United States
Environmental Protection
Agency
Office of
Research and Development
Cincinnati, OH 45268
EPA/540/R-96/503a
June 1997
I Technologies, In
S*AW">^ * •-. 'IMP !8£?' + '.
Introduction
In 1980 the U.S. Congress passed the Comprehensive Envi-
ronmental Response, Compensation, and Liability Act
(CERCLA), also known as Superfund, to protect human health
and the environment from uncontrolled hazardous waste sites.
CERCLA was amended by the Superfund Amendments and
Reauthorization Act (SARA) in 1986. SARA mandates imple-
menting permanent solutions and using alternative treatment
technologies or resource recovery technologies to the maxi-
mum extent possible to clean up hazardous waste sites.
The more than 1,200 sites on the National Priorities List in-
volve a broad spectrum of physical, chemical, and environmen-
tal conditions requiring diverse remedial approaches. The U.S.
Environmental Protection Agency (EPA) has focused on policy,
technical, and informational issues related to exploring and
applying new technologies to Superfund site remediation. One
EPA initiative to accelerate the development, demonstration,
and use of innovative remediation technologies is the Superfund
Innovative Technology Evaluation (SITE) Program.
State and federal agencies and private organizations are ex-
ploring a growing number of innovative technologies for treat-
ing hazardous wastes. The SITE Program provides a forum for
demonstrating the effectiveness of innovative technologies at
hazardous waste sites. The SITE Program evaluates technol-
ogy performance through collection of independent data and
publishes the results of these studies.
EPA Site Technology Capsules summarize the latest informa-
tion available on innovative treatment and site remediation
technologies selected for demonstration in the SITE Program.
The Technology Capsules assist EPA remedial project manag-
ers, EPA on-scene coordinators, contractors, and other deci-
sion-makers in the evaluation of site-specific chemical and
physical characteristics to determine a technology's applicabil-
ity for site remediation.
This Technology Capsule provides the latest available informa-
tion on the EnviroMetal Technologies, Inc. (ETI), process for
metal-enhanced dechlorination of chlorinated volatile organic
compounds (VOCs) in aqueous media. The EPA SITE Pro-
gram evaluated the process in an aboveground reactor at the
SQL Printed Circuits (SQL) site in Wayne, Passaic County, NJ.
Groundwater at the site contains the chlorinated VOCs
tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-
dichloroethene (cDCE). ETI claims that, when properly de-
signed and constructed, the technology can completely
dechlorinate certain chlorinated aliphatic VOCs in water after
one pass through a reactive, zero-valent, iron medium.
This Technology Capsule summarizes the results of the SITE
demonstration and contains the following information:
Abstract
Technology Description and System Design
Technology Applicability
Technology Limitations
Process Residuals
Site Requirements
Performance Data
Summary
Technology Status
Sources of Further Information
Abstract
A metal-enhanced dechlorination processing using reactive,
zero-valent, granular iron to dechlorinate VOCs in aqueous
media was demonstrated at the SQL site in New Jersey. The
developer is ETI of Guelph, ON, Canada. The technology can
be operated as an aboveground reactor or can alternatively
perform in situ groundwater remediation. Chlorinated VOCs
such as PCE, TCE, cDCE, and vinyl chloride are among the
most pervasive groundwater contaminants at hazardous waste
ra§S Printed on Recycled Paper
-------
sites. The metal-enhanced dechlorination process is designed
to degrade chlorinated VOCs to nonhazardous substances,
and therefore offers an alternative to conventional technologies
that simply transfer VOCs from groundwater to other media,
such as air or carbon filters.
The SITE Program evaluated the metal-enhanced dechlorina-
Uon process tn an aboveground reactor during the 13-week
demonstration. About 61,000 gal of groundwater containing
PCE, TCE, and cDCE was treated during the demonstration.
Analysis of influent and effluent groundwater samples indicated
that PCE and TCE were reduced below regulatory levels after
a single pass through the reactive iron medium. The removal
efficiency for PCE was greater than 99.9% throughout the
demonstration.
During the latter portion of the demonstration, cDCE and vinyl
chloride were occasionally detected in the effluent. Several
factors may have contributed to the incomplete dechlorination
ol VOCs. A review of inorganic data indicated that carbonate
and hydroxide minerals precipitated in the reactive iron, and
precipitation of these minerals may have affected system per-
formance. Sedimentation on the reactive iron surface, varia-
tions in reactor temperature, and other factors may also affect
the technology's performance.
The metal-enhanced dechlorination process may be applied at
Superfund and other hazardous waste sites where groundwa-
ter or other liquid wastes are contaminated with chlorinated
VOCs. The aboveground reactor design evaluated during the
SITE demonstration may be used for pilot- or full-scale reme-
dial applications.
Technology Description and System Design
The metal-enhanced dechlorination process is an electrochemi-
cal process that uses zero-valent, reactive iron to dechlorinate
chlorinated VOCs in aqueous media. In the presence of water,
the reactive, zero-valent, granular iron is oxidized and releases
electrons. Water molecules dissociate to produce hydrogen
and hydroxyl ions. The electrons and hydrogen ions react with
chlorinated VOCs present in the water, including substitution of
chlorine atoms by hydrogen atoms, dechlorinating the chlori-
nated VOCs. The dechlorination process yields hydrocarbons
and chloride.
The metaJ-enhanced dechlorination process may be used in an
aboveground reactor supporting a groundwater pump-and-treat
system, or can be applied in situ. For aboveground reactors,
contaminated water is extracted from the source (typically an
aquifer) and transferred to the reactor for treatment. The
aboveground reactor design is appropriate for pilot-scale evalu-
ations or may be used as the full-scale remedial design. For in
situ remediation, the need for extracting contaminated ground-
water before treatment is eliminated. Contaminated groundwa-
ter flows through a permeable iron wall constructed in the
subsurface. For large-scale remediation projects, in situ sys-
tems may either be constructed as a continuous, permeable
treatment zone or as a funnel-and-gate configuration. For "fun-
nel-and-gate" designs, permeable reactive irons walls or "gates"
are flanked by impermeable sheet piling or slurry wall "funnels"
that direct flow through the gate.
The design for the aboveground reactor used at the SQL site
was based on established site-specific conditions and prelimi-
nary bench-scale studies. The highest concentrations of VOCs
occur in a shallow, unconsolidated overburden aquifer; lower
concentrations are present in an underlying, semiconfined,
fractured bedrock aquifer. Groundwater from both zones was
treated during the SITE demonstration. Groundwater was ex-
tracted from the bedrock aquifer using two wells, and pumped
directly to the reactor for treatment. Groundwater was also
passively collected from the overburden zone using two collec-
tion trenches that drained to a common sump, and pumped
from the sump to the reactor.
A schematic diagram of the treatment reactor at the SQL site is
shown in Figure 1. Groundwater pumped from the extraction
wells and the sump passes through a check valve, a 5-micron
water filter, a flow meter, and an air eliminator before entering
the treatment reactor. The water filter removes suspended
solids from influent water, eliminating the need for a layer of
well sand or pea gravel above the reactive iron medium. The
air eliminator releases excess air from the highest elevation of
the influent line when interior pressure exceeds exterior atmo-
spheric pressure. A sight glass and pressure release outlet are
located on top of the reactor. The sight glass allows observa-
tion of the surface of the reactive iron, and the pressure
release outlet prevents a buildup of excessive internal gaseous
pressure in the reactor.
After entering the treatment reactor, the water flows by gravity
through the reactive iron medium. The 8-ft diameter fiberglass
reactor contained a 5.5-ft thick layer of the reactive iron me-
dium. About 39,600 Ib of granular iron was used in the reactor.
The porosity of the iron medium, after placement and settling in
the reactor, was estimated to be about 0.4. The iron rests oil a
6-in. layer of coarse silica sand, referred to as "well sand." The
well sand acts as a strainer, preventing the granular iron from
washing out into the effluent line. An additional layer of pea
gravel or well sand is sometimes placed above the iron to filter
out suspended solids, although this additional layer was not
used during the SITE demonstration.
The reactor drains through a collector line located in the well
sand at the bottom of the reactor, and the collector line directs
the treated water to the effluent line. The volume of water in
the reactor tank is controlled by the configuration of the effluent
line, which is plumbed so that about 2 ft of groundwater
remains ponded inside the reactor above the surface of the
reactive iron medium. During the SITE demonstration, the
treated effluent was returned to the shallow, unconsolidated
aquifer through several monitoring wells modified to serve as
reinjection wells.
Contact time between groundwater and the reactive iron me-
dium is primarily controlled by the thickness of the layer of
reactive iron and by the flow rate. The design of the reactor is
site-specific. The required contact time depends on the half-
lives and concentrations of the contaminants in the influent
water, and the target limits for effluent concentrations. Gener-
ally, higher influent contaminant concentrations require greater
contact time for treatment. The design for the reactor at the
SQL site allowed for a contact time of about 1 day during the
demonstration. The contact time was based on laboratory bench-
scale studies performed using contaminated groundwater from
the SQL site.
Technology Applicability
The metal-enhanced dechlorination technology may be applied
at hazardous waste sites where an aqueous medium, usually
groundwater, is contaminated with chlorinated aliphatic VOCs
such as PCE and TCE. Chlorinated aliphatic VOCs are among
the most pervasive contaminants at hazardous waste sites.
-------
Flow meter
Manhole
Gas vent
—I/
I I Sealing flange
I x/ for top
5.5
6"
• i^r^j^r/Tv^V'^"'?/^^^^
1-jl'i; 'i->v^;V4'^>^4'''^'^'V>V^xV^^' f*"*.'">r •*'•'.'*'•'''^rfo;>• '^fr T-yV^.'^r-^''.*^ .•
O
Sample location
Collector pipe
Figure 1. The metal-enhanced dechlorination process as demonstrated.
Outflow
,3/4"
Effluent line
ETI claims that this process may be applicable for treating
organic compounds other than chlorinated aliphatic hydrocar-
bons. However, the technology's ability to destroy other types
of organic compounds was not evaluated during the SITE
demonstration.
An aboveground reactor, as tested during the SITE demonstra-
tion, may be used to evaluate the metal-enhanced dechlorina-
tion process at pilot scale, allowing for measurement and
optimization of design and operating parameters. Depending
on site-specific factors, aboveground reactors may be operated
as stand-alone treatment units or in conjunction with other
treatment technologies. Aboveground reactors may be espe-
cially applicable for short-term remediation projects at sites
with relatively small amounts of contaminated groundwater, or
for sites where excavation and construction activities in the
immediate vicinity of a contaminated plume are impractical.
In general, the technology applicability is affected by site-
specific factors. The volume of contaminated groundwater re-
quiring treatment may affect the applicability of aboveground
reactors. Groundwater chemistry, contaminant types and con-
centrations, and hydrogeologic conditions may also affect the
technology applicability. Applicability to a specific site should
be evaluated through treatability tests using contaminated
groundwater from the site. Hydrogeologic studies may also be
required, especially for in situ systems where factors such as
depth to groundwater, aquifer thickness, hydraulic gradient and
flow velocity affect the technology's applicability.
For aboveground systems, permits (or waivers) from regulatory
agencies may be required to allow discharge of treated effluent
to surface water or groundwater. Regulations or site-specific
permit stipulations may require additional treatment or "polish-
ing" of system effluent before discharge, depending on system
performance.
The applicability of the technology was evaluated against the
nine criteria used for decision-making in the Superfund feasibil-
ity process. Each criterion and its relevance to the metal-
enhanced dechlorination process's applicability is summarized
in Table 1.
Technology Limitations
The oxidation-reduction reaction that drives the metal-enhanced
dechlorination process creates physical and chemical condi-
tions (high pH and low Eh) that may cause precipitation of
ferrous hydroxide [Fe(OH)J, siderite (FeCO3), calcium carbon-
ate (CaCO3), and other minerals when influent groundwater
contains soluble metal compounds. Precipitation of these min-
erals may eventually reduce the porosity of the granular iron,
decreasing volumetric flow through the system and possibly
inducing channelized flow in the reactor. Precipitates may also
block the available surface area of the reactive iron, increasing
the half-lives of chlorinated compounds in the system and
potentially resulting in incomplete dechlorination. Due to the
potential for precipitation, groundwater containing high concen-
-------
Table 1. Superfund Feasibility Criteria for the Metal-Enhanced Dechlorination Process
Criterion Technology Performance
1
5
6
Overall Protection of
Human Health and the
Environment
Compliance with
Applicable or Relevant
and Appropriate Require-
ments (ARAR)
Long-Term Effectiveness
and Permanence
Reduction of Toxicity,
Mobility, or Volume
Through Treatment
Short-Term Effectiveness
Imptementability
Cost
8 Community Acceptance
9 State Acceptance
The metal-enhanced dechlorination process is expected to protect human health by providing treated water
that has significantly lower concentrations of chlorinated VOCs.
Overall reduction of human health risk should be evaluated on a site-specific basis due to the potential for
formation of harmful treatment byproducts (for example, cDCE and vinyl chloride). However, when properly
designed and implemented, the technology can degrade these byproducts.
Protection of the environment at and beyond the point of discharge should be evaluated based on uses of the
receiving water body, concentrations of residual contaminants and treatment byproducts, and the dilution
factor.
The technology's ability to comply with existing federal, state or local ARARs (for example, maximum
contaminant levels [MCL]) should be determined on a site-specific basis.
The technology's ability to meet any chemical-specific ARARs for byproducts should be considered because
of the potential of forming byproducts such as cDCE and vinyl chloride during treatment. However, when
properly designed and implemented, the technology can degrade these byproducts.
Human health risk can be reduced to acceptable levels by treating groundwater to site-specific cleanup levels;
the time needed to achieve cleanup goals depends primarily on contaminated aquifer characteristics.
The long-term effectiveness of the metal-enhanced dechlorination process applied as an aboveground reactor
may depend on periodically replacing the iron medium or chemical/physical treatment of the system.
The treatment is permanent because the metal-enhanced dechlorination process is a degradation technology.
Periodic review of treatment system performance is needed because application of this technology to
contaminated groundwater at hazardous waste sites is relatively recent and long-term performance data are
not available.
When properly designed and implemented, the technology reduces the toxicity of contaminated groundwater
by lowering total chlorinated aliphatic VOC concentrations and by degrading chlorinated aliphatic VOCs to
nonhazardous substances.
Frequent monitoring of system performance is particularly important for the initial start-up phase, before the
system reaches "steady state."
The site must be accessible to typical construction equipment and delivery vehicles.
The aboveground reactor system used during the SITE demonstration required an area of about 400 ft2. The
actual space requirements will be site-specific and will vary.
In situ systems vary in size and require installation of sheet piling or slurry walls in addition to the reactive iron
wall.
Site-specific needs may dictate the need for additional services and supplies.
Construction and discharge permit requirements will depend on site-specific conditions.
ETI estimates that capital costs for installing an aboveground treatment reactor similar to the one used at the
SQL site are about $48,000. This figure includes costs for all equipment (the reactor tank, reactive iron, piping,
and wiring) and construction costs. Additional costs for hydrogeologic characterization, bench-scale studies,
permitting, and installation of groundwater extraction/reinjection systems are not included. These additional
costs will vary widely depending on site-specific condtions, and may constitute a significant portion of the total
initial cost.
ETI estimates that minimum annual operation and maintenance costs for an aboveground reactor similar to
the one used at the SQL site are about $10,000. This figure includes electrical consumption, expendable
supplies (such as-sediment filters) and maintenance labor costs, but does not include effluent sampling and
analysis. Additional annual costs may be incurred and will vary widely depending on sampling requirements,
useful life of the reactive iron medium, management of process residuals, and other site-specific factors.
This criterion is generally addressed in the record of decision after community responses are received during
the public comment period; because communities are not expected to be exposed to harmful levels of VOCs
noise, or fugitive emissions, community acceptance of the technology is expected to be high.
This criterion is generally addressed in the record of decision; state acceptance of the technology will likely
depend on the concentrations of residual organic contaminants and treatment byproducts.
-------
trations of dissolved metal compounds, inorganic carbon, or
other compounds may impact operation and maintenance (O&M)
requirements.
High concentrations of suspended solids in influent groundwa-
ter may "blind" or accumulate and physically block the reactive
iron medium, reducing flow. Blinding of the top of the reactive
iron layer occurred early in the SITE demonstration. A rake
was used to disturb the layer of gray, silty material that had
formed and improved flow through the reactor.
During the SITE demonstration, algae was observed in the
ponded water above the surface of the iron and on the upper,
exposed portions of the interior reactor walls. Algae in the
ponded water may have retarded flow through the system;
however, the effects of algae and bacterial growth on the
dechlorination reaction are unknown. During the SITE demon-
stration, algal growth was controlled by adding sodium hy-
pochlorite and using an opaque cover on the reactor tank to
block sunlight.
Freezing may affect flow through outdoor aboveground reac-
tors in cold climates. However, although temperatures dropped
below freezing for short periods during the SITE demonstra-
tion, groundwater flow limitations due to icing were not ob-
served.
Data collected during the SITE demonstration indicate that the
temperature of influent groundwater and the reactor were prob-
ably affected by changes in ambient air temperature. Accord-
ing to ETI, temperature may affect the dechlorination reaction
rate for some compounds. If so, ambient temperature may
affect the performance of the metal-enhanced dechlorination
process, especially in aboveground reactors, and site-specific
designs may need to consider potential temperature effects.
The potential effects of ambient temperature on the rate of
PCE dechlorination were not evaluated during the SITE dem-
onstration.
Process Residuals
Process residuals generated by the metal-enhanced dechlori-
nation process during the SITE demonstration consisted prima-
rily of treated effluent water. The New Jersey Department of
Environmental Protection (NJDEP) permitted reinjection of the
treated water to the shallow, unconsolidated aquifer through
reinjection wells. For other sites using aboveground reactors,
site-specific conditions may require alternate management and
disposal methods for treated groundwater.
The reactive granular iron may eventually require replacement
if the iron surfaces become irreversibly blocked with precipi-
tates, or if the iron loses its reactivity. If so, the spent iron
would also constitute a process residual. Disposal options for
the spent reactive iron have not been evaluated. It is possible
that the iron may require management as a hazardous waste.
However, unlike conventional filtering and sorptive material
such as granular activated carbon, the iron degrades contami-
nants to nonhazardous materials, and therefore may not be
hazardous. ETI is also currently evaluating means of regener-
ating spent iron through chemical and physical treatment. In
situ implementation of the technology may not require disposal
of the used granular iron. Extensive long-term data regarding
the useful life of the reactive iron under a wide range of field
conditions are not currently available.
Additional process residuals may be generated depending on
site-specific conditions. If required, use of secondary treatment
for an aboveground reactor could generate process residuals
such as spent carbon. For some sites, it may be necessary to
periodically replace the pea gravel, well sand, or other pretreat-
ment filtration devices if they become completely blocked with
sediments.
During evaluation of the aboveground reactor, air emissions
consisting of PCE and TCE vapors were potentially released
by the pressure release outlet at the top of the reactor. Changes
in temperature or the water volume within the reactor could
force headspace gases out through the opening. Gas samples
collected in the headspace above the water surface in the
reactor indicated the presence of PCE and TCE. If required,
treatment of airborne VOC emissions from aboveground reac-
tors could generate additional process residuals consisting of
spent filtration or sorptive media, such as activated carbon.
Site Requirements
Area requirements for the metal-enhanced dechlorination tech-
nology range from about 400 ft2 for a pilot-scale, aboveground
reactor system to much larger areas for in situ installations.
Additional space for extraction wells or trenches, reinjection
wells, and monitoring wells may be necessary, depending on
site-specific characteristics. Truck access for delivery of the
tank and granular iron (typically in 55-gal drums, 1-ton bags, or
bulk delivery) is also required. Other heavy equipment access
is required for construction, particularly for in situ applications.
The aboveground reactor at the New Jersey demonstration site
was constructed on a concrete pad and was surrounded by a
security fence. Ancillary piping and water and electrical meters
were also housed in the fenced area, which comprised about
400 ft2.
Performance Data
Primary and secondary objectives for the SITE demonstration
were established to provide criteria for evaluating the perfor-
mance of the metal-enhanced dechlorination process. The pri-
mary objectives were to (1) determine if treated effluent met
NJDEP and federal MCL requirements for all chlorinated VOCs
present in influent water or possibly generated as degradation
products and (2) determine the removal efficiency of PCE. The
secondary objectives of the demonstration were to (1) examine
how the concentration of PCE changed as groundwater passed
through the treatment reactor; (2) examine concentrations of
metals, chloride, sulfate, and inorganic carbon to evaluate
precipitation, dechlorination, and biological activities; and (3)
document geochemical changes in the water (specific conduc-
tance, Eh, pH, dissolved oxygen, and temperature) as it passed
through the reactor. As with all SITE demonstrations, data
were gathered to evaluate the operating and design param-
eters, and the costs of using the technology.
To achieve the demonstration objectives, water samples were
collected each week at influent (11) and effluent (E1) sampling
locations and analyzed for VOCs. During weeks 1,5,9, and 13
samples were also collected from intermediate sampling loca-
tions within the reactor (R1, R2, R3, R4, and R5). The sam-
pling locations are shown on Figure 1. Samples collected
during weeks 1, 5, 9, and 13 were analyzed for VOCs, field
parameters, metals, chloride, sulfate, and inorganic carbon.
Analytical results for chlorinated VOCs are shown in Table 2;
select inorganic and field parameter data are shown in Table 3.
To provide additional information on the technology, samples
of gases were also collected and analyzed for VOCs. These
data are shown in Table 4.
-------
Tabla 2. Metal-Enhanced Dechlorination Technology - Preliminary Results: Volatile Organic Compounds
Influent Concentration
Contaminant
PCE
TOE
cDCE
VC
Range*
4,100-13,000
54-590
ND-1,600*
ND
Mean
8,000
160
340"
ND
Detection Limit
25-250
25-250
25-250
25-250
Effluent Concentration
Range'*'
ND
ND
1.3-37
1.2-8.4
Mean
ND
ND
9.2
3.5
Detection Limit
0.9
0.9-1.0
1.0
1.0
Regulatory
Limits
MCL°
5
5
70
2
NJDEP"
1
1
2
5
Notes;
All concentrations in micrograms per liter (ug/L)
ND Not detected
PCE Tetfachtofoethene
TOE TrSchloroethene
cDCE cis-t,29t ol contaminant concentrations detected in weekly samples collected over 13-week demonstration period
*No contaminants detected until week 9
•Fedwal maximum contaminant level
"NJDEP grouxJwaier cSscharjja standards
•Not detected until week 6
Nonzero (detected) values only
Table 3. Metal-Enhanced Dechlorination Technology - Preliminary Results: Inorganic Analytes and Field Parameters
Mean Concentration or Measured Value at Sample Location
Analytes
Barium
Calcium
Magnesium
TIC
pH(SU)
Eh(mV)
Specific
Conductance (jtS)*
11
0,309
73.7
23.8
34
7.9
95.1
407
R1
0.283
69.0
21.6
33
7.8
46.8
367
R2
0.079
43.5
22.0
20
8.2
-198
286
R3
0.082
32.7
19.9
12
8.3
-304
259
R4»
0.108
24.0
12.5
5.7
9.3
-379
226
R5
0.093
23.1
13.8
4.4
9.3
-333
228
E1
0.079
26.7
16.8
5.8
9.4
-272
236
Notes*.
AM concentrations reported are in milligrams per liter (mg/L); the units for measured values are noted.
All concentrations or values based on mean of data collected during weeks 1,5, 9, and 13 unless otherwise noted.
TIC total Inorganic carbon.
SU standard units.
Eh oxidation-reduction potential.
mV millivolts.
nS mlcrosJemens.
•Sampling location R4 was inaccessible during week 13.
*S0ecrfic condoctanea was not measured at any location during week 5; in addition, specific conductance was not measured at sampling location R4 during week 13.
Table 4. Metal-Enhanced Dechlorination Technology - Preliminary Results: Headspace Gas Analyses
Headspace Gas Concentractions (ppb V/V)
Contaminant
Range*
Mean
Detection Limit
PCE
TCE
19,000-39,000
230-650
27,000
440
180-590
180-590
Notes:
ppb parts per billion
V/V volume per volume
"Ranga of contaminant concentrations detected in samples collected during weeks 5,9, and 13.
-------
About 61,000 gal of groundwater was treated during the 13-week
demonstration period. A flow rate of about 0.5 gal/min was
maintained throughout most of the demonstration period.
PCE and TCE were detected in the influent (11) samples through-
out the 13-week demonstration. The average influent PCE and
TCE concentrations were about 8,000 micrograms per liter (p.g/L)
and 160 ng/L, respectively. cDCE was occasionally detected in
the influent samples during the latter part of the demonstration
(after week 6). No other chlorinated VOCs were detected in the
influent samples.
Analysis of the effluent (E1) samples indicated that the technol-
ogy effectively reduced PCE and TCE. Effluent concentrations of
PCE and TCE were consistently below detection limits. Detection
limits in the effluent were 0.9 or 1.0 jig/L; the NJDEP and federal
regulatory limits are 1.0 ng/L or higher (see Table 2).
Removal efficiency for PCE, which is based on comparison of
effluent concentrations to influent concentrations, was greater
than 99.9% for each of the 13 weekly sampling events. Although
TCE and cDCE were detected in the influent groundwater, re-
moval efficiencies were not calculated for these contaminants
because the dechlorination of PCE may introduce TCE, cDCE,
and vinyl chloride at any point in the system. During some weeks,
concentrations of these potential degradation products were higher
at intermediate locations within the reactor than in the influent.
Based on the sampling performed during the SITE demonstra-
tion, it was not possible to account for the quantity of TCE or
cDCE introduced by the dechlorination process.
Effluent cDCE was detected after 9 weeks of operation, and vinyl
chloride appeared in the effluent after 11 weeks of operation. The
maximum concentrations of cDCE and vinyl chloride detected in
the effluent were 37 pg/L and 8.4 ng/L, respectively. Concentra-
tions of cDCE and vinyl chloride occasionally exceeded regula-
tory standards. The presence of these compounds in the effluent
may be due to insufficient contact time with the reactive iron to
carry the dechlorination reaction beyond the formation of cDCE
or vinyl chloride. This effect may have been caused by the parent
compound (PCE) persisting to greater depths in the reactive iron
than anticipated, or by accelerated flow through some parts of
the reactor due to channeling.
Incomplete dechlorination may also have been the result of
reduction of the iron's reactive capacity due to metal precipitates.
These precipitates may limit the surface area of the iron available
for reaction. During the demonstration, PCE concentrations in
lower parts of the reactor steadily increased. For example, PCE
was not detected in the samples collected from location R3
during weeks 1 and 5. At week 9, PCE was detected at 69 |ig/L
in the sample from location R3; by week 13, the PCE concentra-
tion at R3 had increased to 1,600 |o.g/L The increase in PCE
concentrations at R3 suggests that the upper portion of the
reactive iron lost some of its reactive capacity.
Results of the metals and total inorganic carbon analyses, shown
in Table 3, also suggest that precipitates may have been forming
in the reactor. Concentrations of barium, calcium, magnesium,
and total inorganic carbon decreased as groundwater passed
through the reactor. It is possible that metallic-carbonate com-
pounds were precipitating. A high potential for precipitate forma-
tion is consistent with the results of the pH; precipitate
formation is consistent with the results of the pH, Eh and
conductivity analyses (see Table 3), which indicate that chemi-
cal and physical conditions within the reactor were condu-
cive to precipitation of calcium carbonate and other
compounds. Chloride and sulfate concentrations in influent
groundwater were relatively high, but did not change signifi-
cantly as groundwater moved through the reactor.
Summary
The EPA SITE Program evaluated the metal-enhanced
dechlorination process during a 13-week demonstration. The
process effectively dechlorinated PCE and TCE in ground-
water treated during the demonstration. The process also
significantly reduced the total concentration of chlorinated
VOCs in groundwater treated. Two VOCs (cDCE and vinyl
chloride) that appear to have been byproducts of the dechlo-
rination process were detected in the treatment system efflu-
ent during the latter part of the demonstration. Although
site-specific designs for metal-enhanced dechlorination sys-
tems allow for dechlorination of treatment byproducts, the
potential for incomplete dechlorination should be considered
during the system design phase. The design should allow for
system modification and contingent O&M procedures to en-
hance performance, if necessary.
Technology Status
According to ETI, the metal-enhanced dechlorination pro-
cess is currently available for all phases of remediation, from
treatability studies and pilot projects to remedial actions. As
discussed in the Technology Applicability section, extensive
long-term performance data are not yet available. However,
ETI is currently working on several projects that are in
design, construction, or implementation phases. The EPA
SITE Program is evaluating one of these projects, an in situ
funnel-and-gate system, at a New York site. The results of
the New York demonstration will be available in 1997.
Disclaimer
The data and conclusions presented in this Technology Cap-
sule have not been reviewed by the National Risk Manage-
ment Research Laboratory (NRMRL) Quality Assurance
Office. The NRMRL QA office has reviewed the ITER for QA
requirements.
Sources of Further Information
EPA Site Project Manager:
Chien T. (Carl) Chen
U.S. EPA(MS-104)
2890 Woodbridge Avenue, Bldg 10
Edison, NJ 08837-3679
Technology Developer:
EnviroMetal Technologies, Inc.
John L. Vogan, Project Manager
42 Arrow Road
Guelph, Ontario, Canada N1K1S6
-------
United states
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
Please make all necessary changes on the below label,
detach or copy, and return to the address in the upper
left-hand corner.
If you do not wish to receive these reports CHECK HERE D;
detach, or copy this cover, and return to the address in the
upper left-hand corner.
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/R-96/503a
------- |