Loudoun Watershed Watch - Overseeing the Water Resources of Loudoun County, VA

Loudoun Watershed Watch
Overseeing the Water Resources of Loudoun County, VA

Water Quality Standards

Virginia has adopted water quality standards under Section 62.1-44.15(3a) to enforce the federal Clean Water Act. Water quality standards consist of narrative and numeric criteria that describe the water quality necessary for designated uses.

Designated Uses -- All streams in Loudoun County are designated for recreational uses including swimming and boating, and for the support of aquatic life. These designated uses determine the water quality criteria applicable to Loudoun streams. There are chemical and bacteriological criteria for temperature, pH, dissolved oxygen, ammonia, chloride, and fecal coliform bacteria. The Department of Environmental Quality (DEQ) uses these standards to limit the amount of pollutants discharged under permit into surface waters. These standards are listed in Table 1. There are no standards for other parameters such as nitrogen, phosphorous, turbidity, suspended solids, or biological oxygen demand (BOD). These standards are found on-line at: www.deq.state.va.us/Programs/
Water/WaterQualityInformationTMDLs/WaterQualityStandards.aspx.

DEQ Water Quality Standards for Recreational Use in Piedmont Zones. (Source: 9 VAC 25-260-5 et seq. Water Quality Standards, 1/10/97)

Parameter	State Standard (Acute/Chronic)	Significance
Temperature	Maximum = 32⁰C	Affects rates of chemical prossesses in cells and the water’s dissolved oxygen content
pH	6.0 – 9.0	Level of acidity -- affects cell membrane functions
Dissolved Oxygen (DO)	Miniumum = 4 mg/l	Affects biological metabolism
Ammonia	0.86 – 32 mg/l as N acute/ 0.19 – 3.02 chronic¹	Form of nitrogen that in excess causes eutrophication and loss of dissolved oxygen; a toxin
Chloride	860/ 230 mg/l	Indication of salt content
E. coli²Coliform Bacteria	235 cfu/100 ml instantaneous or 126 cfu/100 ml geometric mean	Common bacteria in animals’ digestive tracts. Indicator of human sewage or animal droppings.
Fecal Bacteria		Previous bacterial standard used.

¹Standard varies with temperature and pH

²New standard that replaces Fecal Coliform standard when 12 E. Coli observations available or after June 30, 2008