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Assessment of Water Quality in Virginia's Non-Tidal Streams Using a Probabilistic Sampling Design

George J. Devlin, Jason R. Hill, Mary R. Dail, Michael J. Scanlan and Larry D. Willis

Virginia Department of Environmental Quality, 3019 Peters Creek Road, Roanoke, Virginia 24019

The Virginia Department of Environmental Quality's (VDEQ) biological and ambient water quality monitoring programs have historically used a targeted approach for monitoring the Commonwealth's aquatic resources. This sampling method is necessary for monitoring regulatory compliance of pollution sources and tracking local pollution events. However, the data produced by this sampling method is difficult to estimate water quality conditions across the whole state or in an entire river basin. In 2001, VDEQ began a five-year probabilistic monitoring program (ProbMon) for non-tidal streams. ProbMon incorporates a random tessellation stratified survey design that allows VDEQ to produce an accurate assessment of chemical, physical, and biological conditions in 1st through 6th order streams. This is the first survey that will provide policy-makers and the public with estimates of the status of Virginia's aquatic resources with known statistical confidence. Two years of data results include statewide benthic macroinvertebrate assessments, physical habitat assessments, and water quality data from fall 2001 (n=58) and spring 2002 (n=61).

Keywords: statistical analysis; stream survey design; sampling design; water quality; and aquatic ecosystems.

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