United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-94/000
Dec 1994
EPA Project Summary
Mobility of Dioxins, Furans and
Trace Metals from Stabilized
MSW Combustor Ash in
Seawater
Frank J. Roethel, and Vincent T. Breslin
This report presents the results of a
research program designed to exam-
ine the engineering and environmental
acceptability of stabilizing municipal
solid waste (MSW) combustor ash for
artificial reef construction. MSW com-
bustor ash was combined with Port-
land cement to form solid blocks using
conventional block making technology.
The resultant stabilized combustor ash
(SCA) blocks were used to construct
an artificial habitat in Conscience Bay,
Long Island Sound, N.Y.
Divers periodically returned to the
site to monitor the interaction of SCA
blocks with the marine environment
over a 4.5-yr period. Results show that
the SCA blocks retain their strength
after prolonged seawater exposure.
Contaminants of environmental con-
cern, including metals, dioxins and
furans, were retained within the
cementitious matrix of the SCA blocks
after prolonged seawater submersion.
In addition, organisms growing on the
surfaces of the SCA blocks are not
accumulating contaminants from the
blocks.
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
In May 1985 a research program was
initiated at the Marine Sciences Research
Center to examine the feasibility of utiliz-
ing stabilized MSW combustor ash for ar-
tificial reef construction in the ocean. Re-
sults of these studies showed that
particulate combustion ash could be com-
bined with cement to form a solid block
possessing physical properties necessary
for ocean disposal. The stabilized ash was
subjected to regulatory extraction proto-
cols and in no instance did the metal
concentrations in the leachates exceed
the regulatory limits for toxicilty. Bioassays
revealed no adverse impacts to the phy-
toplankton communities exposed to
elutriate concentrations higher than could
be encountered under normal disposal
conditions. The success of the laboratory
studies resulted in securing the necessary
permits for the placement of an artificial
habitat constructed of stabilized combus-
tor ash in coastal waters.
During April 1987 and again during Sep-
tember 1988 stabilized combustor ash and
concrete control blocks were submerged
in eight meters of water in Conscience
Bay, Long Island Sound, M.Y., to form
reef structures. The primary objectives of
the investigation were to determine:
1) whether prolonged seawater ex-
posure adversely impacts the
structural integrity of the stabilized
combustor ash (SCA) blocks,
2) whether; metals of environmental
concern leach from the SCA blocks,
3) whether organics such as PCDDs
and PCDFs are released into the
marine ; environment from SCA
blocks,
4) whether marine communities that
colonize the artificial habitat
incorporate within their tissues metals
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and/or organics known to be
enriched in MSW combustor ash,
and,
5) whether artificial habitats constructed
from the SCA blocks develop a
diverse biological community of
organisms in a manner similar to a
control structure.
Since the placement of the artificial habi-
tats, divers have periodically returned to
the reef site to study the interactions of
stabilized combustor ash with the marine
environment. Stabilized ash blocks were
retrieved from the reef site for physical
and chemical testing. Compressive
strengths of the ash blocks were mea-
sured to monitor the strengths of the blocks
following prolonged seawater exposure.
Samples of ash blocks, exposed to sea-
water were analyzed for metals, dioxins,
and furans to determine if contaminants
associated with particulate MSW combus-
tor ash are effectively retained within the
stabilized blocks. In addition, divers re-
moved biomass from the surfaces of the
blocks and bivalves that resided within
the crevices of the structures for analysis
of their tissues for possible uptake of met-
als, dioxins and furans.
Materials and Methods
Ash Block Placement and
Sampling Activities
MSW combustor ash for block making
was collected on two separate occasions
from two operational waste-to-energy fa-
cilities: the Westchester Resource Recov-
ery Facility, Westchester County, NY, in
November 1986 and the Baltimore RESCO
facility, Baltimore, MD in August 1988.
Ash block manufacturing was conducted
on two occasions at the research facilities
of the Besser Company at the Alpena
Community College, Alpena, Ml.
The "Narrows" region of Conscience
Bay, Long Island Sound was selected as
the site for the reef placement (Figure 1).
Stabilized ash blocks and concrete con-
trol blocks were submerged to a depth of
eight meters at the site located within Con-
science Bay. Thirty ash blocks and thirty
concrete blocks were submerged on April
27, 1987, while forty ash blocks and forty
concrete blocks were submerged on Sep-
tember 23, 1988 (Figure 2). Compressive
strengths of the blocks at the time of place-
ment were 1120 and 1020 psi for April
1987 and September 1988 ash blocks,
respectively.
Reef sampling activities occurred over
a 4.5-yr period from April 27, 1986, to
September 11, 1991. Reef blocks were
retrieved for the determination of their en-
gineering propeities and dioxin, furan, and
40°59'
40"58'
40°57'
73°08'
73°07'
73°06'
Figure 1. Ash and concrete block placement site, Conscience Bay, Long Island Sound, NY
Concrete blocks
April 1987
Figure 2. Ash and concrete block configuration following the April 1987 and September 1988 <
placement events.
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metal content. Biomass samples were also
retrieved for the analysis of tissue dioxin,
furan, and metal content.
Results and Discussion
Change In Ash Block Properties
Following Soawater
Submersion
Results of the engineering and metals
analyses were normalized to allow the
use of both the April 1987 and September
1988 ash blocks to determine the change
in compressive strength and total metal
content of ash blocks following placement.
The percent retained of a physical or
chemical property was calculated for each
block following each sampling event. Per-
cent retained was calculated as follows:
Percent Retained = P/P0x 100 where;
Pt = block physical or chemical prop
erty at time t.
P0 = initial block physical or chemical
property (Table 1).
The percent retained for each ash or
concrete block property was plotted ver-
Table 1. Elemental Composition of Stabilized Ash Reef Blocks: HF-H^BO3 Acid Digestion
Metal
Al(%)
Si (%)
Fe(%)
Ca (%)
Mg(%)
Na(%)
K(%)
Zn ftig/g)
Pb (ug/g)
Cu ftig/g)
Mn (ug/g)
Ba (fig/g)
Or (ug/g)
Cd (ug/g)
As (pg/g)
Se (ug/g)
Hg (f^g/g)
Ag (ug/g)
April 1987
Ash block
4.17(0.23)*
16.76 (0.22)
7.25 (0.23)
15.70 (1.6)
1.13(0.08)
2.39 (0.03)
0.82 (0.05)
3760 (170)
3580 (160)
1260 (230)
1020 (70)
ND»
178 (15)
23.6 (1.5)
ND
ND
ND
ND
September 1988
Ash block
3.29 (0.11)
21.9 (0.47)
7.45 (0.49)
12.7 (1.0)
1.24 (0.08)
4.51 (0.26)
0.59 (0.02)
2720 (134)
2169 (502)
1400 (300)
1040 (60)
1120(98)
240 (22)
9.44 (2.1)
20.9 (2.7)
<12
<1.0
<6.0
* Values in parenthesis denote the standard deviation (n=3).
b ND = Ms element was not determined.
Table 2. Regression Analysis of Physical and Chemical Ash Block Properties
sus submergence time. A least squares
linear regression analysis was performed
on each data set to obtain a best-fit line.
The significance of the regression analy-
sis for each ash or concrete block prop-
erty was then determined (Table 2).
A student t-test was then used to deter-
mine if the slope of the regression'line
calculated for; each property was signifi-
cantly different from zero. A significant
positive slope indicated an increase in the
property of the block following submer-
sion while a significant negative slope in-
dicated a decrease in the property of the
block following submersion (Table 3).
Effects of Seawater on Ash and
Concrete Block Strength
Linear regression analysis of the com-
pressive strength data yielded negative
slopes for both the ash and concrete
blocks. However, neither the regression
line nor the slope of the line was signifi-
cant for the ash block data (Table 3). In
contrast, both the correlation coefficient
and the slope of the regression line were
significant for the concrete block data.
Ash blocks retained 84% of their initial
compressive strength following 4.5-yr sea-
water submersion (Figure 3). Given the
rate in the decrease in compressive
strength, the compressive strength of the
ash blocks would exceed the minimum
compressire strength criteria for ash blocks
in the sea of 300 psi for 20 yr. In contrast,
the compressive strength of concrete
blocks retrieved from the reef site continu-
ously decreased following placement.
Block Strength
Ash Block
Concrete Block
Block Metals
Aluminum
Arsenic
Barium
Calcium
Cadmium
Chromium
Copper
Iron
Potassium
Magnesium
Manganese
Sodium
Lead
Silicon
Zinc
r2
0.1160
0.8430
0.0176
0.1816
0.3572
0.7092
0.1633
0.3232
0.0029
0.1479
0.1243
0.4981
0.0031
0.0667
0.0029
0.0026
0.4872
F Statistic1
1.700
64.87
0.2247
0.9222
1.579
31.712
2.343
3.175
0.0039
2356
1.844
4.322
0.0406
0.9303
0.0388
0.0341
12.351
F Critical
Value
4.60
4.67
4.67
5.99
5.99
4.67
4.67
4.67
4.67
4.67
4.67
4.67
4.67
4.67
4.67
4.67
4.67
Significance3
:
N.S.
S.
N.S.
N.S. :
N.S.
S.
N.S.
N.S.
N.S.
N.S.
N.S.
N.S.
N.S.
N.S.
N.S.
N.S.
i S.
1 F-Statistic: result of one way, Model IANOVA testing for the significance of regression. Critical values were obtained from a table of critical values of
the F-distribution for a=.05.
2 Regression performed by Least Squares method. '
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Table 3. Determination of the Significance of the Slope of the Best-fit Line for Physical and Chemical Ash Block Properties
Block Strength
Ash Block
Concrete Block
Block Metals
Aluminum
Arsenic
Barium
Calcium
Cadmium
Chromium
Copper
Iron
Potassium
Magnesium
Manganese
Sodium
Lead
Silicon
Zinc
Slope
-0.0082
-0.0738
0.0010
-0.0183
-0.0277
-0.0283
-0.0067
0.0038
-0.0006
0.0101
-0.0249
0.0276
-0.0014
0.0054
-0.0029
0.0015
-0.0108
t Statistic1
1.310
8.050
0.2841
2.5271
3.265
10.992
1.708
1.047
0.109
1.858
5.96
4.657
0.373
1.327
0.706
0.2929
4.123
t Critical
value
2.160
2.160
2.179
2.571
2.571
2.179
2.179
2.179
2.179
2.179
2.179
2.179
2.179
2.179
2.179
2.179
2.179
- Significance?
N.S.
s
N.S.
N.S.
s.
S.
N.S.
; N.S.
: N.S.
N.S.
i S.
S.
N.S.
N.S.
N.S.
' N.S.
S.
1 t-Statistic: result of t-test where null hypothesis states that the slope of the line equals zero: h0:M,=0. Critical t-values were obtained from a table of
critical values of the t-distribution. ;
95% significance level (a=.OS).
175
400
800
Days submerged
1200
1600
Figure 3. Compressive strength versus submergence time for April 1987 (9) and September
1988 (M) ash blocks. Regression line f ) and 95% confidence intervals () are also shown
for the pooled data.
Metal Content of Ash Blocks
Following Seawater
Submersion
Linear regression analysis of the metal
data yielded positive slopes for aluminum,
chromium, iron, sodium, silicon and mag-
nesium while negative slopes were calcu-
lated for arsenic, barium, calcium,
cadmium, copper, potassium, manganese,
lead and zinc (Table 3). However, the
regression line was only significant for cal-
cium and zinc. Results of the students t-
test showed that the slope of the best-fit
line was also! significantly different from
zero for calciuin, and zinc (Table 3).
Calcium and zinc yielded significant re-
gression lines and possessed slopes which
were significantly different than zero.
Therefore, significant decreases in the cal-
cium and zinc content of the ash blocks
was observed as submergence time in-
creased (Figure 4). For the remaining met-
als-aluminum, arsenic, barium, chromium,
cadmium, copper, iron, potassium, man-
ganese, sodium, lead, and silicon no-sig-
nificant trend in the data was observed
(Figure 5).
Metals of environmental concern includ-
ing lead, chromium, copper, and cadmium
were effectively retained within the stabi-
lized ash blocks. The high alkalinity of the
particulate MSW combustor ashes, ihe
Portland type II cement additive, and the
alkalinity of the seawater combine to dre-
ate a favorable environment within the
ash blocks forthe retention of metals. ;
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175
750
125
§ 100
75
SO
25
400
800
Days submerged
1200
1600
Figure 4. Calcium content versus submersion time forApril1987 (9) and September 1988 (U)
ash blocks. Regression line (- ; and 95% confidence intervals () are also shown for the
pooled data.
175
150
125 .t-
§ 100
75 "-
50
25
Y'= -0.0029X'+ 99
r2= 0.0029
400
800
Days submerged
1200
1600
Figure 5. Lead content versus submersion time forApril1987 (; and September 1988 (; ash
blocks. Regression line (- ) and 95% confidence intervals () are also shown for the pooled
data.
Effects of Seawater Exposure
on PCDD/PCDF Mobility
Following ash block submersion,
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1
I
10000
1000
100
223
Days of submersion
following submersion in the sea, suggest
that these organic compounds do not leach
from the SCA:blocks. The biological com-
munity associated with the ash blocks,
when analyzed for the presence of diox-
ins and furans, were found to have con-
centrations of 'these compounds similar to
those found in identical organisms re-
moved from the concrete control blocks.
The data suggest that PCDDs and PCDFs
affiliated w'rth'the stabilized ash blocks are
tightly bound to the ash particle and not
released into the marine environment. In
addition, PCDDs and PCDFs are not ac-
tively assimilated by the attached biologi-
cal reef community.
To date, no adverse environmental im-
pacts have been observed at the Con-
science Bay reef site due to 'the presence
of ash blocks.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. 0R-
815239, by State University of New York
at Stoney Brook, under the sponsorship
of the U.S. Environmental Protecetion
Agency.
601
1082
Figure 6. Mean PCDD/PCDF concentrations measured in submerged ash blocks.
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