xv EPA
U.S. Environmental Protection Agency
Pacific Southwest, Region 9
Land Division
October 2014
Serving Arizona, California, Hawaii, Nevada, the Pacific Island, and 148 Tribes
75 Hawthorne Street, San Francisco, CA 94105
800-EPA-WEST  www.epa.gov/region9
Risk Assessment at Evoqua (formerly Siemens)
October 2014
Evoqua Water Technologies, formerly known as Siemens
Industries, Inc., US Filter, and Westates, operates a hazardous
waste storage and treatment facility on the Colorado River Indian
Tribes' reservation near Parker, Arizona (the "Evoqua Facility").
The Evoqua Facility reactivates spent carbon - carbon which has
been previously used to remove pollutants from water and air.
The spent carbon is reactivated by heating to very high
temperatures under controlled conditions in order to drive off the
contaminants. The contaminants are then captured and further
processed to ensure that they do not pollute the environment.
The newly reactivated carbon product is then ready for reuse.
(See Figure 1)
Carbon Regeneration Cycle
HI
Fill
Carbon filtering site
uses activated
carbon
carbon, no
a hazardou
waste, is re
Figure 1
Spent carbon is
entto Siemens
Siemens
contaminants from
spent carbon
At EPAs request, and as part of the permit process, the Evoqua
Facility completed a human health and ecological risk assessment (risk assessment) in July 2007. The
purpose of the risk assessment was to estimate the Evoqua Facility's current and possible future impacts on the
health of local residents and the
surrounding environment.
Based on the risk assessment results, EPA
concluded that human health impacts
(both carcinogenic and non-cancer)
and ecological impacts from
operations at the Evoqua Facility are
low or insignificant. (See page 4 for an
explanation of what level of risk EPA
considers "insignificant.") Please note that
due to various ownership and name changes
to this facility over time, earlier documents,
including on EPA's website, may show older
names for this facility.
Human health risk: the likelihood that an individual's health
may be affected by exposure to toxic substances in the
environment.
Ecological risk: the likelihood that the ecosystem (e.g. plants,
wildlife) may be affected by toxic substances in the environment.
Carcinogenic vs. non-cancer health impacts: carcinogenic
impacts may cause cancer in humans, whereas non-cancer impacts
are not believed to cause cancer, but may cause other health effects,
such as liver disease.
What is a risk assessment?
-	A scientific study of the various ways individuals and/or the
ecosystem might come into contact with toxic substances
-	A calculation of how likely it is that human health impacts might
occur because of hazardous substances at a site
-	A tool to assist EPA in decision making and in protecting the
community" health and the environment
1

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How will EPA use the risk assessment results in the permit
decision?
EPA cannot deny a permit for the Evoqua Facility based on risk, because the risk assessment determined the
human health and ecological risk of the operations at the facility to be insignificant. However, if EPA decides
to issue the permit, it will not allow the Evoqua Facility to operate under conditions that could have a greater
impact than the conditions evaluated by the risk assessment. For example, the permit would specify
operational conditions, such as the temperature to which the carbon is heated and the amount of carbon
processed.
How was the risk assessment conducted?
EPA provided the Evoqua Facility with guidance and oversight for the risk assessment process, ensured that
the report was sufficiently thorough and extensive, and reviewed the results of the risk assessment. The risk
assessment followed the steps below:
1)	Measured maximum possible concentrations of emissions from the facility by conducting a trial
burn (discussed in greater detail below).
2)	Identified exposure routes by which the emissions could reach potential human and
ecological receptors.
3)	Determined concentrations at which the emissions would reach potential receptors through the
identified exposure routes.
4)	Calculated potential impacts to human and ecological receptors from coming in contact with the
emissions.
Which human and ecological receptors did the risk assessment
consider?
	Facility workers exposed to emissions on the job.
	The community around the Evoqua Facility, particularly the following sensitive receptors:
o The elderly, people with health impairments, pregnant women, women of childbearing ages,
and children.
o Individuals engaging in subsistence fishing, hunting and agriculture, and particularly members
of the above mentioned higher risk population engaging in subsistence activities.
	Plants and wildlife found around the Evoqua Facility.
Which routes of exposure did the risk assessment consider?
	Inhalation (breathing in) of affected air.
	Ingestion (eating) of affected soil (e.g. through soil particles getting onto food or through cultural
practices).
	Eating food that absorbs and accumulates chemicals from the affected air and soil. This food
includes locally-raised produce, beef, chicken and eggs.
	Eating fish potentially affected by waste water discharge from the Evoqua Facility

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Exposure routes - ways in
which particular substances
can reach human and
ecological receptors.
Emissions  All chemical
compounds that leave the
facility
Human receptors
individual-- who may be
affected by substances emitted
by the facility
Ecological receptors -
plants, animals and habitats
in the area that may be
affected by substances from
the facility
What specific information about the
community and the area did the risk assessment consider?
	Information about community activities, such as home gardening, raising of livestock and use of
local plants.
	Information about Tribal cultural and spiritual activities that may increase exposure of community
members to contaminants.
	Information about local and regional weather patterns.
What are the human health impacts from air emissions?
Based on the risk assessment study, the EPA concluded that human health impacts from long-term exposure to
stack emissions, fugitive emissions, as well as the combination of the two, were below EPA's acceptable
thresholds.
Stack emissions: To measure stack emissions, the Evoqua Facility conducted a trial burn under specific
operating conditions (e.g. temperature of the furnace, amount of carbon being processed by facility,
contaminants present in the spent carbon). The concentrations of contaminants coming out of the stack were
measured during the trial burn. Computers helped model how emitted substances would disperse (spread)
throughout the air and soil in a 154 square mile area surrounding the facility.
Fugitive emissions: Fugitive emissions are generated during unloading of the spent carbon that comes into
the Evoqua Facility (see Figure 2). The risk assessment determined levels of fugitive air emissions from
information on amounts of spent carbon that Evoqua handles, as well as the concentrations of contaminants in
that spent carbon.
3
Incoming Spent
Carbon
Siemens Process Diagram
Fugitive
Emissions
emissions
Regenerated
Carbon Product
Pre-treated
Wastewater to
Joint Venture

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What are the impacts to water and fish?
The Evoqua Facility sends its waste water (mostly from
air pollution control devices) through a pipeline to the
Colorado River Sewage System Joint Venture, a
treatment plant. The treatment plant processes waste
water from the Evoqua Facility along with waste water
from the surrounding community. It then releases the
treated water to the Main Drain - a channel that flows to
the Colorado River.
Currently, CRIT does not have EPA-approved surface
water quality standards. As any discharge from the
treatment plant may eventually flow into the Colorado
River, the discharge must meet EPA-approved
downstream standards established by the State of
Arizona Water Quality Standards. The analysis found
that waste water from the Evoqua Facility does not cause
the discharge from the treatment plant to exceed the
State's most stringent water quality standards. It also
found that the discharge from the Joint Venture is not
toxic to aquatic organisms.
The risk assessment did not evaluate the overall risks of eating fish from the Main Drain, so EPA cannot
conclude whether or not the fish are safe to eat. However EPA supports the risk assessment's conclusion that
the Evoqua Facility has no significant effect on how safe the fish are for human consumption.
What are the ecological impacts?
The ecological risk assessment concluded that the stack emissions from the Evoqua Facility do not pose an
unacceptable risk to wildlife considered to be the most sensitive in the area.
How does EPA decide what level of risk is "insignificant"?
To decide on an insignificant risk of cancer in a community from a combustion facility such as the Evoqua
Facility, EPA typically uses the threshold of "one in one hundred thousand." The "one in one hundred
thousand" threshold indicates that for every one hundred thousand residents exposed to facility emissions, at
most one additional case of cancer may develop over the course of a 70-year lifetime. This additional case of
cancer would be in addition to cancers in the community caused by factors unrelated to the facility, such as
smoking, diet, pesticide use, or naturally occurring radon.
When we apply the "one in one hundred thousand" threshold to a community with fewer than one hundred
thousand residents (such as Parker with about 3,000 residents), we would expect less than one additional case
of cancer to develop in that community due to emissions from the facility.
4

Figure 3
Evoqua Stack Gas Composition (Typical):
 49.2% Steam
 42.2% Nitrogen
 4.7% Oxygen
 3.9% Carbon Dioxide
 0.006% Other
0
0.005 Nitrogen Oxides
0
0.00023% Hydrogen Chloride and

Chlorine
0
0.0002% Carbon Monoxide
0
0.00007% Ash
0
0.0000004% Metals
0
0.0000005% Organics (estimated)
0
0.0000000000001% Dioxins

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Please contact the following with questions or comments
Mr. "Mike" Mahfouz Zabaneh, Project Manager
75 Hawthorne St., LND-4-2
San Francisco, CA 94105
(415) 972-3348 or zabaneh.mahfouz@epa.gov
Mr. Patrick Wilson, Senior Toxicologist
75 Hawthorne St., LND-4-1
San Francisco, CA 94105
(415) 972-3354 or wilson.patrick@epa.gov
The complete text of the risk assessment is available online at
http://www.epa.gov/regionQ/waste/evoqua/risk.html

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