_	Draft Baseline Ecological Risk Assessment
O tMr\	Upper Animas Mining District
fuel sheet
United States Environmental Protection Agency • Regions • April 2015
Background
The Animas River originates in the mountain peaks
northeast of Silverton, in San Juan County, Colorado,
near the ghost town of Animas Forks. It ends in
Farmington, New Mexico, where it empties into the San
Juan River.
The Animas River and many of its tributaries are
impacted by high concentrations of hazardous
substances (heavy metals) from both acid rock/mine
drainage at mine sites and from natural sources not
impacted by mining.
Introduction
The purpose of this fact sheet is to summarize the
results of the Draft Baseline Ecological Risk Assessment
of the Upper Animas Mining District (BERA), which
examined water and sediments in the Animas River
from approximately two miles upstream of Silverton,
Colorado, to approximately 30 miles downstream of the
town. Two tributaries of the Animas River, Cement
Creek and Mineral Creek, were also studied.
This evaluation did not attempt to separate natural
contamination from past mining-related contamination,
but assessed the total risk from all sources combined.
Due to natural processes, it is unlikely that Cement
Creek and portions of Mineral Creek ever supported
fish communities. However, these tributaries were
investigated as sources of contamination in the Animas
River.
EPA is soliciting comments on the BERA until June 30,
2015.
Assessment
A baseline ecological risk assessment is the process for
evaluating how likely it is that the environment may be
impacted as a result of exposure to one or more
environmental stressors.
The surface water data represents samples collected
from the waterways between May 2009 and September
2014. The sediment data was collected from May 2012
to September 2014.
This BERA evaluated the likelihood that the following
metals in the water and sediments of the investigated
waterways would impact the environment: aluminum,
arsenic, beryllium, cadmium, chromium, copper, iron,
lead, manganese, nickel, selenium, silver, and zinc.
The BERA estimated the risk under current conditions in
the waterways to:
•	Benthic invertebrates (small organisms that live in
or on the bottom sediments of rivers and streams)
that are exposed to sediments.
•	Fish that are exposed to surface water.
•	Wildlife that eat or drink surface water, sediments
and food from the waterways.
Goals
The benthic invertebrates (insects and other small
organisms), fish, three species of birds and one species
of mammal all represent valued ecological resources to
be protected in the Animas River, Cement Creek and
Mineral Creek.
The data provided by the BERA evaluates if the
waterways examined can maintain stable and healthy
benthic invertebrate and fish communities as well as
stable and healthy bird and mammal populations. This
information will support risk management decision
making for those waterways.

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Lines of Evidence
Three different lines of evidence were used in the
BERA: hazard quotient, toxicity testing, and
community surveys.
The hazard quotient (HQ) is the ratio of a chemical
concentration (e.g. heavy metals) in an environmental
media (e.g. water) and the level at which harmful
effects are expected. Therefore, if an HQ is less than
one, no harmful effects are expected. If the HQ is
greater than one, harmful effects might be found.
Toxicity testing involves taking a environmental media
(e.g. water, sediments) from a site and exposing
laboratory organisms to it to determine if there are
harmful effects. The results of this testing can be
extrapolated to predict if that substance will produce
similar effects on organisms at the site.
Community surveys involve quantifying populations
and communities of organisms on site. This is an
informative line of evidence as it provides the most
realistic and relevant measure of what is occurring in
the Animas River.
Results of these lines of evidence are weighed to
develop a conclusion regarding the potential for
harmful effects on the organisms being evaluated.
Results and Conclusions
Benthic Invertebrates
A diverse benthic invertebrate community is
important for maintaining a healthy fishery. Evidence
from HQs, sediment toxicity testing and a survey of
community structure and function indicates that the
benthic invertebrate community is impaired in most
sections of the Animas River, Cement Creek and
Mineral Creek. Effects are less severe as one moves
further downstream from the site, but are apparent
down to Bakers Bridge.
Fish
The evidence collected to evaluate potential negative
effects on fish included: HQs, toxicity testing with
rainbow trout, and fish community surveys. The
evidence suggests that water in the Animas River from
Arrastra Creek to approximately Cement Creek is likely
toxic to all trout species with the exception of Brook
trout. Brook trout living in this reach, however, are
likely stressed much of the year.
Metals concentrations in the Animas River below
Mineral Creek have eliminated virtually all fish down
to Elk Creek and all cutthroat and rainbow trout down
to Cascade Creek, where only a small community of
brook and brown trout exist. This prediction, based
on HQs, is supported by surveys conducted by
Colorado Parks and Wildlife between 1992 and 2014.
HQ results also predict fish populations are likely
impaired down to at least Bakers Bridge.
Wildlife
Wildlife populations foraging in the Animas River were
evaluated by measuring, or making conservative
predictions of, metals concentrations in food items
and comparing those to levels causing harmful effects.
Based on this evidence, it is unlikely that birdlife or
mammal populations are experiencing significant
negative effects from metals in the Animas River.
FOR MORE INFORMATION OR TO REQUEST A COPY OF THE BERA, PLEASE CONTACT THE FOLLOWING:
Dan Wall
Toxicologist
303-312-6560
wall.dan@epa.gov
U.S. Environmental Protection Agency, 1595 Wynkoop St., Denver, CO 80202
Liz Fagen
Remedial Project Manager
303-312-6095
fagen.liz@epa.gov
Paula Schmittdiel
Remedial Project Manager
303-312-6861
schmittdiel.paula@epa.gov
Cynthia Peterson
Community Involvement Coordinator
303-312-6879
peterson.cynthia@epa.gov
April 2015
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