The TREX (Two-dimensional Runoff Erosion and Export) model can be used to simulate spatial and temporal concentrations of contaminants like selenium by integrating field sampling results with environmental fate processes. This allows for environmental hazard assessments and evaluation of risk management measures. HDR|HydroQual has extensive experience investigating the fate and effects of chemicals like selenium in diverse environments. They have expertise in assessing bioavailability, hazards and risks to aquatic organisms. Their experience includes modeling the speciation, fate and transport of metals, developing bioaccumulation models, conducting field sampling, analyzing project data, and providing guidance on wastewater treatment and regulatory issues for selenium.

1. WATERSHED MODEL FOR FATE AND TRANSPORT
Diffuse, distributed contaminant sources in a watershed can contribute to potentially toxic exposures. The TREX
(Two-dimensional Runoff Erosion and Export) model can be used to integrate field sampling results with envi-
ronmental fate processes to simulate multi-media temporal and spatial concentrations needed to perform environ-
mental hazard assessments for selenium and to evaluate risk management measures.
HDR|HydroQual
Mahwah Office
1200 MacArthur Boulevard  First Floor
 Mahwah, New Jersey 07430
Phone: 201-529-5151  Fax: 201-529-5728
New York Office
HDR|HydroQual Environmental Engineers & Scientists, P.C.
6700 Kirkville Road  Suite 101
East Syracuse, New York 13057
Phone: 315-484-6220  Fax: 315-484-6221
Central New Jersey Office
720 King Georges Post Road
Woodbridge Township,
Fords, New Jersey 08863
Phone: 732-738-0244  Fax 732-738-3829
www.hdrinc.com
INTERNATIONAL
Dubai Office
P.O. Box 231205  Dubai, UAE
Phone: 971-4-330-6320
Fax: 971-4-330-6321
Laboratory
65 Ramapo Valley Road
Mahwah, New Jersey 07430
S ELENIUM-RELATED EXPERIENCE AT
For More Information on HDR|HydroQual's
Experience and Capabilities with Selenium, Please
Contact Aaron Redman at
435-213-4188 or Aaron.Redman@hdrinc.com

2. HDR|HydroQual Inc. personnel have extensive experience investigating the fate and effects of a
wide range of chemicals in diverse physical settings including selenium (Se). We are experts in
assessing bioavailability, hazards and risks of chemicals to aquatic organisms. We have helped
“write the book” describing the State of the Practice on selenium in industrial wastewater. The mate-
rial in this document outlines our direct and relevant experience on the important issues associated
with selenium.
ENVIRONMENTAL FATE
One issue that makes selenium hazard assessments so diffi-
cult is its complex chemistry which affects its environ-
mental fate. Selenium can naturally occur in several different
chemical forms, each of which has unique chemical properties
that affect its speciation and environmental fate.
HDR|HydroQual has internationally recognized expertise in
relating chemical speciation and fate of metals to their environ-
mental fate properties. Examples of this expertise include
development of speciation and partitioning models to assess
bioavailability, fate and transport of metals (Cu, Zn, Pb, Cd,
As, Hg, etc.) in urban settings, from mining materials and in
support of laboratory research.
Bioaccumulation of selenium is a key fate process due to the
potential for toxicity. HDR|HydroQual has extensive experi-
ence developing and applying various bioaccumulation mod-
els for metals and organics, which can be used to predict the uptake of inorganic and organic forms of selenium in
biota. These bioaccumulation models have been extended to describe complex physiological processes such as regu-
lation of metals (Cu and Se) in aquatic organisms. We have also helped industrial clients examine potential impacts
that selenium in wastewater discharges have on receiving water quality and aquatic life.
HDR|HydroQual has the capability to evaluate the fate of selenium from the screening level to comprehensive
assessments that track the fate, transport, and transformation of selenium throughout a site.
FIELD WORK
Selenium can have measure-
able effects in the environ-
ment so field surveys to char-
acterize biological status and
exposure levels can be impor-
tant. The use of clean metal
sampling techniques and
appropriate analytical meth-
ods are necessary to properly
characterize the exposure conditions of selenium to aquatic
life since background concentrations can be low relative to
conventional analytical methods.
HDR|HydroQual has substantial experience using clean
metal sampling techniques in the field for a wide range of
chemicals including selenium. Where biological inventory
and impact surveys are required, HDR|HydroQual has
good working relationships with several other technical
service providers with this expertise, which complement
our field capabilities and technical expertise.
TOXIC EFFECTS
In the case of selenium, tissue-based threshold levels are more closely
related to toxic effects, which has resulted in a draft U.S. EPA criterion
for selenium in 2004 (update due in late 2010) that is based on fish tissue
threshold levels. HDR|HydroQual scientists have championed tissue-
based water- and sediment-quality criteria for metals and organics.While
scientifically defensible, implementation of tissue-based thresholds poses
technical challenges to regulated industries. HDR|HydroQual has direct
project experience relating complex bioavailability issues of selenium and
other metals to practical implementation guidance. HDR|HydroQual is
presently refining modeling tools to support conversion of water concen-
trations to tissue concentrations that can be used to support hazard
assessments and regulatory activities such as permitting.
DATA ANALYSIS
HDR|HydroQual effectively utilizes available proj-
ect data. This is
due to our extensive
experience in the appli-
cation of powerful sta-
tistical platforms such
as R, Systat and in-
house analysis pro-
grams that we use to
provide efficient and
insightful data analysis. We also use geostatistical and
GIS methods for characterizing spatial distribution of
contaminants.
WASTE WATER TREATMENT
Low level selenium removal from industrial and min-
ing wastewaters can be challenging due to the com-
plexities in the chemistry and biology of Se. Furthermore,
many sites have limited space or accessibility which com-
plicate the design of adequate treatment streams.
HDR|HydroQual has experience with removal of low lev-
els of trace metals and other complex constituents in
mobile and stand-alone treatment designs at a wide range
of process conditions. HDR|HydroQual personnel co-
authored a recent white paper for the Water Environment
Federation (WEF) that outlines the treatment options that
are available for removal of selenium from industrial
wastewater.
(http://www.wef.org/TPUs/).
SELENIUM-RELATED EXPERIENCE AT HDR|HYDROQUAL
REGULATIONS
The environmental hazards of selenium have
been recognized in recent years and as a result
U.S. EPA has been developing tissue-based thresh-
olds. However, many states are still relying on
water-based criteria. Implementation guidance for
converting between tissue-based criteria and water-
based permit limits is not yet available. This uncer-
tainty places greater pressure on the regulated
industries when respond-
ing to permit or TMDL
requirements.
HDR|HydroQual per-
formed TMDL and per-
mitting reviews in many
states and has participat-
ed in criteria development
at the state and federal level as well as internation-
ally for a variety of constituents including metals
and organics. This combined experience provides a
strong basis for addressing selenium-related techni-
cal and regulatory issues with local and federal
regulatory agencies.
CONCLUSIONS
Selenium poses significant challenges in today’s regulatory environment. The changing state of environmental
regulations combined with the complex chemistry and biology of selenium can create significant uncertainty
regarding a client’s environmental liabilities. HDR|HydroQual has demonstrated experience in the major issues
related to selenium in the environment. This wide range of technical expertise provides HDR|HydroQual with the
flexibility to meet the client’s technical needs and the high level of credibility required when interacting with regu-
latory agencies.