+----------------------------+-----------------------------------------+
| > **\"Nelson, Martina\"    | +----+------------------------------+   |
| > \<martina.n              | | To | > Group Ow-Docket@EPA        |   |
| elson@metc.state.mn.us\>** | +----+------------------------------+   |
| >                          | | cc | > \"Hermes, Leo\"            |   |
| > 12/06/2007 08:27 AM      | |    | > \<l                        |   |
|                            | |    | eo.hermes@metc.state.mn.us\> |   |
|                            | +----+------------------------------+   |
|                            | | b  |                              |   |
|                            | | cc |                              |   |
|                            | +----+------------------------------+   |
|                            | |    |                              |   |
|                            | +----+------------------------------+   |
|                            | | S  | > Attention Docket ID No.    |   |
|                            | | ub | > EPA-HQ-OW-2006-0771        |   |
|                            | | je |                              |   |
|                            | | ct |                              |   |
|                            | +----+------------------------------+   |
|                            | |    |                              |   |
|                            | +----+------------------------------+   |
+----------------------------+-----------------------------------------+

> ![](media/image1.wmf){width="0.46875in" height="0.46875in"}
>
> Mr. Johnston:
>
> The attached document provides MCES' comments on EPA's Preliminary
> 2008 Effluent Guidelines Program Plan. We have also included a summary
> of MCES' Dental Mercury Study, which is referenced in the comments
> document.
>
> Please contact me if you have any questions.
>
> Martina Nelson, P.E.
>
> Senior Engineer
>
> Industrial Waste & Pollution Prevention Section
>
> Metropolitan Council Environmental Services
>
> 390 N Robert St, St Paul, MN 55101
>
> Ph: 651-602-4728 Fx: 651-602-4730
>
> www.metrocouncil.org/environment/IndustrialWaste/
>
> ![](media/image2.wmf){width="1.8020833333333333in"
> height="0.4895833333333333in"}![](media/image3.wmf){width="3.0520833333333335in"
> height="0.4895833333333333in"}

December 5, 2007

Mr. Carey Johnston

Environmental Protection Agency

Mailcode: 4203M\
1200 Pennsylvania Ave NW

Washington, DC 20460

**RE: Comments Related to EPA's 2008 Effluent Guidelines Program Plan**

Mr. Johnston:

Metropolitan Council Environmental Services (MCES) owns and operates
eight wastewater treatment plants and 600 miles of interceptors in the
seven-county Minneapolis/St. Paul Metropolitan Area. In addition, MCES
administers the POTW Pretreatment Program in this area, including
permits for 774 Industrial Users.

MCES hereby provides the following responses on EPA's request for
comments regarding its 2008 Effluent Guidelines Program Plan.

**[Dental Mercury]{.underline}**

With regard to dental mercury, MCES has chosen to comment on the
following items:

1.  In state and localities that have not established dental mercury
    guidance or requirements, what, if anything do dental offices
    currently do to reduce mercury discharges associated with dental
    amalgam? Also, what annual costs are associated with these
    activities?

> **MCES has administered a program in partnership with the Minnesota
> Dental Association (MDA) to have amalgam separators installed. If this
> program was not in place, it is likely that dentists in our area would
> have learned about and followed BMPs put forth by the American Dental
> Association (ADA). Further, some dental offices have reduced or
> eliminated the placement of new amalgam restorations. MCES does not
> have specific cost figures on this topic. Added costs may vary
> significantly, depending on how far along they are on implementing
> BMPs. If everything such as chairside traps and vacuum filters had
> been put in the regular office trash or rinsed down the drain, and
> they switch to collection and transport, they may see a significant
> increase in costs.**

2.  EPA assumed that, at a minimum, all dental facilities have chairside
    traps and/or vacuum pump filters, and that they dispose of the
    amalgam collected in these traps/filters as solid waste (i.e., not
    subsequently rinsed down the drain). EPA solicits comment on this
    assumption.

> **MCES surveyed Minneapolis-St Paul area dental offices in the late
> 1990s, and found that there was quite a wide variety of waste disposal
> methods, which involved treating these wastes as solid waste,
> hazardous waste, or infectious waste, and also disposal by sewering.
> Since state and national dental associations have promoted BMPs, MCES
> believes that there is improved management of these wastes. See WEF's
> 1999 publication "Controlling Dental**
>
> **Facility Discharges in Wastewater: How to Develop and Administer a
> Source Control Program."**

3.  To what extent are the ADA recommended BMPs currently utilized in
    the dental industry? What is the cost effectiveness in reducing
    dental mercury associated with BMPs, and what are the annual costs.

> **MCES does not have specific scientific data. However, based on the
> annual submittal of statements by dental offices in the Minneapolis-St
> Paul metropolitan area, the implementation of BMPs is believed to be
> uniform. The submittal of these statements is a required part of our
> program which promotes the installation of separators and improved
> waste management. In addition, the seven counties of the
> Minneapolis-St Paul metropolitan area, which administer RCRA rules,
> are currently in the process of having dental offices perform self
> audits, which are beginning to be received for review by the
> counties.**

4.  EPA solicits data on the effectiveness of BMP or amalgam separators
    in reducing mercury in POTW influent, effluent and/or sludge. EPA is
    particularly interested in obtaining data from studies that measured
    mercury concentrations in POTW influent, effluent, and/or sludge
    before and after BMP or amalgam separation implementation.

> **Since the implementation of an amalgam separator program in the
> Minneapolis-St Paul metropolitan area in 2003, MCES has seen a 50%
> reduction in mercury measured in the influent at MCES' largest
> treatment plant, the Metropolitan Wastewater Treatment Plant in St
> Paul. Please refer to the attached Figure 1 entitled "Influent Mercury
> Reduction at Metropolitan Wastewater Treatment Plant."**
>
> **In addition, a joint MCES & MDA study performed between 1999 and
> 2001 measured a 29-44% reduction in mercury concentrations in sludge
> at two smaller MCES WWTPs when dental offices installed amalgam
> separators. A summary of this study is included with this mailing. A
> second MCES research study was conducted with the MDA to measure the
> mercury loading coming from dental offices and the effectiveness of
> amalgam separators. This study determined that dental offices generate
> 234 mg/dentist/operating day of mercury, and amalgam separators remove
> 91-99% of mercury.**
>
> **As noted, MCES data show the effect of amalgam separator
> installation. MCES determined that separator installation was
> warranted, and therefore began a separator installation program right
> away. MCES did not have a separate phase of implementing just BMPs,
> and therefore does not have mercury reduction data on the effect of
> BMPs alone.**

5.  EPA solicits information on the cost and burden to POTWs of
    implementing state or local BMP or amalgam separator requirements.
    EPA is also interested in obtaining information on how POTWs have
    implemented such standards.

> **MCES spent many years researching, creating and implementing an
> amalgam separator program for dental offices in the Minneapolis-St
> Paul metropolitan area. Based on staff time and analytical services
> performed, MCES estimates that the cost of this effort is in excess of
> \$500,000. This is a rough estimate, and includes two major research
> studies, investigating separator testing and certification commented
> on below, working with NACWA, revising the ISO 11143 Standard, etc.**
>
> **If a POTW or a state sets up a separator program by taking advantage
> of the tools available, they will greatly minimize their costs. If
> they are not careful, and begin a program without thoroughly
> considering all aspects, they will set themselves up for a lot of
> extra work, such as reviewing ISO test reports and ongoing evaluation
> of future technical changes to separator models.**
>
> **An extremely critical aspect of implementing an amalgam separator
> program deals with understanding laboratory testing and certification
> of separators. The most common way to test separators is by using the
> International Organization for Standardization (ISO) 11143 test
> method. Regulators at the local and state level need to familiarize
> themselves with the basics of testing and certification PRIOR to
> implementing a separator program.**
>
> **The National Association of Clean Water Agencies (NACWA) published a
> white paper in January of 2006 to help POTWs and other regulators
> learn about setting up separator programs, titled "Controlling Mercury
> in Wastewater Discharges from Dental Clinics." A link to this paper is
> <http://www.nacwa.org/images/stories/public/2006-01dmercwp.pdf>**
>
> **Regulators and separator program administrators need to take
> advantage of the ISO tools currently available, such as certification,
> which is a quality control system to ensure that separators are
> manufactured on an ongoing basis that conform with the ISO Standard.
> (A "UL" mark on a product is an example of certification.) To learn
> more about the benefits of certification, please refer to the NACWA
> paper mentioned above.**
>
> **Regulators and program administrators need to understand, and even
> specify, what labs and certification bodies are acceptable, to be sure
> of the test reports and certificates presented to them. By identifying
> labs and certification bodies (CB), and by requiring proper
> accreditation of these labs and CBs, regulators can lay the foundation
> for a rigorous program. These steps help ensure a fair and good
> program for the separator manufacturers competing to sell in any given
> area.**

6.  EPA solicits comment on any known interferences or pass-through
    problems associated with dental mercury discharges?

> **No interferences or pass-through problems associated with dental
> mercury have occurred at any of the eight treatment plants operated by
> MCES.**

7.  EPA solicits additional information on the effectiveness of
    voluntary local programs for reducing mercury discharges from dental
    facilities.

> **MCES and the Minnesota Dental Association (MDA) promoted its amalgam
> separator program as voluntary and it has been extremely successful.
> However, there was a general threat that dental offices may ultimately
> be required to install a separator. The MDA even put out information
> indicating that there was a "deadline" to install. Therefore, the
> program could not be described as completely voluntary.**
>
> **After the majority of the dental offices installed a separator, MCES
> increased the threat of regulation to get the remaining offices to
> install a separator. Offices were told that they would have to apply
> for a discharge permit, meet a mercury limit, conduct semi-annual
> monitoring of their wastewater, submit self-monitoring reports, and
> pay an annual permit fee. While some dental offices did not
> immediately install an amalgam separator, they all eventually complied
> with the voluntary program in lieu of holding an Industrial Discharge
> Permit.**

**[Unused Pharmaceuticals]{.underline}**

1.  EPA solicits identification of any policies, procedures or
    guidelines that govern the disposal of unused pharmaceuticals from
    hospitals; offices of doctors and mental health practitioners;
    nursing, long-term care, rehabilitation, and personal care
    facilities; medical laboratories and diagnostic service facilities;
    and veterinary care facilities.

> **MCES participates in an ongoing partnership with the Solid Waste
> Management Coordinating Board (SWMCB) and the Minnesota Pollution
> Control Agency (MPCA) to establish uniform interpretations and
> guidance on regulatory issues pertaining specifically to the
> healthcare industry. This partnership has developed and routinely
> updates a "Regulatory Consensus on Health Care Issues" document to
> help eliminate some of the confusion and misunderstanding that exists
> in the healthcare industry concerning the disposal of unused
> pharmaceuticals. A copy of this document can be viewed at**
> [http://www.pca.state.mn.us/publications/w-hw3-35.pdf](../redir.aspx%3FURL=http%3A%2F%2Fwww.pca.state.mn.us%2Fpublications%2Fw-hw3-35.pdf).
>
> **The partnership has also established policies and procedures to help
> the health care industry look for alternative methods of disposal for
> unused pharmaceuticals, including incineration where applicable. In
> addition, fact sheets, BMPs and training sessions for hospital and
> surgery center employees were developed and disseminated, resulting in
> improved management and reduced environmental impacts.**

2.  EPA solicits information on the most likely sub-sectors within the
    Health Service sector that would accumulate unused pharmaceuticals
    for management and disposal.

> **MCES believes that there is potential for all the above-mentioned
> sub-sectors within the Health Service sector to accumulate unused
> pharmaceuticals. This is especially true for sub-sectors that receive
> sample pharmaceuticals shortly prior to their expiration date. In
> addition, MCES believes that there are significant amounts of unused
> pharmaceuticals within the residential sector.**

3.  When applicable, to what extent are unused pharmaceuticals disposed
    according to RCRA?

> **Before the partnership between MCES, SWMCB and MPCA was formed, MCES
> believed that unused pharmaceuticals were not disposed of according to
> RCRA. The partnership has strongly encouraged waste minimization in
> the health care industry in the Minneapolis-St Paul metropolitan area.
> Waste minimization practices such as inventory reduction, product
> substitution, and reverse distribution are utilized first. Then if
> unused pharmaceuticals remain, any quantities are disposed of
> according to RCRA and Minnesota Lethal regulations. The Minnesota
> Lethal regulation constitutes an additional hazardous waste
> characteristic beyond RCRA.**
>
> **As for the status of sewered unused pharmaceuticals, MCES currently
> evaluates requests and may grant discharge approval of such items
> under RCRA on a case by case basis. However, as the partnership
> continues its efforts to provide guidance to the health care industry,
> MCES anticipates a reduction in the request for such discharge
> approvals.**

4.  EPA solicits comment and data on: (1) the main factors that drive
    current disposal practices; (2) any barriers preventing the
    reduction or elimination of unused pharmaceuticals to POTWs and/or
    surface waters. In particular, EPA solicits comment on the extent
    that the Controlled Substances Act complicates the design of an
    efficacious solution to drug disposal?

> **In general, MCES believes that regulations, costs, and the ease of
> disposal drives current disposal practices. Historically, unused
> pharmaceuticals were mismanaged and disposed of into solid waste
> (trash) or sewered since generators did not know about applying RCRA
> and Minnesota Lethal regulations. Currently, under the SWMCB guidance,
> generators of unused *hazardous* pharmaceuticals are instructed not to
> sewer them, but manage via an approved method. See the SWMCB
> "Regulatory Consensus on Health Care Issues".**
>
> **Regarding DEA Controlled Substances, the main factor driving current
> disposal practices is that DEA requires that these substances be
> handled in a "chain of custody" manner and then "rendered
> non-recoverable". Therefore, the simplest, most inexpensive method of
> disposal is sewering on-site. If POTWs do not prohibit such disposal,
> or if no new regulations are implemented, this method will likely
> continue.**
>
> **Some pharmaceuticals that have more than one active ingredient may
> be deemed non-hazardous, and therefore might be sewered without full
> consideration as to each of the active ingredients. This multi-active
> ingredient exemption may be viewed as a loophole in the regulations,
> resulting in more pharmaceuticals being sewered. Some waste handlers
> have even suggested adding active ingredients to avoid hazardous waste
> regulations. Wastes should be evaluated on the effect of all active
> ingredients, not simply the number of ingredients.**
>
> **A barrier to reducing the amount of unused pharmaceuticals being
> sewered is a lack of knowledge on the long-term overall effects of
> such disposal. Without this knowledge, the prevailing thought is that,
> "if it is alright to use or ingest a drug, that it must be alright to
> sewer that same drug."**
>
> **POTWs may be able to apply the "precautionary principal" which says
> that "we best err on the side of caution." But given that a hospital
> may ask to sewer hundreds of different pharmaceuticals, how is a POTW
> to know what to accept and what to reject? Maybe some drugs will break
> down, but maybe some will not. Could there be synergistic effects?
> Without good scientific data, POTWs may be under-regulating or they
> may be over-regulating. Questions also exist as to the effect and fate
> of all of the antimicrobials present in liquid and solid soaps
> (triclosan and triclocarban).**

5.  EPA solicits quantitative information on tracking sheets for the
    past year on the disposal of unused pharmaceuticals via the toilet,
    drain, or sewer.

> **MCES does not have specific quantitative data.**

6.  EPA solicits data on how control authorities are currently
    controlling disposal of unused pharmaceuticals via wastewater.

> **MCES utilizes existing federal, state and local regulations, as well
> as outcomes from its partnership with SWMCB and MPCA, to minimize the
> disposal of unused pharmaceuticals to the sanitary sewer in the
> Minneapolis-St Paul metropolitan area. MCES strongly encourages that
> all unused pharmaceuticals, including residential, be made
> unrecoverable prior to disposal as solid waste.**

7.  EPA solicits information on any technologies or BMPs that are
    available to control or eliminate the disposal of unused
    pharmaceuticals to POTWs.

> **In Minnesota, the partnership between MCES, SWMCB and MPCA has
> developed guidance and recommendations for the disposal of unused
> chemotherapy, pharmaceutical, and hazardous wastes that control or
> eliminate such substances from entering the sanitary sewer.
> Specifically, the new practices are inventory tracking, reverse
> distribution, use of drug dispensing machines, dose control, and
> accepting fewer samples by clinics and hospitals.**

8.  EPA solicits any studies or information on the potential for unused
    pharmaceuticals disposed in non-hazardous landfills to contaminate
    underground resources of drinking water.

> **MCES has no comment on this issue.**

**[Centralized Waste Treatment]{.underline}**

EPA requests information on the industries for which it is continuing or
initiating preliminary category reviews of Centralized Waste Treatment.
EPA will need to collect more information for the 2008 annual review.

**MCES currently has four permitted facilities that fall under
Centralized Waste Treatment Pretreatment Standards. Three are subject to
Subpart B - Oils Treatment and Recovery, and one is subject to Subpart
A - Metals Treatment and Recovery. The following information pertains to
the four facilities.**

Specifically, EPA hopes to gather the following information:

1.  What toxic pollutants are discharged from these industries in
    non-trivial amounts on an industry and per-facility basis?

> **Please see attached Tables 1, 2, 3, and 4 to view data that MCES has
> collected on companies subject to CWT regulations. The tables
> represent all data obtained during monitoring projects conducted by
> both MCES and the Permittees since 2004. Please note that the data
> source of "MCES" denotes monitoring conducted by MCES, while "SMR"
> corresponding to monitoring conducted by the Permittee is in relation
> to the submittal of required, routine self-monitoring reports. The
> companies are identified as Company A, Company B, Company C and
> Company D, with these designations applying to the subsequent
> questions.**

2.  What raw material(s) or process(es) are the sources of these
    pollutants?

> **For the Metals Treatment and Recovery Facility the processes are as
> follows:**
>
> **[Company A]{.underline}**

-   **Regeneration of ion exchange resins.**

-   **Treatment and recovery of electroplating and metal finishing
    plating baths and rinses.**

-   **Treatment and recovery of electroless nickel baths.**

-   **Treatment and recovery of various industrial and hazardous wastes
    from a variety of sources.**

> **For the Oils Treatment and Recovery Facilities the processes are as
> follows:**
>
> **[Company B]{.underline}**

-   **Underground tank pumping, cleaning, and removal.**

-   **Flammable Waste Trap Maintenance.**

-   **Spill Cleanup.**

> **[Company C]{.underline}**

-   **Fuel tank and sump bottom dewatering.**

> **[Company D]{.underline}**

-   **Fuel pump unit servicing and fuel tank cleaning and water
    removal.**

3.  What technologies or management practices area available
    (technically and economically) to control or prevent the generation
    and/or release of these pollutants?

> **For the Metals Treatment and Recovery Facility the processes are as
> follows:**
>
> **[Company A]{.underline}**

-   **Chromium reduction**

-   **Metal hydroxide precipitation**

-   **Cyanide oxidation**

-   **pH neutralization**

-   **Electrolytic metal recovery**

-   **Microfiltration.**

> **For the Oils Treatment and Recovery Facilities the pretreatment
> systems are as follows:**
>
> **[Company B]{.underline}**

-   **Gravity oil/water separator**

-   **Plate oil/water separator**

-   **pH adjust with air sparger**

-   **Bag filtration**

-   **Fiber element filtration**

-   **Carbon canister for emulsified oil**

-   **Carbon canister for VOCs**

-   **Ion exchange canister for lead**

-   **Ion exchange canister for mixed metals.\
    **

> **[Company C]{.underline}**

-   **Oil/water separator followed by air stripper.**

> **[Company D]{.underline}**

-   **Dual gravity oil/water separators in series.**

**[Comments on Effluent Guidelines Program Plan]{.underline}**

1.  EPA solicits comment on whether EPA used the correct evaluation
    factors, criteria, and data sources in conducting its annual review
    and developing this preliminary Plan. EPA also solicits comment on
    other data sources that EPA can use in its annual reviews and
    planning biennial planning process.

> **MCES has no comment on this issue.**

2.  EPA solicits comment on whether, and if so how, the Agency should
    provide EPA Regions and States with permit-based support instead of
    revising effluent guidelines (e.g., when the vast majority of the
    hazard is associated with one or a few facilities). EPA solicits
    comment on categories for which the Agency should provide
    permit-based support.

> **MCES in general supports efforts by EPA to provide support and
> guidance related to the industrial categories identified, rather than
> promulgating additional effluent limitations guidelines. MCES
> believes, however, that some revisions as stated in Item 4 below
> should be undertaken by EPA.**

3.  EPA solicits comment on the methodology for grouping industrial
    sectors currently not subject to effluent guidelines or pretreatment
    standards for review and prioritization, and the factors and
    measures EPA should consider for determining whether to identify
    such industries for a rulemaking. EPA solicits comment on other data
    sources and approaches EPA can use to identify industrial sectors
    currently not subject to effluent guidelines or pretreatment
    standards for review and prioritization.

**MCES has no comment on this issue.**

4.  EPA solicits comment on implementation issues related to existing
    effluent guidelines and pretreatment standards.

> **MCES suggests that EPA consider errors and omissions in a number of
> existing Effluent Limit Guidelines (ELGs), rather than revising all
> parts. **
>
> **MCES again requests that EPA consider eliminating the Part 413
> Electroplating Category, and instead bring the affected Industrial
> Users (IUs) under the Part 433 Metal Finishing Category.**
>
> **In addition, when EPA finalized the Streamlining of the CFR 403
> General Pretreatment Regulations they provided a definition and
> adjusted requirements for Non Significant Categorical Industrial Users
> (NSCIUs).  MCES strongly feels EPA should amend CFR Part 403 to allow
> the NSCIUs, as defined, to be subject to POTW Local Limits only, and
> should be exempt from the applicable Categorical Pretreatment
> Standards.  At less than 100 gallons per day of process wastewater
> discharge per day, the effect of this change on water quality would be
> minimal, and the reduction in administrative burden would be
> considerable.**
>
> **MCES also requests that EPA review the rationale for following
> existing regulations:**

-   **Metal Molding and Casting (Part 464) --There is a lack of a set of
    Pretreatment Standards for the casting cleaning operations in the
    Zinc Subcategory, whereas there is a set of Pretreatment Standards
    for casting cleaning in the Aluminum Subcategory. It has been MCES's
    experience that most IUs that fall under the Aluminum Subcategory
    also fall under the Zinc Subcategory, and clean both types of
    castings in the same machinery.**

-   **Centralized Waste Treatment (Part 437) -- The unusually high (and
    potentially dangerous) Pretreatment Standard for Cyanide of 500 mg/l
    at the end of Cyanide Treatment in Subpart A-Metals Treatment and
    Recovery.**

-   **Centralized Waste Treatment (Part 437) -- The choice of the
    organic parameters of concern in Subpart B-Oils Treatment and
    Recovery, due to the difficulty in finding independent laboratories
    able to analyze for the listed parameters.**

    1.  EPA solicits comment on its evaluation of categories of indirect
        dischargers without categorical pretreatment standards.
        Specifically, EPA solicits wastewater characterization data
        (e.g., wastewater volumes, concentrations or discharged
        pollutants), current examples of pollution prevention, treatment
        technologies, and local limits for all industries without
        pretreatment standards. EPA also solicits comment on whether
        there are industrial sectors discharging pollutants that cause
        interference issues that cannot be adequately controlled through
        the general pretreatment standards.

> **Regarding the overall Effluent Limit Guideline program, MCES feels
> that the use of current ELGs (current Categorical Pretreatment
> Standards) and POTW Local Limits have effectively reduced point source
> pollution. Therefore, MCES believes that EPA resources should be
> redirected towards the identification and reduction of non-point
> pollutant sources. This will result in the greatest benefit to the
> nation's water environment.**

If you have immediate questions, please contact Tina Nelson at
651.602.4728 or via e-mail at
[martina.nelson@metc.state.mn.us]{.underline}.

Sincerely,

Leo H. Hermes, P.E.

Industrial Waste Manager

Metropolitan Council Environmental Services

Industrial Waste & Pollution Prevention Section

390 N Robert St, St. Paul, MN 55101

Attachments: Figure 1: Influent Mercury Reduction at Metropolitan
Wastewater Treatment Plant

Table 1: Analytical Results at Company A (Subject to Part 437 Subpart D
-- Metals

> Treatment and Recovery)

Table 2: Analytical Results at Company B (Subject to Part 437 Subpart B
-- Oils

> Treatment and Recovery)

Table 3: Analytical Results at Company C (Subject to Part 437 Subpart B
-- Oils

> Treatment and Recovery)

Table 4: Analytical Results at Company D (Subject to Part 437 Subpart B
-- Oils

> Treatment and Recovery)

Figure 1: Influent Mercury Reduction at Metropolitan Wastewater
Treatment Plant

![](media/image4.wmf){width="7.745275590551181in"
height="4.084645669291339in"}

**Table 1: Analytical Results at Company A (Subject to Part 437 Subpart
D -- Metals Treatment and Recovery**)

  ------------ ---------- ------------ ------------ ----------- ----------- ------------ ---------- ---------- ------------ ---------- ----------- ---------- ---------- ---------- ------------ ------------
  **Sample     **Data     **Sample     **Antimony   **Arsenic   **Cadmium   **Chromium   **Cobalt   **Copper   **Cyanide,   **Lead     **Mercury   **Nickel   **Silver   **Tin      **Titanium   **Vanadium
  Location**   Source**   Date**       (mg/L)**     (mg/L)**    (mg/L)**    (mg/L)**     (mg/L)**   (mg/L)**   total        (mg/L)**   (ug/L)**    (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**     (mg/L)**
                                                                                                               (mg/L)**                                                                          

  Process      MCES       1/5/2005     0.007        0.041       0.001       0.014        0.004      0.038      0.33         0.003      \<0.060     0.161      0.0002     0.008      \<0.025      \<0.010

                          1/6/2005     0.005        0.017       0.003       0.029        0.004      0.084      0.18         0.003      0.027       0.241      0.002      0.026      \<0.025      \<0.010

                          1/7/2005     0.006        0.011       0.01        0.052        0.002      0.084      0.23         0.009      \<0.024     0.157      0.003      0.082      \<0.025      \<0.010

                          2/8/2006     \<0.010      0.014       \<0.0008    0.031        0.019      0.092      3            0.012      0.248       0.151      0.0009     0.033      0.671        0.035

                          2/9/2006     \<0.010      0.014       \<0.0008    0.026        0.007      0.046      0.69         0.002      \<0.120     0.18       0.001      0.03       0.557        0.027

                          2/10/2006    \<0.020      0.038       \<0.0016    \<0.008      0.014      0.085      0.28         \<0.003    \<0.6       0.498      \<0.0008   0.012      1.55         \<0.040

                          1/17/2007    0.021        0.049       \<0.0004    0.02         0.006      0.148      0.42         0.003      \<0.024     0.272      0.001      0.012                   0.034

                          1/18/2007    0.011        0.021       \<0.0004    0.018        0.031      0.076      5.6          \<0.0007   \<0.120     0.217      0.0005     0.035                   0.04

                          1/19/2007    0.013        0.015       \<0.0004    0.04         0.015      0.0174     \~5.6        0.002      \<0.120     0.355      0.0006     0.008                   0.019

               SMR\*      1/14/04      0.008        0.013       0.005       0.101        0.004      0.159      0.3          0.009      0.25        0.375      0.003      0.07       \<0.001      0.004

                          2/10/04      0.002        0.004       0.003       0.11         0.003      0.184      0.19         0.009      0.2         0.241      0.015      0.157      \<0.001      0.028

                          3/10/04      0.031        0.009       0.004       0.027        0.002      0.111      0.05         0.003      0.08        0.099      0.001      0.03       \<0.001      0.013

                          4/24/04      0.01         0.011       \<0.001     0.221        0.002      0.459      0.27         0.004      \<0.01      0.28       0.004      0.055      \<0.001      0.025

                          5/11/04      0.044        0.004       \<0.001     0.127        0.01       0.156      \<0.01       0.002      0.2         0.402      0.003      0.044      \<0.001      0.006

                          6/16/2004    0.007        0.011       0.002       0.035        0.003      0.14       0.3          0.012      0.08        0.381      0.001      0.036      0.027        0.008

                          7/27/2004    0.007        0.012       0.004       0.071        0.006      0.205      2.11         0.013      0.01        0.381      0.006      0.03       \<0.001      0.001

                          8/11/2004    0.069        0.003       0.002       0.041        0.003      0.093      0.56         0.008      0.01        0.593      0.004      0.069      \<0.001      0.001

                          9/16/2004    0.039        0.009       0.001       0.48         0.007      0.269      0.02         0.008      0.28        0.919      0.006      0.031      \<0.001      0.012

                          10/21/04     0.003        \<0.001     0.006       0.093        0.001      0.177      0.21         0.008      \<0.03      0.139      0.001      0.046      \<0.001      \<0.001

                          11/3/04      0.203        0.005       0.002       0.428        0.003      0.18       1.16         0.021      \<0.01      0.44       \<0.001    0.0196     0.006        0.096

                          11/10/04     0.014        0.016       0.003       0.041        0.005      0.272      0.4          0.004      \<0.01      0.664      0.001      0.044      0.027        0.047

                          11/16/04     0.014        0.012       \<0.001     0.054        0.002      0.213      0.24         0.007      0.11        0.252      0.003      0.017      0.055        0.032

                          12/14/04     0.05         0.042       0.003       0.14         0.003      0.232      0.21         0.013      0.27        0.139      0.025      0.05       0.008        \<0.001

                          1/27/05      0.004        \<0.001     0.002       0.054        0.002      0.31       0.27         0.012      0.23        0.158      0.004      0.037      0.011        \<0.001

                          2/1/05       0.004        0.004       0.005       0.083        0.003      0.201      0.37         0.008      0.35        0.229      0.006      0.039      0.006        \<0.001

                          2/2/05       0.013        0.001       0.005       0.51         0.002      0.275      0.56         0.005      0.19        0.501      0.017      0.036      0.005        \<0.001

                          2/3/05       0.027        \<0.001     0.012       0.173        0.004      0.374      0.6          0.01       0.29        0.693      0.008      0.045      0.001        \<0.001

                          2/4/05       0.013        \<0.001     0.016       0.0604       0.008      0.265      0.39         0.006      0.28        1.109      0.009      0.028      0.008        0.013

                          2/7/05       0.069        \<0.001     0.015       1.155        0.004      0.304      0.58         0.006      0.23        0.455      0.004      0.07       0.011        \<0.001

                          2/8/05       0.018        0.019       0.006       0.312        0.003      0.269      1.33         0.004      0.19        0.481      0.004      0.022      0.014        0.027

                          2/9/05       0.007        0.009       0.002       0.052        0.003      0.133      0.98         0.004      0.13        0.102      0.07       0.05       0.019        0.342

                          2/10/05      0.004        0.01        0.001       0.056        0.004      0.175      0.32         0.007      0.09        0.29       0.002      0.102      0.001        \<0.001

                          10/25/2005   0.011        0.008       0.006       0.224        0.002      0.128      0.71         0.002      0.23        0.161      0.004      0.017      0.005        0.009

                          11/9/2005    0.008        0.004       0.002       0.029        0.002      0.096      0.07         0.002      0.13        0.257      0.007      0.022      0.03         0.018

                          12/16/2005   0.01         0.002       0.005       0.269        0.032      0.064      0.66         0.002      0.13        0.265      0.007      0.017      0.005        0.001

                          1/18/2006    0.013        \<0.001     0.002       0.6          0.002      0.142      \<1          0.003      0.32        0.259      0.023      0.013      0.009        0.019
  ------------ ---------- ------------ ------------ ----------- ----------- ------------ ---------- ---------- ------------ ---------- ----------- ---------- ---------- ---------- ------------ ------------

# Table 1: Analytical Results at Company A (Subject to Part 437 Subpart D -- Metals Treatment and Recovery) -- continued

  ------------ ---------- ------------ ------------ ----------- ----------- ------------ ---------- ---------- ------------ ---------- ----------- ---------- ---------- ---------- ------------ ------------
  **Sample     **Data     **Sample     **Antimony   **Arsenic   **Cadmium   **Chromium   **Cobalt   **Copper   **Cyanide,   **Lead     **Mercury   **Nickel   **Silver   **Tin      **Titanium   **Vanadium
  Location**   Source**   Date**       (mg/L)**     (mg/L)**    (mg/L)**    (mg/L)**     (mg/L)**   (mg/L)**   total        (mg/L)**   (ug/L)**    (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**     (mg/L)**
                                                                                                               (mg/L)**                                                                          

  Process      SMR        2/15/2006    0.01         0.006       \<0.001     0.25         0.003      0.094      \<1          0.002      0.7         0.478      0.01       0.011      \<0.005      0.018

                          3/8/2006     0.03         0.006       0.008       0.123        0.004      0.138      \<1          0.005      0.45        0.2        0.011      0.065      0.015        0.015

                          4/18/2006    0.009        0.004       0.005       0.094        0.024      0.291      \<2          0.007      0.36        0.388      0.008      0.07       \<0.005      0.019

                          5/11/2006    0.006        0.02        0.005       0.066        0.003      0.119      \<1          0.001      0.16        0.365      0.006      0.029      \<0.005      0.009

                          6/28/2006    0.022        0.098       0.004       0.08         0.02       0.263      \<1          0.015      0.14        1.357      0.027      0.08       \<0.005      0.051

                          7/18/2006    0.022        0.019       0.008       0.098        0.057      0.576      \<1          0.005      0.34        1.02       0.008      0.038      \<0.005      0.047

                          8/24/2006    0.008        0.007       0.004       0.055        0.003      0.079      \<1          0.003      0.36        0.419      0.01       0.016      \<0.005      0.049

                          9/7/2006     0.021        0.01        0.012       0.37         0.016      0.33       \<1          0.008      0.47        0.955      0.025      0.11       \<0.005      0.033

                          10/17/06     0.007        0.005       0.003       0.051        0.01       0.306      0.22         0.005      0.55        0.719      0.003      0.026      \<0.005      0.017

                          10/24/06     0.011        \<0.001     \<0.001     0.051        0.006      0.048      0.59         0.072      0.45        0.294      0.002      0.08       0.008        0.011

                          11/7/06      0.007        0.005       0.007       0.091        0.005      0.118      0.3          0.005      0.36        0.485      0.002      0.022      \<0.005      0.013

                          11/14/2006   0.004        0.002       0.003       0.096        0.007      0.09       \<0.01       0.002      0.41        0.419      0.005      0.015      0.005        0.013

                          11/21/2006   0.009        0.004       0.003       0.064        0.005      0.143      0.05         0.01       0.39        5.86       0.008      0.025      0.005        0.011

                          11/28/2006   0.065        0.003       0.002       0.047        0.014      0.046      \<0.01       0.002      0.34        0.299      0.002      0.014      \<0.005      0.01

                          12/7/2006    0.008        0.013       \<0.01      0.051        0.013      0.125      \<0.01       0.007      0.3         0.187      0.003      0.011      \<0.005      0.061

                          12/13/2006   0.055        0.033       \<0.002     0.138        0.014      0.425      0.08         0.005      0.32        0.939      0.001      0.028      \<0.005      0.053

                          1/18/2007    0.006        0.02        \<0.001     0.011        0.017      0.208      0.17         \<0.001    0.52        0.307      \<0.001    0.009      \<0.005      0.026

                          2/21/2007    0.006        0.01        \<0.001     0.12         0.003      0.106      0.06         \<0.001    0.03        0.909      \<0.001    0.006      \<0.005      0.014

                          3/6/2007     0.034        0.012       \<0.001     0.122        0.008      0.153      0.01         0.002      0.02        0.364      \<0.001    0.011      \<0.005      0.025

                          4/18/2007    0.01         0.009       \<0.001     0.028        0.003      0.194      0.09         \<0.001    0.17        0.244      0.033      0.033      \<0.005      0.011

                          5/22/2007    0.12         0.013       0.002       0.085        0.006      0.143      0.2          0.002      0.03        0.158      \<0.005    0.066      \<0.005      0.016

                          6/7/2007     0.087        0.005       0.002       0.08         0.004      0.197      \<0.01       0.002      0.05        0.171      0.099      0.117      \<0.005      0.003

                          7/25/2007    0.009        \<0.001     0.009       0.103        0.042      0.198      0.42         0.015      0.14        0.883      0.003      0.011      0.007        0.001

                          8/16/2007    0.014        0.032       \<0.001     0.033        0.005      0.156      0.06         0.005      \<0.010     0.28       0.004      0.013      \<0.005      0.01

                          9/24/2007    0.07         \<0.001     0.007       0.425        0.009      0.191      0.09         0.007      0.07        0.362      0.004      0.034      \<0.005      \<0.001
  ------------ ---------- ------------ ------------ ----------- ----------- ------------ ---------- ---------- ------------ ---------- ----------- ---------- ---------- ---------- ------------ ------------

\* SMR denotes self-monitoring conducted by Company A.

Table 2: Analytical Results for Company B (Subject to Part 437 Subpart D
-- Oils Treatment and Recovery

  ------------ ---------- ---------- ------------ ---------- ---------- ---------- ---------- ---------- ------------------------------ ------------- ---------------- ------------ ----------------
  **Sample     **Data     **Sample   **Chromium   **Cobalt   **Copper   **Lead     **Tin      **Zinc     **Bis-2(ethylhexyl)phthalate   **Carbazole   **Fluoranthene   **n-Decane   **n-Octadecane
  Location**   Source**   Date**     (mg/L)**     (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**   (ug/L)**                       (ug/L)**      (ug/L)**         (ug/L)**     (ug/L)**

  Process      MCES       8/4/04     0.1          0.01       0.227      0.1        0.003      0.934      7.48                                         \<4.301                       

                          8/5/04     0.014        0.002      0.197      0.011      0.001      0.133      15.02                                        \<4.167                       

                          8/6/04     0.013        0.002      0.224      0.017      0.002      0.206      62.6                                         \<4..255                      

                          4/27/05    0.149        0.01       1.27       0.511      0.067      3.85       394.9                                        27.5                          

                          4/28/05    0.176        0.04       1.04       0.967      0.05       5.9        769.2                                        \<40.0                        

                          4/29/05    0.025        0.004      0.272      0.045      \<0.002    0.409      279.4                                        \<40.0                        

                          10/11/06   1.6          0.001      0.048      0.025      0.004      0.302      205.92                         \<2           \<41.6           \<2          \<14.87

                          10/12/06   1.36         0.002      0.077      0.033      0.003      0.291      113.3                          \<2           \<41.2           \<2          34.94

                          10/13/06   1.12         0.003      0.08       0.008      0.0001     0.516      104                            \<2           \<41.6           \<2          19.38

               SMR\*      03/09/04   0.023        \<0.032    0.231      1.27       \<0.167    1.19       54                             \<10          \<10             1300         570

                          03/10/04   0.061        \<0.032    0.34       1.99       \<0.167    1.49       64                             \<10          \<10             1200         470

                          11/3/04    \<0.013      \<0.032    0.065      \<0.140    \<1.00     0.046      \<11                           \<11          \<11             \<11         \<11

                          11/4/04    \<0.013      \<0.032    0.135      \<0.140    \<1.00     0.06       \<11                           \<11          \<11             \<11         \<11

                          3/8/05     0.074        \<0.032    0.248      \<0.14     \<0.167    0.879      29                             \<50          \<50             0.2          0.2

                          3/9/05     0.032        \<0.032    0.371      \<0.14     \<0.167    0.237      73                             \<20          \<20             0.075        0.11

                          6/7/05                             0.17       \<0.1                 0.22                                                                                  

                          6/8/05                             0.13       \<0.1                 0.16                                                                                  

                          6/9/05                             0.22       0.2                   0.7                                                                                   

                          6/10/05                            0.079      0.11                  0.26                                                                                  

                          6/13/05                            0.04       0.03                  0.11                                                                                  

                          6/16/05                            0.37       0.04                  0.85                                                                                  

                          6/17/05                            0.29       0.04                  0.31                                                                                  

                          6/20/05                            0.26       0.04                  0.35                                                                                  

                          6/22/05                            0.18                                                                                                                   

                          6/23/05                            0.12                                                                                                                   

                          6/24/05                            0.37                                                                                                                   

                          6/28/05                            0.15                                                                                                                   

                          6/29/05                            0.36                                                                                                                   

                          12/7/05    \<0.01       \<0.005    0.029      0.18       \<0.020    0.2        29                             \<1           \<5.0            12           \<1

                          12/8/05    \<0.01       \<0.005    0.024      0.14       \<0.020    0.2        17                             \<1           \<5.0            \<1          \<1

                          12/9/05    \<0.01       \<0.005    \<0.02     0.073      \<0.020    0.1        27                             \<1           \<5.0            8.3          \<1

                          4/10/06    0.02         0.02       0.074      0.13       \<0.100    0.17       4.9                            \<40          \<9.0            10           20

                          4/11/06    \<0.025      \<0.050    0.15       0.16       \<0.100    0.14       6.3                            \<40          \<9.0            18           27

                          10/3/06    0.026        \<0.005    0.079      0.062      \<0.020    0.44       \<200                          \<1           \<200            \<1          28

                          10/4/06    0.047        \<0.005    0.09       0.072      \<0.020    0.44       \<190                          \<1           \<190            \<1          34

                          10/5/06    0.46         \<0.005    0.071      0.081      \<0.020    0.45       \<190                          \<1           \<190            \<1          46

                          5/23/07    \<0.01       \<0.005    0.078      0.04       \<0.020    0.45       \<19                           \<19          \<19             \<19         \<19

                          5/24/07    \<0.01       \<0.005    0.042      0.035      \<0.020    0.32       \<19                           \<19          \<19             34           73
  ------------ ---------- ---------- ------------ ---------- ---------- ---------- ---------- ---------- ------------------------------ ------------- ---------------- ------------ ----------------

\* SMR denotes self-monitoring conducted by Company B.

Table 3: Analytical Results at Company C (Subject to Part 437 Subpart B
-- Oils Treatment and Recovery)

  ------------ ---------- ---------- ---------- ------------ ---------- ---------- ---------- ---------- ------------------------------ ------------- ----------------
  **Sample     **Data     **Sample   **Cobalt   **Chromium   **Copper   **Lead     **Tin      **Zinc     **Bis-2(ethylhexyl)phthalate   **Carbazole   **Fluoranthene
  Location**   Source**   Date**     (mg/L)**   (mg/L)**     (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**   (ug/L)**                       (ug/L)**      (ug/L)**

  Process      MCES       8/31/04                                                                        \<4.16                                       \<4.16

                          9/1/04                0.009        0.088      0.017      \<0.002    4.4                                                     

                          7/28/05               0.019        0.051      0.009      \<0.002    0.86       \<4.16                                       \<4.16

                          12/13/06   0.001      0.075        0.083      0.018      0.003      2.46       \<8.0                                        \<8.0

                          10/11/07   \<0.0005   0.005        0.027      \<0.001    \<0.005    0.451                                                   

               SMR\*      10/27/04                           0.151      0.0217     \<0.075    1.16                                                    

                          6/12/05                            0.0904     0.0143     \<0.075    2.89                                                    

                          10/17/05              \<0.01       0.084      0.0072     \<0.075    0.771      \<0.01                         \<0.01        \<0.01

                          6/14/06                            0.0709     0.0082                0.585      \<0.01                         \<0.01        \<0.01

                          10/25/06                           0.0512     0.0154     \<0.075    2.99       \<0.102                        \<0.102       \<0.102

                          6/18/07    \<0.010    \<0.01       0.179      0.0763     \<0.075    2.01       \<0.011                        \<0.011       \<0.011
  ------------ ---------- ---------- ---------- ------------ ---------- ---------- ---------- ---------- ------------------------------ ------------- ----------------

\* SMR denotes self-monitoring conducted by Company C.

**Table 4: Analytical Results at Company D (Subject to Part 437 Subpart
B -- Oils Treatment and Recovery)**

  ------------ ---------- ---------- ---------- ------------ ---------- ---------- ---------- ---------- ------------------------------ ------------- ---------------- ------------ ----------------
  **Sample     **Data     **Sample   **Cobalt   **Chromium   **Copper   **Lead     **Tin      **Zinc     **Bis-2(ethylhexyl)phthalate   **Carbazole   **Fluoranthene   **n-Decane   **n-Octadecane
  Location**   Source**   Date**     (mg/L)**   (mg/L)**     (mg/L)**   (mg/L)**   (mg/L)**   (mg/L)**   (ug/L)**                       (ug/L)**      (ug/L)**         (ug/L)**     (ug/L)**

  Process      MCES       11/15/06   0.003      0.008        0.037      0.078      0.004      0.244      24.44                                        \<4.82                        

                          11/16/06   0.004      0.009        0.021      0.072      0.001      0.302      44.06                                        \<4.6                         

                          11/17/06   0.005      0.012        0.042      0.158      0.002      0.453      34.78                                        \<4.32                        

               SMR\*      11/17/05   \<0.005    \<0.006      0.008      \<0.015    \<0.05     0.13       0.011                          \<0.01        \<0.01           0.001        0.002

                          11/18/05   \<0.005    \<0.006      \<0.005    \<0.015    \<0.05     0.056      0.011                          \<0.01        \<0.01           0.001        0.002

                          11/19/05   \<0.005    \<0.006      \<0.005    \<0.015    \<0.05     0.062      0.014                          \<0.01        \<0.01           0.001        0.001

                          7/14/06    0.006                   0.049      0.051      \<0.026    0.928      0.013                          \<0.01        \<0.01           0.027        0.062

                          11/30/06   \<0.004                 0.023      0.04       \<0.023    0.241      0.015                          \<0.01        \<0.01           0.079        0.032

                          5/4/07     0.0058     0.015        0.033      0.024      \<0.020    0.3        0.083                          \<0.011       \<0.011          0.083        0.5
  ------------ ---------- ---------- ---------- ------------ ---------- ---------- ---------- ---------- ------------------------------ ------------- ---------------- ------------ ----------------

\* SMR denotes self-monitoring conducted by Company D.

**Community-Wide Dental Mercury Study**

**PROJECT SUMMARY December 13, 2001**

Claude T. Anderson, MCES-EPE

# Introduction

Since the control of mercury sources is an important environmental issue
for state and federal regulators, the regulated community, including
Metropolitan Council Environmental Services (MCES) is continually facing
increasing pressure to reduce mercury emissions to the environment. As a
result, this study was conducted cooperatively between MCES and the
Minnesota Dental Association (MDA). A complete project report is
available from Claude Anderson at (651) 602-8291.

# Objectives

The Community-Wide Study was conducted to quantify the amount of mercury
discharged from dental clinics to MCES\' wastewater treatment plants
(WWTPs). This was accomplished by an intensive sludge sampling and
analysis program at the Hastings and Cottage Grove WWTPs before and
during the time period amalgam removal equipment was in place treating
wastewater at the dental clinics upstream of the WWTPs.

# Methods

The Community-Wide Study was conducted in three phases; each phase
included at least three months of data collection. The daily sludge
sampling at the Hastings and Cottage Grove WWTPs was conducted between
June of 1999 and August of 2001. The time periods and major activities
for each phase were:

[Phase I: Establish baseline at both treatment plants. June 18, 1999 to
October 14, 2000]{.underline}

-   Baseline was established for sludge mercury concentrations and mass
    loadings at the Hastings and Cottage Grove WWTPs.

-   No amalgam removal equipment in place at any of the dental clinics.

[Phase II: Hastings test phase. October 15, 2000 to February 17,
2001.]{.underline}

-   Amalgam removal equipment was in placed in all dental clinics in the
    Hastings WWTP service area (6 clinics).

-   No amalgam removal equipment in the Cottage Grove dental clinics.

-   Additional Cottage Grove WWTP sludge baseline monitoring.

-   At the end of this phase, amalgam removal equipment was removed from
    the Hastings dental clinics.

[Phase III: Cottage Grove test phase. April 8, 2001 to July 21,
2001]{.underline}

-   Amalgam removal equipment was in place at all but one of the dental
    clinics in the Cottage Grove WWTP service area (7 of 8 clinics).

-   Additional Hastings WWTP sludge baseline monitoring.

During the transition periods between Phase II and Phase III, and after
Phase III, sludge monitoring continued at the WWTPs even though
equipment was being removed or installed at the dental clinics.

**Results**

During the study, a 44 % reduction in mercury loading to the Hastings
WWTP sludge was measured while the amalgam removal equipment was in
place in the Hastings dental clinics. The mercury sludge reduction at
Cottage Grove was found to be 29% while the amalgam removal equipment
was in place in Cottage Grove. These removals are represented
graphically below.

Two possible reasons for a smaller reduction at Cottage Grove include

\(1\) one clinic (with one dentist) in Cottage Grove did not
participate, and (2) the grit removal system at the Cottage Grove WWTP
removes above normal quantities of grit, which may have resulted in less
mercury reaching the sludge.

Based on the measured mercury sludge reductions at the wastewater
treatment plants, and estimating the WWTP mercury grit removal rates,
efficiency of the amalgam removal equipment in the dental offices and
the number of days each clinic operated, a mercury loading from dental
clinics was estimated. The mercury loading from dental clinics was
estimated at

120 mg/dentist/operating day for each of the Hastings and Cottage Grove
WWTP service areas. (Note that even though the calculation for each set
of clinics within each service area was done independently, the result
of 120 mg/dentist /operating day was the same.)

**Major Conclusions and Recommendations**

-   This study found that significant decreases in mercury, as measured
    in wastewater treatment plant sludge, could be realized by
    installing amalgam removal equipment in dental clinics.

-   The installation and operation of amalgam removal equipment in the
    13 clinics did not result in any significant operating problems for
    the dental clinics during the three month installation period,
    either in terms of the amalgam removal equipment or the clinic
    vacuum systems.

-   During the time period that amalgam removal equipment was in place
    upstream of the WWTP, the average reduction in the mass of mercury
    present in the sludge was 29 % at the Cottage Grove WWTP and 44 % at
    the Hastings WWTP. The reductions were estimated based on sludge
    volumes, moisture content, and mercury concentrations.

-   Using the study data, a statistical comparison looked at the ratios
    of Hastings to Cottage Grove WWTP sludge mercury concentration and
    mass loadings with and without amalgam removal equipment in place.
    This comparison found that the differences observed for these ratios
    were statistically significant for both WWTPs when the amalgam
    removal equipment was in place.

-   Based on the measured mercury sludge reductions and estimated grit
    removal rates at the wastewater treatment plants, the mercury
    loading from dental clinics was estimated to be\
    120 mg/dentist/operating day for the Cottage Grove and Hastings
    WWTPs.

-   It was possible to get very high participation from the dentists in
    this study. This was possible because of the extensive pre-project
    involvement and support from the MDA and the dentists, in addition
    to the study's attention to minimizing adverse impacts on the
    dentists' practice. However, since involvement in this study was
    voluntary, it was not possible to get universal participation from
    all the dentists in the WWTP service areas.

-   The Community-Wide Study demonstrated that significant reductions in
    WWTP sludge mercury loadings could be achieved if dental clinics
    treat their wastewater to reduce the amount of amalgam and mercury
    wastes prior to discharge to the sanitary sewer system. Therefore,
    it is recommended that a program to reduce dental clinic mercury be
    implemented. Development and implementation of a program should
    involve MCES, MDA, and possibly other state and local agencies.

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