Virginia’s freshwater and estuarine ProbMon programs provide an important complement to the fixed station network. ProbMon data from randomly selected stations provide an unbiased regional or statewide characterization of water resources with a known degree of statistical confidence. The freshwater ProbMon design includes smaller-order streams in addition to large-order waters, and is one of the few programs that gathers data from smaller streams. ProbMon data has many applications, including:

  • Enabling broad regional assessments of overall ambient conditions.
  • Establishing baseline water quality conditions.
  • Identifying problem areas for follow-up monitoring.
  • Answering questions about statewide and regional water quality conditions. For example, “what are the primary water quality problems in VA?”, “how widespread are these problems?”, and “what pollutants cause the greatest environmental stress to VA’s waters?”
  • Meeting requirements under section 305(b) of the CWA to make water quality condition estimates and “submit…a report which shall include a description of water quality of all navigable water…”
  • Rendering assessments for the aquatic life designated use.
  • Improving monitoring sufficiency and efficiency since it is impossible to use the fixed monitoring network to assess all of Virginia’s streams.

Since 2001, Virginia has evaluated nearly 1000 freshwater and 800 estuarine probabilistic sites. Given the robustness of the ProbMon dataset, DEQ scientists have used it to develop new tools, which have been critical to providing support for decision-making within the agency. Some examples of ProbMon applications include the following:

  • Data collected at freshwater ProbMon sites reveal the estimated extent of stressors that may be degrading benthic macroinvertebrate communities. Stressor thresholds that have been developed for various parameters through the ProbMon program indicate the most probable stressor(s) causing benthic macroinvertebrate impairments. These Virginia-specific parameter stressor thresholds have been programmed into a stressor tool that facilitates in-house stressor identifications at no cost to the agency.
  • The statewide or basin-wide perspective on water quality highlights patterns in improvement from TMDL implementation efforts that can be more widespread and not always targeted to where the exact impairment is located (e.g., implementation in upstream portions of the watershed).
  • ProbMon is the only program that collects fish community data and dissolved water column metals. These data are essential when determining background conditions in response to environmental emergencies (e.g., 2014 Dan River coal ash spill), and in turn help the agency be responsive to public concerns.
  • The estuarine ProbMon program is focused on determining the effects of toxic sediment pollutants on benthic macroinvertebrates. Benthic macroinvertebrates are a sensitive indicator group affected by pollution from the past as well as the present. Sediment contamination can affect not only benthic communities, but entire ecosystems. The objective of the program is to evaluate benthic macroinvertebrate communities, lab-based sediment toxicity tests, and sediment chemistry to assess the aquatic life designated use in Virginia’s estuaries.
  • WMA staff are collaborating with permitting staff to use ProbMon data to help establish baseline water quality conditions, which is especially important in areas where there are no fixed stations located near permit outfalls.

Reports and Data Sets