In the mid-1980s, Virginia’s General Assembly studied water quality issues in the Chesapeake Bay. As part of that effort, the body charged the State Water Control Board (SWCB) (now the Virginia Department of Environmental Quality), with developing water quality standards (WQS) to protect the bay and tributaries from nutrient enrichment. SWCB expanded that charge to include waters statewide. The board developed a strategy to protect state surface waters from nutrient enrichment and convened a technical advisory committee (TAC) to provide advice on developing WQS for nutrient-enriched waters. The TAC provided input on major issues via three questionnaires and used that information to come up with recommendations during a workshop. The TAC considered four parameters as possible indicators of in-stream nutrient enrichment in freshwater lakes: chlorophyll a, DO, TP, and TN and selected two—chlorophyll a and TP.

To identify waters with excessive nutrients, the TAC examined waters with average seasonal concentrations of chlorophyll a exceeding 25 µg/L, DO fluctuations, and high water column concentrations of TP. The TAC determined that for chlorophyll a, a planktonic measure would be easy to sample and would accurately reflect eutrophic conditions of the lake. Measurements were to be taken at ½ Secchi depth (as long as that depth was greater than 1 foot). The TAC recommended that, for freshwater lakes, the state consider a chlorophyll a criterion of 25 µg/L (monthly average) with a one-time exceedance level of 50 µg/L, and a TP criterion of 50 µg/L (weighted mean) or 25 µg/L (mixed layer mean). The TAC also recommended that the numeric chlorophyll a criterion for lakes be combined with narrative language to address taste, odor, and other issues caused by high levels of chlorophyll and DO problems in lakes.

The state did not adopt statewide numeric criterion for chlorophyll a or TP because appropriate values could vary by water body type. Rather, on a site-specific basis, the two parameters can be measured and used to designate a water as a nutrient-enriched water, as codified in the state’s WQS. The assessment endpoint, along with historical water quality data, has been used to designate several site-specific water bodies as nutrient-enriched waters (USEPA 2000a).

Reference:

USEPA. 2000a. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs. EPA-822-B-00-001. U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Washington, DC. Accessed October 2016. https://nepis.epa.gov/Exe/ZyPDF.cgi/20003COV.PDF?Dockey=20003COV.PDF.

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