United States
                    Environmental Protection
                    Agency
                    Research and Development
  Risk Reduction
  Engineering Laboratory
  Cincinnati, OH 45268
  EPA/600/SR-93/167    October 1993
or EPA       Project  Summary

                    Evaluation  of  Solidification/
                    Stabilization  Treatment
                    Processes  for Municipal  Waste
                    Combustion  Residues

                   David S. Kosson, Teresa T. Kosson, and Hans van der Sloot
                    The investigations described in this
                   report were carried out to compare and
                   evaluate the effectiveness of solidifica-
                   tion/stabilization  (S/S) processes as
                   treatment  technologies for residues
                   from  municipal  waste combustion
                   (MWC). A  full, factorial, experimental
                   design was used  to evaluate five S/S
                   processes. The two experimental fac-
                   tors were the residue type to be treated
                   and the S/S process. The three experi-
                   mental  levels within the residue type
                   factor were (1) bottom ash, (2) air pol-
                   lution control (APC) residue, and  (3)
                   combined ash. The six experimental lev-
                   els within the S/S  process factor were
                   the  untreated residue, a Portland-ce-
                   ment-only  control process, and four
                  selected vendor processes. Thus, 2 ex-
                  perimental  factors at 3 and 6 experi-
                  mental levels, respectively, resulted in
                  the evaluation of 18 experimental cases.
                    Evaluation of each experimental case
                  included analysis of chemical compo-
                  sition, physical properties, durability,
                  and leaching characteristics. The test-
                  ing included moisture content, loss on
                  ignition, bulk density, modified Proctor
                  density, particle size distribution, per-
                  meability, specific surface area, po-
                  rosity, cone penetrometer, unconfined
                  compressive strength, pozzolanic ac-
                  tivity, unconfined compressive strength
                  after immersion, wet/dry, freeze/thaw,
                  toxicity characteristic leaching proce-
                  dure (TCLP),  availability leach  test
                  (ALT), distilled water leach test (DWLT),
                  acid neutralization capacity (ANC), and
                  the monolithic leach test (MLT).
   Based on comparison  of untreated
 residues with treated residues, the S/S
 processes evaluated generally did not
 decrease the potential for the release
 of target contaminants.  A phosphate
 process did, however, reduce the po-
 tential for lead to be released. Whether
 treated or not, the typical release po-
 tential for metals was a small fraction
 of the total metal concentration present
 in the residues.
   This Project Summary was developed
 by EPA's Risk Reduction Engineering
 Laboratory, Cincinnati, OH, to announce
 key findings of the  research  project
 that is fully documented in a separate
 report of the same title  (see  Project
 Report ordering information at back).

 Introduction
   The proper management of MWC resi-
 dues is necessary to ensure that the use
 of combustion as a solid waste manage-
 ment method protects human health and
 the environment. Although recent Federal
 regulations for  municipal  solid waste
 (MSW) and landfills (Federal Register, Oct.
 9, 1991) address the disposal of MWC
 residues, regulations specific to ash dis-
 posal generally remain the responsibility
 of individual  states.  Recently, the  U.S.
 Congress has considered legislation that
 would require the U.S. Environmental Pro-
 tection Agency (EPA) to develop compre-
 hensive national ash disposal, treatment,
 and utilization standards. To have the sci-
entific data available to support possible
future legislative requirements to promul-
gate technical guidance and/or regulations
                                                                 Printed on Recycled Paper

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for the proper management of MWC resi-
dues, the EPA  initiated studies  on MWC
ash characteristics, ash disposal facilities,
and ash management practices. This study
adds to that database.

Specific Objectives and
Approach
  The investigations described in this re-
port  were  carried out to compare and
evaluate the effectiveness  of  S/S pro-
cesses as treatment technologies for bot-
tom ash, APC residue, and combined ash.
Rather than determine how ash charac-
teristics are affected by municipal waste
combustor designs, operating conditions,
and waste input, the program emphasized
the evaluation of S/S treatment  technolo-
gies. Therefore, the residues included in
the study were limited to those from a
single, modern, waste-to-energy  facility.
The specific objectives of this study were
to:
   1. define residue sampling, preparation,
     and characterization protocols to
     permit bench and pilot-scale
     demonstrations  of  S/S treatment
     processes  with  representative
     residues;
   2. carry out MWC residue S/S  treatment
     process  demonstrations  under
     carefully controlled  and monitored
     conditions;
   3. determine how the  S/S  treatment
     process  affects the fundamental
     physical and chemical properties of
     the MWC  residues;
   4. compare  the effects  of  the S/S
     processes on leaching properties of
     MWC  residues through laboratory
     procedures,  which include the TCLP
     and other tests  that  can  estimate
     contaminant  release potential and
     release rate  over a prolonged period
     of   time   and   under   diverse
     environmental conditions; and,
   5. evaluate the physical  durability  of
     the treated  MWC  residues  during
     aggressive  environmental cycling
     tests.
  A full factorial design was used to evalu-
ate five S/S processes for treating MWC
residues.  The  two  experimental factors
were the residue  type to  be treated and
the S/S  process.  Residue types  tested
were  (1) bottom  ash, (2) APC residue,
and (3)  combined ash.  The six experi-
mental levels within the S/S process fac-
tors were the untreated residue, the Wa-
terways Experiment Station (WES) Con-
trol (Portland cement only) S/S  process,
and four selected vendor  S/S processes.
Thus, 18 experimental cases were evalu-
ated in triplicate.
  The three residue types were obtained
during a single composite sampling taken
from a typical, state-of-the-art, mass-burn
municipal  waste combustor.  The facility
has a lime-slurry spray drier (wet-dry), an
acid gas scrubber, and a fabric filter par-
ticulate removal  system.  Bulk residue
samples  were dried, size reduced,
screened,  and homogenized  before  use
in this program. Thus  all process demon-
strations,  testing, and evaluations were
carried  out on preprocessed  residues to
facilitate laboratory-scale testing and the
comparisons of treatment effects.
  Five  S/S processes  were evaluated.
Four  of the processes  were proprietary
modifications of four different  generic S/S
processes. The four proprietary processes
evaluated  were:
  •   Portland cement  and  polymeric
    additives or other proprietary additives
    (Process 1);
  •  Portland cement and soluble silicates
    (Process 2);
  •  Cement  kiln dust  and  proprietary
    additives (Process 3);
  •  Addition  of soluble phosphates
    (Process 4).
  The fifth process (WES) used Type 1
Portland cement  only  (control  process).
The Type  1 Portland-cement-only process
was selected to provide a baseline com-
parison of the treatment effects of Port-
land cement without vendor additives.
  All  vendors  demonstrated their specifi-
cally  designed S/S processes  on each
residue type. The vendors were provided
approximately 50  Ib of each residue type
to develop optimum formulas before the
process demonstrations. They were also
provided a list of test and program objec-
tives that would be used to evaluate each
process. The vendors were not provided
specific performance criteria to which the
residue should be  treated; performance
criteria were  left to the vendor's discre-
tion. Based on analysis of results, vendor
process optimization may have  focused
on minimizing  contaminant release based
on TCLP, concurrent with minimizing cost,
and not on maximizing the physical prop-
erties of the treated  residue.
  Demonstrations were conducted under
the  observation  of  EPA representatives
and  U.S.  Army Corps of Engineers per-
sonnel.  Each demonstration, done in trip-
licate,  consisted of the vendor  carrying
out  the  specified process to produce ap-
proximately 100 Ib of treated residue. Each
experimental case was analyzed for chemi-
cal  composition  and tested for  physical
properties, physical  durability, and leach-
ing characteristics with the use of the fol-
lowing tests:   moisture content,  loss  on
ignition, bulk density, modified Proctor den-
sity, particle size distribution, permeability,
specific surface area  and porosity, cone
penetrometer,  unconfined compressive
strength, pozzolanic activity,  unconfined
compressive strength after immersion, wet/
dry, freeze/thaw, TCLP, ALT, DWLT, ANC
test, and MLT.

Summary of Leaching Tests
  The leaching tests were selected to pro-
vide a broad  understanding of contami-
nant release under a  variety of potential
environmental conditions. The primary ob-
jective was to evaluate fundamental leach-
ing properties rather than to simulate spe-
cific environmental exposure  scenarios.
These fundamental  leaching  properties
were  (1) release potential, (2) elemental
solubility as  a function  of pH,  and  (3)
release rate under diffusion-controlled con-
ditions. This approach permits  the use of
leaching data to estimate contaminant  re-
lease for a  variety of environmental condi-
tions  instead of only the particular expo-
sure scenario tested. TCLP also was car-
ried out on  untreated and treated residues
for  comparison purposes. Untreated resi-
due samples were tested after mechani-
cal processing steps,  which  included
screening,  size reduction, and homogeni-
zation. Therefore, results from testing the
untreated residues may  not be indicative
of the behavior of "as disposed" residues,
which have not been mechanically pro-
cessed. The leaching tests and the basis
for  selecting each are discussed in  the
following paragraphs.
  The TCLP was selected to allow these
results to be compared with a broad data-
base of results from tests of other materi-
als. The TCLP was carried out in accor-
dance with the method  outlined in  the
U.S. Code of Federal  Regulations,  Title
40, Part 268, Appendix 1.1988. In this test,
a solid  sample  is crushed to  a sample
size less than  9.5 mm  and is extracted
with dilute  acetic acid at  a 20:1 liquid-to-
solid ratio. The extraction solution is either
buffered  or unbuffered depending on the
alkalinity of the material to be tested. Only
a fixed  quantity of acid  is used for  the
extraction,  and therefore, the final pH of
the extract  may vary widely. Thus, metals
concentrations observed in the  extract  of-
ten reflect the pH-dependent solubility con-
straints of the specific element. The con-
taminant  concentrations in  the  test
leachate are compared with a published
list of limits  that apply to hazardous wastes
(not MWC residues).
  The ALT was selected to assess  the
maximum amount of specific elements or
species that could be  released under  an

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  assumed "worst case" environmental sce-
  nario. This test, originally  developed by
  the Netherlands Energy Research Center,
  is carried out on a sample size reduced to
  less than 300 nm. Two serial  extractions
  are carried out, each at a 100:1 liquid-to-
  solid ratio, with the use of distilled water.
  The pH is controlled to pH 7  during the
  first  extraction  and to pH  4  during the
  second extraction by using an automatic
  pH controller that delivers  dilute nitric acid.
  Thus, the final extraction  pH is controlled
  rather than the amount of acid used. The
  first and second extracts are combined for
  analysis. The very large liquid-to-solid ra-
  tio ensures that the contaminant release
  is not constrained by  its  solubility  at the
  final pH and that the amount of contami-
  nant extracted is the maximum amount
  that would be available at  that pH. This
  test generally extracts all species not tightly
  bound in a mineral or glassy matrix. The
  test does not provide  information  on the
  rate of contaminant release.
    The DWLT  was selected to assess the
  amount of specific elements or species
  that might be released under  continued
  exposure to rainfall or to clean water per-
  colation. Synthetic acid rain solutions were
  not selected because the  very high natu-
  ral alkalinity of the residues  would  signifi-
  cantly limit the effects of acid rain acidity.
  The DWLT was carried out in accordance
  with procedures of the sequential  batch
  leaching test used at the Environmental
  Laboratory, U.S. Army Corps  of Engineers.
 A sample, crushed in size to  less than 2.0
 mm, is extracted four times in succession,
 each at a 10:1  liquid-to-solid  ratio with the
 use of distilled water as  the extractant.
 Acid is not added nor is  pH controlled.
 Thus, the natural buffering  capacity of the
 material controls the final extract pH, which
 was typically between pH  10 and  12 for
 the materials tested. The first and second
 extracts were  combined for  analysis, as
 were the third and fourth extracts. Results
 are used to estimate the amount of con-
 taminant released over prolonged  expo-
 sure to the leachant and to  provide limited
 information on the rate of contaminant re-
 lease.
  The ANC test assesses the solubility of
 specific metals over a  broad pH range.
 The test was  carried  out  on a  residue
 sample crushed and size reduced to less
 than 300 urn. Eleven separate extractions
 are performed using separate samples at
 a liquid-to-solid ratio of 5:1. The low liq-
 uid-to-solid ratio results in  the extraction
being  solubility-constrained for  some
analytes. Each  extraction receives a dif-
  ferent amount of dilute nitric acid, varying
  from 0 to 12 meq/g dry residue, resulting
  in a range of final pHs. A titration curve
  also is obtained for each material tested.
    The MLT was used to  assess the re-
  lease rate  of specific elements and  spe-
  cies from the untreated and treated  resi-
  dues under diffusion controlled conditions.
  This would be the case under field condi-
  tions where the flow  of infiltration or  con-
  tacting  water is  predominantly  around
  monolithic  structures (e.g., blocks, other
  forms, or low permeability,  compacted fill).
  The  MLT was  carried out  based on a
  modification of the  American Nuclear So-
  ciety (ANS), American National  Standard
  Measurement of the Leachability of Solidi-
  fied Low-Level  Radioactive Wastes by a
  Short-Term  Test  Procedure  (ANSI-
  16.1,1986). A 4-cm diameter by 4-cm long
  cylindrical,  monolithic sample was tested
  instead of the specified size test speci-
  men. The monolithic samples were ex-
  tracted by  contacting them  with  8.47 L
  distilled water for up to 64  days. Contact-
  ing water was replaced with fresh distilled
  water at 1,  2, 4, 8, 16, 32, and 64 days
  and analyzed for metals and other spe-
  cies.
    A new  test method was  developed for
  evaluating compacted granular materials.
  Release rate data were obtained for  un-
  treated bottom ash and combined ash by
  compacting  each ash at optimum mois-
  ture content,  using  modified  Proctor
  compactive  effort,  in  4"  diameter by  4"
  long cylindrical polyethylene molds. Speci-
  mens were cured in the mold for 28 days
 at  24°C and 98% relative  humidity.  The
 exposed face of the  specimen  in  each
 mold was covered with  a 22-mm-thick layer
 of  3-mm-diameter glass beads and con-
 tacted with 8.47 L distilled water. Contact-
 ing water was replaced with fresh distilled
 water at 6 hr and at  1, 2, 4,  8, 16, and 32
 days.
   Modeling  of the release  data in con-
 junction with the  results of the availability
 leach test was used to determine effective
 diffusion coefficients, tortuosity, and chemi-
 cal retention factors for  estimating long-
 term  release rates for selected species.
 The full report provides the results of each
 of these determinations for each element
 assayed and for each S/S  process and
 residue type  evaluated.

 Test Results
  When the extracts from laboratory leach
tests are  chemically analyzed, the con-
centration in  the aqueous phase  can be
determined.  However,  transforming the
  concentration data into element or spe-
  cies release (e.g., the mass of an element
  or species emitted from the solid matrix
  into  the extract per  unit mass  of  solid
  extracted) permits normalization  and the
  comparison  of data obtained from differ-
  ent leach tests. The  TCLP,  DWLT, and
  ALT are all intended to assess the poten-
  tial for (or the maximum extent of) species
  release  under different extremes of leach-
  ing conditions.  Each  test, however, em-
  ploys different  liquid-to-solid ratios  and
  extraction conditions.  Only the TCLP has
  a defined concentration basis for interpre-
  tation of resulting extract concentrations.
  Thus, data  interpretation  on an extract
  concentration basis is of limited  value.
  Using additives for each treatment  pro-
  cess and varying treated residue moisture
  contents may result in  dilution effects, fur-
  ther confounding direct comparison of ex-
  tract concentration data.  To provide more
  uniform  data interpretation  from  these
  leaching tests, extract concentration data
  were transformed to a basis of release
  per mass of residue  extracted. Results
  are based on a comparison of  treated
  residues with the untreated  results. The
  typical release potential for metals was a
  small fraction of the total metal concentra-
  tion present in the  residues.  Detailed re-
  sults for  each element assayed for each
  process and  residue type are provided in
  the full report.
   The TCLP, DWLT, and the ALT leach-
  ing data  are interpreted on a release ba-
  sis  because these test results most fre-
  quently are  viewed as the  potential for
  release under the extreme conditions rep-
 resented  by the testing procedures. The
 ANC  test is  the principal exception  to
 leaching  data interpretation on a release
 basis. The ANC test was performed at a
 low liquid-to-solid ratio (5:1)  to  facilitate
 determining pH titration curves and satu-
 rated solution concentrations of a variety
 of elements as a function of  pH. There-
 fore, it was most  useful to  present ANC
 data on a concentration basis. In addition,
 extract data also have been presented on
 a concentration basis for  cadmium, cop-
 per, lead,  and  zinc from  TCLP extractions.
  Table 1 summarizes  the  levels of im-
 mobilization achieved by each process for
 each of the target elements in all three
 residues, as obtained by the most aggres-
 sive of all leaching procedures used, the
 ALT. These levels ranged from total im-
 mobilization of aluminum in APC residue
 by Process 4 to no immobilization at all of
cadmium  in the same  residue by  Pro-
cesses 1,  2, 3, and WES control.  No one

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Table 1. Fractions of Elements Released in the Availability Leach Test after Treatment



A PC Residue
Aluminum
Cadmium
Calcium
Chloride
Copper
Lead
Sodium
Potassium
Zinc
Bottom Ash
Aluminum
Cadmium
Calcium
Chloride
Copper
Lead
Sodium
Potassium
Zinc
Combined Ash
Aluminum
Cadmium
Calcium
Chloride
Copper
Lead
Sodium
Potassium
Zinc
Total"
Concentration
(mg/kg ash)

25,586
137
290,725
90,325
515
2,969
20,467
15,598
17,453

51,749
35
1 13,087
24,301
1,477
1,563
19,777
9,510
6,793

56,083
32
123,357
28,922
1,734
1,054
21,678
13,245
6,172
Process
1
(%)

16
>100f
>100f
>100f
30
40
>100f
>100f
38

5
23
53
61
5
9
17
21
10

11
>100f
>wot
55
14
24
32
52
27
Process
2
(%)

31
>100f
95
>100f
55
72
>wot
>100f
62

10
29
>100f
>100f
18
10
>100f
48
>100f

27
63
>100f
>wot
23
47
>100f
57
21
Process
3
(%)

33
>100f
>100f
>100f
76
76
>100f
>100f
69

11
46
>100t
>100f
13
20
38
>100f
24

21
63
>100f
>100f
22
>100f
34
>100f
32
Process
4
(%)

1
87
85
>100f
25
0.1
94
>100f
38

1
49
78
71
15
3
17
24
27

1
81
85
>100f
14
4
24
36
35
WES
Control
(%)


>100f
>100f
>100f
>wot
>100f
>100t
>100f


9
51
92
>100f
10
21
23
47
31

9
75
>100f
>100f
19
32
24
43
34
 * All total element concentrations are based on NAA results except lead, which is based on SW-846 results.
 t  Values nominally greater than 100% were calculated because of either contributions from process additives or correction for process dilution.
process  demonstrated  superiority  over
other processes for all  elements.  Note,
however, that Process 4 retained lead in
all the treated residue types significantly
better than did the other processes.
  Data from the other leaching tests, al-
though not given in this Project Summary,
are presented in detail in the full  report.
No  clear  pattern could  be  noted  other
than that no  single  process demonstrated
clear superiority over the other processes
for all target elements as was noted with
the ALT,  except for lead  in Process 4.
  Another measure of immobilization used
in this study  is the  level  of total dissolved
solids (IDS) released during  the DWLT.
Data obtained from this  test showed that
all processes were comparable to one an-
other with releases ranging  from  4%  to
32%. Significantly  more TDS were re-
leased from the APC residue compared to
the  other ash  types. Many of the  treat-
ments  resulted in  increased  release  of
TDS when compared to the untreated resi-
dues. Table 2 shows the releases from all
three residues by each of the processes
as well as the control and the untreated
samples.

Conclusions
  Based  on the results presented in the
full report of all the testing conducted  on
the  untreated  and treated residues, the
key findings and conclusions are as fol-
lows:
  •  The   S/S  processes   evaluated
    generally  did not  decrease the
    potential   for  release  of  target
    contaminants based  on comparison
    of untreated residues with treated
    residues.  The  phosphate  process,
    however, did reduce the potential for
    lead  to be released.
  •  Whether the  MWC  residues were
    treated  or  not, the  typical  release
    potential for metals (lead,  cadmium,
 zinc, etc.) was a small fraction of the
 total  concentration  present in the
 residues. Release  rates  of the
 elements  were  very   low  for
 compacted,  granular,  untreated
 bottom  ash  and  combined  ash.
 Release rates also were very low for
 bottom ash and combined ash treated
 by processes that produced physically
 durable specimens.
The S/S processes evaluated did not
 successfully treat  the residues to
 reduce  the  potential  for  release of
 TDS and soluble salts. Whether the
 MWC residues were  treated or not,
 the release potential and release rates
 were  high for TDS and the salts of
 calcium, sodium, potassium, chloride,
 and sulfate. The total amounts of
 these constituents released typically
 approached the total concentration in
 the MWC residues. In  the case of the
 APC   residues,   the   treatment

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Table 2. Comparison of Total Dissolved Solids Released for the Distilled Water Leach Test
        (g release/kg ash, dry solid), and the Weight % of the Material Released *n parenthesis).
Sample source

Untreated
Process 1
Process 2
Process 3
Process 4
WES control
Bottom Ash
   58 (6%)
   53 (4%)
 187 (12%)
  126 (7%)
   47 (4%)
   59 (5%)
A PC Residue

  289 (29%)
  640 (32%)
  565 (26%)
  578 (24%)
  194 (15%)
  671 (30%)
   processes  increased the  release
   potential of the salts.
 • The  high concentration and  ultimate
   fate  of soluble salts in MWC residues
   should be carefully considered in the
   design of treatment  processes and
   the use and disposal  of the residues.
 • Based on results from the program,
   ARC residues have the least potential
   for use  in  applications  requiring
   structurally  durable  products.  The
   physical  retention  values for the
   treated ARC residues indicated limited
   or no physical retention. The major
   contaminant  release  from  the ARC
   residue was  salts. In  excess of 30%
   of the total mass  was released in the
   form of sodium, calcium, chloride, arid
   sulfate salts.
 •  The use  of  proprietary additives in
   the evaluated S/S processes did not
   enhance the strength of the treated
   residues.  The  Portland-cement-only
   (WES control) process produced test
   specimens    with     unconfined
   compressive  strengths greater than
   or equal to those of all the processes
  with proprietary additives.  It should
  be noted, however, that high strength
  probably was not  an objective of the
  vendor's  processes.  Process  4
  developed a granular product.
•  Evaluation  of  S/S process design,
  performance, and treatment efficiency
  should be based on a matrix of several
  testing protocols. No single test, such
  as  TCLP, can  provide  all  the
  information  required  to evaluate
 contaminant  release  potential,
 contaminant release rate, and physical
 durability. An appropriate test matrix
 to evaluate S/S processes shoulc
 include tests that will address  these
 factors.
 Formulas   for  most  processes
 evaluated in this study were probably
 developed  on  a limited  number  of
 testing  procedures. Variations  in
 Portland-cement-based  and other
 S/S  technologies will  influence the
Combined Ash

     60 (6%)
     54 (4%)
   208 (13%)
    144 (8%)
     56 (5%)
     79 (6%)
                          degree  of  durability and chemical
                          leaching   potential.   Therefore,
                          substantial  improvements  in  S/S
                          process  optimization  may   be
                          obtainable  by  optimizing  process
                          design  based on results  of multiple
                          test criteria.
                        •  The  Portland-cement-based proc-
                          esses can be formulated to  produce
                          S/S test specimens of MWC bottom
                          and combined  residues  with  high
                          structural  integrity  and  increased
                          resistance to weathering. These types
                          of processes, if properly designed,
                          are likely to be successful in producing
                          monolithic products  with physical
                         properties acceptable for various uses.
                         This does not mean, however, that
                         the chemical  characteristics would
                         also be acceptable. Physical durability
                         or possessing a  monolithic structure
                         does   not   ensure  acceptable
                         performance  with   respect  to
                         contaminant release.
                       • The release  rate of most potentially
                         toxic metals  will be  very slow to
                         negligible  for  S/S-treated  MWC
                         residues, at least those  that  have
                         minimal leachability in the raw state.
                       • The unconsolidated, granular nature
                        of the ash  material required that  a
                        method  for  estimating  diffusion-
                        controlled  release from compacted
                        granular materials  be developed. Such
                        a  method was  developed for this
                        evaluation, and the application of a
                        modified  MLT to  determine intrinsic
                        leaching  properties  for   granular
                        materials has proven very consistent.
                        The data  are comparable with  results
                        from  other   types   of   diffusion
                        measurements. The tortuosity data
                        obtained  in the experimental  setup
                        are  consistent   with   diffusion
                        measurements using radiotracers.
                       TCLP was  not  a  good indicator of
                        release from  untreated and treated
                        residues for several reasons. Variable
                       end-point pH for the  extraction
                       resulted in wide variation in estimated
       metals release  because  of pH-
       dependent solubility constraints. The
       low liquid-to-solid  ratio  for the  TCLP
       (20:1)  also may  have resulted  in
       solubility limitations for many elements
       of concern.  Finally,  TCLP does not
       provide for determination of the total
       release of soluble  salts  and anions.
     •  The most durable  test specimens  to
       the cyclic  weathering tests and the
       immersion tests were those with the
       highest unconfined compression
       strength (UCS). Thus,  UCS may be
       useful as  a preliminary indicator  of
       physical durability.
     •  The MLT for construction  materials
       and stabilized products  provides
       intrinsic information  on  long-term
       leaching effects and  usefulness  in
       relation to  product quality.  The  MLT
       also provides useful information for
       improving product quality. By focusing
       on the controlling parameter requiring
       adjustment, initial estimates of release
       rates and fluxes for varied application
      scenarios  can  be obtained.  The
      distinction between physical retention
      and chemical retention   and  the
      release mechanisms (dissolution,
      wash-off, and diffusion) can be made.'
      Existing regulatory  tests do  not
      provide such useful information.
    •  Physical  retention  was  directly
     correlated  with  the compacted,  dry
     densities of the material for the bottom
     and  combined  ashes. The  test
     specimens with the greater densities
     had more physical retention.
    • The EPA-recommended  methods of
     chemical analysis (SW-846) were not
     comparable in many cases to  the
     neutron activation chemical  analysis
     (NAA)   for    total    elemental
     concentrations in the raw  and treated
     residues. The  EPA method results
     indicated significantly lower elemental
     concentrations than did the  NAA
     methods; this  suggests that only
     partial analytical recoveries occurred.
     This discrepancy warrants  further-
     investigation into  the  chemical
     analysis methods to investigate and
     develop more applicable methods  for
     similar type solid matrices.
   The full report was submitted in partial
fulfillment of CR 818178-01-0 by Rutgers
The State University of New Jersey CR
813198-01-0  by the New Jersey  Institute
of Technology and an interagency agree-
ment between the U.S. Environmental Pro-
tection Agency and the U.S. Army Corps
of Engineers, Waterways Experiment Sta-
tion, under the sponsorship of the  U  S
Environmental Protection Agency
          GOVERNMENT PRINTING OFFICE: W3 - 750-07I/JJOW3

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David S. Kosson is with Rutgers, The State University of New Jersey,
  Piscataway, NJ 08855; Teresa T. Kosson is with the U.S. Army Corps of
  Engineers, Vicksburg, MS 39180; and Hans van der Sloot is with the
  Netherlands Energy Research Foundation (ECN), Petten, The Netherlands
  1755ZG.
Car/ton Wiles is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Solidification/Stabilization  Treat-
    ment Processes for Municipal Waste Combustion Residues," (Order No.
    PB93-229 870/AS; Cost: $61.00, subject to change)  will be available only
    from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Risk Reduction Engineering Laboratory
        U.S. Environmental Protection Agetncy
        Cincinnati, OH 45268
   United States
   Environmental Protection Agency
   Center for Environmental Research Information
   Cincinnati, OH 45268

   Official Business
   Penalty for Private Use
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         EPA
   PERMIT No. G-35
   EPA/600/SR-93/167

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