&EPA
United States
Environmental
Protection Agency
Office of Research
and Development
Washington, DC 20460
EPAA620/R-01/004d
February 2002
EMAP-West Communications
How Reference Condition is Used in Surface Water Monitoring
EPA's Environmental Monitoring and Assessment Program is
designed to develop the tools to measure the status and trends in
the condition of the Nation's surface waters. One of the most
important of these tools is a methodology to interpret the ecologi-
cal indicators being measured by comparing them against a bench-
mark or "reference condition". Multiple definitions exist for refer-
ence condition - each has its own use and interpretation. One of
the purposes of EMAP-West is to work collaboratively with the
western states and tribes to develop a consistent approach for the
development and use of reference condition. This approach will be
used in collecting data to support quantitative description of refer-
ence condition and, ultimately, in the interpretation of data across
the 12 states covered by EMAP-West. After its successful conclu-
sion, this effort should serve as a template for the rest of the Nation.
EMAP-West will rely on two definitions of reference condition for
setting benchmarks against which to compare the condition of the
streams and rivers being sampled.
Minimally Disturbed Condition (MDC) - the condition of water
bodies in the absence of significant, or with minimal, human
disturbance. MDC will change little over time, mostly due to
natural processes, and thus provides a stable benchmark. Historical
information may be used to help describe MDC.
Least Disturbed Condition (LDC) - the best available physical,
chemical, and biological conditions given today's state of the
landscape. LDC will change overtime as landuse and management
practices change thus is not a "target" or upper bound of water
quality potential.
In evaluating the ecological condition of streams across 12 western
states, EMAP-West is faced with a challenge: how to apply the
best scientific principles to assessing reference condition and, at
the same time, adopt an approach that is pragmatic; that is, one that
can be implemented across the diverse landscape of the West in the
timeframe of the Program. EMAP-West has chosen to develop a
rigorous, consistent, and repeatable method for describing LDC
across multiple states/ecoregions/stream types. Since LDC will
change over time, we are also conducting research on techniques to
estimate MDC where such conditions do not exist - in fact most areas.
EMAP-West's objectives are summarized as:
1. Adopt the LDC approach for application everywhere in the
12-state region covered by EMAP-West. EMAP will define
selection criteria, select, and sample at least 20 reference sites
in each state during the time period 2000-2004.
2. To estimate MDC, EMAP will choose 3 pilot areas (one
each in Regions 8, 9, and 10) to explore several different
approaches to developing MDC.
3. Use the information gathered from the LDC and MDC
approaches to stimulate public and scientific discussion about
determining the highest achievable goals given the existing
degree of human disturbance and the potential for restoration -
the significant part of setting management goals.
When completed, the work on reference condition in EMAP-West
will form the foundation for a more quantitative and defensible
process for conducting the analyses of water bodies necessary to:
1. designate their uses, 2. support assessments of condition,
and 3. establish targets for protection and restoration. State
and tribal water quality managers are responsible for bringing to a
public forum an analysis that predicts the best ecological condition
that can be achieved. This analysis must be informed by a rigorous
evaluation of reference conditions, and tempered by economic
conditions and societal values. A process for establishing reference
condition that is transferable across state, tribal, or ecoregional
boundaries will greatly improve our ability to meet the require-
ments of the Clean Water Act.
For further information, contact:
John Stoddard Stoddard.John@epa.gov
Surface Water Lead (541 )754-4441
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