006 67 277 102 3.26 1.24 2.65 3 Influent Effluent

### Appendix A: POTW “B”

90 Sample

Date H g (mg/kg, dry) Sample Date H g (mg/kg, dry) Sample Date H g (mg/kg, dry) Sample Date H g (mg/kg, dry) 07/01/03 1.7 8/3/2004 0.57 8/2/2005 0.88 11/1/2005 1.11 07/08/03 2.1 8/10/2004 1.11 8/9/2005 4.96 11/8/2005 2.30 07/15/03 0.9 8/17/2004 2.09 8/16/2005 1.93 11/15/2005 1.07 07/22/03 1.6 8/24/2004 1.25 8/21/2005 3.30 11/22/2005 0.46 08/05/03 0.5 8/31/2004 0.91 8/22/2005 3.09 11/29/2005 2.27 08/12/03 1.0 9/7/2004 0.36 8/23/2005 2.22 12/6/2005 0.36 08/19/03 0.2 9/14/2004 0.49 8/24/2005 2.60 12/11/2005 0.35 08/26/03 0.9 9/21/2004 0.88 8/25/2005 2.05 12/12/2005 0.31 09/02/03 1.9 9/28/2004 1.55 8/26/2005 2.69 12/13/2005 0.58 09/09/03 1.6 10/5/2004 0.56 8/27/2005 5.10 12/14/2005 0.38 09/16/03 1.3 10/12/2004 0.55 8/28/2005 5.22 12/15/2005 0.36 09/23/03 2.5 10/19/2004 1.74 8/29/2005 4.51 12/20/2005 0.53 09/30/03 0.8 10/26/2004 0.42 8/30/2005 1.87 12/27/2005 0.30 10/07/03 0.9 11/2/2004 0.47 9/1/2005 4.78 1/3/2006 0.56 10/14/03 0.1 11/9/2004 1.07 9/2/2005 3.00 1/24/2006 0.14 10/21/03 0.5 11/16/2004 0.42 9/3/2005 2.00 2/7/2006 0.61 10/28/03 0.7 11/23/2004 0.56 9/4/2005 1.75 2/14/2006 0.91 11/04/03 0.74 11/30/2004 1.00 9/5/2005 2.60 2/21/2006 38 11/11/03 0.70 12/7/2004 0.46 9/6/2005 5.02 2/28/2006 25.25 11/18/03 0.70 12/14/2004 0.51 9/7/2005 3.45 3/7/2006 1.76 11/25/03 0.70 12/21/2004 0.44 9/8/2005 14.02 3/14/2006 1.39 12/02/03 0.40 12/28/2004 0.70 9/9/2005 2.60 3/21/2006 0.56 12/09/03 0.37 1/11/2005 0.65 9/10/2005 10.68 3/28/2006 0.59 12/16/03 0.56 1/18/2005 0.73 9/11/2005 1.62 04/02/06 4.39 12/23/03 1.49 1/25/2005 0.30 9/12/2005 2.73 04/03/06 0.57 12/30/03 0.45 2/1/2005 0.36 9/13/2005 3.17 04/04/06 0.43 01/06/04 0.42 2/8/2005 1.32 9/14/2005 2.67 04/05/06 1.25 01/13/04 0.28 2/15/2005 1.12 9/15/2005 3.58 04/06/06 0.42 01/20/04 0.60 2/22/2005 0.44 9/16/2005 1.24 04/11/06 0.66 01/27/04 0.27 3/1/2005 0.97 9/17/2005 1.13 04/18/06 1.46 02/03/04 0.40 3/8/2005 0.77 9/18/2005 1.19 04/23/06 0.12 02/10/04 0.30 3/15/2005 0.65 9/19/2005 0.88 04/24/06 0.46 02/17/04 0.42 3/22/2005 0.36 9/20/2005 1.43 04/25/06 0.37 02/24/04 0.59 3/29/2005 0.72 9/21/2005 5.21 04/26/06 0.11 3/2/2004 0.36 4/5/2005 0.42 9/22/2005 1.61 04/27/06 0.30 3/9/2004 0.28 4/12/2005 0.81 9/23/2005 1.69 04/28/06 0.18 3/16/2004 0.29 4/19/2005 1.54 9/24/2005 2.15 04/29/06 0.26 3/23/2004 0.18 4/26/2005 0.50 9/25/2005 1.48 5/2/2006 0.46 3/30/2004 0.45 5/3/2005 0.88 9/26/2005 1.83 5/9/2006 0.38 4/6/2004 0.33 5/10/2005 1.45 9/27/2005 1.96 5/16/2006 0.25 4/13/2004 0.71 5/17/2005 0.48 9/28/2005 2.49 5/21/2006 1.64 4/20/2004 0.62 5/24/2005 0.64 9/29/2005 5.27 5/22/2006 0.46 4/27/2004 0.55 5/30/2005 0.54 9/30/2005 4.00 5/23/2006 0.43

5/4/2004 0.30 6/7/2005 1.44 10/1/2005 2.83 5/24/2006 0.73 5/11/2004 0.29 6/14/2005 5.54 10/2/2005 2.32 5/25/2006 0.41 5/18/2004 0.63 6/14/2005 3.56 10/3/2005 1.32 5/26/2006 0.67 5/25/2004 0.67 6/14/2005 3.76 10/4/2005 1.81 5/27/2006 0.57

6/1/2004 0.38 6/15/2005 1.51 10/5/2005 2.61 5/30/2006 0.81 6/8/2004 0.86 6/16/2005 2.50 10/6/2005 1.74 6/6/2006 1.07 6/15/2004 0.73 6/17/2005 18.49 10/7/2005 1.88 6/13/2006 0.80 6/22/2004 0.63 6/18/2005 0.45 10/8/2005 2.68 6/18/2006 0.59 6/25/2004 0.5 6/19/2005 5.61 10/9/2005 2.70 6/19/2006 0.54 6/26/2004 0.99 6/21/2005 0.90 10/10/2005 2.24 6/20/2006 0.34 6/27/2004 0.84 6/28/2005 2.27 10/11/2005 2.64 6/21/2006 0.73 6/29/2004 0.40 7/5/2005 1.17 10/12/2005 5.32 6/22/2006 0.66 7/14/2004 0.60 7/13/2005 0.88 10/13/2005 2.94 6/23/2006 0.68 7/21/2004 0.31 7/20/2005 4.96 10/18/2005 3.72 6/24/2006 6.11 7/28/2004 2.27 7/27/2005 1.93 10/25/2005 3.11 6/27/2006 0.57 Biosolids Biosolids Biosolids Biosolids

### Appendix A: POTW “B”

91 Percent of Dental Facilities Operating Dental Amalgam Separators

July 1, 2003 5 January 1, 2004 6 July 1, 2004 7 January 1, 2005 8 July 1, 2005 9 January 1, 2006 9 July 1, 2006 9

Influent Mercury EPA 1631, Rev. E Effluent Mercury EPA 1631, Rev. E Biosolids Mercury EPA 245.1 Effluent Turbidit y 2130B (Std. Methods 18th Ed.) Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “C”

92 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR Hg (ng/L) D i ssolved Hg (ng/L) Turb i d i ty (NTU) T SS (mg/L) 07/09/03 40.8 18.5 102 2 0.86 6 08/07/03 23.4 54.6 116 2.01 1.33 4 09/04/03 23.7 44.9 123 1.97 0.9 4 10/02/03 33.2 58.5 75 2.92 0.894 3.99 3 11/06/03 20.6 185 189 3.47 1.04 3.33 4 12/03/03 25.5 46.6 83 3.72 1.27 3.96 5 01/08/04 27.8 50.0 77 3.16 1.04 5.46 3.9 02/05/04 27.4 29.6 84 3.24 1.12 3.2 5 03/04/04 36.1 29.7 111 2.68 0.967 3.18 4.8 04/06/04 31.2 62.4 146 3.45 1.26 3.35 4 05/06/04 28.9 23.6 110 0.51 0.415 2.47 4 06/03/04 25.4 37.2 85 2.61 1.06 3.14 3 07/07/04 24.3 34.75 80 1.94 0.973 1.58 2.9 08/05/04 23.3 80 117 2.70 1.16 1.99 1.8 09/13/04 22.4 57 88 1.80 0.97 2.14 2 10/07/04 19.9 115 119 2.15 1 2.66 3 11/10/04 19.1 78.7 129 2.85 1.01 1.9 2 12/08/04 23.4 42.7 67 2.98 0.94 3.3 5 01/05/05 77.8 39.8 54 4.52 0.86 3.44 5 02/02/05 24.1 62.1 90 1.88 0.892 3.86 5 03/03/05 27.5 42.6 110 2.60 0.78 4.23 8 04/06/05 28.9 49.5 68 2.02 0.96 2.89 4 05/03/05 28.3 23.7 71 2.24 0.86 3.43 5 06/13/05 27.9 137 117 1.65 0.851 2.1 4 07/07/05 20 177.5 291 2.12 1 1.26 3 08/03/05 20.6 481 70 1.36 0.78 1.31 4 09/13/05 20.8 51.5 250 1.61 0.98 1.73 2 10/05/05 19.5 72.2 146 2.29 1.07 2.06 4 11/02/05 21.1 62.3 123 1.98 0.85 2 4 12/08/05 20.1 38.1 119 2.45 1.3 3.09 5 01/12/06 22.1 60.9 82 2.43 0.95 2.68 6 02/09/06 24.5 37.3 60 3.22 0.92 3.3 8 03/06/06 19.4 27 90 2.34 0.82 4.05 6 04/06/06 19.9 32.8 68 2.74 1.05 2.3 4 5/3/2006 18.3 41.55 92 2.32 1.2 2.37 6 6/7/2006 19.2 79 103 3.48 1.38 2.38 4 Influent Effluent

### Appendix A: POTW “C”

93 S am p le

Date H g (mg/kg, dry) S am p le Date H g (mg/kg, dry) S am p le Date H g (mg/kg, dry) S am p le Date H g (mg/kg, dry) 07/07/03 0.6 03/15/04 0.5 12/13/2004 0.5 9/12/2005 0.6 07/14/03 0.6 03/22/04 0.7 12/20/2004 0.4 9/19/2005 0.8 07/21/03 2.2 04/05/04 0.4 12/27/2004 0.8 9/26/2005 0.85 08/04/03 1.1 04/12/04 0.6 1/3/2005 0.5 10/10/2005 1.61 08/11/03 0.7 04/19/04 0.6 1/10/2005 0.5 10/17/2005 0.58 08/18/03 0.5 04/26/04 0.8 1/17/2005 0.4 10/24/2005 1.13 08/25/03 1.5 05/03/04 0.5 1/24/2005 0.4 11/7/2005 0.68 09/01/03 1.3 05/10/04 0.5 2/7/2005 0.8 11/14/2005 0.46 09/08/03 0.9 05/17/04 0.7 2/14/2005 0.4 11/21/2005 0.62 09/15/03 0.6 05/24/04 0.7 2/21/2005 0.4 11/29/2005 0.82 09/22/03 1.2 5/31/2004 0.8 3/7/2005 0.5 12/5/2005 0.75 09/29/03 0.9 6/7/2004 0.3 3/14/2005 0.4 12/12/2005 0.57 10/06/03 0.9 6/14/2004 0.5 3/21/2005 0.8 12/19/2005 0.47 10/13/03 0.6 6/22/2004 0.6 3/28/2005 0.4 12/26/2005 0.34 10/20/03 0.6 7/5/2004 0.6 4/11/2005 0.4 1/2/2006 0.49 10/27/03 0.6 7/19/2004 0.8 4/11/2005 0.4 1/16/2006 0.74 11/03/03 0.7 7/26/2004 0.6 4/18/2005 0.4 1/23/2006 0.59 11/10/03 0.8 8/2/2004 0.8 4/25/2005 0.3 2/6/2006 0.7 11/17/03 0.7 8/9/2004 0.7 5/2/2005 0.4 2/13/2006 0.48 11/24/03 1.1 8/16/2004 0.5 5/9/2005 0.4 2/20/2006 1.14 12/01/03 0.7 8/23/2004 1.1 5/16/2005 0.9 3/6/2006 0.43 12/08/03 0.4 9/6/2004 0.5 5/23/2005 0.4 3/13/2006 0.4 12/15/03 0.3 9/13/2004 0.8 6/6/2005 0.7 3/20/2006 0.56 12/22/03 0.9 9/20/2004 0.9 6/13/2005 0.73 3/27/2006 0.48 12/29/03 1.3 9/27/2004 0.6 6/20/2005 0.88 4/3/2006 0.85 01/05/04 0.8 10/4/2004 0.7 7/4/2005 0.5 4/10/2006 0.68 01/12/04 0.2 10/11/2004 1.0 7/11/2005 0.9 4/24/2006 0.56 01/19/04 0.7 10/18/2004 0.5 7/18/2005 0.8 5/1/2006 0.5 01/26/04 0.5 10/25/2004 0.9 7/25/2005 1.2 5/8/2006 0.79 02/02/04 0.4 11/1/2004 0.5 8/1/2005 1.1 5/15/2006 0.57 02/09/04 0.5 11/8/2004 0.5 8/8/2005 0.5 5/22/2006 0.52 02/23/04 0.5 11/15/2004 0.5 8/15/2005 0.8 6/19/2006 3.2 03/01/04 0.7 11/22/2004 0.6 8/22/2005 1.1 6/26/2006 1.01 03/08/04 0.2 12/6/2004 0.5 9/5/2005 1.0 Biosolids Biosolids Biosolids Biosolids

### Appendix A: POTW “C”

94 Percent of Dental Facilities Operating Dental Amalgam Separators

July 1, 2003 6 January 1, 2004 6 July 1, 2004 6 January 1, 2005 6 July 1, 2005 6 January 1, 2006 6 July 1, 2006 6

Influent Mercury EPA 1631, Rev. E Effluent Mercury EPA 1631, Rev. E Biosolids Mercur y SW-846 7471A Effluent Turbidity 2130B (Std. Methods 18th Ed.) Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “D”

95 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S ample Date Hg ( m g /k g , dr y) 9/17/2003 64 230 420 2.1 n/a n/a NA 9/8/2003 2 10/6/2003 71 160 310 2.0 7.0 10/6/2003 0.8 11/5/2003 193 322 260 3.1 7.5 11/3/2003 0.9 12/2/2003 77 97 360 1.8 5.5 12/8/2003 1.2 1/12/2004 83 230 230 2.2 4.0 1/7/2004 1.4 2/4/2004 85 220 310 2.1 12 2/2/2004 1.6 3/3/2004 158 100 160 3.2 6.5 3/1/2004 0.9 4/7/2004 114 210 300 5.2 8.4 4/6/2004 1.6 5/5/2004 94 240 270 1.8 3.2 5/3/2004 2.1 6/7/2004 115 480 240 1.1 2.0 6/7/2004 0.035 7/14/2004 116 100 380 1.3 2.6 7/7/2004 1.2 8/2/2004 83 110 240 1.5 2.8 8/2/2004 1.3 9/8/2004 74 250 280 2.0 5.8 9/7/2004 1.2 10/13/2004 70 180 340 2.8 5.6 10/4/2004 2.4 11/3/2004 86 380 NA 2.9 NA 11/1/2004 2.1 12/7/2004 139 620 250 2.4 22 12/6/2004 2 1/12/2005 122 250 240 1.8 15 1/3/2005 0.7 2/1/2005 73 220 280 1.5 3.8 2/8/2005 1.3 3/7/2005 180 220 88 2.0 5.6 3/7/2005 0.7 4/11/2005 118 100 200 2.5 6.6 4/4/2005 1.4 5/9/2005 72 84 210 1.6 6.2 5/2/2004 0.7 6/8/2005 78 110 390 1.7 5.0 6/6/2005 0.6 7/6/2005 73 89 170 1.5 3.0 7/5/2005 2.1 8/1/2005 70 57 320 1.6 4.6 8/1/2005 1.2 9/1/2005 78 130 590 1.9 7.4 9/6/2005 2 10/3/2005 74 190 340 1.5 6.3 10/3/2005 2.7 11/2/2005 64 150 650 2.7 10 11/7/2005 0.7 12/1/2005 88 51 350 1.7 5.6 12/5/2005 2.6 1/16/2006 90 84 250 1.5 7.0 1/3/2006 0.7 2/15/06 80 130 220 1.4 4.8 2/6/2006 1 3/8/06 97 100 190 1.7 6.2 3/6/2006 0.80 4/4/06 259 14 64 5.5 20 4/3/2006 1.20 5/4/06 100 160 120 2.5 5.8 5/1/2006 1.10 6/7/2006 85 110 300 1.7 5.2 6/5/2006 1.6 Effluent Biosolids Influent

Percent of Dental Facilities Operating Dental Amalgam Separators

July 1, 2003 0.6 January 1, 2004 1.5 July 1, 2004 6.1 January 1, 2005 16 July 1, 2005 26 January 1, 2006 32 July 1, 2006 38

### Appendix A: POTW “D”

96 Influent Mercur y SW-846 7470A Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity n/a Influent TSS 160.2 (EPA 600/4-79-020) Effluent TSS 160.2 (EPA 600/4-79-020) Analytical Methods

### Appendix A: POTW “E”

97 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S ample Date H g (mg/kg, dry) 9/17/2003 74 87 230 3.0 2.5 9/7/2003 0.43 10/6/2003 66 62 220 2.1 3.5 10/5/2003 0.33 11/5/2003 146 231 280 3.3 5.5 11/2/2003 0.41 12/2/2003 70 24 340 1.5 5.5 12/7/2003 0.29 1/12/2004 76 38 280 1.7 5.5 1/4/2004 0.37 2/4/2004 74 72 340 2.7 7.0 2/1/2004 0.43 3/3/2004 75 72 200 2.0 5.5 3/7/2004 0.36 4/7/2004 81 54 270 2.2 5.2 4/14/2004 0.4 5/5/2004 80 100 250 1.9 6.0 5/2/2004 0.27 6/7/2004 93 220 1.2 5.6 6/6/2004 0.5 7/14/2004 114 140 290 2.6 7.4 7/4/2004 0.31 8/2/2004 79 120 240 1.4 5.4 8/1/2004 0.31 9/8/2004 78 230 310 2.1 3.2 9/5/2004 0.35 10/13/2004 68 440 1.8 5.4 10/3/2004 0.25 11/3/2004 63 70 NA 2.0 NA 11/7/2004 0.45 12/7/2004 153 60 150 3.7 11 12/5/2004 0.23 1/12/2005 183 150 260 2.5 11 1/2/2005 0.17 2/1/2005 70 120 260 2.2 7.8 2/6/2005 0.3 3/7/2005 117 85 220 1.4 7.4 3/6/2005 0.13 4/11/2005 85 100 200 1.4 4.8 4/3/2005 0.6 5/9/2005 86 110 420 1.3 7.4 5/1/2005 0.33 6/8/2005 96 84 220 1.4 3.6 6/5/2005 0.23 7/6/2005 72 74 260 2.5 5.6 7/3/2005 0.35 8/1/2005 67 64 26 1.7 6.6 8/7/2005 0.24 9/1/2005 57 67 410 1.5 7.0 9/4/2005 0.29 10/3/2005 61 370 230 1.9 4.6 10/2/2005 0.21 11/2/2005 64 52 320 2.1 6.8 11/6/2005 0.26 12/1/2005 68 110 250 2.8 6.4 12/4/2005 0.39 1/16/2006 59 47 400 1.7 6.2 1/15/2006 0.31 2/15/06 76 66 250 1.9 5.6 2/19/2006 0.39 3/8/06 99 140 390 1.4 9.2 3/19/2006 0.38 4/4/06 241 76 170 2.8 9.4 4/16/2006 0.4 5/4/06 74 100 92 1.2 2.0 5/21/2006 0.25 6/7/2006 73 87 370 3.7 5.6 6/18/2006 0.31 Effluent Biosolids Influent

Percent of Dental Facilities Operating Dental Amalgam Separators

July 1, 2003 0.6 January 1, 2004 1.5 July 1, 2004 6.1 January 1, 2005 16 July 1, 2005 26 January 1, 2006 32 July 1, 2006 38

### Appendix A: POTW “E”

98 Influent Mercury SW-846 7470A Effluent Mercur y EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity n/a Influent TSS 160.2 (EPA 600/4-79-020) Effluent TSS 160.2 (EPA 600/4-79-020) Analytical Methods

### Appendix A: POTW “F”

99 S am p le

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S am p le Date TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S am p le Date H g (mg/kg, dry) 3/2/2004 41.18 253 287 3/2/2004 2.16 4.4 3/1/2004 1.014 4/6/2004 39.57 211 271 4/6/2004 1.58 4.3 4/1/2004 1.149 5/4/2004 40.24 314 255 5/4/2004 2.89 4.7 5/1/2004 1.225 6/1/2004 52.98 210 280 6/1/2004 1.55 3.8 6/1/2004 1.884 7/13/2004 46.43 213 247 7/7/2004 2.64 5.2 7/1/2004 1.652 8/4/2004 52.39 209 252 8/3/2004 1.72 4.7 8/1/2004 1.547 9/8/2004 42.95 164 251 9/7/2004 1.54 6.1 9/1/2004 1.467 10/5/2004 41.02 319 10/5/2004 2.33 6.4 10/1/2004 1.446 11/16/2004 39.62 176 350 11/2/2004 3.06 5.4 11/1/2004 1.62 12/7/2004 44.34 142 296 12/14/2004 2.8 7.6 12/1/2004 1.164 1/4/2005 39.07 227 235 1/11/2005 1.92 5.4 1/1/2005 1.526 2/1/2005 39.41 173 248 2/1/2005 1.95 4.5 2/1/2005 1.09 3/1/2005 40.54 149 231 3/8/2005 2.2 4.4 3/1/2005 1.148 4/5/2005 41.74 74.7 252 4/12/2005 2.04 4.8 4/1/2005 2.236 5/3/2005 40.33 246 251 5/10/2005 2.32 4 5/1/2005 1.058 6/7/2005 41.78 136 245 6/7/2005 1.97 4.1 6/1/2005 1.843 7/6/2005 39.73 161 244 7/6/2005 1.1 5.2 7/1/2005 2.483 8/3/2005 40.55 149 242 8/2/2005 2.17 5.5 8/1/2005 1.462 9/14/2005 42.34 236 236 9/7/2005 1.98 5 9/1/2005 1.452 10/4/2005 42.65 133 232 10/4/2005 1.89 2.8 10/1/2005 1.336 11/1/2005 38.3 160 265 11/2/2005 6.54 9.1 11/1/2005 1.529 12/7/2005 39.24 126 232 12/13/2005 2.68 6.8 12/1/2005 1.378 1/10/2006 38.81 110 265 1/11/2006 2.28 4.9 1/1/2006 1.04 2/7/2006 41.26 209 231 2/7/2006 4.96 5.5 2/1/2006 1.01 3/7/2006 41.06 136 257 3/7/2006 1.86 4.4 3/1/2006 1.01 4/4/2006 46.12 117 226 4/4/2006 1.86 3.4 4/1/2006 1.05 5/2/2006 44.95 97.9 241 5/2/2006 1.47 4.3 5/1/2006 0.86 6/13/2006 40.17 192 235 6/13/2006 2.42 4.7 6/1/2006 1.06 Biosolids Effluent Influent

Percent of Dental Facilities O p eratin g Dental Amal g am July 1, 2003 0 January 1, 2004 0 July 1, 2004 0 January 1, 2005 0 July 1, 2005 2 January 1, 2006 12 July 1, 2006 20

Influent Mercury EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity n/a Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “G”

100 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S ample Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S ample Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) 7/7/2003 78.27 50 128 1/7/2004 32.75 60 456 7/13/2004 40.68 50 146 7/9/2003 44.83 20 186 1/8/2004 31.74 60 328 7/14/2004 38.79 50 132 7/14/2003 44.91 20 172 1/12/2004 32.16 30 166 7/21/2004 38.74 50 318 7/15/2003 39.04 30 198 1/14/2004 31.77 20 174 7/22/2004 37.95 280 320 7/23/2003 38.12 40 240 1/20/2004 31.92 50 218 7/26/2004 36.28 50 244 7/24/2003 37.22 100 204 1/21/2004 32.93 70 224 7/27/2004 36.03 50 232 7/28/2003 37.29 210 328 1/28/2004 30.73 60 180 8/4/2004 35.83 70 220 7/29/2003 36.66 130 258 1/29/2004 31.69 1910 244 8/5/2004 34.64 60 206 8/6/2003 37.39 70 292 2/2/2004 31.36 90 300 8/10/2004 44.45 50 240 8/7/2003 37.24 80 260 2/5/2004 32.03 180 232 8/12/2004 41.58 40 144 8/11/2003 36.85 70 372 2/11/2004 30.92 230 200 8/16/2004 37.8 70 168 8/12/2003 36.97 30 324 2/12/2004 31.79 160 236 8/17/2004 38.37 40 110 8/19/2003 37.81 80 381 2/17/2004 29.87 100 296 8/23/2004 37.48 100 200 8/21/2003 36.30 20 358 2/18/2004 31.58 150 296 9/1/2004 37.77 80 178 8/26/2003 37.35 50 260 2/23/2004 34.22 90 242 9/7/2004 35.78 40 310 8/27/2003 36.00 50 264 2/24/2004 33.56 550 240 9/8/2004 41.21 190 310 9/3/2003 35.19 60 250 3/3/2004 36.35 80 210 9/14/2004 38.46 200 104 9/4/2003 34.75 200 296 3/4/2004 35.46 220 226 9/16/2004 37.8 150 168 9/9/2003 36.17 90 368 3/8/2004 34.92 50 300 9/20/2004 37.13 50 126 9/16/2003 35.92 170 302 3/10/2004 40.80 60 296 9/23/2004 37.48 50 200 9/17/2003 35.47 100 282 3/16/2004 34.74 70 230 9/27/2004 37.76 40 164 9/24/2003 36.99 450 366 3/17/2004 35.03 50 166 9/28/2004 35.79 60 184 9/25/2003 35.55 90 284 3/24/2004 38.73 90 126 10/5/2004 39.44 30 170 9/29/2003 35.26 90 372 3/25/2004 49.36 140 190 10/6/2004 40.11 80 268 9/30/2003 33.02 120 450 3/29/2004 68.81 50 130 10/12/2004 37.9 100 444 10/6/2003 35.75 100 754 3/30/2004 56.07 50 146 10/13/2004 35.12 140 438 10/7/2003 32.99 70 426 4/7/2004 39.75 80 218 10/18/2004 34.87 170 204 10/15/2003 34.08 90 238 4/8/2004 42.15 70 238 10/19/2004 35.74 90 202 10/16/2003 34.20 60 230 4/14/2004 37.00 60 224 10/25/2004 46.07 80 192 10/22/2003 33.31 50 298 4/15/2004 37.40 50 140 10/28/2004 41.18 90 258 10/23/2003 33.58 90 226 4/19/2004 49.79 220 116 11/3/2004 41.75 40 196 10/27/2003 32.53 90 196 4/20/2004 44.76 110 500 11/4/2004 40.53 50 208 10/28/2003 37.74 40 174 4/26/2004 37.16 100 266 11/8/2004 39.22 60 220 11/5/2003 33.77 30 156 4/27/2004 34.26 70 202 11/9/2004 38.47 90 196 11/12/2003 38.18 90 218 5/4/2004 34.38 80 262 11/15/2004 37.21 50 416 11/13/2003 35.50 90 188 5/10/2004 38.36 100 236 11/18/2004 35.71 70 200 11/17/2003 35.60 60 164 5/13/2004 37.15 90 158 11/22/2004 35.77 60 246 11/18/2003 35.94 50 204 5/19/2004 71.61 50 166 11/23/2004 34.04 60 290 11/24/2003 32.61 50 252 5/20/2004 40.52 50 118 12/1/2004 33.55 40 280 11/25/2003 32.47 50 262 5/25/2004 40.37 290 184 12/2/2004 33.74 30 300 12/1/2003 33.83 80 222 6/1/2004 56.57 50 104 12/8/2004 33.37 830 408 12/2/2003 33.30 150 232 6/2/2004 50.20 80 122 12/9/2004 33.4 130 314 12/9/2003 32.36 70 238 6/7/2004 43.33 100 188 12/13/2004 34.26 50 226 12/10/2003 31.24 210 144 6/8/2004 42.89 100 202 12/14/2004 32.83 60 224 12/17/2003 32.82 60 224 6/14/2004 39.16 190 256 12/20/2004 34.98 640 482 12/18/2003 32.53 40 234 6/17/2004 37.58 420 342 12/21/2004 33.61 30 178 12/22/2003 34.09 60 270 6/23/2004 37.17 60 194 12/27/2004 32.46 260 296 12/29/2003 26.83 50 222 6/24/2004 36.09 50 168 12/28/2004 30.98 70 586 12/30/2003 25.54 60 292 6/28/2004 34.81 70 260 1/3/2005 33.39 30 164

1/1/2004 28.94 60 484 6/29/2004 34.56 130 230 1/4/2005 33.68 50 188 Influent Influent Influent

### Appendix A: POTW “G”

101 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S ample Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S ample Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) 1/11/2005 32.72 50 160 7/6/2005 38.97 50 164 1/10/2006 35.61 80 274 1/12/2005 32.16 30 160 7/7/2005 39.46 50 122 1/17/2006 32.49 330 298 1/19/2005 31.95 70 328 7/13/2005 38.53 130 116 1/18/2006 33.91 120 170 1/20/2005 29.97 50 226 7/14/2005 38.2 220 96 1/23/2006 35.73 140 306 1/24/2005 31.82 50 156 7/18/2005 39.78 100 302 1/26/2006 33.26 100 282 1/27/2005 32.38 50 202 7/19/2005 36.7 120 322 1/30/2006 36.05 110 296 2/1/2005 32.42 50 230 7/25/2005 35.5 160 194 2/2/2006 36.51 60 298 2/3/2005 35.72 30 238 7/26/2005 37.26 50 148 2/7/2006 34.72 100 236 2/7/2005 33.82 40 184 8/4/2005 37.76 100 378 2/8/2006 34.93 90 292 2/8/2005 33.87 20 202 8/9/2005 34.33 160 258 2/13/2006 34.28 1480 274 2/14/2005 34.26 70 156 8/10/2005 35.24 70 210 2/14/2006 33.25 60 328 2/16/2005 34.17 220 284 8/16/2005 30.32 60 240 2/22/2006 34.01 40 258 2/23/2005 32.66 70 274 8/18/2005 33.68 90 122 2/23/2006 33.00 50 334 2/24/2005 33.25 50 204 8/22/2005 35.52 120 546 3/1/2006 40 338 3/1/2005 31.59 90 210 8/29/2005 32.94 70 276 3/2/2006 120 190 3/3/2005 33.27 100 224 8/30/2005 33.81 50 262 3/9/2006 200 208 3/9/2005 35.37 240 236 9/7/2005 35.51 180 822 3/14/2006 60 294 3/10/2005 33 50 274 9/8/2005 35.38 140 298 3/15/2006 210 280 3/16/2005 31.57 50 378 9/14/2005 25.54 190 336 3/20/2006 420 292 3/17/2005 32.05 70 460 9/15/2005 25.64 250 484 3/21/2006 120 220 3/21/2005 34.37 70 326 9/19/2005 34.02 130 358 3/27/2006 60 218 3/22/2005 36.43 180 272 9/20/2005 30.95 170 220 3/29/2006 110 162 3/23/2005 37.87 50 230 9/26/2005 39.4 300 340 4/3/2006 56.94 50 316 3/24/2005 40.78 40 216 9/27/2005 37.75 220 272 4/4/2006 52.92 560 146 3/29/2005 63.98 30 462 10/3/2005 35.24 390 340 4/11/2006 42.6 40 190 4/6/2005 58.76 160 206 10/4/2005 103.97 80 126 4/12/2006 42.06 150 312 4/7/2005 46.88 40 208 10/5/2005 127.56 70 198 4/19/2006 38.49 110 212 4/12/2005 41.83 70 174 10/11/2005 39.5 110 180 4/20/2006 39.12 290 252 4/18/2005 33.66 50 252 10/12/2005 39.63 70 244 4/24/2006 32.3 90 324 4/21/2005 42.46 40 314 10/19/2005 36.69 170 202 4/25/2006 29.53 200 176 4/26/2005 39.61 90 350 10/20/2005 38.81 110 216 5/3/2006 41.99 90 184 4/27/2005 39.27 40 180 10/24/2005 37.87 90 152 5/4/2006 40.33 50 178 5/4/2005 36.67 30 194 10/25/2005 37.08 150 178 5/9/2006 47.38 350 198 5/5/2005 36.31 70 144 11/1/2005 36.47 1220 184 5/10/2006 46.93 60 170 5/10/2005 39.71 70 152 11/2/2005 36.22 570 190 5/15/2006 57.05 30 190 5/11/2005 39.5 40 148 11/8/2005 34.46 120 216 5/16/2006 49.12 50 228 5/16/2005 36.73 70 168 11/9/2005 36.36 100 166 5/22/2006 37.69 120 274 5/19/2005 66.41 30 116 11/14/2005 43.08 130 174 5/24/2006 36.71 50 350 5/23/2005 42.34 40 160 11/19/2005 40.01 60 280 6/5/2006 42.86 90 254 5/24/2005 39.78 100 224 11/21/2005 40.95 90 346 6/6/2006 42.81 130 328 6/1/2005 39.77 100 196 11/28/2005 63.00 250 232 6/7/2006 40.25 70 282 6/2/2005 39.22 90 204 12/1/2005 43.53 60 332 6/8/2006 37.83 70 258 6/7/2005 44.64 70 142 12/5/2005 39.56 70 240 6/13/2006 34.94 160 314 6/8/2005 54.61 40 129 12/6/2005 37.24 230 260 6/14/2006 34.81 70 228 6/13/2005 45.72 200 190 12/13/2005 36.01 60 188 6/20/2006 36.73 90 378 6/14/2005 55.58 210 134 12/15/2005 35.14 50 286 6/22/2006 38.84 60 208 6/20/2005 53.64 760 154 12/19/2005 34.96 180 300 6/26/2006 43.9 120 220 6/23/2005 44.25 50 198 1/4/2006 37.10 100 226 6/27/2006 47.65 100 6/27/2005 39.91 70 174 1/5/2006 37.34 80 260 6/28/2005 37.92 80 216 1/9/2006 36.23 120 258 Influent Influent Influent

### Appendix A: POTW “G”

102 S ample

Date TR Hg (ng/L) D i ssolved Hg (ng/L) Turb i d i ty (NTU) T SS (mg/L) S ample Date TR Hg (ng/L) D i ssolved Hg (ng/L) Turb i d i ty (NTU) T SS (mg/L) 7/2/2003 1.8 2 2 7/9/2005 1.8 4.85 4.6 7/15/2003 1.8 3 3 7/19/2005 5.3 10.13 3 8/1/2003 1.9 4 4 8/9/2005 2.1 12.93 4.6 8/15/2003 2.3 17 6 8/16/2005 3.7 16.2 10.6 9/3/2003 1.4 5 4.4 9/1/2005 3.2 9.63 3.2 9/15/2003 3.4 42 7 9/15/2005 2.5 3.89 7 10/1/2003 3.0 50.34 17.8 9/16/2005 2.2 4.76 10 10/14/2003 3.0 2.3 18.3 10.6 10/6/2005 13.6 15.53 22.4 11/3/2003 2.8 19.55 6.8 11/2/2005 4.9 9.14 3.6 11/17/2003 3.1 9.26 3.6 11/17/2005 2.0 2.97 3.4 12/1/2003 3.0 9.83 2.6 12/8/2005 3.9 40.13 18.2 12/15/2004 2.8 11.37 1.8 12/20/2006 3.4 8.9 5.6

1/5/2004 2.2 11.4 2.4 1/5/2006 1.9 7 4.8 1/15/2004 2.4 11.6 3.0 1/31/2006 1.9 4.8 4.2 2/3/2004 2.8 11.1 4.0 2/7/2006 2.5 2.2 3.4 2.4 2/13/2004 3.3 11.2 2.2 2/23/2006 1.4 1 3.1 3.4 3/1/2004 2.5 10.0 1.4 3/9/2006 1.8 1.2 6.2 3.4 3/15/2004 2.2 10.6 2.6 3/27/2006 2.3 1.3 7.9 4.2 4/1/2004 3.1 2.7 1.4 4/7/2006 2.4 1.4 6.79 1.6 4/16/2004 2.0 1.4 10.8 3.4 4/17/2006 2.2 0.8 8.42 5.2 5/7/2004 1.8 5.9 2.4 4/26/2006 4.7 0.8 9.31 8.4 5/18/2004 2.0 3.8 2.6 5/3/2006 2.5 0.9 4.36 2.2 6/10/2004 4.3 6.4 0.8 5/23/2006 1.7 4.89 3.6 6/15/2004 5.3 7.2 4.8 6/1/2006 2.7 4.28 3.4 7/1/2004 2.6 5.92 5.6 6/5/2006 3.4 4.57 7.2 7/23/2004 1.8 1.2 3.98 5.2 6/7/2006 2.9 5.57 4.4 8/4/2004 2.5 3.82 7.4 8/17/2004 2.2 12.32 4.4 9/1/2004 1.7 3.1 4 9/16/2004 4.1 1.9 3.03 6.4 10/4/2004 1.8 3.17 3.4 10/18/2004 2.1 2.31 3 11/1/2004 2.0 2.51 4 11/15/2004 2.7 3.94 4.6 12/9/2004 2.8 6.94 3 12/20/2004 2.4 11.03 4.6

1/3/2005 2.0 7.14 10.8 1/19/2005 1.2 5.17 2 2/1/2005 2.2 8.73 5 2/18/2005 2.2 3.95 5.8 3/4/2005 3.1 5.5 2.6 3/15/2005 1.7 6.21 4 4/4/2005 11.3 16.7 9.4 4/18/2005 1.5 4.1 3.6 5/2/2005 3.8 8.57 7.2 5/16/2005 3.0 2.99 2.4 6/1/2005 2.6 3.85 3 6/16/2005 2.0 2.36 1 Effluent Effluent

### Appendix A: POTW “G”

103 Sam p le

Date H g (mg/kg, dry) Sam p le Date H g (mg/kg, dry) Sam p le Date H g (mg/kg, dry) 7/9/2003 0.71 7/1/2004 0.48 7/10/2005 0.49 7/14/2003 0.32 7/12/2004 0.6 7/19/2005 0.26 7/22/2003 0.33 7/19/2004 0.63 7/25/2005 0.38 7/28/2003 0.57 7/26/2004 0.55 8/1/2005 0.35 8/4/2003 0.51 8/4/2004 0.35 8/15/2005 0.44 8/11/2003 0.27 8/9/2004 0.36 9/1/2005 0.36 8/18/2003 0.41 8/16/2004 0.20 9/7/2005 0.31 8/26/2003 0.35 8/23/2004 0.29 9/12/2005 0.35 9/1/2003 0.36 8/31/20 04 0.37 9/19/2005 0.52 9/8/2003 0.32 9/8/2004 0.55 9/27/2005 0.54 9/15/2003 0.31 9/13/2004 0.34 10/4/2005 1.08 9/22/2003 0.51 9/21/2004 0.44 10/9/2005 0.66 9/29/2003 0.36 9/28/2004 0.36 10/12/2005 0.37 10/6/2003 0.28 10/5/2004 0.22 10/23/2005 0.51 10/20/2003 0.20 10/12/20 04 0.41 10/24/2005 0.43 10/27/2003 0.26 10/19/ 2004 0.34 11/1/2005 0.66 11/4/2003 0.24 11/1/2004 0.49 11/7/2005 1.11 11/12/2003 0.17 11/15/ 2004 0.3 11/14/2005 0.87 11/17/2003 0.28 11/22/20 04 0.35 11/21/2005 0.42 11/21/2003 0.25 11/29/20 04 0.25 11/28/2005 0.37 12/1/2003 0.24 12/6/2004 0.34 12/6/2005 0.42 12/8/2004 0.71 12/13/2004 0.31 12/12/2005 0.29 12/16/2003 0.22 12/20/20 04 0.27 12/19/2005 0.24 12/23/2003 0.52 12/27/20 04 0.16 12/26/2005 0.20 12/29/2003 0.19 1/3/20 05 0.22 1/3/2006 0.28

1/5/2004 0.18 1/10/2005 0.26 1/6/2006 0.17 1/13/2004 0.26 1/17/2005 0.24 1/16/2006 0.19 1/19/2004 0.27 1/21/2005 0.23 1/24/2006 0.17 1/28/2004 0.21 1/31/2005 0.26 1/30/2006 0.27 2/3/2004 0.34 2/7/2005 0.19 2/6/2006 0.31 2/9/2004 0.44 2/14/20 05 0.23 2/13/2006 0.22 2/16/2004 0.38 2/21/2005 0.23 2/20/2006 0.26 2/23/2004 0.37 2/28/2005 0.19 2/27/2006 0.24 3/1/2004 0.36 3/7/2005 0.34 3/13/2006 0.31 3/10/2004 0.33 3/14/2005 0.29 3/20/2006 0.22 3/15/2004 0.30 3/21/2005 0.38 3/27/2006 0.24 3/22/2004 0.28 3/29/2005 0.37 4/3/2006 0.29 3/29/2004 0.32 4/4/2005 0.33 4/10/2006 0.37 4/5/2004 0.40 4/12/20 05 0.24 4/17/2006 0.30 4/12/2004 0.34 4/18/2005 0.35 4/24/2006 0.12 4/20/2004 0.44 4/25/2005 0.45 5/1/2006 0.35 4/26/2004 0.50 5/2/2005 0.45 5/9/2006 0.36 5/3/2004 0.32 5/8/2005 0.39 5/23/2006 0.30 5/10/2004 0.38 5/16/2005 0.21 5/31/2006 0.30 5/17/2004 0.49 5/24/2005 0.22 6/5/2006 0.54 5/24/2004 0.38 5/30/2005 0.14 6/13/2006 0.33 5/31/2004 0.5 6/6/2005 0.37 6/19/2006 0.44 6/7/2004 0.42 6/13/20 05 0.28 6/26/2006 0.42 6/15/2004 0.74 6/19/2005 0.32 6/21/2004 0.44 6/27/2005 0.36 Biosolids Biosolids Biosolids

### Appendix A: POTW “G”

104 Percent of Dentists Operating Dental Amal g am Se p arators July 1, 2003 44 January 1, 2004 86 July 1, 2004 95 January 1, 2005 98 July 1, 2005 100 January 1, 2006 100 July 1, 2006 100

Influent Mercury EPA 245.1 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity 2130B (Std. Methods 18th Ed.) Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “H”

105 Sample

Date Total Daily Flow

(MGD) Flow Weighted Influent average TR Hg (ng/L) Flow Weighted Influent average

TSS (mg/L) TR Hg (ng/L) Dissolved Hg (ng/L) Turbidity (NTU) TSS (mg/L) Sample Date Hg (mg/kg, dry) 7/28/2003 34.7 72.59 257.13 2.30 1.1 0.81 1 7/28/2003 0.21 8/22/2003 35.86 112.57 283.50 3.30 1.2 2 4.4 8/22/2003 0.334 9/22/2003 36.74 251.25 335.42 4.00 1.4 3 3.19 9/22/2003 1.24 10/27/2003 36.58 146.18 303.58 2.60 2.2 <1.00 10/27/2003 0.925 11/21/2003 33.21 78.38 277.90 2.90 8 5.2 11/21/2003 0.963 12/17/2003 33.04 86.34 248.79 5.10 11.5 14.2 12/18/2003 0.746 1/26/2004 33.72 86.92 267.13 7.10 4.6 14.7 1/26/2004 0.615 2/23/2004 34.77 96.31 286.07 8.20 2.8 4 2/23/2004 0.84 3/18/2004 36.63 70.64 211.39 6.70 2 <1.00 3/18/2004 0.806 4/21/2004 35.06 186.05 351.76 2.30 2 4 4/22/2004 1.12 5/20/2004 37.39 79.99 308.49 3.90 1.2 <1.0 5/20/2004 0.951 6/16/2004 38.07 137.27 218.81 2 <1.0 6/16/2004 1.27 7/22/2004 40.42 79.67 240.78 1.90 na 3.2 Jul-04 1 8/24/2004 36.37 208.83 358.85 2.90 na 9.1 Aug-04 1.11 9/16/2004 33.14 140.27 301.84 4.00 2.3 <1.0 Sep-04 0.9 10/21/2004 33.72 108.98 321.23 3.80 2.96 3.2 Oct-04 1.3 11/30/2004 34.32 114.82 274.87 10.10 3.31 <1.0 Nov-04 1 12/21/2004 33.35 78.15 266.15 2.90 na 2 Dec-04 0.9 1/25/2005 35.54 248.27 282.88 3.10 2.6 4.7 Jan-05 1.2 3/23/2005 35.59 116.03 269.81 3.40 2.8 2.1 Feb-05 1.7 4/22/2005 34.35 127.30 351.61 2.40 <1.0 na 1.7 Mar-05 1.2 6/30/2005 38.78 234.29 1.80 <1.0 na <1.0 Apr-05 1.72 7/27/2005 33.38 85.31 168.48 2.00 1.4 <1.0 May-05 1.2 8/17/2005 38.65 320.15 1.90 2 <1.0 Jun-05 1.1 9/13/2005 34.53 186.49 232.10 2.50 1.5 <1.0 7/27/05 1.2 10/18/2005 32.84 74.50 464.83 2.10 1.6 <1.0 8/17/05 2.1 11/14/2005 33.37 102.56 169.93 3.50 1.5 1 9/13/05 0.9 12/12/2005 34.03 147.22 237.85 2.80 5 4.6 10/18/05 2 1/18/2006 33.76 106.12 255.66 7.00 7 11/14/05 1 2/15/2006 31.08 105.50 215.70 3.5 5.5 7.3 12/12/05 1.1 3/15/2006 31.64 181.69 214.39 11.2 12.5 14 1/18/06 0.7 4/12/2006 31.94 244.15 409.05 9.1 <1.0 15.5 24.9 2/15/06 1.2 5/18/2006 32.61 123.13 384.95 2.1 <1.0 3 <1.0 3/15/06 1.4 6/28/2006 32.68 78.85 189.20 2.2 <1.0 2 <1.0 4/12/06 2.1 5/18/06 2.5 6/7/06 1 Influent Biosolids Effluent

8/24/2004: No associated field blank

Percent of Dentists Operating

Dental Amalgam Control Technologies July 1, 2003 n/a January 1, 2004 60 July 1, 2004 89 January 1, 2005 95 July 1, 2005 95 January 1, 2006 98 July 1, 2006 98

### Appendix A: POTW “H”

106 Influent Mercury EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity ? Influent TSS ? Effluent TSS ? Analytical Methods

### Appendix A: POTW “I”

107 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S ample Date H g (mg/kg, dry) 7/8/2003 2.33 332 228 3.7 6 7/14/2003 3.35 8/12/2003 2.32 247 108 6.2 3.7 5 8/11/2003 0.99 9/9/2003 2.30 156 111 5.6 2.2 4.4 9/15/2003 0.86 10/8/2003 2.27 155 272 5.8 11/7/2003 2.25 82.6 234 5 5.2 11/19/2003 1.44 12/10/2003 3.00 264 4.6 2.4 12/19/2003 0.416 1/13/2004 2.92 169 186 4.6 3.4 2/10/2004 2.61 180 212 8.8 17.2 2/9/2004 0.668 3/9/2004 2.82 538 136 7.3 7 4/5/2004 2.45 144 160 27.0 19 4/13/2004 0.459 5/4/2004 2.28 634 188 6.6 6/8/2004 2.28 305 244 6.8 2.9 6/14/2004 0.62 7/8/2004 2.25 216 4.8 6 7/13/2004 0.616 8/4/2004 2.27 128 232 4.7 4 9/14/2004 1.98 172 194 5.3 6.8 9/17/2004 2.39 171 176 3.9 4.8 9/1/2004 0.823 10/15/2004 2.23 94.2 166 14.5 8.4 10/25/2004 0.554 11/8/2004 2.64 151 114 5.5 3 12/13/2004 3.35 522 114 4 2.8 12/13/2004 0.587 1/11/2005 2.62 861 186 4.4 5.4 1/13/2005 0.319 2/8/2005 2.98 134 126 12.7 20 1/31/2005 0.446 3/15/2005 2.32 154 218 29.4 15.6 2/28/2005 0.641 4/7/2005 2.85 151 162 6.2 2.6 8.4 3/31/2005 0.736 5/10/2005 2.32 117 208 14.1 3.2 17 4/24/2005 0.216 6/6/2005 2.36 148 206 8.9 2.7 21 5/31/2005 0.209 7/7/2005 2.35 136 204 13.4 12.6 6/30/2005 0.101 8/4/2005 2.28 123 200 6.9 13.6 7/30/2005 0.149 9/13/2005 2.25 102 234 4.6 10 8/31/2005 0.149 10/25/2005 2.29 115 242 7.2 14.7 9/30/2005 0.12 11/21/2005 2.36 164 166 7 8.2 10/31/2005 0.404 12/7/2005 2.37 96.6 176 5.4 8.8 11/30/2005 0.144 1/23/2006 2.88 242 4.5 9.8 12/28/2005 0.154 2/6/2006 3.18 56.2 134 5 12.4 1/31/2006 0.123 3/13/2006 2.59 95.3 160 6 5.4 2/28/2006 0.183 4/10/2006 2.52 193 210 3.5 3.4 3/30/2006 0.025 5/23/2006 2.76 156 180 5.4 2.2 6 4/28/2006 0.172 6/6/2006 2.31 123 230 3.8 2.1 4.8 5/31/2006 0.1 6/30/2006 0.122 Effluent Biosolids Influent

6/8/2004: No associated field blank.

Percent of Dental Facilities O p eratin g Dental Amal g am July 1, 2003 93 January 1, 2004 93 July 1, 2004 93 January 1, 2005 93 July 1, 2005 93 January 1, 2006 93 July 1, 2006 93

### Appendix A: POTW “I”

108 Influent Mercury EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 3050B or 3051, EPA 245.7 Effluent Turbidity n/a Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

### Appendix A: POTW “J”

109 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S ample Date H g (mg/kg, dry) 7/15/2003 58.34 172 10.1 6.2 7/14/2003 1.80 8/15/2005 51.64 306 9.3 4.8 08/18/03 1.40 9/25/2003 57.78 89.2 308 10.8 3.3 15.9 25 09/15/03 1.40 10/15/2003 63 219 290 10.3 8 14 10/13/03 1.10 11/13/2003 65.93 95.2 308 9.4 13.4 24 11/17/03 1.20 12/22/2003 84.39 150 285 6.4 6.5 16 12/08/03 1.40 1/15/2004 113.2 225 254 12.5 14 20 01/19/04 0.84 2/5/2004 99.52 91.1 220 6.1 6.3 16 02/16/04 0.93 3/11/2004 78.51 162 328 8.7 8.3 20 03/15/04 1.40 4/16/2004 74.67 174 292 6.6 6.4 14 04/19/04 1.30 5/14/2004 74.95 224 213 7.5 6.7 11 05/17/04 1.20 6/11/2004 60.7 274 312 8.7 10.8 15 06/28/04 3.22 7/9/2004 61.48 783 410 9.9 20 23 07/20/04 2.26 8/19/2004 60.82 95.1 276 11.6 7.1 16 08/09/04 1.30 9/10/2004 52.74 362 304 8.7 11.5 11 09/20/04 1.40 10/21/2004 70.36 95.1 264 10.9 8.2 13 10/18/04 1.40 11/12/2004 75.18 133 319 6.9 11 18 11/16/04 0.90 12/17/2004 90.63 474 335 5.6 6.2 14 12/13/04 1.10 1/14/2005 74.93 130 156 9.4 6.5 12 01/24/05 1.10 2/25/2005 69.36 193 316 7.7 9 16 02/14/05 1.83 3/11/2005 70.94 193 280 5.9 8 10 03/14/05 1.94 4/15/2005 72.90 204 457 8 1.5 6 12 04/18/05 1.60 5/20/2005 77.10 112 236 6.2 1.8 4.1 16 05/16/05 1.20 6/10/2005 66.40 76.4 296 6 1.9 4.1 11 06/20/05 0.92 7/15/2005 63.30 106 238 6.7 10.9 16 07/18/05 0.91 8/5/2005 61.60 139 316 6.8 6.6 10 08/15/05 0.95 9/9/2005 61.40 154 328 6.8 7.2 10 09/19/05 1.10 10/14/2005 60.00 184 384 6.5 4 14 10/17/05 1.60 11/11/2005 80.30 90.8 260 8.8 9.4 19 11/14/05 1.20 12/14/2005 69.00 77.9 280 8 22 12/12/05 1.10 NA 01/23/06 0.96 2/17/2006 85.7 87.1 328 7 9.7 16 02/20/06 0.88 3/10/2006 84.4 273 248 6.4 6.5 13 03/13/06 1.00 4/7/2006 60.3 188 284 9.8 2 10 22 04/17/06 1.50 5/19/2006 58.1 145 358 5 1.4 8.3 12 05/15/06 0.95 6/2/2006 76.9 98.3 252 4.4 1.1 5 9 6/19/2006 0.9 Effluent Biosolids Influent

Percent of Dental Facilities O p eratin g Dental Amal g am July 1, 2003 94 January 1, 2004 97 July 1, 2004 97 January 1, 2005 97 July 1, 2005 97 January 1, 2006 97 July 1, 2006 98

### Appendix A: POTW “J”

110 Influent Mercury EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury EPA 7471A (06-01-004-003) Effluent Turbidity ? Influent TSS ? Effluent TSS ? Analytical Methods

### Appendix A: POTW “K”

111 S ample

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S ample Date H g (mg/kg, dry) 08/15/03 86.89 215 284 36.6 9.4 no data 08/18/03 4.44 09/24/03 84.21 134 276 9.2 3.5 5.8 11 09/15/03 2.48 10/15/03 181.85 161 258 8.9 11 10/13/03 1.72 11/13/03 110.28 109 203 6.8 3.32 6 11/17/03 2.57 12/22/03 89.34 43.1 119 7.3 5.47 8 12/15/03 1.4 01/15/04 136.68 90.3 143 3.9 3.01 6 01/19/04 1.4 02/05/04 108.39 53.4 118 4.3 2.66 9 02/23/04 1.82 03/11/04 87.80 58.2 163 13.0 6.41 9 03/15/04 1.30 04/16/04 76.52 102 189 5.7 4.38 9 04/19/04 1.20 05/14/04 74.35 360 295 7.6 4.99 3 05/17/04 1.30 06/11/04 105.04 107 188 9.0 9.68 13 06/21/04 1.30 07/09/04 84.04 85.6 212 9.9 4.11 8 07/20/04 2.10 08/19/04 84.78 128 241 4 2.94 8 08/16/04 1.20 09/10/04 143.32 82.7 206 8.5 6.39 13 09/20/04 1.20 10/21/04 82.77 103 173 11.0 5.69 14 10/18/04 1.81 11/12/04 70.54 62.8 9.6 5.71 11/16/04 1.30 12/17/04 93.62 89.7 180 5.3 4.82 10 12/13/04 1.20 01/14/05 84.36 106 218 7.6 4.64 7 01/24/05 1.60 02/25/05 71.8 138 179 8.8 5.12 12 02/14/05 1.75 03/11/05 71.71 77.2 202 7.1 3.58 7 03/14/05 1.20 04/15/05 152.55 71 192 4.7 3.6 3.02 6 04/18/05 1.40 5/20/2005 131.82 124 163 3.9 4.92 12 05/16/05 1.50 6/10/2005 80.70 84.3 194 7.8 2.9 6.54 9 06/20/05 1.30 7/15/2005 78.71 69.1 192 7.8 5.2 8 07/18/05 1.30 8/5/2005 73.41 443 208 6.8 4.94 7 08/15/05 1.00 9/9/2005 76.78 169 430 7.5 6.62 10 09/19/05 1.50 10/14/2005 124.72 94.5 209 6.7 4.44 14 10/17/05 1.40 11/11/2005 115.25 51.9 188 4.9 3.44 5 11/14/05 1.10 12/14/2005 70.63 75.1 234 3.4 2.95 5 12/12/05 1.50 01/30/06 1.30 2/17/2006 93.94 128 123 5 3.77 8 02/13/06 1.20 3/10/2006 110.01 35 132 5.3 3.74 4 03/13/06 1.10 4/7/2006 90.49 51.7 206 4.7 2.9 3.12 5 04/17/06 1.10 5/19/2006 91.12 156 198 5 2.2 4.1 15 05/15/06 3.15 6/2/2006 138.89 52.2 167 4.5 1.6 3.59 14 6/19/2006 1.81 Effluent Biosolids Influent

Percent of Dental Facilities O p eratin g Dental Amal g am July 1, 2003 94 January 1, 2004 97 July 1, 2004 97 January 1, 2005 97 July 1, 2005 97 January 1, 2006 97 July 1, 2006 98

### Appendix A: POTW “K”

112 Influent Mercury EPA 245.7 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury EPA 7471A (06-01-004-003) Effluent Turbidity ? Influent TSS ? Effluent TSS ? Analytical Methods

### Appendix A: POTW “L”

113 S am p le

Date Flow ( MGD ) TR Hg ( n g /L ) TSS ( m g /L ) S am p le Date TR H g (ng/L) D i ssolved Hg (ng/L) Turb i d i t y (NTU) T SS (mg/L) S am p le Date H g (mg/kg, dry) 7/29/2003 40.7 145 422 7/30/2003 17.8 6 3.1 5 7/29/2003 0.514 8/5/2003 42.3 137 189 8/6/2003 17.5 7.1 4.53 11 8/5/2003 0.629 8/18/2003 40.4 163 220 8/19/2003 28.6 10.6 5.6 9 8/19/2003 0.783 9/8/2003 41.8 676 190 9/9/2003 31.2 4.2 9 9/9/2003 0.157 10/6/2003 42.9 2040 203 10/7/2003 32.4 13.2 10/8/2003 1.86 11/3/2003 45.1 303 179 11/4/2003 17.9 6.4 10.6 11/4/2003 1.08 12/1/2003 41.28 200 189 12/2/2003 13.0 7.5 12/2/2003 0.777 1/6/2004 48.4 211 164 1/7/2004 20.2 4.41 8 1/7/2004 1.04 2/4/2004 41 77 164 2/5/2004 40.1 8.93 4.97 9 2/5/2004 1.52 3/3/2004 54.86 56 180 3/4/2004 26.6 5.49 9.95 3/4/2004 1.11 4/14/2004 41.35 269 246 4/15/2004 12.9 3.9 3.35 6.5 4/15/2004 1.01 5/3/2004 43.57 617 216 5/4/2004 205.0 4.2 6 5/4/2004 9.15 6/1/2004 42 229 246 6/2/041 22.5 5.88 10 6/1/2004 0.94 7/6/2004 42.7 226 259 7/7/2004 15.5 4.6 7 7/6/2004 0.908 8/12/2004 41.66 565 202 8/13/2004 17.1 4.32 3.36 3 8/12/2004 8.2 9/1/2004 40.7 120 196 9/2/2004 27.6 5.37 10 9/1/2004 1.33 10/7/2004 41.3 397 212 10/8/2004 15.8 3.8 4.15 8 10/7/2004 1.39 11/3/2004 41.1 210 178 11/4/2004 19.2 6.51 9 11/3/2004 1.45 12/1/2004 40 137 206 12/2/2004 20.3 2.1 8.23 7 12/1/2004 1.24 1/10/2005 72.8 103 158 1/11/2005 15.3 13.6 5.18 7 1/10/2005 0.82 2/1/2005 48.1 352 196 2/2/2005 47.7 7.99 5.2 2/1/2005 2.14 3/1/2005 56 120 165 3/2/2005 15.5 3.82 5.6 3/1/2005 0.91 4/5/2005 54.3 74 176 4/6/2005 21.5 3.1 6.4 4/5/2005 1.77 5/3/2005 45.3 317 192 5/4/2005 16.5 3.61 6.8 5/3/2005 0.79 6/1/2005 44.7 262 219 6/2/2005 20.6 6.31 3.58 7 6/1/2005 1.19 7/5/2005 41.1 264 222 7/6/2005 74 11.5 12.7 29 7/5/2005 0.82 8/1/2005 41.5 164 183 8/2/2005 34.2 4.27 6.6 8/1/2005 1.13 9/1/2005 40.8 404 230 9/2/2005 76.3 19.8 7.22 8.2 9/1/2005 1.39 10/3/2005 46.9 154 255 10/4/2005 56.1 8.09 9.6 10/3/2005 1.33 11/1/2005 39.6 180 238 11/2/2005 31.5 15.6 5.06 5.6 11/1/2005 1.86 12/1/2005 56.5 185 301 12/2/2005 23.9 6.75 12.4 12/1/2005 1.19 1/4/2006 89.2 176 89 1/5/2006 15 6.5 14.8 1/4/2006 0.72 2/6/2006 50.4 100 181 2/7/2006 19.7 3.6 6.4 2/6/2006 0.44 3/2/2006 60.4 413 118 3/3/2006 18.3 6.22 4.64 7 3/2/2006 1.03 4/2/2006 72.9 117 135 4/3/2006 14.7 5.78 8 4/2/2006 0.73 5/1/2006 53.7 133 158 5/2/2006 15.3 6 4.64 5/1/2006 0.84 6/5/2006 47.2 100 198 6/6/2006 10.4 5.97 7.4 6/5/2006 0.67 Biosolids Effluent Influent

Percent of Dental Facilities/Dentists O p eratin g Dental Amal g am July 1, 2003 unknown January 1, 2004 unknown July 1, 2004 unknown January 1, 2005 unknown July 1, 2005 unknown January 1, 2006 unknown July 1, 2006 11

Influent Mercury EPA 245.2 Effluent Mercury EPA 1631, Rev. E Biosolids Mercury SW-846 7471A Effluent Turbidity 2130B (Std. Methods 18th Ed.) Influent TSS 2540D (Std. Methods 18th Ed.) Effluent TSS 2540D (Std. Methods 18th Ed.) Analytical Methods

# A PPENDIX 

# B: S UMMARY OF 

# S TATISTICAL 

# A NALYSES FOR 

# C OMBINED 

# D ATA

### Appendix B

115 The following are the results of correlation analyses conducted on data from all the POTWs. Kendall’s tau-b was used as the measure of correlation between variables. Alpha ( α ) was set at 0.05 for these statistical tests.

Figure 4.5A: Median Influent Mercury Con centration versus Dentists per Flow Kendall’s tau-b = 0.405, p = 0.00007. Thus, this correlation is significant. Increasing number of dentists per MGD is associ ated with increasing influent mercury concentration.

Figure 4.5B: Median Effluent Mercury Con centration versus Dentists per Flow Kendall’s tau-b = 0.316, p = 0.002. Thus, this correlation is signifi cant. Increasing number of dentists per MGD is associ ated with increasing effluent mercury concentration.

Figure 4.5C: Biosolids Mercury Concentr ation versus Dentists per Flow Kendall’s tau-b = 0.159, p = 0.121. Thus, this co rrelation is not signifi cant. Number of dentists per MGD is not correlated w ith biosolids mercur y concentration.

Figure 4.6A: Influent Mercury Concentrations versus Number of Dentists without Separators per Flow Kendall’s tau-b = 0.032, p = 0.805. Thus, this co rrelation is not signifi cant. Number of dentists without separators per MGD is not correlate d with influent mercury concentration.

Figure 4.6B: Effluent Mercury Concentrations versus Number of Dentists without Separators per Flow Kendall’s tau-b = -0.352, p = 0.004. Thus, this correlation is signifi cant. Number of dentists without separators per MGD is negatively correla ted with effluent mercury concentration.

Figure 4.6C: Biosolids Mercury Concentrations versus Number of Dentists without Separators per Flow Kendall’s tau-b = 0.456, p = 0.0002. Thus, this correlation is signifi cant. Increasing number of dentists without se parators per MGD is associat ed with increasing biosolids mercury concentration.

Figure 4.7A: Influent Mercury Concentr ation versus Average Plant Flow Kendall’s tau-b = 0.076, p = 0.783. Thus, this correlation is not si gnificant. Average plant flow is not correlated with influent mercury concentration.

Figure 4.7B: Biosolids Mercury Concentr ation versus Average Plant Flow Kendall’s tau-b = 0.308, p = 0.191. Thus, this correlation is not si gnificant. Average plant flow is not correlated with biosolids mercury concentration.

### Appendix B

116 Figure 4.7C: Effluent Mercury Concentr ation versus Average Plant Flow Kendall’s tau-b = -0.107, p = 0.680. Thus, this correlation is not si gnificant. Average plant flow is not correlated with effluent mercury concentration.

Figure 4.8A: Influent Mercury Concentr ation versus Non-Industrial Flow Kendall’s Tau-B = 0.366, p = 0.208. Thus, this co rrelation is not significant. Percent non-industrial flow is not correlated w ith influent mercury concentration.

Figure 4.8B: Effluent Total Mercury Concen tration versus Non-Industrial Flow Kendall’s Tau-B = 0.592, p = 0.036. Thus, this correlation is significant. Increasing percent non-industrial flow is associated with increasing e ffluent mercury concentration.

Figure 4.8C: Biosolids Total Mercury Concen tration versus Non-Industrial Flow Kendall’s Tau-B = 0.479, p = 0.093. Thus, this co rrelation is not significant. Percent non-industrial flow is not correlated with biosolids mercury concentration.

Figure 4.8D: Influent Total Mercury Concentr ation versus Non-Industrial Flow in Separate Sewer Systems Kendall’s Tau-B = 0.733, p = 0.060. Thus, this co rrelation is not significant. Percent non-industrial flow in separate sewer systems is not correlated with influent mercury concentration. Note that the p-value (0.06) is only slightly higher than α (0.05).

Figure 4.8E: Effluent Total Mercury Concentr ation versus Non-Industrial Flow in Separate Sewer Systems Kendall’s Tau-B = 0.733, p = 0.060. Thus, this co rrelation is not significant. Percent non-industrial flow in separate sewer systems is not correlated with effluent mercury concentration. Note that the p-value (0.06) is only slightly higher than α (0.05).

Figure 4.8F: Biosolids Total Mercury Concentr ation versus Non-Industrial Flow in Separate Sewer Systems Kendall’s Tau-B = 0.2, p = 0.707. Thus, this co rrelation is not signi ficant. Percent nonindustrial flow in separate sewer systems is not correla ted with biosolids mercury concentration.

Figure 4.12A: Influent Mercury Concen tration versus Population Density Kendall’s tau-b = -0.215, p = 0.370. Thus, this correlation is not signi ficant. Population density is not correlated with influent mercury concentration.

Figure 4.12B: Effluent Mercury Concen tration versus Population Density Kendall’s tau-b = 0.185, p = 0.449. Thus, this co rrelation is not signi ficant. Population density is not correlated with effluent mercury concentration.

Figure 4.12C: Biosolids Mercury Concen tration versus Population Density Kendall’s tau-b = -0.047, p = 0.890. Thus, this correlation is not signi ficant. Population density is not correlated with biosolids mercury concentration.