&EPA
United States
Environmental
Protection Agency
Office of Research
and Development
Washington, DC 20460
EPAA620/R-01/004C
December 2001
EMAP-WEST COMMUNICATIONS
Survey Designs for Sampling Surface Water Condition in the West
Monitoring the condition of the Nation's waters, as required by the
Clean Water Act (CWA), is an enormous task. The CWA delegates
the bulk of this burden to the states and tribes under the guidance
of the U.S. Environmental Protection Agency. State and tribal
monitoring programs are challenged to meet these requirements as
they are faced with growing monitoring needs and often have no
additional, or in some cases dwindling, resources. Therefore, the
sampling designs used for these monitoring activities must be as
efficient as possible. To help meet this need, EPA's Environmental
Monitoring and Assessment Program (EMAP) has developed a
partnership, called EMAP-West, with the states and tribes of 14
Western states to evaluate and demonstrate the effectiveness of
new aquatic monitoring designs.
It is clearly not economically possible to actually visit and monitor
every single waterbody or stream segment within a state or tribal
nation. The survey designs being developed by EMAP provide a
rigorous way to sample a subset of all waters and then provide an
estimate of the quality of all waters along with a statement about
the uncertainty surrounding that estimate. These designs, also
known as "sample survey designs" or "probability survey
designs," have been in common use in many economic, political,
and social fields as well as in timber inventory and agricultural
crop surveys. EMAP has been among the earliest efforts to apply
these survey designs to aquatic systems. Use of the EMAP design
concepts allow the states and tribes to rigorously defend that their
estimates represent all waters of the state and to estimate the
uncertainty surrounding their assessments.
One of the real advantages of the survey designs developed by
EMAP is that they offer the states and tribes enormous flexibility.
Many states want an overall estimate of the quality of their waters,
but they also may want to focus on aquatic systems in particular
geographic regions or in areas of particularly high public interest.
Probability surveys have the flexibility to provide both. Because of
the rigorous procedure for drawing these subsamples, all of the
data can be used in providing the statewide estimate and then a
separate estimate for the subset of waterbodies of concern. The
figure illustrates how the design is being used for the state of Cali-
fornia in EMAP-West. Statements of condition will be possible for
the entire state as well as for the shaded northern and southern
coastal watersheds individually. The data from the more inten-
sively sampled areas nest within the statewide sample and
improves its reliability.
The survey design can also be integrated with indicators that have
different temporal sampling requirements. For example, many
states collect biological data such as fish and macroinvertebrate
information during a single time of the year. They may, however,
require that chemical indicators be collected on a seasonal or more
frequent basis. The probability survey designs can be developed to
take advantage of indicators collected on either or both of these
temporal sequences.
EMAP-WEST
Perennial Sample
California
OBase
A Intensive
EMAP-West is a demonstration monitoring and assessment project
that encompasses nearly one third of the conterminous U.S. area
and is a dramatic demonstration of the importance and flexibility of
new monitoring designs to aid the states and tribal nations in
meeting their requirements of the Clean Water Act. When
completed, each state will be able to make a statement of condition
of all their streams. The design will also support West-wide assess-
ments as well as large areas such as ecoregions or large river basins.
For further information, contact:
Tony Olsen
Design and Analysis Lead
Olsen.Tony@epa.gov
(541)754-4790
------- |