[Federal Register Volume 68, Number 19 (Wednesday, January 29, 2003)]
[Notices]
[Pages 4481-4489]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-2035]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-7445-4; RCRA-2002-0029]


Land Disposal Restrictions: Treatment Standards for Mercury-
Bearing Hazardous Waste; Notice of Data Availability

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of data availability.

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SUMMARY: This notice of data availability (NODA) makes available to the 
public two studies conducted on the treatment of mercury wastes. The 
studies were initiated to help evaluate whether EPA could propose 
treatment and disposal alternatives to the current land disposal 
restriction (LDR) treatment standard of mercury retorting. The studies 
were performed to assess conditions that affect the stability of waste 
residues resulting from the treatment of high mercury (greater than 260 
mg/kg total mercury) wastes. This NODA also makes available the results 
of the peer review of these studies. As a result of our investigation, 
we have concluded that changes to our national regulations are 
impractical at this time. Additionally, this notice also provides 
information on how to use the existing treatability variance procedures 
to make site-specific choices on alternatives to mercury recovery. The 
treatability studies and the results of the peer review are presented 
here only to provide information--we are not

[[Page 4482]]

requesting comments on the mercury-related issues in this NODA.

ADDRESSES: You may view the supporting materials for this NODA in the 
EPA Docket Center (EPA/DC), B102, EPA West, 1301 Constitution Ave. NW., 
Washington, DC 20460-0002. The docket number is RCRA-202-0029. To 
review file materials, we recommend that you make an appointment by 
calling (202) 566-0270. The EPA/DC is open from 9 am to 4 pm, Monday 
through Friday, excluding Federal holidays. You may copy up to 100 
pages from any regulatory document at no charge. Additional copies cost 
$ 0.15 per page. For information on accessing an electronic copy of the 
treatability study and peer review documents, see the SUPPLEMENTARY 
INFORMATION section.

FOR FURTHER INFORMATION CONTACT: For general information, call the RCRA 
Call Center at 1-800-424-9346 or TDD 1-800-553-7672 (hearing impaired). 
Callers within the Washington Metropolitan Area must dial 703-412-9810 
or TDD 703-412-3323 (hearing impaired). The RCRA Call Center is open 
Monday-Friday, 9 a.m. to 4 p.m., Eastern Standard Time. For more 
information on specific aspects of this NODA, contact Mary Cunningham 
at 703-308-8453, [email protected], or write her at the Office of 
Solid Waste, 5302W, U.S. EPA, Ariel Rios Building, 1200 Pennsylvania 
Avenue, NW., Washington, DC 20460.

SUPPLEMENTARY INFORMATION: 

Table of Contents

I. How Can I Get Copies of This Document and Other Related 
Information?
    A. Docket
    B. Electronic Access
II. What Are the Treatability Studies and Peer Review Results?
    A. Why Is Mercury a Concern?
    B. What Is the Purpose of This NODA?
    C. What Prompted the Treatability Studies?
    D. What Are the Current Treatment Practices for Mercury Wastes?
    E. What Earlier Studies Have Been Performed on Radioactive 
Mercury Waste?
    F. What Treatability Studies Are the Subject of Today's NODA?
    G. What Were the Treatment Technologies Included in Our 
Treatability Studies?
    H. What Were the Study Results?
    I. What Were the Peer Review Results?
    J. What Conclusions Do We Reach From the Treatability Studies?
    K. Why are Treatability Variances an Option for High Mercury 
Wastes?
    L. What Other Implications Arise From the Treatability Studies?

I. How Can I Get Copies of This Document and Other Related Information?

A. Docket

    EPA has established an official public docket for this action under 
Docket Number: RCRA-2002-0029. The official public docket consists of 
the documents specifically referenced in this action and other 
information related to this action. Although a part of the official 
docket, the public docket does not include Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. The official public docket is the collection of materials 
that is available for public viewing at the EPA Docket Center (EPA/DC), 
B102, EPA West, 1301 Constitution Ave. NW., Washington, DC 20460-0002. 
To review file materials, we recommend that you make an appointment by 
calling (202) 566-0270. The EPA/DC is open from 9 a.m. to 4 p.m., 
Monday through Friday, excluding Federal holidays.

B. Electronic Access

    You may access this Federal Register document electronically 
through the EPA Internet under the ``Federal Register'' listings at 
http://www.epa.gov/fedrgstr/.
    An electronic version of the public docket is available through 
EPA's electronic public docket and comment system, EPA Dockets. You may 
use EPA Dockets at http://www.epa.gov/edocket/ to access the index 
listing of the contents of the official public docket, and to access 
those documents in the public docket that are available electronically. 
Although not all docket materials may be available electronically, you 
may still access any of the publicly available docket materials through 
the EPA/DC facility identified above. Once in the system, select 
``search,'' then key in the appropriate docket identification number.

II. What Are the Treatability Studies and Peer Review Results?

A. Why Is Mercury a Concern?

    Mercury is an elemental metal, occurs in certain minerals and is a 
naturally-occurring contaminant of some other natural resources, such 
as certain types of coal. Once released into the environment, inorganic 
forms of mercury may be converted to methylmercury, which is the main 
form of organic mercury found in the environment. Methylmercury may 
accumulate in fish tissue to levels that are unhealthful to humans and 
which harm wildlife. Methylmercury has also been shown to be a 
developmental toxicant, causing subtle to severe neurological effects 
at very low levels of exposure, especially to fetuses and young 
children.\1\ The developing fetus is exposed to mercury if the mother 
eats mercury-contaminated fish during pregnancy. Recent 
data,2 3 indicate that 8% of women of childbearing age in 
the U.S. currently have blood mercury levels higher than EPA considers 
to be a ``safe'' level of exposure.\4\ Children and adults can be 
exposed to mercury if they routinely eat large quantities of 
contaminated fish.
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    \1\ http://www.epa.gov/waterscience/fish/.
    \2\ http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5008a2.htm.
    \3\ http://www.cdc.gov/nceh/dls/report/results/Mercury.htm.
    \4\ http://www.epa.gov/triinter/tridata/tri00/qa.pdf.
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    The problem of mercury-contaminated fish is wide-spread in the U.S. 
As of December 2001, 44 states have issued fish advisories for mercury. 
Twenty-four states have issued statewide advisories.\5\ These 
advisories inform the public that concentrations of mercury have been 
found in local fish at levels of public health concern. State 
advisories recommend either limiting or avoiding consumption of certain 
fish from specific water bodies or, in some cases, from specific water 
body types (e.g., all freshwater lakes or rivers).
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    \5\ http://www.epa.gov/waterscience/fish/.
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B. What Is The Purpose of This NODA?

    Today's notice presents the results of two recent treatability 
studies conducted to assess the feasibility of the treatment of high 
mercury wastes (i.e., wastes containing greater than 260 mg/kg total 
mercury) and elemental mercury destined for disposal. This notice also 
presents the results of the independent peer review of these two 
treatability studies.
    The existing land disposal restrictions (LDR) treatment standards 
require recovery by retorting of high mercury wastes. Based on the 
results of the treatability studies published in today's NODA, we have 
decided not to propose revisions to the existing treatment standards. 
We are concerned that treatment (such as the treatment technologies 
evaluated in our treatability studies) may not result in a waste that 
is stable under some landfill conditions that are within the range of 
normal operations.
    Having said this, we believe there may be site-specific situations 
where treatment and disposal of high mercury wastes or excess elemental 
mercury may be warranted. In these instances, we could grant a petition 
for a site-specific

[[Page 4483]]

variance from the applicable treatment standards under current 
regulations. For a site-specific petition to be granted, it should 
demonstrate that treatment of the waste significantly limits mobility 
of mercury from the treated waste and that the treatment residues are 
stable in the intended disposal environment.

C. What Prompted The Treatability Studies?

    On May 28, 1999, EPA published an advance notice of proposed 
rulemaking (ANPRM) requesting comment to help gain a better 
understanding of the environmental impact of our waste treatment 
standards for mercury-bearing hazardous wastes. In the ANPRM, we 
requested data to support potential alternatives to current LDR 
requirements to reclaim elemental mercury from high mercury subcategory 
wastes (i.e., those wastes that contain greater than or equal to 260 
mg/kg total mercury). However, we did not receive enough information to 
propose changes to any of the mercury treatment standards. Therefore, 
we initiated two research studies to identify the ``currently 
available'' treatment processes and to gather information that could be 
used to potentially change the current mercury treatment standards to 
assure more effective treatment.

D. What Are the Current Treatment Practices for Mercury Wastes?

    In this section, we describe the current regulatory categorization 
for mercury wastes as low mercury subcategory wastes, high mercury 
subcategory wastes, or elemental mercury wastes.
1. What Are the Current Treatment Practices for Low Mercury Subcategory 
Wastes?
    Low mercury wastes are those hazardous wastes containing less than 
260 mg/kg of total mercury. Current regulations require that these 
wastes be treated to achieve a certain numerical level, 0.20 mg/L, 
measured using the Toxicity Characteristic Leaching Procedure (TCLP) 
for mercury residues from retorting, and 0.025 mg/L TCLP for all other 
low mercury wastes. These concentrations are generally met by 
stabilization/solidification treatment. This subcategory of mercury 
wastes was not included in any of the treatability studies described in 
this notice.
2. What Are the Current Treatment Practices for High Mercury 
Subcategory Wastes?
    High mercury wastes are those hazardous wastes that contain greater 
than 260 mg/kg total mercury. Because of this high concentration of 
mercury, they are generally required to undergo roasting or retorting 
(see ``RMERC,'' at 40 CFR 268.42, Table 1). RMERC is defined, in part, 
as: ``Retorting or roasting in a thermal processing unit capable of 
volatilizing mercury and subsequently condensing the volatilized 
mercury for recovery.'' The residuals from the roasting or retorting 
process are then subject to a numerical treatment standard as discussed 
above (if the residues meet the definition of ``low mercury 
subcategory'').
    There may be cases where it is not desirable or practical to retort 
high mercury subcategory wastes. One example of this would be mixed 
radioactive high mercury wastes. See the discussion in Section II.K for 
information on this category of mercury waste.
3. What Are the Current Treatment Practices for Elemental Mercury?
    There are three elemental mercury waste streams that contain most 
of the waste regulated under the LDR program:
    (1) Discarded commercial elemental mercury, off-specification 
elemental mercury, and container and spill residues (RCRA hazardous 
waste code U151) that contain greater than or equal to 260 mg/kg total 
mercury. These waste streams must be treated by roasting or retorting 
(see ``RMERC'' at 40 CFR 268.42, Table 1).
    Additionally, because the uses for elemental mercury in products is 
declining, stockpiles of excess commodity (bulk) mercury currently 
exist; if these stockpiles are deemed to be wastes, then they would 
become subject to the ``RMERC'' standard.
    (2) Elemental mercury contaminated with radioactive materials. 
These waste streams are required to be treated by amalgamation (see 
``AMLGM'' at 40 CFR 268.42 Table 1). AMLGM is defined as: 
``Amalgamation of liquid, elemental mercury contaminated with 
radioactive materials utilizing inorganic agents such as copper, zinc, 
nickel, gold, and sulfur that results in a nonliquid, semi-solid 
amalgam and thereby reducing potential emissions of elemental mercury 
vapors to the air.''
    (3) Characteristically hazardous elemental mercury wastes (RCRA 
hazardous waste code D009) that also are required to be roasted or 
retorted, if they contain greater than or equal to 260 mg/kg total 
mercury.

E. What Earlier Studies Have Been Performed on Radioactive Mercury 
Waste?

    The Department of Energy's (DOE) Transuranic and Mixed Waste Focus 
Area-Mercury Working Group, in conjunction with EPA, has initiated 
studies of the treatability and disposal of mercury wastes resulting 
from nuclear weapons production. These treatability studies have 
evaluated current commercialized state-of-the-art technologies and 
several emerging technologies. To date, DOE and EPA have conducted 
several studies of the treatability of contaminated soils, surrogate 
wastes, and bulk elemental mercury by commercial vendors. The goal of 
the studies has been to identify the range of conditions suitable for 
the disposal of these waste residuals, should direct treatment rather 
than separation be performed. Sepradyne Corporation's vacuum retort 
extraction, Nuclear Fuel Services, Inc. (NFS) DeHg[reg] stabilization 
process, Brookhaven National Laboratory's sulfur polymer 
solidification/stabilization, and ADA Technologies, Inc. (ADA) and 
Allied Technology Group (ATG) sulfur-based solidification/stabilization 
processes have been evaluated.
    A 1999 DOE study \6\ examined the release of mercury from mercury 
amalgams prepared by processes operated by ADA Technologies, Inc. (ADA) 
and Nuclear Fuel Services, Inc. (NFS) as a function of temperature and 
pH. Leachate exposure experiments indicate that amalgams prepared with 
zinc released mercury at high rates into the leachate at acidic (low 
pH) conditions and at lesser rates at neutral pH. These metal-based 
amalgams tended to perform better in alkaline (high pH) solutions. 
Sulfur-based treatment samples showed increased release of mercury 
after two and three months at pH 12.5.\7\ Other studies of mercuric 
sulfide solubility have detected increased solubility of mercury 
sulfide complexes above pH 6 with excess sulfide present.\8\ Mercuric 
sulfide is the product formed from treating elemental mercury with 
sulfur or sulfide salts. The reports for these prior studies are 
available on the internet.\9\
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    \6\ C.H. Mattus, ``Measurements of Mercury Released from 
Amalgams and Sulfide Compounds'', Oak Ridge National Laboratory, 
ORNL/TM-13728, April 1999.
    \7\ Ibid. Table 6, page 17.
    \8\ Jenny Ayla Jay, Francois M. M. Morel, and Harold F. Hemond, 
Mercury Speciation in the Presence of Polysulfides, Environmental 
Science and Technology, 2000, Vol. 34, No. 11, pages 2196-2200.
    \9\ See C.H. Mattus, ``Measurements of Mercury Released from 
Solidified/Stabilized Waste Forms'', Oak Ridge National Laboratory, 
ORNL/TM-2001/17, April 2001, available at http://osti.gov/bridge; 
and F. Sanchez, D.S. Kosson, C.H. Mattus, and M.I Morris, ``Use of a 
New Leaching Test Framework for Evaluating Alternative Treatment 
Processes For Mercury Contaminated Mixed Waste (Hazardous and 
Radioactive)'' http://www.cee.vanderbilt/cee/research_projects.html.

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[[Page 4484]]

F. What Treatability Studies Are the Subject of Today's NODA?

    The studies we just described did not focus on two types of mercury 
waste that we thought were important to address: (1) High mercury 
(containing greater than 260 mg/kg total mercury) waste sludges that 
contain multiple forms of mercury; and (2) bulk elemental mercury.
    We collaborated with DOE to evaluate the ability of commercially 
available treatment processes to reduce the solubility of mercury in 
these two types of waste and to identify stable disposal conditions as 
a potential alternative to current regulations which require the 
reclamation of mercury via roasting or retorting before treatment and 
disposal of the residuals. Because this potential alternative (of 
treatment/disposal as opposed to roasting/retorting) would result in 
much higher concentrations of mercury potentially being land disposed, 
and because of the toxic nature of mercury (see section II.A of this 
notice) and the difficulty of treatment, we decided to evaluate treated 
waste forms using the Toxicity Characteristic Leaching Procedure 
(TCLP),\10\ as well as a constant pH leaching procedure that addresses 
the range of pH conditions that could be expected in hazardous waste 
landfill disposal environments. Because the TCLP only evaluates one pH 
condition that results from the interaction of the waste and the fixed 
acid content of the TCLP leaching solution, we thought it was important 
to supplement the TCLP with the constant pH leaching procedure to 
access the performance of the treatment residuals over the range of 
normal landfill operating conditions. Using this procedure, we examined 
waste solubility over a pH range from 2 to 12. Even though more extreme 
conditions have been observed in landfills,\11\ a recent compilation of 
landfill data finds that approximately 95 percent of all hazardous 
waste landfills are in the 2 to 12 pH range, and more than 90 percent 
are less than pH 10.\12\ By maintaining the pH constant at each level, 
the test simulates the potential for metals to be extracted or 
mobilized from the treated waste form by a large volume of landfill 
leachate passing through and around the waste at the set pH level. This 
also allows treatment performance to be compared at the set conditions. 
An exposure period of 14 days, rather than the 18 hours of the TCLP, 
was chosen to allow all samples time to reach near-equilibrium before 
measurement of the release potential of mercury from the treatment 
residuals. Other factors, such as leachate to solids ratio, oxidation/
reduction potential (eH), particle size, exposure period, and the major 
ions present all affect metal solubility. However, the studies 
presented here primarily focused on the effects of varying pH 
conditions because the solubilities of metals and metal complexes are 
highly pH dependent and the pH conditions of hazardous waste landfills 
are known to vary widely.
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    \10\ See 55 FR 11798, March 29, 1990 for more information on the 
TCLP. The TCLP was originally developed to assess the plausible, 
worst case mismanagement scenario for evaluating industrial waste 
codisposed in a municipal solid waste landfill.
    \11\ 65 FR 37945, June 19, 2000.
    \12\ Characterization and Evaluation of Landfill Leachate 
(Draft), SAIC, September 2000, page 3-33.
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    The results of these two studies are provided in two reports: 
``Technical Background Document: Mercury Wastes--Evaluation of 
Treatment of Mercury Surrogate Waste'' and ``Technical Background 
Document: Mercury Wastes--Evaluation of Treatment of Bulk Elemental 
Mercury,'' available in the docket for today's notice. In this section, 
we provide an overview of these studies.
    The first study evaluated the effectiveness of four technologies to 
stabilize a ``difficult-to-treat'' mercury waste, representing the wide 
range of high mercury wastes that could require treatment. A surrogate 
waste was designed for the study, which included an organic form of 
mercury, elemental mercury, and several mercury salts in an inorganic 
matrix. The surrogate waste was treated by each technology vendor. The 
treated waste was then evaluated for mercury leachability, using both 
the TCLP and an automated, constant-pH leaching protocol. Prior to 
leach testing, waste form particles were reduced in size to 9.5 mm or 
less. The waste forms were exposed to the leaching medium at a 20:1 
liquid to solids ratio, and the pH was monitored and adjusted as 
necessary by computer-controlled addition of acid or base. Constant pH 
leaching was conducted at pH 2, 4, 6, 8, 10, and 12 for 14 days at each 
pH. This leaching procedure and the waste surrogate are described in 
detail in the Technical Background Documents, available in the docket 
for today's notice.
    The second study evaluated the ability of three technologies to 
convert elemental mercury into a stable waste form. The study was 
designed to assist in evaluation of options for disposition of the 
inventory of mercury in the Defense Logistics Agency (DLA) stockpile. 
Bulk elemental mercury was treated by each technology vendor, and the 
treated waste residuals were evaluated for mercury leachability, using 
the same protocols and conditions as those used in the first study.
    In both studies, the total concentration of mercury was measured in 
samples of the untreated starting material (either surrogate waste or 
bulk elemental mercury), in the treated waste form, and in leachates 
(both TCLP and constant pH leaching). In addition, samples of the 
untreated and treated material were characterized, including 
measurements of bulk density, moisture content, percent organic matter, 
cation exchange capacity and particle size distribution.
    Each of the technologies evaluated in these studies relies on 
chemical reactions to minimize volatilization and solubility, rather 
than on recovery or separation technologies which generate a near 
mercury-free residual in addition to concentrated or purified mercury. 
These treatment processes are summarized below.

G. What Were the Treatment Technologies Included in Our Treatability 
Studies?

    Four commercial treatment vendors participated in studies of the 
treatability of the surrogate waste. Because the actual commercial 
amalgamation processes are proprietary, we refer to the aforementioned 
treatment technologies as ``vendors'' to mask their identity. Each of 
the four vendors' processes utilized reagents to bind the mercury forms 
present as various sulfides. The following table presents a comparison 
of these technologies.

[[Page 4485]]



                           Table 1.--Technologies Used for Surrogate Sludge Treatment
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                                                                      Vendor
        Comparison factor        -------------------------------------------------------------------------------
                                           A                   B                   C                   D
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Process Overview................  Sulfur              Formation of        Sulfur              Formation of
                                   amalgamation        mercuric sulfide    amalgamation        mercuric sulfide
                                   followed by         followed by micro-  followed by         followed by
                                   thermoplastic        and                addition of         solidification
                                   encapsulation.      macroencapsulatio   proprietary         with a
                                                       n with              precipitation       proprietary
                                                       proprietary         reagent.            cement-containing
                                                       binders and                             stabilization
                                                       coating agents.                         agent.
Reagents........................  Sulfur polymer,     Sulfide and         Sulfur and          Sulfide and
                                   organic modifier,   proprietary         proprietary         proprietary
                                   and proprietary     binders and         precipitation       cement-containing
                                   additives.          coating agents.     reagent.            stabilization
                                                                                               agent.
Waste Loading\**\ (on dry basis)  30 wt%............  72 wt%............  44.9-47 wt%.......  25.4 wt%.
Final Form......................  Uniform solid mass  Uniform solid mass  Granular..........  Uniform solid
                                                                                               mass.
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** Waste loading is the percentage of waste in the treated residue.

    Three of the vendors also participated in the treatment of 
elemental mercury. Vendor D did not participate in this study. Vendors 
A and B used the same general process for elemental mercury. However, 
Vendor C used a process that differed from what was used in the 
surrogate sludge treatment. The following table presents a comparison 
of the technologies used in the treatment of elemental mercury.

                           Table 2.--Technologies Used for Elemental Mercury Treatment
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                                                                         Vendor
          Comparison factor           --------------------------------------------------------------------------
                                                  A                        B                        C
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Process Overview.....................  Sulfur amalgamation      Formation of mercuric    Amalgamation followed
                                        followed by              sulfide followed by      by addition of
                                        thermoplastic            micro- and               proprietary
                                        encapsulation.           macroencapsulation       precipitation reagent.
                                                                 with proprietary
                                                                 binders and coating
                                                                 agents.
Reagents.............................  Sulfur polymer, organic  Sulfide and proprietary  Amalgamation agent and
                                        modifier, and            binders and coating      proprietary
                                        proprietary additives.   agents.                  stabilization reagent.
Waste Loading\**\ (on dry basis).....  33 wt%.................  44 wt%.................  20.1 wt%.
Final Form...........................  Uniform solid mass.....  Uniform solid mass.....  Uniform solid mass.
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** Waste loading is the percentage of waste in the treated residue.

H. What Were the Study Results?

1. What Were the Study Results for the Surrogate Mercury Waste?
    Presented in Table 3 and discussed below are the constant pH 
leaching results for the surrogate mercury waste. Additional testing 
results (raw data, tables, and graphs) are presented in the report 
``Technical Background Document: Mercury Wastes--Evaluation of 
Treatment of Surrogate Mercury Wastes,'' available in the docket for 
today's notice.

                                                   Table 3.--Surrogate Mercury Waste Treatment Study--Constant Leaching Results (mg/L Mercury)
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                                                   Vendor A \**\                                                          Vendor C                                     Vendor D
                pH                ----------------------------------------------        Vendor B       -----------------------------------------------------------------------------------------
                                          Pellets                Crushed                                       Batch 1                Batch 2                Batch 1               Batch 2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
2\*\.............................  0.00251/               0.00682/               1.92/                  0.356/                 4.39/                  0.127/                0.257/
                                   0.00856                0.00294                0.617                  13.9                   1.11                   0.0775                0.130
4................................  0.00483                0.00555                0.137                  0.0816                 0.0340                 2.63                  4.35
6................................  0.00425                0.0140                 0.102                  0.0441                 0.118                  0.240                 0.289
8\*\.............................  0.0127/                0.00180/               0.0873/                0.0391/                0.0106/                0.0603/               0.0724/
                                   0.00424                0.00139                0.0753                 0.0206                 0.00797                0.0594                0.0658
10...............................  0.00734                0.00378                0.0577                 0.0108                 0.00337                2.17                  0.0204
12\*\............................  0.111/                 0.781/                 0.00885/               0.0353/                0.00239/               0.0156/               0.0250/
                                   0.157                  0.136                  0.00609                0.0336                 0.00264                0.0109                0.0193
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\*\Duplicate analyses were performed at pH levels 2, 8 and 12.
\**\Vendor A provided cast <9mm pellets and a larger material that was crushed to yield a <9 mm form for analysis.

    Each vendor's treatment of surrogate waste achieved a significant 
reduction in mercury release in comparison to the untreated waste form. 
However, there are significant differences in the effectiveness of the 
various technologies. Vendor A's stabilized waste leached less than 
0.025 mg/L \13\

[[Page 4486]]

over the range of pH 2 to 10. However, when exposed to very alkaline 
conditions of pH 12, the waste leached 0.111 to 0.157 mg/L in the 
pellet form and 0.136 to 0.781 mg/L in the crushed form. Vendor B's and 
Vendor C's stabilized wastes leached increasingly higher levels of 
mercury at the acidic conditions of pH 4 and lower. Vendor B's 
stabilized waste achieved 0.025 mg/L only at pH greater than 10. Vendor 
C's stabilized waste achieved 0.025 mg/L only at pH greater than 6 in 
one of the two batches. Vendor D's stabilized waste achieved 0.025 mg/L 
only at pH greater than 10.
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    \13\ The current treatment standard for low-level mercury wastes 
that have not undergone roasting or retorting is 0.025 mg/L mercury, 
as measured by the TCLP. Treatment results are presented relative to 
this numerical benchmark for comparison purposes.
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2. What Were the Study Results for Elemental Mercury?
    Presented in Table 4 and discussed below are the constant pH 
leaching results for the bulk elemental mercury study. Additional 
testing results (raw data, tables and graphs) are presented in the 
report ``Technical Background Document: Mercury Wastes--Evaluation of 
Treatment of Bulk Elemental Mercury,'' available in the docket for 
today's notice.

           Table 4.--Bulk Elemental Mercury Treatment Study--Constant Leaching Results (mg/L Mercury)
----------------------------------------------------------------------------------------------------------------
                                                 Vendor A
               pH               ------------------------------------------       Vendor B           Vendor C
                                       Pellets              Crushed
----------------------------------------------------------------------------------------------------------------
2\*\...........................  0.00542/             0.00658/             0.00105/             29.7/
                                 0.0137               0.0132               0.00156              27.9
4..............................  0.984                0.0621               0.00186              0.315
6..............................  0.0835               16.7                 0.00484              0.0323
8\*\...........................  44.9/                30.8/                0.011/               0.0494/
                                 24.3                 53.5                 0.00832              0.368
9..............................  13.7                 NA                   NA                   NA
10.............................  0.0742               0.0839               0.0118               0.139
11.............................  0.00951/             NA                   NA                   NA
                                 0.0177
12\*\..........................  127/                 74.6/                0.143/               0.0251/
                                 155                  23.5                 0.0672               0.0249
----------------------------------------------------------------------------------------------------------------
\*\Duplicate analyses were performed at pH levels 2, 8 and 12.
NA--Not Analyzed.

    Significant differences were observed between vendors in the 
treatment of elemental mercury. Vendor A's stabilized elemental mercury 
exhibited highly variable leaching as a function of pH. The variability 
observed prompted additional testing at pH 9 and pH 11 to verify and 
better characterize the significant swings in leachate mercury 
concentration. Leaching increased from less than 0.01 mg/L at pH 2 to 
over 24 mg/L at pH 8, reached a minimum of 0.009 mg/L at pH 11, then 
increased significantly as it approached pH 12 (to greater than 127 mg/
L). Vendor B's stabilized elemental mercury shows a gradual increase in 
mercury leaching (from levels of 0.001mg/L to 0.15 mg/L) with the 
increasing pH of the leachate fluid. Vendor C's stabilized elemental 
mercury showed a pattern of decreased leaching with increasing pH, 
approaching the level of 0.025 mg/L only at a pH of 12. These results 
clearly show that there are significant differences in the 
effectiveness of the various treatment technologies. More importantly, 
the results show that leaching of mercury from the stabilized elemental 
mercury is pH dependent.
    One treatment vendor in Europe, Bj[auml]sta [Aring]tervinning, has 
developed a mercury treatment process that results in the formation of 
mercuric selenide. This vendor was one of the treatment vendors that 
submitted proposals to the Department of Defense's Defense Logistic 
Agency (DLA), expressing interest in treating their stockpile of 
elemental mercury. Mercuric selenide is indicated by solubility 
calculations to be one of the more insoluble mercury salts. Even though 
our study was underway, when we learned of Bj[auml]sta 
[Aring]tervinning's proposal to treat the DLA stockpile, we were very 
interested in including their treated waste form in our study. Due to 
logistical difficulties, we were unable to obtain a treated waste form 
from this vendor. We were, however, able to obtain laboratory-grade 
mercuric selenide and conduct limited leachate studies at pH 7 and 10 
which bracket the conditions found at many landfills.\14\ We also 
assessed the effects of the addition of 500 ppm of chloride at pH 7 and 
10. Unlike the other treated waste forms formed from treatment using a 
variety of reagents, the final waste form in this case was a known 
compound: Mercury selenide. Thus, there was readily available 
information on mercuric selenide solubility and the potential 
significant effects of chloride on that solubility. Geochemical 
solubility calculations for the mercuric selenide compound indicated 
that chloride ions would promote the solubility of mercury. Chloride 
ions tend to form strong soluble complexes with mercury, greatly 
increasing mercury's mobility. While mean groundwater chloride 
concentrations are approximately 160 mg/L, landfill leachates range 
from 59 to 6,560 mg/L in industrial landfills and 96 to 31,100 mg/L in 
hazardous waste landfills.\15\ In our study, more than a three-fold 
increase in solubility was observed at both pH conditions with the 
addition of 500 ppm of chloride. At pH 7, the leachate concentration of 
mercury increased with the addition of chloride from 0.006 mg/L to 
0.021 mg/L; at a pH of 10, the concentration of mercury increased from 
0.028 mg/L to 0.11 mg/L. This indicates that major ions present in a 
given disposal environment may significantly impact the release of 
mercury from the treated waste form.
---------------------------------------------------------------------------

    \14\ Characterization and Evaluation of Landfill Leachate 
(Draft), SAIC, September 2000.
    \15\ Ibid.
---------------------------------------------------------------------------

I. What Were the Peer Review Results?

    The complete results of the Peer Review are provided in the docket 
to today's notice (Docket Number: RCRA-2002-0029), along with EPA's 
responses to the Peer Review comments.

[[Page 4487]]

1. What Questions Were Asked of the Peer Reviewers?
    In order to provide a more complete analysis, and in accordance 
with EPA policy, we presented the two new studies for formal, 
independent peer review. The three peer reviewers selected for this 
process are national experts with significant technical expertise in 
hazardous waste leaching, have no prior association with these studies, 
and have no perceived or actual conflict with any impact of the study 
results. The members of the peer review panel were tasked with 
evaluating the adequacy of the experimental design, conduct, and 
conclusions of the two studies. The peer review panel also provided 
information on how the studies can be used to provide a framework to 
determine whether additional protective measures are required to 
prevent loss of mercury to the environment from the treatment and co-
disposal of mercury-bearing wastes in landfills.
    Additionally, the members of the peer review panel were asked if 
additional studies were warranted for other factors that impact 
solubility (e.g., liquid/solid ratio, redox conditions, leachate 
composition) or affect ability to leach (such as use of 
macroencapsulation).
2. What Did the Peer Reviewers Say About the Study of the Treatment of 
Mercury Surrogate Wastes?
    Two of the peer reviewers stated that the experimental design was 
appropriate for the study. One reviewer, however, said the design did 
not follow the Data Quality Objectives (DQOs) process, and argued that 
there is little relationship between the objectives and the design. We 
disagree with this reviewer, however. EPA has developed the DQOs 
process as the Agency's recommended planning process when environmental 
data are used to select between two opposing conditions, such as 
achieving or not achieving a numerical standard.\16\ The DQOs process 
is used to develop qualitative and quantitative statements of the 
overall level of uncertainty that a decision-maker is willing to accept 
in results or decisions derived from environmental data, i.e., Data 
Quality Objectives. The DQOs process entails a seven step systematic 
procedure for defining the criteria that a data collection design 
should satisfy, including when to collect samples, where to collect 
samples, the tolerable level of decision error for the study, and how 
many samples to collect, balancing risk and cost in an acceptable 
manner. When this process is not directly applicable (i.e., the 
experimental objective is estimation, research, or any other objective 
that does not select between two distinct conditions), the Agency 
recommends the use of a systematic planning method for defining 
performance criteria.\17\ For this research project, a systematic 
planning method was used. The project planning process used and the 
planning documents development were guided and overseen by EPA/ORD 
staff, and the Quality Assurance Project Plan (QAPP) was reviewed and 
approved by an EPA/ORD quality assurance expert. EPA believes that the 
project objectives and criteria were logical, given the intended end-
use of the data, well-defined, and achievable.
---------------------------------------------------------------------------

    \16\ See EPA/600/R-96/055; Guidance for the Data Quality 
Objectives Process. http://www.epa.gov/quality/qs-docs/g4-final.pdf
    \17\ Ibid.
---------------------------------------------------------------------------

    The three reviewers all stated that the study was conducted 
properly. The three reviewers also stated that the studies met the 
objectives of: (1) Evaluating the ability of alternative treatment 
technologies to achieve a goal of 0.025 mg/L or less for the 
stabilization of mercury over a range of pH levels from 2 to 12; and, 
(2) to compare constant pH leaching protocol results to standard TCLP 
results. Two of the reviewers evaluated the ability of each treatment 
technology to meet the treatment goal, and concluded that the ability 
of each technology to meet the treatment goal in the constant pH 
leaching was pH-dependent.
    The reviewers suggested additional studies to fill in specific data 
gaps. One reviewer noted that additional extractions up to at least pH 
12.5 are needed to supplement the report. While we agree evaluation of 
a broader range could be helpful, we do not believe that additional 
studies are cost effective, because only a small fraction of hazardous 
waste landfills have been observed to have leachates above pH 12. In 
cases where disposal is proposed at or above pH 12.5, additional data 
for such conditions may be necessary to establish that treatment is 
effective for the expected disposal conditions. (See section II.F of 
today's notice for a discussion of pH levels in hazardous waste 
landfills.)
    Another reviewer suggested that two or more actual wastes (rather 
than surrogates) containing over 260 mg/kg of mercury be subjected to 
stabilization and leaching by the TCLP as well as by the constant pH 
protocols. EPA agrees that using actual wastes, rather than surrogates, 
for treatability tests can be desirable. However, in many cases during 
the history of establishing treatment standards in the BDAT program, 
EPA has used surrogates in lieu of actual wastes, whenever 
representative ``hard-to treat'' wastes were not readily obtainable. 
Specifically, in the case of characteristic wastes, which can be 
extremely variable, using a surrogate allows us to evaluate a ``hard-
to-treat'' waste. Using a ``hard-to-treat'' waste is useful if the 
ultimate treatment results will be used for other forms of that waste, 
which in the case of a characteristic waste like D009, is likely the 
case. In the studies discussed in this notice, where we were trying to 
determine how these forms of mercury would respond to treatment and 
determine how the treated waste forms would react to various pH 
environments, we are comfortable that using surrogate wastes did not 
diminish the value of the studies.
3. What Did the Peer Reviewers Say About the Elemental Mercury Study?
    One of the peer reviewers agreed that the experimental design was 
appropriate for the study. Another reviewer said that a statement of 
acceptable errors should have been included (e.g., a treatment 
technology must be effective on 90% of wastes with a 90% confidence). 
Without such a statement, he said, it is difficult to decide when a 
technology provides adequate treatment. EPA believes that a statement 
of acceptable errors as constructed by the reviewer was not 
appropriate. The objective of the study was to determine how these 
forms of mercury would respond to treatment and to determine how the 
treated waste forms would behave in various pH environments.
    Another reviewer also said the experimental design was generally 
appropriate; however, it failed to confirm that concentrations of 
elemental mercury in the treated wastes were at the values reported by 
the vendors. He added that the recoveries (i.e., measure of total 
mercury present) for treated elemental mercury wastes submitted by 
Vendors A and C are so low that they cast doubt on the results of the 
leach tests. We disagree. The analysis of mercury content of the 
treatment residuals and that of the leachates are two distinct 
analyses. The low recoveries for the treated elemental mercury wastes 
were a result of the difficulty in digesting the solid waste form to 
dissolve the mercury and make it available for analysis; as a result, 
waste loadings reported by the vendors could not be verified. Regarding 
the leach tests, all spike recovery measurements of the leachates 
achieved

[[Page 4488]]

quantitative recoveries between 84% and 109%. Thus, there is no 
evidence of a problem with the analysis of mercury in the leachates. We 
believe this is because the mercury was in solution, and therefore, 
available for analysis.
    All reviewers said that the study was conducted properly. Reviewers 
were then asked whether the stated objectives were adequately met. All 
reviewers agreed that the studies met the objectives of: (1) Evaluating 
the ability of alternative treatment technologies to achieve a goal of 
0.025 mg/L or less for the stabilization of mercury over a range of pH 
levels from 2 to 12; and, (2) to compare constant pH leaching protocol 
results to standard TCLP results.
    The reviewers all agreed that the results of the bulk elemental 
mercury study supported the conclusion that the presence of chloride 
ions in a given disposal environment may significantly impact the 
release from a treated waste form (mercury selenide).
4. What Additional Studies Are Recommended?
    When asked if further studies were recommended for other factors 
that impact solubility, one reviewer recommended additional extractions 
up to at least pH 12.5. Again, as described above, we do not agree that 
additional studies are warranted for this pH range, as few landfills 
have been shown to maintain pH conditions in excess of pH 12. This 
reviewer also recommended that mercuric selenide waste should be 
evaluated over the range of pH 2 to 12.5, with varied chloride content 
in the leachate. We agree that if additional studies were planned, it 
would be useful to further investigate mercuric selenide or elemental 
mercury treated to a mercuric selenide composition across a wider range 
of pH values than the 2 pH conditions in our study. We also believe 
that varying chloride content and other potentially significant 
variables across the pH range for all waste forms would be a useful 
study, and would provide additional information on the potential 
effects of chloride content in landfill leachate.
5. Must Site-Specific Disposal Conditions Be Considered Along With 
Appropriate Treatment Technology as Decisions Are Made About Disposal 
of Mercury Wastes?
    Peer reviewer opinions were mixed as to whether the studies 
supported the assertion that site-specific disposal conditions must be 
considered along with appropriate treatment technology as decisions are 
made about disposal of mercury wastes. One reviewer stated that the 
studies provide useful data on pH and chlorides, but do not provide 
adequate support for an absolute requirement. The reviewer also stated 
that, ``For any disposal of hazardous wastes, treated or untreated, it 
is scientifically preferable to use site-specific information.'' This 
reviewer maintained, however, that requiring the factoring of site-
specific conditions into decision making is not always feasible. 
Another reviewer's comments countered that these research results do 
support the assertion, because they demonstrate that leaching fluids, 
which vary greatly in pH under different disposal conditions, can have 
an important impact on the amount of mercury leached from the treated 
wastes. The third reviewer suggested that if several actual wastes have 
been tested and are shown to be stable at all pH values, then selection 
of stabilization technology would not require any site-specific 
considerations. We do not agree with this reviewer's comment, because 
we believe that there are other factors (redox conditions, presence of 
chlorides, etc.) besides pH, which would likely impact the solubility 
of the treated waste form.
    The complete results of the peer review are provided in Docket 
Number: RCRA-2002-0029, along with EPA's responses to the peer review 
comments.

J. What Conclusions Do We Reach From the Treatability Studies?

    For wastes containing a wide range of mercury compounds, treatment 
can result in a residual of reduced solubility under certain pH 
conditions. Our treatability studies showed that the leaching of 
mercury out of the stabilized waste form varied with pH. We saw that 
some of the vendor's treatment of surrogate waste performed better in 
certain pH ranges. For example, Vendor A performed best (i.e., achieved 
levels less than 0.025 mg/L) except in very alkaline conditions (i.e., 
when the pH was greater than 10), whereas Vendor B's treatment 
performed best only under very alkaline conditions. Because the pH in a 
hazardous waste landfill can vary anywhere from near pH 2 to over pH 
12, it appears that none of the treatment processes tested in the 
studies presented here are effective for the entire range of pH levels 
that could exist.
    We find that the evaluated processes are effective to a degree for 
the treatment of elemental mercury wastes. Several have been 
demonstrated to achieve 0.025 mg/L or better under certain pH 
conditions. However, vapor pressure measurements \18\ and observation 
of small droplets of mercury in some samples of the treated wastes lead 
us to believe that some treatment processes did not result in complete 
treatment of all the elemental mercury in every test sample. We also 
believe that the testing conditions cannot be considered to be worst-
case, because the additional presence of sulfide and chloride ions in 
leachates can promote formation of soluble mercury complexes.
---------------------------------------------------------------------------

    \18\ C.H. Mattus, ``Measurements of Mercury Released from 
Solidified/Stabilized Waste Forms,'' Oak Ridge National Laboratory, 
ORNL/TM-2001/17, April 2001. Available at http://osti.gov/bridge.
---------------------------------------------------------------------------

    The physical properties of elemental mercury present significant 
challenges to its long-term management. Mercury cannot be destroyed. 
Elemental mercury is easily vaporized due to its vapor pressure at 
ambient temperatures. Also, elemental mercury is not significantly 
soluble \19\ and therefore not readily detected by short term leachate 
tests, such as the TCLP. Disposal of large amounts of elemental mercury 
require control of both volatilization losses and any subsequent 
solubilization in leachates. Thus, for protective long-term management 
in a disposal environment, elemental mercury first has to be treated to 
convert it to a form with reduced volatility and solubility, and then 
measures must be put into place to prevent these treatments from being 
degraded once the properties of the treatment residual have been 
determined.
---------------------------------------------------------------------------

    \19\ The solubility of elemental mercury is 0.056 mg/L at 
25[deg]C (MERCK Index).
---------------------------------------------------------------------------

    The physical properties of mercury also present treatment 
challenges. At ambient conditions, mercury is an extremely dense liquid 
with high surface tension. It does not appreciably dissolve into, or 
adhere to, wastes or environmental media, and because of its density 
and surface tension, it is extremely difficult to distribute 
homogeneously through the treatment reagents. Consequently, large 
volumes of treatment reagents are needed to contact and react with the 
elemental mercury, resulting in low waste loadings and large volume 
increases.
    The current treatment standard for high mercury and elemental 
mercury wastes is recovery of mercury followed by land disposal of any 
treatment residuals that pass a leaching standard.\20\ The results of 
the treatability studies outlined in this notice lead us to conclude 
that, at this time, we cannot

[[Page 4489]]

establish a new national treatment standard allowing for disposal of 
high mercury and elemental mercury wastes. We continue to believe that 
the current recovery standard is the most appropriate standard for most 
high mercury waste. No technology demonstrated adequate stability 
across the plausible range of pH conditions found in landfills. We 
recognize that other factors, including leachate salinity, can have a 
significant effect on the solubility of treated mercury wastes. These 
other factors may be the reason that we have not been able to find a 
single technology that is effective in all or many situations.
---------------------------------------------------------------------------

    \20\ Residuals that do not pass the leaching standard would 
require additional treatment to meet the standard for the applicable 
subcategory of mercury waste.
---------------------------------------------------------------------------

K. Why Are Treatability Variances an Option for High Mercury Wastes?

    While these circumstances do not allow us to modify or provide an 
alternative national treatment standard for high-mercury hazardous 
wastes to allow for disposal, we are deferring to our variance process 
for stakeholders who believe it would be appropriate to use an 
alternative treatment technology for their wastes and expected disposal 
conditions. Under 40 CFR 268.44(h), we allow facilities to apply for a 
site-specific variance for wastes generated under conditions specific 
to only one site. In such cases, the generator or treatment facility 
may apply to the Administrator, or EPA's delegated representative, for 
a site-specific variance from a treatment standard.
    In cases where roasting and retorting for a certain waste is 
inappropriate, a generator can consider petitioning for a site-specific 
variance from that treatment standard. At a minimum, the generator 
would want to look for the treatment technology that would be most 
effective in the expected pH range for the chosen disposal site. In 
general, for a site-specific petition to be granted, it should 
demonstrate that treatment has occurred and that the treatment residues 
are stable in the intended disposal environment.
    For example, a variance may be appropriate for a high mercury 
subcategory waste that also is radioactive (i.e., a mixed waste). The 
current regulations require high mercury-organic subcategory mixed 
wastes be treated by retorting (RMERC) or incineration (IMERC) and high 
mercury-inorganic subcategory mixed wastes be treated by RMERC. At the 
time of promulgation, the assumed approach for compliance with these 
regulations was separation of the mercury from the wastes and recycling 
of the pure elemental mercury back into commerce. However, this assumed 
compliance scenario is invalid for mixed wastes containing mercury 
because there is no use for recovered mercury that is radioactively 
contaminated.
    To manage this type of waste, it would appear reasonable to use, on 
a site-specific basis, the ``inappropriate'' variance approach (Sec.  
268.44(h)(2)(i)). A petitioner using this approach would necessarily 
have to describe the specifics and likely effectiveness of the 
stabilization treatment that will be used. As demonstrated by the 
studies described in today's notice, the stability of treated waste 
forms can be highly dependent on pH conditions. In determining whether 
the proposed technology is protective, EPA would expect the petitioner 
to demonstrate the technology's effectiveness under the planned 
disposal conditions.
    LDR variance petitions should be submitted in accordance with the 
procedures in 40 CFR 260.20. Petitions should include, among other 
things, a description of the process that generates the waste, the 
rationale for the variance request, and data on the proposed waste 
treatment process.\21\ Site-specific circumstances often dictate the 
types and amount of information that we will need to evaluate a 
petition, so stakeholders who are considering petitioning for a 
treatment variance should engage EPA early in the process to ensure all 
of the necessary information is, or will be, available.
---------------------------------------------------------------------------

    \21\ Note that when submitting data, petitioners should also 
include evidence that appropriate quality assurance/quality control 
procedures were followed in generating the data. For guidance, see 
Final Best Demonstrated Available Technology (BDAT) Background 
Document for Quality Assurance/Quality Control Procedures and 
Methodology; USEPA, October 23, 1991.
---------------------------------------------------------------------------

L. What Other Implications Arise From the Treatability Studies?

    Because these treated waste forms may be chemically altered by 
environmental conditions, macroencapsulation prior to land disposal 
could be used to provide a barrier against leachate intrusion and 
attack on the treated mercury waste. Macroencapsulation would also 
provide a barrier to reduce emissions of elemental mercury vapors. In 
order to meet the performance requirements of 40 CFR 268.45, Table 1, 
the macroencapsulation treatment must completely encapsulate the waste 
and be resistant to degradation by the waste, its contaminants, and 
materials into which it may come into contact after placement. We 
promulgated such a requirement for wastewater treatment sludge from the 
production of vinyl chloride monomer using mercuric chloride catalyst 
in an acetylene-based process; hazardous waste K175 (65 FR 67068, 
November 8, 2000). For K175 wastes, we estimated that 
macroencapsulation and placement in a hazardous waste landfill 
utilizing high density polypropylene vaults adds an additional $150 to 
$200 per ton of waste disposed to the treatment costs.\22\ For a review 
of the current state of encapsulation technologies and materials being 
used to immobilize elemental mercury, mercury-contaminated wastes, 
soils, or sludges, see the technical report ``Advances in Encapsulation 
Technologies for the Management of Mercury-Contaminated Hazardous 
Wastes,'' Battelle, August 30, 2002, available in the docket for this 
notice.
---------------------------------------------------------------------------

    \22\ Economics Background Document--USEPA Final Rule Listing 
Wastewater Sludges Generated By Chlorinated Aliphatic Chemical 
Manufacturing Facilities, as RCRA Hazardous Waste Codes K174 and 
K175: Industry Profile and Estimation of Regulator Costs; page 74. 
http://www.epa.gov/epaoswer/hazwaste/id/chlorali/ca_ebd.pdf
---------------------------------------------------------------------------

    Having concluded that treatment residues of elemental mercury are 
potentially subject to attack by leachates and that the technologies 
may not have fully reacted with the mercury, we are evaluating whether 
to propose modifying the treatment standards for the radioactive 
elemental mercury waste subcategories of U151 and D009. The current 
treatment standard for these wastes is amalgamation (AMLGM). We could 
propose, for example, to replace this standard with the more 
restrictive requirement of amalgamation followed by macroencapsulation. 
We could also require post-treatment testing to ensure effective 
treatment. If we decide to amend the treatment standards, we would 
publish a proposed rule for public comment.

    Dated: January 22, 2003.
Robert Springer,
Director, Office of Solid Waste.
[FR Doc. 03-2035 Filed 1-28-03; 8:45 am]
BILLING CODE 6560-50-U